GB2026621A - Water Power Device - Google Patents

Abstract

The device is buoyantly supportable and comprises a reaction element 10, Fig. 1, and a plate or membrane element 12 which can move back and forth to react against the reaction element 10. The movement of the plate or membrane element which is caused by the cyclic application of wave forces is converted into a more readily usable form by, for example, an air or hydraulic transmission and electrical generation means driven by the pressure of the air or hydraulic fluid which arises by virtue of the back and forth movement of the plate or membrane element 10. In a preferred arrangement, a single spine 35, Fig. 10, supports a plurality of the said plate elements 36 which are movable individually, and in some applications the individual plate elements are coupled so that, in one case, as certain elements are moving towards the spine, others are being displaced away from the spine, and in other cases the relative displacements of adjacent elements are utilised to provide the pumping of hydraulic fluid or air. The plate elements may be parallel or at an acute angle to oncoming waves, or the plate elements may be plated along both sides of a vessel and extend perpendicular to oncoming waves. <IMAGE>

Description

SPECIFICATION Energy Generating Device This invention relates to energy generating apparatus usable for converting to a usable form the energy in waves in a body of liquid such as the sea or ocean.

There are a number of proposals in existence for the conversion of liquid wave energy, and generally speaking a main class of such proposals involves a primary component which is positioned to come under the influence of the waves to be moved back and forth thereby. The back and forth movement is converted into a more usable form, such as electrical energy, by means of a suitable transmission.

In a particular proposal of this class, the primary component is adapted to rock about an axis, and has a lobe at the waveward side which is displaced up and down by the waves (and because of this, it is called a "duck") whilst as the leeward side it does not have any displacement. It is envisaged that a plurality of such ducks should be arranged on a common spine.

The engineering difficulties of designing and manufacturing such ducks, however, even at 1/1 0th scale, have cast doubt on what otherwise was a promising concept.

There are two further areas of difficulty with the said ducks. First, a spine which is capable satisfactorily of withstanding the anticipated bending moment is required, but does not appear to be available, and secondly there are problems to be solved concerning the primary power takeoff, bearings accessibiiity, and the robustness of the apparatus to withstand "survival" conditions e.g. storm conditions. It is the second area of problems which has led us to apply some radical thinking of the design of a new energy generating apparatus to replace the said ducks.

According to the present invention buoyantly supportable apparatus for use in the generation of energy from the wave motions of a body of liquid comprises a reaction element, and a displaceable plate element operatively connected to the reaction element for back and forth movement to react against the reaction element when the plate element comes under the influence of waves in the body of liquid, and including means for extracting wave energy in another and more readily usable form by virtue of the relative movement between the reaction element and the plate element.

Preferably, the reaction element is part of an elongated spine and there is a plurality of said plate elements disposed along at least one side of said spine when the apparatus is to be used in a position parallel or at an angle (specifically an acute angle) to the wave front from which the energy is to be extracted, or there may be said plate elements arranged side-by-side along each side of the spine when the spine is to be used in a position at right angles to the wave front from which the energy is to be extracted.

The said means for extracting energy from the movement back and forth of the plate elements may be any suitable such as fluid pressure rams with suitable transmission as desired, or the said plate elements may be arranged to act as air pistons to pump air which can be discharged into conduits or menifold in the spine, the pumped high pressure air being used as means for driving an air turbine to produce rotary motion from which, for example, electrical power can be derived.

In order to provide damping for the plate elements, each said displaceable plate element and the spine element may define a cavity the volume of which decreases and increases as the displaceable element moves towards and away from the spine element, the said cavity being capable of having a liquid therein which will act as a variable damping means on the displaceable element swinging movements.

Where there is a liquid in said cavity, it is arranged that its level will increase as each displaceable plate element swings towards the spine element, due to the heave effect of a wave acting on the displaceable member; the increase in level of course means an increase in the head of that liquid and an increase in the force tending to return the displaceable element in a swinging direction away from the spine element.

The two regions respectively of the spine element and displaceable element which face and come together and separate as the displaceable member swings as aforesaid preferably are correspondingly shaped, so that in one extreme position of the displaceable element, the said cavity is of zero volume, or contains only a thin even thickness film of the said liquid.

