[KaLium]

Originally Posted by rajendra1

I have found rise in temperature with constant mass source input. But solution stopping after every iteration. may be I shall check the formula again. But again there is nothing stored in UDM.

I am not really sure whether I shall use DEFINE_EXECUTE_AT_END or DEFINE_ON_DEMAND. please put some light .......what I know is that former is executed at the end of time step and later in the beginning.

Can I define initial values to in C_UDMI using DEFINE_INIT macro?

DEFINE_EXECUTE_AT_END is used at the end.
DEFINE_ADJUST is used at the beginning
DEFINE_ON_DEMAND is used with manual command.

I would use a DEFINE_ON_DEMAND for initialization:

DEFINE_ON_DEMAND (udm_init)
{
  Thread *thread;
  cell_t cell;
  Node *node;
  Domain *domain = Get_Domain(1);
    
   thread_loop_c(thread,domain)
    {
      begin_c_loop(cell,thread)       
      {
      C_UDMI(cell,thread,0) = 0.0;
      C_UDMI(cell,thread,1) = 0.0;
      C_UDMI(cell,thread,2) = 0.0;
      C_UDMI(cell,thread,3) = 0.0;
      C_UDMI(cell,thread,4) = 0.0;
      }
      end_c_loop(cell,thread)

    }

}

You have to run macros like this manual: http://jullio.pe.kr/fluent6.1/help/h...-use-on-demand

You can also use fluent patch panel if you don't want to use UDF: https://www.sharcnet.ca/Software/Flu...g/node1384.htm

[KaLium]

Originally Posted by rajendra1

DEFINE_SOURCE(mass_source,c,t,dS,eqn)
{
dS[eqn] = C_UDMI(c,t,1);
return C_UDMI(c,t,0);
}
DEFINE_SOURCE(energy_source,c,t,dS,eqn)
{
dS[eqn] = C_UDMI(c,t,4);
return C_UDMI(c,t,3);
}

So you have non-zero mass source with this code? how is your solution stopping?

[rajendra1]

Originally Posted by KaLium

So you have non-zero mass source with this code? how is your solution stopping?

Since heat source is dependent on mass source and there is increase in temperature, so I think mass source is positive.

Thank you very much for suggestion regarding DEFINE_ON_DEMAND macro.
I have added it to my udf but again solution is stopping after every time step showing "FLUENT received fatal signal (ACCESS VIOLATION)". It proceeds if I calculate it further but only for single time step.

[KaLium]

Maybe you should replace your execute_at_end macro with adjust-macro.

Also add the thread - loop. Similar than in my define_on_demand code.

[rajendra1]

Originally Posted by KaLium

Maybe you should replace your execute_at_end macro with adjust-macro.

Also add the thread - loop. Similar than in my define_on_demand code.

okay I will try it.

[rajendra1]

Hi KaLium,

I have finally moved forward from the error, thank you very much for your suggestions without your suggestions it would have been very difficult to move further.

I have used DEFINE_EXECUTE_AT_END, should also be possible by using DEFINE_ADJUST, I shall try it.

But again I did not find anything stored in UDM.

[rajendra1]

Originally Posted by KaLium

DEFINE_ON_DEMAND (udm_init)
{
  Thread *thread;
  cell_t cell;
  Node *node;
  Domain *domain = Get_Domain(1);
    
   thread_loop_c(thread,domain)
    {
      begin_c_loop(cell,thread)       
      {
      C_UDMI(cell,thread,0) = 0.0;
      C_UDMI(cell,thread,1) = 0.0;
      C_UDMI(cell,thread,2) = 0.0;
      C_UDMI(cell,thread,3) = 0.0;
      C_UDMI(cell,thread,4) = 0.0;
      }
      end_c_loop(cell,thread)
    }
}

CAN we use your suggested code in this fashion? do we need specify node?

DEFINE_ON_DEMAND (udm_init)
{
real x[ND_ND];
Thread *thread;
cell_t cell;
//Node *node;
int zone = 3;
Domain *domain = Get_Domain(1);
thread =Lookup_Thread(domain,zone);

thread_loop_c(thread,domain)
{
begin_c_loop(cell,thread)
{
C_UDMI(cell,thread,0) = 0.0;
C_UDMI(cell,thread,1) = 0.0;
C_UDMI(cell,thread,2) = 0.0;
C_UDMI(cell,thread,3) = 0.0;
C_UDMI(cell,thread,4) = 0.0;
}
end_c_loop(cell,thread)

}

}

[KaLium]

DEFINE_ON_DEMAND (udm_init)
{
  Thread *thread;
  cell_t cell;
  int zone = 3;
  Domain *domain = Get_Domain(1);
  thread =Lookup_Thread(domain,zone);
    
      begin_c_loop(cell,thread)       
      {
      C_UDMI(cell,thread,0) = 0.0;
      C_UDMI(cell,thread,1) = 0.0;
      C_UDMI(cell,thread,2) = 0.0;
      C_UDMI(cell,thread,3) = 0.0;
      C_UDMI(cell,thread,4) = 0.0;
      }
      end_c_loop(cell,thread)


}

I would try this.

You don't need the "node". I copied that from my old code as a mistake.

[KaLium]

thread =Lookup_Thread(domain,zone);       
begin_c_loop(cell,thread)              
{
      
}
end_c_loop(cell,thread)

is enough if you are using your udf in one cellzone only.

