How to correctly apply additional "numerical correction" force to the mesh, at each timestep?

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Hi,

I am in the case of elastodynamics. I already solving variational form, getting the displacement u_solution and then moving the the mesh doing ALE.move(mesh, u_solution) at each timestep.

→ I also would like to apply an additional force F to surface vertices, but which is purely numerical and which has a priori nothing to do with the variational form.
This force F has to take a new value at each time step.
How should I apply it correctly to the mesh at each timestep?

To do so, I have tested the following process, at each timestep:

  • F = Function(V), with V=VectorFunctionSpace(mesh, “CG”, 1)
  • computation of the value of Fsurface for each surface vertex i
  • from Fsurface (surface vertex indexation) to volume Function F (volume DOFs indexation):
    F.vector()[vertexSurface_to_DOFsVolume_mapping[i]] = Fsurface[i]
  • moving mesh (this is independant from the u_solution displacement move): ALE.move(mesh, F).

But, it seems that F is not applied to the mesh and I do not understand why. Would you have some ideas about that?

Many thanks for your help,
Anne