Preferably, the liquid when provided.in said cavity is the same liquid as that in which the apparatus is buoyantly supported. In such arrangement, it is preferred that the cavity will be such as to provide leakage between the body of liquid and the liquid in the cavity.

According to a preferred feature of the present invention, said plate elements along the length of the spine are such as to be capable of complying with instantaneous wave displacement along the length of the spine, so that different plate elements on the spine can move out of phase, and there is a coupling means interconnecting said plate elements so that when wave forces pushes some plate elements towards the spine, other plate elements on which the wave forces are out of phase are forced away from the spine.

In this arrangement, the plate elements may be sealed relative to the spine in order to prevent flow of liquid into the space between each plate element and the spine when the plate element is displaced from the spine. Alternatively, there may be pump means for pumping liquid out of the spaces between the plate elements and spine.

In another arrangement, plate elements are defined by a continuous flexible membrane supported at intervals along the length of the spine by supports which can displace back and forth with displacement of the flap means and which define the plate element.

The said coupling means may be for example a tensioned cord, cable or the like extending lengthwise of the spine and trained round groups of three pulleys, one group for each plate element, two pulleys of each group being carried by the spine and the third being displaceable in synchronism with the associated plate element.

In an alternative arrangement, the plate elements may each be connected to a hydraulic ram, the rams being connected to a common high pressure main.

The said inter-connecting means preferably is connected to transmission means for converting movement of the plate elements into another form of energy such as rotary motion, fluid pressure energy, or electrical energy.

In the case where it is proposed to have a single spine carrying the said absorbing plate elements side by side and facing the oncoming waves, and to extract energy from the waves by suitable means connected to the absorbing elements, the most commonly proposed energy extracting means comprises hydraulic pumps, such as piston and cylinder devices, which convert the element movements into fluid (suitably the same as the body of water) at high pressure, and such high pressure fluid can of course be used to drive a mechanical device such as a turbine for the eventual production of electrical energy, which is the usual goal of apparatus of the type to which the invention relates.

It has been found that it is desireable to control the displacement of each of the absorbing elements, so that the inertia forces thereof do not become too great, as might arise in high seas, and indeed if the absorbing element were left free to swing back and forth in sympathy with the wave forces the apparatus could be self destructive. It is therefore a preferred proposal that the movements of each absorbing elements should be damped or restrained in dependence upon the instantaneous velocity of the element. It has been shown moreover that damping of the elements in relation to the said velocity also provides maximum wave to hydraulic power conversion efficiency.

Unfortunately, the majority of hydraulic pumping devices are fixed displacement pumps and are designed to operate best against a constant hydraulic pressure, and without modification would not work optimally with a to and fro moving absorbing plate element, whose velocity changes cyclically. Variable displacement pumps can be used in connection with such absorbing plate elements, but are complex, expensive, less efficient than fixed displacement pumps and as they are less robust than fixed displacement pumps, more than likely would have a shorter life in the application in question.

Furthermore, the variable displacement pumps incorporate mechanical actuators or valve control gear to achieve the variation in displacement, and such gear or actuators have to be controlled by a hydraulic and/or electrical servo system from velocity proportional control signals which can be difficult to derive.

The present invention seeks to provide in a preferred arrangement of the apparatus it is possible, as will be explained hereinafter, to use fixed displacement pumps for providing velocity related damping on the movement of the energy absorbing elements.

Thus, according to a preferred form of the present invention each of said plate element is connected to damping means, the damping effect of which is varied depending upon the degree by which the element is positionally out of phase relativele to an adjacent plate element.

As wave forces are applied cyclically and as the wave instantaneous force along the length of the spine will vary cyclically, the positional phase difference between adjacent plate elements is a measure of the instantaneous velocity or relative velocity of the element or elements, and pairs of plate elements can be hydraulically coupled by similar fixed displacement hydraulic piston and cylinder devices coupled through check valves so that when the two plate elements of the pair are positionally in phase, the pistons and cylinder devices are out of phase so that one discharges its displacement into the other and there is no damping. If the adjacent plate elements become out of positional phase by 1 800 on the other hand the damping is a maximum and the devices can be arranged to discharge.

When the spine is long, and there are many of the said plate elements, there will usually always be at least some of the elements positionally out of phase, because the instantaneous wave force will be different along the length of the spine.

Instead of fixed displacement hydraulic pumps, it may be possible to use other forms of energy conversion means.

