Constraints are also extracted from the design responses. Constraints restrict the value of a design response; for example, you can specify that the volume must be reduced by 45% or the absolute displacement in a region must not exceed 1 mm. You can also apply manufacturing and geometric constraints that are independent of the optimization; for example, a structure must be able to be cast or stamped or the diameter of a bearing surface cannot be changed.

When you execute an optimization process, Abaqus generates history output from the constraints you defined in the Optimization module. For volume design responses the history output is always reported as a fraction of the initial value. For all other design responses the history output is reported as an absolute value.

Satisfying the constraints has priority over the minimization or maximization of the objective function. The optimization algorithms start to maximize or minimize the objectives only after the constraints are satisfied.

You can specify only a volume constraint for a condition-based topology or shape optimization, and the volume constraint must be either equal to a fixed value or a fraction of the value before the optimization starts. If the requested volume differs greatly from the initial volume, the Optimization module may need several design cycles to satisfy the volume constraint. A general topology optimization provides more flexibility; and you can select any of the design responses as a constraint, except for the design response that calculates the eigenfrequencies with the Kreisselmaier-Steinhauser formula. The constraint in a general topology optimization can be less than, greater than, or equal to a fixed value or a fraction of the value before the optimization starts. For more information, see “Creating constraints,” Section 18.9, and “Objectives and constraints,” Section 13.2.2 of the Abaqus Analysis User's Guide.