[Turbo_hrf]

I have written a UDF about standard k-e turbulence model and compiled successfully, but when I try to initialize this code, it shows error: received a fatal signal (segmentation fault)
does anyone help me to remove this problem please?

My UDF code are listed below:
#include "udf.h"
/*#include "math.h"*/

/* Turbulence model constants */
const real C1e=1.44;
const real C2e=1.92;
const real C_mu=0.09;
const real SIG_k=1.0;
const real SIG_e=1.3;

/* User-defined scalars */
enum
{
TK,
TE,
N_REQUIRED_UDS
};

/*Define source term in k equation */
DEFINE_SOURCE(TK_SOURCE, c, t, dS, eqn)
{
real source;

dS[eqn]=0.0;
source= C_MU_T(c,t)*C_STRAIN_RATE_MAG(c,t)*C_STRAIN_RATE_M AG(c,t)-C_R(c,t)*C_R(c,t)*C_mu*C_UDSI(c,t,TK)*C_UDSI(c,t,T K)/C_MU_T(c,t);

return source;
}

/* define source term in eplison equation */
DEFINE_SOURCE(TE_SOURCE, c, t, dS, eqn)
{
real source, Pk;

Pk=C_MU_T(c,t)*C_STRAIN_RATE_MAG(c,t)*C_STRAIN_RAT E_MAG(c,t);
dS[eqn]=0.0;
source=C1e*C_UDSI(c,t,TE)*Pk/C_UDSI(c,t,TK)-C2e*C_R(c,t)*C_UDSI(c,t,TE)*C_UDSI(c,t,TE)/C_UDSI(c,t,TK);

return source;
}

/* define diffusion coefficienct */
DEFINE_DIFFUSIVITY(KE_diffusivity,c,t,i)
{
real diff;
real mu_t;
int nscalar=i;

mu_t=C_R(c,t)*C_mu*C_UDSI(c,t,TK)*C_UDSI(c,t,TK)/C_UDSI(c,t,TE);
if (nscalar==TK)
diff= mu_t/SIG_k + C_MU_L(c,t);
else
diff = mu_t/SIG_e + C_MU_L(c,t);
return diff;
}

/*define turbulent viscosity */
DEFINE_TURBULENT_VISCOSITY(turbVis,c,t)
{
real mu_t;
mu_t=C_R(c,t)*C_mu*C_UDSI(c,t,TK)*C_UDSI(c,t,TK)/C_UDSI(c,t,TE);
return mu_t;
}

[pakk]

Fluent tries to initialize the diffusivity, and to do this it needs the values of the user defined scalars, but they are not calculated yet.
The udf that you wrote tries to read data that is not stored yet. Without getting too technical, this is an example of a 'segmentation fault'.

There are two possible solution methods:
1. Re-write your code such that if you are initializing, your code recognizes this and does not try to read undefined user defined scalars. (The preferred method if you were a professional programmer.)
2. Initialize your data without the udf, and attach the udf later. (The quick and easy solution.)

[kmou]

Originally Posted by pakk

2. Initialize your data without the udf, and attach the udf later. (The quick and easy solution.)

Hello,
I tried doing this but I still get a segmentation fault error. Could the error be linked to a non-UDF related problem then?
Thank you

[pakk]

My answer was specific for the code that Turbo_hrf gave.

You (probably) use different code, but get the same warning.
If you want to know if the error is caused by something else than your udf, this is easy to test: don't use the udf, and see if you get the same error.

It is possible that your error has nothing to do with your udf, and that it is caused by a mistake of the Fluent programmers. But it is far more likely that it is a problem in your udf; you are probably telling Fluent to read a value that does not exist.

Without seeing your UDF, I can not help more.

[kmou]

Hi pakk,
thanks for getting back to me so quickly.

Originally Posted by pakk

If you want to know if the error is caused by something else than your udf, this is easy to test: don't use the udf, and see if you get the same error.

I did and I do get the error....which is weird because this would make sense:

Originally Posted by pakk

But it is far more likely that it is a problem in your udf; you are probably telling Fluent to read a value that does not exist.