In a particularly preferred arrangement, when the plate elements are arranged to operate as air pumps the spine may have two common air manifolds, one being a high pressure manifold and the other being a low pressure manifold. Each plate element is associated with the two manifolds respectively by the two one way valves, so that as the plate element swings towards the spine it pumps air from a cavity between the plate element and the spine into the high pressure manifold through the high pressure valve, whilst the valve connecting the cavity to the low pressure valve to the cavity closes. As the plate element moves away from the spine, air flows into the cavity through the low pressure valve, whilst the high pressure valvs is closed and the cycle repeats with each to and fro movement of the plate element.

In a particularly advantageous arrangement of the present invention, the spine is in fact the hull of a motorised vessel, in the nature of a tanker in terms of size, the plate elements being mounted on the vessel sides. An advantage of such an arrangement is that the vessel can be manouvered into the best position related to the wave front from which energy is to be extracted.

There may be return means for returning the plate elements to outward positions after they have been displaced inwards by wave forces, and such means may be for example springs or the like.

The spine element preferably has suitable ballasting to ensure that it floats in a predetermined position in the liquid, and it is preferred that, for stability, the spine is relatively massive compared to an individual plate element.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, which are diagrammatic and in which Fig. 1 is a sectional elevation showing a spine and displaceable plate element of apparatus according to a first embodiment of the invention; Fig. 2 shows relative displaceable plate element positions as related to a wave pattern of the body of liquid; Fig. 3 illustrates one example of how the motion of the displaceable plate element can be converted into rotary motion; Fig. 4 shows how the displaceable plate element can be positioned in survival conditions; Fiy. 5 shows how the spine may move in use; Fig. 6 illustrates how the cavity ends may be sealed in a limited fashion;; Fig. 7 and 8 show alternative cross sectional shapes for the spine, and in the case of Fig. 8, for the displaceable element; Fig. 9 illustrates how the spine element may be tensioned by means of guy ropes or members.

Fig. 10 is a plan view illustrating the principle of another embodiment of the present invention; Fig. 11 is a sectional view showing two arrangements of plate elements; Fig. 12 is a plan of an apparatus according to another embodiment of the invention; Fig. 13 is a plan view of an apparatus according to another embodiment of the invention; and Fig. 14 is a plan view of an apparatus according to a third embodiment of the invention.

Fig. 1 5 is a plan showing a section of a spine with a plurality of energy absorbing devices thereon; and Fig. 16 shows how a pair of the energy absorbing devices shown in Fig. 1 5 may be hydraulically coupled in accordance with another embodiment of the invention; Fig. 17 shows an apparatus for explaining further embodiments of the invention; Figs. 1 8, 1 9 and 20 respectively show the apparatus of Fig. 17 in sectional elevation, the section being taken on the line Il-Il in Fig. 17, and the three Figures respectively showing the apparatus in different positions; Figs. 21, 22 and 23 respectively show, in a manner similar to Fig. 1 8 three embodiments of the invention constructed in accordance with the principle of the apparatus shown in Fig. 17;; Figs. 24,25, and 26 are views similar to Figs.

21,22 and 23 but show different modes of energy conversion; Fig. 27 shows how a spine and plate element may be spatially arranged; Fig. 28 shows how a floating vessel may be provided with plate elements to provide with plate elements to provide an apparatus according to another embodiment of the invention; Fig. 29 shows in enlarged detail how a plate element can be used as an air pump; and Fig. 30 is aview similar to Fig. 29, but sharing a modified form of energy conversion means.

Referring to the drawings, a basic arrangement is shown clearly in Fig. 1. A cylindrical reaction element in the form of a spine 10 has hinged thereto displaceable plate elements 12, referred to herein as flaps, the pivot axis being indicated by 14.

The spine 10 and the flaps 12 are buoyancy members, the spine 10 having ballasting 1 6 to ensure that it will take up the position shown when buoyantly supported in calm water, for example as indicated by water line W.L. The inner face 1 8 of the flap 12 is curved to match the curvature of spine 10 but in the usual calm water position shown in Fig. 1 -a cavity 20 exists between the spine 10 and flap 12. The cavity 20 will normally contain a quantity of liquid 22, which is the same as the surrounding liquid e.g.

sea water.

