Part 2 Load Transfer - RecurDyn, multibody dynamics ...support.recurdyn.com/wp-content/uploads/2015/11/Geneva-Wheel_Par… · Multi-Body Dynamics for Ansys, ... Penetration field

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Part 2

Load Transfer

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Revision History

First printed, March 2015

iii

Table of Contents

Getting Started ......................................................................... 4

Objective ......................................................................................... 4

Audience ......................................................................................... 4

Prerequisites ................................................................................... 5

Procedures ...................................................................................... 5

Implementing GeoSurface Contacts ......................................... 6

Task Objective ................................................................................ 6

Starting ANSYS Workbench ............................................................ 6

Deleting Existing Solid Contacts ..................................................... 8

Creating the GeoSurface Contacts ................................................. 8

Analysis / Review ................................................................... 12

Task Objective .............................................................................. 12

Setting up and Running an Analysis ............................................. 13

Viewing the Animation Results ...................................................... 13

Load Transfer ......................................................................... 18

Task Objective .............................................................................. 18

Setting up the Load Transfer ......................................................... 19

Reviewing and Projecting the Points ............................................. 22

Creating the Contact Surfaces ...................................................... 26

Cleaning up the model in DesignModeler ..................................... 30

Static Structural Analyses ...................................................... 31

Task Objective .............................................................................. 31

Preparing for the Static Analyses .................................................. 32

Suppressing the Gravity ................................................................ 32

Associating the Joint Loads with Geometry................................... 32

Setting Up and Defining the Mesh ................................................. 34

Running the Analysis .................................................................... 38

Repeating the Analysis for the Second Time Instant ..................... 40

Repeating the Analysis for the Third Time Instant ......................... 43

4

Getting Started

Objective

The Geneva Wheel Tutorial introduced the Geneva wheel mechanism and how to define bodies, joints, motions and contacts. This tutorial begins from the end of that tutorial and explains how to use GeoSurface contact and how to consider the loads in the Geneva wheel body, including contact loads.

The focus of this tutorial is to explain how to set up load transfer due to contacts, which may have the added complexity of being located at different locations at different time instants.

Audience

This tutorial is intended for new users of the MBD for ANSYS module who have a basic working knowledge of ANSYS and have completed the Geneva Wheel tutorial. All new tasks are explained carefully.

Chapter

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G E N E V A W H E E L L O A D T R A N S F E R G E T T I N G S T A R T E D

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Prerequisites

We assume that you have a basic knowledge of physics.

Procedures

The tutorial is comprised of the following procedures. The estimated time to complete each procedure is shown in the table.

Procedures Time (minutes)

Implementing GeoSurface Contacts 10

Analysis / Review 5

Load Transfer 25

Static Structural Analysis 15

Total: 55

Estimated Time to Complete

This tutorial takes approximately 55 minutes to complete.

6

Implementing GeoSurface Contacts

Task Objective

Replace the Solid contacts that were defined in the first Geneva wheel tutorial with GeoSurface contacts. Three contacts are used in this model. The first two contacts are the contacts between the two pins on the Drivewheel and the Geneva wheel body. These pins drive the motion of the Geneva wheel assembly. The third contact is between the Drivewheel body and the Geneva wheel body. The outer two curves on the drive wheel serve to keep the Geneva wheel fixed (not rotating) while the pins are disengaged from the slots.


10 minutes

Starting ANSYS Workbench

To start ANSYS Workbench and read in the original Geneva wheel system:

1. On your Desktop, double-click the ANSYS Workbench icon.

2. The ANSYS Workbench window appears. If the Getting Started window appears, click OK to dismiss it.

3. Open the Workbench Project file from the Geneva Wheel tutorial by:

Selecting the Open option in the File menu

Navigating to the folder used to store the files for the Geneva Wheel tutorial.

Selecting the Geneva_Tutorial_1.wbpj file, and

Clicking on the Open button as shown in the figure below.

Chapter

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G E N E V A W H E E L L O A D T R A N S F E R G E O S U R F A C E C O N T A C T S

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4. Click on the No button in the alert box that asks if you want to save the current project.

5. The Multi-Body Dynamics system block for the Geneva Wheel model appears in the Project Schematic window, as shown to the right.

6. Save a new copy of the Workbench Project file for use in this tutorial by:

Selecting the Save As… option in the File menu

Navigating to the folder where you want to save the files for this tutorial.

Changing the file name to Geneva_Tutorial_Loads.wbpj, and

Clicking on the Save button as shown in the figure below.


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Deleting Existing Solid Contacts

The original Geneva Wheel model used Solid contacts. We would like to replace the solid contacts with GeoSurface contacts so that we can obtain a set of contact loads at each active contact, which can be more effectively used as loads in a component stress analysis. We will open the model in ANSYS Mechanical and delete the contacts.

To open ANSYS Mechanical:

1. With the cursor over the Model field in the system,

click the right mouse button and select the Edit… option.

The ANSYS Mechanical application will open in a new window.

To check the units:

Please note that it is expected that mm length units are used with this tutorial. The length units should already be mm with this model, but please check to make sure that this is the case before proceeding with the next step.

