WO2012098357A1

WO2012098357A1 - Wave power apparatus

Info

Publication number: WO2012098357A1
Application number: PCT/GB2012/000050
Authority: WO
Inventors: Allan Robert Thomson; Gart BRYANS
Original assignee: Aquamarine Power Limited
Priority date: 2011-01-21
Filing date: 2012-01-20
Publication date: 2012-07-26
Also published as: GB2505766A; GB201101068D0; GB201312845D0

Abstract

A wave energy conversion device (14) includes at least one upstanding flexible flap portion (26) supported by at least two spaced apart upstanding and independently pivoting support masts (16,18), with one support mast disposed at each end of the flap portion. Each support mast is pivotally connected at its bottom end to a base portion (20) formed and arranged for anchoring to the bed of a body of water in use of the device. The support masts and flap portion are biased to the vertical in use and formed and arranged to oscillate backwards and forwards about the vertical in response to wave motion (28) acting on the faces of the flap portion. At least one of the support masts is coupled to power extraction means for extracting energy from the movement of the flap portion (26) and support masts (16,18).

Description

WAVE POWER APPARATUS

Field of the invention

The present invention relates to an apparatus for generating power by extracting energy from waves and methods making use of the apparatus.

Background to the invention

A large number of devices and methods have been described with the intent of extracting power from the waves in the sea and other bodies of water. Arrangements where there is a seabed mounted or supported structure having a hinged lever attached to a panel for reciprocation motion are described in International publication number WO2004/007953. This arrangement is used in relatively deep water, at a preferred depth of about L/2 where L is the wavelength of the waves expected at the location of use. A somewhat similar arrangement is described in WO03/036081 where a reciprocating body is situated entirely under water in a water basin of intermediate depth.

Yet further arrangements are described in the present applicant's WO2006/100436 which discloses an apparatus for use in relatively shallow water that includes an upstanding flap portion pivotally connected to a base portion. The flap portion is biased to the vertical and oscillates backwards and forwards about the vertical in response to wave motion acting on its faces. Power extraction means is used to extract energy from the movement of the flap portion. In order to extract the maximum amount of energy from the wave motion prevailing at the given location the flap portion and base portion are arranged to present a substantially continuous surface to the wave motion throughout the depth of the water (the water column) throughout the full depth of water from the wave crest to the seabed.

Other arrangements include those of US4,371 ,788 which describes the use of a reciprocating flap arrangement which is provided in the form of a flexible sheet or sheets (a "sail" or sails). The sail-like flap arrangement described therein comprises a sheet of flexible material or sheets of flexible material mounted in a frame generally of rectangular construction. In response to the motion of the waves acting on the flexible sheet, the sheet and frame assembly reciprocates either about a pivot mounted to a base on the sea bed or backwards and forwards along a track.

r^nMEiD Λ ΤΙΠΜ ^nDV Yet further examples of the numerous types of wave power generating apparatus that have been described include, for example, US4,476,397 which describes a flexible (sail-like) flap with a particular arrangement of mast and boom that oscillates whilst keeping the sail-like flap full (taut). Examples also include US7,626,281 which makes use of the flutter effect of a flexible flap mounted in a manner akin to a flag and US2009/0302612 and US2010/0102565 which make use of flexible sheets that are held generally parallel to the flow of a fluid such as water. US2010/011 1609 describes yet another option including a flexible sail type flap that tilts or rotates under the action of wave motion.

Whilst such devices have been previously proposed only a few (such as those in WO2006/100436) appear to have progressed towards commercial realisation. Possible reasons include lack of robustness in a very hostile environment; the need to "over engineer" devices so as to make them suitable for use in hostile environments with consequent cost and maintenance implications; the need to utilise substantial anchorage devices for holding such apparatus in a secure manner on the sea bed; and relatively substantial maintenance and repair costs for such devices.

It is an objective of the present invention to avoid or minimise one or more of the foregoing disadvantages.

Description of the invention

The present invention provides a wave energy conversion device comprising:

at least one upstanding flexible flap portion supported by at least two spaced apart upstanding and independently pivoting support masts, with one support mast disposed at each end of the flap portion;

wherein each support mast is pivotally connected at its bottom end to a base portion formed and arranged for anchoring to the bed of a body of water in use of the device; the support masts and flap portion being biased to the vertical in use and formed and arranged to oscillate in use, backwards and forwards about the vertical in response to wave motion acting on the faces of the flap portion; and

wherein at least one of the support masts is coupled to power extraction means for extracting energy from the movement of the flap portion and support masts.

RnQP74RR-1 -mmr.nhprsnn The at least one flexible flap portion may be made of a flexible sheet material. Alternatively flexibility may be provided to a flap portion by constructing the flap portion of an articulated array of substantially rigid sub portions, as described hereafter. Thus the present invention provides a wave energy conversion device comprising: at least one upstanding flap portion of flexible sheet material supported by at least two spaced apart upstanding and independently pivoting support masts, with one support mast disposed at each end of the flap portion;

Thus the present invention provides a wave energy conversion device comprising: at least one upstanding flexible flap portion supported by at least two spaced apart upstanding and independently pivoting support masts, with one support mast disposed at each end of the flap portion;

wherein the at least one flap portion comprises or consists of an articulated array of substantially rigid sub portions;

A flexible flap portion comprising or consisting of an articulated array of substantially rigid sub portions may also be conveniently employed in other wave energy conversion devices such as those where the support masts are not independently pivoting. A flap portion for use in a wave energy conversion device and comprising or consisting of an articulated array of substantially rigid sub portions constitutes another aspect of the

50927486-1 -mmcpherson present invention, as do wave energy conversion devices incorporating such a flap portion.

