GB2558780A

GB2558780A - Wave energy device

Info

Publication number: GB2558780A
Application number: GB1720178.1A
Authority: GB
Inventors: Bateman William; Hodge Caitlin; Jamieson William; Massoudi Tara
Original assignee: ZYBA RENEWABLES Ltd
Current assignee: ZYBA RENEWABLES Ltd
Priority date: 2016-12-02
Filing date: 2017-12-04
Publication date: 2018-07-18
Also published as: GB201620485D0; GB201720178D0

Abstract

A mounting bracket 300 for supporting a wave energy collector 50 comprises one or more supports 305 for securing the bracket to an underwater ground surface. A shaft 315 is rotatable around a first axis relative to the supports. A cross-piece 310 is fixed to and rotatable with the shaft, and enables the wave energy collector to pivot backwards and forwards relative to the shaft about a second axis perpendicular to the first axis. The shaft enables the collector to roll from side to side thereby reducing side-impact stresses from passing waves, and enabling access for maintenance. An energy converter 55 for converting backwards and forwards movement of the energy collector into useful energy may be fixed to and rotatable with the shaft. The supports may be connected to a base (20, fig 1) via a frame (25, fig 1) that is pivotable relative to the base.

Description

(54) Title of the Invention: Wave energy device

Abstract Title: Mounting bracket for wave energy device (57) A mounting bracket 300 for supporting a wave energy collector 50 comprises one or more supports 305 for securing the bracket to an underwater ground surface. A shaft 315 is rotatable around a first axis relative to the supports. A cross-piece 310 is fixed to and rotatable with the shaft, and enables the wave energy collector to pivot backwards and forwards relative to the shaft about a second axis perpendicular to the first axis. The shaft enables the collector to roll from side to side thereby reducing side-impact stresses from passing waves, and enabling access for maintenance. An energy converter 55 for converting backwards and forwards movement of the energy collector into useful energy may be fixed to and rotatable with the shaft. The supports may be connected to a base (20, fig 1) via a frame (25, fig 1) that is pivotable relative to the base.

310

300

Figure 9

320

217

Figure 2

3/7

4/7 if) Ο

Ο Ο

Xj~ <D

L_

Z3

σ)

ΙμΙμ*

Ο

5/7

Figure 6

Figure 7 in

WAVE ENERGY DEVICE

The present invention relates to wave energy devices, specifically energy devices that collect energy from water waves through backwards and forwards movement, and structures for supporting them and anchoring them to an underwater ground surface .

Oscillating wave surge converters (OWSCs) are a type of wave energy device that typically operate in coastal zones with water depths of 10m to 30m. A collector component oscillates backwards and forwards (i.e. horizontally) as the waves surge and this motion is converted to a useful form by a converter or power take-off (PTO) component. OWSC collectors are often flap-shaped or paddle-shaped such as the device described in WO-A-2012/150437.

OWSCs can be contrasted with heave collectors or point absorbers which oscillate up and down (i.e. vertically) as the waves heave and are usually deployed in deeper waters. Heave collectors often employ floating buoys such as the device described in US2016/0169188

OWSCs can also be contrasted with tidal stream generators which generate energy via the rotation of a turbine. One tidal stream turbine is described in GB2450624.

OWSCs present many challenges in terms of deployment, consistent energy production and maintenance. They must be anchored to the seabed, yet variations in water height and wave conditions require alteration of their position at the surface. The mean water level changes both with tides and weather conditions. Dropping water levels may leave a significant portion of the collector out of the water. Conversely, in high seas, waves can over-top the collector.

Both of these situations lead to reduced energy collection. In extreme seas, the collector may need to be lowered below the water surface to prevent damage and maintenance is simplified if the key working components of an OWSC can be raised above the surface.

Maintenance of OWSCs can be hampered by the energy collector component obstructing access to the PTO component or to brackets or other mounts usually located beneath the collector .

WO-A-2015/088923 describes a wave energy collecting device comprising a wave-energy capturing float connected to a frame by an elongated arm. The frame is tethered to the sea floor by cables and is pitch stabilised by a second float that extends rearwardly from the frame along the still water line. The frame also includes a ballast section. The ballast section can be flooded with water to submerge the device during severe seas or to adjust depth to optimise performance of the float.

