[Jups]

i have a function that need to be plot..
the function is a new variable that i define by myself..
the function is "adsorption capacity"
i am doing ANG case (adsorbed Narutal Gas)
here my UDF

DEFINE_INIT(q_init,d)
{
cell_t c;
Thread *t;

thread_loop_c(t,d)
{
begin_c_loop_all(c,t)
{
C_T(c,t)=300;
C_P(c,t)=100000;
q = 0;
}
end_c_loop_all(c,t)
}
}


turq = k*(qe-q);
q = q+turq*time;

i need to plot the "q"

kindly help,
jups

[Sun]

you can probably use EXECUTE_ON_DEMAND or EXECUTE_AT_END to write the results of "q" in a text file and then use the output to plot "q". e.g.

FILE *fp;
fp=fopen("q_output.txt","w");

cheers!

[Jups]

Originally Posted by Sun

you can probably use EXECUTE_ON_DEMAND or EXECUTE_AT_END to write the results of "q" in a text file and then use the output to plot "q". e.g.

FILE *fp;
fp=fopen("q_output.txt","w");

cheers!

could you help me more?
i still dont get it
this is my full UDF

#include "udf.h"
#define P 3000000
#define T 300
#define e 0.65
#define Rc 500
#define k 0.00013996
#define qe 0.0698337
double q, time, turq;

DEFINE_INIT(q_init,d)
{
cell_t c;
Thread *t;

thread_loop_c(t,d)
  {
    begin_c_loop_all(c,t)
     {
       C_T(c,t)=300;
       C_P(c,t)=100000;
       q = 0;
     }
    end_c_loop_all(c,t)
   }
}



DEFINE_SOURCE(mass_source, cell, thread)
{
real source;
time = CURRENT_TIME;

turq = k*(qe-q);
q = q+turq*time;

source = -((1-e)/e)*turq*Rc;
return source;

}



DEFINE_SOURCE(y_velocity, cell, thread)
{
real source;
time = CURRENT_TIME;

turq = k*(qe-q);
q = q+turq*time;

source = -turq*Rc*C_V(cell,thread);
return source;
}



DEFINE_SOURCE(radial_velocity, cell, thread)
{
real source;
time = CURRENT_TIME;

turq = k*(qe-q);
q = q+turq*time;

source = -turq*Rc*C_V(cell,thread);
return source;
}



DEFINE_SOURCE(energy_source, cell, thread)
{
real ha, source;
time = CURRENT_TIME;

turq = k*(qe-q);
q = q+turq*time;

ha = 15568000;
source = -turq*Rc*H;
return source;
}

or can you edit the function so that the q can be plot?

thankyou for reply

[Sun]

I haven't been using fluent for a while and bit rusty with its syntax...but actually there is a more convenient way of doing it ... you can store your results inside a User Defined Memory (UDM) and if I remember correctly you can have up to 50 UDMs...And the cool thing is you can plot the UDMs vs time or any other independent variables of interest...For example I was looking at my old UDFs where I had stored the bubble Reynolds number inside UDM0...here is the code snippet:

#include "udf.h"

DEFINE_ON_DEMAND(someVariables)
	{
		Domain *mixd;
		
		/*INPUTS*/
		/*A bunch of computations here*/
		/* getting the domains and etc*/
		Thread *t;
		cell_t c;
		Thread *mixt;
		Thread *thread_g;
		Thread *thread_f;
	
		/** Mixture Domain **/	
		mixd = Get_Domain(1);	
		
		thread_loop_c(mixt,mixd)	
			{
				/*Gas and Pulp threads*/
				thread_g = THREAD_SUB_THREAD(mixt,1);
				thread_f = THREAD_SUB_THREAD(mixt,0);
				

/* This is where I am computing the slip velocity */
				begin_c_loop(c,mixt)
				{
					/*Slip velocity*/
					x_vel_f = C_U(c,thread_f);
   					y_vel_f = C_V(c,thread_f);
					z_vel_f = C_W(c,thread_f);
   					x_vel_g = C_U(c,thread_g);
   					y_vel_g = C_V(c,thread_g);
   					z_vel_g = C_W(c,thread_g);
   
   					slip_x = -x_vel_f + x_vel_g;
   					slip_y = -y_vel_f + y_vel_g;
   					slip_z = -z_vel_f + z_vel_g;
   
   					slip_vel = sqrt(slip_x*slip_x + slip_y*slip_y + slip_z*slip_z);
					/*Bubble Reynolds number*/
					re_b = (d_b*slip_vel)/kin_vis;
					
/* This is where I am storing it inside UDMI0 */
                                         
C_UDMI(c,mixt,0) = re_b;
					
/*I think you can do the same with respect to your problem*/
					
					
				}
				end_c_loop(c,mixt)
			}
		
	}

hope it helps.
Cheers!

[Hershey]

It seems to me that your value for q will always stay at zero from your initialization step. If you want to use it across each function then use Sun's suggestion of C_UDMI(cell,thread,0) for q. Then you can use it to plot in fluent. As your code stands right now, I do not see how the value of q will get passed to each function at each time step.