As the support masts and flexible flap portion oscillate backwards and forwards in response to the wave motion, the support masts must at least pivot backwards and forwards in the same general direction as the wave motion. In the description that follows this direction of rotation; about an axis of rotation substantially along the line between the pivot points of adjacent support masts, will be referred to as pitching. As discussed in more detail hereafter the support masts may also be formed to allow pivoting in the direction normal to the pitch axis (adjacent support masts may tilt in towards each other and optionally outwards from each other). This direction of rotation will be referred to as rolling. It will be understood that although the flexible flap portion is biased to the vertical, in some (weak) sea states, or where the wave motion is not regular, the flap portion may from time to time not oscillate through the vertical on every wave motion.

The biasing to the vertical may be provided by use of resilient members such as springs that act on the support masts. The pivots connecting support masts to base portions may themselves include resilient members making use of springs or elastomers to provide the biasing. Alternatively or additionally the biasing to the vertical may be achieved by providing buoyancy. Buoyancy may be provided by: having buoyant support masts (for example less dense than water or including air or gas filled chambers or foam components); attaching buoyant members (floats) to the support masts or flap portion; and providing a flap portion (whether of a flexible sheet material or of an articulated array of substantially rigid sub portions) having gas, air or foam filled chambers or foam filled pockets. Where buoyancy is provided it may be adjustable, for example by displacing air or gas in a chamber or foam with water. The rigidity of the flap portion can also be adjusted in this way to maximise energy production and minimise loads. For example the upper part of a flap of flexible sheet material or other buoyant component of a flexible flap may contain a buoyancy chamber whose rigidity is adjusted by flooding with water.

50927486-1 -mmcp erson Typically, where flexible sheet material is employed, the support masts at each end of the flap portion are used to support generally rectangular or square sheet or sheets of flexible sheet material, with these end support masts being attached to or near opposed edges of the generally rectangular or square sheet or sheets. Thus the pivoting part of the device presents a generally rectangular upstanding flap portion, supported by the masts that can be located on the bed of a body of water with the flap portion transverse to the expected direction of wave motion.

Similarly when an articulated array of substantially rigid sub portions is employed in a flap portion, the support masts at each end of the flap portion are typically used to support a generally rectangular or square array with these end support masts being attached to or near opposed edges of the generally rectangular or square array.

The substantially rigid sub portions of a flap portion may take different forms. For example they may be in the form of rectangular or square plates or three dimensional solid or hollow shapes such as cuboids or cubes each arranged in the array to present a pair of opposed faces as part of the faces ("front" and back") of the flap portion as a whole. Alternatively the sub portions may include curves for example they may take the form of cylinders tubes or pipes of for example, circular or elliptical cross section; or they may be in the form of three dimensional shapes having flat opposed faces forming part of the faces ("front" and back") of the flap portion as a whole, but with curved surfaces connecting those faces.

In a convenient form the sub portions are elongate plates or three dimensional shapes arranged substantially vertically in the array. Typically they run substantially from top to bottom of the flap portion, in a manner akin to vertically disposed slats on a fence. Such an array can be convenient to construct and provides stiffness to each sub portion whilst still allowing the benefits of flexibility to the flap portion.

The sub portions may be formed from any suitably strong material such as metals, plastics and composites (for example glass or other fibre reinforced plastics such as GRP or carbon fibre composites). Conveniently one or more of the sub portions are hollow or are provided with one or more chambers therein to provide buoyancy when

50927486-1 -mmcpherson filled with air, another gas or foam or to provide added mass when filled with solids (e.g. concrete) or liquid (typically seawater). Advantageously chambers may be provided with appropriate valves for input and output of a gas or a liquid so that the buoyancy and mass characteristics can be adjusted to allow more efficient use of the device.

The sub portions are substantially rigid, that is to say they are constructed of material normally considered rigid, at least when not under stress, such as metals or reinforced plastics composites. Thus the sub portions may deform to some limited extent, bending or flexing in response to the forces acting upon them.

The array of substantially rigid sub portions is articulated. That is to say that the sub portions are inter-connected by linkages between adjacent sub portions that can allow the sub portions to move relative to one another. This provides flexibility to the flap portion. Linking may be for example by means of elongate flexible connectors such as chains, ropes or wires. Similar or different linkage means may be used to attach a flap portion to support masts.

Linkage means may be provided as discrete connections between adjacent sub portions. For example short lengths of wire, rope or chain connecting between and terminating at adjacent sub portions. The termination may be for example, by a loop at the end of a wire, rope or chain interconnected with a loop fixing (an eye) on the sub portion. Advantageously, for ease of construction the linkage means of the array may comprise longer lengths of flexible connectors with a plurality or even all the sub portions in an array distributed along the length. Conveniently the flexible connectors may terminate at support masts when running lengthwise along the flap portion. A flexible connector may also pass through or around support masts to continue on as a connector for a subsequent flap portion or part of the flap portion where a device of the invention includes more than two support masts. The sub portions may be attached to the flexible connector by passing it through the sub portions or by attaching a surface of the sub portion to the length of flexible connector, making use of appropriate fixings.

50927486-1 -mmcpherson Where the sub portions are of the "slat" type described above .i.e. are elongate three dimensional shapes arranged substantially vertically in the array, then it may be convenient to construct the array as follows. Each sub portion may be provided with a slot open at one end (conveniently the bottom end of the sub portion) and running vertically, in use. The slot is aligned with the pitch axis of the device. A plurality of elongate flexible connectors such as chains, ropes or wires connect between support masts. A sub portion can then be mounted in the array by locating the slot about the flexible connectors. The sub portion can then be secured in place, from sliding along the flexible connectors, by means of suitable fixings, e.g. by clamping to a rope wire or chain used as flexible connector.

