Problems using modalfit to obtain modal parameters

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Enterprixe 2017-10-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/359538-problems-using-modalfit-to-obtain-modal-parameters

Hello,

I have a problem using "modalfit". In this experiment, the force is always applied on one point, and i have measured on every other point (21 total). So i only need the first column of the frf to obtain the modal parameters. I obtain the H0 (true frf) which is H11, H21, H31,...,H211. The problem is, after i get that, im using modalfit to get a rational function to reproduce these experimental data using the least squares but if fails horribly. I get a fitted frf way above the values it should give and i am clueless about where is the mistake.

Help will be much appreciated.

%clear vars
load 0-3000_group.mat
f = zeros(1,3840)';
H0 = zeros(3840,21);
for i = 1:3840
  for j = 1:21
  f(i) = 0.7814*i;
  H0(i,j) = sqrt(FRF.y_values.values(i,2*j-1)*FRF.y_values.values(i,2*j));
  end
end
H0_mod = abs(H0);
H0_phase = angle(H0);
Modal fitting
frf = H0;
fs = 0.7814;
[fn,dr,ms,ofrf] = modalfit(frf,f,fs,25);
for ij = 1:3
for ji = 1:3
  subplot(3,3,3*(ij-1)+ji)
  loglog(f,abs(frf(:,ji,ij)))
  hold on
  loglog(f,abs(ofrf(:,ji,ij)))
  hold off
  axis tight
  title(sprintf('In%d -> Out%d',ij,ji))
  if ij==3
      xlabel('Frequency (Hz)')
  end
end