General Information about Combined Terms

Combination of values derived from model properties or analysis results could be done getting the maximum or minimum value within a number of load cases or a number of group entities or creating response combinations like relative values, differences or mean values.

In Tosca Structure combination of values can be performed in several ways:

  1. The simplest way to combine terms is using a weighted sum for the objective function, or using a MINMAX formulation with the different weighting of the design responses. See Objective Function for more information.
  2. Combining terms might also be done using an operator - a special design response (DRESP) of the DEF_TYPE = OPER. This should only be done with caution to avoid meaningless optimization tasks. You must also be aware of the difference in the way sensitivity and controller-based algorithms handle the operator. Note that for weighted sums you might as well use the formulations used in Objective Function.
  3. Values of one type from several load cases can be combined directly using load case selection and weighting for the design response (command DRESP, item LC_SET).
  4. Values of one type at several locations (nodes, elements) in the model can in general be combined directly using group operations for the design response (DRESP item GROUP_OPER).

If several of these possibilities to combine values are applied, Tosca Structure operates as follows:

  1. The value over all entities of the group for one load case is calculated. This means that a loop over all entities of the group is executed and then the value of the inner loop is calculated with the operator specified in the GROUP_OPER parameter. If the operator is not defined by the user, a default one will be used.
  2. This value (already combined for the group entities) is calculated for the different load cases specified in the LC_SET parameter. If no LC_SET parameter is present, then all load cases and substeps (frequencies) will be used to determine the value.
  3. Combination of design responses by operators is applied next.
  4. Finally, the combination of design responses in the objective function is applied.