The sub portions of the array are generally aligned with adjacent sub portions close together but spaced slightly apart, to allow the adjacent sub portions to move relative to one another, as the flap portion flexes. Spaces between adjacent sub portions may be covered, for example with a flexible sheet material to increase the capture of power from waves if desired.

A flap portion comprising an articulated array of substantially rigid sub portions has certain advantages. The sub portions can be constructed to be strong and capable of accepting heavy loading from wave action, at the same time the benefits of flexibility in the flap portion as described herein can be obtained. By selecting the type and size of sub portions, type of linkage means and the spacing between sub portions; a flexible flap portion can be designed with an appropriate combination of strength and flexibility for expected sea states at a given location for a device of the invention.

Advantageously the devices described herein may be located in use in relatively shallow water, for example between 6m and 20m, desirably between 8 and 16m. The available surge proportion wave energy at these depths, in typical sea locations, is substantially greater than that found in deeper waters. At the same time these depths allow a flap portion of sufficient height to have an oscillation about the vertical that can extract energy efficiently from the wave motion. In addition these depths are often found relatively close to shore, decreasing the cost of transmitting the extracted energy onto land for use, in comparison with devices located at a significant distance offshore.

50927486-1-mmcpherson To efficiently capture the maximum amount of energy from the wave motion prevailing at a given location the device may be formed and arranged to present a substantially continuous surface to the wave motion throughout the depth of the water (the 'water column'). For a device making use of an articulated array of substantially rigid sub portions to form a flap portion, there will generally be spaces between adjacent sub portions. The loss of power capture in such an arrangement may be acceptable. However, as noted above spaces between sub portions may be covered by flexible sheet material if desired. Any gap between the flap portion and the base portion or base portions of the support masts, or between the flap portion and the bed of the body of water the device is placed upon, may be filled by using a deflector plate or shield running along the bottom edge of the flap portion, at least on the face that faces the direction of approaching wave motion. As an alternative and when the flap portion is of a flexible sheet material the material of the flap may be continued downwards, below the pivot point to the base portion or to the bed of the body of water.

As a yet further alternative a separate sheet or separate sheets of flexible sheet material may be mounted as a relatively inexpensive deflector "plate" to cover any gaps for devices employing either a flap portion of a flexible sheet material or comprising an articulated array of substantially rigid sub portions. The flexible sheet material mounted as a deflector may be, for example, mounted on a frame or pulled taut between bases mounting support masts. Providing a flap portion of a flexible sheet material supported by at least two spaced- apart and independently pivoting support masts has a number of advantages.

Flexible sheet material can be a lightweight and cost effective alternative to providing a rigid flap portion, for example constructed of steel plates or tubing. This is particularly important where a large device or array of devices is to be constructed, in order to extract substantial amounts of energy from waves in a given location. A flexible material can accept forces (e.g. bending) that would distort or otherwise damage a large or long rigid flap.

50927486-1 -mmcpherson The height of the flap portion of flexible sheet material is easily altered to suit the local wave regime and obtain optimal loadings and hence energy production.

The independent pivoting of the support masts provided in flexible flap portion devices described herein means that the device can react to the variation in the waves that may found along the length of a flap, especially differences in the force or the phasing of the waves at different places along the length of the flap.

Oscillating flap devices are located with the flap portion transverse to the expected direction of the waves (i.e. the prevailing wave direction for the selected location). However, for example, even a slight deviation in the wave direction means that the phasing of the waves arriving at a face of the flap portion will be different along the length of even a relatively small flap. Furthermore variations in force of waves at a given point along the length of a flap may be expected, for example caused by differences in the local topography of the sea bed near the site of the device. With a rigid flap device the length of the flap and hence the energy capture is limited by the loads induced by the difference in phase between the waves at each end of the flap. With a flexible flap portion supported by independently pivoting support masts, these forces can be more readily accommodated as each end of the flap can move with some independence and the flexible sheet material or articulated array of sub portions can distort from a planar or near planar form. Therefore longer flap devices and assemblies of flap devices may be contemplated, with the advantage of increased energy capture per device installed. As the support masts are independently pivoted the extent of pitching oscillation of each mast in response to wave action may be greater or less at any one time, dependent on the phase and force of waves acting on the flap portion, local to each support mast. However, the support masts are interconnected by the flexible sheet material or the articulated array of sub portions and their motion is therefore coupled to a greater or lesser extent, depending on the choice of design and of materials employed in the device.

For example, if one support mast pitches forwards from the upstanding (typically, vertical) position to a greater extent than an adjacent support mast then the distance between the top of the two adjacent support masts increases and hence the top edge

50927486-1 -mmcDherson of flexible sheet material, where employed, will tend to become tauter and may tend to extend (stretch). For a given device construction and flexible sheet material there may come a point where the less pitched support mast will tend to be "pulled" to pitch further by the more pitched support mast. A similar situation arises where an articulated array of substantially rigid sub portions is employed. The array will become tauter along its top edge and, for example, linkage means such as wires or ropes running along the top edge or near the top edge may tend to extend or stretch, depending on its characteristics. This situation is illustrated in the perspective drawing of Figure 1 which shows in schematic fashion the increase in distance between the tops of two support masts pitching out of phase. The masts 1 and 2 are shown in an upstanding position with a spacing D1 between their tops (line 3). The arcs 4 swept by their possible pitching motion about pivots 6,8 are shown, with the motion suggested by the curved arrow P. If both masts move (pitch) simultaneously in the same direction and to the same extent, for example to the positions indicated as 1a and 2a then the distance between the tops of the two masts remains as D1 as indicated by the dashed line 10. However if the masts move differently due to wave motion that is out of phase then a different situation may arise.

