Plot and calculate Damping ratio

Hi I want to calculate damping ratio by using the log decrement method, but for my understanding we need to select 2 peaks in order to do it. Can matlab do it by itself ?or I have to do it manually. Here is what I got so far.

[v,T,vT]=xlsread('Velocity_Response_of_Pendulum.xlsx')

Time=v(:,1);

Veloc=v(:,2);

xlabel('Time');

ylabel('Velocity');

plot(Time,Veloc);

%pick the first peak (t,v) (0.372,0.02884)

%pick the 2nd peak (1.826, 0.02883)

damp_ratio=

Answer 1

[Star Strider]

The findpeaks or islocalmax functions can return the information to do the calculations.

[Dai Nguyen]

I see but since I import the data from excel what will be the format for findpeaks. Is it pks=findpeark(Time, Veloc)?

[Star Strider]

I have no idea what is in your Excel file.

Read it using readmatrix, then follow the instructions relevant to it in the documentation I linked to.

[Dai Nguyen]

opps sorry here is my excel. Thank so much for your time

[Dai Nguyen]

I rewrite the code but for some reason it didn't highlight the peaks

A=xlsread('Velocity_Response_of_Pendulum.xlsx');

time=A(:,1);

veloc=A(:,2);

plot(time,veloc)

[pks,locs]=findpeaks(A,time);

[Star Strider]

Try this:

T1 = readtable('Velocity_Response_of_Pendulum.xlsx');

[pks,locs] = findpeaks(T1.velocity, 'MinPeakProminence',1E-2);
exp_dk = @(b,x) b(1).*exp(b(2).*x);

B = fminsearch(@(b) norm(T1.velocity(locs) - exp_dk(b,T1.time(locs))), rand(2,1).*[1;-1]);

figure
plot(T1.time, T1.velocity)
hold on
plot(T1.time(locs), T1.velocity(locs), '^r', 'MarkerFaceColor','r')
plot(T1.time, exp_dk(B,T1.time), '-g', 'LineWidth',1.5)
hold off
grid
ylabel('Amplitude')
xlabel('Time')
title(sprintf('$y(t) = %.4f\\cdot e^{%.6f\\cdot t}$',B), 'Interpreter','latex')

producing:

.

[Dai Nguyen]

Thank you so much

[Star Strider]

My pleasure!

If my Answer helped you solve your problem, please Accept it!

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