Importing the calculated torque into my UDF
 

Hallo,

I'm quite new and still learning this program. I'm trying to simulate a hydrodynamic coupling. It consists of two part, Pump side and Turbine side (A screenshoot of the model is available). The rotational velocity of the pump side is constant. The rotational velocity of the turbine side is changing in respect of time and depends on the value of the working torque (from the fluid to the turbine's blade).

I've made a plane on my turbine's geometry and the working torque (Moment) on the turbine can displyed using 'monitors' and 'reports'.

And now I'm going to use this value, so the turbine's rotational velocity can change in respect of time.

1. How can I Import this value into my UDF? Which variable are used in this case?
2. While I was trying to Interpret my UDF File, this warning came 'line 23: structure reference not implemented'. Can someone Show/tell me the mistakes?
3. Will this UDF executed in every iteration? Or will it just be executed once? I dont know if i should write the looping in the UDF or not.

Here is my UDF File.

************************************************** *********
#include "udf.h"
#define Niter 25 /* iteration update interval */
#define omg_ts 0.0 /* starting omega */
#define omg_tf 600.0 /* final omega */
#define Jt 0.000554 /* Moment Inertia of the Turbin*/

DEFINE_ADJUST(testudf,d)
{
int zoneID;
int iter = (nres==0)?(1):((int)count2[nres-1]);
float omgt;
Thread *tc;
zoneID = 2;
tc = Lookup_Thread(domain,zoneID);
if ( (iter%Niter)==0 )
{
del_omgt = Mt/Jt;
omgt = omg_ts + del_omgt*(iter/Niter);
if ( omgt > omg_tf ) omgt = omg_tf;
THREAD_VAR(tc).fluid.omega = omgt;
}
}

************************************************** **********

I'm new and therefore I really appreciate any Reply and any help. Thanks in advance.

Best regards,
Darma Yuda

Hallo,

I have adjusted my code again. I think it should be better than the last one.

********************************
#include "udf.h"
DEFINE_ADJUST(testudf,d)
{
real omega_ts=0.0; /*starting omega*/
real omega_tf=600.0; /*final omega*/
real Jt=0.000554; /*Moment Inertia of the Turbin*/
real delta_t=0.0001; /*time step simulation*/
real alpha_t; /*angular acceleration, delta t*/
Thread *t;
cell_t c;
t=Lookup_Thread(d,9); /*Zone ID = 9*/
begin_c_loop (c,t)
{
alpha_t= Mt/Jt; /*M = J*alpha, but how can I retrieve the value of Mt?*/
omega_ts+=alpha_t*delta_t;
if (omega_ts > omega_tf)
{omega_ts = omega_tf;}
THREAD_VAR(t).fluid.omega=omega_ts; /*I'm not sure if this Syntax correct*/
}
end_c_loop (c,t)
}
*********************************

1. In this case I'm using cell loop. Is that correct?

2. How should I retrieve the calculated torque Mt and input to my UDF Code? In your case, you have F_Flux(f,t). But I can't find a way to retrieve the torque working on the body. Is there a list of variable for the Fluent Parameter (like rotational velocity and torque) ? Because I can only find a cell and face variable.

I would really appreciate any help and tipps. Thanks in advance.

Best regards,
Darma Yuda

Hallo everyone,

I have found how to retrieve the torque from Fluent. However, there is still error in the code after I intepreted the UDF code. it says "line 14: parse error". I think it is about the macro DEFINE_TRANSIENT_PROFILE. Can somebody help to show me the mistakes about this macro? Thank you very much.

Here is my UDF Code:

************************************************** ***************

#include "udf.h"
DEFINE_ON_DEMAND(wall_forces)
{
Domain * domain = Get_Domain (1); /* For multiphase flow, you need to set the Sub domain */
Thread *t;
real CG[3], force[3], moment[3];
t = Lookup_Thread (domain, 13); /* 13 is the ID of the wall to be determined. */
NV_S (CG, =, 0.0); /* coordinates of the center position to find the moment. */
Compute_Force_And_Moment (domain, t, CG, force, moment, TRUE);
Message("f=(%e, %e, %e), m=(%e, %e, %e)\n", force[0], force[1], force[2], moment[0], moment[1], moment[2]);
/* force [0], force [1], force [2] are respectively x, y, z-direction forces, Is the sum of the force by the force and the shear stress due to pressure. */
}

DEFINE_TRANSIENT_PROFILE(testudf, CURRENT_TIME)
{
real omega_ts=0.0; /*starting omega*/
real omega_tf=600.0; /*final omega*/
real Jt=0.000554; /*Moment Inertia of the Turbin*/
real delta_t=0.0001; /*delta t simulation*/
real CURRENT_TIMESTEP;
real CURRENT_TIME;
real alpha_t; /*angular acceleration*/
Thread *t;
cell_t c;
t=Lookup_Thread(domain,9); /*Cell Zone ID = 9*/

begin_c_loop (c,t)
{
alpha_t= 15*moment[0]/Jt; /*there are 15 blades, x axis as rotation axis*/
omega_ts+=alpha_t*CURRENT_TIMESTEP;
if (omega_ts > omega_tf)
{omega_ts = omega_tf;}
THREAD_VAR(t).fluid.omega=omega_ts;
}
end_c_loop (c,t)
}