<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">CORRECTION in horizontal axis....<div class=""><img apple-inline="yes" id="3BAE6579-8B17-4D92-901A-E368F0C26992" src="cid:AC846983-31DC-4471-B591-0631167B77BA@upc.at" class=""><br class=""><div class=""><br class=""><br class=""><blockquote type="cite" class="">On 18.02.2019, at 11:46, Heinz Nabielek <<a href="mailto:heinznabielek@me.com" class="">heinznabielek@me.com</a>> wrote:<br class=""><br class="">Dear friends and colleagues:<br class=""><br class="">Yann Debray had put my first fragmentary attempt at wind speed analyses on the web: <<a href="https://www.scilab.org/wind-speed-analysis" class="">https://www.scilab.org/wind-speed-analysis</a>>.<br class=""><br class="">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.<br class=""><br class="">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".<br class=""><br class="">Now my question: HOW DO I DO THAT AND HOW I DO IT IN SCILAB?<br class=""><br class="">Best greetings<br class="">Heinz<br class=""><br class=""><br class=""><br class=""><span id="cid:BA28ABF4-2E0B-4DEE-BD7F-58A592504BDF@upc.at"><PastedGraphic-1.tiff></span><br class=""><br class=""><br class=""><br class="">[fd, SST, Sheetnames, Sheetpos] = xls_open('1.xls');<br class="">[v, TextInd] = xls_read(fd, Sheetpos(1));<br class="">clear SST Sheetnames Sheetpos TextInd fd<br class="">n=length(v);<br class="">x=(1:n)';<br class="">z=fft(v);<br class="">plot2d(x,abs(z),logflag='ll',style=3);<br class="">xx=(60:20000)';<br class="">xxx=log(xx);<br class="">M=[ones(xxx) xxx];<br class="">y=log(abs(z(xx)));<br class="">a=M\y<br class=""> 12.513971<br class=""> -0.8530057<br class="">F=exp(a(1)+a(2)*xxx);<br class="">plot(xx,F,'r--');<br class="">xtitle('Fourier analysis of wind speeds from station 1', ...<br class="">'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');<br class="">title('Fourier analysis of wind speeds from station 1','fontsize',3);<br class="">legend('measured wind speed data','fit with slope -0.853',3);<br class=""><br class=""><br class=""><br class="">______________<br class="">Dr Heinz Nabielek<br class="">Schüttelstrasse 77A/11<br class="">A-1020 Wien, Österreich<br class="">Tel +43 1 276 56 13<br class="">cell +43 677 616 349 22<br class="">heinznabielek@me.com<br class=""><br class="">_______________________________________________<br class="">users mailing list<br class="">users@lists.scilab.org<br class="">http://lists.scilab.org/mailman/listinfo/users<br class=""></blockquote><br class=""></div></div></body></html>