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Dynamic Eigenvalues

PERMAS-DEV Dynamic Eigenvalues

The PERMAS-DEV (Dynamics/Eigenvalues) module provides for the calculation of real eigenvalues and mode shapes of the structure. The specification of a number of modes and an upper frequency limit is supported. The very efficient subspace iteration algorithm used is capable of solving very large eigenvalue problems. Rigid body modes are detected automatically or may be explicitly defined and are decoupled prior to the subspace iteration.

Additional tools are available for the further processing of modes:

  • Modal stresses can be derived from modal displacements.
  • In addition, modal potential and kinematic energies can be calculated and exported.
  • For the evaluation of modes, e.g. with respect to local or global mode shapes, energy balances can be determined and exported for all sets in a structure.
  • MAC (Modal Assurance Criterion) factors and other factors are available to compare modes between two different modal analyses
  • As a measure for the completeness of the modal model, effective masses are generated and printed on the result file.

For multi-body simulation programs, the mixture between static mode shapes and free vibration modes is a very frequent application, when flexible FE models are integrated. In case of single component models, two sets of vectors are produced: Static mode shapes and dynamic eigenvectors. These mode sets have to be orthogonalized, e.g. in the MBS system. For large models however, this step is very time consuming. Hence, this orthogonalization may be done within PERMAS. A special procedure is available to facilitate this orthogonalization.