[JERC_UTFSM]

Hello, I am having a SIGSEGV error when trying to use a UDF that I created for evaporation-condensation limited by the vapor pressure. I am using a gas phase (primary) using the methyl-alcohol-air template with density set up as ideal gas and a liquid phase combine with methyl-alcohol-liquid and water-liquid (with density Volume Weight Mixing Law).

I manage to compile the UDF without any warning and, in order to test the UDF, I decide to work with a closed and small 2D plane with a Pressure Operation around 10 MPa and a temperature of 450 K (which are nearly similar to the operation condition I will work with this UDF).

I design the UDF using the template ANSYS provided in their manual as a template and also have that one in order to discard possible errors. Either, by using my UDF and the one in the manual, I still have the SIGSEGV warning.

================================================== ============================

Node 0: Process 13728: Received signal SIGSEGV.

================================================== ============================

The fl process could not be started.

The UDF I created is the following:

#include "udf.h"

/*Constants used in psat_i to calculate saturation pressure using ANTOINE EQUATION*/
/*Provided by NIST*/

#define A_H2O 3.55959
#define B_H2O 643.748
#define C_H2O -198.043

/*user inputs*/

#define MAX_SPE_EQNS_PRIM 5 /*total number of species in primary phase*/
#define index_evap_primary 0 /*evaporating species index in primary phase*/
#define prim_index 0 /*index of primary phase*/

/*end of user inputs*/

/* Computes saturation pressure of vapor pressure */
/* as function of temperature */
/* Equation is taken from ANTOINE EQUATION, */
/* Returns pressure in BAR, given temperature in KELVIN */

DEFINE_HET_RXN_RATE(user_evap_condens_react, c, t, hr, mw, yi, rr, rr_t)
{
Thread **pt = THREAD_SUB_THREADS(t);
Thread *tp = pt[0];
Thread *ts = pt[1];

int i;
real ch2o, csath2o, accum = 0., xh2o, xch3oh, varh2o;

real OP = RP_Get_Float("operating-pressure"); /*OPERATING PRESSURE*/
real P = (OP+C_P(c,tp)); /*PASCAL*/

real T_prim = C_T(c,tp); /*PRIMARY PHASE (gas) temperature*/
real T_sec = C_T(c,ts); /*SECONDARY PHASE (droplet) temperature*/
real diam = C_PHASE_DIAMETER(c,ts); /*secondary phase diameter*/

real Re, Sc, Nu, urel, urelx,urely,urelz=0., mass_coeff, area_density, flux_evap, D_evap_prim;

varh2o = A_H2O - B_H2O / (C_H2O - T_prim);

real psat_h2o = pow(10, varh2o)*1e5; /*VAPOR PRESSURE equation for WATER PASCAL*/

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 * diam * C_R(c,tp) / C_MU_L(c,tp);

for (i=0; i < MAX_SPE_EQNS_PRIM ; i++)
{
accum = accum + C_YI(c,tp,i)/mw[i][prim_index];
}

xh2o = C_YI(c,tp,0)/ mw[0][prim_index] / accum;

ch2o = xh2o * P / UNIVERSAL_GAS_CONSTANT / T_prim ;

csath2o = psat_h2o / UNIVERSAL_GAS_CONSTANT / T_sec ;

area_density = 6. * C_VOF(c,ts) / diam ;

D_evap_prim = C_DIFF_EFF(c, tp, 0) - 0.7 * C_MU_T(c, tp) / C_R(c, tp);
Sc = C_MU_L(c, tp) / C_R(c, tp) / D_evap_prim;

Nu = 2. + 0.6 * pow(Re, 0.5) * pow(Sc, 0.333);

mass_coeff = Nu * D_evap_prim / diam;

flux_evap = mass_coeff * (csath2o - ch2o);
*rr = area_density * flux_evap;
}
}

I tried creating a second .cas file, setting the secondary phase like just liquid water, and working with just one core.

Everytime I got the same error.

