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[Sponsors] |
June 20, 2012, 10:34 |
code request
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#21 |
New Member
Join Date: Jun 2012
Posts: 7
Rep Power: 14 |
Hi everyone,
Can someone please send me the matlab code as well? - sjd1e11@soton.ac.uk. Many Thanks, Steven |
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August 21, 2012, 07:45 |
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#22 |
New Member
Martin Söder
Join Date: Jun 2011
Posts: 8
Rep Power: 15 |
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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November 1, 2012, 01:15 |
turbulence spectrum
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#23 |
New Member
Join Date: Nov 2012
Posts: 1
Rep Power: 0 |
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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November 2, 2012, 09:53 |
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#24 |
New Member
Kevii
Join Date: Nov 2012
Posts: 1
Rep Power: 0 |
wow aye
doing spectum always does my head in everytime :\ i suck at this T__T |
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February 8, 2013, 17:20 |
Autocorrelation Function help
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#25 |
New Member
Kealie Goodwin
Join Date: Feb 2013
Posts: 2
Rep Power: 0 |
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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February 9, 2013, 05:01 |
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#26 |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,882
Rep Power: 73 |
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. |
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February 12, 2013, 13:30 |
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#27 |
New Member
Kealie Goodwin
Join Date: Feb 2013
Posts: 2
Rep Power: 0 |
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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March 23, 2013, 22:54 |
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#28 |
Member
ehk
Join Date: Sep 2012
Posts: 30
Rep Power: 14 |
modes should change from -N/2:N/2.
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May 4, 2013, 13:30 |
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#29 |
Senior Member
Bobby
Join Date: Oct 2012
Location: Michigan
Posts: 454
Rep Power: 16 |
Dear FMDenaro
Thanks for sharing ur code. Last edited by babakflame; May 4, 2013 at 13:50. |
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May 28, 2013, 10:55 |
The code
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#30 |
New Member
martin lindström
Join Date: Apr 2013
Posts: 1
Rep Power: 0 |
Can you please send me the code as well? martinrjl@gmail.com
Thank you in advance! |
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June 20, 2013, 17:07 |
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#31 |
New Member
Join Date: Jun 2013
Posts: 10
Rep Power: 13 |
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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July 10, 2013, 17:07 |
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#32 |
New Member
Nik
Join Date: Jun 2013
Posts: 1
Rep Power: 0 |
Can you send me the matlab code as well please? Thank you very much. My email is nikthomar@gmail.com.
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September 6, 2013, 05:56 |
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#33 |
New Member
Terrence Nguyen
Join Date: Jan 2012
Posts: 13
Rep Power: 14 |
Can anyone also send me the matlab code for the energy spectrum calculation, please??
My email is: sonnyvo018@yahoo.de |
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September 6, 2013, 07:37 |
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#34 |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,882
Rep Power: 73 |
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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November 4, 2013, 13:17 |
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#35 |
New Member
Arne
Join Date: Oct 2013
Posts: 16
Rep Power: 13 |
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November 6, 2013, 17:32 |
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#36 |
Senior Member
cfdnewbie
Join Date: Mar 2010
Posts: 557
Rep Power: 20 |
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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December 4, 2013, 04:06 |
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#37 |
New Member
Christian
Join Date: Dec 2013
Posts: 1
Rep Power: 0 |
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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January 16, 2014, 08:51 |
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#38 |
Senior Member
S.Bogoda
Join Date: Jul 2012
Posts: 133
Rep Power: 14 |
Hi,
Could somebody pls send me the matlab code? sakurabogoda@gmail.com |
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March 24, 2014, 02:38 |
code for energy spectra
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#39 |
Senior Member
chandra shekhar pant
Join Date: Oct 2010
Posts: 220
Rep Power: 17 |
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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April 20, 2014, 22:40 |
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#40 | |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
Rep Power: 14 |
Quote:
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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Tags |
energy spectrum, fft |
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