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
[email protected]
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