Wave Energy Converter

Abstract

A wave energy convertor for extracting energy from ocean waves. The wave energy convertor may include a buoy arranged to oscillate relative to a reference point about an equilibrium position and a negative spring device connected between the buoy and the reference point, wherein the negative spring device is for applying a positive force in the direction of displacement when the buoy moves away from the equilibrium position.

I claim: 
     
         1 .- 30 . (canceled) 
     
     
         31 . A method of extracting energy from ocean waves comprising: allowing a buoy to oscillate, due to wave motion, about an equilibrium position relative to a reference point; and using a negative spring device in the form of at least one mechanical spring, providing a positive force between the buoy and the reference point when the buoy moves away from the equilibrium position, the positive force being in a direction of displacement between the buoy and the equilibrium position. 
     
     
         32 . A method as claimed in  claim 31 , comprising, when the displacement of the buoy away from the equilibrium position is greater than a threshold displacement, providing a positive force between the buoy and the reference point in the direction opposite to a direction of displacement between the buoy and its equilibrium position. 
     
     
         33 . A method as claimed in  claim 31 , wherein the negative spring device is used to counteract the hydrostatic stiffness of the buoy such that the total stiffness of the buoy at the equilibrium position is reduced compared to the buoy without the negative spring. 
     
     
         34 . A method as claimed in  claim 33 , wherein the total stiffness of the buoy at the equilibrium position is reduced by at least a factor of five compared to the buoy without the negative spring. 
     
     
         35 . A method as claimed in  claim 33 , wherein the negative spring device is used to counteract the hydrostatic stiffness of the buoy in order to thereby increase the bandwidth of resonant oscillation of the buoy. 
     
     
         36 . A wave energy convertor for extracting energy from ocean waves in accordance with the method of  claim 31 , the wave energy converter comprising: a buoy arranged to oscillate relative to a reference point about an equilibrium position; and a negative spring device connected between the buoy and the reference point, wherein the negative spring device comprises at least one mechanical spring for applying a positive force in the direction of displacement when the buoy moves away from the equilibrium position. 
     
     
         37 . A wave energy convertor as claimed in  claim 36 , wherein the negative spring device is configured to provide a zero force in a direction of oscillatory motion of the buoy when the buoy is at its equilibrium position. 
     
     
         38 . A wave energy convertor as claimed in  claim 36 , wherein the negative spring device is configured to provide a force that is initially in the same direction as the direction of displacement and increases with the magnitude of displacement of the buoy when the buoy moves away from the equilibrium position, and wherein the negative spring device is further configured such that when the displacement of the buoy away from the equilibrium position is greater than a threshold displacement, then the negative spring device provides a positive force between the buoy and the reference point in the direction opposite to the direction of displacement between the buoy and its equilibrium position. 
     
     
         39 . A wave energy convertor as claimed in  claim 36 , wherein the negative spring device acts to counteract the hydrostatic stiffness of the buoy, when the buoy is in use, such that the total stiffness of the buoy at the equilibrium position is reduced compared to the buoy without the negative spring. 
     
     
         40 . A wave energy convertor as claimed in  claim 39 , wherein the total stiffness of the buoy at the equilibrium position is reduced by at least a factor of five compared to the buoy without the negative spring. 
     
     
         41 . A wave energy convertor as claimed in  claim 31 , wherein the negative spring device acts to counteract the hydrostatic stiffness of the buoy, in use, in order to thereby increase the bandwidth of resonant oscillation of the buoy. 
     
     
         42 . A wave energy convertor as claimed in  claim 36 , wherein the mechanical spring is a coil spring, a torsion spring, a gas spring, a pneumatic spring or a hydraulic spring. 
     
     
         43 . A wave energy convertor as claimed in  claim 36 , comprising multiple negative spring devices. 
     
     
         44 . A wave energy convertor as claimed in  claim 36 , wherein each/the negative spring device comprises a set of springs. 
     
     
         45 . A wave energy convertor as claimed in  claim 44 , wherein the set of springs comprises a V-shaped pair of angled springs that, at the equilibrium position, are symmetrically arranged about a perpendicular to the direction of motion and lie in the same plane as the direction of motion and the perpendicular thereto. 
     
     
         46 . A wave energy convertor as claimed in  claim 31 , wherein the reference point is provided on a support member, the buoy being configured to oscillate relative to the support member; and wherein the buoy is configured to undergo rotational oscillation with an angular displacement about a pivot point external to the buoy. 
     
     
         47 . A wave energy convertor as claimed in  claim 46 , wherein the negative spring device is coupled between the centre of the buoy and the reference point. 
     
     
         48 . A wave energy convertor as claimed in  claim 47 , wherein the negative spring device is connected between the buoy and the reference point by a coupling for hinged rotation of the negative spring device relative to the buoy and the reference point during the oscillating movement of the buoy. 
     
     
         49 . A wave energy convertor as claimed in  claim 48 , wherein the reference point is at, or close to, any position along a line connecting the equilibrium position and the pivot point. 
     
     
         50 . A method of extracting energy from ocean waves comprising use of a wave energy converter as claimed in  claim 36 .