[SOLVED] Internal nodes’ displacements from surface displacement

[Mujika]

I have a volume composed of tetrahedra with StandardTetrahedralFEMForceField. I can set the rest position and the initial position of the volume if I set the positions of all nodes. But I want to set the rest position of all nodes and only the initial position of the nodes in the surface (and let SOFA compute the initial position of the internal nodes). Is it possible? How?
If the structure was a mass-spring structure, would it be possible?

Thank you,

Andoni Mujika

[Weng]

What is initial position ? What is the difference between the rest position and initial position?

[Mujika]

When working with StandardTetrahedralFEMForceField I can set the initial position of the nodes (the position of the nodes in time t=0), setting the attribute “position” of the corresponding MechanicalObject.
The rest position (that can be set in the attribute “rest_position” of the Mechanical Object) is the position where the volume won’t move, i.e. the position that the volume tends to take when it is displaced.

[Alex Bilger]

It looks like you want to apply a boundary condition on the surface, rather than differentiating rest and initial position. If you need to use the resulting geometry, you can save it and use it in another simulation.
One quick trick to test your simulation is to apply strong springs between the surface points in the rest and in the initial configuration. Set the initial position equal to the rest position and use a RestShapeSpringForceField to create the springs which will move the surface points towards the position you want. You can also do that with constraints but the springs are a lot easier to use for testing.

Hope this helps

[Weng]

To the best of my knowledge, SOFA has two position,
(1) rest position, which is loaded or generated before the animation.
(2) free position, which is driven by forcefield,solver, etc.. in the animation.

for your “initial position”, does it mean the rest position ?
for your “rest position”, does it mean the balance position in the animation when the object is undergone some forces (gravity for example)?

Are you actually asking about the volume mesh generation from surface mesh ? If this is what you want, please search tetgen or netgen …

[Hugo]

Thank you @binweng for your detailed reply.
Do you still need help @amujika ?
Did these explanations guide you or would you need further support ?

Cheers,

Hugo

[Author]

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