CFD Online Discussion Forums - solving a conduction problem in FLUENT using UDF

Hi,

I am working on cooling of multi-core processors using core hopping. The way it works is - Say, I have a quad core processor. Initially I power "ON" one core. That core keeps running till it crosses a particular temperature threshold. Once, that temperature threshold is reached, I will turn that core "OFF" and turn "ON" another core in its place. Lets say, I do this for a period of 500 seconds.

I created my model in ICEPAK. I simulated a "core" using a heat source. However, I need to write a UDF to perform the switching of cores based on temperature and, ICEPAK does not allow you to write UDFs. Thats the reason I had to learn to do this in FLUENT. I have no prior experience of working with FLUENT and I need to get this done immediately.

I imported my model into FLUENT by reading in the case file generated by icepak and I did not find any meshing errors. I then wrote my UDF s to perform the switching but when I tried interpreting/compiling them, I found a host of errors that I couldn't resolve. I request you to kindly help me out.

My UDFs are given as follows. I have commented them to try and make them as self-explanatory as possible. I have listed the errors after each UDF. The cores are labelled 1, 14, 5 and 7. What I am trying to simulate through these UDFs is that : Initially - Core 1 is powered ON. If the temperature of core 1 goes above 70 deg C, then turn it off and Turn ON core 14. Similarly, if core 14 goes above 0 deg C, turn ON core 5, if core 5 goes above 70 deg C, turn ON core 7 and if Core 7 goes above 70, go back to Core 1.

I am posting just the UDFs for core 1 and core 14 as the rest are just repeats of the code for core 14 and have the same errors.

1.)

#include"udf.h"
/* function for giving power to core 1 */
DEFINE_PROFILE(core_1_power,t,i)
{
face_t f;
face_t f1;
real temp1;
/* Check Temperature of Core 1 */

begin_f_loop(f,t)
{
temp1=F_T(f,t);
}
end_f_loop(f,t)
while(temp1<343)
{
begin_f_loop(f,t)
{
F_PROFILE(f,t,i)=0.394527e+006; /* As long as temperature of core 1 is < 70 deg C,Keep it turned ON */
}
end_f_loop(f,t)
} /* end of while loop */
if(temp1>343)
{
begin_f_loop(f,t)
{
F_PROFILE(f,t,i)=0; /* If temperature of core 1 is > 70 deg C, turn it OFF */
}
end_f_loop(f,t)

Thread *t1=Lookup_Thread(domain,26); /* Get thread for core 14 */
begin_f_loop(f1,t1)
{
F_PROFILE(f1,t1,i)=0.394527e+006; /* Switch Core 14 ON instead of core 1 */
}
end_f_loop(f1,t1)
}
else
{
begin_f_loop(f,t)
{
F_PROFILE(f,t,i)=0.394527e+006; /* Otherwise Keep Core 1 ON */
}
end_f_loop(f,t)
}
}

Errors :

(37) : error C2275: 'Thread' : illegal use of this type as an expression
(37) : error C2065: 't1' : undeclared identifier
(37) : error C2065: 'domain' : undeclared identifier
(37) : warning C4047: 'function' : 'Domain *' differs in levels of indirection from 'int'
(37) : warning C4024: 'Lookup_Thread' : different types for formal and actual parameter 1
(39) : error C2065: 't1' : undeclared identifier
(39) : error C2223: left of '->nelements' must point to struct/union
(41) : error C2065: 't1' : undeclared identifier
(41) : error C2223: left of '->storage' must point to struct/union

2. Code for Core 14

#include"udf.h"
/* Function for assigning power to core 14 */
/* Core 14 will be turned ON only if Core 1 Exceeds 70 Deg C */
DEFINE_PROFILE(core_14_power,t,i)
{
face_t f;
face_t f1;
face_t f2;
real temp1;
real temp2;
Thread *t1=Lookup_Thread(domain,16); /* Lookup Thread for core 1 */
begin_f_loop(f1,t1)
{
temp1=F_T(f1,t1); /* get temperature of core 1 */
}
end_f_loop(f1,t1)
while(temp1<343)
{
begin_f_loop(f,t)
{
F_PROFILE(f,t,i)=0; /* As long as core 1 is not > 70 deg C, core 14 remains turned OFF */
}
end_f_loop(f,t)
} /* End of while loop */
if(temp1>343) /* Provided Core 1 is > 70 Deg C */
{
begin_f_loop(f,t)
{
temp2=F_T(f,t); /* Get Temperature of core 14 */
}
end_f_loop(f,t)

if(temp2<343)
{
begin_f_looop(f,t)
{
F_PROFILE(f,t,i)=0.394527e+006; /* If core 14 is < 70 Deg C (while core 1 is > 70 Deg C)
turn ON core 14 and keep it ON for as long as it
is below 70 Deg C */
}
end_f_loop(f,t)
}
else
{
begin_f_loop(f,t)
{
F_PROFILE(f,t,i)=0; /* If temperature of core 14 is also > 70 Deg C,
do NOT turn it ON */
}
end_f_loop(f,t)
Thread *t2=Lookup_Thread(domain,19); /* Lookup Thread for core 5 */

begin_f_loop(f2,t2)
{
F_PROFILE(f2,t2,i)=0.394527e+006; /* Turn ON core 5 */
}
end_f_loop(f2,t2)
} /* end of nested if-else loop */
else
{
begin_f_loop(f,t)
{
F_PROFILE(f,t,i)=0; /* If core 1 is not > 70 Deg C, then core 14 power is anyway zero */
}
end_f_loop(f,t)
} /* End of outer if-else loop */
}

Errors:

(16) : error C2065: 'domain' : undeclared identifier
(16) : warning C4047: 'function' : 'Domain *' differs in levels of indirection from 'int'
(16) : warning C4024: 'Lookup_Thread' : different types for formal and actual parameter 1
(45) : error C2143: syntax error : missing ';' before '{'
(52) : error C2059: syntax error : 'else'
(69) : error C2059: syntax error : 'else'
(77) : error C2059: syntax error : '}'

I apologize for the very long post and also if any of my errors are really trivial. I would appreciate any prompt help with this as I dont know of anybody here who has worked with UDF and also, I need to get it done immediately.

Thank you very much.

Regards,
Avinash Raghu.
Graduate Student,
University of Texas at Arlington.