How do I do a quadratic integral to a sine function in Simulink

This is my simulation。I want to find the displacement by integrating an acceleration twice，which is a sin function, but when I take the second integral it's going to be very strange。

“Sin Wave” with the function: f=0.01*sin(pi*t)

Initial condition of the first Integrator is -0.001*pi

Initial condition of the second Integrator is 0

The picture of acceleration and velocity is correct, but then the curve of displacement starts to rise.

Do I miss something?

Answer 1

[Areej Varamban Kallan]

Hi Sihao,

I beleive that there is nothing wrong with the solution computed. The equation you are solving is:

at t = 0.

The solution for this equation is:

.

This solution will grow as 't' increases. If you are not expecting this, please check the initial condition for velocity. Setting initial velocity to -0.01/pi will give steady oscillation.

[Sihao Fan]

Hi Areej,

Thanks for your reply! I solved my question。

But I don't really understand the second term of the solution for the equation.

How did you get this term?