Full vehicle random vibration vs. multi body

M-L

Hello,

 

Currently I'm comparing a multi body simulation in motionview versus a random vibration analysis with optistruct for a simple chassis. 

• The chassis is suspended at 4 points to the road. The suspension is modelled as a 1D spring-damper system and the wheel/tire as a 1D spring. Both in optistruct and motionview.
• Based on ISO8608 random road profiles are generated, which are used as inputs in the MBD-model. The ISO8608 PSD is used as input for the random vibration analysis in optistruct.
• The MBD model is placed on 4 shakers to which these road profiles are applied.
• For the optistruct model the 4 road points are excited seperately with a unit displacement in the frequency range 0,2-30 Hz with steps of 0,2. After which the random vibration is executed with the defined PSD.

 

To compare both results I converted the stress over time results from the MBD model in hyperview to stress over frequency by means of a FFT. The absolute stress results should not be comparable between both models, I should however see peaks at the same frequencies. However, clearly some peaks are missing around 5 Hz in the random vibration model, since no resonance seems to occur in at this frequency.

 

Now I believe I hit a theoretical limitation, but I wanted to verify if I did not make a obvious modelling error. Hence, why I am asking the question here.

Thus, does anyone have an explanation for the missing peaks in the random vibration analysis?

 

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Shiva Kumar

Greetings,

I have the same problem, i am confused with the random vibration and MBD analysis. Which is better and reliable. 

Can i get some help with this problem?

Thankyou

Xiaolei

Hi, 

Can you show the comparison in frequency domain? I don't see it from the picture you posted. 

I think you can compare them in the sequence as below:

1. normal modes, especially check if there is a mode around 5 Hz

2. PSD acceleration/disp/velocity

3. PSD stress

 

I's familiar with OptiStruct analysis, but really not sure how it's done in MV.

I believe you used the smoothed and straight curve in log-log scale. Please make sure log-log interpolation method is used for PSD profile. 

You can also share the OptiStruct model then we can check it easily.  

 

Thanks. 

Xiaolei