Example: Defining Stresses in Constraint Definition

The task for this example is to define a constraint on the maximum von Mises stress.

Note: Each design response definition of type SIG_TOPO_MISES may only be applied once in either the objective or constraint definition. If stresses should be considered both in constraint or the objective (or several stresses should be combined) for each use one separate design response has to be defined.

This task shows you how to:

Define a Mises Stress in Constraint Definition in Tosca Structure.gui
Define a Mises Stress in Constraint Definition in Tosca Extension for ANSYS® Workbench

Define a Mises Stress in Constraint Definition in Tosca Structure.gui

Choose Command > DRESP.
The DRESP menu appears.
Define the SIG_TOPO_MISES as design response in as shown in the following figure:

Define a Mises Stress in Constraint Definition in Tosca Extension for ANSYS® Workbench

Set up a design response first with Stress/Strain as Category and SIG_Topo_Mises as Response Type.
Then add a constraint to the project and select the previously defined von Mises stress design response, set Type to Absolute, Category to Less or equal and set the desired value, as shown in the following figure:

SIMULIA Tosca Structure Parameter File

The design response for stresses for topology optimization is defined as the following:
```
DRESP
  ID_NAME   = TOPO_STRESS_DESIGN_ELEMENTS
  TYPE      = SIG_TOPO_MISES
  DEF_TYPE  = SYSTEM
  EL_GROUP  = <element_group>
  LC_SET    = <load cases>
END_
```
The constraint is then defined as:
```
CONSTRAINT
  ID_NAME   = STRESS_CONSTRAINT
  DRESP     = TOPO_STRESS_DESIGN_ELEMENTS
  MAGNITUDE = ABS
  LE_VALUE  = <stress constraint>
END_
```
Notes:
1. Different optimization settings (STRESS_DRESP_OPT = ON) are applied for updating the design variables (=relative densities) when DRESP is TYPE = SIG_TOPO_MISES. When the stresses are applied as design response (DRESP) in a topology optimization formulation the following default settings are modified:
  1. The move limit (DENSITY_MOVE = 0.10 in OPT_PARAM) on the design variables is decreased from 0.25 to 0.10.
  2. The maximal number of optimization iterations (ITER_MAX = 80 in STOP) is increased from 50 to 80.
2. The default settings are overwritten by setting STRESS_DRESP_OPT=OFF, e.g.
```
        OPT_PARAM
          ......
          STRESS_DRESP_OPT = OFF
          DENSITY_MOVE = 0.15
          DENSITY_UPDATE = CONSERVATIVE
          ......
        END_
        
      
```