Effective Mass from Vibration Plot?

[sarclee]

Hi, can we identify which mode is significant (higher effective mass) from the sine sweep vibration plot?

 

[GregLocock]

Can't really tell from that, if it was a transfer function then the dotted line is the estimated accelerance (inverse of mass) if that is the driving point response. There's a lot of ifs buts and whens in that statement.

Obviously the pair of modes at 150 Hz are the ones of interest, probably some subsystem is acting as a vibration absorber. But you need proper data first (transfer function, with phase) not response rubbish, and more than one accelerometer.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[sarclee]

@GregLocock, do you mean to get the transfer functions with phase from the testing?

 

[GregLocock]

Yes, unless you know the excitation was a constant pk-pk force. If it was then you model the modes using any of the known techniques and that'll tell you which has the biggest modal mass, /at that excitation point/. It's the first one in this case obviously at 150 Hz, and it looks as though you might have a split peak due to a subsystem acting as a harmonic damper. That's probably an unwise amount of info to extract from an amplitude plot, a hammer test survey is much better for establishing modal mass (of which I've seen at least 4 definitions).

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?