Problem plotting bode for a 2nd order system
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Hi, I'm getting started with simulink, I tried to simulate a 2nd order mass spring system but the bode plot seems odd :
K1 = 50
K=1/m1 = 1
I don't know which linear analysis point to choose
This system should have a resonance iif c1 < 1/sqrt(2)
If I choose open loop output, then bode NEVER shows a resonance no matter what c1 is.
If i choose output measurement, bode shows me a resonance if c1 < 9 (instead of 1/sqrt(2))
So, which analysis point should i use ?
4 个评论
Can someone answer me please ? I really need to understand that for next week !
Is anybody here ?!
Jan
2019-5-13
@François Blas: Please do not bump your question repeatedly. Post comments in the section for comments and reserve the section for answers for answers. Thanks.
You cannot expect a forum with voluntary members to react inside a certain time. So please calm down.
It's been 9hours, no one knows how to plot bode in simulink ?
采纳的回答
Sulaymon Eshkabilov
2019-5-13
编辑：Sulaymon Eshkabilov
2019-5-13
0 个投票
Hi Francois,
I have tested and simulated your example and it works as it has to w.r.t. the values of M1, K1, C1. In fact, for your data: K1 = 50, M1 =1, C1 = 2 (e.g). The resonant occurs at the frequency of sqrt(50/1) (approximately 7 Hz) and not @ sqrt(2) as you were anticipating. The selection of output measurement, is the right one. Here is my tested Simulink model. It is in fact correct that the resonant occurs at sqrt(50) => 7Hz that can be seen from the TF of SMD: 1/ (M1s^2+C1s+K1) ==> resonant freq: = sqrt(K1/M1).
Good luck.
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