[Brian_]

Hi,

I wrote a UDF (see attached) to compute the total mass in an axisymmetrc energy equation only model. I use this information to adjust boundary conditions. The UDF works correctly for a simple one cell zone model (if I multiple by 2*pi). UDF results agree exactly with Fluent's result volume mass integral.

But the UDF produces nonsensical results when I have more than 2 cell zones. Result of UDF=3.88563e-07 kg, while Fluent's volume mass integral=8.1350377e-08 kg (which is correct).

In addition, I also need to limit the mass summation to certain cell zones. When I try to limit the tread_loop_c to a specific cell zone IDs it gives the same nonsensical result as above (3.88563e-07 kg).

Any help with either the incorrect mass issue or how to limit tread_loop_c to specific cell zone IDs would be greatly appreciated.

Best Regards,

Brian

[AlexanderZ]

was

		  thread_loop_c(t, d) {
			  begin_c_loop(c, t) {
				  mass_total += C_R(c, t) * C_VOLUME(c, t);
			  } 
			  end_c_loop(c, t);
			  mass_total = 2 * pi*mass_total;  /*axisymmetric requires mult by 2pi to get total mass*/
	  }

try this

thread_loop_c(t, d) {
			  begin_c_loop(c, t) {
				  mass_total += C_R(c, t) * C_VOLUME(c, t);
			  } 
			  end_c_loop(c, t);
			 
		}
		 mass_total = 2 * pi*mass_total;  /*axisymmetric requires mult by 2pi to get total mass*/

best regards

[Brian_]

AlexanderZ,

Thanks for finding my error! That solved the total mass issue. I've been looking at this for the better part of a day.

Limiting the cell zones used in the mass summation is still an issue. In my test model I have two cell zones, id=3 and id=4. If I try to limit thread_loop_c(t, d) with the commands below, the UDF still sums mass over both threads. Thanks again for your help.

Best Regards,

Brian

int id_1 = 4;
Thread *t;
t = Lookup_Thread(d, id_1);

thread_loop_c(t, d) {
begin_c_loop(c, t) {
mass_total += C_R(c, t) * C_VOLUME(c, t);
}
end_c_loop(c, t);

}
mass_total = 2 * pi*mass_total;

[obscureed]

The command "thread_loop_c(t, d){ ... }" is doing what it is meant to do: it is meant to loop over all threads in the domain. So, the first iteration over-writes the value of t that you have set up with Lookup_Thread. Delete the thread_loop_c line (and the corresponding closing brace) and you should be fine.

Ed

[Brian_]

Ed,

Thank you! Works just like I need. There is a bit of a learning curve with UDFs You probably saved me several days of debugging.

Best Regards,

Brian