Velocity vs Pressure in Porous Medium
 

I am solving a problem in a porous bed (1Dimension-unsteady state). At present I am trying to solve for change in concentrations due to convection. I am solving for u1 by fixing value of u1 at each time step, specified through patch in Group 13. But I do not know this velocity to specify at each time step and I have a equation v=(Ke (Del Phi/Del X) + Kh (Del P / Del X), where v is velocity, Ke is electroosmotic conductivity,Kh is hydraulic conductivity, Phi is voltage, P is pressure. Pressure is unknown and at each time step I am calculating through a Gauss Seidel subroutine I made in Ground which uses another equation having all of above defined terms. Now my queries are : 1. Can I use 'gxgauss' subroutine given in gxfiles for Gauss Seidel solver instead of writing my own code as sub-routine in ground? If so how to call it? 2. When I solve for velocity, invariably I will be activating convection terms for my concentrations (c1,c3, c5 etc) in terms and solve for u1 also. But do I need to solve for pressure also (p1)? If p1 has to be solved, do I have to specify the pressures calculated with sub-routine in ground and to be called through patch in group 13 like I am doing for u1?

Infact I tried to calculate the pressures and used them to calculate the velocity and fixed u1 as fixval in group 13 of ground without solving p1. But my velocities at all the points are not equal which means continuity equation is not satisfied. I think I need to do some pressure corrections (SIMPLE METHOD). Do PHOENICS take care of it? If so what are the commands to be activated/solved.

Thanks in advance!!!

Regards,

Sanjay