OS-T: 5080 Global Search Optimization

In this tutorial you will perform a Global Search Optimization (GSO) with shape design variables.

Before you begin, copy the file(s) used in this tutorial to your working directory.
A global search approach will be used to generate the multiple starting points. The structure, consisting of one base panel and the cross shaped ribs, is subjected to a frequency-varying unit load excitation using the modal method. The goal is to achieve the best stiffened structure by changing the shapes of the ribs.

os_5080_model
Figure 1. Model Review
A regular shape optimization has been defined in the model. The formulation of this optimization is stated as:
Objective
Minimize the maximum (minmax) displacement at the node where the excitation load was applied.
Constraints
Mass < 2.0e-3.
Design Variables
Shape design variables.

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.

Import the Model

  1. Click File > Import > Solver Deck.
    An Import tab is added to your tab menu.
  2. For the File type, select OptiStruct.
  3. Select the Files icon files_panel.
    A Select OptiStruct file browser opens.
  4. Select the rib_opt.fem file you saved to your working directory.
  5. Click Open.
  6. Click Import, then click Close to close the Import tab.

Review the Model and Optimization Setup

The shape optimization of the frequency response model has been defined in the model.

  1. In the Model Browser, review the model, loadstep, and optimization setup.

    os_5080_browser
    Figure 2.
  2. From the Analysis page, click the optimization panel.
  3. Click the shape panel to review the shape design variables.
  4. Click animate.
    One of the shapes should be displayed in the simulation= field.
  5. Click linear.
    The animation of that shape displays.
  6. Review the other shapes by clicking next or prev.
  7. Click return to go back to the Optimization panel.

Initiate the Run

  1. From the Analysis page, click the OptiStruct panel.
    The name and location of the rib_opt.fem file displays in the input file: field. The location where the model and result files will be written can be modified.
  2. Click OptiStruct.
  3. After the running process completes, go to the working directory and open the rib_opt.out file. Check the optimization history and the final optimal design.
  4. Go back to the Analysis page.

Define the DGLOBAL Cards

  1. From the Analysis page, click the control cards panel.
  2. In the Card Image dialog, click CASE_UNSUPPORTED_CARDS.
  3. In the Control Card dialog, enter DGLOBAL=1 and click OK.
  4. Click BULK_UNSUPPORTED_CARDS.
  5. In the Control Card dialog, enter DGLOBAL,1 and click OK.
  6. Click return.
Both Subcase and Bulk Data Entries for global search are created with default parameters.

Initiate the Run

  1. From the Analysis page, click the OptiStruct panel.
    The name and location of the rib_opt_global.fem file displays in the input file: field. The location where the model and result files will be written can be modified.
  2. Click OptiStruct.
  3. After the running process completes, go to the working directory and open the rib_opt_global.out file. Check the optimization history and the final optimal design.
  4. Go back to the Analysis page.

View the Results

Post-process the GSO Results

Since the default parameters are used for GSO, OptiStruct determines the number of starting points and number of groups of design variables automatically.
  1. Open the rib_opt_global.out file.
    A general summary of the GSO run is output at the end of the out file. This GSO run completed with 20 starting points. Seventeen (17) unique designs were found, which means three designs were repeated. The best design was found at starting point 3. The table of unique designs and table of designs were also printed with the information of starting point, objective function, constraint violation, times found, and directory suffix.
  2. Compare the best design with the results from the regular optimization approach.
    In the working directory, 17 directories with suffix '_GSO_V1_V2' were created for the unique designs. V1 is the number of the starting point, and V2 is the rank of this design among all unique designs. The optimization results of each starting point can be found in the directory, respectively.
  3. Open the Excel file, rib_opt_global_GSO.slk.
    The tables for unique designs and all designs are printed in the Excel file. The best design among the GSO runs was achieved with the 3rd starting point, and the results of this design were saved in the directory, rib_opt_global_GSO_3_1, and this design was found three times during the global search. In GSO search, if the difference between two designs is under the unique design tolerance, they are considered identical; for example, the designs with starting points 11 and 3. This information can be found in the table of all designs. The statistical information and the optimal design variables for each run are also available.

    os_5080_search_results
    Figure 3.

Post-process the Best Design

The following steps demonstrate how to review the best design of GSO in HyperView.

  1. In the OptiStruct panel, click HyperView.
  2. In the Load Results panel, load the rib_opt_global_des.h3d file located in the /rib_opt_global_GSO_3_1 directory.
  3. Click Apply.
    The h3d file containing optimization results is loaded.
  4. In the Results Browser, select Iteration 10.
  5. On the Results toolbar, click resultsContour-16 to open the Contour panel.
  6. Set the Result type to Shape Change (v).
  7. Click Apply.
The optimized shape at the final iteration displays.

os_5080_final
Figure 4. Best Optimized Shape Design from GSO