Learning Forum

[yingtao]

Hi,

I am working on simulating the impact of a pedestrian human body model with a vehicle. In the simulation, the pedestrian is initially struck by the vehicle, causing the body to rotate around the front end of the vehicle. The vehicle comes to a stop after 200 ms. Following the impact, the pedestrian is expected to fall to the ground due to gravity. However, instead of falling, the pedestrian unexpectedly rises after 200 ms. I applied gravity to the entire model using the *LOAD_BODY_Z keyword, as shown in the code below, the unit is mm-s-ton. In the meanwhile, the energy curve showed suddenly kinetic energy drop at 0.28s, that's because of the vehicle was stopped at 0.28s. However the internal energy increased significantly after 0.28s, the head and pelvis velocity increased at the same time as well. Could you suggest how I can ensure the pedestrian falls to the ground as expected?

$
*LOAD_BODY_Z
$     LCID        SF    LCIDDR        XC        YC        ZC       CID
      1003       1.0         0
$

*DEFINE_CURVE
$:
$: Cross-reference summary for Load-curve 1003
$: -----------------------------------------------
$:
$: Body load definition : Base Z acceleration vs time
$: X axis : Time                       (Units: Time)
$: Y axis : Base Z acceleration        (Units: Acceleration)
$:
$: Usage: Transient analysis
$:
$HMCURVE     2    2 LoadCurve_1003
$     LCID      SIDR       SFA       SFO      OFFA      OFFO    DATTYP     LCINT
      1003         0       1.0       1.0       0.0       0.0         0         0
$                  X                   Y
                 0.0          -9806.6504
                 1.5          -9806.6504
$

Thanks!

[Dennis Chen]

 

 

I don’t know for sure but I suspect you need to apply the gravity load during dynamic relaxation and not just in normal phase alone.   given SIDR=0 in your define_curve, maybe try to include DR and see if your model behaves correctly.

I have to say, I can’t 100% exactly follow your model just through text by reading it once so apologize if DR wasn’t the reason. 

 

 

[ytian]

Gravity applied in such way should be positive, - the cordinate system going up. 

[yingtao]

You're right, the load curve should be positive. I tested it using a simple model, it's working now. Thank you so much!