Study of wave interaction with vertical piles integrated with oscillating water columns

Abstract

Ocean wave energy is a source of abundant renewable and clean energy. However, a host of challenges including construction and maintenance costs and structural reliability have prevented the large-scale commercial application of ocean wave energy converters (WECs). Integrating WECs with shore-protection structures may significantly reduce the costs associated with wave energy utilization. One such integration is vertical piles integrated with oscillating water columns (OWCs), which can help achieve costs sharing and overcome the cost hurdles facing the wave energy industry. This study examines the performance of circular piles integrated with OWC devices (OWC-piles) in terms of wave energy extraction and wave scattering. Two configurations of OWC-piles, a loosely spaced configuration, and a closely spaced configuration, are investigated. For the loosely spaced configuration, the spacing is large enough so that the interference between adjacent OWC-piles can be ignored. So that the performance of the loosely spaced configuration can be studied by examining the performance of a standalone OWC-pile. In chapter 2, the performance of a standalone OWC-pile configuration is investigated theoretically, experimentally, and numerically. A quadratic power takeoff model is implemented in the study. The viscous loss associated with vortex shedding is discussed based on a comparison between the theoretical and experimental results. The possible effects of spatial non-uniformity including resonant sloshing are discussed. The performance of the loosely spaced configuration is discussed. In chapter 3, the study is extended to investigate experimentally the performance of a row of closely spaced OWC-piles in terms of wave energy extraction and wave scattering. A comparative evaluation of the performance of the proposed OWC-pile in both configurations are performed. In chapter 4, a computational fluid dynamics study is presented to understand the detailed hydrodynamics involved in the wave interaction with OWC-piles for both configurations. Chapter 5 reports an experimental study investigating the scour around a row of closely spaced piles without OWC device, which affects the safety of the pile structures, especially in extreme events such as tsunamis. The purpose of this study is to provide understanding of the scour induced by the unsteady jet flow created by the narrow gaps between piles. Future work includes a three-phase simulation of the sediment dynamics around OWC-pile structures, and numerical and experimental studies of the shore protection performance of the closely spaced OWC-piles. The three-phase flow model for these future research can be partially validated using data from chapter 5.