Cfdesign 2009 User Manual

cfdesign

user’s guide

Upfront CFD

Version 9.0

Copyright (C) Blue Ridge Numerics, Inc. 1992-2006

R

Copyright

The CFdesign product is copyrighted and all rights are reserved by Blue Ridge Numerics, Incorporated.

Copyright (c) 1992-2006 Blue Ridge Numerics, Incorporated. All Rights Reserved.

The distribution and sale of CFdesign is intended for the use of the original purchaser only and for use only on the computer system specified at the time of the sale. CFdesign may be used only under the provisions of the accompanying license agreement.

The CFdesign Release Notes may not be copied, photocopied, reproduced, translated or reduced to any electronic medium or machine readable form in whole or part without prior written con-sent from Blue Ridge Numerics, Incorporated. Blue Ridge Numerics, Incorporated makes no warranty that CFdesign is free from errors or defects and assumes no liability for the program. Blue Ridge Numerics, Incorporated disclaims any express warranty or fitness for any intended use or purpose. You are legally accountable for any violation of the License Agreement or of copyright or trade-mark. You have no rights to alter the software or printed materials.

The development of CFdesign is ongoing. The program is constantly being modified and checked and any known errors should be reported to Blue Ridge Numerics, Incorporated.

Information in this document is for information purposes only and is subject to change without notice. The contents of this manual do not construe a commitment by BRNI.

Portions of this software and related documentation are derived from and are copyrighted by Symmetrix and Ceetron.

All brand and product names are trademarks of their respective owners.

Table of Contents

Table of Contents

CHAPTER 1 Getting Started . . . . . . . . . . . . . . . . . 1-11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.2 Overview of Upfront CFD . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.3 Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

1.4 Product Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6

1.5 Starting CFdesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

1.6 The Basic Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10

1.7 CFdesign Client-Server . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11

1.8 CFdesign File Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14

1.9 Compatibility with CFdesign 8 . . . . . . . . . . . . . . . . . . . . . . 1-16

1.10 Contact Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17

CHAPTER 2 The User Interface. . . . . . . . . . . . . . . 2-12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.2 The Basics of the User Interface . . . . . . . . . . . . . . . . . . . . 2-1

2.3 Tool Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.4 File Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

2.5 Help. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19

2.6 Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22

2.7 Entity Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24

2.8 Entity Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26

2.9 Feature Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-27

2.10 Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-30

2.11 Task Dialogs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-37

2.12 Additional Parameters (Flags File) . . . . . . . . . . . . . . . . . . . 2-43

CHAPTER 3 Geometry . . . . . . . . . . . . . . . . . . . . . 3-13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.2 What is Flow Geometry?. . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

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3.3 Pro/Engineer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3.4 Parasolid and Acis Based CAD Systems . . . . . . . . . . . . . . . . 3-12

3.5 CATIA V5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17

3.6 Outlets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

3.7 Lost List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25

3.8 Suppressed Components . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

3.9 Third Party Mesh Import . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

CHAPTER 4 Loads. . . . . . . . . . . . . . . . . . . . . . . . 4-14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.2 Application of Boundary Conditions . . . . . . . . . . . . . . . . . . . 4-1

4.3 Surface Boundary Conditions . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.4 Volumetric Boundary Conditions . . . . . . . . . . . . . . . . . . . . . 4-11

4.5 Transient Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4.6 Physical Boundary Types . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

4.7 Initial Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19

4.8 Graphical Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21

4.9 Feature Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-23

CHAPTER 5 Mesh Sizes . . . . . . . . . . . . . . . . . . . . 5-15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.2 Geometry Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5.3 Fully Automatic Mesh Sizing . . . . . . . . . . . . . . . . . . . . . . . . 5-13

5.4 Automatic/Interactive Mesh Sizing . . . . . . . . . . . . . . . . . . . 5-13

5.5 Optional Step 1: Size Adjustment . . . . . . . . . . . . . . . . . . . . 5-16

5.6 Optional Step 2: Extrusion . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

5.7 Geometric Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-34

5.8 Advanced Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-35

5.9 Manual Application of Mesh Sizes . . . . . . . . . . . . . . . . . . . . 5-37

5.10 Graphical Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-42

5.11 Mesh Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-43

5.12 Meshing by Parts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-46

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5.13 Generating the Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-47

CHAPTER 6 Materials . . . . . . . . . . . . . . . . . . . . . 6-16.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.2 The Materials Database . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.3 Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

6.4 Solids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

6.5 Surface Parts (Shells). . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22

6.6 Resistances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-32

6.7 Internal Fans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-47

6.8 Centrifugal Pump/Blower . . . . . . . . . . . . . . . . . . . . . . . . . 6-54

6.9 Check Valves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-59

6.10 Rotating Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-61

6.11 Compact Thermal Model . . . . . . . . . . . . . . . . . . . . . . . . . . 6-66

6.12 Printed Circuit Boards. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-72

6.13 Graphical Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-79

6.14 Feature Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-79

CHAPTER 7 Motion . . . . . . . . . . . . . . . . . . . . . . . 7-17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.2 Guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7.3 Linear Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

7.4 Angular Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-18

7.5 Combined Linear/Angular Motion . . . . . . . . . . . . . . . . . . . . 7-34

7.6 Combined Orbital/Rotational Motion . . . . . . . . . . . . . . . . . . 7-45

7.7 Nutating Motion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-53

7.8 Sliding Vane Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-63

7.9 Free Motion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-70

CHAPTER 8 Analysis Options . . . . . . . . . . . . . . . . 8-18.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.2 Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

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8.3 Compressibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

8.4 Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

8.5 Optional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6

CHAPTER 9 Analyze . . . . . . . . . . . . . . . . . . . . . . 9-19.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

9.2 The Analyze Dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

9.3 Analyze Mode: Steady State or Transient . . . . . . . . . . . . . . . 9-3

9.4 Transient Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

9.5 Save Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6

9.6 Analyze!. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10

9.7 Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14

9.8 Analysis Queue (Batch Mode) . . . . . . . . . . . . . . . . . . . . . . . 9-14

9.9 Analysis Intelligence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15

9.10 Manual Convergence Tools . . . . . . . . . . . . . . . . . . . . . . . . . 9-21

9.11 Advection Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-22

9.12 Result Output Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . 9-23

9.13 Convergence Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25

CHAPTER 10 Review . . . . . . . . . . . . . . . . . . . . . . . 10-110.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

10.2 Convergence Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

10.3 Monitor Points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5

10.4 Notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8

10.5 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18

10.6 Animate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19

10.7 Report Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-20

CHAPTER 11 Viewing Results . . . . . . . . . . . . . . . . . 11-111.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1

11.2 Results-Specific Icons . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2

11.3 Feature Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-6

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11.4 Entity Blanking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-12

11.5 Results Probing on Surfaces . . . . . . . . . . . . . . . . . . . . . . . 11-12

11.6 Color Legends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-13

11.7 Cutting Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-14

11.8 Cutting Plane - Particle Trace. . . . . . . . . . . . . . . . . . . . . . . 11-27

11.9 Cutting Plane - Bulk Data . . . . . . . . . . . . . . . . . . . . . . . . . 11-36

11.10Cutting Surface - XY Plot . . . . . . . . . . . . . . . . . . . . . . . . . 11-37

11.11Iso Surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-43

11.12Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-44

11.13Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-47

11.14Dynamic Images: Design Communication. . . . . . . . . . . . . . 11-50

11.15Design Review Center (DRC) . . . . . . . . . . . . . . . . . . . . . . 11-56

CHAPTER 12 Results to FEA Loads . . . . . . . . . . . . . 12-112.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1

12.2 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1

12.3 FEA Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3

12.4 Transfer of Multiple Time Steps . . . . . . . . . . . . . . . . . . . . . 12-6

CHAPTER 13 Projects . . . . . . . . . . . . . . . . . . . . . . 13-113.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1

13.2 Definitions and Requirements . . . . . . . . . . . . . . . . . . . . . . 13-1

13.3 Assembling a Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2

13.4 Managing Analyses in a Project . . . . . . . . . . . . . . . . . . . . . 13-5

13.5 Viewing Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-9

13.6 Design Review Server . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-12

CHAPTER 14 Analysis Guidelines . . . . . . . . . . . . . . 14-114.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1

14.2 Incompressible Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-2

14.3 Basic Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-7

14.4 Porous Media Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-11

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14.5 Multiple Fluids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-15

14.6 Boundary Layer Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-16

14.7 Periodic Boundary Conditions . . . . . . . . . . . . . . . . . . . . . . . 14-16

14.8 Transient Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-20

14.9 Height of Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-21

14.10Moist/Humid Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-22

14.11Steam/Water Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-23

14.12Radiation Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-24

14.13Solar Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-40

14.14Compressible Flows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-46

14.15Joule Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-51

14.16Motion Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-53

14.17Rotating Regions: Turbomachinery . . . . . . . . . . . . . . . . . . . 14-55

14.18Moving Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-64

CHAPTER 15 Troubleshooting. . . . . . . . . . . . . . . . . 15-115.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1

15.2 Problems between CAD and CFdesign . . . . . . . . . . . . . . . . . 15-1

15.3 Problems During Meshing . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4

15.4 Startup Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-8

15.5 Divergence Before Iteration 10 . . . . . . . . . . . . . . . . . . . . . . 15-11

15.6 Divergence After Iteration 10 . . . . . . . . . . . . . . . . . . . . . . . 15-11

15.7 Divergence Later in the Analysis . . . . . . . . . . . . . . . . . . . . . 15-12

15.8 Oscillating Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-12

15.9 Contacting Technical Support . . . . . . . . . . . . . . . . . . . . . . . 15-13

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CHAPTER 1 Getting Started

1.1 Introduction

Congratulations and thank you for choosing CFdesign as your Upfront CFD Solution!

CFdesign 9 represents a major step forward for all engineers responsible for prod-ucts that incorporate fluid flow and heat transfer. CFdesign is a design tool, and incorporates many features that make flow analysis a valuable and practical part of the product design process.

CFdesign has been developed from day one for multi-faceted product development teams using MCAD tools such as Pro/Engineer, CATIA, Autodesk Inventor, Solid Edge, Unigraphics, Solid Works, and many others. Powered by proprietary numeri-cal techniques and leading-edge computational methods, CFdesign features a true associative relationship with components and assemblies, and automatically applies the optimal mesh required for accurate fluid and thermal simulations.

The principal Value Drivers of CFdesign are summarized below:

A Tool for the People No specialist skills are required

Collaborative software leveraged by an entire team

Process Continuity CFdesign fits into existing MCAD-driven workflow

Overhead Reduction Department-level expenses decrease

Notable savings in staff time, materials, and need for outside services

Innovation Gateway Allows rapid exploration of new ideas

Promotes better understanding of produce perfor-mance

CFdesign User’s Guide 1-1

Getting Started

1.2 Overview of Upfront CFD

CFdesign is built upon the Upfront CFD Solution Platform. The platform is shown:

There are six fundamental pillars of Upfront CFD, each shown as a separate item in the graphic. Each pillar represents a part in the process of performing a CFD analy-sis. The most significant aspect of this concept is that the process is repeatable--multiple design iterations can be analyzed, compared, and communicated with those in the design chain efficiently and effectively. Each pillar is described in more detail below:

CAD Integration

Starting in the CAD system of your choice, the component or assembly model you build is all CFdesign needs to deliver a reliable fluid flow and heat transfer simula-tion. A direct link to the major geometry engines eliminates the need for IGES, STEP, or STL. Make a change to the model in your CAD system, and the change will be a part of the CFdesign analysis.

1-2 CFdesign User’s Guide

Getting Started

Gettin

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d

Mesh Generation

CFdesign employs finite element mesh generation with numerous intelligent algo-rithms to make the process automatic and transparent. By using automatic, unstructured meshing, CFdesign quickly meshes complicated (real world) geometry without forcing the user to become an expert in the application of mesh generation tools. Assignment of the mesh distribution to geometry is virtually automatic, and is based on a highly detailed geometric interrogation of the geometry.

Tools such as Shell surfaces allow significant reduction in overall mesh sizes by allowing the inclusion of solid surfaces within three dimensional volumes. Mesh Enhancement automatically refines the mesh to focus nodes and elements in areas of high physical gradients. Finally, new technology has been developed to mesh large assemblies more efficiently, using less computational resources.

Simulation Scope

CFdesign solves the mathematical equations which represent heat and momentum transfer in a moving fluid. The finite element method is used to discretize the flow domain, thereby transforming the governing partial differential equations into a set of algebraic equations whose solution represent an approximation to the exact (and most often unattainable) analytical solution. The numerical formulation is derived from the SIMPLER solution scheme introduced by Patanker1. More detail is available in the Technical Reference.

The influence of Fluid-Structure Interaction is a very significant element in many mechanical devices. The CFdesign Motion Module brings this capability to the world of product design as a key element of Upfront CFD. Through simulation, this Module allows understanding the interaction between fluids and moving solids to be inte-gral to the product design process.

The flow analysis is often just the beginning in many analysis-design projects. Results from CFdesign can be applied as structural boundary conditions for subse-quent analysis with many popular FEA packages. Aerodynamic and hydrodynamic- induced pressures as well as temperatures can be interpolated directly onto the FEA

1. Patankar, S.V., Numerical Heat Transfer and Fluid Flow, Hemisphere Publishing, New York, 1980


Getting Started

mesh. This very powerful capability completes the “analysis circle,” and is a major integrating factor of CFdesign into the Design Supply Chain.

Simulation Speed

The intuitive user interface in CFdesign makes setting up the simulation very easy. Using engineering language, the user simply applies the material and operating conditions that are needed. Combined with many intelligent algorithms, analysis set-up is fast and easy for users with no CFD experience.

In many design situations, running many “what if” scenarios is the key to the opti-mal design. Because of time constraints, a single license often just won’t get the job done. With the Fast Track Option, our on-demand licensing plan, engineering groups can temporarily ramp up their analysis capability in order to get the job done quickly. Unlike an ASP or “main frame” scheme, this system allows engineer-ing groups to utilize in-house computer resources without having to send out pro-prietary data over the internet.

Design Review

Results are displayed at every step of the calculation. The user can interact with the model, and view results real-time using cutting planes, iso surfaces, xy plots, and particle traces.

Because CFdesign is a design tool, it is very important that results from multiple analyses be viewed, compared, and contrasted easily. The Design Review Center makes it easy to get a true apples-to-apples comparison between all of the analy-ses in your project.

Project Collaboration

Sharing results with other members of the design supply chain is easy using the Dynamic Image, a part of the Design Communication Center. Using our free plug in, interactive images can be viewed in PowerPoint, Word, and Internet Explorer. The person viewing a Dynamic Image can pan, zoom, and rotate the model, to see your results from every angle.


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1.3 Documentation

There are three books that make up the CFdesign documentation. They are:

This book, the User’s Guide, contains the following chapters:

Book Description

User’s Guide The fundamentals. Discusses geometry require-ments, the user interface, and analysis techniques

Examples Guide Tutorial models in a step-by-step format.

Most facets of using CFdesign are covered.

Technical Reference Verification models, underlying theory, and Script-ing language

Chapter Description

Chapter 1: Introduction Introductory information

Chapter 2: User Inter-face

The CFdesign User Interface is described.

Chapter 3: Geometry Discusses required geometry, some things to avoid, and “inversion” techniques to obtain the flow volume

Chapter 4: Loads Boundary Conditions and Initial Conditions

Chapter 5: Mesh Sizes Mesh sizes and guidelines

Chapter 6: Materials Creating and Assigning materials

Chapter 7: Motion Creating and Assigning solid-body motion

Chapter 8: Analysis Options

Flow parameters

Chapter 9: Analyze Running the analysis, the Fast Track option

Chapter 10: Review Assessing convergence, animation, Report Gener-ation

Chapter 11: Viewing Results

Results Visualization tools; Dynamic Images

Chapter 12: Results to FEA Loads

How to map CFdesign results as loads for FEA analyses


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1.4 Product Configurations

CFdesign Solver comes in three different functionality configurations: Basic, Advanced, and Motion.

Chapter 13: Projects Using projects for setting up multiple analyses; Visualizing results on projects using the Design Review Center

Chapter 14: Analysis Guidelines

Application-specific information

Chapter 15: Trouble-shooting

Problem explanations and solutions

Basic Solver FeaturesAdditional Advanced Features Motion Features

Incompressible and Sub-sonic

Compressible

Full compressible Rotating machinery

Laminar flow Scalar models

(general scalar, steam/water, moist air, vol-ume filling)

Moving objects: Linear, angular, combined lin-ear/angular, orbital, nutating, and sliding vane motion

Turbulent flow Transient Flow-induced Motion

Heat Transfer

(conduction and convection)

Radiation Free Motion with auto-matic collision detec-tion

Steady State Joule Heating

Solar Heating

Chapter Description


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1.5 Starting CFdesign

Direct launchers for Pro/Engineer, Inventor, Solid Edge, and Solid Works are included in the CFdesign installation. Additionally, a new analysis can be created from a Parasolid or Acis file by launching CFdesign from the Desktop or Start Menu. The details of how to use each launcher are discussed in the following table:

1.5.1 New Analysis

A new analysis is always created from geometry.

Pro/Engineer Click Applications_CFdesign

CATIA V5 Click the CFdesign icon in the CATIA Toolbar:

Autodesk Inventor

Click Tools_InventorCFdesign_Launch CFdesign

Solid Edge Click the CFdesign icon in the Solid Edge Toolbar:

Solid Works Click the CFdesign icon in the Solid Works Toolbar:

UGNX Analysis_Launch CFdesign 9.0:

Parasolid (.x_t) or Acis (.sat) file

Start CFdesign from the Desktop using the CFde-sign shortcut icon:


Getting Started

When CFdesign is launched from a CAD system, the following dialog will prompt for an analysis name:

The analysis name can (and often should) be different from the CAD part or assem-bly name. The reason is to allow multiple analyses based on the same CAD model to co-exist in the same directory and not overwrite each other, even though the geometry has changed from one analysis to the next.

When CFdesign is launched from the Desktop to create a new analysis from an existing Parasolid or Acis file, hit the New icon in the CFdesign Toolbar:

and the following dialog will come up:

Make sure the Analysis bullet is selected. Select the desired geometry file (its name will appear in the File Name field after it is picked), and enter an analysis name in the Analysis Name field. Hit OK.


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1.5.2 Existing Analysis

Existing analyses are opened using the Open icon in the toolbar:

The file extension for an existing analysis is “.cfd”. Make sure the Analysis bullet is selected near the bottom of the dialog box.

The only time it is required to open an existing analysis from the CAD system is if the geometry is from Pro/Engineer, AND you intend to construct a new mesh. Oth-erwise, always open existing analyses by starting CFdesign from the Desktop or Start menu, hitting the Open icon, and selecting the desired “.cfd” file. Note: if an existing analysis is launched from the CAD system and run, a new mesh will be generated, even if the mesh definition is not changed.

1.5.3 Projects

A project is a collection of analyses--in the same way an assembly is a collection of parts in most CAD tools. Projects have two primary functions: to facilitate model set up for similar analyses and to facilitate post-processing of similar analyses. Both functions are described in Chapter 11 of this Guide.


Getting Started

Note: An analysis is ALWAYS created from geometry--when CFdesign is launched from a CAD tool, an analysis is always either created or opened. It is NOT possible to go from a CAD system (or a Parasolid or Acis file) directly to a project.

A project can, however, be created or opened from within an open analysis (thereby making the analysis a member of the project):

The opposite is also possible: an existing analysis can be imported into a project.

Additionally, a project can be created or opened outside of an analysis by starting CFdesign and hitting the New or Open icon, respectively, and selecting Project.

More information is presented in the Projects chapter of this guide.

1.6 The Basic Process

This section briefly summarizes the process of setting up, running, and visualizing results with CFdesign. Starting CFdesign from various CAD systems with the direct launchers and from the Desktop is discussed in a prior section. After the analysis is named, the following general steps must be taken:

1. On the Feature Tree, set the Analysis Length Units system.2. Using the Loads Task Dialog, apply boundary conditions and, if required, initial conditions.3. In the Mesh Task Dialog, apply mesh sizes to volumes, and if required for local refinement, to surfaces and edges.

(2) Analysis

(3) Project

(1) CAD

Analysis

Project


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4. Switch to the Materials Task Dialog, and apply materials to all parts in the model. If necessary, create custom materials and add them to the Materials Data-base.5. If the analysis is to include moving solids, switch to the Motion task dialog, and create and assign the motion to the intended parts.6. Using the Options Task Dialog, select the physical model(s) to be used within the analysis.7. In the Analyze Task Dialog, input the number of iterations to run and the Results Save Interval. Hit GO to start the analysis.8. During the analysis, switch to the Results task dialog to view the results as they are calculated. Use the Convergence Monitor to keep an eye on the solution progress.9. When the analysis is finished, use the Review task dialog to assess the final convergence and to ensure that the solution is converged.10. Switch to the Results task dialog to view the results.11. Optional: add this analysis to a new or existing project. Return to the CAD sys-tem and modify the geometry. Launch back into CFdesign, and create a new analy-sis. Place this analysis into the project. Transfer the settings from the first analysis to this one, and run it.

While this may seem like a lot of steps, the User Interface is designed to guide the user through each, in the proper order. A separate icon controls each task dialog, and these icons are arranged vertically on the side of the User Interface. By simply starting at the top-most icon and working down, each task is performed easily and logically.

1.7 CFdesign Client-Server

1.7.1 Introduction

CFdesign is built upon a client-server model. The user interacts with CFdesign through the Interface Client (CFdesign.exe). When the command to start the analy-sis is given, a signal is sent to the Server (CFdserv9.exe) indicating that the analy-sis needs to begin. The Server in turn sends a signal to the Solver (cfdcalc.exe). This last step initiates the transfer of the model data from the Interface to the Solver and then instructs the Solver to commence with the calculation. While the analysis is running, the visual results are transferred from the Solver back to the


Getting Started

Interface to provide for the Run-Time Results Display. When the analysis is com-plete, the Server directs the Solver to send the final results back to the Interface.

On a stand-alone installation, this entire process is transparent to the user. After hitting Go, the analysis runs, the analysis data files are kept in the user’s working directory as the communication between the Server and the Interface and Solver clients is managed automatically.

1.7.2 Fast Track

This client-server model allows CFdesign users to run analyses on a remote (net-worked) computer. This kind of implementation is called Fast Track. The analysis model is constructed and meshed on the local computer (using the CFdesign Inter-face), but the actual calculation occurs on a remote computer. In this situation, the Server directs the Interface to put the analysis model files physically on the remote Solver computer for the calculation. When completed, the Server moves the files back to the Interface (User’s) computer.

1.7.3 Server Manager

For most installations, the Server is configured automatically during the installation process. However, there is a dialog that controls the operation of the Server. Located in the installation directory, this dialog is launched by clicking on serv-man.exe, and is shown:


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The Installation Directory is the CFdesign load point. The Analyze Directory, by default, is a sub-directory within the CFdesign installation but can be any writable directory on the local machine. This is where temporary files are written during the analysis. The Install button registers the Server as a Windows service. This causes the Server to start automatically every time the machine is started. The Installation and Analyze Directory fields are set during the installation. They can be changed manually, if necessary. Additionally, the Server is started for the first time during the Installation.

If the Server must be stopped (such as when installing an update to the Server), open this dialog, and click the Stop button. Be sure to start the service again after the new file is in place.

1.7.4 Installing on a File Server Computer

1.7.4.1 Introduction

CFdesign can be installed such that the installation files reside on a file server machine, and the User Interface and Solver run on users’ local machines. The server process called CFD Server 9 runs locally and manages the communication between the User Interface and the Solver (this is true for a single node installation as well). In this type of configuration, however, the service (running on the local machine) must run under an account that has read-only access on the file server machine. Otherwise, the service will not have the necessary privileges to send com-mands to the executable residing on the file server.

As part of every analysis, temporary files are written to an “analyze” directory located on the user’s machine. Additionally, a small program (the Server Manager) that configures and manages the server process must also be installed on each user’s computer. A separate installation program (ClientofFileServer.exe) is included on the installation CD that installs these items, and must be run on each user’s machine. This is very quick, and installs the Server Manager, creates a local Analyze directory, and creates the necessary environment variables.

1.7.4.2 Installation

As part of the software installation on the file server, be sure to check the Central-ized File Server Install box in the Select Features dialog.


Getting Started

After installing the software on the file server, create a domain user account for the service. (This may require assistance from your Information Technology or Techni-cal Support Group.) This can also be done between two machines within the same workgroup by creating the same account on both machines. This account should have read-write privileges in general, but can have read-only access on the file server. Additionally, this account needs the “Log On As A Service” privilege.

On each user’s machine, as administrator, run the ClientofFileServer.exe found on the Installation CD. This will prompt for:

• A directory on the local machine where the analyze directory and the Server Manager are to be installed.• The UNC path of the CFdesign network installation.• The account name and password of the service account.

If the service account is not automatically granted the “Log On as a Service” right, then it may be necessary to manually perform the following steps on the client machine:

• Starting the Control Panel,• Go to Administrative Tools,• Select Services.• Click on the Cfd Server 9 service.• On the Properties dialog, click the Log On tab.• Click the “This Account” bullet, and enter the account login name and password.• Click Apply.

1.8 CFdesign File Types

Here is a list of files saved for each CFdesign analysis:

Extension Description

cfd The analysis file. All settings, results, and analysis parameters are stored in this file. Parasolid and Acis based geometries are included in this file.

cts Component thermal summary. Lists average, maximum, and minimum temperatures for every part in the model.


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dccrt Report template information. Stores report layout and content info for each analysis. (Reports are modified using the Report dia-log on the Review task.)

res.s# Results file. Binary file containing raw results data from iteration #. This file does not have to be in the working directory to view results, but is required to continue an analysis.

set Setting file. Contains all of the settings applied within an analysis model.

sol Solver file. Contains convergence data for each degree of free-dom for each iteration.

st Status file. Contains a record of the analysis process and error and warning messages, if a problem occurs. Lists residual values for each iteration.

sum Summary file. Contains quantitative information about the analy-sis.

smh Summary history file. This contains all of the summary files from all re-starts.

_client.log Client log file: record of actions taken by the Interface. Describes communications and actions performed before, during, and after an analysis.

_gcp.bmp Bitmap file of Summary Convergence data. Automatically created for use by the Report Generator.

_mesh.log Mesh log file: record of meshing steps. Good file to examine if meshing problems occur.

_mi.vtf Model Image file: Dynamic image of analysis model. Automati-cally created for use by the Report Generator.

_model.log Model log file: Contains geometry-related error messages. Good file to examine if problems occur when reading geometry into CFdesign.

_s.cfd Support file: Automatically created copy of the cfd file containing only settings and geometry (parasolid and acis). Does not contain mesh or results. Useful as a way to share analysis with other team members or with Technical Support.



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Some additional files of interest:

1.9 Compatibility with CFdesign 8

Open your v8 analysis directly into v9. The settings should all migrate into the v9 format. Any settings that were lost due to changes in the Parasolid or Acis geome-try kernels will be listed in the Lost List. This list is accessible by clicking the Show Lost button on the appropriate dialog. If the Show Lost button is not visible, then the migration to v8 did not incur any errors.

Note that for best results, the v8 analysis should be saved in the latest version of v8. For Pro/E analyses, this means that the analysis should have been launched and saved into the latest version of v8. Importing analyses from earlier builds of v8 may result in a few lost settings.

_solver.log Solver log file: Contains a record of actions taken by the Solver. Describes communications and actions performed before, during, and after an analysis.

_partname_motion.cs

v

Motion Summary File: Generated for Motion analyses. Contains a time-summary of the forces, displacements, and velocities of moving solids.


pjt Project file. This lists the analyses in a project.

mdb Material database file. Can be modified and placed in a location of choice. Use File_Preferences to indicate default location.

vtf Dynamic image file

vus View settings file



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1.10 Contact Information

For those customers that have purchased CFdesign directly from Blue Ridge Numerics in the United States and Canada, please contact us for support and licensing using:

For those customers that have purchased CFdesign directly from Blue Ridge Numerics in Europe, please contact us for support and licensing using:

For those customers that have purchased CFdesign directly from Blue Ridge Numerics in Asia, please contact us for support and license using:

Target Number or Address

Phone Support 434.977.2764 (Support = Option 3)

Fax Number 434.977.2714

Support e-mail [email protected]

License Request [email protected]

Sales e-mail [email protected]

web site http://www.cfdesign.com

ftp site ftp://ftp.cfdesign.com


Phone Support +44 (0) 1628 501 570 (Option 2)

Fax Number +44 (0) 1628 826 768


Password Request [email protected]





Phone Support +1 434.977.2764 (Support = Option 3)

Fax Number +1 434.977.2714


Getting Started

Blue Ridge Numerics also has a strong reseller network throughout Europe and Asia. If you purchased CFdesign through a reseller, please contact that reseller directly for support and licensing.








CHAPTER 2 The User Interface

2.1 Introduction

This chapter describes how to use the CFdesign User Interface without going into the technical specifics of the fluid flow and heat transfer analysis process. (This is discussed in later chapters.) Details about customization, the tool buttons, the fea-ture tree and dialog regions as well as entity selection and groups are covered in this chapter.

2.2 The Basics of the User Interface

Graphics

Feature Tree

Task Dialog

File Tool Bar

Region

Display Tool Bar

MenuRegion

Task Tool Bar

Status Bar


The User Interface

The model is shown in the Graphics Region. The background color can be changed using the Background Color tool button (described in the next section).

The File Tool Bar at the top controls file manipulation activities--Creating, Opening, and Saving files. The Display Tool Bar controls the display of the interface and the model. The Task Tool Bar controls which task dialog shows in the Task Dialog Region. The Feature Tree lists the applied parameters, and can be used to modify applied conditions (loads and mesh sizes). Additionally, it is used to control the dis-play of individual parts and materials in the model, and to control the display of results quantities.

The Menu Region contains commands for file manipulation and for setting prefer-ences. The main Help menu is also in the Menu Region. The Task Dialogs contain commands for setting up the analysis.

The default arrangement of the interface is shown in the above graphic. The display and location of the Horizontal Tool Bar, the Feature Tree, and the Task Dialog Region is customizable. To hide any of the entities, single click on the top bar of the Task Dialog Region (or left side of the tool bars):

To resume a hidden object, click on the double lines under the Menu region:

Each of these items can be undocked (moved to a different location) by dragging on the double lines with the left mouse button. If the object is released near an edge of the graphics window, it will become docked (will not block a displayed model). If

Windows2000

WindowsXP


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an object is released away from an edge, then that object will become separate, and will have its own title bar. It can be moved to any desired location, and can occlude the graphics window.

An object can also be hidden by clicking the “X” in the upper right corner. To resume a closed object, right click anywhere on another object (Feature Tree, Task Dialog Region, or Tool Bars), and a menu will appear:

Check the desired object to open it again. Additionally, an object can be hidden by unchecking it on the list.

2.3 Tool Buttons

This section describes the tool buttons on the File and Display Tool Bars. Some additional buttons appear in Results Display mode, and are discussed in the Results Visualization Chapter (11).

NewOpen

Add to Project

Save AnalysisSave Image

Save VTF

Outline ImageShaded Image

Center of Rotation

Reset ViewZ-Clip

Incremental RotationZoom

Previous View

Wireframe NavPerspective View

Coordinate AxisBackground Color

(dynamic image)

Transparent Image

Zoom to Fit


The User Interface

Left: New. This icon is used to create a new analysis or project.Right: Open. This icon is used to open an existing analy-sis or project.

Put the current analysis into a project. This is displayed when an analysis is open, and when pressed, the user is prompted to enter a new project name or to select an existing project.

Bring an analysis into the current project. This is dis-played only when a project is open, and when pressed, the user is prompted to select an analysis to add to the project.

Save the current project. This is displayed only when a project is open. Hitting this icon saves the project and all analyses within the project. (Note: analyses are saved automatically when the software is exited.)

Save the current analysis. When only an analysis is open, this saves the analysis. When a project is open, this saves only the current analysis. (Note: analyses are saved automatically when the software is exited.)

Save image. This saves a jpeg, bitmap, gif, or tif image of the current contents of the Graphics Region.

Select the file type from the Format field, and use the Browse button to specify the destination path and the name of the file. Click Ok to save the image.


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Save Dynamic Image. This saves a “.vtf” file, which is an image that can be viewed in the free viewer distrib-uted with CFdesign. It can also be viewed in PowerPoint, Word, or Internet Explorer if the free plug-in is installed (details in the Results chapter). Unlike a “traditional” image, this image is navigable--it can be panned, rotated, and zoomed.

View as Shaded. The model is shown filled.

View as Outline. The model is shown as an outline.

View as Transparent. The model is shown transparent.

Center of Rotation. This icon launches the following dia-log: Use the slider bars to adjust the center of rotation of

the model. While this command is active, a sphere is drawn on the model, graphically indicating the center of rotation.

Reset View. The model is returned to its default orienta-tion.


The User Interface

Z-Clip and Crinkle Cut Launches the Z-Clip dialog:

Use the slider bars to clip into the model. Parts of the model that are between the plane and the user are made invisible. The following is an example of a clipping plane:

For some models with close parallel surfaces, reducing the Mesh Factor increases the visual clarity of the clipped display.Crinkle Cut is a way to view the mesh inside of the model, and is available in Results Viewing.

Standard Views and Incremental Rotation. This icon launches the following dialog:

The Standard View buttons orient the model using the Cartesian coordinate system. The slider bars rotate the model in discrete increments about the screen axes (pos-itive x is to the right, positive y is up, and positive z is out of the screen), not the model axes.


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Left: Zoom. After clicking this icon, hold down the left mouse button and drag a box around the region to zoom. Release the button when finished dragging. The icon must be clicked again to zoom again.Right: Previous View. Returns the model to the previ-ous orientation and zoom.

Wireframe Navigation. When enabled (pressed in), the model will navigate in outline mode. When disabled, the model display does not change when navigated.

Perspective View Toggle. When enabled, model is shown in Perspective View.

Coordinate Axis Toggle. When enabled, the model coordinate axis and the axis bounding box are shown.

Note: Several functions in the Results task as well as Monitor Points use model coordinates. These coordinates are referenced from the model coordinate axis, which is positioned at the model origin.

Background Color Selection. This dialog allows the background color as well the color scheme to be modi-fied: the colors can be varied from top to bottom, toward the corners, in a radial pattern, or as a constant. A full color palette assists in color selection.

Zoom to Fit. This rescales the model to fit entirely in the Graphics window. The orientation is preserved, but the model is centered within the Graphics window. This is a useful feature when navigating the model extensively to reset the location and size.

model coordinate axis

bounding box axis


The User Interface

2.4 File Menu

2.4.1 _New, _Open

These menu items serve the same function as the New and Open tool buttons.

2.4.2 _Save Analysis, _Save Project

These items perform the same function as the Save Analysis and Save Project tool buttons.

2.4.3 _Save Analysis As

Saves a copy of the current analysis to a new name and/or location. Note that the newly created cfd file is opened, and the originally opened cfd file is saved and closed.

2.4.4 Output_Support

Outputs a version of the cfd file that contains just the settings and the geometry, but no mesh or results. This is a very small file, and is suitable for e-mailing to our CFdesign Technical Support Engineers. Such a file has an “_s” appended to its name.

2.4.5 Output_Results Share

A “.cfd” file containing the settings and results, but not the mesh. This is useful for sharing your entire results set with someone else in the organization because it is significantly smaller than the original cfd file. If the user opens such a file, they will be able to view results, but not run. Hitting Analyze_Go will result in the mesh being generated, and the solution starting back at iteration 0. Results Share files have an “_r” appended to the original analysis name.


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2.4.6 Output_Archive

An Archive file contains the settings, mesh, and only the last saved results set. This is useful for analyses in which numerous results or time steps were saved dur-ing the run, but only the last set needs to be saved. Also, the last results file (job-name.res.s# or jobname.res.t#) is saved. An “_a” file can be continued simply by hitting Analyze_Go. This file is most suitable for archival purposes IF intermediate result sets or time steps are not required.

2.4.7 _Export

CFdesign can write out the model and results in several formats for use in other tools. Prior to Version 8, data was saved in these formats by setting a flag entry in the external flags file. This menu contains the following output file formats:

_Universal Mesh Exports only the mesh in Ideas Universal file format

_Tecplot Results Exports the results in Tecplot file format

_FieldView Results Exports the results in FieldView file format

_Nodal Results Exports the results on every node in the model (csv format)


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2.4.8 _Preferences_User Interface

This is a way to set preferred defaults and to customize the interface. The Prefer-ences dialog is shown:

Modifiable Parameter Description

Dialog Placement Sets the default location of the Dialog Region. Select the left or right side of the interface. If the Feature Tree is positioned on the same side, then the Top and Bottom bullets become active, allow-ing placement near the top or bottom of the interface.

Feature Tree Placement Sets the default location of the Feature Tree. Select the left or right side of the interface. If the Dialog Region is positioned on the same side, then the Top and Bottom bullets become active, allowing placement near the top or bottom of the interface.


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Material database This sets which materials database CFdesign reads. (The default material database is the one included in the CFdesign installation folder.) If your organization uses custom materials, this option allows use of a centrally located materials database.

Report Settings The items in the Report Settings section allow control of several parameters affecting Report generation. Use these settings to specify the locations and names of the default analysis and project report templates, to locate a corporate logo file and to set a user name. A set of default templates are included in the CFdesign installation folder, and the default User Name is the account login name. The default logo is left blank. These items are described in detail in the Review chapter of this manual.

Background Color The two default choices are black and white. Use the Background color icon to further customize the background color.

Startup Length Units The choices are the standard length units sys-tems: meters, cm, mm, feet, inch-BTU/s, and inch-Watt.

Perspective view Choose to enable perspective view or disable it.

Navigate as wireframe Choose to navigate in outline mode or in the cur-rent display mode.

Navigation Mode Choose mode 1 or mode 2. These modes are described in the next section (Navigation).

Preserve Blanking when Change Selection Mode

“Yes” causes blanking to not reset when the selection mode is changed.

Blank Edges when Blank Volumes

“Yes” causes edges to blank when the associated volume is blanked. This is especially useful for very complex geometries.

Show Coordinate Axes “Yes” displays the coordinate axes by default.

Modifiable Parameter Description


The User Interface

All settings are invoked as soon as OK is hit. The exception is the Startup Length Units, which is applied only when an analysis is created

2.4.9 _Preferences_Settings Rules

Many analysis models are based on assemblies having multiple instances of the same part. Every instance of the part typically has the same settings, and are used repeatedly in numerous analyses.

This feature allows the automatic assignment of a volumetric boundary condition and a material based on the part name. For many analysis models this feature will greatly simplify and streamline the set-up process because it automates application of key volumetric settings to a large number of parts, eliminating the burden of having to apply a large number of settings manually. This feature should greatly impact electronics cooling analyses in particular due to the large number of repeated parts in electronic devices.

Rules defined with this dialog are automatically applied when an analysis is created if the “Apply” box is checked. Rules are not automatically applied when an existing analysis is opened.

Settings that can be applied as rules include volumetric boundary conditions and materials that do not require any directional inputs in their definitions.

Settings rules are stored with other preferences in the cfdesign90.usr file. This file is contained in the Documents and Settings\account\.cfdesign folder, where account is the name of login account.

2.4.9.1 Boundary Conditions

Heat generation and Total heat generation conditions can be applied as settings rules. Conditions can be defined as steady state or transient, and can be assigned as temperature dependent. Note that temperature dependent conditions use the temperature of the local part (and not a remote location) as the sensing location.

2.4.9.2 Materials

The materials available for application as settings rules are:

• Fluids


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• Solids• Compact Thermal Model component• Printed Circuit Boards

Note that materials must currently exist in the Materials database before they can be used in a setting rule.

2.4.9.3 Usage

To define a settings rule, click File_Preferences_Settings Rules. The Settings Rules dialog will open:

To create a new rule:

1. Click the New button, and specify the name of the rule when prompted.

2. Specify the part name or a portion of the part name in the Part Name field. The rule will be applied to parts that contain the specified name as a part of the com-plete name.

3. Define settings that will be applied to every part having or containing the speci-fied part name

4. Check the Apply box to automatically apply the rule when a new analysis is cre-ated.

5. Click the Save button to save the rule.

6. Optional: Click the Apply Now to apply the rule to the current model.

7. Click the Exit button to close the dia-log or specify an additional rule by clicking the New button and repeating the process.

Step 2

Step 3

Step 5

Step 4

Step 7

Step 1

Step 6


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To modify an existing rule:

1. Select the desired rule from the Rule Name menu.2. Make changes as necessary.3. Click the Save button.Click Exit to close the dialog.

To copy an existing rule to a new rule:

1. Select the desired rule from the Rule Name menu. 2. Click the Save As button.3. Enter a name for the new rule.

Click Exit to close the Settings Rules dialog.

To delete a rule:

1. Select it from the Rule Name menu.2. Click the Delete button.

2.4.10 _Preferences_Results Units

Use this dialog to specify the default units of result scalars. In previous versions, the units for any result scalar can be changed by right clicking on a scalar quantity, selecting Units, and picking the desired unit system. Many companies have guide-lines dictating how results are communicated internally, so in some cases, it was necessary to always manually change the unit for displayed result quantities.

This dialog allows default units to be defined.


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The dialog appears below:

The units for each quantity are listed in the adjacent combo menu.

The choice “Default” is the first item for every quantity, and is shown if no unit sys-tem is selected. Quantities with the “Default” selection are displayed using the default units of the current units system.

The default units selected for a quantity will be applied to all related quantities as well. For example, if the mm/h is selected as the default for velocity, then all veloc-ity components as well as absolute velocity (and components) will be displayed in mm/h. Related quantities are shown in the table:

Velocity Velocity Magnitude

U-Velocity

V-Velocity


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2.4.11 _Analysis Notes

When conducting design studies, keeping accurate records about each analysis is very important, especially when comparing results from a large number of models. Recording the specific conditions of an analysis, as well as any adjustments and important findings, is key to repeatability and organization of a large project.

Every engineer has their own particular way of maintaining information about their analysis models. Some use spreadsheets, some use notebooks, and some use

W-Velocity

Absolute Velocity Magnitude

Absolute Velocity in X-dir

Absolute Velocity in Y-dir

Absolute Velocity in Z-dir

Pressure Static Pressure

Total Pressure

Absolute Static Pressure

Viscosity Viscosity

Effective Viscosity

Conductivity Conductivity

Effective Conductivity

Temperature Temperature

Total Temperature

Shear Stress Shear Stress

Wall Shear Stress


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scraps of paper. The CFdesign Notes file is a useful addition to the engineer’s record-keeping tool-kit for, and is kept within the analysis file itself:

Located in File_Notes, the Notes text editor provides a convienent way of record-ing information about a particular analysis. The contents of the file are internal to the analysis “cfd” file, so they can be easily accessed after the analysis is archived. An external copy of the file can be saved by clicking the Save button.

Modifications made to the text file outside of CFdesign will not be accessible in the CFdesign interface. This option is provided to save a copy of the notes to allow quick access without having to open the “cfd” file.

2.4.12 _Print

A print utility has been added to the File menu to allow printing the image in the Graphics window to either a file or to a printer. The background color is automati-cally set to white, and text is shown as black for visibility.


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To use this, click File_Print. The Print dialog will open:

There are several options that allow printer selection, printing to a file, and the number of copies. Click the Preferences button for additional options controlling the page layout, size, and printer options.

Click the Print button to send the job to the printer.

2.4.13 _Recent Analyses

The last five most recently opened analyses are listed. Click on one to open the file. This improves the work-flow by allowing quick selection of an analysis that was recently opened.

2.4.14 _Recent Projects

The last five most recently opened projects are listed. Click on one to open the file. This improves the work-flow by allowing quick selection of an analysis that was recently opened.


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2.4.15 _Exit

Closes the CFdesign User Interface. If the analysis is not running, it will be auto-matically saved. If an analysis is running, the Exit command shuts down only the Interface--the analysis will continue to run.

2.5 Help

The CFdesign Help System has been overhauled to make it much easier to use and to provide a comprehensive set of information directly and conveniently to the user. The complete documentation set has been integrated with the CFdesign product, and is accessed on a context-sensitive basis using the Help button on every dialog in the Interface. The complete manual set is also accessible from the Help menu item from the Main Menu.

All manuals are packaged in Adobe “pdf” format. The Adobe Acrobat Reader is included with the CFdesign interface, and is opened when Help buttons or items in the Help menu are selected. The manuals can also be viewed outside of CFdesign using Acrobat Reader. Note that the documentation is fully indexed, and includes a table of contents. Acrobat Reader includes full search capability as well.

Most dialogs in the CFdesign User Interface contain a Help button. Pushing a Help button opens the User’s Guide to the appropriate location to describe the relevant dialog or function.

2.5.1 _CFdesign Help Topics

Opens the User’s Guide in Acrobat Reader. The Guide is fully indexed, and includes a table of contents. Links within the document connect sections and chapters where appropriate.

2.5.2 _On-Line Tutorial

Opens the CFdesign Examples Guide. Presented in Acrobat Reader, the Guide has been formatted so that it can easily be positioned adjacent to the CFdesign inter-face while working through the examples. This is a convenient resource for learning how to operate CFdesign.


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2.5.3 _Technical Reference

Opens the CFdesign Technical Reference. This manual contains the suite of Verifica-tion analyses as well as a detailed description of the theoretical foundation of CFde-sign.

2.5.4 _Release Notes

Opens the Release Notes which contains detailed descriptions of new functionality in the current version.

2.5.5 _Check for Updates

Connects to the Download site of the User Portal. This area contains the current and all previous releases of CFdesign v9. This is a great place to check for the latest build as updates are released.

A user account is required to access the User Portal. If you do not have an account, please follow the instructions on the User Portal dialog.

2.5.6 _Knowledge Base

Connects to the on-line CFdesign Knowledge Base and User Portal. This highly use-ful resource contains up-to-date, topical information about using CFdesign as well as the current bug list.

2.5.7 _About

Shows the build number of the current installation. You may be asked for this by a CFdesign Technical Support Engineer.

2.5.8 _Licensing

This item brings up a dialog that shows the current license status. This is a very useful tool for troubleshooting license problems. The dialog indicates which license


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server the software is looking to for a license. It also indicates the number of Inter-face and Solver licenses available.

The Preferences button brings up a dialog that allows selection of a specific func-tionality level if the floating (network) license contains a combination of different functional levels.

To provide a high level of flexibility in licensing for larger installations with network licenses, CFdesign includes the ability to check out a specific funtionality tier from a mixed pool of licenses.

For example, if a corporate site-license includes four Advanced licenses and one Motion license, this function allows the user to select a Motion license only when the Motion functionality is required. For analyses that do not include solid-body motion, the user would select an Advanced license. This would leave the Motion licenses available for other engineers that do need the Motion capability.

For a heterogeneous CFdesign license (a license that contains seats with different funtionality levels), the License Preferences dialog will pop up automatically when CFdesign is started:

This dialog lists the licenses that are available, and prompts the user to select which type of license they will use. If, for example, Advanced is selected, then the Motion functionality will be unavailable in the CFdesign interface. If Motion is selected, the Motion license is checked out, and the Motion functionality will be available. (Note that Motion includes the advanced functionality set as well.)


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By default, this dialog will appear every time CFdesign is started. Uncheck the check box to make the setting permanent (and to prevent the dialog from display-ing every time). To change the setting simply click Help_Licensing_Preferences.

For node-locked licenses and homogeneous network license (meaning that all of the seats are at the same functionality level) the License Preferences dialog does not appear. No input is required for such a license installation.

2.6 Navigation

There are four mouse navigation modes. The default is mode 1:

Navigation Mode 1 Navigation Mode 2

Ctrl + Left Mouse Button = zoom Left Mouse Button = zoom

Ctrl + Middle Mouse Button = rotate Middle Mouse Button = rotate

Ctrl + Right Mouse Button= pan Right Mouse Button = pan

Scroll Wheel = zoom Scroll Wheel = zoom

Left Mouse Button = select/deselect (when in a command)

Cntl + Left Mouse Button = select/deselect (when in a command)

Right Mouse Button = Blank entity Cntl + Right Mouse Button = Blank entity

Middle Mouse Button = Unblank Cntl + Middle Mouse Button = Unblank

Shift = cutting plane probe in Results Shift = cutting plane probe in Results

Shift + Control = surface probe in Results



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2.6.1 Mouse Scroll Wheel Zoom

The mouse scroll wheel now acts as a zoom function. Scroll away to zoom out, scroll toward the user to zoom in.

This new feature in CFdesign simplifies user/mouse interaction as well as improves consistency with many CAD tools.

Navigation Mode 3 (Wildfire) Navigation Mode 4 (Solid Works)

Ctrl + Middle Mouse Button = zoom Shift + Middle Mouse Button = zoom

Middle Mouse Button = rotate Middle Mouse Button = rotate

Shift + Middle Mouse Button = pan Ctrl + Middle Mouse Button = pan

Scroll Wheel = zoom Scroll Wheel = zoom



Right Mouse Button = Blank entity Right Mouse Button = Blank entity

Ctrl + Right Mouse Button = Unblank Ctrl + Right Mouse Button = Unblank

Shift = cutting plane probe in Results Shift = cutting plane probe in Results




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2.7 Entity Selection

The selection mode (on the Loads and Mesh dialogs) controls which type of entity is selectable: volume, surface, or edge.

The Selection Mode can be changed on the Loads and Mesh dialogs, but on Mate-rials, it is set to only Volumes or Surfaces (3D or 2D models, respectively).

The Selection Basis allows for associative selection and the selection of groups. Associativity is based on geometry, and provides a quick way to select multiple entities that are related to the Selection Basis type (surfaces owned by a volume, for example). Entities of the type shown in the Selection Basis menu will highlight as the mouse is moved over them. When picked, all of the items of the current selection mode that are associated with the picked item will be selected. Groups will be discussed later in this chapter.

The Selection Basis modes for each selectable entity are:

Entity Selection Basis

Volume Direct -- Volumes are highlighted and are selected

By Material -- All volumes that have the same material are highlighted and selected together.

Surface Direct -- Surfaces are highlighted and are selected

By Volume -- Volumes are highlighted, and all surfaces touching a picked volume are selected.

Edge Direct -- Edges are highlighted and are selected

By Surface -- Surfaces are highlighted, and all edges touching a picked surface are selected.

By Volume -- Volumes are highlighted, and all edges touching a picked volume are selected.

Selection Mode

Selection Basis


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The four buttons adjacent to the Selection Basis drop menu simplify selection and deselection of multiple entities:

When the mouse hovers over an entity, it turns green. When an entity is selected, it turns red. When the mouse hovers over an already selected entity, it turns yel-low.

To deselect an entity, simply click on it again, or highlight it in the Selection List and hit the Deselect button.

To be selectable, an entity must not be occluded by another entity. If there is an entity blocking the line of sight to the desired entity, use the right mouse button to blank its display (see the next section).

When an item is selected, its label is shown in the Selection List. Multiple selected

items can be highlighted in the list using the Windows “standard” selection meth-ods--hold down the control key while clicking on items to select multiple items; hold down the shift key while clicking on items to select a range.

Select All entities

Deselect highlighted Deselect All selected entities

Select Previously selected entities

(in the Selection List) entity


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2.8 Entity Visibility

2.8.1 Blanking

An entity can be blanked by right clicking the mouse on it. Only entities of the type in the current selection mode will be blanked. To redisplay all blanked entities, right click the mouse somewhere off of the model. Shown is a model with some surfaces blanked. Note how the surface underneath is now visible, and therefore pickable.

Blanking entities is very useful when applying boundary conditions and mesh sizes to allow easy access to objects in the background.

2.8.2 Blanking Undo

Clicking the middle mouse button in Mouse Mode 1 (which is also the scroll wheel on some mouse devices) will undo blanking commands in the opposite order that they were issued. Use the Ctrl+Middle mouse button in Mode 2. In Mouse Modes 3 and 4, undo blanking with the Ctrl+Right mouse button.

This action will also undo the redisplay of all hidden entities. If the user had blanked several parts in an effort to gain access to an internal part, but accidently redis-plays the entire assembly, they now can simply hit the middle mouse button, and undo the redisplay command.


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2.9 Feature Tree

The Feature Tree has several functions that assist in setting up and running a CFde-sign analysis. Some of the branches allow certain analysis settings to be made.

Other branches list existing settings, and allow them to be modified easily. Most of the branches will be described with their relative chapters (the Boundary Conditions and Initial Conditions branches will be discussed in the Loads chapter, for exam-ple). This section describes the branches that are specific to the Feature Tree, and are not associated with a Dialog Task.

2.9.1 Units

When an analysis is created, the default units system will be meters (unless the default was changed using File_Preferences).

For Pro/Engineer and CATIA v5 geometries, changing the units system only changes the analysis length unit--it DOES NOT convert any dimensions in the model.

For geometries originating in other CAD systems that are Parasolid or Acis based, the Units branch works slightly differently. Because most CAD systems output geometry in meters (converted from the working units system), CFdesign will set the analysis units to meters, when it reads in the geometry file. Unless the geome-try was originally built in meters, the model will have different dimensions in CFde-sign than in the CAD system. To convert the units system, simply select (left


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click on) the desired units system from the Length Units branch of the Fea-ture Tree.

To make this process easier, it is recommended that you set the default units system in File_Preferences to the working units system in your CAD sys-tem. When geometry is read into CFdesign for a new analysis, the analysis units system will automatically be set, and the length dimensions of the model will be the same as in the CAD system (they will be automatically converted from meters to the default units system during the import).

When reading in a geometry file and the dimensions are correct but the unit system is not, change just the units system (without changing any model dimen-sions) by right clicking on the desired unit system, and selecting Change Length Unit Only. This is applicable if the CAD system does not convert the units to meters when exporting geometry. Autodesk Inventor behaves this way.

2.9.2 Coordinate Systems

For three dimensional analyses, Cartesian (XYZ) is the only available coordinate system.

For two dimensional analyses, the choices are Cartesian and Axisymmetric about the X and Axisymmetric about the Y.

A two dimensional Cartesian geometry is always assumed to have a unit depth.

An axisymmetric geometry is a three dimensional geometry that is uniform in the tangential direction. Because of this uniformity, a single slice through the geometry can be simulated as a two dimensional model. The nice thing about axisymmetric modelling is that a two dimensional analysis can give correct results for a three dimensional model. An example of axisymmetric geometry is a straight pipe.

It is recommended that axisymmetric geometries be constructed in the first quad-rant. Geometries that are axisymmetric about the x-axis cannot cross the x-axis because the x-axis is the center-line. Likewise, geometries that are axisymmetric about the y-axis cannot cross the y-axis. A unit radian depth is always assumed for axisymmetric geometries.


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2.9.3 Parts

Every part in the CAD model will be listed as a branch in the Parts section. The main function of this branch is to set individual part view parameters and to allow selec-tion of parts.

Left click on a part to highlight its display.

Right click on a part to bring up a menu with the following items: Select, Outline, Transparent, and Add to Group.

Select a part from the Parts or Materials branch of the feature tree by right clicking on its entity label and picking Select from the menu. Use the Windows standard (shift or ctrl keys) to select multiple parts.

In Analyze (during the run), Review, and Results modes, the Parts branch is not displayed in the Feature Tree. Individual part display attributes are set using the Materials branch.

2.9.4 Naming Entities with Assigned Conditions

Geometric entities with assigned conditions can be renamed in the Feature Tree. This feature is applicable to surfaces and edges for 3d models and edges for 2d models that have boundary conditions, initial conditions, or mesh sizes. (Note that part names cannot be changed within the CFdesign interface.)


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To change the name of an entity, right click on the current name in the feature tree, and select Change Name. Enter the new name in the dialog that appears, and hit OK. The entity will be renamed in the feature tree, and the name will persist in other branches of the tree if other settings are applied to the entity.

2.10 Groups

2.10.1 Introduction

Geometric entities such as volumes, surfaces, or edges can be grouped based on part name, material, common mesh size or boundary condition. Groups of entities can then be selected with a button click to add additional settings. Groups of sur-faces can also be selected for assessing wall results (post processing).

A Group is a homogeneous collection of entities: volumes, surfaces, or edges. A group cannot contain a combination of entities (such as a mixture of volumes and surfaces, for example).


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2.10.2 Creating Groups

Create a group by right clicking on the main Group branch in the feature tree, and select “Create Group”

A dialog will come up prompting for a group name. To group geometric enti-ties (parts, surfaces, edges), select Geometric as the Type. To group parts by Motion (for linked motion), select Motion as the type. (This is described in the Motion chapter of this manual.)

Groups can be created on the fly if desired. This can occur when entities are added to groups, and will be described in the next section.


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2.10.3 Adding Entities (and Creating Groups on the Fly)

2.10.3.1 Adding Parts from the Feature Tree

2.10.3.2 Adding Parts by Name

1. Parts can be added to groups by right clicking on part ids listed in the Parts branch of the feature tree.

(Note that multiple selection of entities in the tree using shift key-Windows standard multiple picking is supported.)

2. After selecting the desired parts, right click, and select “Add to Group.” 3. A menu will come up listing avail-able groups. Select the desired group from the list.4. To create a group on the fly, select “Create Group.” The Create Group dia-log will prompt for a name. After enter-ing the name, the selected parts are added to the group.

1. Parts can also be added to an exist-ing group by right clicking on a group name, and selecting Add by Name. 2. Use a regular expression to type in part of the name that is common to the parts to be added to the group. (Be sure to check the Regular Expression box.)

For example, to add multiple parts with the word “chip” in their name, enter “*chip*”, and all parts that have the word chip somewhere in their name will be added to the group.


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2.10.3.3 Adding Entities with Applied Conditions

2.10.3.4 Adding Multiple Entities From The Selection List

Any volume, surface, or edge that has an applied mesh size or boundary condi-tion can be added to a group:1. Right click on an entity with an applied condition in the feature tree, and select “Add to Group”. 2. All entities with the same applied setting can be added to a group by right clicking on an applied condition under an entity in the feature tree, and select “Add by Value to Group.”

When applying loads, mesh sizes, or mate-rials, the currently selected entities can be added to a group by right clicking in the Selection window, and selecting Add to Group.


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2.10.4 Removing Entities from Groups

2.10.5 Deleting Groups

2.10.6 Displaying Grouped Entities

Right click on an entity (or entities) under the Group branch, and select Delete. This will remove the item(s) from the group.

Delete an individual group by right clicking on it in the Group branch of the feature tree.

Delete all groups by right clicking on the top level Groups branch of the tree, and selecting Delete All.

To show only the contents of a group, right click on the group label (under the Groups branch), and select Display Group Only.

To re-display the rest of the model, right click in the graphics window, off of the model.


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2.10.7 Hiding Groups

A new menu item, “Hide Group,” has been added to the right-click group menu in the feature tree. Click this menu item to blank (hide from view) all entities within a certain group.

Right clicking anywhere on the Graphics window will restore the visibility of the objects.

2.10.8 Selecting Multiple Groups

Selecting multiple groups allows an easy way to display, blank, or delete more than one group at a time. Select multiple groups from the feature tree by using the Win-dows standard shift and control keys and clicking on the desired groups. Use the right-click menu to execute the desired command.


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2.10.9 Combining Groups

Combine the contents of groups by right-clicking on a group, and selecting the Add Group menu item:

The other groups containing the same entity type are listed. Click one of the groups from the list to add its contents into the current group.

The group that is selected from the pop-out menu is not altered. (Only the group that was right-clicked is modified.)

For example, to add the volumes of Group2 (as in the above graphic) into Group1, right click on Group1, select Add Group, and then select Group2 from the list.

Group 1 will then contain all of its original entities plus those in Group2. Group2, however, will not be changed.


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2.10.10 Using Groups

Groups of surfaces can be selected for use with a Wall Results calculation. The group must have existed during the last run (if it did not exist, simply run 0 itera-tions prior to examining wall results). To access a group of surfaces, right click in the Wall Results dialog Selection list, and select the appropriate group. The sur-faces in the group will be added to the Selection list, and wall results on those sur-faces will be reported.

2.11 Task Dialogs

The Task Dialogs shown in the Task Dialog Region are activated by clicking on one of the tool buttons in the vertical tool bar. A good sequence to follow when setting up an analysis is to work vertically through the tool buttons.

On the Loads, Mesh, and Materials dialogs, groups are listed in the Selec-tion Basis menu. Only groups contain-ing the type of entity of the current selection type are listed.When a group is selected, the entities are added to the Selection List. Individual items can be deselected or additional items added.

LoadsMesh Sizes

MotionOptions

Analyze

Review

Load Transfer

Results

Materials


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Below is a brief description of each task. The following chapters in this Guide dis-cuss much more detail about the use and application of each of these dialogs.

Loads

Boundary conditions and initial condi-tions are applied with the Loads Command Dialog.Items such as velocity, pressure, and tem-perature are applied to the surfaces of a model (to edges in 2D models).Volumetric heat generation and total heat generation are applied to volumes (to sur-faces in 2D models).Select the units for each boundary and initial condition type. Transient (time-dependent) boundary condi-tions are also applied and defined in the Loads task.Please see the Loads chapter for more infor-mation.

Mesh Sizes

A mesh has to be constructed which divides the entire geometry into small pieces, or elements. Each element has four nodes, one at each corner. The finite element equations are then solved at each node in the model.This dialog provides tools to automatically define a mesh as well as identify potential problem areas within the geometry.The Mesh Enhancement parameters are adjusted by clicking the Mesh Enhancement button.Please see the Meshing chapter for more information.


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Materials

The physical material of each part is assigned with this dialog. A materials data-base including fluids and solids is included with the software, and the entries are selected from the Name drop menu.Materials can be modified and added to the materials database by clicking on the Create/Edit Material button.This dialog is also used to define and assign distributed resistances, internal fans, check valves, rotating regions, component thermal models, and printed circuit boards.

Please see the Materials chapter for more information.


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Motion

The definition and specification of solid motion are controlled with this dia-log. Several types of engineering motions are supported: linear, angular, combined linear-angular, orbital, nutating, sliding vane, and free motion. All can be defined through user-input, and most can be flow-driven.A Motion Editor is accessed by clicking the Create/Edit Motion button. This dialog allows specification of non-geometric-dependent quantities such as velocity, displacement, or driving or resistive forces.Geometric-based parameters such as initial position of the object, the direction of travel, and the limits of the motion are defined on the main Motion task dialog.

See the Motion chapter for more information.

Options

The physics to be solved in an analysis are set in the Options dialog. The defaults are good for many analyses--flow, incompress-ible, no heat transfer--but are easily changed if necessary.The Turbulence button allows the user to change the turbulence model.The Solar button opens the Solar Heating dia-log which allows specification of solar loading.The Scalars button allows the user to enable one of the scalar models (general scalar, steam, and humidity.)

Please see the Analysis Options chapter for more infomation.


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Analyze

After the analysis is set up, use this dialog to start the calculation.Set the Analysis Mode to Steady State (the default) or Transient. The Results and Sum-mary Output Intervals are also set.The Analysis Computer is chosen here. This is for the Fast Track Option. Stop the analysis by clicking the Stop button (which replaces the Go button during the analysis).Select additional output quantities from the Result Quantities dialog.

Please see the Analyze chapter for more infor-mation.

Review

This dialog contains numerous func-tions. Before the analysis, it is used to set up Monitor Points (points in space on which con-vergence can be monitored). After the analysis the Summary and Status files are accessible from the Notes tab. These files contain information about the results as well as the analysis.The Results tab lists all saved results (and time) steps, and provides a way to include them in an animation.The Animate tab animates the results sets made active in the Results tab.

Please see the Review chapter for more infor-mation.


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Results

The Results dialog contains a great deal of post-processing functionality. The Cutting Plane, a 2D slice through the model on which color results and/or vectors are shown, is the primary tool, and is the basis for particle traces, XY plots, and bulk data out-put.The Iso Surface is a surface of constant value, and is a great way of visualizing flow and tem-perature distributions.Flow-induced forces, convection coefficients, temperatures, and pressures on walls are cal-culated using the Wall tab.Settings for cutting plane and vector display are set with the Settings tab.

Please see the Viewing Results chapter for more information.

Transfer

This dialog makes it easy to convert CFdesign flow results (pressures and tempera-tures) to boundary conditions in several FEA structural codes.Ansys, Nastran, Abaqus, Mechanica, Cosmos, and FEMAP, and I-DEAS are supported.

Please see the Results Transfer chapter for more information.


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2.12 Additional Parameters (Flags File)

There are some additional parameters that control output of optional files as well as provide additional control to the way geometry is handled. These parameters must be in a file called cfdesign_flags.txt, which is located in the installation directory. The default location of the file is the CFdesign installation directory. An environment variable called CFDESIGN90TEMP must point to the location of this file.

This file can be moved to a different location, but the environment variable must be updated to point to the new location.

The variables in the flags file, their parameters, and their meanings are shown:

use_spaceball This entry enables support the Spaceball navigation device. There are no arguments--if the entry is in the flags file, the Spa-ceball is supported.

protool fillvoids A A = 0: off;A = 1: on(ON by default)

Controls automatic creation of core volume for Pro/E geome-tries. (See chapter 3 for more details.)

CATIA fillvoids A A = 0: off;A = 1: on(ON by default)

Controls automatic creation of core volume for CATIA geome-tries. (See chapter 3 for more details.)

PARASOLID SET_DISP_TOLER A B C

A = 0: off; A = 1: onB = 0C = tolerance value

Controls the display resolution of parasolid geometry. The model is displayed with a higher resolu-tion for smaller tolerance values. Display processing time will go up as the tolerance value is reduced.


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ACIS SET_DISP_TOLER A B C

A = 0: off; A = 1 onB = 0C = tolerance value

Controls the display resolution of acis geometry. The model is dis-played with a higher resolution for smaller tolerance values. Display processing time will go up as the tolerance value is reduced.

DISCRETE EDGEANGLE_THRESHOLD A B C

A = 0: off; A = 1: onB = 0C = tolerance value

For mesh files created in third-party meshing tools and imported into CFdesign, this parameter controls the crease angle tolerance between edges. Smaller values (0.001) results in more breaks between element edges, producing more “geomet-ric” pickable edges.

load_xfer_all_res A A = 0: off;A = 1: on

Enables output of loads file (con-taining interpolated results) for every saved result or time step. Default of 0 causes only last saved result or time step to be output.

ViewFactorUpdate A A = number between 1 and 100

Controls how often radation view factors for moving objects are updated. A is the percentage of the maximum diagonal of the model. The default is 2, meaning view factors are recomputed when the object has moved a distance equal to 2% of the diagonal.

rad_model_1 A A = 0: off;A = 1: on

Enables old radiation model. New radiation model is on by default.

FORCED_EXTRA A A = number of iterations

Controls number of thermal-only iterations when Staged Forced Convection is enabled. The default is 10.


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enthalpy_humid A A = 0: off;A = 1: on

Enables old ethalpy-based humidity model. The new, tem-perature-based model is on by default.

CFDESIGN USE_VIZSERVER A

A = 0: off;A = 1: on

Controls the Design Review Server. The Design Review Server is enabled by default, but setting a value of 0 for this entry will disable it.


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CHAPTER 3 Geometry

3.1 Introduction

CFdesign has very strong ties to most of the CAD tools used in industry today. By using the same geometry engines found in these CAD systems, CFdesign reads the native model without the need for Step or IGES translations. Parametric changes to the geometry are read directly into CFdesign, and model settings from similar anal-yses are automatically applied to the modified geometry.

This functionality allows two things to occur very easily: The first is that multiple design alternatives can be analyzed very easily--without having to go to great lengths to fix IGES or Step translations for each “what if” scenario. The second is that corporate PLM/PDM initiatives are supported--geometry manipulation occurs ONLY in the CAD system, where it can be tracked and archived. When geometry is manipulated in a third party system (such as many of the other CFD tools), changes often get lost, or simply have to be re-created in the CAD system--thereby doubling the work. With CFdesign, such issues are not a problem.

This chapter describes the type of CAD geometry needed to successfully run a flow analysis. Guidelines for what is needed, techniques for how to obtain it, and trou-bleshooting tips are presented. Guidelines specific to Pro/Engineer and to Parasolid/Acis based CAD systems are discussed.

3.2 What is Flow Geometry?

Geometry used for a typical fluid flow analysis is often different than that used in a structural analysis. There are two broad classifications of flow geometry: internal and external. Examples of internal flows include pipe flow, valve flow, and flow in electronic enclosures. Examples of external flows, also called submerged flows, include flow over a car, an airplane wing, or a missile.


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For internal flows, a flow “core” must be created from the existing surrounding geometry. The outer walls of the volume are omitted (unless they are to be used as part of a heat transfer calculation) and the interior volume of the pipe is modeled.

In contrast, in a structural analysis the walls of the pipe would be meshed and the interior would be omitted from the calculation domain:

Another description of the interior volume is this: a pipe is filled with water and the water is allowed to freeze. Now, imagine that the pipe walls are removed, and all that remained was the solid volume of ice. This volume is where the fluid exists, and is the geometry that would be created and meshed for a CFD analysis of flow through that pipe.

For external flows, it is customary to “invert” the geometry, meaning that the object will be made stationary and the flow will be blown over it at the equal and opposite speed of the object. To implement this as analysis geometry, two pieces of


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geometry are needed: the object itself (missile, car, bullet, etc.) and a large calcu-lation domain in which the object is positioned:

The shape of the domain is usually not very critical, and can be a circle, semi-circle, rectangle, sphere, or box. Because the flow all around the object is being modeled, it is a good idea to make the computational domain substantially larger than the object itself. More detail about the relative size of the calculation domain will be dis-cussed in Chapter 12 of this Guide.


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3.3 Pro/Engineer

This section discusses geometry considerations specific to Pro/Engineer.

3.3.1 Automatic Flow Volume Creation in Pro/E

Many models constructed in Pro/E consist of just the physical solids (the pipe wall, for example). In earlier versions of CFdesign, it was necessary to manually create the flow volume in Pro/E. To reduce the amount of time and effort needed to pre-pare a Pro/E geometry for analysis, CFdesign has the ability to convert a fully enclosed void into a meshable volume.

3.3.1.1 Applying Void Filling

In the following example, the pipe wall and two internal parts were created in Pro/Engineer:


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To prepare this for a flow analysis, simply add a cap to both ends of the pipe:

The Pro/E geometry shown above consists of five parts: the pipe wall, the two internal components, and the two end caps. In this example, the caps are con-structed using the inner diameter of the pipe wall, and extruded into the pipe. Alternatively, the caps could have been extruded out of the pipe, or have been built using the outer diameter of the pipe wall.

When brought into CFdesign, the internal volume is automatically created:

The two internal parts are automatically cut from the newly created flow volume.


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3.3.1.2 Invoking Void Filling

Pro/E Void Filling is enabled by default. To deactivate it, make the following entry in your cfdesign_flags.txt file. A value of 1 activates fill voids, a value of 0 disables it:

PROTOOL FILLVOIDS 0

The cfdesign_flags.txt file can be placed anywhere on your local computer. Be sure to set an environment variable called CFDESIGN90TEMP to point to the location of your flags file. Its default location is in the CFdesign installation directory.

3.3.1.3 Guidelines

Components built in Pro/E must not interfere, so care must still be taken to elimi-nate part interferences from the Pro/E model.

There are a few guidelines that should be observed or the automatic void creation will not work:

• Parts that are inside of the void must not protrude through the outer wall of the geometry. If this occurs, the void filling will fail. This is shown:

Part must not protrudethrough end cap


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• End caps must not extend beyond the geometry surrounding an open-ing. In this pipe example, the cap must not extend beyond the outer diam-eter of the pipe. An example that will fail is shown:

3.3.2 Volume and Surface Regions

There are situations in two and three dimensional geometry where it is advanta-geous to divide a surface or volume into smaller areas. This is especially useful for boundary condition placement, and sometimes for greater control over mesh den-sity. In Pro/E, create a surface region to divide a surface into smaller surfaces or a volume region to divide a volume into smaller volumes. CFdesign will read in these divisions, and allow boundary conditions and mesh definitions on the new surfaces and edges.

