Translation of a time signal in space by FFT and IFFT

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Twevers 2018-4-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/395698-translation-of-a-time-signal-in-space-by-fft-and-ifft

Dear all,

Currently i am looking to translate my time signal, which has been taken at point 'X' to point 'X+1.875'. The way i am doing this is as follows:

Applying a FFT to get each individual wave
For each individual wave, determine the wave number 'k'
Determine the phase per fase
determine the phase shift (length x k)
determine the new waves at the new point
inverse fft of new waves

But by doing this, the amplitude decreases significantly of my wave crests and increases in my wave through. Can anyone spot a mistake?

if true
S=fft(wle);
T=length(wle)/Fs;
f=[0:1/T:1/2*Fs 1/2*Fs-(1/T):-1/T:1/T];
figure, plot(f,sqrt(S.*conj(S)));
hold on; plot(f,abs(S));
kd = 0:0.001:10000;
w2d=g*kd.*tanh(kd*h);
w=2*pi*f;
k=interp1(w2d,kd,w.^2);
figure, plot(k,sqrt(S.*conj(S)))
hold on; plot(k, abs(S))
Z = angle(S);
L = -1.875 ;% (somehow it translated 1.875m forward when L is set negative....)
da = L.*k';
amp2 = abs(S);
S_sh2 = amp2.*cos(Z+da) + i*amp2.*sin(Z+da);
S_sh2 = [S_sh2(1:561);conj(S_sh2(560:-1:2))];
wle_sh2 = ifft(S_sh2,'symmetric');
plot(t,wle,'r',t,wle_sh2,'k')
end