FLUENT - Tutorial - Dynamic Mesh - Submarine Docking Simulation

Tutorial: Submarine Docking Simulation Using MDM Model

Purpose

The purpose of this tutorial is to provide guidelines for the creation, setup, and solutionprocedure to solve the flow around a small submarine in a given time frame using MovingDeforming Meshes (MDM).

In this tutorial you will learn how to:

• Import the geometry, create the required MDM domain and surface mesh usingGAMBIT.

• Model the small submarine movement using MDM model in FLUENT.

• Set up, run, and postprocess the solution using FLUENT.

• Save the animation using FLUENT.

Prerequisites

This tutorial assumes that you are familiar with the FLUENT and GAMBIT user interface. Italso assumes that you have a good understanding of the basic setup and solution procedures.This tutorial does not cover the mechanics of using the MDM model, but the focuses onsetting up problem for the submarine and solving it. If you have not used the MDM modelbefore, Chapter 10: Modeling Flows in Moving and Deforming Zones in FLUENT 6.2 User’sGuide will provide you the necessary information.

Problem Description

This tutorial considers a simplified 2D model of a model scale (9 m) submarine advancingat constant speed. An ASDS approaches this submarine along a prescribed attitude andpath. The tutorial case is setup to understand the flow field, forces, and moments actingon the large submarine and the ASDS, while they dock.

c© Fluent Inc. March 16, 2005 1

Submarine Docking Simulation Using MDM Model

Geometry Setup and Mesh Generation in GAMBIT

Step 1: CAD Import and Domain Creation

1. Start GAMBIT with ID as sub-initial.

2. Read in the database file provided with this tutorial, sub-initial.dbs.

File −→Open ...

3. Create a region of fine meshing.

Create a region of very fine mesh compared to the rest of the domain. This region willserve as the remeshing region for the MDM calculations.

(a) Create a square face.

Operation−→ Geometry−→ Create Real Rectangular Face

i. Specify a value of 150 for Width and 100 for Height.

ii. Set Direction as XY Centered.

2 c© Fluent Inc. March 16, 2005

Submarine Docking Simulation Using MDM Model

(b) Move the rectangular face (face.8), by 10 units in the X direction and by 30units in the Y direction.

Operation−→ Geometry−→ Move/Copy Faces

i. Pick the rectangular face, face.8 and turn on Move.

ii. Under Operation, select Translate.

iii. Under Global, specify a value of 10 for x: and 30 for y:.

These distances are chosen such that the rectangular box covers both thesubmarines.

4. Split the parabolic face (face.7) with the rectangular face (face.8).

Operation−→ Geometry−→ Split Face

(a) Select face.7 in the upper Face picklist.

This is the face that will be split.

(b) Keep default selection of Face (Real) for Split With.

(c) Keep the default selection of Connected.

(d) Select face.8 in the lower Face picklist.

This is the face that will be used to split previously selected face.

c© Fluent Inc. March 16, 2005 3

Submarine Docking Simulation Using MDM Model

(e) Click Apply.

5. Subtract the two submarine faces (face.1 and face.4) from the inner rectangularface (face.8).

Operation−→ Geometry−→ Subtract Real Faces

(a) Select face.8 in the Face picklist.

(b) Select face.1 and face.4 in the Subtract Faces picklist.

4 c© Fluent Inc. March 16, 2005

Submarine Docking Simulation Using MDM Model

Step 2: Mesh Generation

1. Mesh the submarine edges.

Operation−→ Mesh−→ Mesh Edges

(a) Select the edges of both the submarines.

(b) Specify a value of 0.5 for Interval Size.

2. Mesh the outer edges of the rectangular face, face.8.

(a) Select the outer four edges of the rectangular face..

(b) Specify a value of 1.4 for Interval Size.

c© Fluent Inc. March 16, 2005 5

Submarine Docking Simulation Using MDM Model

3. Mesh the rectangular face.

Operation−→ Mesh−→ Mesh Faces

(a) Select the rectangular face, face.8.

(b) Mesh the face with Tri/Pave meshing scheme.

4. Create Sizing Function.

Operation−→ Tools−→ Create Size Function

(a) Set Type as Fixed.

(b) Set Source as Faces, and select face.8 (Rectangular face) as source face.

(c) Set Attachment as Faces, and select face.7 (Parabolic face) as attachment face.

(d) Under Parameters, specify a value of 1.4, 1.05, and 13 for Start size, Growth rate,and Size limit respectively.

