Problem with CG Motion
 

I'm having a little trouble with the Define_CG_Motion macro. I'm trying to do a simulation of a cylinder moving as a result of pressure and shear forces. This is an image of the problem:

http://i39.tinypic.com/1zg4yo3.jpg

I'm using this UDF, but a moment after I'm starting the calculation an "access violation" error appear..

#include "udf.h"
#include "stdio.h"
#include "stdlib.h"
#include "math.h"
#include "dynamesh_tools.h"
#include "storage.h"

static real v0_prev = 0.0;
static real v1_prev = 0.0;
static real v2_prev = 0.0;

DEFINE_CG_MOTION(CoGRAVITY_M,dt,vel,omega,time,dti me)
{
Thread *t;
face_t f;
real NV_VEC(A);
real force0, force1, force2;
real dv0, dv1, dv2;
real mass = 0.5;

/* reset velocities */
NV_S(vel, =, 0.0);
NV_S(omega, =, 0.0);

if (!Data_Valid_P()) /* Do nothing if gradient isn’t allocated yet. */
return;

/* get the thread pointer for which this motion is defined */
t = DT_THREAD(dt);

/*reset forces*/
force0 = 0.0;
force1 = 0.0;
force2 = 0.0;

begin_f_loop(f,t)
{
F_AREA(A,f,t);
force0 += F_P(f,t)*A[0] + F_STORAGE_R_N3V(f,t,SV_WALL_SHEAR)[0];
force1 += F_P(f,t)*A[1] + F_STORAGE_R_N3V(f,t,SV_WALL_SHEAR)[1];
force2 += F_P(f,t)*A[2] + F_STORAGE_R_N3V(f,t,SV_WALL_SHEAR)[2];
}
end_f_loop(f,t)

/* compute change in velocity, i.e., dv = F * dt / mass velocity update using explicit Euler formula */
dv0 = dtime * force0 / mass;
dv1 = dtime * force1 / mass;
dv2 = dtime * force2 / mass;

v0_prev += dv0;
v1_prev += dv1;
v2_prev += dv2;

/* sets the components of velocity */
vel[0] = v0_prev;
vel[1] = v1_prev;
vel[2] = v2_prev;
printf ("force0 = %f, force1 = %f, X_force2 = %f\n", force0, force1, force2);
}

I've defined all dynamic mesh zones as "deforming" except for the solid interface zone "contact_region-trg" which is defined as "rigid body" with the above UDF.

Any help in this regard will be very appreciated.

with kind regards,
Jessica.