OS-T: 3010 Topography Optimization of an L-bracket

In this tutorial you will perform a topography optimization on a L-bracket modeled with an attached mass.

The bracket is modeled with shell elements. The objective is to maximize the frequency of the first mode by introducing beads or swages to the bracket. This can be achieved by using topography optimization. The regions around the holes are specified as non-designable, while the bulk of the bracket is available for developing stiffening beads.

3010_l_bracket
Figure 1. L-bracket Layout
The optimization problem for this tutorial is stated as:
Objective
Maximize 1st frequency mode.
Constraints
Bead dimensions and layout.
Design Variables
Perturbation of nodes normal to the shell's mid-plane.

Launch HyperMesh and Set the OptiStruct User Profile

  1. Launch HyperMesh.
    The User Profile dialog opens.
  2. Select OptiStruct and click OK.
    This loads the user profile. It includes the appropriate template, macro menu, and import reader, paring down the functionality of HyperMesh to what is relevant for generating models for OptiStruct.

Open the Model

  1. Click File > Open > Model.
  2. Select the Lbkttopog.hm file you saved to your working directory from the optistruct.zip file. Refer to Access the Model Files.
  3. Click Open.
    The Lbkttopog.hm database is loaded into the current HyperMesh session, replacing any existing data.

Set Up the Optimization

Define Topography Design Variables

For a topography optimization, a design space and a bead definition need to be defined.

In this step, the values of a bead width of 15mm, a bead height of 5mm, and draw angle of 85 degrees will be used. Symmetry of the bead pattern should be forced along the symmetry line of the design space.

  1. From the Analysis page, click the optimization panel.
  2. Click the topography panel.
  3. Create a topography design space definition.
    1. Select the create subpanel.
    2. In the desvar= field, enter topo.
    3. Using the props selector, select design.
    4. Click create.
    A topography design space definition, topo, has been created. All elements organized into the design component collector(s) are now included in the design space.
  4. Create a bead definition for the design space topo.
    1. Select the bead params subpanel.
    2. Verify the desvar = field is set to topo, which is the name of the newly created design space.
    3. In the minimum width= field, enter 15.0.
      This parameter controls the width of the beads in the model. The recommended value is between 1.5 and 2.5 times the average element width.
    4. In the draw angle= field, enter 85.0 (this is the default).
      This parameter controls the angle of the sides of the beads. The recommended value is between 60 and 75 degrees.
    5. In the draw height=, enter 5.0.
      This parameter sets the maximum height of the beads to be drawn.
    6. Select buffer zone.
      This parameter establishes a buffer zone between elements in the design domain and elements outside the design domain.
    7. Toggle draw direction to normal to elements.
      This parameter defines the direction in which the shape variables are created.
    8. Set boundary skip to load and spc.
      This tells OptiStruct to leave nodes at which loads or constraints are applied out of the design space.
    9. Click update.

    A bead definition has been created for the design space topo. Based on this information, OptiStruct will automatically generate bead variable definitions throughout the design variable domain.

  5. Adding pattern grouping constraints.
    1. Select the pattern grouping subpanel.
    2. Click desvar = and select topo.
    3. Set the pattern type to 1-pln sym.
    4. Click anchor node, and enter 337 in the id= field.
    5. Click first node, and enter 613 in the id= field.
    6. Click update.
  6. Update the bounds of the design variable.
    1. Select the bounds subpanel.
    2. Verify the desvar = field is set to topo, which is the name of the design space.
    3. In the Upper Bound= field, enter 1.0.
      Upper bound on variables controlling grid movement (Real > LB, default = 1.0). This sets the upper bound on grid movement equal to UB*HGT.
    4. In the Lower Bound= field, enter 0.0.
    5. Click update.
    The upper bound sets the upper bound on grid movement equal to UB*HGT and the lower bound sets the lower bound on grid movement equal to LB*HGT.
  7. Click return to go to the Optimization panel.

Create Optimization Responses

  1. From the Analysis page, click optimization.
  2. Click Responses.
  3. Create the frequency response.
    1. In the responses= field, enter FREQ.
    2. Below response type, select frequency.
    3. For Mode Number, enter 1.0.
    4. Click create.
    A response, FREQ, is defined for the frequency of the first mode extracted.
  4. Click return to go back to the Optimization panel.

