Modal truncation effects

To account for modal truncation effects in your solution, retain all modes that are within your lower-frequency and upper-frequency bounds. For more accuracy, retain up to twice the frequency of the upper bound.

Example:

If the frequency response analysis must be between 200 Hz (lower bound) and 2,000 Hz (upper bound), you should retain, at a minimum, all modes whose resonant frequencies are in this range. For better accuracy, however, you should retain all modes from 0 to at least 4,000 Hz.

If you do not retain enough computed modes for your frequency response range to account for modal truncation effects in your Nastran SOL 103 Real Eigenvalues solution, do one of the following:

• Set RESVINER to YES in the Solution Parameters dialog box. This adds the following setting to your structural solution:PARAM,RESVINER,YES

• In the Solution dialog box, on the Case Control page, click Create Modeling Object next to Residual Vectors. From the Inertia Relief Load list, select INRLOD. To check your selection, click Preview at the top of the Solution dialog box, and look for the following request: RESVEC(APPLOD,RVDOF,INRLOD,DAMPLOD,DYNRSP) = YES

Accounting for modal truncation effects creates additional modes in the Laminate Dynamics Details View subpanel. Similar to all other modes, you can choose to include or exclude them from the random solution. Because the laminate dynamics solver does not differentiate residual vector modes from regular flexible modes, both mode types participate dynamically in the response.

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Create a dynamic simulation

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Modal truncation effects, Simcenter 3D 2021.1 Series

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