FRF plot on acceleration data

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Gorg
Gorg 2015-11-23
编辑： Justine Nyakundi 2017-7-18
Hi all, I have a range of acceleration reading output at every 0.02s and would like to get a Frequency Response Function plot. Any body can help with the suitable code in Matlab? Thanks

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回答（2 个）

Star Strider
Star Strider 2015-11-23
If you know the input of the system as a function of time as well, and the data for both the input and output were collected over the same time interval at the same sampling times, you can calculate the frequency response function as:
FRF = fft(output)./fft(input);
See the documentation on fft for details.
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Gorg
Gorg 2015-11-23
Thank you for your prompt reply. There is a free vibration test in which an applied load is suddenly released. Therefore, there is no input towards the actual readings for acceleration output. What is your suggestion now? Thanks
Star Strider
Star Strider 2015-11-23
My pleasure.
That corresponds to a step response, so I would just use the fft of the output.
Also, the fft documentation I linked to in my original Answer is to the R2015a version, and easier to understand and use than the current version of the documentation.

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Justine Nyakundi
Justine Nyakundi 2017-7-18
编辑：Justine Nyakundi 2017-7-18
depends on your application. But personally I have used Gaussian white noise with a mean of zero to find FRF. But really it depends on what you gonna use the FRF for, and if you know what causes the acceleration, in my case it was random excitation of a beam. there is a MATLAB function for that just check wgn on help

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