MATLAB: FFT for the given data to find the dominant frequency

dominant frequencyfftlift coefficient

hello everyone,

I have a data file containing a variable called "Lift coefficient" collected over a period of 1.25 seconds with time steps of 1e-5. I am performing the FFT but i'm not getting the desirable result. I am using the following code. Please find the data file also. Thankyou in advance

x=Cl;
plot(t,x)
t=VarName1;
y=fft(x);
f = (0:length(y)-1)*(10000)/length(y);
plot(f,abs(y))

Best Answer

Try this:

[D,S] = xlsread('forcecoefficients1.xlsx');
t = D(:,1);
Cl = D(:,2);
Ts = mean(diff(t));
Fs = 1/Ts;
Fn = Fs/2;
L = numel(t);
Clm = Cl-mean(Cl);                                  % Subtract Mean (Mean = 0 Hz)
FCl = fft(Clm)/L;
Fv = linspace(0, 1, fix(L/2)+1)*Fn;
Iv = 1:numel(Fv);
[pks,locs] = findpeaks(abs(FCl(Iv))*2, 'MinPeakHeight',0.01);
figure
plot(Fv, abs(FCl(Iv))*2)
grid
xlim([0 1E3])
text(Fv(locs), pks, sprintf('\\leftarrow Dominant Frequency = %.2f', Fv(locs)), 'HorizontalAlignment','left')

The dominant frequency appears to be 226.4.

EDIT —

Added plot image:

FFT for the given data to find the dominant frequency- 2019 05 03.png

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Try not using so many elements - too many to display.

Try this:

clc;
close all;
clear;
workspace;
format long g;
format compact;
fontSize = 15;
%variables
Am=5; %message signal amplitude

Ac=10; %message signal amplitude
t= linspace(0, 0.04, 1500); %period
Fm=50; %message frequency
Fc=1000; %carrier frequency
%output graph preparation
m=Am*cos(2*pi*Fm*t); % Signal equation
c=Ac*cos(2*pi*Fc*t); % Carrier equation
%plot m(t) and its amplitude
subplot(2,3,1);
plot(t,m);
xlabel('time', 'FontSize', fontSize);
ylabel('m(t)', 'FontSize', fontSize);
title('Signal Equation', 'FontSize', fontSize);
% Put x axis in the right place.



ax = gca
ax.XAxisLocation = 'origin'
subplot(2,3,2);
plot(t,abs(m));
xlabel('time', 'FontSize', fontSize);
ylabel('m(t)', 'FontSize', fontSize);
title('Signal Amplitude', 'FontSize', fontSize);
%plot c(t) and its amplitude
subplot(2,3,3);
plot(t,c);
xlabel('time', 'FontSize', fontSize);
ylabel('c(t)', 'FontSize', fontSize);
title('Carrier Equation', 'FontSize', fontSize);
% Put x axis in the right place.
ax = gca
ax.XAxisLocation = 'origin'
subplot(2,3,4);
plot(t,abs(c));
xlabel('time', 'FontSize', fontSize);
ylabel('c(t)', 'FontSize', fontSize);
title('Carrier Amplitude', 'FontSize', fontSize);
% Put x axis in the right place.
ax = gca
ax.XAxisLocation = 'origin'
%Sketch the magnitude of the multiplication of m(t) with c(t).
y=m.*c;
subplot(2,3,5);
plot(t,y);
xlabel('time', 'FontSize', fontSize);
ylabel('m(t) .* c(t)', 'FontSize', fontSize);
title('Multiplication of m(t) with c(t)', 'FontSize', fontSize);
% Put x axis in the right place.
ax = gca
ax.XAxisLocation = 'origin'
subplot(2,3,6);
plot(t,abs(y));
xlabel('time', 'FontSize', fontSize);
ylabel('y(t)', 'FontSize', fontSize);
title('Amplitude of the multiplication', 'FontSize', fontSize);
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')

Best Answer

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