Design Variables

For each optimization problem, the design variables represent the values to be changed during the optimization. The density of each individual element in the design space is a design variable in topology optimization in SIMULIA Tosca Structure. The densities change during the optimization in order to fulfill the optimization goals. The Young’s modulus of each element is coupled with the density.

This task shows you how to:

Related Topics
In Other Guides
DV_TOPO

Define a Design Variable in Tosca ANSA® environment

Before you begin:

Valid design elements are 2D and 3D elements, including shell elements. Bars can be used as design variables, but not within mixed groups. The list of valid element types for the topology optimization is given in Solver Specific Features for the different FE solvers.

  1. To choose the design element group, select DESIGN_AREA > Edit .

  2. In the appeared dialog, set the field EL_GROUP to GROUP_DEF and press "?" key in GROUP_DEF field.

    The SET HELP window opens, where all existing groups are listed.

  3. If needed, create a new element group by using New command of this window.

Define a Design Variable in Tosca Structure.gui

  1. Choose Command > DV_TOPO.

  2. Assign a previously defined element group to be the design element group for the topology optimization as shown in the following figure:

    The element group has to be a group of elements which are allowed as design elements for the topology optimization.



    The resulting command is the DV_TOPO command. For more information, see DV_TOPO.

    DV_TOPO
 ID_NAME = dv_design_elem
 EL_GROUP = design_elem
END_

Define a Design Area in Tosca Extension for ANSYS® Workbench

  1. To add a Design Area to the project, select Topology > Design Area in the toolbar.

  2. In the Design Area dialog, select the Geometry as shown in the following figure:

    The part of the geometry that is assigned will be optimized. It is also possible to assign a predefined Named Selection.

Use Results from Previous Runs as Initial Material Distribution

Before you begin: The RESTART File containing the initial material distribution must be located in the start directory of the optimization job. The format of the RESTART File has to be ONF (Optmization Neutral File).

  1. If you want to use results of already performed optimizations as start solution for the current optimization task, use the option INITIAL_DV_FIELD within the DV_TOPO command:

    Important: This option is currently not supported from the Tosca ANSA® environment.

    DV_TOPO
 ID_NAME = dv_design_elem
 EL_GROUP = design_elem
 INITIAL_DV_FIELD = <my_initial_mat_distribution.ONF>
END_

    This option leads to the use of the material distribution stated in the result file instead of a homogeneous material distribution in the design area.

  2. The initial material distribution is extracted from the datablock 740 with the title MAT_PROP_NORMALIZED.

    Important:
    • When using a material distribution of a previous optimization run (file TP_XXX.onf ) for the new optimization it is recommended to rename the file (e.g. to INITIAL_MAT.onf). Otherwise name conflicts with the running optimization (with newly generated material distribution files TP_YYY.onf) may lead to confusion in the postprocessing: the start file TP_XXX.onf may be considered and shown as last iteration (if XXX is larger as the last iteration in the actual optimization).
    • Depending on the state used as initial material distribution and depending on the differences in the optimization definition between the used solution and the current task the convergence can be speeded up significantly. If the changes are too big then the usage of the initial distribution may lead to a higher number of iteration.
    • The restart is not available for the controller-based approach due to the fact that this approach is already very efficient and the use of previously defined material distributions does not lead to a speedup of the optimization process.