[AlexanderZ]

you have an equation for 3D case, but running it in 2D

change to

#if RP_3D
urelz = C_W(c,tp) - C_W(c,ts);
#endif
urel = sqrt(urelx*urelx + urely*urely ); /*relative 
#if RP_3D
urel = sqrt(urelx*urelx + urely*urely + urelz*urelz); /*relative 
#endifvelocity*/

[JERC_UTFSM]

Originally Posted by AlexanderZ

you have an equation for a 3D case, but running it in 2D

change to

#if RP_3D
urelz = C_W(c,tp) - C_W(c,ts);
#endif
urel = sqrt(urelx*urelx + urely*urely ); /*relative 
#if RP_3D
urel = sqrt(urelx*urelx + urely*urely + urelz*urelz); /*relative 
#endifvelocity*/

Thanks for the observation, I tried what you said, but it still gave me the SIGSEGV error. I deleted any 3D equation related to the UDF, but it didn't work.

Thanks anyway for the help. Much appreciate.

[JERC_UTFSM]

Originally Posted by AlexanderZ

you have an equation for 3D case, but running it in 2D

change to

#if RP_3D
urelz = C_W(c,tp) - C_W(c,ts);
#endif
urel = sqrt(urelx*urelx + urely*urely ); /*relative 
#if RP_3D
urel = sqrt(urelx*urelx + urely*urely + urelz*urelz); /*relative 
#endifvelocity*/

Can it be the fact I, initially, did not have a secondary phase?

EDIT: I tried with a few if for the secondary phase and it still didn't work.

[pakk]

Maybe you forgot to enable the energy equation?

[JERC_UTFSM]

Originally Posted by pakk

Maybe you forgot to enable the energy equation?

It can't be. Energy equation is enable.

EDIT: I just realize Fluent become buggy just after the error is presented. Everywhere I click the text is all over the place.

Captura.jpg

[AlexanderZ]

problem could be here

real OP = RP_Get_Float("operating-pressure"); /*OPERATING PRESSURE*/

to be

real OP = RP_Get_Real("operating-pressure"); /*OPERATING PRESSURE*/

its strange, that you have the error while using code from manual, probably something wrong with your case

[JERC_UTFSM]

Originally Posted by AlexanderZ

problem could be here

real OP = RP_Get_Float("operating-pressure"); /*OPERATING PRESSURE*/

to be

real OP = RP_Get_Real("operating-pressure"); /*OPERATING PRESSURE*/

its strange, that you have the error while using code from manual, probably something wrong with your case

It didn't work. I tried to create another case and I still getting the same SIGSEGV error. I also tried to define the Universal Gas Constant but I am still getting the same error no matter what I try.

I use the Visual Studio compiler because the build-in doesn't work properly, so I doesn't know if it may be related.

[AlexanderZ]

try simplified udf with constant output

#include "udf.h"

DEFINE_HET_RXN_RATE(user_evap_condens_react, c, t, hr, mw, yi, rr, rr_t)
{
*rr = constant value here;
}
}

[JERC_UTFSM]

Originally Posted by AlexanderZ

try simplified udf with constant output

#include "udf.h"

DEFINE_HET_RXN_RATE(user_evap_condens_react, c, t, hr, mw, yi, rr, rr_t)
{
*rr = constant value here;
}
}

I simplified the UDF. I also specified the diameter of the droplet. I could manage to get rid of the SIGSEGV error, but now I am having trouble with the solver.

This is the UDF:

#include "udf.h"

/*Constants used in psat_i to calculate saturation pressure using ANTOINE EQUATION*/
/*Provided by NIST*/

#define A_H2O 3.55959
#define B_H2O 643.748
#define C_H2O -198.043
#define R 8.314

/* Computes saturation pressure of vapor pressure */
/* as function of temperature */
/* Equation is taken from ANTOINE EQUATION, */
/* Returns pressure in PASCAL, given temperature in KELVIN */

DEFINE_HET_RXN_RATE(user_evap_condens_react, c, t, hr, mw, yi, rr, rr_t)
{
Thread** pt = THREAD_SUB_THREADS(t);
Thread* tp = pt[0];
Thread* ts = pt[1];

int i;

real OP = RP_Get_Real("operating-pressure"); /*OPERATING PRESSURE*/
real P = (OP + C_P(c, tp)); /*PASCAL*/

real T_prim = C_T(c, tp); /*PRIMARY PHASE (gas) temperature*/
real T_sec = C_T(c, ts); /*SECONDARY PHASE (droplet) temperature*/