Define the Objective Function

  1. Click the objective panel.
  2. Verify that max is selected.
  3. Click response and select FREQ.
  4. Using the loadsteps selector, select STEP.
  5. Click create.
  6. Click return twice to exit the Optimization panel.

Save the Database

  1. From the menu bar, click File > Save As > Model.
  2. In the Save As dialog, enter Lbkttopog.hm for the file name and save it to your working directory.

Run the Optimization

  1. From the Analysis page, click OptiStruct.
  2. Click save as.
  3. In the Save As dialog, specify location to write the OptiStruct model file and enter Lbkttopog for filename.
    For OptiStruct input decks, .fem is the recommended extension.
  4. Click Save.
    The input file field displays the filename and location specified in the Save As dialog.
  5. Set the export options toggle to all.
  6. Set the run options toggle to optimization.
  7. Set the memory options toggle to memory default.
  8. Click OptiStruct to run the optimization.
    The following message appears in the window at the completion of the job:
    OPTIMIZATION HAS CONVERGED.
FEASIBLE DESIGN (ALL CONSTRAINTS SATISFIED).
    OptiStruct also reports error messages if any exist. The file Lbkttopog.out can be opened in a text editor to find details regarding any errors. This file is written to the same directory as the .fem file.
  9. Click Close.
The default files that get written to your run directory include:
Lbkttopog.hgdata
HyperGraph file containing data for the objective function, percent constraint violations, and constraint for each iteration.
Lbkttopog.hist
The OptiStruct iteration history file containing the iteration history of the objective function and of the most violated constraint. Can be used for a xy plot of the iteration history.
Lbkttopog.html
HTML report of the optimization, giving a summary of the problem formulation and the results from the final iteration.
Lbkttopog.oss
OSSmooth file with a default density threshold of 0.3. You may edit the parameters in the file to obtain the desired results.
Lbkttopog.out
OptiStruct output file containing specific information on the file setup, the setup of the optimization problem, estimates for the amount of RAM and disk space required for the run, information for all optimization iterations, and compute time information. Review this file for warnings and errors that are flagged from processing the Lbkttopog.fem file.
Lbkttopog.sh
Shape file for the final iteration. It contains the material density, void size parameters and void orientation angle for each element in the analysis. This file may be used to restart a run.
Lbkttopog.stat
Contains information about the CPU time used for the complete run and also the break-up of the CPU time for reading the input deck, assembly, analysis, convergence, and so on.
Lbkttopog_des.h3d
HyperView binary results file that contain optimization results.
Lbkttopog_s#.h3d
HyperView binary results file that contains from linear static analysis, and so on.
Lbkttopog.grid
An OptiStruct file where the perturbed grid data is written.

View the Results

Shape contour information is output from OptiStruct for all iterations. In addition, Eigenvector results are output for the first and last iteration by default. This section describes how to view those results in HyperView.

View a Transient Animation of Shape Contour Changes

  1. From the OptiStruct panel, click HyperView.
    HyperView launches within the HyperMesh Desktop and loads the Lbkttopog_des.h3d file.
  2. On the Animation toolbar, set the animation mode to Transient.

    transient_menu
    Figure 2.
  3. Click animationStart-24 to start the animation.
  4. Click animationOptions-24 to open the Animation Controls panel.
  5. Move the Max Frame Rate slider to adjust the animation speed.

Review the Optimized Frequency Difference

  1. In the top, right of the application, click pageNext-24 to proceed page 3, which contains the results for first and the last iterations.
  2. In the Results Browser, select the first iteration (Iteration 0).
The frequencies of all of the modes requested from the analysis are shown in the Subcase drop-down.

os_3010_iter0
Figure 3. Frequency of the First Mode for Iteration 0
Look at the frequency values for the last iteration. Upon observation, the frequency for the first mode has changed from around 48 Hz to around 93 Hz for first and last iterations, respectively.

os_3010_iter12
Figure 4. Frequency of the First Mode for Iteration 12

Apply Optimized Topography

  1. In the top, right of the application, click pageNext-24 to go back to the Design History page (page 2).
  2. On the Animation toolbar, click animationFastForwardEnd-24 to set the Current time to the last step.

    3000_topog_results
    Figure 5. Topography Results