Hi all,

I have just begun looking at using UDMs for the first time and have hit a fairly major stummbling block. To describe my situation right now, I'm trying to apply one of the simplest UDM examples from the Fluent UDF manual to a pre-solved 3d case.

The script (udmres1.c) is listed below.

I tried to interpret the script, but that failed with syntax errors, so I tried to compile it instead. The script compiles, and, so long as I allocate enough UDMs the ON_LOAD part works fine. I can see the memories, and they are named. However, when I try to execute the ON_DEMAND part, I get a SEGMENTATION VIOLATION. I have no idea what this means.

If I replace the C_UDMI() function with a Message() function everything works as expected, however nothing I do with C_UDMI() in place makes any difference.

I am sufficiently new to all of this that the problem could be anything, so any advice would be greatly appreciated.

Thanks in advance,

Chris

PS If relevant, I'm using Fluent 6.2.16.

--

#include "udf.h"

#define NUM_UDM 3

static int udm_offset = UDM_UNRESERVED;

DEFINE_EXECUTE_ON_LOADING(on_loading, libname)

{

if (udm_offset == UDM_UNRESERVED) udm_offset = Reserve_User_Memory_Vars(NUM_UDM);

if (udm_offset == UDM_UNRESERVED) Message("\nYou need to define up to %d extra UDMs in GUI and then reload current library %s\n", NUM_UDM, libname);

else

{

Message("%d UDMs have been reserved by the current library %s\n",NUM_UDM, libname);

Set_User_Memory_Name(udm_offset,"lib1-UDM-0");

Set_User_Memory_Name(udm_offset+1,"lib1-UDM-1");

Set_User_Memory_Name(udm_offset+2,"lib1-UDM-2");

}

Message("\nUDM Offset for Current Loaded Library = %d",udm_offset);

}

DEFINE_ON_DEMAND(set_udms) {

Domain *d;

Thread *ct;

cell_t c;

int i;

d=Get_Domain(1);

if(udm_offset != UDM_UNRESERVED)

{

Message("Setting UDMs\n");

for (i=0;i<NUM_UDM;i++)

{

thread_loop_c(ct,d)

{

begin_c_loop(c,ct)

{

C_UDMI(c,ct,udm_offset+i)=3.0+i/10.0;

}

end_c_loop(c,ct)

}

}

}

else Message("UDMs have not yet been reserved for library 1\n");

}

have you run at least one solver iteration before executing the ON_DEMAND macro to initialise the UDM's?

Hi Alec,

I thought that I had, but to make sure, I tried again. I still get the same failure.

It has been suggested to me that the problem might be that I'm compiling on a 64-bit machine and that I should try on a 32-bit machine.

Does this sound reasonable? I do have capacity to do this - but it requires a bit of effort!

Chris

Update:

I'm now able to use the UDMs. I have determined that by loading the case file, setting up the UDMs, initialising the case, loading the data file, and then trying to use the UDMs it all works.

Slightly more effort than I might like, but it works.

Thanks Alec for pointing me in this direction.

Chris

Hi, I think it also helps this: before executing the on demand function, try to display that udm on any surface (there will be zeros) and then execute your function.

Martin