OptiStruct_01_Design Concept for a Structural C-Clip

Design Concept for a Structural C-clip - OS-2000

Using the topology optimization technique yields a new design and optimal material distribution. Topology optimization is

performed on a baseline design, resulting in a design that is lighter in most cases, and also performs better than the

baseline one. Topology optimization allow designers to start with a design that already has the advantage of improved

material distribution and is ready for fine tuning with shape or size optimization.

In this tutorial, topology optimization is performed on a model to create a new topology for the structure, removing any

unnecessary material. The resulting structure is lighter and satisfies all design constraints.

The optimization problem for this tutorial is stated as:

Objective: Minimize volume fraction.

Constraints: Translation in the y-axis for node A < 0.07mm.

Translation in the y-axis at node B > -0.07mm.

Design variables: The density of each element in the design space.

In this tutorial, you will:

• Set up the model in HyperMesh

• Analyze the baseline model

• Set up the optimization

• Post-process the optimization results

Exercise

Set Up the Model in HyperMesh

Step 1: Launch HyperMesh and Set the User Profile

1. Launch HyperMesh through the start menu.

The User Profiles dialog will appear by default.

2. Choose the OptiStruct user profile by selecting the radio button beside it.

3. Click OK.

This loads the user profile. It includes the appropriate template, macro menu, and import reader, paring down the

functionality of HyperMesh to what is relevant for generating models in Bulk Data Format for RADIOSS and

OptiStruct.

Step 2: Open the cclip.hm File

1. Click the Open .hm File button .

2. Select the cclip.hm file.

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3. Click Open.

The cclip.hm database is loaded into the current HyperMesh session, replacing any existing data. The database

only contains geometric data and the mesh.

Step 3: Create Materials and Properties; Assign to Components

Since components need to reference a material, the materials collectors should be created first.

1. Select the Model tab.

2. Right click inside of the Model Browser window, activate the menu over Create, and click Material.

When in this popup, do not press the Enter key until you are done.

3. In the Name: field, type Steel.

4. Select MAT1 as Card Image:.

5. Click Create/Edit.

The MAT1 card image pops up.

6. For E, enter the value 2.0E5.

7. For Nu, enter the value 0.3.

8. For RHO, enter the value 7.85E-9.

9. Click return.

10. Right click inside the Model Browser window, activate the menu over Create, and click Property.

11. In the Name: field, type prop_shell.

12. Select PSHELL as the Card Image:.

13. Select Steel as the Material.

14. Click Create/Edit.

The PSHELL card image appears.

15. Activate the thickness field for the shell component by clicking [T].

This allows you to edit this field. The acceptable default of 1.0 is shown.

16. Click return to go to the main menu.

17. From the Collectors pull down menu, activate the menu over Edit, and click Components.

18. Click on comps, check the box comp_shell, and click select.

19. Toggle <no property> to property=.

20. Double click on property= and select prop_shell.

21. Click update.

22. Click return.

Step 4: Create Load Collectors

Next we will create two load collectors (Constraints and Forces) and assign each a color. Follow these steps for each

load collector.

1. Right click inside the Model Browser window, activate the menu over Create, and click LoadCollector.

When in this popup, do not press Enter on the keyboard until you are completely done.

2. In the Name: field, type Constraints.


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3. Leave the Card Image: field set to None.

4. Select a color from the palette.

5. Click create.

6. Using the same method, create a LoadCollector named Forces.

Step 5: Create Constraints

For the three nodes that show constraints in the following figure, we need to create the constraints and assign them to

the spc load collector as outlined in the following steps.

1. From the Model Browser, expand LoadCollectors, right click on constraints, and click on Make Current.

2. From the Analysis page, enter the constraints panel.

3. Select nodes and corresponding dofs, and click on create to create constraints as shown below.

Mesh showing the boundary conditions applied on the c-clip.

4. Click Return.

Step 6: Create Forces


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In this step, we load the structure with two opposing forces of 100.0 N at the opposite tips of the opening of the c-clip.

1. From the Model Browser, under (expanded) LoadCollectors, right click on Forces, and click on Make Current.

2. From Analysis page, enter the forces panel.

3. To create the force at the top of the opening, click on the node at the top of the opening (A) of the c-clip as in the

figure below.

Opposing forces created at the opening of the c-clip.

4. Click magnitude=, enter 100.0, and press ENTER.

5. Set the switch below to y-axis.

6. Click create.

An arrow, pointing up, should appear at the node on the screen.

7. Similarly, to create the force at the bottom of the opening, click on the node at the bottom of the opening (B) of the

c-clip.

8. Click magnitude=, type -100.0, and press ENTER.

9. Verify that the y-axis is selected.

10. Click create.

An arrow, pointing down, should appear at the node on the screen.

11. To provide a separation between the arrows, select uniform size=, type 7, and press ENTER.

12. Click return to go back to the Analysis page.

Step 7: Create Load Cases

The last step in establishing boundary conditions is the creation of a subcase.

