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Old   June 20, 2012, 09:34
Default code request
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Hi everyone,

Can someone please send me the matlab code as well? - sjd1e11@soton.ac.uk.

Many Thanks,

Steven
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Old   August 21, 2012, 06:45
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Martin Söder
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Hi,
I would also be interested in the code, and would be very thankful if I could get it
martins@mech.kth.se

/Martin
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Old   November 1, 2012, 01:15
Default turbulence spectrum
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hi,

i'm doing my undergrad final year prjct on simulation of atmospheric boundary layer in wind tunnel.....have to measure wind profile, turbulence intensities and turbulence spectrum....

can anybody help with the turbulence spectrum....what i need to measure...how to get the plot?

thank you in advance
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Old   November 2, 2012, 09:53
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wow aye
doing spectum always does my head in everytime :\
i suck at this T__T
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Old   February 8, 2013, 17:20
Default Autocorrelation Function help
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Kealie Goodwin
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I am also trying to compute the turbulence energy spectrum for some velocity data I have.

My data are taken with a profiling ADV so I have u, v, w velocities for 12 points along a depth profile. These data are collected over time, which is used for a x-space proxy.

In short, I have u, v, w velocity data spatially distributed across x and z dimensions (only one point in y-direction). So, 3 matrices that are 1501 (x) by 12 (z), one each for u, v, w.

I understand all the steps of calculating the energy spectrum. My only problem is that I'm not sure I completely understand the autocorrelation step in Pope, especially with respect to my data.

R_ij(r, x) = <u_i(x) u_j(x+r)>
The <> notation is an average, correct? What does this mean for a scalar? Or is this the dot product notation? Again what does this mean for a scalar?

If anyone has any matlab code for this portion that they are willing to share, it would be helpful.

Thanks!
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Old   February 9, 2013, 05:01
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Filippo Maria Denaro
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just consider a 3d Cartesian mesh and (j,k) some fixed positions. This is some lines of my Matlab code for the energy spectrum

% ____________ E_uu (stream-wise)______________
% ff is a dump array for using the FFT of the field u(i,j,k)
for i = 1:np+1, ff(i) = u(i,j,k); end
% Discrete transform: computation of the Fourier coefficient
c=fft(ff,np); for q = 1:np, c(q)=c(q)/np; end
% Computation of the modulus squared. Cycle for all the wavenumbers
for q=1:np, cu(q,k)=c(q)*conj(c(q)); end

Then, you must simply plot your power spectrum.
Generally, the computed spectrum are also computed along the whole homogeneous directions (e.g. for all the k) and then averaged to have a statistically meaning.
mgg, GiulioS and smog like this.
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Old   February 12, 2013, 13:30
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Kealie Goodwin
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Thank you for your code, FMDenaro. However, it's difficult for me to understand your process without your data. Does anyone have the math formulas they used for the autocorrelation? Again, the steps I'm using are:
1. Calculate autocorrelation to get signal into wave number space
2. Take fft
3. Calculate energy
E(k) = E(k) + abs(V(i,j,m))^2 + abs(U(i,j,m))^2 + abs(W(i,j,m))^2;
4. plot energy vs wave number
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Old   March 23, 2013, 22:54
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modes should change from -N/2:N/2.
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Old   May 4, 2013, 12:30
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Bobi
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Dear FMDenaro

Thanks for sharing ur code.

Last edited by babakflame; May 4, 2013 at 12:50.
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Old   May 28, 2013, 09:55
Default The code
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martin lindström
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Can you please send me the code as well? martinrjl@gmail.com
Thank you in advance!
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Old   June 20, 2013, 16:07
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If somebody can share the code for energy spectrum calculation I would greatly appreciate that. My email is: alexbn024@gmail.com
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Old   July 10, 2013, 16:07
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Can you send me the matlab code as well please? Thank you very much. My email is nikthomar@gmail.com.
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Old   September 6, 2013, 04:56
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Terrence Nguyen
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Can anyone also send me the matlab code for the energy spectrum calculation, please??
My email is: sonnyvo018@yahoo.de
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Old   September 6, 2013, 06:37
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Filippo Maria Denaro
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there is nothing else to do that loading the data in matlab, calling the built-in FFT and plotting the modulus of the Fourier coefficients versus the frequencies
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Old   November 4, 2013, 13:17
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Arne Eggers
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Hey

could someone please send me the code.
my email adress : arne-eggers@web.de


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Old   November 6, 2013, 17:32
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The question has been answered in the posts above by FMDenaro, including the code! It is 3 lines in Matlab, that should be doable...
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Old   December 4, 2013, 04:06
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Christian
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Hi Everyone,

I am currently trying to perform a problem similar to this one except with a different geometry. Could someone please forward me the matlab code harish sent? My email is combustion.spot@gmail.com

Thank you in advance
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Old   January 16, 2014, 08:51
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S.Bogoda
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Hi,
Could somebody pls send me the matlab code? sakurabogoda@gmail.com
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Old   March 24, 2014, 02:38
Default code for energy spectra
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chandra shekhar pant
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Can anyone send the code for energy spectra to me also. chandukec@gmail.com
It will be a great help. Thanks in advance
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Old   April 20, 2014, 21:40
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Huang Xianbei
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Quote:
Originally Posted by FMDenaro View Post
just consider a 3d Cartesian mesh and (j,k) some fixed positions. This is some lines of my Matlab code for the energy spectrum

% ____________ E_uu (stream-wise)______________
% ff is a dump array for using the FFT of the field u(i,j,k)
for i = 1:np+1, ff(i) = u(i,j,k); end
% Discrete transform: computation of the Fourier coefficient
c=fft(ff,np); for q = 1:np, c(q)=c(q)/np; end
% Computation of the modulus squared. Cycle for all the wavenumbers
for q=1:np, cu(q,k)=c(q)*conj(c(q)); end

Then, you must simply plot your power spectrum.
Generally, the computed spectrum are also computed along the whole homogeneous directions (e.g. for all the k) and then averaged to have a statistically meaning.
Hi,Filippo
I think the third line should be: cu(q)=c(q)*conj(c(q))
As known, the velocity spectrum tensor is
phi[i,j](k)=cu(k),the energy spectrum is integrated to
E(k)=1/2*cu(k)*dS(k)
where S(k) is the sphere's surface area with radius mag(k)
is this means to calculate E(k)=1/2*cu(k)*4*pi*k^2?
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