OS-4010_ Size Optimization of a Welded Bracket

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    HyperWorks Tutorials

    OS-4010: Size Optimization of a Welded Bracket

    This tutorial demonstrates how to perform a size optimization on a welded bracket modeled with shell elements. The

    structural model with loads and constraints applied is shown in the figure below. The objective is to minimize the

    amount of material used in the model subject to certain stress specificat ions. The gauge changes of the bracket are

    linked to each other so that the gauge is identical for both sides at the optimal design.

    Structural model of the welded bracket.

    The structural model, as shown, is loaded into HyperMesh. The constraints, loads, material properties, and

    subcases (loadsteps) are already defined in the model. Size design variables and optimization parameters are

    defined and the OptiStruct software is used to determine the optimal gauges. The results are then reviewed in

    HyperMesh.

    The optimization problem is stated as:

    Objective: Minimize volume.

    Constraints: Maximum Von Mises Stress of the brackets < 100 Mpa.

    Design variables: Gauges of the brackets.

    The following exercises are included:

    Setting up the size optimization problem in HyperMesh

    Submitting the job

    Viewing the results

    Exercise

    Step 1: Launch HypeMesh Desktop, set the User Profile and Retrieve the Database File

    1. Launch HyperMesh Desktop.

    2. Choose OptiStructin the User Profile dialog and click OK.

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    This loads the OptiStruct user profile. It includes the OptiStruct template, macro menu, and import reader,

    paring down the functionality of HyperMesh to what is relevant for use with OptiStruct.

    User Profiles can also be accessed from the Preferences pull-down menu on the toolbar.

    3. Select the Open Model toolbar button .

    4. Browse to the bracket_size.hm file, located in the HyperWorks installation directory under

    /tutorials/hwsolvers/optistruct/ and click Open.

    The bracket_size.hm database is loaded into the current HyperMesh session, replacing any existing data.

    Step 2: Define the Design Variables

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

    2. Select the size panel.

    3. Select the desvarsubpanel using the radio buttons on the left-hand side of the panel.

    4. Click desvar = and enterpart1.

    5. Click initial value = and enter2.5.

    6. Click lower bound = and enter1.0.

    7. Click upper bound = and enter2.5.

    8. Set the move limit toggle to move limit default.

    9. Click create.

    A design variable, part1, has been created. The design variable has an initial value of 2.5, a lower bound of 1.0,

    and an upper bound of 2.5.

    10. Repeat steps 4 through 9 to create the design variable part2 using the same initial value, lower, and upper

    bounds.

    11. Select the generic relationship subpanel using the radio buttons on the left-hand side of the panel.

    12. Click name = and enterpart1_th.

    13. Click the entity selection switch and chooseprop.

    14. Clickprop and selectpart1 from the list of component collectors.

    A property selection switch now appears below the comp button.

    15. Click the property selection switch and select Thickness Tfrom the pop-up menu.

    16. Click on designvars.

    The list of design variables appears.

    17. Check the box next to part1.

    Note that the linear factor (value is box beside part1) automatically gets set to 1.000.

    18. Click return.

    19. Click create.

    A design variable to property relationship, part1_th, has been created relating the design variable part1 to the

    thickness entry on the PSHELL card for the component part1.

    20. Repeat steps 12 through 19 to create the design variable to property relationship part2_th relating the design

    variable part2 to the thickness entry on the PSHELL card for the component part2.

    21. Click return to go to the Optimization Setup panel

    Step 3: Link the Design Variables

    1. Select the desvar linkpanel.

    2. Click on dlink = and type link1.

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    5. Click return to return to the Optimization Setup panel.

    Step 6: Define Constraints

    A response defined as the objective cannot be constrained. In this case, you cannot constrain the response volume.

    Upper bound constraints are to be defined for the responses stress1 and stress2.

    1. Select the dconstraints panel.

    2. Click constraint = and enterstress1.

    3. Click response = and select stress1 from the list of responses.

    A loadsteps button should appear in the panel.

    4. Click loadsteps.

    5. Check the box nest to STEP and click select.

    6. Check the box next to upper bound =.

    7. Click upper bound = and enter100.

    8. Click create.

    A constraint is defined on the response stress1. The constraint is an upper bound with a value of 100. The

    constraint applies to the subcase STEP.

    9. Click constraint = and enterstress2.

    10. Click response = and select stress2from the list of responses.

    11. Click loadsteps.

    12. Check the box next to STEP and click select.

    13. Check the box next to upper bound =.

    14. Click upper bound = and enter100.

    15. Click create.

    A constraint is defined on the response stress2. The constraint is an upper bound with a value of 100. The

    constraint applies to the subcase STEP.

    16. Click return twice to go to the main menu.

    Step 7: Save the HyperMesh Database

    1. From the File pull-down menu, click on Save As.

    A Save file browser window pops up.

    2. Select the directory where you would like to save the database, enter the name bracket_size.hm for thedatabase, and click Save.