WO-A-2013/083976 describes a mounting for underwater turbines that generate power from water currents. The mounting includes a rigid, Y-shaped tether, the apex of which is connected to an underwater anchorage. The buoyancy of the mounting is adjustable to pivot the mounting around the tether between a deployment condition and an operating condition. The connection between the tether and the anchorage permits 360° rotation about a vertical axis, up and down movement about a horizontal axis, and side-to-side rolling.

Embodiments of the present invention support and anchor oscillating wave surge collecting devices, improve their efficiency when extracting energy from waves and simplify deployment and subsequent maintenance.

In one aspect, the present invention provides a mounting bracket for supporting a wave energy collector comprising: one or more supports for securing the bracket to an underwater ground surface; a shaft rotatable around a first axis relative to the one or more supports; and a cross-piece fixed to and rotatable with the shaft, the cross-piece for supporting a wave energy collector and for enabling the wave energy collector to pivot backwards and forwards relative to the shaft about a second axis perpendicular to the first axis.

In this way, embodiments of the present invention enable a wave energy collector of an oscillating wave surge convertor to pivot back and forth to generate energy from water waves while also being able to roll around a perpendicular axis (i.e. an axis in line with the expected wave direction in use). By rolling from side to side, the effect of side impacts by waves is reduced. Being able to roll the collector to one side also aids with maintenance since the collector can be moved out of the way of other components.

Preferably, the mounting bracket further comprises an energy convertor for converting backwards and forwards movement of an energy collector into useful energy, the energy convertor fixed to and rotatable with the shaft. The energy convertor, or power take-off component (e.g. a piston) is connected between the shaft and the energy collector so that it also rolls from side to side with the shaft.

Preferably, the first axis is pitched downwards relative to the horizontal in an expected water wave direction in use. Pitching the first axis downwards results in the collector yawing (i.e., rotating about a vertical axis) with incoming waves as it rolls from side to side, further reducing impact stresses. The pitch angle is preferably approximately 15° to achieve a suitable balance between rolling and yawing.

In another aspect, the present invention provides a device for collecting energy from water waves, comprising: a base securable in position relative to an underwater ground surface; a frame connected to the base and pivotable relative to the base; and an energy collector connected to the frame, the collector configured to pivot backwards and forwards relative to the frame to collect energy from water waves when at least partially submerged in water; wherein, when the device is submerged in water, buoyancy supports the energy collector at the water surface causing the frame to pivot up and down relative to the base as the energy collector rises and falls.

Advantageously, embodiments of this aspect of the present invention anchor an oscillating wave surge convertor to the seabed or other underwater ground surface and buoyancy supports the collector at a desired position at the surface of the water. As the water level changes, with either passing waves or changing tides, the frame automatically pivots up and down around the base, maintaining the collector in a suitable vertical position as the collector oscillates horizontally.

Preferably, the device further comprises a heave plate connected to the frame. The heave plate resists motion of the frame through the water and is subject to hydrodynamic forces from passing waves. This constrains the up and down movement of the frame about the base, improving the energy harvesting efficiency of the collector.

Preferably, the heave plate is positioned behind the energy collector relative to a water wave direction so that it is subject to hydrodynamic forces which positively counter the forces on the collector and maintain the collector in the desired position.

Preferably, the device further comprises means for adjusting the buoyancy of the heave plate. Controlling the buoyancy of the heave plate is an effective wave of tuning buoyancy to support the collector in the desired position at the surface of the water.

Preferably, the frame extends behind the base relative to a water wave direction. Having the frame stretching out behind the base rather than leading the base is a more stable position in the face of oncoming waves.

Preferably, the base is pivotable about a vertical axis relative to the underwater ground surface. In this way, if the direction of incoming waves changes, the device will automatically align itself with the new wave direction.

Preferably, the base is securable in position relative to the underwater ground surface with one or more weights. This permits the device to be secured to the seabed without the use of divers. Preferably the base comprises a cage containing one or more weights, enabling the device to be placed and secured in position on the seabed in a single lift.

Preferably, the frame is an A-frame, and the collector is connected to the frame at or near the apex of the A. An Aframe is more stable and less likely to roll under the influence of waves from the side than a frame connected to the base at a single point.

