# How do i create time dependent flows on UDF?

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 December 9, 2010, 16:22 How do i create time dependent flows on UDF? #1 New Member   Nuril Join Date: Dec 2010 Posts: 17 Rep Power: 9 How do I create this conditon using a UDF? I want the velocity at the pipe inlet to be 10m/s from t=0 to 5 then i want the v=20m/s from t=5 to 6, then i want the velocity again to be 10m/s from t =6 to 11 How do i set the time ticking ticking on the UDF? and what is the varaible for time? Thanks

 December 9, 2010, 20:56 #2 Senior Member   Real Name :) Join Date: Jan 2010 Location: United States Posts: 192 Rep Power: 9 nha1g08, Try something like this. Inevitably I'm missing a semicolon in the following, but it should be relatively simple to fix. Interpret (or better, compile) this UDF, then hook it to your face velocity boundary condition. This loops over all cell faces at the inlet boundary and sets them to the given velocity depending on the simulation time. Make sure you run transient! Regards, ComputerGuy DEFINE_PROFILE(velocity_magnitude, t, i) { real velocity; real the_current_time; face_t f; the_current_time = CURRENT_TIME; if ((the_current_time>=0) && (the_current_time<5)) { velocity=10; } if ((the_current_time>=5) && (the_current_time<6)) { velocity=20; } if ((the_current_time>=6)) { velocity=10; } begin_f_loop(f,t) { F_PROFILE(f,t,i) = velocity; } end_f_loop(f,t) }

 December 12, 2010, 04:20 #3 New Member   zhuliang Join Date: Nov 2010 Location: China Posts: 13 Rep Power: 9 I want the pressure of the pressureinlet to be 0 form 0 to 5 second and the pressure of 8Mpa from 5 to 6 second is it similar? thank you in advance

 December 12, 2010, 09:24 #4 Senior Member   Real Name :) Join Date: Jan 2010 Location: United States Posts: 192 Rep Power: 9 bright181, Yes. You have to change the udf slightly and hook it to a different place on the inlet boundary conditions panel, but it's effectively the same. I have changed variable names for clarity. ComputerGuy Code: ```#include "udf.h" DEFINE_PROFILE(pressure_magnitude, t, i) { real pressure_mag; real the_current_time; face_t f; the_current_time = CURRENT_TIME; if ((the_current_time>=0.0) && (the_current_time<5.)) { pressure_mag=0.0; } if ((the_current_time>=5.0) && (the_current_time<6.0)) { pressure_mag=8.0e6; } begin_f_loop(f,t) { F_PROFILE(f,t,i) = pressure_mag; } end_f_loop(f,t) }``` Last edited by ComputerGuy; December 12, 2010 at 11:27. Reason: Changed pressure from 10 --> 8 MPa

 January 5, 2011, 00:42 #5 New Member   ekkapong Join Date: Oct 2010 Posts: 18 Rep Power: 9 Dear computerGuy how to hook your codes to Fluent and how to set time in fluent please give me your suggestion thank

 January 5, 2011, 00:48 #6 New Member   ekkapong Join Date: Oct 2010 Posts: 18 Rep Power: 9 Could I have one question? I'd like to know that how to define current time at fluent ?

 June 17, 2013, 03:03 #7 New Member   Sakshi Sharma Join Date: Jun 2013 Posts: 1 Rep Power: 0 I want to inject a fluid at every 6 mins. I prepared a code, but ther seems to be an error in line 10 saying:" line 10: invalid type for integral binary expression: double % int." Can anyone give me a solution to this? Thankyou. Here's the code: #include "udf.h" DEFINE_PROFILE(insulin_inlet,thread,position ) { face_t f; begin_f_loop(f,thread) { real t = RP_Get_Real("flow-time"); if (t%360==0) F_PROFILE(f,thread,position) = 0.1; else F_PROFILE(f,thread,position) = 0; } end_f_loop(f,thread) }

 July 9, 2017, 11:10 sakshi1632 #9 New Member   saman Join Date: Jul 2017 Posts: 1 Rep Power: 0 I want to inject a fluid at every 6 mins. I prepared a code, but ther seems to be an error in line 10 saying:" line 10: invalid type for integral binary expression: double % int." Can anyone give me a solution to this? Thankyou. Here's the code: #include "udf.h" DEFINE_PROFILE(insulin_inlet,thread,position ) { face_t f; begin_f_loop(f,thread) { real t = RP_Get_Real("flow-time"); if (t%360==0) F_PROFILE(f,thread,position) = 0.1; else F_PROFILE(f,thread,position) = 0; } end_f_loop(f,thread) } hi, did you know what was the problem of your code?

 September 21, 2017, 07:57 #10 New Member   madan Join Date: Sep 2017 Posts: 5 Rep Power: 2 Hi everybody, I am doing a transient simulation of conjugated heat transfer problem. In that I have a solid that plays a role of heat generation(W/m3) varying with time (q=q(t)). Since i am weak in codings, I need a help to write a udf for heat source varying with time. value is q=6.75e11 Thank you.

 September 22, 2017, 08:57 #11 Senior Member   Join Date: Nov 2013 Posts: 1,162 Rep Power: 15 If q=6.75e11, it is not varying in time but constant... So I think you should be more clear in what you want.

September 22, 2017, 14:37
#12
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Join Date: Sep 2017
Posts: 5
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Quote:
 Originally Posted by pakk If q=6.75e11, it is not varying in time but constant... So I think you should be more clear in what you want.
Hi,

I found out the example source. When I tried to run transient simulation with this udf. It doesnt looklike its working. The heat generation source is increasing for every 100 sec. But when i see the avearge temperature of heat source its was almost the same for all timesteps. Hereby I have attached the Udf. Please tell me what are the mistakes I have did.
Thank You.

#define Q1 2e10
#define Q2 2.97e10
#define Q3 3.80e10

DEFINE_SOURCE(qgen_source,c,t,dS,eqn)
{
real source;
real time = CURRENT_TIME;

if (time <= 100) /* time 0-100 q = Q1 */
{
/* source term */
source = Q1;

/* derivative of source term. */
dS[eqn] = 0.;
}
if (time > 100 && time < 200) /* time 100-200 q = Q2 */
{
source = Q2;

dS[eqn] = 0.;
}
if (time >= 200 && time < 300) /* time 200-300 q = Q3 */
{
source = Q3;

dS[eqn] = 0.;
}
if (time >= 300 && time <400) /* time 300 -400 q = 0 */
{
source = dS[eqn] = 0.;
}

return source;
}

 September 25, 2017, 10:09 #13 Senior Member   Join Date: Nov 2013 Posts: 1,162 Rep Power: 15 What makes you think that you made a mistake?

September 25, 2017, 16:58
Regarding entropy generation due to heat transfer and fluid friction.
#14
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Join Date: Sep 2017
Posts: 5
Rep Power: 2
Quote:
 Originally Posted by pakk What makes you think that you made a mistake?
Hi pakk,

I figured out the mistake.that was is in timestep size when iam iterating it..

And I have a another doubt in the entropy generation for 3d problem. I am trying to calculate entropy generation for heat transfer and fluid friction using custom field functions.
from the literature i have found that the entropy for heat transfer can be found out from following formula but for fluid friction i dont know how to implement that formula..herby i have attached the photo.

Thanking you.
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