UDF works in 2D but not in 3D? Suggestions?

Brian

I have a simple UDF to simulate sloshing of a tank. It works in 2D but not 3D. Anyone know why? I can't seem to find any documentation on 3D and UDF's. The UDF is below as a source term that I use in the BC's to the momentum eqn.

#include "udf.h"

#define period 1.689

#define amplitude 0.005

DEFINE_SOURCE(cell_x_source, cell, thread, dS, eqn) {

real source;

source =(-1.0*amplitude)*pow((2.0*M_PI/period),2.0)*C_R(cell,thread)*sin((2.0*M_PI/period)*CURRENT_TIME);

dS[eqn] = 0.0;

return source; }