Preferably, an energy convertor is fixed between the frame and the energy collector for converting movement of the energy collector into useful energy.

Preferably, the energy collector is connected to the frame via a cylindrical shaft, the shaft being rotatable along its axis to enable side to side rolling of the energy collector. Enabling the collector to roll from side to side reduces stresses imparted by waves coming from the side and simplifies maintenance .

Preferred embodiments of the present invention will now be described by way of an example and with reference to the accompanying drawings, in which:

Figure 1 illustrates a wave energy device;

Figure 2 is a detailed view of the junction between an anchoring structure and a wave energy convertor of the wave energy device;

Figure 3 illustrates a method of deploying the wave energy device;

Figure 4 illustrates the wave energy device under the influence of a passing wave;

Figures 5 and 6 illustrate a heave plate;

Figure 7 illustrates a range of heave plate arrangements; and

Figures 8 and 9 illustrate and alternative bracket for connecting an anchoring structure to a wave energy collector.

Figure 1 illustrates a wave energy device comprising an anchoring structure 10 for carrying and anchoring a wave energy convertor 15.

The anchoring structure 10 comprises a base 20 that is securable in position relative to the seabed or other underwater ground surface. Preferably, the base 20 rests on the seabed and is secured with bolts, tethers or similar fasteners, and/or is secured by weight. For example, the base 20 may comprise a large concrete slab or block. Alternatively, concrete blocks or other weights such as heavy chains are placed on top of the base 20 to hold it down. In another alternative, the base comprises a cage which contains one or more weights. The base 20 is optionally capable of rotation about a vertical axis in response to changing wave directions. For example, the base may comprise a lower part that is fixed to the seabed and an upper part that is free to rotate relative to the lower part. In this arrangement, the upper part of the base aligns itself automatically with the incoming wave direction.

A frame 25 is connected to the base 20 via one or more connection points 30. Each connection point 30 is a hinge or similar connection that permits the frame 25 to pivot relative to the base 20 about a horizontal pivoting axis. The frame 25 is substantially rigid so that its full length rotates about the hinged connection rather than flexing significantly. Preferably, the frame 25 comprises two struts 25a, 25b to form an inverted V or A-frame. At the base of the A, each strut 25a, 25b is connected to the base 20 at a separate connection point 30, the connection points being spaced apart along the pivoting axis. This improves structural strength and reduces side-to-side and/or rolling movements of the frame 25 relative the base 20 compared to an arrangement with a single connection point 30. Optionally, the struts 25a, 25b are joined by one or more crossbars 27 for increased strength and rigidity.

The height of the frame 25 depends upon the depth of the water into which the device is submerged. The frame 25 is taller than the depth of the water above the base 20 such that at least part of the frame emerges out of the water when the frame 25 is standing vertically. This enables the top of the frame 25 to be raised out of the water for maintenance of the wave energy convertor 15 and other components. In normal use, the frame 25 remains submerged and extends behind the base 20 relative to the incoming wave direction, forming an angle of less than 90° and preferably less than 60° to the seabed.

A support bracket 35 is secured to the frame 25. The bracket 35 is located at the opposite end of the frame 25 from the base 20. Where the frame 25 is an A-frame, the bracket 35 is located at or near to the apex of the A.

As shown in more detail in Figure 2, the bracket 35 includes a cross-piece 40 and one or more struts 45 for supporting the wave energy convertor 15.

The wave energy convertor 15 comprises a collector component such as a flap or paddle 50 and a power take-off (PTO) component 55. The collector 50 illustrated in Figure 1 is a curved paddle having a concave front surface that, in use, faces incoming waves and a convex back surface. The collector 50 is connected to the cross-piece 40 of the bracket 35 and is free to pivot about the cross-piece 40. This enables the collector 50 to move backwards and forwards relative to the bracket 35 and to the frame 25.

Preferably the collector 50 is buoyant in water so that, when submerged, it is supported by buoyancy in an average operating position above the cross-piece 40. The collector 50 optionally has internal spaces which can be filled with air to adjust the buoyancy of the collector 50. Preferably, for ease of construction, the collector 50 is moulded from a solid piece of buoyant material, the buoyancy of the collector 50 being determined by its thickness.

