Combined Topology and Topography Optimization of a Slider Suspension - OS-3100



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This tutorial performs a combined topology and topography optimization on a slider suspension 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.

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:

Element densities and shape variables in design space.

image\3100_1.gif

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.

The specific steps taking in this tutorial include:

·      Loading the finite element model

·      Setting up the optimization deck using HyperMesh

·      Defining the design space for optimization

·      Defining OptiStruct parameter cards

·      Solving combined topology and topography optimization to determine the bead locations and the optimal material distribution

·      Post-processing the results

Optimization Setup

To import the file:

  1. In HyperMesh, clear any previously created models.

  2. From the Preferences pull down menu, select User Profiles….

  3. Choose HyperMesh in the field next to Application and select the radio button next to OptiStruct and click on OK to load OptiStruct user profile.

This sets the HyperMesh environment for the OptiStruct solver

  1. Select the Files panel toolbar button image\files_panel.gif.

  2. Select the import subpanel.

  3. Click FE and select OptiStruct.

  4. Click import…, select combined.fem, and click Open.

  5. Click return to go back to main page.

To set up the topology design space:

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

  2. Select the topology subpanel.

  3. Verify you are in the create subpanel.

  4. Click comps, select 1pin, and click select.

  5. For desvar =, assign the name pin.

  6. Change type: to PSHELL.

  7. Verify base thickness is 0.0.

  8. Click create.

  9. Click comps, check only 3bend and click select.

  10. For desvar =, assign the name bend.

  11. Verify base thickness is 0.0.

  12. Click create.

  13. Click return.

To set up the topography design space:

  1. Click topography.

  2. Verify you are in the create subpanel.

  3. Click comps, check 1pin and 3bend, and click select.

  4. For desvar=, assign the name tpg.

  5. Click create.

  6. Select the bead params subpanel.

  7. For minimum width=, assign 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.

  1. Select the pattern grouping subpanel and set pattern type: to 1-plane sym.

  2. Click anchor node, type 41, and press Enter.

  3. Click first node, type 53, and hit Enter.

  4. Click update.

  5. Select the bounds subpanel.

  6. Verify the bounds are as follows:

upper bound = 1.0, lower bound = 0.0.

  1. Click update.

  2. Click return.

To 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. For response =, assign 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 compliance index.

  8. Click loadsteps and activate force.

  9. Make sure that the option to define normalizing factor is toggled to autonorm.

  10. Enter the mode numbers and their corresponding weights using the following chart.

Mode

Weight

1

1.0

2

2.0

3

1.0

4

1.0

5

1.0

6

1.0

  1. Click create.

  2. Click return.

To 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 the frequency checkbox, then click select.

  6. Click create.

  7. Click return.

To define the objective function:

  1. Click objective.

  2. Verify that objective is set to min.

  3. Click response = and select comb.

  4. Click create.

  5. Click return.

To define minimum member size control:

Minimum member size is generally recommended to avoid checkerboarding. It also ensures that 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.

To 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 Analysis page.

To 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 that 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.

  6. Note that the PARAM button highlighted, indicating that it is active.

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

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.

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 the 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 <prefix>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.

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, estimates for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. Review this file for warnings and errors that are flagged from processing the sshield_analysis1.fem file.

comb_complete_des.h3d

The HyperView results file. Contains shape, thickness and density information for all iterations. Contains the element and possible nodal, material density or topography information for all iterations.

comb_complete_s1.h3d

The HyperView results file. Contains stress, displacement, for all load cases.

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.

Post-processing the Results

  1. Once you see the message Process completed successfully in the command window, close the command window to return to HyperMesh.

  2. Click HyperView to launch HyperView.

The HyperView GUI window opens and the results get loaded automatically in HyperView. A message window appears to inform about the successful loading of the model and result files in to HyperView. Click Close to close the message window

To view the shape result:

  1. Click on the Deformed toolbar button image\def.gif.

  2. By clicking on the pull-down menus next to each option, select Shape Change(v) for Result Type, Scale factor for Scale:, and Uniform for Type. Also choose 1.0 for Value.

  3. Below the Undeformed shape: section, click on the pull-down menu next to Show: and select None.

  4. Click Apply to display the shape change because of topography optimization.

  5. At the bottom of the GUI, click on the name Design or Iteration 0,
    image\3100_desi_iter.gif,
    to activate the Load Case and Simulation Selection dialog and select the 25th iteration by double clicking on Iteration 25.

image\3100_2.gif

Topography result applied on slider suspension

To view a static contour plot:

  1. Click the Contour toolbar button image\contour.gif.

  2. Select the first pull-down menu below Result Type and select Element Thicknesses [s].

  3. Select the second pull-down menu below Result Type and select Thickness.

  4. Select Simple in the filed below Averaging method:.

  5. Click Apply to display the density contour.

To view an isosurface plot:

  1. Click the Iso Value toolbar button image\iso.gif.

  2. Choose Element Densities [s] in the first filed below Result Type and Density in the second field below Result Type.

  3. Below the Display options:, make sure that Above is selected in the field next to Show:.

  4. Click Apply to display the density iso-surface plot.

  5. Enter 0.3 in the field next to Current value and press enter key in your keyboard.

An iso-surface plot is displayed in the graphics window. Those parts of the model with a density greater than the value of 0.3 are shown in with density contour, the rest are removed from the display.

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