End cap extends beyond outeredge of geometry.

This will NOT produce a flowvolume.


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An example in Pro/E is shown:

The procedure to create a surface region follows (volume region creation is simi-lar):

1. Click on Applications_Mechanica.2. On the Mechanica menu, select Structure.3. Select Model_Features_Surf Region_Create. At this point, click either Sketch to sketch the region, or Select if datum curves already exist which define the region. Click Done.4. If Sketch was selected, you will be prompted to select a sketch plane and to orient it.5. You will then be in Sketch mode. Draw and dimension the region.6. After completing the section, you will be asked to select the surface(s) to be split. Do so, then hit Done Sel and Done.

Note that your Pro/E license must allow access to the Mechanica FEM mode to use Simuation Features.

When CFdesign is started, you will see the region as another surface.

3.3.3 Two Dimensional Geometry

Often two dimensional geometry is useful for simulating axisymmetric geometry or for a simply “first crack” at an analysis. To create a two dimensional feature, do the following:


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1. Click Feature_Create_Surface_Flat.2. Position the drawing (the XY plane is the recommended orientation).3. If the geometry is an axisymmetric model, be sure to position it relative to the x or y axis properly. If the geometry is axisymmetric about the x axis, it cannot cross the x axis. If it is axisymmetric about the y axis, it cannot cross the y axis. We recommend that axisymmetric geometry be constructed in the first quadrant of the coordinate axis.4. Proceed into CFdesign exactly as you would for a three dimensional model.

3.3.4 Interferences

When working with assemblies, it is very important in Pro/Engineer geometries that no parts interfere (take up the same volume). If two or more parts do interfere, the mesher will fail.

Very often there are parts that are physically inside other parts. Care must be taken to ensure that internal parts are first cut out of surrounding parts, and that they do not interfere. On the screen it may appear that the model is correct simply by placing a solid inside another (that’s what one would do physically!), but in Pro/E, it is necessary to first cut out internal solids from the surrounding air. Once that is done, the internal part and the surrounding parts do not interfere.

Shown is an example of two parts that interfere

To check for interference in Pro/E, do the following:

1. From the Pro/E main menu, click Analysis_Model Analysis.2. Select Global Interference from the Type menu.3. Hit the Compute button.


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Any parts that interfere will be highlighted. To fix an interference, it may be neces-sary to move one or more parts, cut one part from another (see Section 3.3.2), or to delete parts. Every model is different, so the solution will be dependent on the goal of the analysis. Shown are a couple of examples of fixed geometry:

3.3.5 Accuracy

When working with assemblies, it is recommended that all the parts in the assem-bly (and the assembly itself) have the same absolute accuracy. In many cases, it might not matter, but if you try to launch into CFdesign, and both Pro/E and CFde-sign crash, you should adjust the accuracies of the parts and assemblies in your model.

By default, absolute accuracy is not enabled in Pro/E. To turn it on, a configuration setting called enable_absolute_accuracy needs to be set. To do this:

1. From the Pro/E main menu, click on Utilities_Preferences.2. Click on the Find button, and search for the keyword “accuracy”. Select enable_absolute_accuracy, and change the value to Yes.

To set the absolute accuracy for the parts and assembly, first find out what the absolute accuracy is for the smallest part, then change the absolute accuracy of the other parts to that of the smallest:

1. Open the part, and click on Setup_Accuracy (from the Part or assembly menu).


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2. Pro/E will prompt for a relative accuracy, so click the ESC key, and select Abso-lute Accuracy.3. Select Absolute, and Enter Value, and enter the value for absolute accuracy.4. Click the Check mark, and the part will regenerate.

Modifying the part and assembly accuracy to absolute is not always necessary, but if there are parts with very small features and larger parts in the same assembly, it can be very useful for preventing crashes.

Also, if automatic void filling is enabled but fails to create the internal volume (assuming that the guidelines in the void filling section of this chapter are fol-lowed), it may be necessary to modify the accuracy on the parts and assembly to be absolute. If the void filling still fails, using a smaller accuracy value might correct the problem.

When using simulation volume regions (particularly in Wildfire), if they do not appear as a separate volume from the surrounding part (in CFdesign), then setting the accuracy to absolute (and then using a smaller value if necessary) will often cause the volume region to be considered as a separate part.

3.3.6 When Pro/E Must be Running

For a new analysis, CFdesign MUST be launched from Pro/E. When you do this, you will see that Pro/E minimizes, and is in a “sleep” state. You will also notice that when you hit the GO button on the Analyze window in CFdesign, Pro/E comes back, but is working. The mesh is actually being generated by CFdesign by reading the part geometry from the Pro/E database. It is accessing the part and assembly infor-mation in the same way that Pro/Mesh accesses it. For this reason, CFdesign must be launched from Pro/E when the goal is to generate a mesh.

Once CFdesign returns, the analysis proceeds automatically. Pro/E returns to a “sleep” state, and cannot be accessed. To access Pro/E, do one of the following:

1. Set the number of iterations to 0, so that after meshing and pre-processing, the analysis does not proceed. Exit out of CFdesign, and then exit out of Pro/E. Start CFdesign from the Desktop, open the analysis, and run it.2. While the analysis is running shut down the CFdesign interface. (The analysis will continue to run.) After the interface is shutdown, Pro/E can be accessed or shut down as required.


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If a mesh exists, and if the goal is to do anything (modify boundary conditions, materials, run more iterations, view results, etc.) other than generate a new mesh, CFdesign can be started from the Desktop or Start Menu. Open the “.cfd” file.

3.3.7 Split Surfaces in Pro/E

When a three dimensional part is divided by another part into multiple volumes, the result will be “split surfaces.” The problem with split surfaces is that they are con-sidered by the Pro/E model to be a single surface (even though there are discon-nected). When a boundary condition is applied to one of these surfaces, it may be lost or will jump to the other surface when the analysis is saved. An example is shown:

An easy fix is to add a protrusion or cut feature to one of the volumes so that the surfaces are unique. This will prevent conditions from jumping or being lost.

3.4 Parasolid and Acis Based CAD Systems

This section discusses geometry issues that are specific to the Parasolid and Acis-based CAD systems. Such systems include Inventor (Acis), Solid Edge (Parasolid), Unigraphics (Parasolid), Solid Works (Parasolid), Solid Designer (Acis), and CAD-Key (Acis).

Original partOriginal part, divided by anadditional part.

Two surfaces, but consideredto be the same by Pro/E. Settingsapplied to one surface may be lost “jump” to the other.


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3.4.1 The Internal Flow Volume

The internal flow volume will be created by CFdesign provided that the internal vol-ume is completely enclosed. This means that when the open ends of an internal flow geometry are capped with either a surface or volume and then read into CFde-sign, the internal core will be generated automatically. This is illustrated below:

Step 1: Pipe geometry--only the physical solids exist (pipe wall and poppet):

Step 2: Pipe geometry with newly-created volumes at the ends (pipe wall, poppet, and two end caps). The end caps were created by extruding the inner-radius curves of the pipe. This extends the flow volume slightly, but they can be omitted from the meshing if necessary.


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Note: For Acis geometries, it is recommended that the end caps be larger than the ends. The following graphic shows this:

Step 3: Geometry read by CFdesign--the flow core has been created automatically, and is shown as the highlighted volume. Notice that there are now five volumes listed in the Materials branch of the Feature Tree--the pipe wall, the poppet, the two end caps, and the flow volume.

If there are objects inside of the flow volume (like a poppet for example), they will automatically be embedded into the flow volume. This means that it is not neces-sary to cut out submerged objects from their surrounding geometry.

For Solid Works-based analyses, if a geometric change is made to an existing anal-ysis model such that the topology of an internal core volume is changed, the vol-ume settings (volume mesh size and material definition) will be lost from that core volume. Such a change would be the addition or removal of a part or features of a part that are inside the void. The reason for this is that core volumes are not cre-ated in the CAD tool, they are created by CFdesign when the geometry is read in. Because of this, there is no direct geometric link between the core volume and the original CAD model. Settings on geometric entities created in the CAD tool will be preserved for most topological changes, however.

If it is not necessary (or desirable) to mesh various solids in a model (the pipe wall and poppet, for example), then a no-mesh condition can be applied to them during the mesh definition step. (This is covered in more detail in the Meshing chapter). In the preceding example, because the flow volume was created based on the solid geometry, the poppet is cut out from the flow volume, and fluid will not pass through this region even if the poppet is not meshed.


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3.4.2 Submerged Objects and External Flows

Many analysis models are built have physical solids that are submerged in the flow. Such objects are often involved in a heat transfer analysis, and may carry a heat load. The method for dealing with submerged objects is very simple: Place them in the desired location within the surrounding volume. It is not necessary to remove interferences or to cut an internal part from the surrounding volume. CFdesign will do this automatically. The following graphics illustrate this.

Step 1: An empty box representing the air in an electronics box.

Step 2: Components are simply placed inside the box in the appropriate locations.

Step 3: As the model is read into CFdesign, the components are automatically cut from the air to remove all geometric interferences. Proper connectivity between all contacting parts is automatically ensured.


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In our example, the air volume in the CAD system was only a box. As CFdesign read the geometry, voids for the internal components were cut into the air. This is why the internal curves highlight when the air volume is selected.

This applies to both internal flows with submerged objects (examples include valves with poppets and electronic packages), and for external flows simulating the flow over a moving object. To include the obstruction as a meshable volume in the anal-ysis model, simply place it in the surrounding volume at the desired location.

3.4.3 Two Dimensional Geometry

Often two dimensional geometry is useful for simulating axisymmetric geometry or for simply an initial attempt at an analysis. A Parasolid or Acis surface in the XY plane is necessary for such an analysis.

Axisymmetric geometries must be constructed relative to the x or y axis properly. If the geometry is axisymmetric about the x axis, it cannot cross the x axis. If it is axisymmetric about the y axis, it cannot cross the y axis. We recommend that axi-symmetric geometry be constructed in the first quadrant of the coordinate axis.

3.4.4 Part Names

Part names assigned in Parasolid- and Acis-based CAD tools will now appear in the CFdesign feature tree. Only part names are listed in the Parts branch of the feature tree; assemblies are not listed.

From Solid Works, the naming convention of a part is based on the parent assembly and any parts that surround that part. For example, a part called small-chip is a member of a sub-assembly called left-board_asm. This part is also surrounded by a part called test-box. The part name in the feature tree would then be:

TEST-BOX_U_SMALL-CHIP-4@LEFT-BOARD_ASM

The “U” indicates that the part SMALL-CHIP is surrounded by the part TEST-BOX.

If a part is used multiple times in an assembly, an instance number will be attached to the part name. In the example above, this part was the fourth instance of the part SMALL-CHIP.


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If the geometry was not launched from Solid Works, the part names will be a com-bination of the CAD part name and any part that completely surrounds it. The name of the part listed above would be:

TEST-BOX_U_SMALL-CHIP^4

In some cases, the actual part name (without the surrounding part or assembly) will be listed in the feature tree. This is typically because the part is surrounded by an automatically-created flow volume.

Note that internal core parts that are created by CFdesign will be assigned the generic name “volume”. This is because such parts were not created in the native CAD tool, and hence did not have a name. Also, the name of internal core parts will not be used within the names of other parts they completely surround.

3.5 CATIA V5

The CFdesign interface for CATIA is designed to work with V5R14, V5R15, and V5R16. This is an associative interface that reads the geometry directly from the CATIA database--it does not rely on file translations. Meshing is performed by CFdesign directly on the CATIA geometry.

After launching CFdesign from CATIA, the CATIA interface will minimize (but CATIA will continue to run). The CFdesign interface will start, and will prompt for an anal-ysis name. The analysis model is then set up according to standard practices out-lined in the CFdesign documentation. When the analysis is started (by hitting the GO button on the Analyze task) the CFdesign interface will minimize and the CATIA interface will reappear. Meshing status messages are written to the Status bar in the CATIA interface. After meshing is completed, the CFdesign interface will reap-pear, and the analysis will continue.

3.5.1 Part Names

The names assigned to CATParts remain with them when the model is brought into CFdesign.


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3.5.2 Interferences

Interferences between CATIA geometry are not supported in the CFdesign inter-face. Please ensure that all interferences are removed before launching into CFde-sign. The result of not removing them is likely a crash either when CFdesign is first launched or when the mesh is generated.

3.5.2.1 Clash Detection

These are some general steps to detect for interferences between parts in CATIA:

1. Click Analyze_Clash. The Clash Detection dialog will appear. 2. Select Contact+Clash as the Type, and select Between all Components. Click Apply.3. Interfering parts will highlight in orange, and will be listed in the Check Clash dialog.

3.5.2.2 Removing Interferences

This is a simple procedure to cut interfering parts from one another:

1. Click Insert_Assembly Features_Remove2. Select the part that is to be cut out. 3. A dialog will appear that lists all parts that may be affected by this cut out. Select the desired part to be cut from, and move it from the Parts Possibly Affected area to the Affected Parts area.4. Click OK on the Remove dialog (to verify the cut out).

3.5.3 Automatic Flow Volume Creation

Many models constructed in CATIA consist of just the physical solids (the pipe wall, for example). To analyze the flow, however, the volume comprising the flow vol-ume must also exist in the analysis. To reduce the amount of time and effort needed to prepare a solid-only geometry for analysis, CFdesign has the ability to convert a fully enclosed void into a meshable volume automatically.


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In the following example, the pipe wall and two internal parts were created in CATIA:

To prepare this for a flow analysis, simply add a cap to both ends of the pipe:

The CATIA geometry shown above consists of five parts: the pipe wall, the two internal components, and the two end caps. In this example, the caps are con-structed using the inner diameter of the pipe wall, and extruded into the pipe. Alternatively, the caps could have been extruded out of the pipe, or have been built


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using the outer diameter of the pipe wall. In many cases, it has been found that extending the outer edges of the cap beyond the outer edge of the flow vessel is the recommended method of automatically generating the flow volume.

When brought into CFdesign, the internal volume is automatically created:

The two internal parts are automatically cut from the newly created flow volume.

Automatic Flow Volume Creation is enabled by default. To disable it, add the follow-ing entry in your cfdesign_flags.txt file. A value of 1 enables volume creation, a value of 0 disables it:

CATIA FILLVOIDS 0

The cfdesign_flags.txt file can be placed anywhere on your local computer. Be sure to set an environment variable called CFDESIGN90TEMP to point to the location of your flags file. Its default location is in the CFdesign installation directory.

3.5.4 Model Changes

An important capability that CFdesign provides to the product design process is the ability to conduct analyses of multiple geometric configurations. Using the Projects feature in CFdesign greatly facilitates the management of multiple analyses, each of which can be based on a variation of the design geometry.


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The CFdesign interface to CATIA supports both parametric and topological changes to the geometry. Parametric changes are modifications to dimensions that do not result in a change in the number of parts, surfaces, or edges. Topological changes are a broader scope of changes, and include the addition or removal of parts or fea-tures.

Specifically, if a change is made to the geometric model, settings from a similar analysis can be mapped to the modified geometry. If the geometric change causes a significant change to an area (such as the removal of a feature), then locally those settings cannot be applied. Such settings are listed in the Lost List, and can be re-applied manually.

3.5.5 Multi-Body Parts

The use of multiple-body parts is not supported. Only the geometry from the first body will be read into CFdesign.


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The following graphic shows a CATIA feature tree with both an empty part body and multiple part bodies in the same part:

Alternatively, it is possible (and allowed) to create a part body consisting of several separate regions (volumes). An example is a sketch consisting of several non-touching outlines that is then extruded. The resulting single part body will consist of several volumes that will then be recognized properly by CFdesign.


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3.5.6 Face/Edge Intersections and Tangency

The intersection of a face and only an edge is not supported. The following geomet-rical situation should be avoided:

In this case, only the edge of one volume contacts the surface of another volume. This will cause an error in transferring the geometry from CATIA to CFdesign, and should be corrected by the user prior to launching CFdesign.

The surfaces of two (or more) volumes can touch one another without error, how-ever.:


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A similar geometric situation that should also be avoided is a perfect tangency. An example is shown:

In this example, a work-around would be to offset the cylinder slightly into the block, and cut off the interfering piece.

3.5.7 Units

The default units system in CATIA is mm. Additionally, mm is the underlying units system for the geometry engine in CATIA. Because of this, geometry read by CFde-sign from the CATIA database is always in mm, even if the geometry was con-structed in any other units system.

In the Units branch of the CFdesign feature tree, left click on mm to set the units system to mm. Doing this will not convert any dimensions in the model, however.

A future enhancement to the CATIA CFdesign launcher will be to allow units conver-sions of geometry constructed in other units systems.

3.6 Outlets

More information about boundary conditions will be supplied in the Loads chapter, but it is worth pointing out some important geometric considerations regarding out-lets. CFdesign assumes that flow is normal to the outlet and that there are no gra-dients in the normal direction.

For this reason, it is important to create flow outlets away from sudden turns or contractions. If the outlet is too close, the flow cannot reach a fully developed state, which is the condition assumed by CFdesign. Also, if the outlet is too close to an expansion area, reversed flow could result (flow re-entering).


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This may cause convergence difficulties:

3.7 Lost List

When changes are made to a geometry (often as the next design alternative), a new analysis is created and added to a project containing previous analyses of sim-ilar geometry. The settings (boundary conditions, mesh sizes, materials, options) can be read from an existing analysis and applied to a new analysis with a simple command on the feature tree. (See the Projects chapter of this Guide for more details.)

If the geometric change was parametric in nature (dimensional change), then set-tings will be applied to the new geometry. If the change was topological in nature (added or deleted geometric features), then some settings may not be applied automatically, and will have to be applied manually. An example is if a part with an assigned heat generation load was removed from the model. The heat generation boundary condition would be lost from the model.

In this case and for the case in which an analysis is re-opened after geometric changes, any settings that are lost are now listed in a small dialog. The user can

NO YES


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reassociate these settings to the model by selecting the geometric entity and then the setting from the list.

If settings are lost (either because a topological change eliminated some geometry or because the topology was changed too much), a “Show Lost” button will appear on the appropriate dialog (based on the type of settings that were lost):

The Show Lost button will only appear on a dialog if settings of the dialog type are lost.

When the Show Lost button is hit, a window will come up listing the lost settings:

The number to the right of the setting indicates how many instances of the condi-tion were lost. Lost conditions can be applied to as many entities as desired, how-ever.

For lost mesh sizes, the type of entity the condition was applied to (volume, sur-face, or edge) will be indicated in the list.

To reassign a lost setting, first select the entity (or entities) in the model. Select the desired setting from the list of lost settings. Hit Apply on the task dialog.

All lost lists will be cleared from the analysis when the analysis is saved.


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3.8 Suppressed Components

Components that are suppressed when starting the CFdesign analysis will not be read by CFdesign.

3.9 Third Party Mesh Import

This feature allows the import of a mesh generated in a tool other than CFdesign. Meshes in the I-DEAS “.unv” format and the Nastran “.nas” and “.dat” formats can be read in by clicking File_New, and changing the File Type to CAD Mesh Files.

The model will come into CFdesign and appear as it did in the meshing tool. Sepa-rate parts in an assembly must be meshed with unique material ID’s in the third party meshing tool. Otherwise, parts will not be differentiated from one another.

In CFdesign, set up of the model is standard, with the exception that the Mesh task dialog is not available. Mesh Enhancement is allowed, however. When the analysis is started, the meshing step will be omitted.


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CHAPTER 4 Loads

4.1 Introduction

This chapter describes both the physical significance of loads as well as how to the correctly assign them in the CFdesign user interface. Loads can be classified into two categories: boundary conditions and initial conditions. The former can be a known velocity or flow rate at an inlet, a specified temperature, or a heat flux, for example.

Boundary conditions are enforced through the entire course of an analysis. Initial conditions, however, are often applied to larger regions of a geometry, but are only enforced at the beginning of an analysis. Initial conditions are often the starting point for a transient analysis.

4.2 Application of Boundary Conditions

The Loads dialog is broken into two tabbed sections: Boundary Conditions and Ini-tial Conditions. Boundary conditions are the most commonly used, and define the condition at a location on the model throughout the entire analysis. Initial condi-tions, conversely, only enforce a condition at the beginning of the analysis, and are mostly used for transient (time-dependent) analyses.


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Shown is the Boundary Condition tab, and instructions for its use:

1. Set the Selection Mode, and select only the Surfaces or Volumes to which the intended boundary con-dition will be applied. (Chapter 2 con-tains more information about entity selection.)

2. In the Boundary Condition Group, select the Type of boundary condi-tion, the Units, and choose between Steady State and Transient (time varying).

3. Most of the Boundary Condition types have certain parameters you will need to select. For example, the direction of a velocity condition is set either Normal to the selected sur-face or by specifying Components. Also, enter the necessary value(s).

4. Click the Apply button to finish setting the condition.

5. Other commands: The Delete button will remove the boundary con-dition of the type shown in the Type drop menu from the selected entity or entities. The Delete All button removes all boundary conditions from the model.

Step 1

Step 2

Step 3

Step 4


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4.3 Surface Boundary Conditions

4.3.1 Velocity

A normal velocity component is applied to an inlet (or outlet) surface by selecting the Normal bullet. (This is only available when planar surfaces are selected.) An arrow will be drawn on the surface to indicate the direction of flow. To reverse the flow, click the Reverse Direction button. Enter the velocity magnitude in the Magni-tude field, and hit Apply.

To apply velocity components, select the Components bullet, and check the desired component(s). Enter the velocity values in the appropriate boxes, and hit Apply.

Note: The Vx, Vy, and Vz components will be directed in the global X, Y, and Z directions, respectively.

4.3.2 Rotational Velocity

This condition applies a rotating velocity to a wall. It is applied by specifying a point on the axis of rotation, the direction of the axis of rotation, and the Rotational Velocity. This condition is used for simulating a rotating object in a surrounding flow. An example is the rotating disks in a computer hard drive. This condition does not induce flow caused by rotation (as in a pump impeller), and is not a turbo-machinery condition.

4.3.3 Volume Flow Rate

A volume flow rate is applied to an inlet (or an outlet, if the applied direction is out of the model). This condition can only be applied planar entities. When applying flow rate to multiple openings at the same time, the flow direction (in or out of the model) must be the same.


Loads

4.3.4 Mass Flow Rate

Mass flow rate can be applied at an inlet or an outlet (by specifying the correct flow direction). When mass flow rate is applied to multiple openings concurrently, the flow direction (in or out of the model) will be the same for all applied openings. Modifications to individual openings can be made as necessary. Mass flow rate boundary conditions can only be assigned to planar surfaces.

4.3.5 Pressure

Choose between Gage or Absolute. Gage is a relative pressure, and Absolute is the sum of the gage and the reference pressure (set in Materials). Also select either Static or Total. (Total is the sum of the static pressure and the dynamic pressure, and should only be used for compressible analyses. It should not be used for incompressible analyses.)

The recommended pressure condition for most analyses is Gage, Static.

Please see the discussion below in the Outlets part of the Physical Boundary Section of this chapter.

4.3.6 Temperature

Select either Static or Total. Static is the recommended temperature for most analyses. Total temperature should only be used as an inlet for compressible analy-ses with heat transfer.

Enter the value and hit Apply.

A temperature condition constrains the applied region to that temperature through-out the entire analysis. It can also constrain the temperature of incoming flow.

4.3.7 Slip/Symmetry

Hit the Apply button to set a slip condition on selected surfaces. There is no value associated with the slip condition.


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The slip condition allows fluid to flow along a wall (as opposed to stopping at the wall as in a non-slip condition). The fluid is prevented from flowing through the wall, however.

This boundary condition can be used with a very low viscosity to simulate Euler or inviscid flow.

Slip walls are also useful for defining a symmetry plane. The symmetry region does not have to be parallel to a coordinate axis.

For axisymmetric analyses, the symmetry condition along the axis is automatically set, and does not need to be applied manually.

4.3.8 Unknown

Hit the Apply button to set an unknown condition on selected surfaces. There is no value associated with the unknown condition.

This is a “natural” condition meaning that boundary is open, but no other con-straints are applied.

This is most used for supersonic outlets where the outlet pressure or velocity is not known, and applying either condition would result in shock waves or expansion waves at the outlet.

4.3.9 Scalar

This is a unitless quantity ranging between 0 and 1 that represents the concentra-tion of the tracking (scalar) quantity.

4.3.10 Humidity

This is a unitless quantity ranging between 0 and 1 that represents relative humid-ity (1 corresponds to a humidity level of 100%).


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4.3.11 Steam Quality

This is a unitless quantity ranging between 0 and 1 that represents the steam qual-ity (1 corresponds to a quality of 100%--pure steam).

4.3.12 Heat Flux

Heat flux is a surface condition that imposes a given amount of heat directly to the applied surface.

Select the desired units, and enter a heat value divided by area. For example, if the heat input is 10W, and the area is 5 sq. inches, then the applied value will be 10W/5 sq. inches = 2 W/sq. inch.

Heat flux can be applied to outer walls, to solid-solid interfaces, and to fluid-solid interfaces.

4.3.13 Total Heat Flux

This is a heat flux condition that is applied directly without having to divide by the surface area. This is very important because it allows the user to make parametric changes that might change the area, and not have to worry about recalculating the heat flux boundary condition.

To use, select the surface or surfaces, select the units, enter the value of the heat (not divided by area) in the Total Heat Flux field, and hit Apply.

Total heat flux can be applied to outer walls, to solid-solid interfaces, and to fluid-solid interfaces.

4.3.14 Film Coefficient

Select the desired units, and specify a film coefficient (convection coefficient). Also, enter the reference temperature in the desired units.

This condition is most often used to simulate a cooling effect.


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4.3.15 Radiation

This condition simulates the radiative heat transfer between the selected surface(s) and a source external to the model. The surface emissivity and the background temperature are the required inputs.

This is a sort of “radiation film coefficient” in that it exposes a surface to a given heat load using a source temperature and a surface condition.

4.3.16 External Fan

Click the Edit Flow Rate/Pressure Curve button to specify the values of the known fan curve. Click Insert Row to add rows between defined rows. Click the Plot

button to view the plot--to check your work. The Import button imports a comma separated variable (CSV) file, and the Save button saves the curve information to a CSV file. To enter a fan that pulls flow (at an outlet), enter all flow rate and pres-sure values as negative.

If desired, specify the Rotational Speed of the fan. A tangential component of velocity is then added to the inlet flow to simulate the effect of rotating blades. The units of rotational speed (RPM or rad/sec) is set in the Units field. Use the Reverse Direction button to change the direction of rotation. The rotational direction is set according to the right-hand rule convention.

A Slip Factor can also be specified. The slip factor is the ratio of the true rotational speed of the flow to the rotational speed of the fan blades. Due to inefficiencies in the fan, slip can result in a slower flow tangential flow velocity than expected. CFdesign determines the flow tangential velocity component by multiplying the slip factor by the user-supplied fan rotational speed.


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The default slip factor is 1.0. This means that the rotational speed of the flow is the same as the rotational speed of the fan. The permitted range of slip factor values is between 0 and 1. Values outside of this range are not allowed by the User Inter-face.

4.3.17 Current

Used only to define a Joule heating analysis, apply the current to one end of the solid through which Joule heating is occurring. The current condition to apply is a total current, not a current density.

Joule heating is the generation of heat by passing an electric current through a metal. Also known as resistance heating, this feature allows the user to simulate stove-top burner elements as well as electrical resistance heaters.

4.3.18 Voltage

Another condition used only for a Joule heating analysis. Apply a voltage to the other end of the heated solid. A value of 0 Volts is often used. Alternatively, a volt-age difference can be applied to the solid: a higher voltage on one side and a lower voltage on the other. In this case, omit the applied current condition.

4.3.19 Periodic

The periodic boundary condition values are the Pair ID and the Side ID. Use the same Pair ID for both members of a pair, and use different Side IDs for each mem-ber of a pair. On the inlet periodic pair, for example, use a Pair ID of 1 on both sides, and assign one side a Side ID of 1 and the other a Side ID of 2. On the outlet, assign a pair ID of 2 to both members of the pair, but use a Side ID of 1 for one side and a Side ID of 2 for the other. Do not use the same pair ID for surfaces that are not periodic with one another.

Periodic boundary conditions (cyclic symmetry) enable users to model a single pas-sage of an axial or centrifugal turbomachine or of a non-rotating device with repeating features (passages).


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Periodic boundaries are always applied in pairs; the two members of a periodic pair have identical flow distributions. The two members of a periodic pair must be geo-metrically similar.

Periodic pairs are used at the inlet and outlets of repeating devices:

Periodic boundary conditions are a convenient way to include the effect of multiple repeating features in a simplified model. Because of the repeating geometry, the flow upstream and downstream of a device will be the same for each passage.

4.3.20 Transparent

The radiation model introduced in CFdesign v9 allows for the computation of radia-tive heat transfer through transparent media. The level of transmissivity of such media is defined as a material property on the Materials Task dialog. To simulate transparent media that is completely immersed in the working fluid, only the mate-rial transmissivity needs to be specified. To simulate transparency through surfaces on an exterior solid, the Transparent boundary condition is also required.

This boundary condition is used to indicate that an exterior surface of a solid part is transparent, allowing radiative energy to pass through it (such as through a window). Exterior wall surfaces that do not have this condition are con-sidered opaque, and will not allow radiative energy to pass through them, regard-less of the value of transmissivity assigned to the material.

The only parameter associated with the Transparent condition is the Background Temperature. This is the temperature of the environment outside of the analysis domain.

Periodic Pair 1

Periodic Pair 2


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An example of the application of this condition is to simulate a room heated by sun-light coming in through a window on an external wall of the model:

The temperature specified with this boundary condition is used to define the incom-ing radiation flux according to this equation:

Transparent BCs should only be applied to external boundaries so that the incoming flux is external to the analysis domain. This boundary condition can only be used with transparent parts--parts that have a non-zero value of transmissivity.

Solar heating problems should not use transparent BCs because the set up of the solar heating problem requires a sky dome and ground structure that define the entire external boundaries. If windows are modeled in these cases, these transpar-ent materials would be internal to the analysis domain which would make transpar-ent boundary conditions inappropriate.

If an external transparent part is not assigned a transparent boundary condition, the emissivity and transmissivity will automatically be set to 0 because the follow-ing relation is observed:

reflection = 1 - emissivity - transmissivity.

In such a case, the external boundary will be perfectly reflective (like a silver back-ing on a mirror) with the exterior of the model. This is done to conserve energy; because no background temperature is defined, the heat loss or gain cannot be computed.

Note that radiation must be enabled (on the Options dialog) for the Transparent boundary condition to work.

Window (solid part),Ambient Temperature = 30 C

Room Temperature = 20 C

q"" σ Tbackground( )4=


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The Background Temperature can be varied with time by clicking the Transient bul-let, and specifying the time function.

4.4 Volumetric Boundary Conditions

Heat generation is a volume condition that applies an amount of heat to a geomet-ric volume. This is most often used to simulate the presence of heat-dissipating components in electronics assemblies.

4.4.1 Volumetric Heat Generation

This is a volume-based boundary condition, and is available if the selection mode is set to Volume. The applied condition is the amount of heat divided by the volume of the part.

4.4.2 Total Heat Generation

This is a volume-based boundary condition, and is available if the selection mode is set to Volume. The applied condition is the amount of heat on the part, and is not divided by the volume.

4.4.3 Temperature Dependent Heat Generation

This allows the heat generation to vary with temperature. Physically, such a condi-tion is a thermostat, and allows for the simulation of a heating device that shuts off (or greatly de-powers) once a target temperature is reached. Temperature-depen-dent heat generation is available for both volumetric and total heat generation boundary conditions. The location of the sensing temperature can be set to be either the centroid of the part or at some other user-selected location.


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A temperature-dependent heat generation allows for the simulation of industrial processes that operate within a narrow temperature band by adjusting the heat input to maintain the target temperature.

Note: Heat Generation cannot vary with temperature and time simultaneously.

To apply a Heat Generation or Total Heat Generation boundary condition with a remote sensing location:

1. Select the part or parts to be assigned the boundary condition, and specify the units.2. Check the Temperature Depen-dent box.3. Select the units of temperature, the variation method, and click Define to specify the parameters of the varia-tion.4. Select either Part Centroid or Pick on Surface from the Sensing Location menu.

Part Centroid, uses the temperature of the part as the driving temperature.

Pick on Surface uses the average tem-perature at the selected surface as the driving temperature.

5. Select a sensing location in the model by graphically picking a surface. Click OK on the Pick Sensing Location dialog to finish selection.6. Click Apply.

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4.5 Transient Conditions

4.5.1 Constant

The Constant variation method causes the boundary condition to remain static throughout the calculation. The condition does not change, unless the value is changed by the user.

To make a boundary condition vary with time:

1. Click the Transient bullet2. Select the time variation method3. Hit the Define button to set up the variation.There are seven variational methods, each described below:

• Constant• Ramp Step• Periodic• Harmonic• Polynomial• Inverse Polynomial• Power Law• Piecewise Linear

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4.5.2 Ramp Step

4.5.3 Periodic

The Ramp-Step function combines a lin-ear ramp function with a flat step func-tion.

Refer to the sketch below for the param-eter meanings. The T# values are the times that inflections occur. The F# val-ues are the min and max of the vari-ables. One cycle of this function goes from T4 to T4.

The ramp step function should be speci-fied such that the maximum value (F1) occurs first at time T1. At time T2, the value starts to ramp down. At time T3, the function hits its minimum value (F2). At time T4, the value starts to ramp up.

The Periodic type of boundary condition is exponential in time. The Functional Form is shown in the dialog.

Note that the function can be decaying in time by entering negative values for the “B1” or “B2” parameters. Also, only one set of values is required, either “A1”, “B1” and “C1” or “A2”, “B2” and “C2”. The default for all the parameters is zero.


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4.5.4 Harmonic

4.5.5 Power Law

The Harmonic type of boundary condi-tion is similar to the Periodic except that the variable is a function of sine and cosine functions. As in Periodic, only one set of values need to be specified: either the cos or the sin values. Note that the cos and sin functions do change sign, so negative values of the variable can result if improper parameters are entered on this dialog.

The Power Law function raises time to an exponent value.


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4.5.6 Polynomial and Inverse Polynomial

4.5.7 Piecewise Linear

The Polynomial and Inverse Polyno-mial variational methods rely on a table of data points. A curve is fitted to the data using the specified order. Care should be taken with higher order func-tions: Such polynomials contain inflec-tion points which may cause the data to change sign.

To check the curve fit of the polynomial or inverse polynomial, click the “Plot” button.

The Piecewise Linear function type connects the inputted data points with linear segments, and interpolates between them.

To make a function repeat for all time, check the Repeating box.


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4.6 Physical Boundary Types

This section describes the different kinds of physical boundaries and relates them to the boundary condition types available in CFdesign.

4.6.1 Inlets• Inlets are most often defined with either non-zero velocity components or a gage static pressure, or...• An inlet can be a fan. The inlet flow rate will vary with the pressure drop through the device, or...• Volumetric flow rate can be assigned as an inlet condition, or...• Mass flow rate can be assigned as an inlet condition, or...• Total Pressure can be used at the inlet of supersonic flow models if that is the only quantity known.• For heat transfer analyses, specify the temperature at all inlets.• For subsonic conditions at the inlet, specify velocity OR pressure, not both.• For supersonic inlet conditions, specify both the velocity and the static pressure. This is necessary only if the inlet is nearly sonic or faster. For more information about Compressible analyses, please see the Analysis Guidelines chapter of this manual.• For compressible flow analyses that include heat transfer, specify a total temperature as well as a velocity and pressure.• When using a general scalar, specify the scalar at all inlets, even if the value is zero.• To include swirl (an out of plane velocity component) in a 2D axisym-metric analysis, specify the third component of velocity (usually the z-com-ponent). • It is not necessary to specify turbulence quantities at any inlet. The inlet turbulence intensity used to calculate the turbulent kinetic energy and turbulent energy dissipation is set in the Turbulence menu launched from the Options dialog.


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4.6.2 Outlets• The recommended (and most convenient) outlet condition is a gage static pressure with a value of 0. If this condition is used at an outlet, then no other conditions should be applied to that outlet.• If the outlet velocity, mass flow rate, or volumetric flow rate is known, then any of these conditions can be applied to the outlet. If this is done, then a pressure must be specified at the inlet.• An external fan boundary condition pulling flow from the model can be applied to an outlet.• If the outlet flow is supersonic, the Unknown boundary condition is often the recommended condition. Unknown is a “natural” condition mean-ing that such an outlet is simply open, and no other conditions (velocity or pressure) are enforced.• Outlet conditions should be positioned far enough downstream from sudden turns or contractions to allow the flow to reach a fully developed state, which is the condition assumed by CFdesign. Furthermore, if the out-let is too close to a sudden expansion, flow will come back in through the outlet. This may cause convergence difficulties:

4.6.3 Walls• AutoWall sets wall conditions automatically on all surfaces that are not defined as inlets, outlets, symmetry, slip, or unknown.• It is not necessary to set a zero velocity (no-flow) condition at any fluid/solid interface.

NO YES


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• Wall turbulence conditions are set automatically by CFdesign.• For heat transfer calculations, walls with no specified thermal boundary conditions will be considered perfectly insulated.

4.7 Initial Conditions

Unlike boundary conditions, initial conditions are only enforced at the beginning of an analysis. They are primarily used for transient analyses, but sometimes they are useful for steady state analyses (temperature, in particular).

It is generally not recommended to apply a velocity initial condition to a steady-state flow analysis. Studies have shown that the best initial velocity for most steady-state flow calculations is the default of 0.

Shown is the Initial Condition dialog (accessible by selecting the Initial tab at the top of the Loads dialog) and instructions for its use:


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There are six quantities that can be applied as initial conditions: Velocity, Pressure, Temperature, Scalar, Humidity, and Steam Quality. An additional initial condition, Height of Fluid, can be applied only to volumes. Applying a Height of Fluid condition marks a region as containing fluid, and activates the Height of Fluid function in the Solver. See Chapter 12 for more details about Height of Fluid analyses. Details for the other quantities are described in the preceding Boundary Condition sections.

This Re-Initialize check box allows the user to reset a result quantity in all or part of an analysis model. This box is accessible only after the analysis has been run at least once.

1. Set the Selection Mode, and select only the Surfaces or Volumes to which the intended initial condition will be applied. (Chapter 2 contains more information about entity selection.)

2. In the Initial Condition Group, select the Type of initial condition and the Units.

3. Most of the initial condition types have certain parameters you will need to select. For example, the tempera-ture can be either Static or Total. Also, enter the value.

4. Hit the Apply button to finish set-ting the condition.

5. Other commands: The Delete but-ton will remove the boundary condition of the type shown in the Type drop menu from the selected entity or enti-ties. The Delete All button removes all boundary conditions from the model.

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Normally, initial conditions only take effect on a model when the analysis is first started (either from iteration 0 or from time 0). When the Re-initialize box is checked, however, all of the applied initial conditions will take effect again. This allows the user to discard a result quantity on an analysis while preserving other results fields. It also allows the user to apply an initial condition to all or part of the model mid-run--even though some iterations have already been completed.

An example of the use of this feature is if a flow solution is run to completion, and then the user realizes that an initial temperature condition is necessary for the sub-sequent transient thermal portion of the analysis. To accomplish this, simply apply the desired temperature initial condition, check the Re-initialize box, and run the thermal portion of the analysis. The initial condition will be applied to the model, and the analysis will proceed.

The Re-initialize check box will be cleared automatically after the analysis is started. This is to prevent unwanted re-initialization in subsequent re-starts of the analysis.

4.8 Graphical Indications

Unlike most other analysis packages that use vectors or some number of symbols to indicate the presence of a boundary condition, CFdesign uses colored stripes to


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mark boundary conditions. The colors are defined in a legend that appears in the top left corner of the Graphics Window. Shown is an example:

In this case, a white stripe on the inlet face means that a Velocity Normal is applied. The yellow stripe on the outlet means that a pressure is applied. The green stripes along the outer surfaces mean that a film coefficient is applied.

There is no need to memorize the meaning of the colors because they are always defined in the legend. This legend only shows boundary condition types that have been applied to the current model.


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4.9 Feature Tree

All applied boundary conditions are listed on the feature tree:

These listings are very helpful for checking, editing, and deleting loads.

• To highlight an entity with an applied condition, left click your mouse on an entity ID--it will appear green in the Graphics window. • To edit an applied condition, right click on the condition, and select Edit.

• To delete an applied condition, right click it and select Delete.

• To delete all applied conditions, right click on the top-level Boundary Conditions branch, and select Delete All.


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CHAPTER 5 Mesh Sizes

5.1 Introduction

Prior to running a CFdesign analysis, the geometry has to be broken up into small, manageable pieces called elements. The corner of each element is called a node, and it is at each node that a calculation is performed. All together these elements and nodes comprise the mesh (also known as the finite element mesh).

In three dimensional models, each element is a tetrahedral: a four sided, triangu-lar-faced element. In two dimensional models, each element is a triangle. Both are shown:

Constructing these elements into the geometry is done automatically by the soft-ware, so that step does not require any work on the part of the user. What the user needs to do, however, is tell the software what element size(s) to use, and where to use them. There is a lot of flexibility to this, and the following sections help to define what sort of mesh size is required and how to apply it.

To help identify and locate problem areas in CAD geometry, CFdesign incorporates a new Geometry Diagnostics utility into the analysis process. This function interro-gates the geometry in a very detailed manner to determine the location of potential problem areas. These areas may cause difficulty in the determination of mesh sizes, the mesh generation, and even in the solution stability of the analysis.

One of the questions most often asked by new (and experienced) users of CAE tools (including CFdesign), is what mesh sizes should they apply to their analysis models.


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Techniques based on geometry shape as well as anticipated flow behavior have been developed and communicated, but mesh sizing is still an area that confounds many casual users.

In CFdesign, a geometry-based, automatic mesh sizing facility has been developed that solves this problem. This facility performs a comprehensive topological interro-gation of the geometric model, and assigns mesh sizes based on curvature, geo-metric gradients, and neighboring features. Building on this automation, extrusion meshing has also been implemented to greatly facilitate the meshing of long, skinny parts such as pipes and heat sinks.

5.2 Geometry Diagnostics

The Diagnostics function searches for surfaces that are extremely thin and edges that are extremely small relative to the rest of the model. In many cases, these entities are caused by poor geometry creation practices, a lack of design intent, or are the result of multiple format conversions throughout the life of the design model.

Diagnostics is a tab on the Meshing task. The controls for each selection mode per-form different actions, but all are designed to help identify problems and/or simplify the analysis model.


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5.2.1 Part Mode Diagnostics

In previous versions of CFdesign, parts were omitted from an analysis by assigning a mesh size of 0. In CFdesign v9, this has been made more intuitive, and is per-formed by Suppressing parts in Diagnostics:

Suppressed parts will appear with the word “Suppressed” in the Mesh branch of the feature tree.

They will also be colored light blue to differentiate them from active parts.

When parts are suppressed or resumed after mesh sizes are assigned, a recalcula-tion of the mesh distribution will automatically occur on the modified model. If the suppressed or resumed parts do not appreciably change the Minimum Refinement Length, then the mesh distribution will automatically be recalculated after leaving the Part mode of the Diagnostics tab.

If the Minimum Refinement Length is affected, then a message will come up indi-cating this, and the mesh distribution will not be recalculated until another task is opened or the analysis is saved. This allows modification of the Minimum Refine-

Set the Selection mode to Part. (In 2D, surfaces will be selected and can be sup-pressed.)

Select a part or parts that are to be excluded from the analysis model.

Click the Suppress Selected Part(s) button.

To resume a suppressed part, select it, and click the Resume Selected Part(s) button.

To resume all suppressed parts, click the Resume All Parts button.


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ment Length on the Edge mode. The mesh distribution can be rebuilt by opening the Automatic tab, and clicking either the Automatic Size or Play Macro button or by changing tasks.

5.2.2 Surface Mode Diagnostics

Surface mode Diagnostics identifies potentially problematic surfaces that may lead to meshing difficulties. Examples of such surfaces include slivers, very thin annular surfaces, and surfaces with a “cusp” or tangency region.

5.2.2.1 Problematic Surfaces

Surfaces are deemed “problematic” based on the separation distance between edges. The variation of separation distances is assessed to determine a minimum threshold. All surfaces with an edge separation distance below this threshold are considered potentially problematic, and are shaded.

Extremely high-aspect ratio surfaces such as slivers and annuli have edges that are very close to each other within the separation distance. Surfaces that contain tan-gencies may be mostly well formed, but can be considered problematic because of the tangency between two or more edges.

Problematic surfaces have been the reason for many meshing failures or solution problems due to a badly distorted mesh. Identifying and locating them before attempting to run the analysis is essential to reducing wasted time and effort. This dialog provides two ways of dealing with problematic surfaces: identification and refinement.

Sliver Annulus Cusp


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5.2.2.2 Identification

The first function, identification, is performed by coloring the surfaces orange. A slider on the dialog varies the edge separation distance from the threshold to the minimum. By moving the slider to the left, the display is restricted to progressively smaller surfaces until the far left position--which shows the very smallest surface or surfaces. Displayed problematic surfaces can then be added to a group and saved to an external text file for reference. The text file makes it convenient to locate the surfaces in the CAD model and apply a fix.

Keep in mind that the principal objective of Surface Diagnostics is to locate the smallest surfaces in the model. Such surfaces are often unintentional surfaces that will make meshing difficult or impossible. However, there are situations in which small surfaces are intentional, and cannot be removed. In some cases, surfaces may be identified that are simply the smallest surface in the model, without having any inherent flaw. In this case, they will likely be ignored by the Automatic Refine-ment. In other cases, very small surfaces are identified that are truly high aspect- ratio slivers, and will be refined automatically to ensure the successful creation of a quality mesh.

5.2.2.3 Automatic Refinement

The second function is Automatic Refinement. This is an attribute that is assigned to high aspect-ratio surfaces that causes them to be refined automatically by the


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Automatic Mesh Sizing facility. This is used primarily for surfaces that fit the follow-ing criteria:

• Very high aspect-ratio (longer and thin)• Close proximity to larger surfaces

This function is fully automatic, and only affects high aspect-ratio surfaces. Its pur-pose is to ensure that such surfaces are meshed finely enough so that the specified mesh sizes do not significantly exceed the dimensions of the surface. These reduced length scales are then propagated to the surrounding entities, resulting in a smooth transition.

After Automatic Mesh sizing has occurred, surfaces that will be automatically refined are shaded in an olive color.

Extreme transitions have been found to have a detrimental effect on both the gen-eration of the mesh as well as the solution accuracy.


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5.2.2.4 Surface Diagnostics Process

When the CAD model is first read into CFdesign, the geometry is scanned and prob-lematic surfaces are identified. If found, the controls in the dialog are available to identify and store them to a text file or group:

The Status group indicates if any prob-lem surfaces are found. Only problem surfaces are then displayed, and are col-ored orange for clarity. The Arrows check box toggles arrows that point to the small surfaces. (Note: the surfaces highlighted by default are considered for automatic refinement.) See Note 1 below.

Use the Highlight Surfaces slider to vary the edge separation distance. Mov-ing to the left reduces the separation distance, and shows the smallest sur-faces.

Change the displayed maximum edge separation by keying a new value in the Max Size field. This is useful for show-ing more surfaces. Restore the default value with the Restore Default Max button.

Save the displayed surfaces to an exter-nal text file with the Save to a Text File button. See Note 2 below.

Add surfaces identified as problematic to a group with the Save to a Group but-ton.


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Note 1: All surfaces are blanked except the problem surfaces, right clicking in the Graphics window will redisplay all surfaces; clicking on the slider will blank all but the problem surfaces again.

Note 2: The filename of the text file containing small surfaces is the analysis name followed by the word “surface”. If the analysis name is “run1”, then the text file will be “run1-surface.txt”.

5.2.3 Edge Mode Diagnostics

Edge Mode Diagnostics locates edges that are extremely small relative to other edges in the geometry. Variations in edge length greater than several orders of magnitude are often indicative of a geometric problem which may cause difficulty for the mesher. The distribution of edge length values throughout the model is also calculated, and is then used to determine the “Minimum Refinement Length” as used by the mesher.

The Minimum Refinement Length is the threshold edge size that will be allowed to influence the mesh in neighboring features. Edges that are below this size will be meshed, but will only have a node at each end. Such small edges are meshed with a single small element, but that small element size will not propagate to other fea-tures in the model.

The Edge Mode dialog provides two mechanisms for dealing with extremely small edges: Identification of small edges and Adjustment of the Minimum Refinement Length.

5.2.3.1 Small Edge Identification

When the model is first opened, all edges that are three orders of magnitude or more smaller than the largest edge in the model are identified, and the slider can be used to vary the highlighted size.

A default Minimum Refinement Length is automatically determined based on relative edge lengths throughout the model. This value is shown in the Min Refine-ment Length field in the dialog, and is the default slider position. When the slider is at this position, all highlighted edges fall below this value, and will only be meshed with two nodes.


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Note: If a large number of edges are smaller than the Minimum Refinement Length, it may be necessary to reduce its value. In such cases, the Mesh task dialog will open directly to the Edge Diagnostic panel, and many edges will be marked with arrows. Reducing the Minimum Refinement Length will improve the chances of successfully generating a mesh.

Edges that are the current size indicated by the slider and smaller are highlighted.

If no edges are less than three orders of magnitude smaller, then the slider will be grayed out.

5.2.3.2 Adjustment of the Minimum Refinement Length

The Minimum Refinement Length provides control over whether (and to what extent) smaller length scales propagate throughout the mesh. This feature does not remove small features, but can limit their effect upon local length and mesh scales.


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As an example, the model shown has four very small edges at the corners of the cut-out. Each edge is highlighted, and is identified with an arrow:

Edges that are shorter than the default Minimum Refinement Length are meshed coarsely, and do not affect neighboring geometry

This will improve the mesh on very small features, but may increase the number of nodes and elements in your analysis model. This is necessary if significant edges fall below the default Minimum Refinement Length. In the image below, the Mini-mum Refinement Length is set to be smaller than the length of the four small edges. Notice their effect on the mesh:

To increase the refinement on small edges, and hence INCLUDE their effect in the model:

Reduce the Minimum Refine-ment Length to a value LESS than the length of the particu-lar edge.


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Edges that are longer than the default Minimum Refinement Length are meshed finer, and do affect neighboring geometry.

In the image below, the Minimum Refinement Length is set to be larger than the small edges. The mesh distribution will be considerably more coarse. The edges will be meshed, but will not strongly affect the mesh on surrounding geometry:

Changes to the Minimum Refinement Length affect the model globally, and are not isolated to a particular location. Care must be taken so that the Minimum Refine-ment Length is not accidently made larger than other important edges elsewhere in the model. Doing so will effectively remove their influence on the mesh, and may lead to accuracy issues.

Note that if the Minimum Refinement Length is changed after applying Automatic Mesh Sizing, the mesh distribution must be reapplied by clicking the Automatic Size button. Otherwise, the new Minimum Refinement Length will not affect the mesh distribution.

To decrease the refinement on such an edge, and hence EXCLUDE its effect on the model:

Increase the Minimum Refine-ment Length to a value GREATER than the length of the particular edge.


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5.2.3.3 Edge Diagnostics Process

When the CAD model is first loaded, all edges are scanned and a Minimum Refine-ment Length is determined. If any edges are shorter than this length, the controls in the dialog are active, and the edges are highlighted.

The Status group indicates that edges three orders of magnitude smaller than the longest edge exist with the message “Potential Prob-lems Found.” The Arrows check box toggles arrows that point to all small edges to help locate them.

Use the Highlight Edges slider to vary the edge length. Move to the left to reduce the length; the far left position shows the small-est edge in the model.

Change the maximum displayed edge length by keying a new value in the Max Size field. This is useful for showing more edges. Restore the default value with the Restore Default Max button.

Save the displayed edges to an external text file with the Save to a Text File button. The text file containing edges will be automati-cally named: analysisname-edges.txt.

Add the displayed edges to a group with the Save to a Group button.

If necessary, change the Minimum Refine-ment Length by either keying in a new value or by clicking the Use Highlight Length but-ton. The default value can be restored with the Restore Minimum Length Scale but-ton.


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5.3 Fully Automatic Mesh Sizing

CFdesign provides a completely automatic mode of mesh definition. By completely skipping the Mesh dialog from your analysis set-up, the mesh distribution will auto-matically be computed when the analysis is started. The process is automatic and seamless.

Specifically, the Interface detects that the Automatic Size button has not been pressed, and that no mesh sizes were assigned manually. The default Minimum Refinement Length will be used, and all critically small surfaces will automatically be compensated for in the mesh (using the Surface Refinement scheme described in Surface Diagnostics).

5.4 Automatic/Interactive Mesh Sizing

The controls in the Automatic tab of the Mesh task dialog allow automatic mesh size assignment, local user-controlled refinement (or coarsening), and mesh extrusion for linear, uniform cross section parts.

The benefits to this facility are numerous:

• Greatly simplified set-up of analysis models resulting in less time spent assigning mesh sizes.• More efficient mesh distributions--the mesh is fine where required, and coarse where it can be.• Improved solution accuracy due to better mesh quality and mesh tran-sitions.• Improved solution robustness--good mesh transitions lead to a well-posed mathematical model.


Mesh Sizes

Assigning mesh sizes is now a one step process (with two optional steps):

With a push of the Automatic Size button, CFdesign performs a comprehensive topological interrogation of the analysis geometry and determines the mesh size and distribution on every edge, surface, and volume in the model. Geometric cur-vature, gradients, and proximity to neighboring geometry are all considered when assigning element sizes and mesh distributions.

It does not matter which selection mode (volume, surface, or edge) is active when this button is clicked.

This process is fast, but can take a few minutes for larger geometries containing 3000 or more edges.

1. Click the Automatic Size button.


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Models with Automatic Sizing mesh distributions are shown:


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The mesh distributions on each of these cases were computed automatically simply by clicking the Automatic Size button. Note that surfaces and edges with high cur-vature are meshed finer, and those with little or no curvature are meshed coarser. Edges that are close to other edges are assigned smaller element sizes which can even vary along the span of the edge.

Note that if the Minimum Refinement Length (on the Edge Diagnostics panel) is changed after applying Automatic Sizing, a message will prompt the user to reapply Automatic Sizing. If Auto Sizing is not invoked again, the mesh distribution will not be affected by the modified Minimum Refinement Length.

The cyan dots drawn on the model indicate how the actual mesh will appear on the model. The location and spacing of the dots does not change if the Selection Mode is changed. If there are edges in a model that do not have cyan dots, this is a sign that the surfaces are not meshable. This is usually caused by extremely thin sur-faces or some other geometric flaw. This should be corrected in the CAD model prior to running the analysis.

After sizing is invoked, there are two optional steps available:

• Select entities for refinement by switching the selection mode, and graphically selecting them. Use the Size Adjustment slider.• Select volumes for extrusion meshing. The Extrusion controls are avail-able only when volumes eligible for extrusion are selected.

5.5 Optional Step 1: Size Adjustment

The underlying criteria for the Automatic Mesh Sizing facility is the geometry. Mesh is automatically concentrated in regions of high curvature and rapid size variation. In certain situations, however, significant flow gradients in a simple geometric region may require a finer mesh than assigned by the Facility.

An example is a volume constructed in the wake region in an aerodynamics model. The volume is quite simple, so its automatically-defined mesh will be coarse.


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Because the flow will be quite energetic, and will have high gradients, a finer mesh is required:

A mechanism is provided that allows for the local adjustment of automatically assigned mesh sizes on volumes, surfaces, and edges after Automatic Sizing has been invoked.

1. Set the selection mode (Volume, Sur-face, or Edge), then select the desired entities.

2. Use the Size Adjustment slider to refine or coarsen the mesh on the selected entities. The size preview points will update as the slider is moved.

3. To apply a uniform mesh on a part, click the Use Uniform button.

4. Click the Apply button to confirm the changes.

5. All adjustments (including Uniformity) since the last Spread Changes can be undone by clicking the Cancel button.

6. When all adjustments are made, click the Spread Changes button. This func-tion recalculates the mesh distributions throughout the model to reconcile applied changes with the mesh on neighboring geometry.

Step 1

Step 2

Step 4

Step 3

Step 6

Step 5


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The process is illustrated:

5.5.1 Slider

The slider uses a parametric scale that extends between 0.2 and 5, with a default position of 1.0. This allows the mesh size to be reduced to 1/5th or increased to as much as 5 times the original size. To apply a value that exceeds the minimum or maximum range, (smaller than 0.2 or larger than 5), type the scaling value into the field to the right of the slider.

As the slider is moved, the modified distribution updates dynamically. After decid-ing on a desired slider position, click the Apply button. This ensures that the set-ting will be available in the replay Macro file (used for rebuilding the mesh distribution and when settings are applied to modified geometry).

The Cancel button will return the slider position to 1--effectively undoing any adjustments made to an entity after either the automatic size specification or since the last Spread Changes command.

Note that the mesh quality constraints embedded in this system may override adjustments that excessively coarsen the mesh. This is done to prevent a mesh definition that will result in a poor-quality or failed mesh.

5.5.2 Spread Changes

When the Spread Changes button is pushed, all modified settings are resolved with neighboring settings to ensure proper element transitions. The slider position for each adjusted entity resets to 1--the middle of the slider range. This means that

Original mesh size on wake region. Mesh refined to 0.4 on wake region.


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the newly assigned size becomes the default size for subsequent adjustments. Note that the slider does not reset when the Apply button is pressed.

In general, however, the Spread Changes button should be used sparingly because pushing it initiates a complete recalculation of the mesh distribution. If Spread Changes is not pressed prior to leaving the Meshing dialog, the function will be invoked automatically when the analysis is started or when the analysis is saved.

5.5.3 Uniform Sizing

A uniform mesh distribution can be applied to an entity by selecting it, and clicking the Use Uniform button. This command modifies the underlying length scales throughout the entity to be the same, based on the smallest length scale on the object. It is not necessarily persistent, however, and subsequent changes to neigh-boring entities can cause the mesh to again vary. For this reason, we recommend that Uniformity is applied after other adjustments have been made.

After the Use Uniform button is clicked, the slider will reset to 1. This allows subse-quent modification of the size on the entity.

Uniformity can be removed from an entity by selecting it and clicking the Cancel button IF this is done prior to hitting the Spread Changes button. After Spread Changes is clicked, Uniformity cannot be removed directly from the model.

5.5.4 Play Macro

The relationship between size adjustment on entities and the recalculation of neigh-boring length scales when the Spread Changes button is selected is quite complex. This makes it potentially difficult to exactly recreate a mesh distribution on a com-plicated model if multiple adjustments occurred.

To facilitate this process, a log file containing all size adjustment commands is automatically recorded when Automatic Sizing is invoked. Every size adjustment and instance of the Spread Changes button is recorded, and can be played back to exactly reproduce a mesh distribution on a given model.

The file is first created when the Apply button is clicked after adjusting a size, and commands are automatically appended as they are issued. When the Delete All


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button is hit, the mesh distribution is removed from the model, and the Play Macro button becomes active. Click it to re-assign the mesh distribution to the model.

Invoke the file by clicking the Play Macro button. The button is available when a mesh distribution containing adjustments did exist, but was deleted. It is also avail-able if the distribution is deleted, and the Automatic Size button is pressed, and will overlay saved adjustments over the default mesh distribution.

This assigns the exact mesh distribution that was previously saved. Note that a specific macro should only be applied to the same geometry. Applying this file to a different geometry will lead to unexpected results.

The file is named with the analysis name with the extension “.meshlog”. To use a mesh log with another analysis based on the same geometry, copy the meshlog file to the new analysis name, and click the Play Macro button.

The macro file is stored with the analysis file, and a copy is extracted to the working directory when the analysis is opened. If a macro file exists for that analysis, it will be overwritten by the one extracted from the analysis file. When an analysis is closed, the macro file in the working directory is copied into the analysis file. If there is no macro file in the working directory, then any macro file in the analysis file will be deleted. If the analysis is closed but not saved, the external copy of the macro file is not packed into the analysis file.

A macro file can be deleted through the CFdesign interface in these three ways:

1. Click the Automatic Size button when the model has a distribution that has been adjusted with the Size Adjustment slider. This resets the distribu-tion throughout the model to the default, deleting the macro file.

2. After deleting the mesh distribution, click the Automatic Size button, and adjust sizes. The first click of the Automatic Size button can be followed by clicking the Play Macro button to overlay it on the model. If, however, sizes are adjusted after hitting the Automatic Size button but prior to hitting the Play Macro button, the macro will be removed because a new adjustment strategy is assumed.

3. After deleting the mesh distribution, click the Automatic Size button twice. As mentioned in step 2, the first click of the Automatic Size button can be followed by clicking the Play Macro button. If the Automatic Size button is clicked again, however, the macro is removed.


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5.5.5 General Guidelines

This is a summary of the areas in which manual refinement is often recommended:

• Distributed Resistance Regions: In general, three elements through the width of a distributed resistance is recommended for best accuracy. For very thin geometry, this may not be practical. Some modifications were made in CFdesign v9 that improve the accuracy through a coarse mesh in a distributed resistance to about 20% or better.• Internal Fans: The mesh distribution in an internal fan should be adjusted to produce at least two elements in the flow direction of the fan.• Centrifugal Blowers: Try to attain at least five elements in the axial direction of the blower. Also, you may have to refine the inlet face slightly to ensure adequate flow into the device. This example has a few more than five nodes in the axial direction:

• Wake Regions: Illustrated above, geometry constructed in high-velocity or high-gradient regions should be refined to ensure adequate rep-resentation of the flow physics. In some models, a uniform mesh distribu-tion is useful, especially if the default distribution has a lot of variation. Use the Use Uniform button to apply a uniform mesh.• Motion Path: The mesh distribution in the path of a moving object should be refined as described in the Motion Chapter of the User’s Guide. This will allow the velocity and pressure distributions to be calculated prop-erly and prevents mesh “bleed-through.” A uniform mesh is often recom-mended for the motion path, and is prescribed using the Use Uniform button.• Rotating Regions: A uniform mesh should be used when possible on a rotating region. This is recommended because the default automatic sizing


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will often cause the initial position of the impeller to influence the mesh on the rotating region, potentially causing problems as the impeller rotates. With a uniform mesh on the region, the mesh will not skew the results.

5.6 Optional Step 2: Extrusion

5.6.1 Introduction

Historically, tet-meshing high-aspect-ratio geometry requires a large number of elements, and a long calculation time. In CFdesign v9, a much more efficient method for meshing such geometry is introduced in the form of extrusion meshing.

The extrusion function in CFdesign stretches triangular faces into multiple layers of wedge (prism) elements through the length of three dimensional parts with a uni-form cross section. Extrusion meshing often greatly reduces the element count in high aspect-ratio parts, and improves flow accuracy in models dominated by form drag, such as pipe flow.

Extruded meshes are structured meshes, but can contact or even be immersed in regions meshed with unstructured tetrahedrals. This is called “non-conformal” meshing, and is a condition in which the nodes in the extruded section do not line up automatically with the surrounding mesh. CFdesign detects and deals with this situation automatically. Because of the bookkeeping that this requires, it is not pos-sible to change the mesh in a model containing extruded regions and continue from a saved analysis. When the mesh is changed, it is necessary to start the analysis back at the beginning.

Assuming the geometric constraints are met, extrusion meshes can be used on moving objects and for solids in rotating regions (such as fan blades), but not the rotating region itself.

Extrusion meshes cannot, however, be used for models with radiation.

The default advection scheme is recommended when using extrusion.


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5.6.2 Examples

Some examples of extruded meshes are shown:

A pipe with extruded mesh contact-ing a tet-meshed block. The element faces on the circular end of the pipe that contacts the block are extruded down the length of the pipe.

This heat sink is extrusion meshed: It is immersed in air that is tet meshed. The nodes do not line up, but the two parts are automatically linked computa-tionally.

A rectangular box is extrusion meshed. There are three extrusion directions available for this box, and the Extrusion dialog allows selection of the desired one.


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5.6.3 Assigning Extrusion

In its most automatic form, the Extrusion capability computes both the end mesh distribution and layer growth based on the geometry. Manual controls are also pro-vided that enable control of layer growth, end biasing, and the number of extrusion layers.

Available after Automatic Mesh Sizing has been invoked, select one or more vol-umes for extrusion, and click the Extrude Mesh button:

The Extrude Mesh button is active only when at least one volume eligible for extru-sion has been selected. A set of guidelines describing extrusion eligibility are given below.

Clicking the Extrude Mesh button opens the Extrusion dialog.

The Automatic check box controls the operation of the dialog: when it is enabled, the Automatic Sizing controls the number of layers and the end layer sizes. When disabled, additional controls are available.


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5.6.3.1 Automatic Enabled

In this mode, the Automatic Sizing feature matches the layer sizes originating at each end of the part with the length scales used in the surface mesh at each respective end.

Note: Before applying extrusion to multiple identical parts in which it is critical that the mesh be identical, select the end surfaces of each channel, and click the Use Uniform button. This will help ensure that the mesh through passages such as heat sink channels or pipe rows will be equivalent.

1. Modify the growth with the Growth slider if more or less layer stretching is desired. The default is 1.3.2. Select the Extrusion Direction, if applicable. 3. While this dialog is open, the interac-tive Extrusion Preview line will show on the model.4. Click OK.

OK closes the dialog, and assigns Extru-sion to the selected part(s).


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5.6.3.2 Automatic Disabled

In this mode, more control is provided for the layering.

5.6.3.3 Extrusion PreviewA Preview Line is drawn through the part to indicate the layers. This is interactive, and updates as settings in the Extrusion dialog are adjusted. While this dialog is open, surfaces will blank on the active parts by right clicking on them to allow visi-bility of the preview. The Preview line below shows the extrusion for a Growth set-ting of 1:

1. Modify the growth with the Growth slider if more or less layer stretching is desired. The default is 1.3.2. Select the Extrusion Direction, if applicable.3. Select the type of End Layering.4. Select the number of Layers.5. While this dialog is open, the interac-tive Extrusion Preview line will show on the model.6. Click OK.

OK closes the dialog, and assigns Extru-sion to the selected part(s).


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5.6.3.4 GrowthThe Growth slider controls the degree of layer stretching through the part. When Automatic is enabled, the amount of acceptable growth also determines the num-ber of layers. The growth value is a constraint which governs the maximum rate which the element layers can grow from one element to the next. The range of this slider is from 1.0 to 2, with a default of 1.3. At the minimum setting (1.0), the lay-ers will be nearly the same size:

At the default growth (1.3), the layers will be approximately 30% larger in the part center:

The amount of growth from one layer to the next can be described with this equa-tion:

= amount of growth of a layer

= amount of growth of next layer

g = growth parameter

∆y( ) g( ) ∆x( )×≤∆x∆y


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At the maximum setting (2), the layers will be quite large relative to the ends:

When Automatic is unchecked, the number of layers is controlled with the Layers slider. The Growth parameter behaves differently than when Automatic is enabled, and does not represent a constraint. Growth values in the range of 20-50 are not considered extreme in many cases.

5.6.3.5 Extrusion Direction

The Extrusion Direction menu is available if:

• A single part is selected AND• There are multiple possible extrusion directions, such as in a box.

If multiple parts with more than one potential extrusion direction are selected, CFdesign will automatically select the extrusion direction that is most closely aligned with the longest dimension of the part bounding box. If the variation in part bounding box dimensions is minimal, then the direction most closely aligned with the maximum dimension of the assembly bounding box is used.


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The Extrusion Direction menu lists each possible direction, and the preview line updates to correspond to the selected direction:

5.6.3.6 End Layering

Available only when Automatic is unchecked, the End Layering menu controls the “biasing” of layers through the extrusion path. When a single part is selected, the options are:

• Uniform• Small at End• Small at Start• Small at Both• Large at Both

The determination of the Start and the End of the part is based on the internal topological direction of the part, and is not user-controllable. The Preview line graphically indicates on which end the layers will be smaller.

When multiple parts are selected, only the Small at Both and Large at Both options are available.


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5.6.3.7 Layers

Available only when Automatic is unchecked, the Layer slider controls the number of extrusion layers. The slider range is between 10 and 100, but it is possible to key-in a value as small as 2, or as large as 500.

5.6.4 Extrusion Geometry Guidelines

The Extrusion button on the Mesh task dialog is active only when the following con-ditions are met:

• Automatic Sizing has been invoked• One or more extrudable parts have been selected.

An extrudable part is defined as:

• a part whose cross-section is uniform (the topology of the part must be invariant in the extrusion direction)• a part that has a linear extrusion path• a part that is three dimensional• a part whose surfaces are uniform in at least one extrusion direction • a part whose ends are parallel to each other• a part that is topologically identical between the endcaps--it must have the same number and orientation of bounding edges on both surfaces

There are three physics limitations regarding extrusion meshing:

• Rotating regions cannot be extrusion meshed.• Analyses with radiation cannot have any extruded-meshed parts.• Surface parts cannot contact parts that are extrusion meshed.

Each of these points is explained:


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5.6.4.1 Uniform Cross-Section

For a part to be extrudable, it must have the same cross-section in at least one direction. If a part consists of an extrudable region connected to another region with a different cross section, the part is not extrudable:

In this example, because all three regions are in the same part, the part is not extrudable. The pipe and channel protruding out from the box would be extrudable if they were separate parts forming an assembly.

5.6.4.2 Linear Path

Only parts that have a linear extrusion path are eligible for extrusion. Parts that bend, even if the cross section is uniform, are not extrudable:

Not Extrudable

Not Extrudable


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5.6.4.3 Three Dimensional Parts

Only three dimensional parts are supported by extrusion. Two dimensional surfaces in 2D analyses must be free meshed.

5.6.4.4 Uniform Surfaces in at Least One Direction

It is not possible to extrude in a direction if edges on a surface are normal to that direction:

The edge on the top surface of this box prevents extrusion in the two directions marked “No” because the surface is not uniform in those directions. The other direction is fine because the edge is uniform through the entire extrusion direction.

No

No

Yes

This edge is the culprit!


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5.6.4.5 Ends that are Parallel to Each Other

The surfaces at the ends of an extrudable part must be parallel to each other. This is an extension of the uniform cross-section rule, and explicitly applies the rule to the ends of the volume:

5.6.4.6 Rotating Regions

Objects within a rotating region that have a uniform cross-section that satisfy the requirements for mesh extrusion can be extruded. The mesh inside of the rotating region, however, cannot be extruded because the interface between the rotating region and the adjacent stator must be a conformal (matching) mesh.

5.6.4.7 Radiation

Extruded meshes are not compatible with radiation calculations. An error will be issued if objects are extrusion meshed and Radiation is enabled.

5.6.4.8 Surface Parts

Surface parts cannot touch parts that are extrusion meshed. This limitation applies to surface parts used as obstructions (solids), contact resistance, and distributed resistances.

Not Extrudable


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5.7 Geometric Changes

When geometry is changed in the CAD tool and launched back into an analysis or when settings are transferred between analyses in a project, the entire model will be Automatically Sized, and any customizations to the mesh distributions will be applied back to the model.

This process is performed by automatically sizing the modified geometry, and then replaying the Macro mesh file. Automatically sizing the model accounts for dimen-sional changes and ensures that newly introduced parts will have a mesh distribu-tion. Replaying the macro ensures that adjustments to the mesh distribution on any parts, surfaces, or edges are also preserved.

Additionally, when transferring settings in a project, the minimum refinement length is adjusted proportionally based on the modified geometry and the value set in the source analysis.

The entire process is automatic, and is designed to ensure that the mesh distribu-tion is preserved as much as possible when modifications are made to the model. There are three potential status messages that can occur:

Model entity map was complete. Full Macro played. This means that a com-plete one-to-one correspondence existed between the original and the modified geometry. All adjustments to the original model were transferred to the modified model.