To delete the solid contacts:

1. Delete the SCont_Pin1 solid contact by:

In the Outline window, expand the Contacts group under the Multi-Body Dynamics group.

Select the SCont_Pint1 entity.

Click the right mouse button and select the Navigate to the tutorial files and select the Parasolid file

Delete as shown in the figure.

Click on the Yes button to confirm that you want to delete the solid contact.

2. Repeat the operations of the prior step to delete contact entities SCont_Pint2 and

SCont_Geneva_DrvWhl.

Creating the GeoSurface Contacts

To create the Pin1 GeoSurface contact:

1. In the MBD Entities toolbar,

pull down the Contacts menu and select the


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GeoSurface option.

2. Select the GenevaWheel body (G_Geneva geometry) as the Base Body and the

G_Pin1 geometry as the Action body.


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3. In the Details window, go the Base

Body section, select the Show

Geometry Info field, pull down the

menu and select the Show Options item.

4. Select the Plane Tolerance Factor

field and change the value from 3 to 1. This factor controls the resolution of the contact calculations. By using a value of 1 we will have a higher resolution surface for contact modeling and the results will include more contact forces, which is helpful in doing a component stress analysis. The Details window should appear as shown.

5. Repeat Steps 3-4 for the Action Body.

6. Make the following changes in the Properties section of the Details window:

Make sure the value of the Maximum

Penetration field is 0.8 (0.8 mm, this should be the default value).

Change the value of the Maximum

Stepsize Factor from 10 to 2.

Change the value of the No. of Max Contact Points from 50 to 200. This factor controls the maximum number of separate contact forces that will be reported at each output time for this contact.

To create the Pin2 GeoSurface contact:

1. In the MBD Entities toolbar, pull down the Contacts menu and select the

GeoSurface option.


G_Pin2 geometry as the Action body.

3. In the Details window, go the Base Body section, select the Show Geometry Info

field, pull down the menu and select the Show Options item.

4. Select the Plane Tolerance Factor field and change the value from 3 to 1. This factor controls the resolution of the contact calculations.


6. In the Properties section of the Details window:


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Make sure the value of the Maximum Penetration field is 0.8 (0.8 mm).

Change the value of the Maximum Stepsize Factor from 10 to 2.

Change the value of the No. of Max Contact Points from 50 to 200.

To create the GenevaWheel to DriveWheel GeoSurface contact:

1. In the MBD Entities toolbar, pull down the Contacts menu and select the

GeoSurface option.


G_DriveWheel geometry as the Action body.

3. In the Details window, go the Base Body section, select the Show Geometry Info

field, pull down the menu and select the Show Options item.

4. Select the Plane Tolerance Factor field and change the value from 3 to 1. This factor controls the resolution of the contact calculations.


6. In the Properties section of the Details window:

Make sure that the value of the Maximum Penetration field is 3 (3 mm).

Change the value of the Maximum Stepsize Factor from 10 to 2.

Change the value of the No. of Max Contact Points from 50 to 200.

To check and rename the contacts:

1. The list of contacts in the Outline window should appear as shown. If any of the contacts do not have a check mark, please review the instructions above and make sure that the base body and action body are defined for that contact.

1. In the Outline window click on each contact name. The base body and the contact icon will highlight. Click the right mouse button and select Rename (or press the F2 key). Type in the name of the contact as given in the table below. The list of contacts in the Outline window should appear as shown after the renaming is complete

To save the project:

Back in the Workbench window, click the Save icon.

Default Name Rename to:

GeoContact1 GCont_Pin1

GeoContact2 GCont_Pin2

GeoContact3 GCont_Geneva_DrvWhl

12

Analysis / Review

We can now run a simulation (analysis) with this model and then review an animation of its motion and plot some of the outputs.

Task Objective

You will learn to:

Set up and run a simulation.

View the motion of the Geneva wheel mechanism


5 minutes

Chapter

3

G E N E V A W H E E L L O A D T R A N S F E R A N A L Y S I S / R E V I E W

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Setting up and Running an Analysis

To set the parameters controlling the analysis:

1. In the Outline window, select the Analysis

Settings item in the Multi-Body Dynamics group.

2. In the Details window make sure the End Time value is

set to 3.

3. Make sure that the number of steps in the Step field is

set to 1200. This sets the number of animation output steps that are saved in the results files. When you play an animation you will see a maximum of this number of steps. Also, plots will contain this number of data points.

4. Set the Maximum Time Step field to 0.005. This will make sure that there are at least 400 steps per second taken by the integrator, which matches the frequency of the request output steps.

The Details window should appear as shown in the figure above.

To run an analysis:

1. Select the Solve Icon in the ANSYS Mechanical toolbar.

After a pause (5-10 seconds) the ANSYS Workbench Solution Status box will appear and provide ongoing feedback on the progress of the solution.

Viewing the Animation Results

An external viewer is provided in order to show animations and MBD output plots with high performance and capability.

To invoke the results viewer:

1. In the MBD Post toolbar, pull down the View menu

and select the RecurDyn Viewer option. At this point all of the geometry and results are being prepared and written to several files for use by the viewer. A startup image will appear and then 5-10 seconds later the RecurDyn Viewer for Multi-Body Dynamics (hereafter


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referred to as the RecurDyn Viewer) will appear with the Geneva wheel mechanism model loaded as shown in the figure.

