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From: Michael Klein on 7 Jul 2010 05:21
Dear all,

I am facing a mathematical problem, which I want to solve with Matlab.

I designed a 2 DoF vehicle mass-spring-damper system in Simulink with
nonlinear damper characteristics realized with a lookup table. All the other
parameters are linear. The input respectively the excitation of the system
is a predefined random road signal.

Now, I am interested in the frequency response of this nonlinear system,
more precisely the transfer functions such as (vehicle mass
acceleration)/(input signal) or (wheel load fluctuation)/(input signal). I
started calculating these transfer functions with several methods (such as
fast-fourrier transformation fft, transfer function estimate tfestimate or
bode function) but I figured out that these compute the magnitude and phase
of the frequency response based on Linear Time-Invariant LTI models.

I have some doubts whether these linear models are suitable for my Simulink
model described above because of the nonlinear damping characteristics.
Which kind of methods does Matlab have in order to analyze my system? Do I
have to use the system identification toolbox with models such as SISO
Nonlinear ARX and Hammerstein-Wiener?

For any help I would be really thankful.

Regards. Michael


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