Defining eigenvalue extraction data for Nastran analyses

In Nastran, you use the EIGR, EIGRL, and EIGC bulk data entries to define the data necessary to perform real or complex eigenvalue analysis. These bulk data entries let you control the numerical approach Nastran uses to solve for natural frequencies and modes shapes.

In Pre/Post, you can create Real Eigenvalue-Householder, Real Eigenvalue-Lanczos, and Complex Eigenvalue modeling objects to define eigenvalue data. The type of modeling object you need to create depends upon your selected solution type.

• For SOL 107 analyses, you must create a Complex Eigenvalue object.

• For SOL 111 and SOL 112 analyses, you must create either a Real Eigenvalue-Householder or Real Eigenvalue-Lanczos object.

• For SOL 110 analyses, you can create a Complex Eigenvalue object as well as a Real Eigenvalue-Householder or Real Eigenvalue-Lanczos object.

Defining real eigenvalue extraction data

Create a Real Eigenvalue-Lanczos or Real Eigenvalue-Householder modeling object to define the data needed to perform a real eigenvalue analysis with either the Lanczos or Householder method. This modeling object lets you specify a number of options, including the number of desired modes and the frequency range. When you solve or export your model:

• The options on the Real Eigenvalue-Lanczos dialog box define an EIGRL bulk data entry.

• The options on the Real Eigenvalue-Householder dialog box define an EIGR bulk data entry.

For more information see:

• Real Eigenvalue (Lanczos or Householder) dialog box

• Methods of Computation in the Simcenter Nastran Basic Dynamic Analysis User's Guide

Defining complex eigenvalue extraction data

In a Nastran SOL 107 (direct complex eigenvalue analysis) or SOL 110 (modal complex eigenvalue analysis) solution, you can create a Complex Eigenvalue modeling object to define the data necessary to perform complex eigenvalue analysis. You can use the Complex Eigenvalue dialog box to control options such as the complex eigenvalue extraction method as well as the desired number of modes. The options in the Complex Eigenvalue dialog box correspond to the fields in the EIGC bulk data entry.

For more information, see Complex Eigensolutions in the Simcenter Nastran Advanced Dynamic Analysis User's Guide.

Where do I find it?

• Choose Home tab→Properties group→Modeling Objects and then choose the appropriate eigenvalue extraction method object from the Type menu.

• Choose Insert→Modeling Objects and then choose the appropriate eigenvalue extraction method object from the Type menu.

How do I

Reduce response errors with residual vectors

Learn more

Dynamic analysis

Simcenter Nastran dynamics workflow

Specifying forcing frequencies for a frequency response analysis

Assigning frequencies from all loads to subcases

Limiting frequency response output to peak responses

Residual vector loads in a SOL 103 Real Eigenvalue solution

Quick links

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Pre/Post video examples

Bulk Entry Descriptions

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Defining eigenvalue extraction data for Nastran analyses, Simcenter 3D 2021.1 Series

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