To adjust the view in the viewer:

The RecurDyn Viewer has its own methods for controlling the view on the screen. In the RecurDyn Viewer graphics window, click on the right mouse button and the pop-up menu that appears contains information about view control, as shown in the figure. You can see the typical Translate, Rotate and View commands. Each view command can be accessed in three ways:

1. Select the icon associate with each view command from the toolbar on the left of the screen, just below the ribbon.

2. Use the keyboard equivalent for each command, as shown in the figure.

3. Click the right mouse button to display the pop-up menu and then select the view command.

Note that each view command is not persistent. Once the view command is given the user can click and hold down on the left mouse button and perform the view command. Once the left mouse button is released the cursor mode reverts back to select.

Use the RecurDyn Viewer view commands to position the model at a good angle to see the 3D animation, as shown in the figure.

To play the animation:

1. At the left side of the Ribbon, there is an Animation Control group. The buttons can be used to play the


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animation following standard conventions. Click the Play button in order to see the motion of the Geneva wheel mechanism. Because of the large number of output

frames you may also want to use the FastPlay button (double arrowheads) to review the animation.

To identify times of interesting loads:

The next step is to identify the time instants of interesting loads for the Geneva Wheel body. Loads are applied to the body at the revolute joint in the center of the body as well as contact loads in the slots and at the perimeter of the Geneva Wheel (contact with the Drive Wheel). Loads in the Geneva Wheel body will change as the pins move down the slots. We want to identify the load cases during the portion of the work cycle where the pin travels down and back along the slot. Then we can use ANSYS to do a set of linear statics stress analyses, using the Static Structural systems in Workbench.

During the load transfer process there will be an opportunity to review the loads that act on the Geneva Wheel. Before starting the load transfer it may be useful to review some model results in order to understand the loading that occurs during the work cycle of the system.

1. An important indicator of loads on the Geneva Wheel is the angular acceleration of the wheel during the work cycle. Do the following to review and better understand the angular acceleration:

Under the Viewer Ribbon, go to the Plot group and click on the Plot icon.

In the Plot Database window expand the Bodies group. Then expand the

G_Geneva group and double-click on the Acc_RZ item.

Double-click on the X-Axis. In the dialog box that appears change the maximum X-value to 1.0. Click OK.

Double-click on the Y-Axis. Change the maximum Y-value to 150 and the minimum Y-value to -150. Click OK to obtain a plot similar to the figure below.

Observe a fairly steady rise of acceleration as the pin moved down the slot towards the center of the Geneva Wheel.

Notice that as the pin exits there is substantial noise. The noise in the acceleration is due to the clearance from the sides of the slot to the outer surface of the pin.

2. It is also useful to directly plot the contact forces that act on the Geneva Wheel. Do the following:

Go to the Page group in the ribbon and click on the Add icon in the ribbon in order to create a new plot page.


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In the Plot Database window expand the Contact group. Then expand the Geo

Contact group and later the GCont_Pin1 group. Double-click on the

FM_GeoContact item.

Now expand the GCont_GenevaDrvWhl group and double-click on the

FM_GeoContact item.

Double-click on the X-Axis. In the dialog box that appears change the maximum X-value to 1.0. Click OK.

Double-click on the Y-Axis. Change the maximum Y-value to 5000 and the minimum Y-value to 0. Click OK to obtain a plot similar to the figure below.

Note that the two contacts do not have non-zero contact forces at the same time.

Given the plot results there are three time instants of interest:

~0.55 seconds – Pin has moved most of the distance down the slot and the Geneva Wheel is seeing full acceleration.

~0.68 seconds – Severe bounce impact as the pin moves up the slot and hits the other side of the slot.

~0.94 seconds – Impact of the Geneva Wheel with the Drive Wheel.

To observe the mechanism at the selected times:

1. Use the Animation Control group to step through the animation using any or all of the following techniques:

Dragging the slide on the slide bar

Clicking the single frame icons (the single forwards and backwards arrows with the number 1 in the icon) to move within the animation one frame at a time.

Clicking the Play button and the Pause button in order to get the animation to the approximate time of interest.


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The figures that follow show the Geneva Mechanism at the estimated times of interest.

0.55 Seconds:

0.68 Seconds:

0.94 Seconds:

G E N E V A W H E E L L O A D T R A N S F E R L O A D T R A N S F E R

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Load Transfer

The purpose of transferring loads for use in ANSYS Static Structural systems is to assess component reliability. A sudden failure could occur if a peak stress exceeds the yield stress of the component material. With cyclic loading the damage to the component is a function of the variation of stress throughout the component during the work cycle of the assembly.

In this section we are going to do the load transfer for the Geneva Wheel body. Loads are applied to the body at the revolute joint in the center of the body as well as on the slots (contact loads). Loads in the Geneva Wheel body will change as the pins move down the slots. We want to identify the load cases during the portion of the work cycle where the pin travels down and back along the slot. Then we can use ANSYS to do a set of linear statics stress analyses, using the Static Structural systems in Workbench.

Task Objective

You will learn to:

Set up the transfer of the load cases of interest.

Use DesignModeler to project the contact load point to the surface of the geometry.

