How to compute the forces at the tip and at the distal end of a catheter?

[SangbaekYoo]

I am currently working on implementing a catheter simulation.
This time, I have a question that is more about the physics rather than the code.

I’ve finally success to get every contact forces acting on the catheter through the constraint matrix.
However, my goal is to compute the net force exerted at the insertion point (i.e., the end of the catheter).

It seems that I might need to calculate this explicitly myself.

1. Or is there a way to obtain it directly without having to compute it myself?

2. If I should implement myself, I don't know how to calculate this physically.
   It might seem to simply sum all the forces applied to the catheter, but since the catheter is not a rigid body, I don’t think the calculation is that straightforward.

[hugtalbot]

Dear @SangbaekYoo

Sorry for keeping you waiting so long.
Several discussions addressed this topic :

• one on the old SOFA forum "Getting forces generated by a collision"
• one on the recovery of contact forces with Rigid degrees of freedom How to access the contact forces when using constraint resolution based on Lagrange multipliers #3812
• one on the recovery of contact forces with Vec3 degrees of freedom Contact using lagrange multiplier for deformable body #4415

I need to find some time to update these with a more recent piece of codes.
Anyway you should find inspiration there. To detail the how to :

1. access the Lagrange multipliers (see the data "constraintForces" from the ConstraintSolver)
2. access the Jacobian matrix from the associated object you are looking at (see the data "constraint" from the MechanicalObject)
3. Multiply them to get the contact forces in the 3D (x,y,z) coordinate system
4. Project the force at the basis of the catheter to compute the resulting torque
   

Let us know if you successfully implemented something on your end since your post
Hope this helps

[hugtalbot]

Hi @SangbaekYoo

For your information, I just created an example as a PR in the SofaPython3 repository describing how to easily access (and visualize) contact forces, when using the response method "FrictionContactConstraint".

See ➡️ https://github.com/sofa-framework/SofaPython3/pull/514/files

[github-actions[bot]]

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@SangbaekYoo
Feedback has been given to you by the project reviewers, however we have not received a response from you. Without further news in the coming weeks, this discussion will be automatically closed in order to keep this forum clean and fresh 🌱 Thank you for your understanding

[github-actions[bot]]

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@SangbaekYoo
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