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Is it possible? Changing BC from wall to pressure-outlet with an UDF trigger

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Old   June 2, 2015, 15:06
Question Is it possible? Changing BC from wall to pressure-outlet with an UDF trigger
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Juan Man
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Hi everyone, I don't know if the title is clear enough.

This is what I want to do:

I have a tank (circle, BC=wall) subject to a wave. I want to monitor the pressure on the wall, and if it is greater than a limit value I want to simulate the breaking of the tank by changing its boundary-condition to pressure-outlet.
Is this possible with UDFs or Scheme?

To monitor the pressure I'd use something like this:
Code:
DEFINE_ADJUST(test_de_explosion,domain)
{    
    int ID = 7;
    int exploded = 0;

    Thread *thread = Lookup_Thread(domain,ID);

    face_t f;

    begin_f_loop(f, thread)
    {
        if ( F_P(f, thread) > 700000.0)
        {
            exploded = 1;
        }
    }
    end_f_loop(f, thread)

    if (exploded == 1)
    {
        printf("Explosion\n");
    }
    else
    {
        printf("Nothing\n");
    }
}
I hope you can help me

Juan
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Old   June 2, 2015, 18:12
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Yes, it's possible. First, try converting your UDF to a Scheme file and run this script at each time step. Use the corresponding TUI commands for changing boundary conditions and implement them with ti-menu-load-string. Alternatively, if you can't code the face loops (or similar) in Scheme (there's a number of limitations I've come across with Scheme), use a flag with a rp-variable or text file to inform the Scheme script when to convert the boundary condition.
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Old   June 3, 2015, 15:54
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Juan Man
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Hi `e`, thanks for your answer.

I understand the part about the TUI commands for changing the BC.
What I don't get is how i could convert the UDF to a Scheme file, I couldn't find any information about that in the manual. How would i access simulation results with Scheme? Maybe with a monitor?

If not possible, I'm going to try with an rp-variable.
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Old   June 3, 2015, 18:59
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I'm not sure if it'd be possible to convert your UDF to a Scheme file directly (I've had similar issues and couldn't find a solution); however, this approach would be the most elegant which is why I suggested to try it first. The alternative approach with an rp-variable would be the second best method (I believe rp-variables are accessible by both Scheme and UDFs).

What I've done (because it required more information than a single flag) was write a Scheme file from inside a UDF and run this script at every time step (Calculation Activity); defaults to empty, but otherwise has a number of commands.

This question of coupling UDFs with Scheme files have been appearing frequently on these forums so I might post a tutorial in the future.
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Old   June 8, 2015, 13:00
Default Did it!
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Juan Man
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Thanks `e`, I did it!

This is how I managed, in case someone encounters a similiar issue:


This is the UDF that checks the pressure on the wall that I wanted to monitor:
Code:
#include "udf.h"

DEFINE_ON_DEMAND(pres_check)
{
int ID;
face_t f;
real maxPressure;
Thread *thread;
Domain *d;

ID = 6;
maxPressure = 1.0;

d = Get_Domain(1);

thread = Lookup_Thread(d, ID);

begin_f_loop(f, thread)
{
    if (F_P(f, thread) > maxPressure) maxPressure = F_P(f, thread);

}
end_f_loop(f, thread)

printf("Max Pressure = %f \n",maxPressure);

RP_Set_Real("pressure_on_wall",maxPressure);

}
I interpreted or compiled it and then I run this Scheme script:

Code:
(rp-var-define 'pressure_on_wall 0.0 'real #f)
(rp-var-define 'explosion_time 0.0 'float #f)
(define exploded #f)
(define limit 100000)
(define ts 50)


(do ((i 1 (+ 1 i) ))((> i ts))


	(ti-menu-load-string "solve dti 1 10")

	(cond((eq? exploded #f)
		(%udf-on-demand 'pres_check);### CHECK UDF NAME!!! ###

		(display "Limit Pressure Not Yet Reached")
	
		(cond((> (%rpgetvar 'pressure_on_wall) limit)
			(display "Limit Pressure Reached")
			(set! exploded #t)
			(rpsetvar 'explosion_time (%rpgetvar 'flow-time))
			
			(ti-menu-load-string "def bc mz zt 6 pi");### CHECK ZONE ID ###
			(ti-menu-load-string "def bc pi 6 , , 300000 , , , , , , , , ,");### CHECK ZONE ID ###
		))
	))

)
It works great, though it's a bit slow when evaluating the UDF
I hope this thread is useful to everyone.
Regards,
Juan
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Old   June 25, 2018, 06:32
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Hello World,

This is an old post, but it might be useful to see what changes are needed in that UDF code to make it work in parallel:


Code:
#include "udf.h"
 
