OptiStruct Concept Design Using Topology and Topography Optimization

Altair OptiStruct ®

®

Concept Design Using Topology and Topography Optimization

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Table of Contents

Chapter 1: Topology Optimization of a Structural C-Clip .........................................................3 Chapter 2: Topology Optimization of an Automotive Control Arm........................................25 Chapter 3: Topology Optimization with Manufacturing Constraints .....................................49 Chapter 4: Optimal Rib Pattern for an Automotive Splash Shield .........................................69 Chapter 5: Topography Optimization of a Torsion Plate.........................................................81 Chapter 6: Combined Topology and Topography Optimization of a Slider Suspension ....93

OptiStruct 7.0

Concept Design Using Topology and Topography Optimization i Proprietary Infromation of Altair Engineering, Inc.

Table of Contents

ii Concept Design Using Topology and Topography Optimization Proprietary Information of Altair Engineering, Inc.

OptiStruct 7.0

Preface Who should attend This course is designed for individuals who want to become familiar with optimization techniques using OptiStruct. It is recommended that students attend HyperMesh Basic training and be familiar with one of the finite element packages. This course covers the optimization portion of the software and the analysis part is blended within the optimization exercises. This course covers the basics of topology, topography, shape and size optimization and their implementation in OptiStruct. Each section includes "hands-on" exercises to help the students become comfortable with the techniques presented. This course introduces the principles of optimization and helps to develop familiarity with various types of optimization problems.

Manual notations This manual uses the following notations. •

courier for text that you type in and file names.

•

bold italic for panel names, button names, and subpanel names.

Information that is of importance or warning messages will appear in a note box.

.

This is an example of a note box. Important information appears here.

For more help For additional help with material in this course, see the back of the title page of this manual for contact information. Comments about this manual may be directed to [email protected].

OptiStruct 7.0

Concept Design Using Topology and Topography Optimization Proprietary Information of Altair Engineering, Inc.

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Preface

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OptiStruct 7.0

Chapter 1

Topology Optimization of a Structural C-Clip Purpose This exercise involves performing topology optimization using OptiStruct. The topology optimization technique provides us with a new design and optimal material distribution. Topology optimization is performed on a concept design and the resulting design space is returned to the designer for suitable modifications. The optimized design in most cases is lighter and performs better than the concept design. The modified design from the designer can be further fine-tuned using shape or size optimization. We perform topology optimization on this model to create a new boundary for this structure and remove any unnecessary material. This optimization normalizes each element according to its density and lets you remove elements that have low density. This exercise describes the steps to define topology optimization for the surface model of a c-clip with shell elements with a single subcase (loadstep). The exercise describes the steps to perform a finite element mesh; define force, boundary conditions, and optimization parameters using HyperMesh; conduct a linear static analysis using OptiStruct; and perform its optimization. The resulting structure is lighter and satisfies all constraints.

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A

B

Figure 1-1: Design space with conditions and design constraints


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Chapter 1: Topology Optimization of a Structural C-Clip

Problem Statement Perform structural optimization on a structural c-clip (see Figure 1-1) ensuring that a minimum amount of material is used and movement at the end nodes of the opening (see A and B in Figure 1-1) does not exceed 0.14mm in the y-direction. Objective function

Minimize volume

Constraints

1)

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

2)

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

Design Variables

Element densities

Optimization Process The process to complete a topology optimization using OptiStruct is a three-part process. •

Use HyperMesh to create the appropriate input deck

•

Run OptiStruct using the created input deck

•

Examine the results

These are the steps the exercise follows. 1. Load the geometry into HyperMesh. 2. Define the material properties and components. 3. Generate a finite element mesh. 4. Apply loads and boundary conditions. 5. Create load case. 6. Set up optimization problem using HyperMesh. 7. Define the design space for optimization. 8. Define optimization responses, constraints, and objective function. 9. Solve topology optimization using OptiStruct to determine the optimal material distribution. 10. Post-process the results.

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Create FE Model Step 1: Load the geometry into HyperMesh 1. Launch HyperMesh. 2. Go to Geom page and click user profile…. 3. From the pull-down menu, select OptiStruct and click OK. 4. This sets the HyperMesh environment for the OptiStruct solver. 5. From any main page in HyperMesh, select the files panel. 6. Select retrieve …, locate the file, cclip.hm, and click Open. Sample directory name where input files are located: /altair/tutorials/os/ (Note: The instructor will mention the location of the training file for classroom instruction. Otherwise, the files are in the tutorials section of the installation CD). 7. Click return to go back to the main page.

Step 2: Define the material properties and components Because components need to reference a material, create material collectors first. At any time, you can modify the card images and materials for collectors from the collectors panel. For card images, use the card image subpanel. For a different material, use the update subpanel. 1. From any main page of HyperMesh select the collectors panel. 2. Click the radio button to the left of create to access the create subpanel. 3. To the right of collector type:, click the switch. From the pop-up menu, click mats. 4. Click name =. In the text box, type steel. 5. Click card image = and from the pop up menu select MAT1. 6. Click create/edit to load the MAT1 card image for the material steel. 7. Click E to select it and enter the value of 2e5 and in a similar fashion select NU and set it to the value of 0.30. 8. Click return to go to the collectors panel. 9. Change collector type: to comps using the switch.

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10. Click name = and type shells. 11. Click card image = and from the pop up menu select PSHELL. 12. Click material =. You will see a list of materials you just created. 13. Click steel. 14. Click color and select yellow (color12). 15. Click create/edit to load the PSHELL card image for the component shells. 16. Enter the thickness for the shell component by clicking T, clicking in the text box, and typing 1. 17. Click return to go back to the collectors page. 18. Click return to go to a main page.

Step 3: Generate a finite element mesh Use the automesh module to create a quad dominant mesh. Since the shells component you just created is your current component, any elements you generate are organized into that component. 1. Access the automesh panel. (Select the 2D page, then automesh or press F12). 2. Click the check box to the left of reset meshing parameters to:. 3. Click element size =, type 2.5, and press ENTER to set element size. 4. Use the switch under element size to set element type to mixed. 5. Select the top half of the surface by clicking any line in that surface. 6. Click mesh. The mesh density is displayed on the surface. 7. Click mesh again. The automesher should create about 560 shell elements. See the HyperMesh Message Bar for the message.

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Figure 1-2: Quad mesh created from automesh panel

8. Click return to save the mesh into the shells component. Note the mesh color corresponds to the color selected for the current component. 9. Click return to go to the main panel.

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Step 4: Create a mirrored duplicate of the upper surface elements 1. Click Tool to select the tool page. 2. Select the reflect panel. 3. Click the switch under the Reflect heading and, from the pop up menu, select elems. 4. Click elems button and select displayed from the pop up menu. 5. Click elems again and from the pop up menu select duplicate, and from the next pop up menu select original comp. 6. Click the switch in the center of the page. From the pop up menu, select the normal direction of the reflection plane (the y-axis in this case). 7. Click base and select the node as shown in Figure 1-3. The node is needed to reflect the mesh about the y-axis.

Figure 1-3: Node to select as base to reflect elements

8. Click reflect. Mesh appears in the lower half of the image. 9. Click return. 10. To refresh the screen, from the permanent menu click p (or press P on the keyboard).

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Step 5: Equivalencing duplicate nodes between the meshes The nodes on the edges shared by the two surfaces are defined for each edge. They need to be equivalenced. 1. Select the edges panel. 2. With the left mouse button, click any of the elements in the figure to select it and place its component into the comps buffer. 3. Click preview equiv. This highlights the twenty-one nodes defining the seam between the two sets of elements. 4. Click equivalence. The message “21 nodes were equivalenced” appears. 5. Click return to go back to the Tool page.

Define Loads Step 1: Create load collectors Create two load collectors and assign each a color: spc (green) and forces (red). Follow these steps for each load collector. 1. Go to the BCs page. 2. Click collectors. 3. Verify the create subpanel is active. 4. Click the switch to the right of collector type: and select loadcols from the menu. Use steps 4 – 8 to create each load collector and assign its name and color per the diagram. 5. Click name = and type in the name of the load collector. 6. Press enter.

Load Collectors and Display Color Load Collector

Color

spc

green

forces

red

7. Click color and select assigned color from the pop-up menu. 8. Click create.

It is not necessary to assign a card image for these load collectors. 9. When both collectors are created, click return to go back to the BCs page. OptiStruct 7.0


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Step 2: Apply loads and boundary conditions For the three nodes in Figure 1 - 4 that show constraints, we need to create these constraints and assign them to the spc load collector. To do that, follow these steps.

Figure 1-4: Mesh showing the boundary conditions applied on the c-clip

1. From the permanent menu, click global. 2. Check the current setting of loadcols =. If it is not spc, click loadcols = and select spc. 3. Click return to go to the BCs page. 4. Select the constraints panel. 5. Left click on the node at the center of the left edge of the design space to select it (see Figure 1-4). Active degrees of freedom contain a check in the box to the left of their label. 6. Verify dof1, dof2, and dof3 are active. 7. De-select dof4, dof5, and dof6 by clicking in the check box to remove the check. 8. Click create to apply this constraint to the selected node. Note a triangle with a number for each dof selected appears at the node. 9. Left click the node at the center of the c-clip curve (see Figure 1-4). 10


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Degree of freedom (dof)

Definition

dof1

Translation about X-axis

dof2

Translation about Y-axis

dof3

Translation about Z-axis

dof4

Rotation about X -axis

dof5

Rotation about Y -axis

dof6

Rotation about Z -axis

10. Set only dof2. 11. Click create. 12. Left mouse click on the node at the upper left corner of the c-clip design space (see Figure 1-4). 13. Set only dof3. Unselect any other dof that might be active. 14. Click create. Your image should appear as in Fig 1-4. 15. Click return.

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Step 3: Apply force boundary conditions Load the structure with two opposing forces of 100.0 N at the opposite tips of the opening of the c-clip as shown in Figure 1-5. 1. Click global (permanent menu). 2. Click loadcol =. 3. Select the forces collector. 4. Click return. 5. From the BCs page, select the forces panel.

Figure 1-5: Opposing forces created at the opening of the c-clip

6. To create the force at the top of the opening, left mouse click on the node at the top of the opening (A) of the c-clip (see Figure 1-5). 7. Click magnitude =, type 100.0 and press ENTER. 8. Click the switch to the left of N1, N2, N3 and from the pop up menu select y-axis. 9. Click create. An arrow (pointing up) should appear at the node on the screen. 10. To create the force at the bottom of the opening, left mouse click on the node at the bottom of the opening (B) of the c-clip (see Figure 1-5). 11. Click magnitude = , type -100.0 and press ENTER. 12


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12. Verify the y-axis is selected (under magnitude =). 13. Click create. 14. An arrow (pointing down) should appear at the node on the screen. 15. To provide a separation between the arrows, select uniform size=, type 7 and press ENTER. 16. Click return to return to the BCs page.

Step 9: Create load case The last step in establishing boundary conditions is the creation of an OptiStruct subcase (a load step to HyperMesh). 1. From the BCs page, click load steps. 2. Click name=, type opposing forces and press enter. 3. Click loadcols and select spc and forces from the collector list. 4. Click select. 5. Click create. 6. Click return to go back to the BCs page.

Analysis of FE Model Step 1: Perform analysis We perform linear static analysis on this cclip before defining the optimization process. An analysis identifies the responses of the structure before optimization. This ensures constraints defined for the optimization are reasonable. 1. From the BCs page select the OptiStruct panel. This panel exports the deck, runs the analysis/optimization and then loads the results files into HyperMesh after the job is complete. 2. Click save as…. and enter cclip_analysis.fem as the file name and click Save. 3. Click the switch below Run Options: and select analysis. 4. Click optistruct to run the analysis. Running OptiStruct from this panel automatically loads the results file after the job is done. 5. Close the DOS window or shell window and click return. OptiStruct 7.0


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Step 2: Post-process analysis results 1. From the Post page, select the contour panel. 2. Click simulation= and select opposing forces. 3. Click data type= and select Displacements. 4. Change from total disp to y comp. 5. Activate min/max titles and info title. 6. Click contour. What is the displacement at Nodes A and B (upper node and lower node, respectively see Figure 1-4)? ________________________________________________________ 7. Click return.