Model entity map was partially complete. Partial macro played. This means that the number of components differs between the original and the modified geometries. Mesh distribution adjustments are transferred, but there are either new parts that have the default mesh distribution or parts were removed.

Model entity map failed. Macro deleted. This means that none of the original components were found in the model after updating the geometry. The result of this is that the model will be auto-sized, but no size adjustments from the original model will be transferred to the new one.

The following mesh attributes are also transferred between analyses in a project:

• The Minimum Refinement Length, but may be scaled from the source value based on the geometry modifications in the target model


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• The fact that the mesh was defined using Automatic Sizing.• Extrusion data if the corresponding source surfaces can be determined.

5.8 Advanced Parameters

Several additional parameters are contained on the Advanced dialog, accessible by clicking the Advanced button:

These define constraints that affect the behavior of the Automatic Mesh Sizing facil-ity globally. These parameters should be used with caution as they may have a sig-nificant impact on the resulting mesh.

5.8.1 Resolution Factor

The Resolution Factor controls the relative fineness of the mesh in response to the curvature detected on the model entities. Though this parameter has global scope, the effects are localized to regions of high curvature. Smaller values result in a finer mesh on model entities with curvature. Regions with no curvature are not affected by this parameter.

The default value is 1.0, and the acceptable range is between 0.1 and 3.0. Values outside of this range are rejected.


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5.8.2 Local Stretching

This parameter controls the quality of the distribution computed by Automatic Siz-ing. It is a constraint on the rate at which point distributions may expand or con-tract along an edge. Smaller values cause slower variation in the distribution from regions of high to low curvature. A value of 1.1 represents a permissible growth rate of 10% between adjacent elements within a distribution on a model edge. A value of 1.5 represents a growth rate of 50%.

This parameter influences distributions along individual edges as well as distribu-tions between edges. The net effect is that controlled blending is introduced along and across model entities.

The default Local Stretching value is 1.1, and the acceptable range is 1.01 to 2.0.

5.8.3 Minimum Points on Edge

For entities lacking curvature, a minimum level of resolution is guaranteed by this parameter. Increasing this value increases the minimum number of nodes on an edge. This is a constraint and not a prescription on the computed resources. If a small edge is in close proximity to a highly curved entity, these smaller length scales may drive the resolution on the small edges to be higher than the prescribed minimum value.

5.8.4 Points on Longest Edge

This parameter controls the minimum number of points on the longest edge in the model. It is most relevant for geometry with no curvature such as the surrounding box for an external flow model. This setting may be superseded by the influence of length scales on other model edges in conjunction with how the local stretching constraint dictates a smaller length scale. This may cause more points on the long-est edge than the value specified by the Points on Longest Edge parameter.

5.8.5 Surface Limiting Aspect Ratio

This parameter introduces an additional constraint during Automatic Sizing that affects the distributions on edges which bound high aspect surfaces as described in Surface Mode Diagnostics. During Automatic Sizing, surfaces identified by the diag-


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nostics facility are examined to ensure that the distributions generated for the bounding edges reflect length scales whose size is no greater than the product of the computed separation distance and the Surface Limiting Aspect Ratio. This limit-ing length scale may be smaller than that derived from the local curvature, and if so, the distributions are based on this constraint.

With this parameter, the user can introduce a further constraint on length scales ensuring that they are not larger than a specified factor of the dimensions of the surface. This can significantly enhance the robustness of the meshing operation.

Any value greater than or equal to 1 is permitted for this parameter.

5.9 Manual Application of Mesh Sizes

5.9.1 The Principle Guidelines

Leaning how to create a “good” mesh definition can sometimes be the most intimi-dating part of the analysis process. It does not need to be. There are two funda-mental rules that should always be considered when defining the mesh on any model.

The first rule is that the geometric shapes must be adequately defined. It is very important that the mesh sizes that you define on a model be such that none of the geometric features are mis-represented. An example is the mesh definition on a round tube. Too few elements (too large an element size) and that round tube will be approximated as a square duct:

The other principle guideline is that elements need to be concentrated where flow gradients occur. Where there is a lot of fluid movement, there needs to be more elements. Where there is little fluid activity (all the fluid moving in one direction, for example), the mesh can be a little more coarse.


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5.9.2 Basic Strategy

To ensure that a mesh definition is fine enough without being so fine that computa-tional resources are wasted, the following steps are recommended when perform-ing any CFD analysis:

• First, determine if there are any symmetries, and divide the geometry in the CAD system as appropriate. Look for geometric symmetries, but be sure that the flow will be symmetric as well.• Determine if the analysis can be modeled as a 2D or an axisymmetric geometry. A 2D approximation may be a good place to start, especially if you are unsure of how to solve a particular type of flow problem. • Examine the geometry, identifying probable high and low gradient regions for all solution variables (u, v, w, P, T, k and ).• Identify solid material zones and fluid zones and keep them as separate geometric entities or parts.• If there are areas with small, repeating geometric details (such as per-forated plates or baffles), try using distributed resistances to model these zones, instead of meshing the detail.• Assign mesh sizes to all volumes in the model, and then apply finer sizes to surfaces and edges where necessary in order to capture strong flow gradients or to represent complicated geometric features.• Perform an analysis on a “coarse” mesh (no more than 25,000 nodes) to qualitatively assess the flow features present and identify meshing needs in high gradient regions without a severe time penalty.• Looking at the results on the coarse mesh, refine the mesh in the high gradient regions.• To ensure that the final solution is not “mesh-dependent,” compare the two solutions from the coarse and fine meshes. If they are substantially dif-ferent, then it is a good idea to construct a mesh that has at least 10% fewer nodes than the fine mesh, obtain a solution and compare. The idea is to have two meshes that vary in number of nodes by 10% or more and that give the same solution. This solution is then said to be “mesh-indepen-dent”.

In any finite element analysis, more elements are required in areas where spatial gradients of the solution variables are high. In CFD, an additional physical phenom-enon called velocity-pressure coupling must also be accurately represented on the mesh to ensure continuity of fluid mass over the entire solution domain. This dis-tinction elicits the following two requirements:

ε


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• Many more elements must occupy the domain than in a typical struc-tural analysis.• Transitions in element size must be relatively smooth so that the area or volume of adjacent elements does not vary substantially.

In attempting to satisfy these criteria, engineers sometimes construct very large CFD finite element models, particularly when the geometry is complex. Typical 2D fluid flow analyses will require anywhere from 1,000 to 25,000 nodes; 3D analyses often range from 15,000 to 1,000,000 nodes! These ranges are exceeded in some applications. With computing hardware evolving so rapidly, expect to see these numbers continue to climb.

5.9.3 Locations of Mesh Refinement

This section contains information about where you should pay close attention to your mesh definitions. The underlying theme of this discussion is that the mesh should be fine enough to capture gradients and changes in the flow. Gradients may be due to geometric features, boundary conditions, or distributed resistance areas.

Solid Boundaries

Spatial gradients for velocity, pressure, turbulent kinetic energy and turbulent energy dissipation will generally be highest near a solid boundary, typically a con-tainment wall or the surface of an immersed body. This is particularly true if the flow is constrained by a tight clearance, forced to turn around a sharp corner or suddenly brought to rest at a stagnation point. Accordingly, mesh density must be greatest in these regions.

When analyzing turbulent flow, the element size adjacent to a solid boundary is particularly important for accurate prediction of shear stress. This ultimately affects the calculation of pressure drop across the solution domain. The k- and RNG tur-bulence models in CFdesign compute a non-dimensional distance from the wall, y+, at all nodes adjacent to a solid boundary. This value is useful in determining whether the elements adjacent to solid boundaries are sufficiently sized.

The y+ values may be viewed as a results quantity. In general, they should be kept within the range 35<y+<350. It is impractical and unnecessary for all y+ values to be within this range, but it is a good general guideline. This range is most critical for flows that experience a great deal of pressure drop due to shear. Examples of such situations are the flow through long pipes and flow over aerodynamic bodies.

ε


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In flows where form drag dominates the pressure drop, the y+ criteria is not nearly as important. The use of Boundary Mesh Enhancement and Boundary Mesh Adaptation is strongly recommended to ensure that the mesh is fine enough near all walls of the domain.

See Section 5.3.4 for more information about Mesh Enhancement, and to learn how CFdesign automatically takes care of the considerations discussed above.

Inlet/Outlet Passages

In general, elements should be concentrated at inlet openings to allow solution gra-dients to develop. In some situations (compressible flows, for example), the regions near outlets should also have a fine mesh. If the outlet has been placed far enough out from the solution domain, no refinement is necessary. The goal is that the outlet should not strongly affect the solution.

Thermal Boundaries

Similar to the inlet passages, elements should be concentrated near walls with thermal boundary conditions. Usually near these boundaries, the heat transfer rate (which is the temperature gradient) is the highest. You should also try to concen-trate nodes at the edges of these boundaries so the discontinuity in heat transfer can be captured accurately.

Sudden Change in Boundary Conditions

The area surrounding the separation point between two boundary condition types must have a refined mesh to adequately resolve the discontinuity. An example is the point at the intersection of an insulated wall and a specified heat flux boundary in a convection analysis.

Near Distributed Resistances/Porous Media Elements

Because of the extra pressure drop across distributed resistance/porous media ele-ments, you should refine the mesh in and around these regions to resolve the velocity and pressure gradients.

Rotating Regions


Mesh Sizes

Mesh

Size

s

It is good practice to concentrate the mesh on rotating regions and solids enclosed within a rotating region. The flow gradients are typically quite high within rotating regions, and the geometric shapes are often very intricate.

Moving Solids

The fluid region surrounding a moving solid (and in the intended path of the solid) are areas in which the mesh should be focused. The fluid gradients that occur as a result of a moving solid can be quite severe, and the mesh must be fine enough to capture them. Please see the Motion chapter of this manual for more detail about the meshing requirements of motion analyses.

5.9.4 Manually Applying Volumes and Surface Mesh Sizes

1. Set the Selection Mode, and select only the Surfaces or Volumes to which the intended mesh size will be applied. (Chapter 2 contains more information about entity selection.)

(Note: it is always good practice to assign volume sizes to ALL volumes in the model. Use surface and edge sizes to refine the mesh as necessary.)

2. Enter the Element Size (in the length units of the analysis).

3. As mesh sizes are applied to the geometry, the approximate number of ele-ments to be generated is shown.

This estimate updates automatically as element sizes are added, removed, and modified. Note that the estimated mesh size is only available for manual mesh siz-ing.

4. Click the Apply button.

Other commands: The Delete button will remove the mesh size on the selected entity or entities. The Delete All button removes all mesh sizes from the model.

The steps for applying mesh sizes on surfaces is the same as for volumes.

5.9.5 Manually Applying Edge Mesh Sizes

Set Edge as the selection type, and select the edges in your model.


Mesh Sizes

1. Select to enter an Element Size or the Number Of Elements.2. If the Number of Elements is entered, then elements can be biased (clustered) along the edge. Be sure to enter a Bias Factor (a value greater than 1.0). When biasing, elements can be concentrated at the Start, End, in the Middle, or at Both Ends of the edge.3. Hit Apply.

5.9.6 Which Size Wins?

Because an edge can have so many different element sizes, it is critical to know which size will actually be used by the mesher:

The smallest size on an entity will be used by the mesher.


Once a mesh size is applied, reference points appear along all the edges of the part. These points indicate nodal locations, once the mesh is generated. (They do not

appear when any task other than Mesh Sizes is active.)

To turn off the display of mesh reference points, right click on the Mesh Size branch of the Feature Tree, and uncheck Show Sizes.


Mesh Sizes

Mesh

Size

s

If Automatic Sizing was used, the reference points will appear where the nodes will be generated, independent of the selection mode.

If sizes were assigned manually, reference points for each selection mode will appear independently. For example, if a certain size is applied to the volumes of a model, there will be corresponding reference points on all the curves of those vol-umes. If a smaller size is then applied to some of the surfaces, then when in Sur-face Selection mode, only the reference points for those surface definitions will appear. Likewise, if some other size is applied to some of the edges, then when in Edge Selection mode, only the reference points for those edge definitions will appear.

All applied mesh sizes are listed on the feature tree:

These listings are very helpful for checking, editing, and deleting mesh sizes. To highlight an entity with an applied condition, left click your mouse on it--it will appear green in the Graphics window. To edit an applied condition, right click it, and select Edit. To delete an applied condition, right click it and select Delete.

To delete all applied mesh sizes, right click on the top-level Mesh Size branch, and select Delete All. To disable the visibility of mesh reference points, right click on the Mesh Size branch and un-check Show Sizes.

5.11 Mesh Enhancement

Mesh Enhancement is a powerful feature that considerably simplifies the mesh def-inition process. Mesh Enhancement automatically constructs layers of prismatic ele-ments (extruded triangles) along all walls and all fluid-solid interfaces in the model, based on the tetrahedral mesh that you define. These additional elements serve two primary purposes:


Mesh Sizes

The first is that elements are concentrated in the boundary layer region, where high velocity, pressure, and turbulence gradients most often occur.

The second benefit is that enough nodes are automatically placed in all gaps (area between walls) in the model. Recall that the two principal guidelines were to define the shapes and to allow/account for flow activity. Adequately meshing all of the small gaps and crevices in a complicated geometry is not an issue the user must be concerned with, thanks to Mesh Enhancement.

The graphic on the left shows a mesh without Mesh Enhancement, and the graphic on the right shows the enhanced mesh:

Mesh Enhancement parameters are controlled with the Mesh Enhancement dialog, launched from the Mesh Enhancement button on the Meshing dialog:

The default settings are appropriate for the vast majority of analysis models. An explanation of the settings follows:


Mesh Sizes

Mesh

Size

s

5.11.1 Number of Element Layers

As mentioned, three layers is satisfactory for most analyses. However, when work-ing with turbulent flows that are in the lower Reynolds number range (less than 10,000), it may be necessary to reduce the number of layers to one. The reason is that the generation of three layers creates nodes that are too close to the wall, resulting in y+ values that are too low due to the low overall Reynolds numbers.

5.11.2 Boundary Layer Thickness Factor

The Boundary Layer Thickness Factor controls the total height of the inflation layer relative to the original near-wall elements. A value of 0.45 allows the total height of the inflation layer to be one half the size of the original elements. A value of 0.2, for example, allows the total height of the inflation layer to be one fifth the size of the original elements. This is shown in the following graphic:

If an error occurs during model processing due to Mesh Enhancement, it can often be fixed by adjusting the Boundary Layer Thickness Factor. Try 0.4 and succes-sively smaller values until it does work.

5.11.3 Boundary Mesh Adaptive Scheme

This feature works in conjunction with Boundary Mesh Enhancement, and is useful for high speed aerodynamic flows where the distance between the near-wall node and the wall-node is critical for accuracy. To use this, click on both Enhance Boundary Mesh On Input, and Automatic Layer Adaptation. A minimum of three Enhancement layers is required.

This feature is ideal for external flows such as vehicle aerodynamics and hydrody-namics. It is not so useful for slower speed internal flows. The way it works is that starting at iteration 37 (after the flow has had a chance to become established), the y+ values throughout the domain are inspected. The near wall node positions are then moved closer or away from the walls in order to make the y+ value fall within

Factor = 0.45 Factor = 0.2


Mesh Sizes

the optimum range for turbulent flow. The near-wall nodal positions are adjusted with every successive iteration. There is only a slight time penalty for this adjust-ment scheme.

If you have run an inflated mesh analysis but did not activate Boundary Mesh Adap-tation at the beginning, it can be turned on any time during the analysis. If Adapta-tion is activated mid-run, be sure to run the analysis for at least another 50 iterations.

5.12 Meshing by Parts

For multi-part assemblies, a memory limitation may be encountered when using the standard procedure of meshing all parts simultaneously. This new feature causes parts to be meshed sequentially so that only the memory required to mesh the current part is required.

The meshing process appears the same to the user, and the only outward differ-ence is that the meshing status messages are repeated for each part.

A toggle on the Mesh Enhancement dialog enables the feature:

Meshing by Parts is Off by default.

Some important notes regarding Meshing by Parts include:

• Meshing times will always be longer with Meshing by Parts than with Standard meshing.


Mesh Sizes

Mesh

Size

s

• Meshing by Parts is best suited for assemblies consisting of roughly 30 or fewer parts. For such assemblies, Meshing by Parts will use less memory than Standard meshing. • Meshing by Parts an assembly with more than 30 parts with a coarse mesh size will require more memory than Standard meshing (because Standard meshing uses very little for a coarse mesh). Meshing by Parts the same assembly with a fine mesh, however, will require less memory than Standard meshing (because Standard meshing requires a great deal of memory for the finer mesh).• Because Meshing by Parts can create much larger meshes (more ele-ments) than Standard meshing, it is possible to create a mesh that exceeds the memory requirements of the CFdesign Solver. If this occurs, an error message will be given during the initial processing of the analysis model.

5.13 Generating the Mesh

The dialog discussed in this chapter is used only for mesh size definition on the geometry. The generation of the mesh is part of the analysis, and is not a separate step. When the GO button on the Analyze dialog is hit, CFdesign will construct the mesh according to the element sizes prescribed using this dialog. If a mesh already exists (and you are simply continuing the analysis), then a new mesh will not be created.

To view the mesh prior to running the analysis, simply set the number of iterations to 0, and hit GO. After the mesh is generated, the Solver will stop, and the mesh can be examined carefully.

To help diagnose meshing problems, please consult the Analysis Guidelines chapter of this manual.


Mesh Sizes


CHAPTER 6 Materials

6.1 Introduction

Materials are physical substances, and are key to the CFdesign analysis. There are eight distinct material types available in an analysis: fluids, solids, internal fans, centrifugal fans, resistances, check valves, rotating regions, and moving solids. Each material type will be discussed in this chapter.

The work flow for assigning materials is very similar to the other model set-up tasks (Loads and Mesh Definition): pick a part (volumes for three dimensional mod-els and surfaces for two dimensional models), make selections on the dialog, and hit Apply. Visual indication is given by coloring parts by material (a legend defines the color-material correspondence). Also assigned materials are listed on the fea-ture tree for additional reference.

The Material Editor makes creating and editing materials very convenient. Numer-ous property variations are available, allowing for great flexibility when creating materials.

As part of the installed CFdesign package, the Material Database includes several variations of air, water, and numerous solid materials. Additional materials can be added to the database at the push of a button. The materials database file can be placed anywhere in a company’s network to allow easy standardization for all CFde-sign users to company-specific materials.

6.2 The Materials Database

• To store a new material to the Materials Database, click the Save but-ton in the Database group on the Materials dialog.• Materials that are not saved to the database will have a “*” prepended to their names. They will be saved in the cfd file, but will not be available for other analyses unless they are saved to the Materials Database.


Materials

• If a material saved to the database is edited (remember that the default (installed) materials cannot be edited), a “*” will appear before the name, indicating that the material is different from the one in the database. When the Save button is hit, a prompt will ask for confirmation that you want to save the edited material.• When an existing analysis containing a material not stored in the Mate-rial Database is opened, the word “local” will be appended to the material name. This material will exist in the analysis, and can be used. Hit the Save button to add it to the Materials Database (and the word “local” will disap-pear the next time the analysis is opened).• If an analysis is opened that contains a material that has the same name as a database material, but has different properties, the name of the analysis will be appended to the material name to prevent the two different materials from conflicting.• The default location of the Materials Database is in the CFdesign instal-lation folder. If this location is not appropriate (for sharing with multiple users, for example), then the database can be placed elsewhere on the net-work. Use File_Preferences to indicate the location of the database file. This setting will be saved, and will not have to be altered every time the soft-ware is used.


Materials

Mate

rials

6.3 Fluids

6.3.1 Assigning Fluid Materials

6.3.2 Installed Database Materials

Several variations of air and water are included with the software. As mentioned,

1. Select the parts to which the fluid will be applied.

2. Select Fluid from the Type pull-down menu.

3. Select the specific material from the Name pull-down menu.

4. If the desired fluid does not exist, create a new material by hitting the Create/Edit Material button, and use the Material Edi-tor to enter the necessary proper-ties.

5. If a new material was created or modified, save it to the Material Database (optional).

6. Click Apply to apply the material.

Note: Care should be taken to avoid placing two different fluids in direct contact. Different fluids can exist in the same analysis if they are separated by a solid.

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6


Materials

these materials cannot be edited, but each can be selected as the “Read From” material when creating a similar new material.

Material Description

Air Constant

Water Constant

The properties do not change

Air Buoyancy

H2O Buoyancy

Density changes with temperature. A buoyancy property should be selected when solving for natural convection--where the density of the fluid changes with the tempera-ture.

Air Not STP

H2O Not STP

A Not STP property should be used when temperature and/or pressure are far from standard conditions.

Air Moist Useful for humidity (moist air) calculations. These proper-ties are only of the gas, not the gas/liquid mixture. (The liquid properties are determined using the steam tables.) If a new material is created based on moist air, pay spe-cial attention to the gas constant, the reference proper-ties, and the specific heat.

H2O Steam/Liquid Useful for analyses of steam/water mixtures. Change the Reference Pressure if your operating conditions are at a different pressure.

Steam Buoyancy Sets the properties of steam, but only allows density to vary with equation of state, not the steam tables. No other properties vary.

Steam Constant Sets the properties of steam, but does not allow for any property variation. This is useful if the temperature and pressure variations are small.

Ammonia Constant

Blood non-Newtonian

CO2 Buoyancy

CO2 Constant

Ethylene Glycol Constant

Freon Constant

Glycerin Constant

Helium Buoyancy


Materials

Mate

rials

6.3.3 Creating Fluid Materials

Shown is the Material Editor dialog for Fluids:

1. The Type is set on the main Materials dialog. To create or edit a fluid, select Fluid as the type.2. Assign a name to the material. The names of the default database materials cannot be used for new materials. To modify a default database material, save it to a new name. Note: Spaces are not permitted in material names.

Helium Constant

Hydrogen Buoyancy

Hydrogen Constant

Mercury Constant

Nitrogen Buoyancy

Nitrogen Constant

Oxygen Buoyancy

Oxygen Constant

Step 1Step 2

Step 3

Step 4

Step 5

Step 6


Materials

Note that it is possible to select a similar material from the Read From drop menu. This is a convenient starting-point for creating new materials.

3. Click the property button that is to be defined.4. Select the Variation Method from the Input Region, and enter the appropriate Values and units for the selected property. Click the Apply button.5. Modify the Reference Properties, if necessary. If these parameters are modi-fied, care should be taken to modify them for all fluids in a model.6. When all properties are defined, click the OK button. This will make the new material available for only the current analysis.

6.3.3.1 Fluid Properties

The Material Editor is used to create materials different from those supplied with the software. There are six basic properties that are needed to define a fluid. Most of these properties can be made to vary with temperature, pressure or scalar, in several different ways. The following table lists the properties and the available variational methods.

Property Variational Methods

Density:

the amount of mass per volume

Constant, Equation of State, Polynomial, Inverse Polynomial, Arrhenius, Steam Table, Piecewise Linear, and Moist Gas

Viscosity:

dynamic (absolute) viscosity is used

Constant, Sutherland, Power Law, Polyno-mial, Inverse Polynomial, Non-Newtonian Power Law, Hershel-Buckley, Carreau, Arrhe-nius, Piecewise Linear, and Steam Table, First Order Polynomial, Second Order Polynomial

Conductivity:

the thermal conductivity

Constant, Sutherland, Power Law, Polyno-mial, Inverse Polynomial, Arrhenius, Steam Table, Piecewise Linear

Specific Heat Constant, Polynomial, Inverse Polynomial, Arrhenius, Steam Table, Piecewise Linear


Materials

Mate

rials

Bulk Modulus

The bulk modulus and the density of a liquid are key to determining the speed of sound through that liquid:

The definition of bulk modulus is: .

Given that the speed of sound, a, is defined as: , this works out to be:

Source: White, F. M., “Fluid Mechanics,” McGraw Hill, New York, New York, 1986.

The bulk modulus is used only for compressible liquid (water hammer) analyses. The value of bulk modulus is automatically set for the liquid materials included in the Material Data Base. For user-defined materials, the correct value of bulk modu-lus is only required if liquid compressibility is to be analyzed. An example of a liquid compressibility, water hammer, is described:

Compressibility Choice of:

Cp/Cv (gamma, the ratio of specific heats) -- useful only for compressible gas analyses or

Bulk Modulus -- useful only for compressible liquid analyses. See note below about Bulk Modulus.

Emissivity -- useful for radiation analyses. The emissivity speci-fied on a fluid is assigned to con-tacting walls. Note that the emissivity assigned to a solid will take override the value assigned to a contacting fluid.

Constant, Piece-wise Linear variation with temperature. (This is useful for spectral radi-ation analyses.)

See Guidelines Chapter for more details on Spectral radiation.

Wall Roughness -- useful for applying variable roughness height to include effects of fric-tion

Constant.

See note below about the Wall Roughness property.


K ρ∂p∂ρ------=

a2 ∂p∂ρ------=

a Kρ----=


Materials

Water is flowing through a straight pipe at 10 in/s. At a certain time, a valve at the end of the pipe is suddenly closed. A pressure pulse will move through the water at the speed of sound through water. This phenomena is called a “water hammer”, and is analyzed with a transient analysis to predict the movement of the pressure wave through the water. Instead of using the Ideal Gas Law and the ratio of specific heats to determine the sound speed, we will use the density and the bulk modulus of the water.

Wall Roughness

Enter a physical dimension (in the units available in the drop menu) of the rough-ness height. Such heights are typically very small--cast iron pipes, for example, have a typical wall roughness height of 0.0102 inches.

A value of wall roughness height specified on a fluid is automatically applied by the Solver to the wetted walls touching that fluid. A value of wall roughness height specified on a solid is applied to all wetted surfaces (surfaces contacting a fluid) of the part. A non-zero wall roughness height applied to a solid will prevail over a wall roughness applied to a fluid that touches it.

Wall roughness heights are implemented into the turbulence wall model, and do not affect the geometry. The flow must be turbulent for wall roughness heights to take effect. They will be ignored for laminar flows.

Specified wall roughness heights work best when closely adhered to the Turbulent Law of the Wall. This means that the non-dimensional distance (y+) from the wall node to its near-wall node must be between 35 and 350. The easiest way to enforce this constraint is by checking the Automatic Layer Adaptation box on the Mesh Enhancement dialog (found on the Meshing task). This will allow the Solver to adjust this near wall node distance along all walls in the model, based on the local flow conditions.


Materials

Mate

rials

6.3.3.2 Property Variation Methods

Property variation methods used for both fluid and some solid properties are described here:

Constant

Enter the value and units as appropri-ate.

Power Law

enter a Reference Value (of the property) = ,

the Power Law Exponent = n

and a Reference Temperature (in the Reference Properties group).

(Note: The Reference Temperature is only used at start up to calculate an initial reference density. The field value of temperature is used during the calculation to determine density.)

ααo------ T

To-----⎝ ⎠⎛ ⎞ n

≈

αo


Materials

Equation of State

Enter P = Reference Pressure,

R = Gas Constant,

and T = Reference Temperature.

The Reference Temperature is only used at start up to calculate an initial reference density. The field value of temperature is used during the calcu-lation to determine density.

The Reference Pressure is used both to calculate an initial reference density and also throughout the calculation to determine the absolute pressure. See the Technical Reference Guide for more information.

For adiabatic compressible analyses, the static temperature used to calcu-late density is determined from both the local stagnation and dynamic tem-peratures. See the Technical Refer-ence for a discussion of Adiabatic Compressible Flow.

ρ PRT-------=


Materials

Mate

rials

Arrhenius

Enter a property Reference Value =

and the Activation Energy = E.

Sutherland

Enter a property Reference Value = ,

the Sutherland constant=S

and a Reference Temperature in the Reference group)

ααo------- e

E–RT-------

=

αo

ααo------ T

To-----⎝ ⎠⎛ ⎞ 1.5 To S+

T S+---------------≈

αo


Materials

Note: Non-Newtonian fluids are often described in terms of a power law index, n. The quantity to be entered here, the power law exponent, is related to the power law index as p = n-1. (A power law index of 1 describes a Newtonian fluid.

Non-Newtonian Power Law

Enter the Viscosity Coefficient =

and the Power Law Exponent = p

(an exponent of 0 describes a Newto-nian fluid).

Note that the viscosity coefficient is the viscosity reference value.

If a viscosity cutoff is not applicable, simply enter values for the Viscosity Coefficient and the Power Law expo-nent and leave the Cutoff Strain rate at the default. Make the Cutoff Vis-cosity = the Viscosity Coefficient.

To model a non-Newtonian fluid with a constant viscosity that starts to vary at a given strain rate, input this viscosity and the strain rate in the Cutoff Viscosity and Cutoff Strain Rate fields, respectively.

Enter the constant k in the Viscosity Coef (k) field.

µµo----- γp=

µo

µµo----- kγp=


Materials

Mate

rials

Herschel-Buckley (viscosity variation)

Enter the Yield Stress = ,

the Flow Behavior Index = ,

and the Consistency Factor =

Carreau (viscosity variation)

Enter the Zero Strain Viscosity = ,

the Infinite Strain Viscosity = ,

the Time Constant = ,

and the Power Law Index = n.

τ τy kmγnm+=

τynm

km

µ µ∞–µo µ∞–------------------ 1 λγ( )2+[ ]

n 1–( )2

----------------

=

µoµ∞

λ


Materials

First Order Polymer (viscosity)

Enter the Viscosity factor = A,

the Shear factor = B,

and the Temperature factor = C.

= shear rate calculated during the analysis

T = temperature calculated during the analysis

Note: the coefficients must be entered in SI units, regardless of the analysis length units system.

Second Order Polymer (viscos-ity)

ln( )=A1 + A2ln( ) + A3T + A4[ln( )]2 + A5[ln( )]T + A6T

2

The constants A1, A2, A3, A4, A5, and A6 are constants that define the mate-rial.

= shear rate calculated during the analysis

T = temperature calculated during the analysis

Note: the coefficients must be entered in SI units, regardless of the analysis length units system.

µ AγB CT( )exp=

γ

µ γ γγ

γ


Materials

Mate

rials

Polynomial and Inverse Poly-nomial

Data points are required for a poly-nomial or inverse polynomial prop-erty variation.

Density, conductivity, and specific heat can vary with temperature, pressure, or scalar.

Viscosity can vary with temperature, pressure, scalar, or strain rate.

Each data point is entered on a sepa-rate line. To insert a data point between two existing lines, click on the point after the desired new point and click on the Insert button. All the subsequent data points will be pushed down one row.

The range of values should encom-pass the range of the independent variable (temperature, pressure, or scalar) of your analysis. CFdesign will automatically clip the property value if it exceeds the upper or lower values of the independent variable.

The polynomial order is specified in the Order field. The order should be less than the number of data points to get a good fit. It is always a good idea to plot the property values to ensure they follow the expected trends using the Plot but-ton. Polynomial orders greater than 3 are generally not useful because of unex-pected inflection points.

Data in “.csv” format can be imported using the Import button. Data is saved to a “.csv” file using the Save button.


Materials

6.3.3.3 Reference Properties

The Reference Temperature is only used at start up to calculate an initial refer-ence density. The field value of temperature is used during the calculation to deter-mine density.

The Reference Pressure is used both to calculate an initial reference density and also throughout the calculation to determine the absolute pressure. See the Techni-cal Reference Guide for more information.

For adiabatic compressible analyses, the static temperature used to calculate den-sity is determined from both the local stagnation and dynamic temperatures. See the Technical Reference for a discussion of Adiabatic Compressible Flow.

Piecewise Linear

The Piece Wise Linear variation uses a linear interpolation between entered data points. Data points are entered into the table in the same manner as polynomial and inverse polynomial data (see above).

Density, specific heat, and conductiv-ity can be varied with temperature, pressure, or scalar.

Viscosity can vary with temperature, pressure, scalar, and strain rate.

The choice of independent variable is made using the drop menu (showing Temperature in the above example).

Use the Plot button to check the data.



Materials

Mate

rials

6.4 Solids

6.4.1 Assigning Solid Materials

6.4.2 Installed Database Materials

Several solid materials are included with the software. As mentioned, these materi-als cannot be edited, but each can be the “Read From” material when creating a

1. Select the parts to which the solid will be applied.

2. Select Solid from the Type pull-down menu.

3. Select the specific material from the Name pull-down menu.

4. If the desired solid does not exist, create a new material by hitting the Create/Edit Material button, and use the Material Edi-tor to enter the necessary proper-ties.

5. If a new material was created or modified, save it to the Material Database (optional).

6. Click Apply to finish.

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6


Materials

similar new material.

Material Description

Aluminum Con-stant

The properties do not change

Copper Variable Conductivity varies with temperature

Glass Constant The properties do not change

Iron Constant The properties do not change

PCB 12 Layer X, Y, or Z

Effective conductivities are used to represent the layers of a printed circuit board. The direction is the component normal to the board--the conductivity is considerably less than the other two (in plane) components

PCB Plastic for Laminate Constant

The constant properties of printed circuit board plastic

Steel Variable Conductivity varies with temperature

Brick Constant

Glass Wool Constant

Gold Constant

Gold Variable

Gypsum-Board Constant

Hardwood Constant

Lead Constant

Magnesium Constant

Mercury Constant

Nickel Constant

Particle Board Constant

Platinum Constant

Plywood Constant

Polystyrene Constant

Silicon Constant

Silicon Variable

Silver Constant


Materials

Mate

rials

6.4.3 Creating Solid Materials

Shown is the Solids Material Editor:

1. The Type is set on the main Materials dialog. To create or edit a solid, select Solid as the type.2. Assign a name to the material. The names of the default database materials cannot be used for new materials. To modify a default database material, save it to a new name. Note: Spaces are not permitted in material names.

Tin Constant

Titanium Constant

Tungsten Constant

Wood (soft) Constant

Zinc Constant

Step 1

Step 2

Step 3

Step 4

Step 5


Materials

Note that it is possible to select a similar material from the Read From drop menu. This is a convenient starting-point for creating new materials.

3. Click the property button to be defined.4. Select the Variation Method from the Input Region, and enter the appropriate Values and units for the selected property. Click the Apply button.5. When all properties are defined, hit the OK button. This will make the new material available for only the current analysis.

6.4.3.1 Solid Properties

The Material Editor is used to create additional materials not supplied with the soft-ware. There are four basic properties that are necessary to define a solid for use with CFdesign. Most of these properties can vary with temperature, pressure or scalar, in several different variational methods; these properties and methods are listed in the following table:


Conductivity -- the same value for thermal conductivity can be used for all three directions, or each component can be differ-ent.

Constant, Polynomial, Inverse Polynomial, Piecewise Linear.

Y and Z directions also have: Same as X-Dir.

Density -- only needed for tran-sient analyses.


Specific Heat -- only needed for transient analyses.


Emissivity -- useful for radiation analyses. The emissivity speci-fied on a solid will override the value assigned to contacting fluid.

Constant, Piecewise Linear variation with temperature (useful for spectral radiation analyses.)

Transmissivity -- useful for radi-ation analyses; see note below

Constant, Piecewise Linear variation with temperature


Materials

Mate

rials

Transmissivity

Transmissivity is a measure of how much radiative energy can pass through an object. A value of 1 indicates that the object is completely transparent, and that radiative energy can pass completely through it. A value of 0 means that the object is opaque. The permissible range of transmissivity values is between 0 and 1.

Two variation methods are available for transmissivity: Constant and as a Piecewise Linear table varying with temperature. Transmissivity is a unitless parameter. The default value is 0.

The sum of Transmissivity and Emissivity must be less than or equal to 1.

If the sum of these two values exceeds 1, an error message will be displayed when the analysis is started.

Transmissivity can only be assigned to solids. The radiation model considers fluids to be non-participating, so it is not possible to simulate radiative heat transfer through dark or “muddy” fluids.

To simulate a transparent object completely immersed within a fluid:

• Model the object as a solid and mesh it (it cannot be a suppressed part).• Assign a transmissivity value between 0 and 1 to the solid material to allow radiation to pass through the object.

To simulate radiative heat exchange between a transparent solid and the environ-ment, such as a window:

Electrical Resistivity -- only needed for Joule heating analy-ses.

Constant, Polynomial, Inverse Polynomial, Piecewise Linear (varies with temperature).

Wall Roughness -- useful for applying variable roughness height to include effects of fric-tion

Constant. Please see note in Section 6.3.3.1 about Wall Roughness.


ε τ 1≤+


Materials

• Model the window as a solid in the model.• Assign a transmissivity value to the material for that solid.• Assign a Transparent boundary condition to that surface. This boundary condition includes a background temperature

Surface parts cannot be used to simulate transparent media. A non-zero value of transmissivity applied to surface parts will be ignored. Likewise, non-zero values of transparency assigned to moving solids are ignored--transparency is not supported for moving solids or within rotating regions.

Note that absorption of radiation energy by transparent solids is not included in the radiation model.

Electrical Resistivity

The resistance per area multiplied by the length of the device. A value for resistivity is required for any solid that is heated by the Joule effect.

The relationship between resistivity and resistance is:

• R = resistance (ohms)• r = resistivity (ohms-length unit)• L = length of the device• A = cross sectional area

For more information, please consult the Joule Heating section of the Analysis Guidelines chapter of this manual.

6.4.3.2 Solid Property Variational Methods

Variational methods are described in the Fluid Property Variation section: 6.3.3.2.

6.5 Surface Parts (Shells)

6.5.1 Thin Obstructions

Surface Parts are two dimensional surfaces incorporated into three dimensional geometry. They are typically used to simulate very thin objects such as guide vanes

R r L×A

-----------=


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or sheet metal that the flow must pass around. They are useful because they elimi-nate the need to model very thin geometry with three dimensional volumes. Mesh-ing such volumes can be very difficult and can result in very large meshes. The reason is that an element that is small enough to represent the thickness will be so small that a huge number of them are required across the other dimensions of the object. By representing such objects only with surfaces, the elements only need to be small enough to represent the shape of the object, eliminating the thickness from the model.

This is shown in the following graphics. The model on the left contains a thin-walled obstruction that is modeled as a volume. The element size needed to represent this volume is quite small (because the part is so thin), so the element count is large (about 158,000 elements in this example). The model on the right, however, uses a Surface Part to represent the thin obstruction. The element size on the surface part is not vastly different from that of the surrounding air, and the overall element count (model size) is considerably smaller (about 38,000 elements for this exam-ple):

6.5.2 Contact Resistance with Surface Parts

Surface Parts can be used to conduct heat as well as obstruct flow. They will exhibit the same heat transfer characteristics as three dimensional volumes in that they will conduct heat in all directions. For this reason, a thickness value is required

Sheet metal obstruction modeled witha 3D volume.

Sheet metal obstruction modeled witha Surface Part.


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when defining Surface Parts. This is discussed in the Specifying Surface Parts sec-tion.

In addition to obstructions, Surface Parts can be used to simulate the contact resis-tance in thin layers of material between or within chip packages. Layers of epoxy or other substances are commonly used between thermal components, and the effect of their contact resistance must be included. A Surface Part material can be applied to a surface that represents an epoxy layer, eliminating the need to model the sub-stance with a thin three dimensional volume. This approach will still account for the thermal conduction between the chip components, but will greatly simplify the modeling process and reduce the size of the mesh (analysis model size).

The Solid Material Editor dialog allows specification of thermal conductivity or resis-tance. If the conductivity of the layer is known, select Conductivity in the dialog,


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and enter the appropriate value. Alternatively, if the resistance is known, select Resistance, and enter the value:

6.5.3 Rotating Machinery

Another application for Surface Parts is the analysis of thin-bladed turbomachinery devices using Rotating Regions. Surface Parts can greatly simplify the modeling of thin sheet-metal fan blades. Instead of meshing around very thin three-dimen-sional blade volumes, represent the blades as surfaces within the rotating region, and assign a Surface Part material to them.

6.5.4 Assigning Surface Parts

Surface parts can be constructed in two different ways in the CAD model: as fea-tures or separate parts or by using surfaces on existing volumes. Assigning a Sur-face Part material in CFdesign is very easy using the Materials task dialog. This is discussed later in this section.

6.5.4.1 Surface Parts using CAD Surface Features

Surface parts are always assigned to surfaces. In many cases, it is practical to con-struct floating surfaces within the three dimensional model. Some CAD tools allow such surfaces to be separate components in an assembly. Others require that these


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surfaces just be features within a part. An example of a surface feature or part is shown:

The surface is not part of a closed region, but if a solid material is assigned to it (as described above), it will obstruct the flow:

6.5.4.2 Surface Parts on Surfaces of Volumes

In some situations, it is easier to include a volume within an assembly, and assign one or more surfaces to be Surface Parts. In such a situation, the part itself will be a fluid (and hence not an obstruction), but the surface or surfaces will be solids, and will block flow.


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When assigning Surface Parts to represent an epoxy layer in an electronic chip set, it is not necessary to create a separate surface in the CAD model. Simply select an appropriate surface on one of the chips, and assign a solid material to it. The ther-mal resistance and the physical thickness are then included in the analysis, without having to complicate the geometry with very thin volumes or creating a huge finite element mesh.

An example of a surface that is part of a volume is shown:

The volume is assigned a fluid material, but because the two front surfaces are assigned a solid material, they are considered to be Surface Parts, and will obstruct the flow:


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6.5.4.3 Additional Guidelines

A few additional notes regarding Surface Parts:

• Surface Parts are not applicable to edges in two dimensional models.• It is not necessary to assign a Surface Part material to surfaces that are walls. If a surface is on a solid part, it is a wall. If a surface is on an external boundary (no material on one side of it), then it is wall.• CFdesign does not support a Surface Part material assigned to the external surfaces of a flow volume. (Some attempt this in an effort to simu-late a sheet metal thickness.) Application of external heat transfer bound-ary conditions (such as heat flux and film coefficient) is also not recommended. The reason is that Surface Parts that are on external bound-aries are not completely incorporated into the calculation--their material and thickness information will not be included. Because of this, there will not be a thermal gradient calculated across external Surface Parts. An alternative to applying Surface Parts for external wall surfaces is to leave the external surface unspecified, making it a wall by default. When this is done, externally-applied heat transfer boundary conditions will then be properly incorporated into the simulation.• Multiple layers of material cannot be represented by applying multiple layers of Surface Parts. To represent a laminate of thin materials, apply a single Surface Part material that uses an effective thermal conductivity based on the conductivity values of the laminate materials.• Surface Parts must be completely enclosed in a 3D volume. Surface Parts cannot extend outside of the 3D model.• We do not recommend dividing an opening with a surface part, as shown in the following image if the two sections are to have different boundary conditions.:

If such a situation is required, then the two boundary conditions should either be the same value OR they should both be mass flow or volume flow conditions. If other conditions are applied, there will be “bleed through” from one side to the

Surface Part

BoundaryCondition 1 Boundary

Condition 2


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other within the Mesh Enhancement layers contacting the surface part, which will cause unexpected results.

• It is not possible to change the mesh on a model containing surface parts and continue the analysis from a saved iteration. When the mesh is changed, the analysis must be started back at the beginning (iteration 0).• Surface parts must not contact parts that are extrusion meshed.

6.5.4.4 Specifying Surface Parts in the Materials Dialog

The Material task dialog has been modified to include the option to select surfaces for material assignment.

6.5.4.5 Shell Thickness

The Shell Thickness value is required, but is only used in the calculation of con-duction heat transfer. The thickness value will not modify the geometry in any way, and there will be no graphical representation of the thickness value.

1. Select Surface as the Entity Selection type.2. Select the surfaces from the model.3. Select Solid as the Type. Select or create a solid material.4. Specify a Shell Thickness and select the desired units.5. Click Apply.

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6.5.5 Visualization of Surface Parts

The standard visualization tools in CFdesign work with Surface Parts. Cutting planes and iso surfaces will display results caused by the presence of Surface Parts. Using shift+ctrl, results on Surface Parts can be probed by hovering the mouse.

The displayed value of pressure on Surface Parts depends on which side of the Sur-face Part is viewed. The leading side of a Surface Part will show high pressure, and the wake side will show lower pressure:

When visualizing results, Surface Parts are listed in the Feature Tree under the Materials branch. They are listed separately from volume parts--even those with the same material. Additionally, every Surface Part is listed twice--this is because each surface part is duplicated within the model to allow results to vary from the leading to the trailing side.

Surface Parts can be used as the source surfaces for non-planar cutting surfaces. This is discussed in more detail in the Results Visualization chapter of this manual.


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Wall results are assessed on Surface Parts by selecting the appropriate side of the surface. In the example above, selecting the leading side would show a higher wall force than selecting the drag side.

6.5.6 CAD Guidelines

Different behavior regarding the inclusion of Surface Parts as surfaces that are not connected to volumes has been observed in several CAD tools. These guidelines are described below.

6.5.6.1 Pro/E Wildfire

Surfaces that are to be Surface Parts should be created as separate parts and added to an assembly consisting of the surrounding flow volume part and any other Surface Part and 3D parts. If a Surface Part is included as a quilt feature in a part, the part may either not come into CFdesign correctly or it will incur meshing diffi-culties. Also, Surface Parts must not interfere, and must not cross one another. Multiple Surface Parts can meet along an edge, however.

Surface Parts that are not connected (completely disjointed) must be created as separate parts, and included as components in the assembly.

6.5.6.2 Solid Works

Surface Parts can be created as either separate parts in an assembly or as surface features in a 3D part. Surface Parts can interfere with one another, and disjointed surfaces can be included in the same part.

6.5.6.3 Solid Edge and Inventor

We have found that the most convenient way to include Surface Parts is to create a 3D part with the surface shape of the desired Surface Part. Mesh the volume as a fluid, and assign a Surface Part material to the surface, as described in the preced-ing section called Surface Parts on Surfaces of Volumes.

6.5.6.4 CATIA v5

We have found that the most convenient way to include Surface Parts in CATIA models is to create a 3D part with the surface shape of the desired shell. Mesh the


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volume as a fluid, and assign a Surface Part material to the surface, as described in the preceding section called Surface Parts on Surfaces of Volumes.

6.6 Resistances

In some analyses, the actual flow geometry may contain a large number of holes or obstructions. For example, baffles are used in many electronics packages, and often have hundreds of holes through which the air must pass. To model each and every hole would be tedious, expensive and unnecessary.

The alternative is to simulate the presence of such holes or obstructions with a dis-tributed resistance region. In this method, the mesh elements in this region are assigned a resistance parameter usually using either the free area ratio (proportion of free to total area) or a loss coefficient based on the known pressure drop. This resistance simulates the effect of the obstructions without using an inordinate num-ber of elements. Other examples of porous media include radiators, vents, screens, filters and packed beds.


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6.6.1 Assigning Resistances

There are three different methods of assigning the flow direction through a resis-tance region: aligned with a Cartesian direction, not aligned with a Cartesian direc-tion, through a cylindrically shaped region.

Note: distributed resistance regions should not contact an external boundary condi-tion. Likewise, it is not recommended to apply boundary conditions to any surface of a distributed resistance material. Doing so may cause convergence difficulties and will affect the flow rate reported in the summary file. If a distributed resistance

1. Select the part or parts.2. Choose Resistance as the Type.3. Select the Material Name.

(If the material does not exist, see the following section for how to create resistance materials.)

4. Select the flow direction through the resistance. Select the two direc-tions normal to the flow direction. See below for further detail.

5. Hit Apply to apply the material.

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contacts an external boundary, it is good practice to add an extension onto the region (so that the boundary condition is not applied directly to it).

6.6.1.1 Aligned with Cartesian

Use one of the Cartesian directions (Global X, Global Y, or Global Z) if the flow direction through the resistance region is aligned with a Cartesian direction. Select the remaining directions for the other two directions.

6.6.1.2 Not Aligned with Cartesian

Resistance values for the normal directions specified on the Resistance Material Edi-tor will be used by the Solver. The following image shows flow passing through a resistance object that is inclined at an angle to the flow. In this example, the Flow

1. Use Pick on Surface to specify the flow direction through the resistance region by selecting a surface that is normal to the direction of flow. After selecting it, click OK on the Device Flow Direction dialog. 2. Specify the direction of Normal Direction 1 by either selecting the available Cartesian direction(s) or by selecting Pick on Surface, and picking a surface that is normal to the desired direction3. The direction for Normal Direction 2 is automatically determined from the two specified directions, and is not available for modification. The resis-tance for Normal Direction 2 (normal to the plane of the page) is automatically set to a high value.

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and Normal Direction 1 resistances were set to the same value. Obviously, the val-ues can be different if desired:

The flow is turned slightly, but is not completely realigned to be normal to the resis-tance object.

To force the flow to be normal to a resistance (to produce a “vent” resistance), set the Normal Direction resistances to be at least three orders of magnitude greater

Flow Direction

Normal Direction 1

Select this surfaceas the normal surface

Select this surfaceas the normal surface

for the Flow Direction.

for the Normal Direction


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than the Through Flow K. This will cause the flow to turn so that its direction is nor-mal to the resistance object.

6.6.1.3 Cylindrically Shaped Region

Use Radial for the Flow Direction to simulate a cylindrically-shaped resistance. The other two directions will automatically be set to Axial and Tangential. A prompt will come up to select a surface normal to the axial direction. The code requires this for correct calculation of the orientation of the material object.

Another application for the Radial flow direction resistance is for a bank of resistive cylinders over which the flow must pass. In this case, the flow direction is again

Surface normal toFlow enters axially, but must pass through radialresistance region

Flow Inlet

Resistance Region(annulus)

axial direction


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Radial, and an axial direction (select a surface normal to the axis of the cylinder) must be selected:

6.6.1.4 Resistance Surface Parts

Surface parts can also be used as distributed resistance regions. Applications include very thin baffles, perforated plates, and any type of very thin obstruction that would be very cumbersome and computationally expensive to model as a vol-ume.

Shown are examples of a baffles modeled with surface parts:


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On the Materials task, the Resistance material type is available when Surface selec-tion mode is invoked:

Unlike volumes, Surface parts cannot be used to simulate pressure drop within the plane of the object (secondary losses). All pressure loss will be in the direction nor-mal to the plane, and the flow will be constrained to be normal to the surface. To allow for secondary-direction flow through a resistance, a volume must be used for the resistance region.

A nodal reorganization is performed during startup processing to ensure connectiv-ity between the distributed resistance region and the surrounding mesh. This means that it is not possible to change the mesh and continue the analysis from a saved iteration. If the mesh is changed in a model containing a distributed resis-tance surface part, the analysis must be started back at the beginning (iteration 0).

1. Set Surface as the Selection Mode2. Select the surface(s) from the model.3. Change the Type to Resistance.4. Select a resistance material from the Name menu or click the Create/Edit Material button to create one.5. Specify a Shell Thickness.6. The flow direction through a surface part will automatically be normal to the part, so no further directional assign-ments are necessary.7. Click Apply.

Cross-flow resistance is automatically set very high so that all flow is aligned normal to the surface.

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Distributed resistance surface parts are very flexible, and can contact the surround-ing wall on one or more edges and even be completely submerged within the fluid:

It is very important that the fluid mesh between the edge of a floating resistance surface and the neighboring wall have at least a single row of nodes between them. If no nodes exist in this region, an error will be issued:

Distributed resistance surface parts can be planar or arbitrarily shaped. The flow direction will always be locally normal to the surface part. Note that there are limi-tations to the shape of a surface part. Very high curvature surfaces are not suitable

Surface Part Resistance

Region between edge andwall must have more than 1 row ofnodes.


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for use as distributed resistances, and an error will be given. An example of an unsuitable surface is shown:

The recommended shapes for resistance surface parts are planes and hemispheres:

Multiple resistance surface parts cannot be joined together to form a “composite” resistance region, and cannot touch other surface parts. A resistance must be com-posed of a single surface part. Surface parts that share an edge will cause an error in the analysis processing:

Note: surface parts are not available for 2D models.

Too much curvatureto be used as a resistancesurface part.


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6.6.2 Creating and Editing Resistances

No resistance materials are included in the installed Materials Database, so it is necessary to create at least one before using a resistance. The Material Editor for resistances is shown:

The Variation Method and Value for each component is entered separately, but it is recommended that the same variation be used for all three components.

Creating Resistance Materials is similar to creating fluid and solid materials:

1. The Type must be set to Resistance (this is set on the Main Materials dialog).2. Enter a material name. Note: spaces are not permitted in material names.3. Hit the button of the component to define (Properties group).4. Select the Variation Method.5. Enter the Value(s).6. Hit the Apply button.7. Hit OK when all information is entered.

A Resistance material definition does not reference specific Cartesian components. Instead, the values are saved as the Through-Flow, and the two Normal Compo-nents. The specific Cartesian orientation of the material is specified when a resis-tance material is applied to a part.

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A thermal conductivity can also be assigned to a resistance material. This can be different from the surrounding fluid, and is important for heat transfer analyses in which the material will play a thermal role.

No other fluid property information is required to define a resistance. The Solver automatically applies the fluid property information from the surrounding fluid to the resistance. For this reason it is very important that a resistance region only contact one fluid material type. If, for example, a resistance contacts air on one side and water on the other, an error will result, and the analysis will not run.

There are five different resistance variational methods:

1. Constant Loss Coefficients2. Free Area Ratio3. Friction Factor4. Pressure-Flow Rate Curve5. Permeability Coefficient (Darcy equation)

6.6.2.1 Constant Loss Coefficient:

Losses through a media can be expressed in terms of an additional pressure gradi-ent:

where Ki is the loss coefficient in the global i coordinate direction. Each global coor-dinate direction can have its own unique loss coefficient.

Loss coefficients in CFdesign are expressed without units, and are independent of the length of the resistance in the model. The equation describing these losses is written in terms of a pressure drop instead of a pressure gradient:

Values for can be found in many fluids texts and the hydraulic resistance refer-ence, Handbook of Hydraulic Resistance, 3rd Edition by I.E. Idelchik, published by CRC Press, 1994 (ISBN 0-8493-9908-4).

Alternatively, this is a good method to use if measured data for pressure drop ver-sus flow rate is available. Use the equation for Delta P shown above: substitute in

p∂xi∂

------- Kiρui

2

2------=

∆p ζiρui

2

2-----=

ζ


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the known values of pressure and velocity to determine a value. Enter this value for the Through-Flow K.

To input a loss coefficient, select the desired direction and choose Constant as the Variation Method. Enter the appropriate value of (as described above) in the Through-Flow K Value field.

Often the normal direction coefficients will be 50-100 times larger than the through flow loss value. This simulates a flow straightener.

The Permeability value can be specified in conjunction with the Constant resistance method as well as the Friction Factor method. This allows a resistance to be speci-fied in the form:

Where is the viscous resistance term, which is the reciprocal of permeability.

The value of permeability is required in the resistance Material Editor, and is used in the pressure drop equation in the following manner:

where is the value of permeability. The unit of permeability is the Darcy, and is expressed in terms of length squared.

The term (in the above equation) is the standard loss coefficient.

The combined pressure drop equation is then:

Where:

• is the permeability, in units of length squared.• V is the velocity• L is the length over which the resistance acts• is the viscosity• is the loss coefficient• is the fluid density

ζ

ζ

P1 P2– αµVL ζρV2

2------------+=

α

α 1κ---=

κ

ζ

P1 P2– 1κ---µVL ζρV2

2------------+=

κ

µζρ


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The value of permeability specified for one component is automatically applied to the other components.

To enter a constant resistance or a friction factor without the contribution of a per-meability, simply leave the Permeability value 0. Likewise to apply a permeability value without a constant loss coefficient or friction factor, change the Variation Method to Permeability, and enter the appropriate value of permeability. More detail about this method is described in the Darcy Equation description, below.

Note: In version 7, specified values of permeability were used as a viscous resis-tance term in the above equation. For this reason, when such a model is opened in CFdesign 8, the value of permeability will be inverted, and the reciprocal shown in the field. This will cause the resultant pressure drop with version 8 to be the same as with version 7. However, care should be taken to ensure that the correct value of the permeability is entered in the version 8 interface.

6.6.2.2 Free Area Ratio

An easy way to represent a perforated plate or a baffle that has a known open (free) area is to use a free area ratio.

The free area ratio is the ratio of the open area to the total area of an obstruction:

To input a free area ratio, select the desired direction and choose Free Area Ratio as the Variation Method. Enter the appropriate ratio in the Value field. A value of 1 indicates that the region is completely open, and the flow will encounter low resis-tance. The two normal directions are typically closed, so use a value of 0 to indi-cated a completely closed--high resistance condition.

6.6.2.3 Friction Factor

The friction factor method can be used to simulate a long length of tube or pipe. In this method, the excess pressure drop is written as:

fAopen

Atotal-------------=

p∂xi∂

------- fDH-------Lρ

ui2

2------=


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where f is the friction factor and DH is the hydraulic diameter. On the Material Edi-tor, select the desired direction, and choose Friction Factor as the Variation Method:

Enter the Hydraulic Diameter and the simulated Pipe Length (as well as the desired units).

Select the friction factor calculation method: Moody or the equation , where Re is the Reynolds number based on the hydraulic diameter of the pipe.

In the Moody method, the Moody formula is used to calculate the friction factor. The obstruction Roughness height must be entered in the correct length units.

In the equation method, enter the coefficients a and b, as shown in the equation above.

6.6.2.4 Head Capacity Curve

A head capacity table controls the flow rate based on the calculated pressure drop.

f aRe b–=


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To input a head capacity curve, select the desired direction and choose Head Capacity Curve as the Variation Method. Enter the pressure and flow rate values in the following table:

Click the Insert button to create a new line between two existing lines. Use the Import button to bring in data in Excel “.csv” format. Save a table of data to a “.csv” file using the Save button.

A set of controls on the dialog allows the selection of the driving (independent) variable: pressure or flow rate. For the other distributed resistance methods, the pressure is determined as a function of the velocity. However, because in previous versions of CFdesign, the flow rate was a function of the pressure when using the Head Capacity curve, this toggle has been added.

By default, this toggle is set so that the pressure is a function of the flow rate (mak-ing flow rate the independent variable). This variation method is more consistent with the other resistance variation methods, and will produce pressure drop results that are consistent with expected values.

Analyses that are converted from previous versions of CFdesign will have this tog-gle set to Pressure as the independent variable when opened into CFdesign 8.0.


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6.6.2.5 Permeability

A permeability can be input using the Darcy equation. Unlike loss coefficients which have different resistance values in the three directions, a permeability provides a constant resistance in all directions. An example is a packed bed of stones.

The governing equation for pressure drop as a function of permeability is:

where C is the viscosity coefficient, is the viscosity (of the surrounding fluid) and ui is the velocity in the global i coordinate direction.

To represent a porous media, select Permeability from the Variation pull-down menu, and enter just the value of the permeability, , as shown in the following equation:

The units of permeability are length squared.

Note that the length over which a permeability acts must be represented accurately in the geometry. The reason is that the Length term in the above equation is deter-mined from the meshed geometry. Unlike the loss coefficient (K) variation method, the length over which a permeability acts is not divided out of the equation.

6.7 Internal Fans

Internal fans simulate an axial momentum source within the interior of the geome-try. Fans can have a constant flow rate, or the flow rate can vary with a head-capacity curve so that the fan operating point depends on the pressure drop through the device.

p∂xi∂

------- Cµui=

µ

κ

P1 P2– 1κ---µVL=


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6.7.1 Assigning Axial Fans

Note: internal axial fans should not be placed on an external boundary. Likewise, it is not good practice to apply boundary conditions to any surface of an internal fan material. Doing so may cause convergence difficulties and will affect the flow rate reported in the summary file. If an internal fan contacts an external boundary, it is better to either create an extension onto the fan inlet (so that the boundary condi-tion is not applied directly to the fan) or simply use an external fan boundary condi-tion instead of an internal fan material.

1. Select the part or parts.2. Choose the Internal Fan/Pump as the Type, 3. Select the Material Name.

(If the material does not exist, see the following section for how to create fan materials.)

4. Select the Flow Direction of the fan by selecting either a Cartesian direction or by selecting Pick on Surface.

If Pick on Surface is selected, you will be prompted to pick a planar surface on the fan part that is nor-mal to the flow direction.

Use the Reverse button to change the flow direction if necessary.

5. If the fan is to be temperature dependent, click the Thermostat button, and define the tempera-ture behavior as described below.

6. Click Apply to apply the mate-rial.

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6.7.2 Thermostatic Controls

This allows internal fans (and blowers) to be dependent on a temperature within the model. The fan will run as long as this “trigger temperature” is above (or below) a pre-defined cut-off. When the temperature at the thermostat location is below (or above) the cut-off, respectively, the fan will not run.

Click the Thermostat button on the Internal Fan/Pump Materials task to open the Internal Fan Thermostat dialog. This dialog allows for specification of a Trigger tem-perature and a thermostat location:

The average temperature on the surface is used as the sensing temperature. (Any surface in the model can be used.) While this dialog is open, the interface allows for the selection of a surface. Only one surface can be used as a sensing surface, so selecting a new surface will update the selection list. The surface ID is written in the space called “Surface ID,” and the surface in the model is highlighted.

1. Click the Enabled box to activate an internal fan thermostat.2. Set the thermostat location by selecting a surface on the model. 3. Select the fan dependence on tem-perature--operating below the trigger temperature (to keep things warm) or...

above the trigger temperature (to keep things cool).

4. Specify the Trigger Temperature and the associated units.5. Click OK to finish.

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6.7.3 Creating and Editing Axial Fans and Pumps

No internal fans are included in the installed Materials Database, so it is necessary to create at least one before using a fan. The Material Editor for internal fans is shown:

Creating Fan Materials is similar to creating fluid and solid materials:

1. The Type must be set to Internal Fan/Pump (this is set on the Main Materials dialog).2. Enter a material name. Note: spaces are not permitted in material names.3. Hit the button of the Property to define.4. Select the Variation Method.5. Enter the appropriate Value(s).6. Click the Apply button.7. Click OK when all information is entered.

A Fan material definition does not reference specific Cartesian components. Instead, the Through-Flow-Rate is entered. The specific Cartesian orientation of the fan is specified when a fan material is applied to a part.

No other fluid property information is required to define an internal fan. The Solver automatically applies the fluid property information from the surrounding fluid to

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the fan. For this reason it is very important that a fan part contact only one fluid material type. If, for example, a fan contacts air on one side and water on the other, an error will result, and the analysis will not run.

6.7.3.1 Flow

There are three ways to specify the flow: as a constant value, a head-capacity (PQ) curve, or as a specified velocity profile:

Constant

Enter the Flow Rate Value and appropriate units.

Fan Curve

Enter the Flow Rate and Pressure into the table. This information often comes from fan manufacturer data.



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In some instances, certain fans such as large industrial units deliver a non-standard velocity distribution. When several such fans are present, the default uniform velocity distribution provided by the internal fan material does not adequately pre-dict the flow profiles and the interaction between the fans. This information, how-ever, is required for a complete understanding of the overall flow distribution throughout the enclosure.

The Velocity Profile flow variation method allows the specification of the velocity profile for an internal fan. It provides a mechanism to apply the velocity distribution computed from a detailed rotating region fan analysis to a simple geometric repre-sentation of that fan in a subsequent system-level analysis.

A velocity profile distribution can be computed from a separate rotating region analysis by creating a radial line of monitor points from the center to the outer edge

Velocity Profile

The table allows input of radius, axial velocity, swirl velocity (cir-cumferential), and radial velocity.

Enter velocity profile data in the table. Values for Radius and Axial Velocity are required. Values for Swirl Velocity and Radial Velocity are optional. Alternatively, data can be read in from a comma-separated file (“.csv”). Data can be prepared in an Excel spreadsheet and saved to a “.csv” format.

More information is given below.


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of the fan. These monitor points should be created prior to running the analysis so that a time history of velocity is generated.

Create the line of monitor points along a Cartesian axis, if possible. This will greatly facilitate determining the radial position of each point. In the example shown above, the points all have the same y and z coordinates, and the origin is at the center of the fan. The radial position of each point is its x coordinate.

If the points are aligned along a Cartesian axis, then each velocity component will directly correspond to a component needed for the fan profile: axial, radial, and swirl. In the example above:

• x coordinate = radius• x velocity component = radial velocity• y velocity component = swirl• z velocity component = axial

After the analysis is complete (so that the velocity values are converged on a time averaged basis), save the velocity components for each monitor point from the Convergence Motor table into an Excel spreadsheet, and save as a “.csv” file.

x

yz


Materials

6.7.3.2 Rotational Speed

The rotational speed is an optional parameter, and can only be entered as a con-stant value.

6.7.3.3 Slip Factor

The slip factor is the ratio of the flow rotational speed to the fan blade rotational speed. Due to inefficiencies in the fan, slip can cause the tangential velocity of the flow to be slower than that of the fan blades. CFdesign will determine the tangential velocity of the flow by multiplying the slip factor by the specified fan rotational speed.

The default slip factor is 1.0. This will cause the rotational speed of the flow to be the same as the rotational speed of the fan. The permitted range of slip factor val-ues is between 0 and 1. Values outside of this range are not allowed by the User Interface.

6.8 Centrifugal Pump/Blower

A complement to the axial fan device, this is a material type that changes the flow direction from axial to radial. The user specifies a flow rate (constant or a fan curve) as well as an optional rotational speed.

This device models the flow through the impeller of a centrifugal device, so the volute geometry is required. Flow can also be made to enter radially/tangentially and exit axially (as in a radial in-flow turbine).


Materials

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6.8.1 Assigning Centrifugal Pumps and Blowers

(If the material does not exist, see the following section for how to create the mate-rial.)

1. Select the part or parts.2. Choose the Centrifugal Pump/Blower as the type.3. Select the Material Name.

4. Select the Axis of Rotation by click-ing the Axis of Rotation button. This opens a dialog prompting for a surface that is normal to the axis of rotation. Select the surface, and reverse the direction if necessary, using the right hand rule convention.

5. Select the inlet surface or surfaces by clicking on the Inlet button. This will bring up a dialog prompting you to select the inlet surface(s). After selecting the surface(s), hit OK on the Inlet Face Selection dialog.

6. Select the outlet surface or surfaces by clicking on the Outlet button. This will bring up a dialog prompting you to select the outlet surface(s). After selecting the surface(s), hit OK on the Outlet Face Selection dialog.

7. If the fan is to be temperature dependent, click the Thermostat button, and define the temperature behavior as described in the Axial Fan section.

8. Click Apply finish.

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Materials

For a pump or blower-type device, the inlet is typically the axial surface. Care should be taken when constructing the geometry that the inlet surface does not touch the outlet surface.

This is shown

Alternatively, the device may be an annulus, like a squirrel cage. In this case, the inlet would be the interior annular surfaces, and the outlet would be the exterior cylindrical surfaces (as shown above).

Inlet Surface Outlet Surfaces

Centrifugal BlowerSurroundingFlow Volume


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6.8.2 Creating Centrifugal Pumps and Blowers

No centrifugal pumps are included in the installed materials, so it is necessary to create at least one before using a pump. The Material Editor for centrifugal pumps is shown:

1. The type must be set to Centrifugal Pump/Blower (this is set on the main Mate-rials dialog).2. Enter a material Name. (Note: no spaces.)3. Hit the button of the Property to define.4. Select the Variation Method.5. Enter the appropriate Values.6. Click the Apply button.7. Click OK when all information is entered.

The Flow Rate and the Rotational Speed are necessary inputs. The specific direction of flow and rotational direction are not part of the material definition. These set-tings are entered on the Material task dialog, making them particular to the assigned geometry.

No other fluid property information is required to define a centrifugal pump. The Solver automatically applies the fluid property information from the surrounding fluid to the pump. For this reason, it is very important that a pump contact only one fluid material type.

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There are two ways to input flow rate: as a constant value or as a head-capacity (PQ) curve.

6.8.2.1 Flow Rate

6.8.2.2 Rotational Speed

The rotational speed is an optional parameter, and can only be entered as a con-stant value.

Constant

Enter the Flow Rate Value and the appropriate units.

Fan Curve

Enter the Flow Rate and Pressure Head data into the table. This infor-mation often comes from fan manu-facturer data. Data in “.csv” format can be imported using the Import button. Data is saved to a “.csv” file using the Save button.


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6.9 Check Valves

Check valves shut when the flow rate reaches a user-specified minimum value, and are often used to prevent back flow. Check valves can be represented using a resis-tance parameter, reducing the need to model the geometry.

6.9.1 Assigning Check Valves

If Pick on Surface is selected, you will be prompted to pick a planar surface on the part. This surface will be normal to the flow direction.

Use the Reverse button to change the flow direction.

1. Select the part or parts.2. Choose Check Valve as the Type.3. Select the Material Name.

(If the material does not exist, see the following section for how to create the material.)

4. Select the Flow Direction of the check valve by selecting either a Cartesian direction or by selecting Pick on Surface.

5. Click Apply to apply the mate-rial.

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6.9.2 Creating and Editing Check Valves

No check valves are included in the installed Materials Database, so it is necessary to create at least one before assigning one. The Material Editor for check valves is shown:

Creating Check Valve Materials is similar to creating fluid and solid materials:

1. The Type must be set to Check Valve (this is set on the Main Materials dialog).2. Enter a material name. Note: spaces are not permitted in material names.3. Hit the button of the Property to define.4. Select the Variation Method.5. Enter the appropriate Value(s).6. Click the Apply button.7. Click OK when all information is entered.

A Check Valve material definition does not reference specific Cartesian compo-nents. Instead, the flow direction is specified when a check valve material is applied to a part.

No other fluid property information is required to define a check valve. The Solver automatically applies the fluid property information from the surrounding fluid to the check valve material. For this reason it is very important that a check valve material contact only one fluid material type. If, for example, a check valve con-tacts air on one side and water on the other, an error will result, and the analysis will not run.

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Two parameters are required to define a check valve: the Full Open K Factor and the Cutoff Flow Rate.

The Full Open K factor is used to simulate the fact that even a wide open valve causes loss to the flow. This value can be very small, but it is not recommended to use a value of 0.

The Cutoff flow rate is the flow rate at which the valve begins to close.

6.10 Rotating Regions

Part of the CFdesign Motion Module, the Rotating Region allows for the analysis of rotating machinery such as pumps, turbines, and mixers. The rotating region is an “envelope” that surrounds a spinning device. Throughout the analysis, the rotating region rotates about its center-line, and any solids within the region will rotate as well.

There are numerous ways to define the rotation using a rotating region. Such methods include a user-defined rotational speed, a driving torque, and a fluid-driven approach that spins because of the hydrodynamic (or aerodynamic) forces imparted by the flow.

Please consult the Guidelines chapter of this Guide for more information about Rotating Machinery analyses.

6.10.1 Assigning a Rotating Region

A new material type has been added to the Material Task Dialog: Rotating Region. When defining a rotating region, select this type from the Type drop down of the


Materials

Material Task dialog. To create or edit a Rotating Region, hit the Create/Edit Mate-rial button to bring up the Material Editor.

The center of rotation will be calculated automatically based on the geometry of the rotating region. For this reason, it is important that the rotating region and the solid (or cut-out) rotor have the same center.

Note: Solids embedded in a rotating region should be assigned a solid material. CFdesign will rotate such a solid because it is embedded in a rotating region.

1. Select the part or parts. 2. Choose Rotating Region as the Type.3. Select the Material name.

(If the material does not exist, create one using the Create/Edit button.)

4. Choose the Axis of Rotation by selecting either a Cartesian direction or by selecting a surface that is nor-mal to the rotational axis (Pick on Surface).

If Pick on Surface is selected, you will be prompted to pick a planar surface on the rotating region part that is normal to the axis of rotation.

Use the Reverse button to change the axis direction if necessary. The Right Hand Rule Convention is used.

5. Click Apply to apply the material to the part.

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6.10.2 Creating and Editing Rotating Regions

No rotating region materials are included in the installed Materials Database, so it is necessary to create at least one before designating a part as a rotating region. The Material Editor for rotating regions is shown:

Creating a rotating region is similar to creating fluid and solid materials:

1. The Type must be set to Rotating Region on the Main Materials dialog.2. Enter a material name. Note: spaces are not permitted in material names.3. Select the Analysis type: Known Rotational Speed, Known Driving Torque, or Free Spinning.4. Click the Property button to define.5. Select the Variation Method.6. Enter the appropriate Values.7. Click the Apply button.8. Click OK when all information is entered to close the dialog.

