Deformable liver on flat surface with gravity

[LichtiL]

Hello everyone,

I am new to SOFA and I would like to model and simulate a deformable liver which falls onto a flat surface/floor/table and then stays there.
For that I have a created a volumetric mesh of the liver and added a floor to the simulation. I also inserted a simple sphere to collide with the liver and with the floor.

In my current simulation the sphere collides and bounces off the liver and the floor as intended, but I have encountered some problems on which I am stuck on:

1. The liver does not bounce off the floor, it just goes straight through. (See screenshot)
   

2. It seems like the applied gravity acts like a normal force on each of the nodes of the liver model separately rather than on the volumetric mesh as a whole. (See screenshot with fixed constraints on some nodes of the liver mesh)
   

3. It would also be nice if the surface could be rigid & not effected by gravity.

Attached you can find my code and the volumetric mesh that I am using. Thanks to any help in advance!
LiverFloorGravity.zip

[hugtalbot]

Hi @LichtiL

Welcome on the SOFA forum!
In fact your simulation is using penalities as a contact response. This kind of method has a strong limitation, namely the contactStiffness has to be fine tuned for each object. You should change the contactStiffness of your deformable floor.

In general, when you have multiple colliding objects, it is advised to use Lagrangian multipliers to solve the constraint/contact problem.

About the gravity, just know that it is computed using the gravitational acceleration global to the scene and the mass component specified for each object.

I hope this helps.
Best wishes,

[LichtiL]

Hi @hugtalbot

Thank you for your advice! I switched the contact response to Lagrangian multipliers, the collision between the sphere and the liver works just fine, but the liver still does not collide with the floor and now the sphere does not bounce off the floor (although I can see that there certainly is a contact which shows up in the scene graph).

I also took a look at the mass component I specified for the liver: Even though I am using MeshMatrixMass the issue remains as described above (gravity acts like a normal force on each node).

Best,

[hugtalbot]

Hi @LichtiL

How things are going? Could you please share an updated version of your scene?