1. From the Analysis page, enter the loadsteps panel.

2. Click name=, type opposing forces, and press ENTER.


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3. Check the box preceding SPC.

An entry field appears to the right of SPC.

4. Click on the entry field and select constraints from the list of load collectors.

5. Check the box preceding Load and select forces from the list of load collectors.

6. Select type as linear static.

7. Click Create.

8. Click return to go back to the Analysis page.

Analyze the Baseline Model

Step 8: Run the Analysis

A linear static analysis of this c-clip is performed prior to the definition of the optimization process. An analysis identifies

the responses of the structure before optimization to ensure that constraints defined for the optimization are reasonable.

1. From the Analysis page enter the RADIOSS panel.

2. Click save as6 following the input file: field.

3. Select the directory where you would like to write the OptiStruct model file and enter the name for the model,

cclip.fem, in the File name: field.

.fem is the recommended extension for Bulk Data Format input decks.

4. Click Save.

Note the name and location of the cclip.fem file displays in the input file: field.

5. Set the export options: toggle to all.

6. Click the run options: switch and select analysis.

7. Set the memory options: toggle to memory default.

8. Set the options: field to blank.

9. Click Radioss.

Step 9: View Displacement Contour

1. From the Radioss panel, click on HyperView.

HyperView launches the cclip.h3d file which contains the model and the results.

2. From the Graphics pull down menu, click on Contour. Choose Displacement as the Result type and set the

pull-down menu below Displacement to Y.

3. Click Apply.


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This shows the contour of Y displacements.

4. Verify if the values are equivalent to those in the image above.

5. From File pull-down menu, click on Exit to quit HyperView.

6. Back in HyperMesh, click return to exit the panel.

Set Up the Optimization

The preliminary finite element model, consisting of shell elements, element properties, material properties, and loads and

boundary conditions has been defined. Now a topology optimization will be performed with the goal of minimizing the

amount of material to be used. When reducing material in an existing mesh with the same loads and boundary

conditions, it follows for the model to be less stiff and more prone to deform. Therefore, the optimization process needs

to be constrained with a displacement so that a balance between material and overall stiffness is achieved.

The forces in the structure are applied on the outer nodes of the opening of the clip, making those two nodes critical

locations in the mesh where the maximum displacement may happen. We applied a displacement constraint on the

nodes so that they would not displace more than 0.07 in the y-axis.

Step 10: Create the Topology Design Variables

1. From the Analysis page, enter the optimization panel.

2. Select topology to enter the topology panel

3. Make sure the create subpanel is selected using the radio buttons on the left-hand side of the panel.

4. Click DESVAR=, type d_shell, and press ENTER.

5. Click props and choose prop_shell from the list of props; click select.

6. Choose type: PSHELL.

7. Verify that the base thickness is 0.0.

A value of 0.0 implies that the thickness at a specific element can go to zero, and therefore becomes a void.

8. Click Create.

9. Click return to go back to the optimization panel.

Step 11: Create a Volume Response

1. Enter the responses panel.

2. Click response= and type volfrac.

3. Change response type: to volumefrac.

4. Click create.


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Step 12: Create a Displacement Response

To create a displacement as a response, you will need to supply a meaningful name for the response, set the response

type to displacement, select the node for the response, and select the type of displacement (dof).

1. Click responses.

2. Click response= and type upperdis.

3. Change the response type: to static displacement.

4. Click the node labeled A (upper opening of c-clip) as shown in the figure to select it.

5. Choose dof2 for the node.

6. Click create.

7. Click response= and type lowerdis.

8. The response type: should still be static displacement.

9. Click the node labeled B (lower opening of the c-clip) as shown in the figure.

10. Select dof2 and create the response.


Step 13: Create Constraints on Displacement Responses

In this step we set the upper and lower bound constraint criteria for this analysis.

1. Select the dconstraints panel.

2. Click constraint= and enter c_upper.

3. Check the box for upper bound only.

4. Click upper bound= and enter 0.07.


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5. Select response= and set it to upperdis.

6. Click loadsteps.

7. Check the box next to forces.

8. Click select.

9. Click create.

10. Click constraint= and enter c_lower.

11. Check the box for lower bound only.

12. Click lower bound= and enter -0.07.

13. Select response= and set it to lowerdis.

14. Click loadsteps.

15. Check the box next to forces.

16. Click create.


Step 14: Define the Objective Function

1. Click objective.

2. The switch on the left should be set to min.

3. Click response= and select volfrac.

4. Click create.

5. Click return twice to exit the optimization panel.

Step 15: Run the Optimization Problem

1. From the Analysis page, click on control cards.

2. Click next twice.

3. Click on SCREEN and return.

This will make OptiStruct output the optimization iterations to the output window.