[Jups]

sun, may i have your email?
so that i can consult with you more intensive..
thankyou before sun


Hersey, i think the q value only at start is zero because i put zero value only for initialize,, in my mind, initialize is the initial condition or the beginning condition.. am i wrong?
i have so much complicated thing in this fluent cause i only learn it 3 months ago,, my lecturer ask me to do this thing for my graduate.. i hope u could help me more Hersey.. I really really need someone help right now..



in this problem i need to define the q value for beginning is 0
then the next q value is the function below :

q = q + turq*time

i have turq value, i have time...
so the next q is
q = 0 (the intial q that zero) + turq*time
then we have new q value, let's we say it 10..
then the next q is
q = 10 + turq*time
like looping..
i confused to make this... after that, i need to plot the q function...



thanks before SUN and HERSHEY
i really really thank for you two )

[Mohawk]

In fluent .go to define and choose custom field functions

[Sun]

let's keep the conversation in the forum, so others can join, benefit and contribute...but in case if the problem needs more talks on the details I can send you my email add. BTW, have you tried the UDMI ?

[Mohawk]

I haven't tried udmi

[Jups]

Originally Posted by Sun

let's keep the conversation in the forum, so others can join, benefit and contribute...but in case if the problem needs more talks on the details I can send you my email add. BTW, have you tried the UDMI ?

okay.. benefit and contribute..
i tell you later if the case gets more and more complicated..
im still thinking, where should i link the UDMI?
Should i make a new UDF only for q then i link it to UDMI?

[Jups]

Originally Posted by Mohawk

In fluent .go to define and choose custom field functions

could you tell me more specific about custom field funtions mohawk?

thankyou before mohawk

[Sun]

Originally Posted by Jups

okay.. benefit and contribute..
im still thinking, where should i link the UDMI?
Should i make a new UDF only for q then i link it to UDMI?

you don't need to create a separate UDF for the UDMI. Just store the "q" ...like the example I shared

/* This is where I am storing it inside UDMI0 */
                                         
C_UDMI(c,mixt,0) = re_b;
					
/*I think you can do the same with respect to your problem*/

Have a look at this page to figure out how to link/define the UDMI:
http://aerojet.engr.ucdavis.edu/flue...udf/node96.htm

Cheers!

[Jups]

Originally Posted by Sun

you don't need to create a separate UDF for the UDMI. Just store the "q" ...like the example I shared

/* This is where I am storing it inside UDMI0 */
                                         
C_UDMI(c,mixt,0) = re_b;
                    
/*I think you can do the same with respect to your problem*/

Have a look at this page to figure out how to link/define the UDMI:
http://aerojet.engr.ucdavis.edu/flue...udf/node96.htm

Cheers!

i have try UDMI, it's work
thankyou very much sun..

but i have another problem right now,, i think the problem is q..
when the plot of q shown,, the q value from 0 suddenly increase to 0,069 (maksimum value for q in my case)..
q value should increase slowly, example..
0 then 0,00005 then 0,00006 then ..... then 0,069 (maksimum)..
do you have any idea?

[Sun]

Since the "q" mostly depends on time, reduce your time step and I think you should be able to see the gradual increase of this factor.
Cheers!

[Jups]

Originally Posted by Sun

Since the "q" mostly depends on time, reduce your time step and I think you should be able to see the gradual increase of this factor.
Cheers!

the time step i use is 1 second..
should i reduce it again sun? hmm,, make it about 0.5 second?
max iterations per time step is 1.

[Hershey]

Your problem is that each source udf is being called at each iteration. So every iteration, the value of q is changing. Then this factor is changing for each source term. I would recommend using a DEFINE_ADJUST udf to calculate the q value at the current time step, save it to the C_UDMI and then call the C_UDMI in each of the source udf. There is a way to only calculate q for the first iteration of the timestep, but I am not at my computer to look up the reference. I will get back to you.

[Sun]

Originally Posted by Jups

the time step i use is 1 second..
should i reduce it again sun? hmm,, make it about 0.5 second?
max iterations per time step is 1.

I would probably change the time step to something around 1E-4 or 1E-5.

[Jups]

Originally Posted by Hershey

Your problem is that each source udf is being called at each iteration. So every iteration, the value of q is changing. Then this factor is changing for each source term. I would recommend using a DEFINE_ADJUST udf to calculate the q value at the current time step, save it to the C_UDMI and then call the C_UDMI in each of the source udf. There is a way to only calculate q for the first iteration of the timestep, but I am not at my computer to look up the reference. I will get back to you.

Hersey, you mean, i have to calculate q in DEFINE_ADJUST then save it to C_UDMI.. and then in DEFINE_SOURCE i call the C_UDMI for the q?
so i separate q and source? like that?
okay Hersey, i wait patiently
thankyou Hersey...

[Jups]

Originally Posted by Sun

I would probably change the time step to something around 1E-4 or 1E-5.

later i will try to change the time step.. i will tell you the result soon Sun..
thankyou very much Sun

[Hershey]

Originally Posted by Jups

Hersey, you mean, i have to calculate q in DEFINE_ADJUST then save it to C_UDMI.. and then in DEFINE_SOURCE i call the C_UDMI for the q?
so i separate q and source? like that?
okay Hersey, i wait patiently
thankyou Hersey...

Yes. Since your equation for q is the same in each source, it would be better to define it in DEFINE_ADJUST by saving the value as C_UDMI(c,t,0) = q. Then in the DEFINE_SOURCE you should just reference C_UDMI(c,t,0) instead of q.

In the DEFINE_ADJUST, there are a couple things you must do:

1. You must use begin_cell_loop(c,t) to loop through the cells for C_UDMI. Try looking at Google to fine this and an example.

2. Finally, since DEFINE_ADJUST is called at the beginning of every iteration (not time step), you will want to only calculate q for the first iteration. Look at the following link on how to do that:

http://www.cfd-online.com/Forums/flu...luent-5-a.html