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SIGSEGV error when running UDF

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Old   November 24, 2020, 08:25
Default SIGSEGV error when running UDF
  #1
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Tyler Richardson
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Hi,

I'm trying to calculate the heat transfer coefficient at the interface between my solid and fluid mesh (simple pipe, CHT)

The following code seems to fail every time with a SIGSEGV error. In fact, it wont even print out my messages within begin_f_loop. The output i get is "Begin F loop" (as i message out), and then the SIGSEGV error. I originally thought this was due to trying to loop along some solid faces, so i put a little if statement to omit any threads other than the one i am interested in.

I am totally lost. any help would be greatly appreciated.

Thanks!

Code:
#include "udf.h"
#include "sg.h"
#include "mem.h"


DEFINE_ON_DEMAND(on_demand_calc)
{

   /* Initialize face data */
   real kt, dTx, dTy, dTxRG, dTyRG, dTr, dTrRG;


	/* Initialize heat Transfer Coefficient*/
	real whtc, whtcRG;

   /* Initialize Temp, Q */

   real TWall, TBulk, QWall, QWallRG, TWadj;

   Domain *d; /* declare domain pointer since it is not passed as an argument to the DEFINE macro */
   Thread *t, *t0;
   cell_t c0;
   face_t f;

   d = Get_Domain(1);
   /* Loop over all boundary zones in the domain */
   thread_loop_f(t,d)
   {
   	Message ("Cell Thread %d \n", t);
      Message (THREAD_NAME(t));
      if (strcmp(THREAD_NAME(t),"pipe_fluid")!=0)
      {
         Message ("skipping thread \n");
         continue;
         /* break; */
      }
   	/* function that returns TRUE if Thread *t is a boundary face thread */
   	if (BOUNDARY_FACE_THREAD_P(t)) /* (WALL_THREAD_P(t))*/
      {
            Message ("Begin F loop \n");
            /* Loop over all faces */
            begin_f_loop(f,t)
            {
               if (f==0)
               {
                  Message ("Beginning face loop \n");
               }
               /* c0 and t0 identify the adjacent cell */
               c0 = F_C0(f, t);
               t0 = THREAD_T0(t);

      			/* Properties */
      			kt = C_K_L(c0,t0);
               Message ("kt = %g \n",kt);

               /* Cell Gradients */
               dTx = C_T_G(c0,t0)[0]; /* returns the x-component of the cell temperature gradient vector */
               dTy = C_T_G(c0,t0)[1]; /* returns the x-component of the cell temperature gradient vector */

               Message ("dTx = %g \n",dTx);
               Message ("dTy = %g \n",dTy);

               dTxRG = C_T_RG(c0,t0)[0]; /* returns the x-component of the cell temperature gradient vector */
               dTyRG = C_T_RG(c0,t0)[1]; /* returns the x-component of the cell temperature gradient vector */

               Message ("dTxRG = %g \n",dTxRG);
               Message ("dTyRG = %g \n",dTyRG);

               dTr = pow(pow(dTx,2)+pow(dTy,2),0.5);
               dTrRG = pow(pow(dTxRG,2)+pow(dTyRG,2),0.5);

               Message ("dTr = %g \n", dTr); 
               Message ("dTrRG = %g \n",dTrRG);

               QWall = -kt*dTr;
               QWallRG = -kt*dTrRG;

               Message ("Qwall = %g \n", QWall);
               Message ("QwallRG = %g \n",QWallRG);


      			/* Retrieve bulk temperature & Wall Adjacent Temperature */
      			TBulk = RP_Get_Real("ref/temperature");
               TWadj = F_T(f,t);

               Message ("TBulk = %g \n",TBulk); 
               Message ("TWadj = %g \n",TWadj);


               /* Calculate heat transfer coefficient */

               whtc = QWall/(TWadj-TBulk);
               whtcRG = QWallRG/(TWadj/TBulk);

               /* TWall = QWall/(-kt*dTr) + TWadj */

               Message ("Store data \n");

               C_UDMI(c0,t0,0) = whtc;
               F_UDMI(f,t,0) = whtc;

               C_UDMI(c0,t0,1) = QWall;
               F_UDMI(f,t,1) = QWall;

               C_UDMI(c0,t0,2) = QWallRG;
               F_UDMI(f,t,2) = QWallRG;

               C_UDMI(c0,t0,3) = TBulk;
               F_UDMI(f,t,3) = TBulk;

               C_UDMI(c0,t0,4) = TWadj;
               F_UDMI(f,t,4) = TWadj;

               C_UDMI(c0,t0,5) = whtcRG;
               F_UDMI(f,t,5) = whtcRG;


      		}
            end_f_loop(f,t)
      }
   }
}

Cell Thread 89742640
pipe_solid-non-overlappingskipping thread
Cell Thread 89581616
pipe_fluid-non-overlappingskipping thread
Cell Thread 89420592
pipe_interface-wall1-1-1skipping thread
Cell Thread 89903664
pipe_interface-wall1-1-1-shadowskipping thread
Cell Thread 86909472
interior-fluidskipping thread
Cell Thread 87070496
inletskipping thread
Cell Thread 87231520
outletskipping thread
Cell Thread 87392544
pipe_fluidBegin F loop
Cell Thread 88369344
interior-solidskipping thread
Cell Thread 88518224
wall-solidskipping thread
Cell Thread 88667104
pipe_solidskipping thread
Cell Thread 88828128
htfx_bcskipping thread

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

Node 0: Process 381551: Received signal SIGSEGV.

================================================== ============================
The fluent process could not be started.
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Old   November 24, 2020, 14:18
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Do you get the same if you replace

kt = C_K_L(c0,t0);

By

kt = 0.0;

?
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Old   November 26, 2020, 11:27
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Tyler Richardson
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Quote:
Originally Posted by pakk View Post
Do you get the same if you replace

kt = C_K_L(c0,t0);

By

kt = 0.0;

?
Thanks for looking into this!

Turns out the problem was as follows:

1) I was retrieving gradient data (C_T_G) and that is only stored if you request it
2) I was storing calculations to UDMI_F() on an interface… you can only store face values to walls and boundaries….
pakk and Aj_45 like this.
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