Defining Design Variables for Topology Optimization

You can define Design Variables that 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 Tosca Structure.

This task shows you how to:

Define a Design Variable in Tosca Structure.gui
Use Results from Previous Runs as Initial Material Distribution

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.

Define a Design Variable in Tosca Structure.gui

Choose Command > DV_TOPO.
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 must 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_
```

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 must be ONF (Optimization Neutral File).

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

The initial material distribution is extracted from the data block 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 (for example, to INITIAL_MAT.onf). Otherwise name conflicts with the running optimization (with newly generated material distribution files TP_YYY.onf) might lead to confusion in the post-processing: the start file TP_XXX.onf might be considered and shown as the last iteration (if XXX is larger as the last iteration in the actual optimization).
Depending on the state used as the initial material distribution and depending on the differences in the optimization definition between the used solution and the current task, the convergence can be accelerate significantly. If the changes are too big, the usage of the initial distribution may lead to a higher number of iteration.
The restart is not available for the controller-based approach because this approach is already very efficient and the use of previously defined material distributions does not lead to a speedup of the optimization process.