clarification on damping broadening peak

[electricpete]

I came accross an old thread and wanted to make a small comment, but thread is closed:

Here is the thread

http://www.eng-tips.com/viewthread.cfm?qid=160351

It was stated:

Bear in mind that damping will broaden the peak as well as reducing its height, so increasing the damping can actually increase the response at a particular speed.

This seems incorrect to me, at least by study of a SDOF system: Here is an example (which I'm sure is nothing new to anyone here).

http://home.comcast.net/~electricpete/eng-tips/SDOF_VaryDamping.pdf

Increasing the damping does broaden the shape of the peak, but the amplification at any given frequency is lower as we increase damping, correct?


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[GregLocock]

You are right of course, for an SDOF system.

"so increasing the damping can actually increase the response at a particular speed."

was wrong, for your simple SDOF system.

BUT, there are many more complex systems where adding damping does increase the off-resonant response, eg increasing the damping levels in a shock absorber. You see the same in engine mounts, diff mounts and suspension bushes.

Nice catch.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[electricpete]

Thanks. That makes sense.

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[GregLocock]

In fcat thinking baout it it seems to depend on whether you have a base excitation system, or are looking at the transmissibility through a system.

So, in the case of a driveshaft, it might well be closer to yuor SDOF example.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.