Define rigid-body mode tolerance for Simcenter Nastran

The model or part of the model may be displaced without stress if it is not sufficiently constrained. These stress-free displacements are called rigid-body modes. If your model is unconstrained, the first six modes of your solution are the rigid-body modes.

You can define the frequency tolerance under which Simcenter Nastran considers a mode to be a rigid-body mode in its damping calculations. For example, if you define this tolerance value at 0.001 Hz, the modes generated up to this frequency are considered to be rigid-body modes and are excluded from damping calculations.

1. In the Solution dialog box (when creating or editing the SOL 103 – Response Dynamics solution), expand the SOL 103 – Response Dynamics group.

2. In the Rigid Body Modes Below box, enter the frequency below which Simcenter Nastran should consider modes to be rigid-body modes. The solve excludes these rigid-body modes from modal damping calculations. If you leave this value blank, the solver uses a value of 10-3 for the tolerance.

3. Click OK.

Note:

When you create your Response Dynamics solution process, you can also specify the rigid-body mode frequency for use in the response evaluations. This tolerance value overrides the solution-level tolerance value. See Create a Response Dynamics solution process for more information.

How do I

Define Response Dynamics result types

Define the frequency range and number of modes to solve

Filter out modes according to their modal effective mass fraction

Import results and event data from I-deas

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Defining the Simcenter Nastran solution

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Define rigid-body mode tolerance for Simcenter Nastran, Simcenter 3D 2021.1 Series

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