[Cooper24]

Hello all!! I am new to writing UDFs and am trying to model Selective Laser Melting making use of UDF for moving laser as a source term in the energy equation. I am using volume of fluid for this. I have written a UDF for this. The UDF compiles without any error and initializes also without any error. It's just that when I try to run the simulation, FLUENT crashes. I have attached the equation which I am trying to add as a source term, the screenshot of the error and my UDF also. I think there is some issue with the DEFINE_ADJUST which I am using to get gradient of volume fraction.
I request you all to please help me. I would be really grateful as I am facing a lot of difficulty and running out of time.
Thanks in advance.

#include "udf.h"
#include "sg_mphase.h"
#include "mem.h"
#include "sg_mem.h"
#include "math.h"
#include "flow.h"
#include "unsteady.h"
#include "metric.h"

#define A 0.4 // Absorption coefficient
#define P 200 // Laser power
#define R 80e-6 // spot radius
#define v 0.1 // scan speed of laser
#define h 25 // Heat transfer coefficient
#define Ta 298 // Ambient air temperature
#define s 5.67e-8 // Stefan Boltzmann constant
#define e 0.5 // Emmisivity
#define Pi 3.1415926535
#define Ts 1658 // Solidus temperature
#define Tl 1723 // Liquidus temperature
#define x0 100e-6 // Initial x position of the laser
#define y0 0.0 // Intiial y position of the laser
#define domain_ID 3 // Domain ID of metal substrate


DEFINE_INIT(volume_fraction, mixture_domain)
{
int phase_domain_index = 1;
cell_t c;
Thread *t;
Domain *subdomain;
real xc[ND_ND];
sub_domain_loop(subdomain, mixture_domain, phase_domain_index)
{
if(DOMAIN_ID(subdomain) == 3)
thread_loop_c(t,subdomain)
{
begin_c_loop_all(c,t)
{
C_CENTROID(xc,c,t);
if(xc[0] > -0.5e-3 && xc[0] < 0.5e-3 && xc[1] > -0.25e-3 && xc[1] < 0.25e-3 && xc[2] < 0 && xc[2] > -0.3e-3)
C_VOF(c,t) = 1.0;
else
C_VOF(c,t) = 0.0;
}
end_c_loop_all(c,t)
}
}
}




DEFINE_ADJUST(adjust_gradient, mixture_domain)
{
int phase_domain_index = 1;
Thread *t;
cell_t c;
Domain *subdomain = DOMAIN_SUB_DOMAIN(mixture_domain,phase_domain_inde x);

sub_domain_loop(subdomain, mixture_domain, phase_domain_index)
{
if(DOMAIN_ID(subdomain) == 3)
thread_loop_c(t, subdomain)
{
begin_c_loop(c,t)
{
C_UDSI(c,t,0) = C_VOF(c,t);
C_UDMI(c,t,1) = C_UDSI_G(c,t,0)[0];
C_UDMI(c,t,2) = C_UDSI_G(c,t,0)[1];
C_UDMI(c,t,3) = C_UDSI_G(c,t,0)[2];
C_UDMI(c,t,4) = sqrt(C_UDMI(c,t,1)*C_UDMI(c,t,1) + C_UDMI(c,t,2)*C_UDMI(c,t,2) + C_UDMI(c,t,3)*C_UDMI(c,t,3));
}
end_c_loop(c,t)
}
}
}



DEFINE_SOURCE(heat_source, c, t, dS, eqn) // The name of the UDF is heat_source
{
Thread *pri_th;
Thread *sec_th;
real source;
real x[ND_ND], time; // Define face centroid vector, distance, time, exponential for laser and volume to get cell volume
time = RP_Get_Real("flow-time"); // Acquire time from Fluent solver
C_CENTROID(x, c, t); // Acquire the cell centroid location
real T = C_T(c,t);
pri_th = THREAD_SUB_THREAD(t, 0);
sec_th = THREAD_SUB_THREAD(t, 1);

if(C_VOF(c,t)>0.05 && C_VOF(c,t)<1)
{
source = (((2*A*P)/(Pi*R*R))*exp((-2*(pow(x[0]-x0-v*time,2.0) + pow(x[1]-y0,2.0)))/(R*R)) - h*(T-Ta) - s*e*(pow(T,4) - pow(Ta,4)))*C_UDMI(c,t,4);
dS[eqn] = 0.0;
}
else
{
source = 0.0;
dS[eqn] = 0.0;
}
return source;
}

[AlexanderZ]

I've received an error while compiling your code,
try to use following

DEFINE_SOURCE(heat_source, c, t, dS, eqn) // The name of the UDF is heat_source
{
Thread *pri_th;
Thread *sec_th;
real source;
real x[ND_ND], time, T; // Define face centroid vector, distance, time, exponential for laser and volume to get cell volume
time = RP_Get_Real("flow-time"); // Acquire time from Fluent solver
C_CENTROID(x, c, t); // Acquire the cell centroid location
T = C_T(c,t);
pri_th = THREAD_SUB_THREAD(t, 0);
sec_th = THREAD_SUB_THREAD(t, 1);

if(C_VOF(c,t)>0.05 && C_VOF(c,t)<1)
{
source = (((2*A*P)/(Pi*R*R))*exp((-2*(pow(x[0]-x0-v*time,2.0) + pow(x[1]-y0,2.0)))/(R*R)) - h*(T-Ta) - s*e*(pow(T,4) - pow(Ta,4)))*C_UDMI(c,t,4);
dS[eqn] = 0.0;
}
else
{
source = 0.0;
dS[eqn] = 0.0;
}
return source;
}

[Cooper24]

Thanks for your reply. Actually I want to multiply tha heat equation term with magnitude of gradient of volume of fraction, as you can see in the attached image in which equation is shown. That is why I have used UDMI for storing the gradient and magnitude of gradient. When I am compiling, it compiles without any error. FLUENT just crashes when I run the simulation. Can you tell if it is the right way to use and multiply with volume fraction gradient??

Thanks