[pranab_jha]

Hello Everyone,

Been a regular visitor to this site. Recently started playing with UDFs. I am stuck at this one. I have to model a pressure boundary condition similar to a hydrostatic pressure at the inlet.
My problem is that I am not able to get the pressure already available at the first time step at every face of the inlet thread (I use a steady state solution as my initial condition for the unsteady case) and then compute its average. I have to store this as the initial pressure. Then I have to decrease the initially calculated volume Q0 at the inlet with the volume flux and compute pressure P1 using the new remaining volume Q1 to be stored in a user defined memory location (MEM2) and use it in the next time step.

Can anyone take a look and help me out here.

Thanks,
Pranab


#include "udf.h"

DEFINE_PROFILE(pv1, t, index)
{
face_t f;
int n = N_TIME; /*no. of time steps*/
real P1;
real P_sum=0;
real P_avg=0;
real Q0, Q1;
real vol_out;
real mass_flux=0;
real mass_flux_tot=0;
real MEM1, MEM2, MEM3;
Thread *t1;
int d;

int Zone_ID = 22; /*look up the id from the boundary conditions panel*/
d=Get_Domain(1); /*domain*/

t1=Lookup_Thread(d,Zone_ID);

/**Initialize UDM to face-pressure at the first time-step**/
if(n==1) {printf("\nFirst timestep\n");
begin_f_loop(f,t1)
{
P_sum = P_sum + F_P(f,t1);
P_avg = P_sum / 7;

F_UDMI(f,t1,0) = P_avg; /*constant for all iterations*/

Q0 = (P_avg * 10000)/(0.6679 * 9.81); /*initial volume*/

F_UDMI(f,t1,1) = Q0;

F_UDMI(f,t1,2) = Q0; /*constant for all iterations*/

}end_f_loop(f,t1)
}


/**Assign all UDM's to a variable to be used later**/
MEM1 = F_UDMI(f,t1,0);
MEM2 = F_UDMI(f,t1,1);
MEM3 = F_UDMI(f,t1,2); /

begin_f_loop(f,t1)
{
mass_flux = mass_flux + F_FLUX(f,t1);
}end_f_loop(f,t1)

mass_flux_tot = mass_flux;

vol_out = 0.0001* mass_flux_tot/0.6679;

/**Calculate remaining volume & new pressure**/
Q1 = MEM2 - vol_out; /**new volume**/

P1 = Q1 * MEM1 / MEM3; /**new pressure**/
printf("New Pressure = %f\n", P1);

begin_f_loop(f,t1)
{
/**Apply new pressure on the face**/
F_PROFILE(f,t1,index) = P1;
}end_f_loop(f,t1)

/**Update the udm with new Q1**/
F_UDMI(f,t1,1) = Q1;

}