Create the Contact Surfaces

Clean up the model in DesignModeler


25 minutes

Chapter

4


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Setting up the Load Transfer

To select the Geneva Wheel body for load transfer:

1. In the MBD Post toolbar, pull down the Load Transfer menu and select the

1. MBD Load Transfer Config. item.

2. A Load Transfer Configuration item will appear in

the Outline Window, within the Solution group.

3. In the Details window make sure the

Scoping Method field is set to Geometry

Selection. If not, pull down on the menu in

the field and select Geometry Selection.

4. Define the Geneva Wheel as the body to receive the loads by doing the following:

Click in the new Geometry field that appears.

Select the Geneva Wheel body and click the

Apply button.

The Geometry field shows that one body has been selected.

To select the time instants for the load transfer:

1. Click in the Show Information Dialog field

and click on the Apply Button that appears.

The window below will then be displayed.


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You can see that the List Control section in the upper right contains a list of the model entities that apply loads on the Geneva Wheel body:

Fix_Geneva_Flywheel- the fixed joint that attaches the Geneva Wheel to the Flywheel.

Rev_Geneva- the revolute joint that attaches the Geneva Wheel to the BasePanel.

GCont_Geneva_DrvWhl- the contact between the Geneva Wheel and the Drive Wheel..

GCont_Pin2- the contact between the Geneva Wheel and the Pin2 body..

GCont_Pin1- the contact between the Geneva Wheel and the Pin1 body..

Given the previewing of the forces acting on the Geneva Wheel body in the previous chapter, it is sufficient to display the loads in the table and select the Time Instants of

interest. You can use the Table columns of the List Control section to display the forces for the 1200 output points that were saved from the simulation. You will review the loads of interest for the Geneva Wheel body and select three times where the locally maximum forces can possibly produce the maximum stresses in the Geneva Wheel.

2. In the List Control section, go to the GCont_Pin1 row and click the box in the

Table column. Now the table function under the Loads Acting on Body tab in the upper left of the Load Transfer dialog box will be used to pick the time instants.

3. The first time instant occurs at approximately 0.55 seconds when the GCont_Pin1 force values are at a local maximum. Scan the values in the table that are near to that time. You will find that the local maximum forces occur at 0.5525 seconds. Click in

the Select box for that row, as shown in the figure.

4. The second time instant occurs at approximately 0.68 seconds when the

GCont_Pin1 force values are at a local maximum. Again, scan the values in the table. You will find that the local maximum forces occur at 0.685 seconds. You can see that the globally maximum values of TM (Torque Magnitude) and TX (Torque about the

global X axis) occur at that same time. Click in the Select box for that row, as shown in the figure.


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5. In the List Control section, go to the GCont_Geneva_DrvWhl row and click the

box in the Table column.

6. The second time instant occurs at approximately 0.94 seconds when the

GCont_Geneva_DrvWhl force values are at a local maximum. Scan the values in the table. You will find that the local maximum forces occur at 0.9475 seconds. Click in

the Select box for that row, as shown in the figure.

You may have noticed that as you have click on the Select box that the time instants were being added to

the list in the Time Instant section of the dialog box. There are now four time instants in the list, as shown in the figure.

7. Now that all of the time instants have been

identified you can click on the Apply button in

the Load Transfer window. All of the time instant values are shown in the Details window for the Load Transfer Configuration as shown in the figure.

To set contact load transfer parameters:

1. Scroll down in the Details window to the Setting of LT section. Set the Tolerance

field to 0.5 (1 mm should be the default), which means that the separate contact forces that are applied within this distance will be merged when they are located within 0.5 mm of each other.

2. Make sure that the Area Searching Method is set to Manual, using the pull-down menu. This is the best option for most cases at this time. Methods that are more automated are being investigated and will be recommended once they are sufficiently robust.

To execute the load transfer:

1. Scroll back up in the Details window to the

Method section. The default option is to use the inertia relief method. The default value of

Yes is good and should not be changed.

2. Click in the Load Transfer? field and click the Apply button. Wait 5-20 seconds for the load transfer to complete.


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3. When the load transfer is completed check the Workbench window and you can see that a new linear statics project has been created for each of the three time instants that were designated as shown in the figure below.

4. Close the Mechanical Application.

5. In the Workbench window, select the Save icon in the toolbar.

Reviewing and Projecting the Points

You will notice that a DesignModeler session has been automatically started (if you don’t see the DesignModeler session then check your Windows taskbar). This happens whenever the load transfer body includes contact loads. The usage of the DesignModeler session is explained in the next section.

To review the points:

MBD for ANSYS has done the following to prepare to create contact surfaces where needed:

A DesignModeler session has been automatically started.

In the DesignModeler session a point set has been defined for each location on the Geneva Wheel body where a contact force occurred and for all of the Time Instants.

The following steps should be followed to define the contact surfaces:

1. In the DesignModeler application you will see a new Point1 entity in the Tree Outline window. Click on the

Point1 entity and you will see the points on the Geneva Wheel highlight. .


