[Lyapunov]

Hi everyone, I'm modeling a 2D gas-solid fluidized bed in TFM. The geometry is a simple rectangle with structural mesh.
The BCs:
velocity inlet with only air in
pressure outlet
no-slip for gas phase at wall
partial slip for solid phase at wall
The simulation runs well for several seconds. However, it suddenly crashes with AMG solver divergence and floating point exception. Besides, when the problem appears, the solid phase seems to be blown away by the gas phase. I've checked the mesh, decreased URFs, lowered the time step and changed some parameters of solid phase but it still doesn't work.
Any advice would be very appreciated.
Thanks in advance.

[Lyapunov]

Anyone can help?