This tutorial demonstrates how to perform 1-D topology optimization. The model is a simple welded hat section. The welding is modeled using CWELD elements.
The necessary file can be found in <install_directory>/tutorials/os/. Copy the files from this directory to your working directory.
The steps in the tutorial are:
· Define the design space
· Set-up the optimization problem
· Run OptiStruct
· Post-process the results
The following file is needed to perform this tutorial:
hut.hm Original HyperMesh database containing the analysis model.
The objective is to minimize the weighted compliance through all three load cases. The volume fraction of the weld component is limited to 0.3. The design space is the spot weld component.
Initial model.
To load the model in HyperMesh:
Start HyperMesh.
Choose OptiStruct in the User Profile dialog and click OK.
User Profile… can also be accessed from the Preferences pull-down menu on the toolbar.
Select the hm file subpanel using the radio buttons on the left side of the panel.
Click retrieve… and use the file browser to locate the file hut.hm. in <install_directory>/tutorials/os/.
Click Open.
The hut.hm database is loaded into the current HyperMesh session, replacing any existing data.
Note that the location of the file is now displayed in the file: field.
Click Return.
To define the design space:
Go to the Analysis page.
Click optimization.
This brings up the optimization module.
Click topology.
Set the radio button to create.
Set the selector to type PWELD.
This action makes the props selection box show up.
Click props.
Select the tick box PWELD_500.
Click return.
Enter desvar = tpl.
Click create.
This defines the design space.
Click return.
To define the responses:
Click responses.
Select response type: volumefrac.
Select by entity.
This action makes the yellow selection box show up.
Switch the yellow box to the props box.
Click props.
Select the tick box PWELD_500.
Click return.
Enter response = volfrac.
Click create.
This defines the volume fraction response.
Enter response= wcomp.
Select the pull-down menu below response type: to open a window listing all responses that are available for optimization in OptiStruct.
Click the arrow icon 
to go to the second page.
Click weighted comp to select it as the response type and return to the response panel.
Click loadsteps.
Turn on all three tick boxes for the subcases.
Change the weighting factors for SUBCASE2 and SUBCASE3 to 100.0.
This increases the influence of the two bending load cases vs. the torsion load case SUBCASE1, which is kept at 1.0.
Click return.
Click create.
This defines the weighted compliance response.
Click return.
To define the constraint and objective:
Click dconstraints.
Select response = volfrac.
Select the tick box upper bound = and enter 0.3.
Enter constraint = volfrac.
Click create.
This defines the volume fraction constraint.
Click return.
Click objective.
Select response = wcomp.
Select min as the objective.
Click create.
This defines the weighted compliance objective.
Click return.
This concludes the definition of the optimization problem. Some optimization parameters should be modified to achieve a good result.
Click opti control.
Select the tick box DISCRETE = and enter 20.0.
This increases the penalty factor to the density method to achieve a discrete result.
Select the tick box OBJTOL = and enter 1.e-5.
This reduces the objective tolerance that is checked for convergence.
Click return twice.
To perform the OptiStruct run:
Click OptiStruct to enter the panel to run OptiStruct.
Click save as… following the input file: field.
A Save file… browser window pops up.
Select the directory where you would like to write the OptiStruct model file and enter the name for the model, hut.fem, in the File name: field.
The .fem filename extension is the suggested extension for OptiStruct input decks.
Click Save.
Note the name and location of the hut.fem file now displays in the input file: field.
Select run options: optimization.
The input file name should be hut.fem
Click OptiStruct.
This will export the input deck and start the execution of OptiStruct in a DOS or Unix window.
To visualize the new spot weld configuration:
To post-process the results, the weld elements will be sorted by density into different components.
Click files.
Use browse to find the output hut.HM.comp.cmf from your OptiStruct run.
Click Open.
Click execute.
As a result, four of the welds are in the DENS 0.9-1.0 component, all others are in the DENS 0.0-1.0 component.
To do a reanalysis with the new weld configuration, un-display the components with low density (DENS 0.0-0.1 to DENS 0.8-0.9) and rerun the analysis with export options: set to displayed in the OptiStruct panel.
Final configuration.
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