Optimization Setup Step 1: Topology optimization We have defined the preliminary finite element model consisting of shell elements, element properties, material properties, and loads and boundary conditions. Now we will perform topology optimization with the goal of minimizing the amount of material to be used. However, when using less material in the existing mesh with the same loads and boundary conditions, we would expect the model to be less stiff and deform more than it did. Therefore, we need to constrain the optimization process with a displacement so that we achieve a balance between the material to be used and the overall stiffness of the material. 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. We applied a displacement constraint on the end nodes so they would not displace more than 0.07 in the y-axis. Define the design space for topology optimization from the optimization panel in HyperMesh using the topology subpanel. The optimization process is as follows: 1. Define the design space for optimization and thereby, the design variables. 2. Define all responses for the optimization (in this tutorial, the responses would be volume fraction and displacement). 3. Define the displacement at the end nodes of the c-clip as constraints. 4. Define volume fraction as the objective function.

. 14

Defining the same response as the objective function and a constraint is not allowed.


OptiStruct 7.0


Step 2: Define the topology design variables 1. From the BCs page, select optimization. 2. Select topology to access the topology optimization subpanel. 3. Select create. 4. Click comps and select shells and click select. 5. Choose type : to be PSHELL. 6. Assign a name of shells in DESVAR= and press ENTER. 7. Verify base thickness is 0.00. A value of 0.0 implies that the thickness at a specific element can go to zero and therefore it becomes a void. 8. Click create. 9. Click return to go back to optimization panel.

Step 3: Define responses for optimization The three responses for this problem need to be defined. The first response is the volume fraction, which forms the objective function, and two responses for the displacements because the two nodes move in opposite directions.

Define volume as a response 1. Click Responses.

2. In response=, assign the name Vol. 3. Change the response type: to volumefrac. 4. Verify the toggle below response type: is total. 5. Click create.

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Define displacement as a response To create a displacement as a response you need to: supply a meaningful name to the response, set the response type to displacement, select the node for the response, and select the type of displacement (dof). 1. In response=, assign a name upperdis. 2. Change the response type: to displacement. 3. Click the node labeled A (upper opening of c-clip) in Figure 1-5 to select it. 4. Choose the dof2 for the node. 5. Click create. 6. In response=, assign a name lowerdis. The response type: is still displacement. 7. Click the node labeled B (lower opening of the c-clip) in Figure 1-5 to select it. 8. Select dof2 and create the response. 9. Select review to see the list of responses you just created. 10. Click return to leave this panel. 11. Click return to go back to optimization panel.

Define constraints Set the upper and lower bound constraint criteria for this analysis. 1. Select dconstraints to access the constraints panel.

2. In constraint=, assign a name const1. 3. Activate upper bound=. 4. In upper bound=, assign a value of 0.07. 5. Select response= and set it to upperdis. 6. Select loadsteps. 7. Activate opposing forces. 8. Click select. 16


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9. Click Create. 10. In constraint=, assign a name const2. 11. De-activate upper bound=. 12. Activate lower bound=. 13. In lower bound=, assign a value of –0.07. 14. Select response= and set it to lowerdis. 15. Click loadsteps. 16. Select opposing forces. 17. Click select. 18. Click create. 19. Select Review to see a list to the newly created constraints. 20. Click return. 21. Click return to go back to optimization panel.

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Define objective function 1. Click objective.

2. Verify Objective is set to min. 3. Click response= and select vol. 4. Click create. 5. Click return twice to exit the Optimization panel.

Solve the problem 1. From the BCs page, select OptiStruct to access the OptiStruct solver. This panel exports the deck, runs the analysis/optimization and then loads the results files into HyperMesh after the job is completed. 2. Click save as…., enter cclip_complete.fem as the file name, and click Save. This indicates to OptiStruct what file name is to be associated with the various outputs it creates and where to locate the files. The actual save occurs at the completion of the optimization run. 3. Click the switch below Run Options: and select Optimization. 4. Click Optistruct to run the optimization. Running OptiStruct from this panel automatically loads the results file after the job is done. When you click the optistruct button, OptiStruct: writes out the OptiStruct input file, solves the optimization, and loads the results into HyperMesh for postprocessing. You no longer need to export the file with the OptiStruct template, manually initiate the solver, and import the results file for post-processing. The message “….Processing complete” appears in the window at the completion of the OptiStruct job. OptiStruct also reports error messages, if any. If error messages appear, open the file cclip_complete.out in a text editor to look for details about the error. The cclip_complete.out file is written to the same directory as the .fem file. 5. Close the DOS window or shell and click Return.

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Default files written to your directory on a successful run cclip_complete.res The HyperMesh binary results file. cclip_complete.HM.ent.cmf A HyperMesh command file that organizes elements into entity sets based on their density result values (only used with OptiStruct topology optimization runs). cclip_complete.HM.comp.cmf A HyperMesh command file that organizes elements into components based on their density result values (only used with OptiStruct topology optimization runs). cclip_complete.out the OptiStruct output file containing specific information on the file setup, the setup of your optimization problem, estimate 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.fem file. cclip_complete.sh The shape file for the final iteration contains the material density, the 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 notation and constraints 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. Clip_complete_hist.mvw This file contains the iteration history of the objective, constraints and the design variables and can be used to plot curves in HyperGraph, HyperView, and MotionView. Clip_complete.stat This file contains information about the CPU time utilized for the complete run and also the break up of the CPU time for reading the input deck, assembly, analysis, convergence etc…

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View Results Step 1: Post-process the results OptiStruct gives you density information for all iterations. OptiStruct also gives you displacement and Von Mises Stress results for your linear static analysis in iteration0 and iteration29. This section describes how to view those results in HyperMesh.

View a deformed shape It is helpful to first view the deformed shape of your model to determine if the boundary conditions have been defined correctly and also to check if the model is deforming as expected. 1. Select the Post page. 2. Select the deformed panel. 3. Click simulation =. You will notice that there are many simulations. At the end of the simulation list, you see opposing forces - ITERATION 0 and opposing forces - ITERATION 29. 4. Select opposing forces - ITERATION 0. 5. Verify the datatype = is pointing to displacements. 6. Toggle model units = to scale factor =. 7. Set the scale factor to 100.000. 8. Click deform to view a deformed plot of your model overlaid on the original, undeformed mesh. (Figure 1-6 shows the plot from a top view). Does the deformed shape look correct for the boundary conditions you applied to the mesh?

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Figure 1-6: Deformed plot overlaid on original undeformed mesh. Scale factor is set to 100.000. The darker mesh is the deformed plot and the lighter mesh is the original location.

9. Click return.

View a transient animation of density results This step views how the material distributes during the optimization. 1. From the permanent menu select the options panel. 2. Select the graphics subpanel. 3. Toggle the graphics engine mode to standard. 4. Click return. 5. From the Post page in HyperMesh, select the transient panel. 6. Set start with = DESIGN-ITER0. 7. Set end with = DESIGN–ITER29, the last iteration. 8. Set data type = to Element Density. 9. Click transient.

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10. Set the following options located on the left side of the animation panel. mode

hidden line

color

contour

lights

smooth

mesh

on

11. Use the slower button to slow down the animation if the frames animate too quickly. 12. Click exit when you are finished viewing the animation. 13. Click return.

View a static contour plot This plot assigns density to all the elements in the model. 1. From the Post page in HyperMesh, select the contour panel. 2. Set simulation = to DESIGN–ITER29. 3. Click data type = and select Element Density. 4. Click assign to see the element densities of each element at the end of optimization. The regions with high element densities indicate the areas where material is needed and the regions with low element densities are areas with scope for mass reduction. 5. Click return.

View an isosurface plot This plot provides the information about the element density. Isosurface retains all the elements at and above a certain density threshold. Pick the density threshold providing the structure that suits your needs. 1. From the permanent menu, select the options panel. 2. Select the graphics subpanel. 3. Toggle the graphics engine mode to per (performance). 4. Click return. 5. From the Post page in HyperMesh, select the contour panel. 6. Set your simulation to DESIGN–ITER29. 7. Click data type = and select Element Density. 8. Click the radio button to the left of isosurface to select the subpanel. 22


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9. Activate show. 10. Toggle the mode from legend based to value based. 11. Set the iso surface = field to 0.300. 12. Activate include faces above. 13. Click contour.

Figure 1-7: Isosurface plot of an optimal layout of the designable material

14. On the triangle shown in the legend (currently pointing to a value representing 0.300 for your density), click and hold the left mouse button then scroll up and down to change the threshold surface. You will see the isosurface 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.

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Review 1. Have most of your elements converged to a density of 1 or 0? If there are many elements with intermediate densities, you may need to adjust the discrete parameter. The DISCRETE parameter (set in the opti cntl panel) can be used to push elements with intermediate densities towards 1 or 0 so that a more discrete structure is given. 2. Is the max = field showing 1.0e+00? In this case, it is. If it is not, your optimization has not progressed far enough. Allow more iterations and/or decrease the OBJTOL parameter (set in the opti cntl panel).

Conclusion The exercises in this tutorial covered:

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•

Creating a finite element mesh using HyperMesh.

•

Creating loads and boundary conditions.

•

Performing linear static analysis and topology optimization.

•

Post-processing topology results using isosurfaces in HyperMesh.


OptiStruct 7.0

Chapter 2

Topology Optimization of an Automotive Control Arm Purpose This exercise involves performing topology optimization using OptiStruct. Topology optimization is a technique that provides a new design boundary and optimal material distribution. Topology optimization is performed on a concept design and the resulting design space is returned to the designer for suitable modifications. The optimized design will always be lighter and usually stiffer than the concept design. The modified design from the designer can then be further fine-tuned using shape or size optimization. This exercise describes the steps involved in defining a topology optimization for an automotive control arm modeled with solid elements and with three subcases (loadsteps). The exercise describes the steps to define force, boundary conditions, and optimization parameters using HyperMesh. The optimization is carried out with constraints for three different subcases. The resulting structure is lighter and satisfies constraints for all subcases.

Problem statement Perform topology optimization on an automotive control arm. The optimization problem for this exercise is: Objective:

minimize volume

Constraints:

resultant displacement at node id 2699 induced by subcase 1 < 0.05. resultant displacement at node id 2699 induced by subcase 2 < 0.02. resultant displacement at node id 2699 induced by subcase 3 < 0.04.

Design variables:

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element density


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Chapter 2: Topology Optimization of an Automotive Control Arm

Figure 2-1: Finite element mesh containing designable and non-designable material

Optimization Process The process to complete a topology optimization using OptiStruct is a three-part process. •

Use HyperMesh to create the appropriate input deck.

•

Run OptiStruct using the created input deck.

•

Examine the results.

This tutorial will follow the steps outlined below: 1. Load the model into HyperMesh. 2. Define material properties and assign materials to the components. 3. Apply load and boundary conditions. 4. Setup the optimization problem using HyperMesh. 5. Define the design space for optimization. 6. Define optimization responses, constraints, and objective function. 7. Solve topology optimization using OptiStruct to determine the optimal material distribution. 8. Post-process the results.

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Load the Model Step 1: Set up the FEA model in HyperMesh 1. Delete the current model by pressing F2 to access the delete panel and selecting delete model. 2. From any main page in HyperMesh, select the files panel. 3. Select hm file. 4. Click retrieve …, select carm.hm, and click Open. 5. Click return. 6. From the Geom page, select user prof…. 7. Select optistruct from the list and click OK. This sets the HyperMesh environment for the OptiStruct solver .

Step 2: Set up material properties The components for this exercise have already been created. The next step is to create the material collectors and assign to each component the appropriate material.

