[antton]

Hello,

I am writting an UDF to calculate the density of my mixture taking into account the temperature and species mass fraction.

When I consider only the temperature change the simulation is OK. However when I consider both (temperature and species mass fraction) I have problems solving the simulation.

Can someone help me?

Thanks

*****

DEFINE_PROPERTY(density_mixture,c,t)
{
/* Definir variables */

int i = 0;
Material *sp;

real density;
real temp;
real conc;

real alpha;
real beta;
real homogeneous_density;
real homogeneous_concentration;

alpha = 0.001222587;
beta = 0.275;
homogeneous_density = 748.435;
homogeneous_concentration = 0.5167;

/* Temperatura & concentracion de celda */

temp = C_T(c,t);

mixture_species_loop(THREAD_MATERIAL(t),sp,i)

{
conc = C_YI(c,t,i);
}

/* Ecuación */

density = homogeneous_density*((1)-(alpha*(temp- 298.16))+(beta*(conc-0.5167)));

/* Result return */

return density;
}

[pakk]

"problems solving the simulation"

This can mean many things... Crash, doesn't converge, converges too slow, converges to a wrong solution... What do you mean here?

[antton]

I have problems with the simulation because it does not convergence, the residuals go up.

The question is that if I put in the UDF only the part of the temperature and alpha and eliminate the part of the concentration the simulation convergence correctly. Why can happen this?

I want to consider both parts (temperature and concentration) and I dont know where is the error.

Thanks

[Guvennergiz]

You want to read overall temperature of mixture or temperature of every fractions in the mixture?

[antton]

Hi

I want to read the temperature of each cell and also the mass fraction of each cell. Ones I know that information, I want to calculate the density using the UDF that I send.

If I consider only the temperature, the simulation runs correctly but when I use the mass fraction macro the simulation doesnt convergence.

Thanks

[pakk]

But the mass fraction of what? Your code is not clear about it.

You have a mixture. Your mass fractions will sum to 100%. In your code, you calculate them all, and use the last calculated mass fraction. You're lucky if that is the one you want...

[antton]

Hi

I want use the mass fraction of my first component in each cell to calculate the density later.

conc = C_YI(c,t,i);

With this can I calculate that eliminating the loop part?

I want to know the mass fraction of my first component (i) in each cell.

Thanks

[pakk]

The first component is i=0.

conc = C_YI(c,t,0);

[antton]

Yes I know that and in the UDF I define int i = 0. So if I eliminate the loop the other part is correct in the UDF? If I eliminate the loop am I considering the mass fraction in each cell of the first species to calculate then the density?

Thanks

[pakk]

If with "the loop" you mean "mixture_species_loop(THREAD_MATERIAL(t),sp,i) ", then yes.

[antton]

Hi again,

I eliminte the "loop" part butI have the same problems, the simulation doesnt convergence.

If I only consider the temperatura and I delete the part in wich I take into account the mass fraction of my first species, the UDf that I use is the following one and the simulation convergence correctly:

#include "udf.h"

DEFINE_PROPERTY(density_mixture,c,t)
{
/* Definir variables */

int i = 0;
Material *sp;

real density;
real temp;
real conc;

real alpha;
real beta;
real homogeneous_density;
real homogeneous_concentration;

alpha = 0.001222587;
beta = 0.275;
homogeneous_density = 748.435;
homogeneous_concentration = 0.5167;

/* Temperatura & concentracion de celda */

temp = C_T(c,t);

/* Ecuación */

density = homogeneous_density*((1)-(alpha*(temp- 298.16)));

/* Result return */

return density;
}

Why can happen this? Maybe is because the density and mass fraction equations are related and is not posible to calculate the density taking into account the mass fraction?

Thanks