Divergence detected in AMG solver
 

Hello. everyone!
I am doing numerical simulation of the 2D VIV of a cylinder. The mesh is divided by Gambit, see below.There is a 3D*3D tri mesh zone around the cylinder. The outside is quad mesh zone. I want to produce a 2 degree freedom vibration of the cylinder through UDF and dynamic mesh. The UDF have been compiled into the fluent. The problem now is that it will diverge when the calculation reaches a certain number of steps, appears" Error: Divergence detected in AMG solver: x-momentum; Error Object:#f". I don't know what the specific problem happened. Will it be an error in the UDF, or the parameter settings are incorrect? Can you give help to me? Thanks!