Learning Forum

[Zwernjayden]

I want my udf to update the surface tempurature to T(f), and the mass flow inlet to m_dot at the end. When try and use the DEFINE_ADJUST macro it crashes and says "999999: mpt_accept: error: accept failed: No error." The current code below compiles and works at printing the values (although they aren't really what I expected). I have also attached the pseudo code of what I am trying to do.

#include "udf.h"

#include

DEFINE_EXECUTE_AT_END(print_heat_flux)

{

    Domain *d;

    Thread *t;

    face_t f;

    real Ts, heat_flux, Hv, r, Ts_old, Ts_new, m_dot, T;  // Declare all variables at the top of the block

    real error;

    int iter;

    d = Get_Domain(1);  // Adjust the domain ID as per your case

 

    /* Loop over all face threads in the domain */

    thread_loop_f(t, d)

    {

        /* Check if this is the boundary with the ID you're interested in */

        if (THREAD_ID(t) == 6)  // Adjust the surface ID as per your case

        {

            /* Loop over all faces in this thread */

            begin_f_loop(f, t)

            {

                Ts = F_T(f, t);           // Get the temperature at face f

                heat_flux = BOUNDARY_HEAT_FLUX(f, t); // Calculate the heat flux

                printf("Heat flux on face %d: %g W/m^2\n", f, heat_flux);

Ts_old = Ts;

iter = 0;

error = 1;

while (error>1e-6 && iter <10)

{

Hv = 2033631 + 310000 + 1500;

r = heat_flux/(Hv*900);

Ts_new = 20557.188 / (8.314 * (log(0.01104) - log(r)));

error=fabs(Ts_new-Ts_old);

iter++;

}

T(f)=Ts+0.1*(Ts_new-Ts);

r = heat_flux/(Hv*900);

printf("Regression Rate: %g\n", r);

m_dot=900*r;

printf("M_dot: %g\n", m_dot);

            }

            end_f_loop(f, t)

        }

    }

}

 

[Rob]

We'd normally use DEFINE_PROFILE to set boundary conditions. Is this for a transient flow?

[Zwernjayden]

Its steady state. Would it be like this? Im a bit confused how the arguments for the F_PROFILE work. What does the i and the i+1 do? It says its supposed to determine which profile is which but I don't see a way to actually select it in the GUI.

#include "udf.h"

#include

 

DEFINE_PROFILE(combined_surface_and_mass_flow_profile, t, i)

{

    face_t f;

    real Ts, heat_flux, Hv, r, Ts_old, Ts_new, m_dot, error;

    int iter;

   

 

    begin_f_loop(f, t)

    {

        if (THREAD_ID(t) == 6)  // Select fuel grain surface

        {

            // Initial values and heat flux retrieval

            Ts = F_T(f, t);

            heat_flux = BOUNDARY_HEAT_FLUX(f, t);

 

            // Iterative calculation for new surface temperature

            Ts_old = Ts;

            iter = 0;

            error = 1;

            while (error > 1e-6 && iter < 10)

            {

                Hv = 2033631 + 310000 + 1500 * (Ts_old - 298);  // Update Hv formula as needed

                r = heat_flux / (Hv * 754);  // Regression rate calculation

                Ts_new = 20557.188 / (8.314 * (log(0.01104) - log(r)));  // New surface temperature calculation

                error = fabs(Ts_new - Ts_old);  // Compute error

                Ts_old = Ts_new;  // Prepare for next iteration

                iter++;

            }

            // Update the surface temperature profile at the face

            F_PROFILE(f, t, i) = (Ts + 0.1 * (Ts_new - Ts));

    r = heat_flux / (Hv * 754);

            // Compute mass flow rate based on the final regression rate

            m_dot = 754 * r;  // Use the same r calculated for temperature

            F_PROFILE(f, t, i+1) = m_dot;  // Assuming 'position + 1' is the correct slot for mass flow rate

        }

    }

    end_f_loop(f, t)

}

 

[Rob]

i , i+1 , i++ are generally integers and used to count up for "something". I'm not sure you should be using them like that in  F_PROFILE(f, t, i+1)  as i may be the surface ID: check the macro. 

In a steady case you're trying to update a boundary at each iteration so effectively you're changing the problem. If there's no damping you may find you oscillate around a value until the solver fails. 

Rather than trying to write ever more complex code, take a step back and figure out exactly what you're trying to acheive. Can it be done by running a model and manually altering a value to then run it again?