Tetsu Memita

SPH-LES MODEL FOR NUMERICAL INVESTIGATION OF WAVE INTERACTION WITH PARTIALLY IMMERSED BREAKWATER

The reflection and transmission characteristics of regular waves by a partially immersed curtain-type breakwater have been studied by the experiment and numerical model in the paper. Non-overtopping and overtopping of the breakwater by the incident wave were considered to compare different wave dissipation efficiencies. An incompressible Smoothed Particle Hydrodynamics (SPH) theory combined with a Large Eddy Simulation (LES) model was employed as the numerical tool. The SPH method is robust for tracking free surfaces without numerical diffusion and the LES model is capable of analyzing turbulence and eddy vortices during wave-breakwater interactions. A good agreement between computational and experimental wave profiles verifies the accuracy of the SPH-LES model. The computations also disclose that the wave energy dissipation is mainly attributed to the turbulence production and vortex shedding during the wave transmission and reflection processes.

LAGRANGIAN PARTICLE METHOD FOR SIMULATION OF WAVE OVERTOPPING ON A VERTICAL SEAWALL

A particle method, or a gridless Lagrangian method, shows the high performance in describing the complicated behavior of water surface with the fragmentation and coalescence of water. In this paper, a wave overtopping process on a vertical seawall is numerically simulated on the basis of the Navier-Stokes equation with surface-tension term, which is discretized by the MPS (moving particle semi-implicit) method belonging to the category of the particle method. An improvement of the listing process of neighboring particle is introduced to reduce the computational load. Wave overtopping process in the experiments are well reproduced by the MPS method. The predictions of the MPS method of the overtopping volume agree well with the experimental results.

Stem waves along vertical wall due to random wave incidence

Abstract This study investigates stem waves, propagating along a vertical wall, due to obliquely incident random waves through laboratory experiments and numerical simulations. Attention is paid to the difference or similarity between the stem waves due to periodic waves and random waves, the nonlinear and linear characteristics, and the effect of wave breaking on the evolution of stem waves. The following were found from this study: as the incident angle of waves become large or the nonlinearity of the incident waves become small, the significant stem wave height, normalized by the incident significant wave height, becomes large. This tendency is the same as that generated by the Stokes waves or cnoidal waves. However, regardless of the nonlinearity of incident waves, the width of stem waves is almost the same. This is a different point between the stem waves due to periodic and random waves. The wave breaking suppresses the growth of the stem waves.

Gridless Numerical Analysis of Wave Breaking and Overtopping at Upright Seawall

A wave breaking and an overtopping at an upright seawall are simulated based on the particle method, which is the Lagrangian gridless model completely different form the ordinary Eulerian ones. The behavior of a wave breaking and an overtopping has been well simulated by the MPS (Moving Particle Semi-implicit) method, which is categorized as the Lagrangian particle method. Especially, the existence of splash, which was difficult to be simulated by the former Eulerian methods such as the VOF, is clearly simulated by the MPS method. The difference of velocity fields for the different hydraulic conditions and the geometrical conditions of a crown of seawall has been numerically investigated. The overtopping quantities estimated by the MPS method show good agreement with the Godas experimental curve.