For example, if mast 1 moves to 1a but mast 2 remains at or near its original upstanding position then the distance between the mast tops will increase to that indicated by line 12, denoted D2 on the figure. If a flexible sheet material is suspended between the two masts then it will become tauter along its top edge and may stretch and/or pull mast 2 in the direction of position 2a.

This coupling effect can be varied in a number of different ways which may be employed individually or in combination to provide desired operational characteristics for a device of the invention. Thus devices of the invention may be designed to provide a good power output whilst coping robustly with expected variation in wave force and phasing.

Examples of means of controlling (selecting) the degree of coupling between support masts include:

50927486-1 -mmcpherson Flexible sheet material employed in the flap portion between adjacent support masts may have elasticity. The stretching of the material allows the support masts to pitch to different extents;

Flexible sheet material employed in the flap portion between adjacent support masts may have fullness or a flap portion comprising an articulated array of substantially rigid sub portions may have fullness i.e. when adjacent masts are in a neutral upstanding position (typically vertical) the flap portion is not held fully taut between the masts but has some slack. When the adjacent support masts pitch to different extents the slack is taken up;

Linkage means provided in a flap portion comprising an articulated array of substantially rigid sub portions may have elasticity. The stretching of the linkage means allows the support masts to pitch to different extents;

The support masts, or at least some of the support masts, are arranged to pitch in the roll direction as well as in the pitch direction. This allows the top of adjacent masts to move inwards towards each other as they pitch to different extents and the flexible sheet material or articulated array of sub portions becomes taut along its top edge. If only two support masts are employed in a device then optionally, if desired, only one of the two may be arranged to pivot in the roll direction to achieve this effect. Where only three support masts are employed in a device then optionally, if desired, only the outermost two of the three may be arranged to pivot in the roll direction to achieve the effect. For outermost support masts (at the end of a flap) the pivoting in the roll direction may be arranged to be only in the inwards (towards the flap) roll direction. Support masts that pivot in the roll direction as well as the pitch direction may be pivotally connected to their base portions in a number of ways. For example by means of a universal joint, such as a ball and socket arrangement, or by means of two, typically close together orthogonal pivot bearings, one allows the pitch motion; the other allows the roll motion. A universal joint including elastomeric or spring members can conveniently be employed in some circumstances.

Where support masts are formed to allow pivoting in the roll direction, only a limited degree of roll may be required or desired and the pivot in the roll direction of at least the outermost masts should be limited. For example complete freedom to inwards roll could result in collapse of the flap portion. This effect is avoided if the biasing of the

50927486-1 -mmcpherson flap portion to the vertical is sufficient to prevent it. However the roll pivoting may also be limited by the design of the pivot. For example, by providing a pivot that has a stop to the pivot action after a limited angle of roll. Where a limited pivot action in the roll direction is required then pivots may be employed to provide only the few degrees of roll required. For example making use of a resilient member made of or including, for example, an elastomer or a spring, rather than by use of conventional bearings.

Other means of avoiding excessive movement in the roll direction can include providing stays on support masts. For example outermost support masts may be stayed from moving excessively inwards towards each other.

As a yet further and convenient alternative adjacent support masts, with flexible sheet material or an articulated array of substantially rigid sub portions connecting them may also be interconnected by a compression member. The compression member controls the inwards roll (towards each other) of the adjacent support masts by providing a resistance in compression. The compression member may also control outwards roll of the support masts by providing a stop to that motion. Alternatively where outwards roll of support masts is required or desired the compression member may be formed allow outwards roll to a selected extent and may control it by providing resistance in tension.

The compression member may be, for example a tube or beam including a portion or portions that can compress (and optionally extend to allow outwards roll). For example the compression member may include a portion having elastomers, springs or piston in cylinder dampers to allow compression. Typically a portion at or towards each end of the compression member is arranged to compress (and optionally extend). As an alternative the compression member may be formed to bend or have a portion that bends as compressive force is applied, thereby allowing inwards roll motion of the support masts. The compression member is flexibly connected (for example by a universal joint) to the support masts to allow their independent pivoting. The compression member provides a coupling between the support masts in similar fashion to that provided by the flexible sheet material of the flap portion or the articulated array of sub portions as discussed above. The resistance in compression (or tension) or the compression member may be selected to provide a selected degree of damping to optimise the coupling between

50927486-1 -mmcpherson support masts (allow the desired degree of phase difference in pitch between support masts).

Typically the compression member will be attached at or near the top of each of the support masts but other positions may be envisaged. Flexible sheet material of a flap portion (or an articulated array of sub portions when employed) may be attached to the compression member to provide it with additional support.

Where a compression member is employed to control the inwards roll of support masts, the corresponding outwards roll may be limited or prevented by providing stays mounted between support masts as illustrated hereafter with reference to a specific embodiment.

Wave energy conversion devices described herein may further comprise dynamic damping means, operable to adjust damping of at least a part of a flap portion over time.

Advantageously the motion of support masts of devices of the invention may be damped in a controlled fashion, with the amount of damping adjusted in response to the forces acting on the device. Support masts that are dynamically damped, at least in the pitch direction, can provide notable advantages. Dynamic damping in both the pitch and the roll direction may be provided or even only in the roll direction. As noted above as the support masts are independently pivoted the extent of pitching oscillation of each mast in response to wave action may be greater or less at any one time, dependent on the phase and force of waves acting on the flap portion, local to each support mast. Where such a situation arises the power capture obtained across a flap portion or part of a flap portion may be optimised by dynamic damping, applying different degrees of damping to different support masts over time. The damping applied provides resistance to motion of a given support mast. The part of the flap portion local to the support mast can thus be set to capture power more efficiently, depending on the local wave phasing and strength.

