ABSTRACT

For developing an OWC device to capture wave energy efficiently, it is important to investigate its hydrodynamic performance and even could do some amelioration. To against a large wave force on OWC device as storm wave impacts, Tsai (2016) proposed an improved OWC device which is installed by a nonconventional wave damping structure in front of OWC chamber. The improved OWC was purposed to not only reduce the wave force impact but also promote the wave energy capture. This study conducted preliminary experiments in a wave flume to investigate the hydrodynamic characteristics of the improved OWC, including the wave pressure on the front wall of OWC chamber, the oscillating water column profile, and the airflow velocity generating by OWC. The experimental results showed that the improved OWC has better hydrodynamic performance than the conventional OWC and a U-shaped OWC.

INTRODUCTION

Nowadays, it has gradually become an important issue all over the world in seeking clean, pollution-free and sustainable use of renewable energy, even the development of new technologies. Wave power is one of the considerable renewable energies. Wave power means that uses various types of devices to capture wave energy and convert it into electrical power, in which the Oscillating Water Column (OWC) device is evidently one of the most efficiency. The OWC device consists of a chamber partially submerged and an air-duct connecting the chamber to the atmosphere. The periodic motion of the waves causes the water column oscillating in the chamber, and then sucks and extrudes air to drive a self-rectifying turbine.

A large number of studies have investigated the hydrodynamic characteristics of OWC devices since 1970's. Evans (1978) derived a simple approximate analytical solution based on small amplitude wave theory for the efficiency of wave energy absorption of an OWC device. Also based on the linear water wave theory, Evans and Porter (1995) investigated hydrodynamic properties of OWC device consisting of a thin vertical surface-piercing barrier next to a vertical wall in finite depth water. Weber and Thomas (2000) extended the theory of Evans (1995) by modelling into the importance of the air chamber design of an OWC device. Thanks to the development of computational fluid dynamics, many studies carried out numerical simulations for investigating the hydrodynamic and aerodynamic characteristics of OWC devices in recent years. Zhang et al. (2007) presented a numerical method to investigate the effect of the various wave conditions and configuration of the OWC chamber on the efficiency of wave energy extraction. Liu et al. (2008) and Liu et al. (2009) explored the effect of the nozzle at the opening of the OWC device on the energy extraction efficiency by Fluent CFD software. Also by using Fluent code, Marhani et al. (2008) devoted to simulate the flow characteristics of the components of an OWC system. Iturrioz et al. (2014) employed OpenFOAM code to simulate the hydrodynamic characteristics and efficiency of different aperture sizes of a fixed detached OWC towards a floating multi-chamber device. Ning et al. (2015) investigated the hydrodynamic performance of an OWC device using a fully nonlinear higher-order boundary element method. Based on Fluinco model, Torres et al. (2016) presented a hydrodynamic-aerodynamic coupled model to investigate the turbine power output of an OWC device.

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