[lbj007]

Can UDF achieve the following function: monitor the minimum value of a physical quantity, obtain its values at the nth and (n-1)th iteration steps, and when the difference approaches zero, switch a boundary condition mounted with a UDF, such as replacing DEFINE_PROFILE(uright0,f_thread,position) with another DEFINE_PROFILE(uright1,f_thread,position). or maybe scheme can achieve it?

[Siba11]

Originally Posted by lbj007

Can UDF achieve the following function: monitor the minimum value of a physical quantity, obtain its values at the nth and (n-1)th iteration steps, and when the difference approaches zero, switch a boundary condition mounted with a UDF, such as replacing DEFINE_PROFILE(uright0,f_thread,position) with another DEFINE_PROFILE(uright1,f_thread,position). or maybe scheme can achieve it?

Hi. Yes, it can be done.

Firstly, write a UDF that calculates the difference between the nth and (n-1)th iteration. Simultaneously, define an RP variable in the console (check this page).

Now, when the difference approaches zero, change the value of this RP variable via your first UDF. (using "RP_set_integer").

Now, you can write a second UDF (a DEFINE_PROFILE UDF) with a switch case statement. At some nth iteration, when the RP variable will change its value, it will be detected by the 2nd UDF. And from that iteration onwards, it will switch the boundary condition (using the switch-case statement).

[lbj007]

Originally Posted by Siba11

Hi. Yes, it can be done.

Firstly, write a UDF that calculates the difference between the nth and (n-1)th iteration. Simultaneously, define an RP variable in the console (check this page).

Now, when the difference approaches zero, change the value of this RP variable via your first UDF. (using "RP_set_integer").

Now, you can write a second UDF (a DEFINE_PROFILE UDF) with a switch case statement. At some nth iteration, when the RP variable will change its value, it will be detected by the 2nd UDF. And from that iteration onwards, it will switch the boundary condition (using the switch-case statement).

Hi, Thank you for your detailed explanation, but there's one more thing I'm not sure, how can I obtain the variable's values at the nth and (n-1)th iteration steps in real time? More specially, how can I store the value of the previous iteration step？I know there are previous time step Macros, such as C_T_M1(c,t) for transient calculations, but what can be used for steady simulations?

[Siba11]

Hi. You can use an array (or even pointers) to store the values at each iteration using the in-built macro N_ITER.

[lbj007]

Originally Posted by Siba11

Hi. You can use an array (or even pointers) to store the values at each iteration using the in-built macro N_ITER.

Hi, can you give me a simple example for how to use it? I'm not sure what do you mean. N_ITER is just a number, how can it be used to monitor the current step and the previous step in real-time?

[Siba11]

Originally Posted by lbj007

Hi, can you give me a simple example for how to use it? I'm not sure what do you mean. N_ITER is just a number, how can it be used to monitor the current step and the previous step in real-time?

Hi. you can do something like this :

int A[100];

if (N_ITER == 1)
A[N_ITER] = C_T(c,t); // assuming you are working with temperature.

if (N_ITER > 1)
{
A[N_ITER] = C_T(c,t);
diff = A[N_ITER] - A[N_ITER - 1];
 
  if ('diff' satisfies the tolerance)
    RP_Set_Integer ("rp-variable", 1);
}

When the rp-variable will change, it will be detected by the console. You can use a DEFINE_ADJUST UDF for this task.

[lbj007]

Originally Posted by Siba11

Hi. You can use an array (or even pointers) to store the values at each iteration using the in-built macro N_ITER.

Originally Posted by Siba11

Hi. you can do something like this :

int A[100];

if (N_ITER == 1)
A[N_ITER] = C_T(c,t); // assuming you are working with temperature.

if (N_ITER > 1)
{
A[N_ITER] = C_T(c,t);
diff = A[N_ITER] - A[N_ITER - 1];
 
  if ('diff' satisfies the tolerance)
    RP_Set_Integer ("rp-variable", 1);
}

When the rp-variable will change, it will be detected by the console. You can use a DEFINE_ADJUST UDF for this task.

Hi, a new question, I didn't see the reason for using the 'rp' variable here. Following your steps, we could define a global variable in the udf to achieve the same functionality.