EIGVSAVE

Subcase Information Entry The EIGVSAVE command can be used to output eigenvalue and eigenvector results of a Normal Modes, Modal Frequency Response, or Modal Transient Analysis run to an external data file (.eigv).

Format

EIGVSAVE = integer

Definitions

Argument Options Description
integer <integer>

No default

 Outputs eigenvalues and eigenvectors obtained from a Normal Modes, Modal Frequency Response, or Modal Transient Analysis run to an external data file.

The external eigenvalue data file name is of the form:

<prefix>.#.eigv

Where,
<prefix>
Is defined by the EIGVNAME I/O Options Entry.
#
The integer argument defined. 4

Comments

  1. Only one occurrence of EIGVSAVE per subcase is permitted.
  2. If EIGVSAVE is not present, eigenvalue and eigenvector results do not get exported to an external data file.
  3. EIGVSAVE is not supported for fluid elements.
  4. The integer argument specified here is used as part of the name of the .eigv file as:

    In an input file named testfile.fem, if EIGVSAVE=50 is specified, without EIGVNAME entry, then the eigenvalue and eigenvector results are exported to the testfile.50.eigv file. You can see that the input file name is used as the default file name for the .eigv file when the EIGVNAME entry is not specified.

  5. In the case of an EIGVRETRIEVE run with Modal Frequency Response or Modal Transient Analysis:
    • If partial-model eigenvectors are saved via EIGVSAVE, then EIGVRETRIEVE can be used only with AMSES (EIGRA) and AMLS eigen solvers.
    • If full-model eigenvectors are saved via EIGVSAVE, then EIGVRETRIEVE can be used with Lanczos (EIGRL), AMSES (EIGRA), and AMLS eigen solvers.
  6. There are several scenarios under which EIGSAVE and EIGVRETRIEVE can be used for Modal Frequency Response and Modal Transient Analysis. Recommended approaches for two of the most common use cases are as follows:
    1. Save partial model eigenvectors in .eigv file: Saving eigenvectors only for a partial set of degrees of freedom in the .eigv file during the EIGVSAVE run can help improve performance. This approach is feasible if you need to request output for only these partial degrees of freedom (or a subset of them) in the EIGVRETRIEVE run.
      • Currently the only approach for saving eigenvectors for partial degrees of freedom in the EIGVSAVE run is by using AMSES and DISP=SET (where SET represents the degrees of freedom for which eigenvectors need to be saved in the *.eigv file).
      • The type of EIGVSAVE analysis depends on how RESVEC generation is handled, which in turn depends on the type of loading that will be used during the EIGVRETRIEVE run. AMSES can still be used in EIGVRETRIEVE run. For instance:
        • If FORCE load is applied in EIGVRETRIEVE run, the EIGVSAVE run is recommended to be a Normal Modes analysis. RESVEC=YES can be defined along with USET consisting of the corresponding FORCE dofs. This saves the unit-load RESVECs in the *.eigv file.
          Note: An alternative approach is to have the EIGVSAVE run be a full setup Modal FRF/Transient analysis with the corresponding FORCE loads applied. However, this involves additional runtime when compared to the recommended normal modes EIGVSAVE run).
        • If SPCD load is applied in EIGVRETRIEVE run, the EIGVSAVE run should be a full setup Modal Frequency Response or Modal Transient analysis (similar to the EIGVRETRIEVE run). The unit-displacement RESVECs required for SPCD load in EIGVRETRIEVE run can only be calculated by a EIGVSAVE run with full-setup Modal Frequency or Modal Transient analysis (instead of a Normal Modes analysis, which only can generate unit-load RESVECs). In the EIGVRETREIVE run with SPCD, retain the SPCDs on all EIGVSAVE SPCD dofs. Otherwise, the modal space will change and the EIGVSAVE modal space cannot be used for this EIGVRETRIEVE run). However, you can change the applied SPCD constraint value on these dofs to a different value or set them to zero.
        • If distributed static loads via PLOADi/GRAV/RFORCE are applied in EIGVRETREIVE run, the partial eigenvectors option is not allowed. In this case, refer to the next use case.
    2. Save full model eigenvectors in .eigv file: Saving eigenvectors for a full set of degrees of freedom in the .eigv file during the EIGVSAVE may require more runtime than requesting a partial set of eigenvectors. However, it may be required as part of the application use case or selected loading. With this approach, you can request output for all degrees of freedom in the EIGVRETRIEVE run.
      • The recommended approach for saving eigenvectors for full degrees of freedom in the EIGVSAVE run is by using AMSES and DISP=ALL (wherein all eigenvectors are saved in the *.eigv file).
        Note: An alternative approach is to use Lanczos in EIGVSAVE run to save the full eigenvectors set, but using AMSES may provide better performance.
      • Since the full set of eigenvectors are saved in the *.eigv file during EIGVSAVE run, the recommended simple approach is to use Lanczos for the EIGVRETRIEVE run. This way, RESVECs are recalculated in the EIGVRETRIEVE run and do not need to be included in the *.eigv file during EIGVSAVE run. This also works consistently for any type of loading in EIGVRETRIEVE run (FORCE, SPCD, or distributed loading via PLOADi/GRAV/RFORCE).