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2. There are three sets of points, including points on both the top and bottom edges of the Geneva Wheel:

The points on the leading edge of the slot representing the contact as the pin has traveled most of the distance down the slot (Time Instant 0.5525, label 1)

The points on the trailing edge of the slot representing the contact as the pin starts to move out of the slot (Time Instant 0.6825, label 2)

The points on the perimeter of the Geneva Wheel representing the contact with the Drive Wheel after the pin has exited the slot (Time Instant 0.9475, label 3)

3. In the Details View you can observe that 47 Points were generated but no Mates were generated. We will use the Projection function to project the points onto the surface. We will use the projected points to define three contact surfaces on adjacent faces.

To project the points to the first contact surface:

1. Zoom in on the points near the bottom of the leading edge of the slot (near label 1 in the previous image). When the Point1 entity is selected you should see this image where 12 points are highlighted as shown.

2. Project the points to the surface using the following steps:

In the Display Toolbar, make sure that the

Display Points icon is active (selected).

Pull down on the Tools menu and select the

Projection command.

2

1

3


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In the Details View window, click in the Type

field, pull-down on the menu and select the Point

On Face option.

Click in the Points field.

Choose the Box Select option.

Draw a box around the 12 points. All 12 points will highlight.

Select the Apply button in the Points field.

Click in the Target field.

Choose the Single Select option.

Make sure the Selection Filter: Faces is turned on.

Select the face that the points are to be projected on and click on the Apply button in the Target Field.

Point at the Projection1 item in the Tree

Outline window and click the right mouse button.

Click on the Generate Option.

Tip: Understanding the need to project the points onto the surface

When the RecurDyn solver is doing the contact calculations the curved surfaces are represented with a set of triangles. In addition a penalty method algorithm is used which allows a small penetration between the contacting geometries.

Therefore the location of the application of contact forces will not lie exactly on the surface due to the approximated contact geometry and the penetration. A projection step is needed for the contact points so that they will lie precisely on the surface because these points are going to be seeds for the mesh that we will create later.

To project the points to the second contact surface:

1. Zoom in on the points near the bottom of the trailing edge of the slot (near label 2 in the previous image). When the Point1 entity is selected you should see this image where 22 points are highlighted as shown.


Pull down on the Tools menu and select the Projection command.

In the Details View window, click in the Type field, pull-down on the menu

and select the Points On Face option.


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Choose the Box Select option..

Draw a box around the 22 points (all 22 points will highlight) and select the

Apply button in the Points field.




Select the face that the points are to be projected on and click on the Apply button in the Target Field.

Point at the Projection2 item in the Tree Outline window, click the right

mouse button and click on the Generate Option.

To project the points to the third contact surface:

1. Under the View menu select the Wireframe option.

2. Zoom in on the points near the entrance of the slot (near label 3 in the previous image), as shown in the figure. When the Point1 entity is selected you should see this image where 13 points are highlighted as shown.


Pull down on the Tools menu and select the

Projection command.

In the Details View window, click in the Type field, pull-down on the menu

and select the Point On Face option.



Select the first point, then press and hold the Ctrl (Control) key and select the other 12 points (all 13 points will highlight).

Click on the Apply button in the Points field.



Select the face that the points are to be projected

on and click on the Apply button in the Target Field.

Point at the Projection3 item in the Tree Outline window, click the right

mouse button and click on the Generate Option.

Under the View menu select the Shaded Exterior and Edges option.


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Creating the Contact Surfaces

Contact surface will be created by defining 3D curves and projecting them onto the face. The projected curves will form boundaries that will define the contact surfaces. The contact surfaces will be grouped into named selections in order to define the active contact surfaces for each time instant.

To create the 3D curves:

1. Adjust the model view to see the points of the first contact area (at Projection1) and create 3D curves to define the boundary of the contact area using the following steps:

From the Concept menu select the 3D

Curve command.

Select the three points to create a curve from the lower left corner to the upper left corner, as shown in the figure.

Click on the Apply button.

In the Tree Outline window, click the

right mouse button on the Curve1

item and select the Generate command.

From the Concept menu select the 3D Curve command.

Select the three points to create a curve from the lower right corner to the upper right corner, as shown in the figure.


In the Tree Outline window, click the right mouse button on the

Curve2 item and select the Generate command.

The curves, when both are selected, will appear as shown in the figure.

2. Adjust the model view to see the points of the second contact area (at Projection2) and create 3D curves to define the boundary of the contact area using the following steps:


Select the three points to create a curve from the lower left corner to the upper left corner, as shown in the figure.


In the Tree Outline window, click the right mouse button

on the Curve3 item and select the Generate command.



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Select the three points to create a curve from the lower right corner to the upper right corner, as shown in the figure.


In the Tree Outline window, click the right mouse button

on the Curve4 item and select the Generate command.

The curves and points, when selected, will appear as shown in the figure.

3. Move back to the points in Projection3 and repeat the steps above to create the 3D curves that surround all of points in the group. Use the Wireframe viewing option if you cannot see the points.


Select a series of point to create a curve from the upper right corner to the lower right corner, as shown in the figure.


In the Tree Outline window, click the right mouse

button on the Curve5 item and select the Generate command.

The curve and points, when selected, will appear as shown in the figure.

