CONSTRAINT

Definition of an equality or inequality (less or equal/ greater or equal) constraint. The constraint is defined with respect to a design response.

This page discusses:

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About Constraints

ID_NAME

= <name_of_constraint>

Name of the CONSTRAINT definition.

DRESP

= <name_of_dresp>

Name of the design response that should be restricted.

MAGNITUDE

= ABS

= REL

Constraints can be given in absolute or relative values.

EQ_VALUE

= <value>

Value of equality constraint.

GE_VALUE

= <value>

Value of greater or equal constraint.

LE_VALUE

= <value>

Value of less or equal constraint.

Remarks

  1. Only one item of the following list of items can be used within a constraint definition:
    • EQ_VALUE
    • GE_VALUE
    • LE_VALUE
  2. MAGNITUDE: relative values always refer to the design response of the start model for the optimization. Example: The relative value 0.8 represents 80%.

    Please note: In topology optimization, the start model for the optimization is the model used for the first finite element analysis in the optimization procedure (iteration 0). The element densities might differ from the initial model (for example, when no volume constraint is present they are set to 50% of the original density). Take this into account when defining, for example, relative displacement or frequency constraints.

    This behavior can be controlled by the user with the parameter DENSITY_INITIAL in the OPT_PARAM command.
  3. For EQ_VALUE only a value greater equal to zero can be set for MAGNITUDE=REL.
  4. For shape optimization, a volume constraint might be defined for an element group which contains the complete mesh_smooth area.
  5. Inequality constraints can only be used for the sensitivity-based bead, sizing, shape and topology optimization.
  6. Equality constraints can be used for controller-based shape, bead, and topology optimization. If accidentally an equality constraint is defined for a sensitivity-based optimization an error message is shown.
  7. Special care must be taken when using relative magnitude in an inequality constraint with a negative start model design response value: When converting the relative magnitude to absolute, the inequality is multiplied with a negative number and thus the constraint type changes from "lesser equal" to "greater equal" and vice versa. This behavior can be changed with the OPT_PARAM parameter MOD_NEG_REL_CONSTR.

Examples

For sensitivity-based topology optimization:


CONSTRAINT
 ID_NAME   = my_constraint
 DRESP     = volume_part_1
 MAGNITUDE = REL
 LE_VALUE  = 0.8
END_

For controller-based bead optimization: 


CONSTRAINT
 ID_NAME   = bead_height_constraint
 DRESP     = dresp_bead_height
 MAGNITUDE = ABS
 EQ_VALUE  = 20.0
END_