회절을 고려한 장대구조물에 작용하는 파력 예측

Abstract

In this study, analytical solutions for the wave force acting on a vertical-type breakwater are suggested considering diffraction. A semi-infinite breakwater is analyzed. The wave force of a regular wave on a vertical breakwater is investigated considering diffraction in front of the vertical breakwater and on the lee side of the vertical breakwater. A comparison of the term of included in Goda’s formula and the diffraction effect is described in this paper. The relative wave force acting on a breakwater is 0.5 for diffraction when the incident wave angle is 90° and this is consistent with Goda’s formula. The wave forces as functions of incident wave angle and position on the breakwater are suggested. The wave forces acting on vertical porous breakwaters are also investigated in this research. A new analytical solution of the wave force is derived that additionally considers the transmission and reflection rate of the breakwater and the transmission of diffracting waves. The results of the analytical solution have good agreement with the results of the numerical model of the Boussinesq equations. The relationship of the wave force to the porosity, inertia coefficient, and friction coefficient are described in the research. An analytical solution of the wave force acting on long structures is also suggested in this study. The wave forces on long structures are evaluated for monochromatic, uni-directional random, and multi-directional random waves. The analytical solution of Penney and Price (1952) is used to generate diffracting waves. Diffraction effects in front of the breakwater and on the lee side of the breakwater are considered. The wave force on a long structure becomes zero when the relative length of the breakwater is zero. The diffraction effects are relatively strong when the relative length of the breakwater is less than 1.0, and the wave forces decrease greatly for long structure when the relative length of the breakwater is larger than 0.5. Therefore, it is necessary to consider diffraction effects when the relative length of the breakwater is less than 1.0, and the relative length of the breakwater must be at least 0.5 in order to obtain a reduction of wave force on long structures.