CORRECTION in horizontal axis....
> On 18.02.2019, at 11:46, Heinz Nabielek <[email protected]> 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 > [email protected] > > _______________________________________________ > users mailing list > [email protected] > http://lists.scilab.org/mailman/listinfo/users
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