Fluid Structure Interaction simulation fails at constriction with inverted mesh and ALE errors

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Hello Team COMSOL,

I'm working on a 2D FSI model using Laminar Flow + Solid Mechanics (Neo-Hookean hyperelastic) + Moving Mesh with a fully coupled solver with automatic remeshing.

The model contains a deformable hyperelastic object moving through a microchannel with a constriction. The simulation runs normally until the object reaches the constriction, where it consistently fails with errors such as:

  1. Inverted mesh element
  2. Undefined value found in the stiffness matrix
  3. NaN in comp1.spatial.u and comp1.spatial.v
  4. Failed to find consistent initial values
  5. Last time step is not converged

I've already tried:

  1. Refining the mesh near the constriction
  2. Adding fillets to the constriction
  3. Automatic remeshing
  4. Different Newton solver options
  5. Verifying mesh and boundary conditions

The failure always occurs at the constriction.

Has anyone encountered a similar issue? Are there any recommended ALE/remeshing settings or solver strategies for large-deformation Fluid Structure Interaction in narrow constrictions?

I have attached the design for reference. Any suggestions would be greatly appreciated.

Thank you.



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