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UDF to measure Mass Flow Rate

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Old   August 14, 2013, 11:42
Default UDF for keep water height constant at inlet for a VOF model
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Tanjina Afrin
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Hi, does anybody have UDF for keeping the water height constant at inlet for VOF ( 2 phase) model? Or can anyone can give an idea from where I can learn how to write UDF ?


I badly need of it. It will be very great if anyone can help me . Thanks a ton in advance.
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Old   February 15, 2014, 02:18
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Quote:
Originally Posted by Tanjina View Post
Hi, does anybody have UDF for keeping the water height constant at inlet for VOF ( 2 phase) model? Or can anyone can give an idea from where I can learn how to write UDF ?


I badly need of it. It will be very great if anyone can help me . Thanks a ton in advance.
If you show a specific picture, Maybe I can help you
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Old   September 26, 2017, 12:50
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Quote:
Originally Posted by a.lynchy View Post
Hi Kartn
The problem with the previous code that I posted was in getting the value for the variable “flow” from the DEFINE_EXECUTE_AT_END section and using it in the DEFINE_PROFILE. The way it was set as a global variable was okay but what was happening was it was been set to zero after the DEFINE_EXECTUE_AT_END loop so the DEFINE_PROFILE function was seeing a value of flow=0. Sorry if what I am saying is hard to follow, but I have attached the working code below and maybe from comparing the two you will be able to understand.
The only real different is in introducing the flow_tot variable as the global variable instead of using the flow variable.

#include"udf.h"
real flow_tot;
real p ;

DEFINE_EXECUTE_AT_END(funny)
{
Domain *d;

real flow;
cell_t c;
Thread *t;
face_t f;
d = Get_Domain(1);
t= Lookup_Thread(d, 12);

begin_f_loop(f,t)
{
flow+=F_FLUX(f,t);
}
end_f_loop(f,t)
p = C_P(c,t);
printf(
"static pressure = %g\n", p);
printf(
"MASS Flow Rate: %g\n",flow);
flow_tot =flow;
flow=0.;
}

DEFINE_PROFILE(pressure_out,t,i)
{
real set_point = 1;
real pressure;
face_t f;




printf(
"MASS Flow Rate: %g\n",flow_tot);
if (flow_tot < set_point)

pressure = p - 1;

elseif (flow_tot > set_point)

pressure = p + 1;

else
pressure = p;



begin_f_loop(f,t)
{
F_PROFILE(f,t,i) = pressure;
}
end_f_loop(f,t)
printf(
"Adjusted pressure = %g\n", pressure);
}

Hope this helps!
I tried to use this UDF initially and modify according to my case. Prior to any modification, I got the following error after the first iteration on "DEFINE_EXECUTE_AT_END".

Code:
==============================================================================

Node 0: Process 13808: Received signal SIGSEGV.

==============================================================================

==============================================================================

Node 1: Process 17288: Received signal SIGSEGV.

==============================================================================

==============================================================================

Node 3: Process 17844: Received signal SIGSEGV.

==============================================================================

==============================================================================

Node 999999: Process 16332: Received signal SIGSEGV.

==============================================================================

==============================================================================

Node 5: Process 12176: Received signal SIGSEGV.

==============================================================================

==============================================================================

Node 6: Process 17444: Received signal SIGSEGV.

==============================================================================
MPI Application rank 0 exited before MPI_Finalize() with status 2
 The fl process could not be started.
How can I fix this error?!!
Thanks.
PS: I interpret the UDF.
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Old   January 6, 2018, 13:50
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Hello everyone i am using the similar UDF to alter the inlet boundary condition of my simulation. Basically i am also calculating the mass flow rate at the outlet of my valve and using this flow rate to calculate the pressure drop in feed line. Can someone help to find out what is problem wit this UDF..


Following UDF i am using to modify the inlet pressure......
#include "udf.h"
FILE *fp;
real flow_tot;

DEFINE_EXECUTE_AT_END(pressure)
{
Domain *d;
float flow;
cell_t c;
Thread *t;
face_t f;
d = Get_Domain(1);
t= Lookup_Thread(d, 12);

begin_f_loop(f,t)
{
flow+=F_FLUX(f,t);
}
end_f_loop(f,t)

flow_tot =flow;
flow=0.;
}
DEFINE_PROFILE(inlet_pressure, thread, position)
{
face_t f;
float P_i=903063;/* 199625Pa steady state pressure drop in feed circuit*/
real t= CURRENT_TIME;/* steady state inlet pressure 703438Pa*/
/*float flow_t=0;*/
float Del_P=0;
fp = fopen("output.txt","a");
fprintf(fp,"MASS Flow Rate: %f kg/s \n",flow_tot);
fclose(fp);
Del_P=(0.79215*flow_tot*flow_tot);
begin_f_loop(f, thread)
{

F_PROFILE(f, thread, position)=P_i-Del_P;
}
end_f_loop(f, thread)
}
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Old   January 6, 2018, 13:53
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can someone tells why i am getting Pi=9 bar at t=0 when mass flow is max. this should be 7.0 bar (Pi-Delta_p) but at t=0 i am getting initial pressure as 9.0 bar........where is the problem????can anyone tell....

Delta_P in steady state is given by Del_P=(0.79215*flow_tot*flow_tot); hence in steady state flow rate is maximum hence Pi should be minimum but surface monitor will start reading from 9.0 bar
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Old   January 8, 2018, 12:13
Default UDF for mass flow rate at a pressure outlet
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Can someone find where is the mistake in following udf. It is always printing zero flow rate at all time steps while mass flow rate from surface monitor is coming total different....???