Create a material called steel 1. From the Geom page select the collectors panel. 2. Select the create subpanel. 3. Specify the collector type to be mats by clicking the switch to the right of collector type: and from the pop up menu choose mats. 4. Select name =, type steel in the text box, and press ENTER. 5. Select card image = and, from the pop up menu, choose MAT1. 6. Click create/edit to load the MAT1 card image for the new material, steel. 7. Set the values for E to 2E5 and NU to 0.300. To establish values in these fields: Select the field name, click in the text box, type in a value, and press ENTER.

.

Since this problem is a linear static analysis with volume as a response, you do not need to define a density value. Density values are required for a normal modes analysis or if mass is used as a response.

8. Click return. OptiStruct 7.0


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Assign the material to the components 1. Remain in the collectors panel, and select the update subpanel. 2. Change the collector type to comps. 3. Click the yellow comps button. 4. Activate components, design and non-design (click the box on the left of each). 5. Click select. 6. Click material= and select steel. 7. Click the green update button. 8. Activate material id. 9. Click update. The MID fields for both components should now be set to 1 since only one material is defined. The following steps allow you to verify the card image for each component to ensure the MID fields are updated. 10. Select the card image subpanel. 11. Click name = twice and select nondesign. 12. Select card image = and choose PSOLID. 13. Click load/edit. 14. Verify MID is 1. 15. Click return. 16. Repeat 10 through 15 for the design component. 17. Click return.

Step 3: Apply boundary conditions and loads Create the load collectors This problem requires four load collectors, one for boundary conditions and three for forces in the x, y, and z-axis at node 2699. To accomplish this, give each collector a meaningful name, assign it a color, then create it. The following steps take you through this process for all four collectors. 1. On the collectors panel, select the create subpanel. 2. Set the collector type: to loadcols (click on the switch to the right of collector type: and choose loadcols from the pop up menu). 3. Click name = and type spc. 28


OptiStruct 7.0


4. Click color and select green (color 10). 5. Click create. 6. Click name= and type brake. 7. Click color and select yellow (color 12). 8. Click create. 9. Click name= and type, corner. 10. Click color and select orange (color 13). 11. Click create. 12. Click name = and type, pothole. 13. Click color and select red (color 15). 14. Click create. 15. To review all of the collectors, click name = twice and read through the list. Then click return to bring up the collectors panel. 16. Click return to go back to the main screen.

Apply constraints to the model The model needs to be constrained using single point constraints at the two bushing locations. Apply constraints dof1, dof2 and dof3 at one end of the bushing and dof2, dof3 at the other end. Apply constraint dof3 on node 3239. 1. Click global in the permanent menu, then click loadcol=. 2. Select spc from the list. 3. Click return. 4. From the BCs page, select the constraints panel. 5. Select the foreground node at one end of the bushing (see Figure 2-2) and constrain dof1, dof2 and dof3. DOFs

Definition

1

Translation on x-axis.

2

Translation on y-axis.

3

Translation on z-axis.

4

Rotation on x-axis.

5

Rotation on y-axis.

6

Rotation on z-axis.

Make sure dofs 1,2 and 3 have been checked. OptiStruct 7.0


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6. Select create to apply these constraints to the selected node.

Figure 2-2: Constraining dof1, dof2 and dof3 at one end of the bushing

7. Select the background node at the other end of the bushing (see Figure 2-3) and constrain dof2 and dof3.

Figure 2-3: Constraining dof2 and dof3 at the other end of the bushing

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8. Make sure the check boxes to the left of dofs 2 and 3 have checks. 9. Select create to apply these constraints to the selected node. 10. From the permanent menu, click f to fit the model to the screen. 11. Click nodes, then select by id. 12. Type 3239 and press ENTER to select node ID 3239. Move mouse off pop-up menu to close the menu. See Figure 2-4.

Figure 2-4: Constraining dof3 on node id 3239

13. Select dof3 to activate it. 14. Select create to apply the constraint to the selected node. 15. Click return to bring up the BCs menu page in HyperMesh.

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Step 4: Apply forces to the model At node 2699, load the structure with three separate forces in the x, y, and z directions organized into the three load collectors brake, corner, and pothole. Use the following table values to set the forces. Use the instructions below for each force. Node Id

Collector

Magnitude

Axis

2699

brake

1000

x-axis

2699

corner

1000

y-axis

2699

pothole

1000

z-axis

Create forces by node 1. From the BCs page, access the forces panel. 2. Select the create subpanel. 3. Click global in the permanent menu. 4. Click loadcol = to access the list of collectors. 5. Select the appropriate collector from the table provided. 6. Click return to go back to the forces panel. 7. Click the yellow nodes button. 8. Choose by id. 9. Enter the id number (from the table provided) and press ENTER and move the mouse to release the pop up menu. 10. Click magnitude =, type in the value from the table, and press ENTER. 11. Set the vector definition switch below magnitude = to the appropriate axis according to the table. 12. Click create. 13. Repeat Steps 3 -13 for the remaining forces. 14. After you have created all three forces, click return to go back to the BCs panel. Your forces should appear as in Figure 2-5.

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Figure 2-5: Three separate forces in load collectors brake, corner and pothole

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Set up loadsteps The last step in setting up the boundary conditions is to create OptiStruct subcases (loadsteps in HyperMesh). The procedure is to name the loadstep and associate the appropriate load collectors to the loadstep. 1. From the BCs page of HyperMesh, access the load steps panel. 2. Click name =, type brake, and press ENTER. 3. Select loadcols and activate spc and brake from the collector list. 4. Click select. 5. Click create. 6. Click name =, type corner, and press ENTER. 7. Select loadcols and activate spc and corner from the collector list. 8. Click select and then click create. 9. Click name =, type pothole, and press ENTER. 10. Select loadcols and activate spc and pothole from the collector list. 11. Click select. 12. Click create. 13. Verify the creation of all three loadsteps by clicking review. 14. Click return to go back to the load steps panel. 15. Click return to go back to the BCs page.

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Prepare for Optimization Step 1: Set up topology optimization Define topology design space for solid elements These steps define the whole component of design as a designable region. The component non-design is not affected when optimization is performed. 1. From the BCs page, select the optimization panel. 2. Click topology. 3. Select the create subpanel. 4. Select comps. 5. Activate design. 6. Click Select. 7. Select the component type by selecting the type: switch and choosing PSOLID from the popup menu. 8. To desvar = assign the name solids. 9. Click create. 10. Click return to go back to the optimization set up panel.

Define responses for optimization The objective of this exercise is to remove material from the control arm. Three different forces are applied at one end of the control arm and that node has the maximum displacement in the structure. Therefore define the optimization deck with the objective function of minimizing the volume and constraints as the displacement of node 2699 at the application of the forces.

.

Since all three load cases use the same node and direction of displacement, we need to define only one response for the displacement.

1. From the optimization panel, select the responses panel. 2. For response =, assign the name vol. 3. Set the response type: to volumefrac by clicking the switch and selecting volumefrac from the pop up menu. 4. Click create. OptiStruct 7.0


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5. For response =, assign the name disp. 6. As the response type:, select displacement. 7. Click nodes and select by id and enter the node 2699. 8. Below the nodes button activate total disp as the direction of displacement. 9. Click create. 10. Click return to go back to the optimization set up panel.

Figure 2-6: Displacement response defined on node 2699

Define constraints for optimization 1. From the optimization set up panel, select the dconstraints subpanel. 2. To constraint =, assign the name brake. 3. Activate upper bound and assign the value 0.05. 4. Click response =. 5. Select disp. 6. Click loadsteps button.

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7. Activate brake. 8. Click select. 9. Click create. 10. At constraint=, assign the name corner. 11. At upper bound =, assign the value 0.02. 12. Click loadsteps. 13. Activate corner. 14. Click select. 15. Click create. 16. At constraint =, assign the name pothole. 17. At upper bound =, assign the value 0.04. 18. Click loadsteps. 19. Activate pothole. 20. Click select. 21. Click create. 22. You can use the review button to see the constraints you created. 23. Click return to go back to the optimization set up panel.

Define objective function 1. From the optimization panel, select the objective subpanel. 2. Verify the switch is set to min. 3. Click response = and select vol. 4. Click create. 5. Click return. 6. Click return again to return to the BCs page.

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Step 2: Set up a check run for OptiStruct During the check run, OptiStruct checks the syntax of the input deck, calculates a recommended amount of RAM, and estimates the required disk space for the model. OptiStruct also scans the input deck verifying the parameters required to run the analysis and optimization. 1. From the BCs page select OptiStruct. From this panel you can export the deck, run the analysis/optimization, and then after the job completes load the results files into HyperMesh. A check run can also be performed from this panel. 2. Click save as…, enter carm_check.fem as the file name, and click Save. 3. Click the switch below Run Options: and select Check. 4. Click optistruct to run the check run. The check run for this model should take approximately 5 to 10 seconds of processing time. Once the processing completes, view the file carm_check.out at the UNIX prompt or through a Windows utility. The OptiStruct output file contains specific information on the file setup, the setup of your optimization problem, an estimate 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 possible warnings and errors that are flagged from processing the carm_check.fem file. 5. Close the DOS window or shell and click return.

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Check for correct setup of your optimization problem Review your report and check the objective function and constraints (Figure 2-7).

Figure 2-7: Portion of carm_check.out showing the optimization problem setup

1. What is the recommended amount of RAM for an In-Core solution? 2. Do you have enough disk space to run the optimization? 3. Close carm_check.out.

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Request both H3D (*.h3d) and HyperMesh binary result output (*.res) The FORMAT control card allows you to create multiple result files. An H3D file is a compressed result format used for post-processing in HyperView and HyperView Player. 1. From the BCs page, select the control cards panel. 2. Select the FORMAT subpanel. 3. Set number_of_formats = to 2. In the area above the card image, a second FORMAT card appears. The default value is HM. 4. Select the top HM button and change it to H3D. The lower HM button signifies the production of a .res file. 5. Click return. 6. Notice the Format button is green, indicating it is active. 7. Click return to go back to the BCs page.

Run the optimization 1. From the BCs page and select OptiStruct to go the optistruct panel. This panel exports the deck, runs the analysis/optimization, and then loads the results files into HyperMesh once the job is complete. 2. Click save as…, enter carm_complete.fem as the file name, and click Save. 3. Click the switch below Run Options: and select Optimization. 4. Click optistruct to run the optimization. Running OptiStruct from this panel causes the results file to load automatically when the job finishes. The full topology optimization should take approximately 10 to 15 minutes for 25 iterations (about 25 seconds for each finite element analysis). Actual performance depends on your processor, available RAM, and time required for system communications. After processing is complete, you should see a new file carm_complete.out in the directory from where HyperMesh was invoked. The file is a good place to look for error messages to help you debug your input deck for any errors. 5. Close the DOS window or shell. 6. Click return.

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Default files written to your directory on a successful run carm_complete.res The HyperMesh binary results file. carm_complete.HM.ent.cmf A HyperMesh command file used to organize elements into entity sets based on their density result values (only used with OptiStruct topology optimization runs). carm_complete.HM.comp.cmf A HyperMesh command file used to organize elements into components based on their density result values (only used with OptiStruct topology optimization runs). carm_complete.out The OptiStruct output file containing specific information on the file setup, the setup of your optimization problem, estimate 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 carm_complete.fem file. carm_complete.hgdata HyperGraph file containing data for the objective function, percent constraint violations and constraint for each iteration. carm_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. carm_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. The .sh file may be used to restart a run and, if necessary, run OSSmooth files for topology optimization. Carm_complete_hist.mvw This file contains the iteration history of the objective, constraints and the design variables and can be used to plot curves in HyperGraph/HyperView/MotionView Carm_complete.stat This file contains information about the CPU time utilized for the complete run and also the break up of the CPU time for reading the input deck, assembly, analysis, convergence etc…

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Post-process OptiStruct provides density information for all iterations. OptiStruct also provides displacement and von Mises Stress results for linear static analysis in the first and last iteration. This section describes how to view those results using HyperMesh.