    Step 8: Launch OptiStruct

    1. Select the OptiStructpanel on the Analysis page.

    2. Click save as following the input file: field.

    A Save file browser window pops up.

    3. Select the directory where you would like to write the OptiStruct model file and enter the name for the model,

    bracket_size.fem , in the File name: field.

    .fem is the suggested file extension for OptiStruct input decks.

    4. Click Save.

    Note the name and location of the bracket_size.fem file displays in the input file: field.

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    5. Set the memory options: toggle to memory default.

    6. Click the run options: switch and select optimization.

    7. Set the export options: toggle to all.

    8. Click OptiStruct.

    This launches the OptiStruct job. If the job was successful, new results files can be seen in the directory where

    the OptiStruct model file was written. The bracket_size.out file is a good place to look for error messages

    that will help to debug the input deck if any errors are present.

    The default files written to the directory are:

    bracket_size.hgdata HyperGraph file containing data for the objective function, percent

    constraint violations and constraint for each iteration.

    bracket_size.his_dat OptiStruct iteration history file containing the iteration history of the

    objective function and of the most violated constraint. Can be used for

    an xy plot of the iteration history.

    bracket_size.html HTML report of the optimization, giving a summary of the problem

    formulation and the results from the final iteration.

    bracket_size.out OptiStruct output file containing specific information on the file set-up, the

    set-up 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. This file contains compliance,

    volume calculations, and gauge information for each optimization

    iteration. It is highly recommended this file be reviewed for warnings and

    errors.

    bracket_size. prop OptiStruct property output file containing all updated property data from

    the last iteration for size optimization.

    bracket_size.h3dHyperView binary results file.

    bracket_size.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.

    bracket_size.stat Summary of analysis process, providing CPU information for each step

    during analysis process.

    Viewing the Results

    Size optimization results from OptiStruct are given in two places. The bracket_size.out file contains gauge and

    volume information for each iteration. The bracket_size.h3d file contains the element thickness for all five

    iterat ions and Displacement and Stress results for the linear stat ic analysis for iteration 0 and iteration 3. This

    section describes how to review all results. The results contained in the HyperMesh binary results file will be

    examined first. The gauge history in the bracket_size.out file will then be reviewed.

    Step 9: View the Stress Results

    After the size optimization, the stress value should be reviewed to make sure the stress constraints are not violated.

    1. Once you see the message Process completed successfully in the command window, click the green

    HyperViewbutton.

    This launches HyperView and opens the results. A message window appears to inform about the successful

    loading of the model and result files into HyperView. Notice that all of the h3d files get loaded, each into a

    different page in HyperView. The files bracket_size_des.h3d and bracket_size_s2.h3d get loaded in

    pages 2 and 3, respectively.

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    2. Click Close to close the message window.

    3. Click the Next Page toolbar button .

    The third page has the results loaded from the bracket_size_s1.h3d file. Note that the name of the page is

    displayed as Subcase 1 STEP to indicate that the results correspond to subcase 1.

    4. Click the Contourtoolbar button .

    5. Select the first pull-down menu below Result type: and select Element Stresses [2D & 3D] (t).6. From the second pull-down menu, select vonMises.

    7. Select None in the field below Averaging method:.

    8. ClickApply.

    A contoured image representing von Mises stresses should be visible. Each element in the model is assigned a

    legend color, indicating the von Mises stress value for that element resulting from the applied loads and boundary

    conditions. If you did not change the Iteration step you should be contouring the stress of the initial step. To

    contour the final step, set the last iteration of that loadcase using the Status Bar.

    9. Click either the first or second field on the right side of the Status Bar.

    This brings up the Load Case and Simulation Selection window.

    10. Click the last Iteration # in the Simulation: list.

    Notice only two iterations are displayed; the First and Last (FL) is the default setting for optimization runs. To

    change this setting, add an OUTPUT control card with a frequency setting of ALL.

    11. Click OK.

    This will now contour your final iteration of that loadcase. Review the stress to see that it is under the proper

    constraints.

    Step 10: View the Thickness Results

    1. Click the Previous Page toolbar button to move to the First page.

    2. Make sure Result type: is set to Element Thicknesses (s).

    3. Also make sure that you select Iteration 2from the Load Case and Simulation Selection window

    4. ClickApply.

    Alternatively, you can also open the bracket_size.prop file in a text editor to view the final gauge

    thicknesses of the two parts.

    Review

    The .out file contains a summary of the optimization process. From the information in the .out file, you can seehow the objective, constraints, and design variables are changing from one iteration to the next.

    Has the volume been minimized for the given constraints?

    Have the stress constraints been met?

    What are the resulting gauges for the two parts?

    Did the design variable linking work?

    Go To

    OptiStruct Tutorials

    4010: Size Optimization of a Welded Bracket http://www.altairhyperworks.com/hwhelp/Altair/hw11.0/help/hwtut/os...