Reply To: coupled simulation of vehicle and fluid tank

[vikram chahal]

#include "udf.h"

#include // Include the standard I/O library for file operations

DEFINE_ADJUST(coupled_simulation1, d)

{

    real simulation_time = CURRENT_TIME; // Get the current simulation time

    real dt = RP_Get_Real("flow-time-step"); // Get the flow time step

    real end_time = RP_Get_Real("flow-time-end"); // End time of simulation

    real braking_duration = 2.0; // Duration of braking force (seconds)

    // Open file for writing

    FILE *fp;

    fp = fopen("E:\coupled trial 3\50 prcnt_files\dp0\FFF\Fluent\libudf6\result\simulation_results.txt", "w");

    if (fp == NULL) // Check if file was opened successfully

    {

        Message("Error opening file.\n");

        return -1; // Exit initialization function

    }

    Domain *domain = Get_Domain(3); // Replace 1 with the appropriate domain ID

    if (!domain)

    {

        Message("Error: Unable to obtain domain.\n");

        fclose(fp); // Close the file before returning

        return -1; // Exit initialization function

    }

    // Define vehicle parameters

    real m_truck = 5450.0; // Mass of the truck (kg)

    real I_truck = 5000.0; // Moment of inertia of the truck (kg*m^2)

    real k1 = 2.86e10; // Front spring stiffness (N/m)

    real k2 = 3.870e5; // Rear spring stiffness (N/m)

    real l1 = 0.2; // Distance of front axle from CG (m)

    real l2 = 0.8; // Distance of rear axle from CG (m)

    real F_braking = 27000.0; // Braking force (N)

    // Define fluid parameters

    real fluid_density = 1000.0; // Density of the fluid (kg/m^3)

    // Initial conditions for vehicle motion

    real x = 2.0; // Initial vertical displacement

    real theta = 2.0; // Initial angular displacement

    real x_dot = 0.0; // Initial vertical velocity

    real theta_dot = 0.0; // Initial angular velocity

    real fluid_force_x, fluid_force_y, fluid_force_z, fluid_moment_x, fluid_moment_y, fluid_moment_z;

    Thread *t;

    cell_t c;

    face_t f;

    // Main simulation loop

    while (simulation_time < end_time)

    {

        // Step 1: Calculate vehicle response to braking force

        real F_brake = (simulation_time < braking_duration) ? F_braking : 0.0; // Apply braking force only within the braking duration

        real x_ddot = (-k1 * (x - l1 * theta) - k2 * (x + l2 * theta) + F_braking) / m_truck;

        real theta_ddot = (-k1 * l1 * (x - l1 * theta) + k2 * l2 * (x + l2 * theta)) / I_truck;

        // Step 2: Apply vehicle response in terms of x(t) and theta(t) to fluid domain as a body force in the source term

        real vehicle_force_x = 0.0; // Body force in x-direction    

        real vehicle_force_y = 0.0; // Body force in y-direction

        real vehicle_force_z = 0.0;  // Body force in z-direction

        real vehicle_moment_x = 0.0; // vehicle moment in x-direction

        real vehicle_moment_y = 0.0; // vehicle moment in y-direction

        real vehicle_moment_z = 0.0; // vehicle moment in z-direction

        // Update the body force components based on vehicle response

        // For simplicity, assuming all the force acts in the z-direction

        vehicle_force_y = -m_truck * x_ddot;

        vehicle_moment_z = -k1 * l1 * (x - l1 * theta) + k2 * l2 * (x + l2 * theta);

        // Apply the body force to the fluid domain

        t = Lookup_Thread(domain, 3); // Assuming FLUID_THREAD_ID is the ID of the fluid thread

        thread_loop_c(t, d)

        {

            C_UDMI(c, t, 0) = vehicle_force_x;

            C_UDMI(c, t, 1) = vehicle_force_y;

            C_UDMI(c, t, 2) = vehicle_force_z;

           

             // Apply the moment components based on vehicle response

            // Here, we'll assume all the moments act around the z-axis

            C_UDMI(c, t, 3) = 0.0; // Moment about x-axis

            C_UDMI(c, t, 4) = 0.0; // Moment about y-axis

            C_UDMI(c, t, 5) = vehicle_moment_z; // Moment about z-axis

        }

        // Step 3: Calculate fluid forces and moments

        fluid_force_x = 0.0;

        fluid_force_y = 0.0;

        fluid_force_z = 0.0;

        fluid_moment_x = 0.0;

        fluid_moment_y = 0.0;

        fluid_moment_z = 0.0;

        // Loop over fluid cells

        thread_loop_c(t, d)

        {

            begin_c_loop(c, t)

            {

                real A[ND_ND], F[ND_ND], F_area[ND_ND];  // Add F_area vector to store face area

                real p = C_P(c, t); // Pressure of the cell

                C_CENTROID(A, c, t); // Centroid of the cell

                for (int i = 0; i < ND_ND; i++)

                {

                    F[i] = 0.0; // Initialize force vector

                }

                // Loop over faces of the cell using C_FACE macro

                for (int f = 0; f < C_NFACES(c, t); f++)

                {

                    face_t face = C_FACE(c, t, f);

                    F_AREA(F_area, face, t); // Face area vector

                    // Calculate face force

                    for (int j = 0; j < ND_ND; j++)

                    {

                        F[j] += p * F_area[j]; // Use F_area instead of calling F_AREA macro multiple times

                    }

                }

                // Accumulate forces and moments

                fluid_force_x += F[0];

                fluid_force_y += F[1];

                fluid_force_z += F[2];

                fluid_moment_x += (A[1] * F[2] - A[2] * F[1]);

                fluid_moment_y += (A[2] * F[0] - A[0] * F[2]);

                fluid_moment_z += (A[0] * F[1] - A[1] * F[0]);

            }

            end_c_loop(c, t);

        }

        // Step 4: Update vehicle response based on fluid forces and moments as excitation force on vehicle equations

        x_dot += fluid_force_y / m_truck * dt;

        theta_dot += fluid_moment_z / I_truck * dt;

        x += x_dot * dt;

        theta += theta_dot * dt;

        // Update simulation results in the file

        fprintf(fp, "%.4f, %.4f\n", x, theta);

       

        printf("Time: %.2f, x: %.4f, theta: %.4f\n", simulation_time, x, theta);

        // Increment simulation time

        simulation_time += dt;

    }

    // Close the file after simulation

    fclose(fp);

    return 0; // Successful initialization

}

now this code is getting compiled and hooking, but during simulation i am getting very low value of force in order of 0.4 N. i have doubt regarding macro i have used. could you please suggest me use of define_adjust macro is suitable for this coupled simulation or not??