[Scilab-users] wind speed analyses via fft power spectral density investigations

[Heinz Nabielek]

CORRECTION in horizontal axis....



> On 18.02.2019, at 11:46, Heinz Nabielek <heinznabielek at me.com> wrote:
> 
> Dear friends and colleagues:
> 
> Yann Debray had put my first fragmentary attempt at wind speed analyses on the web: <https://www.scilab.org/wind-speed-analysis>.
> 
> Based on ca. 55.000 hub-level wind speed measurements at 10-min-intervals, I am investigating the power spectral density of wind speed - diagram and code below - with the help of the Scilab 'fft' function and that worked very well.
> 
> One famous Japanese wind professor [he is now away for several months] had suggested "Using an arbitrary phase shift as random number into Inverse FFT, you can generate similar natural wind numerically, having the same spectrum".
> 
> Now my question: HOW DO I DO THAT AND HOW I DO IT IN SCILAB?
> 
> Best greetings
> Heinz
> 
> 
> 
> <PastedGraphic-1.tiff>
> 
> 
> 
> [fd, SST, Sheetnames, Sheetpos] = xls_open('1.xls');
> [v, TextInd] = xls_read(fd, Sheetpos(1));
> clear SST Sheetnames Sheetpos TextInd fd
> n=length(v);
> x=(1:n)';
> z=fft(v);
> plot2d(x,abs(z),logflag='ll',style=3);
> xx=(60:20000)';
> xxx=log(xx);
> M=[ones(xxx) xxx];
> y=log(abs(z(xx)));
> a=M\y
>    12.513971
>   -0.8530057
> F=exp(a(1)+a(2)*xxx);
> plot(xx,F,'r--');
> xtitle('Fourier analysis of wind speeds from station 1', ...
> 'f r e q u e n c y    [ c y c l e / 1 0 min. ]','p o w e r   s p e c t r a l   d e n s i t y');
> title('Fourier analysis of wind speeds from station 1','fontsize',3);
> legend('measured wind speed data','fit with slope -0.853',3);
> 
> 
> 
> ______________
> Dr Heinz Nabielek
> Schüttelstrasse 77A/11
> A-1020 Wien, Österreich
> Tel +43 1 276 56 13
> cell +43 677 616 349 22
> heinznabielek at me.com
> 
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