(e) Click Apply to create a sizing function.

6 c© Fluent Inc. March 16, 2005

Submarine Docking Simulation Using MDM Model

5. Mesh the parabolic face using Tri/Pave meshing scheme and retain the other defaultparameters.

Figure 1: Mesh

c© Fluent Inc. March 16, 2005 7

Submarine Docking Simulation Using MDM Model

Step 3: Specify Boundary and Continuum Types

1. Specify the boundary types.

Zones−→ Specify Boundary Types

(a) Under Entity, select Edges.

(b) Specify boundary types using following table:

Name Type Edges

sub small WALL Edges of the small submarinesub big WALL Edges of the large submarinev inlet VELOCITY INLET Curved edge of the parabolic facep outlet PRESSURE OUTLET Straight edge of the parabolic face

8 c© Fluent Inc. March 16, 2005

Submarine Docking Simulation Using MDM Model

2. Specify the continuum types.

Zones−→ Specify Continuum Types

(a) Under Entity, select Faces.

(b) Select face.8 (Rectangular face) and name it as deforming.

(c) Select face.7 (Parabolic face) and name it as stationary.

3. Save and export the mesh file, sub-final.msh.

File −→ Export −→Mesh...

Turn on Export 2D (X-Y) Mesh while exporting the mesh file.

c© Fluent Inc. March 16, 2005 9

Submarine Docking Simulation Using MDM Model

Solution Using FLUENT

Step 4: Grid

1. Start the 2D version of FLUENT.

2. Read the mesh file, sub-final.msh.

File −→ Read −→Case...

3. Check the grid.

Grid −→Check

FLUENT will perform various checks on the mesh and will report the progress in theconsole. Make sure the reported minimum volume is a positive number.

4. Scale the grid.

Grid −→Scale...

(a) Scale the grid using Scale Factors of 0.1 for both X and Y.

The maximum domain extent in X direction should be 50 m and minimum shouldbe approximately - 40 m.

Step 5: Models

First get a steady state solution, which will serve as an initial solution for the unsteadyMDM case.

1. Keep the default solver settings.

Define −→ Models −→Solver...

2. Turn on standard k-epsilon turbulence model.

Define −→ Models −→Viscous...

(a) Under Model, turn on k-epsilon (2-eqn).

(b) Keep the other default values.

Step 6: Materials

Define −→Materials...

1. Click Fluent Database... in the Materials panel to open Fluent Database Materials panel.

(a) Under Fluent Fluid Materials, select water-liquid (h2o<l>).

(b) Click Copy and close the Fluent Database Materials panel.

2. Click Change/Create and close the Materials panel.

10 c© Fluent Inc. March 16, 2005

Submarine Docking Simulation Using MDM Model

Step 7: Boundary Conditions

Define −→Boundary Conditions...

1. For stationary and deforming fluid zones specify the Material Name as water-liquid.

2. Set the boundary conditions for v inlet.

(a) Select Magnitude and Direction as Velocity Specification Method.

(b) Specify a value of 0.5 for Velocity Magnitude.

(c) Specify a value of 1 for X-Component of Flow Direction.

(d) Select Intensity and Viscosity Ratio as Turbulence Specification Method.

(e) Specify a value of 2 for Turbulence Intensity and a value of 1 for Turbulent ViscosityRatio.

3. Specify the similar turbulent boundary conditions for p outlet.

4. Keep the other default boundary conditions.

c© Fluent Inc. March 16, 2005 11

Submarine Docking Simulation Using MDM Model

Step 8: Solution

1. Enable the plotting of residuals.

Solve −→ Monitors −→Residuals...

2. Initialize the solution.

Solve −→ Initialize −→Initialize...

(a) Select all-zones from the Compute From drop-down list.

(b) Click Init and close the panel.

3. Start the solution with 1000 iterations.

Solve −→Iterate...

The case should converge in around 300 to 400 iterations.

4. Save the case and the data files, steady.gz.

File −→ Write −→Case & Data...

Step 9: Unsteady MDM Setup

1. Read the velocity profile velnew.prof using TUI command.

/>file/rtttransient-table file name []’’ velnew.prof

2. Switch to unsteady solver.

Define −→ Models −→Solver...

(a) Under Options, select Unsteady.

12 c© Fluent Inc. March 16, 2005

Submarine Docking Simulation Using MDM Model

3. Define the dynamic mesh parameters.

Define −→ Dynamic Mesh −→Parameters...

