[shubham]

Hello all,
I have a problem in defining Density. I am simulating multiphase simulation where density is a function of Temperature and composition. For that I want to define two different density calculation formula in two different cell zones.

For this I am using the following UDF:



#include "udf.h"
#include "math.h"
#include "materials.h"
#include "threads.h"

/* I want to define two different DENSITY variation in two different cell zones. */

DEFINE_PROPERTY(cell_density,c,t)
{
real rho;
int i;

real T;
real xch4;
Material *sp;
Domain *mixture_domain;
mixture_domain = Get_Domain(3); // domain id of liquid phase = 3
Thread *tc1,*tc2;
tc1 = Lookup_Thread(mixture_domain,14); //14 is Domain id of bottom zone
tc2 = Lookup_Thread(mixture_domain,15); //15 Domain id of middle zone


if (t == tc1) //when thread pointer at bottom zone xch4 remain constant
{
mixture_species_loop(THREAD_MATERIAL(t),sp,i)

{
T = C_T(c,t);
xch4 = 0.89;
rho = (-0.8292 - (0.5407*xch4))*(T - 100) - (250.15*xch4) + 690.73;

}
//return rho;

}

else if (t == tc2) //when thread pointer at middle zone Temperature remain constant
{
mixture_species_loop(THREAD_MATERIAL(t),sp,i)

{
T = 111.67;
xch4 = C_YI(c,t,1);
rho = (-0.8292 - (0.5407*xch4))*(T - 100) - (250.15*xch4) + 690.73;
}
//return rho;

}

return rho;


}







The UDF compiles without any problems. However, as soon as it starts,
the simulation begins to diverge. Without UDF, the simulation runs without a hitch.
I can't seem to figure out what the issue is.
Does anyone have an idea what this can be due to?

Many thanks in advance.

[AlexanderZ]

i think you don't need these lines:

mixture_species_loop(THREAD_MATERIAL(t),sp,i)

most likely concentration macro leads to error

xch4 = C_YI(c,t,1);

it is possible, that at 0 moment concentration is not defined yet, but you are trying to use it for calculations, that will lead to problems if that is the case.
You may try to define some specific value for initialization (when time = 0) explicitly to bypass possible issue.

make sure you are using correct index for material either, which you put as 1