The PTO component 55 is connected between the collector 50 and the struts 45 of the bracket 35. In use, when the collector 50 is at least partially submerged in water, water waves cause backwards and forwards motion of the collector 50 and this motion is converted into useful energy by the PTO component 55.

In the Figures, the PTO component is represented as a piston 55 having one end connected to the struts 45 of the bracket 35 and the other end connected to the collector 50. Many other types of PTO component are known. The PTO component 55 may convert oscillating motion of the collector 50 into electrical energy which is carried by wires along the frame 25 to the base 20, and from there to any desired location.

Alternatively, the PTO component 55 may be a hydraulic pump. Hydraulic pressure can be used in situ to power desalination equipment, for example, or to pump fluids along pipes on or under the seabed.

The bracket 35 also supports a heave plate or damper 60. In normal use, the heave plate 60 is submerged beneath the water. The heave plate 60 increases the resistance to motion through the water of the frame 25, damping oscillating motion of the frame 25 about its connection 30 to the base 20. The heave plate 60 and collector 50 are also subjected to varying forces as waves pass, causing the frame 25 to pivot up and down relative to the base 20. The motion of the frame 25 in response to passing waves and the effects of the heave plate 60 will be described in detail in connection with Figure 4.

One or more air tanks 65 are attached to the heave plate 60. Preferably there are at least two air tanks 65 arranged symmetrically beneath the heave plate 60. The amount of air inside the air tanks 65 is adjustable to control and tune the buoyancy of the heave plate 60. When the device is submerged, increasing or decreasing the buoyancy of the heave plate 60 raises or lowers the frame 25 in the water. Air tanks 65 may alternatively, or in addition, be attached to the frame 25 and/or bracket 35.

Figure 3 is a sequence of images illustrating a method of deploying a wave energy device comprising an anchoring structure 10 and wave energy convertor 15. The device is deployed onto the seabed 100, under the water 105. Deployment is carried out via a ship or crane vessel 110 having a crane or winch 115.

Initially, in Figure 3(a), the anchoring structure 10 is lowered into the water 105 while the bracket 35 and/or heave plate 60 are tethered to the ship 110 by a chain, rope or other suitable tether 120. The bracket 35 is made to float at the surface of the water 105 by filling the air tanks 65 (not shown in Figure 3) with air to increase buoyancy.

Optionally, internal spaces in the collector 50 are filled with air to increase its buoyancy and support the bracket 35 at the surface. Preferably, however, the wave energy convertor 15 is lifted out of the water by the bracket 35 beneath it to facilitate access to the working components of the convertor 15.

Next, in Figure 3(b), the base 20 is lowered towards the seabed 100 by the crane 115 while the bracket 35 floats on the surface of the water 105. As illustrated in Figure 3(c), the frame 25 is tall enough that the bracket 35 remains at the surface even when the base 20 is in place on the seabed 100. This facilitates access to the energy convertor 15, bracket 35, heave plate 60 and other components located near to the apex of the frame 25.

In Figure 3(d), the crane 115 has been disconnected from the base 20 which is now resting on the seabed 100. If additional weights 125 are required to secure the base 20 in position on the seabed 100, these are lowered by the crane 115, as illustrated in Figure 3(e). Advantageously, this method of securing the base 20 to the seabed 100 does not require human divers and is therefore safer and more cost-effective than other methods of securing the base 20 such as tethers.

In Figure 3(f) the tether 125 has been released from the bracket 35 allowing the frame 25 to pivot freely about the hinged connection 30. Air is let out of the air tanks 65 to reduce buoyancy, causing the bracket 35 and heave plate 60 to sink beneath the water. The buoyancy is fine-tuned so that the collector 50 is partially submerged to its optimal operating position. To perform subsequent maintenance, the buoyancy of the device is increased by filling the air tanks 65, raising the frame 25 and lifting the collector 50, bracket 35 and heave plate 60 out of the water 105.

Figure 4 is a sequence of images illustrating movement of the wave energy device under the influence of a passing wave 200. The average height of the water, i.e. the zero-crossing point of the wave, is indicated by a dotted line 205. The wave 200 moves from left to right by 1/4 of a wavelength between each image (a) to (d) such that the sequence of four images shows a full wavelength.

