ROTATING WAVE ENERGY ABSORBER

Abstract

A wave energy absorber is provided for use with a wave energy converter, the absorber having one or more body portions arranged to engage hydrodynamically with a water flow from waves of a body of water, the one or more body portions having a rotational axis about which the one or more body portions are arranged to rotate. The one or more body portions are asymmetrical about the rotational axis. The present invention aims to provide an improved energy capturing member for use with the wave energy converter which allows a pressure difference to be created by the wave energy absorber that is ultimately converted into useful energy, done using a smaller and lighter structure.

Claims

1. A wave energy absorber, the absorber comprising: one or more body portions arranged to engage hydrodynamically with a water flow from waves of a body of water, the one or more body portions each comprising a rotational axis about which the body portion is arranged to rotate, the body portion being asymmetrical about the rotational axis.

2. The wave energy absorber of claim 1, wherein the absorber further comprises: a linkage arranged to couple the one or more body portions to a wave energy converter (WEC), the one or more body portions being rotatable about the rotational axis relative to the linkage.

3. The wave energy absorber of claim 2, wherein the linkage is arranged to define a cyclic trajectory of the rotational axis.

4. The wave energy absorber of claim 3, wherein the cyclic trajectory is an orbital trajectory.

5. The wave energy absorber of claim 3, wherein the one or more body portions comprises a plurality of angles of rotation about the rotational axis, the angles of rotation defining a rotation arc of the one or more body portions about the rotational axis.

6. The wave energy absorber of claim 5, wherein each of the plurality of angles of rotation corresponds to a flow direction of the flow of water impinging on a flow engaging surface of the one or more body portions.

7. The wave energy absorber of claim 6, wherein the one or more body portions are shaped to assume a rotational position about the rotational axis according to a direction of the impinging flow of water.

8. The wave energy absorber of claim 5, wherein the one or more body portion comprises a predefined array of the angles of rotation, each angle of rotation in the array is associated with a position of the rotational axis along the cyclic trajectory.

9. The wave energy absorber of claim 8, wherein the absorber further comprises an adjustment member arranged to urge a rotation of the one or more body portions according to the angle of rotation, the angle of rotation selected from the predefined array.

10. The wave energy absorber of claim 9, wherein the rotation by the adjustment member is arranged to be controlled by a controller.

11. The wave energy absorber of claim 1, wherein the one or more body portions comprises a hydrofoil shape.

12. The wave energy absorber of claim 1, wherein the one or more body portions of the absorber comprise: a first body portion having a first longitudinal axis; and a second body portion having a second longitudinal axis; each of the first and second body portions being rotatable about the rotational axis relative to one another.

13. The wave energy absorber of claim 12, wherein the first and second body portions are arranged to rotate about respective first and second loci on the rotational axis; wherein the first and second loci are collocated or proximate one another.

14. The wave energy absorber of claim 12, wherein the absorber further comprises a rotational actuator arranged to rotate the first and second body portions between a first position in which the first and second longitudinal axes are non-parallel, and a second position in which the first and second longitudinal axes are substantially parallel.

15. A wave energy converter system arranged to convert wave energy into useful energy, the system comprising: a buoyant platform; and a drive assembly mounted on the buoyant platform and arranged to capture and convert wave energy, the drive assembly comprising a wave energy absorber as claimed in any one of the preceding claims.

16. The system of claim 15, wherein the rotational axis of the one or more body portions of the wave energy absorber is positioned at a location relative to an upper surface of the buoyant platform.

17. The system of claim 16, wherein the drive assembly is arranged to adjust the location along a cyclic trajectory.

18. The system of claim 17, wherein the cyclic trajectory is an orbital trajectory.

19. The system of claim 17, wherein the adjustment of the location by the drive assembly is independent of a working stroke of the drive assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the detailed description herein, serve to explain the principles of the invention. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. The foregoing and other objects, features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

[0049] FIG. 1 shows a side view of an example WEC system in accordance with the second aspect comprising a wave energy absorber in accordance with the first aspect;

[0050] FIG. 2 shows an example cyclic (orbital) trajectory of the wave energy absorber of the embodiment of FIG. 1;

[0051] FIG. 3A shows a snapshot of a wave profile at a first point along the trajectory of FIG. 2, and both the wave propagation forces and water flow direction forces at the snapshot;

[0052] FIG. 3B shows a side view of a position of the system of FIG. 1 at the snapshot of FIG. 3A;

[0053] FIG. 4A shows a snapshot of a wave profile at a second point along the trajectory of FIG. 2, and both the wave propagation forces and water flow direction forces at the snapshot;

[0054] FIG. 4B shows a side view of a position of the system of FIG. 1 at the snapshot of FIG. 4A;

