# [Scilab-users] wind speed analyses via fft power spectral density investigations Classic List Threaded 2 messages  Dear friends and colleagues:Yann Debray had put my first fragmentary attempt at wind speed analyses on the web: .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 greetingsHeinz [fd, SST, Sheetnames, Sheetpos] = xls_open('1.xls');[v, TextInd] = xls_read(fd, Sheetpos(1));clear SST Sheetnames Sheetpos TextInd fdn=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  -0.8530057F=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 NabielekSchüttelstrasse 77A/11A-1020 Wien, ÖsterreichTel +43 1 276 56 13cell +43 677 616 349 22[hidden email]_______________________________________________ users mailing list [hidden email] http://lists.scilab.org/mailman/listinfo/users CORRECTION in horizontal axis.... On 18.02.2019, at 11:46, Heinz Nabielek <[hidden email]> wrote:Dear friends and colleagues:Yann Debray had put my first fragmentary attempt at wind speed analyses on the web: .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 greetingsHeinz[fd, SST, Sheetnames, Sheetpos] = xls_open('1.xls');[v, TextInd] = xls_read(fd, Sheetpos(1));clear SST Sheetnames Sheetpos TextInd fdn=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  -0.8530057F=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 NabielekSchüttelstrasse 77A/11A-1020 Wien, ÖsterreichTel +43 1 276 56 13cell +43 677 616 349 22[hidden email]_______________________________________________users mailing list[hidden email]http://lists.scilab.org/mailman/listinfo/users_______________________________________________ users mailing list [hidden email] http://lists.scilab.org/mailman/listinfo/users