Step 1: View deformed results It is helpful to first view the deformed shape of your model to determine if the boundary conditions have been defined correctly and also to check if the model is deforming as expected. 1. From the Post page, select the deformed panel. 2. Click simulation =. You will notice that there are many simulations. At the end of the simulation list, you will see brake - ITER0, brake – ITER21, corner - ITER0, corner - ITER21, pothole ITER0 and pothole - ITER21. 3. Select brake – ITER21. 4. Set data type to displacements. 5. Toggle model units= to scale factor=. 6. Set your scale factor to 10.00. 7. Click linear to view a deformed animation for brake – ITER21. In what direction is the load applied for the subcase named brake? ______________________________________________ Which nodes have degrees of freedom constrained? ______________________________________________ Does the deformed shape look correct for the boundary conditions you applied to the mesh? ______________________________________________ 8. View the linear animation for the 2nd and 3rd subcases (iteration 21). Second subcase named corner: In what direction is the load applied for the subcase named corner? ______________________________________________ Which nodes have degrees of freedom constrained? ______________________________________________ 42


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Does the deformed shape look correct for the boundary conditions you applied to the mesh? ______________________________________________ Third subcase named pothole: In what direction is the load applied for the subcase named pothole? ______________________________________________ Which nodes have degrees of freedom constrained? ______________________________________________ Does the deformed shape look correct for the boundary conditions you applied to the mesh? ______________________________________________ 9. Click exit. 10. Click return.

Step 2: View a static contour plot You may wish to mask your rigid elements before using the contour panel. Density results are not given for 1D elements. 1. Press F5 (function key on your keyboard) to access the mask panel. 2. Click the yellow elems button. 3. Select by config. 4. Click config =. 5. Select rigid. 6. Click select entities. 7. Click mask. 8. Click return. 9. From the Post page, access the contour panel. 10. Set simulation = to DESIGN - ITER21. 11. Click data type = and select Element Density.

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43


12. Click assign. Have most of your elements converged to a density close to 1 or 0? If there are many elements with intermediate densities, you may need to adjust the discrete parameter. The DISCRETE parameter (set in the opti control panel) can be used to push elements with intermediate densities towards 1 or 0 so that a more discrete structure is given. In this model, refining the mesh should provide a more discrete solution; however, for the sake of this tutorial, the current mesh and results will be sufficient. Regions that need reinforcement will tend towards a density of 1.0. Areas that do not need reinforcement will tend towards a density of 0.0. Is the max= field showing 1.0e+00? In this case, it is. If it is not, your optimization has not progressed far enough. Allow more iterations and/or decrease the OBJTOL parameter (set in the control cards panel). If adjusting your discrete parameter, refining the mesh, and/or decreasing the objective tolerance does not yield a more discrete solution (none of the elements progress to a density value of 1.0), you may wish to review the setup of the optimization problem. Perhaps some of the defined constraints are not attainable for the given objective function (or visa-versa).

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Step 3: View an isosurface plot 1. Access the options panel in the permanent menu. 2. Select the graphics subpanel. 3. Toggle the graphics engine mode to performance. 4. Click return. 5. Select the contour panel from the Post page in HyperMesh. 6. Set your simulation to DESIGN–ITER 21. 7. Click data type = and select Element Density. 8. Select the isosurface subpanel. 9. Activate show. 10. Toggle the mode from legend based to value based. 11. Set the iso surface= 0.150. 12. Activate include faces above. 13. Click assign.


14. Use the isosurface post-processing feature in HyperMesh for viewing your density results from OptiStruct. Click and hold the left mouse button on the triangle shown in the legend (currently pointing to a value representing 0.150 for your density), then scroll up and down to change the threshold surface. You will see the isosurface in the graphics window interactively update 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. 15. Click return. OptiStruct 7.0


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Step 4: View result using HyperView Player 1. Go to the current working directory and locate the file carm_complete.html. 2. Right-click carm_complete.html and select Open. The system web browser application (Netscape or Internet Explorer, for example) initializes displaying the OptiStruct report in HTML format. 3. Review the HTML report. 4. From the results summary section of the report, select the blue Click here hyperlink. This displays the OptiStruct H3d in HyperView Player. You can select the simulation type, result type and simulation id to review results. 5. Exit the web browser application.

Step 5: View results using command files OptiStruct creates two HyperMesh command files carm_complete.HM.ent.cmf and carm_complete.HM.comp.cmf that could be used to organize the elements into entity sets and components based on their density results values. 1. From any page in HyperMesh select the files panel. 2. Select the command subpanel. 3. Select the file carm_complete.hm.ent.cmf. 4. Click execute. 5. Repeat steps 3 and 4 for file carm_complete.hm.comp.cmf. 6. Click return. 7. Press F5 to activate the mask panel. 8. Click elems and select by sets. 9. There are 10 different entity sets from 0.0-0.1, 0.1-0.2, 0.2-0.3 and so on. 10. Select the entity sets 0.0-0.1 and 0.1-0.2 and click select. 11. Click mask. Only elements with densities above 0.2 are displayed. The elements with density levels greater than 0.2 may be masked also using the masking panel and the appropriate entity sets. 12. Click Unmask all and click return. 13. The elements with different density levels grouped into different components may be observed by clicking disp on the permanent menu and turning off the components 0.0-0.1, 0.1-0.2 by right clicking the check box. 14. Click return. 46


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Step 6: Running OSSmooth The isosurface plot provides a graphic image of the material with different density levels. Once you decide on the density level to be used for the optimized model, the geometry surface of the desired optimized density can be obtained by running OSSmooth. The execution of OSSmooth results in creation of an iso-density surface in the format of NASTRAN triangular elements, surface patches in IGES format, STL format, MotionView triangles, and H3D format. It requires both .fem and .sh files from the optimization run. 1. From the post page, click OSSmooth. 2. Click browse…, and select the file carm_complete.fem. 3. Change the output code to IGES. 4. Change the density threshold to 0.15. 5. Verify surface reduction is on. 6. Set surface code to laplacian smoothing. 7. Click OSSmooth. 8. The message “carm_complete.oss file exists. Overwrite? (y/n)” appears, click Yes. OSSmooth reads in geometry automatically. OSSmooth starts and after the program terminates, close the OSSmooth command window (MS-DOS for Windows and ksh for UNIX). The iges file is automatically imported. 9. Click disp in permanent menu. 10. De-activate comps nondesign and design (use a right-click). 11. Click return.

Review 1. Has the objective function been satisfied? 2. Have any constraints been violated?

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Conclusion You have completed exercises that:

48

•

Create constraints, loads and organize into three different subcases

•

Define optimization parameters and describe the optimization problem for solid elements

•

Submit an OptiStruct check run from within HyperMesh

•

Look at an optimal material layout from the OptiStruct topology optimization for three subcases.

•

Recovering the iges format of the iso-density surface using OSSmooth.


OptiStruct 7.0

Chapter 3

Topology Optimization with Manufacturing Constraints Introduction Using topology optimization can optimize design characteristics such as weight and stiffness. Performing topology optimizations early in the project assists in generating a good baseline design and a shorter design cycle. However, sometimes the design suggested by the initial topology optimization creates a design that can be hard to manufacture. Here are some common problems encountered in topology optimization related to manufacturing: •

Discreteness of the solution The optimized design may have several intermediate density elements or checkerboards. These occurrences bring difficulties in both interpreting the topology results and manufacturing the design.

•

Unsymmetrical design The design suggested by topology optimization will not be symmetric even if the finite element mesh and loads and boundary conditions are symmetric. Sometimes it may be necessary to introduce constraints on the model to obtain a symmetrical result.

•

Casting problems Depending on the load and boundary conditions, topology optimization may suggest a design with an interior void. Such designs are difficult to manufacture, especially if it is a casting part.

•

Extrusion problems For extruded parts, it is often desirable to have constant cross-sections. It may be necessary to introduce extrusion manufacturing constraints on the model in order to obtain constant cross-sections.

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Chapter 3: Topology Optimization with Manufacturing Constraints

OptiStruct offers several methods to account for manufacturability when performing topology optimization, including: −

Minimum member size control

−

The ability to combine symmetry constraints with draw direction constraints.

−

Extrusion constraints

Minimum member size control method This procedure provides some control over the member size in the final topology design by defining the least dimension required in the final design. Achieve a discrete solution by eliminating the intermediate density elements and checkerboard density pattern, resulting in a discrete and better-reinforced structure.

Combining symmetry constraints with draw direction constraints This technique produces a symmetric design. A symmetric mesh is not necessary. OptiStruct produces results very close to identical across the plane(s) of symmetry. Symmetry can be attained for solid models regardless of the initial mesh, boundary conditions, or loads. In other words, symmetry can be enforced by using the symmetry constraints. On the other hand, applying drawing constraints allows you to impose casting feasibility constraints so that the determined topology optimization result allows the die to slide in a specified direction. Transformation of such a design proposal to a manufacturable design is easy and practical. So, combining the symmetry constraints with the draw direction constraints in a topology optimization run will yield a design that is both symmetric and also easy to cast.

Extrusion constraints method The extrusion constraint will be of use in situations requiring a design be characterized by a constant cross-section along a given path, as in the case of parts manufactured by an extrusion process. The extrusion constraints can be applied on a component level and can also be defined in conjunction with minimum member size control constraints. The three exercises in this chapter discuss these techniques of topology optimization. The first optimization uses minimum member size control on a C-clip. The second uses symmetry and draw direction constraints on an automotive control arm, and the third uses extrusion constraints on a curved rail.

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Minimum Member Size Control Method Purpose This optimization problem applies the technique of minimum member size control on the elements of the model to achieve a discrete solution.

Problem statement Apply a minimum member size factor on a structural c-clip. The related bulk data cards are: DOPTPRM:

Design Optimization Parameters

MINDIM:

Minimum diameter of members

MINMETH:

Method of minimum member size control

.

The definitions for all card images appear in the online help. See the Bulk Data Section of the OptiStruct online help.

Optimization Process The process to complete an OptiStruct topology optimization with minimum member size control contains three parts: •

Use HyperMesh to setup the minimum member size control problem

•

Run OptiStruct

•

Examine the results

The exercise covers the following: 1. Loading the model file. 2. Defining the minimum member size control parameters. 3. Using OptiStruct to solve the topology optimization to determine the optimal material distribution. 4. Post-processing the results.

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Step 1: Set up the FEA model in HyperMesh In this step, import the geometry and invoke the OptiStruct template. 1. Delete the current model by pressing F2 to access the delete panel and selecting delete model. 2. From any main page in HyperMesh, select the files panel. 3. Select the import subpanel. 4. Select FE and set the translator to Optistruct. 5. Click import…, select cclip_complete.fem, and click Open. 6. Go to the Geom page and select user profile…. 7. Select OptiStruct from the dialog box and click OK. 8. This sets the HyperMesh environment for the OptiStruct solver. 9. Click Return.

Step 2: Apply minimum member size control parameters 1. From the BCs page, click optimization. 2. Click opti control. 3. Click F4 to bring up the distance panel. 4. Click the radio button to the left of two nodes to select it. N1 is highlighted, indicating it is active. 5. Select any node on the screen. N2 is highlighted, indicating it is active. 6. Select another node on the same element. 7. Repeat steps 4 through 6 a few times using different elements to obtain an average element size. The average element size for this model is about 2.9. The MINDIM value must be larger than this average element size. 8. Click return to go back to opti control panel. 9. Activate MINDIM and set the value to 5.

.

Recommendation: Do not set MINDIM to a value less than the average element size. You can assign a multiple of the average element size for MINDIM.

10. Click return. 52


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Request H3D and HyperMesh binary results files 1. From the BCs page, select control cards. 2. Select the FORMAT subpanel. 3. Set the number_of_formats = to 2. In the above the card image a second HM button appears. 4. Select the top HM button and from the list of available formats select H3D. This button creates the .h3d format. The HM button creates the .res file. 5. Click return twice to return to the BCs page.

