Figure. Strain energy minimization performed if the combined load cases contain only Stress analysis types.
ProTOp can currently compute two objective functions: total strain energy and lowest eigenfrequency. Consequently, two individual objectives are supported as follows:
In order to choose a particular objective, the user has to select appropriate FE analysis type, as follows
In ProTOp these two objectives can be addressed either individually or combined. In the latter case, the two objectives are combined into a single one and a weighting factor is engaged to define the relative importance of one objective against the other.
Minimization of the structural strain energy is selected automatically by ProTOp if the combined load cases contain only the Stress analysis types. The number of load cases with Stress analysis types is not limited; the number of combined load cases with EigFrq analysis type has to be zero.
Figure. Strain energy minimization performed if the combined load cases contain only Stress analysis types.
Maximization of the structural lowest eigenfrequency is selected automatically by ProTOp if the only combined load case contains the EigFrq analysis type. Note that only exactly one combined load case with the EigFrq analysis type is allowed; the number of combined load cases with Static analysis types has to be zero.
Figure. Lowest eigenfrequency maximization is performed if the combined load case contains the EigFrq analysis type.
In order to run eigenfrequency optimization, the structure has to be normally supported (as for the static analysis). Maximizing the eigenfrequencies of free structures (without any displacement boundary conditions) is not supported.
NOTE. Only supported structures can be addressed in eigenfrequency maximization.
While maximizing the structural lowest eigenfrequency, the lowest and the second lowest eigenfrequencies may become close (multiple eigenfrequencies). This may introduce some numerical instabilities; usually, in such a situation it does not make much sense to run the optimization further because the gains are typically minor. Multiple lowest eigenfrequencies are easily observed by eigenmodes being changed significantly from one optimization cycle to another.
NOTE. After encountering multiple lowest eigenfrequencies, the optimization should usually be ended; the gains of further optimization would typically be rather minor.
Figure. Indication of multiple close lowest eigenfrequencies: eigenmodes are being changed significantly from one optimization cycle to another.
Mixed optimization is selected automatically by ProTOp if the actual combined load cases contain both, the Stress and the EigFrq analysis types. Note that the number of load cases with Stress analysis types is not limited; the number of load cases with EigFrq analysis types has to be exactly one.
Figure. Mixed optimization: strain energy minimization and lowest eigenfrequency maximization.
In mixed optimization, both objectives are addressed: strain energy minimization and lowest eigenfrequency maximization. The relative importance of these two objectives can be set or changed interactively at any stage of the optimization process.