Reply To: coupled simulation of vehicle and fluid tank

March 26, 2024 at 8:15 am

vikram chahal

Subscriber

#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??

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