Question about pre-deformed bellow actuator

[Benjamin]

Hi everyone,

I have a question about loading pre-deformed geometry, similar to the an old post

https://www.sofa-framework.org/community/forum/topic/pre-deformed-beam/#post-14323

. I want the initial state of a hollow bellow actuator in a compression condition and then running other simulation based on this initial state. One end of actuator will be fixed on a wall or floor and the other end will attach to an object so that after animation running, there will be a force generated by bellow to push the object.

My questions are how to make the bellow compressed and load the pre-deformed state at the beginning of simulation.

For the first question, I added a rigid plane on one side to compress the bellow while the other side is fixed on a wall. However, as the bellow acts like a spring, when I move the position of the plane, it will be pushed back by the force from bellow. The forcefield applied on bellow is TetrahedronFEMForceField. Does anyone has suggestion about this problem?

For the second problem loading the pre-deformed state at beginning of simulation, the old post suggested set the reset_position. I don’t really understand this. Is the pre-deformed object drawn in a CAD firstly, then loaded in a simulation with the stress-free position as the reset_position? But this solution doesn’t consider the initial stress energy stored in the object and the new deformed geometry will get a different mesh (nodes number and position) from the old geometry.

Thanks for help.

Regards,

[Hugo]

Hi @wzdy4444

I really apologize for the delay of my reply.
I am sorry I am not sure to get your first question.

In your case, if you are only looking for inducing forces by your compressed actuator, a solution could indeed be to define different position (the deformed configuration) and rest_position (undeformed). The actuator material should thus induce forces on your object so that the actuator recovers its rest shape.

In general, saving the whole mechanical state and restart from a deformed state is not that simple in SOFA. Especially because several vectors/matrices/tensors are saved in C++ components, but not exposed.

Best

Hugo

[Author]

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