[Oula]

Hi everyone

One of the CFD-ONLINE users helped me to write a C++ code for a monitoring user-defined function. The code consists of two functions, the first one is to store value in UDMI during the transient simulation and the other function is to write data that were stored in the first one to a (.txt) file for time and temperature.

We expected the file to be like, see below (A). But what happened is that the time data has not been recorded at all and the faces counting was seperate from the temperature value see below (B) a sample of the written data.

I have checked the ANSYS UDF manual but I couldn't find any example on writing files using DEFINE_EXECUTE_AT_END macro to identify the mistake and why I'm not getting what I expect. The other thing is that the file's size became super big I couldn't open it even in excel. Do you have any experience with this regards? Any help is much appreciated and sorry for the long post

A)
time face000 face001 face002 ...
0.1 300.0 301.0 302.0 ...
0.2 300.2 300.8 301.5 ...

B)
time face000 face001 face002 face003 face004 face005 face006 face007 face008 face009 face010 face011 face012 face013 face014 face015 face016 face017 face018 face019 face020 face021 face022 face023 face024 face025 face026 face027 face028 face029 face030 face031 face032 face033 face034 face035 .....
..... 0.00000e+00 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02 2.93000e+02


The code is
#include "udf.h"
#define ID 8

/* Solution a: store value in UDMI */
/* Both the face thread and their adjacent cells */
/* of the UDMI are set for proper visulazation in FLUENT */
DEFINE_EXECUTE_AT_END(wall_temp)
{
#if !RP_HOST
face_t f;
real temp, tmax, tmin;
real value;
Domain *domain = Get_Domain(ROOT_DOMAIN_ID);
Thread *t = Lookup_Thread(domain, ID);
begin_f_loop(f,t)
{
temp = F_T(f,t);
value = (temp - tmin) / (tmax-tmin);
F_UDMI(f,t,0) = value;
F_UDMI(F_C0(f, t), t->t0, 0) = value;
}
end_f_loop(f,t);
#endif
}

/* Solution b: write data to file */
FILE* fptemp = NULL;
DEFINE_EXECUTE_AT_END(write_temp_to_file)
{
#if !RP_HOST
face_t f;
real temp, tmax, tmin;
real value;
real time;
Domain *domain = Get_Domain(ROOT_DOMAIN_ID);
Thread *t = Lookup_Thread(domain, ID);
int cnt;
char header[16];
if (!fptemp)
{
fptemp = fopen("temp-vs-time.txt", "w");
fprintf(fptemp, "%16s", "time");
for (cnt = 0; cnt < t->nelements; ++cnt)
{
sprintf(header, "face%03d", cnt);
fprintf(fptemp, "%16s", header);
}
fprintf(fptemp, "\n");
}
time = CURRENT_TIME;
fprintf(fptemp, "%16.5e", time);

begin_f_loop(f,t)
{
temp = F_T(f,t);
value = (temp - tmin) / (tmax-tmin);
fprintf(fptemp, "%16.5e", value);
}
end_f_loop(f,t);

fprintf(fptemp, "\n");
fflush(fptemp);
#endif
}

[AlexanderZ]

your code

#include "udf.h"
#define ID 8

/* Solution a: store value in UDMI */
/* Both the face thread and their adjacent cells */
/* of the UDMI are set for proper visulazation in FLUENT */
DEFINE_EXECUTE_AT_END(wall_temp)
{
#if !RP_HOST
face_t f;
real temp, tmax, tmin;
real value;
Domain *domain = Get_Domain(ROOT_DOMAIN_ID);
Thread *t = Lookup_Thread(domain, ID);
begin_f_loop(f,t)
{
temp = F_T(f,t);
value = (temp - tmin) / (tmax-tmin);
F_UDMI(f,t,0) = value;
F_UDMI(F_C0(f, t), t->t0, 0) = value;
}
end_f_loop(f,t);
#endif
}

ID 8, check this ID value -> in Fluent gui go to boundary conditions and manualy click one by one all your boundaries, find ID = 8 for your model, is this surface is what you want?

F_UDMI(f,t,0) = value;
F_UDMI(F_C0(f, t), t->t0, 0) = value;

you rewrite first UDMI value with the second.
you may use

F_UDMI(f,t,0) = value;
F_UDMI(F_C0(f, t), t->t0, 1) = value;

if you think you need them both, in that case you will have 2 udms, was 1.

