Full vehicle random vibration vs. multi body

M-L
M-L Altair Community Member
edited February 15 in Community Q&A

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?

 

<?xml version="1.0" encoding="UTF-8"?>MBD_freq_stress.thumb.png.7ca4cbf7c3c7c5c177ab451511af24a7.png<?xml version="1.0" encoding="UTF-8"?>Random_freq_stress.thumb.png.75d21b77b017bb7e6142e4c221e5c827.png

<?xml version="1.0" encoding="UTF-8"?>MBD_model.png

<?xml version="1.0" encoding="UTF-8"?>Random_model.png

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Answers

  • Shiva Kumar
    Shiva Kumar Altair Community Member
    edited February 15

    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
    Xiaolei
    Altair Employee
    edited February 15

    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

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