Step 3: Run the optimization As we saw previously clicking the optistruct button allows OptiStruct to combine into one step writing out the OptiStruct input file, solving the optimization, and loading the results into HyperMesh for post-processing. This eliminates the need to use the files panel to export the file with the OptiStruct template, manually initiate the solver, and import the results file for post-processing. 1. From the BCs page in HyperMesh, select the OptiStruct panel. 2. Click save as…., enter cclip_complete_min_member.fem as the file name, and click Save. 3. Click the switch below Run Options: and select optimization. 4. Click optistruct. At the end of processing, close the DOS window or shell. 5. Click return. The result file loads automatically into HyperMesh on completion of the run, so you can proceed directly to the post-processing step.

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Step 4: Post-process the results In this step, we view the isosurface plot using HyperView. 1. Launch HyperView. 2. Click the open folder icon and load the file cclip_complete_min_member_des.h3d. 3. Click Apply.

Figure 3-1: Isosurface plot of a C-Clip layout of the topology optimization with minimum member size control

4. There are several menus along the status bar at the bottom of the interface. Select Model Step to activate the Load Case And Simulation Selection list.

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5. Scroll to and select ITER 47 and click OK.

Figure 3-2: The dialog box to select an iteration to view

6. Select the Iso Value defined).

panel and verify Iso value Mode: is set to Single (User

7. Select Result type: as Element Densities and click Apply. 8. Set Current value: to 0.3 and hit ENTER. 9. Compare this image to Figure 1-7.

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The iso value plot displayed is similar to the one we saw previously in HyperMesh. Notice the smaller members in the original isosurface plot are replaced by more discrete rib patterns. The design in Figure 3-3 is easier to manufacture.

Figure 3-3: The Isosurface contour

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Combining Symmetry and Draw Direction Constraints Purpose The topology optimization performed in this tutorial combines symmetry constraints with draw direction constraints to demonstrate one of the valuable new features implemented with the release of Optistruct 7.0. The optimization will produce a symmetric final design which is also manufacturable via the casting process.

Problem statement A topology optimization will be performed on an automotive control arm with the simultaneous application of the symmetric and draw direction constraints. The DTPL (Design Variable for Topology Optimization) bulk data card is used to enter information relevant for this method. This tutorial will use the same optimization problem considered in Chapter 2, except that a refined mesh will be used on the automotive control in order to better capture the effect of simultaneously applying symmetric and draw manufacturing constraints. The model used for this tutorial has a pre-defined refined mesh.

Optimization Process The basic two part process involved in topology optimization including the application of both symmetry and draw direction constraints is as indicated below: •

Setup the topology optimization problem with symmetry and draw direction constraints.

•

Examine the results produced by Optistruct.

This exercise covers the following aspects: 1. Loading the model file into HyperMesh. 2. Defining the symmetry and the draw direction control parameters. 3. Exporting the Optistruct input deck. 4. Loading the results file and post-processing the results.

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Step 1: Load the FEA model into HyperMesh 1. Delete the current model, if any, by pressing the F2 key on the keyboard to access the delete panel and press the delete model button. 2. From any main page in HyperMesh, select the files panel. 3. Select the template subpanel and load the OptiStruct template. This can also be done using the user prof… panel from the Geom/Tool page. 4. Select the import subpanel and select the model carm_draw_symm.fem. The finite element model is shown in Figure 3-4. The constraints, loads, material properties, and subcases are already defined in the model. 5. Click Open.

Figure 3-4 Finite element model of the refined control arm

Step 2: Apply symmetry and draw direction constraint parameters These steps allow you to define the cutting plane for the symmetry constraints and the direction for the draw direction constraints. 1. From the BCs page, click optimization. 2. Click topology. 3. Double click desvar = and select solid. 4. Select the pattern grouping radio button.

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5. From the pull-down menu under pattern-type:, select 1-pln sym (one plane symmetry). 6. Click anchor node and input node id = 3241 and press ENTER. 7. Click the switch button to the left of first node and input the node id = 3877 and press ENTER. The plane of symmetry is perpendicular to the vector from the anchor node to the first node and passes through the anchor node. 8. Click update to update the design variables. 9. Select the draw radio button. 10. This is where the draw direction is defined. 11. Double click desvar = and select solid. 12. Change draw type: to single. 13. Click the anchor node button, input node id = 3165, and press ENTER. 14. Click on first node, input node id = 3753, and press ENTER. The anchor node, in conjunction with the first node, sets the draw direction, or the direction of the movement of the die during casting. 15. Click the update button to update the design variables. 16. Click return twice to go back to the BCs page.

Step 3: Export the file 1. Click files. 2. Select the export subpanel. 3. Select template. 4. Click write as…. 5. Set filename to carm_draw_symm_complete.fem. 6. Click Save. 7. Click return.

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Step 4: Load results file and post-process results 1. From any main page in HyperMesh, select the files panel. 2. Select the results subpanel. 3. Click browse… and select the file carm_draw_symm_complete.res. 4. Click return.

Step 5: View deformed shape Viewing the deformed shape of a model can determine if the boundary conditions are defined correctly and can also show if the model is deforming as expected. 1. Select the deformed panel on the Post page. 2. Click simulation=. Notice that there are numerous simulations: DESIGN - ITER 0, …, DESIGN - ITER 40, brake - ITER 0, brake - ITER 40,………., pothole-ITER 40. 3. Select brake - ITER 40. 4. Click data type= and select Displacements. 5. Toggle model units= to scale factor=. 6. Click scale factor= and enter a value of 1000.00. 7. Click linear. A deformed animation for the first subcase should be displayed. 8. Click exit to stop the animation. Animations of the deformed shapes can be observed for other subcases as well. Observe the animations and see if the deformed shapes look correct considering the boundary conditions applied to the mesh.

Step 6: View an isosurface plot 1. Select options from the permanent menu in the lower right-hand corner of the HyperMesh interface. 2. Select graphics. 3. Toggle the graphics engine: mode to performance. 4. Click return to exit options. 5. From the Post page, select the contour panel.

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6. Click simulation= and select DESIGN – ITER 40. 7. Click data type= and select Element Density. 8. Select the iso-surface subpanel. 9. Check the box next to show. 10. Toggle the mode from legend based to value based. 11. Click iso-surface= and enter 0.3. 12. Check the box next to include faces above. 13. Click assign. An isosurface plot is displayed in the graphics window. As shown in Figure 3-5, parts of the model with a density greater than the value of 0.3 are shown in color, and the other parts are transparent.

Figure 3-5 Isosurface plot of Control Arm for topology Optimization with Draw Direction and Symmetry manufacturing constraints

14. Click and hold the left mouse button on the triangle shown in the legend (currently pointing to a value representing 0.3 for the density). Then, scroll up and down to change the threshold surface. Use the isosurface tool to get a better look at the material layout and the load paths from Optistruct. 15. Click return to go to the main menu. OptiStruct 7.0


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Extrusion Constraints Method Purpose The extrusion constraints method allows you to perform an optimization problem with extrusion constraints to obtain a constant cross section along a given path, particularly in the case of parts manufactured through an extrusion process. By using extrusionmanufacturing constraints in topology optimization, constant cross-section designs can be obtained for solid models – regardless of the initial mesh, boundary conditions or loads. The exercises show the steps involved in defining topology optimization over a curved beam, simulating a rail, over which a vehicle is moving. Both ends of the beam are supported. A point load is applied over the length of the rail in seven independent load cases, simulating the movement of the vehicle. The rail should be manufactured through extrusion. The steps taken to define the topology design space, extrusion-manufacturing constraints and optimization parameters (responses, objective and constraints) using HyperMesh are shown.

Problem statement In this tutorial, you will perform topology optimization on a curved beam so that the extruded rail will be stiffer and have less material. The finite element mesh of the curved beam is shown in Figure 3-6. Objective:

minimize weighted compliance

Constraints: Volume fraction < 0.3 Design variables:

element density

The DTPL (Design Variable for Topology Optimization) card is used for this optimization.

Figure 3-6: Finite element mesh of the curved beam showing loads and boundary conditions

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Optimization Process The three-part process to complete an OptiStruct topology optimization with extrusion constraints includes: •

The use of HyperMesh to setup extrusion constraints

•

The set up the design optimization problem – responses, objective and constraints

•

An examination of the results

The exercises cover the following: 1. Loading the file. 2. Setting up the extrusion constraint and the extrusion path. 3. Setting up the optimization problem. 4. Loading the results file and post-processing the results.

Step 1: Set up the FEA model in HyperMesh In this step, you will import the input file and invoke the OptiStruct translator. 1. Delete the current model by pressing F2 to access the delete panel and selecting delete model. 2. From any main page in HyperMesh, select the files panel. 3. Select the import subpanel. 4. Click import… and select the file rail_complete.fem. 5. Click Open. 6. Verify that the optistruct template is selected.

Step 2: Set up topology optimization with extrusion constraints Define the topology design space for solid elements: 1. From the BCs page, click optimization. 2. Click topology. 3. Select the create subpanel 4. Select comps. 5. Activate new_solid. OptiStruct 7.0


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6. Click Select. 7. Select the component type by selecting the type: switch and choosing PSOLID from the popup menu. 8. Click desvar= and assign the name solids. 9. Click create. 10. Click return twice to return to the main menu.

Define extrusion problem and extrusion path: 1. From the Tools page, select the numbers panel. 2. Click nodes and select by id. 3. Enter numbers 71559,70001 and hit ENTER, then click on. 4. The numbers 71559 and 70001 should be displayed on the screen. 5. Click return. 6. From the BCs page, click optimization. 7. Click topology. 8. Click extrusion. 9. Double click desvar = and select solids. 10. Switch the toggle under desvar to no twist. Extrusion constraints can be applied to domains characterized by non-twisted crosssections or twisted cross-sections by using the NOTWIST or TWIST parameters respectively. 11. Select the extrusion path by selecting node list and click by path. It is necessary to define a 'discrete' extrusion path by entering a series of grids. The curve between these grids is then interpolated using parametric splines. The minimum amount of grids depends on the complexity of the extrusion path. Only two grids are required for a linear path, but it is recommended that at least 5-10 grids be used for more complex curves. 12. First, select node 71559 and then select node 70001. 13. Click update. A line of nodes starting from 71559 and ending with node 70001 should be highlighted, indicating the extrusion path. You do not have to select as many nodes to define the curve. This is an exercise to show that the nodes by path option can also be used. 14. Click return to go back to the optimization panel. 64


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Define responses for optimization: 1. From the optimization panel, select the responses panel. 2. Click response= and assign the name vol. 3. Set the response type: to volumefrac. 4. Click create. 5. Click response= and assign the name wcompl. 6. Change the response type: to wcomp. 7. Click loadsteps and activate step1, step2, step3, step4, step5, step6 and step7 by checking them. 8. Click return. 9. Click create. 10. Click return.

Define constraints for optimization: 1. From the optimization panel, select the dconstraints subpanel. 2. Click constraint= and type the name volume. 3. Activate upper bound and assign the value 0.3. 4. Click response=. 5. Select vol. 6. Click create. 7. Click return.

Define objective function: 1. From the optimization panel, select the objective subpanel. 2. Verify the switch is set to min. 3. Click response= and select wcompl. 4. Click create. 5. Click return. 6. Click return again to return to the BCs page.

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Step 3: Export the file 1. Click files. 2. Select the export subpanel. 3. Select template. 4. Click Write as…. 5. Set file name to rail_complete_extrusion.fem. 6. Click Save. 7. Click return.

Step 4: Load results file and perform post-processing Solving time for this extrusion constraint problem takes about 2 hours and 45 minutes. Rather than solving this geometry in class, we will pick up the process by loading the solution results file. 1. From any main page in HyperMesh select the files panel. 2. Select the results subpanel. 3. Click browse… and select rail_complete_extrusion.res. 4. Click return.

