3.9.2. Reusing Eigenmodes
Mechanical APDL analyses that require the eigenmodes from the modal analysis can reuse the modes
from an earlier modal analysis solution.The user can reuse the Jobname.MODE (or Jobname.MODESYM)
file that is created in a modal analysis for use in the following modal based methods:
- Spectrum Analysis (ANTYPE,SPECTRUM) (p. 68)
- Modal Transient Analysis/Harmonic Analysis (p. 68)
- QR Damp Complex Modes Extraction (p. 68)
This section outlines the procedures for saving and reusing the eigenmodes from an earlier modal
analysis.
3.9.2.1. Spectrum Analysis (ANTYPE,SPECTRUM)
To run a spectrum analysis, users must first perform a modal analysis to generat e the MODE file. For
multiple spectrum analyses, a unique MODE file can be used when the modeReuseKey on the SPOPT
command is activated. This prepares the database and the necessary files for a new spectrum analysis
that reuses an existing Jobname.MODE.
3.9.2.2. Modal Transient Analysis/Harmonic Analysis
To use new load vectors, residual vector, and/or enforced motion in modal transient or modal harmonic
analyses with existing modal analysis results, refer to Restarting a Modal Analysis (p. 69)
3.9.2.3. QR Damp Complex Modes Extraction
In QRDAMP eigensolver the solution occurs in two steps. First the Block Lanczos eigensolver is used to
extract the symmetric matrix eigenmodes. These eigenmodes then are used in the second pass to build
the modal subspace (see QR Damped Method) matrix of the non-symmetric eigensystem and compute
the complex eigenmodes.
When an existing Jobname.MODESYM containing the eigenmodes of the symmetric eigensolution of
the model is available, it can be reused in the second pass by turning on the reuse flag (ReuseKey)
in the QRDOPT command.
3.9.3. Generating and Using Multiple Loads in Mode-Superposition Analyses
In a mode-superposition harmonic, transient, or PSD analysis, only nodal forces can be defined directly
during the analysis. The other loads (SF,SFE,BF,ACEL,OMEGA, etc.) must be defined in the modal
analysis. They can then be retrieved, scaled, and applied using the LVSCALE command in the mode-
superposition analysis. Spring preloads, initial strains, pretension loads, and thermal loads are ignored
and do not generat e a load.
Nodal forces can also be applied more efficiently using this multiple loads generation method.
3.9.3.1. Understanding the Multiple Loads Method
To use the multiple loads method, you must first generat e load vectors in the modal analysis. You can
use any of these modal analysis mode-extraction methods:
- Block Lanczos (MODOPT,LANB)
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