system identification
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For a second order differential equation of a mechanical system m*(xdbldot) + c*(xdot)+k*(x)=F1*t)+F2*exp(i*2*omega*t) the unknown parameters 'c' which represents system damping and F1 and F2 which represent forcing functions need to be estimated. I have vibration signature in frequency domain to be used for input. How do i use system identification in Matlab for the same ?
Thanks, Sumit.
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Rajiv Singh
on 28 Mar 2012
By vibration signature, do you mean the frequency responses from the two inputs to the output? Are F1 and F2 constants? Is the system of equations complex (you show exp(i*2*omega*t) which is a complex number)?
Given frequency response measurements, there are various functions that can produce a model that fit the measured response - n4sid, oe, pem, and in R2012a, also tfest, procest, ssest. For structured estimation, you can also use grey box modeling techniques (idgrey/pem in R2011b or earlier, greyest in R2012a), but for simple systems like yours (unless I missed something; see questions above), functions like OE and PEM can deliver the results, provided you do have the right data.
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Rajiv Singh
on 1 Apr 2012
So what type of data do you have? It is FFT of complex time-domain input and output measurements (possibly complex)? If so, the standard identification methods that I mentioned before still apply. You can package the data as iddata object with domain = frequency. You will need to generate FFT values for a frequency range that is symmetric around origin. The result of estimation will be a complex model.
Perhaps you could post some example data to put the discussions to more concrete terms?
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