Step 5: View a static contour and an isosurface plot 1. From the macro menu, select disp. 2. Click the per button next to gfx to activate performance graphics. 3. From the Post page in HyperMesh, select the contour panel. 4. Set your simulation to DESIGN – ITER41 (the last iteration). 5. Click data type = and select Element Density. 6. Click contour. The regions with high element densities indicate areas where material is needed. 7. Select the isosurface subpanel. 8. Activate show. 9. Toggle the mode from legend based to value based. 10. Set the iso surface= field to 0.300. 11. Activate include faces above. 66


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12. Click contour. See following image for contour.

Figure 3-7: Isosurface plot of a curved beam rail layout of the topology optimization with extrusion constraints

As expected, the result with manufacturing extrusion constraints permits a constant cross section for the entire length of the model.

Step 6: View a section cut The section cut panel allows you to cut planar sections through a model. This is useful when you want to see details inside of a model. 1. De-activate show. 2. Select the cutting subpanel. 3. Activate xz plane. 4. Click contour. See following image for contour.

Figure 3-8: Contour plot of a section cut on x-z plane of the curved beam OptiStruct 7.0


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5. Toggle the single button on the right of xz plane to double as shown in the following image.

6. Assign a value of 100 to t=. This will bring up an additional section about 100mm from the first section. By changing the value of t, the contour of the section at different intervals along the length of the beam should be possible. It should also be possible to view the contour of the sections at different intervals of the beam by clicking the mouse at any one of the eight corners of the section and moving the mouse along the length of the beam. As expected, the result with manufacturing extrusion constraints shows constant cross section through the length of the model.

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Chapter 4

Optimal Rib Pattern for an Automotive Splash Shield Purpose This exercise describes the steps involved in performing a topology optimization on an automotive splash shield to arrive at optimal rib patterns. The model is optimized for a normal modes analysis. The baseline analysis provides the initial frequencies, which are then increased using topology optimization. The high-density regions from the topology results are then reinforced with ribs.

Problem statement Increase the natural frequency of an automotive splash shield by introducing ribs in the designable region (the light gray region in Figure 4 -1).

Figure 4-1: Finite element mesh containing designable (light gray) and non-designable (dark gray) material OptiStruct 7.0


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Chapter 4: Optimal Rib Pattern for an Automotive Splash Shield

This is the optimization problem for this exercise. Objective:

maximize frequency of mode number 1

Constraint:

equality constraint of 30% for the designable volume

Design variables:

element densities

Optimization Process This tutorial is divided into sections in which you will perform a normal modes analysis in OptiStruct using HyperMesh, then view the results.

Perform Normal Modes Analysis in OptiStruct Using HyperMesh Step 1: Retrieve the file and load the OptiStruct user profile 1. From any main page in HyperMesh, select the files panel. 2. Click import. 3. Select the FE subpanel and select optistruct. 4. Click import…. and select sshield_opti.fem and click Open. 5. Go to the Geom page and select user profile…. 6. Select OptiStruct from the dialog box and click OK. This sets the HyperMesh environment for the OptiStruct solver.

Step 2: Create load collectors 1. Access the collectors panel. 2. Select the create subpanel. 3. Set the collector type to loadcols. 4. Click name= and type constraints. 5. Set the color to yellow (color12). 6. Click create. (This creates the load collector where you will put your constraints). 7. Click name= again and type eigrl. 8. Click card image= and select EIGRL. 9. Set the color to gray (color1). 70


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10. Click create/edit to set values on the card. To enter a value for a field in the card image, click on the number field and type in the number. 11. Set V1=0.000, V2=3000.000 and ND=2. Setting the above values will find two roots (or less) in the range 0.00 to 3000.00. 12. Click return once the values have been entered. 13. Click return again to return to the HyperMesh pages.

Step 3: Create constraints In this step, constraints are created on two points at the same time. 1. From the global panel, set load col = to constraints. 2. Click return. 3. From the BCs page, access the constraints panel. 4. Click the yellow nodes button and select by id. 5. Type 1075, then press the ENTER key. 6. Type 1076, then press the ENTER key. 7. Activate dof1 through dof6. (Make sure dofs 1-6 are checked). 8. Click create. The selected constraints apply to both ids. You should see them on the image. 9. Click return.

Step 4: Create loadstep 1. From the BCs page of HyperMesh, access the load steps panel. 2. Select name = and type frequencies. 3. Select loadcols and activate constraints and eigrl from the collector list. 4. Click select. 5. Click create. This step sets up an OptiStruct subcase incorporating the constraints and eigrl load collectors. Therefore, a normal modes analysis (from the EIGRL card) will run with the constraints you placed into the constraints collector in Step 3. 6. Click return. OptiStruct 7.0


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Step 5: Set up OptiStruct parameter cards 1. From the BCs page, access the control cards panel. 2. Select analysis. OptiStruct only runs an analysis (if this card is defined) and ignores all optimization parameters. 3. Click return. Notice the ANALYSIS button is green, indicating it is active. 4. Click return again.

Step 6: Run the analysis using OptiStruct 1. From the BCs page in HyperMesh, select the OptiStruct panel. 2. Click save as…., enter sshield_analysis1.fem as the name, and click Save. 3. Click the switch below Run Options: and select Analysis. 4. Click optistruct to run the analysis. Running OptiStruct from this panel causes the results file to be automatically loaded at the completion of the job. This command launches the OptiStruct job. After processing completes, you should see a new file sshield_analysis1.out in the directory where HyperMesh was invoked. This file is a good place to look for error messages that will help you debug your input deck if any errors are present. 5. Close DOS window or shell. 6. Click return. Default files written to your directory on a successful run sshield_analysis1.res The HyperMesh binary results file. sshield_analysis1.out The OptiStruct output file containing specific information on the file setup, the setup of the optimization problem, estimate 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 sshield_analysis1.fem file. sshield_analysis1.stat This file contains information about the CPU time utilized for the complete run and also the break up of the CPU time for reading the input deck, assembly, analysis, convergence etc. 72


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Step 7: View the modal shape 1. From the Post page, select the deformed panel. 2. Click simulation=. You should see two simulations: MODE 1 - F=4.33E+01 MODE 2 - F=6.82E+01 3. Select MODE 1 - F=4.33E+01. (This is the mode you will optimize). 4. Select modal to begin the animation. 5. Click return when you are done viewing the animation. 6. Click return to return to the main panel.

Set up the Optimization Decks in Hyper Mesh and View Results Step 1: Assign designable regions 1. From any main panel in HyperMesh, access the collectors subpanel. 2. Set your subpanel to card image. 3. Select the collector type switch and click comps. 4. Click name = twice and select nondesign. 5. Click edit. 6. Verify your thickness (T) is 0.300 and click return. 7. Click name = twice and select design. 8. Click edit. 9. Set T to 1.0. 10. Click return twice to return to the HyperMesh main page.

Step 2: Turn off the ANALYSIS parameter 1. From the BCs page, access the control card panel. 2. Select delete then the card(s) to delete, in this case ANALYSIS. 3. Click return. OptiStruct 7.0


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Step 3: Define the design space 1. From the BCs page, select the optimization panel. 2. Click topology. 3. To desvar =, assign the name rib. 4. Click comps. 5. Activate design and click select. 6. Set component type: to PSHELL. 7. Change toggle selection from base thickness = 0.0 to base thickness =. 8. To base thickness =, assign the value 0.3. 9. Click create to create the design variable. 10. Click return.

Step 4: Define the responses We are attempting to maximize the first frequency with 30% designable volume freedom as a constraint. Therefore we need to create two responses, volumefrac and frequency. 1. Click responses. 2. In response =, assign the name vol. 3. Change the response type to volumefrac. 4. Click create. 5. In response =, assign the name freq. 6. Change the response type to frequency. 7. Verify the mode number is one. 8. Click create. 9. Click return.

Step 5: Define the constraints for optimization 1. Click dconstraints. 2. For constraint =, assign the name vol. 3. Activate upperbound and assign a value of 0.3.

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4. Click response = and click vol. 5. Click create. 6. Click return.

Step 6: Define objective function 1. Click objective. 2. Click the switch and select max. 3. Click response = and select freq. 4. Click loadstep and select frequencies. 5. Click create. 6. Click return.

Step 7: Change objective tolerance 1. Click opti control. 2. Activate objtol and assign a value of 0.001. 3. Click return twice.

Step 8: Run the optimization 1. Go to the BCs page in HyperMesh. 2. Click OptiStruct. 3. Click save as…., enter sshield_optimization.fem as the file name, and click Save. 4. Click the switch below Run Options: and select Optimization. 5. Click optistruct to run the optimization. Running OptiStruct from this panel automatically loads the results file at the completion of the job. When processing is complete, you should see a new file sshield_optimization.out in the directory where HyperMesh was invoked. The file is a good place to look for error messages to help you debug your input deck if any errors are present.

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6. Close the DOS window or shell and click return. Default files written to your directory on a successful run sshield_optimization.hgdata HyperGraph file containing data for the objective function, percent constraint violations and constraint for each iteration. sshield_optimization.HM.comp.cmf A HyperMesh command file used to organize elements into components based on their density result values (only used with OptiStruct topology optimization runs). sshield_optimization.HM.ent.cmf A HyperMesh command file used to organize elements into entity sets based on their density result values (only used with OptiStruct topology optimization runs). sshield_optimization.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. sshield_optimization.out The OptiStruct output file containing specific information on the file setup, the setup of your optimization problem, the estimate 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 sshield_analysis1.fem file. sshield_optimization.res The HyperMesh binary results file. sshield_optimization.sh Shape file for the final iteration. Contains the material density, void size parameters and void orientation angle for each element in the analysis. The .sh file may be used to restart a run and, if necessary, run OSSmooth files for topology optimization. sshield_optimization_hist.mvw This file contains the iteration history of the objective, constraints and the design variables and can be used to plot curves in HyperGraph, HyperView, or MotionView sshield_optimization.stat This file contains information about the CPU time utilized for the complete run and also the break up of the CPU time for reading the input deck, assembly, analysis, convergence etc… 76


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View Results of the Optimization Step 1: View a static contour plot 1. From the permanent menu, access the disp panel and turn off the nondesign, and misc1 components. 2. Click return. 3. From the Post page in HyperMesh, access the contour panel. 4. Click simulation =. 5. Set the simulation to DESIGN-ITER9. 6. Click data type = and select Element Density. 7. Click assign. Have most of your elements converged to a density close to 1 or 0? If there are many elements with intermediate densities, you may need to adjust the discrete parameter. The discrete parameter (set in the cntl cards panel) can be used to push elements with intermediate densities towards 1 or 0 so that a more discrete structure is given. Regions that need reinforcement will tend towards a density of 1.0. Areas that do not need reinforcement will tend towards a density of 0.0. Is the max= field showing 1.0e+00? In this case, it is. If it is not, your optimization has not progressed far enough. Increase the iterations and/or decrease the OBJTOL parameter (set in the control card panel). If adjusting your discrete parameter, incorporating a checkerboard control, refining the mesh, and/or decreasing the objective tolerance does not yield a more discrete solution (none of the elements progress to a density value of 1.0), you may wish to review the setup of the optimization problem. some of the defined constraints may not be attainable for the given objective function (or visa-versa). Where would you place the ribs? ___________________________________________ 8. Click return.

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Step 2: View an isosurface plot 1. From the permanent menu, access the options panel. 2. Select the graphics subpanel. 3. Toggle the graphics engine mode to performance. 4. Click return. 5. From the Post page in HyperMesh, select the contour panel. 6. Set your simulation to DESIGN – ITER9. 7. Click data type = and select Element Density. 8. Select the isosurface subpanel. 9. Activate show. 10. Toggle the mode from legend based to value based. 11. Set iso surface= to 0.750. 12. Activate include faces above. 13. Click assign.


14. Click and hold the left mouse button on the triangle shown in the legend (currently pointing to a value representing 0.750 for your density), then scroll up and down to change the threshold surface. You will see the isosurface in the graphics window interactively update when you scroll to a new value. Use this tool to get a better look at the material layout from OptiStruct. 15. Click return. 78


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Set up the Final Normal Modes Analysis and View the Results Step 1: Retrieve the model containing the ribs Next, you will retrieve a model containing a preliminary design of ribs based on the topology results you’ve just viewed. 1. Press the F2 function key, click delete model. At the prompt “Do you wish to delete the current model? (y/n) “ click yes to confirm the delete, and then click return. 2. From any main page in HyperMesh, select the files panel. 3. Click import. 4. Click the radio button to the left of FE and select optistruct. 5. Click import…, select sshield_newdesign.fem, and click Open. 6. Click return.

