Modal frequency response analysis

Hi sir,

I performed modal analysis and I got natural frequencies starting from 322 Hz and so on (pic is attached). And when I perform modal FRA I am getting peak values starting from 500Hz. But I should get the peak value at natural frequencies. I don't know what's going wrong

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Altair Forum User

That is because the applied load is resonant at that particular frequency.

Altair Forum User

What should I do to get peaks at natural frequencies?

Altair Forum User

If not 322Hz, it should have given me the peak near 322Hz....say 300Hz or 350Hz

Altair Forum User

Hi Mayur,

Can you share both input decks?

Altair Forum User

The files have been sent sir

Altair Forum User

Hi Mayur,

Thank you for sharing files. But it is taking long to run.

Can you check if there are any modelling issues at your end?

gopal_rathore

Hi,

For resonance to occur, the natural frequency should match with operating frequency and also the external load should be able to generate the same mode shape at that frequency. The load direction can create peaks at other frequencies as it might not be exciting the mode shape at lower frequencies

Thus, both frequency and mode shape needs to be checked.

Altair Forum User

Hi,

For resonance to occur, the natural frequency should match with operating frequency and also the external load should be able to generate the same mode shape at that frequency. The load direction can create peaks at other frequencies as it might not be exciting the mode shape at lower frequencies

Thus, both frequency and mode shape needs to be checked.

Yes, exactly. Since the model is an assembly, this could be due to modelling errors.

I would also suggest to use FREQ1 instead of FREQ and make sure that natural frequency falls in the calculation.