The image sequence of Figure 4 illustrates that, as the collector 50 pivots backwards and forwards in response to a passing wave, the frame 25 also pivots up and down around the base 20, raising and lowering the collector 50. This combined movement increases the energy collecting efficiency of the collector 50 and has other unexpected beneficial effects.

For the purposes of illustration, the motions of the frame 25 and the paddle 50 are greatly exaggerated in Figure 4. Only a simplified theory of operation is described to enable an understanding of the advantages of the present invention. The motion of the system is highly complex, depending on many different factors including buoyancy, hydrodynamic forces, resistance to movement through the water, and inertia.

For example, in the arrangement shown in Figure 4, the heave plate 60 is approximately 1/4 of a wavelength behind the collector 50, supported on an elongated bracket 35. In a simplified model, this is the hypothetical optimum position for the heave plate 60. In reality, however, the heave plate 60 may be in a range of different positions behind the collector 50 and still provide similar advantages. Even in the absence of a heave plate 60, the buoyancy of the collector 50 and anchoring structure 10 may still be tuned to obtain beneficial rising and falling of the collector 50.

One key factor in the motion of the device is buoyancy. The buoyancy of the collector 50 changes over a wave cycle as the water surface intersects the collector 50 at different heights. The buoyancy of fully submerged components, such as the heave plate 60, remains relatively constant.

A second key factor in the motion of the device is hydrodynamic force, particularly the hydrodynamic force 210 on the collector 50 and the hydrodynamic force 215 on the heave plate 60. One source of these hydrodynamic forces 210, 215 is pressure arising from particle motions of the water. As the wave 200 travels from left to right, water particles move clockwise in an approximately circular shape and exert pressure on objects in the water. The radius of the circles decreases with depth such that energy within the wave 200 is concentrated towards the surface. Another source of hydrodynamic force is the resistance to motion of the device through the water, particularly the resistance to motion of the heave plate 60.

The buoyancy of the collector 50 and heave plate 60, and the hydrodynamic forces 210, 215 apply a time-varying moment to the frame 25 about its connection 30 to the base 20. This time-varying moment causes forced oscillation of the frame that raises and lowers the collector 50, the oscillation being damped by the resistance to movement through the water.

In Figure 4(a), the collector 50 is located in a trough of the passing wave 200 such that the hydrodynamic force 210 on the collector 50 is opposite to the direction of wave travel.

Force 210 rotates the collector about the cross-piece 40 in an anti-clockwise direction 220, as indicated by dotted outlines.

The heave plate 60, being 1/4 of a wavelength behind the collector 50, is in line with a zero crossing point of the wave 100 as it drops from a crest to a trough. The hydrodynamic force 215 on the heave plate 60 is consequently in a downward direction.

Force 210 creates an anti-clockwise moment on the frame 25 about the connection 30 and force 215 creates an opposing clockwise moment on the frame 25. The direction of movement of the frame is also in an anti-clockwise direction, and this creates an additional downward resistance force on the heave plate 60 as it rises.

In Figure 4(b), the collector 50 is located at a zero-crossing point of the wave 200 and is subject to an upward hydrodynamic force 210. Compared with the position in Figure 4(a), more of the collector 50 is submerged resulting in larger upward buoyancy force. The heave plate 60 is in line with the wave trough and is subject to a hydrodynamic force 215 opposite to the direction of wave travel.

Compared to Figure 4(a), the hydrodynamic forces 210, 215 in Figure 4(b) are not directed at the wide surfaces of the collector 50 or heave plate 60 so have less impact on the device. Nevertheless, the combined moment on the frame 25 is in an anti-clockwise direction, with buoyancy and both hydrodynamic forces 210, 215 all acting in the same direction. Consequently, the collector 50 is lifted with the anticlockwise rotating frame 25 as the wave crest approaches.

In Figure 4(c), the collector 50 is positioned in a crest of the wave 200. The frame 25 is at approximately its greatest anti-clockwise rotation and the collector 50 is consequently at approximately its greatest height. The collector 50 is subject to a hydrodynamic force 210 in the direction of wave travel. Force 210 rotates the collector about the cross-piece 40 in a clockwise direction 225, as indicated by dotted outlines .

The heave plate 60 is in line with the zero-crossing point of the wave 200 and is subject to an upward hydrodynamic force 210 .

