Frequency Domain, Modal
The Frequency Domain, Modal () study and study step are used, for example, to compute the response of a linear or linearized structural mechanics model subjected to harmonic excitation for one or several frequencies.
The Frequency, Domain Modal study consists of two study steps: an Eigenfrequency study step for computing the eigenfrequencies and eigenmodes of the structure followed by a second Frequency Domain, Modal study step for computing the modal response. In the mode superposition analysis, the deformation of the structure is represented by a linear combination of the structure’s eigenmodes. This means that the frequencies to be studied are limited by the frequencies of the computed eigenmodes. A Frequency, Domain Modal study usually results in a faster computation than a direct solution using the Frequency Domain study.
The following sections describe the settings for the Frequency, Domain Modal study step. See Eigenfrequency for information about the settings for the Eigenfrequency study step.
The Frequency, Domain Modal study step node corresponds to a modal frequency sweep for systems with frequency-based loads. It gives a Modal Solver.
The Include geometric nonlinearity check box and Mesh Selection are described in Common Study Step Settings. There is also detailed information in the Physics and Variables Selection and Values of Dependent Variables sections.
Study Settings
Specify the frequencies to use for the frequency sweep. Select the unit to use from the Frequency unit list (default: Hz). Enter the frequencies in the Frequencies field using space-separated numbers or the range function.
Use the Load parameter values field to select a file with parameter values. Click the Browse button () to browse the file system. You can also click the downward arrow beside the Browse button and choose Browse From () to open the fullscreen Select File window. Click the downward arrow for the File Location Actions menu () to choose Show in Auxiliary Data () to move to the row for this file in the Auxiliary Data window, Copy File Location (), and (if you have copied a file location) Paste File Location (). After selecting a file, click the Read File () button to load the parameter values into the Frequencies field.
Use the Parameter list type list to control how to interpret the parameter values entered in the Parameter values field. Select:
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Frequency (the default setting) to use the parameter values without modification.
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Fraction to multiply the parameter values by the absolute value of the largest eigenvalue in the reduced model divided by two.
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Spread to treat the parameter values as an interval around each eigenvalue in the reduced model. That is, the absolute value of each eigenvalue is multiplied by the parameter values and the resulting parameter value vectors are concatenated into one.
For information about the Reuse solution from previous step list, see Reuse Solution from Previous Step List.
With the Structural Mechanics Module, see Various Analyses of an Elbow Bracket, Application Library path Structural_Mechanics_Module/Tutorials/elbow_bracket.