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Prepare Fourier Amplitude Spectrum from ground motion record (Peak-Acceleration vs time-period)

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Parvesh
Parvesh 2024 年 4 月 24 日
コメント済み: Star Strider 2024 年 4 月 27 日
Prepare Fourier Amplitude Spectrum from ground motion record (Peak-Acceleration vs time-period) with the input .txt files which contains peak-acceleration in 1st column & time-period in 2nd column.

回答 (1 件)

Star Strider
Star Strider 2024 年 4 月 24 日
Perhaps this —
T1 = readtable('india.19911019...at_output.txt');
T1.Properties.VariableNames = {'Peak Acceleration','Time'}
T1 = 1808x2 table
Peak Acceleration Time _________________ ____ -0.0146 0.02 0.0116 0.04 -0.0029 0.06 0.0296 0.08 0.0185 0.1 0.0295 0.12 -0.0229 0.14 -0.0848 0.16 -0.0696 0.18 -0.048 0.2 -0.0352 0.22 -0.0146 0.24 -0.00165 0.26 0.0493 0.28 0.0701 0.3 0.0688 0.32
[FTs1,Fv] = FFT1(T1.('Peak Acceleration'),T1.Time);
[PeakVal,idx] = max(abs(FTs1)*2);
fprintf('\nMaximum acceleration of about %.4f mm/s^2 occurs at about %0.4f Hz\n', PeakVal, Fv(idx))
Maximum acceleration of about 0.0585 mm/s^2 occurs at about 1.9775 Hz
figure
plot(Fv, abs(FTs1)*2)
grid
xlabel('Frequency')
ylabel('Magnitude')
function [FTs1,Fv] = FFT1(s,t)
t = t(:);
L = numel(t);
if size(s,2) == L
s = s.';
end
Fs = 1/mean(diff(t));
Fn = Fs/2;
NFFT = 2^nextpow2(L);
FTs = fft((s - mean(s)) .* hann(L).*ones(1,size(s,2)), NFFT)/sum(hann(L));
Fv = Fs*(0:(NFFT/2))/NFFT;
% Fv = linspace(0, 1, NFFT/2+1)*Fn;
Iv = 1:numel(Fv);
FTs1 = FTs(Iv,:);
end
Experiment!
.
  4 件のコメント
Parvesh
Parvesh 2024 年 4 月 27 日
編集済み: Parvesh 2024 年 4 月 27 日
Thank you for your response. Although I've a deveoped a similar code which gives almost same result as of yours but the problem is when I'm comparing these results from the one obtained from 'Sesimo-Signal' software, the response is completely different. For comparison, I'm uploading the ordinates for the reference purpose.
Star Strider
Star Strider 2024 年 4 月 27 日
My pleasure!
I would not say that the response is completely different, however your non-MATLAB software gives a different magnitude result than my MATLAB code.
Taking ths of that result gives —
SeismoSignalVal = log10(1.4939)
SeismoSignalVal = 0.1743
MyCode = 10^(0.0585)
MyCode = 1.1442
These are not strictly comparable, however they are reasonably close. I am not certain what the ‘SeismoSignal’ code does, or how it produces its Fourier transform results. It also appears to use a 25 Hz lowpass filter prior to calculating the Fourier transform, since there is no energy higher than that in the ‘SeismoSignal’ record. I did not use any filters in my code.
Also, the ‘SeismoSignal’ Bode magnitude plot uses a truncated logarithmic frequency axis. (I have reproduced that here.) My plot uses a simple linear frequency axis.
For all intents and purposes, the ‘SeismoSignal’ result and my result are the same.
My analysis —
figure
imshow(imread('Screenshot 202...27 092404.png'))
title('Image of the ‘SeismoSignal’ Fourier Magnitude Plot')
T2 = readtable('FAS_Ordinates.xlsx', 'VariableNamingRule','preserve')
T2 = 2048x5 table
Frequency Period Fourier Amplitude Fourier Phase Power Spectrum _________ ______ _________________ _____________ ______________ 0.02441 40.96 0.02911 -0.22077 6e-05 0.04883 20.48 0.03319 -1.2565 8e-05 0.07324 13.653 0.03426 0.7691 8e-05 0.09766 10.24 0.01155 -0.37581 1e-05 0.12207 8.192 0.01922 -0.93403 3e-05 0.14648 6.8267 0.02871 -1.4569 6e-05 0.1709 5.8514 0.08533 0.18696 0.00051 0.19531 5.12 0.10611 -1.1405 0.00079 0.21973 4.5511 0.14562 1.3089 0.00149 0.24414 4.096 0.18425 0.44059 0.00238 0.26855 3.7236 0.1323 -0.18164 0.00123 0.29297 3.4133 0.15615 -0.7626 0.00171 0.31738 3.1508 0.28456 1.5609 0.00568 0.3418 2.9257 0.09585 -1.527 0.00064 0.36621 2.7307 0.18708 0.26333 0.00246 0.39063 2.56 0.11011 0.65927 0.00085
VN2 = T2.Properties.VariableNames;
figure
plot(T2.Frequency, T2.('Fourier Amplitude'))
grid
xlabel(VN2{1})
ylabel(VN2{3})
title('Linear Frequency Axis')
[PeakVal,idx] = max(T2.('Fourier Amplitude'));
fprintf('\nMaximum acceleration of about %.4f mm/s^2 occurs at about %0.4f Hz\n', PeakVal, T2.Frequency(idx))
Maximum acceleration of about 1.4939 mm/s^2 occurs at about 1.9775 Hz
figure
semilogx(T2.Frequency, T2.('Fourier Amplitude'))
grid
xlabel(VN2{1})
ylabel(VN2{3})
title('Logarithmic Frequency Axis')
figure
semilogx(T2.Frequency, T2.('Fourier Amplitude'))
grid
xlabel(VN2{1})
ylabel(VN2{3})
xlim([1 max(T2.Frequency)])
title('Truncated Logarithmic Frequency Axis')
.

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