[rajendra1]

Originally Posted by KaLium

thread =Lookup_Thread(domain,zone);       
begin_c_loop(cell,thread)              
{
      
}
end_c_loop(cell,thread)

is enough if you are using your udf in one cellzone only.

interesting ..thanks for clarification.


I have tried to use DEFINE_ADJUST instead of DEFINE_EXECUTE_AT_END but not fruitful so far, however it solves problem when I use DEFINE_EXECUTE_AT_END and also storing values in UDM.

[KaLium]

Do you mean that your code is working now?

[rajendra1]

yes it is working.

[KaLium]

Ok! Then you can forget the Define_adjust and just use the code that works.

How did you fix the code?

[rajendra1]

Originally Posted by KaLium

Ok! Then you can forget the Define_adjust and just use the code that works.

How did you fix the code?

I was not using thread loop, so just added it and it worked.

[rajendra1]

so basically I have used DEFINE_INIT and DEFINE_EXECUTE_AT_END .........and apparently the problem was with DEFINE_EXECUTE_AT_END macro ie. the missing thread loop as I have said.

[maitray]

Originally Posted by rajendra1

Dear Friends,

I am trying to solve heat transfer problem.
The geometry is shell and tube type. please see attachment for the picture of model.
Problem description:
heat is generation takes place in tube and it is to be transferred to the shell side through the cylinder wall. There is no problem when I am trying to solve the problem in fluent (workbench project) by giving constant heat source as input. BUT when I am trying to calculate mass generation and heat generation with the help of UDF, fluent says: fluent received fatal signal (access_violation). I have tried different ways to rectify the error but failed so far.

Boundary conditions are,
gas inlet (tube (inner) inlet) at 20e+05 Pa. pressure, 300 K temp.
gas outlet (tube (inner) outlet) adiabatic wall (so there is no outlet only inlet on tube side)
coolant inlet (shell side (annular section)) 300 K temp.
coolant outlet (shell side (annular section))
Convetive wall (inner cylinder surface)
Convetive wall Shadow (inner cylinder surface)
Adiabatic wall (outer cylinder surface)

I have coupled convective wall and its shadow in boundary conditions. Also tried to calculate heat flux on the convective wall using DEFINE_HEAT_FLUX macro.
I have tried to give initial values using DEFINE_INIT MACRO in the gas tube because I want uniform pressure in the tube.

I am trying to calculate mass source and hence heat source using DEFINE_SOURCE MACRO

I am using Interpreted UDF. It gets interpreted, in fluent initialization gets done but it again gives same error ie. "fluent received fatal signal (access_violation)".

I need help from you guys, please see the code and tell me where I am wrong, I will be very grateful for you suggestions.

UDF CODE:

/************************************************** *************
UDF for initializing flow field variables
************************************************** **********/


DEFINE_INIT(my_init_func,d)
{
cell_t c;
Thread *t;
real xc[ND_ND];

/* loop over all cell threads in the domain */
thread_loop_c(t,d)
{

/* loop over all cells */
begin_c_loop_all(c,t)
{
C_CENTROID(xc,c,t);

C_T(c,t) = 300.;
C_P(c,t) = 2000000.;
C_U(c,t) = 0.;
C_V(c,t) = 0.;
C_W(c,t) = 0.;
}
end_c_loop_all(c,t)
}
}
/************************************************** ************/

/* UDF for specifying an absorption source term in a pressure and temperature*/

DEFINE_EXECUTE_AT_END(source_calculation)
{
Domain *d;
Thread *t;
cell_t c;
real time = CURRENT_TIME;
real temp, Pg, Peqa, mab, m;
int zone=7;
d=Get_Domain(1);
t=Lookup_Thread(d,zone);
begin_c_loop(c,t)
{
temp=C_T(c,t);

Pg=C_P(c,t);

Peqa=1000*exp(Aab-Bab/temp);

mab=-Ca*exp(-Ea/(Rg*temp))*log(Pg/Peqa)*(Psat-Pemp-C_UDMI(c,t,2)); /* mass rource kg/m^3 S*/

m=mab;

C_UDMI(c,t,0) = m;

C_UDMI(c,t,1) = 0.0; /*derivative term in mass source*/

C_UDMI(c,t,2) = -C_UDMI(c,t,0)*CURRENT_TIMESTEP+C_UDMI(c,t,2);

C_UDMI(c,t,3) = C_UDMI(c,t,0)*(delta_H+temp*(C_pg-C_ps));

C_UDMI(c,t,4) = 0.0;/*derivative term in energy source*/
}
end_c_loop(c,t);
}
DEFINE_SOURCE(mass_source,c,t,dS,eqn)
{
dS[eqn] = C_UDMI(c,t,1);
return C_UDMI(c,t,0);
}
DEFINE_SOURCE(energy_source,c,t,dS,eqn)
{
dS[eqn] = C_UDMI(c,t,4);
return C_UDMI(c,t,3);
}
/************************************************** ***********/

/**************udf for Wall Heat flux on convective wall *************************** */

real h = 0.0; /* heat transfer coefficient (W/m^2 K)
*/

DEFINE_ADJUST(htc_adjust, domain)
{
/* Define the heat transfer coefficient. */

h = 120;
}

(heat_flux, f, t, c0, t0, cid, cir)
{
cid[0] = 0.;
cid[1] = h;
cid[2] = h;
cid[3] = 0.;
}

I thank you in advance.

For this metal hydride absorption problem, why are you giving initial pressure to all cell zone instead to giving the pressure at the inlet of cylinder?