Re: Modal Analysis!!!!

Dear Friend,

I disagree with your explanations about Modal Analysis.

What you are talking about is a Harmonic Analysis and not Modal Analysis.

Modal Analysis does not involve any forcing function. It is just the calculation of system natural frequencies. The modal analysis results give the mode shapes which are associated with the particular frequency (see the name, Modal analysis which means calculation of modes, and a mode is only linked with the mass distribution in the system, it is independent of external force). The results does not give the displacement in absolute value, but its the relative displacement. Say, the maximum displaced node is assumed to be 100% and then relative to this, displacement of all the other nodes are calculated. Since there are no external forces involved, it does not indicate the resonance condition. In modal analysis only the mass of the system is taken into consideration.

In Harmonic Analysis, there is a periodic (sinusoidal) forcing function (e.g. unbalance in rotating equipment) involved and we have to calculate the natural frequencies of the system to evaluate the system response, which is often given in terms of node displacements. And here, the displacements are the absolute displacement of the node. We check for resonance in this type of analysis What you are talking about is this type of analysis.

Regards,
Kaustubh Received on Tue Jul 30 00:56:00 2002