Numerical Simulation on a Sand Erosion under Wave in 2D by Lattice Boltzmann Method

Abstract

Coastal waves and nearshore currents are crucial hydrodynamics for coastal sediment transport. As wave propagates from deep ocean to shallow water, it occurs shoaling, diffraction, refraction and breaking due to the influence of bathymetry, and wave energy is usually lost to turbulence generated in the process of breaking. To predict sediment transport in coastal environment is of particularly importance for analyzing coast erosion and deposition accurately and solving the corresponding coast protection engineering problems further more. In this thesis, Lattice Boltzmann Method is applied for fluid simulation. The wave generation in the numerical wave tank is done by internal mass source function method, flap-typed and piston-typed wave maker method. As for the plane type wave maker, the movement of wave paddle, either piston or flap, is accomplished by coupling with immersed boundary condition at the paddle to generate linear waves. By using different source function at the designed region, generations of different types of wave trains can be done. The regular wave, second-order stokes wave, cnoidal wave and solitary wave are generated and validated with the analytical solutions. Sediment model is comprised of mechanism of sediment transport, deposition and erosion. These mechanisms are designed by implementing the concept of multi-particle cellular automata (CA). Sand particles are allowed to move at regular lattice nodes along with fluid particles at discrete time steps. The change of bed profile can be revealed by switching on the sediment model. The sand erosion under the pipe is investigated and compared with the experiment data. The cnoidal wave trains approaching the beach slop with vertical wall is simulated and the result in the sand erosion at the wall toe is predicted.