To create the contact surfaces:

The contact surfaces are created by projecting the 3D Curves into the face. Once the surfaces are created they must be included within Named Selection entities with specific names so that the contact s surfaces can be identified by the MBD for ANSYS script for load transfer.

1. The first contact surface is created by following the steps below:

Adjust the view to clearly see the points in Projection1.

From the Tools menu select the Projection command.

Click in the Type field and pull-down to select the

Edges on Face option.

Click in the Edges field and select one of the two 3D Curves that were created earlier.


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Hold down the Ctrl (Control) key and then select the second curve

Click on the Apply button. This field should contain the number 2, indicating that two edges (curves) were selected.


Make sure the Selection Filter is set to Faces and select the face of the slot.

Click the Apply button

In the Tree Outline window click the right mouse

button on the Projection4 entity and select the

Generate command. A selectable contact surface has been created, as shown in the figure.

From the Tools menu select the Named

Selection command.

Change the name in the Named Selection field to con_area1. The MBD for ANSYS load transfer process will look for named selections that have names of the form con_areaX where X is the number of the particular time instant. This surface is the only contact surface with loads for the first time instant, so only this area will be included in this named selection.

Click in the Geometry field and select this contact surface.

Click the Apply button. The Details View window should appear as shown on the right.

In the Tree Outline window click the right mouse

button on the con_area1 entity and select the

Generate command.

2. The second contact surface is created by following the steps below:



Click in the Type field and pull-down to select the Edges on Face option.

Click in the Edges field and select one of the two 3D Curves that were created earlier.

Hold down the Ctrl (Control) key and then select the second curve

Click on the Apply button. The field should contain the number 2, indicating that two edges (curves) were selected.




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In the Tree Outline window click the right mouse button

on the Projection5 entity and select the Generate command. A selectable contact surface has been created, as shown in the figure.

From the Tools menu select the Named Selection command.

Change the name in the Named Selection field to

con_area2 because this surface is the only contact surface with loads for the second time instant.


Click the Apply button.

In the Tree Outline window click the right mouse button on the con_area2

entity and select the Generate command.

3. The third contact surface is created by following the steps below:



Click in the Type field and pull-down to select the Edges on Face option.

Click in the Edges field and select the 3D Curve that were created earlier.





In the Tree Outline window click the right mouse button

on the Projection6 entity and select the Generate command. A selectable contact surface has been created, as shown in the figure.

From the Tools menu select the Named Selection command.

Change the name in the Named Selection field to

con_area3 because this surface is the only contact surface with loads for the third time instant.



In the Tree Outline window click the right mouse button on the con_area3

entity and select the Generate command.


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Cleaning up the model in DesignModeler

To clean up the model:

The curve creation related to contact surface definitions left behind 5

Line Bodies as shown in the figure. These bodies need to be suppressed in order to avoid error messages in the subsequent steps.

1. Click the right mouse button over the first

Line Body entity and select the Suppress option:

2. Repeat for the other four Line Bodies.

3. The Tree Outline window should appear as shown in the figure.

4. Close DesignModeler

5. Save the project.

G E N E V A W H E E L L O A D T R A N S F E R S T A T I C S T R U C T U R A L

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Static Structural Analyses

Now we can use ANSYS to do a set of linear statics stress analyses, using the Static Structural systems in Workbench.

Task Objective

You will learn to:

Associate joint loads with the geometry of the Geneva Wheel body.

Mesh the Geneva Wheel Geometry

Run the linear statics analysis and review the results.

Evaluate the results and determine the need for changes to the Geneva Wheel design.


25 minutes

Chapter

5


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Preparing for the Static Analyses

To open Mechanical with the MBD system:

1. Click the right mouse button on the Model line of the first Static Structural system

block (for time = 0.5525 seconds) and select the Edit option in order to open the model in Mechanical.

2. In the MBD Post toolbar, pull down on

the LoadTransfer menu and select the

2. Set FE Boundary Cond. option. This command will run for 5-20 seconds. The components of the MBD model other than the Geneva Wheel geometry will be suppressed. You may need to select the Geneva Wheel geometry item in order for the graphics window to refresh and show that body.

Suppressing the Gravity

To suppress the Gravity Transformed Entity:

No gravity vector was defined in the multi-body dynamics model, therefore the Gravity

Transformed entity under the Static Structural_at t=05525 sec (B5) can be ignored. Suppress this entity by doing the following:

1. Click the right mouse button over the Gravity Transformed entity and select the

Suppress command.

2. The Gravity Transformed entity should now be marked with an X, as shown in the figure.

Associating the Joint Loads with Geometry

To associate the transferred joint loads with the appropriate geometry:

Four new entities related to the transferred loads have been added under the first Static Structural group in the Outline window as shown. The four items correspond to the forces and moments of the fixed joint to the flywheel and the revolute joint to the frame.


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1. Each of the four loads needs to be associated with geometry on the Geneva Wheel body. Both the Force and the Moment entities of the fixed joint will be associated with the bottom of the hole at the bottom of the Geneva wheel. To do this:

Select the Fix_Geneva_Flywheel_Force

Acting on Body entity

In the Details window click in the Geometry field

Select the surface side of the hole at the bottom of the Geneva wheel.


Repeat the same process with the Fix_Geneva_Flywheel_Moment Acting on

Body entity.

