How can rigid body modes be determined in a Natural Frequency (Modal) analysis in Simulation Mechanical?
Determine visually the first 6 modes are in fact rigid body motion. One way to determine is to output Normalized stress on the Analysis Parameter Output tab. In cases with rigid body motion there are no large stress values present. This along with viewing the animations of each mode lead and the low frequencies would me to believe which modes are rigid body modes.
For more on parameters for frequency analyses visit the following online help documentation.
Natural Frequency (Modal)
Although the results from a Natural Frequency (Modal) analysis include displacements, use these displacements only to visualize the mode shape. The magnitude of the displacements is relative to each other. The natural frequency is a theoretical result due to unspecified dynamic loads, so the results cannot contain absolute displacements.
After performing the modal analysis, perform a vibration analysis in which loads are applied to the model, and the displacement results will have a physical value.
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