Specifying forcing frequencies for a frequency response analysis

Frequency response analysis is a method that you can use to compute the response of a structure to steady-state oscillatory excitation, such as in rotating machinery, unbalanced tires, or helicopter blades. In Nastran, you use:

• SOL 108 to perform a direct frequency response analysis.

• SOL 111 to perform a modal frequency response analysis.

In a frequency response analysis, the excitation is explicitly defined in the frequency domain. All the applied forces are known at each forcing frequency. You must specify the frequencies at which Nastran performs the analysis.

In Pre/Post, you create a Forcing Frequencies or Forcing Frequencies-Modal modeling object to specify the list of forcing frequencies to be solved in frequency response problems (SOL 108 and SOL 111). This modeling object lets you specify options such as the starting frequency, the increment between frequencies, and the number of increments. You can also create a Forcing Frequencies modeling object from a Peakout Frequencies Plots scenario.

When you solve or export your model, the options on the Forcing Frequencies or Forcing Frequencies-Modal dialog boxes define a FREQUENCY case control command and FREQ, FREQ1, FREQ2, FREQ3, FREQ4, or FREQ5 bulk data entries, depending upon the options you choose.

For more information, see:

• Forcing Frequencies dialog box (Nastran)

• Overview of Frequency Response Analysis in the Simcenter Nastran Basic Dynamic Analysis User’s Guide

• Solution Frequencies in the Simcenter Nastran Basic Dynamic Analysis User’s Guide

• Peakout Frequencies Plots scenario

Where do I find it?

Creating modeling objects

Application	Pre/Post
Prerequisite	A Simulation file as the work part and displayed partMSC Nastran as the specified solverStructural as the specified analysis typeSOL 108 Direct Frequency Response or SOL 111 Modal Frequency Response as the specified solution typeSimcenter Nastran as the specified solverStructural, Acoustic, or Vibro-Acoustic as the specified analysis typeSOL 108 Acoustic Transfer Vector, SOL 108 Direct Frequency Response, or SOL 111 Modal Frequency Response as the specified solution typeSimcenter 3D Acoustics BEM as the specified solverDirect Acoustic, Indirect Acoustic, or Indirect Vibro-Acoustic as the specified analysis type
Simulation Navigator	Right-click the Modeling Objects node→Modeling Objects
Command Finder	Modeling Objects
Location in dialog box	Modeling Objects Manager dialog box→Type list

Creating a Peakout Frequencies Plots scenario

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSupported results
Command Finder	Scenario Setup (Results tab)

How do I

Reduce response errors with residual vectors

Learn more

Dynamic analysis

Simcenter Nastran dynamics workflow

Assigning frequencies from all loads to subcases

Limiting frequency response output to peak responses

Defining eigenvalue extraction data for Nastran analyses

Residual vector loads in a SOL 103 Real Eigenvalue solution

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

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Specifying forcing frequencies for a frequency response analysis, Simcenter 3D 2021.1 Series

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