The parameters that define a Rotating Region are based on the type of analysis to be run. There are three different scenarios: Known Rotational Speed, Known Driv-ing Torque, and Free Spinning. The type is selected from the drop menu as described in Step 3, above.

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6.10.2.1 Analysis Type: Known Rotational Speed

Enter the rotational speed of the rotor in either radians per second or RPM.

A variable rotational speed can be entered by changing the Variation Method to Table, and entering data points for rota-tional speed vs. time.


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6.10.2.2 Analysis Type: Known Driving Torque

This method is useful for modeling a device that is rotated by a known driv-ing torque (such as from a motor). Torque can be entered as a constant value or as varying with time or RPM using a piece-wise linear data table.

(The direction of applied torque is set as the rotational direction on the main Material Task dialog.)

If there is a resistive torque acting on the device, subtract that from the Known Torque value. For example, if the known motor torque is 100 N-m, and the resistive torque is 5 N-m, then apply a value of 95 N-m.

In addition to torque, enter the inertia of the rotating device. This is commonly the rotational inertia of the rotor and shaft and anything that is connected to the shaft (such as a motor or flywheel if the rotating device is a turbine). An easy way to determine an approximate iner-tia is to multiply the combined mass of the rotor, shaft, and shafted accessories by the average radius squared. This approach is reasonable if the intent of the analysis is to run the device to a steady state condition.

If the intent of the analysis is to obtain a detailed time history of the rotational speed, then a more precise value of inertia is necessary.


Materials

6.10.2.3 Analysis Type: Free Spinning

6.11 Compact Thermal Model

6.11.1 Introduction

A new material type, “Compact Thermal Model,” has been added that allows the simulation of integrated circuits using a two resistor compact thermal model. Com-pact models provide a geometrically simple way to simulate the performance of electronic components using a resistor network.

This modeling method uses very simple geometry to represent a very complicated device. A more rigorous method uses the entire geometry of the device, and is often referred to as a “detailed model.” Detailed models typically produce the high-est degree of accuracy, but due to their complexity, require a large mesh and hence require long analysis times.

The following chip configurations are supported by this type of modeling:

• BGA (ball grid array)

In this case, the rotor starts with no rota-tional speed, and will “spin up” based on the applied fluid loading. Specify the inertia of the mechanical components and the rotor. The steady rotational speed will occur when the net hydraulic torque is zero.

If the device is free spinning, but a known resistive torque exists:

1. Set the Analysis Type to Known Driving Torque, 2. Apply the resistive torque as a negative value.This will cause the device to spin up due to the surrounding flow, and will find a steady rotational speed when the net hydraulic torque is zero.


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• PBGA (plastic ball grid array)• TBGA (taped ball grid array)• FC-BGA (flip chip ball grid array)• QFP (quad flat pack)• PQFP (plastic quad flat pack)• NQFP (no-lead quad flat pack)• SOIC/SOP (small-outline IC/ small-outline package)

Note that vertical chips such as the TO200 are not supported by this model. It is recommended to model such chips using a detailed model.

The typical two resistor compact thermal model consists of just three nodes: the junction, the case, and the board. The junction is also referred to as the die or the chip. The case is the top surface of the package, and is where a heat sink may be mounted to the package. The board node is a single point of contact between the board and the package. The nodes are connected by a thermal resistance between the case and junction (Theta jc), and a resistance between the junction and the board (Theta jb). The resistor network is shown:

In the two resistor compact model, heat transfer is only computed at the three nodes (case, junction, and board). The sides of a two resistor compact model are considered adiabatic. Only the case and board sides allow heat transfer to their sur-roundings. The case and board sides of the device are isothermal, and are modeled with a high conductivity in the in-plane direction.

Note that the two resistor compact model is a simplified representation of an actual device, and the literature indicates that they are typically accurate to about 10-30%. This model is a simplification, but one that is acceptable for many design-level “what if” analyses.

Case

Junction

Board

Theta jc

Theta jb


Materials

The resultant quantities of a two resistor compact model analysis are the tempera-tures at the board, junction, and case. In addition, the heat flux to the case and the board are provided.

Unlike a detailed component model, the two resistor compact model is modeled as a simple six-sided shape. The device must contact a PCB part, and a heat sink may be attached to the case side of the component.

An example is shown:

Heat loading on a two resistor compact model is typically applied as a total heat generation boundary condition. Note that a transient heat generation condition can be applied, but because the specific heat and density of the component are not included in the material definition, a time-accurate solution will not be available.

Because the heat transfer computation is only performed on the three nodes of the network, a finite element mesh is not constructed through the device. The outside surfaces are meshed to provide connectivity between the two resistor device and the surrounding geometry.

PCB

Compact ThermalModel Component


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6.11.2 Assigning Compact Thermal Materials

A requirement of the compact thermal model implementation is that the device must contact either a PCB material (described in the previous section) or a solid material with “PCB” in its name. From this, the orientation of the device is deter-mined automatically. The side of the component touching the PCB material is the board side, and the board node is at the center of the board surface of the compo-nent. The opposite side is the case side.

1. Select the component part or parts from the model.

2. Choose Compact Thermal Model as the Type, and select the material from the Name combo menu if it exists.

3. If the material does not exist, see the following section for how to create 2 Resistor Component materials.

No direction data is required when assigning a 2 Resistor Component material. CFdesign automatically determines the orientation based on the location of the contacting PCB.

4. Click Apply to apply the material.

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PCB

board sidecase sidecompact thermalmodel component


Materials

An error is given if a 2-Resistor Electronic Material does not contact a PCB material (or a solid material with PCB in its name) when the user leaves the Materials task dialog.

6.11.3 Creating a Compact Thermal Material

Only two parameters are required to define a two resistor Compact Thermal Model on the Material Editor: the resistance between the junction and the board “Theta JB” and theresistance between the junction and the case, “Theta JC.”

1. Select Compact Thermal Model as the Type on the Material Task dialog.2. Enter a name for the material in the Name field on the Material Editor. (Spaces are not allowed for material names.)3. Click either the Theta JB or Theta JC button.4. Enter a value and appropriate units. (Note that the only available variation method is Constant.)5. Click Apply. 6. After specifying both values, click OK to close the dialog.

Values for the resistances (Theta JB and Theta JC) can often be obtained from the component manufacturer’s specifications.

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6.11.4 Data Extraction and Visualization

For visualization purposes, the device is divided into two regions--the junction and the case. Each region of the component has its own temperature which is governed by the resistance values and the surrounding conditions. A single rectangular ele-ment comprises each layer, and is shown:

For every two resistor component, the following data is available:

• Board Temperature• Junction Temperature• Case Temperature• Heat transfer between the junction and the board• Heat transfer between the junction and the case

This data is viewed with these methods:


Materials

• Left click on the component name in the Materials branch of the feature tree. This will show a pop-up window on the component listing the data:

• Open the Component Thermal Summary from Review_Notes.• View the Component Thermal Summary by generating a report from Review_Report.

6.12 Printed Circuit Boards

Printed circuit boards (PCB) are used in a wide variety of electronics applications. Because PCBs play an important role in the temperature and heat flux distribution within a device, it is important to accurately represent their thermal characteristics accurately.


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PCBs are typically constructed of multiple layers of copper foil and a dielectric material (a glass-reinforced polymer called FR4):

Because of the complexity of these components, it is often desirable to model them using simple geometry in conjunction with effective properties to simulate the heat transfer. Two conductivity values are needed: the normal conductivity (knormal) and the in-plane conductivity (kin-plane). These values are computed as shown:

• N = the maximum number of layers• k = layer conductivity• t = thickness• C = metal content• E = coverage exponent

A new material type, Printed Circuit Board, has been added to the Materials dialog of the CFdesign interface. The PCB is represented as a simple geometric volume (even though physically PCBs can be quite complicated). The geometric physical specifications of the PCB such as the layer thickness and the amount of metal per

Component Trace20% Copperthickness, t = 0.07 mm

Component Planes95% Copperthickness, t = 0.035 mm

Component Trace20% Copperthickness, t = 0.07 mm

Total PCB thickness = 1.6 mm

Dielectric layers

kin plane–

ti ki CiE⋅ ⋅

i 1=

N

∑

ti

i 1=

N

∑---------------------------------= knormal

ti

i 1=

N

∑

ti

ki Ci⋅-------------

i 1=

N

∑-----------------------=


Materials

layer are specified as material attributes, and the effective conductivities are then computed automatically and applied to the geometry throughout the analysis.

This material type provides a convenient way to include the thermal effects of a PCB in a simple, homogeneous geometry without having to include the geometric details of the various layers, traces, and planes:


Materials

Mate

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6.12.1 Assigning a Printed Circuit Board Material

As with all materials, PCB materials are stored with the analysis file, even if the material is not saved to the material database. Clicking the Save Database button on the Material Task dialog will save existing PCB materials to the database for use with later analyses.

6.12.2 Creating a Printed Circuit Board Material

No PCB materials are included in the installed Materials Database, so it is necessary to create at least one prior to applying a PCB material. There are three steps neces-sary to create a PCB material:

1. Specify the Total PCB Thickness. In this step, the total physical thickness of the circuit board is specified.

1. Select the PCB part or parts from the model. PCBs should be modeled as three dimensional volumes having the same physical size and shape as the actual PCB. No internal layers should be modeled within the PCB.

2. Choose Printed Circuit Boards as the Type, and select the material from the Name combo menu if it exists.

3. If the material does not exist, see the previous section for how to create PCB materials.

No direction data is required when assigning a PCB material. CFdesign automatically determines the through and planar directions based on the rel-ative dimensions of the part.

4. Hit Apply to apply the material.

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2. Define the trace layers. In this step, the solid material that makes up the traces is selected from the Solid Material library. This material is typically copper, and is available by default in the Solid Material library. Additionally, the thickness and per-centage of metal of each layer are specified.3. Define the dielectric material. The solid material that makes up the dielectric is selected from the Solid Material database. This material is listed in the Solid Mate-rial database under the name: PCB_Plastic_for_Laminate

Each step is described in detail below:

Step 1: Total PCB Thickness

1. Click the Total PCB Thickness button.2. Enter the thickness of the printed circuit board in the Thickness field as well as the units. Constant is the only variation method for PCB thickness.3. Click Apply to save the value.

The thickness can easily be obtained from the CAD model or from the actual device. Using this value and the sum of the trace layer thicknesses, the thickness of the dielectric layer is automatically computed.

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Step 2: Traces and Planes

In this step, the solid material that makes up the traces and planes is selected from the Solid Material library. Additionally, the thickness and percentage of metal of each layer are specified.

1. Click the Traces and Planes button.2. Select the trace material from the Material drop-down menu. This menu lists all of the solid materials stored in the material database. Copper is the most com-monly used material for PCB trace layers. If a material that has variable properties is selected, a median value will be used for the PCB material. This property value will be constant throughout the analysis.

Note: To use a material that is not in the list, close this dialog, and switch to Solid Materials on the Material task dialog. Create the desired solid material using the Solid Material Editor. This material will then be available on the PCB Material drop-down menu.

3. Enter a line for each layer, and specify the thickness and the percent metal con-tent. For example, if the 35% of the layer is copper, enter “35” in the “% Metal” column.4. Add additional rows by clicking the Insert button; remove rows with the Delete button.

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5. A two-column table of data in “.csv” format can be imported by clicking the Import button. Likewise, input data can be saved to a “.csv” file by clicking the Save button.6. The Coverage Exponent is a weighting function used to account for the effect of the configuration and concentration of copper within the board on the in-plane con-ductance. The default value is 2. A value of 1 is most applicable for strips or grids; a value of 2 is applicable for spots or islands.7. Click Apply to save the values and to activate them with the equivalent proper-ties calculation.

Step 3: Dielectric

The dielectric layer is typically a glass-reinforced polymer that gives the PCB its rigidity, and surrounds the copper layers. In this step, the solid material that makes up the dielectric layer is selected from the Solid Material database:

1. Click the Dielectric button.2. Select the trace material from the Dielectric Material drop-down menu. This menu lists all of the solid materials stored in the material database. FR4 is the most commonly used material for PCB trace layers.

If a material that has variable properties is selected, only the value for the x-direc-tion conductivity will be used for the PCB dielectric material. This property value will

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be constant throughout the analysis. Note: anisotropic dielectric conductivity is not supported.

To use a material that is not in the list, close this dialog, and switch to Solid Materi-als on the Material task dialog. Create the desired solid material using the Solid Material Editor. This material will then be available on the PCB Material drop-down menu.

3. Click the Apply button to activate the material.4. Click OK to finish.

The effective normal and in-plane conductivity values are computed when the Apply button is clicked. The effective density and specific heat are also computed for the PCB. These values are used by CFdesign during the heat transfer calculation to determine the temperature distribution throughout and around the PCB.


Parts are colored by their applied materials. The legend in the upper left corner defines the color for each material. All parts with the same material are colored the same except for parts contained within rotating regions. Parts that are enclosed within rotating regions will be colored differently from other parts of the same material.

6.14 Feature Tree

All applied materials are listed on the feature tree. These listings are for informa-tional and for view attribute control only. All material definition is controlled through the task dialog:


Materials

These listings are very helpful for checking materials and for changing the visibility of materials. To highlight all parts of a material, left click on the material name branch--the parts will highlight in the Graphics window. To change the appearance of materials and parts, right click on either a material or a part branch; the part can be displayed in Outline mode or as Transparent. In the Results task, further visibility choices are available on the Materials branch and sub-branches of the fea-ture tree.


CHAPTER 7 Motion

7.1 Introduction

The CFdesign Motion Module provides the ability to analyze the interaction between solid objects in motion and the surrounding fluid. The effect of the motion on the fluid medium as well as the flow-induced forces on the object can both be analyzed efficiently and quickly.

The Motion Module was first introduced in CFdesign version 7, with the introduction of user-prescribed Linear motion. Since then, six motion types have been added, resulting in support for seven varieties of motion:

• Linear• Angular• Combined Linear/Angular• Combined Orbital/Rotational• Nutating• Sliding Vane• Free Motion

For all but two of the motion types, movement is either prescribed using input parameters or is driven by the flow. (Sliding Vane is user-prescribed only, and Free Motion is flow-driven only.) Each motion type is defined by specifying only the applicable properties and directions, but does not require definition of all six degrees of freedom. The displacement, velocity, or location of objects in motion is either explicitly prescribed by the user or is driven by the forces imparted from the surrounding flow. In the case of the latter, externally applied driving and resistive forces (such as springs) can be defined that influence the motion of the object.

A new task dialog just for Motion has been added to the CFdesign interface. This was done to reduce the complexity of the Materials task. However, as in Materials, color coding of objects with motion and Feature Tree listings allows easy identifica-tion of applied settings.


Motion

7.2 Guidelines

7.2.1 Basic Process

This is an overview of the steps necessary to assign motion to a solid object.

Note that a moving solid cannot pass through more than one fluid type.

Only objects that are solids (as assigned on the Materials dialog) can be assigned motion. Solids will appear shaded in the Motion task, all other materials will appear in outline mode.

1. Select the object or objects that are to move. (Objects that are assigned motion simultaneously will have the same motion.)2. Select the type of motion from the Type pull-down menu. The choices are: Linear, Angular, Combined Linear/Angular, Combined Orbital/Rota-tional, Nutating, and Sliding Vane, and Free Motion.3. Indicate if one or both components of the motion are to be flow driven by check-ing the appropriate Flow-Driven check box.4. Click the Create/Edit Motion but-ton. This brings up the Motion Editor. The parameters of the motion are entered on this dialog. Each motion type has specific motion parameters that are required. These are described in each section.5. Enter the model-dependent informa-tion such as Direction Vector, Initial Posi-tion, and Bounds (for flow-driven only).6. Click Apply.

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Motion

Mo

tion

The following topics are discussed in the Guidelines chapter of this manual:

• Geometry• Meshing• Surface Parts in Motion• Solid Motion Solution Strategy• Radiation for Moving Parts• Time Step Determination• Continuing after making changes

7.2.2 Previewing Motion

The path of motion is verified prior to the analysis by clicking the Preview button. The Preview function is available as soon as the motion is defined, and can be used prior to clicking the Apply button on the task dialog. To preview the motion of all defined moving solids in a model, click the Preview button when no parts are selected.

The Preview button will bring up the dialog shown below:

Use the slider bar to step the object through the defined path to ensure that the specified parameters satisfy the analysis intent. The time span is given based on the defined motion. A pseudo-time span is used for flow-driven motion so that the defined path can be examined.

7.2.3 Groups of Motions (Linked Motions)

In many devices, two or more objects that are driven by the flow are physically connected in some manner so that their motions are related. Examples include

• Hydraulic rams that slide linearly together through multiple cylinders• Gears in a gear pump rotate in opposite directions at the same rota-tional speed


Motion

Because of a mechanical linkage between the object, the motion of one is depen-dent on the motion of the others.

To link the motion of two or more objects, use the Group functionality available in the Feature Tree. Add the parts whose motions are to be linked. When creating the group, select Motion as the type on the Group Creation dialog:

Grouping is only applicable to flow-driven motions that are assigned the same motion type. If a linear and an angular motion are grouped together, for example, the linking is not possible, and will hence be ignored.

The linking functionality depends on the direction(s) of motion for the relevant parts being fully defined. Objects with linked motions can move in different direc-tions or even rotate in opposite directions. In the case of a gear pump, for example, the two gears rotate in opposite directions from one another. Assign the directions for both objects as appropriate, and add the two motions to the same group. As the flow moves them, they will move with the same rotational velocity, but in the assigned directions.

Note: objects with linked motions do not have to physically touch one another in the CFdesign analysis.

7.2.4 Visual Dominance

When visualizing results for some motion analyses, the moving solid will appear “behind” another part as it is animated through it. This other volume is often the


Motion

Mo

tion

flow volume, so this situation makes it very difficult to see the moving part. An example of this is shown:

A new visualization setting has been introduced in v9 that causes moving solids to appear over non-moving solids. This allows a clear view of the moving solid and the flow surrounding it:

Enabled by default for Moving Solids, the setting is controlled through the Materials branch of the feature tree when displaying results:


Motion

7.3 Linear Motion

7.3.1 Description

Linear motion is the motion of a solid in a straight line. Examples include a piston moving in a cylinder, a hydraulic ram in a chamber, and objects on a conveyor belt moving through a curing process. The linear motion of solids can be fully pre-scribed, or it can be driven by the flow. If flow-driven, additional parameters are required including the bounds of motion and relevant resistive or driving forces. Examples of flow-driven linear motion include the above items, as well as the simu-lation of valves opening and closing.

7.3.2 Assigning Linear Motion

1. Select the object or objects that are to move. (Objects that are assigned motion simultaneously will have the same motion.)2. Select Linear as the type of motion from the Type pull-down menu. 3. Indicate if the motion is to be flow-driven by checking the Flow-Driven box.4. Click the Create/Edit Motion but-ton. This brings up either the User-Pre-scribed Motion Editor or the Flow-Drive Motion Editor. The parameters of the motion are entered on this dialog. These parameters are described in the next sections.5. Specify the Linear Motion Parame-ters: Direction Vector, Initial Position, and Max and Min bounds (for flow-driven only).6. Click Apply.

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7.3.2.1 Direction Vector

This sets the direction of travel of the object. The pull-down menu contains the three Cartesian directions: Global X, Global Y, and Global Z, Key-in Location, as well as a “Pick” option. If Pick is chosen, a dialog will prompt for the graphical selection of a surface normal to the direction of motion. Only planar surfaces may be selected.

An arrow will indicate the direction of travel; click the Reverse button to switch the direction.

The specified direction of travel is the reference direction, and all directional-depen-dent parameters are relative to it. Specified positive displacements will move the object in the reference direction. Negative displacements will move the object in the opposite direction.

Flow-driven parameters such as driving forces and resistive forces reference this direction as well. Positive values of a driving force will act in the direction of the Direction Vector; negative values will act in the opposite direction. In contrast, pos-itive resistance forces will act in the opposite direction of the Direction Vector; neg-ative resistance forces will act in same direction as the Direction Vector.

7.3.2.2 Initial Position

This slider is used to modify the initial position of the object from the as-built loca-tion in the CAD model. This is very useful for fine-tuning the model if the position of the object in the CAD is different from the true starting position.

The positive direction of adjustment is in the Direction of Travel. Use the slider to move the object in the Direction of Travel in both the positive and negative direc-tions.

X

Y

Direction of Travel

Select either “Global X” or“Pick”, and select a surfacenormal to the direction of travel.


Motion

7.3.2.3 Minimum and Maximum

Use the Minimum and Maximum pull-down menus to set the bounds of motion for flow-driven motion. (This is only required (and available) for flow-driven motion.) The choices available for each menu are: Unbounded, Key-In Location, and Slider.

• Unbounded does not stop the object from moving along its path.• Key-In Location brings up a dialog for the input of a distance the object can travel. For example, if 1.5 inches is entered as a minimum value, then the object can not go beyond 1.5 inches in the negative direction of travel. This distance is relative to the initial position of the object.• Slider brings up a dialog and a graphical plane normal to the direction of travel. Use the slider to position the plane at the desired boundary. All locations are relative to the initial position.

The Min and Max boundaries can be specified using different methods.

Note that the bounds are relative to the initial position specified with the Initial Position Slider.

7.3.3 Defining User-Prescribed Linear Motion

In this section, methods to define linear motion are described. When an object moves according to a fully-prescribed linear motion, it does not react to the flow.


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The object will move in the direction and across distances that are explicitly speci-fied.

1. On the Motion task dialog, set the Type to Linear, and be sure Flow-Driven is unchecked.2. The only property for user-prescribed linear motion is the Distance.3. Select the Variation Method (described below).4. Enter the appropriate values.5. Click the Apply button.6. Click OK when all information is entered to close the dialog.

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7.3.3.1 Distance Variation Methods

7.3.4 Defining Flow-Driven Linear Motion

In this section, methods to describe objects in motion that respond to the sur-rounding fluid flow are described. The motion of such objects is influenced by the flow as well as user specified driving and resistive forces. The origins of such forces

ReciprocatingThis method causes the object to oscillate linearly along a prescribed distance, in a specified time.

The Half Period Time is the time it takes the object to move from the start position to the end of the stroke.

The Distance is the length of the stroke.

TableThe Distance is relative to the Initial Posi-tion prescribed on the Motion task Dialog.

Enter Distance and Time data into the table.

The Cyclical box defines the motion by repeating only forward passes through the distance table.

The Reciprocating box defines the motion by alternating forward and reverse passes through the distance table.

Distance

Start End


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do not have to be included in the analysis model--the forces act on the object in a user-prescribed manner to either push the object in its prevailing direction or to impede its progress.

In several places in this section, the Direction Vector of the object is referenced. This is the direction specified on the Motion task dialog. Because the true direction of flow-driven motion is not always known prior to the analysis, this direction is really the Reference Positive Direction. Directions of driving and resistance forces are then relative to this direction.

Flow-driven objects may start off moving at a known velocity, and either speed up or slow down based on their interaction with the surrounding fluid (and applied forces).

1. On the Motion task dialog, set the Type to Linear, and be sure Flow-Driven is checked.2. Three properties are available, but entries are not required: Initial Velocity, Driving Force, and Resistive Force.3. For each property, select the Variation Method...4. ...and enter the appropriate values, as necessary. The Variation Methods are described below.5. Click the Apply button.6. Click OK when all information is entered to close the dialog.

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7.3.4.1 Initial Velocity Variation Method

7.3.4.2 Driving Force Variation MethodsDriving forces are forces that are positive when acting in the direction of motion specified on the Motion task dialog. A negative driving force will act in the opposite direction.

Examples of driving forces include electromagnetic and other body forces as well as forces imposed by objects omitted from the analysis geometry. The force will act in the same direction as the direction of motion (as specified on the Motion task dia-log).

A driving force can be used to represent the force of gravity on an object by speci-fying the weight of the object as the driving force, if gravity is acting in the direc-tion of travel.

ConstantIf the object is in motion at the beginning of the calculation (and not starting from a dead-stop), the initial velocity should be specified. The object will travel at this velocity at the on-set of the calculation, and will react to the flow forces appropri-ately.

F

Direction Vector:(Reference Direction)


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7.3.4.3 Resistive Force Variation MethodsApplied resistive forces affect the motion of the object by acting against its speci-fied direction of travel, impeding its progress. A positive value of a resistive force acts in the opposite direction of travel; a negative value acts in the direction of travel.

ConstantEnter a constant force value to apply an unchanging force to the object throughout the entire analysis.

TableIf a driving force is to vary with time, enter the time history as a table of driving force and time.

As with all table entries, the values can be retrieved from an Excel “.csv” file or like-wise saved to one.


Motion

In addition to constant and tabular specification, resistive forces can be specified as a spring. This is a virtual spring, and does not exist in the geometry model.

A resistive force can be used to represent the force of gravity on an object by spec-ifying the weight of the object as the resistive force, if gravity is acting opposite the direction of travel.

ConstantEnter a constant force value to apply an unchanging resistive force to the object throughout the entire analysis.

F

Direction Vector:(Reference Direction)


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TableIf a resistive force is to vary with time, enter the time history as a table of resis-tive force and time.


SpringFour parameters are required to specify a spring:

Engagement Displacement: the dis-tance traveled before touching the spring

Compression Displacement: the dis-tance traveled before fully compressing the spring (relative to the starting point). This is the limit of travel, and is considered a hard stop.

Engagement Force: the amount of force the spring exerts at the engagement dis-placement. (This is the spring pre-load. If none exists, enter 0).

Compression Force: the amount of force the spring exerts at the compression dis-placement.


Motion

Recall that the Direction Vector specified for flow-induced motion is the reference positive direction. Depending on the flow, the true direction of the object may change. However the Direction Vector specified on the Motion task dialog is really a Reference Direction for the signs of applied forces and displacements.

Because springs are typically a resistive force, a positive spring force will act in the direction opposite of travel of the object’s reference direction; a negative spring force acts in the reference direction.

Likewise, a positive displacement is in the reference direction; a negative displace-ment value is opposite to the reference direction.

Note that all spring displacements are relative to the initial position defined using the Initial Position slider on the Motion task dialog.

The following diagrams describe setting up several scenarios involving springs.

If the object is not touching the spring at time = 0, then the configuration may appear as:

Starting PointEngagement Displacement

springCompression

springReferenceDirection

Direction ofSpring Force

Forces and Displacements are positive values.

Displacement


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If the object is touching the spring at time=0, then the engagement displacement is 0:

If at time = 0 the spring is fully compressed by the object, then the compression displacement is zero, and the engagement displacement is the distance to where the spring is no longer compressed:

Starting Point

spring

Compression Displacement

spring

Forces and Displacements are positive values.

ReferenceDirection


spring

Engagement Displacement

spring

Compression displacement = 0

Spring forces are negative because they act in the Reference Direction.

Starting Point

ReferenceDirection



Motion

If the object has to travel in a direction opposite of its Reference Direction to con-tact a spring, then the displacements should be applied as negative values:

Note that only one spring is allowed on a moving part. Because of this, a forward and backward spring cannot be applied to the same part.

The relationship between the required parameters and the spring constant is given as:

7.4 Angular Motion

7.4.1 Description

Angular motion is the rotation of an object about a centerline. Examples of applica-tions that should be solved with this functionality are positive displacement pumps (such as gear pumps and trichodal pumps), check or reed valves, and other devices with an angular movement. Unlike rotating regions (applied as a material type in the Materials task dialog), objects with an angular motion can have paths that

spring

spring

Compression

Displacements and are entered as negative values.Spring forces are also negative because they act in the Reference Direction.

Starting PointReferenceDirection


Engagement Displacement

Displacement

Fcompression Fengagement–Dcompression Dengagement–-------------------------------------------------------------- K=


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interfere--such as gear teeth in a gear pump or multiple mixing blades in an egg-beater:

Turbomachinery devices (centrifugal, mixed-flow, and axial pumps and turbines) should be analyzed using Rotating Regions:

Assign Angular Motion to devices that move fluid (liquid or gas) using a volume dis-placement or that simply move through fluid. Conversely, surround a rotating

The lobed cam rotates about its center. Its lobes mesh with the static lobes of the sur-rounding piece. Flow is induced through a positive displacement mechanism by changing the volume of the flow region.

Use Angular Motion to define this motion.

The impeller in this centrifugal compresor rotates, but does not touch any other solid object. It induces flow by transferring energy to the fluid (through a momentum transfer, in the classic turbomachinery sense.)

Use a Rotating Region to define this motion.


Motion

device with a rotating region that moves fluid through an energy transfer. Such devices rely on the Coriolis effect and centripetal acceleration.

Rotating regions will produce a more accurate answer, and typically require less computational resources. Moving solids (specified angular motion) are more versa-tile, and can solve a wider variety of applications.

The following table lists several devices, and how the rotational motion should be specified:

Pump Rotating Region

Turbine Rotating Region

Compressor Rotating Region

Fan Rotating Region

Blower Rotating Region

Gear Pump Angular Motion

Positive-Displacement Pump Angular Motion

Cammed Lobes Angular Motion

Egg-beater Angular Motion

Check Valve Angular Motion


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7.4.2 Assigning Angular Motion

7.4.2.1 Axis of Rotation

The rotational direction about the axis of rotation is determined by the right hand rule. Click the Reverse button to reverse the direction of rotation.

The pull-down menu contains the three Cartesian directions: Global X, Global Y, Global Z, Key-in Location, and “Pick”.

If Pick is chosen, a dialog will prompt for the graphical selection of a surface normal to the axis of rotation. (Only planar surfaces may be selected.) The object will

1. Select the object or objects that are to move. (Objects that are assigned motion simultaneously will have the same motion.)2. Select Angular as the type of motion from the Type pull-down menu. 3. Indicate if the motion is to be flow-driven by checking the Flow-Driven box.4. Click the Create/Edit Motion button. This brings up either the User-Prescribed Motion Editor or the Flow-Drive Motion Edi-tor. The parameters of the motion are entered on this dialog. 5. Specify the Angular Motion Parame-ters: Axis of Rotation, Center of Rotation, Initial Position, and Minimum And Maxi-mum Bounds (for flow-driven only).6. Click Apply.

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Motion

rotate about the specified axis that passes through the Center of Rotation (dis-cussed in the next section).

The Direction of Rotation is the reference direction for all directional-dependent parameters. For user-prescribed rotation, a positive angular rotation will rotate the object in the Direction of Rotation. A negative angular rotation will rotate the object in the opposite direction.

Flow-driven parameters such as driving torque and resistive torque reference this direction as well. Positive values of a driving torque will act in the direction of the Axis of Rotation; negative values will act in the opposite direction. In contrast, pos-itive resistance forces will act in the opposite direction of the Direction Vector; neg-ative resistance forces will act in same direction as the Direction Vector.

7.4.2.2 Center of Rotation

The center of rotation is the point through which the axis of rotation passes. There are two ways to specify it: as the centroid of a selected surface or by keying-in coordinates. Select the desired method from the Center of Rotation pull-down menu.

• Centroid of Surface: The axis of rotation will pass through the cen-troid of the selected surface. If the axis does not pass through the centroid, specify an offset distance and direction:

Global Z is the desired axis of rotation, and the direction is positive.

The unit vector = 0 0 1.

Z

X

Y

Z

Axis of rotation

Select surface to set centroid ascenter of rotation

Axis of rotation

Offset from Centroid: x = -a

a

x

y


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• Key-In Location: a dialog will prompt for the x, y, and z coordinates of the center of rotation.


This slider is used to modify the initial angular position of the object from the as-built location in the CAD model. This is very useful for fine-tuning the model in case the initial position of the object in the model is not quite correct.

The positive direction of adjustment is in the direction defined by the Axis of Rota-tion. Use the slider to rotate the object about the axis of rotation in both the posi-tive and negative directions.


Use the Minimum and Maximum pull-down menus to set the bounds of rotation for flow-driven angular motion. (This is only required (and available) for flow-driven rotation.) The choices available for each menu are: Unbounded and Key-In Loca-tion.

• Unbounded does not stop the object from moving along its path.• Key-In Location allows specification of an angular limit. Multiple revo-lutions can be defined by entering the total angular sweep that is permit-ted.

The minimum and maximum boundaries can be specified differently, if necessary.



Motion

7.4.3 Defining User-Prescribed Angular Motion

In this section, methods to define angular motion are described. When an object moves according to a fully-prescribed angular motion, it does not react to the flow. The object will rotate in the specified direction at the prescribed angular velocity.

1. On the Motion task dialog, set the Type to Angular, and be sure Flow-Driven is unchecked.2. The only property for user-prescribed angular motion is the Angle through which the object will sweep.3. Select the Variation Method (described below).4. Enter the appropriate values.5. Click the Apply button.6. Click OK when all information is entered to close the dialog.

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7.4.3.1 Angle Variation Methods

ConstantEnter the angular speed at which the object will rotate throughout the analysis. The units pull-down menu allows selection of either radians per second or RPM.

OscillatingThis method causes the object to oscillate angularly through a prescribed angle, in a specified time.

The Half Period Time is the time it takes the object to rotate from the start position to the end position of the angular displace-ment.

The Angular Displacement is the included angle of the stroke.

Start

End

AngularDisplacement

Center of Rotation(specified on theMotion task dialog)


Motion

7.4.4 Defining Flow-Driven Angular Motion

In this section, methods to define rotating objects that respond to the surrounding fluid flow are described. The motion of such objects is influenced by the flow as well as user-specified driving and resistive torques. The origins of such torques do not have to be included in the analysis model--they act on the object in a user-pre-scribed manner to either accelerate the rotation of the object or to slow it down.

In several places in this section, the direction of rotation of the object is refer-enced. This is the rotational direction specified as part of the axis of rotation on the Motion task dialog. Because the true rotational direction of flow-driven motion is not always known prior to the analysis, this direction is really the reference positive direction. Directions of driving and resistance forces are then relative to this direc-tion.

TableThe table allows for specification of an angular position at specific times.

The angle is relative to the Initial Position prescribed on the Motion task dialog.

Enter Angle and Time data into the table.

The Cyclical box defines the motion by repeating only forward sweeps through the angle table.

The Reciprocating box defines the motion by alternating forward and reverse sweeps through the angle table.


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Flow-driven objects may start off rotating at a known velocity, and either speed up or slow down based on their interaction with the surrounding fluid (and applied forces).

1. On the Motion task dialog, set the Type to Angular, and be sure Flow-Driven is checked.2. Three properties are available for specification, but entries are not required: Initial Angular Velocity, Driving Torque, and Resistive Torque.3. For each property, select the Variation Method...4. ...and enter the appropriate values, as necessary. The Variation Methods are described below.5. Click the Apply button.6. Click OK when all information is entered to close the dialog.

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7.4.4.1 Initial Angular Velocity Variation Method

7.4.4.2 Driving Torque Variation MethodsA driving torque is positive when applied in the reference direction of motion (as specified on the Motion task dialog). A negative driving torque will act in the oppo-site direction.

Examples of driving torque include electromagnetic and other body torque as well as torque imposed by objects omitted from the analysis geometry. The torque will act in the same direction as the direction of motion (as specified on the Motion task dialog).

A driving torque can be used to represent the force of gravity on an object if gravity is acting in the direction of travel. Specify a driving torque that is the product of the weight of the object and the length of the moment arm connecting the centroid to the center of rotation.

ConstantIf the object is rotating at the beginning of the calculation (and not starting from a dead-stop), the initial velocity can be specified.

The object will rotate at this velocity at the on-set of the calculation, and will react to the flow forces appropriately.

Direction of Rotation(as defined on the

Driving Torque

Motion task dialog)


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7.4.4.3 Resistive Torque Variation MethodsApplied resistive torque affects the rotation of the object by acting against its spec-ified rotational direction, impeding its progress. A positive value of a resistive torque acts in the opposite direction of rotation; a negative value acts in the direc-tion of rotation.

ConstantEnter a constant torque value to apply an unchanging torque to the object through-out the entire analysis.

TableIf a driving torque is to vary with time, enter the time history as a table of driving torque and time.



Motion

In addition to constant and tabular specification, resistive torque can be specified as a torsional spring. This is a virtual spring, and does not exist in the geometry model.

A resistive torque can be used to represent the force of gravity on an object if grav-ity is acting opposite the direction of travel. Specify a resistive torque that is the product of the weight of the object and the length of the moment arm connecting the centroid to the center of rotation.

ConstantEnter a constant torque value to apply an unchanging resistive torque to the object throughout the entire analysis.

Direction of Rotation:Resistive Torque

(Reference Direction)


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Recall that the angular direction defined by the Axis of Rotation is the reference positive direction. Depending on the flow, the actual rotational direction may

TableIf a resistive torque is to vary with time, enter the time history as a table of resis-tive torque and time.


SpringFour parameters are required to specify a torsional spring:

Engagement Angle: the rotation before touching the spring

Compression Angle: the rotation before fully compressing the spring (relative to the starting point). This is the limit of travel, and is considered a hard stop.

Engagement Torque: the amount of torque the spring exerts at the engage-ment angle. (This is the spring pre-load. If none exists, enter 0).

Compression Torque: the amount of torque the spring exerts at the compres-sion angle.


Motion

change. Note, however that the signs of applied torque and angular displacement values are defined by this rotational direction.

Because torsion springs are considered a resistive force, a spring force with a posi-tive value will act in the direction opposite to the object’s reference rotational direc-tion (it is impeding the forward progress of the object, therefore it is a resistance). Likewise, a negative spring torque acts in the object’s reference rotational direc-tion. (The spring is aiding the forward progress of the object, and is hence acting not as a resistance but as a driver, so its sign is negative).

A positive spring angle is in the reference direction; a negative angle value is oppo-site to the reference direction.

The following diagrams describe setting up several scenarios involving torsional springs.

Note that all specified displacements will act relative to the initial position specified with the Initial Position slider on the Motion task dialog.

If the object is not touching the spring at time = 0, then the configuration may appear as:

If the object is touching the spring at time=0, then the engagement angle is 0:

Engagement CompressionAngleReference

RotationalDirection Direction of

Spring Torque

Spring Torque and Angles are positive values.

Angle

Direction ofSpring Torque

ReferenceRotationalDirection

Spring Torque and Angles are positive values.

CompressionAngle

EngagementAngle = 0


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If at time = 0 the spring is fully compressed by the object, then the compression angle is zero, and the engagement angle is the angle to where the spring is no longer compressed:

If the flow is such that the object rotates in an angle opposite of its reference angle to contact the spring, then the engagement and compression angles should be applied as negative values:

Note that only one torsional spring is allowed on a moving part. Because of this, multiple torsional springs acting in different directions cannot be applied to the same part.

The relationship between the required parameters and the spring constant is given as:

As shown, Spring Torque and Angles are negative values.

Starting PointReferenceRotationalDirection


EngagementAngle Compression

Angle = 0

Spring Torque and Angles are negative values.

ReferenceRotationalDirection


EngagementAngle

CompressionAngle

Tcompression Tengagement–θcompression θengagement–------------------------------------------------------------ K=


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7.5 Combined Linear/Angular Motion

7.5.1 Description

In Combined Linear/Angular motion, the object translates linearly along the path specified on the Motion task dialog. The instantaneous linear position of the object is determined either by user-specification or as a result of flow-induced forces.

As the object translates, it will also rotate about a user-specified axis. The direction of rotation is either determined by the user or is a result of flow-induced forces. For flow-induced rotation, developed torque is used to compute angular accelerations.

If both motions are flow induced, it is assumed that the two motions are uncoupled and work independently. The linear translation equations update the center of rota-tion over time and the rotation equations update the directional cosines over time, thus yielding a combined motion.

The location of the axis of rotation is determined by the translation of the object. Conversely, the direction of translation is not affected by the rotation. (This kind of motion is implemented using the Sliding Vane motion type, described later in this chapter.)

Examples of combined motion include an object sliding along a path and rotating about its center axis. The center of rotation is translating with the object:

Another example is an oscillating piston whose axis of rotation is its direction of travel. This is a typical configuration found in many flow meters.

Time A Time A+1

Direction of Translation

Rotation Direction

Direction of Translation


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7.5.2 Assigning Combined Motion

7.5.2.1 Linear Motion Parameters

Direction Vector

This sets the direction of travel of the object. The pull-down menu contains the three Cartesian directions: Global X, Global Y, and Global Z, Key-in Location, as well as a “Pick” option. If Pick is chosen, a dialog will prompt for the graphical

1. Select the object or objects that are to move. (Objects that are assigned motion simultaneously will have the same motion.)2. Select Combined Linear/Angular as the type of motion from the Type pull-down menu. 3. Indicate if either motion (or both) are to be flow-driven by checking the appro-priate Flow-Driven box(es).4. Click the Create/Edit Motion button. This brings up either the Motion Editor for User Defined or for Flow Driven. The parameters of the motion are entered on this dialog. These parameters are described in the next sections.5. Specify the Linear Motion Parameters: Direction Vector, Initial Position, and Maxi-mum and Minimum bounds (for flow-driven only). 6. Click the Angular tab, and specify the Angular Motion Parameters: Axis of Rota-tion, Center of Rotation, Initial Position, and Minimum And Maximum bounds (for flow-driven only). 7. Click Apply.

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Step 4

Step 5 Step 6

Step 7

Step 6: Angular Tab


Motion

selection of a surface normal to the direction of motion. Only planar surfaces may be selected.



Flow-driven parameters such as driving forces and resistive forces reference this direction as well. Positive values of a driving force will act in the direction of the Direction Vector; negative values will act in the opposite direction. In contrast, pos-itive resistance forces will act in the opposite direction of the Direction Vector; neg-ative resistance forces will act in same direction as the Direction Vector.

Initial Position

This slider is used to modify the initial position of the object from the as-built loca-tion in the CAD model. This is very useful for fine-tuning the model if the position of the object in the CAD is different from the true starting position.


X

Y

Direction of Travel



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Linear Minimum and Maximum

Use the Minimum and Maximum pull-down menus to set the bounds of motion for flow-driven motion. (This is only required (and available) for flow-driven motion.) The choices available for each menu are: Unbounded, Entity, and Slider.

• Unbounded does not stop the object from moving along its path.• Entity brings up a dialog allowing graphical selection of a geometric surface. This surface sets a limit of travel, and the moving object cannot pass through or by it.• Slider brings up a dialog and a graphical plane normal to the direction of travel. Use the slider to position the graphical plane at the desired boundary. The dialog will have an adjustment for resolution, to allow fine tuning of the bounding location. An additional field allows the entry of an exact bounding location, if desired. All locations are given in absolute model coordinates.



7.5.2.2 Angular Motion Parameters

Axis of Rotation

The rotational direction about the axis of rotation is determined by the right hand rule. Click the Reverse button to reverse the direction of rotation.

The pull-down menu contains the three Cartesian directions: Global X, Global Y, Global Z, Key-in Location, and “Pick”.

If Pick is chosen, a dialog will prompt for the graphical selection of a surface normal to the axis of rotation. (Only planar surfaces may be selected.) The object will


Motion

rotate about the specified axis that passes through the Center of Rotation (dis-cussed in the next section).


Flow-driven parameters such as driving torque and resistive torque reference this direction as well. Positive values of a driving torque will act in the direction of the Axis of Rotation; negative values will act in the opposite direction. By contrast, pos-itive resistance forces will act in the opposite direction of the Direction Vector; neg-ative resistance forces will act in same direction as the Direction Vector.

Center of Rotation




Z

Global Z is the desiredaxis of rotation, and the direction is positive.The unit vector = 0 0 1.

X

Y

Z

Axis of rotation


Axis of rotation

Offset from Centroid: x = -a

a

x

y


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Initial Position

This slider is used to modify the initial position of the object from the as-built loca-tion in the CAD model. This is very useful for fine-tuning the model if the angular position of the object in the CAD model is different from the true starting position.

The positive direction of adjustment is the positive Direction of Rotation. Use the slider to rotate the object about the axis of rotation in both the positive and nega-tive directions.

Angular Minimum and Maximum

Use the Minimum and Maximum pull-down menus to set the bounds of rotation for flow-driven angular motion. (This is only required (and available) for flow-driven rotation.) The choices available for each menu are: Unbounded and Key-In Loca-tion.




7.5.3 Defining Combined Motion

The two elements of Combined motion, Linear and Angular, are defined indepen-dently as User-prescribed or Flow-driven. The Flow-Driven check boxes on the Motion task dialog govern how each element is defined on the Material Editor. The possible combinations of user-prescribed and flow-driven are listed:

• User-Linear/User-Angular• Flow-Linear/User-Angular• User-Linear/Flow-Angular• Flow-Linear/Flow-Angular


Motion

The following sections describe how to set up User-prescribed and Flow-driven motions. Only the Material Editors for completely user-defined and completely flow-driven are shown, but the variation methods described are applicable to the two user-defined/flow-driven combinations, as well.

7.5.3.1 Defining User-Prescribed Motions

In this section, methods to prescribe linear and angular motions are described. When an object moves according to a fully-prescribed motion, it does not react to the flow. The object will move and rotate only in the specified directions, across dis-tances that are explicitly specified, and at prescribed angular velocities.

If one of the two motion elements is to be user-prescribed, then only that one will be defined using the User-prescribed properties (as shown below). The other will be defined using the Flow-Driven properties (as shown in the next section).

The Material Editor for User-Prescribed-Linear/User-Prescribed-Angular is shown:

1. On the Motion task dialog, set the Type to Combined Linear/Angular. (If Flow-Driven is unchecked for both types of motion, then both types will be User-prescribed.)2. Click the Distance property button for Linear Properties.3. Select the Variation Method for Distance.4. Enter the appropriate values.5. Hit Apply.

Step 2Step 4

Step 3

Step 5

Step 1


Motion

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tion

6. Click the Angle property button for Angular Properties. (This defines the angle through which the object will sweep.)7. Select the Variation Method for Angle.8. Enter the appropriate values. 9. Hit Apply.10. Hit OK when all information is entered to close the dialog.

7.5.3.2 Variation Methods for User-Prescribed Motions

The following table lists the variation methods for User-Prescribed properties for Linear and Angular motion. More details and illustrations for both types of motions are contained in the preceding Linear and Angular sections, respectively.

Linear Motion

Distance Reciprocating

Please see section 7.3.3.1 for a detailed description.

Linear Motion

Distance Table


Angular

Motion

Angle Constant


Step 6

Step 7Step 8

Step 9

Step 10


Motion

7.5.3.3 Defining Flow-Driven Motions

In this section, methods to describe objects in linear and angular motion that respond to the surrounding fluid flow are described. The motion of such objects is influenced by the flow as well as user-specified driving and resistive forces and torque. The origins of such forces do not have to be included in the analysis model--they act on the object in a user-prescribed manner to either accelerate the object in its direction and angle travel or to slow it down.

In several places in this section, the Direction Vector and the Direction of Rota-tion of the object are referenced. These are the directions specified on the Motion task dialog. Because the true direction of flow-driven motion is not always known prior to the analysis, this direction is really the Reference Positive Direction. Direc-tions of driving and resistance forces are then relative to this direction.

Flow-driven objects may start off moving at a known velocity, and either speed up or slow down based on their interaction with the surrounding fluid (and applied forces).

The Material Editor for Flow-Driven-Linear/Flow-Driven-Angular is shown:

Angular

Motion

Angle Oscillating


Angular

Motion

Angle Table


Step 2

Step 3Step 1

Step 4

Step 5


Motion

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tion

1. On the Motion task dialog, set the Type to Combined Linear/Angular. (If Flow-Driven is checked for both types of motion, then both types will be flow-driven.)2. Define each of the Linear properties by first clicking on the desired property button: Initial Velocity, Driving Force, and Resistive Force. (It is not required to specify any or all of the properties.)3. For each property, select the Variation Method.4. Enter the appropriate values, as necessary5. Hit the Apply button.

6. Define each of the Angular properties by first clicking on the desired property button: Initial Angular Velocity, Driving Torque, and Resistive Torque. (It is not required to specify any or all of the properties.)7. For each property, select the Variation Method.8. Enter the appropriate values, as necessary.9. Hit the Apply button.10. Hit OK when all information is entered to close the dialog.

Step 6

Step 7Step 8

Step 9

Step 10


Motion

7.5.3.4 Variation Methods for Flow Driven Motions

Linear Motion

Initial Velocity

Constant


Linear Motion

Driving Force

Constant


Linear Motion

Driving Force

Table


Linear Motion

Resistive Force

Constant


Linear Motion

Resistive Force

Table


Linear Motion

Resistive Force

Spring


Angular

Motion

Initial Angular Velocity

Constant


Angular

Motion

Driving Torque

Constant


Angular

Motion

Driving Torque

Table


Angular

Motion

Resis-tive Torque

Constant


Angular

Motion

Resis-tive Torque

Table


Angular

Motion

Resis-tive Torque

Spring



Motion

Mo

tion

7.6 Combined Orbital/Rotational Motion

7.6.1 Description

Combined Orbital/Rotation motion is another double motion--the object rotates about its axis of rotation, and also orbits about an axis parallel to its axis of rota-tion. Rotational motion is described in the Angular Motion section of this chapter.

Orbital motion is the circular displacement of an object about an axis. The orienta-tion of an object in pure orbit (with no rotational component) does not change. This is shown below:

Time = a Time = a+1Time = a+2


Motion

The combined rotation and orbital motion is shown below (in this graphic the rota-tion and orbital speeds are the same).

The orbital speed is often slower than the primary rotational speed, however.

A typical application for Combined Orbital/Rotational motion is a pump shaft with an eccentric orbit (or whirl) component. The shaft rotates about its centerline, but also has an eccentric rotation about an additional axis. By specifying an orbit on an object, it is possible to understand the force imbalance imparted on bearings and other fixtures as a result of a shaft orbit.

Both motions can be either user-prescribed or flow-driven. If the orbit is flow-driven, then the forces acting on the moving object are summed and appropriate accelerations are computed. Velocities and displacements are limited to the circular orbital path using the following relationships.

Time = a Time = a+1Time = a+2

Orbital Direction

Rotation Direction

Center of Rotation

Center of Orbit


Motion

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tion

7.6.2 Assigning Orbital Motion

The parameters required for the Orbital and the Rotation definition are specified in the same manner as angular motion. Descriptions of these parameters are dis-cussed in Sections 7.4.2.1 through 7.4.2.4 of the Angular Motion section of this chapter.

1. Select the object or objects that are to move. (Objects that are assigned motion simultaneously will have the same motion.)2. Select Combined Orbital/Rota-tional as the type of motion from the Type pull-down menu. 3. Indicate if either the rotation or the orbit (or both) are to be flow-driven by checking the appropriate Flow-Driven box(es).4. Click the Create/Edit Motion button. This brings up either the Motion Editor for User Defined or for Flow Driven. The parameters of the motion are entered on this dialog, and are described in the next sections.5. Specify the Orbital Parameters: Orbit Axis, Center of Orbit, Initial Position, and Maximum/Minimum Bounds (for Flow-Driven).6. Click the Rotational tab, and specify the Rotational Parameters: Rotation Axis, Center of Rotation, and Initial Position, and Maximum/Minimum Bounds7. Click Apply.

Step 1

Step 2Step 3

Step 4

Step 5Step 6

Step 7

Step 6: Rotational Tab


Motion

7.6.3 Defining Combined Orbital/Rotational Motion

The two elements of Orbital motion, the rotation and the orbit, are defined indepen-dently as User-Prescribed or Flow-Driven. The Flow-Driven check boxes on the Motion task dialog govern how each element is defined on the Material Editor. The possible combinations of user-prescribed and flow-driven are listed:

• User-Prescribed Rotation/User-Prescribed Orbit• Flow-Driven Rotation/User-Prescribed Orbit• User-Prescribed Rotation/Flow-Driven Orbit• Flow-Driven Rotation/Flow-Driven Orbit

The following sections describe how to set up User-Prescribed and Flow-Driven Orbital motion. Only the Material Editors for completely user-defined and com-pletely flow-driven are shown, but the variation methods described are applicable to the two user-prescribed/flow-driven combinations, as well.

7.6.3.1 Defining User-Prescribed Orbital and Angular Rotation

In this section, methods to prescribe both angular motions (the orbit and the rota-tion) are described. When an object moves according to a fully-prescribed motion, it does not react to the flow. The object will orbit and rotate only about the specified axes, and at prescribed angular velocities.

If one of the two motion elements is to be user-prescribed, then only that one will be defined using the User-Prescribed properties (as shown below). The other will be defined using the Flow-Driven properties (as shown in the next section).


Motion

Mo

tion

The Material Editor for User-Prescribed Orbit/User-Prescribed Angular is shown:

1. On the Motion task dialog, set the Type to Combined Orbital/Rotational. (If Flow-Driven is unchecked for both types of motion, then both types will be User-prescribed.)2. Click the Angle property button for Orbital Properties.3. Select the Variation Method for Orbit.4. Enter the appropriate values.5. Hit Apply.6. Repeat for the Angular Rotation property.7. Hit OK when finished to close the dialog.

7.6.3.2 Variation Methods for User-Prescribed Orbital Motion

Since both elements in an orbital motion are angular rotations, both use the same angular property variations described earlier in this chapter. The following table

Step 2

Step 3

Step 4

Step 5

Step 6

Step 7

Step 1


Motion

lists these variation methods for User-Prescribed Orbital motion, and lists where to find more details and illustrations about each.

7.6.3.3 Defining Flow-Driven Orbital and Angular Rotation

In this section, methods to describe orbital and angular motions that respond to the surrounding fluid flow are described. The motion of such objects is influenced by the flow as well as user-specified driving and resistive forces and torque. The ori-gins of such forces do not have to be included in the analysis model--they act on the object in a user-prescribed manner to either accelerate the object or to slow it down.

In several places in this section, the Direction of Rotation of the object are refer-enced. These are the directions specified on the Motion task dialog. Because the true rotational direction of flow-driven motion is not always known prior to the analysis, this direction is really the Reference Positive Direction. Directions of driv-ing and resistance forces are then relative to this direction.

Angle Constant


Angle Oscillating


Angle Table



Motion

Mo

tion

The Material Editor for Flow-Driven Orbit/Flow-Driven Angular Motion is shown:

1. On the Motion task dialog, set the Type to Orbital. (If Flow-Driven is checked for Orbital and Angular, then both types will be flow-driven.)2. Define each of the Orbital properties by first clicking on the desired property button: Initial Angular Velocity, Driving Force, and Resistive Force. (It is not required to specify any or all of the properties.)3. For each property, select the Variation Method.4. Enter the appropriate values, as necessary.5. Hit the Apply button.6. Repeat for the Rotation properties.7. Hit OK when all information is entered to close the dialog.

Note that forces (instead of torques) are used to describe the Orbital motion. This is done because the orbit is really a displacement motion, so force, displacements, and velocities are more applicable than torque and angular displacements, and angular velocities. The relationship between torque and force for the orbit is expressed in terms of the eccentricity radius (eps):

• Torque = force * eps• Omega = velocity / eps• Theta = displacement /eps

Step 2

Step 3

Step 4

Step 5

Step 6

Step 7

Step 1


Motion

7.6.3.4 Variation Methods for Flow-Driven Orbital Motion

The orbital motion element uses forces, and the angular rotation element uses torque. The following table lists these variation methods for Flow-Driven Orbital motion, and lists where to find more details and illustrations about each:

Note: Springs are not available for either motion element in combined orbital/rota-tional motion.

Initial Angular Velocity

Constant


Driving Force

(Orbital)

Constant


Driving Force

(Orbital)

Table


Resistive Force

(Orbital)

Constant


Resistive Force

(Orbital)

Table


Driving Torque Constant


Driving Torque Table


Resistive Torque Constant


Resistive Torque Table



Motion

Mo

tion

7.7 Nutating Motion

7.7.1 Description

Nutation is a type of motion used in several types of liquid flow meters. A nutating object is inclined at an angle to a reference axis. As the normal vector of the object rotates about the reference axis, the angle between the normal vector and the ref-erence axis remains constant. The result is that the object actually wobbles about the reference axis, but does not change angular position relative to it. A coin wob-bling along its edge as it slows from a spin is a good example of nutating motion.

The image above describes nutating motion. The three quantities that are defined through the User Interface are the Tilt Axis, the Axis of Nutation (Nutating Axis), and the Center of Nutation. The Tilt axis is normal to the disk, and rotates about the Nutating axis through the Nutating Angle. The Nutating Axis is typically a global Cartesian axis, but is not required to be one. The Center of Nutation is typically the center of the disk. This point is often constructed at the origin or some other easily defined point. The other quantities shown in the graphic above are determined automatically, and do not require explicit definition.

Center of Nutation


Motion

The series of images below show a nutating disk. The disk wobbles about its axis, but it does not actually rotate. The angular position of the slot in the disk does not change throughout the nutation.


Motion

Mo

tion

7.7.2 Assigning Nutating Motion

7.7.2.1 Tilt Axis

The tilt axis is the axis normal to the disk. As the disk nutates, this is the axis that is pinned at the Center of Nutation and rotates about the Axis of Nutation. There are several choices for selecting the Tilt Axis: Global X, Global Y, Global Z, Key-In, and Pick. If Pick is chosen a dialog will appear prompting for selection of a sur-face normal to the intended axis.

1. Select the object or objects that are to nutate. 2. Select Nutating as the type of motion from the Type pull-down menu. 3. Indicate if the motion is to be flow-driven by checking the Flow-Driven box.4. Click the Create/Edit Motion button. This brings up either the Motion Editor for User Prescribed or for Flow-Driven. The parameters of the motion are entered on this dialog. These parameters are described in the next sections.5. Specify the Nutating Motion Parame-ters: Tilt Axis, Axis of Nutation, Center of Nutation, Initial Position, and Minimum And Maximum bounds (for flow-driven only). These parameters are not available until a Motion is created in the Motion Edi-tor. The parameters are described below.6. Click Apply.

Step 1

Step 2Step 3

Step 4

Step 5

Step 6


Motion

The Tilt Axis on an actual nutating device is shown:

The absolute orientation of the tilt axis will change as the object nutates, but the orientation relative to the object will remain constant. The direction of this axis determines the direction of Nutation according the right hand rule convention.

7.7.2.2 Axis of Nutation

The Axis of Nutation is the axis that remains constant throughout the nutation pro-cess. This axis is selected using any of the following options: Global X, Global Y, Global Z, Key-In, and Pick. Because this axis does not move, it is often conve-nient to construct the model such that a Cartesian axis is the Axis of Nutation. This allows easy specification of the axis. The Axis of Nutation is shown:

In this case, the Axis of Nutation is the Global Y axis.

select this surfaceas the surfacenormal to the Tilt Axis.

The resultant TiltAxis at the currentposition of the disk

Using the Pick Option,

z

yx


Motion

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7.7.2.3 Center of Nutation

The Center of Nutation is the center point of the nutating object. There are two ways to specify this: by Keying In the coordinates or as the centroid of a selected surface. The center point is the center of motion, and is typically the center of the object. Because of this, it is often convenient to construct the CAD model such that the center of the nutating object is at a known coordinate. In the example shown below, the Center of Nutation is actually the origin (0,0,0), which made defining it very easy:


This slider is used to modify the initial angular position of the object from the as-built location in the CAD model. This is very useful for fine-tuning the model in case the initial position of the object in the model is not quite correct.

The positive direction of adjustment is in the direction defined by the Axis of Nutat-ing. Use the slider to rotate the object about the axis of nutation in both the posi-tive and negative directions.


Use the Minimum and Maximum pull-down menus to set the bounds of rotation for flow-driven nutating motion. (This is only required (and available) for flow-driven nutating.) The choices available for each menu are: Unbounded and Key-In Loca-tion.

The Center of Nutationin this model is atthe origin.


Motion




7.7.3 Defining User-Prescribed Nutation

In this section, methods to define nutating motion are described. When an object moves according to a fully-prescribed nutating motion, it does not react to the flow. The object will nutate in the specified direction at the prescribed nutation velocity.

1. On the Motion task dialog, set the Type to Nutating, and be sure Flow-Driven is unchecked.2. The only property is the Nutating Angle through which the object will sweep.3. Select the Variation Method (described below).4. Enter the appropriate values.5. Hit the Apply button.6. Hit OK when all information is entered to close the dialog.

Step 2

Step 1 Step 3

Step 4

Step 5

Step 6


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7.7.3.1 Nutation Angle Variation Methods

7.7.4 Defining Flow-Driven Nutation

In this section, methods to define nutation that responds to the surrounding fluid flow are described. The motion of such objects is influenced by the flow as well as user-specified driving and resistive torques. The origins of such torques do not have to be included in the analysis model--they act on the object in a user-prescribed manner to either accelerate the object or to slow it down.

Constant Nutating Angular SpeedEnter the angular speed at which the object will nutate. The units pull-down menu allows selection of either radians per second or RPM.

TableThe table allows for specification of a Nutation Angle position at specific times.

The angle is relative to the Initial Position prescribed on the Motion task dialog.

Enter Nutation Angle and Time data into the table.

The Cyclical box defines the motion by repeating only forward sweeps through the angle table.

The Reciprocating box defines the motion by alternating forward and reverse sweeps through the angle table.


Motion

In several places in this section, the direction of nutation of the object is refer-enced. This is the nutation direction determined by the direction of the Tilt Axis or the Axis of Nutation (as defined on the Motion task dialog.) Because the true nuta-tion direction of flow-driven motion is not always known prior to the analysis, this direction is really the reference positive direction. Directions of driving and resis-tance forces are then relative to this direction.

Flow-driven objects may start off with an initial nutation velocity, and either speed up or slow down based on their interaction with the surrounding fluid (and applied forces).

1. On the Motion task dialog, set the Type to Nutating, and be sure Flow-Driven is checked.2. Three properties are available for specification, but entries are not required: Initial Nutation Velocity, Driving Torque, and Resistive Torque.3. For each property, select the Variation Method...4. ...and enter the appropriate values, as necessary. The Variation Methods are described below.5. Hit the Apply button.6. Hit OK when all information is entered to close the dialog.

Step 2

Step 1 Step 3

Step 4

Step 5

Step 6


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7.7.4.1 Initial Nutation Velocity Variation Method

7.7.4.2 Driving Torque Variation MethodsA driving torque is positive when applied in the reference direction of motion (as applied on the Motion task dialog). A negative driving force will act in the opposite direction.

Examples of driving torque include electromagnetic and other body torques as well as torque imposed by objects omitted from the analysis geometry. The torque will act in the same direction as the direction of motion (as specified on the Motion task dialog).

ConstantThe object will nutate at this velocity at the on-set of the calculation, and will react to the flow forces appropriately.

If the object starts from rest, leave this value specified as 0.

ConstantEnter a constant torque value to apply an unchanging torque to the object through-out the entire analysis.


Motion

7.7.4.3 Resistive Torque Variation MethodsApplied resistive torque affects the nutation of the object by acting against its spec-ified nutation direction, impeding its progress. A positive value of a resistive torque acts in the opposite direction of nutation; a negative value acts in the direction of nutation.

TableA driving torque that varies with time is specified using the table of torque vs. time.


ConstantEnter a constant torque value to apply an unchanging resistive torque to the object throughout the entire motion.


Motion

Mo

tion

7.8 Sliding Vane Motion

7.8.1 Description

Sliding Vane is a variation of Combined Linear/Angular motion. In the Combined Linear/Angular motion type, the path of linear translation is specified by the user, and is not changed by the rotational motion. Sliding Vane motion is the opposite: the location of the axis of rotation is specified by the user, does not change, and controls the direction of linear translation.

The most common application of this type of motion is found in sliding-vane posi-tive displacement pumps. Vanes or pistons rotate about the center-line of the

TableIf a resistive torque is to vary with time, enter the time history as a table of torque and time.



Motion

impeller, but translate radially. The direction of linear travel changes at every angu-lar position. The axis of rotation, however, remains constant. This is shown:

Sliding vane motion is specified only as a user-prescribed motion. Flow-driven slid-ing vane motion is not currently supported.

Direction oftranslation changesbased on angular position.


Motion

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7.8.2 Assigning Sliding Vane Motion

7.8.2.1 Linear Motion Parameters

Direction Vector

This sets the direction of travel of the object. The pull-down menu contains the three Cartesian directions: Global X, Global Y, and Global Z, Key-in Location, as well as a “Pick” option. If Pick is chosen, a dialog will prompt for the graphical

1. Select the object or objects that are to move. (Objects that are assigned motion simultaneously will have the same motion.)2. Select Sliding Vane as the type of motion from the Type pull-down menu. 3. Click the Create/Edit Motion button. This brings up the Motion Editor. The parameters of the motion are entered on this dialog, and are described in the next sections.4. Specify the Linear Motion Parameters: Direction Vector and Initial Position. 5. Click the Angular tab, and specify the Angular Motion Parameters: Axis or Rota-tion, Center of Rotation, and Initial Posi-tion. 6. Click Apply.

Step 1

Step 2

Step 3Step 4

Step 5

Step 6

Step 5: Angular Tab


Motion

selection of a surface normal to the direction of motion. Only planar surfaces may be selected.



Initial Position

This slider is used to modify the initial position of the object from the as-built loca-tion in the CAD model. This is very useful for fine-tuning the model if the position of the object in the CAD model is different from the true starting position.


7.8.2.2 Angular Motion Parameters

Axis of Rotation

The rotational direction about this axis is determined by the right hand rule. Click the Reverse button to reverse the direction of rotation.

The pull-down menu contains the three Cartesian directions: Global X, Global Y, Global Z, Key-In Location, and “Pick”.

X

YDirection of Travel



Motion

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tion

If Pick is chosen, a dialog will prompt for the graphical selection of a surface normal to the axis of rotation. (Only planar surfaces may be selected.) The object will rotate about the specified axis that passes through the Center of Rotation (dis-cussed in the next section).


Center of Rotation




Z

Global Z is the desiredaxis of rotation, and the direction is positive.The unit vector = 0 0 1.

X

Y

Z

Axis of rotation


Axis of rotationOffset from Centroid: x = -a

a

x

y


Motion

Initial Position

This slider is used to modify the initial position of the object from the as-built loca-tion in the CAD model. This is very useful for fine-tuning the model if the angular position of the object in the CAD model is different from the true starting position.

The positive direction of adjustment is the positive Direction of Rotation. Use the slider to rotate the object about the axis of rotation in both the positive and nega-tive directions.

7.8.3 Defining Sliding Vane Motion

In this section, methods to specify the linear and angular components of Sliding Vane motion are described. When an object moves according to a fully-prescribed motion, it does not react to the flow. The object will move and rotate only in the specified directions, across distances that are explicitly specified, and at prescribed angular velocities.

The Linear properties on the Sliding Vane Material Editor are shown:

1. On the Motion task dialog, set the Type to Sliding Vane.2. Click the Distance property button for Linear Properties.3. Select the Variation Method for Distance.

Step 2

Step 1 Step 3

Step 4

Step 5


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4. Enter the appropriate values.5. Hit Apply.

6. Click the Angle property button for Angular Properties. (This defines the angle through which the object will sweep.)7. Select the Variation Method for Angle.8. Enter the appropriate values. 9. Hit Apply.10. Hit OK when all information is entered to close the dialog.

Step 6

Step 7

Step 8

Step 9

Step 10


Motion

7.8.4 Variation Methods for Sliding Vane Motions

The following table lists the variation methods for the linear and angular compo-nents of Sliding Vane motion. More details and illustrations for both types of motions are contained in the preceding Linear and Angular sections, respectively.

7.9 Free Motion

7.9.1 Description

A general motion type, Free Motion, has been added to CFdesign v9. Unlike the other motion types (linear, angular, combined, etc.), Free Motion allows for motion in any direction. This is the most flexible of the motion types, and can be used to simulate the unconstrained (or partially constrained) movement of objects within an active flow field.

The motion is always flow driven, and is defined by enabling or disabling any of the six degrees of freedom. Limits can be defined for each degree of freedom, but colli-sions with walls, static and other moving solids are automatically detected.

Linear Motion

Distance Reciprocating


Linear Motion

Distance Table


Angu-lar

Motion

Angle Constant


Angu-lar

Motion

Angle Oscillating


Angu-lar

Motion

Angle Table



Motion

Mo

tion

Forces can be applied to objects in free motion as well as gravity. Freely-moving solids can be subjected to initial linear and/or angular velocities as well.

Care should be taken when defining the mesh for free motion analyses. For the constrained motion types, the path of the object is known, and the mesh can be refined within that path. This often reduces the mesh requirements on other areas of the model that do not directly influence the motion. In a free motion analysis, however, the path is often less certain, so a higher mesh density may be required throughout more of the model in order to adequately resolve the motion of the object. Please consult the User’s Guide for more information on the mesh require-ments for motion analyses.

Objects in free motion cannot pass through other solids, walls, symmetry or sur-faces with periodic conditions. They will, however, be allowed to pass through openings (such as fluid boundaries with specified velocities, flow rates, or pressure conditions).

As an object in free motion moves through a flow field, CFdesign tracks the forces and torque acting on it, and uses this information to update its position. When a collision occurs, the forces, torque, and location of impact are computed, and are used to determine the reaction. A coefficient of restitution of 0.5 is used to compute the momentum exchange between objects as they collide. Reactions include bounc-ing, glancing, and spinning:

More details about collisions are presented at the end of this section.

Bounce

Glance

Spin


Motion

7.9.2 Assigning Free Motion

7.9.2.1 Specifying Active Degrees of Freedom

By default, objects in free motion can move in any direction. Each of the six degrees of freedom is enabled by default, indicating that the object is free to move

1. Select the object or objects that are to move. (Objects that are assigned motion simultaneously will have the same motion.)2. Select Free Motion as the type of motion from the Type pull-down menu. 3. Click the Edit Motion Properties but-ton. This brings up the Motion Editor, which allows specification of initial linear and angular velocities of the object. This dialog is described in the next section.4. Specify the applicable Free Motion Parameters with the tabbed dialogs: Active degrees of freedom (DOF), Applied Force, and Gravity.5. Click Apply.

Step 1

Step 2

Step 3

Step 4

Step 5


Motion

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in that direction or rotate about that axis. Unchecking a degree of freedom prevents motion in that direction (or about that axis).

For two-dimensional models, the Z translation, X and Y rotations are inactive because motion in these directions is not possible for models oriented in the xy plane.

Translation

By default, objects in free motion are free to move in the X, Y, and Z directions. Unchecking a translation degree of freedom will prevent the object from moving in that direction.

Limits of travel are set for each degree of freedom by clicking the Set Bounds but-ton. This will bring up a dialog that allows for specification of the minimum and maximum limits of travel:

The choices for the minimum and maximum limits are Unbounded, Key-In, and Slider:

• Unbounded: the object can move without limit in the direction. This is the default for all degrees of freedom.• Key-In Location: A dialog will appear for the input of a distance the object can travel. For example, if 1.5 inches is entered as a minimum value, then the object cannot go beyond 1.5 inches in the negative direction of travel. This distance is relative to the initial position of the object.• Slider brings up a dialog and a graphical plane normal to the direction of travel. Use the slider to position the plane at the desired boundary. All locations are relative to the initial position.

The Min and Max boundaries can be specified using different methods.


Motion

Rotation

By default, objects in free motion are free to rotate about the three Cartesian axes. Unchecking a rotation degree of freedom will prevent rotation about that particular axis.

Limits of rotation can be set for each degree of freedom by clicking the Set Bound button. The choices for the minimum and maximum are Unbounded and Key-In value:

• Unbounded causes the object to rotate about the axis without a limit.• Key-In Location allows specification of an angular limit. Multiple revo-lutions can be defined by entering the total angular sweep (in degrees) that is permitted.


7.9.2.2 Applied Force

This set of controls provides a way to specify an optional force acting on the object. There are three basic parameters required to specify a force on an object in free motion: The force direction, the force magnitude, and the location of force applica-tion on the object.