Step 2: Submit the job 1. From the BCs page in HyperMesh, select the OptiStruct panel. 2. Click save as…., enter sshield_newdesign.fem as the file name, and click Save. 3. Click the switch below Run Options: and select Analysis. 4. Click optistruct to run the analysis. Running OptiStruct from this panel causes the results to automatically load when the job is done. 5. Close the DOS window or shell. 6. Click return.

Step 3: View the mode shape 1. From the Post page, select the deformed panel. 2. Click simulation=. You should see two simulations: MODE 1 - F=8.38642E+01 MODE 2 - F=1.14202E+02 OptiStruct 7.0


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3. Select MODE1 - F=8.38642E+01. 4. Click modal. 5. When you are done viewing the animation, click return. 6. Click return.

Review 1. What is the percentage increase in frequency for your first mode (sshield_analysis1.fem vs. sshield_newdesign)? _______________________________________________ 2. The new part has how much additional mass (check the mass of your ribs in the mass calc panel in the Tool page)? ____________________________________________ 3. What is the percentage increase in mass? ______________________________

Conclusion This concludes the lesson, you have completed exercises that:

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•

Setup a normal mode analysis.

•

Run a topology optimization to maximize frequency by introducing ribs in the structure.

•

Compare the frequency change between a design without ribs to design with ribs.


OptiStruct 7.0

Chapter 5

Topography Optimization of a Torsion Plate Purpose This exercise involves performing topography optimization using OptiStruct on a torsion plate (Figure 5-1). Topography optimization is a method used to determine optimal bead patterns distribution on a given structure. Topography optimization, unlike topology, does not remove material but instead generates beads based on perturbations of nodes in the designable region. These beads in turn make the structure stiffer thereby increasing stiffness or frequencies. We perform topography optimization on this model and make it stiffer by generating beads. The beads can be easily stamped on the torsion plate. This exercise describes the steps involved in defining topography design space for a model comprised of shell elements. Further, this exercise also shows the user-controlled factors to define a bead such as pattern grouping, the bead width, height, angle, and symmetry options, if any. The resulting bead patterns are linear.

Problem statement Figure 5-1 shows a finite element model of the torsion plate with loads and constraints applied. The objective is to minimize the displacement of the node where the force is applied in the positive z-direction. This problem assumes that the part is to be formed using a stamping process. To achieve this objective, apply a bead pattern to reinforce the structure. Objective:

minimize nodal displacement at a given grid

Design variables:

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shape variables on the designable space


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Chapter 5: Topography Optimization of a Torsion Plate

Figure 5-1: Finite element model of the torsion plate with loads and constraints

Optimization process This tutorial follows these steps. 1. Load the finite element model . 2. Set up bulk data cards for topography optimization. 3. Solve topography optimization using OptiStruct to determine bead reinforcements on the structure. 4. Post-process the results.

Set up the Problem in HyperMesh Step 1: Retrieve the file and define the OptiStruct template 1. From any main page in HyperMesh, select the files panel. 2. Select the hm file subpanel. 3. Click retrieve…, select torsion_plate.hm, and click Open. 4. Go to the Geom page and select user prof…. 5. Select OptiStruct from the dialog box and click OK. This sets the HyperMesh environment for the OptiStruct solver.

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Step 2: Set up the topography optimization 1. From the BCs page select the Optimization panel. 2. Select the Topography subpanel. 3. In desvar=, assign the name bead. 4. Click comps. 5. Activate design. 6. Click select. 7. Click create.

Step 3: Define the parameters to create bead patterns on the torsion plate 1. Select the bead params subpanel. 2. Set minimum width = to 5.0. 3. Set draw angle = 60. 4. Set draw height= 10.0. 5. Click the switch under boundary skip: and select none. 6. Click update. 7. Select the pattern grouping subpanel. It is possible to generate several different bead patterns for a given structural member. However, we will generate linear bead patterns for this torsion plate, as the structure is square and coplanar. Further, for the bead patterns to enhance and simplify die design for stamping, we will use a 1-plane symmetry. 8. Set Pattern type: to linear. 9. Click the switch to the left of subtype: and select 1-plane. 10. Click anchor node, type 2551, and press ENTER. 11. Click first node, type 1177, and press ENTER. 12. Click second node, type 2425, and press ENTER. 13. Click update. 14. Select the bounds subpanel. 15. Verify Upper bounds is 1 and Lower bounds is 0. 16. Click update. 17. Click return. 18. Click return to leave the optimization panel. OptiStruct 7.0


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This describes the data format of the DTPG (Design Variable for Topography Optimization) card and what the values mean. (1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

DTPG

ID

TYPE

PID1/ DVID

PID2

PID3

PID4

PID5

PID6

MW

ANG

BF

HGT

Norm/XD

YD

ZD

SKIP

PATRN

TYP

AID/XA

YA

ZA

FID/XF

YF

ZF

PATRN2

UCYC

SID/XS

YS

ZS

BOUNDS

LB

UB

(10)

Table 5-1: DTPG card for topography design variable.

Where: Field

Contents

ID

Each DTPG card must have a unique ID.

TYPE

Indicate whether DTPG card is defined for PSHELL, PCOMP or DVGRID.

PID/DVID

If TYPE is PSHELL or PCOMP, this entry is a property identification number. Use ALL if it applies to all properties of type PTYPE in the model. Numerous PIDs may be given. If TYPE is DVGRID, this entry is the design variable number for a set of DVGRIDs. Only one DVID may be given.

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MW

Bead minimum width. This parameter controls the width of the beads in the model (recommended value between 1.5 and 2.5 times the average element width).

ANG

Draw angle in degrees. This parameter controls the angle of the sides of the beads (recommended value between 60 and 75 degrees).

BF

Buffer zone ('yes' or 'no'; default = 'yes'). This parameter will establish a buffer zone between elements in the design domain and elements outside of the design domain.

HGT

Draw height. This parameter sets the maximum height of the beads to be drawn. This field is only valid if TYPE is PSHELL or PCOMP.

norm/XD,Y D,ZD

Draw direction. If the norm/XD field is 'norm', the shape variables will be created in the normal directions of the elements. If all of the fields are real, the shape variable will be created in the direction specified by the xyz vector defined by the three fields. The X, Y, and Z values are in the global coordinate system. This field is only valid if TYPE is PSHELL or PCOMP.


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Field

Contents

SKIP

Boundary skip. This parameter tells OptiStruct to leave certain nodes out of the design domain. If ‘none’, all nodes attached to elements whose PIDs are specified will be a part of the shape variables. If ‘bc’ or ‘spc’, any nodes which have SPC or SPC1 declarations are omitted from the design domain. If ‘load’, any nodes which have FORCE, FORCE1, MOMENT, MOMENT1, or SPCD declarations are omitted from the design domain. If ‘both’, nodes with either ‘spc’ or ‘load’ declarations are omitted from the design domain. This field is only valid if TYPE is PSHELL or PCOMP.

PATRN

PATRN flag indicating that variable pattern grouping is active. Indicates that information about the pattern group will follow.

TYP

Type of variable grouping pattern. Required if any symmetry or variable pattern grouping is desired. If zero or blank, anchor node, first vector, and second vector definitions are ignored. If less than 20, second vector definition is ignored.

AID/XA,

Variable grouping pattern anchor point (Real in all three fields or integer in field 15; default = blank). These fields define a point which determines how grids are grouped into variables. The X, Y, and Z values are in the global coordinate system. You may put a grid ID in the AID/XA field to define the anchor point.

YA,ZA

FID/XF, YF,ZF

Direction of first vector for variable pattern grouping. These fields define an xyz vector which determines how grids are grouped into variables. The X, Y, and Z values are in the global coordinate system. You may put a grid ID in the FID/XF field to define the first vector. This vector goes from the anchor point to this grid. If all fields are blank and the TYP field 20 is not blank or zero, OptiStruct gives an error.

PATRN2

PATRN2 flag indicating variable pattern grouping continuation card. This card is only required when a second vector is needed to define the pattern grouping.

UCYC

Number of cyclical repetitions for cyclical symmetry. This field defines the number of radial “wedges” for cyclical symmetry. The angle of each wedge is computed as 360.0 / UCYC.

SID/XS,

Direction used to determine second vector for variable pattern grouping. These fields define an xyz vector which, when combined with the first vector, form a plane. The second vector is calculated to lie in that plane and is perpendicular to the first vector. The second vector is sometimes required to determine how grids are grouped into variables. The X, Y, and Z values are in the global coordinate system. You may put a grid ID in the SID/XS field to define the second vector. This vector goes from the anchor point to this grid. If all fields are blank and the TYP field contains a value of 20 or higher, OptiStruct gives an error.

YS,ZS

BOUNDS OptiStruct 7.0

BOUNDS flag indicating that information on upper and lower limits are to follow. Concept Design Using Topology and Topography Optimization Proprietary Information of Altair Engineering, Inc.

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Field

Contents

LB

Lower bound on variables controlling grid movement (Real < UB, default = 0.0). This sets the lower bound on grid movement equal to LB*HGT.

UB

Upper bound on variables controlling grid movement (Real > LB, default = 1.0). This sets the upper bound on grid movement equal to UB*HGT. Bead Width

Draw Angle

Draw Height

Figure 5-2: Illustration of the DTPG parameters

Note

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Refer to the on-line help for bead patterns. In HyperMesh, click Help/Altair HyperWorks/OptiStruct/User's Guide/Optimization/Topography Optimization.


OptiStruct 7.0


Step 4: Create responses for optimization The objective is to define a bead pattern on the structure to minimize the z-displacement of the node at which the force is applied. Therefore, we need only define one response. Optimization constraints, even though valid, are not required as the bead cards act as constraints. 1. Select the responses subpanel. 2. Set response = to disp. 3. Change the response type to displacement. 4. Click nodes, choose by id, and enter 2500 as the point at the application of the force. 5. Select dof3. 6. Click create. 7. Click return.

Step 5: Define objective function 1. Select the objective panel. 2. Verify the objective switch is min. 3. Click response and select disp. 4. Click loadstep and select torsion. 5. Click create. 6. Click return.

Submit the Job First, write your OptiStruct input deck (usually specified with the .fem filename extension) before you run OptiStruct.

Step 1: Write the file 1. Go to the BCs page in HyperMesh. 2. Click OptiStruct. 3. Click save as…., enter torsion_plate.fem as the file name, and click Save. 4. Click the switch below Run Options: and select optimization.

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5. Click optistruct to run the optimization. Running OptiStruct from this panel causes the results file to load automatically when the job is done. 6. Click return. This launches the Optistruct job. If the job is successful, you should see a new results file in the directory where HyperMesh was invoked. The torsion_plate.out file is a good place to look for error messages to help you debug your input deck if any errors are present. Default files written to your directory on a successful run torsion_plate.res The HyperMesh binary results file. torsion_plate.grid An OptiStruct file where the perturbed grid data is written. torsion_plate.out The OptiStruct output file containing specific information on the file setup, the setup of your optimization problem, estimate for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. It is highly recommended to review this file for warnings and errors that are flagged from processing the torsion_plate.fem file. torsion_plate.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. torsion_plate_hist.mvw This file contains the iteration history of the objective, constraints and the design variables and can be used to plot curves in HyperGraph, HyperView, and MotionView torsion_plate.stat This file contains information about the CPU time utilized for the complete run and also the break up of the CPU time for reading the input deck, assembly, analysis, convergence etc. torsion_plate.hgdata HyperGraph file containing for each iteration data for the objective function, percent constraint violations and constraints. torsion_plate.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. The .sh file may be used to restart a run and, if necessary, run OSSmooth files for topology optimization. 88


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View the Results OptiStruct gives you contour (shape change) information for all iterations. OptiStruct also gives you displacement and Von Mises Stress results for your linear static analysis for iteration 0 and iteration 6. This section describes how to view those results in HyperMesh. First, load your HyperMesh binary results file.

