Modal Setup

Modal Setup is available whenever running a modal based analysis such as Normal Modes, Prestress Normal Modes and Modal Transient.

To go to the Modal Setup, right-click on Modal Setup under your Subcase in the Autodesk Nastran In-CAD tree and select Edit.

• Name: Specifies name of modal setup.
• Number of Modes: The solver finds the specified number of natural frequencies and mode shapes.
• Lowest Frequency: Specifies the lowest frequency of a frequency range to be analyzed for natural frequencies and mode shapes.
• Highest Frequency: Specifies the highest frequency of a frequency range to be analyzed for natural frequencies and mode shapes.
• Extraction Method:
  • Auto: The program picks the best method based on the RAM directive setting (Parameters-Memory Management Directives) and model size.
  • Subspace Iteration: Selects the subspace eigensolver.
  • Lanczos Iteration: Selects the high performance PCGLSS block Lanczos eigensolver. This eigensolver is recommended for large problems and will generally be faster than the subspace eigensolver.
• Mass Representation:
  • Diagonal: Requests the generation of diagonal mass matrices. Diagonal, or lumped, mass matrices contain uncoupled, translational components of mass.
  • Coupled: Requests the generation of coupled mass matrices for elements with coupled mass capability. Coupled mass matrices contain translational components of mass with coupling between the components. This option may be more accurate than lumped diagonal mass.
  • Element Type Default: Will use the coupled mass formulation when rigid elements are specified in the model.
• Modal Database: Controls the storage and retrieval of modal data such as eigenvalues and eigenvectors used in dynamic response analysis. You have 4 options:
  • Delete: The default value will purge all modal data when the program terminates normally.
  • Store: The modal database is stored in a single file with the name you specify by selecting the browse option and a .MDB file extension.
  • Fetch: The database specified by the browse option is retrieved and the eigenvalue extraction phase is skipped.
  • Update: The modal database will be retrieved and stored.