I'm trying to get the natural frequencies of accelerometer data used to do seismic testing on a structure.

Hi,

I have a set of accelerometer data I've collected from a seismic test subjected to a structure. I'm trying to determine the natural frequencies using the accelerometer data retrieved from the tests. How would I be able to do that with MATLAB?

So far I've tried using the FFt function but not sure if I'm doing it correctly. Can anyone help? I've attached my Sinesweep testing data below.

% Load SineSweep Testing Data

load("SineSweep.mat")

% Accelerations of Structure

a_tSWF=AccTopFSW; %Acceleration of SW Fixed

a_t1SW=AccTop1stSW; % Acceleration of SW 1st Isolator

a_t2SW=AccTop2ndSW; % Acceleration of Sw 2nd Isolator

% Plots Acceleration vs Time data for sinesweep

figure(1)

plot(tFSW,a_tSWF,"b")

hold on

plot(t1stSW,a_t1SW,"r",'LineWidth',3)

hold on

plot(t2ndSW,a_t2SW,"g",'LineWidth',3)

hold on

title('SineSweep on Structure')

legend('Fixed','1st Iso','2nd Iso')

xlabel('Time in s')

ylabel('Acceleration in g')

% Fourier Transform to get Natural Frequency

dt=0.002;

n=length(tFSW);

fSW=fft(a_tSWF,n);

PSD=fSW.*conj(fSW)/n;

freq=1/(dt*n)*(0:n);

L=1:floor(n/2);

figure(3)

plot(freq(L),PSD(L),'r')

xlabel('Acceleration')

ylabel('Hz')

[Askic V]

I suggest you to check this out:

https://www.mathworks.com/matlabcentral/fileexchange/50988-frequency-domain-decomposition-fdd