You can define stress (factor of safety) and frequency values as design
constraints for a Topology
study.
For example, run a Topology study to find the optimal shape of a model
with the largest stiffness for a 50% weight reduction and a maximum permissible stress
condition. A stress constraint enforces the condition that a model after optimization
cannot experience stresses larger than a percentage factor of the material's yield
strength.
To specify a stress constraint, in the
Goals
and Constraints PropertyManager, select
Stress/Factor of Safety Constraint. For
Type, select either
Stress
Constraint, or
Factor of Safety
Constraint.
Stress
Constraint 
Specified value

Enter the maximum permissible von Mises
stress value for the optimized geometry.

Specified factor

Enter the maximum permissible von Mises
stress value as a percentage of the material's yield
strength.


Factor
of Safety Constraint 
Enter the minimum acceptable
factor of safety for the optimized geometry. The maximum permissible
von Mises stress is calculated from the material's yield strength
divided by the userdefined factor of safety. The maximum von Mises
stress is the default FOS criterion used in this case. 
To specify a frequency constraint, in the Goals
and Constraints PropertyManager, select Frequency Constraint. Enter a lower or upper, frequency limit, or range
of permissible frequencies for the selected mode shapes.
Run a frequency study with the original model (maximum design
space), before you run a topology study with frequency constraints, to evaluate the
range of permissible natural frequencies.
Select Mode tracking to instruct
the optimization solver to track the order of the selected mode shapes derived from the
original geometry (throughout the optimization iterations) when enforcing frequency
constraints.
When Mode tracking is cleared, the
solver tracks the current order of mode shapes as derived for each optimization
iteration. For example, it is possible for an optimization goal of a 50% mass reduction
and a frequency constraint on the first mode shape. The first mode shape of the original
geometry becomes the second or third mode shape of the optimized geometry.
For example, you add a frequency constraint on a distinct mode shape
of a plate (the first mode in the original plate geometry). As the model shape changes
during iterations, this mode may move down in the frequency list. By selecting
Mode tracking, the solver keeps track of the
same mode as it moves positions in the list of frequencies, and enforces the constraint
on the same mode shape. When you clear Mode
tracking, another mode shape replaces the original first mode in the
course of iterations. The solver then applies the frequency constraint on this new mode
that replaces the old mode.
For a Topology study with a specified frequency constraint only:
 Applied loads or prescribed displacements (including remote loads, translations,
and rotations) are not considered in the calculation of the resonant
frequencies.
 In the Remote Load/Mass
PropertyManager, select to apply a remote mass. Any remote mass you apply with option
is ignored by the solver.