# Energy spectrum to physical domain

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 March 8, 2012, 17:52 Energy spectrum to physical domain #1 Member   HJ Join Date: Nov 2011 Posts: 30 Rep Power: 7 i am wondering can i get real velocity from energy spectrum function (frequency domain), which can have a form like sinusoid function? Can i set temporal difference equal to zero in the autocorrection function? In this way i think i can only get the mean value of u_i square. or is there any other way? Thanks

March 9, 2012, 04:58
#2
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Filippo Maria Denaro
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Quote:
 Originally Posted by wanghaojie i am wondering can i get real velocity from energy spectrum function (frequency domain), which can have a form like sinusoid function? Can i set temporal difference equal to zero in the autocorrection function? In this way i think i can only get the mean value of u_i square. or is there any other way? Thanks
is your spectrum derived from a temporal signal? In general, you can construct a velocity field in space with a prescribed spectrum, however you need to prescribe other condition in order to construct all the Fourier coefficients

March 10, 2012, 11:42
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HJ
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Quote:
 Originally Posted by FMDenaro is your spectrum derived from a temporal signal? In general, you can construct a velocity field in space with a prescribed spectrum, however you need to prescribe other condition in order to construct all the Fourier coefficients
Thanks. I havent start the experiment yet. I think i will get temporal signal instead of spatial. And can you please tell me what other conditions do I need?

March 11, 2012, 15:14
#4
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Filippo Maria Denaro
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Quote:
 Originally Posted by wanghaojie Thanks. I havent start the experiment yet. I think i will get temporal signal instead of spatial. And can you please tell me what other conditions do I need?
since your velocity field is v(x,t) = Sum_p,q,r Cpqr(t) exp (i k .x ) you need to know the real and imaginary part of your Fourier coefficients

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