BilateralInteractionConstraint with Caribou Solver

[Jan]

Hello everyone!

I want to simulate a tilting actuator that uses an expanding bellows (see picture below). The hyperelastic bellows is connected to the rigid top frame with BilateralInteractionConstraint and is fixed on the bottom. The node of the bellows uses the BackwardEulerODESolver and LDLTSolver of the caribou plugin and UncoupledConstraintCorrection.

For the node of the rigid top frame the EulerImplicitSolver, ShewchukPCGLinearSolver and UncoupledConstraintCorrection are used. The rigid top frame is constrained so it can only rotate around the z-axis. The flexible bottom frame uses EulerImplicitSolver, SparseLDLSolver and LinearSolverConstraintCorrection. The bottom frame is fixed on the bottom.

The problem is that the BilateralInteractionConstraint does not work properly when the caribou solvers are used for the bellows. Some connection points are drifting apart (see picture) and I don’t know what causes that only some points drift apart.

Picture of the scene:

View post on imgur.com

Best regards
Jan

[jnbrunet]

Hey Jan,

Could you try replacing the BackwardEulerODESolver of Caribou by a EulerImplicitSolver of SOFA, but keep the LDLTSolver solver of Caribou. Does it work? If not, can you replace the LDLTSolver of Caribou with the SparseLDLSolver of SOFA. Does it work now?

I’m just trying to determine which component of Caribou makes it fail. This will help me debug the issue.

J-N

[Jan]

Hey Jean-Nicolas,

thanks for your response. When using Caribou solvers in the scene independent of the combination the constraints do not work properly. When using the NeoHookeanMaterial of Caribou with EulerImplicitSolver and ShewchukPCGLinearSolver (Preconditioner: SparseLDLSolver) of SOFA it will work for low pressures.
But for now, I’m using the TetrahedronFEMForceField with the SOFA solvers because it seems that it would be the most stable solution with the constraints described above.

Best regards
Jan

[Hugo]

Let’s poke @jnbrunet but @sidaty as well on this Caribou topic 😉

Best

Hugo

[jnbrunet]

Hey @Hugo and @Jan,

Yes, sorry for the late reply rate. I have some time issues these days, but who doesn’t right? ^^

I’ve created an issue here to follow the development. It is on my top priority for caribou, I hope I’ll find some time in the next 2 weeks to look at it. But if someone wants to tackle it (could be a good opportunity to learn about the constraint solving and matrix assembly process in SOFA), that would be awesome. I will of course offer my full support.

J-N

[Author]

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