PERMAS-DEVX Extended Mode Analysis
This module provides additional methods for dynamic eigenvalue analysis:
- Dynamic condensation
- Complex mode analysis
- Eigenfrequencies over rotational speed for rotating structures
Dynamic Condensation
It includes dynamic condensation due to the Craig-Bampton method. The method uses fixed-interface vibration modes and the static deflections
due to unit displacements of the interface degrees of freedom for the dynamic reduction of the substructures.
Like for the Guyan's reduction, an explicit and an iterative scheme is available in order to achieve good performance.
The functionality is important for the following types of solution:
- Structural dynamics
- Acoustics
- Coupled fluid-structure acoustics
Two condensation options are available for coupled fluid-structure acoustics:
- Dry Interface
- Solution of a coupled eigenvalue problem on subcomponent level, i.e. isolation of the acoustic component. External modes are coupled modes.
- Global solution may be a mechanical vibration analysis.
- Wet Interface
- Separate computation of mechanical and acoustic modes on subcomponent level.
- Global solution is a coupled vibration analysis.
- Condensation of the fluid-structure interface can also be made.
Complex Mode Analysis
This includes the calculation of complex eigenvalues and eigenvectors in modal coordinates. This method is based
on a previous solution of the real eigenvalue task.
The results of this analysis are as follows:
- Frequency
- Complex eigenvalues
- Complex eigenfrequency (damping coefficient and circular frequency)
- Equivalent viscous damping ratio
- Complex mode shapes with physical and modal representation. The modal displacements of the complex modes represent the modal participation of the underlying real modes.
A suitable post-processor (like MEDINA) can be used to visualize and animate complex mode shapes.
Eigenfrequencies of Rotating Systems
For rotational systems it is often required to generate a so-called Campbell diagram, which relates the eigenfrequencies to the rotational speed. The values of such a diagram can be generated automatically in one single run. From these values all frequencies of interest can be selected for a subsequent frequency response analysis.