I agree. I have variables which are not yet initialised in the UDF:

DEFINE_HET_RXN_RATE(char_o2,c,t,hr,mw,yi,rr,rr_t)
{
     Thread **pt = THREAD_SUB_THREADS(t); 
     Thread *tp = pt[0];        /* gas phase or primary phase */ 
     Thread *ts = pt[1];        /* solid phase or secondary phase */ 
 
 
     real T_p = MAX(293.,C_T(c,tp));    /* primary phase temperature */    
     real T_s = MAX(293.,C_T(c,ts));    /* secondary phase temperature */ 
     T_p = MIN(T_p,TMAX); 
     T_s = MIN(T_s,TMAX); 
 
     const real Rgas = 8.314;        /* ideal gas constant Joule/mol.K */  
                    /* UNIVERSAL_GAS_CONSTANT = 8314 J/kmol.K;*/  
 
     real p_o2 = 0.;            /* pressure in Pa = N/m^2 = kg/m.s^2 */  
     real k_c, k_d;            /* coefficients related diffusion and kinetic */  
     real D_p = C_PHASE_DIAMETER(c,ts); /* solid particle diameter FLUENT macro */ 
     const real Ac = 0.052;              /* kg/(m^2 . s . Pa^0.5) */  
     const real Ec = 6.1e7;              /* J/kmol */  
     real Re, Sc, Sh, urel, urelx,urely,urelz=0.;

     real Dk = C_DIFF_EFF(c,tp,index_primary) - C_MU_T(c,tp)/(0.7*C_R(c,tp)); 
 
     *rr = 0.0e0; /* reaction rate */ 
 
     C_UDMI(c, t, 20) = 0.0e0;  
     C_UDMI(c, t, 21) = 0.0e0; 
 
     if(C_VOF(c, tp) < eps_g_small && yi[INDEX_PHASE_C][INDEX_SPECIES_C] > spe_small && yi[INDEX_PHASE_O2][INDEX_SPECIES_O2] > spe_small) 
     { 
         p_o2 = C_R(c,tp) * UNIVERSAL_GAS_CONSTANT * C_T(c,tp) * yi[index_primary][INDEX_SPECIES_O2] / 32.0e0; /* kg/m.s^2 */ 
          
         if(C_VOF(c, ts) <= 0.0e0)  /* for negative volume fraction from wrong calculations */  
         { 
                *rr = 0.0e0; 
         } 
         else 
         {  
 
                k_c = Ac * exp( -1.0e0 * Ec / UNIVERSAL_GAS_CONSTANT / T_s ); /* kinetic coefficient */ 
 
                /* Calculation of Sherwood number and then reaction rate */
           if(Data_Valid_P())
        { 
                     urelx = C_U(c,tp) - C_U(c,ts); 
                     urely = C_V(c,tp) - C_V(c,ts); 
                #if RP_3D
                urelz = C_W(c,tp) - C_W(c,ts); 
                #endif 
                   urel = sqrt(urelx*urelx + urely*urely + urelz*urelz);  /* relative velocity*/ 
                      Re = urel * D_p * C_R(c,tp) / C_MU_L(c,tp); 
                     Sc = C_MU_L(c,tp) / C_R(c,tp) / Dk ;           
                Sh =  2. + 0.6 * pow(Re, 0.5)* pow(Sc, 0.333);  
    
 
 
                       k_d = (Dk * mw[INDEX_PHASE_C][INDEX_SPECIES_C] * Sh ) / (T_p * UNIVERSAL_GAS_CONSTANT * D_p); /* diffusion coefficient */ 
 
 
            *rr = (-1.0e0 * k_c) + sqrt(k_c * k_c + 4.0*k_d*k_d*p_o2); 
 
            *rr = *rr * ( (6.0*C_VOF(c,ts)*k_c) / (2.0*D_p*k_d)); 

 
            *rr = *rr / mw[INDEX_PHASE_C][INDEX_SPECIES_C];  
 
                    C_UDMI(c, t, 20) = *rr; 
                    C_UDMI(c, t, 21) = yi[INDEX_PHASE_C][INDEX_SPECIES_C] * volume_p(D_p/2.0) * C_R(c,ts);  
        } 
         }   
     } 
  }

But now I am using

if(Data_Valid_P())

and it still does not work. I also tried Initialising before loading the UDF but it fails to do so, it does not give me an error message it just hangs there...