In this paper, computational fluid dynamics (CFD) simulations are carried out for the purpose of finding the optimal design parameters of a spiral-reef overtopping device. In order to maximize the overtopping flow rate, geometrical parameters of the device were systematically examined in numerical computations. In all simulations, the commercial CFD program FLOW3D was used. In this study, regular waves with a period range of 4~6 seconds (which are very common in the Korean southern sea) are considered. In the first phase of the study, two-dimensional parameters including device ramp angle, ramp shape and draft were investigated. Fully three-dimensional CFD simulations were then conducted to understand wave flow over the device and the guide-vane effect on overtopping on it. The calculation results show different overtopping processes between 2D and 3D simulations, and optimal design parameters were identified based on numerical results. These findings can be incorporated in the design of an overtopping device to obtain better overtopping performance.
There are many kinds of wave energy converters. They can be categorized as being one of three basic types; a movable body type, an oscillating water column (OWC) type and a wave overtopping type. The overtopping type makes use of the potential energy of overtopping water via water turbines. Only a few overtopping wave energy converters have been studied. Among them, the Wave Dragon (Nielsen & Kofoed, 1997) is the most practical and pioneering model. It consists of two wave reflectors, a reservoir and a number of hydro turbines. The wave reflectors focus the incoming waves towards a ramp, and a reservoir captures the overtopping water above sea level. Low-head hydro turbines generate power by using the hydraulic head of the stored water. The Wave Dragon is a floating converter that is placed in an offshore area with a mooring line.