1. Force Direction

The direction of force is specified by either selecting a Cartesian direction, keying-in a direction vector, or by selecting a surface that is normal to the force direction. Additionally, the force vector can be constant or vary with position of the object.

1. Select the direction or method of specification. Change the direction with the “+/-” button if necessary. If Key-In is selected, a dialog will prompt for a unit vec-

Step 1Step 2

Step 3


Motion

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tor. If Pick is selected, a dialog will prompt for selection of a surface on the object. This surface is normal to the applied force.2. The force direction is shown in the field below the direction menu. This is an editable field, so the unit vector can be modified directly in this field.3. The force direction can either be a Constant Vector with respect to the ground, or can Vary By Orientation relative to the ground (while remaining con-stant with respect to the object).

• If Constant Vector is selected, the direction of force will not change even as the object orientation changes. The force direction remains con-stant, even if the object rotates about an axis. This is shown:

• If Vary by Orientation is selected, the direction of force will vary rela-tive to the coordinate system, but will remain constant relative to the object. This is the recommended way to apply a constant torque to an object in motion. This is shown:

Initial Position. Force is appliedin the negative x direction.

Object rotates because of torque about

in the negative x direction. The resultantobject center. Force is still directed

torque will vary as the object changesorientation.

Initial Position. Force is appliedin the negative x direction.

Object rotates because of torque.

but varies relative to ground.Force is constant relative to the object,

The resultant torque remains constantas the object moves.


Motion

2. Force Magnitude

The magnitude of the applied force can either be constant or vary with time.

1. Select if the force is Constant in Time or if it is Varying In Time.2. If the force is constant, enter the value in the field. If the force is time varying, click the Define button. This will open a dialog allowing specification of a piece wise linear table between force and time.3. Select the units of force in the third menu.

3. Location

The final step is to specify the location of the applied force on the object. There are two methods: select the Centroid of a Surface or by Key-In Location:

Step 1Step 2

Step 3

Step 1

Step 3

Step 2


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tion

When Centroid of Surface is selected, a dialog will prompt to pick a surface on the moving part:

Select a planar surface on the part. The point of application will be the centroid of the selected surface. Offset the location of force from the centroid by entering the x, y, and z components of the distance in the Offset group of the dialog. Click OK to close the dialog.

When Key-In Location is selected, a dialog will prompt to enter the coordinates of the point of force application:

This point must be on or in the moving object. A specified point of application that does not contact the object in its initial location will cause the force to not act on the object throughout the analysis.

7.9.2.3 Gravity

The Gravity tab allows for specification of a gravitational acceleration to act on the object. On the Gravity tab, check the Earth box to indicate that the object is sub-jected to the Earth’s gravitational pull. Enter a unit vector to indicate the direction of the gravitational force:


Motion

To define a gravitational pull that is different from that of Earth, uncheck the Earth box, and enter the gravitational acceleration in the appropriate direction. The units of this value will be in terms of the analysis length unit.

7.9.3 Defining Free Motion

Most of the parameters governing free motion are defined directly on the Motion Task dialog. The exception are the initial linear and angular velocity components. These values are assigned on the Motion Editor, which is accessible by clicking the Edit Motion Properties button:

By default objects in free motion start from rest. To define a free motion state that has an initial velocity or rotation:

1. Select the velocity or angular velocity component from the Properties list.2. The variation method for all initial velocity values is “Constant.”3. Enter the appropriate value and select the units.4. Click the Apply button.5. Click the OK button to close the dialog.

7.9.4 Collision Detection

As mentioned, objects in Free Motion will react with walls and solids when they col-lide, thereby preventing penetration with other objects.

Step 1

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• Collision detection is enabled only for collisions involving at least one object in free motion.• If a free motion object strikes another object in free motion, both objects will adjust their paths to avoid penetration. The impulse exchanged during the collision as well as a contact path are calculated. The contact force (which is the impulse divided by the time step) is applied to both objects at their respective contact points.• If a free motion object strikes an object in user-specified motion, the free motion object will adjust to avoid penetrating the other object. The forces from the collision are applied to both objects, respectively, but will not affect the motion of the object in user-specified motion. (The collision force is included in the motion output data for both parts, however.)• If a free motion object strikes an object in fluid-driven motion, the free motion object will adjust to avoid penetrating the other object. Forces from the collision are applied to both objects, and will move the fluid-driven part in its constrained path of motion.• The mesh must follow the guidelines described in the User’s Manual for the motion path. If the mesh is too coarse, the moving object may pass through an obstruction instead of colliding with it.• Collision detection is sensitive to the time step size. If the time step is too large, moving objects may pass through an obstruction instead of col-liding. A good guideline is the time step size indicated by the Estimate func-tion on the Analyze dialog.

If an object in free motion strikes a wall or static solid, a collision will also occur, and the object will bounce or deflect appropriately.


Motion


CHAPTER 8 Analysis Options

8.1 Introduction

The Options dialog is used to set basic conditions and parameters of the analysis.

8.2 Flow

If flow is turned On, the pressure and momentum equations for the fluid motion will be solved. Turn flow Off for conduction-only heat transfer analyses.

The default settings define an incompress-ible, turbulent flow analysis, with no heat transfer. The parameters are all engineer-ing in nature, and are discussed in this chapter:

• Flow• Compressibility• Heat Transfer• Radition• Gravity• Turbulence• Solar Heating• Scalars


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Note: For forced convection analyses, the flow and heat transfer calculations can be run separately (although it is not required). After the flow analysis finishes, turn flow to Off, and turn Heat Transfer On (discussed below). For natural convection analyses, flow and heat transfer must be run concurrently.

8.3 Compressibility

8.3.1 Incompressible

Characterizes any flow for which the maximum Mach number is less than 0.3. For more information about incompressible flows, please refer to the Incompressible Flows section of the Analysis Guidelines chapter of this manual.

8.3.2 Subsonic Compressible

Subsonic compressible flows are flows that are compressible but contain no shocks.

In particular, the fluid velocity must be low enough so that heat generation due to viscous shearing work on the fluid is negligible. Typically, a Mach number of 0.7-0.8 is the maximum for which this is true.

If there is heat transfer, the static Temperature equation is solved. This equation neglects viscous dissipation and pressure work effects. If there is no heat transfer, the total temperature is held constant and the static temperature is determined from:

Be sure to enter a value for Total Temperature for subsonic compressible flows without heat transfer. This constant value of total temperature will be used in the equation shown above.

Additionally, be sure to define a material in which density varies with Equation of State (see the Materials chapter, Chapter 6, for more information).

T0 TstaticV2

2cP---------+=


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8.3.3 Compressible

Compressible flows are flows that have a Mach number greater than 0.8 with or without heat transfer and shocks.

If there is heat transfer, the total Temperature equation is solved. This equation includes terms for viscous dissipation and pressure work. The static temperature is determined from the equation shown above.

For compressible flows without heat transfer, enter a value for Total Temperature.

Additionally, the density of the fluid must vary with Equation of State (see the Materials chapter for more information).

If water is chosen as the material and compressible is selected, then the water hammer problem will be solved.

For more detailed information about running compressible analyses, please refer to the Analysis Guidelines Chapter of this manual.

8.4 Heat Transfer

The default setting of Off considers the calculation to be adiabatic, and will not solve for any heat transfer effects.

When Heat Transfer is turned On, conduction, forced convection, mixed convection, and natural convection are computed as appropriate. To include internal radiation, check the Radiation box on the Radiation group. If Joule heating boundary condi-tions (current and/or voltage) are applied, heat transfer must be enabled to solve for Joule heating.

For more information about heat transfer, please see the Heat Transfer section of the Analysis Guidelines chapter of this manual.

8.4.1 Forced Convection Automation

In forced convection analyses, flow and heat transfer can be run separately because the flow does not depend on the temperature distribution. This is an effi-


Options

cient approach because it saves time by not having to run flow and heat transfer together throughout the entire analysis.

Staged Forced Convection controls this the automation of forced convection analyses.

The following occurs after GO on the Analyze dialog is pressed:

1. The analysis will run as Flow-only (heat transfer is disabled) until either the analysis converges (as determined by the Automatic Convergence Assessment) OR the prescribed number of iterations is complete.2. Flow will then be disabled and heat transfer enabled, and the analysis will run an additional ten iterations (heat transfer only) or until the solution reaches conver-gence.

To change the number of thermal-only iterations, add this entry to your CFdesign flags file:

FORCED_EXTRA #

where # is the number of thermal-only iterations the Solver should run. Note that this entry is case sensitive.

To automatically run a forced convection analysis in separate flow and heat transfer stages:

1. Enable Flow and Heat Transfer on the Options dialog.2. Check the Staged Forced Convection box.3. Specify the number of iterations for the flow-only solution on the Analyze dia-log. 4. Click GO on the Analyze dialog.

Note that both Flow and Heat Transfer must be enabled on the Options dialog. The Staged Forced Convection check box will not be active if any properties vary with temperature or if thermostatically-controlled internal fans are used.


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If the Stop button is pressed during the flow-only portion, the analysis will end after the current iteration, and will not run the heat-transfer portion of the calculation.

8.4.2 Radiation

Turn Radiation On to include surface-to-surface radiation effects in a heat transfer analysis. Radiation is typically most relevant when the field temperatures are very high. The radiation model is a non-participating model, meaning that radiation occurs between the walls and the fluid medium (the air) is not directly affected by the radiation. When radiation is activated, the start-up processing of the analysis will generally take longer due to the view factor calculation.

Radiative heat transfer through transparent media is supported, as well as geomet-ric symmetry. The radiation model computes radiative heat transfer to moving sol-ids and moving surfaces, and is the basis of the solar heating model. The radiation model has very rigorous “book-keeping” to keep track of the radiative energy bal-ance, and reports the amount of heat transfer due to radiation and the radiative energy balance for each part in a model. The result is that reciprocity is enforced, to ensure that the radiative heat transfer between parts with large size differences is computed accurately.

The radiation model is designed for use with all of the supported geometry types: two and three dimensional Cartesian and axisymmetric about the X and Y axes.

Be sure to set the emissivity of the walls and solids (in the Materials dialog). Emis-sivity set as a fluid property is automatically applied to all contacting wall surfaces. Because the radiation model is non-participating, emissivity values set on fluid materials are not relevant to the fluids. Emissivity set on a solid material overrides any specified value on the contacting fluid.

For more information about radiation, please see the Radiation section of the Anal-ysis Guidelines chapter of this manual.

8.4.3 Gravitational Vector

Use the Gravity Vector for buoyancy driven flows (natural convection). (You should NOT specify a gravity vector for forced convection flows.) Because most natural convection analyses occur on Earth, all that is required to set up gravity is to make sure the Earth box is checked (it is by default) and to indicate the direction of grav-


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ity in your model with a unit vector. For example, if your model is constructed such that “down” is in the negative Y direction, then the unit vector for gravity should be:

X = 0; Y = -1; Z = 0

For buoyancy driven flows on other planets (or where the gravity is different from that on Earth), uncheck the Earth box, and enter the magnitude (in the analysis units) and the direction of the gravity vector.

Note: be sure to choose a buoyancy material or set the density to vary with equation of state on the Material Dialog

To include gravity as a force acting on a moving solid, do not specify gravity on the Options dialog. Alternatively, assign a driving or resistive force equal to the force imparted from gravity. The gravitational force may be added to some additional driving or resistive force, if necessary.

8.5 Optional

There are three additional sets of controls on the Options dialog: Turbulence, Solar Heating, and Scalars. These controls are accessed by clicking their respec-tive buttons on the Options Dialog.

8.5.1 Turbulence

The Turbulence dialog is used to toggle turbulence on and off, to select the turbu-lence model and to modify the default values for the turbulence model parameters.


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If Laminar is selected, then the flow will be solved as laminar. If Turbulent is selected (the default) then the analysis will be solved as turbulent. Most engineer-ing flows are turbulent, however. If there is some uncertainty about which setting to use, then first try laminar. If the flow should be solved as turbulent, the calcula-tion will typically diverge within the first ten to fifteen iterations.

Turb Model

Five turbulence models are available:

• k-epsilon, the default turbulence model, is typically more accurate than the constant eddy viscosity, but more computational intensive and slightly less robust. It is not as resource intensive as the RNG model, but still gives good results.• Low Re k-epsilon is well suited for low speed, but turbulent flows. The Reynolds number of such flow is typically between 1,500 and 5,000.

This turbulence model is well suited for pipe flows and external aerody-namic flow in the transition between laminar and turbulent as well as flow situations that have both high speed and low speed areas. Other flow situa-tions that perform well with the Low Reynolds turbulent model include:

1. A high-speed jet entering a large room. The jet is highly turbulent when it first enters the room, but the flow slows down considerably, and the Reynolds number drops. These types of flows can be very unstable when run with k-epsilon. 2. Buoyancy-driven (natural convection) flows that are barely turbulent.

Because this turbulent model does not use wall functions, Mesh Enhance-ment should be always be enabled when using Low Reynolds k-epsilon. We recommend increasing the number of mesh enhancement layers to 5 (using the Mesh Enhancement controls on the Meshing dialog).

Note that analyses run with this turbulence model may not be as stable as those run with the k-epsilon model. Because of this, the Intelligent Solution Control should be enabled (the switch is located in the Solution Control dia-log launched from the Analyze task dialog.) Likewise, analyses run with this model may take more iterations to reach a fully converged solution.

High Reynolds flows that are run with the Low Reynolds turbulence model will generally produce the same solution as would the k-epsilon model. Likewise, laminar flows that are run with this model will produce similar results to a solution run as laminar.


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• The RNG turbulence model is more computational intensive, but some-times slightly more accurate than the k-epsilon model, particularly for sep-arated flows. This model works best for predicting the reattachment point for separated flows, particularly for flow over a backward-facing step. When using the RNG model, it is often recommended to start with the k-epsilon model and after this model is fairly well converged, enable the RNG model. • The constant eddy viscosity model is slightly less rigorous than the other two models, but more numerically stable. This is a good choice for lower speed turbulent flows and some buoyancy flows. This is also useful if one of the other two models caused divergence.• The Mixing Length turbulence model is primarily designed for internal natural convection analyses. Use of the mixing length model, in some cases, has been shown to reduce run times and provide better accuracy than the default turbulence model for internal buoyancy-driven flows.

Auto Startup

Auto Startup controls the Automatic Turbulent Start-Up (ATSU) algorithm.

This algorithm goes through a number of steps to obtain turbulent flow solutions. The algorithm starts by running 10 iterations using a constant eddy viscosity model, so the k and epsilon equations are not solved. With this solution as an initial guess, the two-equation turbulence model is started. At iteration 10, a spike in the convergence monitoring data will appear for the k and epsilon equations. Other steps are then taken to gradually arrive at the converged result. These steps may involve spikes in the convergence monitoring data at iterations 10, 20 and 50. After 50 iterations, the ATSU is turned off automatically.

If Lock On is selected, the ATSU stays on during the entire analysis until the user manually clicks it off. If there are convergence difficulties after iteration 50 (diver-gence within 10 iterations), then you should enable Lock On. If the ATSU is turned on, you should run at least 200 iterations to ensure convergence of the turbulent flow solution.

If Extend is selected, an extended version of the ATSU is activated. This method is useful for difficult analyses, particularly compressible analyses. The minimum num-ber of iterations that should be run with this algorithm is 400.

Turb/Laminar Ratio


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The Turb/Laminar Ratio is the ratio of the effective (turbulent) viscosity to the laminar value. This is used to estimate the effective viscosity at the beginning of the turbulent flow analysis. In most turbulent flow analyses, the effective viscosity is 2-3 orders of magnitude larger than the laminar value. The default value is gen-erally suitable for most flows.

For some flows, it is helpful to increase the Turb/Lam Ratio to 1000 or even 10,000. Such flows typically involve a small, high speed jet shooting into a large plenum. Such flows are typically momentum-driven, and benefit from a larger turbulent vis-cosity at the beginning of the calculation.

Additionally, this affects the value of viscosity when the constant-eddy viscosity turbulence model is used.

Turbulence Intensity

The Turbulence Intensity Factor controls the amount of turbulent kinetic energy in the inlet stream. Its default value is 0.05 and should rarely exceed 0.5. The expression used to calculate

turbulent kinetic energy at the inlet, , is:

where I is the Intensity Factor and u, v and w are velocity components.

Advanced

The quantities in the Advanced dialog are described in detail in the CFdesign Tech-nical manual.

8.5.2 Solar Heating

Solar heating plays a significant role in the reliability and performance of many mechanical and electronic devices that are subjected to outside environmental con-ditions. In some situations, the worst-case solar loading during the hottest part of the day is of interest. In other situations, the intent is to understand the periodic temperature variation that occurs from diurnal heating (multiple cycles of day and night).

The Solar Heating functionality allows study of both scenarios. Solar heating can be run as a steady state analysis to learn the temperature distribution caused by solar

kin kin12---I2 u2 v2 w2+ +( )=


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loading at a particular instant in time. Alternatively it can be run as a transient analysis to study the time history of the temperature distribution over several days and nights.

The Solar model only works in conjunction with the new radiation model, and as such supports radiative heat transfer through transparent media. With solar heat-ing, the effect of shadowing on other objects is also supported. The Solar Heating dialog allows for specification of specific geographical locations as well as input of latitude and longitude. The date, time, compass direction, and object orientation relative to the sky are also specified. A full report of the radiative energy balance similar to the reports shown in the previous section is provided during and after the analysis.

Radiation must be enabled to run a solar heating analysis. Solar heating is not sup-ported unless both Heat Transfer and Radiation are enabled on the Options dialog.

To configure solar heating, click the Solar Heating button on the Options dialog. Note that this button is not active unless both Heat Transfer and Radiation are enabled. The Solar Heating dialog is shown:

1. Check the Enable Solar Heating box to include solar heating in an analysis. The dialog is grayed out unless this box is checked.


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2. Select the geographical location. There are two ways to do this. Method 1 is to select the country and city from the drop-down menus. Method 2 is to check the Manual box, and enter the Latitude and Longitude coordinates and offset from Greenwich Mean Time (in the GMT box). The GMT offset is used to accurately deter-mine the time zone.

When specifying the location manually

• The latitude must be between -90 and 90 degrees.• The longitude must be between -180 and 180 degrees.• The GMT must be between -12 and 12.

3. Set the Date and Time. Change each value by clicking on it, and use the up and down arrows to modify the value. (Direct entry in these fields is not supported.) Note that all times are considered to be Standard Time--Daylight Savings Time is not supported due to the wide variation of its use throughout the world.

4. Specify the orientation of the model. The Compass Direction defines which way the model is facing. The Celestial Orientation defines which way is up by selecting either the direction of the sky or the ground. For both directions, select the conve-nient direction or orientation, and select the direction from the adjacent menu. The direction can either be a Cartesian axis or specified by selecting a direction graphi-cally on the model.

5. Click the OK button to close the dialog.

Method 1Method 2

Click the value Change with the arrows

Define as aDirection and

OrientationCartesian axis

or graphically


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For more information about setting up and running solar heating analyses, please see the Solar Heating section of the Analysis Guidelines chapter of this manual.

8.5.3 Scalars

The Scalars dialog controls the calculation of the scalar quantity:

The default is No Scalar meaning that the scalar calculation is not part of the anal-ysis.

The transport of a general scalar variable will be modeled when General Scalar is selected. This scalar might be the salinity in a seawater fluid flow analysis, a mix-ture fraction in a multi-species analyses or some marker.

The Diffusion Coefficient controls the mass diffusivity of the scalar quantity into the surrounding fluid. A value of 0 will prevent any diffusion of the scalar quantity. This quantity is in Fick’s Law:

where jA is the mass flux of species A. This is how much of A is transferred (per time and per unit area normal to the transfer direction). It is proportional to the mixture mass density, and to the gradient of the species mass fraction, mA. The units of the Diffusivity coefficient are length squared per time.

Select Humidity to account for moist gas. Both the relative humidity and the con-densed water can be post-processed. Note that the condensation of a moist gas can

DAB

jA ρDAB∇mA–=


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be modeled by CFdesign, but the evaporation of water into a gas stream cannot. Heat transfer must be turned On. If the relative humidity is dependent upon the pressure, you should also enable Subsonic Compressible. Remember to enter the correct properties for the gas (only the gas, not the moist mixture) on the Materials Dialog. A summary of the steps for setting up a humidty (moist air) analysis are:

1. Assign humidity boundary conditions to all inlets.2. Assign a moist-air property to the flow region (or regions).3. Select Humidity from the Scalar sub-dialog on the Options task.

Please consult the Moist/Humid Flows section of the Analysis Guidelines chapter for more information about humidity analyses.

Select Steam Quality to enable the fluid to be a homogeneous mixture of water and steam. The scalar is the steam quality (0 if no steam, 1 if all steam). Properties are calculated using the steam tables. Heat transfer must be turned On. For this type of flow, the energy equation is written in terms of enthalpy. Enthalpy can also be post-processed.

Please consult the Steam/Water Flows section of the Analysis Guidelines chapter for more information about humidity analyses.


Options


CHAPTER 9 Analyze

9.1 Introduction

At this point, the model should be set up and ready to run. The Analyze dialog con-tains controls to run the analysis, and also launches the Convergence Monitor. The Convergence Monitor allows an easy way to monitor the performance of the calcu-lation. The Fast Track Option is also discussed.

After the analysis is finished, the Review dialog is the place to go for information about the calculation. The Review dialog provides access to the Status and Sum-mary files, and provides tools to organize saved results sets and time steps for ani-mation.

Prior to the analysis, use the Review task dialog to set up monitor points. During the analysis, convergence data will be plotted for monitor points, and allow the user to track the flow and thermal behavior at exact locations throughout the model.

9.2 The Analyze Dialog

This dialog contains the commands to start and stop the calculation. The analysis mode can be set to steady state (the default) or transient. The Results and Sum-mary Output Intervals are set on this dialog. The analysis computer is also set here. This is for the Fast Track Option--the ability to run the analysis on a computer different from the one used to build the analysis. The analysis can always be


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stopped by hitting the Stop button (which replaces the Go button during a calcula-tion.)

1. Select either Steady State or Transient. 2. If Transient, set the Transient Parameters (time step size, etc.)3. Set the Results and/or Sum-mary Save Intervals4. Select the Analysis Computer (the local computer is the default).5. If continuing an analysis, select the iteration or time step to Continue From.6. Enter the number of Itera-tions to Run.

7. Optional: select additional Result Quantities.

8. Hit GO to start the analysis.

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9.3 Analyze Mode: Steady State or Transient

The default selection, Steady State, causes the analysis to be independent of time. Switching to Transient causes the analysis to be time-dependent. It is possi-ble to switch between the two modes during an analysis. Transient boundary condi-tions are set up on the Loads dialog. Note that all Motion analyses (rotating machinery and moving solids) are run as transient.

9.4 Transient Parameters

Three parameters are necessary for transient analysis: Time Step Size, Stop Time, and Number of Inner Iterations.

9.4.1 Time Step Size

The Time Step Size is always in seconds. The correct choice of time step depends on the time scale of the analysis. For non-motion flow analyses, the time step size is a fraction of the mean flow velocity, and should be at least a tenth of the time needed to traverse the length of the device. In many cases a much smaller time step size will be required to adequately resolve the flow.

For non-motion heat transfer analyses, the time scale is usually much larger, so a larger time step size can be used. The time step should be no more than one tenth of the expected heat-up time. In cases involving diurnal solar heating, a much larger time step can be used because the time scale is typically a day or more. A time step for a typical diurnal heating analysis can be on the order of 100 seconds or more.

If Intelligent Solution Control is enabled, CFdesign automatically calculates a time step size based on convergence progression and the mesh. This time step size is usually quite small, and often a larger step size can be used effectively.

9.4.2 Estimate: Time Step for Rotating and Motion

For Rotating analyses, a time step size ranging from individual blade passages to complete revolutions can be used effectively. Smaller time step sizes are recom-


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mended for devices with large number of blades to resolve the interaction between blades and surrounding, non-rotating geometry.

To facilitate this, a time step calculator has been added to the Analyze task dialog that computes the time step size based on either a prescribed number of degrees per time step or the number of blades. Open the dialog by clicking the Estimate button on the Analyze dialog when a rotating region is present:

Specify either the Degrees per Time Step or the Number of Blades, and the time step will be computed based on the rotational speed specified as part of the Rotating Region. If the number of blades is specified, the time step size will be computed using a single time step per blade passage.

If the model contains multiple rotating objects, the fastest rotational speed is used as the basis for the time step size computed in this dialog.

More details about proper time step size are presented in the Guidelines chapter of this manual.

The time step size for moving solids analyses is computed based on the specified motion parameters and the mesh size. When the Analyze dialog is first opened after assigning Motion parameters, the time step size is computed automatically. If changes are made to the flow or motion velocities, click the Estimate button to recalculate the default time step.

This will not conflict with the time step size determined by Intelligent Solution Con-trol, but rather computes a reasonable starting time step size.


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9.4.3 Stop Time

For transient analyses, the user can specify whether the analysis should stop when a specific time has been reached, after a certain number of time steps, or which-ever comes first.

Enter a specific time (in seconds) in the Stop Time field to indicate when the solu-tion should stop. This is a very useful way to end certain transient analyses in which Intelligent Solution Control is enabled. An example is the simulation of flow-driven motion because it is not known how many time steps will be required to complete a certain amount of time. If it is not desired to stop the analysis at a certain time, enter “-1” in the Stop Time field, and be sure to specify the number of time steps to run.

Enter the number of steps to run in the Time Steps To Run field. After completing the indicated number of time steps, the solution will stop. This is a recommended way to run transient analyses whose time step size will not likely change. If the number of time steps to run is not important (only reaching the stop time is), then enter “-1” as the number of time steps to run, and be sure to specify a Stop Time.

If both a Stop Time and the number of Time Steps To Run are specified, then the first of the two that is met will cause the analysis to stop. For example: the user wants to run a transient for 3 seconds, but doesn’t want to exceed a total number of time steps of 1000. The user would set the Stop Time as 3, and the Number of Time Steps to 1000. If 1000 time steps are calculated, but only 2.5 seconds have


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passed, the solution will stop. Alternatively, the solution would stop if 3 seconds is reached in only 450 time steps.

9.4.4 Number of Inner Iterations

This controls the number of inner iterations for each time step during a transient analysis.

Because CFdesign uses an implicit method to discretize the transient terms in the governing equations, the calculation has to be iterated at each time step. This tran-sient inner iteration is similar to a global steady state iteration. The governing equations are solved at each inner iteration as they are at each global iteration in a steady state analysis. The difference is that far fewer inner iterations are needed in a transient time-step because the transient equations are much more numerically stable.

Typically, 10-20 inner iterations per time step are sufficient for a transient analysis. If the convergence monitor indicates that this is not enough (the convergence plot does not flatten), this number can be increased. If the convergence monitor shows that this is too many inner iterations (curves are flat for several iterations), you can decrease this number.

For Motion (Rotating and Moving Solid) analyses, we recommend only one inner iteration per time step. This has been found to work very well for a wide variety of Motion analyses.

9.5 Save Intervals

Sets how often the results and summary information are stored to the disk.

When the Results Output Interval is set to the default value of 0, results are saved only when the analysis stops (either completing the specified number of iterations or because the Stop button was pressed). For complicated analyses, it is recom-mended to set a non-zero Results Output Interval. (Be careful that your Results Output Interval is not so small as to exceed your hard-drive capacity.)

These saved results sets/time steps can be used for continuing the analysis from an earlier result set if there is a problem--in effect returning to an earlier saved state


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of the analysis without having to run it out again from the beginning. Results from saved result sets or time steps can also be animated.

The intermediate summary information is available in the summary file (analysis-name.sum). Summary information from intermediate iterations is appended to the summary history file (analysis-name.smh). This information is useful for tracking the progress of an analysis.

9.5.1 Steady State

For steady state analyses, simply select the interval of Steps to be saved.

9.5.2 Transient

For transient analyses, however, results can now be saved at either a specified interval of time steps or at a specified interval of seconds. The principal reason for this feature (besides greater flexibility) is that when Intelligent Solution Control varies the time step size (as described above) for transient analyses there is no way to ensure that results are saved at the desired times. This feature provides the ability to save transient results at exactly the desired times.

The Save Intervals group of the Analyze dialog was modified as shown:

When transient results are saved by specifying a time interval, the time step size will be adjusted automatically (assuming Intelligent Solution Control is on) such that a result will be calculated at the desired time. Intelligent Solution Control

Specify if resultsshould be savedat intervals of Stepsor at specific Times.


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includes the specified time save interval as part of its criteria in determining time step size.

For example: the user wishes to save results every 3 seconds. However, as Intelli-gent Solution Control varies the time step (to ensure stability) it finds that a time step size of 1.7 seconds is optimal. The first time step is then calculated at 1.7 sec-onds. Knowing that the user wants to save the results at 3 seconds, the next time step is adjusted from 1.7 (which would put the solution at 3.4 seconds) to 1.3 sec-onds. This forces a result to be calculate at 3 seconds so that the desired result is saved.

If Intelligent Solution Control is not enabled, the time step size is not changed automatically. Because of this, if the time save interval does not correspond to the user-specified time step size, only results solved at the specified time step are saved.

For example: the user specifies a time step size of 2 seconds, but disables Intelli-gent Solution Control. However, they also enter a time save interval of 1 second. As the solution progresses, results are only calculated every 2 seconds, so the result at 1 second is not saved. Likewise, the result at 3 seconds and 5 seconds, etc., are not saved either. Only results at 2, 4, 6, etc. seconds are saved.

The summary file can also be saved using an interval of results steps or of time.

9.5.3 Save Table (Steady State or Transient)

In addition to saving results and summary data at a constant interval as described above, a table capability has been added that allows saving iterations or time steps


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at varying intervals. Checking Table and clicking the Edit button brings up a table for input of step (or iteration) number and the save interval.

For example: tabular data for steps and save frequencies was entered as shown above. The result will be that from step 0, output is saved every 5 steps. At step 30, output is stored every 10 steps. Finally, from step 100, output is saved every 100 steps. If 300 steps were run, results from the following steps would be saved to the disk:

In the example above, the intervals led to the next interval definition quite natu-rally. If, however, the table looks like:

5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300

From step 0,save every 5




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If the analysis is run 300 steps, results will be saved at:

5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300

which is the same as the first example because changes in the save frequency occur only at steps in which data is saved.

The table can be used to specify a save frequency based on time as well. When a time on the table is reached, the save frequency will change. For example, in the table shown below:

every step is saved from time 0 until time=2 seconds. At 2 seconds, results are saved every 5 steps. Finally, at 10 seconds, results are saved every 20 steps.

9.6 Analyze!

9.6.1 Analysis Computer, Server Monitor, and Fast Track

CFdesign is built upon a client/server architecture. This enables an analysis to be built on one machine, the User Interface Computer, and run on another machine, the Analysis Computer.

For a single-seat installation, the default setting shown in the Analysis Computer drop menu is the name of the machine. This means that analyses will run locally without requiring any additional steps. During the analysis, CFdesign can be shut down and the analysis will continue to run. (Check the Task Manager.) When the


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CFdesign interface is started again and that analysis opened, either the current sta-tus of the analysis will show, or it will be completed and the final results will be available.

Note: Care should be taken to NOT shut down CFdesign until after the first iteration is completed.

Building upon these concepts, CFdesign features the Fast Track Option.

The Fast Track Option is a way to run analyses on remote computers (on your net-work). It is a way to temporarily ramp up analysis capability by using (often under-utilized) in-house computer resources. This is not an ASP model nor is it distributed computing. Alternatively, it is an innovative way to run multiple analyses on multi-ple computers. Temporary Solver licenses can be leased for a few weeks or a few months at a time. (Consult your Account Manager for details.) With these licenses, you can perform numerous analyses simultaneously, offering a great way to explore all those “what if” scenarios that are critical to a successful design effort.

The analyses are set up locally (on the Interface Computer), but assigned to run on the machine chosen in the Analysis Computer drop menu. Every machine on the network that is set up as an Analysis Computer will be listed here. The Server Monitor, accessible by hitting the Server Monitor tab, lists all available Analysis computers and their status:

Detailed set-up instructions are provided in Fast-Track.pdf, found in your CFdesign installation folder. To summarize the set up of an analysis computer: install the CFdesign software (select the Solver-only option) and configure the licensing. Ensure that the process called cfdserv9.exe is running (if not, click on the file called servman.exe to start it).

On the Interface computer, the host-name of each available Analysis Computer must be added to the server.cfg file found in the CFdesign installation folder. This


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will cause each Analysis Computer to be listed in the Server Monitor on the Inter-face Computer.

To run an analysis on an eligible Analysis Computer, select its name from the Anal-ysis Computer drop menu (on the Interface machine), and hit GO. The model data will transmit to the waiting Analysis Computer, and the analysis will proceed. As the analysis runs, results will be sent back to the interface machine (where the model was built), for viewing with the Results tools. During the analysis, the model can be closed and CFdesign shut down on the local (Interface) machine.

Care should be taken to NOT shut down CFdesign on the Interface machine until after the first iteration is completed.

Later, when the analysis is opened on the Interface machine, the current progress or the finished results will automatically be sent from the Analysis machine.

9.6.2 Continue From

The default entry in the Continue From drop menu is the last saved iteration or time step. When GO is hit, the analysis will continue from the value shown in this drop menu.

If a previous iteration or time step is chosen, then all subsequent saved iterations or time steps will be deleted from the analysis (after a prompt is displayed confirm-ing that this is OK).

Changes made to the mesh definitions, boundary conditions, or materials will be automatically incorporated into the analysis. If a mesh size is changed, but the Continue From menu is not reset to 0, a new mesh will be generated, the current results will be interpolated onto this new mesh, and the analysis iteration count will be reset to 0. Note: all intermediate saved results files (and time steps) will be deleted. The analysis will then proceed with the saved results mapped to the new mesh except for analyses containing the following features:

• Extruded elements• Surface parts (solid or distributed resistance)• Motion (moving solids)• Rotating region• Periodic boundary conditions


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Note: for existing analyses originally launched from Pro/Engineer but opened sub-sequently from the Desktop, the Mesh Size task-dialog will not be available. Fur-thermore, if the existing mesh sizes are deleted (through the Feature Tree), the Analyze dialog will be grayed out. This is because the analysis MUST be opened from Pro/Engineer to generate a new mesh.

9.6.3 Iterations (or Time Steps) to Run

This is the number of additional iterations or time steps to be run once GO is hit.

9.6.4 Starting and Stopping

Hitting the GO button starts the analysis. Once the analysis is started, it changes to the STOP button. Hitting the STOP button will stop the analysis at the end of the current iteration.

For a new analysis, the mesh will be generated prior to any iterations being solved. For analyses started from Pro/Engineer or CATIA, meshing occurs in the CAD inter-face--causing CFdesign to minimize while the CAD tool appears. All status mes-sages will appear in the List region of the CAD interface. After the mesh is generated, the CAD tool will minimize and CFdesign will come back up and the analysis will proceed. During the analysis, the CAD tool will remain in a minimized state, and can not be accessed. To shut down the CAD tool (to free up more mem-ory), shut down the CFdesign interface--the analysis will continue to run--and then shut down the CAD tool. CFdesign can then be started again, and the running anal-ysis opened. The analysis will continue to run even when the CFdesign interface is shut down.

For Acis and Parasolid based CAD systems, the CFdesign interface does not mini-mize during the meshing, and status messages are listed in the Information field of the Analyze dialog.

To just generate the mesh and not run any iterations (this is sometimes useful to inspect the mesh prior to running a large analysis) set the number of iterations to 0, and hit GO. The mesh will generate, but the analysis will not proceed. The mesh can be inspected using the Results dialog. (Note: it is not necessary to assign boundary conditions, materials, or set up any analysis options if the goal is just to generate the mesh. Obviously these tasks must be completed prior to running the analysis.)


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9.7 Information

In this window on the Analyze dialog, status messages are written out during the generation of the mesh and model pre-processing. Every pre-analysis calculation performed on the model is listed here. A small summary of the model is also pre-sented, and lists the number of inlets and outlets, number of nodes and elements, and the units systems. If an error occurred during processing, it will be stated here. Also be sure to check the Status window found in the Review dialog, Notes tab for error messages.

9.8 Analysis Queue (Batch Mode)

The Analysis Queue in CFdesign allows the user to run multiple analyses in series, in much the same way as a batch process can be made to automate a succession of events. Instead of relying on a DOS batch file, however, the analysis queue requires no special steps, and is managed through the user interface.

To add analyses to the queue, simply hit the Go button on the Analyze dialog. The first analysis will start to run immediately. Close the CFdesign interface (the analy-sis will continue to run). Open a subsequent analysis, and hit Analyze_Go to add it to the Queue. When Go is hit, the analysis will not run immediately. Instead, it will be added to the queue, and the word “Queued” will appear in the Status bar in the lower left corner of the Interface. Queued analyses will be run in the order that they were submitted.

It is highly recommended that you generate the mesh for each analysis prior to launching the first analysis for solving. To do this, simply run each analysis 0 itera-tions. This will generate the mesh and helps to locate any errors in the set up prior to running the analyses.

Analyses in the queue will be listed in the Server Monitor tab of the Analyze task dialog. When an analysis is completed, it will be removed from the list.

At any time while an analysis is running, it can be opened in the CFdesign interface and the current state of the solution will be loaded for display.

To remove an analysis from the queue, open it in the CFdesign interface. A mes-sage in the Status bar will indicate that the analysis is in the queue. To remove it,


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simply hit the Stop button on the Analyze dialog. That analysis will then be removed from the queue and will be removed from the list in the Server Monitor.

If an analysis diverges or stops because of errors, the next analysis in the queue will start.

When the analysis is completed, open it in the CFdesign interface. When you exit the interface, be sure to save the analysis when prompted.

9.9 Analysis Intelligence

Accessed with the Solution Control button on the Analyze dialog, a set of tools exists which allow control over the rate of solution progression. The purpose of these solution controls is to provide control over how quickly the solution field progresses, to ensure a robust, converged solution. In addition to the manual con-trols, CFdesign contains a great deal of Analysis Intelligence which automatically controls the rate of convergence as well as determines when the analysis is no longer changing (converged).

This automation is described first, and then the manual controls and the theory behind them are described subsequently.

9.9.1 Intelligent Solution Control

This capability greatly improves the robustness of the CFdesign solution. By employing elements of control theory to examine the trends of each degree of free-dom, CFdesign automatically adjusts the convergence controls and the time step size to attain a solution. If the solution is changing too quickly from one iteration to the next, this algorithm automatically slows down progress in an effort to maintain stability. Alternatively, if the solution is stable and progressing too slowly, the algo-rithm will allow the calculation to evolve quicker, resulting in reduced solution times.


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Intelligent Solution Control is enabled by default for several analysis types (as described below), but can be disabled on the Solution Controls dialog (launched from the Analyze task dialog):

The convergence control values that Intelligent Solution Control chooses can be plotted on the Convergence Monitor by selecting Relax Parm from the third pull-down menu:

The convergence control values are shown for all degrees of freedom over the range of iterations.

If an analysis simply will not converge even with Intelligent Solution Control enabled, then the mesh should be evaluated to determine if a finer mesh concen-tration is needed. Also, the applied conditions and materials need to be inspected to ensure that the physics are being simulated correctly. If modifications to the mesh


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and/or physics still do not produce a converged solution with Intelligent Solution Control, please contact your technical support representative.

The application of Intelligent Solution Control with different types of analyses is described:

9.9.1.1 Steady State Analyses

Intelligent Solution Control adjusts the time step size and the convergence control settings to achieve solution stability. The result is that even very physically demanding analyses that would have required manual adjustment of convergence controls will now run with virtually no manual intervention.

Steady state analyses are run internally as transient solutions when Intelligent Solution Control is enabled. Each time step consists of only one inner iteration, so solution times are not significantly longer (as is often the case in true time-varying transient analyses). Because of this, each time step is considered a single iteration. Saved results files follow this naming convention:

analysisname.res.s#.

where analysisname is the name of the CFdesign analysis, and # is the number of the time step (effectively the iteration number for steady state analyses). Note that the same convention is used when Intelligent Solution Control is disabled.

To run steady state analyses, ensure that Steady State is the selected Analysis Mode on the Analyze dialog (it is by default). Also, when specifying how often results are saved to the disk, the default save interval is expressed in terms of iter-ations (instead of seconds).

Intelligent Solution Control behaves slightly differently when solving for tempera-ture. Unlike the other solution variables in which the convergence controls and time step are adjusted, for temperature, only the time step is adjusted. Because of this, the value of the convergence control for temperature (as set in the dialog) will affect the rate of convergence of the energy equation. By varying the time step internally, Intelligent Solution Control enforces and maintains stability of the Energy Solver throughout the analysis. The default value for temperature conver-gence control has been increased to 1.0 in CFdesign 8.0 in an effort to reduce solu-tion times of heat transfer analyses.


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9.9.1.2 Transient without Motion

For transient analyses that do not include moving objects, Intelligent Solution Control adjusts only the time step size, and does not modify any convergence con-trol settings. This is done to prevent artificially affecting the time accuracy of the solution. (Reducing the convergence control slows down solution progression by the Solver, so it is always a good idea to use the default convergence control settings for non-Motion transient analyses.)

We have found that in some cases the time step size that Intelligent Solution Con-trol selects can be smaller than truly necessary for convergence, which may result in significantly longer solution times. For this reason, Intelligent Solution Control is disabled by default for transient analyses. It is recommended to manually assign a time step size based on the physics of the analysis model.

9.9.1.3 Transient with Motion

For solid motion analyses, Intelligent Solution Control is disabled by default (although it can be enabled if necessary). Because it will only reduce the time step size, if the motion is user-prescribed, enabling it will generally result in longer solu-tion times, with only a fairly small increase in stability.

For motion analyses that include flow-driven moving objects, we recommend that you enable Intelligent Solution Control. This will adjust the time step size to ensure that the object passes through only one element per time step. As the velocity of the object increases the time step will be automatically reduced to ensure stability. As the motion of the object slows, the time step size will be increased, but will not exceed the time step size manually set in the Time Step Size field on the Analyze dialog.

Intelligent Solution Control has been optimized for use with transient analyses involving moving objects, and, as such, is recommended for use with flow-driven Motion.

9.9.1.4 Transient with Rotating Regions

For rotating region analyses, Intelligent Solution Control is disabled by default (although it can be enabled if necessary). Because it will only reduce the time step size, if the rotational speed is known, enabling it will generally result in longer solu-tion times, with only a fairly small increase in stability.


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We recommend that you enable Intelligent Solution Control for rotating analyses that are either free-spinning or driven by a known torque. This will automatically determine and vary the time step size throughout the analysis. The time step size will be modified to ensure that no more than three degrees of rotation pass for each time step. This criteria has been found to be quite stable for rotating analyses.

9.9.2 Automatic Convergence Assessment

Automatic Convergence Assessment determines when a solution is converged--when the solution stops changing--and automatically halts the calculation. It exam-ines small and large frequency changes throughout the solution field, and evaluates the local and global fluctuations of each degree of freedom.

Automatic Convergence Assessment is automatically enabled for the same types of analyses as Intelligent Solution Control. Automatic Convergence Assessment is enabled or disabled by clicking the Advanced button on the Solution controls dialog, and checking or unchecking the Automatic Convergence Assessment box:

Automatic Convergence Assessment removes the guess-work of knowing when a solution is completed. Four different parameters are evaluated, and the threshold criteria levels can be changed with the slider bar. By default, the criteria are set to be moderate--between Loose and Tight. This will provide reasonable convergence for a wide variety of analysis types. “Reasonable” means that the convergence cri-teria are rigorous, but not exhaustively so. They will consider a 1% variation in the


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Summary trends to be converged. This is appropriate for most analyses with excep-tions listed below.

Change the slider setting to Loose for a “preliminary” analysis in which extremely high accuracy is not the goal. Such analyses are very useful for identifying trends in a design. Convergence will typically occur with fewer iterations, but the results may not be as accurate. Change the slider to Tight to invoke more rigorous convergence criteria. This is useful for a final analysis in which a high level of convergence and accuracy is necessary.

It has been observed that in some analyses in which aerodynamic- or hydrody-namic-induced forces are of interest, the solution may be considered converged and stopped by Automatic Convergence Assessment before the forces have actually stopped changing. The forces in such analyses (such as aerodynamic flows over thin bodies) often require many hundreds of iterations to reach fully converged force values, and may require additional iterations beyond where Automatic Con-vergence Assessment will stop the calculation. In such cases, it is recommended to disable Automatic Convergence Assessment and run additional iterations. Monitor the forces manually to ensure that they have stopped changing.

Additionally, flows that rely only on shear drag for their pressure drop, such as flow through a pipe, tend to require more iterations to converge. In such analyses, the default slider setting may halt the calculation prematurely. For this reason, it is rec-ommended to change the setting to Tight for pipe flow analyses that do not contain any form-drag.

Reliance on Automatic Convergence Assessment is not recommended for transient analyses that will not reach a steady-state solution such as Rotating, Motion, or vortex shedding analyses. By their nature, none of these types of analyses will ever typically reach a numerically converged state that satisfies Automatic Convergence Assessment. For this reason, it is recommended that the stopping criteria be evalu-ated manually based on the desired time span of the analysis or other physical objective.

For more information about these Convergence Criteria, please consult the CFde-sign Technical Reference.


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9.9.3 Intelligent Solver Selection

Because certain numerical solvers are better suited than others for various analysis types, CFdesign now uses an algorithm to automatically select the optimal solver for every analysis. Certain model attributes such as the aspect ratio of the flow pas-sages, the number of flow passages, and the overall length of the device all play a role in which solver is selected.

Using condition numbers and several parameters in the coefficient matrix, CFdesign selects the solver best suited for the given analysis type. The result of this is a sig-nificant reduction in calculation time, and greater calculation efficiency. There are no user-modifiable controls associated with this feature.

9.10 Manual Convergence Tools

The Solution Control dialog controls the solution progression rate so that the chance of divergence is minimized. Values are adjusted by moving the slider bar toward “Slower” or “Faster” between 0 and 0.5 (or in some cases, 1.0). Note that if you specify 0, the degree of freedom will not be allowed to progress with the solu-tion at all.

The default values are the best settings for most analyses. However, if Intelligent Solution Control is disabled, solution difficulties can often be resolved by manually reducing the progression rate for pressure to 0.1-0.3. This is generally the most effective way to minimize solution difficulties, particularly if they occur in the early iterations of a calculation. Reducing the rate on the velocity components, in con-junction with pressure, to 0.1-0.3 may be necessary in some cases.

The progression rate on variables and properties can be adjusted only for those quantities that are changing in the analysis. For example, the temperature rate can only be adjusted if Heat Transfer is turned On on the Options dialog. Likewise, the progression rate on the Density, Specific heat (Cp), and Conductivity properties can only be adjusted if these properties are variable, as set in the Material Editor.

The progression rate is applied to the solution in the following manner:

φ rφnew 1 r–( )φold+=


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where r is the control parameter, is the dependent variable, the new subscript refers to the latest solution and the subscript old refers to the previous solution. Values greater than 0.5 (default) are not used for most solution variables.

For compressible analyses, an additional method of control is also available: Pres-sure Control and Temperature Control. (Temperature Control is available for incompressible analyses as well.) A value between 1e-3 and 1e-6 can be selected for these parameters. They are necessary for compressible analyses because the numerical conditioning for such analyses can often be poor. For most compressible analyses, a value of 1e-3 is adequate for pressure (and temperature if Heat Transfer is enabled in the Options dialog). However, if convergence difficulties persist, it may be necessary to reduce the value.

The value set for Pressure and Temperature control is a sort of pseudo-transient relaxation that is implemented in the solution in the following manner:

This sort of solution control is most often referred to as “inertial relaxation.”

9.11 Advection Schemes

The advection scheme can be changed by clicking the Advection button, and select-ing the scheme of choice. A brief description of the recommended applications of the four advection schemes is given:

ADV 1: This is the default scheme for nearly all analyses (except rotating regions). It is the “work horse,” and is recommended as a starting point for all analysis types except for those listed below.

ADV 2: This is the default scheme for rotating regions (not moving solids, however) analyses. It is better for pressure-driven flows (no specified velocity or flow rate). Also, it works well for many compressible analyses.

ADV 3: Although not automatically set as a default for any type of analysis, this scheme has been found to work well for external aerodynamic analyses. In con-

φ

Ai i,

ρi N Ωd∫∆tinertia------------------------+

⎝ ⎠⎜ ⎟⎜ ⎟⎛ ⎞

φi Ai j, φjj i≠∑+ Fi

ρi N Ωd∫∆tinertia------------------------φi

old+=


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junction with a fine mesh around the body, this scheme does a good job producing drag and lift values. It can be less stable than the other schemes, although with Intelligent Solution Control invoked this will not likely be problematic. Note that Mesh Enhancement must be enabled when using ADV 3. Without it, the accuracy advantages will be negated.

ADV 4: This scheme is similar to ADV 2, but is not recommended for rotating anal-yses. ADV 4 is optimized for the analysis of flow through long, skinny pipes. It also performs well when calculating heat transfer in devices with multiple skinny gaps.

9.12 Result Output Quantities

This dialog lists the results quantities that are available for viewing after the analy-sis is completed.

The default quantities are the most widely used, but additional quantities are avail-able if needed.


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After running the analysis, to output additional quantities, select them from this list, set the number of iterations to 0, and hit GO. These additional quantities will be available for viewing on the Results dialog.

By default, the film coefficient result quantity is calculated based on heat transfer results (thermal residual). However, sometimes it is advantageous to obtain film coefficient data based on the flow solution. This is accomplished by using an empir-ical correlation. The dialog is accessed by clicking the Options button on the Optional Post-Processor Output dialog. The dialog is shown:

This dialog allows the film coefficient to be calculated in two ways.

The first uses the energy equation solution in the fluid and calculates the residual heat going to the walls.

The second uses an empirical formulation of the form:

Nu is the Nusselt number, Re is the local Reynolds number, and Pr is the Prandtl number. The flow solution is used to calculate the Reynolds and Prandtl numbers. Use either the default values for a, b, and c, or select new values. Note that the definition of Reynolds number and Nusselt number requires a length constant. If you are unsure what to use for these length scales, use the default of 1.

Note: Vorticity is the measure of the spin (angular speed) of a fluid particle. The mathematical definition of vorticity is the curl of the velocity vector. Another way to look at it is that vorticity is twice the angular rotation (omega). Since omega is a measure of the net angular rotation, vorticity is a measure of the local spin of the fluid particle. (If omega, the angular velocity, = 0, then the flow is irrotational and the vorticity is zero.)

Nu cReaPrb=


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9.13 Convergence Monitor

While the analysis is running the Convergence Monitor is displayed below the Graphics window. A detailed description of the Monitor is given in the Review chap-ter of this manual.


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CHAPTER 10 Review

10.1 Introduction

The Review dialog contains tools to help assess convergence throughout the entire calculation domain as well as at individual monitor points. Additionally it provides access to several files that contain summary, status, and results information. Use the Review dialog to animate multiply saved results sets or time steps as well as produce Reports that summarize the analysis setup and results.

The Report Generator is a direct extension of the Design Communication Center, and provides a very easy to use way to create and customize reports for sharing CFdesign results.

Operation of the Review Dialog is not as sequential as some of the other functions. Alternatively, there are several useful tools available to help assess and understand analysis results.


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10.2 Convergence Monitor

After the analysis is finished, the Convergence Monitor is displayed by clicking the View Conv. Monitor button on the Review task dialog:

The primary criteria for determining convergence is that the change of each degree of freedom is minimized over a large range of iterations. The curves shown in the Convergence Monitor are plots of the average value of each degree of freedom throughout the entire calculation domain. More details about convergence assess-ment and the Automatic Convergence assessment function are included in the Ana-lyze chapter of this manual.

10.2.1 Degrees of Freedom

A very helpful way to look at this data is to examine each degree of freedom individually. Select a degree of freedom from the Quantity drop menu (it says


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“All” by default). The maximum and minimum values of the quantity will be shown on the Y-axis of the plot:

10.2.2 Iteration Range

Adjust the displayed range of iterations by changing the Start and/or End iter-ation values. After changing a value, hit the keyboard Enter to implement the change. This is especially helpful for removing the first 50 or so iterations from the convergence plot. Before iteration 50, the quantities are typically changing too much to be considered when assessing convergence.

By default the average value of each degree of freedom is plotted. To view the maximum and minimum values, select Min. or Max. from the menu at the right side of the dialog.

The Table tab (shown just above the Start and End fields) shows a table of the plot-ted data. When an individual degree of freedom is selected, the table shows only values for that quantity.


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10.2.3 Plot Quantities and Error Estimation

Several different parameters can be plotted with the Convergence Monitor to aid in understanding the progress of an analysis.

Available in a pull-down menu on the Convergence Monitor, the following quantities are available: Avg., Min., Max, Resid In, Resid Out, Solv Iter, Relax Parm, and DPhi/Phi.

These quantities are used by the Intelligent Solution Control and Automatic Conver-gence Assessment algorithms, which are described in the Analyze chapter. A brief description of each is given:

• Avg: The average value of the plotted quantities.• Min: The minimum value of each quantity over the displayed range of iterations.• Max: The maximum value of each quantity over the displayed range of iterations.• Resid In: This is the residual value of each degree of freedom, and is the measure of how much the quantity is changing. This is the residual quantity that was plotted in previous versions of CFdesign.• Resid Out: This value should be quite small, and is the value of the residual over the entire field after the last iteration.• Solv Iter: The number of sweeps per iteration required by the solver for each degree of freedom.• Relax Parm: The under-relaxation value invoked by the Intelligent Solution Control for each quantity. If Intelligent Solution Control is not enabled, then these are the values specified on the Convergence Controls dialog.


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• DPhi/Phi: The fluctuation value of each field variable. This is used by Intelligent Solution Control and Auto Stop to assess the analysis rate of change.

10.3 Monitor Points

Monitor points are available in two forms: Runtime and Post. Runtime points track convergence (of the basic degrees of freedom) at a user-specified point for every iteration of the analysis. For this reason, Run-Time points must be selected prior to running iterations. Note that there is a limit of 100 run-time monitor points in an analysis.

Post Monitor points are used to create XY plots of any output quantity at any loca-tion in the model for the saved time steps or iterations. These locations can be cho-sen after the analysis, but only results data for saved iterations or time steps can be plotted. (Recall that the Results Output Interval on the Analyze dialog can be used to save results sets during the analysis.)


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10.3.1 Runtime Monitor Points.

Monitor points can not be chosen while the solver is running, and must be created prior to running iterations. Convergence data at monitor points created after itera-tions have been run will be of subsequent iterations as the analysis is continued--not from previous iterations.

Likewise, if a point is removed and the analysis is continued, then no subsequent data will be available for the removed point.

Go to the Review dialog task, and select the Monitor Points tab.

1. Ensure that the Runtime Monitor tab is showing.2. Use the X, Y, and Z sliders to navigate to the desired location. Specific coordinates can be entered in the fields adjacent to the sliders. 3. Hit the Add button to finish the point definition.4. Points and their locations will be displayed in the List Region.5. Plot the point graphically by hit-ting the Show Points button.

Step 1Step 5

Step 3

Step 4

Step 2


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When a completed analysis is started over from the beginning, all monitor point data for the previous analysis will be removed.

Convergence data for each monitor point is plotted in the Convergence Monitor in the same manner as the global convergence data. Select a specific monitor point from the drop menu on the right side of the Convergence Monitor:

10.3.2 Post Monitor Points

Post monitor points can be created after the analysis is finished, but are only plot-ted for saved results sets or time steps (recall that the Results Save interval is set on the Analyze task dialog).

Go to the Review dialog task, and select the Monitor Points tab.

1. Ensure that the Post Monitor tab is showing.2. Use the X, Y, and Z sliders to navigate to the desired location. Specific coordi-nates can be entered in the fields adjacent to the sliders. 3. Hit the Add button to finish the point definition.4. Points and their locations will be displayed in the List Region.5. Plot the point graphically by hitting the Show Points button.

Plot the saved results at a point by first selecting it from the list and then hitting the View Plot button.

Note: Select the desired results sets to plot using the Review_Results tab. Only the results sets added to the Active group will be plotted.

When the View Plot button is hit, an XY plot of the data will be presented. A drop menu on the plot window lists all the saved output quantities for the analysis, and any of these can be plotted against iteration number.


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10.4 Notes

The Notes tab provides access to several informational files created during and after the analysis. Additionally, user-defined annotations can be created and assigned from the Notes dialog:

10.4.1 Status File

The status file contains descriptions of any errors that occurred during the analysis. If a message saying “Errors occurred, Review Status File” appears in the Analyze Dialog Information field, this is where you should go to view the error.

Additionally, this file contains the messages displayed during startup (the initial cal-culations) as well as the residuals for each degree of freedom for each iteration.

By default, the status and summary files are written out to the working directory as separate text files. However, if they are deleted or if the cfd file is moved without either file, the status and summary data are still accessible through the Review dia-log. To create a separate text file for either file, click the Save button on the bot-tom of the dialog frame.

Files for viewing:

• Status• Summary• Summary History• Component Thermal Summary• Setup Parameters• Rotating Region Results• Motion Results

Annotations


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10.4.2 Summary File

This file contains tabulated minimum, maximum, and average nodal values for selected variables. It also contains global summary calculations such as mass flow through inlet and outlet passages, bulk pressures and temperatures, Reynolds number, wall heat transfer, a global energy balance and the fluid forces. Addition-ally, analysis times and the amount of RAM used in the analysis are shown.

<jobname>.sum is a simple text file that can be viewed in any text editor.

The calculation units as well as the units for every variable are included in the file. When working in the inch-lb-s and inch-Watt-K units systems, the mass flow rate will be given in both the consistent units as well as in lbm/s.

Energy Balance

Line 1: The difference in energy in the fluid from the outlet to the inlet. This is the sum of the residuals over the entire fluid domain. It represents the total energy needed to sustain all of the fluid boundary conditions. This should match up with the quantity: .

Line Fluid Energy Balance Informa-tion:

1 Energy Out - Energy In

2 Heat Transfer from Wall to Fluid

3 Heat Transfer Due to Sources in Fluid

4 Sum Radiant Heat Transfer to Fluid Walls

Solid Energy Balance Informa-tion:

5 Heat Transfer from Exterior to Solid

6 Heat Transfer Due to Sources in Solid

7 Heat Transfer From Fluid to Solid

m· cp∆T


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Line 2: This is how much energy the fluid picked up from heat transfer boundary conditions on the wall, and is the sum of the residuals at all of the wall nodes, including those nodes on the interface of the solid materials. In the case where all of the external fluid walls (not touching any other volume or surface) are adiabatic, this represents the amount of energy the fluid gets from the solid materials. If there are thermal boundary conditions on these external fluid walls, Line 2 will include those conditions as well as the energy being transferred from the solid materials.

Line 3: This is the summed energy from heat sources in only the fluid elements/volumes.

Line 4: The residuals calculated in Lines 1-3 and Lines 5-7 do not include the radi-ative fluxes. This line sums the radiative fluxes from every wall surface.

Line 5: This is how much energy is transferred to (or from) the solids to (or from) an exterior boundary. This is the sum of the residuals on the external faces of the solid materials. These are faces that do not touch any other material. In certain cases, where the solid material has say a heat generation applied to it and some external faces, this Line may contain a finite number which is the sum of the resid-uals on these external nodes. In this case, this number can be interpreted as the energy that would seep into the environment from that material. In the case where the external faces have a thermal flux-type condition or a specified temperature, this Line represents the amount of energy needed to sustain those boundary condi-tions.

Line 6: This is the summed energy from the heat sources in only the solid material elements/volumes.

Line 7: This is the energy that crosses the interface of the solid materials into the fluid elements. For adiabatic fluid external walls, this Line should be matched up with Line 3.

For the Fluid Energy Balance, the following values should match:

Energy Out - Energy In = Heat Transfer from Wall to Fluid + Heat Transfer Due to Source in Fluid + Radiant Heat Transfer to Fluid Walls

or

Line 1 = Line 2 + Line 3 + Line 4


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For the Solid Energy Balance, the following values should match:

Heat Transfer Due to Sources in the Solid = Heat Transfer from Exterior to Solid + Heat Transfer From Fluid to Solid + (some radiation)

or

Line 6 = Line 5 + Line 7 + (some radiation)

For radiation calculations, Line 7 will be larger than Line 6 because the radiative energy leaving the solids is not included.

Why don’t they exactly match? Remember, we are summing the residuals of the energy equation at every node in the model. If the energy equation is not con-verged, there will not be a balance. Even at convergence, the energy balance may still contain some errors due to numerical roundoff and mesh inaccuracies.

Inlets/Outlets

Recall that for book-keeping purposes, any specified velocity boundary condition is labeled an “inlet,” and any specified pressure boundary condition is labeled an “out-let.”

For a pressure-driven flow, with a pressure at the inlet and a pressure at the outlet, the summary file will report that there are zero inlets, and two outlets. The physi-cal inlet will have a positive mass flow rate however, and the physical out-let will have a negative mass flow rate. Also note that the “Total Mass Flow In” and the “Total Mass Flow Out” will be 0. This is because there are no specified velocity conditions (no labeled inlets), and the total mass flow from the labeled out-lets cancels (one is positive, and the other is negative).

Temperature Statistics

For analyses with heat transfer, statistics for temperature distribution are included in the summary file. These statistics show how much (as a volume percentage) of the model has a temperature within a given range.


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Summary of Fluid Forces on Walls

The cumulative force components are reported in the Summary file as Shear and Pressure results. These values are the summed force values from all walls in the model. Use the Wall Calculator in the Results task dialog to compute forces at indi-vidual surfaces.

Shell Forces

If an analysis contains shells (solid surface obstructions), then force, temperature, and heat transfer information for each surface is listed in the summary file.

10.4.3 Summary History File

This is a collection of all the summary files created for this analysis. Each time the analysis is continued, a new summary file is appended.

10.4.4 Component Thermal Summary

The component thermal summary file automatically saved at the conclusion of every analysis. This file contains the mean, max, and minimum temperature data for each solid part in the analysis model. This information is provided for each time step in a transient analysis.

Additionally, temperature and heat flux information for two-resistor components are also listed.


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This information is also saved to an external file, and is named after the analysis with a “.cts” extension.

10.4.5 Setup Parameters File

The Setup Parameters File is automatically saved at the conclusion of every analy-sis. This file contains a listing of all applied analysis conditions such as mesh sizes, materials, and boundary conditions.

This file is named after the analysis with a “.set” extension.

10.4.6 Rotating Region Results

This is a time history of the behavior of rotating regions in a Rotating analysis. The hydraulic torque, rotating speed, and hydraulic force components for each rotating object are listed.

This data is also written to a “.csv” file named after the analysis name with the word “torque” appended to it. For example, an analysis named Centrif-Pump would produce a torque file called:

CENTRIF-PUMP_torque.csv.

10.4.7 Motion Results

This is a time history of the behavior for every moving object in a Motion analysis. The linear and angular velocities, the linear and angular displacements, the force, and the torque for each time step are listed. This information is very useful for understanding the dynamic state of each part throughout the analysis. Each part is listed on a separate tab.

Note that the linear and angular displacements are relative to the initial position of the object as specified using the Initial Position slider on the Motion task dialog. Pay particular attention to this if the initial position differs from the as-built location in the CAD model.

This file is also saved to the working directory, and is named using the analysis name and the part name and the word “motion.” For example, the motion file for


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an analysis called Heating-Process that contains a moving solid called Product would be called:

HEATING-PROCESS_PRODUCT_1_motion.csv.

Note that the “force” and “torque” values are the net values, and include driving, resistance, collision, contact forces as calculated in the Motion module. The hydrau-lic force and torque are just the force and torque imparted on the object by the fluid, and do not include any forces specified in the motion definition. The hydraulic values are reported in the Wall dialog.

10.4.8 Annotations

This feature allows text notes to be added to the results display of an analysis. There are two forms of graphics: static notes and model notes. Static notes are used primarily as titles and general information text on a model, and do not change position on the Graphics window. Model notes are attached to geometry and display objects (such as cutting planes), and navigate with the model.

10.4.8.1 Creation and Placement of Notes

On the Review task dialog, click the Notes tab.

To create a note:

1. Type the text in the field in the Anno-tations section.2. Click the Place Text button.

Step 1 Step 2


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10.4.8.2 Modification of Notes

All notes are listed under the Annotations branch of the feature tree (which is only shown when the Results and Review task dialogs are active). A right mouse button

To place a note:

1. Click on the desired location on the Graphics window or the model. 2. Text placed on the model (or on results entities such as cutting planes) will be a model note.3. Text placed off of the model will be a static note.

static note

model note


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menu is available for each note that allows the note to be moved, changed, deleted, or displayed with a frame:

A note cannot change form after it is created. If a note is first placed on the model, it will remain a model note. If moved, it must be placed on a model entity. The same is true of static notes--if a model entity is selected as a new location, it will remain a static note.

10.4.8.3 Saving and Retrieving Notes

The View Settings File

The text and locations of all notes in a model are saved in the View Settings File. Save a View Settings File by clicking this tool button:

When a View Settings File is opened into a results display using the tool button at the right, all stored notes will be placed on the Graphics window in the locations where they were saved.

The Graphics Text File

To move a note, right click on the note in the feature tree, and select Move. Click on the new location.

To show a frame around a static note, select Frame from the menu.

To edit a note, click Change. The note will be editable on the feature tree. Modify the note as necessary, and then hit Enter on the keyboard. The modified note will appear in the Graphics window.

To delete a note, click Delete. It will be removed from the feature tree and from the Graphics window.


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Only the text from notes is saved in the Graphics Text file (“.gtx”).

10.4.8.4 Design Review Center

Static notes displayed on a model will be shown for all models when the Design Review Center is active. Model notes, however, are only shown on the model on which they were created.

Click the Save All button to store the text from all notes in a model.

Text locations are not stored in this file, but when opened into a model, each note can be placed individually.

Click the Retrieve button to open a Graphics Text file to add text to a Results display.

A dialog will appear listing each note. Select a note, and press OK. Its text will be placed in the Annotations field of the Notes task dialog.

Click the Place Text button and then a location in the Graphics window or the model to place the note.

(Text retrieved from a Graphics Text File can be applied as either a static note or a model note. The original type of the note is not saved.)


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10.5 Results

Result sets that are added to the Active group can be animated. This is very useful for visualizing time dependent data. The next section describes animation of time steps.

The Results dialog lists saved results sets and/or time steps in the Available group.

1. Move sets from the Available group to the Active group to make them part of the animation.There are three ways to select sets:

• Directly from the list (Win-dows-standard control-left click to select certain sets) and hit the Down button to move.• Enter the range and incre-ment in the Parametric Selec-tion section and hit the Move button.• Hit the All Down button.

2. After selections are made, hit the Apply button.3. After an animation occurs, hit the Reset button to regain control in the dialog.

To clear the Active list, hit the All Up button. To remove certain steps, select them and hit the Up button.

Step1

Step3Step2


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10.6 Animate

Once result sets are made Active on the Results tab, hit the Animate tab to view the animation:

Use the “VCR” controls to control the animation. Animated files can be played for-ward or in reverse as well as stopped, paused, and advanced by frame forward or reverse. Click the Cycle box to alternate between playing the animation forward and then in reverse.

The speed of the animation is controlled with the Frame Interval value (in millisec-onds).

Use the controls on the Results task dialog to set up the view. Results objects can be added, removed, and manipulated during the animation. Additionally, cutting plane bulk data can be output for all active sets during an animation.

Stop

Play Forward

Single Frame

Pause

AdvanceReverse

Play In Reverse

Single Frame


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10.7 Report Generation

10.7.1 Introduction

This is an important evolution in the Design Communication Center first introduced in CFdesign 6. A report template consisting of sections for the introduction, model description, analysis summary, results, and conclusions is included by default. The order and content of the sections is fully modifiable, and text files, graphics, and additional sections can be added as well. Items can be removed from the template or suppressed from the report. There are several placeholders for text files which can be used to describe the model, annotate graphics, and summarize conclusions.

A summary of the model parameters (jobname.set file) is created automatically for the analysis, and is a part of the report. The summary and status files as well as images of the model and the convergence graph are also automatically created and included in the report. User-created VTF files will automatically appear in the Graphics section of the report, and each has a placeholder for an associated text file for description. Modifications to the report layout can be stored for future use, and can be designated as the default template through a setting in File_Preferences.

To create the report in HTML format, simply click the Generate Report button. The document is created and saved in a sub-folder of the working directory. This HTML document contains the VTF files, which allow image navigation and animation of time steps and multiple results frames.

A report can be created at the project level as well. This report contains setup, analysis summary information, and the graphics for each analysis in the project. Report formatting for each analysis is also imported into the project report.


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10.7.2 Entity Types and Basic Usage

A default report template is automatically created for every analysis after the anal-ysis is processed (run for 0 iterations or more). Located under Review_Report, the template lists the items that will be placed into a report when it is generated:

Items can be modified, suppressed, and moved within the template. New items can be added as well. This section describes the basic process of manipulating the con-tents of a report and a description of the entities in the report template.


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10.7.2.1 Template Columns

The template layout is divided into two columns: the Template Items on the left and the Values on the right. The names of the Template Items and the Value of default items cannot be changed. Values of user-created Items can be changed, however.

10.7.2.2 Entity Types

There are two primary types of entities in the report template: Text Lines and Referenced Files.

Text Lines

Text Lines are single lines of text, and include the Report Title, Report Date, Author name, Analysis Name, and Section names. The contents of each text line is shown in the Value column in the report template.

Note that the Report Date, Analysis Name, and Section names of default sections cannot be changed. (The names of user-created sections are modifiable, however.) These items can be suppressed from the report by right clicking on the item, and unchecking Include.

Referenced Files

File References are references to external files that are to be included in the report. They are typically descriptive text files, vtf files, graphics files, and output files such as the Summary file.

The Referenced Files that are included by default are:

The two User Text Entries do not contain any text, and are not part of the report until the user adds text and saves them. A “?” beside the entry indicates that the

Corporate Logo Summary File Setup Parameters

Model Image Convergence Plot

Conclusion User Text Entry

Model User Text Entry Thermal Sum-mary


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file does not exist. After text is added and the file saved, the “?” will disappear from the report template.

10.7.2.3 Basic Usage

Exclude a Referenced File or Text Line

Right click on file name, and uncheck Include. To include a suppressed file, right click and check Include.

Exclude a Section Right click on the section name, and uncheck Include. To include a suppressed section, right click and check Include.

Change the order of entities Click on an entity, and click the Up or Down but-tons near the bottom of the task dialog. Move an entire section by first clicking on the section header, and then hitting the Up or Down but-tons.

Create a new Text File Click the Create Text button near the bottom of the task dialog. Enter text in the text editor that appears. Save the text file when finished.

Add an existing Referenced File (text or graphic)

Click the Add Existing button near the bottom of the task dialog. A browse window will prompt for a file name and location. Files added will be placed below the currently selected item in the template.

Delete a Referenced File (text or graphic)

Only files that are added to the report can be deleted from the report. Right click, and hit Delete.

Modify or view a User Text Entry or a user-created Ref-erenced (text) File

Right click on the text line, select Edit/View. A text editor will come up allowing text to be entered or changed.

View a Referenced File

(default text file or graphic)

Right click on the entity, and select View. Text files will appear in a Text Editor (input deacti-vated). Graphics files (bmp, tif, etc.) appear in a graphics viewer. VTF files are viewed in the CFde-sign Communication Center.


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10.7.3 Default Report Sections

By default, analysis reports consist of five sections: Creation Info, Model Descrip-tion, Analysis Summary, Graphics Files, and Conclusions. All sections are included by default in the report except Graphics. The Graphics section is enabled automati-cally, however, if there are vtf files named according to the convention described in the Graphics section description.

