[aestas]

hi,friends,i am still work on a MHD problem, i defined current density of three dimensions,Jx,Jy,Jz, and treated them as UDM. Every iteration i put them in UDF DEFINE_ADJUST to update.
the UDM i put in the DEFINE_ADJUST is cell value such as
#define Jx C_UDMI(c,t,0)

One problems are confusing me:
on the boundary of cathode(zone_ID=1), the current density should be treated as evenly distributed as current I/(pi*r^2),how should i define this in UDM?
my ADJUST marco is as follows

DEFINE_ADJUST(uds,d)
{
	Thread *t;
	cell_t c;
	face_t,f;

	/* Make sure there are enough user defined-scalars. */
	if (n_uds < N_REQUIRED_UDS)
		Internal_Error("not enough user-defined scalars allocated");
	thread_loop_c(t,d)
	{
		begin_c_loop_all(c,t)
		{
			Be=e*Bad/me*3.0e10*pow(1.5,3./2.)/(Zi*Zi*C_R(c,t)/mi)
			Jx=sigma*(-C_UDSI_G(c,t,phi)[0]+k*Te/e)*Nz*C_R(c,t)/mi);
			Jy=sigma/(1+Be*Be)*(-C_UDSI_G(c,t,phi)[1]+(k*Te/e)*Ny*C_R(c,t)/mi);
			Jz=Be*Jy;
			J=sqrt(Jx*Jx+Jy*Jy+Jz*Jz);	
		}
		end_c_loop_all(c,t)


	}
}

[aestas]

I came up with one using THREAD_ID to decide how to do in the loop:

DEFINE_ADJUST(uds,d)
{
	Thread *t;
	cell_t c;
	face_t,f;
	int zone_ID;
	/* Make sure there are enough user defined-scalars. */
	if (n_uds < N_REQUIRED_UDS)
		Internal_Error("not enough user-defined scalars allocated");
	thread_loop_c(t,d)
	{
		zone_ID=THREAD_ID(t);
		if zone_ID==1
		{
			begin_c_loop_all(c,t)
			{
				Jx=6.4e5;
				Jy=0;
				Jz=0;
				J=sqrt(Jx*Jx+Jy*Jy+Jz*Jz);	
			}
			end_c_loop_all(c,t)

		}
		else
		{
			begin_c_loop_all(c,t)
			{
				Be=e*Bad/me*3.0e10*pow(1.5,3./2.)/(Zi*Zi*C_R(c,t)/mi)
					Jx=sigma*(-C_UDSI_G(c,t,phi)[0]+(k*Te/e)*Nz*C_R(c,t)/mi);
				Jy=sigma/(1+Be*Be)*(-C_UDSI_G(c,t,phi)[1]+(k*Te/e)*Ny*C_R(c,t)/mi);
				Jz=Be*Jy;
				J=sqrt(Jx*Jx+Jy*Jy+Jz*Jz);	
			}
			end_c_loop_all(c,t)


		}
	}
}

but i don't know whether it's right or wrong,and i am not sure whether a boundary zone has cell values or just has face value.I need the cell value of current denesity to calculate other varibles. So help me,my friends

[Lin_wg]

DEFINE_PROFILE(current_density,thread,position)
{
real x[ND_ND],x1,y1,r;
face_t f;

begin_f_loop(f,thread)
{
F_CENTROID(x,f,thread);
x1=x[0],y1=x[1];
r=sqrt(x1*x1+((y1-0.0055)*(y1-0.0055)));
if(r<0.003)
{
F_PROFILE(f,thread,position)=-1.2e8*exp(-1920.88*r);
}
else
{
F_PROFILE(f,thread,position)=0;
}
}
end_f_loop(f,thread)
}
I think you can try like this