[aashna@iitp]

I am trying to write C-code for specifying rheology model of grease. For this, I am using the Herschel-Bulkley model. But my UDF has three compilation errors. I have attached my codes here.
If anyone has any idea about it, please let me know.

[AlexanderZ]

put here your code, NOT PICTURE

you need math.h library,
make all variable types the same (double or float)
2 and 3 lines are confusing

where is information about error you've gotten?

best regards

[aashna@iitp]

#include ''udf.h''
double pow(double, double);
double exp(double);
float yst = 189;
float m = 1;
float k = 4.1;
float n = 0.797;
define VISCOSITY(cell_viscosity,c,t)
{
float visco;
float rate;
rate= (C_STRAIN_RATE_MAG(c,t));
visco =(((yst/rate)*(1-exp((-1)*m*rate)))+(k*pow(rate,(n-1))));
return visco;
}

The errors displaying are:
1. unable to open include file 'UDF.H'
2. For line8, Declaration syntax error

In the Ansys user guide manual, it was given to use udf.h for defining all udfs.

[AlexanderZ]

you should set appropriate environment variables (windows environment variables)
https://www.cfd-online.com/Wiki/Fluent_FAQ
read User-Defined Function (UDF) Related carefully

best regards

[aashna@iitp]

As suggested, I set up the environment variables and then compiled the UDF. It is getting compiled and I am able to successfully hook it to fluent and use it to set the viscosity variation as per the modified Herschel-Bulkley rheology model.

But when the software solves it, an error message pops up. It reads: ''floating-point exception. Divergence detected.''

This is after the first iteration itself. Can anyone suggest me where am I wrong? Are my codes incorrect or there is any problem with the way it is being hooked?

[AlexanderZ]

when you a telling, that there were no errors during compilation, what did you mean?

I've told you, you must put here your code and console output each time!

use code

#include "udf.h"
#include "math.h"

float yst = 189;
float m = 1;
float k = 4.1;
float n = 0.797;
DEFINE_PROPERTY(cell_viscosity,c,t)
{
float visco;
float rate;
rate= (C_STRAIN_RATE_MAG(c,t));
visco =(((yst/rate)*(1-exp((-1)*m*rate)))+(k*pow(rate,(n-1))));
return visco;
}

best regards

[bloodflow]

It likely diverges becauses the equation or coefficients are wrong, from what I have looked up on the Herschel-Bulkley model I cant understand your equation, can you post a link to the paper you get these values and equations from?