energies Article Experimental Study of a Moored Floating Oscillating Water Column Wave-Energy Converter and of a Moored Cubic Box Minghao Wu 1, * , Vasiliki Stratigaki 1, *, Peter Troch 1 , Corrado Altomare 1 , Tim Verbrugghe 1 , Alejandro Crespo 2 , Lorenzo Cappietti 3 , Matthew Hall 4 and Moncho Gómez-Gesteira 2 1 Department of Civil Engineering, Ghent University, Technologiepark 60, B-9052 Zwijnaarde, Belgium; peter.troch@ugent.be (P.T.); corrado.altomare@ugent.be (C.A.); timl.verbrugghe@UGent.be (T.V.) 2 Environmental Physics Laboratory, Universidade de Vigo, 36310 Pontevedra, Vigo, Spain; alexbexe@uvigo.es (A.C.); mggesteira@uvigo.es (M.G.-G.) 3 Department of Civil Engineering, Università degli Studi di Firenze - UniFI, Via di Santa Marta 3, 50139 Florence, Italy; lorenzo.cappietti@unifi.it 4 School of Sustainable Design Engineering, University of Prince Edward Island, Charlottetown, PE C1A 4P3, Canada; mthall@upei.ca * Correspondence: minghao.wu@ugent.be (M.W.); vicky.stratigaki@ugent.be (V.S.) Received: 24 April 2019; Accepted: 9 May 2019; Published: 15 May 2019   Abstract: This paper describes experimental research on a floating moored Oscillating Water Column (OWC)-type Wave-Energy Converter (WEC) carried out in the wave flume of the Coastal Engineering Research Group of Ghent University. This research has been introduced to cover the existing data scarcity and knowledge gaps regarding response of moored floating OWC WECs. The obtained data will be available in the future for the validation of nonlinear numerical models. The experiment focuses on the assessment of the nonlinear motion and mooring-line response of a 1:25 floating moored OWC WEC model to regular waves. The OWC WEC model motion has 6 degrees of freedom and is limited by a symmetrical 4-point mooring system. The model is composed of a chamber with an orifice on top of it to simulate the power-take-off (PTO) system and the associated damping of the motion of the OWC WEC model. In the first place, the motion response in waves of the moored floating OWC WEC model is investigated and the water surface elevation in the OWC WEC chamber is measured. Secondly, two different mooring-line materials (iron chains and nylon ropes) are tested and the corresponding OWC WEC model motions and mooring-line tensions are measured. The performance of these two materials is similar in small-amplitude waves but different in large wave-amplitude conditions. Thirdly, the influence of different PTO conditions is investigated by varying the diameter of the top orifice of the OWC WEC model. The results show that the PTO damping does not affect the OWC WEC motion but has an impact on the water surface elevation inside the OWC chamber. In addition, an unbalanced mooring configuration is discussed. Finally, the obtained data for a moored cubic model in waves are presented, which is a benchmarking case for future validation purposes. Keywords: moored floating wave-energy converter; oscillating water column; wave flume experiment; nonlinear wave condition; 6 degrees of freedom motion; mooring-line tension 1. Introduction The Oscillating Water Column (OWC) is a Wave-Energy Converter (WEC) which mainly consists of a hollow chamber, open below the water level, in which a column of water is forced to oscillate once excited by the external incident waves. The oscillation of water surface inside the chamber Energies 2019, 12, 1834; doi:10.3390/en12101834 www.mdpi.com/journal/energies