#define FACE_ZONE_ID 6

DEFINE_ON_DEMAND(pres_check)
{
  int ID;
  face_t f;
  real maxPressure;
  Thread *thread;
  Domain *d;

  maxPressure = -9.99e30;

  d = Get_Domain(1);

  thread = Lookup_Thread(d, FACE_ZONE_ID);

  begin_f_loop(f, thread)
  {
    if (F_P(f, thread) > maxPressure)
      maxPressure = F_P(f, thread);
  }
  end_f_loop(f, thread)

  /* In parallel, get the combined max pressure across all nodes: */
#if RP_NODE
  maxPressure = PRF_GRHIGH1(maxPressure);
#endif

  Message0("\nMax Pressure = %f \n",maxPressure);

  /* In parallel, send the combined max pressure to the host: */
  node_to_host_real_1(maxPressure);

  /* In parallel, only the host sets RP variables: */
#if !RP_NODE
  if(RP_Variable_Exists_P("pressure_on_wall")) {
    RP_Set_Real("pressure_on_wall",maxPressure);
  }else{
    Message("\nThe UDF would like to set the RP-var 'pressure_on_wall\n");
    Message("but this RP-var does not currently exist.\n");
  }
#endif

}
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Old   June 25, 2018, 07:10
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Oh, and if your only reason for running this is to get the maximum pressure of a face zone called "wall_example" in a Scheme command, then you could do that directly in Scheme like this:
Code:
(pick-a-real "/rep/surf/facet-max (wall_example) pressure n")
For example:
Code:
(define limit 100000)
(if (not (rp-var-object 'explosion_time))
  (rp-var-define 'explosion_time -999.9 'double #f)
  ())

(if (< (%rpgetvar 'explosion_time) 0.0)
  (if (> (pick-a-real "/rep/surf/facet-max (wall_example) pressure n") limit)
    (begin
      (display "Limit Pressure Reached.  ")
      (rpsetvar 'explosion_time (%rpgetvar 'flow-time))

      (ti-menu-load-string "/def/bc/mod-zones/zone-type wall_example pressure-inlet")
      (ti-menu-load-string "/def/bc/pressure-inlet wall_example , , 300000 , , , 300 , , , , , , , , , , , , , ,")
      )
    (display "Limit Pressure Not Yet Reached.  ")))
Some things to note:
++ You can put face zone numbers into the /report/surface command... BUT, whatever numbers are used there, they are not the same numbers as zone ID numbers. (Yeah, I was surprised, too.) So I have avoided the zone ID altogether and used the name only.
++ My command for changing the pressure-inlet boundary condition is different from the previous one, because I have temperature and species in my test case. The conclusion is to remember that this command is strongly case-dependent.
++ You could put that longer set of Scheme commands into a file called check_pres.scm, and then run it with a TUI command /file/read-macro check_pres.scm. I cunningly made sure that the RP-variable is not re-defined every time.

Enjoy!
Ed
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Old   October 1, 2018, 13:46
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Hi,

Thank you for providing good insights. I have one question - should the Scheme script be put in a so-called journal file?

Thank you once again.
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Old   October 4, 2018, 17:12
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Hi wc34071209,


No, Scheme commands belong in a .scm file. You can run a .scm file from Fluent's top menu File...Read Macro -- or see the TUI command that I mention in the final point of that previous post.


Good luck!
Ed

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Old   October 5, 2018, 04:16
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Hi obscureed,

Thank you so much for your reply.

I run Fluent on a cluster and give Fluent command through a journal file. I think I should use TUI command you mentioned to hook the Scheme commands.

But I still have one question. Is the Scheme command executed every iteration/time step or is it run only once?
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Old   October 5, 2018, 04:40
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Quote:
Originally Posted by wc34071209 View Post
Hi obscureed,

Thank you so much for your reply.

I run Fluent on a cluster and give Fluent command through a journal file. I think I should use TUI command you mentioned to hook the Scheme commands.

But I still have one question. Is the Scheme command executed every iteration/time step or is it run only once?
it runs once

best regards
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Old   October 5, 2018, 05:03
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Hi Alexander,

Thank you very much for your kind reply. Do you know how to make it to run every iteration/time-step?

Best,
Yuehan

Quote:
Originally Posted by AlexanderZ View Post
it runs once

best regards
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Old   October 5, 2018, 12:40
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You can put a TUI command in Calculation Activities...Execute Commands, to run at a specified frequency. I would recommend using a TUI command to access the Scheme file directly (for example "/file/read-macro check_pres.scm"), rather than going via a journal file. A journal file to read a Scheme file seems like a pointless extra level of bureaucracy. (Also, there is a restriction that you cannot read a journal file while writing a journal file.)
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