The resultant moment on the frame 25 is in a clockwise direction. Consequently, the frame 25 is rotated clockwise and the collector 50 lowered as the wave crest passes.

In Figure 4(d), the collector 50 is located at a zero-crossing point of the wave 200 and is subject to a downward hydrodynamic force 210. The heave plate 60 is in line with a wave crest and is subject to a hydrodynamic force 215 in the direction of wave travel.

The combined moment on the frame 25 is in a clockwise direction, with both hydrodynamic forces 210, 215 acting in the same direction. Consequently, the collector 50 is lowered as the wave trough approaches, returning to the position in Figure 4(a).

From the foregoing description, it will be seen that one benefit of the device is that the oscillation motion of the frame 25 raises and lowers the collector 50 as each wave 100 passes. The collector 50 is raised with wave crests. This prevents overtopping of the collector 50 by the wave, which would reduce the energy harvested. Conversely, the collector 50 is lowered during a wave trough. This enables the collector 50 to harvest more energy from the wave trough compared to a static collector 50.

Additionally, lowering the frame 25 during a wave trough ensures that the bracket 35 and PTO component 55 are always submerged. These components are typically made from steel or similar metals and would corrode quickly if located in a splash zone in contact with both air and sea water. Ensuring these components are always submerged during normal use extends their working lives.

A further surprising advantage of the device is its behaviour in extreme weather conditions. As waves become higher and/or stronger, the hydrodynamic forces 210, 215 on the device exerted by wave crests become relatively higher than those exerted by wave troughs. This imbalance rotates the frame 25 further clockwise, submerging the whole device, including the collector 50, under the water. This natural response protects the collector 50 from damage from large waves.

To ensure that the motion of the frame 25 raises and lowers the collector 50 by the desired amount, the device is tuned. The distribution of buoyancy between the collector 50 and the submerged elements, particularly the heave plate 60, can be adjusted to control the dynamic response of the device. For example, if the heave plate 60 is relatively more buoyant than the collector 50, the system will be slow to react to changing water elevations. Conversely, a more buoyant collector 50 (e.g. a collector made from a thicker piece of buoyant material) will respond quickly to changing water elevations, and less buoyancy in the submerged elements is required for the collector 50 to float at the desired level. Buoyancy can be distributed across the device to optimise the position of the collector 50 relative to the incoming waves so that it can harvest the most energy. Tuning of the device can also be achieved by changing the size, shape, angle and position of the heave plate 60, as will be discussed below.

In addition to responding to the changing height of the water with individual waves, the device also responds to changing water height over longer periods of time. For example, as the height of the water changes with changing tides, the average angle between the frame 25 and the seabed will change correspondingly, keeping the collector 50 in approximately the same position relative to the water surface.

Figures 5 and 6 illustrate a preferred design of heave plate 60 in more detail. Figure 5 shows the heave plate 60 and attached air tanks 65 from behind the device and Figure 6 is a perspective view.

The heave plate 60 is curved with a convex upper surface and a concave lower surface. This increases the effect of upward hydrodynamic forces 215 on the heave plate 60 in lifting the collector 50, and reduces the effect of downward hydrodynamic forces. It also reduces the resistance to motion in the upward direction. Consequently, the responsiveness of the device to approaching wave crests is increased, ensuring the collector 50 is not overtopped by waves, which represents a significant loss in harvested energy. It further means that the collector 50 is rising and advancing into an oncoming wave crest more quickly, increasing the power stroke harvested from the wave crest.

The upper and lower surfaces of the heave plate 50 are preferably in a smooth curve to spread forces out evenly. Alternatively, the heave plate could be shaped as an inverted V or a convex upper surface and concave lower surface can be formed from several straight portions. Yet another configuration is a flat upper surface with downward pointing edges to create a cavity in the lower the surface.

A disadvantage of a curved or angled heave plate 60 is that waves coming from the side put stresses on the bracket 35 and frame 25. The amount of curvature is therefore limited by structural tolerance considerations. A flat, thin heave plate 60 presenting only a small surface to waves from the side would reduce sideways stresses on the device and may be desirable in some situations. The sideways pointing edges of a flat heave plate are preferably smoothed and tapered to minimise the impact of waves from the sides.

