Learning Forum

[neabar]

Hi,

I am trying to set up a simple simulation in LS-DYNA (S-ALE) involving a rigid sphere immersed in a water domain ([-3,3]x[-3,3]x[-10,10]).
The objective is to validate that the sphere floats, sinks, or remains suspended depending on its density relative to water.

The water is modeled using a *MAT_NULL  material with a density of 1025 kg/m³.
The sphere is fully submerged at the start of the simulation. It has a radius of 0.61 m. 
Gravity is applied using a downward acceleration vector (- Z direction). 

I have tested different sphere densities, expecting it to:

• Sink for densities higher than water,

• Remain suspended for equal density,

• Float upwards for lower density.

However, in all cases, the sphere sinks, regardless of its density. I have not been able to determine the cause of this behavior.

Additionally, I was not able to find any tutorials or examples addressing the hydrostatic equilibrium of a simple object (like a sphere) in an ALE fluid domain. Could you please provide any guidance, references, or example input decks that could help me obtain physically meaningful results?

Thank you in advance.

[Dennis Chen]

Do you have cards like Initial_hydrostatic_ALE in your model?  I've not tested this but it is actually on my list to make a video about.    

[neabar]

Hi, 

Thanks for your reply. Great news to have a video about this topic. 

I use ambient elements and thus *Ale_Ambient_Hydrostatic to initialize hydrostatic pressure. 

 

[Dennis Chen]

have you tried to probe pressure to see if you can see the pressure gradient?  also, if it starts immersed in water at t=0, I am not 100% sure that's how buoyance works as water needs to be displaced.    I will play around with this topic maybe this weekend or maybe next month but it's actually a topic on my mind for a while now so if you figured out what to do properly, please post it here and let me know as well!

thank you!