divergence always happen while UDF was used
 

im working on the simulation about the navier slip boundary condition, and i used a UDF to make this boundary condition. i set the wall condition:

"shear condition"->"no slip"
"wall motion"->"moving wall"-> "X-velocity:udf wall_velocity_x"and the udf code is here:

#include "udf.h"

DEFINE_PROFILE(wall_velocity_x, thread, position)
{
face_t f;
Thread *t0;
cell_t c0;
double VC[ND_ND];
double lambda=100E-6;
double dudy;

begin_f_loop(f, thread)
{
t0 = THREAD_T0(thread); /* adjacent cell thread to f */

c0 = F_C0(f, thread);

dudy = C_DUDY(c0,t0);


VC[0]=-lambda*dudy;

VC[1]=0; /* stress vector's y componant*/



F_PROFILE(f, thread, position)=VC[0];

}

end_f_loop(f, thread)
}



why "divergence detected in AMG solver:pressure correction" always showed?

I think the meshing is ok, coz I tried using "no slip"and "stationary wall" condition to solve that question and it worked. but every time i used this udf with a large "lambda", it would divergent.

Any people has any idea? plz help...