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

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Sihao Fan
Sihao Fan 2019-1-19
评论： Sihao Fan 2019-1-21
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。
捕获.PNG
“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.
捕获3.PNG
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捕获2.PNG
Do I miss something?

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采纳的回答

Areej Varamban Kallan
编辑：Areej Varamban Kallan 2019-1-21
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.
  1 个评论
Sihao Fan
Sihao Fan 2019-1-21
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.
捕获2.PNG
How did you get this term?

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