FFT to IFFT issue with going back to time-domain

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Luka David Dilas 2018-5-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/398817-fft-to-ifft-issue-with-going-back-to-time-domain

编辑： Matt J 2018-5-3

Im trying to obtain displacements from frequency response function (I have data for acceleration and force) and with that information to obtain displacements by going back to time-domain with IFFT. I have issues with inverse Fourier transform, I know that I need some pre-conditioning regarding sizing but I couldnt find the solution. I get like mirror-image of the signal when I use ifft. I provided the code and functions for frequency response function along with data. Any help much appreciated!

Main Code:

file='accela2.txt'
data =load(file);
acc_1 = detrend(data(:,1)); %Acceleration is in g's
force_1 = (data(:,2)); %Force is in Newtons
Fs=1000; %Sampling Frequency (Hz)
%-------------Using My_FRF function to get FRF-acceleration---------------%
time=linspace(0,3,2049); %FRF  function produces a vector (therefore size 2049)
[freq, HaMag] = My_FRF(acc_1,force_1,Fs);  %My_FRF function - acceleration
FRFaccel=HaMag
% plot(freq,FRFaccel); xlim([0 30]); %Check on FRF graph
%--------Calculation of Radial (Force) Frequency-My_FFT function----------%
%Use Force_1 and Fs as input in My_FFT --> get force_1 frequency (f1)
%Multiply f1(omega) by 2*pi to convert to rad/s 
[f1,m_wave1, psd_1] = My_FFT(force_1,Fs);
omega=transpose(f1).*(2*pi); % Hz to rad/s for force frequency
%----------------FRF-Displacements(from Acceleration FRF)----------------%
   FRFdisp=FRFaccel./(-omega.^2);
   FRFdisp=abs(FRFdisp);
   Disp=ifft(FRFdisp);
figure(1);
plot(time,Disp);
xlabel('Time(s)')
ylabel('Displacements(m)')