Performance of a distensible-tube wave attenuator in a slender focusing channel

A wave energy device utilizing a water-filled distensible tube aligned head to waves is analyzed. The wave-excited pressure bulges in the tube activate a stationary forward-bent circular oscillating water column (OWC) at its stern. This system has been extensively tested in wave-tank, at different scales. However, further improvements to its efficiency are possible. The present research assesses its performance at 1:20 scale, while operating in a slender focusing channel. Complementarily, two other situations are considered: one at the nearshore, where the system is assembled to a bottom-standing jacket structure, and an onshore design where the tube operates in front of a sea wall in constant depth or over a sloping bottom. Deep and intermediate regular waves of small and finite amplitudes are generated in the wave-tank, representing the wave climate in the Occidental Group of the Azores islands. A non-linear power take-off impedance is imposed by a set of calibrated orifice plates and its characteristic is then obtained assuming compressible airflow. Measurements of air pressure in the pneumatic chamber, OWC free-surface displacement, and incident wave-field provide estimates of energy capture-width, which are then compared with analytical predictions and benchmark test results. Photographs further help to understand the physics underlying the tube’s working modes. Moreover, the performance of the system is obtained with and without the tube and then compared with standard values for OWCs. It is demonstrated that the addition of a distensible tube and a suitable focusing channel can significantly improve the capacity factor of a conventional OWC system.

Ocean wave energy, Azores, Distensible tube, Focusing channel, Wave-tank tests

10.1007/s40722-023-00297-8

2198-6444

745-766

Mendes, Antonio C.

f7b162d3-2b06-45e7-be7a-5a1d964c2d87

Braga, Francisco P.

266099dd-0d7c-4911-aa15-f008904ccae3

Chaplin, John R.

d5ed2ba9-df16-4a19-ab9d-32da7883309f

Mendes, Antonio C.

f7b162d3-2b06-45e7-be7a-5a1d964c2d87

Braga, Francisco P.

266099dd-0d7c-4911-aa15-f008904ccae3

Chaplin, John R.

d5ed2ba9-df16-4a19-ab9d-32da7883309f

Mendes, Antonio C., Braga, Francisco P. and Chaplin, John R. (2023) Performance of a distensible-tube wave attenuator in a slender focusing channel. Journal of ocean Engineering and Marine Energy, 9 (4), 745-766. (doi:10.1007/s40722-023-00297-8).

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Accepted/In Press date: 2 August 2023

e-pub ahead of print date: 17 August 2023

Additional Information: Funding Information: The work was partially funded by the Portuguese Foundation for Science and Technology (FCT) and the European Union, within the framework of Programme COMPETE. The present study follows the work done under FCT Project PTDC/EME-MFE/111763, developed from 2012 to 2016 within the framework of the COMPETE Programme, partially funded by the Portuguese Foundation for Science and Technology and the European Union. The research was carried out in the experimental facilities of the Laboratory of Fluid Mechanics and Turbomachinery of Universidade da Beira Interior, in Portugal, with the collaboration of the University of Southampton in the UK. The authors are grateful to FCT and UBI for their support of the research activities. Furthermore, the valuable contribution of Mr. Morgado and of the Electromechanical Engineering Msc students that have helped to develop and assemble the experimental apparatus is acknowledged. The first author also wishes to acknowledge the valuable teachings of the late Professor Francis Farley, whose enthusiasm will always be remembered.

Keywords: Ocean wave energy, Azores, Distensible tube, Focusing channel, Wave-tank tests