RIASSUNTO
ABSTRACT
This paper studies, through physical model experiments, the attenuation performance of a new type of box-type free-surface breakwater with symmetrical wavy bottom. A series of experiments were carried out with changing the box immersion depth and the wave steepness. The transmission coefficient, reflection coefficient and energy dissipation coefficient versus B/L (B is model width and L is wave length) with different immersion depth and wave steepness were showed. The research results show that the transmission coefficient of the symmetrical wavy-bottom free-surface breakwater is obviously affected by the immersion depth and less affected by the wave steepness, the reflection coefficient is just the opposite. In addition, the symmetrical wavy-bottom free-surface breakwater has a stronger energy dissipation for longer wavelengths. Box-type free-surface breakwater with symmetrical wavy bottom has better wave attenuation performance than flat bottom.
INTRODUCTION
Breakwater, as an oceanic protection facility at ports, wharves and coasts, could maintain the even operation environment through decreasing waves which transfer from the offshore to the inshore. Compared with the traditional bottom-mounted dam breakwater, free-surface breakwater adapts to the characteristics of wave energy distribution. According to the different main structures of the free-surface breakwater, it can be divided into box type, pontoon type, raft type and other types (Shen et al. 2016). The design and manufacture of box-type free-surface breakwater is simple and easy, and the cost is relatively low. In addition to wave attenuation, box-type free-surface breakwaters can sometimes double as roads, warehouses, anchor boats, or fishing pier (Dong 2009). Based on the above advantages, box-type free-surface breakwater has been widely concerned and researched, and is gradually applied to engineering projects (Arami et al. 2006).
The bottom of the box-type free-breakwaters are mainly flat contour. Yan et al. (2005) used the characteristic function method to analyze the wave attenuation performance of a single box-type free-surface breakwater, a mathematical model of the interaction between a single box-type free-surface breakwater and waves was established, hydrodynamic performance of a single box-type free-surface breakwater was analyzed by solving the velocity potentials of each part of the watershed. Subramaniam and Al-Banaa (2014) studied the variation of the transmission, reflection, and energy dissipation coefficients of a single box-type free-surface breakwater with the relative width, and found that with the increase of the relative width, the transmission coefficient of the breakwater gradually decreased, while the reflection and energy dissipation coefficients gradually increased. Williams and Abul-Azm (1997) studied the hydrodynamic performance of the dual box-type free-surface breakwater based on the potential flow theory and applied the boundary element method, the research showed that the dual box-type form can improve the wave attenuation effect of the breakwater.