[murthya3]

hi
i am writing a UDF(FLUENT) for VISCOSITY, in which the equation contains inverse hyperbolic function of sin. what is the syntax for the inverse hyperbolic functions.

Thanks in advance

[`e`]

The function for the inverse hyperbolic function of sin is asinh(x), and you may need to include the math library:

#include "math.h"

[murthya3]

Originally Posted by `e`

The function for the inverse hyperbolic function of sin is asinh(x), and you may need to include the math library:

#include "math.h"

thanks 'e'
although, i add math library to my UDF i am getting error like" unresolved external symbol asinh referenced in function cell_viscosity", any library i need to add?
the usage of 'asinh' in the following equation

Flow_stress=(1/alpha)*(asinh(pow((Z/A),(1/n))));

[`e`]

I've tested the asinh function with and without including the math header file and it worked fine both times (possibly this function is included elsewhere in Fluent as well). First, add trailing dots to your numbers (for example, "1.") so the fractions aren't rounded incorrectly. Second, try solving a simpler number: asinh(5) which should return 2.31...

I've now tried interpreting the UDF and it's returning the same error. Compile your UDFs.

[murthya3]

Originally Posted by `e`

I've tested the asinh function with and without including the math header file and it worked fine both times (possibly this function is included elsewhere in Fluent as well). First, add trailing dots to your numbers (for example, "1.") so the fractions aren't rounded incorrectly. Second, try solving a simpler number: asinh(5) which should return 2.31...

I've now tried interpreting the UDF and it's returning the same error. Compile your UDFs.

Thanks 'e'
i have tried everything what you have posted. still i am getting same error. Here i am posting my program please tell me where i made mistake.


and also i am getting error: 'not all control paths return a value'

[Bruno Machado]

Originally Posted by murthya3

Thanks 'e'
i have tried everything what you have posted. still i am getting same error. Here i am posting my program please tell me where i made mistake.

This is the program for creating viscosity for a material
#include "udf.h"

#include "math.h"

#define Q 232560.0 //J/mol
#define A 7.86e+06
#define n 5.37
#define R 8.314 //J/molK
#define alpha 0.038e-06
#define Temp 578.5 //K
DEFINE_PROPERTY(cell_viscosity,c,t)
{
double mu_lam;
double strain;
double Z;
double Flow_stress;
begin_c_loop(c,t)
{
strain = C_STRAIN_RATE_MAG(c,t);
Z=strain*exp(Q/(R*Temp));
Flow_stress=(1./alpha)*(asinh(pow((Z/A),(1./n))));
mu_lam = Flow_stress/(3.*strain);
if(mu_lam>0)
return;
else
return 0;
}
end_c_loop(c,t)
}

and also i am getting error: 'not all control paths return a value'

you are returning nothing. i think you want it to be

return Flow_stress;

[murthya3]

Originally Posted by Bruno Machado

you are returning nothing. i think you want it to be

return Flow_stress;

not flow stress, i should get viscosity(mu_lam), hence return mu_lam, is it wrong?

i have written logarithamic formula for an inverse hyperbolic sine function, but while running it flow is getting reversed, without UDF which means with a constant value of viscosity flow is taking place by keeping boundary conditions same. What would be the reason?

Thanks.

[Bruno Machado]

Originally Posted by murthya3

not flow stress i should get viscosity(mu_lam), hence return mu_lam, is it wrong?

yes, sorry. type it quickly and did not realize it was wrong. you should return the mu_lam value.

return mu_lam;

[murthya3]

Originally Posted by Bruno Machado

yes, sorry. type it quickly and did not realize it was wrong. you should return the mu_lam value.

return mu_lam;

Thanks, Bruno Machado;

yes I did it, and the flow is reversed as stated in previous post.
is that program is correct for getting strain rate from each cell, evaluating viscosity and assigning viscosity to the cell?

[`e`]

Originally Posted by `e`

I've now tried interpreting the UDF and it's returning the same error. Compile your UDFs.

If you're still getting that same error, try compiling your UDF.