Abstract
The possibility of absorbing wave energy using a submerged balloon fixed to the sea bed is investigated. The balloon is in the form of a fabric encased within an array of meridional tendons which terminate at a point at the top of the balloon and at some radius at the bottom. The expansion and contraction of the balloon in waves pump air via a turbine into and out of a chamber of constant volume. A more refined model than that used by Kurniawan and Greaves [Proc. Second Offshore Energy and Storage Symp., 2015] predicts a similarly broad-banded response, but the maximum absorption is less than previously predicted. Both approaches are compared and discussed.
Highlights
To optimally absorb energy from ocean waves, it is well-known that a wave energy device needs to oscillate with optimum amplitude and phase [1, 2]
The device needs to operate as close as possible to the two optimum conditions not just for a single wave amplitude and a single wave period, but for a range of wave amplitudes and periods, typically from 5 to 15 seconds. This challenge is pertinent for point absorbers, which by definition are much smaller than the incident wavelengths [3]
A conventional rigid-bodied point absorber has an inherently narrow resonance bandwidth and without any phase control is not able to capture a significant portion of energy available beyond its natural period
Summary
To optimally absorb energy from ocean waves, it is well-known that a wave energy device needs to oscillate with optimum amplitude and phase [1, 2]. The device needs to operate as close as possible to the two optimum conditions not just for a single wave amplitude and a single wave period, but for a range of wave amplitudes and periods, typically from 5 to 15 seconds This challenge is pertinent for point absorbers, which by definition are much smaller than the incident wavelengths [3]. The mode shape was taken as the difference between the static profile of the tendons at the mean pressure and that at a slightly different pressure Such approach predicted a broad-banded response whose magnitudes were almost proportional to the volume of the chamber. The purpose of this paper is to extend the previous analysis to allow the tendons to deform more naturally without any apriori assumption on the mode of deformation Both the previous and the present approaches rely on the prediction of the static behaviour of the balloon in still water, and this will be first examined.
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