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Segmentation fault when execute on demand udf

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Old   November 8, 2015, 22:15
Default Segmentation fault when execute on demand udf
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Dantong Shi
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Hello,

I'm calculating dimensionless temperature using a udf (shown in the following). After I interpreted it, I click the execute on demand. Then the error appear. It says "Segmentation fault". I don't know how to solve it? Where is the fault in my udf?
The following is my udf.

Thanks!

#include "udf.h"

DEFINE_ON_DEMAND(dimentionless_temperature)
{
Domain *d;
real dimentionless_t;
real twall = 400;
real temp;
real xmin = 0;
real xmax = 0.2667;
real deltax = 0.01;
//int n= (xmax-xmin)/deltax;
real tbulk[27];
Thread *t;
cell_t c;
real x[ND_ND];
int i;
C_CENTROID(x,c,t);
d = Get_Domain(1); /* Get the domain using ANSYS Fluent utility */

thread_loop_c(t,d)
{
for(i=0; i<=26; i++)
{
begin_c_loop(c,t)
{
if (x[0]>=xmin+i*deltax && x[0]<=xmin+(i+1)*deltax)
{tbulk[i] += (C_T(c,t)*C_U(c,t)*C_VOLUME(c,t))/(C_U(c,t)*C_VOLUME(c,t));
temp = C_T(c,t);
dimentionless_t = (temp-twall)/(tbulk[i]-twall);
C_UDMI(c,t,0) = (temp-twall)/(tbulk[i]-twall);
}
end_c_loop(c,t)
}
}
}
}
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Old   November 9, 2015, 03:36
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When you write C_CENTROID(x,c,t);, neither c nor t are initialized.

C_CENTROID(x,c,t); must be included in the loop of cells, such as:

d = Get_Domain(1); /* Get the domain using ANSYS Fluent utility */

thread_loop_c(t,d)
{
for(i=0; i<=26; i++)
{
begin_c_loop(c,t)
{
C_CENTROID(x,c,t);
if ((x[0]>=xmin+i*deltax) && (x[0]<=xmin+(i+1)*deltax))//better write more parentheses
{tbulk[i] += (C_T(c,t)*C_U(c,t)*C_VOLUME(c,t))/(C_U(c,t)*C_VOLUME(c,t));
temp = C_T(c,t);
dimentionless_t = (temp-twall)/(tbulk[i]-twall);
C_UDMI(c,t,0) = (temp-twall)/(tbulk[i]-twall);
}
end_c_loop(c,t)
}
}
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Old   November 9, 2015, 10:29
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Dantong Shi
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Thank you for your help. I revised the udf as you suggested. Then I interpreted it and execute on demand. Another error appear.

It says:
Node 0: Process 7280: Recieved signal SIGSEGV.
Node 1: Process 7288: Recieved signal SIGSEGV.

MPI Application rank 1 exited before MPI_finalize() with status 2
The f1 process could not be started.

Fatal error in one of the compute processes.

Do you know what's wrong this time?

Thank you very much!
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Old   November 16, 2015, 08:20
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If you are working in parallel, first try to get it working in serial. Only if that works, go to parallel.
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Old   June 19, 2017, 05:20
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Shravan
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Hello,
I dont know if this might help you now. But usually we get segmentation error in UDM when we have used it in a UDF but havent set the number of UDMs in fluent GUI.

When we compile a UDF in which we use a UDM, before compiling we should go to DEFINE->User Defined->Memory and Set the number as you wish
Just make sure you have done this before clicking Execute on Demand. Thanks
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Old   June 30, 2017, 03:03
Default Received a fatal Signal ( Segmentation fault )
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Muhammad Furqan Ali
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Hi everyone !

I hope you are fine. I am using UDF in VOF model in ANSYS FLUENT, although, my VOF model without UDF is running fine. The UDF is written by my friend used it successfully. He has graduated last year after getting the results from same UDF. The UDF was working well on his server. He was using Fluent 6.3 on Linux system. When I am using same case, date and UDF on my laptop the case is not running, although UDF compilation is very fine. I also check it on Linux system too. During or after initialization, Error occurred segmentation fault error. It is very strange that same case and UDF is not working on his office now. Main error occurred when I am hooking ADJUST and EXECUTE-AT-END UDFs. May be there is some problem of writing/calling style is different in Windows and Linux system with 32bit and 64bit. ( this is just my opinion).

I hope you can understand the situation and have a try to fix the problem. I would be highly thankful if you guide me that where is the problem. I can send UDF by email if needed..

Thanks in Advance,
Regards,
M. F. ALi
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