Dynamic damping may be obtained by use of an appropriate control system. For example the controller of the control system directs changes in damping at a given support mast in response to input signals reflecting the action of the waves and/or the

50927486-1 -mmcpherson behaviour of a flap portion or associated equipment such as the support masts, or power extraction means, as they change with time.

For example sensors, such as pressure or motion sensors, detect water motion or pressure and/or changes in such properties of the water. Alternatively or additionally sensors on the flap portion or support masts may detect pressure on, or motion of, one or more of those components and report to the controller. As a yet further addition or alternative sensors detecting changes in the pressure and/or flow rates in a hydraulic power extraction system, where one is employed, may be used to monitor the behaviour of the system. In response to the input signals from the sensors the controller, for example a microprocessor based controller, directs changes in the damping. For example a particular support mast may be provided with more resistance to pitching. Thus the dynamic damping method may comprise:

monitoring at least one of the group consisting of wave motion, wave pressure, flap portion motion, pressure on a flap portion, support mast motion, pressure on a support mast, pressure in a hydraulic power extraction system and flow rate in a power extraction system; and

adjusting the damping forces applied to at least one support mast in response to the results of the monitoring.

Typically the damping force at more than one support mast, even all the support masts present in a device will be adjusted. For example where a device has two support masts, one at each end of a flexible flap, both will be dynamically damped to enhance power capture of the flap portion between them.

The dynamic damping effect may be provided, for example by adjusting hydraulic resistance in a hydraulic power take off circuit used as power extraction means and coupled to a support mast. For example, a valve may close or partially close, operating in response to a signal or signals from the controller. Where a hydraulic power extraction means includes a hydraulic displacement motor, the control of valve positions in such a motor may conveniently be employed to adjust damping dynamically. Alternatively dynamic damping may be by, for example, adjusting a

50927486-1 -mmcpherson damping device fitted to a support mast, such as a separate hydraulic damper arrangement.

Advantageously, a number of flap portions may be laid out in a line, with a support mast that is connected to adjacent flap portion edges being provided between each flap portion. Thus a long assembly of flap portions and interconnecting masts (a mast in common between adjacent flaps) is constructed. The use of common masts between the flap portions reduces the cost in comparison with individually sited flap portions which each require at least two end support masts.

Alternatively, a flap portion may have several masts fitted at intervals along its length as well as those at each end. Thus a long flap portion of flexible sheet material or an articulated array of sub portions may be utilised to make a large device. As a yet further alternative, any combination of the above two options may be provided. For example, a number of flap portions, each having several masts fitted at intervals along its length, may have in common masts to link them together, thus forming a long assembly of long flap portions. As the flap portions are constructed of flexible sheet material or of an array of sub portions the size of flap portion is easily adapted to suit the planned location of the devices of the invention. For example where an assembly of flap portions is placed in a location with varying water depth and/or varying sea bed geology, the height and/or the lengths of the flap portions can be varied along the assembly. The most suitable anchoring locations for support masts can then be chosen, without having to space them evenly to suit a standard flap portion length. Similarly the height of flap portions can be varied with water depth to allow optimal output from the assembly.

The use of long flap portions or long assemblies as described above allows a reduction in the costs of collecting the power extracted in comparison with rigid flap devices. The length of rigid flap devices is constrained as described above. Therefore to extract substantial power at a given location an array of rigid flap devices may be employed. To avoid power losses caused by disruption to the wave motion at edges of the flaps (eddies) the flaps must be spaced apart. This spacing increases the complexity and

50927486-1 -mmcpherson quantity of power transmission cables or hydraulic pipes that are required to collect the extracted power from the array for delivery to a site of use.

A flexible flap portion of flexible sheet material may be of any suitable flexible sheet material. For example it may be in the form of a woven or knitted textile. For example aramid, polyethylene or polyester fibres or mixtures thereof may be employed to make a suitable textile material. For example sheet materials constructed from or comprising commercially available fibres such as Twaron®, Dacron®, Kevlar®, Spectra®, Technora®, Certran®, Vectran® and Dyneema® or mixtures thereof may be employed. The flap portion may have gas or air filled chambers to provide buoyancy and/or rigidity. The filling of the gas or air filled chambers may be adjustable in use so as to adjust the buoyancy and/or rigidity as desired.

Other means of modifying the behaviours of the flap portion material may include constructing different sections of the flap portion of different materials (for example with more or less flexibility and/or elasticity); providing sections of the flap portion, where a fexible sheet material is employed, with more than one layer of material which may be the same or different (for example, reinforcing certain sections of the flap portion with a more rigid material than used for the bulk of the flap); and providing the flap portion with battens. Battens may be made of elongate thin sections of material, such as steel, plastics or composite which can be attached to flexible sheet material, where used, or inserted into pockets formed in or on the flap portion in a manner akin to battens employed in yacht sails, in order to provide stiffness at selected locations. Other reinforcing techniques may be employed, for example where the flexible sheet material is a woven or knitted textile, different materials may be employed in different directions of weave or in different portions of a particular sheet. For example aramid fibres may be employed to add strength.

The support masts are mounted to pivot on base portions. Support masts may share a base portion. For example a device having only two support masts may conveniently make use of a single base portion running below the bottom edge of the flap portion.

The base portion or portions support the device and thus generally include anchorage to the bed of the body of water which may be means of piles for example.

Conveniently, each support mast may have a separate base portion that includes a pile or piles that anchors the base portion by being driven into the bed of the body of water.

