[paolofug87]

Hi all,
I would like to create an udf for calculating the time integral of a variable (i.e. CO concentration) and allocating it in a UDM. Nothing special, just multiply the new value for dt and adding the one calculated in the previous step.
I know how to write udf but this time it seems that I need to declare a global variable and I don't now where I have to hook it in the model.

Thank you in advance

Paolo

P.s. is there any precaution to use this udf in parallel computing?

[LuckyTran]

Why can't you use the built-in data sampling for time statistics option? You should have the option of selecting species.

If you cannot select it, I think it is much easier to define a custom field function, set it equal to the [CO] and then sample this custom variable again using the data sampling option.

Originally Posted by paolofug87

I know how to write udf but this time it seems that I need to declare a global variable and I don't now where I have to hook it in the model.

I don't know how to decipher that to understand what your problem is.

[paolofug87]

Sorry for my English, I wish to have a field variable that is the cumulative of the co concentration in time for each cell. The aim is to show contour of FED (fractional effective dose) in all the domain.
I figured out that I have probably to set two udm, one for storing the [CO] in the previous time step (let's say udm0) and one for the last time step (udm1) and then sum udm0+udm1 each time step updating the first one (udm0=udm1). My problem is to write the udf that does this task and where to hook it (probably in the udf hook panel in one of the options).

Thank you

[paolofug87]

Furthermore I wish to run the simulation in parallel, I know that loops over cells require some precaution

[LuckyTran]

This doesn't require a UDF afaik. Just turn on data sampling for time-statistics.

[AlexanderZ]

Originally Posted by paolofug87

Hi all,
I would like to create an udf for calculating the time integral of a variable (i.e. CO concentration) and allocating it in a UDM. Nothing special, just multiply the new value for dt and adding the one calculated in the previous step.
I know how to write udf but this time it seems that I need to declare a global variable and I don't now where I have to hook it in the model.

Thank you in advance

Paolo

P.s. is there any precaution to use this udf in parallel computing?

Hello

For UDF use ANSYS Fluent Customization Manual

For your case you may use this code for single cell as a basis, modify it

#include "udf.h"
DEFINE_EXECUTE_AT_END(execute_at_end)
{
Domain *d;
Thread *t;
/* Integrate dissipation. */
real integral=0.;
real dtime;
real temperature;
cell_t c;
d = Get_Domain(1); /* mixture domain if multiphase */
dtime = CURRENT_TIMESTEP;	 		/* get time step value */
thread_loop_c (t,d)
{
/* Loop over all cells */
	begin_c_loop(c,t)
	{
		/* Calculate volume of JR */
		temperature = C_T(c,t); 			/* get temperature*/
		integral += temperature*dtime;		/* calculate integral */
		C_UDMI(c,t,0) = integral;			/* write to UDM */
	}
	end_c_loop (c,t)
}
Message("Temperature time integral: %f\n", integral);
}

Save this as a .c file. Compile.
Then load in fluent. Hook DEFINE_EXECUTE_AT_END function (User-Defined -> function hooks)
Add UMD ( User-Defined -> Memory -> Set memory locations 1)

Best reagards

[paolofug87]

Thank you very much!
I was able to do my task modifiyng the code like here below.
Obviously is only an example, in my code I'll use the CO concentration instead of temperature.
Now I just need to change the UDM name, for the parallel computing it seems that I don't need any change (looking at results).

Thank you again, hope this post could help someone else.

Cheers

Paolo

#include "udf.h"
DEFINE_EXECUTE_AT_END(execute_at_end)
{
Domain *d;
Thread *t;
/* Integrate dissipation. */
real integral=0.;
real dtime;
real temperature;
cell_t c;
d = Get_Domain(1); /* mixture domain if multiphase */
dtime = CURRENT_TIMESTEP; /* get time step value */
thread_loop_c (t,d)
{
/* Loop over all cells */
begin_c_loop(c,t)
{
/* Calculate volume of JR */
temperature = C_T(c,t)*dtime; /* get temperature*/
C_UDMI(c,t,0) = C_UDMI(c,t,0) + temperature; /* write to UDM */

}
end_c_loop (c,t)
}
Message("Temperature time integral: %f\n", integral);
Message("Temperature time integral: %f\n", dtime);
}