## Abstract

The theoretical limit for absorption of energy in monochomatic water

waves of wavelength $\lambda$ by axisymmetric wave energy converters

operating in rigid-body motion was established in the 1970s. The

maximum mean power generated by a device absorbing due to heave motion is

equivalent to that contained in $\lambda/2\upi$ length of incident wave

crest. For devices absorbing through surge and/or pitch motions the

so-called capture width doubles to $\lambda/\upi$. For devices absorbing

in both heave and surge/pitch the capture width increases further to

$3\lambda/2\upi$. In this paper it is demonstrated it is theoretically

possible to extend the capture width for axisymmetric wave energy

converters without bound through the use of generalised (non-rigid body)

modes of motion. This concept will be applied to vertical cylinders whose

surface is surrounded by an array of narrow vertical absorbing paddles.

A continuum approximation is made to the paddle motion which simplifies the

problem and allows strategies to be developed for setting the springs

and dampers that control the power absorption. Results demonstrate

the main result: a cylinder of fixed size can absorb as much power as

demanded from a plane incident wave although there are practical

considerations which are also discussed. The continuum approximation

is tested against a discrete paddle simulation for accuracy.

waves of wavelength $\lambda$ by axisymmetric wave energy converters

operating in rigid-body motion was established in the 1970s. The

maximum mean power generated by a device absorbing due to heave motion is

equivalent to that contained in $\lambda/2\upi$ length of incident wave

crest. For devices absorbing through surge and/or pitch motions the

so-called capture width doubles to $\lambda/\upi$. For devices absorbing

in both heave and surge/pitch the capture width increases further to

$3\lambda/2\upi$. In this paper it is demonstrated it is theoretically

possible to extend the capture width for axisymmetric wave energy

converters without bound through the use of generalised (non-rigid body)

modes of motion. This concept will be applied to vertical cylinders whose

surface is surrounded by an array of narrow vertical absorbing paddles.

A continuum approximation is made to the paddle motion which simplifies the

problem and allows strategies to be developed for setting the springs

and dampers that control the power absorption. Results demonstrate

the main result: a cylinder of fixed size can absorb as much power as

demanded from a plane incident wave although there are practical

considerations which are also discussed. The continuum approximation

is tested against a discrete paddle simulation for accuracy.

Original language | English |
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Journal | Journal of Fluid Mechanics |

Publication status | Accepted/In press - 5 Jul 2021 |