Frequency analysis software for structure borne noise
Frequency analysis software for structure borne noise
(OP)
I am looking for some data analysis software for calculating the structural mobility/impedance based on modal hammer and random vibration exciter measurements. Meaning I am going to collect a bunch of high frequency data with a bunch of high bandwidth accelerometers and I need some way to analyze impedance of the structure between 6 and 20 khz. I'm still working on the method of testing and I'm trying to determine how to analyze the data. I'm not looking for resonances, though I am looking for how well those frequencies are transmitted through the structure. If anyone has any suggestions on what software I should be using and how best to analyze the data I would appreciate it.





RE: Frequency analysis software for structure borne noise
However what you are trying to do thereafter is trickier and until you decide wat you are actually trying to do then it is hard to say, B&K and LMS probably have modules to do what you want, but again rolling your own might be worth it, for which I'd use Octave or Matlab.
The general field is called statistical energy analysis, and you are probably interested in structural intensity, which is directly analagous to acoustic intensity. The marvelous thing about intensity is that it tracks the flow of something human beings can't detect and don't care about.
Cheers
Greg Locock
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RE: Frequency analysis software for structure borne noise
Most of my experience is in injury analysis and dynamic/quasi static events. This whole vibration analysis is a bit new to me, thanks for the input. Another question kind of on topic, I've been exploring the FFT function averaging and overlap. I have no idea what is standard for frequency analysis at such high frequencies. Increasing the block size (points per fft) decreases the frequency step(bin size), though it "clutters" the plot. Is there a good average, standard resolution that is commonly used? Or do you go with what looks good.
RE: Frequency analysis software for structure borne noise
14 response channels and 1 input is well within the capabilities of any serious laptop based system, but the front end will obviously cost more than a 4 channel unit, I'd GUESS $2000 per channel.
"Another question kind of on topic, I've been exploring the FFT function averaging and overlap. I have no idea what is standard for frequency analysis at such high frequencies. "
There is no standard. Your frequencies aren't especially high, in the next office they work at 20 kHz all day. Many people will run 50% or 75% overlap, there is no penalty (but little advantage) in going to 99% except for calculation time.
"Increasing the block size (points per fft) decreases the frequency step(bin size), though it "clutters" the plot. Is there a good average, standard resolution that is commonly used? Or do you go with what looks good."
Typically 400 lines usable (ie 1024 samples/frame), or 800. But that very much depends on what you are trying to do, sometimes I use 16, other times 10240.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Frequency analysis software for structure borne noise
X(w)*2*pi*f*i V(w)
--------------- = -----
F(w) F(w)
Can I integrate the acceleration channel to velocity first and then use the fft of that to calculate mobility with a spectrum H0. H1 is standard FRF for noise at the output which is what I was using for my impact testing.
and if I wanted impedance I could choose F(w)/V(w) = Z(w)
Spectrum H0 DIAdem calculates the transfer frequency response by dividing the FFT of the output signal (A) by the input signal (E): FFT(A)/FFT(E). DIAdem averages the amplitudes of the individual transfer functions.
Spectrum H1 DIAdem specifies the cross spectrum and the auto spectrum for each signal pair. DIAdem calculates the transfer frequency response by dividing the averaged spectra: Middle(cross(A,E))/middle(auto(E)). DIAdem does not average phases, because phases can delete each other.
Spectrum H2 DIAdem specifies the cross spectrum and the auto spectrum for each signal pair. DIAdem calculates the transfer frequency response by dividing the averaged spectra: Middle(auto(A))/middle(cross(E,A))
RE: Frequency analysis software for structure borne noise
(X(w) * 9.807)/(2*Pi*f) gets me m/s
ht
page 57
RE: Frequency analysis software for structure borne noise
A->V is just a 1/(j*w) weighting, once you are in consistent units.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Frequency analysis software for structure borne noise
- Steve
RE: Frequency analysis software for structure borne noise
Walt
RE: Frequency analysis software for structure borne noise
it's not quit a hammer at all
http://www.pcb.com/spec_sheet.asp?model=086E80
I would never use it to hammer anything, it's so tiny.
Steve,
I have not gotten that far, and I hope to find a paper/primer/technote/website on conversions and correction factors. It seems like my math software can do it... it's just not in a black box function.
RE: Frequency analysis software for structure borne noise
If you haven't done a hammer survey before then you have a whole new skill to learn, and if you haven't done a high frequecy survey before then you will need to practice a lot.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Frequency analysis software for structure borne noise
Walt
RE: Frequency analysis software for structure borne noise
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Frequency analysis software for structure borne noise
Walt
RE: Frequency analysis software for structure borne noise
We are not looking for frequency modes of resonance. We need to induce some energy in the 6-20 kHz range and find the best path for those frequencies through the test article.
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RE: Frequency analysis software for structure borne noise
Once you have good coherence your next check is reciprocity, which helps to define if your system is linear. If you do not get good reciprocity then all may not be lost but you are outside my field of experience when it comes to analysis. There can be several reasons for poor reciprocity.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?