#include "udf.h"
FILE *fp;
real flow_tot=0.;
DEFINE_EXECUTE_AT_END(fun)
{
Domain *d;
real flow=0.;
cell_t c;
Thread *t;
face_t f;
d = Get_Domain(1);
t= Lookup_Thread(d, 12);

begin_f_loop(f,t)
{
flow+=F_FLUX(f,t);
}
end_f_loop(f,t)
printf("MASS Flow Rate is: %g kg/s \n",flow_tot);
flow_tot =flow;
flow=0.;
}
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Old   January 11, 2018, 09:14
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Hi Wasim_03,

Your latest question is easy: you are printing the value of "flow_tot" *before* you copy the value of "flow" into it -- it should be after.

I haven't looked in detail at your previous questions. I do know that commands involving writing to file (fopen(fp...) fprintf(fp...)) are dangerous in parallel. Much better to print to the Fluent window using Message(...), which has a similar syntax to printf(...).

You are presumably trying to print out the value of "flow_tot" because you are not sure whether the value calculated by one UDF will survive when the next UDF is called. This is a valid concern -- you probably want to declare "static real flow_tot=0.;".

I worry whether your intended linkage between flowrate and pressure will be stable -- you might want to apply some home-made under-relaxation. (If you do this, you should be aware that DEFINE_PROFILE is sometimes called many times per iteration, for reasons that are not clear to me.)

The other stability issue is that DEFINE_PROFILE will be called before DEFINE_EXECUTE_AT_END, so the first iteration might go mad.
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Old   January 16, 2018, 08:58
Default Udf
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Hi OBSCUREED....Thanks for your reply...

i am able to compiled and run this UDF, your concerned regarding initial time step i have well taken care when Define_profile is called and Execute_at_end is still on hold and to be called subsequently, at this time i have implemented if else logic to define the initial value flow rate to avoid the function go made and both function are working perfectly.......


Thanks and regards
Wasim
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Old   August 9, 2018, 10:04
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Quote:
Originally Posted by Kanarya View Post
Hi ALL,

I want to calculate solid phase mass flow rate at outlet and I wrote following code to it but it only read primary phase even though I pointed secondary phase. is there any one to help me why?
thanks a lot!!
#include "udf.h"
DEFINE_EXECUTE_AT_END(measure_mass_flow)
{
real mass_flow;
real abs_v;
Domain *d=Get_Domain(2);
face_t f;
Thread *mixture_thread = Lookup_Thread(d,2);
Thread **pt = THREAD_SUB_THREADS(mixture_thread);
Thread *tp = pt[0];
Thread *ts = pt[1];

mass_flow=0.;
mp_thread_loop_f(tp,d,pt)
{
if( THREAD_ID(tp) == 4 )

{
begin_f_loop(f,tp)
{

mass_flow+=F_FLUX(f,tp);

}
end_f_loop(f,tp)
}



}
Message("mass_flow:%g/n",mass_flow);
}
thanks again..
Hi, Kanarya,
i'm trying to build a circulating fluidized bed, and encourtered a problems like yours. can you plz give some suggestions?
thanks a million in advance
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Old   October 4, 2018, 13:56
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Quote:
Originally Posted by a.lynchy View Post
Hi everyone,
I am trying to measure the mass flow rate through a pressure outlet using a UDF. I realise there are easier way to get the mass flow rate at the outlet, rather than using the UDF but this is to be incorperated into a larger UDF later (hopefully ). I have attached the code below that i have writen. The UDF interpetes okay and runs, however the problem is this code is giving me the mass flow rate throughout the whole volume and not at the pressure outlet ID 12 as required. I believe the problem is to do with the line: Lookup_Thread(d, 12);

#include "udf.h"
DEFINE_EXECUTE_AT_END(measure_mass_flow)
{
Domain *d;
real flow=0.;
face_t f;
Thread *t;
t= Lookup_Thread(d, 12);
d = Get_Domain(1);

thread_loop_f(t,d)
{
begin_f_loop(f,t)
{
flow+=F_FLUX(f,t);
}
end_f_loop(f,t)
}
printf("MASS Flow Rate: %g\n",flow);
flow=0.;
}

Please can anyone point me in the right direction?
Hi
Is the mass flow rate that you tried to measure is an output of the simulation?
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Old   October 4, 2018, 14:01
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Quote:
Originally Posted by a.lynchy View Post
Hi everyone,
I am trying to measure the mass flow rate through a pressure outlet using a UDF. I realise there are easier way to get the mass flow rate at the outlet, rather than using the UDF but this is to be incorperated into a larger UDF later (hopefully ). I have attached the code below that i have writen. The UDF interpetes okay and runs, however the problem is this code is giving me the mass flow rate throughout the whole volume and not at the pressure outlet ID 12 as required. I believe the problem is to do with the line: Lookup_Thread(d, 12);

#include "udf.h"
DEFINE_EXECUTE_AT_END(measure_mass_flow)
{
Domain *d;
real flow=0.;
face_t f;
Thread *t;
t= Lookup_Thread(d, 12);
d = Get_Domain(1);

thread_loop_f(t,d)
{
begin_f_loop(f,t)
{
flow+=F_FLUX(f,t);
}
end_f_loop(f,t)
}
printf("MASS Flow Rate: %g\n",flow);
flow=0.;
}

Please can anyone point me in the right direction?
Hi a.lynchy
Is the mass flow rate that you tried to measure is an output of the simulation?
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Old   October 4, 2018, 14:10
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Hi Oula,

You seem to be replying to the original post -- this is confusing, because that post was answered completely by coglione in 2010. If you have your own question, it is probably better to start a new thread. (The content of a.lynchy's question was good, by the way, and worth emulating -- it included descriptions of the goal, the current progress, the problem and a possible route towards a solution.)

Good luck!
Ed
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