Transient cavity dynamics in the oblique water entry of a cylinder at a constant velocity is investigated. The drag force exerted on the cylinder is measured by a force sensor, and the evolution of a cavity is recorded simultaneously by a high-speed camera. A simple theoretical model, based on the decomposition of gravity force, is proposed to describe the asymmetric cavity formed in the oblique water entry. Theoretically predicted cavity shapes compare favorably with the experimental and numerical results. Moreover, it is found that with a factor indicating the effect of entry angle, the pinch-off time and position in oblique and vertical water entry problems follow the same scaling law.

The Herschel-Bulkley rheological theory is used to describe the viscoplastic debris landslide flow. The shallow water equations considering the time-dependent deformation of the seafloors are adopted to simulate the generation, propagation, and run-up of the landslide induced tsunami. The one-way coupled method of the landslide induced tsunami is implemented through satisfying the kinematic bottom boundary condition. The 1998 Papua New Guinea landslide tsunami is simulated to validate the numerical model by comparing with measurements. We found that the mechanism of the 1992 Hainan Island tsunami in the South China Sea is due to a submarine landslide by comparing the numerical results between earthquake and landslide. With respect of the Baiyun slide, the effects of remolding rate, initial, and residual yield strength on landslide and tsunami are studied numerically. To distinguish the potential landslide tsunami hazard in the South China Sea, the scenarios of the landslides with the volume of 10, 50, 100, and 200 km³ in the Baiyun slide and 1200 km³ in the Brunei slide are presented. Comparison with the nondeformation model in the near-field illustrates the crucial role of rheological property in the landslide tsunami modeling. Furthermore, the characteristics of the propagation of the landslide tsunami in the South China Sea and coastal hazards are analyzed.

The vertical water-entry of a cylinder with a flat bottom at a high-speed impact velocity is investigated numerically in this paper. The multiphase solver is based on the reduced five-equation model and adopts a pressure relaxation method. The fluid is assumed as inviscid and compressible. The effect of gravity is neglected because of the high Froude number and short loading period. A series of numerical experiments are conducted, and the influence of the impact velocity and aeration effect on the slamming loads are studied. The results show that the compressibility of the fluid is important as the impact velocity increases and the acoustic pressure underestimates the maximum impact pressure. Moreover, as the aeration level grows, both the impact loads and the affected area will decrease. Simplified theoretical equations based on the shock jump relation are proposed to predict the maximum impact loads, showing a good agreement with the numerical results. The dimensional analysis results show that the impact loads in pure and aerated water follow the same relation vs Mach number, which can be used to measure the high-speed impact force at a lower impact velocity in aerated water.

A parallelized three-dimensional (3D) boundary element method is used to simulate the interaction between an incoming solitary wave and a 3D submerged horizontal plate under the assumption of potential flow. The numerical setup follows closely the setup of laboratory experiments recently performed at Shanghai Jiao Tong University. The numerical results are compared with the experimental results. An overall good agreement is found for the two-dimensional wave elevation, the horizontal force and the vertical force exerted on the plate, and the pitching moment. Even though there are some discrepancies, the comparison shows that a model solving the fully nonlinear potential flow equations with a free surface using a 3D boundary element method can satisfactorily capture the main features of the interaction between nonlinear waves and a submerged horizontal plate.