modelfrf, experiment, naturel frequecies, magnitude
3 Ansichten (letzte 30 Tage)
Ältere Kommentare anzeigen
Gloria
am 18 Jan. 2021
Kommentiert: Mathieu NOE
am 19 Jan. 2021
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 Kommentare
dpb
am 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?
Akzeptierte Antwort
Mathieu NOE
am 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 Kommentare
Mathieu NOE
am 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
Weitere Antworten (0)
Siehe auch
Kategorien
Mehr zu Spectral Measurements finden Sie in Help Center und File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!