Product: Abaqus/Standard
Benefits: In transient modal dynamic analyses, you can use undamped rigid body and/or undamped low frequency eigenmodes, even if damping is specified in the model or within the procedure. You can also exclude damping being applied; for example, damping can be excluded for eigenmodes extracted for secondary base motions due to the use of the big mass approach.
Description: A low frequency cutoff value can now be specified to control damping of the low frequency eigenmodes in transient modal analyses. This control is useful for free structures and models with secondary base motions, and it controls all sources of damping including the modal damping. To include low frequency eigenmodes, set the low frequency cutoff value to a small negative value. To exclude them, either provide a low frequency cutoff value or allow Abaqus to calculate it; it will be six orders of magnitude smaller than the eigenfrequency of the first deformable eigenmode.
References: