Learning Forum

[Zery Triputra]

Hi everyone, I'm having trouble initializing my model. 
My fluent crash when i try to initialize my model. 
I use UDS and UDF, my simulation is 2D, single phase. \
I aim to get the simulation results in the form of the distribution of Dissolved Oxygen in the pond. 
Is there anyone can check my UDF is wrong or not ?

My UDF :

#include "udf.h"

DEFINE_PROFILE(inlet_velocity, thread, position)
{
    real x[ND_ND];
    real vel = 0.32; // Kecepatan masukan inlet (m/s)

    face_t f;
    begin_f_loop(f, thread)
    {
        F_CENTROID(x, f, thread);
        F_PROFILE(f, thread, position) = vel;
    }
    end_f_loop(f, thread)
}

#define Cs 0.0085  //  dissolved oksigen concentration saturated (kg/m^3)
#define C_initial 0.003  // l C (kg/m^3)
#define a 22.34  // coefficient source item (1/s)

DEFINE_SOURCE(mass_source, c, t, dS, eqn)
{
    real S, C;
    real time = CURRENT_TIME;

    // Calculation of value S (mass source item) based on the one degree reaction model
    S = a * (Cs - C_initial);

    // deficit value S
    S *= exp(-0.1 * time);  // Nilai penurunan dapat disesuaikan

    // update value C
    C = C_initial + (Cs - C_initial) * (1 - exp(-a * time));

    // stop iteration when C is maximum ( saturated)
    if (C >= Cs) {
        C = Cs;
        S = 0.0;
    }

    // Assign value C to UDS (User Defined Scalar)
    C_UDSI(c, t, 0) = C;

    dS[eqn] = 0.0; // 
    return S;
}

[Rob]

How many scalars did you tell Fluent you were using?  Check the lines

  // deficit value S
    S *= exp(-0.1 * time);  // Nilai penurunan dapat disesuaikan

[Zery Triputra]

i use 2 scalars in this simulation 

[Rob]

And did you assign memory for that in User Defined tab? 

If you did. Turn off the source terms, run a few iterations/one time step and try again. If any of those data calls don't have a value you may have a problem. Also, using 1-3 letter variables can cause problems if they're also used in Fluent somewhere else, hence I often use real/integer over DEFINE for coefficients.