4. From the Analysis page, select OptiStruct.

5. Click save as6, enter cclip_complete.fem as the file name, and click Save.

6. Click the run options: switch and select optimization.

7. Click OptiStruct to run the optimization.

The message 6Processing complete appears in the window at the completion of the job. OptiStruct also reports

error messages if any exist. The file cclip_complete.out can be opened in a text editor to find details

regarding any errors. This file is written to the same directory as the .fem file.

8. Close the DOS window or shell and click return.

The default files that get written to your run directory include:

cclip_complete.res HyperMesh binary results file.

cclip_complete.h3d HyperView binary results file.


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cclip_complete.HM.comp.cmf HyperMesh command file used to organize elements

into components based on their density result values.

This file is only used with OptiStruct topology

optimization runs.

cclip_complete.out OptiStruct output file containing specific information on

the file setup, the setup of the optimization problem,

estimates for the amount of RAM and disk space

required for the run, information for each optimization

iteration, and compute time information. Review this file

for warnings and errors that are flagged from

processing the cclip_complete.fem file.

cclip_complete.sh Shape file for the final iteration. It contains the material

density, void size parameters and void orientation angle

for each element in the analysis. This file may be used

to restart a run.

cclip_complete.hgdata HyperGraph file containing data for the objective

function, percent constraint violations, and constraint for

each iteration.

cclip_complete.oss OSSmooth file with a default density threshold of 0.3.

The user may edit the parameters in the file to obtain

the desired results.

cclip_complete_hist.mvw Contains the iteration history of the objective,

constraints, and the design variables. It can be used to

plot curves in HyperGraph, HyperView, and MotionView.

cclip_complete.stat Contains information about the CPU time used for the

complete run and also the break up of the CPU time for

reading the input deck, assembly, analysis,

convergence, etc.

Post-process the Optimization Results

OptiStruct provides density information for all iterations, and also gives displacement and von Mises stress results for

your linear static analysis. This section describes how to view those results in HyperView.

Step 16: View an Iso Value Plot of Element Densities

This plot provides the information about the element density. Iso Value retains all of the elements at and above a certain

density threshold. Pick the density threshold providing the structure that suits your needs.

1. From the OptiStruct panel, click the HyperView button.

This will launch HyperView and open the section file cclip_complete.mvw which contains two pages with the

results from two files:

Page 1 - cclip_complete_des.h3d: Optimization history results (element density).

Page 2 - cclip_complete_s1.h3d: Subcase 1 results; initial and final (displacement stress).

2. On page 1, in the bottom portion of the GUI, click in the area circled below to activate the Load Case and

Simulation Selection dialog.


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3. Select Design under the Load Case section and the last iteration listed under Simulation and click OK.

4. From Graphics pull down menu, click on Iso Value and choose Element Densities as the Result type.

5. Set the Current Value: to 0.3.

6. Click on Top view orientation to set the correct view.

7. Click Apply.

Iso value plot of element densities.

7. Move the slider below Current value: to change the density threshold.

You will see the iso value in the graphics window update interactively when you scroll to a new value. Use this tool

to get a better look at the material layout and the load paths from OptiStruct.

Step 17: Compare Static Contour of Original to the Optimized Material Layout

1. In HyperView, click on the Next Page arrow toolbar button to go to page 2.

This will bring up the cclip_complete_s1.h3d file, which contains the static subcase results for the first and last

iteration steps.

2. Divide this page into two vertical windows using the Page Layout toolbar icon shown below.


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3. Click on Top view orientation to set the correct view.

4. From Graphics pull down menu, click on Contour; choose Displacement as the Result type, and set the pull-down

menu below Displacement to Y.

5. Click Apply.

6. Click on the Deformed toolbar button .

7. On the Deformed shape panel, change the scale value to 100, the unperformed shape to edges, and click Apply.

8. From Edit pull down menu, click on Copy Window then click on the empty window.

9. Again, from the Edit pull down menu, click Paste Window.

10. Switch the animation mode from Transient to Linear Static .

11. In the bottom portion of the GUI, with the second window selected, click in the area circled below to activate the

Load Case and Simulation Selection dialog.

12. Select Iteration 28 under Simulation and click OK.

Y-Displacement at iteration 0 and at the last iteration.

The Note toolbar button has been improved to allow for display manipulation.

13. From Edit pull down menu, click on Copy Page.

14. From the Edit pull down menu again, click Paste Page.

This will create a 3rd page on this report.

15. Now click on the first window and click on the Contour button .


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16. Change the result type to Element Stresses (2D & 3D) (t) and click Apply.

17. Click with the right button on the first window; choose Apply Style To, then Current Page, and select Contour.

These stress results can be used only as reference to help understanding how far from the limits the design is.

Remember that topologic optimization will show you a concept shape and the stress results should be validated

during the next design phases.

Go To

RADIOSS, MotionSolve, and OptiStruct Tutorials


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Documents

OptiStruct_01_Design Concept for a Structural C-Clip