how to define F=R1*vis*Laplace(vel) as source term
 

hi everyone

I am modeling the 3D two phase flow of Solid-Gas and I want to define the following formulation for internal-force between solid particles:

F = VolumeFraction * Viscosity * Laplace(Vel)

I defined the solid phase as 1st phase in the model and I am thinking of using FNDSDX function with DUDX for calculation of Laplace(vel). I am wondering how to do it? I could not figure out from POLIS so I am posting this in here if anyone can help me with this.

Tanx
/Reza