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 list (default: Hz). Enter the frequencies in the field using space-separated numbers or the range function.

Use the field to select a file with parameter values. Click the button (

) to browse the file system. You can also click the downward arrow beside the button and choose (

) to open the fullscreen window. Click the downward arrow for the menu (

) to choose (

) to move to the row for this file in the window, (

) (if the location is a database), (

), and (if you have copied a file location) (

). After selecting a file, click the (

) button to load the parameter values into the field.

Use the list to control how to interpret the parameter values entered in the field. Select:

•

(the default setting) to use the parameter values without modification.

•

to multiply the parameter values by the absolute value of the largest eigenvalue in the reduced model divided by two.

•

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 list, see Reuse Solution from Previous Step List.

Values of Linearization Point

Use the settings under to specify a linearization point.

From the list, choose (the default) to use linearization point settings controlled by the physics interfaces. Choose to specify the linearization point using the list. Select:

•

to use the expressions specified on the nodes under a specific physics interface as a linearization point.

•

to use a solution as a linearization point.

Use the list to specify which solution to use from the available studies. Select:

•

to use a linearization point that is identically equal to zero.

•

Any other available solution to use it as a linearization point. It can be the current solution in the sequence, or a solution from another sequence, or a solution that was stored with the Solution Store node. You select a stored solution by changing to the name of the stored solution. Choose a solution using the list (see under Common Study Step Settings).


	With the Structural Mechanics Module, see Various Analyses of an Elbow Bracket, Application Library path Structural_Mechanics_Module/Tutorials/elbow_bracket.