(a) Turn on Dynamic Mesh.

(b) Under Mesh Methods, turn on Smoothing and Remeshing.

(c) Select Smoothing tab.

i. Set the Number of Iterations to 10.

ii. Keep the other default parameters.

(d) Select Remeshing tab.

i. Set the following parameters:

Parameter ValueMinimum Length Scale (m) 0.03757772Maximum Length Scale (m) 0.1Maximum Cell Skewness 0.55Size Remesh Interval 1

(e) Click OK to close the panel.

Note: For information about length scale, click Mesh Scale Info.... This will openMesh Scale Info panel which displays values of Minimum Length Scale, Max-imum Length Scale, Maximum Cell Skewness, and Maximum Face Skewness.The maximum length specified for the deforming zone in the Dynamic Meshpanel is very small compared to the maximum length scale in the domain(which is outside the deforming zone).

c© Fluent Inc. March 16, 2005 13

Submarine Docking Simulation Using MDM Model

4. Define the dynamic mesh zones.

Define −→ Dynamic Mesh −→Zones...

(a) Select sub small in the Zone Names drop-down list.

(b) Under Type, select Rigid Body.

(c) Under Motion Attributes tab, select vel dataper from the Motion UDF/Profiledrop-down list.

(d) Under Meshing Options tab, specify a value of 0.025 for Cell Height.

(e) Click Create.

5. Save the case and data files, sub-mdm-setup.gz.

14 c© Fluent Inc. March 16, 2005

Submarine Docking Simulation Using MDM Model

6. Preview the mesh motion.

Solve −→Mesh Motion...

(a) Specify a value of 0.5 for Time Step Size and a value of 100 for Number of TimeSteps.

(b) Click Preview.

You can see how FLUENT restructures the mesh after every time step.

7. Read the previously saved case and data files, sub-mdm-setup.cas.gz andsub-mdm-setup.dat.gz .

Step 10: Animation

1. Define the animation.

Solve −→ Animate −→Define...

c© Fluent Inc. March 16, 2005 15

Submarine Docking Simulation Using MDM Model

(a) Specify a value of 1 for Animation Sequences.

(b) Under Name, enter velocity and under Every enter 25.

(c) Under When, select Time Step and click Define...

i. Under Storage Type, select In memory.

ii. Set Window to 1 and click Set.

iii. Under Display Type, select Contours to open the Contours panel.

iv. Using the Contours panel, display the filled contours of Velocity Magnitudeand close the panel.

v. Close the Animation Sequence and Solution Animation panels.

vi. In the graphics window, zoom in the region showing both the submarines.

2. Iterate the solution.

Solve −→Iterate...

(a) Specify a value of 0.5 for Time Step Size.

(b) Specify a value of 1450 for Time Steps.

Until the small submarine docks into the big submarine.

(c) Keep the default value of 20 for the Max iterations per time step.

3. View the animation.

Solve −→ Animate −→Playback...

(a) Select Hardcopy Frames in the Write/Record Format drop-down list.

(b) Click Hardcopy Options... and select TIFF as hardcopy format in the resultingpanel.

(c) Click Write in the Playback panel to save the hardcopy of the contour display atthe specified intervals.

(d) View the animation of these hardcopy frames using any Image Viewer tool.

16 c© Fluent Inc. March 16, 2005

Submarine Docking Simulation Using MDM Model

Contours of Velocity Magnitude (m/s) (Time=1.2500e+01)FLUENT 6.2 (2d, segregated, dynamesh, ske, unsteady)

Mar 16, 2005

7.18e-016.82e-016.46e-016.10e-015.74e-015.38e-015.02e-014.67e-014.31e-013.95e-013.59e-013.23e-012.87e-012.51e-012.15e-011.79e-011.44e-011.08e-017.18e-023.59e-020.00e+00

Figure 2: Velocity Contours — Before Docking

Contours of Velocity Magnitude (m/s) (Time=7.2500e+02)FLUENT 6.2 (2d, segregated, dynamesh, ske, unsteady)

Mar 15, 2005

8.56e-018.13e-017.70e-017.28e-016.85e-016.42e-015.99e-015.56e-015.14e-014.71e-014.28e-013.85e-013.42e-013.00e-012.57e-012.14e-011.71e-011.28e-018.56e-024.28e-020.00e+00

Figure 3: Velocity Contours — After Docking

c© Fluent Inc. March 16, 2005 17