50927486-1 -mmcDherson Advantageously a single pile is used with each base portion. This allows relatively convenient construction of a device in a selected location. For example piles are driven into selected locations and then the base portions with or without attached support masts are connected to the piles. After the support masts are located in position the flexible flap material or articulated array of sub portions may be attached to them. Alternatively support masts may be fitted with flexible sheet material or an array of sub portions on shore and the support mast/flap portion assembly delivered to the selected location. The power extraction means may comprise, for example, a hydraulic piston and cylinder arrangement mounted to at least one of the support masts. The hydraulic piston and cylinder arrangement reciprocates in response to the motion of the mast and the hydraulic power generated may be transmitted in the form of fluid motion to a generator that may be located under water, on shore or on a fixed or floating platform nearby the wave power energy conversion device. Thus electrical energy may be obtained from wave motion.

The devices described above are used to provide methods of extracting energy from waves.

Thus the present invention also provides a method of extracting energy from waves comprising:

providing a wave energy conversion device comprising:

wherein at least one of the support masts is coupled to power extraction means for extracting energy from the movement of the flap portion and support masts;

and

50927486-1 -mmcpherson locating the device on the bed of a body of water with the flap portion transverse to the expected direction of wave motion.

The present invention also provides a method of extracting energy from waves comprising:

providing a wave energy conversion device comprising:

at least one upstanding flap portion of flexible sheet material supported by at least two spaced apart upstanding and independently pivoting support masts, with one support mast disposed at each end of the flap portion;

wherein at least one of the support masts is coupled to power extraction means for extracting energy from the movement of the flap portion and support masts; and

locating the device on the bed of a body of water with the flap portion transverse to the expected direction of wave motion.

providing a wave energy conversion device comprising:

50927466-1-mmcpherson and

locating the device on the bed of a body of water with the flap portion transverse to the expected direction of wave motion. Brief description of the drawings

Further preferred features and advantages of the present invention will now be described with reference to the accompanying drawings in which:- Figure 1 illustrates the pitching motion of a device of the invention as discussed above: Figures 2 and 2a shows in schematic perspective and plan views a wave energy conversion device with a flap portion of a flexible sheet material;

Figure 3 shows in schematic elevation view a wave energy conversion device with multiple support masts;

Figure 4 shows in schematic perspective a support mast fitted with a piston and cylinder hydraulic power extraction means; and

Figures 5, 5a and 5b show in schematic elevation further devices of the invention;

Figure 6 shows in schematic perspective view a wave energy conversion device comprising a flap portion of an articulated array of substantially rigid sub portions; Figure 6a shows a sub portion of a flap portion; and

Figure 7 shows a schematic flow diagram of dynamic damping of a wave energy conversion device.

Description of some embodiments

Figure 2 shows in schematic perspective a device 14 of the invention, comprising two upstanding and biased to the vertical support masts 16, 18 mounted to pivot on bearings connecting to bases 20, each of which in this example is anchored to the bed 22 of a body of water by a pile (not shown). A generally rectangular flap portion 26 of flexible material is attached by opposite edges to the support masts. The device 14 is mounted with the flap portion transverse to the expected wave direction indicated by the double headed arrow 28. In response to the action of waves the flap portion 26 and support masts 16, 18 pitch backwards and forwards as indicated by the curved arrows P.

A power extraction means (not shown, but see figure 4 as an example) extracts power from the reciprocating motion of the flap and masts assembly. The masts 16, 18 and

50927486-1 -mmcp erson flap portion 26 are biased to the vertical; in this example by the provision of air or gas filled chambers in the upper section of the masts 16, 18.

Figure 2a illustrates in schematic plan view the device 14 of figure 2, with one of the support masts 16 pitched from the vertical to a further extent than the other 18. In this example the masts 16,18 are formed so as to be able pivot inwards to each other, in the roll direction as indicated by the double headed arrows R.

The extent of inwards rolling of the masts shown by the angles A made with respect to the lines 32 showing the direction of pitch is determined by the length and elasticity of the taut top edge 34 of the flap portion 26; together with the amount of roll pivoting allowed by the design of the mast pivots; and any elasticity provided in the mast pivots, for example by using elastomeric bearings. Figure 3 shows in elevation a device 14 similar in construction to that of figures 2 but including an assembly of three support masts, two 16,18 to either end of the assembly and a third 36 provided between two flap portions 26, 26a of a flexible sheet material. Similar assemblies with more flap portions 26,26a and support masts 36 in common between pairs of flap portions may be constructed as desired. Alternatively a single continuous flap portion may be employed with the support mast or masts 36 attached to one face or other of the flexible sheet. A combination of these alternative arrangements may be employed to make a long assembly of long flap portions.

In this example all three masts 16, 18, 36 are able to pivot in the roll and in the pitch directions. The extent of roll of the masts 16, 18 at the ends of the assembly is limited by the stays 38, cables running from near the top of the support masts 16, 18 and anchored to the bed 22 of the body of water. The stays 38 have elasticity sufficient to allow some inwards roll of the masts 16, 18. Figure 4 shows a support mast 16 such as may be employed in the devices of figures 2 and 3. The support mast is pivotally connected to a base 20 by means of two pivots or bearings 40, 42. One pivot 40 allows pitch motion indicated by the arrow P, the other 42 roll motion as indicated by the arrow R. Attached to the mast 16 is a twin piston and cylinder hydraulic power extraction means. The pitch motion P causes the pistons inside the cylinders 44 to move backwards and forwards. The hydraulic power thus

50927486-1 -mmcp erson generated can be transferred by a suitable hydraulic circuit to drive a hydraulic motor which can be used to power an electrical generator in the known fashion.

