I am trying to plot acceleration-time graph by using a txt file but I got error.

clear all;close all;clc;

%%%%%%%LOAD ACCELERATION%%%%%%%

[filename]=textscan('at2.txt','%s');

for i=1:1:length(filename)

file=fopen(filename{i});

line1=fgetl(file);

line2=fgetl(file);

line3=fgetl(file);

line4=fgetl(file);

line5=fgetl(file);

line6=fgetl(file);

line7=fgetl(file);

acc=fscanf(file,'%e',[2,inf]);

fclose(file);

acc=acc';

t=acc(:,1);

a=acc(:,2);

dt=0.01;

%%%%%%%%VELOCITY%%%%%%%%

vel=dt*cumtrapz(a);

%%%%%%DISPACEMENT%%%%%%%%

disp=dt*cumtrapz(vel);

figure

plot(t,a,'linewidth',2);title(['Acceleration Time History for Point',num2str(i)]);

ylabel('Acceleration, cm/sec^2');xlabel('Time, sec');grid on;

saveas(gcf,['acc_p',num2str(i)],'jpg')

figure

plot(t,vel,'linewidth',2);title(['Velocity Time History for Point',num2str(i)]);

ylabel('Velocity, cm/sec');xlabel('Time, sec');grid on;

saveas(gcf,['vel_p',num2str(i)],'jpg')

figure

plot(t,disp,'linewidth',2);title(['Displacement Time History for Point',num2str(i)]);

ylabel('Displacement, cm');xlabel('Time, sec');grid on;

saveas(gcf,['dis_p',num2str(i)],'jpg')

figure

subplot(311)

plot(t,a,'linewidth',2);title(['TIME HISTORIES FOR POINT',num2str(i)]);

ylabel('Acceleration, cm/sec^2');grid on;

subplot(312)

plot(t,vel,'linewidth',2);

ylabel('Velocity, cm/sec') ;grid on;

subplot(313)

plot(t,disp,'linewidth',2);grid on;

ylabel('Displacement, cm');xlabel('Time, sec')

saveas(gcf,['TH_p',num2str(i)],'jpg')

% %%%%%%%%%FOURIER SPECTRUM%%%%%%%%%%%

% [FA,f]=fr_amp(a,dt);

%

% figure

% loglog(f,FA,'linewidth',2);grid on;

% xlabel('Frequency, Hz'); ylabel('Fourier Amplitude, cm/sec');

% title(['FOURIER AMPLITUDE SPECTRA of POINT',num2str(i)]);

% saveas(gcf,['FAS_p',num2str(i)],'jpg')

end

[Askic V]

Please attach your file: 'at2.txt', this way you increase your chances to get quick help.

[Muhammet Emin Sari]

It is done.

[Askic V]

First of all, this is more elgant way to read the file:

filename = 'at2.txt';

A = readmatrix(filename);
acc = A(:,1); % first column represents acceleration
time = A(:,2); % second coolumn represent time

Form teh data in the file, it seems that second column is time, because the difference is constant and 0.005, so sample time is 5 ms?

Do you need something like this?

filename = 'at2.txt';

A = readmatrix(filename);
acc = A(:,1); % first column represents acceleration
time = A(:,2); % second coolumn represent time

% time difference is equal to time(2)-time(1)
t_diff = diff(time);
dt = sum(t_diff)/numel(t_diff); 
% dt = time(2)-time(1); % same result as above

% plot
subplot(3,1,1)
plot(time, acc)
subplot(3,1,2)
vel = dt * cumtrapz(acc);
plot(time, vel);
subplot(3,1,3)
disp = dt * cumtrapz(vel);
plot(time, disp);

[Muhammet Emin Sari]

Thank you for your comment. It looks easier to understand and it really helped me to solve my problem. <3

But I couldn't understand the problme in my code.

Answer 1

[Star Strider]

The columns are reversed from your assignments. The first column is the signal, and the second column is the time vector.

Try something like this —

acc = readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1254552/at2.txt');
t = acc(:,2);
a = acc(:,1);

vel = cumtrapz(t,a);
dspl = cumtrapz(t, vel);

figure
subplot(3,1,1)
plot(t, a)
grid
ylabel('Acceleration (cm \cdot s^{-2})')
subplot(3,1,2)
plot(t, vel)
grid
ylabel('Velocity (cm \cdot s^{-1})')
subplot(3,1,3)
plot(t, dspl)
grid
ylabel('Displacement (cm)')
xlabel('Time (s)')

Fs = 1/mean(diff(t));
Fn = Fs/2;
L = numel(t);
NFFT = 2^nextpow2(L);
FTa = fft(a,NFFT)/L;
Fv = linspace(0, 1, NFFT/2+1)*Fn;
Iv = 1:numel(Fv);

figure
plot(Fv, abs(FTa(Iv))*2)
grid
xlabel('Frequency (Hz)')
ylabel('Magnitude Of Acceleration Signal')

I am not certain what the Fourier transform is supposed to be. Make appropriate changes to that part of the code to get the desired result.

.