Double wall wave barriers for small craft and marina applications

Wave protection for small craft harbours and marinas has for many years utilised floating breakwaters and/or vertical impermeable wave barriers or screens. Typically the wave barriers are not full depth but penetrate to a chosen ratio of the water depth consistent with the desired reduction in wave height in the lee of the structure. In recent years , for a range of reasons the vertical wave barriers supported on piles have been preferred over floating breakwaters. There have been quite a number of single panel barriers constructed successfully within Australia. More recently an additional vertical barrier appropriately spaced seaward of a more typical single barrier design has been adopted to reduce wave reflections to acceptable local environmental criteria - this design being developed after extensive 2D wave flume and 3D wave basin physical model testing. The interaction between the incident, transmitted and reflected waves and the barrier structure is a major concern of engineers in the design process. An eigenfunction expansion, numerical model is presented in the paper, which simulates wave interaction with a thin, vertical, double-walled, rigid wave barrier. The barrier partially penetrates the water column from the water surface down. The mathematical analysis is based on linear wave theory, supplemented by the appropriate external and internal boundary conditions to determine the velocity potential throughout the flow domain. The model predicts the influence of various wave barrier characteristics (such as wall penetration ratio and the spacing between the two walls) on the performance of the barrier over a broad range of water depths and wave conditions. The main advantage of this model is that the time variant solution across the flow domain allows wave forces and pile moments to be calculated.