[0055] FIG. 5A shows a snapshot of a wave profile at a third point along the trajectory of FIG. 2, and both the wave propagation forces and water flow direction forces at the snapshot;

[0056] FIG. 5B shows a side view of a position of the system of FIG. 1 at the snapshot of FIG. 5A;

[0057] FIG. 6A shows a snapshot of a wave profile at a fourth point along the trajectory of FIG. 2, and both the wave propagation forces and water flow direction forces at the snapshot;

[0058] FIG. 6B shows a side view of a position of the system of FIG. 1 at the snapshot of FIG. 6A;

[0059] FIG. 7 shows a side view of an alternate example WEC system in accordance with the second aspect comprising a wave energy absorber in accordance with the first aspect; and

[0060] FIG. 8 shows a side view of a position of the system of FIG. 7 at a snapshot of a wave profile along a trajectory similar to that shown in FIG. 2.

DETAILED DESCRIPTION FOR CARRYING OUT THE INVENTION

[0061] All of the presently described embodiments comprise a wave energy absorber in accordance with the first aspect as part of a WEC system in accordance with the second aspect. The embodiments each have substantially the same general structure which is summarised briefly here. The system comprises a cylindrical buoyant platform supporting a drive assembly on an upper surface thereof. The drive assembly comprises a first lower pair of opposing elongate rigid lever arms coupled at one end at a lower hinge positioned centrally on the upper surface of the platform. The other end of each lever arm of the first lower pair is rotably affixed to one end of a corresponding rigid lever arm of a second upper pair of lever arms. The second upper pair of lever arms are coupled at an upper hinge. The drive assembly further comprises a wave energy absorber in accordance with the first aspect, affixed to the upper hinge. Each lever arm of the first lower pair of lever arms is affixed to an energy converter, which for illustrative purposes takes the form of hydraulic ram, but may comprise any suitable energy converter such as a rotational generator.

[0062] In use, the platform and the wave energy absorber are submerged in a body of water using a mooring and anchoring system (not shown). In the in-use configuration, the wave energy absorber is arranged to move following a substantially orbital trajectory as a result of wave forces impacting thereon. As the wave energy absorber moves, the consequential movement of the lever arms drives the corresponding energy converters.

[0063] The extent of the ability of the wave energy absorber to capture wave energy is generally proportional to the availability of wave forces acting on the device. For a wave energy absorber, the wave forces include a vertical component according to the crest and trough periods of a wave cycle, and a horizontal component according to the wave propagation direction. For a wave energy absorber which is designed to be submerged in-use, the wave forces also include an additional directional component corresponding to a direction of water particle flow occurring beneath the surface of the waves, which typically tracks an orbital trajectory throughout a wave cycle. In order to maximise capture of the wave energy available, the present invention aims to make optimum use of all the components of the directional forces available.

[0064] Referring to FIG. 1 and FIG. 2, a first embodiment 100 of the present invention is shown, and functions substantially as previously described. The embodiment 100 comprises a WEC system 100 in accordance with the second aspect comprising a buoyant platform 102 supporting a drive assembly 104 mounted on an upper surface thereof. The drive assembly 104 comprises a first lower pair of rigid lever arms 106 and a second upper pair of rigid lever arms 108 as previously described. The drive assembly 104 comprises energy converters 110 affixed to the lower pair of lever arms 106. Coupled to the second pair of lever arms 108, the drive assembly 104 further comprises a wave energy absorber 112. In the embodiment 100 shown, the absorber 112 comprises a single hydrofoil body portion having a positively body 114 and an elongate metal appendage 116 extending from a position thereof closer to a leading edge 117 of the hydrofoil body 114. The absorber 112 further comprises an adjustment mechanism (not shown) which comprises a motor arranged to be driven electrically according to a controller. In an in-use configuration as shown in FIG. 1, the motor of the adjustment mechanism is arranged to drive a rotation of the body portion 114, 116 about a rotational axis 121 thereof. In the in-use configuration shown, the rotational position of the hydrofoil body 114 provides an optimal angle of attack relative to a water flow direction 115 of water impinging on the leading edge thereof, such that the body 114 maximises hydrodynamic lift 119 causing the body 114 to drive the rotational axis thereof in an upward motion, extending the lever arms 106, 108 of the drive assembly 104 to drive the energy converters 110.

[0065] The angle of attack would be expected to reach a steady equilibrium during the unidirectional flow 115 shown, however as the water flow is generated by waves, the direction of the subsurface water flow is constantly changing in a circular or orbital pattern. Therefore, the body 114 is able to rotate about the rotational axis 121, maintaining a consistent angle of attack with the water flow.