2. The forces of the revolute joint need to be associated with the shoulder at the top of the Geneva wheel. To do this:

Select the Rev_Geneva_Force Acting on

Body entity

In the Details window click in the Geometry

field

Select the surface of the shoulder at the top of the Geneva wheel.


Repeat the same process with the Rev_Geneva_Moment Acting on Body entity.

3. Set the origin of the two forces to the global origin as shown in the following steps:

Expand the Coordinate Systems group in the Outline window.

Select the Fix_Geneva_Flywheel_Origin entity

Set the origin to the global origin by setting the

Origin X, Origin Y, and Origin Z fields

to 0 (0 mm)

The result will be as shown in the figure.

Repeat this operation for the

Rev_Geneva_Origin entity’


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Setting Up and Defining the Mesh

To review the contact areas and mesh seeds:

The Named Selections that were defined in DesignModeler continue to be defined in Mechanical. The points that were projected onto the surface in DesignModeler are defined as vertices in Mechanical.

1. Review the definition of the contact surfaces by selecting the entity in the Named Selections group and viewing the highlighted surfaces.

2. Turn on the Show Vertices option in the Graphics Options toolbar by clicking on the icon as shown in the figure below.

For example, selecting contact surface con_area1 results in the image to the right. Note that there are 12 vertices but there are 19 forces in the list of Contact Forces in the Outline Window. This is the result of the Tolerance value of 0.5 mm that was defined during the load transfer. The 19 contact forces from the RecurDyn MBD solver were grouped into a total of 12 vertex locations.

To define the mesh – global settings:

1. Adjust some of the global settings of the mesh by:

Selecting the Mesh entity in the Outline window.

In the Details window changing the

Relevance field to 100.

Expanding the Sizing group, pulling-down

the menu in the Relevance Center field,

and selecting the Medium option.

The Details window should appear as shown in the figure.

To define the mesh – inserting:

When meshing thick-walled solid geometry it is good practice to use hexahedral elements as much as possible. Another good practice is to define more elements near areas of stress concentration, which in this model are in the vicinity of the applied loads. The mesh that will be defined will follow these good practices.


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1. Set up the mesh to use hexahedral elements as much as possible by:

Placing the cursor over the Mesh name in the Outline window and clicking on the right mouse button

Selecting the Insert option.

Selecting Method.

In the Detail window

click in the Geometry field and select the G_Geneva geometry.

Pull down the menu in the Method field and

select the Hex Dominant option.

2. Control the overall element sizing in the mesh by:

Placing the cursor over the Mesh name in the Outline window and clicking on the right mouse button.


Selecting Sizing.

In the Detail window click in the Geometry field and select the G_Geneva geometry.

Click in the Element Size field and set the value

to 8 (8 mm).

3. Control the mesh refinement in the fixed joint top hole surface by:

Placing the cursor over the Mesh name in the Outline window and clicking on the right mouse button.


Selecting Refinement.

In the Detail window click in the Geometry field and select the face at the bottom of the hole on the underneath side of the Geneva wheel.


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Click in the Refinement field and set the value to 1.

4. Control the refinement in the mesh at the revolute joint shoulder surface by following the same steps as given above.

In the Detail window click in the Geometry field and select the shoulder surface at the boss on top of the Geneva wheel.

Again, make sure the Refinement field is set to 1.

5. Rename the three refinement entities as Refine_Fix, and

Refine_Rev. The Outline window should appear as shown.

To define the mesh – local settings:

1. Control the mesh refinement in the first contact surface by:

Selecting the first contact surface.

Pulling-down on the Mesh Control menu in the Mesh toolbar and

selecting the Sizing option.

The Details window will show that the contact geometry (1 Face) has already been selected.

Click in the Element Size field and set the

value to 1 (1 mm)

2. Control the mesh refinement in the surface to the left of the first contact surface by:

Selecting the surface to the left of the first contact surface.

Pulling-down on the Mesh Control menu in

the Mesh toolbar and selecting the Sizing option.


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Clicking in the Element Size field and set

the value to 1.5 (1.5 mm).

3. Control the mesh refinement in the surface to the right of the first contact surface by:

Selecting the surface to the right of the first contact surface.

Pulling-down on the Mesh Control menu in the Mesh toolbar and

selecting the Sizing option.

Clicking in the Element Size field

and set the value to 1.5 (1.5 mm).

4. Rename the three refinement entities as Face Sizing 1,

Face Sizing 1L, and Face Sizing 1R,. The Outline window should appear as shown:

To generate the mesh:

1. Create the mesh as follows:

Place the cursor over the Mesh and click on the right mouse button.

Select the Generate Mesh option.

The mesh will appear on the geometry as shown when the Mesh item is selected. The mesh has approximately 134,000 nodes and 87,000 elements. The mesh refinement near the loading surface for the revolute joint can be seen.


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The mesh refinement in the face with contact area #1 can be seen.

Running the Analysis

To run the structural analysis and retrieve stresses:

It is often a good practice to examine von-Mises stresses when taking the first look at the stresses in a component under 3D loading. You will request the display of von-Mises stress and perform a solve of the component.