In the arrangement of Figures 5 and 6, the heave plate 60 is located directly behind the collector and is approximately the same length and width as the collector 50. The heave plate 60 and collector 50 therefore present a similar surface area to pressure-causing water particles and have a similar lever distance to the connection point 30 between the frame 25 and the base 20. This arrangement helps to balance the forces acting on the device.

Figure 7 illustrates a range of different angles and positions for the heave plate 60 relative to the collector 50.

In Figure 7(a), the heave plate 60 is located directly behind the collector 50 and below the connection between the collector 50 and bracket 35 at the cross-piece 40.

Furthermore, the heave plate 60 is approximately at right angles to the average collector 50 position and is approximately horizontal when the frame 25 is in its average position. This is substantially the arrangement depicted in Figures 5 and 6 and has the features and advantages described above .

In Figure 7(b), the heave plate 60 is spaced away from and behind the collector 50 on an extended arm or strut of the bracket 35. The heave plate 60 may be offset behind the collector 50 by as much as 1/4 of the expected wavelength of passing waves. The greater the distance between the collector 50 and the heave plate 60, the greater the phase difference in water particle motions experienced by each component. At 1/4 of a wavelength distance, the motion of the water particles at the collector 50 and at the heave plate 60 are 90° out of phase. This corresponds with the situation described in Figure 4 where the different hydrodynamic forces 210 and 215 work together to raise and lower the collector 50.

Another advantage of spacing the heave plate 60 behind the collector 50 is that it increases the length of the lever arm to the connection 30 between the frame 25 and the base 20. The size of the heave plate 60 can therefore be reduced and will nevertheless provide the same contribution to the turning moment. However, the stresses on the bracket 35 increase with distance and structural considerations may limit the distance between the collector 50 and heave plate 60. Furthermore, some sea waves have wavelengths of around 100m. Spacing the heave plate 60 1/4 of a wavelength behind the collector 50 is unlikely to be feasible in such conditions.

In Figures 7(c) and 7(d), the heave plate 60 is angled away from the horizontal when the frame 25 is at its average rotation. This alters the angle at which the heave plate 60 presents a perpendicular surface to the direction of water particle motions. Effectively, this changes the phase difference between the water particle motions at the heave plate 60 and at the collector 50 for a given horizontal spacing. Changing the angle of the heave plate 60 relative to the frame 25 also changes the effect that forces acting on the heave plate 60 have on the turning moment of the frame 25 about the connection 30.

In Figure 7(c) , the heave plate 60 is closer to being parallel with the frame 25. This increases the moment on the frame 25, increasing the turning effect of hydrodynamic pressures 215 on the heave plate. However, the phase difference between particle motions at the collector 50 and at the heave plate 60 is effectively reduced.

In Figure 7(d) the heave plate 60 is closer to being at right angles to the frame. This increases the phase difference between the collector 50 and the heave plate 60, but reduces the turning effect on the frame 25 of hydrodynamic forces 215 on the heave plate 60.

In Figure 7(e) the height of the heave plate 60 relative to the base of the collector 50 is changed. If the heave plate is raised, as in Figure 7 (e), the hydrodynamic forces 215 on it increase since water particle motions are greater near the surface. The forces 215 on the heave plate are consequently a greater counter to the large surface-level hydrodynamic forces 210 on the collector 50. The length of the level arm is also increased. If the heave plate is lowered, the hydrodynamic forces 215 on it decrease, but the water at greater depths is calmer such that the forces 215 will be more consistent.

In general, the location and arrangement of the heave plate 60 is changed to adapt the device to different expected wave conditions and to balance different competing factors.

Figures 8 and 9 illustrates an alternative bracket 300 for mounting the wave energy convertor 15 either to a frame 25 as described above or to any other fixed or movable base that is securable to the seabed.

The bracket 300 includes several support struts 305 fixed securely to the frame 25 or other base (not shown in Figures 8 and 9) or otherwise secured directly to the seabed. The bracket 300 further includes a cross-piece 310 and a shaft 315 at right angles to one another. The shaft 315 is cylindrical and fixed securely to the cross-piece 310.