Figure 5 shows in schematic elevation a device similar to that of figures 2, but incorporating as a compressive member a beam 46, flexibly connected (e.g. by ball and socket joints) to the support masts 16,18. The beam 46 includes a portion 48 that is compressible (e.g. including elastomers, springs or a piston in cylinder arrangement) thus allowing and controlling the. inwards roll of the support masts 16, 18 as indicated by the arrows 50 and in similar fashion to that illustrated in figure 2a. Unwanted outwards roll motion of the support masts is prevented by the stays 38, in this example fitted between the support masts in a crosswise arrangement, each stay attaching to near the top of one support mast and near the bottom of the other.

Figure 5a shows in schematic elevation a similar arrangement to that of Figure 5 but in this example the compression member is a beam 46 provided with two compressible portions 48, 49, one towards each end of the beam. In this example the compressible portions 48,49 are formed to allow some extension, permitting outwards roll of the support masts 16,18 as indicted by the arrows 52. Thus both inwards and outwards roll is controlled by the beam 46 and can be damped to the desired extent by suitable construction of the compressible portions.

Figure 5b shows a similar arrangement to that of figure 5a except that the compression member is a beam 46 formed to bend in response to expected compressive forces as indicated in figure 5c which shows the arrangement of 5b in a view comparable to that of figure 2a.

Figure 6 shows an alternative wave energy conversion device 14. The device 14 has four support masts, two 16, 18 at either end, and two other masts 36 in intermediate positions. Each support mast is mounted on a base 20 via pivots 40, 42 (not shown in any detail here but see figure 4 as an example) allowing pivoting in both the pitch and roll directions. The support masts support three flap portions 26,26a and 26b. Each flap portion comprises an articulated array 54 of substantially rigid sub portions 58.

The sub portions 58 are elongate cuboids, in this example, running vertically and presenting opposed faces 60 (only one visible in this view) to the direction of wave

50927486-1 -mmcpherson motion indicated by arrow 28. The sub portions are hollow and of glass reinforced plastic (GRP) for example. The sub portions are mounted on and linked together by elongate flexible connectors, ropes 56 in this example. The connection together by rope allows the flap portions 26,26a and 26b a degree of flexibility. The ropes 56 run spaced apart and parallel from one end support mast 16 to the other 18. In this example ropes 56 pass through intermediate support masts 36 and through sub portions 58. The sub portions 58 may be provided with chambers therein. These can provide buoyancy (biasing to the vertical) when gas filled and/or mass when water filled. The support masts 16, 8, 36 are provided with power extraction means (not shown in this figure, see for example figure 4). The support masts are dynamically damped to improve power capture, for example by a valve controlling the flow of hydraulic fluid in a piston and cylinder arrangement such as in figure 4 or in an associated hydraulic circuit and motor arrangement (not shown). Figure 6a shows in partial perspective view an alternative sub portion 62 which has flat faces 60 but curved edges 64. A slot 66 passing through the sub portion 62 from edge to edge and open at the bottom 68 is shown in this example, allowing the sub portion 62 to be dropped onto a set of elongate connectors such as the ropes 56 shown in figure 6, during construction of a device. The ropes 56 may then be secured to the sub portion 62 by suitable fixings

Figure 7 shows a flow diagram of a system for dynamic damping such as may be applied to flexible flap portion devices described herein. One or more sensors 70 monitors the situation, for example monitoring at least one of wave motion, wave pressure, flap portion motion, pressure on a flap portion, support mast motion, pressure on a support mast, pressure in a hydraulic power extraction system and flow rate in a power extraction system.

The sensor or sensors 70; send data to controller 72, typically a microprocessor. In response to the data from sensors, the controller 72 then directs changes in damping. In this example the controller directs changes in a hydraulic power extraction system 74. For example valve settings are changed to alter pressure and or flow in a part of the hydraulic circuit. The resulting changes in resistance to motion of at least one support mast alters the behaviour of the part of the flap portion local to that support mast or support masts.

60927486-1 -mmcp erson Thus the behaviour of the wave energy conversion device 14 (of which 74 is a part) is affected. Feed back (suggested by dashed arrows 76) obtained from appropriately placed sensors 70 e.g. in the hydraulic system 74 or on part of the flap portion or support masts of device 14 may be used to supply information to the controller 72 about the behaviour and disposition of the power extraction system 74 or the device 14.

As an alternative suggested by arrow 75, the controller 72 may direct changes to some other part of device 14 to affect damping. For example a separate hydraulic damping device attached to a support mast.

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

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Claims

1. A wave energy conversion device comprising:

2. A wave energy conversion device according to claim 1 wherein the flap portion comprises an articulated array of substantially rigid sub portions.

3. A wave energy conversion device according to claim 1 wherein the flap portion comprises flexible sheet material.

4. A wave energy conversion device according to any one of claims 1 to 3 further comprising dynamic damping means, operable to adjust damping of at least a part of a flap portion.

5. A wave energy conversion device according to claim 4 wherein the dynamic damping means adjusts the damping of at least one support mast.

6. A wave energy conversion device according to claim 5 wherein the damping of the at least one support mast is by means of a control system that directs changes in damping at a given support mast in response to input signals from sensors monitoring at least one of the action of waves, the behaviour of the flap portion, the behaviour of at least one of the support masts, or the behaviour of the power extraction means.

7. A wave energy conversion device according to claim 5 or claim 6 wherein the power extraction means comprises a hydraulic power circuit associated with the at

50927486-1 -mmcpherson least one support mast and dynamic damping of the at least one support mast is obtained by adjusting at least one valve in the hydraulic power circuit.

8. A wave energy conversion device according to any preceding claim wherein the support masts are formed and arranged to pivot only in the pitch direction.