This section describes the default contents of each section.

Edit a Text Line (such as Author name)

Right click on the line, and select Change Value. Modify the text directly on the value line.

Create a Section Click the Add Section button near the bottom of the task dialog. The new section will be placed below the currently highlighted section. If no sec-tion is highlighted, then a new section will not be created. A “U” will appear adjacent to the Section header indicating that it is user-created.

Delete a Section Only user-created sections can be deleted. Right click on the section name, and select Delete. Default sections can be suppressed from the report, if desired.

Refresh the template If the Report task dialog is showing when a prop-erly named vtf file is created, click the Refresh button to automatically add it to the Graphics section.

Create a Report Click the Generate Report button. This is described in more detail in the Generating the Report section of this chapter.


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10.7.3.1 Introduction

This section contains basic information about the origin of the report.

10.7.3.2 Model Description

This section contains information about the analysis model.

Corporate Logo: The file and location of this graphical file are set in the User-Pref-erences dialog, found under the File main menu item.

Report Title: The analysis name is used by default, but can be changed.

Report Date: The current time and date when the report is generated.

Author name: The account login name is used by default, but a different name can be set in File_Preferences. This value can also be changed as described in the Text Line section.

Analysis Name: The name assigned to the analysis when it was created.

Model Image: A vtf file showing the anal-ysis model. This is automatically created.

Model Description User Text Entry: A blank text file that can be used to enter a description of the analysis model. (The “?” adjacent to the entry means that no text has been saved to the file.)

Setup Parameters: An output file that is automatically saved when the analysis is run. This file contains a list of all of the user-applied settings such as boundary conditions and mesh sizes.


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10.7.3.3 Analysis Summary

The files containing the text files describing the analysis results are included in this section.

Summary File: An output file that is automatically saved. It contains a sum-mary of the analysis results, results at openings, and energy balance.

Convergence Plot: A bitmap of the Con-vergence Monitor.

Thermal Summary: An output file that is automatically saved. It contains the tem-perature data for every solid in the analy-sis model.


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10.7.3.4 Graphics Files

Images showing the results are typically contained in this section.

10.7.3.5 Conclusions

This section provides a place to summarize the pertinent findings of the analysis.

Graphics Files: This section is populated automatically by vtf files found in the working directory.

VTF files must be named in the following manner to automatically be included in the report:

analysis-name_g_graphic-name.vtf

“analysis-name” = the name of the anal-ysis.

“graphic-name” = descriptive filename.

The “_g_” must come between the analy-sis name and the graphic name.

A corresponding text file is automatically created for each graphic, allowing text to be entered that describes the graphic. This file doesn’t actually exist until text is saved to it.

Other graphics files types (bmp, jpg, gif) and vtf files named differently can be imported by hitting the Add Existing but-ton. The accompanying text file will not be added automatically, but can be created by clicking the Create Text button.

Conclusions User Text Entry: A blank text file that can be used to enter conclu-sions. The “?” adjacent to the entry means that no text has been saved to the file.


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10.7.4 Generating the Report

To view the report that is defined by the template, click the Generate Report but-ton near the bottom of the task dialog. An HTML-based report will then be created and will open in Internet Explorer, if available. All of the items contained in the template (but not suppressed) will be included in the report. A table of contents with linked entries is included on the left side of the window for easier navigation. Part of a sample report is shown:

All vtf files will be navigable, and will contain any animation present at the time of file creation. Because the vtf files use an ActiveX plug-in to be viewed within the HTML document, the CFdesign Communication Center must be installed on a com-puter to view the vtf files. This is automatically installed as a part of the CFdesign installation. To view a report on a computer without a CFdesign installation, down-load the CFdesign Communication Center from the CFdesign web site (www.cfde-sign.com).

Note that Internet Explorer (by Microsoft) is required to view the report. This is due to the fact that the vtf files require an ActiveX plug-in (described above) for viewing in applications other than the CFdesign Viewer. When a report is opened in IE, a security message may appear prompting for approval to show the images. This is a


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Windows security measure, but you should select the choice allowing the images to show.

All included and generated files in the report are placed into a sub-folder of the working directory created when the report is generated. This sub-folder is named:

Analysis_Report_analysis name_0001

where “analysis name” is the name of the CFdesign analysis model. The number appended to the folder name is incremented each time the report is generated. This means that each time a report is generated, it is a new report, and does not over-write a previous version.

This folder contains all of the files needed to view the report. To send the report to another person, simply send all of the contents of the report folder.

10.7.5 Saving and Opening Templates

A default template (or report layout) is included with the CFdesign installation. However, to save a modified template for use with other reports, click the Save button from the Template group in the task dialog:

This will prompt for a template name, which will have the extension “.dcctmp”. (This stands for Design Communication Center Template.) This file will contain every item in the customized report in the same order.

User-created and added Referenced files (graphics and text files) will not be explic-itly saved in a template, but blank entries for them will. A “U” will appear adjacent to each user-added or created entity.

User-created sections are included in the template as well. When a saved template is applied to a new report layout (by clicking the Open button) user-created section names appear in the template.


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To make a customized template the default template for all subsequent reports, enter the location and name in the File_Preferences dialog:

The template that is created or used for a report is saved as part of the analysis to a separate file called analysis-name.dccrt. This file is read when the analysis file is opened, and all template settings applied automatically. The reason for this is to allow easy modification of a report. Because it is not possible to edit an HTML docu-ment, modification of a report is performed within the CFdesign analysis file by manipulating the report template. Modification, relocation, addition, or removal of referenced files is performed directly on the template. When completed, simply generate a new report.

10.7.6 Project Reports

A report format for projects is available by clicking the Project Report box at the bottom of the task dialog. Note that this option is only available while a project is open.

When unchecked, the report template will be for the current analysis. It behaves as described above.


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However, when checked, the report format changes so that project-specific infor-mation can be added. The Creation Info section is still positioned at the beginning of the report, but it is followed by a Project Description section. This consists of the project name and a User-Text Entry line for description.

A single graphics section automatically includes all of the graphics from the Graph-ics section of each analysis in the project. This is the ideal place to include vtf files that show animation of Design Review Center results. They can be created in any analysis file, and should be named with the appropriate naming convention to ensure inclusion in the report.

Additionally, the Model Description and Analysis Summary sections from each anal-ysis report are automatically added to the Project report.

Creation Info section describing the Project

Project Name

Project Description section

Single Graphics sectionconsisting of all graphicsfrom included analyses

Model Description andAnalysis Summary for eachanalysis in the project


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This is a powerful way to compare results from many analyses in a design study.

The Model Description and Analysis Summary sections are read directly from the respective analysis report templates. Customizations made to either of these sec-tions will be included in the Project report. Likewise, any modifications made to one of the sections while in the Project report mode will be migrated back to the Analy-sis report template.

As in an analysis report, text files can be created or added to the report. If placed in an analysis-specific section, they will be included in that analysis report. If a vtf file is created using the naming convention described in the Graphics section above, then it will be included in the appropriate analysis report as well.

Project templates can be customized as well. Sections can be moved, items can be added and removed. Project templates can be saved using the Save button in the Template group. A project template can be applied to subsequent projects by click-ing the Open button in the Template group or by setting the default Project Tem-plate in File_Preferences.


CHAPTER 11 Viewing Results

11.1 Introduction

CFdesign has a powerful set of results visualization tools to help view, extract, and present analysis results quickly, easily, and efficiently. An integrated feature tree lists display entities, and several ways to output graphical images and data make communicating your analysis results with other members of the design supply chain very easy.

The Results dialog task is more than just a post-processor: it is the way to view results during the calculation. CFdesign has had Run-Time Results viewing capabil-ity for several years, but this is the first time that the run-time results viewing envi-ronment is the same as the post-analysis results environment.

The Results-specific icons, the Feature Tree, and the Results dialog task are all dis-cussed in this chapter. There are several icons that are unique to the Results task, and make viewing results easier. The Feature tree contains a summary of the set-tings that were in effect for the displayed results. Finally, the Results dialog task is divided into four tabs: Cut Surface, Iso Surface, Wall, and Settings. Most of these tabs are divided into further sub-tabs for clarity.


Viewing Results

11.2 Results-Specific Icons

Most of the icons in the user interface are discussed in Chapter 2 -- the User Inter-face Chapter. However, there are several icons that are specific to post-processing, and are discussed here:

Save Image. This saves a jpeg, bitmap, gif, or tif image of the current contents of the Graphics Region.

Save Dynamic Image. This saves a “.vtf” file, which is an image that can be viewed in the free viewer distrib-uted with CFdesign. It can also be viewed in PowerPoint, Word, or Internet Explorer if the free plug-in is installed (details later in this chapter). This image is navigable--it can be panned, rotated, and zoomed by the viewer.

Left: Save View Settings. This saves post-processing views and objects such as cutting planes and iso sur-faces.

Right: Open View Settings: This retrieves and applies saved views and objects. A settings file can be opened on a model different from the original model.

Note: non-planar cutting surfaces (described later) can-not be saved to a View Settings file.


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Shaded Image. The model is shown filled.

View Lines. The mesh lines are shown

Outline Image. The outline of the model is shown.

Transparent. This works in conjunc-tion with a shaded image, and makes the model transpar-ent.


Viewing Results

Show Mesh. Dis-plays surface mesh. (Shaded Image should be enabled.)

Peel by Surface. Toggles between surface and volume blanking (with the right-mouse-but-ton). Default is vol-ume blanking.

(Note: surface peel-ing is not available for parts with assigned motion (Moving Solids).)


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Crinkle Cut

The Crinkle Cut provides a three-dimensional interior

view of the analysis mesh. This is a visually interesting and very useful way to examine the element distri-bution, transitions, and shape within the model.

This view is controlled with the Z-Clip dialog. Check the Crinkle-Cut box to show the model in this man-ner

When crinkle-cut is enabled, the model is automatically shown in shaded mode, and the mesh is dis-played.

The cut is only updated as the slider on the Z-Clip dialog is moved. Unlike the standard z-clip, the crin-kle-cut will not update when the model is navigated.

Closing the Z-Clip Control and Crin-kle-Cut dialog will disable the crin-kle-cut view from the model.

This method provides a more visu-ally accurate method of viewing the mesh inside a three dimensional model than showing the mesh lines on a cutting plane.


Viewing Results

11.3 Feature Tree

The Results Task Feature Tree behaves differently from the Feature Tree shown in the other tasks. Most of the branches are informational only, and do not allow any modification to assigned settings. The Length Units, Coordinate System, Boundary and Initial Conditions, and Mesh Size branches behave this way.

Mirror

Part mirroring reflects displayed geometry about a plane. This is

very useful for results on models that have been divided by symmetry.

The Mirror icon opens the Mirror dialog box.

Check the Mirror Enabled box to acti-vate mirroring.

A model can be reflected about a single plane at a time.

There are two ways to set the reflection plane:

• Select any planar surface on the model when this dialog is open.• Click the X-Y, Y-Z, or Z-X buttons to reflect the model about the Cartesian planes.

Mirroring is active after the dialog is closed, if it was not disabled.

When mirroring is active, results visual-ization entities (cutting planes, particle traces, iso surfaces, etc.) that are visible in the original model will also be shown in the reflection.

Disable mirroring by unchecking the Mir-ror Enabled box.


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Additionally, each of the branches lists the settings that were assigned to produce the current results. If a boundary condition or mesh size is changed after results are obtained, they will not be listed on branches of the Results Feature Tree until the analysis is run with the new settings. However, any new settings will be listed on the feature tree for the other tasks.

11.3.1 Analysis Settings

The Boundary Conditions, Initial Conditions, and Mesh Size branches list the settings for the current analysis, and left clicking on the entity label (volume, surface, or edge label) will cause that entity to highlight. This is a convenient way to determine the location of settings while viewing Results. Click the label again to turn off the highlighting.

11.3.2 Materials

The Materials branch lists each material and the associated parts.

Left clicking on a part label causes that part to highlight in the Graphics region. To remove the highlighting, left click again on the part label.

Right clicking on a specific material branch brings up a menu with display con-trols that are applied to all parts with that material.


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Right clicking on a part label brings up the same display control menu but applies only to that part.

11.3.3 Results

The result selected from the Scalar branch of the Feature Tree is the globally dis-played result. The result selected here will show on all surfaces of the model. This is important to note because cutting planes and iso-surfaces can display a result different from the global result.

If a desired quantity does not appear in the Results_Scalar list, then you should return to the Analyze task, and click the Result Quantities button. Select which quantity you want displayed, and run the analysis zero iterations (ensure the last iteration is shown in the Continue From menu). When you return to Results, the quantity will be available in the Feature Tree.

Most of these commands are view settings, and perform the same function as the tool-bar icons described earlier.

Additionally:

Visible toggles the visibility of the part.

Transparent displays the part with transpar-ent surfaces.

Set Transparency Value opens a dialog allowing control of the transparency level. A value of 0% is opqaue; a value of 100% is completely transparent.

Show Results toggles the display of analysis results on the part.

Show Color opens a Color Palette dialog for assigning colors to parts. Results are not shown on a part when it is colored.


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Results

Scalars

All the entries under the Scalars heading are single-component quantities, and do not have a direction. Toggle between quantities simply by clicking on the desired one.

The right click menu for each scalar quantity looks like

If an analysis has multiple saved results sets or time steps, by default the last set will be visible. To select a different set to view, go into the Results task, and right click on the Results branch of the Feature Tree. A menu will appear showing all the saved results sets and time steps.

Select the desired set from the list. Results from the selected set will then be displayed.

Reference Frame is described below.

Visible controls the visibility of the quantity (also toggled by left-clicking on the Scalars branch).

Settings calls up the Scalar Settings menu tab on the Results dialog. This is covered later.

Units lists the available display unit types. The analysis unit system will be marked as the default.

Contours controls the display of contour lines on the surfaces of the model--contour lines do not appear on cutting planes.

Textured Fringes controls display of the fringe display method. Textured fringes show discreet divisions in the colors. When disabled, fringe colors blend together smoothly.


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Note that values on XY plots, the bulk calculations, and wall results always use the analysis units system, and will not be updated when a different units system is chosen from the Feature Tree menu.

Reference Frame is only available for Velocity Magnitude. This allows the user to toggle between the Absolute and Relative velocity frames. Applies to velocity magnitude fringe display and velocity vector display. This is most applicable for rotating analyses:

relative velocity = absolute velocity - rotating component.

Vectors

The Vectors branch has multiple components. Click on a vector quantity to control its visibility in the Graphics Window. Note that this controls only the visibility of vec-tors on surfaces of the model. Vector display throughout the interior of the model is controlled by the cutting plane and iso surface dialogs.

Each vector quantity has a right-click menu:

Visible controls the visibility of vectors on the model surfaces. Uncheck to turn off the vector display.

Settings toggles the Vector Properties dia-log. This dialog will be discussed in the Set-tings section of this chapter.


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Iso Surfaces and Cutting Planes

All iso surfaces and cutting planes are listed in the Feature Tree. The appearance of each can be controlled independently by right clicking on the cutplane or iso surface branch:

Cutting planes and iso surfaces can be created from the Feature Tree by right click-ing on either the Cutplanes or Isosurfaces branches, respectively, and selecting Add from the menu. Selecting Settings from this menu brings up the corresponding task dialog.

11.3.4 Groups

The groups branch lists every group that had been created prior to running the most recent set of iterations or time steps. Because groups are composed of geo-metric entities, and the displayed entities in Results mode are all based on the anal-ysis mesh, there is no facility for direct visualization or manipulation of groups or group entities through the feature tree.

Groups of surfaces can be used in the Wall Calculator, however, by right clicking in the List region of the Wall dialog, and selecting the appropriate group of surfaces.

11.3.5 Annotations

Annotations (written descriptions on the Graphics window) are listed individually under the Annotations branch. Each entry can be modified, deleted, and moved directly through the feature tree. More information about Annotations is presented in the Review chapter of this manual.

Visible/Shaded controls the visibility of an entity.

Vectors toggles the display of vectors on a cutting plane or iso-surface.

Textured Fringes toggles the display of textured fringes (discreet coloring).

Delete removes the entity.


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11.4 Entity Blanking

In the default mouse mode, right clicking on an object will cause it to be blanked (hidden) from view. Click the right mouse button off of the model to re-display all blanked items. Click the middle mouse button to re-display the last blanked item or to undo a total re-display command.

By default, right clicking on the model blanks the volume that it touches. To enable surface blanking, click the Volume/Surface toggle tool button to Surface (pressed in):

An unobstructed “view” of an object must exist to blank it. If a cutting surface or an iso surface is in front of the intended object to be blanked, it will not blank. Move or delete the cutting or iso surface, and then blank the object.

Note: surface blanking is not currently available for parts that are assigned motion (Moving Solids). This is a capability that will be added in a later version of CFde-sign. Also, surfaces that are blanked will not appear blanked when saved to a View Settings file or to a Dynamic Image. Blanked volumes, however, will be blanked in both.

11.5 Results Probing on Surfaces

Result values can be probed on any surface--walls, openings, slip faces, internal fluid surfaces, etc. To probe on any surface: Hover the mouse over the area of interest and hold down the shift and control keys simultaneously.


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The value of the active scalar will be displayed in the Status bar:

11.6 Color Legends

Each time the global result is changed in the Feature Tree, the color legend updates to show the new quantity. Additionally, because each cutting plane and iso surface can show a unique result quantity, a new color scale is drawn for each unique quan-tity.

The following graphic shows a model with velocity magnitude as the global result (which only shows on the surfaces of the model), static pressure as a cutting plane


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quantity, velocity magnitude is shown on the other cutting plane, and u-velocity as an iso-surface quantity:

Each color legend has a title that indicates which display entity is displaying the result, and the units of the result quantity

11.7 Cutting Surfaces

Cutting surfaces are the primary post processing tool for visualizing data on three dimensional models. Traditionally, cutting surfaces have been used simply to visu-alize fringes or vectors on a planar slice through the model. In CFdesign, cutting surfaces have several additional roles:

• They can present results data on planar and non-planar surfaces• They provide a seed plane for particle traces• They provide a method to extract bulk data through any cross section• They serve as a basis for XY-plots.

In addition to the user-interface roles of the cutting surface, results can be probed at any location on a planar cutting surface by holding down the shift key, and posi-tioning the mouse at the point of interest. The value at that location will be shown


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in the status bar at the bottom of the interface. The units of this value correspond to the units selected from the Scalar branch of the Feature Tree.

Shown are examples of a planar (left) and a non-planar cutting surface (right) showing fringe (color) results:


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The Cut Surface tab of the Results dialog is shown:

The basic cut surface controls are always visible on the dialog. Additional controls and other functionality such as particle traces, bulk values, and xy plots are accessed through tabbed dialogs on the Cut Surface dialog.

Basic Cut Surface Tools:Location, orientation, and displayedresult

Advanced Cut Surface Controlsand dependent functionality tabs.

Selection of Cut Surface shape:Planar or Surface


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11.7.1 Cut Surface - Tools

The Cut Surface Tools control the basic location and orientation of the cut surface, and can be accessed when any of the cut surface sub-tabs is active:

11.7.2 Cut Surface - Controls

The Controls tab contains advanced options for controlling cutting surface appear-ance. This tab provides controls for the appearance of scalar and vector data as well as the creation of non-planar cutting surfaces

1. Create a cutting surface with the Add button. When a cutting surface is created, the model will automatically be shown in outline mode. 2. Select the desired scalar quantity from the Scalar menu. 3. Enter a Normal vector to set its orientation.4. Adjust the location with the slider bar.5. All cutting surfaces are listed in the List Region. The controls only apply to the highlighted plane.6. The Save Table button will export a “.csv” file containing tabular data on the cutting plane. The active quantity in the Scalar menu will be written to the file. Data is listed in a uniform grid throughout the cutting plane. The density of the grid is set by the Vector Spacing slider bar. This is only avail-able for planar cutting surfaces.7. If necessary, delete a cutting sur-face using the Delete button.

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11.7.2.1 Appearance

• Shaded toggles visibility of the cut-ting surface. (Uncheck to make cut-ting surface disappear.)

• Vectors toggles display of vectors.• Color by Scalar toggles the display

of the scalar quantity on the cutting surface.

• Clip cuts the model with the planar cut surface.

• Show Grid toggles the display of the vector display grid. This is only avail-able for planar cutting surfaces.

• Show Mesh toggles the display of the mesh on the cutting surface. For pla-nar cutting surfaces, this is the inter-polated mesh at the current location of the surface. For non-planar cutting surfaces, this mesh is the mesh that was on the source surface(s).


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11.7.2.2 Vector Spacing

11.7.2.3 Position, Orientation, and Shape: Planar

This slider adjusts the density (in the length units of the analysis) of the ordered grid of vectors. If a finer or coarser grid spacing is needed than the defaults provide, they can be keyed into the Max. or Min. fields, respectively.

Note that this control is only available for planar cutting surfaces. The vector den-sity on non-planar cutting surfaces is based on the mesh density of the source surface(s).

• When Shift RightClick to Align to Surface is checked, the planar cutting surface is aligned to a surface by hold-ing the Shift key and right clicking on that surface.

• Use the Key-In Plane Location to specify the exact coordinates of the cutting surface location.


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11.7.2.4 Position, Orientation, and Shape: Non-Planar

Creating Non-planar Cutting Surfaces

1. Click the Add button in the tools group.2. Select Surface from the Shape pull-down menu.3. To define the shape of the cutting surface, click the Source Surface(s) button.4. The Select Source Surface(s) dialog will come up. Select surfaces on the model by left clicking on them.5. Click the OK button to end the selection process.The cutting surface will then be created, and will overlay the source surface(s). As it is moved through the calculation domain, it will be colored by the Cut Surface Scalar at its local position.

When picking surfaces to be source sur-faces, it is helpful to move the existing planar cutting plane out of the way. It is not possible to pick through it, so unchecking Shaded will not help.

Blank surfaces if necessary by changing the Surface Peel toggle to Surface, and right clicking on them to hide them.

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Moving Non-Planar Cutting Surfaces

There are three ways to move non-planar cutting surfaces: either along a specified direction, by morphing between a source and a target, or by offsetting from the source.

Specified Direction

When moving a cutting surface along a specified direction, the surface main-tains the shape of the source sur-face(s).

1. Ensure that the Movement Type pull-down menu is set to Specified Direction.2. The direction of travel is set by defining a unit vector in the Normal field. The default value is based on the average normal of the cutting surface. Change it as necessary.3. Use the slider bar to move the cut-ting surface.

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Morphing

Morphing a cutting surface means that its shape will change as it is moved between the source and the target. One of the steps described below is how to define the target.

1. Set the Movement Type pull-down menu to Morph to Target Surface(s).2. Click the Select Target Sur-face(s) button.3. Select one or more surfaces that will be the target.4. Click the OK button in the Target selection widget.

5. Move the slider to “morph” (con-vert) the cutting surface from the source to the target.

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Distortion may occur when morphing surfaces if the angle between the source and target is greater than approximately 110 degrees. The reason is that the transfor-mation rays between the source and target can be multi-valued. Below is an exam-ple of this. The source was the roof of the car; the target was the planar surface cutting through the car.

In the following graphics, the source was the roof of the car, but the target was the surface of the wind tunnel opposite the car. The surface is shown at four positions of its morph:


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As mentioned, the choice of source and target surfaces plays a significant role in the level of distortion that will occur during the morph. Reasonable morphing can really only be obtained in the following two scenarios:

If the surfaces to be morphed completely surround a volume, then source and tar-get surfaces must completely enclose their respective volumes without any gaps. The best types of volumes are shaped such that a direct line of sight exists between every face and the centroid of the volume.

If the morphing surfaces do not completely enclose a volume, then the source and target surfaces must be shaped such that they can be mapped (or projected) onto a flat plane. The key is that there must be a one-to-one correspondence to get a use-ful mapping. An example of a surface that does not meet this criteria is shown:

Points A and B both map to point C. This produces a non-unique mapping which will result in a lot of distortion.

A B C

cylinderplane


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A non-planar cutting surface that has been offset is shown: Both the expanded (left) and shrunk surfaces (right) are shown:

Note: non-planar cutting surfaces cannot be stored as part of a View Settings file. Any non-planar cutting surfaces saved as part of a view settings file will not be restored when the View Settings file is open on a model.

Offset Surface

This mode scales a non-planar cutting sur-face while preserving its original shape.

1. Change the Movement Type to Offset Surface.2. Use the slider in the Tools group to change the size of the surface. Moving the slider to the right expands the surface; to the left shrinks it.

The direction of movement is always nor-mal to the source surfaces.

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11.7.2.5 Rotate

The tools in the Rotate group allow the user to rotate a cutting surface about its centroid, any of the Cartesian axes, or a user-defined axis.

The Centroid selections mean that the cutting surface will rotate about an axis in the x, y, or z direction that passes through the centroid of the surface.

The Global axis selections cause the cutting surface to rotate about the selected global axis. This can be very useful for cutting surfaces in an impeller that rotates about a Cartesian axis. These selections are only available for non-planar cutting surfaces.

1. Select the axis of rotation from the Axis pull-down menu. The available choices are:

• User Defined• Centroid X• Centroid Y• Centroid Z• Global X• Global Y• Global Z

Each option is explained below.

2. If User Defined is chosen, enter an axis point and an axis direction.3. Use the slider to rotate the cutting surface. 4. Clicking on the slider bar rotates the surface 10 degrees. Change this incre-ment with the increment control to the right of the slider.5. Clicking on the slider arrow rotates the surface 1 degree.6. Click the Reset to Original button to position the cutting surface back at its default location and orientation.

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Note: The Axis Pt. and Axis Dir fields are grayed out when any of the Centroid or Global components are selected.

The User Defined option will cause the Axis Point and Axis Dir fields to be editable. Specify the axis of rotation by entering a point through which the axis passes (Axis Point) and the direction of the axis by entering a unit vector (Axis Dir). Both entries can be entered by separating the three components with spaces or commas.

11.8 Cutting Plane - Particle Trace

Particle Traces are similar to an injected dye in the flow. They are a very useful method of visualizing the flow distribution. Hit the Trace tab on the Cutting Plane dialog for particle trace controls. There are three sub-tabs for particle traces: Sets, Attributes, and Mass. Each is discussed below:


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11.8.1 Sets

Seed points must first be created. The particle traces will pass through these points. There are four ways to create seed points:

• Pick on Plane: Graphically select seed point locations directly on the cutting plane. The coordinate loca-tions will appear in the Seed Point field. Hit the Add Traces button to draw the traces. Sets are listed in the Sets field.

• Rectangular Grid: A rectangle drawn anywhere on the cutting plane encloses a matrix of points. Three locations are selected: the two top corners and a lower corner. Enter the number of points in the length and width grid directions on the plane. Hit the Add Traces button to draw the traces.

See the note about Residence Time below.


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Settings made on these two tabbed dialogs apply to the trace set highlighted on the Sets field.

11.8.1.1 Residence Time

The time that each trace takes to traverse through the model is its residence time. This value is listed in the Edit Sets region of the Particle Trace dialog for each trace. This value will be changed depending on whether the trace has mass or not.

Each trace is listed within its group. Groups of particle traces are listed as well. When a trace is selected from the list, it will change color in the Graphics window to provide a graphical indication of its location.

• Circular Grid: Specify a distribution of particle trace seed points using a circular grid.

The first value is the number of points in the circumferential direction. The second value is the number of points in the radial direction.

On the active cutting plane, define the extent of the grid by first clicking on the center of the circular grid, and then click again at the outer radius of the grid.

• Key In: Key in the exact X,Y, and Z coordinates. Separate each coordinate with a comma. These coordinates do not have to lie on the cutting plane. Hit the Add button

(The Remove All and Remove buttons delete all or just the selected seed points from the Point Field.)

Circumferential Radial


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11.8.1.2 Deletion of Particle Traces

Delete individual particle traces by selecting the trace from the list, and click the Delete button:

Delete an entire trace set by highlighting the group name and clicking the Delete button.

1. Select the desired trace to delete.2. Click the Delete button.

A trace with a considerably longer resi-dence time than the rest in the set will affect animation of the entire set. It will appear to animate very slowly followed by a very rapid animation of the others. Deleting this longer trace will make the animation appear much better.

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11.8.2 Attributes:

11.8.3 Massed Particles

By default, particle traces are the traces a particle without mass would take if it were released in the flow. A more physically real visualization technique is to include the effects of mass on the particle. The resulting trace will behave more like a physical substance within a flow system.

Massed particle traces are only drawn forward, not backward, so it is best to posi-tion the seed points near the inlet of the geometry.

Inertial and drag effects are taken into account, and if a particle has too much iner-tia to turn a corner, it will hit the wall. Massed particles will bounce when they strike a wall. They will also bounce when they strike a symmetry surface. The coefficient of restitution can be specified to control the amount of bounce in a collision.

• Show as Lines: Display the trace as a line. Adjust the width bigger to display rib-bons.

• Show as Points: Display the trace as points; Adjust the point size as desired.

• Not Shown: Toggles the visibility of the traces.

• Max Steps: Controls the length of the trace; 5000 is good for most, but for very finely meshed models, increase this value if traces stop mid-field.

• Start button: Starts and stops animation• Reset button: Causes the animation to

start back at the beginning when Start is clicked again.

• Animate Incrementally: Draws the trace as the animation occurs (unchecked and a “worm” crawls along the completely drawn trace).

• Color by Result: Displays active scalar quantity on drawn traces.


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There are several capabilities that allow a great deal of flexibility to the visualization of massed particles. The most basic is the ability to select units required quantities: particle density and particle radius. Other functionality include a user-prescribed initial path, the inclusion of gravity, and the ability to customize the drag correla-tion by modifying the coefficients.

These features are located in the Mass sub-tab of the Trace dialog:


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11.8.3.1 Units Options for Required Quantities

11.8.3.2 Coefficient of Restitution

Enter the density and radius of the parti-cle, and select the desired units for both quantities, respectively. The default den-sity is the fluid density, and the default radius is based on the bounding box of the model.

This coefficient of restitution is a measure of the amount of “bounce” between two objects. Specifically, it is the ratio of the velocities of the objects before and after an impact, and can be described mathe-matically as:

where V1 is the velocity of the first object, V2 is the velocity of the second object, and the i and f subscripts indicate initial and final velocity, respectively. In the case of massed particles, the other “object” is a static wall, so the equation reduces to:

The range of values of the coefficient of restitution is between 0 and 1. A value of 0 is an inelastic collision, and the particles stick when they hit the wall.

A value of 1 is a perfectly elastic collision, and particles have the same velocity (and kinetic energy) after the collision.

The default value is 0.5.

CV2f V1f–V2i V1i–--------------------=

CV2f

V2i-------=


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11.8.3.3 Initial Path

11.8.3.4 Gravity

11.8.3.5 Modifiable Drag Correlation

Check the Set Initial Velocity box to input an initial velocity and direction for the trace.

This allows the visualization of the interac-tion between the flow and a particle injec-tion with a known velocity and trajectory. An example is an aerosol injection of parti-cles into a flow stream.

Check the Enable Gravity for Massed Parti-cles to include the effects of body forces on particle traces. Enter the components of the force in the X, Y, and Z boxes.

For Earth’s gravity, check the Earth box, and enter a unit vector to indicate the direction in which gravity acts.

The drag correlation used for massed par-ticles is shown:

The coefficients a, b, and c can be modi-fied to effect the drag as appropriate.

Cd24Re------ a bRec+( )=


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11.8.4 Examples of Particle Traces

Massed particles with a Coefficient of Restitution value of 0 are shown on the left. The traces on the right have a value of 1:

Shown is an example of a rotating model with particle traces:

For Rotating Region analyses, select Relative Velocity from the Feature Tree to show particle traces in the relative frame. To do this, right click on Velocity Magni-tude from the Results branch, and select Relative Velocity. This will show the flow with the rotating velocity component subtracted out. An example is shown on the right above.

Particle Traces in the absolute frame. Particle Traces in the relative frame.


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11.9 Cutting Plane - Bulk Data

This feature quickly calculates and shows bulk-weighted results on a planar cutting surface. Bulk (mass-weighted) results are automatically updated as the active cut-ting surface is moved:

Notes:

• Volume Flow Rate is the product of velocity and area.• Thrust is the pressure integrated over an area (This is an area-weighted pressure. The pressure value produces a mass-weighted pressure value).• Velocity components are displayed by selecting Velocities.

1. Position the cutting surface at the cross section of interest.2. If a cutting surface divides a geometry in more than one location--resulting in multiple discreet regions, each region will be listed in the High-light Region drop menu. Select one to view it in the model.3. Select the desired variables and units to output. 4. The selected bulk quantities for all regions will be listed in the Output region.5. Optional: Hit the Save button to write results to a text file (.cvs exten-sion).

To obtain bulk data for multiple results sets while animating, hit the Save button. A text file will be saved with data for each result set or time step that is in the active animation set. (See the Review chapter for more details about animation.)

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• Bulk output files are saved in Excel comma separated variable (csv) format instead of a simple text format. This allows bulk output files to be readily opened into Excel for further results processing.

11.9.1 Bulk Output from Multiple Analyses

The Design Review Center (DRC) is an easy, powerful tool for assessing results from multiple analyses in a project. The DRC has now been extended to the Bulk calculator so that bulk data from multiple analyses can be saved to a single output file. When the DRC is active, click the Save button on the Bulk dialog. An Excel CSV file will be written that contains the bulk data from the active cutting plane for every active analysis in the project.

11.10 Cutting Surface - XY Plot

11.10.1 Creating a Plot

An XY plot can be created through points selected graphically on a cutting surface, through keyed-in points, or through points saved from a previous plot.


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1. Select the method of point selec-tion: Add by Picking, Add by Key-in, or Read from File.

To Add by Picking, click on loca-tions on the cutting plane through which the xy plot will pass. Points are shown in the Point List Region. (A minimum of two points is required.)

2. A title can be given to the plot using the Title field.3. The number of divisions in each data segment (a segment is between two entered points) is set to 20 by default, but can be changed if neces-sary.4. To create the plot, hit the Plot button.

To Add (points) by Keying In, enter X, Y, and Z coordinates (sepa-rated by a comma) in the field and hit the Add button. Points are shown in the Point List Region.

Point List Region

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11.10.2 The XY Plot

The resulting plot of the data will appear in a separate window:

The locations of points used in an xy plot can be saved to a file by clicking the Save Points button on the XY Plot dia-log

Once plot point locations are saved, an xy plot can be constructed using the point locations by clicking the Read from File bullet on the XY Plot dialog and clicking the Browse button.

A file selection dialog will appear prompting the user to select the appro-priate “xyp” file.

A plot through saved point locations can be constructed on an analysis different from the original model.


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There are several tools to modify the XY plot:

11.10.2.1 Changing the Plot Quantity

The plot quantity is selected from the Quantity pull-down menu:

This is the quantity plotted on the Y axis. The X axis quantity is the parametric dis-tance along the path between selected points.

11.10.2.2 Changing the Units on Axis Labels

The Y axis label of XY plots now shows the units of the dependent variable:

This adds clarity to the plot, and improves communication of CFdesign results with others.


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The units can be changed by right clicking anywhere on the XY plot, and selecting Units from the menu. Choose the desired units for the dependent variable from the list:

The Y-axis label will be modified to show the new label, and the Y-axis values will be converted to the selected units.

11.10.2.3 Changing the Axis Label Text

The labels for both axes can be changed by right clicking on the plot, and selecting either Change X-Axis Label or Change Y-Axis Label:


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A dialog will appear that allows new text to be entered:

Pressing the Set Default button will return the axis label to its default value.

The Display Min/Max Values box controls the appearance of the axis extremes. Unchecked, the min and max values will be removed from the label.

11.10.2.4 Changing the XY Plot Background Color

The plot background color can be changed from the default blue by right clicking on the plot, and selecting Background Color:


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This brings up the standard color selection tool:

Customize the color to make the plot easier on the eyes or easier to print.

11.11 Iso Surface

An iso surface is a surface of constant value of a quantity. Shown is an example of a velocity magnitude iso surface:

Iso surfaces are a three dimensional visualization tool that show a value as well as the physical shape of the flow characteristics. They are very useful for visualizing velocity distributions in complicated flow paths in addition to temperature distribu-tions in thermal analyses. Iso surfaces can be used to determine the locations of the maximum and minimum values in a model.


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The Iso Surface tab of the Results dialog task is shown:

11.12 Wall

The Wall tab of the Results dialog task provides a way to calculate flow-induced wall forces on wall surfaces of the model. Such forces are useful in many situations. Examples include assessing the hydrodynamic force on internal valve components for determining spring rate as well as calculating the lift and drag on aerodynamic bodies.

In addition, this utility calculates wall temperatures, pressures, heat flux, and film coefficients on walls. The torque about an axis as well as the center of force are also calculated.

1. Create iso surfaces by clicking the Add button. Iso surfaces are listed in the List region, and the high-lighted iso surface is controlled by the dialog.2. The iso quantity is changed by selecting from the Iso Quantity drop menu. This variable controls the shape of the iso surface. If it is different from the results selected on the Results Feature Tree, then an additional color legend will be dis-played.3. The iso surface can be colored by a different result than the iso quan-tity by selecting from the Color by Result drop menu.4. The value of the iso quantity is changed by moving the Value slider bar. This value can be manually entered in the field adjacent to the slider.5. Display vectors on an iso surface by checking the Show Vectors box.

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The Wall Results tab is broken into two sub-tabbed dialogs: Selection-and-Result and Output. The former is used for selecting surfaces and the desired calculation value. The latter displays the results.

11.12.1 Wall - Selection and Result Quantities

When this dialog is invoked, surfaces on the model will highlight when the mouse is hovered near them.

1. Select desired surfaces. Pickable surfaces are any wall surface as well as openings (inlets and outlets). The IDs of selected surfaces are shown in the List Region.

When the Selection Mode is Volume, vol-umes will highlight when hovered over, and can be selected. Note that the sur-faces belonging to the picked volume are actually be added to the selection list.

2. Groups of surfaces are selected from the Selection Basis menu.Note that the group must exist prior to running the last set of iterations. If not, simply run 0 iterations to force the model to re-pro-cess.

3. Select the quantities and desired units to output. Choices include Forces, Temperature, Heat Flux, Pressure, Film Coefficient, and Torque. (Description of each follows.)

4. Click the Calculate button.

Wall results are shown on the Output tab.

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(List Region)

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• Forces are the overall stress tensor--both pressure and shear are inte-grated over the surface. Force components and magnitude are output for each surface. Total force for all selected surfaces is also given. To remove very low wall pressures from the force calculation (which may indicate the on-set of cavitation), check the Cutoff Pressure box, and enter a mini-mum pressure value. All pressure values that fall below the Cutoff (on the selected surfaces) will be re-assigned to the cutoff pressure value for the wall calculation. (This cutoff does not affect the displayed results fringes or any other output quantity.)• For moving solids, the computed force and torque are the hydraulic val-ues, and do not include the effect of specified driving and resistance forces or torque as part of the Motion definition.• Pressure is the average pressure exerted by the fluid on the wall sur-face.• Temperature is the average temperature on the wall surface. Note that temperatures values from intermediate saved iterations or time steps are not accessible on the Wall dialog.• Calculated Heat Flux is based on the thermal residual from the heat transfer solution. Note that heat flux values from intermediate saved itera-tions or time steps are not accessible on the Wall dialog.• Film coefficient can be calculated in two ways: Enter a value for the reference temperature or use the near wall temperature at every wall node as the local reference temperature. The latter is done by checking the Use near-wall temperatures box.

If a reference temperature is entered, the film coefficient will be calculated based on the heat flux and the temperature difference between the speci-fied reference temperature and the wall temperature. If near wall tempera-tures are used, then the film coefficient will be based on the difference between the wall temperature and temperature at the closest non-wall (flow) node for every node on the wall.

• To calculate the Torque about an axis, enter the coordinates of one point on the axis of revolution in the Point on Axis group, and enter a unit vector that defines the orientation of the axis (in the Direction group). When Forces is selected, the wall forces, the center of force about each glo-bal axis, and the torque about the selected axis will be displayed.


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11.12.2 Wall - Output

To view calculated wall results, click the Output tab:

11.13 Settings

The Settings tab of the Results dialog contains numerous settings for customizing the display of scalars and vectors. Items such as the legend fringe range and the vector sizing are controlled here.

The requested values from the Selection and Result tab are dis-played on this dialog for every selected surface.

A Summary section lists the total quantities for all of the selected surfaces.

This data can be saved to an Excel csv file by hitting the Write to File button. The default extension of the file will be “csv”.

Hitting the View File button will prompt to select a previously saved wall results file. When selected, the contents of the file will be shown in the Output region.


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11.13.1 Settings - Scalar

• Fringe Range: Change the Minimum and Maximum values to modify the color range of the global result quantity (as selected on the Feature Tree). While the analysis, is running, check the User Specified box to modify these quantities.

• Set to Part is described below• Contour Lines control the display of

and the number of contour lines:• Filtering controls the display for a

given scalar range. Areas of the model that fall outside of the filter range will not be displayed.

• The Show Legend check box toggles the display of the color legend.

• The number of color bars in the color legend is controlled with the Legend Levels box.

• Hit the Apply button to implement settings.


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Part Dependent Legend Range

The legend range can be adjusted to span between the minimum and maximum values of the active scalar of a selected part.

1. On the Settings tab of the Results dia-log, click the Set to Part button.2. Click on the desired part in the analy-sis model.

Note that the Volume/Surface toggle must be set to Volume in order to blank vol-umes to gain access to internal volumes.

The legend range will change to corre-spond to the minimum and maximum val-ues found on the selected part. Additionally, the name of the selected part will be displayed on the Settings dialog

Click the Reset button to return the legend range to its default values.

This is especially useful for electronics assemblies in which the temperature pro-file through individual parts needs to be understood thoroughly.


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11.13.2 Settings - Vector

11.14 Dynamic Images: Design Communication

Traditionally, communicating analysis results was accomplished by creating numer-ous images in an attempt to convey the whole story to an audience (or a man-ager!). The creator of such images often has to create additional images once the intended viewer decides they want to see the results from a different orientation or they want to zoom in on a particular detail.

CFdesign takes Design Communication to a new level. With the introduction of the Design Communication Center and the Dynamic Image, CFdesign users not only share images, they can share the whole story. Unlike traditional bitmap, tif, and

• Attributes: Control the length of vec-tors with the Scale Factor. If the Scale Relative to Model box is checked, this value is between 0 and 1. Unchecked, and it can be greater than 1.

The Arrowhead size can be varied from 0 (no arrow heads) to as big as neces-sary. The default size of 1 is based on the average vector length.

• Clamping: Sets maximum and mini-mum cut off values for vectors. Vectors that fall outside of this range will be resized to the length corresponding to the maximum or minimum value, as appropriate.

• Filtering limits the display of vectors to only those that fall within the specified range.

• Same Length: If enabled, all vectors will be displayed as the same length. The slider bar controls this length.

• Hit the Apply button to implement settings.


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jpeg formats, a Dynamic Image can be navigated--panned, zoomed, and rotated. Dynamic Images can contain animation of transient results as well as animated particle traces.

Dynamic Images can be created, shared, and viewed very easily.

11.14.1 Creation of Dynamic Images (VTF Files)

After setting up a view that you want to share, click the Dynamic Image icon:

You will be prompted to enter a name and location of the file. The extension is “.vtf”.

11.14.2 Viewing Dynamic Images

Dynamic Images can be viewed in the Design Communication Center, in a CFdesign HTML Report, MicroSoft PowerPoint presentations, and Microsoft Word documents.

To view a Dynamic Image on a machine that does not contain a CFdesign installa-tion, it is first necessary to run the Design Communication Center installation. This file is called CFdesign-Communication-setup.exe, and is part of the CFdesign installation (located in the Design-Communication-Center subfolder of your CFdesign installation). It can be shared with anyone that wants to view Dynamic Images. It can also be downloaded from the CFdesign web site. This will install the Design Communication Center (the free viewer) and a few other files necessary for viewing Dynamic Images.

If CFdesign is installed on your computer, then all of these files can be found in the Design-Communication-Center sub-folder in your CFdesign installation folder, and it is not necessary to run the CFdesign-Communication-setup.exe file.


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Design Communication Center

Included in the CFdesign installation (Design-Communication-Center sub-folder) is a file called Design-Comm-Center.exe. Dynamic images can be viewed with this tool. This three megabyte file is a free viewer that can be given to anyone with whom you wish to share your results. Additionally, it can be downloaded from the CFdesign web site at www.cfdesign.com by following the links on the web site.

Images in the Design Communication Center can be navigated using the mouse (Left mouse button = pan, Middle mouse button = zoom, and Right mouse button = rotate). The integrity of the Dynamic Image is preserved in that display objects such as cutting planes cannot be moved or deleted.

CFdesign Report

The Review_Report dialog contains a template for the CFdesign Report. The layout of the report can be changed by using the right mouse-button menu for each item to change its visibility, with the Up and Down buttons to change the order of items and sections, and by adding additional text files and images.


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Dynamic Images that are named according to this naming convention will automat-ically be included in the report:

analysis name_g_image name

where analysis name is the name of the analysis (car, for example), and image name is whatever descriptive name you want to use. Be sure to separate the two names with the “_g_”.

Dynamic Images are automatically added to the Graphics section of the report. When the report is generated, an HTML document is created that includes the Dynamic Images:

To view a CFdesign report, you should have the Design Communication Center installed. (This is done automatically when CFdesign is installed). Use the CFdesign-Communication-setup.exe file to install it on other computers. This file is included in the CFdesign installation (Design-Communication-Center folder), and can be sent to anyone; additionally the file can be downloaded from the CFdesign web site.

CFdesign reports can only be viewed with Microsoft Internet Explorer. Care should be taken to ensure that your browser security settings will allow the ActiveX plug-in to display the Dynamic Images. If your images cannot be viewed from a CFdesign


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report, check the security settings of your browser. If Dynamic Images do not appear in your report, and you see the warning message shown in the following graphic, then click on the warning message, and select the option to allow content:

PowerPoint

Prior to adding an image into PowerPoint, add the CFdesign dynamic image macro. This adds a button into the PowerPoint menu, and makes adding images much eas-ier:

1. Start PowerPoint, and hit Tools-Add Ins. 2. Click the Add New button. 3. Browse to the Design-Communication-Center subfolder of the CFdesign installation, and select the add-in called ppt-dyn-img.ppa. This add-in uses a macro, so a warning will come up about macros.4. If the button does not appear, then you should reduce the security settings of PowerPoint.

To add an image to a PowerPoint presentation:

1. Click the CFdesign Image button in the PowerPoint menu:

2. A frame will be drawn in the presentation. Right click on the frame, and select Properties.


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3. On the Properties dialog, enter the name of the image in the FileURL field. Dynamic image files (files with the vtf extension) must reside in the same directory as the PowerPoint presentation.

4. The image will show when the Slide Show is presented.

Word

To add an image to a Word document:

1. Select View, ToolBars, and select Control Toolbox. 2. On the Control Toolbox dialog, select the More Controls icon:

3. From the list of controls, select GLView 3D Plugin, and position the frame in the document as appropriate.4. On the frame, hit the right mouse button, and select Properties.


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5. On the Properties dialog, enter the name of the image in the FileURL field. It is recommended that the dynamic image files (files with the vtf extension) reside in the same directory as the document file.

6. Click the Exit Design Mode button to view the images:

11.15 Design Review Center (DRC)

When the Results dialog task is invoked when a Project is open (instead of an anal-ysis), an additional dialog will appear below the Graphics Window:

This is the Design Review Center, and is used to view results from all the analyses in a project.

By setting up a view on one analysis and hitting the DRC-Compare button, all of the analyses in a project will be presented with the exact same view attributes. Using this dialog, one can flip from one analysis to the next manually, or hit the


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“Play” button on the VCR controls to automatically flip through all of the analyses. The beauty of this is that each analysis is presented with the same color legend scale and in the same manner--with the same cutting planes, iso surfaces, etc.

This is a great way to visualize results data from multiple design concepts, without having to create dozens (or even hundreds) of static images. Also, because each analysis is presented in the same manner, it eliminates having to set up multiple viewing panes on the screen and trying to make each one look the same.

More information about the Design Review Center is presented in the Projects chap-ter of this Guide.


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CHAPTER 12 Results to FEA Loads

12.1 Introduction

CFdesign results can be applied as boundary conditions for FEA analyses using sev-eral popular FEA tools: Nastran, Abaqus, Ansys, Pro/Mechanica, I-DEAS, and Cos-mos, as well as FEMAP. This capability showcases one of the strengths of the finite element approach, in that results can be shared across analysis platforms and used for subsequent calculations quickly and easily. The ability to transfer results to loads in this manner greatly strengthens the bond between flow and structural analysis, making for a more comprehensive and useful analysis suite. As a critical element in this suite, CFdesign allows flow analysis to be an integral part of the product design process.

Pressure and temperature results are interpolated onto the FEA model, meaning that the FEA mesh does not have to coincide with the CFdesign mesh. Most of the time, these two meshes will be very different, as required by the particular analysis tool. Additionally, the element types used in the FEA analysis do not have to be the same as in the CFdesign analysis.

This chapter discusses the procedure for converting CFdesign results to FEA bound-ary conditions. Specific details for each supported FEA tool are presented.

12.2 Procedure

Steps 1 through 4 need to be completed in the FEA tool. Steps 5 through 9 are per-formed in CFdesign. Step 10 is performed in the FEA tool.

1. Prepare the FEA geometry. The model geometry must be in the same position and orientation as the CFdesign analysis model.2. Build the appropriate finite element mesh for your structural analysis. The mesh does not have to have the same density or use the same element types as the CFdesign mesh. Only those regions critical to the FEA analysis have to be meshed.


Results to FEA Loads Transfer

3. Apply pressures or temperatures to the appropriate locations in the FEA model. The specified value does not matter-they will be overwritten with values calculated by CFdesign.4. Export an analysis deck. The type of file for each FEA tool is shown:

10. A new deck will be written with results interpolated to the appropriate bound-aries. This deck will have the words “_new BC” appended to the original name. Return to the FEA tool, and import the new deck. The boundary condition values will be the result values from CFdesign, and they will be interpolated to the new nodal and/or elemental locations.

FEA Tool Analysis Deck

Nastran .nas (or.dat)

Abaqus .inp

Ansys .ans (or cdb)

Pro/Mechanica No input file needed

FEMAP .neu

Cosmos .gfm

I-DEAS .unv

5. In the completed CFdesign analysis, go to the Transfer task

6. Select the FEA deck using the Browse button.7. Select the Results type to Map (pressure or temperature).8. Indicate if the direction of pres-sure should be reversed. (This is specific to FEA tools--some direct positive pressure inward, some out-ward.)9. Hit the Map Results to BC but-ton.

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12.3 FEA Details

12.3.1 Nastran• Nodal temperatures and elemental pressures are supported.• The output deck is the “.nas” or “.dat” file.• The converted deck from CFdesign has the words “_newBC” appended to its name.• Supported element types are:

• CTRIA (3 and 6 node triangles)• CQUAD (4 and 8 node quadrilaterals)• CTETRA (4 node and 10 node tetrahedra)• CHEXA (8 node hexahedra)• CPENTA (6 node prisms)

• When the converted deck is read back into Nastran, the new loads are added to the current load set.

12.3.2 Abaqus• Nodal temperatures and elemental pressures are supported.• The output deck is the “.inp” file.• The converted deck from CFdesign has the words “_newBC” appended to its name.• Abaqus files generated in Patran, Pro/E, FEMAP, I-DEAS, and Abaqus CAE are supported.• Supported element types include most of the 2D and 3D solid, contin-uum elements including:

• 3D Solid Elements: C3D4*, C3D6*, C3D8*, C3D10*• Axisymmetric Elements: CAX3*, CAX4*, CAX6*, CAX8*• 2D Plane Strain Elements: CP3E*, CPE4*, CPE6*, CPE8*• 2D Plane Stress Elements: CPS3*, CPS4*, CPS6*, CPS8*

• When the converted deck is read back into Abaqus, the new loads are added to the current load set.



12.3.3 Ansys• Ansys versions higher than 6.0 are supported.• The output deck is the “.ans” or “.cdb” file. Use the command “cdwrite” in Ansys to create an “.ans” file. This command is entered in the command line. The arguments are:

CDWRITE option, Fname, Ext

Use “All” for “Option”. Enter the filename with directory (if not the working direc-tory) for “Fname”. The default extension is “cdb”. Alternatively, enter “ans” as the extension.

• Nodal temperatures and elemental pressures are supported.• Supported Ansys element types:

• PLANE2, 13, 25, 35, 42, 55, 67, 75, 77, 78, 82, 83, 141, 145, 146, 162, 182, 183

• SHELL28, 41 , 43 , 57 , 63 , 93 , 131 , 132 , 143 , 150 , 157 , 163 , 181

• SOLID5 , 45 , 46 , 62 , 64 , 65 , 69 , 70 , 72 , 87 , 90 , 92 , 95 , 96 , 97 , 98 , 117 , 122 , 123 , 127 , 128 , 142 , 147 , 148 , 164 , 168 , 185 , 186 , 187

• Linear varieties of these elements are supported; additionally, 10-node tetrahedrals are supported. No other non-linear Ansys elements are sup-port.• The converted deck from CFdesign has the words “_newBC” appended to its name.• When the converted deck is read back into Ansys, the new loads are added to the current load set.

12.3.4 Pro/Mechanica• No input deck is required. An “.fnf” file with the same name as the anal-ysis is output automatically for every analysis based on a Pro/E geometry.• Import the “.fnf” file into your Pro/Mechanica model.• Temperatures and pressure are included in this file. • CFdesign will output two versions of the fnf file format: one that is com-patible with Pro/E 2001 and one that is compatible with Wildfire.



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12.3.5 FEMAP• FEMAP neutral file version 7.1 is supported• Nodal temperatures and elemental pressures are supported.• Supported element types are:

• 2 (3 node triangles)• 4 (4 node quadrilaterals)• 6 (4 node tetrahedra)• 7 (6 node prisms)• 8 (8 node hexahedra)• 10 (10 node tetrahedra)

• The output deck is the “.neu” file.• The converted deck from CFdesign has the words “_newBC” appended to its name.• When the converted deck is read back into FEMAP, the new loads are added to the current load set.

12.3.6 Cosmos/M• Nodal temperatures and elemental pressures are supported.• Supported element types are:

• 3 node triangles• 4 node quadrilaterals• 4 node tetrahedrals• 5 node pyramids• 6 node prisms• 8 node hexahedrals• 10 node tetrahedrals

• The output deck is the “.gfm” file.• The converted deck from CFdesign has the words “_newBC” appended to its name.• When the converted deck is read back into COSMOS, the new loads are added to the current load set.

12.3.7 I-deas• I-deas versions 9 and higher are supported.



• Nodal temperatures and elemental pressures are supported.• Supported element types are:

• 40 (plane stress elements) • 50 (plane strain elements) • 80 (axisymmetric solids)• 90 (thin shell elements) • 110 (3D solid elements)The output deck is the “.unv” file.

• The converted deck from CFdesign has the words “_newBC” appended to its name.• When the converted deck is read back into I-deas, the new loads are added to the current load set.

12.4 Transfer of Multiple Time Steps

The primary application of this is for transient (time-dependent) analyses in which results from many analyses are saved. This function provides a convenient way to export and convert each result set (or time step) to a separate FEA load set for a series of structural analyses.

By default, only the results from the last saved result set or time step are converted to an FEA load set. To convert all saved result sets to FEA load sets, add the follow-ing entry to your cfdesign_flags.txt file located in your CFdesign installation direc-tory:

load_xfer_all_res 1

With this flag entry set, follow the procedure described above to create an FEA deck containing a mesh and applied (dummy) loads and to map the results using the Load Transfer dialog in the CFdesign interface. A separate file containing the inter-polated results as loads for each time step will then be exported. Each file will fol-low this naming convention:

deckname_newbcs_t#.filetype

• deckname = the name assigned to the deck when it was saved from the FEA tool• filetype = the appropriate extension of the deck (could be “.inp,” “.ans,” “.nas,” “.unv,” “.neu,” “.gfm”)



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The conversion of results to Pro/Mechanica loads is not performed through this dia-log--a Mechanica “.fnf” file is saved automatically at the conclusion of every Pro/E-based analysis that contains solid materials. If the flag mentioned above is enabled, then a Mechanica file for each time step is automatically saved to the disk.




CHAPTER 13 Projects

13.1 Introduction

Most of the description in this guide has been about setting up, running, and post-processing an individual analysis. CFdesign has made this process very easy. In fact, if product design was accomplished with just one or two analyses, our work would be done. The reality of the situation however, is that design engineering requires many analyses and a great deal of information to attain that much sought-after final design.

Most “traditional” CFD tools are aimed at the dedicated analyst whose goal is often to complete one large-scale, complicated analysis at a time. CFdesign is different. CFdesign is a CFD package whose mission is to accelerate product development. It is a design tool, and is developed for the product design engineer that isn’t satisfied with completing just one analysis--the product design engineer might require one hundred analyses! The information learned from a single analysis is often not enough to design a product--information from a multitude of analyses is required.

This is why the concept of the project was introduced into CFdesign 6. A project is a collection of analyses--much like a CAD assembly is a collection of parts. The link between analyses in a project is a strong one, and one that makes setting up, run-ning, and post-processing a multitude of analyses a practical part of the product design process.

13.2 Definitions and Requirements

13.2.1 Definitions

An analysis is an individual simulation performed on a single geometric model. The preceding chapters in this Guide discuss the components of a single analysis: geometry, boundary conditions, mesh, materials, options, iterations, and results.


Projects

When the flow and/or heat transfer through or around an object is calculated, an analysis has been performed.

A project is a collection of analyses. The components that make up a single analy-sis can be shared with other analyses in a project. Projects provide a convenient means of staging a large number of analyses for simultaneous execution using the Fast Track Option (see the Analyze and Review chapter, Chapter 8). Projects fur-thermore simplify post-processing multiple analyses.

13.2.2 Requirements

All analyses in a project must reside in the same folder or directory.

Analyses are always created outside of a project, but are often set-up inside a project. The first component of an analysis is geometry, of course. It does not mat-ter if geometry comes from a CAD system or is a file in the working directory, it is the foundation of the analysis, and is always first read into a CFdesign analysis. Once an analysis is created, it can be set up and run as an individual analysis OR it can be brought into a project to be set-up and run.

13.3 Assembling a Project

13.3.1 Project Creation

There are two primary ways to create a project.

The first is to hit the New icon, select Project from the Browse window, and type in a name. The results will be an empty project.

The second method is to create a project from within an analysis. To do this, hit the Place Analysis In Project icon:

A browse window will appear prompting for the name of the project. After entering it and hitting the Save button, the project will be created. The analysis


Projects

Pro

jects

from which the project was created will be in the project. The Feature Tree will look something like:

When in a project, the project name is shown as the top branch of the Feature Tree. Each analysis is a sub-branch. The settings for each analysis (mesh sizes, boundary conditions, etc.) are listed as sub-branches for each analysis.

13.3.2 Adding Analyses to a Project

There are two primary ways to add an analysis to a project.

The first is to put an analysis into a project.

Starting from an analysis, click the Place Analysis in Project icon. This was described in the previous section as a way to create a new project from an existing analysis, but it is also a method to launch an analysis (contain-ing nothing more than geometry) into an existing project.

A common scenario for this command is something like this:

1. An analysis is run to completion. 2. While viewing results, a problem is identified, and a change to the design is contemplated. 3. Before returning to the CAD system, create a new project from this completed analysis using the Place Analysis in Project icon, and save the project using the Save Project icon.4. Shut down CFdesign, and return to the CAD system. Make the geomet-ric change, and launch back into CFdesign. 5. Create a new analysis.6. Hit the Place Analysis in Project icon, and select the project that was just created.

Project Name

Analysis Name

Analysis Settings


Projects

7. Now the project has two analyses, and the new analysis can be set up by read-ing settings from the first analysis (see the next section).

The second way is to bring an analysis into a project.

Starting from a project, hit the Add Analysis into a Project icon, and select an existing analysis from the browse window. The analysis can be completely set-up, or just contain geometry. This method is less convenient for bringing in and setting up analyses because it requires the user to leave the analysis, open the project and then bring in the analysis. The method described above is easier for assembling new analyses for set-up and running. This command is more useful for bringing in completed analyses, and assembling them for post processing. A typical scenario might look like:

1. Several analyses are run to completion outside of a project.2. Create a project by starting CFdesign from the Desktop icon or Start Menu, and hit the New icon. Select Project on the Browse window, and give the project a name.3. Hit the Add Analysis into a Project icon, and select an analysis from the browse window.4. Once in the project, the analyses can be opened using the Feature Tree (see the next section). Results from all of the analyses can be viewed using the Design Review Center (discussed in a later section in the chapter).

Note: Individual analyses in a project can be saved by hitting the Save Analysis icon. The entire project can be saved by hitting the Save Project icon. This automatically saves all of the analyses in the project as well.


Projects

Pro

jects

13.4 Managing Analyses in a Project

13.4.1 Opening an Analysis

All analyses in a project are listed in the Feature Tree. The analysis with the “+” beside its name is the open analysis. To open a different analysis, right click on its name, and select Open.

The open analysis is the active one, and it can be interacted with as if it were open as a single analysis outside of a project. Controls to set up, run, and view results can be applied to the analysis. When a different analysis is opened, the previous one is closed, and all settings and results shown are for the open one only.

Note: if an analysis is created from Pro/E and added to a project, only that analysis corresponding to the active Pro/E session can be meshed. If a different analysis is opened, it cannot be meshed. We recommend that on Pro/E models, the mesh be generated (run 0 iterations) prior to opening any other analyses in the project.

13.4.2 Sharing Settings Between Analyses

One of the major strengths of the project is the ability to share settings between analyses. All of the settings (analysis units, loads, mesh sizes, materials, and options) can be imported from a completed analysis to a new one simply by using the Feature Tree.

The open analysis


Projects

The new analysis (we’ll call it the target) has to be open. Right click on its Analysis branch in the Feature Tree, and hit Import Settings From. This will show a list of all

the other analyses in the project. Simply select the analysis that has the settings that are to be applied to the new one, and they will be applied automatically.

This settings transfer works best if the two analyses are topologically similar. Para-metric changes can exist between the two, but if the change was topological in nature (added or deleted geometric features), then some settings may not be applied automatically, and will have to be applied manually. An example is if a part with an assigned heat generation load was removed from the model. The heat gen-eration boundary condition would be lost from the model.

In this case and for the case in which an analysis is re-opened after geometric changes, any settings that are lost are now listed in a small dialog. The user can reassociate these settings to the model by selecting the geometric entity and then the setting from the list.

If settings are lost (either because a topological change eliminated some geometry or because of because the topology was changed too much), a “Show Lost” button will appear on the appropriate dialog (based on the type of settings that were lost):

The Show Lost button will only appear on a dialog if settings of the dialog type are lost.


Projects

Pro

jects

When the Show Lost button is hit, a window will come up listing the lost settings:

The number to the right of the setting indicates how many instances of the condi-tion were lost. Lost conditions can be applied to as many entities as desired, how-ever.

For lost mesh sizes, the type of entity the condition was applied to (volume, sur-face, or edge) will be indicated in the list.

To reassign a lost setting, first select the geometric entity (or entities) in the model. Select the setting from the list of lost settings. Hit Apply on the task dialog.

All lost lists will be cleared from the analysis when the analysis is saved.


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13.4.3 Changing the Order of Analyses in a Project

The position of an analysis within a project is changed by moving it up or down in the project. Do this by right clicking on an analysis, and selecting the appropriate action:

This affects the order of the analyses when the Design Review Center is invoked.

13.4.4 Removing an Analysis

An analysis can be removed from a project by right clicking on the analysis name in the Feature Tree, and selecting Remove from the menu. This will not delete the analysis from the disk, but will only remove it from the project.

13.4.5 Running Analyses in a Project

If an analysis is running, another analysis can be opened, and will appear in its cur-rent state. The running analysis will continue to run, although results and conver-gence information are not available for viewing until the analysis is opened again. When it is opened, the results and convergence information from the current itera-tion will be displayed.

In conjunction with the Fast Track option (described in the Analyze chapter, Chap-ter 8), projects can serve as a central hub for running multiple analyses. Each anal-ysis can be run on a selected analysis computer, and can be monitored from the project. To inspect the progress of an analysis, simply open it from the Feature Tree. That analysis will open in its current state, and can be interacted with while running. It will continue to run even when a different analysis is opened for inspec-tion.


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When finished, results from all the analyses can be viewed in a truly novel man-ner...

13.5 Viewing Results

In “traditional” CFD tools, examining results from a large number of analyses (assuming that a large number of analyses could be run) is a daunting chore. Often it requires setting up two, three, or four viewing panes on the computer screen and setting up the results view for each analysis in the same way. A great deal of time is often spent trying to show each model in the same orientation and with the same display entities and the same color legend range.

The alternative is not much better: Paper. Images are created and printed out, but again, a great deal of care has to be put into making sure that each analysis is shown in the same manner. The result is a great deal of time lost and a whole lot of paper. Now the design team has to lay all these images out on a large table and peruse them in search of the best design. This alone can be pretty time consuming.

CFdesign introduces a better way. The Design Review Center.

13.5.1 The Design Review Center (DRC)

When the Results task dialog is invoked in an analysis in a project, the Design Review Center controls appear below the Graphics window:

This simple dialog provides the ability to automatically apply a view from a single analysis to all the analyses in the project.

Instead of toiling over multiple results panes to create the same view or printing out a forest of paper, the Design Review Center makes it possible to view results from a multitude of analyses quickly and easily. It is called the “Design Review Cen-ter” because it acts like an engineering design review meeting. By presenting results from each analysis in exactly the same manner, everyone involved in the


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design process gets a good apples-to-apples comparison of the performance of every design alternative.

Set up the view with any of the results tools available--cutting planes, vectors, par-ticle traces, iso surfaces, etc. Click the DRC-Compare button. The project will enter the DRC mode. Use the slider bar on the DRC controls to manually flip between analyses. Use the “VCR” controls to automatically flip between analyses.

While in the DRC mode, the model can be navigated (panned, zoomed, and rotated). To change a display object (move a cutting plane, for example), hit the Reset button (Reset replaces DRC-Compare while in DRC mode) to leave DRC mode, and return to a regular interactive state with the analysis. The analysis that is shown when the DRC is turned off (by hitting the Reset button) will automatically be opened.

When the DRC is activated, the scalar fringe range on the current model will be applied to all analyses in the Project. This is done so that all analyses can be viewed with the same scale. When the DRC is reset, the scalar fringe range will not be reset to the extrema of the current analysis. To reset the scalar fringe range, hit the Settings_Scalar tab, and hit the Reset button in the Fringe Range group.

It is not necessary for geometric models to be the same for the DRC to work. It is not necessary for geometry to be in the same location, or to be the same size, or have the same orientation. The DRC applies to all analyses in a project that have results, and does not discriminate based on size, location, or orientation.

There are two things that should be the consistent across all analyses to be com-pared in the DRC:

• Each analysis should be run with the same length unit.• Each analysis should have the same result output quantities.

13.5.2 XY Plotting

An XY plot over a path can be created for all analyses in a project. Create the plot on the active analysis, and start the DRC. Curves will be added to the plot showing results along the same path for each analysis in the project. A legend on the plot indicates the analysis for each curve.


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13.5.3 Bulk Results

Bulk Results on a cutting plane are shown for each analysis in the DRC. To view the results, create and position a cutting plane, and switch to the Bulk tab (under Cut-planes). Start the DRC. The Bulk results text information will update as the DRC scroll bar is manually dragged between analyses. The text information will not update if the frames are animated using the VCR play button.

13.5.4 Selecting a Specific Result Set/Time Step

If an analysis has multiple saved results sets or time steps, by default the last set will be viewed in the DRC. To select a different set to view, go into the Results task, and right click on the Results branch of that feature tree. A menu will appear show-ing all the saved results sets and time steps:

Select the desired set from the list. Results from the selected set will be displayed immediately, and when the DRC is invoked. This can be done for any analysis in the project. The selected result set will be remembered, even when a different analysis is opened.

13.5.5 Removing an Analysis From the DRC

By default all analyses in a project will be shown when the DRC is invoked. To pre-vent an analysis from being part of the DRC, right click the Analysis name, and select “Remove from DRC” from the menu. To include it again in the DRC, select “Add to DRC” from the right mouse button menu.


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13.6 Design Review Server

The Design Review Server is an innovative union of Fast Track and the Design Review Center. Fast Track is a system that distributes analyses to remote comput-ers for running multiple analyses concurrently; as discussed, the Design Review Center allows direct results comparison of multiple analyses in a consistent, easy-to-use environment.

The Design Review Server distributes the results processing of analyses in a project across available networked computers. Instead of opening and computing the results visualization for every analysis on a single machine, the Design Review Server transfers completed analyses to networked computers for computation of the “data model.” This spreads out the computational burden of opening the analy-ses and computing the results visualization. The end result is a convenient way to compare analysis results from numerous large analyses.

13.6.1 Set Up

The Design Review Server relies on computers on the same network, and is config-ured in the same manner as Fast Track. For a computer to be accessed by the Design Review Server, it must satisfy all of the requirements to be a Fast Track Analysis computer:

• The software must be installed and licensed.• The CFdesign Server Manager (cfdserv9.exe) must be running.


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• Each remote computer must be listed in the server.cfg file of User’s Interface computer. • The Interface and remote computers must be on the same subnet, and on a Windows network. Novell networks, etc. are not supported.

If the conditions listed above are met, the Design Review Server will be enabled by default. To disable the Design Review Server, add the following entry to your cfdesign_flags.txt file:

CFDESIGN USE_VIZSERVER 0

13.6.2 Distribution of Analyses

Most of the functions performed by the Design Review Server are transparent to the user. The only user interaction is to assign analyses to available Design Review Server computers on the network.

When a project containing completed analyses is either opened or an analysis is added, a dialog will open that lists the available Design Review Server computers as well as the analyses in the project. Existing analysis computer assignments are listed (either from previous assignments or from their last Fast Track run). The amount of memory on each computer is shown to assist in making new assign-ments or modifying existing ones.

The dialog and usage are shown:

• To assign an analysis to a different computer, drag its name and drop it onto the desired computer.• To assign all analyses to the local machine, click the Reset to Local button.• When all assignments are made, click the Open Project button. This will automatically distribute the display model for each analysis to the assigned computer.• Check the Save Server Assignments box to store the assigned com-puters.• The Cancel button will assign all analyses to the local machine and close the dialog.


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13.6.3 Launching the Design Review Server

The specific scenarios that cause this dialog to open are described. Note that the term “finished analysis” refers to an analysis with results.

Open a project with two or more finished analyses. The Configuration dialog will open, and default assignments are shown. (These are either saved assignments or the original Analysis computer of the analysis.) Change assignments as neces-sary based on required memory and available memory on each machine.

From a project with one or more finished analyses, add a finished analysis. The Configuration dialog will open, and the existing assignments will be shown. The new analysis will be assigned to its analysis computer, but can be reassigned as appropriate.

From a project with two or more finished analyses, add a a new analysis. The Configuration dialog will open to allow assignment of the finished analyses. The new analysis will not be listed on the Configuration dialog, but is assigned by selecting the desired Analysis Computer on the Analyze dialog.

From a finished analysis, place into a project with one or more finished analyses. The default assignment will be the analysis computer, but can be reas-signed to a different available computer. Other assignments can be changed if nec-essary.

From a new analysis, place into a project with one or more finished analy-ses. The saved assignments for the completed analyses will be listed on the Config-uration dialog, and can be modified. The new analysis will not be listed in the Configuration dialog, but is assigned by selecting the desired Analysis Computer on the Analyze dialog.

13.6.4 Fast Tracked Analyses

When an analysis is run on a Fast Track machine, the results visualization is com-puted on that machine as well. In previous versions of CFdesign, the display view was computed on the local machine based on data sent back from the Solver machine. This change is a by-product of the architecture of the Design Review Server, and is more efficient, and better leverages the resources of the Solver machine.