The collector 50 is connected to the cross-piece 310 of the bracket 300 and is configured to pivot about the cross-piece 310, enabling backwards and forwards movement of the collector 50. The PTO component 55 is connected between the collector 50 and the shaft 315 of the bracket 300 to convert backwards and forwards motion of the collector 50 into useful energy.

The support struts 305 are connected to the cylindrical shaft 315 via one or more circular clamps 320 that encircle the shaft 315. Preferably two clamps 320 are provided at opposite ends of the shaft 315, either side of the connection between the PTO component 55 and the shaft 315.

The shaft 315 is free to rotate or roll around its longitudinal axis within the circular clamps 320. Since the cross-piece 310 is fixed relative to the shaft 315, rolling motion of the shaft 315 also causes the cross-piece 310 to roll and this in turn allows the collector 50 and PTO component 55 to roll from side to side. In other words, the cross-piece 310 defines an axis of rotation for the collector 50 to pivot backwards and forwards and the shaft 315 defines a perpendicular axis of rotation for the collector 50 to roll from side to side. In use, the collector 50 will often be subjected to waves from a range of directions, including from the side. Enabling the collector 50 to roll with such waves reduces stresses on the pivoting connection between the collector 50 and the cross-piece 310.

Additionally, when the frame 25 is raised for maintenance, lifting the collector 50 out of the water, the collector 50 will naturally roll to one side, improving access to components beneath it. By rolling to the side, the collector 50 also remains partially submerged even when the cross-piece 310 and other components below the base of the collector 50 are lifted out of the water. It is therefore not necessary to support the whole weight of the collector 50 out of the water, which reduces the lifting force required and, consequently, reduces the size of the air tanks 65 required to raise the frame 25.

When the frame 25 is at its average rotation in the water, the shaft 315 is preferably at an angle to the horizontal. The connection between the cross-piece 310 and the collector 50 is higher than the connection between the shaft 315 and the PTO component 55. As an example, in Figures 8 and 9 the shaft 315 is at an angle of approximately 15° to the horizontally aligned heave plate 60.

Angling the shaft 315 changes the direction of the forces on the PTO component 55 caused by backwards and forwards movement of the collector 50. Depending on the configuration of the device, the angle of the shaft 315 is adjusted to optimise power collection. Additionally, angling the shaft 315 means that the collector 50 yaws about a vertical axis as it rolls from side to side. By pitching the shaft 315 downwards in the direction of wave travel, the direction of the yaw is the same as the direction of the waves, further reducing impact stresses on the collector 50.

Tapered bearings prevent longitudinal movement of the shaft 315 relative to the clamps 320.

If desired, the shaft 315 can be locked in place to prevent rolling. This can be achieved using, for example, locking pins inserted through aligned holes in the clamps 320 and the shaft 315.

As described above, the alternative bracket 300 of Figures 8 and 9 provides several advantages when used with the wave energy device of the present invention. It will be apparent, however, that the bracket 300 may also be used to support and enable side-to-side rolling movement of any oscillating wave energy/surge converter, including a converter having a fixed position in the water.

Claims

CLAIMS :

1. A mounting bracket for supporting a wave energy collector comprising:

one or more supports for securing the bracket to an underwater ground surface;

a shaft rotatable around a first axis relative to the one or more supports; and a cross-piece fixed to and rotatable with the shaft, the cross-piece for supporting a wave energy collector and for enabling the wave energy collector to pivot backwards and forwards relative to the shaft about a second axis perpendicular to the first axis.

2. The mounting bracket of claim 1 further comprising an energy convertor for converting backwards and forwards movement of an energy collector into useful energy, the energy convertor fixed to and rotatable with the shaft.

3. The mounting bracket of claim 1 or claim 2 wherein rotation of the shaft enables a wave energy collector supported on the cross-piece to roll from side to side about the first axis.

4. The mounting bracket of any preceding claim wherein the shaft is cylindrical.

5. The mounting bracket of any preceding claim wherein the first axis is pitched downwards relative to the horizontal in a water wave direction.

6. The mounting bracket of any preceding claim wherein the one or more supports are connected to a base that is securable to an underwater ground surface.

7. The mounting bracket of claim 6 wherein the one or more supports are connected to the base via a frame, the frame being pivotable relative to the base.

Intellectual

Property

Office

Application No: GB1720178.1 Examiner: Rachel Smith