Acceleration and velocity patterns

Altair Forum User
Altair Forum User
Altair Employee
edited October 2020 in Community Q&A

Hi Experts,

 

In a typical full frontal crash simulation I plotted a graph between time and acceleration/velocity of one of the parts in my model. The graph was haphazard and not uniform. I mean there were many peaks and valleys in the graph through out the simulation run time ( the results are unfiltered). I would like to know the reason behind this. Could anyone explain why the pattern is haphazard and not uniform ? Is it because of the crash phenomena or because of time step instability or because of interface stiffness......

 

Thank you in advance..

Tagged:

Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited April 2017

    Hi Raghav,

    Normally for a crash analysis the acceleration vs time plot will not be like a uniform curve, For a case like where the acceleration is increasing and decreasing significantly over short periods of time, the motion would feel jerky, and there will be rate of change of acceleration.

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited April 2017

    Hi,

    Thank you for the answer. But my question why does it happen has not been clarified. Could you elaborate ?

     

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited April 2017

    Hi Raghav,

    Full-scale vehicle crash tests are performed globally to assess vehicle structure and restraint system performance. The crash pulse, captured by accelerometers mounted within the occupant compartment, measures the motion of the vehicle during the impact event. These time histories have shape, amplitude, and duration characteristics.There are numerous factors that can effect the characteristics of a crash pulse. Some of these include the vehicle shape, vehicle structure, vehicle mass, collision partner, crash mode, and amount of engagement. Normally for rear impact cases, crash pulses normally have typically unimodal or bimodal sinusoidal shapes. Unimodal shapes are commonly characterised by an initial sudden rise followed by a gradual descent in acceleration, whereas the bimodal ones are commonly characterised by an initial sudden rise with a high peak, followed by a lower peak and a gradual descent in acceleration.

    There are numerous open resources available on web regarding crash pulse. I recommend you to go through for various impact cases.

Categories