[0066] The hydrofoil body 114 generates a lift force which pulls the rotational axis 121 in the same direction; as the direction of the lift force is changing in circular cycle caused by the waves (and the corresponding subsurface flow), the rotational axis 121 is caused to move in an orbital path 121 as shown FIG. 2. This orbital motion is exploited by the drive assembly 104 to generate power.

[0067] Referring to FIG. 2, an overall expected orbital trajectory 120 of the rotational axis 121 of the body portion 114, 116 is shown, along which the rotational axis 121 will travel throughout a wave cycle of the body of water in which the system 100 is submerged.

[0068] The embodiment 100 is shown in use in FIG. 3A to FIG. 6B. FIGS. 3A, 4A, 5A and 6A pictorially represent a snapshot of a wave profile of a body of water in which the embodiment 100 is submerged, at a specific point during a wave cycle. Throughout FIGS. 3A, 4A, 5A and 6A, the wave profile 122 is propagated 124 continuously in a principal horizontal direction, while the subsurface water particle flow direction 126 changes throughout the wave cycle following a circular, or orbital, pattern. FIGS. 3B, 4B, 5B, and 6B each show a corresponding position of the embodiment 100 at the snapshot, and when presented by wave forces acting at the snapshot and throughout the wave cycle.

[0069] Referring to FIG. 3A, the wave profile 122 is such that subsurface water particle flow forces 126 act in a principally vertical upward direction, such that the hydrofoil body 114 in FIG. 3B of the absorber 112 is oriented with the flow engaging surface of the leading edge 117 positioned opposing the principal directional forces 126 such that hydrodynamic lift is provided in a left direction (relative to the depiction shown) driving the rotational axis 121 of the absorber 112 along the orbital trajectory 120 to the left. Such movement of the absorber 112 causes a corresponding movement of the drive assembly 104 and a consequential driving of a portion of a working stroke of the corresponding energy converters 110 relative to the extent of the movement.

[0070] Referring to FIG. 4A, the wave profile 122 is such that subsurface water particle flow forces 126 act in a principally horizontal right direction, such that the hydrofoil body 114 in FIG. 4B of the absorber 112 is oriented with the flow engaging surface of the leading edge 117 positioned opposing the principal directional forces 126 such that hydrodynamic lift is provided in a upwards direction (relative to the depiction shown) driving the rotational axis 121 of the absorber 112 along the orbital trajectory 120 upwards, and thus completing a half-cycle of the orbital trajectory 120 of the rotational axis 121. Such movement of the absorber 112 causes a corresponding movement of the drive assembly 104 and a consequential driving of a portion of a working stroke of the corresponding energy converters 110 relative to the extent of the movement.

[0071] Referring to FIG. 5A, the wave profile 122 is such that subsurface water particle flow forces 126 act in a principally vertical downward direction, such that the hydrofoil body 114 in FIG. 5B of the absorber 112 is oriented with the flow engaging surface of the leading edge 117 positioned opposing the principal directional forces 126 such that hydrodynamic lift is provided in a right direction (relative to the depiction shown) driving the rotational axis 121 of the absorber 112 along the orbital trajectory 120 to the right. Such movement of the absorber 112 causes a corresponding movement of the drive assembly 104 and a consequential driving of a portion of a working stroke of the corresponding energy converters 110 relative to the extent of the movement.

[0072] Referring to FIG. 6A, the wave profile 122 is such that subsurface water particle flow forces 126 act in a principally horizontal left direction, such that the hydrofoil body 114 in FIG. 6B of the absorber 112 is oriented with the flow engaging surface of the leading edge 117 positioned opposing the principal directional forces 126 such that hydrodynamic lift is provided in a downwards direction (relative to the depiction shown) driving the rotational axis 121 of the absorber 112 along the orbital trajectory 120 downwards, and thus completing a cycle of the orbital movement 120 of the rotational axis 121. Such movement of the absorber 112 causes a corresponding movement of the drive assembly 104 and a consequential driving of a portion of a working stroke of the corresponding energy converters 110 relative to the extent of the movement.

[0073] In describing the movement of the absorber 112 in the present embodiments, the terms left, right, upwards and downwards are used. These terms will be understood in the context of the exemplary two-dimensional depictions shown in the present figures, and it will be appreciated that such terms may refer in practice to a more complex movement in any relative direction corresponding to a three-dimensional absorber in-use.

