The wave attenuation characteristics of two surface-piercing fixed box structures are studied by the Desingularized Boundary Integral Equation Method (DBIEM). The accuracy analysis of DBIEM is carried out by comparing with the experimental results of a single fixed box. Considering the effect of such main factors as the relative width w/ h (box width w, water depth h ), the relative draft d / h (box draft d ) and the relative gap size S / h (gap size S ) of two boxes, calculate the wave fields that regular waves propagate through two box structures, and show the curves of transmission coefficients and reflection coefficients versus dimensionless parameter kh (wavenumber k ) or 2L /λ (two boxes space L, wavelength λ ). The Bragg resonance is also paid attention to, especially to the shift characteristics of Bragg condition where Bragg resonance would occur. This study is a primary step for next to improve the wave attenuation performance of free surface breakwater by taking advantage of Bragg resonance.

INTRODUCTION

As a kind of protective facility for coastal and offshore construction, breakwater is mainly used to attenuate waves and reduce the impact of waves on coastal and offshore constructions. Breakwater mainly includes bottom mounted breakwater and free surface breakwater according to the location of main body. The free surface breakwater has gained more attention in recent years. Its main body locates near free surface where the wave energy is concentrated, and its effect on water circulation and coastal erosion is relatively weak. It also could be applicable to deep water and soft geological seabed area.

A box-type is usually a basic configuration of free surface breakwater main body. Abul-azm and Gesraha (2000) used the eigenfunction expansion method to analyze the interaction between the single surfacepiercing fixed box and the oblique linear incident waves under the finite water depth, and obtained the corresponding linear analytical solution. Huang et al. (2014) conducted a comparative experimental study of the wave attenuation characteristics of a rectangular free surface breakwater between with and without slotted barriers. Delavari and Mostafa Gharabaghi (2017) used the weakly compressible smoothed particle hydrodynamic method to analyze the wave scattering by a free surface box-type breakwater. The reflection coefficients and the dynamic response of the breakwater were compared with the experimental results.

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