[Jinming Wu]

Hello, everyone! I have some problems with my 3D dynamic mesh, multi-phase simulation. I use FLUENT to simulate the buoy dynamics in water and air surface. However, the simulation always diverges when the buoy touches the free surface, No matter how small is the time step (0.00001s), and how small is the cell size. I have tried 2D simulation with the same parameters, and there are no such problems, although near the free surface, the convergence time may be longer than in other regions.
Pic. 1 is the buoy and the water surface (Blue for volume fraction of water to be 0, green for 0.5, and red for 1). If the buoy is placed above the free surface, then it will be no problem until the buoy touches the surface. If the buoy is placed intersecting the free surface, then the simulation will diverge very quickly after 3 or 4 time steps.
Pic. 2 is the overall mesh, while Pic. 3 shows the inner mesh.
Thank you for your suggestions.