three phase modelling (air sand water )

Gunjan kumar

hi I am trying to simulate a two-dimensional flow over weir with a sluice gate inlet ,a simlified version of the three-dimensional flow over a weir .sand is laid on the bottom and water flows over it . As the water starts to flow over the initially flat erodible sand bed,the scouring potential of moving water, created by incoming high velocity, is usually so strong that sand grains are immediately dislodged from the surface and transported downstream . i want to get the scour profile i tried VOF and eulerian model,but didnt get desired result ,because both model requires viscosity of sand which is unknown to me in Eulerian model, iteration didnt proceed after 500 iteration it is giving message "Turbulent viscosity limited to viscosity ratio of 1.0000e+05 in 9017 cells. Error :-Floating point error invalid number " please suggest me remedy and which model is suitable for my problem . thanks for ur cooperation