Frequency Response Results - Transient vs Sinusoidal

AM_20700
AM_20700 Altair Community Member
edited August 2022 in Community Q&A

I'm analyzing a vibrating system that operates at 15 Hz. The analysis is simulating a ramp up from 0 Hz to 15 Hz. There is resonance at 3 Hz. I'm specifically looking at the force through the upper crossbeams.

If I set a measure at the crossbeam RBE3 element central node, and animate the results in transient mode, I get a spike at 3 Hz with a value of 7072 N:

image

However, if I set the subcase load to 3 Hz and animate the results in sinusoidal mode, I get a max value of 6943 N.

image

What's going on?

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Answers

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited August 2022

    does it make any difference if you increase the step size in the animation of your sinusoidal result (in the 'gear' options for animation).

    Maybe some interpolation is not getting the right value, I guess.

     

    Results should match in both cases.

    Anyway, by looking at your FRF, it looks like you need to request more points in your FREQ1 card, as you're using 1Hz step right now.

    You would probably benefit a lot of using FREQ4 if this is a modal FRF, as it would go exactly into your current frequency.

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