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When an analysis is run on a Fast Track machine, the machine assignment (set on the Analyze dialog) is stored, and is the default Design Review Server assignment if that analysis is opened within a project.


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CHAPTER 14 Analysis Guidelines

14.1 Introduction

This chapter presents guidelines for various types of flow analyses. While the previ-ous chapters in this Guide discussed the general operation of the software, this chapter discusses some of the specific physical details of various flow conditions. The suggestions offered should be used in conjunction with the Examples Manual. The following analysis types are discussed:

• Internal and External Incompressible Flows• Basic Heat transfer (conduction and convection)• Porous Media Flows• Multiple Fluids• Boundary Layer Flows• Periodic Boundary Conditions• Transient Flows• Height of Fluid• Moist/Humid Flows• Steam/Water Flows• Radiation Heat Transfer• Solar Heating• Internal and External Compressible Flow• Joule Heating• Motion Analyses

Note that the first six items make up the “Basic” configuration. The “Advanced” configuration is made up of the next eight items. The “Motion Module” is required for Motion analyses. (The Advanced configuration is a pre-requisite for the Motion Module.)


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14.2 Incompressible Flows

14.2.1 Internal Flow

Internal flow is a very general category which describes the flow of a fluid that is contained by and passes through a solid structure. There may be one or several openings through which fluid enters and leaves the device. The solutions to internal flow problems are among the most difficult to achieve in “typical” CFD (CFdesign is hardly typical!), particularly for turbulent and compressible flows with complex geometry. The reason is that there are often several flow regimes throughout dif-ferent regions of the device, and hence the mathematical characteristics vary widely through the calculation domain.

CFdesign has several tools to aid convergence for a wide range of internal flow problems. These tools include the Automatic Turbulent Start-Up algorithm, Auto-Convergence Control, and Auto-Stop. These algorithms work to prevent solution instability or divergence, particularly in the early iterations.

Notes regarding incompressible internal flow:

1. Mesh Density in Gaps: When using any turbulence model there should be at least five elements across inlet and outlet passages so that gradients can be prop-erly resolved. Mesh Enhancement automatically ensures that this criteria is met.2. Mesh Refinement: It is good practice to refine the mesh near openings so that the boundary conditions correctly influence the flow in the interior. Generally Automatic Mesh Sizing ensures this requirement is satisfied, but if not, the mesh should be adjusted.3. Outlet Configuration: At the outlet, where a uniform pressure is commonly applied, there must not be any flow features which will conflict with this uniform pressure boundary. Additionally, the flow should be approximately normal to the


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plane of the outlet. Sometimes the boundary must be extended to achieve this result. The following figure illustrates these concepts.

4. Outlets at Corners: Pressure boundary conditions should not be specified on surfaces that meet at a corner. This often causes flow recirculation zones that can lead to analysis instability. It is not physically possible to maintain the specified pressure uniformly over all surfaces of a corner. The work-around is to extend the opening and to apply the boundary condition to only one surface of the extension. 5. High Speed Jet: For flow situations in which a small, high speed jet of fluid is blowing into a relatively large region filled with fluid, it has been found to be helpful to change the Turb/Lam Ratio to 1000 or greater (the default is 100). This control is accessed with the Turbulence button on the Options dialog task. An alternative approach is to change the turbulence model to the Low Reynolds model. This will resolve both the high and low levels of turbulence throughout the domain.6. Pressure drop prediction of flow in a long straight pipe: When the pres-sure drop is caused by shear losses along the pipe walls instead of form drag due to obstructions, the following technique should be used to calculate an accurate pres-sure drop:

• Use an entry length of approximately 25 pipe diameters upstream of the test section. This is to ensure fully developed flow at the entry of the test section.• Use symmetry to reduce overall model size, if possible.• Apply a surface mesh size to the pipe wall such that there are eight nodes for every 90 degrees of arc. Apply a volume mesh size to the pipe that is two times the surface mesh size.• On the Mesh Enhancement dialog, select Automatic Layer Adaptation.• On the Analysis task dialog, click the Solution Control button, click the Advection button, and select ADV3.


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• Also on the Solution Control dialog, click the Advanced button in the Intelligent Solution Control group. Move the slider to Tight. These analyses require more iterations to converge than models with form drag.• Run the analysis at least 600 iterations.

7. Internal Fans with fan curves: When a fan curve is used to describe an internal fan material object, it is recommended to apply convergence control to pressure if Auto-Convergence is not enabled. This will allow the solver to match the correct flow rate from the curve to the system pressure drop in a stable manner. When this occurs too quickly, the flow rate produced by the fan may oscillate which in turn causes the system pressure to change too quickly. Additionally, if the inter-nal fan is causing instability, refine the inlet and outlet surfaces of the fan part. 8. Low Pressure Limit: CFdesign provides a numerical solution of the Navier-Stokes (N-S) equations. The N-S equations assume that the fluid can be treated as a continuum, and this assumption becomes inaccurate as the characteristic dimen-sion of the flow path drops below 10 times the mean free path of the fluid. The Knudsen number (Kn) is the ratio of the mean free path to the characteristic length.

• Kn < 0.01: The N-S equations are accurate without any special treat-ment.• - 0.01 < Kn < 0.1: The N-S equations can be used in conjunction with slip-wall boundary conditions.• - Kn > 0.1: The N-S equations no longer apply because the fluid cannot be considered a continuum. This regime is often called molecular flow or rarefied gas flow, and other equations and techniques are required. Physi-cally, the regime occurs primarily with high-altitude flight, strong vacuum applications, and flow through very small passages (such as in MEMs appli-cations).

9. Bivarient non-Newtonian setup: To properly set up a bivarient non-Newto-nian Fluid, you first need to curve fit your data to fit the following model:

ln( )=A1 + A2ln( ) + A3T + A4[ln( )]2 + A5[ln( )]T + A6T2

When curve fitting data, ensure that the resulting surface is well defined beyond the extremes of the data set. This is typically difficult with natural logs in the equation without the addition of artificial (non physical) data points added to the original data set.

With the data set in metric units, a linear regression can be performed using each multiplier of the equation to determine the coefficients for input into CFdesign. For example in Excel, create columns for the natural log of the viscosity in Pa-s, the natural log of the shear rate in inverse seconds,

µ γ γ γ


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the temperature in C, the natural log of the shear rate in inverse seconds squared, the natural log of the shear rate in inverse seconds multiplied by the temperature in C, and the temperature in C squared. Use the add-in for data analysis and select Linear Regression with the y value as the first col-umn, and the x values as the remaining columns. The six coefficients will be output.

14.2.2 External Flow

External flows are characterized by a solid body immersed in fluid that is moving relative to the body. Nearly all engineering aerodynamic problems are external flows. Examples include noise generated by a car mirror at highway speeds, the drag on a motorcycle fairing, and the lift on a missile. Additionally, wind tunnel models are usually considered external flows.

These problems generally require the greatest number of nodes of any CFD calcula-tion since the velocity and pressure boundary conditions applied at the exterior of the flow domain must not affect flow features around the immersed body.

1. Calculation Domain Size: Generally, the exterior or “far-field” boundary must be at least 5 to 10 chords upstream and 10 to 20 chords downstream of the body. Higher Reynolds number flows will require far-field distances in the upper portion of this range.2. Meshing Strategy: It is important to transition the element sizes in the mesh quite substantially to conserve nodes. It is common for elements on the body sur-face to be several thousand times smaller than elements at the far-field. Lift and drag forces calculated by CFdesign will be dependent upon the mesh size near the body. Transitioning must be smooth for solution stability and accuracy, as described in the Meshing chapter and care must be taken to avoid creating tetrahedral ele-ments with very high aspect ratios. Sometimes embedding fluid volumes around the object of interest is very useful for concentrating many elements around it. This “Russian Doll” approach helps transition the mesh from very small elements around the object to larger elements further away from the object.3. Boundary Condition Placement: For incompressible and subsonic compress-ible flow problems with subsonic inlets, velocity and pressure boundary conditions are applied on the far-field boundary as shown in the following figure. To aid con-


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vergence, it is useful to specify the velocity boundary condition around a greater portion of the flow domain than for pressure, as shown in the following figure:

Apply slip conditions to any surfaces that are not openings unless the boundary layer or ground effects are of interest against the wall.

4. Convergence: Note that convergence will often be slow, and the monitor will show relatively flat lines well before the flow field is fully developed around the body. Subtle differences in the pressure distribution may not be visible by only reviewing the convergence monitor. This is why it is recommended to adjust the Automatic Convergence Assessment to Tight when running external incompressible analyses.5. Accuracy of Drag Calculation: CFdesign has been used to calculate the drag on aerodynamic bodies with a very high degree of accuracy. Such drag is due almost entirely to form drag. Such calculations can be very sensitive to the applied conditions in the model, and care must be taken to represent the physics as care-fully as possible. This sensitivity is not unique to CFdesign, but is inherent to all CFD tools. Some suggestions to improve accuracy of the drag calculation include:

• The region around the object must be meshed with a very fine mesh. More streamlined bodies require the mesh near the stagnation point of the body to be highly refined to capture the rapidly changing coefficient of pres-sure.• Change the turbulence intensity to 0.01 (from the default of 0.05) for wind tunnel analyses. This will more accurately represent the conditions in an actual wind tunnel.• Reduce the turb/lam ratio to 10 (from the default of 100). • Use the ADV 3 advection scheme.


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• Enable Automatic Layer Adaptation.• Use the K-epsilon turbulence model for the first 1000 iterations, and then switch to the RNG model for an additional 1000 iterations.

6. Altitude Effects: To simulate the effect of altitude, we recommend that you consult tables of atmospheric data to identify the static pressure and temperature based on a geometric and/or geopotential altitude. From the pressure and temper-ature, the density of the air can be computed and specified as a constant property. If properties are held constant (hence you are not solving for compressible or ther-mal effects) the density is the only parameter that needs to be modified on the Material Editor. Keep in mind that the actual effect that is simulated at different alti-tudes is that of the Reynolds number.

14.3 Basic Heat Transfer

This section discusses conduction and the different types of convection. Radiation is discussed in a subsequent section in the “Advanced” part of this chapter.

There are several variations of heat transfer analyses that can be performed using CFdesign. They include: conduction, natural convection, forced convection and mixed convection. Some of these can occur together in the same analysis. For example, conjugate heat transfer includes both convection through a fluid and con-duction through a solid. The following discussions present information about per-forming each of these types of heat transfer analysis.

14.3.1 Conduction

A conduction heat transfer analysis can be performed on fluid materials, solid mate-rials, or a combination of both. For all cases, the correct properties (particularly thermal conductivity) are necessary. Be sure to define the material properties on the Material dialog task. Also, select Laminar from the Options_Turbulence dialog. This will ensure that the correct conductivity is used in the fluid.

On the Options dialog, you should turn Flow to Off and Heat Transfer to On. Click the Turbulence button, and turn turbulence Off (on the Options dialog). This will use the laminar conductivities of the materials in the model. Additionally, the tem-perature convergence should be set to 1.0 on the Solution Control dialog launched from the Analyze task (it is by default). If the material properties are not varying with temperature, the analysis should only require 10 iterations to converge.


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14.3.2 Natural Convection

Natural and free convection flows are largely dominated by buoyancy forces. The buoyancy forces are generated by density gradients which vary primarily with tem-perature since pressure gradients are relatively small in these flows. Natural con-vection flows may be laminar or turbulent depending on the Grashof number associated with the flow. The Grashof number is defined as

where g is the local acceleration of gravity, is the thermal coefficient of volume expansion, L is a characteristic length of the surface in the direction of gravitational acceleration, is the temperature difference between the heated surface and the undisturbed fluid and is the kinematic viscosity.

The Grashof number is a measure of the ratio of net buoyancy forces to viscous forces. Transition to turbulence occurs at around .

Some prefer to use the Rayleigh number to characterize the flow. The Rayleigh number is the product of the Grashof and Prandtl numbers. The Prandtl number is defined as

For most gas flows, .

1. Calculation Domain: For fully-enclosed mixed or natural convection flows, construct a box (the calculation domain) around the device. The box should be wide enough so that the flow is not artificially accelerated. (If the side walls are too close to the heated object, the flow may accelerate as in a nozzle). The top of the box should be farther away than the base to allow for eddie currents downstream of the object as the hot air rises. A good guideline for the size of this box is a height 10 times the vertical dimension of the device, and a width and depth that are 5 times the respective width and depth of the device. 2. Boundary Condition Placement: Apply a pressure (of 0 gage) and a temper-ature to the top surface of the air domain, and leave the bottom surface a wall. In addition, apply a temperature or a low convection coefficient value to the sides of the box. This approach will produce correct flow and temperature patterns near the object if the domain is large enough, even though in reality air may come from all directions, not just the top.

Gr gβL3 T∆ν

--------------------=

β

T∆ν

Gr 4 108×≈

PrµCp

k----------=

Pr 1≈


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3. Alternative Boundary Condition Placement: Apply a constant pressure to the top and bottom openings of the domain, and a temperature to the bottom. In most cases, air will flow in through the bottom-most opening (hence the applied temperature), and out through the top-most opening. The surrounding surfaces should be left as walls or have an applied slip condition.4. Need for a Specified Temperature: It is very important that a temperature be specified somewhere in the model (in addition to the known heat loadings). This can be an applied temperature boundary condition, but can also be the reference temperature for a film coefficient or radiation boundary condition. Without a speci-fied temperature somewhere in the model, the temperature solution will not con-verge. 5. Need for a Specified Pressure: For some complicated geometries, it has been found that a specified pressure somewhere in the model considerably helps convergence as well. If possible, specify pressure on an outer solid surface, or on some location that fluid cannot pass through. If no such convenient location exists in the model, apply pressure AND a zero value velocity condition to some external surface.6. Convergence: While an external natural convection analysis is running, the temperatures will often initially climb quite high (because the air is still moving very slowly) and then will settle back down as the flow field develops. Natural convection analyses usually require more iterations than internal flow problems to reach a steady-state solution. The number of iterations required, and hence the total solu-tion time, will be longer for a natural convection than for a pressure-driven flow analysis. Solution progression is slowed by the fact that buoyancy forces are gener-ally significantly larger than pressure forces.7. Convection with Liquids: Because a larger temperature gradient is required to cause buoyancy-driven movement in liquids, overall solution times can be reduced by first inducing a temperature gradient through the fluid prior to running the flow and thermal analysis. Do this by running 10 iterations thermal only (with-out flow). After a thermal gradient is achieved, flow and thermal should be run simultaneously.8. Meshing: When defining the mesh for buoyancy-driven analyses, more ele-ments will be required in the interior of the domain (away from the solid bound-aries) than for a pressure driven flow. The reason is that accurate representation of the small density gradients is critical to computing the driving buoyancy forces cor-rectly.9. Analysis Setup: Some basic guidelines for setting up a natural convection analysis include:

• Be sure to select a property with Buoyancy on the Material task or select Equation of State as the density variation in the Material Editor.


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• On the Options dialog, be sure to set Heat Transfer to On and to set a Gravity vector. • In the Options_Turbulence dialog, it may be necessary to set the Turb/Lam Ratio to a higher value, at least 2-5 times the default. Alterna-tively, use the Low Reynolds turbulence model.• It is also helpful to initialize the temperature field to a value close to what is expected. Do this by applying the initial temperature on the Initial Conditions tab of the Loads task dialog.• Adjust the Automatic Convergence Assessment slider to Tight.

14.3.3 Forced Convection

If the heated or cooled air is being blown (by a fan, for example) through the solu-tion domain, this is usually forced convection. In forced convection heat transfer, the temperature does not influence the fluid material properties.

For this reason, the energy equation can and should be solved alone (Flow is Off on the Options window) after the flow solution (velocity, pressure) has converged. The problem with running flow and thermal together is that the thermal solution will evolve very slowly due to the very small time scale required for the flow solution. The thermal solution will converge much slower if run concurrently with flow. When run separately, a larger time scale is used, and the thermal solution will typically converge very rapidly.

As with the conduction heat transfer analyses, ten thermal-only iterations are typi-cally sufficient for thermal convergence.

Note that you should not specify a gravity vector for forced convection analyses (leave the gravity components set to 0).

14.3.4 Mixed Convection

In some heat transfer analyses, the heated or cooled air is blown but may contain local temperature gradients that will cause some appreciable buoyancy effects. This type of heat transfer is known as mixed convection, since it has features of both natural and forced convection. There is not a good way to tell prior to the analysis if the heat transfer is mixed or forced. To check, you should run a mixed convection analysis after the forced convection analysis is finished. The steps required are:


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1. Get a converged flow solution with Thermal set to Off on the Options window and constant fluid properties on the Materials dialog.2. Turn Flow to Off, and turn Heat Transfer to On on the Options window and run 5 iterations.3. Set Flow to On, keep Heat Transfer On, and set the Gravity vector on the Options dialog. Select a fluid property with Buoyancy in its name from the fluid property data base or choose Equation of State for the functional form for density. For the latter, set the appropriate parameters for this functional form.4. Run 25 - 50 more iterations and examine the results for changes.

Many electronic cooling applications are in the mixed convection regime. The above steps are recommended for these analyses. Temperature results should be reviewed carefully after step 2 to ensure that unrealistically high temperatures have not been predicted. This is generally an indication that buoyancy effects are significant. In this case, continue on to step 3, BUT choose the previous iteration from the Starting At menu on the Analyze dialog to start the thermal solution from a constant temperature field instead of the unrealistic values.

14.3.5 Conjugate Heat Transfer

For conjugate heat transfer analyses, the solid material conduction and the fluid convection are analyzed simultaneously. For this type of analysis, the type of fluid convection (natural, forced or mixed) determines the analysis parameters. For forced convection, you should again get a converged flow solution and then run the forced convection analysis with the flow turned off for a few more iterations. If the fluid convection is natural convection, you need to run the thermal equation analy-sis with the flow turned on for all iterations. For mixed fluid convection, follow the steps outlined above.

14.4 Porous Media Flows

Multiple obstructions in a geometry (holes in a baffle plate, for example) can conve-niently be modeled using distributed resistance (porous media) materials. This eliminates the need to mesh around every finite obstruction, thereby resulting in a more efficient mesh.

Assign a distributed resistance material to a part by selecting the part and indicat-ing the through-flow and cross directions. If such a material does not exist, create


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one using the Material Editor. In the Material Editor, the through-flow and cross-direction resistances are required, as is the thermal conductivity. If the object that is being represented with distributed resistances has a different thermal conductiv-ity than the surrounding fluid, enter that value in the Material Editor as well. An example of such a situation is air through a porous ceramic filter. The ceramic material has a different conductivity from that of the surrounding fluid, and that is entered as a property of the material.

There are 5 ways to enter flow resistances for these obstacles:

14.4.1 Constant K-factor approach

A good reference for calculating or estimating K-factors is: Handbook of Hydraulic Resistance, 3rd edition by I.E. Idelchik, published by CRC Press, 1994 (ISBN 0-8493-9908-4). To use this data, enter the value of the loss coefficient as K.

If measured data for pressure drop versus flow rate is available, this can be used to calculate the K-factor. This is done using the following equation:

If you know the pressure drop, the velocity, and the density, you can back out the value of . Enter this value for K.

In many situations, the loss in one direction will be significantly less than the loss in the other two directions. To represent this, enter the calculated or estimated loss coefficient for the through flow direction and some value four or five orders of mag-nitude higher in the cross directions. This will allow the flow to go in the desired direction, and impede it in the other directions.

The Permeability value can be specified in conjunction with the Constant resistance method as well as the Friction Factor method. This allows a resistance to be speci-fied in the form:

Where is the viscous resistance term, which is the reciprocal of permeability.

The value of permeability is required in the resistance Material Editor, and is used in the pressure drop equation in the following manner:

∆P ζiρui

2

2-----=

ζ

P1 P2– αµVL ζρV2

2------------+=

α


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where is the value of permeability. The unit of permeability is the Darcy, and is expressed in terms of length squared.

The term (in the above equation) is the standard loss coefficient.

The combined pressure drop equation is then:

Where:

• is the permeability, in units of length squared.• V is the velocity• L is the length over which the resistance acts• is the viscosity• is the loss coefficient• is the fluid density

The value of permeability specified for one component is automatically applied to the other components.

14.4.2 Friction Factor Approach

In this method, the pressure drop is expressed as:

where f is the friction factor and DH is the hydraulic diameter of the obstructions. Both of these values must be entered as material properties.

The friction factor can be calculated in one of two ways:

In the first method, the friction factor is calculated with the Moody formula. The obstruction roughness height must be entered in the correct length units.

In the second method, the friction factor is determined from:

α 1κ---=

κ

ζ

P1 P2– 1κ---µVL ζρV2

2------------+=

κ

µζρ

∂p∂xi------- f

DH-------Lρ

ui2

2-----=


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where Re is the Reynolds number based on the hydraulic diameter of the obstruc-tion. If this method is chosen, the values for a and b are required. For this case, note that the friction factor is dimensionless but the hydraulic diameter should be entered in the correct length units.

Note that for both methods, the hydraulic diameter and the simulated pipe length are required properties of the material.

14.4.3 Free Area Ratio

To represent a perforated plate or a baffle that has a known open (free) area, use a free area ratio. The free area ratio is the ratio of the open area to the total area of a perforated plate:

A value of 0 represents a completely closed direction. Enter a free area ratio for each component direction.

14.4.4 Pressure-Flow Rate Curve

A head capacity table controls the flow rate based on the calculated pressure drop.

14.4.5 Darcy Equation Approach

A permeability can be input using the Darcy equation. Unlike loss coefficients which have different resistance values in the three directions, a permeability provides a constant resistance in all directions. An example is a packed bed of stones.

where C is the viscosity coefficient, is the viscosity (of the surrounding fluid) and ui is the velocity in the global i coordinate direction.

f aRe b–=

fAopen

Atotal-------------=

p∂xi∂

------- Cµui=

µ


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To represent a porous media, select Permeability from the Variation pull-down menu, and enter just the value of the permeability, , as shown in the following equation:

The units of permeability are length squared.

Note that the length over which a permeability acts must be represented accurately in the geometry. The reason is that the Length term in the above equation is deter-mined from the meshed geometry. Unlike the loss coefficient (K) variation method, the length over which a permeability acts is not divided out of the equation.

14.5 Multiple Fluids

CFdesign has the ability to handle multiple fluids in one model. Note that fluids with different materials cannot come in physical contact with each other unless one or more is a distributed resistance. Non-distributed resistance fluids can be connected thermally (separated by a solid material).

To implement multiple fluids into an analysis, assign the fluids as appropriate, ensuring that no fluids come in contact.

Examples where this is useful include an air-water heat exchanger or flow blown over a sealed electronics component box. In the latter example, natural convection might be important inside the sealed box, and forced convection may play a role outside the box.

Note that a pressure boundary condition must be set in all fluid regions. For a totally enclosed area with no inlets or outlets, it is a good idea to specify the pres-sure on at least one surface somewhere in the enclosure. If necessary, specify a 0-value velocity to the same surface to prevent it from being treated as an opening. This will decrease the analysis time significantly.

κ

P1 P2– 1κ---µVL=


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14.6 Boundary Layer Flows

Boundary layer flows are performed in a fashion similar to external flows with one important exception. Since the pressure field is generally uniform throughout the domain in these types of flows, the nodal pressures must be initialized to the same value (usually zero) and not updated during the calculation. The solution relaxation for pressure must be set to zero to maintain the initial pressure field.

Note that there will be finite , and terms in the governing flow equations since “intermediate” pressures are used in their computation. “Intermediate” refers to a point in the middle of a sequential solver iteration when pressure gradients are established to conserve mass. At the end of each sequential solver iteration, these pressure gradients will not be present since pressure relaxation is set to zero.

14.7 Periodic Boundary Conditions

Periodic boundary conditions (cyclic symmetry) enable users to model a single pas-sage of an axial or centrifugal turbomachine. It is not a sliding mesh implementa-tion (like the full rotating device), but will capture the flow within the blade passage. Periodic boundary conditions can also be used to simulate non-rotating devices such as a single blade passage through a stator cascade.

For such an analysis, only a single blade passage is modeled. Additional volumes are added to the inlet and the outlet of the model. These should be distinct volumes from the blade passage as they do not rotate. Periodic boundary conditions are always applied in pairs, typically to surfaces on the inlet and outlet extensions that are not walls or openings.

Note that models containing periodic boundary conditions cannot be remeshed and continued from a saved iteration. If the mesh is changed, the model must be started from the beginning (iteration 0). This is due to the nodal reorganization that occurs at the onset of analyses containing periodic boundary conditions.

14.7.1 Boundary Conditions

The sides of the extensions must be translated or offset from each other in the same manner. For example, if the sides of the inlet extension are rotated 30

∂P∂x------ ∂P

∂y------ ∂P

∂z------


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degrees from each other, then the sides of the outlet extension must be rotated 30 degrees from each other as well. Alternatively, if the periodic sides of the inlet extension are translated in the Y direction 3 inches, then the periodic sides of the outlet must be translated 3 inches in the Y direction as well.

At least one set of periodic surfaces in the model must be planar. As long as one set is planar, the other surfaces can be curvilinear.

In 2D models, edges in a periodic pair must be within three degrees of each other, and must be the same length. Additionally, all normals from one surface must pierce the other, and vice versa.

When applying a periodic condition, a pair ID is required. Use an integer value for the pair ID, and use the same value on the periodic surfaces of each extension. Additionally, a unique side ID is required for each member of a pair. For example, one surface of a periodic pair might have pair ID =1 and side ID =1. The corre-sponding surface in the pair would have pair ID =1, and side ID = 2.

The side ID should be consistent from one region to the next. This is shown:

Being consistent with the sides from one region to the next will greatly speed-up startup processing. If side IDs are not marked consistently, the start-up processing of the analysis will take considerably longer.

side 1

side 2


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14.7.2 Geometry Configuration

There are two ways to configure the rotating region based on the blade passage. One approach is for the passage to be exactly between the blades (extending from the suction side of one blade to the pressure side of the other):

This approach is better for most centrifugal devices and axial devices that have a large number of blades or high degree of blade curvature.

Alternatively, the rotating region can extend from the mid-point of one passage to the mid-point of the neighboring passage. In this case, a single blade will run

Inlet PeriodicExtension

Outlet Periodic

Extension

Rotating Region(Blade passage,

Periodic Pair 1

Periodic Pair 2

Side 1

Side 1

pressure and suction sides of blades)

Side 2

Side 2


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through the middle of the rotating region. The blade should either be a cutout or should be a solid:

Turbomachinery analyses using periodic conditions are only useful for blade pas-sages. Such analyses are not appropriate for geometries in which a non-moving solid is included, such as a centrifugal pump surrounded by a volute.

The blade passage will be set up as a rotating region, and the rotational speed and direction of rotation must be defined. Periodic boundary conditions are required on the sides of the rotating region as well, if the blade is centered within the region. If the sides of the rotating region are the pressure and suction sides of the blade, then it is not necessary to assign periodic conditions to the sides of the rotating region.

Periodic boundary conditions can also be used for non-rotating devices, such as a stator cascade. Periodic pairs are required at the inlet and outlet extensions:

pair 1, side 1

pair 1, side 2

pair 2, side 1

pair 2, side 2

pair 3, side 2

pair 3, side 1

Pair ID 1

Pair ID 2

Blades

Inlet

Outlet


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Analyses with periodic boundary conditions that include a rotating region must be run transient. For analyses of non-rotating devices, it is not required to run as a transient analysis.

Note that periodic boundary conditions are included in the Basic configuration, but the Motion Module is required to analyze rotating machinery passages with periodic boundaries.

Advanced Functionality:

The following functionality items are the additional items in the “Advanced” configu-ration.

14.8 Transient Flows

In fluid flow analyses, transient refers to both periodic in time (albeit steady) and the usual time-varying flow solution. For transient flows, initial conditions must be set. The default initial condition will be zero for all variables except temperature. Assign initial conditions using the Initial tab of the Loads dialog task.

1. Transient Boundary Conditions: Time-varying boundary conditions are often necessary. The steps for setting a time-varying boundary condition are outlined in the Loads chapter of this guide.2. Unit of Time: Note that the time unit is always seconds for transient analyses. This unit of time is consistent with that used for the properties. Even for transients which take days or longer, the time step size should still be entered in seconds.3. Inner Iterations: Because CFdesign uses an implicit method to discretize the transient flow equations, iterations must be run for every time step. This inner iter-ation is similar to the amount of work required for a single steady state iteration. However, the inner iterations in a transient analysis are almost always better-condi-tioned mathematically than a steady state iteration. For this reason, far fewer inner iterations per time step (typically 10) are required than iterations for a steady state solution.

For Motion analyses, the recommended number of inner iterations per time step is one. Little benefit has been found from using more iterations per time step.


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4. Divergence: If the transient calculation is diverging, the time step size will likely need to be decreased. For most situations, reducing the time step size is a better approach than adjusting the convergence controls because doing so will affect the time-accuracy of the solution. The convergence controls will artificially slow down the time history of the calculation.5. Intelligent Solution Control: If invoked, it adjusts only the time step size, and does not modify any convergence settings. This is done to prevent artificially affecting the time accuracy of the solution. (Convergence settings slow down solu-tion progression so it is always a good idea to use the default settings for non-Motion transient analyses.) We have found that in some cases the time step size that Intelligent Solution Control selects can be smaller than truly necessary for con-vergence, which may result in significantly longer solution times. For this reason, Intelligent Solution Control is disabled by default, and it is recommended to assign a time step size for transient analyses that do not involve the Advanced functional-ity physics.6. Pressure Waves: When running a transient analysis with time-varying pres-sure boundary conditions, the analysis should be set to compressible. The tran-sient terms in the pressure equations can only be accurately determined if the density is allowed to vary. Namely, pressure waves always have to be modeled as a compressible flow phenomenon.7. Compressible Liquids: In water hammer analyses, the density does not vary. Compressible and Transient must still be invoked however to solve a water hammer analysis.8. Animation: Transient results sets can quickly be animated in the Results dia-log. This is described in the Review chapter of this Guide.

14.9 Height of Fluid

Designed to track the fluid level for a tank filling or emptying operation, the Height of Fluid (HOF) function is a transient-based formulation that works for two and three dimensional geometries as well as axisymmetric.

To implement HOF into an analysis, simply apply the Height of Fluid initial condition to those regions of the model that contain fluid at Time 0. Regions that do not have this condition are considered empty at the onset of the analysis. The geometry should be oriented such that the filling or emptying direction is the “Y” coordinate direction.


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Additionally, be sure to select Transient on the Analyze dialog, and set an appropri-ate time step.

The filling or emptying process must be driven by an applied velocity boundary con-dition. The hydrostatic head of the water column will not cause the water to sponta-neously empty from a tank.

Note: the Residence Time scalar quantity can be selected for results viewing, and is often useful for HOF analyses. This is selected from the Results Quantities dialog available on the Analyze dialog. Note also that an HOF analysis can have a scalar quantity as part of the calculation. This is useful for modeling the concentration of additives to the water.

14.10 Moist/Humid Flows

To model the effect of moisture on a gas flow, specify a relative humidity and a temperature boundary condition at every inlet.

Additionally, it is often helpful to apply the initial value of temperature and humidity to the model. Use one of the inlet values as the initial condition value.

On the Materials dialog, select one of the Air_Moist properties from the fluid mate-rial database, or define a new material using a Moist Gas density variation. The val-ues that can be changed are the Reference Pressure and Gas Constant. The reference pressure is the sum of the partial pressures of the gas and the water vapor. You should also enter the carrier gas viscosity, conductivity and specific heat.

Also, select the Humidity option on the Scalar dialog on the Options task, and set Heat Transfer to On on the Options dialog.

For incompressible flows, only the temperature affects the fluid properties (includ-ing relative humidity). If pressure effects are to be considered, select Subsonic Compressible from the Options dialog task.

When continuing an analysis from existing results, there may be a blip in the con-vergence monitor for temperature and scalar due to some internal conversion vari-ables.


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Note: CFdesign can model the condensation process but not the evapora-tion process. The amount of liquid condensed and the calculated field values of relative humidity can be viewed as results. The condensed liquid is calculated as a mixture fraction, i.e., the mass of the condensed liquid divided by the total mass of the liquid, vapor and carrier gas.

It is often helpful to apply Convergence Control to the following variables for moist/humid analyses: pressure, temperature, and density. Values of 0.1-0.25 are appro-priate.

Be sure to enable output of the Scalar quantity on the Result Quantities dialog (available from the Analyze dialog). This will allow humidity to be viewed as a result quantity.

14.11 Steam/Water Flows

To model a two-phase mixture of steam and water, specify the steam quality and static temperature (as well as the appropriate flow condition) at all inlets. If the inlet fluid is 100% liquid water, then the steam quality is 0.

Select the H2O_Steam/Liquid property from the Fluid list on the Material dialog. If operating far from STP, create a new steam/water material, and change the Ref-erence Pressure accordingly. The actual values of the fluid properties will be deter-mined during the analysis using the steam tables and the specified reference pressure.

On the Options dialog, turn Heat Transfer On, and select Steam Quality from the Scalar dialog.

For incompressible flows, only the temperature and reference pressure will affect the fluid properties (including the steam quality). If local pressure effects need to be considered, select Subsonic Compressible flow on the Options dialog.

In the case of steam/water flows, CFdesign assumes a homogeneous two-phase mixture. The energy equation that is used is written in terms of enthalpy. Tempera-ture is determined using the steam tables. Both temperature and enthalpy results can be viewed in the Results dialog task (make sure both quantities are enabled on the Output Quantity dialog on the Analyze dialog).


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For steam/water analyses, we recommend that Auto-Convergence should be invoked. To run such an analysis without Auto-Convergence, it is necessary to apply convergence control to the following variables: pressure, temperature, density, and specific heat. Control values of 0.1-0.2 are appropriate for most flows.

14.12 Radiation Heat Transfer

The radiation model uses a true view factor calculation which provides as accurate energy balance because it enforces reciprocity between solids. Temperature and energy balance accuracy are ensured for geometries with widely varying feature sizes.

Radiative heat transfer through transparent media is supported, as well as geomet-ric symmetry. The radiation model computes radiative heat transfer to moving sol-ids and moving surfaces, and is the basis of the solar heating model. The radiation model has very rigorous “bookkeeping” to keep track of the radiative energy bal-ance, and reports the amount of heat transfer due to radiation and the radiative energy balance for each part in a model. The result is that reciprocity is enforced, to ensure that the radiative heat transfer between parts with large size differences is computed accurately.

Radiation works with all of the supported geometry types: two and three dimen-sional Cartesian and axisymmetric about the X and Y axes.

14.12.1 True View Factor Calculation

The new radiation model computes true view factors for every part. This is more accurate than the flux-based method used in the radiation model in previous ver-sions. The view factors between every part are written to the “.sol” file, and should sum to 1 for each part. Tables of view factors are produced for opaque as well as transparent materials.

A sample view factor list for one part in an assembly is shown:

Opaque Part-To-Part View Factors

Part 1 viewing Part 1, VF = 0

Part 1 viewing Part 2, VF = 0.00870629


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Because this new model uses a true view factor calculation, it can more accurately solve the radiative heat transfer for models with parts that have large size differ-ences. Surface to surface reciprocity is enforced to ensure a more accurate energy balance.

14.12.2 Modeling Guidelines

To use radiation, specify an emissivity for every solid material type in the model. If there are no solids present, specify an emissivity for the surrounding walls by set-ting an emissivity on the fluid material. (You will have to create a new material, but it can be based on a database material.) Because the radiation algorithm does not allow the fluid medium to participate, emissivity specified on a fluid material is automatically applied to the walls touching the fluid.

Note that the default value of 0 as the emissivity is not generally recommended because it indicates a perfectly reflective surface. Such a case may cause analysis instabilities and convergence difficulties.

Enable Heat Transfer and Radiation on the Options dialog.





Part 1 sum of all view factors = 1


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Radiation can be run with or without flow, but should be run with Heat Transfer set to On.

An important modeling consideration is that fluid and parts that contact each other should not be extrusion meshed. The reason is that if either (or both) use extruded elements, the interface between the extrusion faces and the tetrahedral faces, also known as a non-conformal interface, is not supported by the radiation model. The radiation model must have a matching mesh at all fluid-solid interfaces. This guide-line applies to solid-solid interfaces as well if one or both of the solids is a transpar-ent medium.

When an assembly is enclosed by an air volume, it is very important that a non-zero value of emissivity be assigned to the air (which then gets applied to the walls). If a value of 0 is used, the wetted surfaces (that do not touch solids) will behave as perfect mirrors, and no energy will be lost to the environment--a non-physical situation. Apply a temperature boundary condition to the external air sur-face that represents the correct environmental temperature, and specify a realistic emissivity for the air.

14.12.3 Transmissivity

The new radiation model supports radiative heat transfer through transparent solid media. A new material property, transmissivity, defines the level of transparency of a solid object. Radiative heat transfer through a transparent solid object that is completely surrounded by fluid can be simulated by assigning a non-zero transmis-sivity property to the material. Opaque solids that are enclosed by transparent sol-ids can be modeled as well. This even allows “nesting” of multiple layers of opaque and transparent solids.

Note that transmissivity cannot be assigned to surface parts.

In the new radiation model, radiative energy that passes through a transparent solid does not experience an attenuation effect--there is no absorption of radiative energy into the media. There is no accounting for spectral effects within a transpar-ent object, and energy leaves the object in a diffuse manner. Energy may, however, be absorbed through the surface and then emitted (emissivity = absorptivity). The energy balance for radiative heat transfer looks like:

r 1 ε– τ–=


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where = reflectivity, = emissivity, and = transmissivity. Note that transmis-sivity can only be applied to solids. Fluids are non-participating media for all radia-tion simulations.

14.12.3.1 Internal Transparent Parts

To include radiative heat transfer through a transparent solid that is completely sur-rounded by the fluid, assign a transmissivity value to the material using the Mate-rial Editor on the Material task dialog.

r ε τ


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Note that the sum of transmissivity and emissivity must be less than or equal to 1.

14.12.3.2 External Transparent Parts

To include radiative heat transfer through a transparent surface on the external wall, such as a window:

1. Model the transparent region as a solid part. 2. Assign a transmissivity value to the material using the Material Editor on the Material task dialog. (Note that the part must have a non-zero transmissivity prop-erty to be considered transparent.)3. Assign a Transparent boundary condition to the external surface:

The temperature specified with this boundary condition is used to define the incom-ing radiation flux according to this equation:

Air cavity

Object with

emissivity <= 1

Emissivity of walls set

Transparent parttransmissivity > 0

heat source

Object heatedby radiativeheat transfer

if opaque, transmissivity = 0

as property of air

Air cavity

Internal solid part

Transparent parton exterior of model.Transmissivity > 0

Transparent BC with Background Temperatureapplied to external surface(s)


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Transparent BCs should only be applied to external boundaries so that the incoming flux is external to the analysis domain. They must be assigned to a solid material; assignment to a fluid material will result in an error.

Solar heating problems should not use transparent BCs because the set up of the solar heating problem requires a sky dome and ground structure that define the entire external boundaries. If windows are modeled in these cases, these transpar-ent materials would be internal to the analysis domain which would make transpar-ent boundary conditions inappropriate.

If a transparent material with surfaces on an external boundary are not assigned a transparent boundary condition, the emissivity and transmissivity will automatically be set to 0. Because reflection is the difference between 1 and the sum of emissiv-ity and transmissivity, the external boundary will be perfectly reflective (like a silver backing on a mirror) with the exterior of the model. This is done to conserve energy. Because no background temperature is defined, the heat loss/gain cannot be computed.

14.12.4 Symmetry

The new radiation model supports geometric symmetry. Symmetric divisions must be such that the model is a true fraction of the complete model. For example, a half symmetric model is valid if the other half makes up the complete device. Likewise, a quarter symmetry is valid if it encompasses 90 degrees of the actual device, and if the other three quarters would make up the complete device.

q σ Tbackground( )4=


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A slip condition that does not divide a model along a geometry symmetry would not produce accurate radiative heat transfer results. Examples of valid symmetry/slip divisions are shown:

These two examples show valid half and quarter symmetry geometries, but much smaller symmetry can be used, if it is valid. As an example, an 18 degree wedge could be analyzed from a disk. This corresponds to a 1/20th symmetry! The key is to apply the symmetry (slip) boundary conditions so that they properly define the symmetry.

When working with a symmetric model, care should be taken to ensure that the model uses pure rotational symmetry. A combination of rotational and mirrored symmetry is not supported. For example, if the complete geometry looks like the image on the left, then a valid quarter symmetry would be as shown on the right:

Half Symmetry Quarter Symmetry

Symmetry Plane

Model

Cut-away half

Model

Cut-away Quarters

Symmetry Plane


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But, if the actual geometry did not contain pure rotational symmetry, and looked like the image on the left (below), then the symmetry shown in the middle image would be wrong. The image on the right is the correct way to invoke symmetry on such a model:

To properly model symmetry, it must be possible to rotate the symmetric model through 360 degrees and arrive at the original geometry. This is to ensure that the effects of shadowing and reflection are accurately accounted for by the radiation model.

The new radiation model also supports 2D axisymmetric models. Such models must be axisymmetric about either the x or y axis.

Rotational Periodic symmetry is also supported by the new radiation model. The wedge angle must be at least three degrees, and periodic faces are marked using the periodic boundary conditions on the Loads dialog. Translational periodic sym-metry, however, is not supported.

14.12.5 Motion

Radiation is now supported for moving solids. When radiation is enabled for a motion analysis, the view factors will automatically recompute when the moving part has traveled 2% of the maximum diagonal of the domain bounding box. This value can be changed with a flags file entry:

ViewFactorUpdate VALUE

QuarterSymmetryNOT VALID

Half SymmetryVALID


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where VALUE is the percent of the diagonal. To recompute view factors every 5%, for example, place this entry in your flags file:

ViewFactorUpdate 5

NOTES:

• Moving objects that experience radiation heat transfer must not touch any stationary object or wall at any point in the analysis. This includes the as-built location as well as anywhere in the motion path.• Moving objects must not leave the enclosure.• Radiation cannot be used for rotating regions--it is only for moving sol-ids.• Moving parts must be opaque. They cannot have a non-zero value of transmissivity in their material definition.

14.12.6 Invoking

The new radiation model is enabled by default. To use the CFdesign v8 radiation model, add this setting to your cfdesign_flags.txt file:

rad_model_1 1

14.12.7 Resource Usage

The fact that the new radiation model computes view factors and reciprocity between every face of every part leads to a high level of accuracy and a good energy balance for radiation calculations. The model is, however, resource inten-sive. During initial startup, a view factor is calculated between all element faces of every part with a line of sight. Additionally, the radiation matrix must be built that tracks all of this data.

The required amount of RAM increases with the square of the number of surface element faces. Depending on the number of surfaces in a geometry, the amount of RAM required to compute the view factors may be in excess of 1 Gigabyte. The amount of time required to compute the view factors at startup can be quite signif-icant as well. A progress bar indicates the relative progress of this calculation dur-ing initial startup.


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The radiation model automatically adjusts the accuracy of the computation as a function of the available RAM. The algorithm probes the system to determine how much RAM is available, and then it will adjust the optical sampling rate so that the final radiosity matrix will fit into the available RAM. It will also determine whether it should use in-memory or out-of-core storage of view factors, radiosity matrix terms, and even the type of solver employed. So even with only 256 Mbytes of memory, it is possible to run radiation calculations. It will take longer and be less accurate than results generated on a machine with 4 Gbytes of RAM, however.

If, however, the analysis model simply cannot be run with the available RAM, an error will be given advising that the radiation model cannot be run due to the lack of system resources.

Fortunately, this calculation is only performed at the beginning of an analysis. It does not occur for subsequent restarts of the analysis if the mesh does not change. Because the new radiation model employs a surface integral method, it has been shown to not require a high mesh density to provide accurate results. Please be sure to balance the meshing requirements of the other physical phenomena in an analysis model as appropriate.

14.12.8 Spectral Radiation

The radiation model can include the effects of temperature-dependent emissivity. This allows the simulatation of the effects of spectral radiation. This variation is in the form of a piece-wise linear table, and is entered on the Material Editor by hitting the Emissivity button, and selecting Piecewise Linear on the Variation Method drop menu.


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To account for the spectral characteristics of a surface, use the radiation functions in the following table to construct a second table of total emissivity as a function of temperature to be used in CFdesign:

0 0 0.0 10,200 5666.7 0.70754

1000 555.6 1.70e-8 10,400 5777.8 0.71806

1200 666.7 7.56e-7 10,600 5888.9 0.72813

1400 777.8 1.06e-5 10,800 6000 0.73777

1600 888.9 7.38e-5 11,000 6111.1 0.74700

1800 1000 3.21e-4 11,200 6222.2 0.75583

2000 1111.1 0.00101 11,400 6333.3 0.76429

2200 1222.2 0.00252 11,600 6444.4 0.77238

2400 1333.3 0.00531 11,800 6555.6 0.78014

2600 1444.4 0.00983 12,000 6666.7 0.78757

2800 1555.6 0.01643 12,200 6777.8 0.79469

3000 1666.7 0.02537 12,400 6888.9 0.80152

3200 1777.8 0.03677 12,600 7000 0.80806

3400 1888.9 0.05059 12,800 7111.1 0.81433

3600 2000 0.06672 13,000 7222.2 0.82035

3800 2111.1 0.08496 13,200 7333.3 0.82612

λTµm °R–

λTµm °K–

Eb0 λT–

σT4-----------------

λTµm °R–

λTµm °K–

Eb0 λT–

σT4-----------------


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4000 2222.2 0.10503 13,400 7444.4 0.83166

4200 2333.3 0.12665 13,600 7555.6 0.83698

4400 2444.4 0.14953 13,800 7666.7 0.84209

4600 2555.6 0.17337 14,000 7777.8 0.84699

4800 2666.7 0.19789 14,200 7888.9 0.85171

5000 2777.8 0.22285 14,400 8000 0.85624

5200 2888.9 0.24803 14,600 8111.1 0.86059

5400 3000 0.27322 14,800 8222.2 0.86477

5600 3111.1 0.29825 15,000 8333.3 0.86880

5800 3222.2 0.32300 16,000 8888.9 0.88677

6000 3333.3 0.34734 17,000 9444.4 0.90168

6200 3444.4 0.37118 18,000 10,000 0.91414

6400 3555.6 0.39445 19,000 10,555.6 0.92462

6600 3666.7 0.41708 20,000 11,111.1 0.93349

6800 3777.8 0.43905 21,000 11,666.7 0.94104

7000 3888.9 0.46031 22,000 12,222.2 0.94751

7200 4000 0.48085 23,000 12,777.8 0.95307

7400 4111.1 0.50066 24,000 13,333.3 0.95788

λTµm °R–

λTµm °K–

Eb0 λT–

σT4-----------------

λTµm °R–

λTµm °K–

Eb0 λT–

σT4-----------------


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Radiation functions from R.V. Dunkle, Trans. ASME, 76, p549, 1954

For example, if you know the range of temperatures for your model is 100F

to 1200F and the emittance of the surface is 0.3 ( ) below 3 and is 0.8

7600 4222.2 0.51974 25,000 13,888.9 0.96207

7800 4333.3 0.53809 26,000 14,444.4 0.96572

8000 4444.4 0.55573 27,000 15,000 0.96892

8200 4555.6 0.57267 28,000 15,555.6 0.97174

8400 4666.7 0.58891 29,000 16,111.1 0.97423

8600 4777.8 0.60449 30,000 16,666.7 0.97644

8800 4888.9 0.61941 40,000 22,222.2 0.98915

9000 5000 0.63371 50,000 27,777.8 0.99414

9200 5111.1 0.64740 60,000 33,333.3 0.99649

9400 5222.2 0.66051 70,000 38,888.9 0.99773

9600 5333.3 0.67305 80,000 44,444.4 0.99845

9800 5444.4 0.68506 90,000 50,000 0.99889

10,000 5555.6 0.69655 100,000 55,555.6 0.99918

λTµm °R–

λTµm °K–

Eb0 λT–

σT4-----------------

λTµm °R–

λTµm °K–

Eb0 λT–

σT4-----------------

ε1 µ


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( ) at the longer wavelengths, you would create the following table, and

enter this data in the Piecewise Linear property table in CFdesign:

The emissivity in the above table is determined using the equation:

Substituting the numbers above and interpolating values from the table:

So, the emissivity at 100 F is:

For the emissivity at 1200F:

So, the emissivity at this temperature is:

T Emissivity Temperature (F)

1680 9.888e-5 0.8 100

4980 0.220354 0.69 1200

ε2

λ

Eb0 λT–

σT4-----------------

εEb0 λT–

σT4-----------------⎝ ⎠⎛ ⎞ ε1 1.0

Eb0 λT–

σT4-----------------–⎝ ⎠

⎛ ⎞ ε2+=

T 100 F( ) λT 3 560× 1680= =( )→=( )Eb0 λT–

σT4----------------- 9.888e 5–=⎝ ⎠⎛ ⎞→

ε 9.888e 5–( ) 0.3( ) 1.0 9.888e– 5–( ) 0.8( )+ 0.80= =

T 1200 F( ) λT 3 1660×=( ) 4980=( )→=( )Eb0 λT–

σT4----------------- 0.220354=⎝ ⎠⎛ ⎞→

ε 0.220354 0.3( ) 1.0 0.220354–( ) 0.8( )+ 0.69= =


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14.12.9 Energy Balance

For every iteration, a radiosity matrix is form and solved. A complete record of the energy balance is provided for every part in the model. This data is written to the “.sol” file for every iteration during the analysis, and to the summary file after the last iteration. This section describes the information that is provided, and discusses the differences for models using transparent boundary conditions and solar heating.

14.12.9.1 Radiation with no Transparent BC or Solar

The following is a sample energy balance from a radiation analysis containing five parts. There are four parts immersed in an air cavity (part 5). None of the parts has transmissivity. Comments about the meaning of certain items are written below the line and are preceded by a “>>>>” symbol.

Radiosity Solution has converged

Iter=12 ResNorm = 5.85774E-013

CPU time to solve radiosity matrix = 0.719

Radiation heat balance = 2.3363e-008/ 20.437 = 1.1431e-007%

>>>> The 2.3363e-008 is the sum of the radiative energy. This value should be 0 or very close. The 20.437 is the sum of the absolute values of the radiative energy. The 1.1431e-007% is the total radiative energy divided by the sum of the absolute values. This is an indicator of the error in the radiative energy balance.

Radiation Heat Loads by Part ID

ID Radiation

Heat Load

(Watts)

Area

(mm^2)

Surface

Tempera-ture

(K)

Emissivity Transmissivity

1 -2.583 5959.3 365.23 0.94 0

2 -2.5318 5959.2 363.07 0.94 0

3 -2.5806 5959.3 365.56 0.94 0

4 -2.5148 5959.3 364.2 0.94 0


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>>>>Parts 1-4 are each losing about 2.5 Watts through radiation, and part 5, the enclosure, is receiving that radiant energy. The totals indicate that the total heat lost equals the sum of the heat gain, indicated by the total heat load summing to 0. The temperature for each part is an area-weighted temperature, and the total tem-perature is average temperature for all of the parts.

14.12.9.2 Radiation with Transparent Boundary Conditions

When transparent boundary conditions are included in a radiation analysis, the energy balance information is presented slightly differently as shown in the radia-tive energy balance from such an analysis. Comments about the meaning of certain items are written below the line and are preceded by a “>>>>” symbol.

Radiation heat balance = -4.5792e-008/ 226.96 = -2.0176e-008%

>>>>As in the previous example, the -4.5792e-008 value is the net radiative heat exchange within the model. A very small value means that a good energy balance has been attained.


5 10.21 1.2296e+005

298.25 0.7 0

Totals 2.3363e-008

1.4679e+005

309.01

ID Radiation

Heat Load

(Watts)

Area

(mm^2)

Sur-face Temp

(K)

Emissivity Transmissiv-ity

2 -36.289

/ 0 transparentBC

6.917e+005

1268.5 0.94 0

3 -32.062

/ 0 transparentBC

1599.3 1015.7 0.94 0

4 0.18324

/ -76.557 transpar-entBC

1767.8 980.85 0.05 0.8


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>>>> Parts 2 and 3 are losing about 36 and 32 Watts, respectively. Part 6, the enclosure, is losing about 8 Watts. The sum of the energy lost from these three parts equals the energy lost through the transparent boundary condition. The transparent part, part 4, is only picking up a small amount of energy because it is losing most of its energy through the transparent boundary condition. Note that the total transparent BC heat load = total radiation heat load. This indicates a good energy balance.

14.13 Solar Heating

The Solar model only works in conjunction with the new radiation model, and as such supports radiative heat transfer through transparent media. With solar heat-ing, the effect of shadowing on other objects is supported as well. The Solar user interface dialog allows for specification of specific geographical locations as well as input of latitude and longitude. The date, time, compass direction, and object orien-tation relative to the sky are also specified. A full report of the radiative energy bal-ance similar to the reports shown in the previous section is provided during and after the analysis.

14.13.1 Geometry

To properly compute the solar heating of an object, it must be fully enclosed by a larger volume that represents the environment. A volume representing the ground can also be included in the model, but is not required. The purpose of both regions (environment and ground) is to properly simulate the effects of reflected and emit-ted radiative heat transfer between the object and its surroundings. These two ele-ments in a solar model allow for proper simulation of the indirect solar flux to and from the ground and the radiative energy loss and/or gain to the sky.

The ground volume should be approximately a meter thick. The thickness is signifi-cant only if diurnal heating over several days is studied, in which case it is neces-

6 -8.3889

/ 0 transparentBC

2.029e+005

1270.7 0.94 0

Totals

-76.557/ -76.557 8.980e+005

1268


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sary to compute the thermal inertia of the ground. The ground part should be approximately 20 times wider than the studied object.

The shape of the environment volume is not critical, and a hemisphere or cube are the most convenient choices. The environment volume should extend at least 10 times the height of the objects in the analysis model. A smaller environment can be used, but if natural convection is analyzed, a small volume will influence and poten-tially complicate the buoyancy-induced flow. Also, if diurnal heating is analyzed, a cold sky temperature that is too close to the object will artificially cool the object through conduction.

Note that only three dimensional geometry is supported for solar analyses because the motion of the sun is a function of its altitude and its East-West (azimuth angle) orientation. Since the solar energy flux is a function of three dimensional space, CFdesign does not convert this energy into an equivalent energy load in two dimen-sional models. For example, for a model that is axisymmetric in the Y axis, solar input only exists on one side of this object. This conflicts with the condition of sym-metry about the Y axis because the solar heating is non-symmetric by its very nature.

The relative locations of objects in an analysis model are important because shad-owing is computed by the Solar Heating model. When an object blocks solar flux (either partially or completely) from hitting another object, that blocked object is

Environment Volume

Ground

Object

Volume

2 meters

1 meter

40 meters

20 meters


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shadowed. Such an object is still subject to receiving indirect radiant heat flux from the sky, the ground, and surrounding objects.

14.13.2 Analysis Settings

Temperature boundary conditions and emissivity values should be specified for both the ground and sky.

The ground temperature depends on the location on the Earth, and should be spec-ified on the external surface of the ground volume. The emissivity of the ground should be specified as a property of the ground material. This value depends on the type of material. Grass surfaces, for example, may have an emissivity of about 0.3, while asphalt may have an emissivity of about 0.8. White surfaces such as an air-

If solar flux

comes from here...

This object is in

the shadow of

the bigger object

Ground temperatureGround emissivity

Sky temperature

Sky emissivity


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port tarmac, are highly reflective, and would tend to have very low emissivity val-ues.

During the day, the sky temperature is nearly the ambient temperature. At night, however, the sky temperature falls to about 0 C. On very cloudy nights in warm cli-mates, the sky temperature may be warmer than this. On clear nights in cold cli-mates, the sky temperature can be as cold as -15 C.

The amount of cloud cover and the amount of ambient light affect the amount of radiant energy that is reflected off the sky and back to earth (the albedo). Use the value of emissivity specified on air to control the emissivity of the sky (and hence the reflectivity). The emissivity controls the amount of reflected energy: (reflection = 1-emissivity).

• A clear sky with little or no cloud cover has a higher emissivity value (and hence lower reflectivity) than a cloudy sky. • At night, a clear sky might have an emissivity as high as 1, but because of the low night-time sky temperature, it acts as an emitter that is cold, so little heat is emitted back to the object and ground.• A cloudy night sky will have a lower emissivity (higher reflection), so the clouds reflect the radiation emission from the ground, and will limit the heat loss of the ground.

To study diurnal heating, specify the sky temperature as a transient boundary con-dition, and assign the emissivity of the air (which is automatically assigned to the exterior surface of the environment volume) as a function of temperature. During the day, high sky temperature corresponds to lower emissivity. During the night, low sky temperature corresponds to higher emissivity values.

Transparent objects such as windows can be incorporated into solar heating analy-ses. Assign a transmissivity property value to such parts in the Material Editor. Because all parts are internal to a solar heating analysis, the transparent boundary condition should not be used in a solar heating model. This boundary condition is used for setting an external temperature on objects that are on the exterior of a model, so it is not appropriate for objects in the interior of a solar analysis.

Please see the Solar Heating section of the Options chapter of this manual for infor-mation about the Solar Heating dialog.


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14.13.3 Running a Solar Heating Analysis

There are two ways to run a solar heating analysis: as steady-state or as transient. When run as steady state, the time specified on the Solar Heating dialog does not change throughout the calculation. This is ideal for computing the “worst case” solar heat loading on an object during the heat of the day. Also, this regime is use-ful for determining seasonal variations in the peak solar loading.

To study the variation of solar loading over a longer period of time (either within a single day or over multiple days and nights), a solar heating model can be run tran-sient. The time and date specified on the Solar Heating dialog are that at the begin-ning of the simulation. If analyzing diurnal heating over a long period of time (several days, for example), we have found that it is convenient to divide a day into 100 time steps. This is a time step size of 864 seconds. Such a large time step should be very effective if Flow is disabled on the Options dialog. If buoy-ancy effects are to be studied, then a significantly smaller time step will be neces-sary.

When running a diurnal solar analysis, it will likely be important to vary the sky temperature with time so that the appropriate value is used during day and night. Likewise, define the sky emissivity to be temperature-dependent to properly repre-sent the reflective effects of ambient light and cloud cover.

The two result quantities that provide the most insight into the effects of solar load-ing are temperature and solar heat flux. Solar heat flux is enabled automatically, and is available from the Scalar branch of the feature tree:


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14.13.4 Radiation Energy Balance with Solar Heating

A complete reporting of the radiation energy balance is also provided in the Sum-mary file when running Solar Heating. Below is a sample of such a report. Com-ments about the meaning of certain items are written below the line and are preceded by a “>>>>” symbol.

Simulation Time 1.728000e+003 seconds, year = 2006, month = 2, day = 1 hour = 12 minute = 25 second = 5

>>>>Time, date, and duration when the position of the sun is computed.

Altitude 72.6 Azimuth 3.2 Night 0 Direct Solar Flux 7.239663e-004 sun_pointer 0.298570 -0.016760 0.954241

>>>>Position of the sun

L2 Norm of residual before solve = 1.06209e-003

Radiosity Solution has converged

Iter=10 ResNorm = 6.36236E-014

CPU time to solve radiosity matrix = 4

Radiation heat balance = 4.1933e-010/ 86.259 = 4.8613e-010%


ID Radiation

Heat Load

(Watts)

Area

(mm^2)

Surface

Tempera-ture

(K)

Emissiv-ity

Transmissiv-ity

1 0.1875/ 0 solar 5959.3 298.43 0.7 0

2 0.19787/ 0 solar

5959.3 298.83 0.7 0

3 12.858/ 14.379 solar

1.56e+005

303.46 0.2 0.6


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>>>> Part 3 is picking up 14.379 Watts through incoming solar flux, but its net increase is only 12.858. This means that this part lost about 1.5 Watts to its sur-roundings. Part 6, conversely, has a slightly higher net influx than it received from solar. This means that it picked up additional radiant energy from its surroundings. Note that the total solar heat load = total radiation heat load, indicating a good radiation energy balance.

14.14 Compressible Flows

Physically, the fluid density of compressible flow varies with pressure. In CFdesign, the distinction between subsonic compressible and full compressible is that in the former, the relationship between pressure and density is weak, and in the latter, the relationship is quite strong. In compressible flow, the pressure strongly affects the density.

Subsonic Compressible flow contains no shocks. The local Mach number is always less than 1.0.

Compressible flow may have shocks and regions where the local Mach number is greater than 1.0. This type of flow may be either transonic or supersonic. In super-sonic flows, pressure effects are transported downstream. The upstream flow is not affected by downstream conditions.

If the flow accelerates through a geometrically converging section to sonic speed, the flow is considered to be choked. When choked, no additional mass can pass through the constriction region, even as the pressure drop is increased (by lowering the outlet back pressure). The flow downstream of the throat can then expand and become supersonic.

4 0.57946/ 0.51806 solar

5959.3 300.24 0.7 0

5 0.78074/ 0.69285 solar

5959.3 301.29 0.7 0

6 71.656/ 70.67 solar

1.21e+005

303.73 0.94 0

Total 86.259/ 86.259 3.01e+005

303.27


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Please note that compressible analyses can vary considerably from one to the next, and that they can be much more sensitive to applied parameters than incompress-ible analyses. It is very important that the physics of the model be represented cor-rectly. Discrepancies between the model set up and the actual physical situation can cause significant differences in the results, and may affect analysis stability.

Some general guidelines for running compressible analyses are listed:

1. Inlet Boundary Condition: If the inlet Mach number is known, specify a velocity and gage static pressure (=0). The inlet velocity is calculated as:

Where M = Mach number, and a = speed of sound:

Where =1.4 for air, R = gas constant, and T = reference static tempera-ture (in absolute units).

Note: The reference temperature is the static temperature at the inlet of the domain.

If the source of the flow is a pressurized plenum, specify a total pressure.

2. Exit Boundary Condition: If the outlet flow is supersonic, the outlet boundary should be the Unknown boundary condition. If the outlet flow is subsonic, then apply a pressure of 0 gage. Ensure that a specified pressure is far enough from any supersonic regions so as not to cause any artificial influence.3. Materials: Use a material with a density that varies with equation of state. It is very important to use the correct fluid reference quantities. The reference static pressure and static temperature are used to initialize the density. Because of this, the reference temperature needs to be reasonable and the pressure needs to be exact for the gage reference point to be correct.4. Meshing: To capture physical elements such as shocks, the mesh size will have to be quite fine in critical areas. The mesh can be less fine in non-critical areas. A good guideline governing mesh transition is that the mesh size should not transition by more than a factor of four between neighboring fluid volumes. 5. Total Temperature: If heat transfer is not solved for, it is necessary to specify a Total temperature in the Options dialog. The equation for total temperature is:

or

V aM=

a γRT=

γ

Tt TVi

2

2Cp---------+= Tt T 1 γ 1–

2-----------M2+⎝ ⎠

⎛ ⎞=


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It is very important that the total temperature is specified correctly. A good test is to run zero iterations and check that the Mach number at the inlet is the expected value. If not, adjust the total temperature and inlet boundary conditions accordingly.

6. Heat Transfer: To include heat transfer in a compressible analysis, apply Total (stagnation) temperature boundary conditions instead of static temperatures. Set Heat Transfer to On in the Options dialog. The value of Total Temperature on the Options dialog will be ignored if heat transfer is enabled.

Note that when heat transfer is present in a compressible analysis, viscous dissipation, pressure work, and kinetic energy terms are calculated. It is only necessary to enable heat transfer if you are solving for heat transfer or for Mach numbers greater than 3. The latter condition is applicable only if viscous dissipation is important.

To capture a very crisp shock, account for viscous heating, or run a thermal problem, heat transfer must be turned enabled. The inlet total temperature of the fluid must be specified.

7. Advection: for pressure driven flows, ADV2 is the recommended scheme. The default of ADV1 is recommended for most other situations. Note that ADV2 will often produce higher resolution shock results than ADV1, so if the location of shock waves is an important result, use ADV2.8. Intelligent Solution Control: The use of Intelligent Solution Control is rec-ommended for compressible analyses. Such analyses have historically been chal-lenging to solve, and have required a great deal of manual intervention to adjust control parameters and materials. Intelligent Solution Control applies controls auto-matically, resulting in a more efficient analysis process.

14.14.1 Internal Flow

The practices outlined in the Incompressible flow section about internal flow model-ing should be followed for compressible flows as well, with the important exception of the boundary conditions.

1. Boundary Conditions For Supersonic Openings: For compressible flows, if the inlet is supersonic, pressure and velocity must be specified at the inlet because pressure signals only travel downstream in a supersonic flow. If the outlet flow is supersonic, then it is not a good idea to specify the outlet pressure for the same reason. The Unknown boundary condition is a better outlet condition for supersonic outlet flow.


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2. Boundary Conditions For Subsonic Openings: There are situations, how-ever, in which the inlet and/or the outlet may be subsonic, while flow within the domain is supersonic.

• For a subsonic inlet that is well below sonic, it is a good idea to specify only velocity. • For a subsonic inlet that is near sonic, both velocity and pressure can be specified. • If the outlet is very far downstream of supersonic flow, specify a pres-sure. In some instances it is possible to add an extension to the exit to be able to set a uniform pressure at the domain exit. If such an extension is used, it is good practice to set the slip condition on the walls of the exten-sion to prevent any Fanno flow effects. • If, however, the outlet is fairly close to supersonic flow, you should set the Unknown boundary condition.

3. Running: The analysis sequence for internal flows that have some internal compressibility effects is:

• Run 15-40 iterations with Incompressible selected on the Options dia-log. (The solution should become stable and flow should be entering the domain.) Also, set density to vary with equation of state. This will allow the density to approach the correct value prior to switching to compressible.• After the first 15 iterations, run the remaining iterations with Com-pressible enabled. This sequence allows the flow to get established throughout the calculation domain prior to introducing compressibility effects.

14.14.2 External Flow

Please refer to the general information about external flows in the Incompressible flow section of this chapter for basic geometric guidelines.

1. Boundary Conditions: The key difference between incompressible and com-pressible external flow modeling is the boundary conditions. For supersonic flows,


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specify both pressure and velocity upstream of the object. Downstream of the object, set the Unknown boundary condition. An example of this is shown:

Note that if the domain is not large enough, you may have to make the inlet condi-tion (velocity and pressure) extend over a greater portion of the domain.

2. Subsonic compressible: Specify velocity and pressure upstream of the object and pressure downstream of the object. This is valid if the domain is at least 50 chord lengths away from the object.

The analysis sequence for this type of analysis is to run 50 iterations as subsonic compressible then switch to full compressible and run for at least 300 more iterations. (If Auto-Convergence is not invoked, Convergence Control should be set to 0.1-0.2 for velocity and pressure.) This method has been found to be quite stable for flows around Mach 1.

3. Supersonic Compressible: Higher velocity flows (greater than Mach 1.2) should be run with Velocity and Static Pressure specified upstream and the Unknown set downstream (as shown in the preceding figure). (If Auto-Convergence is not invoked, Pressure Control should be set to 0.001 and Convergence Control on velocity and pressure should be set to 0.1 in the Control_Convergence window.)4. Calculation Domain Shape: Sometimes it might be more convenient to use a rectangular shaped domain instead of a semi-circular or spherical shape. This has been found to work quite well for some situations, and the boundary conditions should be applied as shown in the following graphic:


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5. Automatic Convergence Assessment: External compressible analyses typi-cally require more iterations than incompressible analyses to converge. For this reason, we recommend that you adjust the Automatic Convergence Assessment slider to Tight.

14.15 Joule Heating

Joule heating is the generation of heat by passing an electric current through a metal. Also known as resistance heating, this feature allows the user to simulate stove-top burner elements as well as electrical resistance heaters. User-supplied inputs include current, voltage, and the resistivity of the metal.

Two boundary conditions are available to help define a Joule heating condition: cur-rent and voltage. The typical way to define the loading is to set a current on one


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end of the solid through which electricity is passing and a voltage of 0 on the other end:

Alternatively, a potential (voltage) difference can be applied across the device, and the current boundary condition can be omitted.

A new material property has also been added: Resistivity. This is the resistance times the area divided by the length of the device. A value for resistivity is required for any solid that is heated by the Joule effect.

The relationship between resistivity and resistance is: or

• R = resistance (ohms)• r = resistivity (ohms-length unit)• L = length of the device• A = cross sectional area

A non-zero value for resistivity should always be specified for solids experiencing Joule heating. For non-conductive materials or materials in which Joule heating does not occur, specify 0 as the resistivity value. As with any heat transfer analysis, a temperature needs to be specified somewhere in the model (either as a tempera-ture boundary condition or as a surrounding temperature for a film coefficient boundary condition).

Care should be taken that the mesh on any object heated by the Joule effect should have two layers of elements across the object. This will ensure that there are enough nodes to calculate the heating in the object.

Joule heating is invoked automatically if the Current and Voltage Boundary Condi-tions and the Resistivity Material Property are set. Additionally, heat transfer must

Flow VolumeElectrically Heated Object

Current on surface Voltage = 0 on surface

R r L×A

-----------= r R A×L

-------------=


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be enabled on the Options task dialog. There is not a separate button to invoke Joule Heating.

14.16 Motion Module

14.16.1 Introduction

The mission of the Motion Module is to analyze the effects of solids moving through or within a fluid.

The interaction between a solid body in motion and the surrounding fluid is a key aspect to the design of many mechanical devices. The CFdesign Motion Module brings this capability to the world of product design as a key element of Upfront CFD. Through simulation, this Module allows understanding the interaction between fluids and moving solids to be integral to the product design process.

There are two principal ways of simulating the motion of solid objects with the Motion Module: with Rotating Regions and as Moving Solids.

14.16.2 Rotating Regions

Rotating Regions are used to simulate turbomachinery devices such as pumps, turbines, compressors, and fans. They are best suited for simulating rotating objects that do not contact any other solid objects. Such devices are typically impellers or fan blade/hub assemblies that induce flow by transferring energy to the fluid through a momentum transfer.

A Rotating Region is actually a fluid material region that completely envelopes a solid impeller. The motion parameters (rotational speed, inertia, etc.) are assigned to the rotating region instead of to the impeller. During the analysis, the entire rotating region (and the impeller that it surrounds) rotate relative to the surround-ing analysis domain. The mesh within the region rotates as well.

Rotating Regions should be used to simulate turbomachinery devices that induce flow through energy transfer. Such devices rely on the Corollas effect and centripe-tal acceleration. For turbomachinery devices, rotating regions will produce a more accurate answer, and typically require less computational resources.


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14.16.3 Moving Solids

Unlike Rotating Regions in which a special region surrounds the object in motion, Moving Solids are solid objects that have motion assigned directly to them. Moving Solids are more versatile than Rotating Regions, and there are several different types of motion available:

• Linear motion is the motion of a solid in a straight line. Examples include a piston moving in a cylinder, a hydraulic ram in a chamber, and objects on a conveyor belt moving through a curing process. The linear motion of solids can be fully prescribed, or it can be driven by the flow. If flow-driven, additional parameters are required including the bounds of motion and relevant resistive or driving forces. Examples of flow-driven lin-ear motion include the above items, as well as the simulation of valves opening and closing.• Angular motion is the rotation of an object about a centerline. Exam-ples of applications that use angular motion are positive displacement pumps (such as gear pumps and trichodal pumps), check or reed valves, and other devices with an angular movement. Unlike rotating regions (described above), objects with an angular motion can have paths that interfere--such as gear teeth in a gear pump or multiple mixing blades in an egg-beater. The Motion chapter of this guide contains more information about the use of rotating regions and angular motion for different applica-tions.• Combined Linear and Angular motion allows objects to translate as well as rotate about a user-specified axis. Examples of applications include certain flow meters that rely on both components of motion.• Combined Orbital and Angular: A typical application for Combined Orbital/Rotational motion is a pump shaft with an eccentric orbit (or whirl) component. The shaft rotates about its centerline, but also has an eccentric rotation about an additional axis. By specifying an orbit on an object, it is possible to understand the force imbalance imparted on bearings and other fixtures as a result of a shaft orbit.• Nutation is a type of motion used in several types of liquid flow meters. A nutating object is inclined at an angle to a reference axis. As the normal vector of the object rotates about the reference axis, the angle between the normal vector and the reference axis remains constant. The result is that the object actually wobbles about the reference axis, but does not change angular position relative to it. A coin wobbling along its edge as it slows from a spin is a good example of nutating motion.


