Learning Forum

[AaronJackson21]

Hi everybody,

I am using explicit dynamics for my masters research to try and understand the correlation between impact force and the resulting internal pressure of a human head model when subject to impact. Our simplified model is a hollow ellipsoid that is filled with water and impacted with a ball from the front flying at an initial velocity. I am using the ALE method by designating my water body as Eulerian and the rest of my bodies as Lagrangian. I have successfully modeled the impact simulation and am able to see the pressure wave propagation from the front of the head to the back of the head once impact occurs. However, numerous studies in this realm show that once the impact happens, there should be a positive pressure in the front of the head (which I see) and an equally negative pressure in the back of the head (which I do NOT see).

Does anybody have any recommendations as to how I can capture this negative pressure? My thought would be to see if there is a reaction force/stress on the interior of the ellipsoid wall that is negative, however I am unable to see the forces/stresses induced on the wall interior due to the water moving within. I will add that I am unable to use the Reaction Force probe as it gives an error because I am using an Eulerian body.

Any help is greatly appreciated and please let me know if I can clarify any information about my simulation. Thanks!

[Ram Gopisetti]

have you used PRESSURE equation user defined result scoped to the ALE bodies and need if you can variation of the pressure. Scope the Wall to the force reaction and see if you can justify. post some images for better response.
Cheers, Ram

[AaronJackson21]

I now believe my issue is that I am viewing the wrong type of pressure. Since the stress tensor is equal to the deviatoric pressure plus the hydrostatic pressure, I only need to view the hydrostatic pressure component ( 1/3*(sigxx+sigyy+sigzz)). I am trying to use a hydrostatic pressure command to store these values in an ETABLE for plotting, but I am having an error occur when I run my simulation. From my understanding of the documentation the ETABLE command should take the following format: ETABLE,Lab,Item,Comp,Option
The command I am trying to implement to view the minimum hydrostatic pressure is:
ETABLE,HSP,NL,HPRES,MIN
I am new to writing ANSYS commands so any help would be greatly appreciated. Thanks!!