[Eanna.Kennedy]

I am trying to calculate the standard deviation of particles about the centre of a channel at a sampling plane near the exit and I am having trouble getting my UDF to work. The UDF compiles and loads fine, but it causes fluent to crash when i try to run it. I have included my code below. I think the problem is probably due to the need to loop through all particles in a Macro that doesn't take in any DPM arguments. Any advice would be really appreciated. Thanks.

#include "udf.h"
#include "dpm.h"
#include "surf.h"
#include "dpm_types.h"
#include "dpm_laws.h"

/************************************************** ****************/
/* UDF records Standard Deviation of all particles on a plane */
/************************************************** ****************/

double Standard_Deviation = 0.0; /* intitialise standard deviation as global variable*/

/*Creates Output Parameter Standard Deviation*/
DEFINE_REPORT_DEFINITION_FN(standard_deviation)
{
return Standard_Deviation;
}

DEFINE_ON_DEMAND(Get_Particle_Positions)
{
double d = 0.0;
double y = 0.0;
double z = 0.0;
double dbar = 0.0;
double deviation = 0.0;
double counter = 0.0;
int zone_ID = 3; /* initialise zone id for sampling plane*/
Thread *c_thread; /* c_thread is declared as a variable */
Domain *domain; /* domain is declared as a variable */
Tracked_Particle *tp; /* tp declared as identifier for tracked particles */
cell_t c; /* c declared as identifier for cells */

domain = Get_Domain(1); /* returns fluid domain pointer */
c_thread = Lookup_Thread(domain,zone_ID);
tp = 0;

/* Loop calculates sum of particle-to-centre distances, allows mean distance to be calculated later*/

begin_c_loop(c, c_thread) /* loops over cells in a cell thread */
{
while(NULLP(tp)){ /* checks that tp points to actual particle*/
y = TP_POS0(tp)[1];
z = TP_POS0(tp)[2];
d += sqrt((y*y) + (z*z));
tp ++;
counter ++;
};
}
end_c_loop(c, c_thread)

dbar = d / counter; /* calculate mean particle-to-centre distance*/
tp = 0; /* reset particle pointer*/

/* Loop to calculate sum of squared particle-to-mean distances */
begin_c_loop(c, c_thread)
{
while(NULLP(tp)){ /* checks that tp points to actual particle*/
y = TP_POS0(tp)[1];
z = TP_POS0(tp)[2];
d = sqrt((y*y) + (z*z));
deviation += pow((dbar - d), 2);
tp ++;
};
}
end_c_loop(c, c_thread)

Standard_Deviation = deviation / counter;
}