Assessing the efficiency of a distensible-tube wave attenuator at three different scales considering aero and hydro-elastic effects
Assessing the efficiency of a distensible-tube wave attenuator at three different scales considering aero and hydro-elastic effects
A water-filled floating distensible tube connected to a forward-bent oscillating water column is here considered in the context of harnessing energy from sea waves. Based on wave-tank experiments conducted at three different scales, under intermediate and deep-water incident regular waves of small and finite amplitudes, the present study addresses important aspects that determine the energy capture-width of the system. The comparison be- tween the results obtained at the three scales reveals non-linear and aero-hydroelastic scale effects inherent in modelling the device. The following issues are also tackled: (i) the occurrence of various working modes of the floating tube and their contribution to its performance; (ii) the compressibility of the airflow through the orifice power take-off system; (iii) the viscous-effects associated with the Reynolds and Keulegan-Carpenter numbers. The parameters that govern the system’s efficiency are the tube’s length, the OWC natural period and the bulge wave tuning period. The system becomes very efficient not only at the OWC resonance, but also when the incident wavelength is equal to or twice the tube’s length. Video frames further provide evidence of the rela- tionship between the tube’s working modes and its performance. An iterative algorithm based on Buckingham’s formula, with an empirical expansibility factor, provides adequate estimates of the compressible flow through the power take-off. Viscous losses closely related to the Reynolds and Keulegan-Carpenter numbers are found to be important even for waves with moderate steepness. Finally, the experiments suggest that a single distensible- tube system in open sea has a maximum capture-width of no more than 2 tube-diameters.
Air compressibility, Distensible tube, Scale effects, Wave energy, Wave-tank tests
Mendes, Antonio C.
9bd6a10d-c97d-4df5-8859-3666b45c4bca
Braga, Francisco P.
eb2e8e04-3c27-4e10-841c-34e0181b057b
Chaplin, John R.
d5ed2ba9-df16-4a19-ab9d-32da7883309f
December 2023
Mendes, Antonio C.
9bd6a10d-c97d-4df5-8859-3666b45c4bca
Braga, Francisco P.
eb2e8e04-3c27-4e10-841c-34e0181b057b
Chaplin, John R.
d5ed2ba9-df16-4a19-ab9d-32da7883309f
Mendes, Antonio C., Braga, Francisco P. and Chaplin, John R.
(2023)
Assessing the efficiency of a distensible-tube wave attenuator at three different scales considering aero and hydro-elastic effects.
Applied Ocean Research, 141, [103792].
(doi:10.1016/j.apor.2023.103792).
Abstract
A water-filled floating distensible tube connected to a forward-bent oscillating water column is here considered in the context of harnessing energy from sea waves. Based on wave-tank experiments conducted at three different scales, under intermediate and deep-water incident regular waves of small and finite amplitudes, the present study addresses important aspects that determine the energy capture-width of the system. The comparison be- tween the results obtained at the three scales reveals non-linear and aero-hydroelastic scale effects inherent in modelling the device. The following issues are also tackled: (i) the occurrence of various working modes of the floating tube and their contribution to its performance; (ii) the compressibility of the airflow through the orifice power take-off system; (iii) the viscous-effects associated with the Reynolds and Keulegan-Carpenter numbers. The parameters that govern the system’s efficiency are the tube’s length, the OWC natural period and the bulge wave tuning period. The system becomes very efficient not only at the OWC resonance, but also when the incident wavelength is equal to or twice the tube’s length. Video frames further provide evidence of the rela- tionship between the tube’s working modes and its performance. An iterative algorithm based on Buckingham’s formula, with an empirical expansibility factor, provides adequate estimates of the compressible flow through the power take-off. Viscous losses closely related to the Reynolds and Keulegan-Carpenter numbers are found to be important even for waves with moderate steepness. Finally, the experiments suggest that a single distensible- tube system in open sea has a maximum capture-width of no more than 2 tube-diameters.
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Assessing the Efficiency of a Distensible-Tube Wave Attenuator at Three Different Scales Considering Aero and Hydro-elastic Effects
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Accepted/In Press date: 28 October 2023
e-pub ahead of print date: 17 November 2023
Published date: December 2023
Additional Information:
Funding Information:
The present study was carried out at the Laboratory of Fluid Mechanics and Turbomachinery of Universidade da Beira Interior, in Portugal, in close collaboration with the University of Southampton in the UK. It follows the work done under FCT Project PTDC/EME-MFE/111763, developed within the framework of the Programme COMPETE, partially funded by the Portuguese Foundation for Science and Technology and the European Union. The support of FCT and UBI in the research activities are acknowledged, as well as the skills and goodwill of Mr. Morgado in the manufacture and testing of the physical models. The first author wishes to acknowledge the constant encouragement received from the late Professor Francis Farley, with whom fruitful discussions were held in Southampton on course of previous experiments.
Publisher Copyright:
© 2023 Elsevier Ltd
Keywords:
Air compressibility, Distensible tube, Scale effects, Wave energy, Wave-tank tests
Identifiers
Local EPrints ID: 485521
URI: http://eprints.soton.ac.uk/id/eprint/485521
ISSN: 0141-1187
PURE UUID: 3d47cdcc-9886-4ab7-a4a5-ee01b2d5c6b7
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Date deposited: 08 Dec 2023 17:30
Last modified: 18 Mar 2024 02:51
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Contributors
Author:
Antonio C. Mendes
Author:
Francisco P. Braga
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