Fluid dynamics simulation

[1904288070]

I used to have a small surface in the model, but after modifying the simulation generated mesh, there was no such problem Non-manifold. However, this time when I modified the model, there was no small surface, but the problem occurred again. What is the reason for this. But removing that thread and turning it into a cylinder will generate a solid mesh without any problem.

[Rob]

Non-manifold means you have a surface-surface contact with no area. So chances are you have a tangential contact somewhere that may or may not be linked to the small surface.