UDF for output temperature
 

Hi I am attempted to use UDF to define dimensionless temperature in order to use it in post processing results I wrote it as below :

#include "udf.h"

DEFINE_ON_DEMAND(on_demand_calc)
{
Domain *d; /* declare domain pointer since it is not passed as an
argument to the DEFINE macro */
real th = 298.3899;
real tc = 297.6101;
real temp;
Thread *t;
cell_t c;
d = Get_Domain(1); /* Get the domain using Fluent utility */

/* Compute temperature function and store in user-defined memory*/
/*(location index 0) */

begin_c_loop(c,t)
{
temp = C_T(c,t);
C_UDMI(c,t,0) = (temp-tc)/(th-tc);
}
end_c_loop(c,t)

}


I interpreted it successfully but when I select execute for demand it give me the following error:

Warning: E:\\Project current year\\paper work\\output.C: line 9:
Error: received a fatal signal (Segmentation fault).

So is there problem with the UDF? any reply please?

regards,
mariam

Did you allocate memory to store the UDM? Go to "User Defined" -> "Memory" and the set "Number of User-Defined Memory Locations" to 1.

Hi Thanks for the reply. I set the memory to 1 from the user defined menu but nothing appear at display >contours>User defined memory see pict? what the problem?

User defined memory indices start at 0. Assuming to did re-run the simulation,

You can also (in Fluent) go to File > Export > Solution Data...

The set "CFD-Post Compatible" as File Type. And choose User Memory 0 in the "Quantities list" (and whatever other things you want to store). Then click write and store in somewhere you want.

The use the CFD-Post to read that file.

I interpreted the UDF at first then change the memory to 1 then I initialize the solution and run the case after that when I view the user memory contours nothing appears to me same as the pict I sent in my previous reply?

User Memory 1 (the one you're trying to draw contours for in the picture) shouldn't even exist for your simulation. As I said, User Defined memory Indices start at 0, so you should have a User Memory 0. Can you find this or not?

Cannot find User Memory 1 ? just User Memory 0 exist and nothing appear with it? maybe my steps was wrong or my UDF not interpreted successfully? may you repeat the procedure to me step by step? Currently do I need to apply execute on demand option or not need it?

Ok, so you have your UDF exactly as you posted, it is correct.

First you allocate the User Defined Memory Location (For you UDF you only need to allocate 1 memory location for UDMI(c,t,0)).

Second, you interpret (or compile, whatever you prefer) your UDF.

Third, run the code. It is a execute on command, so go to User Defined > Execute on command... then select your code and hit "execute".

Now it should be written.

Also after viewing your first post again, I see that you use Fluent to also draw the contours. You have not selected a surface for fluent to draw them on, so it wont draw anything. You'll probably want to select "Interior_surface_body".

I hope this will work for you.

When I go to User Defined > Execute on command
it still give me the error I mentioned at my first post i.e.

Warning: E:\\Project current year\\kefayati paper\\output.C: line 9:
Error: received a fatal signal (Segmentation fault).

I assume line 9 is "real temp;", nothing seems to be wrong there at all.

What I think is going wrong now is that the thread pointer (*t) is never actually set to anything.

I will assume that you want to loop over all cells in the domain. To do this try the following code:

#include "udf.h"

DEFINE_ON_DEMAND(on_demand_calc)
{
Domain *d; /* declare domain pointer since it is not passed as an
argument to the DEFINE macro */
real th = 298.3899;
real tc = 297.6101;
real temp;
Thread *t;
cell_t c;
d = Get_Domain(1); /* Get the domain using Fluent utility */

/* Compute temperature function and store in user-defined memory*/
/*(location index 0) */

thread_loop_c(t,d) /* This will loop over all threads in the domain */
{
begin_c_loop(c,t) /* This will loop over all cells in a thread */
{
temp = C_T(c,t);
C_UDMI(c,t,0) = (temp-tc)/(th-tc);
}
end_c_loop(c,t)
}
}

Use as I described before.