Mesh isues

[CMeg9]

I'm trying to simulate the aero of the f1 2026 prototype but im having some problems with the mesh, like parts disapearing or things that shoudn't apear idk if this is caused by the limitations of the grid or some thing else .
This part on the nose need to appear .

This "lines" should not.


Also having problems with moving boundaries on the wheels but that is not critical right now.

[ProjectPhysX]

Hi @CMeg9,

please see #303 (comment). Closing as duplicate. Feel free to reply here if issues persist.

Kind regards,
Moritz

[CMeg9]

I tried the direction = 2u, and also checking the mesh but neither of those solved it.
This is my setup:
void main_setup() {
// ##################################################################
// Define simulation box size, viscosity, and volume force
// ##################################################################
const uint3 lbm_N = resolution(float3(5.0f, 1.0f, 1.0f), 1000u); // Grid resolution
const float lbm_u = 0.075f; // LBM velocity
const float lbm_length = 0.8f * (float)lbm_N.y; // LBM length scale
const float si_T = 0.25f; // Simulation time in seconds
const float si_u = 100.0f / 3.6f; // Physical velocity in m/s
const float si_length = 5.5f, si_width = 2.0f; // Physical dimensions
const float si_nu = 1.48E-5f, si_rho = 1.225f; // Physical viscosity and density

// Set units for conversion
units.set_m_kg_s(lbm_length, lbm_u, 1.0f, si_length, si_u, si_rho);
const float lbm_nu = units.nu(si_nu); // LBM viscosity
const ulong lbm_T = units.t(si_T); // LBM time steps

// Print Reynolds number
print_info("Re = " + to_string(to_uint(units.si_Re(si_width, si_u, si_nu))));

// Create LBM object
LBM lbm(lbm_N, 1u, 1u, 1u, lbm_nu);

// ##################################################################
// Load and prepare meshes
// ##################################################################
// Load meshes
Mesh* body = read_stl(get_exe_path() + "./stl/F12026.stl");
Mesh* front_wheels = read_stl(get_exe_path() + "./stl/frontwheel.stl");
Mesh* back_wheels = read_stl(get_exe_path() + "./stl/rearwheel.stl");

// Scale meshes to fit the domain
const float scale = lbm_length / body->get_bounding_box_size().y;
body->scale(scale);
front_wheels->scale(scale);
back_wheels->scale(scale);

// Translate meshes to the correct position
const float3 offset = float3(
    lbm.center().x - body->get_bounding_box_center().x,
    1.0f - body->pmin.y + 0.25f * back_wheels->get_min_size(),
    4.0f - back_wheels->pmin.z
);
body->translate(offset);
front_wheels->translate(offset);
back_wheels->translate(offset);

// Set mesh centers for rotation
body->set_center(body->get_bounding_box_center());
front_wheels->set_center(front_wheels->get_bounding_box_center());
back_wheels->set_center(back_wheels->get_bounding_box_center());

// ##################################################################
// Voxelize meshes in all three axes (x, y, z)
// ##################################################################
// Voxelize the car body (stationary)
lbm.voxelize_mesh_on_device(body, TYPE_S, body->get_center(), float3(0.0f), float3(0.0f));

// Voxelize the front wheels (rotating around x-axis)
const float lbm_radius = 0.5f * back_wheels->get_min_size();
const float omega = lbm_u / lbm_radius; // Angular velocity
lbm.voxelize_mesh_on_device(
    front_wheels,
    TYPE_S,
    front_wheels->get_center(),
    float3(0.0f), // Linear velocity
    float3(omega, 0.0f, 0.0f) // Rotational velocity (x-axis)
);

// Voxelize the back wheels (rotating around x-axis)
lbm.voxelize_mesh_on_device(
    back_wheels,
    TYPE_S,
    back_wheels->get_center(),
    float3(0.0f), // Linear velocity
    float3(omega, 0.0f, 0.0f) // Rotational velocity (x-axis)
);

// ##################################################################
// Set initial conditions and boundary conditions
// ##################################################################
const uint Nx = lbm.get_Nx(), Ny = lbm.get_Ny(), Nz = lbm.get_Nz();
parallel_for(lbm.get_N(), [&](ulong n) {
    uint x = 0u, y = 0u, z = 0u;
    lbm.coordinates(n, x, y, z);

    // Set free stream velocity in x-direction
    if (lbm.flags[n] != TYPE_S)
        lbm.u.x[n] = lbm_u;

