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Old   January 20, 2016, 10:31
Exclamation Compile UDF for Fluent
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Ganesh K C
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I need to include Lorentz force equation as a source term in my model. how can i compile a UDF and use it in fluent ?
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Old   January 20, 2016, 17:03
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Use the DEFINE_SOURCE macro for specifying a custom source term (ensure the units are of the form generation rate per volume, e.g. kg/m^3/s for the continuity equation), there are a couple of examples in the UDF manual to get you started (ask back here if you get stuck). As for compiling UDFs, see the reply in your duplicate thread.
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Old   January 21, 2016, 12:42
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Ganesh K C
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respected sir,
could suggest me what mistake i do in this code as given below ?

#include "udf.h"
#define mu 1.26*(10e-6)
#define I 300
#define reff 0.008
#define r 0.005
/*--------------------------------------------------------
Momentum source term in x
----------------------------------------------------------*/
DEFINE_SOURCE(xmom_source,c,t,dS,eqn)
{
float x[ND_ND], source;
face_t f;
F_CENTROID (x,f,t);
source =-((mu*I*I)/(4*3.14*3.14*reff*reff*r)) * (exp (-r*r / (2*reff*reff))) * (1-(exp (-r*r / (2*reff*reff)))) * pow((1-(x[1]/t),2) * (x[0]/r);
dS[eqn] = 0;
return source;
}
/*--------------------------------------------------------
Momentum source term in y
----------------------------------------------------------*/
DEFINE_SOURCE(ymom_source,c,t,dS,eqn)
{
float x[ND_ND], source;
face_t f;
F_CENTROID (x,f,t);
source = -((mu*I*I)/(4*3.14*3.14*r*r)) * pow((1-(exp (-r*r / (2*reff*reff)))),2) * (1-(x[1]/t));
dS[eqn] = 0;
return source;
}
/* HEAT INPUT CODE */
DEFINE_PROFILE(Gauss,t,i)
{
real x[ND_ND], c[ND_ND];
face_t f;
real r;
r = 0.0035;
begin_f_loop(f, t)
{
F_CENTROID (x,f,t);
F_PROFILE (f,t,i) = (3*(300*14*0.7) / (3.14*pow(r,2))) * exp (-3*(x[0]*x[0])/ pow(r,2));
}
end_f_loop(f,t)
}
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Old   January 21, 2016, 18:48
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For starters, use a trailing dot for real numbers (otherwise the compiler will read them as integers), for example:

Code:
F_PROFILE (f,t,i) = (3.*(300.*14.*0.7) / (3.14*pow(r,2))) * exp (-3.*(x[0]*x[0])/ pow(r,2));
Next, be specific. Show us any errors and explain what result you're expecting compared to what you're actually achieving.
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Old   January 29, 2016, 06:46
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i have modified the format with trailing dot as suggested. the UDF is given below and it gives the error: Line 27: invalid type for binary expression: float / pointer to structure.

how can i rectify the error in the following udf ?

/*------ HEAT FLUX -------- */
#include "udf.h"
DEFINE_PROFILE(Gauss,t,i)
{
real x[ND_ND], c[ND_ND];
face_t f;
real r;
r = 0.005;
begin_f_loop(f, t)
{
F_CENTROID (x,f,t);
F_PROFILE (f,t,i) = (3.*(300.*14.*0.7/0.001) / (3.14*pow(r,2.))) * exp (-3.*(x[0]*x[0])/ pow(r,2.));
}
end_f_loop(f,t)
}
/*--------- Lorentz Force ----------*/
/*-------- x momentum source ------*/
#DEFINE mu 0.00000126;
#DEFINE I 300.;
#DEFINE reff 0.006;
#DEFINE r 0.005;
DEFINE_SOURCE(xmom,c,t,dS,eqn)
{
real x[ND_ND];
real mu, I, reff, r, source;
C_CENTROID(x,c,t);
source = -((mu*I*I)/(4.*3.14*3.14*reff*reff*r)) * (exp (-r*r / (2.*reff*reff))) * (1.-(exp (-r*r / (2.*reff*reff)))) * pow((1.-(x[1]/t),2.) * (x[0]/r));
dS[eqn]=0;
return source;
}
/* ----------- y momentum source ------------*/
DEFINE_SOURCE(ymom,c,t,dS,eqn)
{
real x[ND_ND];
real source;
C_CENTROID(x,c,t);
source = -((mu*I*I)/(4.*3.14*3.14*r*r*c)) * pow((1.-(exp (-r*r / (2.*reff*reff)))),2.) * (1.-(x[1]/t));
dS[eqn]=0;
return source;
}
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Old   January 29, 2016, 09:29
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One of your problems is here:

Code:
#DEFINE mu 0.00000126; 
#DEFINE I 300.; 
#DEFINE reff 0.006;
#DEFINE r 0.005;
...
real mu, I, reff, r, source;
"#DEFINE mu 0.00000126;" means: everywhere where you write "mu", the compiler should read "0.00000126;". So the last line that I copied becomes:
Code:
real 0.00000126;, 300.;, 0.006;, 0.005;, source;
This not what you want. You should choose. Option 1: use #define in the right way:
Code:
#DEFINE I 300.
Note: no ; after the number! And don't try to redefine I as real.

Option 2: don't use #DEFINE:
Code:
real mu=0.00000126, I=300, ...
There may be other problems.
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