1. Request Equivalent (von-Mises) stresses by:

Making sure that the Geneva Wheel geometry is selected

Placing the cursor over the Solution item in the Outline window and clicking on the right mouse button,

Selecting Insert, Selecting Stress, and Selecting Equivalent (von-Mises)

Check the Details window to make sure that the Scope section shows that 1 Body has been selected. If not, click in the Geometry field and select the Geneva Wheel geometry. Note that if an edge or vertex is selected then the results will not be displayed properly.

2. The analysis is now ready to run. Invoke the solve by:

Placing the cursor over the Solution item under the Static Structural_at

t=0.5255 sec (B5) group, clicking on the right mouse button, and

Selecting the Solve item

The results will be ready in 2-4 minutes, depending upon the computer.


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Tip: Understanding the warning messages

You may note that there are two warning messages that occur when the analysis is run.

The first error message, shown to the right, informs us that there are multiple boundary conditions on a common face. This is the result of applying one of a joint loads on a surface that wraps around the geometry such that the leading and trailing edges are the same. This warning can be safely ignored.

The second warning is related to the unconstrained condition of the Geneva wheel body, which is acceptable because we are using the inertial relief option. This warning message can also be safely ignored.

To display the results:

1. Display the Equivalent (von-Mises) stresses and adjust the display settings by:

Clicking on the Equivalent Stress item in the Solution Group.

Since the Geneva Wheel is stiff we do not need to view the magnified deformation of the geometry. Request the display of the un-

deformed shape by going to the Result toolbar, pulling down the menu and selecting

the 1.0 (True Scale) option.

In the same toolbar pull down on the Contour menu and

select the Smooth Contours option.

Also pull down on the Edge menu and select the No

Wireframe option.

Click the right mouse button over the number within the stress

legend that is below the Max stress number and select the Edit option. Change the value of the number to 16 and press the Enter key. The stress legend will be redefined as shown in the figure.


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The undeformed Geneva wheel body with stress contours is displayed as shown in the figures. The local stresses due to the contact load are apparent, but there are also some stresses at the root of the slot. It is also interesting to see stresses at the hub. This is due to the resistive inertia of the flywheel body that is attached to the Geneva wheel.

Repeating the Analysis for the Second Time Instant

The following operations need to be done for each of the other two load cases:

- Suppress the transformed gravity

- Repeat the operations on the four load entities for the two joints.

- Request von-Mises stresses

- Run the Analysis

Before working with the second time instant it is recommended that the first time instant section be collapsed to a single line. This is done by clicking on the box with the minus sign in

front of the entity Static Structural_at t = 0.5525 sec (B5).


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Suppress command.

2. The Gravity Transformed entity should now be marked with an X.

To associate joint loads to the appropriate geometry for the second case:

Four entities related to the joint loads are included within the second Static Structural group in the Outline window as shown.

1. Both the Force and the Moment entities of the fixed joint will be associated with the bottom of the hole at the bottom of the Geneva wheel. To do this:







Body entity.



Body entity


field




To request the von Mises stresses:





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To run the analysis:

1. The analysis is now ready to run. Invoke the solve by placing the cursor over the

Solution item under the Static Structural_at t=0.6825 sec (C5) group, clicking

on the right mouse button, and selecting the Solve item





Click the right mouse button over the number within the stress

legend that is below the Max stress number and select the Edit

option. Change the value of the number to 56 and press the Enter key. The stress legend will be redefined as shown in the figure.

The undeformed Geneva wheel body with stress contours is displayed as shown in the figures. As in the first case the local stresses due to the contact load, stresses at the root of the slot and stresses at the hub can be observed.


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Repeating the Analysis for the Third Time Instant

Before working with the third time instant it is recommended that the first and second time instant section be collapsed to a single line. This is done by clicking on the box with the minus

sign in front of the entities Static Structural_at t = 0.5525 sec (B5) and Static

Structural_at t = 0.6825.



Suppress command.

2. The Gravity Transformed entity should now be marked with an X.

To associate joint loads to the appropriate geometry for the second case:

Four entities related to the joint loads are included within the second Static Structural group in the Outline window as shown.

3. Both the Force and the Moment entities of the fixed joint will be associated with the bottom of the hole at the bottom of the Geneva wheel. To do this:







Body entity.



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Body entity


field




To request the von Mises stresses:






To run the analysis:

1. The analysis is now ready to run. Invoke the solve by placing the cursor over the

Solution item under the Static Structural_at t=0.9475 sec (D5) group, clicking

on the right mouse button, and selecting the Solve item





The undeformed Geneva wheel body with stress contours is displayed as shown in the figures. Due to the contact loads at the tip of the slot there are noticeable surface stresses down most of the length of the arm between the contact point and the slot. As we would expect, the higher stresses occur on the surface where the material thickness is reduced and there is some distance from the forces at the contact surface so that a moment can be developed. It is interesting to observe some stress at the root of the adjoining slot as shown in the upper figure.


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Even with this simple example the power of using MBD for ANSYS to produce loads for use in ANSYS is evident. MBD for ANSYS calculates loads throughout the work cycle, the user selects of load cases of interest, and ANSYS calculates the stresses so that the engineer can easily understand the worst case conditions for the selected component.

Thanks for participating in this tutorial!

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