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An eigenfrequency step will give you a list of all (or as many as you request) the natural frequencies of your system. You can then look at the deformed mode shape to see what displacement will be qualitatively. The normalization used in an eigenvalue problem is somewhat arbitrary. However, it is likely that the largest displacement will correspond to the lowest mode. Once you have performed an eigenfrequency step to find all potential modes, you must then perform a frequency domain step where you apply a load or displacement over a range of frequencies and measure the displacement. You don't have to sweep over a huge band once you've done the eigenfrequency, since you know where the resonant modes are; you might only have to sweep over a band of a few frequencies centered about the one you get from the eigenfrequency step.

Hi

I would just add that if you have no damping in the model, you might not manage to pass the resonance as the Q factor (or resonance finess might too steep for the solver. So consider adding some damping, even if this is a delicate value to estimate correctly

And note that with damping your response might well become complex so you must consider absolute value and angle (argument with arg() or an atan2(imag(),real()) check the doc/help )
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Good luck
Ivar

Hi Geoffrey Moss,

Thanks for your explanation. I am also working on the problem. I still have a question.
Do i define eigenfrequency step and frequency domain step in one study type or they should be in two different study types? Does really matter if frequency domain step is defined by eigenfrequency study step?

Hi Sarah,

Eigenfrequency and frequency domain analyses are different studies that are independent of each other. There is another study type though which is frequency domain modal. That one performs a frequency domain analysis based on the modal (eigenfrequency) solution. COMSOL has a predefined study type for this one that creates an eigenfrequency step and automatically links its output to the frequency domain step.

Nagi Elabbasi
Veryst Engineering

Sir, i am actually working on design of fbar. i needed to know how to find out the 3rd and the 4th harmonic frequency of the fbar designed

That needs an eigenfrequency analysis.

sir, how to proceed further? i have done eigenfrequency analysis for finding fundamental mode frequency.