[0074] The embodiment 100 shown has a body 114 which is rotated by a controller (not shown) actuating a motor. The controller is arranged to rotate the body 114 by the motor based on a corresponding position of the rotational axis 121 along the orbital path 120. Thereby, the controller is arranged to optimise driving of the working stroke by maximising hydrodynamic lift in a required direction. Other embodiments may include a flow direction sensor which may inform the controller of a water flow direction, such that a corresponding adjustment of the rotation may be performed in order to optimise the hydrodynamic lift in a desired direction. Additionally, embodiments may be envisaged comprising a sea state monitor or a wave force sensor arranged to detect excessive sea forces which may lead to damage to the drive assembly through excessive or chaotic movement of the absorber 112. In such embodiments, dynamic adjustment of the rotation may be performed in order to provide sufficient hydrodynamic lift to drive the working stroke, while operating within a safe window of hydrodynamic lift such that excessive wave forces are not exposed to the absorber 112. Such an embodiment may be advantageous for providing a storm survival configuration.

[0075] In the example 100 shown, the body 114 or the body portion 112 is distanced from the rotational axis 121 by the appendage 116. Embodiments will be appreciated, wherein the rotational axis is positioned on the body itself.

[0076] A second embodiment 200 of the invention is show in FIG. 7 and FIG. 8. The second embodiment 200 comprises a WEC system substantially as shown in FIG. 1 to FIG. 6B, but having a wave energy absorber 202 having a first body portion 204 and a second body portion 206, each formed of an elongate bar affixed to a common rotational axis 208 at a first end thereof. The first and second body portions 204, 206 are arranged to be rotated about the rotational axis 208 by a controller driving a motor (not shown) in the same manner as that described in the embodiment 100 of FIG. 1. The controller is arranged to drive the rotation 210 of the body portions 204, 206 independently of one another such that a custom flow engaging surface may be formed of the body portion 204, 206 as required, thereby providing an embodiment with dynamic hydrodynamics and lift adjustment capabilities as required.

[0077] In the configuration shown in FIG. 7, the body portions 204, 206 for an asymmetrical ‘v’-shaped absorber 202. The common rotational axis 208 at the point of the ‘v’ shape means that the absorber 202 will naturally tend to align into the water flow direction 212 with the point of the ‘v’ facing the flow direction.

[0078] As the direction of the water flow 212 changes with the wave cycle as described herein, the absorber 202 will continuously align itself to the water flow direction 212, which in a wave cycle will follow a circular path dictated by the waves.

[0079] The water flow over the absorber 202 will cause a pressure force on the flow engaging surface of the absorber 202 pointing into the water flow direction 212 and this pressure force will cause the absorber 202 to rotate about the rotational axis 208 corresponding to the flow direction 212. The circular path direction of the resultant force from the absorber 202 will cause the rotational axis 208 to move in an orbital motion, and this orbital motion will be exploited by the drive assembly affixed thereto to generate power in the same manner as described for the embodiment 100 of FIG. 1.

[0080] The angle of the ‘v’ can be adjusted by the controller to adjust the pressure force on the absorber 202 and therefore the amount of energy absorbed from the waves. This can be used to both optimise energy capture in small waves and limit forces impinging on the absorber 202 during large waves.

[0081] With reference to FIG. 8, the body portions 204, 206 can be caused by the controller to converge such that the longitudinal axes thereof are substantially parallel. Such a configuration may be used to dramatically reduce wave forces impinging on the absorber 202 during storms. This can, in some embodiments, be further combined with a retraction of the absorber 202 further underwater, more proximate the platform, using the drive assembly.

[0082] Further embodiments within the scope of the present invention may be envisaged that have not been described above, for example, the buoyant platform is illustrated as a fixed block in all of the described embodiments for illustration purposes only, but embodiments will be appreciated, wherein the platform is any suitable structure arranged to remain relatively stationary in the body of water relative to the energy absorber. For example, the platform may comprise a buoyant underwater platform that is moored to the seabed; or any buoyant/non-buoyant structure that directly affixes to the seabed.

[0083] The energy converter in all described embodiments, for illustrative purposes only, is shown to be a simplified hydraulic cylinder combined with a separate spring unit. Embodiments will be appreciated, wherein in any suitable form of energy converter may be used, for example: a linear electrical generator; a rotational electrical or hydraulic generator; or any kind of rotational generator which may be combined with a mechanism that converts rotational motion to linear motion such as a rack and pinion.

[0084] The adjustment members described take the form of a motor driving rotation. Any suitable adjustment mechanism, including any suitable mechanical mechanism, will be appreciated, such as any hydraulic mechanism, a rack and pinion gear or a ratchet and pawl mechanism.

[0085] The body portions of the described embodiments take the form of a hydrofoil or an elongate bar shape, but embodiments will be appreciated, wherein any shape of body portion may be used.

[0086] The invention is not limited to the specific examples or structures illustrated and will be understood to be any embodiment falling within the scope of the appended claims.