The error "Failed to respect boundary element on geometry face" occurs.
First, due to continual improvements in meshing, make sure to use the latest version of COMSOL Multiphysics: Product Download
The mesh generator failed in making the elements compatible with the geometry object’s edges. The reason for this could be that the face mesh is too coarse or contains adjacent elements with large differences in scale. Another reason can be that some domains in the geometry are too narrow with respect to the rest of the geometry. Try to avoid creating small and narrow domains and very short boundary segments that are adjacent to longer boundary segments. Use Remove Details and Virtual Operations to clean up the geometry. Check the information in the error message for details about location and possible cause of the problem. Also see the section "Troubleshooting Free Tetrahedral Mesh Generation" in the COMSOL documentation.
If possible, send the model file which is causing the issue to COMSOL Technical Support.
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