#if !RP_HOST
#endif

which version of fluent do you use, if less than 19.0 you may delete it, this macro is for parallel computation, you don't need it for single core.

tmax
tmin
ARE NOT DEFINED!

best regards

[AlexanderZ]

your code

/* Solution b: write data to file */
FILE* fptemp = NULL;
DEFINE_EXECUTE_AT_END(write_temp_to_file)
{
#if !RP_HOST
face_t f;
real temp, tmax, tmin;
real value;
real time;
Domain *domain = Get_Domain(ROOT_DOMAIN_ID);
Thread *t = Lookup_Thread(domain, ID);
int cnt;
char header[16];
if (!fptemp)
{
fptemp = fopen("temp-vs-time.txt", "w");
fprintf(fptemp, "%16s", "time");
for (cnt = 0; cnt < t->nelements; ++cnt)
{
sprintf(header, "face%03d", cnt);
fprintf(fptemp, "%16s", header);
}
fprintf(fptemp, "\n");
}
time = CURRENT_TIME;
fprintf(fptemp, "%16.5e", time);

begin_f_loop(f,t)
{
temp = F_T(f,t);
value = (temp - tmin) / (tmax-tmin);
fprintf(fptemp, "%16.5e", value);
}
end_f_loop(f,t);

fprintf(fptemp, "\n");
fflush(fptemp);
#endif
}

first of all delete

#if !RP_HOST #endif

tmax, tmin are not defined

time = CURRENT_TIME;
fprintf(fptemp, "%16.5e", time);

printing time works well, but it write only ONCE, you may put it inside the loop to the the time in each face

so you may get something like this, NOT TESTED

FILE* fptemp = NULL;
DEFINE_EXECUTE_AT_END(write_temp_to_file)
{
#if !RP_HOST
face_t f;
real temp, tmax, tmin;
real value;
real time;
Domain *domain = Get_Domain(ROOT_DOMAIN_ID);
Thread *t = Lookup_Thread(domain, ID);
int cnt;
char header[16];
time = CURRENT_TIME;
if (!fptemp)
{
	fptemp = fopen("temp-vs-time.txt", "w");
	fprintf(fptemp, "%16s", "time");
		for (cnt = 0; cnt < t->nelements; ++cnt)
		{
			sprintf(header, "face%03d", cnt);
			fprintf(fptemp, "%16s", header);
		}
	fprintf(fptemp, "\n");
	
	begin_f_loop(f,t)
	{
	fprintf(fptemp, "%16.5e ", time);
	}
	end_f_loop(f,t);
	
	fprintf(fptemp, "\n");
	
	begin_f_loop(f,t)
	{
		temp = F_T(f,t);
		value = (temp - tmin) / (tmax-tmin);
		fprintf(fptemp, "%16.5e ", value);
	}
	end_f_loop(f,t);

fprintf(fptemp, "\n");
}
fflush(fptemp);
#endif
}

you should define tmin tmax as well

best regards

[Oula]

Many thanks Alexander. It is just the face counting that I'm not sure about. I wish if there is any way to stop the counting and give the average. What do you think is this possible?

Best Regards

[AlexanderZ]

check 2.2.9. DEFINE_ON_DEMAND in Ansys Fluent Customization manual.
There you may find example, how to calculate average temperature, you may you it as a basis
number may be different, depending on version.

best regards

[pavankonchada]

Hi alexander
When I am trying to interpret 6th degree polynomial I am getting different answer when normally calculating with calculator

[Oula]

Originally Posted by pavankonchada

Hi alexander
When I am trying to interpret 6th degree polynomial I am getting different answer when normally calculating with calculator

Hi pavan, could you explain more? is it the polynomial equation is to fit a curve of original data?

Regards

[pavankonchada]

I am trying to write udf for variable dynamic viscosity for PCM as shown below
DEFINE_PROPERTY(PCM_Dynamicviscosity,cell,thread)
{
real tempe2,mu,bt;
tempe2 = C_T(cell,thread);
bt=(6722811.795)-(67319.37*tempe2)+(224.7*tempe2*tempe2)-(0.25*tempe2*tempe2*tempe2);
printf("bt=%f \n",bt);
if (tempe2 < 298.6)
mu=180000;
if ((tempe2 >= 298.6) && (tempe2 <= 300.6))
mu=0.001798(1+((100000(1-bt)*(1-bt))/((bt*bt*bt)+0.001)));
else
{
mu=0.001798;
}
return mu;
}
the value of bt is 0.011 and hence mu value is 175632.39
but the value I am getting for bt when initializing is 1.5 and dynamic viscosity is coming wrong
Problem is
0.25*tempe2*tempe2*tempe2=6655940.5 (fluent value)
0.25*tempe2*tempe2*tempe2=6655941.9189(Actual value)