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PSD Analysis Question

PSD Analysis Question

PSD Analysis Question

(OP)
I'm performing a number of PSD runs on a structure with approximately 1 million DOF and between 0-2000 Hz it has 700 modes.  To cut back run time and .rst file size during the mode combination step I am specifying different values of for significance value (command is PSDCOM,SIGNIF,,) and I've noticed that a value of 0.001 and 0.01 for SIGNIF produces nearly identical one sigma displacements and stresses.  I think the SIGNIF command is based on covariance values normalized to 1 for the maximum mode if memory serves.  All modes with values equal or less than SIGNIF are not considered.  What I want to know is there a way to tell how many modes are actually being considered for each different SIGNIF value?  I didn't see anything mentioned about this in the output file.  Any help would be greatly appreciated.

Thanks in advance,
-Brian

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