## Resonance of mechanical structure

## Resonance of mechanical structure

(OP)

Hi

I am designing an electrical machine which has 3 cubical of size (30”x20”x10”) connected together side by side. Eaxh cubical has a fan for cooling.

I was told that I should find out the natural frequency of the structure so that it does not create resonance with the FAN frequency.

My question is:

Can any one tell me how the natural frequency of this type of structure is calculated and also if possible tell me material to read for my knowledge in this area.

Thanks in advance,

nkb

I am designing an electrical machine which has 3 cubical of size (30”x20”x10”) connected together side by side. Eaxh cubical has a fan for cooling.

I was told that I should find out the natural frequency of the structure so that it does not create resonance with the FAN frequency.

My question is:

Can any one tell me how the natural frequency of this type of structure is calculated and also if possible tell me material to read for my knowledge in this area.

Thanks in advance,

nkb

## RE: Resonance of mechanical structure

You might also want to predict the acoustic modes inside the enclosure.

If you're looking for software then EDS/SDRC/MTS I-DEAS will do all of the above.

## RE: Resonance of mechanical structure

Can u please tell me how to test the hardware using modal analysis.

Thanks once again.

Nkb

## RE: Resonance of mechanical structure

A tricky part is determining where to whack and where to monitor. You will want to try several combinations that you think will excite modes in the frequency range you are concerned about.

## RE: Resonance of mechanical structure

Step 2 - Excite the structure with an instrumented hammer or exciter at the minimum number of locations which excite all modes of interest.

Step 3 - Measure response, usually with an accelerometer at enough locations to describe the modeshapes over the frequency range of interest.

Step 4 - Measure at extra response locations to make your test model look like the test article.

Step 5 - Curve fit the frequency response funtions (frfs) between all excitation and response locations to provide a modal model of natural frequencies, modeshapes, damping, modal mass.

Step 6 - Synthesise frfs from modal model and compare with measured data to check accuracy of model.

Step 7 - If appropriate, perform correlation studies (frequency difference, modal assurance criteria, orthogonality) with FE model.

## RE: Resonance of mechanical structure

## RE: Resonance of mechanical structure

Regards,

NKB