[tomdillon97]

Hi everyone,

I'm working on writing a UDF for a windkessel model (a flow-dependent pressure outlet boundary condition). This model can be thought of as an elastic bag, whose pressure increases as flow is integrated at the outlet at each timestep. To perform this integration, I am using user defined memory function F_UDMI to update the pressure from one time iteration to the next. I am reserving memory, initialising memory values, initialising my pressure using define_init, applying the windkessel model, and saving my pressure at the end of each iteration.

However, when I run the solver, define_profile always thinks the initial value of F_UDMI(f,thread,0) is 0, despite the fact that I have initialised it to be 980 Pa in the functions below. Why would the solver be ignoring my initialisation functions / am I using F_UDMI correctly? Thanks so much
Tom


#include "udf.h"

#define NUM_UDM 1
static int udm_offset = UDM_UNRESERVED;

DEFINE_EXECUTE_ON_LOADING(on_loading, libname)
{
if (udm_offset == UDM_UNRESERVED)
udm_offset = Reserve_User_Memory_Vars(NUM_UDM);

if (udm_offset == UDM_UNRESERVED)
Message("\nYou need to define up to %d extra UDMs in GUI and "
"then reload current library %s\n", NUM_UDM, libname);
else
{
Message("%d UDMs have been reserved by the current "
"library %s\n", NUM_UDM, libname);

Set_User_Memory_Name(udm_offset, "lib2-UDM-0");

}
Message("\nUDM Offset for Current Loaded Library = %d", udm_offset);
}


DEFINE_ON_DEMAND(set_udms)
{
Domain* d;
Thread* ft;
face_t f;
int i;

d = Get_Domain(1);

if (udm_offset != UDM_UNRESERVED)
{
Message("Setting UDMs\n");

for (i = 0; i < NUM_UDM; i++)
{
thread_loop_f(ft, d)
{
begin_f_loop(f, ft)
{
if (NUM_UDM > 0 && BOUNDARY_FACE_THREAD_P(ft))
{
F_UDMI(f, ft, udm_offset + i) = 980.0;
printf("The UDM value is %g \n ", F_UDMI(f, ft, udm_offset + i));
}

}
end_f_loop(f, ft)
}


}

}
else
Message("UDMs have not yet been reserved for library 1\n");
}

DEFINE_INIT(init_func, domain)
{
face_t f;

Thread* ft = Lookup_Thread(domain, 7);

begin_f_loop(f,ft)
{
F_P(f,ft)= 980.0;

}
end_f_loop(f,ft)
}

DEFINE_PROFILE(unsteady_pressure, thread, position)
{

face_t f;
real flow = 0.0f;
real C = 1.0f;
real deltat = CURRENT_TIMESTEP; //should be current timestep?
real R = 0.3f;

real integrated;



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



begin_f_loop(f, thread)
{

integrated = F_UDMI(f,thread,0) + ((1 / C) * (flow * deltat) * (10 ^ 4));
F_PROFILE(f, thread, position) = integrated;

}
end_f_loop(f, thread);

}


DEFINE_EXECUTE_AT_END(pressure_save)
{
Domain* domain = Get_Domain(1);
Thread* thread = Lookup_Thread(domain, 7);
face_t f;

begin_f_loop(f, thread)
{
F_UDMI(f, thread, 0) = F_P(f, thread);
}
end_f_loop(f, thread)
printf("Step Pressure Recorded!");
}

[qazmlp223]

I would like to ask you if this problem has been solved. I am also working on the Windkessel boundary problem.Can you share the code?thank you

[AlexanderZ]

code above should be modified
In define_init macro author doesn't change the value of F_UDMI(f,thread,0)

[qazmlp223]

Originally Posted by AlexanderZ

code above should be modified
In define_init macro author doesn't change the value of F_UDMI(f,thread,0)

Could you please tell me how to modify it in detail？ best regards

[AlexanderZ]

if you want to get help here, you are expected to do following:
describe your model in details
show the code you have
show log file after compiling
describe problems