modeling MHD with COMSOL

Hi Aoki, I read your two papers about MHD with salty water flow. Can you hellp me? At first I want do modeling your MHD with COMSOL (4.3b) and later I will be able other modeling of MHD. I do all of work that you write in the papers I do it. But i can´t put the Lorentz force in simulation and term of inlet velocity U(0;y;z) = 2U0*U*1*s1*(1-s1)*s2*(1-s2). I used 2 electrodes (20*20*3mm) and 2 magnets (70*20*10mm) and salt water in the middle of them.
I would be grateful if you help me.