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Random Response Analysis Incorrect PSD Output

Random Response Analysis Incorrect PSD Output

Random Response Analysis Incorrect PSD Output

(OP)
Dear all,

I am using Femap as pre/post-processor and MSC Nastran as solver for a random response analysis to study PSD response at certain locations.

However, the PSD response results on certain areas seem to be incorrect/unrealistic.

The whole response output spectrum is lower then input spectrum by an order of magnitude at certain node locations. I have tried this on the Femap default random response example (hingemodel), I can re-create the result given in documentation (on Node 44), however if in the same model I post process some other nodes, I get the same issue in PSD response output. I have attached the result plots for readers to look clearly.

(Please note, the discrepancy due to acceleration unit and output (use of scale factor), I have already take care of it, so that is not the issue).

I have uploaded the result. Anyone who has done Femap example can see the result on Node 44 is as given in the documentation. Node 289 is the input one, which is also correct. Additionally I am post-processing two other node locations (Node 130 and 118) and you can clearly see that they have the same behavior but they are lower than the input by orders of magnitude!. There is something wrong. I have tried different models and methods and I get the same result.

Does anyone have similar experience or any experience person can guide me what can actually be going wrong?

I'll be thankful, because I am quite stuck at this in work. Thanks in advance.

Umer

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