[usr0830]

Hello everyone,
I am new to Fluent and UDFs and c. I hope the community can help me with fixing the errors in my first UDF.

I am trying to sample the components of velocity at two points close to a rotating airfoil at every timestep. Firstly, I find the location of the sampling points in global coordinates as a function of theta (which is dependent on time). Then, I use CX_Find_Cell_With_Point to find the cells with these points. Once the cells are found, the centroid is calculated and the velocities are extracted.

I have compiled the udf successfully in Fluent but when I start the simulation, at the end of the first timestep, I get an error message saying the fluent process could not be started. I have already tried checking it with both single and parallel processing and also with and without double precision as suggested by some on this forum with no success.
I have attached the udf and the error message here. Kindly help me resolve this issue.
Thank you.

Code:

#include "udf.h"
#include "cxndsearch.h"
static ND_Search *domain_table1 = NULL;
static ND_Search *domain_table2 = NULL;
static float c_centroid1[2];
static float c_centroid2[2];
static int starting_dt = 200; /* Setting the starting time step. */
static float R = 0.25; /* Radius */
static cell_t c1;
static cell_t c2;
static Thread *t1;
static Thread *t2;
static CX_Cell_Id *cx_cell1;
static CX_Cell_Id *cx_cell2;
real pt1[3];
real pt2[3];
real U_vel1;
real V_vel1;
real U_vel2;
real V_vel2;
real xTheory;
real yTheory;
real theta;
FILE *velocity_t1;
FILE *velocity_t2;
real current_dt;

DEFINE_EXECUTE_AT_END(execute)
{
#if !RP_HOST
        Message("UDF begin execution");
	current_dt = CURRENT_TIMESTEP;
	Message("Current timestep acquired");
	if (current_dt <=starting_dt)
	{
		theta = 0;
	}
	else
	{
	  theta = (current_dt - starting_dt)* 0.004363323; /* dtheta = 0.004363323 rad. Change if dt changes)*/
	}
	xTheory = 0 - R * sin(theta); /* Point at the mounting point of the airfoil */
	yTheory = 0 + R * cos(theta);

/* Evaluation point near the LE*/
	if (theta <= M_PI) 
	{
		pt1[0] = xTheory - 0.0375; 
	} 
	else
	{
		pt1[0] = xTheory + 0.0375;
	}
	if (yTheory >= 0)
	{
		pt1[1] = yTheory + 0.05;
	}
	else 
	{
		pt1[1] = yTheory - 0.05;
	}
	
	pt1[2] = 0.0;

	/* Evaluation point near the TE*/
	if (theta <= M_PI) 
	{
		pt2[0] = xTheory - 0.0375;
	} 
	else
	{
		pt2[0] = xTheory + 0.0375;
	}
	if (yTheory >= 0)
	{
		pt2[1] = yTheory - 0.05;
	}
	else 
	{
		pt2[1] = yTheory + 0.05;
	}
	
	pt2[2] = 0.0;

	domain_table1 = CX_Start_ND_Point_Search(domain_table1,TRUE,-1); 
	cx_cell1 = CX_Find_Cell_With_Point(domain_table1,pt1,0.0);

	if (cx_cell1) {
		c1 = RP_CELL(cx_cell1);
		t1 = RP_THREAD(cx_cell1);
		C_CENTROID(c_centroid1,c1,t1);
		U_vel1 = C_U(c1,t1);
		V_vel1 = C_V(c1,t1);
	} else {
		Message("Could not find cell!\n"); 
	}
	domain_table1= CX_End_ND_Point_Search(domain_table1);

	domain_table2 = CX_Start_ND_Point_Search(domain_table2,TRUE,-1); 
	cx_cell2 = CX_Find_Cell_With_Point(domain_table2,pt2,0.0);
	if (cx_cell2) {
		c1 = RP_CELL(cx_cell2);
		t1 = RP_THREAD(cx_cell2);
		C_CENTROID(c_centroid2,c2,t2);
		U_vel2 = C_U(c2,t2);
		V_vel2 = C_V(c2,t2);
	} else {
		Message("Could not find cell!\n"); 
	}
	domain_table2 = CX_End_ND_Point_Search(domain_table2);
	Message("UDF run finished");
#endif


#if !RP_HOST
velocity_t1=fopen("velocity1.txt","ab+");
fprintf(velocity_t1,"%15.4f\t%15.6f\t%15.6f\t%15.6f\t%15.6f\t%15.6f\t%15.6f\t%15.6f\t\n",CURRENT_TIMESTEP,theta,xTheory,yTheory,c_centroid1[0],c_centroid1[1],U_vel1,V_vel1);
fclose(velocity_t1);

velocity_t2=fopen("velocity2.txt","ab+");
fprintf(velocity_t2,"%15.4f\t%15.6f\t%15.6f\t%15.6f\t%15.6f\t%15.6f\t%15.6f\t%15.6f\t\n",CURRENT_TIMESTEP,theta,xTheory,yTheory,c_centroid2[0],c_centroid2[1],U_vel2,V_vel2);
 fclose(velocity_t2);
#endif
}

Error message:
Node 0: Process 48048: Received signal SIGSEGV.

================================================== ============================

The fluent process could not be started.

[usr0830]

As mentioned in the title, I managed to fix the issue. It was because of the wrong use of CURRENT_TIME macro.