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How to resolve error # 5408 while performing Modal Frequency Response Analysis?

Hello,

I am going through a Modal Frequency Response Analysis on a Crankshaft. The frequency range is 0 Hz - 1000 Hz for which I have used FREQi card image load collector. I have applied the load on the specific nodes of the crank pin using DAREA load type in the constraints panel. And I have also linked the load (with a table that I have created using TABLED1) using RLOAD2 card image load collector. And I have also input the frequency range i.e. 0 Hz as initial frequency, 1000 Hz as final frequency and 10 No. of mode shapes in EIGRL card image load collector. And finally, I created the loadstep for freq. resp. (modal) accordingly. But when I click on Optistruct Solver for results, an error #5408 occurs.

Messages for the job:

*** ERROR # 5408 ***
Aborting analysis because no structural modes have been
computed in the modal dynamic subcase 1.

*** PROGRAM STOPPED: FATAL ERROR(s) ENCOUNTERED.

How can I resolve this error and successfully achieve the results?

Thank You!

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Adriano Koga_20259

have you run a modal analysis upfront in your model?

What is your 1st mode frequency?

In EIGRL you have specified ND 10 modes, correct? what are the frequencies of these modes?

For running FRF modal, a rule of thumb is to use at least 1.5x the frequency of interest for normal modes extraction. If your interested in 1000Hz, then your EIGRL card should point to an upper range frequency of at least 1500Hz. This would ensure representativity of your modal space to run the FRF.

Try removing the ND 10 of your EIGRL and use upper bound of 1500...2000Hz instead.

Anees Sunesra

Thanks a lot for your reply!

So you mean that in the EIGRL card image I should input V0= 0 HZ and V1= 1500 Hz and keep ND blank right?