/* Mass fraction from the primary phase. */
real wh2o = C_YI(c, tp, 0);
real wch3oh = C_YI(c, tp, 1);
real wh2 = C_YI(c, tp, 2);
real wco2 = C_YI(c, tp, 3);
real wco = C_YI(c, tp, 4);
real wn2 = C_YI(c, tp, 5);

real mh2o = mw[0][0];
real mch3oh = mw[0][1];
real mh2 = mw[0][2];
real mco2 = mw[0][3];
real mco = mw[0][4];
real mn2 = mw[0][5];

/* Accumulation base from the primary phase. */
real mmix = wh2o / mh2o + wch3oh / mch3oh + wh2 / mh2 + wco2 / mco2 + wn2 / mn2 + wco / mco;

/* Mole fraction from the primary phase. */
real yh2o = (wh2o / mh2o) / mmix;
real ych3oh = (wch3oh / mch3oh) / mmix;
real yh2 = (wh2 / mh2) / mmix;
real yco2 = (wco2 / mco2) / mmix;
real yco = (wco / mco) / mmix;
real yn2 = (wn2 / mn2) / mmix;

real diam = 0.00015; /*secondary phase diameter*/

real Re, Sc, Nu, urel, urelx, urely, mass_coeff, area_density, flux_evap, D_evap_prim;

real varh2o = A_H2O - B_H2O / (C_H2O - T_prim);

real psat_h2o = pow(10., varh2o) * 1e5; /*VAPOR PRESSURE equation for WATER PASCAL*/

if (Data_Valid_P())
{
urelx = C_U(c, tp) - C_U(c, ts);
urely = C_V(c, tp) - C_V(c, ts);

urel = sqrt(urelx * urelx + urely * urely);

Re = urel * diam * C_R(c, tp) / C_MU_L(c, tp);

real ch2o = yh2o * P / R / T_prim;

real csath2o = psat_h2o / R / T_sec;

area_density = 6. * C_VOF(c, ts) / diam;

D_evap_prim = C_DIFF_EFF(c, tp, 0) - 0.7 * C_MU_T(c, tp) / C_R(c, tp);

Sc = C_MU_L(c, tp) / C_R(c, tp) / D_evap_prim;

Nu = 2. + 0.6 * pow(Re, 0.5) * pow(Sc, 0.333);

mass_coeff = Nu * D_evap_prim / diam;

flux_evap = mass_coeff * (csath2o - ch2o);

*rr = area_density * flux_evap;
}
}

Now I am getting errors with the AMG solver, more precisily the temperature.

Stabilizing temperature to enhance linear solver robustness.
Stabilizing temperature using GMRES to enhance linear solver robustness.

Divergence detected in AM
Error at Node 3: floating point exception

Error at Node 1: floating point exception

Error at Node 2: floating point exception

Error at Node 0: floating point exception
G solver: temperature
Divergence detected in AMG solver: temperature
Divergence detected in AMG solver: temperature
Divergence detected in AMG solver: temperature
Error at host: floating point exception

Error: floating point exception
Error Object: #f

Tried with both, stationary and transient model.

[AlexanderZ]

when did you get this error, on the very first time step?

you may try to decrease timestep. make it small enough.
check your mesh quality

[JERC_UTFSM]

Originally Posted by AlexanderZ

when did you get this error, on the very first time step?

you may try to decrease timestep. make it small enough.
check your mesh quality

I perform a mesh quality evaluation. I was reading somewhere the best is to keep the minimum orthogonal quality above 0.1, but I don't if there is something wrong with my mesh.

Mesh Quality:

Minimum Orthogonal Quality = 1.00000e+00 cell -1 on zone -1 (ID: 0 on partition: 3) at location ( 0.00000e+00 0.00000e+00)
(To improve Orthogonal quality , use "Inverse Orthogonal Quality" in Fluent Meshing,
where Inverse Orthogonal Quality = 1 - Orthogonal Quality)

Maximum Aspect Ratio = 1.41422e+00 cell 262 on zone 2 (ID: 172 on partition: 3) at location ( 1.92500e-02 3.57500e-02)

Decreasing the time step does nothing. I tried with my default 1e-3 and decrease it with a 1e-5 time step and still got the same error.

Btw, the error happens in the first iteration.