9. A wave energy conversion device according to any one of claims 1 to 7 wherein at least one support mast is formed and arranged to allow pivoting in the roll direction.

10. A wave energy conversion device according to any one of claims 1 to 7wherein all the support masts are formed and arranged to allow pivoting in the roll direction.

11. A wave energy conversion device according to any preceding claim wherein the biasing of the support masts and flap portion to the vertical is obtained by buoyancy.

12. A wave energy conversion device according to claim 6 wherein the buoyancy is adjustable.

13. A wave energy conversion device according to claim 11 or claim 12 wherein the buoyancy is provided by at least one of:

at least one buoyant support mast;

attaching buoyant members to a support mast or the flap portion; and providing a flap portion having gas, air or foam filled chambers or foam filled pockets.

14. A wave energy conversion device according to any one of claims 1 to 11 wherein the biasing of the support masts and flap portion to the vertical is provided by use of resilient members acting on a support mast.

15. A wave energy conversion device according to any preceding claim wherein the device is formed and arranged to present a substantially continuous surface to the wave motion throughout the depth of the water from the wave crest to the bed of the body of water.

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16. A wave energy conversion device according to any preceding claim wherein the degree of coupling between adjacent support masts is controlled by at least one of: providing a compression member interconnecting the adjacent support masts; providing stays on support masts; and

providing at least one support mast formed and arranged to pitch in the roll direction as well as in the pitch direction.

17. A wave energy conversion device according to any one of claims 9 to 16 wherein at least one support mast pivots in the roll direction by means of:

providing a universal joint; or

providing two orthogonal pivot bearings, one allowing pitch motion; the other allowing pivoting in the roll direction.

18. A wave energy conversion device according to any one of claims 9 to 17 wherein pivoting in the roll direction of at least one support mast is limited.

19. A wave energy conversion device according to claim 18 wherein pivoting in the roll direction is limited by at least one of;

providing a pivot that has a stop to the pivot action after a limited angle of roll; providing a pivot comprising an elastomer or a spring;

providing at least one stay on at least one support masts; and

providing a compression member between adjacent support masts.

20. A wave energy conversion device according to claim 19, comprising a compression member:

wherein the compression member comprises a portion having elastomers, springs or piston in cylinder dampers to allow compression; or

wherein the compression member is formed and arranged to bend as compressive force is applied.

21. A wave energy conversion device according to any preceding claim wherein a plurality of flap portions are laid out in a line, with a support mast that is connected to adjacent flap portion edges being provided between each flap portion.

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22. A wave energy conversion device according to any one of claims 1 to 20 wherein a flap portion has at least one support mast fitted between the support masts disposed at each end of the flap portion.

23. A wave energy conversion device according to any one of claims 1 to 20 comprising a plurality of flap portions, with a support mast that is connected to adjacent flap portion edges being provided between each flap portion and wherein each flap portion has at least one support mast fitted between the support masts disposed at each end.

24. A wave energy conversion device according to any preceding claim wherein each support mast has a separate base portion that includes at least one pile for anchoring the base portion to the bed of a body of water.

25. A wave energy conversion device according to any preceding claim wherein each base portion has a single pile for anchoring to the bed of a body of water.

26. A wave energy conversion device according to any preceding claim wherein the power extraction comprises a hydraulic piston and cylinder arrangement mounted to at least one of the support masts.

27. A wave energy conversion device according to claim 2 wherein the support masts at each end of the flap portion are used to support a generally rectangular or square array with the end support masts being attached to or near opposed edges of the generally rectangular or square array.

28. A wave energy conversion device according to claim 2 or 27 wherein the substantially rigid sub portions of the array are in the form of rectangular or square plates or three dimensional, solid or hollow, cuboids, cubes or cylinders.

29. A wave energy conversion device according to claim 2 or 27 wherein the substantially rigid sub portions of the array are in the form of elongate plates or three dimensional shapes arranged substantially vertically in the array.

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30. A wave energy conversion device according to claim 2 or 27 wherein the linking means joining the substantially rigid sub portions comprises elongate flexible connectors such as chains, ropes or wires.

31. A wave energy conversion device according to claim 30 wherein the elongate flexible connectors run lengthwise along the flap portion with sub portions of the flap portion distributed alon the length.

32. A wave energy conversion device according to claim 3 wherein the support masts at each end of the flap portion are used to support generally rectangular or square sheet or sheets of flexible sheet material, with these end support masts being attached to or near opposed edges of the generally rectangular or square sheet or sheets.

33. A wave energy conversion device according to claim 3 or 32 wherein the degree of coupling between adjacent support masts is controlled by:

the elasticity of the flexible sheet material employed in the flap portion;

providing fullness to the flexible sheet material employed in the flap portion whereby when adjacent masts are in a neutral upstanding position the flap portion is not held fully taut;

34. A wave energy conversion device according to claim 3 or 32 wherein the flexible sheet material of a flap portion is in the form of a woven or knitted textile.

35. A wave energy conversion device according to claim 3 or 32 wherein the behaviour of a flap portion is modified by at least one of:

constructing different sections of the flap portion of different materials;

providing sections of the flap portion with more than one layer of material; providing the flap portion with battens; and

where the flexible sheet material is a woven or knitted textile, employing different materials in different directions of weave.

36. A method of extracting energy from waves comprising:

providing a wave energy conversion device according to any one of claims 1 to 35; and

50927486-1-mmcphereon locating the device on the bed of a body of water with the flap portion or flap portions transverse to the expected direction of wave motion.

37. A method of dynamic damping of a wave energy conversion device according to any one of claims 1 to 35, the method comprising:

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