[jreiter164]

Hello all,

I am a new FLUENT user and am having an issue getting a UDF I wrote to work. I am trying to create user defined functions for density and viscosity as a function of concentration. The code is as follows:

#include "udf.h"

#define rhoC3 -70.481
#define rhoC2 239.64
#define rhoC1 -383.15
#define rhoC0 995.08

DEFINE_PROPERTY(mixture_density,c,t)
{
real ethanol_mf, rho;

ethanol_mf=C_YI(c,t,0);

rho=rhoC3*pow(ethanol_mf,3)+rhoC2*pow(ethanol_mf,2 )+rhoC1*ethanol_mf+rhoC0;

return rho;
}

#define muC4 -1e-5
#define muC3 4e-5
#define muC2 -3e-5
#define muC1 1e-5
#define muC0 8e-7

DEFINE_PROPERTY(mixture_viscosity,c,t)
{
real ethanol_mf, mu;

ethanol_mf=C_YI(c,t,0);

mu=muC4*pow(ethanol_mf,4)+muC3*pow(ethanol_mf,3)+m uC2*pow(ethanol_mf,2)+muC1*ethanol_mf+muC0;

return mu;
}

It interprets fine and I can hook it into my mixture properties, but when I try and initialize I get the following error message:

FLUENT received fatal signal (ACCESS_VIOLATION)
1. Note exact events leading to error.
2. Save case/data under new name.
3. Exit program and restart to continue.
4. Report error to your distributor.

Does anyone know to fix this issue? Help will be greatly appreciated.

[maverick123]

Hi,

Instead #define , initialize your constants in
DEFINE_PROPERTY()
{
real rhoC3 = -70.481;
}

and it is better to use only alphabets to name a variable/constant. You may consider to rename the constant name as well.

Best Luck!

Originally Posted by jreiter164

Hello all,

I am a new FLUENT user and am having an issue getting a UDF I wrote to work. I am trying to create user defined functions for density and viscosity as a function of concentration. The code is as follows:

#include "udf.h"

#define rhoC3 -70.481
#define rhoC2 239.64
#define rhoC1 -383.15
#define rhoC0 995.08

DEFINE_PROPERTY(mixture_density,c,t)
{
real ethanol_mf, rho;

ethanol_mf=C_YI(c,t,0);

rho=rhoC3*pow(ethanol_mf,3)+rhoC2*pow(ethanol_mf,2 )+rhoC1*ethanol_mf+rhoC0;

return rho;
}

#define muC4 -1e-5
#define muC3 4e-5
#define muC2 -3e-5
#define muC1 1e-5
#define muC0 8e-7

DEFINE_PROPERTY(mixture_viscosity,c,t)
{
real ethanol_mf, mu;

ethanol_mf=C_YI(c,t,0);

mu=muC4*pow(ethanol_mf,4)+muC3*pow(ethanol_mf,3)+m uC2*pow(ethanol_mf,2)+muC1*ethanol_mf+muC0;

return mu;
}

It interprets fine and I can hook it into my mixture properties, but when I try and initialize I get the following error message:

FLUENT received fatal signal (ACCESS_VIOLATION)
1. Note exact events leading to error.
2. Save case/data under new name.
3. Exit program and restart to continue.
4. Report error to your distributor.

Does anyone know to fix this issue? Help will be greatly appreciated.

[pakk]

I think your #define's are fine, and there is nothing wrong with your variable names.

The problem is, I think, in the line

ethanol_mf=C_YI(c,t,0);

When you start to initialize, you don't have any data yet. But your code tries to get the species mass fraction anyway. Fluent does not know what to do.

You can try to test if I am right by changing that line to:

ethanol_mf=0.25;

If your code then runs without problems, it is due to C_YI.

If that is the case, you should fix the code by first checking if C_YI is set; if it is set, read it, if it is not set, choose a default value (e.g. 0.0). I don't remember the Fluent macro to check if a value is set, but it exists.

[jreiter164]

Thanks Pakk,

I think you are right about the source of the error, when I put in a constant value for ethanol_mf the simulation initialized fine.

I would like to implement your solution of checking to see if C_YI has a value or not prior to defining the mass fraction for the cell. I am having difficulty doing that.

Does anyone know how to perform this? Also, is there a "command window" or something like that where I can just put in a line of code and see its effect? I am used to having this in MATLAB.