EDIT: Tried to refine mesh from 0,5 mm to 0,1 mm element size. It didn't work.

[AlexanderZ]

you may try to run same case but with simplified heating rate

#include "udf.h"

DEFINE_HET_RXN_RATE(user_evap_condens_react, c, t, hr, mw, yi, rr, rr_t)
{
*rr = constant value here;
}
}

put reasonable value as "constant value here" and run simulation

[JERC_UTFSM]

Originally Posted by AlexanderZ

you may try to run same case but with simplified heating rate

#include "udf.h"

DEFINE_HET_RXN_RATE(user_evap_condens_react, c, t, hr, mw, yi, rr, rr_t)
{
*rr = constant value here;
}
}

put reasonable value as "constant value here" and run simulation

I tried what you suggest but with no success... It gaves me the following errors:

Stabilizing x-momentum to enhance linear solver robustness.
Stabilizing x-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: x-momentum Stabilizing y-momentum to enhance linear solver robust
Error at Node 3: floating point exception

Error at Node 1: floating point exception

Error at Node 2: floating point exception

ness.
Error at Node 0: floating point exception
Stabilizing y-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: y-momentum Stabilizing pressure correction to enhance linear solver robustness.
Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction Stabilizing k to enhance linear solver robustness.
Stabilizing k using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: k Stabilizing epsilon to enhance linear solver robustness.
Stabilizing epsilon using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: epsilon Stabilizing vapor-species-0 to enhance linear solver robustness.
Stabilizing vapor-species-0 using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: vapor-species-0 Stabilizing vapor-species-1 to enhance linear solver robustness.
Stabilizing vapor-species-1 using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: vapor-species-1 Stabilizing vapor-species-2 to enhance linear solver robustness.
Stabilizing vapor-species-2 using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: vapor-species-2 Stabilizing vapor-species-3 to enhance linear solver robustness.
Stabilizing vapor-species-3 using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: vapor-species-3 Stabilizing vapor-species-4 to enhance linear solver robustness.
Stabilizing vapor-species-4 using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: vapor-species-4 Stabilizing liquid-species-0 to enhance linear solver robustness.
Stabilizing liquid-species-0 using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: liquid-species-0 Stabilizing temperature to enhance linear solver robustness.
Stabilizing temperature using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: temperature Stabilizing vof-1 to enhance linear solver robustness.
Stabilizing vof-1 using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: vof-1
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: k
Divergence detected in AMG solver: epsilon
Divergence detected in AMG solver: vapor-species-0
Divergence detected in AMG solver: vapor-species-1
Divergence detected in AMG solver: vapor-species-2
Divergence detected in AMG solver: vapor-species-3
Divergence detected in AMG solver: vapor-species-4
Divergence detected in AMG solver: liquid-species-0
Divergence detected in AMG solver: temperature
Divergence detected in AMG solver: vof-1
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: k
Divergence detected in AMG solver: epsilon
Divergence detected in AMG solver: vapor-species-0
Divergence detected in AMG solver: vapor-species-1
Divergence detected in AMG solver: vapor-species-2
Divergence detected in AMG solver: vapor-species-3
Divergence detected in AMG solver: vapor-species-4
Divergence detected in AMG solver: liquid-species-0
Divergence detected in AMG solver: temperature
Divergence detected in AMG solver: vof-1
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: k
Divergence detected in AMG solver: epsilon
Divergence detected in AMG solver: vapor-species-0
Divergence detected in AMG solver: vapor-species-1
Divergence detected in AMG solver: vapor-species-2
Divergence detected in AMG solver: vapor-species-3
Divergence detected in AMG solver: vapor-species-4
Divergence detected in AMG solver: liquid-species-0
Divergence detected in AMG solver: temperature
Divergence detected in AMG solver: vof-1
Error at host: floating point exception

Error: floating point exception
Error Object: #f


I define a constant around 1.5*1e(n), varying the n value from -3 to -10.

[AlexanderZ]

I have no experience in condensation/evaporation simulations
but for me this error means, you do probably have problems with case settings (boundary conditions, may be material properties, mesh, others) as you are using simplified UDF.

If you don't have any other thoughts you may try to simplify your case, may be start with just 2 species, find convergence and go step but step to your real case.