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

[Heinz Nabielek]

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







[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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.scilab.org/pipermail/users/attachments/20190218/e632ba13/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: PastedGraphic-1.tiff
Type: image/tiff
Size: 34006 bytes
Desc: not available
URL: <https://lists.scilab.org/pipermail/users/attachments/20190218/e632ba13/attachment.tiff>