ABSTRACT

This work presents a numerical investigation of the attenuator type of Wave Energy Converter (WEC) that uses the immersed ‘one-fluid’ formulation in two dimensions. In the ‘one-fluid’ framework, the multiple connected rigid bodies are treated as different phases of a fluid, and their motions are solved by a unified equation like those governing the air and water. The results suggest that the unified one-fluid equation can predict the dynamic response of the attenuator type of WEC.

INTRODUCTION

The potential for extracting and using the energy in waves is huge. Waves have the potential to provide a completely sustainable source of energy, which can be captured and converted into electricity by Wave Energy Converter (WEC) machines (Folley, 2016). In the last decade, many projects for development of WEC have emerged (Babarit, 2013). Attenuators received the most funding of any design (Hannon, 2017), for example, the Pelamis. The Pelamis is an offshore, floating, slack-moored wave energy converter consisting of a set of semi-submerged cylinders linked by hinged joints (Henderson, 2006). Ocean waves perform work on the Pelamis by moving cylinder section relative to each other across two degree of freedom joints. There is need to develop a predictive numerical tool for understanding of how multiple moving parts interact with each other and their environment.

The hydrodynamic interaction between WECs and ocean waves is complex nonlinear process and there is some simplified model, such as potential flow theory, which may be justified by the viscous and turbulent effects does not play a significant role. The frequency-domain models (Evans, 1982), time domain models (Damaren, 2000) and semi-analytical model (Child, 2010) is based on linear wave theory. Fully nonlinear potential wave equation can be solved by boundary element methods (Payne, 2008) for the WEC developments.

The simplification of the fluid using potential flow models limits the applications. With a significant advancement in computational fluid dynamics (CFD) and computing power, the use of CFD model is a viable approach for simulating the WECs. Ideally, the CFD model can be used to study the design, virtual testing parameters and optimise the dynamic response for different waves loading. However, the general WEC dynamics involves complex physical process which is still challenges for CFD modelling. The main practical limitation of CFD is the computational efficiency.

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