Frequency response functions

  • Thread starter arpwpagr
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  • #1
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Main Question or Discussion Point

Hi all,
I have input force data and output acceleration data to calculate frequency response functions. As these data are in time domain I converted it to frequency domain using fft function in MATLAB. This is the procedure I used.
As an example Let's think, Force matrix =a
Acceleration matrix= b
c=fft2(a)./fft(b);
d=real(c);
There are 24 sensors in the system and I used all data once by using a matrix. I am not sure whether this is correct or not. Should I use one data at once or matrix is correct. Can anyone help me? It is a great help for me.
Thank you!!!
 

Answers and Replies

  • #2
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Since you have the input and output relationship in the frequency domain, I think you would be better off leaving the matrices alone and leaving them a lookup table to interpolate with.

Or you could divide the two expressions given and pass your values through the resulting expression.

What you are doing is conceptually wrong.
 
  • #3
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I have input and output values in the time domain and I want to convert it to frequency domain to find frequency response functions. Then I used fft function in MATLAB to do that. I have 8192 data points from 24 locations which means dimension of acceleration matrix is 8192*24 and force matrix is 8192*1.
I used this formula
The basic formula for a frequency response function is
H(f)=Y(f)/X(f)

Where H(f) is the frequency response function.

And Y(f) is the output of the system in the frequency domain.

And where X(f) is the input to the system in the frequency domain.
 
  • #4
272
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Ok yes I take back what I said earlier, reviewing the equations that operation does give you the frequency response of your system. I was thinking you were doing matrix division not a scalar division (missed the dot next to the division sign " ./ " ).
 

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