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• Sliding Vane: The most common application of this type of motion is found in sliding-vane positive displacement pumps. Vanes or pistons rotate about the center-line of the impeller, but translate radially. The direction of linear travel changes at every angular position. The axis of rotation, how-ever, remains constant.

14.17 Rotating Regions: Turbomachinery

CFdesign includes the ability to analyze rotating devices surrounded by a static (non-rotating) frame of reference. By physically rotating the device and the region immediately surrounding it, this capability offers greater flexibility for analyzing rotating machinery. Examples include pumps, fans, blowers, and turbines. Centrifu-gal, axial, and mixed configurations are supported. Multiple rotating components in a device (such as the pump and turbine in an automotive torque converter) can be analyzed.

This functionality gives the user the ability to analyze the flow within the blade pas-sages of a rotating device. It also allows study of the interaction between rotating and non-rotating geometry. A classic example is the interaction between the rotor and the stator in an axial compressor or turbine. Another example is the influence of a volute cutwater (tongue) on the exit flow from a centrifugal pump impeller.

14.17.1 Geometric Considerations

The CFdesign rotating machinery capability analyzes rotating devices using a locally rotating frame of reference. This region completely surrounds a rotating object, and is called the rotating region.

Areas in the model that are not rotating are analyzed in a static (absolute) frame of reference. These regions are called static regions. (Obviously fluid in a static region can move, but the volume itself does not rotate in space.)

The following points summarize the geometric considerations for setting up rotating analyses:

• All rotating objects must be completely immersed in a rotating region. Such a region will rotate using its own relative rotating frame of reference.


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• The mesh that is generated in a rotating region will physically rotate along with the parts that are immersed.• Immersed parts can be modeled as voids in the rotating region, or they can be included as solids. (Solid objects in a rotating region will rotate at the same speed as the rotating region.)• The interface between a rotating and a static region is called the periphery zone. Within a periphery zone, the outer element faces of the rotating region will slide along the neighboring element faces of the static region.• The shape of a rotating region needs to correspond (loosely) to the shape of the rotating device. Rotating regions are usually fairly simple cylindrical shapes. This allows the element faces on both sides of the periphery zone to “fit” together easily.• The rotating region should extend to roughly the mid-point between the outer blade tips and the closest point of the surrounding non-rotating wall. • Do not apply any boundary conditions to nodes on the periphery zone. Care should be exercised when constructing fluid geometry to avoid such a condition.• Rotating regions from multiple rotating components must not overlap. Devices such as gear pumps or the beaters of a kitchen mixer cannot be modeled with the rotating machinery capability because their rotating regions overlap.• All rotating devices must have a rotating region and a static region that interact via the periphery zone. In other words, a rotating region cannot directly contact a non-rotating solid region, even if the solid is not inside of the rotating region. An example is a solid annulus surrounding the outside of rotating region. The result will be that the solid annulus (which is sup-posed to be static) will rotate. The resultant images will be very unex-pected.• Objects within a rotating region that have a uniform cross-section that satisfy the requirements for mesh extrusion can be extruded. The mesh inside of the rotating region, however, cannot be extruded.


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The following graphics illustrate these principals:

Rotating Region

Static Regions

Axial Fan(solid or cut-out)


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• If the blade tip clearance is extremely small (often because of tight seals), the surrounding static region can be eliminated. An example is shown:

• A rotating region must not be in direct contact with a solid region. The outer edge of the rotating region must either be a fluid or an exterior boundary.

Rotating RegionStatic Region

Periphery Zone

Pump Impeller

DischargeVolute

Rotating RegionImpeller

Inlet Outlet

Static Regions


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14.17.2 Boundary Conditions

If the rotational speed of the rotor is known, then pressures will often be specified. In many cases, the purpose of the analysis is to determine the flow rate generated by the device for a given pressure. Apply a pressure rise across the device. This will impose the resistance faced by the rotor. Note that it is recommended to start such an analysis with equal pressures assigned to both the inlet and outlet. As the impel-ler starts rotating and moving flow, the pressure rise can be gradually imposed. This can be done either manually or with a time-varying boundary condition.

Another situation involving a known rotational speed is that the flow rate is known, and the pressure drop is the desired output quantity. For such a model, specify a pressure of 0 gage at the inlet and the flow rate at the outlet. This method will often solve faster than specifying a pressure on both the inlet and outlet.

If the rotational speed of the rotor is unknown (as in the case of the torque-driven or the free-spinning scenarios), then a specified velocity or flow rate is most often appropriate. Recall that a pressure MUST be assigned to at least one opening in the model unless the model is fully enclosed.

Heat transfer boundary conditions can be applied as appropriate to conduct a heat transfer analysis.

14.17.3 Running Rotational Motion Analyses

Rotating device analyses are always run transient (varying with time). This is because the mesh of the rotating region physically rotates relative to the static regions in the model. Transient will be set automatically on the Analyze dialog when a part is designated as a rotating region.

A Time Step Calculator computes the ideal time step size for a known rotational speed. The time step size is computed to be the amount of time per blade passage.

For cases in which the rotational speed is not known (for known torque and free spinning analyses), use Intelligent Solution Control to automatically determine and vary the time step size throughout the analysis. The time step size will be modified to ensure that no more than three degrees of rotation pass for each time step. This criteria has been found to be quite stable for rotating analyses.


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In addition to the time step size, CFdesign automatically invokes several other set-tings for rotating devices: The number of iterations per time step is set to 1. The Automatic Turbulence Startup is set to the “Extend” mode.

Be sure to set a Results Output frequency. This controls how frequently the time steps are saved to the disk. Saved time steps can be used to animate the results after the analysis is completed. Care should be exercised when setting the output frequency to avoid saving so many results sets that your hard drive fills up.

As the analysis runs, the rotation of the rotating region (and any solids within the region) will appear both computationally and visually in the run-time results viewer.

At the conclusion of an analysis, a comma separated variable file (jobname_torque.csv) containing a time history of velocity and torque is written to the working directory. This information is also accessible on the Review_Notes task dialog.

Note that it is not possible to change the mesh and continue a rotating region anal-ysis from a saved iteration. If the mesh is changed, the analysis must be started from iteration 0 (the beginning). This is a consequence of the nodal organization and book-keeping that occurs during the initialization of a rotating region analysis.

14.17.4 Analysis Notes

The purpose of many rotating analyses is to obtain the flow rate for a known head or pressure rise. The most basic approach to such a problem is to apply the pres-sure rise across the device as inlet and outlet boundary conditions, and then spin the rotor or impeller at its known rotational speed. The problem with this approach is that solution accuracy may be compromised because of the unrealistically fast start-up of the device. Rotating analyses can be quite sensitive to instantaneous changes in the rotational speed or to the back pressure.

14.17.4.1 Time Step Size for Known Rotational Speed

For many rotating devices, we have found that using a time step size equal to the blade pass time allows a practical way to run enough revolutions to achieve accu-rate flow rate and/or pressure head prediction.

An example is a pump impeller with six blades. Using the blade pass time as the time step size, a complete revolution is completed in just six time steps. Some


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devices require as many as 100 revolutions before reaching a steady-state condi-tion. This time step strategy allows this requirement to be satisfied in a practical manner.

To facilitate this, a time step calculator has been added to the Analyze task dialog that computes the time step size based on either a prescribed number of degrees per time step or the number of blades. Open the dialog by clicking the Estimate button on the Analyze dialog when a rotating region is present:

Specify either the Degrees per Time Step or the Number of Blades, and the time step will be computed based on the rotational speed specified as part of the Rotating Region. If the number of blades is specified, the time step size will be com-puted using a single time step per blade passage.

If the model contains multiple rotating objects, he fastest rotational speed is used as the basis for the time step size computed in this dialog.

The Time Step Calculator is performing the following calculation to determine the time step size:

where t = time step (in seconds)

D = number of degrees per time step:

(for a time step size = to a blade passage)

N = rotational speed (in RPM)

t DN 6⋅-----------=

D 360NumberofBlades--------------------------------------------=


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When using this approach, the impeller will not appear to move because with each time step it rotates a complete blade passage. Additionally, this approach will not produce a time-accurate solution for the interaction between the rotor and a stator or a static volute. (It will produce accurate results for steady-state quantities such as resultant flow rate.) To save results with a finer resolution or to obtain a time accurate solution for the rotor-stator interaction, reduce the time step size to three degrees per time step and run an additional revolution after completing the set of multiple revolutions.

14.17.4.2 Non-Impulsive Startup

When a constant rotation speed is prescribed, an impulsive start means that the impeller accelerates from a stop to its rated speed in just one time step.This is hardly a realistic condition! In some devices, an impulsive start has been found to create large separation zones on the pressure side of the blade passage.

These separation areas prevent the blades from pumping as much fluid as they would in reality. The forces and vortex generation is quite large when this happens. In some cases, these vortices will be carried out of the impeller and a normal flow field will evolve over time. However, in some instances the vortices and the separa-tion remain and the flow rate through the device is greatly under predicted.

To prevent an impulsive start up, prescribe the impeller speed as a function of time using a table. A good guideline is to set the rotation speed at 0 RPM at time 0, and allow it to increase over the next 30 time steps to its full rated speed. If using a time step size that allows the rotation of one passage per time step (as described in the previous section), then multiply the time step size by 30 to determine the time at which the impeller should be rotating at its full speed.

For example, if a six bladed fan is to rotate at 1000 RPM, the time step size would be such that 60 degrees of rotation occurs per time step. At 1000 RPM, this works out to a time step of 0.01 seconds. If the impeller is to ramp up over the first 30 time steps, then our ramp up time is 30 x 0.01 = 0.3 seconds. The rotational speed table would then look like:

Impeller Speed (RPM)

Time, sec

0 0

1000 0.3

1000 100


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(The last line is to hold the rotational speed constant through the duration of the analysis.)

14.17.4.3 Flow Initialization Approach

The approach described in the previous two sections works well for most applica-tions, but if flow reversal throughout the device is a problem and is not washed out, then an additional approach is to first run two revolutions with a known flow rate running through the device. The boundary conditions would include a velocity or flow rate on one opening and a pressure on the other. (The placement of the flow rate and pressure should be based on numerical stability. Place the specified pres-sure where it makes sense to do so--not too close to the impeller if possible.) After two revolutions, replace the flow rate boundary condition with a pressure condition (to impart the specified head rise), and continue the analysis for another two or three revolutions. The flow rate will then adjust slightly, resulting in a better overall solution.

The challenge with this approach is knowing the appropriate flow rate with which to start the analysis with. This can usually be calculated using velocity triangles based on the known rotating speed and the blade angle, and the assumption of ideal flow. This initial flow just needs to loosely approximate the operating condition, and will provide a much better starting condition for the device than an impulsive no-flow start.

14.17.5 Visualization Notes

Results from a rotating analysis are viewed using the visualization tools described in the Results Visualization chapter of this guide. It is often useful to animate results to more fully understand the rotational effects and the interaction between the rotating and static geometry.

Velocity can be presented in the relative frame with the Feature Tree sub menus: On the Results_Scalar_Velocity Magnitude branch, right click on Velocity Magnitude, and select Reference Frame. The choices are Absolute and Relative. Absolute is the default. Relative is the velocity flow field with the rotational component (r omega) subtracted out. This is very useful for visualizing the flow within the impeller blade passages. Note that particle traces will show the relative velocity if this selection is made.


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Wall results data on the surfaces of rotating regions can be obtained for any time step. Prior to going into the Wall Results dialog however, it is necessary to first go to Review_Results, and activate those times steps on which wall results are required. After doing this, select the desired time step by right-clicking on the Results branch of the Feature Tree, and then selecting the time step from the Iterations/Time Step menu.

14.18 Moving Solids

The support motion types are described in the introduction to the Motion section. For all but sliding vane, the option to prescribe the motion manually or to let the flow drive the motion is available. (Sliding vane only allows user-prescribed motion.)

To define motion, the basic movement parameters are specified in the Motion Edi-tor. Such quantities include the speed or displacement/position with time as well as driving and resistive forces for flow-induced motion. All geometry-dependent parameters are specified on the main Motion task dialog. These items include the direction of travel, the center of rotation, as well as the initial position and the bounds of movement for flow-induced motion.

14.18.1 Geometric Considerations

Unlike Rotating Objects, a special “envelope” is not necessary around the moving object.

Because the initial position of moving objects can be set in the Motion task dialog, objects can be constructed in the CAD model where it is convenient. When prepar-ing the analysis model in CFdesign, the object can then be moved to its correct starting location. Note that all bounds information (for flow-driven analyses) will be relative to the selected starting position.

Moving objects can start completely inside the flow volume, partially inside, or completely outside. Moving objects can pass through the flow volume, and exit completely. If the moving solid starts outside of the flow volume but overlaps or


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even touches it, then the volume outside of the flow volume will be maintained as part of the flow volume, even after the solid leaves that region. This is illustrated:

When an object moves through the fluid volume, the mesh of the object will appear to overlap the flow mesh. The solid elements will block out the fluid elements, and the velocity of the moving solid will be transferred to the nodes of the underlying fluid.

If heat transfer is of interest, then the energy equation is solved between the fluid and the solid nodes. Obviously the heat transfer between the moving solid and the fluid will be a function of the respective materials as well as the velocity of the solid and of the fluids.

The motion of a moving solid can be described such that the solid will collide with static solids. The solver will allow this type of motion, and care should be taken to ensure that physically real solid motion is defined. A Preview function is provided that allows the motion to be “practiced” prior to running the analysis. This is described in the Motion chapter of this guide.

14.18.2 Meshing Guidelines

CFdesign uses a “masking” technique to model the interaction between moving sol-ids and the fluid through which the solids move. As a moving solid passes through fluid, its elements mask the fluid nodes, meaning that the velocity on those nodes is governed by the motion of the solid. The mesh density of a moving solid and the


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fluid in its path must be fine enough to adequately represent the interaction between the solid and the fluid.

The graphic on the right is an example of a fluid mesh that is much too coarse. As the solid moves through the fluid, there are times when the solid elements do not mask any fluid nodes. The result is that the solid has no effect on the fluid.


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If the fluid mesh is refined so that there is one row of masked nodes within the solid, the mesh is still too coarse.

Because of the motion of the solid, a pres-sure gradient will exist through it. With only one row of masked fluid nodes, only one pressure value can be transferred to the fluid at any given location. The gradi-ent will be lost.

The velocity results are shown for this mesh. The velocity field along the solid object is very irregular, and should appear all blue. The red areas are the fluid results “bleeding through” because of an inade-quate fluid mesh.

The pressure field with this mesh is highly irregular as well.


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To adequately mesh the moving solid and fluid path in this example, a minimum of two rows of masked nodes throughout the fluid path are required.

A more universal guideline is that the moving solid must be meshed finely enough to resolve gradients through it, and the fluid path must be meshed with a similar element size.

Such a strategy will allow proper masking of fluid nodes, and will support gradients within the pressure field.

The velocity field for this finer mesh is shown. No “bleed-through” occurred, and the results appear quite plausible.

The multiple layers of masked nodes allow the pressure gradient to be resolved well, as shown on the right. As the object moves upward, high pressures on the top surface and lower pressure on the bottom surface are apparent.


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14.18.3 Moving Surface Parts

When thin volumes are set into motion, the mesh requirements in the part itself and in the motion path in the flow can be quite severe. The moving volume must have a mesh that is fine enough to resolve the gradients through its thickness, and the flow path must have a correspondingly fine mesh.

To provide a more convenient method of analyzing the motion of thin objects, the Motion Module support moving surface parts. This reduces the meshing require-ments on both the moving part (because it is a surface part) and the motion path in the surrounding fluid:

On the Materials task dialog, create a surface part by assigning a solid material to the intended surface. The properties of the material and the shell thickness are used to compute the mass of the part, and influence the movement for flow-driven motion. For user-prescribed motion, the physical properties do not influence the motion. On the Motion dialog, change the selection mode to Surface, and select the surface or surfaces that are to move.

Guidelines• Any of the motion types can be applied to moving surfaces. The motion can be user-prescribed or flow-induced.• Surface parts cannot be coupled with moving solids using Motion Groups. Surface parts can, however, be grouped with other surface parts in Motion groups.• Moving surface parts cannot contact moving solids at their starting location.• Moving surface parts can fully enclose a region.• Moving surface parts do not have to be planar--they can be arbitrarily shaped.


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• Moving surface parts must not come into contact with parts that are extrusion meshed. The interaction between surface parts and extrusion meshed parts is not supported.• While moving surface parts can initially touch non-moving solid parts, they should not be in complete contact with a solid at their starting point. The reason is that after a small amount of movement, fluid will be trapped between the surface and the solid, and the pressure in the fluid may be very high.• To add clarity when visualizing the results of a motion analysis with a moving surface part, the moving surface is shown with a virtual thickness. This thickness is purely graphical, and does not influence the motion or the flow around the part.• The meshing requirements in the path of a moving surface are signifi-cantly reduced compared to the path of a moving volume. Unlike moving volumes, the solid elements do not mask the underlying fluid elements, and the fluid mesh does not have to be fine enough to resolve the solid.

The mesh should, however, be fine enough to resolve the pressure gradients on the surface. Likewise, the mesh within the fluid surrounding the moving shell should be fine enough to allow flow to pass around the surface as it moves.

In the image on the left, the 3D mesh surrounding the moving shell is quite coarse. As the valve opens due to the force of the fluid, very little fluid can pass around it until it has opened about half way. In reality, fluid would leak past such a valve at the onset of motion, and is shown in the model with a finer mesh on the right:


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Keep in mind that the amount of “bookkeeping” necessary to track the motion of a moving surface is similar to that of a moving solid. Because of this, moving surface motion analyses are as resource intensive as moving solid analyses, for a given mesh density. The advantage of moving surfaces is that the mesh in the motion path does not have to be as dense as for a moving solid analysis.

14.18.4 Radiation for Moving Parts

Radiation is now supported for moving solids. The view factors on a moving object are automatically recomputed when the part has traveled 2% of the maximum bounding box diagonal of the computation domain. This value can be changed by modifying the following parameter in the CFdesign Flags file:

ViewFactorUpdate A

where A = the percentage of the maximum diagonal. To increase the distance between each view factor update to 5%, for example, add this line to your flags file:

ViewFactorUpdate 5

This would change the tolerance to 5% of the max diagonal.

Increasing the distance between view factor updates will reduce computation time, but may reduce the accuracy of the heat transfer solution if the surrounding static geometry changes shape abruptly. Conversely, if the static geometry is uniform, then view factors between the walls and the moving solid will probably not change quickly, and a larger distance between updates will not adversely affect solution accuracy.

Guidelines • Moving objects that experience radiation heat transfer must not touch any stationary object or wall at any point in the analysis. This includes the as-built location as well as anywhere in the motion path.• Radiation cannot be used for rotating regions--it is only for moving sol-ids.• Moving parts must be opaque. They cannot have a non-zero value of transmissivity in their material definition.


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14.18.5 Automatic Time Step Determination

CFdesign will determine and adjust the time step size (shown on the Analyze dia-log) if Intelligent Solution Control is enabled (which it is by default). Click the Esti-mate button on the Analyze dialog to compute an initial time step size. To manually set the time step size, disable Intelligent Solution Control on the Solution Control dialog.

When Intelligent Solution Control is enabled, the time step for user-prescribed motion is calculated and set automatically based on the specified distance and/or velocity.

The time step for flow-driven motion is calculated automatically by initially using a value based on the surrounding flow velocity and/or the initial velocity of the object. As the object accelerates, the time step will automatically decrease to sat-isfy the basic criterion that an object in motion should not move through more than one element per time step. Adjusting the time step in this way has been shown to balance calculation efficiency with solution accuracy.

Intelligent Solution Control will automatically adjust under-relaxation parameters to remove instabilities from the calculation. We have found that doing this does not affect the time accuracy of the solution appreciably, and that solution stability can be greatly improved.

More information about Intelligent Solution Control is provided in the Analyze/Solve chapter of this book.

14.18.6 Solid Motion Solution Strategy

Solid body motion analyses are always run transient. When a moving solid material is assigned, certain Solution settings are automatically set. Such settings include switching the analysis to transient, setting the time step, and setting the number of internal iterations to one per time step. Additionally, Mesh Enhancement is turned Off. We’ve found that for some Solid Motion analyses, the presence of Mesh Enhancement can cause stability problems during the analysis. Because it is dis-abled, additional care should be taken when defining the mesh size to ensure that the mesh density is adequate for the flow.


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Setting the time step save interval and the number of times steps are left to the user. Be careful not to set a save interval that fills the hard disk with time step results sets.

As an object moves through a fluid, the space that was once occupied by the object is converted to a fluid. With this in mind, it is recommended that when applying slip conditions to a symmetry wall that cuts through a moving solid, that they be applied to the surface of the object that will become a fluid boundary after the solid has moved away. Not applying a slip condition to the surface of the solid (at its starting location) will result in a wall surface within the slip plane.

In most devices with a moving solid, there will be regions of fluid that are isolated from other regions during some point in the movement. An incompressible fluid will not allow pressure waves to travel throughout the medium, and may cause solution instabilities. Additionally, objects that are to move due to flow-induced forces may not move at all. For this reason, the use of compressiblity is recommended for flow-induced motion analyses. Enable Compressible in the Options dialog. For liquids and gases, this will cause pressure waves to move throughout the device, and will produce a much more realistic solution for flow-induced motion.

If Intelligent Solution Control is not used, then it is recommended to apply conver-gence controls to pressure on the Solution Controls dialog. Use of a value of 0.25 for pressure helps stability, and will damp out noise from the calculation.

14.18.7 Continuing after Making Changes

Due to the organization of motion data, it is not generally possible to continue a motion analysis from existing results if changes have been made to the mesh, boundary conditions, or motion parameters. If settings of a motion analysis are modified and the analysis continued from a saved time step, a warning will be given, and the analysis will be prevented from continuing. In particular, Motion changes that cannot be made mid-run include:

• Type of motion (linear, angular, etc.)• Direction of motion (user-prescribed)• Velocity or displacement with time (for user-prescribed)• Whether the motion is Flow-Induced or not• Removing a motion assignment from a solid


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To stop a part with a user-prescribed motion from moving part-way through an analysis, either construct a motion table so that after a certain time its displace-ment does not change (or its velocity is 0). For a flow-driven part, a part can be stopped mid-run by modifying its bounds so that it cannot move from its current location. Alternatively, modify its material density so that it is so heavy that the flow cannot continue to move it.

Obviously, if none of the changes described above are made to the Motion analysis, the solution can be stopped and continued.

There are some parameters, however, that can be changed mid-run, and the analy-sis made to continue:

• Max and Min Bounds (for flow-driven)• Forces (driving and resistance, including spring parameters, for flow-driven)• Material properties (particularly the solid density)

Note that it is possible to run an analysis without motion assignments, stop it, assign motion, and then continue without losing field results. The saved results files, however, will be deleted from the analysis directory after the field results are interpolated onto the analysis mesh.

14.18.8 Output Tables

A “.csv” file is written for every moving solid in a motion analysis that contains a time history of the linear and angular velocity, linear and angular displacement, force and torque. This file is named with the analysis name and the part name and the word “motion.” For example, the motion file for an analysis called Heating-Pro-cess that contains a moving solid called Product would be called:

HEATING-PROCESS_PRODUCT_1_motion.csv.

(In general, this will be the same name as assigned in the CAD model. However, for some models, the name will be a combination of the name of the CAD part and the name of the surrounding part.)

This file lists the linear and angular velocity, the linear and angular displacement, the force, and the torque for each time step of the analysis. This data is very useful for understanding the dynamic state of each part throughout the analysis.


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The linear and angular displacement values are relative to the initial position of the object as specified using the Initial Position slider on the Motion task dialog. Pay particular attention to this if the initial position differs from the as-built location in the CAD model.

Note that the “force” and “torque” values are the net values, and include driving, resistance, collision, contact forces as calculated in the Motion module. The hydrau-lic force and torque are just the force and torque imparted on the object by the fluid, and do not include any forces specified in the motion definition. The hydraulic values are reported in the Wall dialog.

These files are also accessible directly from the User Interface, and are found in the Notes tab of the Review task. Click the Motion Results button to open the Motion file.

If a motion analysis contains multiple moving parts, the data for each part is dis-played on a separate tab, and is selectable from the lower-left side of the dialog.


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CHAPTER 15 Troubleshooting

15.1 Introduction

This section discusses some common problems in three different aspects of the analysis process:

• Bringing geometry from the CAD tool into CFdesign.• Meshing the geometry.• Divergence of the analysis.

15.2 Problems between CAD and CFdesign

15.2.1 Pro/Engineer

15.2.1.1 If a Crash Occurs During Launch• Ensure that all parts have the same absolute accuracy. In some cases, the absolute accuracy may have to be reduced. In some cases, reducing it as low as 0.0001 (or lower) has fixed the issue.• Ensure the model does not have any Geom Checks.• Ensure that no parts are interfering.• Check the analysis-name_model.log file or the session trail file for the location of bad geometry. If necessary, create a construction point at this location to assist in locating the problem.• Suppress all cosmetic features.• If all else fails, systematically suppress components and/or slice away parts of the model until the problem area is isolated.

15.2.1.2 Other Common Errors

This section describes several issues that occur occasionally.


Troubleshooting

Error: Pros model: cannot retrieve regions. Error = 1; Status = 1

When trying to launch from WildFire 2 into CFdesign this error message is shown in the WildFire message window.

This is a licensing issue indicating that neither a Pro/Mesh nor a Mechanica license can be found.

If Wildfire Mechanica is available, (MECBASICENG and MECBASICUI are shown in the PTC license file), Pro/MESH is not required. The Wildfire and Mechanica setup may need to be modified using the following steps:

• Run Ptcsetup out of the wildfire bin directory• Hit next until you get to the “Optional configuration steps” page• Check “Configure other product interoperability” and hit Next• Make sure the mechanica install path is set under “Locate other instal-lation locations”

If Wildfire Mechanica is not available, then a Pro/Mesh license may be required. Please contact CFdesign Technical Support for more information.

Error: Failed to Take Pro/Mesh License

This error is given because Pro/ENGINEER can't find the meshpro.dll file that is called for from the protk.dat file. There is a simple work-around for this issue.

Instead of putting the protk.dat in the Pro/ENGINEER installation directory, you can place it in the default startup directory of the local machine. When starting Pro/ENGINEER, it will look there as well as the text directory, and if meshpro.dll exists on the local machine (which it will if you have CFdesign installed), this error will no longer be reported.

Only Surfaces Can Be Selected in a 3d model...

After launching a 3D model into CFdesign from Pro/E, volumes cannot be selected, and the Volume Selection Mode bullet on the task dialogs is grayed out. Only sur-faces are selectable. This indicates a problem in geometry.


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In the Pro/E model, look for cosmetic features and tiny geometric features that fall below the specified accuracy value.

Check for global interferences. Remove interferences by cutting one part from the other. If an interference is found, but the amount is shown as “???”, reduce the absolute accuracies of the parts that interfere.

A useful diagnostic technique is to reduce the absolute accuracy on every part, sub assembly, and assembly in the model. In some cases, this will cause one or more parts to fail to regenerate. This often indicates which part is problematic. After fix-ing the issue, launch into CFdesign and determine if the volumes are selectable.

If the volumes are still not selectable, then a further technique is to open each part individually into CFdesign to identify which part is causing the problem.

If all parts come into CFdesign properly, then the problem likely is in the assembly relations. To investigate this, place all but two neighboring parts on a layer and blank the layer. When CFdesign is launched, only those parts not blanked will come into CFdesign. This makes it easier to troubleshoot which assembly definition is causing the problem. Sequentially add neighboring parts back into the visible model and launch back into CFdesign until the problem occurs again--indicating which relation or pair of parts is causing the problem.

Another problem may be that a shell surface was included as a surface feature within a part. This will not work with Pro/E Wildfire. Shell surfaces must be added as separate parts to the assembly.

Missing Boundary Conditions

If a Pro/Engineer analysis was set up and run and a specified boundary condition disappeared from the model (or even after re-opening the cfd file), the problem is that a fluid part was divided by a solid part, resulting in a multi-body part. This is a single part that is divided into multiple disjointed volumes. Likewise, the surfaces of the block are divided into multiple disjointed surfaces.

The surfaces on the two disjointed volumes are considered to be the same surface (even though the ID in CFdesign is different, the Pro/E topology thinks they are one). Two seemingly disjointed surfaces have the same ID. When settings are applied to both and the analysis is run (or closed and re-opened), the conditions are mapped back to the surfaces. After applying the condition to the first surface with a given ID, the condition is not applied to the second surface--hence the con-


Troubleshooting

dition is lost. It is not recommended to use multi-body parts in Pro/Engineer for this reason.

15.2.2 Parasolid- and Acis-Based CAD Systems:

These include a large number of tools such as Solid Works, Solid Edge, Unigraphics, and Inventor.

15.2.2.1 If a Crash Occurs during Launch• Search the geometry for obvious errors--check to see if mating compo-nents contact properly, check for any sliver-type volumes or surfaces.• Check the analysis-name_meodel.log file for the location of bad geom-etry. If necessary, create a construction point at this location to assist in locating the problem.• If all else fails, systematically suppress components and/or slice away parts of the model until the problem area is isolated.

15.3 Problems During Meshing

This section contains diagnostic information and an explanation of some of the error messages that occur if CFdesign crashes or gives an error while generating the mesh.

15.3.1 Basic Techniques

15.3.1.1 Geometry from Pro/Engineer• Ensure that there are no interfering parts in the model.• The mesher is pretty good at fixing intersecting elements, but if the geometry is too small, and the element size is too large, then the mesher might falter. Try a smaller element size.• The problem might be caused by one or more components in the model that contain errors. Try to suppress parts systematically to find out which component is the culprit. Once located, it can be fixed.• Check the analysis-name_mesh.log file found in the working directory. Create a datum point in Pro/E to help locate the problem area.


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• Check the Pro/E trail file. This file contains all of the messages written during the meshing process, and will list the coordinates of problem areas.

15.3.1.2 Geometry from Parasolid and Acis CAD Tools• The mesher is pretty good at fixing intersecting elements, but if the geometry is too small, and the element size is too large, then the mesher might falter. Try a smaller element size.• The problem might be caused by one or more components in the model that contain errors. Try to suppress parts systematically to find out which component is the culprit. Once located, it can be fixed.• Check the analysis-name_mesh.log file found in the working directory.

The locations of errors occurring during the meshing of Parasolid and Acis models are reported in the mesh log file (jobname_mesh.log). Specifically, the CFdesign ID of the problematic surface(s) are given in this file. An excerpt from such a file is shown:

With the CFdesign ID, it is convenient to locate exactly where the problem is occur-ring.

An easy technique to find a surface by its ID number is to:

• First, enable surface selection in the Loads dialog• Use the Select All button to add all of the surfaces to the selection win-dow.• Highlight (using Windows-standard multiple selection techniques) all of the surfaces except the desired one, and remove them from the list.• The remaining surfaces are where the meshing problems are, and can be added to a group for easy reference later.

The next step would be to either apply (or refine) a surface mesh size to the surface or to return to the CAD tool and repair the geometry at the indicated location.

15.3.2 Specific Meshing Error Messages

!%CItag = 54, type = Unknown


Troubleshooting

If the last few lines in the trail file or mesh log look something like this:

!%CI(2) face meshing 54/87

!%CItag = 54, type = Unknown

You will need to review the surface topology of the model.

The mesher first meshes the individual surfaces. Failure at this point indicates that the mesher failed to mesh a particular surface. In this example it is likely to be sur-face #54 out of a total of 87 surfaces. You should investigate the surface to deter-mine if there is an error in the geometry, perhaps an unintentional sliver surface, or if just refining the mesh on that surface will suffice. To mesh highly curved surfaces effectively, use an element size that is small enough that a nodes are spaced every 30 degrees along the arc.

fixSelfInter': edge-face intersection

If the last few lines in the trail file or mesh log look something like this:

fixSelfInter': edge-face intersection

!%CItag = 226, type = Plane

!%CI(2) face meshing 227/227

!%CItag = 227, type = Plane

!%CIAfter surf mesh, num faces = 10761

!%CI(2) smoothing surface mesh started

!%CI(2) fixing surface mesh intersections started

!%CI'fixSelfInter': edge-face intersection

!%CI at 1.452821 9.126500 0.485000

!%CIfixSelfInter: edge on type= 2 tag= 227 split !

!%CI'fixSelfInter': edge-face intersection

!%CI at 1.571153 9.126500 0.485000

The mesher has completed meshing the surfaces and is trying to blend the individ-ual surface meshes together. The fixSelfInter error indicates that the mesher is unable to properly blend two surfaces together because the surface mesh is too coarse or there is an error in the geometry. The coordinates of the error are given. Locate the problem area in CFdesign using the Rotation Point dialog or in the native CAD tool.


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Couldn’t find merge use

If the last few lines in the Pro/E trail file contain something like this:

!%CIGEdge::mergeUses - error: couldn't find merge use 41

!Edge Information:

!edge 41 -

In Pro/Engineer, adjust the absolute accuracy of the assembly and parts. This error typically occurs when the default relative accuracy is used and there is a combina-tion of very small and large parts in the assembly. Starting with the small parts, change the absolute accuracy to the smallest value that Pro/E will allow. Then change absolute accuracy of the remaining parts to that same value. It may be necessary to temporarily modify the size of the larger parts to be able to use the same accuracy value. After the value is assigned, revert such parts back to their correct dimensions.

In the message above, the problem is occurring at edge 41. Locate this edge in CFdesign in the Meshing task dialog. (Switch to Edge selection, and enter a select all command. Remove all but the edge of interest from the Selection list.) The edge will be highlighted, and can be located.

You can also use the next piece of information in the log file:

Bounds: (0.01,0.436,1.685) (0.01,0.436,1.78776)

vertices:

vertex 2714 - 20100910 (0.01,0.436,1.78776)

vertex 2716 - 20100CE0 (0.01,0.436,1.685)

These are the vertices of the edge that are having problems. Locate these points in the CAD tool or with the Rotation Point dialog in CFdesign by typing in the coordi-nates (a gray dot will appear at the coordinate location). View the model in Outline mode to see the dot.

Out of Memory

If the last few lines of the trail file or meshing log look something like this:

!%CI0 unsnapped vertices from cavity meshing

!%CI(2) smoothing volume mesh started

!%CI(2) optimizing volume mesh started


Troubleshooting

out of memory

All of the available computer memory (RAM) has been used. Assign larger element sizes or modify the geometry so that fewer elements will be required.

Invalid meshCavity / retriangulation fails

Delaunay Cavity Mesher in progress.

New cavity vertices from "x" faces.

Delaunay insertions of "x" vertices.

Inserting "x" extra vertices by splitting...

Cavity bdry recovered successfully.

Delaunay Cavity Mesher in progress.

New cavity vertices from "x" faces.

Delaunay insertions of "x" vertices.

Inserting "x"extra vertices by splitting...

Cavity bdry recovered successfully.

"x"unsnapped vertices from cavity meshing

Invalid mesh

Cavity retriangulation fails

This error message means that there is insufficient mesh definition on rounded geometry. Refine the mesh definition on rounds and curved surfaces.

15.4 Startup Problems

15.4.1 Before Starting

If the Go button is grayed out and unavailable, the CFdesign server (not the license server) is likely not running. Start Servman (located in the CFdesign installation folder), and click the Install button if it is not installed. Click the Start button if the service is installed, but not running.


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15.4.2 During Initial Processing

Once Go on the Analyze dialog is hit, if an error occurs and the analysis does not start, consult the Status file (Review_Notes) to read the error. Various errors that can occur are:

• Could not connect to server: Make sure that the solver machine has the process cfdserv.exe running. If the analysis is to be solved locally, this process should start automatically, but verify that it did using the Task Manager. Start it manually if necessary opening the server manager (serv-man.exe) in the installation directory, and hit Start.• Could not connect to server: A second solution is to verify that a network connection exists between the local computer and the solver com-puter. Ensure that permissions (including within the firewall) allow reading and writing between both machines. • Licensing problem: Verify that the licensing is configured and operat-ing correctly.• Unable to find the GBI file: chances are the working directory (as set in Pro/E) is not the same directory as where the Pro/E model was saved. Change the working directory and try again, and/or copy the model files into the intended working directory.

15.4.3 Mesh Enhancement Diagnostics

An analysis will sometimes stop during mesh enhancement, before any iterations are completed. A message in the analysis window will indicate that an error occurred during mesh enhancement and direct you to view the status file.

First, take a look at the status file. Click the Notes tab in the Review task to find the Status File button. Typically the error will read that the mesh is too coarse. A list of the nodes and their coordinates are contained in the status file to help locate where the mesh enhancement is failing.

Before re-meshing, try adjusting the mesh enhancement thickness factor. This parameter can be found under the mesh enhancement button at the bottom of the mesh definitions page. Reduce the thickness factor in increments of 0.05 until you reach 0.05. If you must go less than this thickness factor, you may need to investi-gate refining your mesh by changing the mesh size on volumes, surfaces or edges.


Troubleshooting

Note that a Mesh Enhancement error can be an indicator of geometry problems in the CAD model. Be sure to avoid thin slivers as well as tangency between planes and cylinders and/or spheres.

15.4.4 After Initial Processing

Once the analysis phase has started, the start up processing steps are displayed in the information window of the Analysis window. When all input processing is com-pleted, iterations should commence. These are some of the more common errors that may occur after initial processing is complete, but before any iterations are run.

• bicgstab.c, iner product (**,**) equals 0: This means that there is a significant error in the analysis setup. Examine the boundary conditions to determine if they define an ill posed problem (a setup that violates the conservation of mass such as velocities specified on both inlets and out-lets). Check the analysis units. Check the materials and property defini-tions. Check internal fans and distributed resistances definitions. Check rotating regions and moving object definitions. Check the mesh. The solu-tion might be that the mesh needs to be refined somewhere in the model.• If the Analysis hangs: Make sure the program has been installed properly and that all CFdesign files are in the installation directory. Check licensing, and the server using the Servman executable found in the CFde-sign installation folder. For very large analyses, be patient--the first itera-tions may take some time to complete. • If there is not enough in-core memory available for the CFD problem being run, the message “Maximum available memory may have been exceeded” will be printed in the status file. If the memory limit is exceeded, CFdesign can be run using a virtual memory manager to “page” to the hard disk.• Analysis Queued: If CFdesign thinks that there is another analysis running, it will add the current analysis into the Queue. If there was not another model running and the current analysis was added to the Queue, hit the Stop button, and exit out of CFdesign. Start Servman (located in the CFdesign installation folder), and Stop the server. Click the Uninstall but-ton. This will clear the Queue. Install the server, and exit from Servman. Start CFdesign again, and run the current model. If it is added to the queue again, hit the Stop button, exit CFdesign and reboot the computer.


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15.5 Divergence Before Iteration 10

Even with Automatic Solution Control invoked, most of the problems that cause quick divergence have to be fixed by the user.

Check property values and variations (a zero viscosity frequently causes quick divergence) in the summary file or on the Materials dialog. Also, make sure the length unit specified in the Feature Tree is correct (for Pro/E models) or results in the expected dimensional lengths in the geometry.

If you are using variable properties, the temperature should be initialized to some appropriate value. A temperature of zero will definitely cause problems.

If the flow is turbulent, but laminar is selected from the Turbulence dialog on the Options dialog, the solution will diverge quickly. Try turning on a turbulence model. Also, make sure the Automatic Turbulent Start Up is turned On.

Try increasing the Turb/Lam Ratio in the Turbulence dialog on the Options dialog by an order of magnitude.

Ensure that all volumes in a 3D model or surfaces in a 2D model have an assigned mesh size. Any part that does not have an element size will be meshed with a very coarse element size, which could lead to divergence. To cause a part to not be meshed, assign an element size of 0.

15.6 Divergence After Iteration 10

If the inlets or outlets contain recirculation zones, the problem is not well-posed mathematically and may eventually diverge. You may have to move these bound-aries out, as shown in the Boundary Condition section of this chapter.

If there are gaps which have fewer than 3 interior nodes, the solution may also diverge. This is usually only true if the gap is in a critical area of the flow. Make sure Mesh Enhancement is enabled, and that more than one element layer will be gener-ated.


Troubleshooting

15.7 Divergence Later in the Analysis

Intelligent Solution Control will generally prevent divergence in most analyses by slowing down progress of the calculation variables, and eliminating trouble-spots in the solution field. If the analysis does diverge, however, it is likely due to a mesh that is just too coarse for the scope of physics or geometry of the model. Adjust the mesh, refining it in areas of high gradients, and re-run the analysis.

The following manual convergence adjustment steps should be taken if Intelligent Solution Control is not invoked:

If the solution gets a large spike soon after iteration 50 and continues to grow or at least does not converge, you should try choosing Lock On for the Automatic Turbu-lent Startup Procedure (Options_Turbulence).

Though many CFD analyses, including turbulent ones, may be performed with the default CFdesign control settings, some require special treatment to achieve a solu-tion. When necessary, the following steps are recommended to aid convergence, particularly when the solution is unstable or diverging in the early iterations (these steps should be implemented individually in the order given):

1. Lower the convergence control on the pressure equation from the default value to 0.2. This is done on the Convergence Controls dialog on the Analyze task.2. Try setting the Auto Turb to Extend in the Options_Turbulence dialog. This is a variation of the Automatic Turbulent Startup algorithm that is particularly useful for some compressible flow problems.3. Observe the solution results during the analysis in the Results dialog. Errant velocity vectors or splotches of high or low pressures indicate where the solution is having difficulty. Often refining the mesh in these locations solves the problem. If necessary, you may have to re-run the analysis and stop just before divergence occurs (1-2 iterations). The turbulence quantities (TKE and EPS) can also be indica-tors.

15.8 Oscillating Results

There are three scenarios which cause results to oscillate in the Convergence Moni-tor:


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1. The first is that the mesh is not fine enough. By observing where the solution changes while the analysis running, it is easy to quickly locate areas of the model in need of mesh refinement. Show vectors, and note where the directions are chang-ing. Often you will see one or a small number of vectors in some critical location such as a wake oscillating.2. Another scenario which causes this condition is recirculation zones crossing inlet/outlet planes. Again, this can be quickly diagnosed by observing the Results window. If these zones can be eliminated in your model, the solution should con-verge.3. The third cause of oscillating residuals is vortex shedding. If you switch to tran-sient, you should be able to obtain a converged solution.

In some instances, the oscillation amplitude may be small enough that the solution may be converged enough for the purpose of the analysis. Use the Automatic Solu-tion Control and Automatic Stop to determine if such oscillations are not altering the results substantially.

15.9 Contacting Technical Support

If all else fails, please contact Blue Ridge Numerics or your reseller for technical support.

For those customers that have purchased CFdesign directly from Blue Ridge Numerics in the United States and Canada:

Target Number or AddressPhone Support 434.977.2764 (Support = Option 3)

Fax Number 434.977.2714


License Request [email protected]





Troubleshooting

For those customers that have purchased CFdesign directly from Blue Ridge Numerics in Europe:

For those customers that have purchased CFdesign directly from Blue Ridge Numerics in Asia:

Blue Ridge Numerics also has a strong reseller network throughout Europe and Asia. If you purchased CFdesign through a reseller, please contact that reseller directly for support and licensing.

Target Number or AddressPhone Support +44 (0) 1628 501 570 (Option 2)

Fax Number +44 (0) 1628 826 768

Phone Support in German and French

+44 (0) 1628 501 570 (Option 4)






Target Number or AddressPhone Support +1 434.977.2764 (Support = Option 3)

Fax Number +1 434.977.2714







Index

Ind

ex

Index

AAbaqus 12-3absolute accuracy 15-1absolute pressure BC 4-4absolute velocity 11-9,

14-63accuracy in Pro/E 3-10Acis 1-7, 3-12, 9-13, 15-4,

15-5Acis part names 3-16activation energy 6-11add analysis to a

project 13-3add by key-in 11-38add by picking 11-38add existing button 10-

23add section button 10-24adiabatic compressible

flow 6-10, 6-16Advanced 1-6, 14-1Advanced Solution

Control 9-19advanced turbulence

quantities 8-9advection schemes 9-22aerodynamic forces 11-

45albedo 14-43altitude effects 14-7analysis 13-1analysis client 9-10analysis computer 9-10,

9-11Analysis Intelligence 9-

15analysis name 10-25analysis queue 9-14analysis queued 15-10analysis report 10-21analysis server 9-10analysisname.res.s# 9-

17analyze directory 1-13analyze information 9-14Analyze task dialog 2-41angular

displacement 14-74angular motion 7-18, 14-

54angular velocity 14-74animation of particle

traces 11-31animation of results 10-

19animation speed 10-19annotations 10-14, 11-11annulus surfaces 5-4Ansys 12-4Applied Force 7-74archive file 2-9Arrhenius 6-11Arrows 5-12arrows check box 5-7Asia contact

information 1-17, 15-14

asphalt emissivity 14-42associative selection 2-

24attenuation 14-26author of a report 10-25Auto Turb (ATSU) 8-8Automatic Convergence

Assessment 9-19, 14-6

Automatic Mesh Sizing 5-13

Automatic on Extrusion 5-25

Automatic Size button 5-14

automatic wall specification 4-18

axial velocity 6-52axis of nutation 7-56axis of rotation 7-21, 7-37axisymmetric 14-31

Bbackground color 2-7, 2-

11background

temperature 4-9baffles 6-37Basic 1-6, 14-1batch mode 9-14

bias factor 5-42bicgstab 15-10bivarient non-

Newtonian 14-4blade passage 14-61blanking 2-26blanking undo 2-26, 11-12board 6-67boundary conditions 14-

8, 14-59boundary layer flows 14-

16Boundary Mesh

Adaptation 5-45bounds 7-8, 7-23, 7-37, 7-

39, 7-57, 7-73, 7-74Bring Analysis into a

Project icon 2-4Bring analysis into a

project icon 13-4bulk data from

project 11-37bulk flow rate 11-36bulk modulus 6-7bulk output files 11-37bulk results 13-11bulk thrust 11-36bulk velocity

components 11-36buoyancy 14-8

CCAD Integration 1-2CAD-KEY 3-12cannot retrieve

regions 15-2Carreau 6-13case 6-67CATIA 1-7CATIA v5 3-17, 6-31cavitation 11-46Celestial Orientation 8-

11center of nutation 7-57center of rotation 7-22, 7-

38, 11-45Center of Rotation

icon 2-5centrifugal blowers 5-21centrifugal pump mate-

CFdesign User’s Guide I-1

Index

rial creation 6-57centrifugal pump/blower

material 6-54centroid 11-26centroid of surface 7-77CFdesign 7.0 1-16cfdesign90temp 3-6cfdserv7.exe 1-11cfdserv9.exe 9-11change analysis

model 9-12change length unit

only 2-28changing entity

names 2-29check valves 6-59, 6-60city 8-11clamping 11-50clash detection 3-18client/server 9-10cloud cover 14-43collision 7-78collisions 7-71colored stripes for

loads 4-21combined linear/

angular 7-34, 14-54combined orbital and

angular 14-54Compact thermal

model 6-66Compass Direction 8-11component

temperatures 10-12component thermal

summary 6-72compressibility 6-7compressible 9-22compressible flow 8-3

external 14-49internal 14-48

compressible liquid 6-7, 14-21

compression angle 7-31compression

displacement 7-15compression force 7-15compression torque 7-31compressors 14-53conclusions in a

report 10-27condensation 14-23condensed water 8-12conduction 14-7conduction-only 8-1conductivity 6-6, 6-20configurations 1-6conjugate heat

transfer 14-11connection to server 15-

9constant eddy

viscosity 8-8Constant in Time 7-76constant internal fan

flow rate 6-51constant loss

coefficient 6-42constant property

type 6-9Constant Vector 7-75contact information 1-17contact resistance 6-23Continue From 9-12contour lines 11-9, 11-48convection boundary

condition 4-6convection

coefficient 11-46convergence controls 9-

21convergence monitor 9-

25, 10-2convergence plot 10-26Coordinate axis icon 2-7coordinate systems 2-28copper content 6-77copper thickness 6-77corners 14-3corporate logo in a

report 10-25Cosmos 12-5country 8-11Cp/Cv 6-7create analysis 1-7create text button 10-23current boundary

condition 4-8, 14-51curvature 5-16cusp surfaces 5-4

cut surface 11-14cut surface

appearance 11-18cut surface location 11-

17cut surface

orientation 11-17cut surface rotate 11-26cut surface task

dialog 11-16cutoff pressure 11-46cutoff strain rate 6-12cutoff viscosity 6-12cutting surface table 11-

17cyclic symmetry 14-16cyclical 7-10cyclical motion 7-10, 7-

26, 7-59cylindrically-shaped

resistance 6-36

DDarcy 6-43, 14-14Darcy Equation 6-47, 14-

14database materials 6-3,

6-17date in a report 10-25default analysis

options 8-1default units 2-28degrees of freedom 7-70,

7-72Degrees per time step 9-

4, 14-61delete from report 10-23delete particle traces 11-

30deleting a note 10-16deleting a report

section 10-24density 6-6, 6-20Design Communication

Center 1-4, 11-52Design Review 1-4Design Review Center 1-

4, 10-17, 11-37, 11-56, 13-9, 13-12

Design Review

I-2 CFdesign User’s Guide

Index

Ind

ex

Server 13-12dialog placement 2-10die 6-67dielectric 6-78diffuse energy

transfer 14-26direction vector 7-7, 7-35,

7-65displacement 14-74distributed resistance 5-

21, 5-40, 6-32, 6-37, 14-12

diurnal 14-44diurnal heating 8-9divergence

after iteration 10 15-11before iteration 10 15-11

docking of dialogs 2-2documentation 1-5domain shape 3-3down button 10-23drag accuracy 14-6drag correlation 11-34DRC 11-56, 13-9driving force 7-12driving nutation

torque 7-61driving torque 7-28Dynamic Image 1-4, 11-

50Dynamic Images 10-20

EEarth 8-5edge bias factor 5-42edge curvature 5-16edge diagnostics 5-8edge mesh size 5-41editting a note 10-16effective PCB

properties 6-73element 5-1element size criteria 5-42embedded surfaces 6-25emissivity 4-10, 6-7, 6-20,

14-26, 14-42empirical film

coefficient 9-24end layering 5-26

energy balance 10-9, 14-24, 14-38

engagement angle 7-31engagement

displacement 7-15engagement force 7-15engagement torque 7-31equation of state 6-10, 8-

3error estimation 10-4errors during launch 15-

1Estimate button 9-3Euler or invisid flow 4-5European contact

information 1-17, 15-14

existing analysis 1-9exiting CFdesign 2-19export options 2-9extended ATSU 8-8extensions 1-14external fan boundary

condition 4-7external fan rotational

speed 4-7external flow 14-5external flow

meshing 14-5Extrude Mesh button 5-

24extruded fan blades 5-22extrusion 5-22extrusion direction 5-25extrusion guidelines 5-30extrusion layers 5-26

Ffan blades 5-22fan curves 14-4fans 14-53Fast Track 1-4, 1-12, 9-11,

13-14FEA 1-3FEA deck 12-2FEA mesh 12-1feature tree 2-27

loads 4-23materials 6-79

part names 3-16results 11-6

feature tree placement 2-10

FEMAP 12-5Fieldview 2-9file export options 2-9File menu 2-8file types 1-14fill voids in CATIA 3-20fillvoids 3-6film coefficient 11-46film coefficient boundary

condition 4-6film coefficient result 11-

45filtering 11-48, 11-50first order polynomial

property variation 6-14

flags file 2-43flow core in Pro/E 3-2flow driven combo 7-42flow geometry 3-1flow initialization 14-63flow off 8-1flow on 8-1flow types

boundary layer 14-16moist gas 14-22radiation 14-24steam/water 14-23subsonic

compressible 14-46supersonic flow 14-46transonic 14-46

flow volume in acis/parasolid 3-13

flow volume in Pro/E 3-4flow volumes in CATIA 3-

18flow-driven angular 7-26flow-driven linear 7-10flow-driven nutation 7-59flow-driven orbital 7-50fluctuation value 10-5fluid property types 6-6force 14-74force location 7-76


Index

Force Magnitude 7-76forced convection 14-10forces on surface

parts 10-12FR4 6-73frame around a note 10-

16free area ratio 6-44, 14-

14free motion 7-70friction factor 6-43, 6-44,

14-12, 14-13fringe range 11-48

Ggage pressure boundary

condition 4-4gas constant 6-10general scalar

variable 8-12Generate Report 10-28generating a report 10-

24geom checks 15-1geometry inversion 3-2geometry modification 3-

25, 13-3glass 4-9global axis 11-26globally displayed

result 11-8GLView PlugIn 11-55GMT 8-11GO 9-12gotolink ch4_loads.fm

loads chapter 2-38gotolink fan-

thermostat 6-55gotolink options_solar

heating 14-43gotolink

transmissivity 6-20graphics files 10-27graphics region 2-2graphics text file 10-16Grashof number 14-8grass emissivity 14-42gravity 7-71, 7-77, 11-34,

14-10

gravity for moving solids 8-6

gravity vector 8-5grayed out Anayze

dialog 9-13grayed out mesh

dialog 9-13Greenwich Mean Time 8-

11ground volume 14-40groups 2-30, 7-3, 11-11growth 5-25

Hharmonic time curve 4-

15heat flux boundary

condition 4-6heat flux results 11-45heat transfer 14-7, 14-48

conduction 14-7forced convection 14-10gravity 8-5mixed convection 14-10natural convection 8-5,

14-8off 8-3on 8-3radiation 8-5

Height of Fluid 4-20, 14-21

help 2-19Herschel-Buckley 6-13high speed jets 14-3Highlight Edges Slider 5-

12Highlight Surfaces

slider 5-7HTML report 10-20humidity 8-12, 14-22, 14-

23humidity boundary

condition 4-5hydrodynamic forces 11-

45

II-DEAS 12-5

I-DEAS mesh 3-27IGES 1-2, 3-1implicit method 9-6include in report 10-23included fluid

materials 6-3included solid

materials 6-17incompressible flow 8-2

external 14-5internal 14-2

Incremental rotation icon 2-6

industrial fans 6-52infinite strain viscosity 6-

13Information 9-14initial angular velocity 7-

28initial conditions 4-19, 14-

20initial nutation

velocity 7-61initial position 7-7, 7-23,

7-36, 7-39, 7-57, 7-66initial velocity 7-12, 7-78inlet boundary

conditions 4-17external fan 4-17mass flow rate 4-17pressure 4-17scalar 4-17temperature 4-17total pressure 4-17total temperature 4-17velocity 4-17volumetric flow rate 4-17

inlets/outlets 5-40, 10-11inner iterations 9-6, 14-20Intelligent Solution

Control 9-15, 14-21Intelligent Solver

Selection 9-21interface computer 9-10interferences in CATIA 3-

18interferences in Pro/E 3-

9internal fan creation 6-50


Index

Ind

ex

internal fan curveconstant flow rate 6-51pressure-head curve 6-

51, 6-52internal fan rotational

speed 6-54, 6-58internal fans 5-21, 6-47,

14-4internal flow 14-2interval save table 9-8Inventor 1-7, 2-28, 3-12,

6-31, 15-4inverse polynomial prop-

erty variation 6-15inverse polynomial time

curve 4-16iso surface 11-43iso surface vectors 11-44Iterations to Run 9-13

JJoule heating 14-51junction 6-67

Kk-epsilon turbulence

model 8-7key in points 11-29known rotational

speed 6-64Knudsen number 14-4

Llaminar 8-7latitude 8-11launching 1-7layers 5-26layers of surface parts 6-

28legend levels 11-48license status 2-20linear displacement 14-

74linear motion 7-6, 14-54linear springs 7-15linear velocity 14-74linked motion 7-3Loads task dialog 2-38

boundary conditions 4-2initial conditions 4-20

Location 7-76Lock on 8-8longitude 8-11Loose 9-19lost settings 13-7low pressure limit 14-4Low Reynolds

turbulence 8-7, 14-3

Mmass flow rate bound-

ary condition 4-4massed particle

density 11-33massed particle drag 11-

34massed particle

gravity 11-34massed particle initial

path 11-34massed particle

radius 11-33massed particle

traces 11-31material appearance 11-

7material assignment 6-3,

6-17material colors 6-79material creation 6-3, 6-

17material database 2-11materials database 6-1Materials task dialog 2-

39, 6-3, 6-17materials task dialog

centrifugal pump 6-54check valves 6-59internal fan/pump 6-48resistance 6-33rotating regions 6-61

Max Size 5-12Mechanica 12-4mesh density 14-2Mesh Enhancement 5-43,

15-9boundary mesh

adaptation 5-45number of layers 5-45thickness factor 5-45

mesh generation 1-3, 5-47, 9-13

mesh import 3-27mesh inspection 9-13mesh preview dots 5-16mesh reference points 5-

42mesh refinement 5-39,

14-2mesh size estimate 5-41mesh size

fundamentals 5-37mesh size reduction 6-23Mesh Size task dialog 2-

38mesh-independent

solution 5-38meshing by parts 5-46meshing moving

objects 14-65meshing problems 15-4meshing refinement

inlets/outlets 5-40moving solds 5-41porous media 5-40rotating regions 5-40solid boundaries 5-39sudden discontinuity 5-

40thermal boundaries 5-40

meshing strategy 5-38MicroSoft PowerPoint 11-

54MicroSoft Word 11-55min and max 7-8, 7-23, 7-

37, 7-39, 7-57Minimum Refinement

Length 5-8mirror icon 11-6mirrored symmetry 14-

30mixed convection 14-10mixing length 8-8mixture fraction 14-23model change 13-5model image 10-25


Index

model notes 10-15moist gas 8-12, 14-22moment 11-45monitor points 10-5Moody formula 14-13morphing 11-22morphing limitations 11-

24Motion 9-18, 14-1motion groups 7-3Motion Module 1-3, 1-6, 5-

40, 5-41, 6-61, 7-1, 14-53

motion output file 14-74motion output table 14-

74motion path 5-21Motion task dialog 2-40motion with extrusion 5-

22motion with radiation 14-

31mouse modes 2-22moving a note 10-16moving non-planar cut

surf. 11-21moving solids 5-41, 14-

54, 14-64multiple fluids 14-15multiple scalar

legends 11-13

NNastran 12-3Nastran mesh 3-27natural boundary

condition 14-47natural convection 14-8natural convection

boundaries 14-8natural convection

domain 14-8natural convection

guidelines 14-9navigation 2-22near wall

temperatures 11-46new analysis 1-7New icon 2-4, 13-2, 13-4newlink fan-

thermostat 6-49newlink transmissivity 6-

21nodal field data 2-9node 5-1non-Cartesian-oriented

resistance 6-34non-conformal 14-26non-conformal

meshing 5-22non-impulsive

startup 14-62non-Newtonian property

variation 6-12normal directions 6-34number of blades 9-4, 14-

61number of layers 5-45nutation 7-53, 14-54nutation tilt axis 7-55

Oolive surfaces 5-6opaqaue 14-26open analysis 1-9Open icon 2-4Open Project 13-13Open View Settings

icon 11-2optional parameters 2-43Options task dialog 2-40,

8-1orange surfaces 5-5orbital 7-45order of analyses 13-8order of appearance 7-4orientation 11-19, 11-20oscillating motion 7-25oscillating results 15-12outlet boundary

conditions 4-18external fan 4-18pressure 4-18unknown 4-18velocity 4-18volumetric flow rate 4-18

outlet configuration 14-2outlet location 4-18outlets 3-24

outlets at corners 14-3Outline Image icon 2-5Outline image icon 11-3

Pparametric changes 3-1Parasolid 1-7, 3-12, 9-13,

15-4, 15-5Parasolid part names 3-

16part appearance 2-29part blanking 11-12part by part meshing 5-

46part dependent

legend 11-49part interference 15-1part suppression 5-3particle trace 11-27particle trace

appearance 11-31particle trace residence

time 11-29particle traces with

mass 11-31Patankar 1-3PCB material 6-69PCB thickness 6-76Peel Surface icon 11-4percent metal 6-77perforated plates 6-37periodic boundary

condition 4-8periodic boundary

conditions 14-16periodic symmetry 14-31periodic time curve 4-14permeability 6-43, 6-47,

14-12Perspective View icon 2-

7pick on plane 11-28piece-wise linear prop-

erty variation 6-16piecewise linear time

curve 4-16Place analysis in project

icon 13-2, 13-3planes 6-77planetary motion 7-45


Index

Ind

ex

Play Macro button 5-19PLM/PDM 3-1polynomial property

variation 6-15polynomial time curve 4-

16porous media 5-40, 6-32,

14-11position 11-19, 11-20power law exponent 6-12power law index 6-13power law property

variation 6-9power law time curve 4-

15PowerPoint 11-54Prandtl number 14-8preferences 2-10pressure boundary

condition 4-3pressure control 9-22pressure direction 12-2pressure drop in a

pipe 14-3pressure flow-rate

curve 6-45pressure result 11-45, 12-

2pressure waves 14-21pressure-flow rate

curve 14-14pressure-head curve 6-

51, 6-52preview motion 7-3Previous View icon 2-7printed circuit board 6-72Pro/E meshing 9-13Pro/Engineer 1-7, 3-11,

15-1, 15-4Pro/Mechanica 12-4Pro/Mesh license 15-2probe

cut surface 11-14surfaces 11-12

problematic surfaces 5-4project 1-9, 13-2

settings 3-26project bulk data 11-37project report 10-30property variations

Arrhenius 6-11Carreau 6-13constant 6-9equation of state 6-10first order polynomial 6-

14Herschel-Buckley 6-13inverse polynomial 6-15non-Newtonian 6-12piece-wise linear 6-16polynomial 6-15power law 6-9second order

polynomial 6-14Sutherland 6-11

pumps 14-53Put Analysis to Project

icon 2-4

Qqueue 9-14

Rradial velocity 6-52radiation 8-5, 14-24radiation boundary

condition 4-7radiation matrix 14-32ramp step time curve 4-

14Rayleigh number 14-8read from file 11-39recent analyses 2-18recent projects 2-18reciprocating motion 7-

10, 7-26, 7-59reciprocity 14-25rectangular grid 11-28reference frame 11-9, 11-

35, 14-63reference pressure 6-16reference properties 6-

10, 6-16reference

temperature 6-16referenced files 10-22reflection 4-10, 14-31

reflectivity 14-27re-initialize 4-20relative velocity 11-9, 11-

35, 14-63relaxation values 9-16remove analysis from

DRC 13-11renaming entities 2-29repeating (piecewise

linear) 4-16report generation 11-52report settings 2-11report template 10-21reports 10-20Reset to Local 13-13Reset View icon 2-5residence time 11-29Residence Time scalar

quantity 14-22residuals 10-4resistance 6-22resistance directions 6-

33resistance heating 4-8resistance material

creation 6-41resistance methods

constant loss coefficient 6-42, 14-12

Darcy Equation 6-47, 14-14

free area ratio 6-44, 14-14

friction factor 6-44, 14-13

pressure-flow rate curve 6-45, 14-14

resistive force 7-13resistive nutation

torque 7-62resistive torque 7-29resistivity 6-21, 6-23Restore Default Max

button 5-12result quantities 9-23result scale 11-13result set 13-11results


Index

cut planes 11-14project 13-9scalar 11-9vectors 11-10

results display on groups 11-11

results interpolation 12-1results output interval 9-

6results probing 11-12results range 11-48results save table 9-8results share file 2-8Results task dialog 2-42,

11-16results units 11-9resume interface

element 2-2Review task dialog 2-41Review_Animation 10-19Review_Notes 14-74Review_Results

dialog 10-18right hand rule 6-62RNG turbulence model 8-

8rotating machinery 14-55rotating regions 5-21, 5-

40, 6-25, 6-61, 7-20, 9-18, 14-53, 14-71

rotational direction 6-62rotational speed 6-64rotational symmetry 14-

30rotational velocity

boundary condition 4-3

runtime monitor points 10-6, 10-7

SSave analysis icon 2-4Save Dynamic Image

icon 2-5, 11-2Save Image icon 2-4, 11-

2save intervals 9-6Save Project icon 2-4Save Server

Assignments 13-13save table 11-17Save View Settings

icon 11-2saving a note 10-16scalar boundary

condition 4-5scalar filtering 11-48scalar legend 11-13scalar quantities 8-6scalar result quantity 11-

9scalar settings 11-48scalar visibility 11-9scroll wheel zoom 2-23second order polynomial

property variation 6-14

selection 2-24Selection Basis 2-24sensing location 6-49server 1-11server manager 9-11, 15-

9Server Monitor 9-11server.cfg file 9-11, 13-13servman.exe 1-12set to part 11-48, 11-49settings file 10-13, 10-20settings transfer 13-5setup parameters 10-25Shaded Image icon 2-5Shaded image icon 11-3shadowing 8-10, 14-31,

14-40shape 11-19, 11-20shell forces 10-12shell thickness 6-29shells 6-22show legend 11-48show lost 3-26, 13-6Show Mesh icon 11-4shutting down Pro/E 9-13Simulation Scope 1-3Simulation Speed 1-4size adjustment 5-16sky temperature 14-41,

14-43sliding vane 7-63, 14-55slip boundary

condition 4-4slip factor 4-7, 6-54sliver surfaces 5-4solar flux 14-40solar heat flux 14-44solar heating 4-10, 8-9solid boundaries 5-39Solid Edge 1-7, 3-12, 6-31,

15-4solid property types 6-20Solid Works 1-7, 3-12, 6-

31, 15-4solver 1-11specific heat 6-6, 6-20specified pressure

requirement 14-9specified temperature

requirement 14-9spectral radiation 6-7, 6-

20, 14-33Spread Changes

button 5-17, 5-18springs 7-15, 7-31Staged Forced

Convection 8-4stagnation

temperature 8-2Standard Views icon 2-6Start/End iteration 10-3starting and stopping 9-

13startup problems 15-8static notes 10-15static temperature 8-2status file 10-8steady state 9-3steady state analyses 9-

17steam quality 8-13steam quality boundary

condition 4-6steam/water 8-13, 14-23Step 1-2, 3-1step save interval 9-7STL 1-2stop time 9-5structured mesh 5-22submerged objects in

acis/parasolid 3-15subsonic 14-50


Index

Ind

ex

subsonic compressible 8-2, 14-46

subsonic inlet 4-17sudden discontinuity 5-

40summary file 10-9, 10-26

energy balance 10-9inlets/outlets 10-11

summary history file 10-12

summary output 9-7supersonic flow 14-46,

14-50supersonic inlet 4-17support file 2-8suppressed

components 3-27suppressed parts 5-3surface blanking 11-4,

11-12surface cutting entity 11-

20surface diagnostics 5-4surface features 6-25surface mesh size 5-41surface part forces 10-12surface parts 6-22surface regions 3-7Sutherland property

variation 6-11swirl 4-17swirl velocity 6-52symmetry 5-38, 11-6symmetry with

radiation 14-29

Ttable of motion 7-10tangencies 5-4Task Manager 9-10Tecplot 2-9temperature 11-45

stagnation 8-2static 8-2total 8-2

temperature boundary condition 4-4

temperature control 9-22temperature dependent

heat generation 4-11temperature results 12-2temperature

statistics 10-11template for report 10-

21, 10-29tetrahedral element 5-1text lines 10-22textured fringes 11-9thermal boundaries 5-40thermal summary 10-26thermal-only

iterations 8-4thermostat fans 6-49theta jb 6-67, 6-70theta jc 6-67, 6-70thickness factor 5-45thin resistance 6-37thrust 11-36Tight 9-19tilt axis 7-55time save interval 9-7time step 13-11time step size 9-3, 14-60,

14-72time step size for

solar 14-44title of a report 10-25tool buttons 2-3toolbar 2-2torque 11-45, 14-74torsion spring 7-31total heat flux boundary

condition 4-6total heat generation

boundary condition 4-11

Total PCB Thickness 6-76total temperature 8-2traces 6-77Transfer task dialog 2-42transient 9-3, 9-18, 14-20

inner iterations 9-6time step size 9-3

transient boundary conditions 4-13, 14-20

transient loadsharmonic 4-15inverse polynomial 4-16

periodic 4-14piecewise linear 4-16polynomial 4-16power law 4-15ramp step 4-14

transient results transfer 12-6

transmissivity 4-10, 6-20, 14-26

transonic flow 14-46transparency 14-26transparent boundary

condition 6-22, 14-28Transparent icon 11-3Transparent Image

icon 2-5transparent media 4-9,

14-43triangle element 5-1trigger temperature 6-49turb/lam ratio 8-8, 14-3turbines 14-53turbomachinery 6-25, 7-

19turbulence 8-6

auto startup 8-8extend 8-8lock on 8-8

intensity 8-9turb/lam ratio 8-8

turbulence inlet quantities 4-17

Turbulence modelsconstant eddy

viscosity 8-8k-epsilon model 8-7Low Reynolds model 8-7mixing length 8-8RNG model 8-8

two dimensional geome-try

acis/parasolid 3-16Pro/E 3-8

two dimensional models 6-28


Index

Uunconstrained motion 7-

70under-relaxation 9-21Unigraphics 3-12unit of time 14-20units 2-11, 2-27, 11-9units conversion 2-27universal file 2-9unknown boundary

condition 4-5, 14-47up button 10-23Upfront CFD 1-2upgrade from 7.0 1-16Use Uniform button 5-17,

5-19user defined nutation 7-

58user defined orbital 7-48user defined sliding

vane 7-68user text entry 10-25user-created files 10-29user-defined combo 7-40user-prescribed

angular 7-24user-prescribed linear 7-

8

VVary by Orientation 7-75Varying in Time 7-76vector clamping 11-50vector filtering 11-50vector length 11-50vector results

quantity 11-10vector settings 11-50vector spacing 11-19velocity 14-74velocity boundary

condition 4-3velocity components in

bulk 11-36velocity profile 6-52version 2-20Version 8 radiation

model 14-32view factor 14-24, 14-32

view factor for motion 14-71

View Lines icon 11-3view settings file 10-16viscosity 6-6viscosity coefficient 6-12viscous resistance 6-43visible 11-9visual dominance 7-4visualization of surface

parts 6-30voltage boundary

condition 4-8, 14-51volume blanking 11-12volume diagnostics 5-3volume flow rate 11-36volume flow rate bound-

ary condition 4-3volume mesh size 5-41volume regions 3-7volumetric heat genera-

tion boundary condition 4-11

vorticity 9-24vtf files 10-20, 11-50

Wwake regions 5-18, 5-21wall film coefficient 11-

45wall forces 11-45wall heat flux 11-45wall output 11-47wall pressure 11-45wall results 11-44wall roughness 6-7, 6-8,

6-21wall temperature 11-45wall turbulence

conditions 4-19walls 4-18walls (groups) 2-37water hammer 8-3, 14-21window 4-9Wireframe Navigation

icon 2-7Word 11-55

XXY plot axis label 11-41XY plot color 11-42XY plot points 11-39XY plot quantity 11-40XY plot units 11-40XY plots 11-37, 13-10

Yy+ 5-39, 5-45

ZZ-Clip 11-5Z-clip icon 2-6zero strain viscosity 6-13Zoom icon 2-7
