Efficiency and Survivability of a Floating Oscillating Water Column Wave Energy Converter Moored to the Seabed: An Overview of the EsflOWC MaRINET2 Database

Dogan Kisacik,Peter Stansby,José Domínguez,Vasiliki Stratigaki,Moncho Gómez-Gesteira,Irene Simonetti,Matthew Hall,Ricardo Birjukovs Canelas,Alejandro Crespo,Minghao Wu,Corrado Altomare,Peter Troch,Lorenzo Cappietti

doi:10.3390/w12040992

Abstract

Floating oscillating water column (OWC) type wave energy converters (WECs), compared to fixed OWC WECs that are installed near the coastline, can be more effective as they are subject to offshore waves before the occurrence of wave dissipation at a nearshore location. The performance of floating OWC WECs has been widely studied using both numerical and experimental methods. However, due to the complexity of fluid–structure interaction of floating OWC WECs, most of the available studies focus on 2D problems with WEC models of limited degrees-of-freedom (DOF) of motion, while 3D mooring effects and multiple-DOF OWC WECs have not been extensively investigated yet under 2D and 3D wave conditions. Therefore, in order to gain a deeper insight into these problems, the present study focuses on wave flume experiments to investigate the motion and mooring performance of a scaled floating OWC WEC model under 2D wave conditions. As a preparatory phase for the present MaRINET2 EsflOWC (efficiency and survivability of floating OWC) project completed at the end of 2017, experiments were also carried out in advance in the large wave flume of Ghent University. The following data were obtained during these experimental campaigns: multiple-DOF OWC WEC motions, mooring line tensions, free surface elevations throughout the wave flume, close to and inside the OWC WEC, change in the air pressure inside the OWC WEC chamber and velocity of the airflow through the vent on top of the model. The tested wave conditions mostly include nonlinear intermediate regular waves. The data obtained at the wave flume of Ghent University, together with the data from the EsflOWC tests at the wave flume of LABIMA, University of Florence, provide a database for numerical validation of research on floating OWC WECs and floating OWC WEC farms or arrays used by researchers worldwide.

Highlights

Oscillating water column (OWC) wave energy converters (WECs) consist of a partially submerged reservoir with a water column and a column of trapped air
For fixed onshore oscillating water column (OWC) WECs, the incident waves that propagate towards the shallow coastal waters lose part of their energy content due to dissipation mechanisms arising from the wave-bottom interaction
Offshore floating OWC WECs can be a better option in order to exploit a higher wave energy potential

Summary

Introduction

Oscillating water column (OWC) wave energy converters (WECs) consist of a partially submerged reservoir with a water column (open to the sea below the waterline) and a column of trapped air. The incident waves change the water level inside the reservoir, which in turn compresses and decompresses the air column. This trapped air is allowed to flow to and from the atmosphere through a turbine where its rotation is used to generate electricity. OWC WECs can be classified as fixed (onshore) or floating (offshore). For fixed onshore OWC WECs, the incident waves that propagate towards the shallow coastal waters lose part of their energy content due to dissipation mechanisms arising from the wave-bottom interaction. One of the main challenges is related to the mooring system in terms of the lifetime of the floating OWC WEC under extreme wave conditions and implications in the device efficiency. The floating OWC WECs must be able to cope with a wide range of realistic wave conditions, maintaining efficiency despite a significant variation of the incoming wave power flux

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