What does damping mean in a modal analysis?

It depends on the type of modal analysis:

1. In a QRDAMP modal analysis, MP,DAMP is material dependent "beta" damping (K matrix multiplier.) [Ref: Table 5.6 of the Structural Analysis Guide.]

2. In an "undamped" Block Lanczos modal analysis [MODOPT,LANB], material dependent damping input [MP,DAMP] is interpreted as material dependent ratio to critical damping. This is done using the Modal Strain Energy technique.

Note 5 of Table 5.5 of the Structural Analysis Guide should be modified to read, "If specified, an effective damping ratio is calculated for subsequent spectrum and mode-superposition analysis." This value can be retrieved with *GET.

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