[Sinon Lee]

hello, everyone, I am doing the work about a velocity slip boundary condition in a two phase flow, i need to define the different slip lengths of the water and oil in a microchannel. so i use the following UDF to do this work. but the mistake says:
Error:
FLUENT received fatal signal (ACCESS_VIOLATION)
1. Note exact events leading to error.
2. Save case/data under new name.
3. Exit program and restart to continue.
4. Report error to your distributor.
Error Object: ()
will occur after some loops over the channel wall just in the first iteration,


#include "udf.h"
#include "sg_mphase.h"
#define lso 4e-6 /*oil slip length*/
#define lsw 1e-6 /*water slip length*/
#define h 2e-6 /*height of first cell center*/
real x[ND_ND];
real mu;
real vof;

DEFINE_PROFILE(shear_x,t,position)
{

face_t f;
cell_t c0,c2;
Thread *t0=THREAD_T0(t);
Thread *t2=THREAD_SUB_THREAD(t,1);
double ux;
begin_f_loop(f,t)
{
c0=F_C0(f,t);
F_CENTROID(x,f,t);

mu=C_MU_L(c0,t0);
ux=C_U(c0,t0);
Message ("1\n (%f,%f,%f)\n",x[0],x[1],x[2]);
Message ("1\n");
vof=C_VOF(c0,t2);
Message ("2\n");
F_PROFILE(f,t,position)=mu*ux/(lso*(1-vof)+lsw*vof+h);
}
if ((x[0]>=450e-6&&x[0]<=800e-6)&&(x[1]>=98e-6&&x[1]<=100e-6)&&x[2]>=48e-6&&x[2]<=52e-6)
Message ("shear_x=%f\n vof=%f\n mu=%f\n ux=%f\n",mu*ux/(lso*(1-vof)+lsw*vof+h),vof,mu,ux);
end_f_loop(f,t)
}

this is my code, the mistake may be caused by "vof=C_VOF(c0,t2);" debugged by “Message ("1\n");” and “Message ("2\n");”
many thanks for your kindly help.