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How to calculate wavenumber while using fft?

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Old   June 23, 2019, 08:09
Default How to calculate wavenumber while using fft?
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I have 192 grids of two point correlation data of a 3.14(m) length domain.
I use the "fft" command in matlab to plot the energy spectrum. How can I calculate wavenumber(k) of each grid?
Code:
R= load('2pcor.txt');
 PHI = fft(R); 

% K=?? ; 

%loglog(K,abs(PHI));
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Old   June 23, 2019, 12:12
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Quote:
Originally Posted by KevinSpears View Post
I have 192 grids of two point correlation data of a 3.14(m) length domain.
I use the "fft" command in matlab to plot the energy spectrum. How can I calculate wavenumber(k) of each grid?
Code:
R= load('2pcor.txt');
 PHI = fft(R); 

% K=?? ; 

%loglog(K,abs(PHI));



On your grid of Nx=192 nodes you have 192/2=96 resolvable wavenumbers. Each wavelength is k=n*2*pi/L. Thus, if you L is exactly pi (in meters) you have k=2*n. The maximum in your range is the Nyquist frequency pi/h=pi/(L/Nx)=Nx
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Last edited by FMDenaro; June 23, 2019 at 16:16.
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