Sufficient Modes for Random Vibration?

[Lee.Conti]

Hi,

I ran a modal analysis that the Ratio of Eff. Mass to Total Mass exceeds 0.80. However, the max frequency at n-Mode is lower than the maximum frequency of the Random Vibration Profile. For instance, the max frequency at n-mode is 200Hz but the vibration profile for Random Vibration is up to 500Hz. Do I need to run more modes in Modal analysis?

 

[GregLocock]

Yup, although it is a rather optimistic idea that an FEA modal has much specific meaning at 500 hz. You get some sort of modal density and an avergae impedance, but specific mode shapes and frequencies are unlikely to correlate with reality.

Cheers

Greg Locock


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