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Why is the input signal to my suspension model settling at a non-zero value and drift away? Why does the drifting go away when I change a nonlinear damper to a linear one?

Asked by Ryan Vorster on 7 Aug 2018
Latest activity Answered by Christoph Hahn on 7 Aug 2018
Hello, my name is Ryan. I am a student at the University of Victoria in Canada. I have been trying to model a suspension corner of my FSAE car with Simscape blocks and I have run into an issue with how the model is behaving. I would attach the file but apparently the Simulink model filetype is not supported by this forum. I've attached a picture below for reference. The values in the model are realistic for the type of car, but the model behavior described happens with any values.
This is the input signal to the system, swept from 0-20hz of velocity peaking at 100mm/s. I have attached only the first 20s for clarity as to what the input is as it becomes a big yellow block much past that point.
When I run the model as shown above, these are the body acceleration and body position outputs I get. The model is run using the ode23t (mod. stiff/Trapezoidal) solver.
As you can see, the acceleration is behaving as expected, vibrating with the input and having a magnified mode somewhere in the middle at its damped natural frequency. The position however, does not behave as expected and I need help understanding why. The next picture is the measured position of the input signal. You can see it also behaves in a similar manner.
The weirdest part about the whole system is that the input position signal changes when I change the nonlinear damper to a linear damper: it doesn't drift off anymore. See picture below.
In summary, my simscape model of a suspension system is not behaving the way I expect it to and I need help understanding why and how to model the system properly.
Thanks for your help, Ryan

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Answer by Christoph Hahn on 7 Aug 2018

Hi Ryan, thanks for your query. I am neither able to see nor able to download your figures. Would you mind checking. Thanks! Best, Christoph

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