Modal identification using Frecuency domain descomposition

[antonioro]

Hello, I´m spanish, my english is very bad...
I try to make a program that use the method "frequency domain descomposition" (FDD) (Brincker et al. (2000)).
I try to calculate the modal parameters of a cantilever beam. This method take n-signal and make the spectral density matrix. Then compute the singular value descomposition (SVD) for each frequency and take for a new approximation, for the frequency response of my mechanical system, the maximum singular value of each frequency. The eigenvector at the natural frequency is the shape mode, and the damping ratio is estimated from the inverse fft of the svd around the peak of the natural frequency.

I have a problem to calculate the PSD of each signal. I´m usin the command pwelch of MATLAB, that use the welch's method to estimate de PSD. The parameters of this command are the length of the window to average, the overlap of these windows and the number of samples that I anlyze. I see that the spectrum's amplitude and shape change with the value of the length window.

Someone could help me.
Thanks!

 

[EdDanzer]

This question belongs in the Mechanical engineering other topics, or Finite element analysis engineering or Programming language engineering