I have simulated a 2DOF Quarter Car Model (Figure Attached) for Step Input of 0.1m. The Weighted RMS acceleration obtained is 4.768 m/s2 . The Acceleration plot on Time Scale is also attached.
I want to obtain plot between Weighted RMS acceleration Real Amplitude (m/s2) vs Frequency (Hz) Plot to compare it with ISO 2631 standards. I tried to obtain it using Magnitude FFT and Vector Scope block but result is showing very high amplitude of 600.
Simulink Model is Also Attached.
How to Obtain the correct plot?
Don't forget to normalize FFT over its time window (sampling frequency x N of samples).
How to do this, the FFT block used in attached simulink model has no such provision.
You can follow this example and plot it in Matlab: https://it.mathworks.com/help/signal/ug/power-spectral-density-estimates-using-fft.html your Fs is 1/sampling frequency of your first order holder, N is the FFT window you're using (128 samples).
Otherwise you need to add a gain block in simulink. Also with a square and a logaritm you can obtain PSD.
Also, I suggest using a fixed step for integration or, if you want to use a variable solver don't forget to narrow tollerances.
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