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April 20, 2014, 23:58 |
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#41 | |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
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Quote:
Sorry for the second reply.I followed your advice, here is my code in matlab Code:
clear all; [x y z Ux Uy Uz]=textread('U_constantPlane.raw','%f%f%f%f%f%f','headerlines',2); N=32768; Lz=6.28; kz=(2*pi*(1:256)/Lz); kzz=round(kz); w=reshape(Uz,256,128); wk=fft(w); for i = 1:256, for j=1:128, wk(i,j)=wk(i,j)/N; end end for i = 1:256, for j=1:128, R(i,j,kzz)=wk(i,j)*conj(wk(i,j)); end end for j=1:128, E(kzz)=0.5.*R(j,j,kzz(j))*4*pi.*kzz(j)^2; end plot(kzz,E(kzz)) |
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April 21, 2014, 04:17 |
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#42 | |
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Filippo Maria Denaro
Join Date: Jul 2010
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Quote:
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April 21, 2014, 04:33 |
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#43 | |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
Rep Power: 14 |
Quote:
Thank you for your reply, could you please have a look at my previous reply for the code? Also, I tried another case which only contains 1 line of velocity in z direction.The result is still incorrect Code:
clear all; [z Ux Uy Uz]=textread('Zleft_U.xy','%f%f%f%f'); N=128; Lz=6.28; kz=(1:N)*2*pi/Lz; k=round(kz); c=fft(Uz,128); for q = 1:N, c(q)=c(q)/N; end for q=1:N, cu(q)=c(q)*conj(c(q)); end %up to now, the velocity-spectrum is obtained,however, the q~=k, %how to match them? for q=1:N, E(k)=0.5*cu(q)*4*pi*k.^2; end plot(k,E(k)) |
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April 21, 2014, 05:13 |
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#44 |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
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April 21, 2014, 05:18 |
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#45 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,865
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Quote:
w=reshape(Uz,256,128); wk=fft(w) this way, w is a matrix??? |
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April 21, 2014, 05:31 |
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#46 |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
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yes,because z values are ranged in a periodic way(256 values one loop), so 32768 values corresponding to 128 loops, representing the whole value on a plane. Is this resonable?
I'm now confused about the wavanumber k, is this write as: (1:N)*2*pi/Lz each one is connected to a cu value in order? |
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April 21, 2014, 05:40 |
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#47 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,865
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Quote:
Anyway, I suggest checking for a simple test: generate a sin(k*x) function (try for some k value) and store in a vector, after doing the fft plot the spectrum and check if the energy density is located at the right frequency |
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April 21, 2014, 05:56 |
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#48 | |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
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Quote:
what's definition formula of k? 2*pi*n/Lz? Best reguards |
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April 26, 2014, 10:00 |
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#49 |
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Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
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April 29, 2014, 16:40 |
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#50 |
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Amjad
Join Date: May 2012
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April 29, 2014, 22:42 |
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#51 | |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
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Quote:
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July 8, 2014, 02:10 |
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#52 |
Member
SHEIKH NASIRUDDIN
Join Date: Aug 2013
Location: DELHI
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Dear Harishg,
I 'm also facing the same problem and want to plot energy spectra using matlab. Can you send me the code you have used. My e-mail is:nasir.iitd@gmail.com Your help is highly appreciated. nasiruddin. |
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October 27, 2014, 20:42 |
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#53 |
New Member
Purvi
Join Date: Oct 2014
Posts: 4
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Can I get the code for energy spectrum?
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October 27, 2014, 21:08 |
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#54 | |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
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Quote:
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October 27, 2014, 21:08 |
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#55 |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
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October 27, 2014, 21:30 |
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#56 |
New Member
Purvi
Join Date: Oct 2014
Posts: 4
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Yes, that will be great and if you can send me understanding of it too!!!
Thanks Purvi my email address is : p3vdim@yahoo.co.in |
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October 28, 2014, 00:53 |
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#57 | |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
Rep Power: 14 |
Quote:
I have sent you the code. The explaination is not so much for the limited time, hoping this can help you. Xianbei |
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October 28, 2014, 05:34 |
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#58 |
Senior Member
chandra shekhar pant
Join Date: Oct 2010
Posts: 220
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Please send it to me also ..
chandukec@gmail.com |
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October 29, 2014, 15:33 |
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#59 |
New Member
Join Date: Nov 2013
Posts: 3
Rep Power: 13 |
Would you mind sending me the code as well? bmeyer907@gmail.com
Thx in advance! |
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October 29, 2014, 18:55 |
Energy spectra
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#60 |
New Member
Purvi
Join Date: Oct 2014
Posts: 4
Rep Power: 12 |
Hi Guys,
I am also having problems with plotting energy spectrum. Could somebody plz send me the code. My email address is : p3vdim@yahoo.co.in Thanks in advance!! |
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Tags |
energy spectrum, fft |
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