Step 1: View a deformed plot 1. From the Post page, select the deformed panel. 2. Click simulation = and select Torsion – ITER 0. 3. Set data type = to displacements. 4. To view a deformed plot animation of your model, click linear. Does the deformed shape look correct for the boundary conditions that were applied to the mesh? Similarly, you can view the animation of the contour shapes for different iterations. 5. Click exit. 6. Click return.

Step 2: View a transient animation of shape contour changes A transient animation of contour shapes will give a good idea of the shape changes happening through different iterations. 1. From the Post page in HyperMesh, select the transient panel. 2. Set start with = to DESIGN-ITER0. 3. Set end with = to DESIGN–ITER6. 4. Click data type = and select SHAPE. 5. From the macro menu, select std graphics. 6. Click transient. 7. When using standard graphics (selectable through the options panel), set the following: Mode

hidden line

Color

by element

Use the slower button to slow down the animation if the frames animate too quickly. 8. When you are finished viewing the animation, click exit. 9. Click return. OptiStruct 7.0


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Step 3: View applied result plot 1. From the Post page in HyperMesh, select the apply result panel. 2. Set simulation to DESIGN–ITER 6. 3. Select data type = and select SHAPE. 4. Click nodes and select displayed. 5. For mult =, assign a value of 1.00. 6. Click apply. 7. After reviewing the result, click reject.

Figure 5-3: Contour shape of the plate shows the bead pattern at 6th iteration (converged solution)

Review 1. Is the objective function satisfied?

2. Are linear patterns visible in the structure?

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Conclusion This concludes the topography optimization of a torsion plate. The steps in this exercise covered: •

Defining a topography design space.

•

Defining linear pattern groups with 1-plane symmetry.

•

Post-processing topography results using apply results panel in HyperMesh.

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Chapter 6

Combined Topology and Topography Optimization of a Slider Suspension Purpose This exercise involves performing a combined topology and topography optimization using OptiStruct. The objective is to increase the stiffness of the slider suspension and make it lighter at the same time. This requires the use of both topology and topography optimization. This exercise highlights the ability of OptiStruct to perform a combination of optimization techniques at the same time. This exercise describes the steps involved in performing both topology and topography optimizations on a slider suspension. The finite element model of the slider suspension contains force and boundary conditions. The structure is made of quad elements and has both linear statics and normal modes subcases (loadsteps). Steps are described to define topology and topography design space, responses, constraints, and objective function. The optimized structure will be stiffer for both linear statics and normal modes subcases and will have beads and less material.

Problem statement Perform combined topology and topography optimization on a disk drive slider suspension to maximize the stiffness and weighted mode. The lower bound constraint on the seventh mode is 12Hz. Objective function

Minimize the combined weighted compliance and the weighted modes.

Constraints Lower bound on mode number 7 is 12 Hz. Design variables

OptiStruct 7.0

Element densities and shape variables in design space.


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Chapter 6: Combined topology and topography Optimization of a Slider Suspension

Figure 6-1: Disk drive slider

Optimization Process The process to complete an optimization using OptiStruct is as follows. •

Use HyperMesh to create the appropriate input deck.

•

Run OptiStruct using the created input deck.

•

Examine the results.

These are the steps that this tutorial follows. 1. Load the finite element model. 2. Setup optimization deck using HyperMesh. 3. Define the design space for optimization. 4. Define OptiStruct parameter cards. 5. Solve combined topology and topography optimization to determine the bead locations and the optimal material distribution. 6. Post-process the results.

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Optimization Setup Step 1: Import the file 1. In HyperMesh, clear any previously created models. 2. Go to the Geom page and click user prof…. 3. Select OptiStruct from the menu and click OK. This sets the HyperMesh environment for the OptiStruct solver 4. From any main page in HyperMesh, select the files panel. 5. Select the import subpanel. 6. Click FE and select OptiStruct. 7. Click import…, select combined.fem, and click Open. 8. Click return to go back to main page.

Step 2: Set up topology design space 1. From the BCs page, select the optimization panel. 2. Select the topology subpanel. 3. Click comps, select 1pin, and click select. 4. For desvar =, assign the name pin. 5. Change type: to PSHELL. 6. Verify base thickness is 0.0. 7. Click create. 8. Click comps, check 3bend and click select. 9. For desvar = assign the name bend. 10. Verify base thickness is 0.0. 11. Click create. 12. Click return.

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Step 3: Set up topography design space 1. Click topography. 2. Verify you are in the create subpanel. 3. Click comps and check 1pin and 3bend, click select. 4. For desvar=, assign the name tpg. 5. Click create. 6. Select the bead params subpanel. 7. Assign for minimum width=, a value of 0.4; for draw angle=, 60; and for draw height=, 0.15. 8. Toggle draw direction to normal to elements. 9. Toggle boundary skip to load & spc. 10. Activate buffer zone. 11. Click update. We will use 1-plane symmetric beads, as it is the simplest and can be symmetric at the same time. 12. Select the pattern grouping subpanel and set pattern type: to 1-plane sym. 13. Click anchor node, type 41, and press ENTER. 14. Click first node, type 53, and hit ENTER. 15. Click update. 16. Select the bounds subpanel. 17. Verify the bounds are as follows: upper bound = 1.0, lower bound = 0.0. 18. Click update. 19. Click return.

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Step 4: Create responses for optimization Since this problem is a combined linear static and normal mode analysis, we are trying to minimize compliance and increase frequency for the two load cases, while constraining the seventh frequency. Therefore, we define two responses: comb and freq. 1. Select the responses panel. 2. Assign response = the name freq. 3. Change the response type to frequency. 4. For mode number, assign a value of 7. 5. Click create. 6. For response =, assign the name comb. 7. Change the response type to comb. 8. Click loadsteps and activate force. 9. Click return. 10. Enter the mode numbers and their corresponding weights using the chart. Mode

Weight

1

1.0

2

2.0

3

1.0

4

1.0

5

1.0

6

1.0

11. Click create. 12. Click return.

Step 5: Define constraints 1. Click dconstraints. 2. For constraint =, assign the name frequency. 3. Check lowerbound and assign a value of 12. 4. Click response= and select freq. 5. Click loadsteps and click frequency checkbox, then click select. 6.

Click create.

7. Click return. OptiStruct 7.0


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Step 6: Define the objective function 1. Click objective. 2. Verify objective set to min. 3. Click response = and select comb. 4. Click create. 5. Click return.

Step 7: Define minimum member size control Minimum member size is generally recommended to avoid checkerboarding. It also ensures the structure has the minimum dimension specified in this card. 1. Click Opti Control. 2. Click the checkbox for MINDIM to activate it and assign a value of 0.25.

Step 8: Define MATINIT MATINIT declares the initial material fraction in a topology optimization. MATINIT has several defaults based upon the following conditions: If mass is the objective function, the MATINIT default is 0.9. With constrained mass, the default is reset to the constraint value. If mass is not the objective function and is not constrained, the default is 0.6. 1. Click the checkbox for MATINIT to activate it and assign a value of 1.0. 2. Click return. 3. Click return to go back to BCs page.

Step 9: Set up mode tracking During optimization, the frequencies and their mode shape may change order due to the change in element densities and other design changes. To overcome this, define a parameter to track the frequencies so only the intended frequencies are tracked during optimization runs. 1. Click control cards. 2. Click PARAM. 3. Under Card Image check MODETRAK 4. In the card panel, set MODET_V1 to Yes. 5. Click return. Note the PARAM button highlighted, indicating it is active. 6. Click return to go back to the BCs page. 98


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Step 10: Using OptiStruct to solve the problem 1. Click OptiStruct. 2. Click save as…, enter comb_complete.fem as the file name, and click Save. 3. Click the switch below Run Options: and select Optimization. 4. Click optistruct to run the optimization. Running OptiStruct from this panel will automatically load the results file after the job is done. 5. Click return. This launches the OptiStruct job. If the job is successful, you should see a new results file in the directory where HyperMesh was invoked. The following files are written to the directory. Default files written to your directory on a successful run comb_complete.grid The shape file for the final iteration of a topography/shape optimization. Contains the grid point coordinates. The format is that of the GRID card. The .grid file may be used to restart a run. This file is an input file for OSSmooth. comb_complete.hgdata Optimization history file. Contains the iteration history of the objective function, constraint functions, design variables, and response functions. Output is specified by deshis, and hisout in the I/O section. comb_complete.hm.comp.cmf Component generating command file. This is a HyperMesh command file. When executed, it organizes all elements in the model into 10 new components based on their material densities at the final iteration. The components are named 0.0-0.1, 0.1-0.2, 0.2-0.3, and so on, up to 0.9-1.0. All elements with a material density between 0% and 10% are contained in 0.0-0.1, all elements with a material density between 10% and 20% are contained in 0.1-0.2, and so on. This helps you visualize the results by turning components on and off. Since elements cannot be in more than one component in HyperMesh, the original components do not contain any elements. comb_complete.hm.ent.cmf Entity set generating command file. This is a HyperMesh command file. It performs the same function as the comp.cmf file except the elements are organized in entity sets rather than components. The advantage of this method is that the elements remain in their original components but can still be selected and masked by entity set.

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Default files written to your directory on a successful run comb_complete.oss OSSmooth parameter file. Contains default settings for running OSSmooth after a successful topology, topography or shape optimization. comb_complete.out OptiStruct output file containing specific information on the file set up, the set up of the optimization problem, estimate 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 sshield_analysis1.fem file. comb_complete.res The results file. Contains stress, displacement, shape, thickness and density information for all load cases for all iterations specified in the I/O options section. Contains the element and possibly nodal, material density or topography information for all iterations specified in the I/O options section. comb_complete.sh The shape file for the final iteration of a topology optimization. Contains the material density, the void size parameters, and void orientation angle for each element in the analysis. The .sh file may be used to restart a run. This file is an input file for OSSmooth. comb_complete_hist.mvw This file contains the iteration history of the objective, constraints and the design variables and can be used to plot curves in HyperGraph/HyperView/MotionView comb_complete.stat This file contains information about the CPU time utilized for the complete run and also the break up of the CPU time for reading the input deck, assembly, analysis, convergence etc… 6. Click return.

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Post-process Results Step 1: Apply result 1. From Post menu, click apply result. 2. Click simulation= and select DESIGN-ITER 25. 3. Click data type and select Shape. 4. Click nodes and select displayed. 5. Verify mult= is 1.0. 6. Click apply. 7. Click return.

Figure 6-2: Topography result applied on slider suspension

Step 2: View static contour plot 1. Click contour. 2. Click simulation= and select DESIGN-ITER 25. 3. Click data type= and select Element Thickness. 4. Click assign.

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Step 3: View an isosurface plot 1. From the permanent menu, click options. 2. Select the graphics panel by clicking the radio button to the left of graphics. 3. Toggle the graphics panel to performance mode. 4. Click return. 5. Click simulation= and select DESIGN-ITER 25. 6. Click data type and select Density. 7. Click the radio button to the left of isosurface to select the subpanel. 8. Click the check box to the left of show to turn it on. 9. Toggle the mode from legend based to value based. 10. Click the check box to the left of include faces above. 11. Set the iso surface to 0.3. 12. Click contour.

Review 1. Is the objective function satisfied?

2. Have any of the constraints been violated?

Conclusion This concludes the combined topology and topography optimization for a slider suspension. The exercises covered:

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•

Defining the topology and topography design spaces.

•

Defining responses, constraints, and objective function for combined linear statics and normal modes.

•

Post-processing the results for the combined topology and topography optimization. Concept Design Using Topology and Topography Optimization Proprietary Information of Altair Engineering, Inc.

OptiStruct 7.0

OptiStruct Concept Design Using Topology and Topography Optimization

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