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# Frequency Response Functions

## Frequency Response Functions

(OP)
Hello,

I was wondering if it is possible to change a mobility measured FRF to a receptance FRF so I can take advantage of the program I developed to recontruct receptance FRF with a rational fraction method. I thought maybe just simply dividing the Mobility matrix by iω?

Thank you

### RE: Frequency Response Functions

Y(w)=iw*recept(w) but is there not a 90deg out of phase tetaY = teta_receptance -90deg

### RE: Frequency Response Functions

Indeed it is. I'm not quite following the previous answer, but x=1/(j.w)*v

It's not a great way of getting spring rates near zero Hz, but for general NVH frequencies, if your experimental technique is adequate, you'll get useful results. If you want to know receptance near zero Hz, look at trends rather than where your data falls apart in the frequency spectrum, typically 3 Hz or so.

One of our aptitude tests for our technicians (not engineers) was to estimate the stiffness of a steel plate set into a concrete wall with a hammer test. I know the guy who set that test up, he had a weird sense of humour. Anyone who could get that had really been paying attention.

Cheers

Greg Locock

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