[force_95]

Hey everyone, I really need your help !

I'm dealing with a UDF code calculating the viscous force acting on a body. Now I want to extend that code so that the force of particles I want to insert is also calculated and added to the viscous force. If the particles are in my domain I expect the body to slow down very faster because of the particle forces acting on that body.
I wrote a code, but I don't know the mistakes because I'm not familiar with programming in C. I would really appreciate if you could check and help me.

So thats my code :

#include "udf.h"

static real v_prev = 0.3;

DEFINE_CG_MOTION(bubble, dt, vel, omega, time, dtime)
DEFINE_DPM_BC(Particle_Infos,p,t,f,f_normal,dim)
{
#if !RP_HOST
Thread *t;
face_t f;
cell_t p_cell; /* Cells where particles reside */

real p_n; /* Number of particles in a parcel */

real p_mass; /* Mass of each particle */

real pur_vel[ND_ND]; /* Velocity of each particle */

int i; /* vector number*/

flow_time = CURRENT_TIME; /* Get current flow time */

Thread *p_cell_thread;

real NV_VEC(A);
real Wall_Shear_Force;
real viscous;
real force_p;
real dv;


/**** Now calculating force of particles*******/

p_cell = F_C0(f,t); /* return cell thread index in which face thread "t" is */

p_cell_thread = THREAD_T0(t); /* Get the face centroid from ANSYS FLUENT */

F_CENTROID(pur_f_centroid,f,t); /* Get the number of the particles in a parcel from FLUENT */

p_n = P_N(p); /* Get the mass of the particle from ANSYS FLUENT */

p_mass = P_MASS(p); /* Get the velocity of the particle from ANSYS FLUENT */

for(i=0;i<dim;i++)
pur_vel[i] = P_VEL(p)[i]; /* When the particles hit the wall face, mark the cell, which consists
this face.*/

C_UDMI(p_cell,p_cell_thread,0) = PUR_cell; /* Store the number of particles hitting this face all the
time. */

C_UDMI(p_cell,p_cell_thread,1) += p_n;

C_UDMI(p_cell,p_cell_thread,2) += p_n * p_mass; /* mass of particles hitting the face */


C_UDMI(p_cell,p_cell_thread,6) += p_n * p_mass * pur_vel[0]; /* Total impulse of all parcels in x
direction in a cell */

force_p = C_UDMI(p_cell,p_cell_thread,6);

C_UDMI(p_cell,p_cell_thread,17) += 1; /* Store the number of parcels hitting on this face all the
time*/

return PATH_ABORT;
#endif



/**** Now calculating viscous force*******/

/* reset velocities */
NV_S (vel, =, 0.0);
NV_S (omega, =, 0.0);

if (!Data_Valid_P ())
return;

/* get the thread pointer for which this motion is defined */
t = DT_THREAD (dt);

/* compute pressure force on body by looping through all faces */
viscous = 0.0;


begin_f_loop (f, t)
{
F_AREA (A, f, t);

Wall_Shear_Force = -F_STORAGE_R_N3V(f,t ,SV_WALL_SHEAR)[0];

viscous += Wall_Shear_Force ;


}
end_f_loop (f, t)

/* compute change in velocity, i.e., dv = F * dt / mass
velocity update using explicit Euler formula */

dv = dtime * (viscous + 0.000512 + force_p/dtime) / 0.000055;

v_prev += dv;

Message ("time = %f, x_vel = %f, force = %f\n", time, v_prev,
force);

/* set x-component of velocity */
vel[0] = v_prev;
}




Best regards!

[annan]

Dear Jens,

Why do you have two functions ? Namely, DEFINE_CG_MOTION and DEFINE_DPM_BC. A part of your code might be missing here, but there should be only one of them.

DEFINE_CG_MOTION(bubble, dt, vel, omega, time, dtime)
{
Code
}

Or

DEFINE_DPM_BC(Particle_Infos,p,t,f,f_normal,dim)
{
Code
}

Regards,
Annan

[force_95]

Hey annan

thank you for your answer.

I thought I need two functions. One for the motion and one for the Particles...

How can I change that into a right code ?

best regards