Sloshing-2D

Real-time 2D sloshing tank simulator solving the incompressible Navier-Stokes equations with PLIC (Piecewise Linear Interface Calculation) free-surface tracking.

Features

• MAC staggered grid eliminates checkerboard pressure oscillations
• Fractional-step projection method with semi-Lagrangian advection
• PLIC geometric VOF — sharp interface by construction, no numerical diffusion
• Velocity extrapolation into the air band (normal-direction weighted) for accurate free-surface dynamics
• Non-homogeneous Neumann wall BCs folded into the pressure Poisson equation
• Red-Black SOR pressure solver with warm-starting
• CSF surface tension model (Brackbill et al.) with SOLID-aware curvature
• Internal obstacles (baffles) via persistent obstacle mask
• 9 initial conditions selectable at runtime, including OpenFOAM damBreak geometry
• Texture-mapped rendering via OpenGL for efficient visualization
• Interactive controls — move the tank with arrow keys and watch the fluid slosh

Building

Requires CMake 3.20+, a C++20 compiler, GLFW 3.3+, and doctest.

mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
cmake --build .

Running

./build/sloshing_tank           # Default 256x128 grid
./build/sloshing_tank 512 256   # Custom resolution

Controls

Key	Action
Arrow keys / WASD	Accelerate tank
1-9	Select initial condition
T	Toggle surface tension
Space	Pause / Resume
R	Reset
+/-	Speed up / down
Q / Esc	Quit

Initial Conditions

Key	Setup
1	Still water
2	Dambreak
3	Dambreak with baffle (centre)
4	Tilted surface (sloshing mode)
5	Central column
6	Two-column collision
7	Shallow fill
8	Dambreak with baffle (3/4)
9	OpenFOAM damBreak tutorial geometry

Tests

cd build && ctest

Eight physics tests validate the solver against analytical solutions:

Test	Metric	Value
Hydrostatic pressure	RMS error	5.1%
Sloshing frequency	period error	0.8%
Ritter dambreak wavefront	sim/theory ratio	0.71
Thin-film spreading	sim/theory ratio	0.64
Interactive dambreak (256x128)	Ritter ratio at t=0.5s	0.71
Baffle impermeability	leakage	0%
Volume under violent shaking	drift	0%
VOF boundedness	all cells in [0,1]	pass

Project Structure

src/
  grid.{hpp,cpp}        MAC staggered grid, field storage, initial conditions
  solver.{hpp,cpp}      Navier-Stokes fractional-step solver with velocity extrapolation
  vof.{hpp,cpp}         PLIC geometric VOF transport
  renderer.{hpp,cpp}    OpenGL texture-based renderer
  simulation.{hpp,cpp}  Main loop orchestrator
tests/
  test_grid.cpp         Grid data structure tests
  test_solver.cpp       Solver unit tests
  test_vof.cpp          VOF transport tests
  test_physics.cpp      Physics validation tests (8 cases)
docs/
  update-plic.md        Development notes on the PLIC migration

License

Free for personal, academic, and research use. No warranty. Commercial use requires written permission from the author.