Mooring Analysis of a Floating OWC Wave Energy Converter

Alana Pols,Eric Gubesch,Christopher Chin,Irene Penesis,Nagi Abdussamie

doi:10.3390/jmse9020228

Abstract

This investigation focuses on the modelling of a floating oscillating water column (FOWC) wave energy converter with a numerical code (ANSYS AQWA) based on potential flow theory. Free-floating motions predicted by the numerical model were validated against experimental data extrapolated from a 1:36 scale model device in regular and irregular sea states. Upon validation, an assessment of the device’s motions when dynamically coupled with a four-line catenary mooring arrangement was conducted at different incident wave angles and sea states ranging from operational to survivable conditions, including the simulation of the failure of a single mooring line. The lack of viscosity in the numerical modelling led to overpredicted motions in the vicinity of the resonant frequencies; however, the addition of an external linear damping coefficient was shown to be an acceptable method of mitigating these discrepancies. The incident wave angle was found to have a limited influence on the magnitudes of heave, pitch, and surge motions. Furthermore, the obtained results indicated that the mooring restoring force is controlled by the forward mooring lines under the tested conditions.

Highlights

Global interest in the renewable energy industry has steadily increased in recent years, as the fossil fuel industry continues to take criticism with regard to the ongoing environmental impact
Three wave probes were positioned within the basin, and additional six wave probes were attached to the floating oscillating water column (FOWC) model: five within the chamber and one on the front face
The experimental response amplitude operators (RAOs) were derived from results in which the device was moored with the horizontal soft mooring system, the influence of such moorings on the heave and pitch motions was found to be negligible

Summary

Introduction

Global interest in the renewable energy industry has steadily increased in recent years, as the fossil fuel industry continues to take criticism with regard to the ongoing environmental impact. With oceans covering 71% of the earth’s surface, there is a large potential for ocean renewable energy (ORE) to become a viable alternative method of energy production. The main sources of ORE are wave, tidal, and non-tidal ocean currents and offshore wind. An estimate of the wave energy potential for Australia’s southern coastline is 1300 TWh/year, which is roughly five times the nation’s energy requirements [1]. There are currently over 1000 wave energy conversion (WEC) devices with patents worldwide [2], with the majority falling into one of four main device categories: oscillating water columns (OWCs), overtopping devices, pressure differential devices, and wave activated buoys [3]. OWC devices have been suggested to have the highest ratio in terms of efficiency per characteristic width [4] and will be the focus of this investigation

Methods

Results

Conclusion