modelfrf, experiment, naturel frequecies, magnitude
2 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
When I plot the experiment data with modalfrf, the units on the vertical axis are not correct. I gave the result for the experiment with figure 1 and the numerical results with figure 2. I think figure 2 is correct and figure 1 is wrong. Where is my mistake?
B1=xlsread('excel.xlsx',1);
x = B1(1:10000,3:3);
f = B1(1:10000,4:4);
dt = 0.0001;
Fs = 1/dt;
N = 10000;
t = dt*(0:N-1);
wind = hann(N/2);
[frf,f] = modalfrf(f,x,Fs,wind);
plot(f,20*log10(abs(frf)))
2 commentaires
dpb
le 18 Jan 2021
I don't see anything to complain about -- I hadn't realized there was a modal frf function in SP TB; I haven't done much of that sort for a while, so "know nuthink!" about it per Sgt Schultz but it appears it outputs the plot in linear scale and you've converted to a power/dB axis. Somewhat more conventional, but if you got the expected amplitudes, what's to complain?
Réponse acceptée
Mathieu NOE
le 18 Jan 2021
hello
I plotted the time data for channels combos 3/4 (and 1/2)
both shows single (low) frequency sinus type data - so this is not what I expected for a modal frf - I was expecting to see random, random burst , sine dwell (chirp) , but not a lonely fixed freq sinus
not a surprise that the computed frf is completly misleading
also the amplitude of x and f are of very different orders of magnitudes : x is in the 10^-5 and f in the 10^5 , so a ratio like this cannot give a frf modulus like the "good" figure 2 would show between 10^-7 and 10^-4.
7 commentaires
Mathieu NOE
le 19 Jan 2021
you have to introduce some wide frequency range excitation signals , like random (white noise ) or chirps , but do not rely on "operationnal" background noise or narrow band signals like sines to get accurate models
have a good day
Plus de réponses (0)
Voir également
Catégories
En savoir plus sur Spectral Measurements dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!