    // Set side walls and ceiling as equilibrium boundaries
    if (y == 0u || y == Ny - 1u || z == 0u || z == Nz - 1u)
        lbm.flags[n] = TYPE_E;

    // Set outlet as equilibrium boundary
    if (x == Nx - 1u)
        lbm.flags[n] = TYPE_E;
});

// ##################################################################
// Run simulation and export images
// ##################################################################
lbm.graphics.visualization_modes = VIS_FLAG_SURFACE | VIS_Q_CRITERION;

#if defined(GRAPHICS) && !defined(INTERACTIVE_GRAPHICS)
lbm.run(0u, lbm_T); // Initialize simulation

while (lbm.get_t() <= lbm_T) { // Main simulation loop
    if (lbm.graphics.next_frame(lbm_T, 30.0f)) {
        // Camera 1
        lbm.graphics.set_camera_free(
            float3(0.779346f * (float)Nx, -0.315650f * (float)Ny, 0.329444f * (float)Nz),
            -27.0f, 19.0f, 100.0f
        );
        lbm.graphics.write_frame(get_exe_path() + "export/a/");

        // Camera 2
        lbm.graphics.set_camera_free(
            float3(0.556877f * (float)Nx, 0.228191f * (float)Ny, 1.159613f * (float)Nz),
            19.0f, 53.0f, 100.0f
        );
        lbm.graphics.write_frame(get_exe_path() + "export/b/");

        // Camera 3
        lbm.graphics.set_camera_free(
            float3(0.220650f * (float)Nx, -0.589529f * (float)Ny, 0.085407f * (float)Nz),
            -72.0f, 16.0f, 86.0f
        );
        lbm.graphics.write_frame(get_exe_path() + "export/c/");

        // Camera 4 (dynamic angle)
        const float progress = (float)lbm.get_t() / (float)lbm_T;
        const float A = 75.0f, B = -160.0f;
        lbm.graphics.set_camera_centered(A + progress * (B - A), -5.0f, 100.0f, 1.648721f);
        lbm.graphics.write_frame(get_exe_path() + "export/d/");
    }
    lbm.run(1u, lbm_T);
}

#else // GRAPHICS && !INTERACTIVE_GRAPHICS
lbm.run(); // Run interactively
#endif // GRAPHICS && !INTERACTIVE_GRAPHICS
}

Also here is some images of what happens when direction = 2u.



As the images shows part of the structure of the nose that was wrong before now is fine, also those weird structures that appeared on the first images of the issue don't exist anymore. But some crucial parts disappear like, part of the frontwing, rear wing or the floor.

[CMeg9]

By the way this is the stl im using.
F12026.zip

[pk-guest]

Uploading update.zip…

your geometry was not watertight, with update its better. The resolution should also increase.

A better meshing for the future should solve this issues

[CMeg9]

resolution was like that because i was at that moment wiith a laptop that only has processor not dGPU, it was the highest resolution i could use and still move the camera, but i really want to know how to make the geometry watertight.

[ProjectPhysX]

@CMeg9 super high mesh resolution is not beneficial. Ideal for the voxelization is when mesh triangles are about the same size as the grid cells in LBM. Any finer mesh details will get lost in the voxelization anyways. And the mesh has to be watertight - without holes or overlapping triangles. Microsoft 3D Builder can repair non-watertight meshes, and also make them coarser.

[pk-guest]

sorry my wording was wrong, with resolution I mean: the voxelsize was too coarse compare the geometry.

[pk-guest]

You need a open source or commertial CAD tool which can prepair stl files. Than working the voxeling better. But I know its not always so easy. Carlos Megias ***@***.***> schrieb am Sa., 4. Okt. 2025, 18:29:

…

resolution was like that because i was at that moment wiith a laptop that only has processor not dGPU, it was the highest resolution i could use and still move the camera, but i really want to know how to make the geometry watertight. — Reply to this email directly, view it on GitHub <#310 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BJ2YNNAC7B734A6LKRKFPNL3V7YX5AVCNFSM6AAAAACHWUPJQWVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTINJZGIZDSMQ> . You are receiving this because you commented.Message ID: ***@***.***>

[ProjectPhysX]

Microsoft 3D Builder also has a tool to repair meshes, and is free. Usually I don't recommend Microsoft but 3D Builder is actually quite good and useful.

[pk-guest]

update.zip

[CMeg9]

god bless you for this stl, i really need to learn how to make them.