To explain the basic principle of operation, assume that the cavity 20 between flap 12 and spine 10 is partly full of water at the mid-swing position, then the neutrai position will be as shown in Fig. 1 with all weight and buoyancy moments balanced. With an increasing wave height the flap 12 will rotate anti-clockwise and will be resisted by the spring action of increasing water level in the cavity 20. With a decreasing wave height the flap 12 will rotate clockwise, and will likewise be resisted by the spring action of decreasing water level in the cavity 20.

The main water level in the cavity 20 is determined by the dynamic range of the flap 12 with respect to the mean position of the flap.

Under no wave conditions the cavity water level will be mean sea level with the flap angle determined by the spine-flap geometry and weight/buoyancy distribution. With increasing wave height, cavity water will be progressively extruded at the flap peak excursions thereby decreasing the mean water level within the cavity.

Fig. 2 shows a range of flap positions as related to a simple sine wave pattern.

The steady state cavity water level at any particular sea state will be determined by the balance of water extrusion and the leakage, controlled or otherwise, into and out of the cavity.

Inertia and spring rates of the flap 12 are functions of structural geometry and flap mass and the air to water volume ration within the cavity 20 and hence may be tuned to the wave energy frequency band.

In practical example, it is required that there be a means for harnessing the swinging movements of the flap 12. One example is illustrated in Fig. 3.

Referring to Fig. 3, curved power arm 22 fixed to the flap 12 will rotate about the hinge 14 and provide a mechanical power drive within a controlled environmental section 24 on the upper surface of the spine 12. The power arm 22 can be fitted with a toothed rack to drive geared hydraulic pumps or with a road surface for a friction tyre drive. A direct acting sea water pump is not out of the question. Several arms 22, spaced along the length of the flap 12 may be provided, each co-operating with a sliding or gaiter seal at the point of entry into the power module 24.

in very high or storming seas (survival conditions) the angular movement of the flap may get out of control or may decrease the cavity volume towards zero at the peak upward excursions. With decreasing cavity volume the wave loading on the flap will be balanced by the pressure due to restricted water expulsion from the cavity. This non-linear damping of the flap movement will prevent direct impact with the spine over the operational range of the falp 12.

In the case where the flap may get out of control, it may be suitable to lock the flap in position.

If the flap is prevented from moving from the near impact position, the flap will become in effect integral with the spine as far as wave loading is concerned. Wave forces will be transmitted to the spine by the sealing contacts and the hydrodynamic water pressure between flap and spine. Movement of the flap 12 relative to the spine will be prevented by mechanical clamping of the power arm 22 or end sections of the flap 12.

It seems reasonably clear that in use, the spine 12 will also tend to rock or rotate. The rotation of the spine which is due to operational cavity buoyancy, can be used to advantage. In calm conditions the buoyancy-ballast distribution in the spine flap cross-section is such that the cavity is of minimum volume when full of water. With increasing wave height, the flap rotation will increase giving a corresponding increased mean cavity volume. A larger mean cavity volume gives rise to an upward buoyancy force on the wave side of the spine. The force acts as a torque on the spine producing rotation. This spine rotation moves the hinge location to give an effectively higher flap and larger cavity volumes with increased flap inertia. The effect is illustrated in Fig. 5.

It is desirable that the cavity 20 should be sufficiently but not completely sealed relative to the surrounding water so that the cavity 20 can be self-pumping.

Leakage rates of up to say 1/10th of the operational cavity volume per wave cycle can be tolerated and indeed may be required for effective operation. The seal at hinge 14 may be a simple tolerance fit or a full sealed flexible flap. The end seals present a more difficult problem. A possible end sealing arrangement is shown in Fig. 6. A close tolerance sliding seal between flap ends is provided by separating plates 26 neatly fitting between adjacent flap ends. With such an arrangement, the leakage should be tolerable provided that the end gaps are not more than 1 Ocm, which should be sufficient to cope with adjustable construction tolerances and load distortions.

The adoption of a flap as the primary component as opposed to the duck as described herein provides more scope for spine design. A cylindrical spine has been the natural structural shape for the duck and as such has presented a serious design problem. Bending moment considerations dictate the maximum length of a rigid spine to be not more than 250m for 1 0m duck. Longer spine lengths would have to incorporate joints to give two degrees of freedom, an expensive engineering challenge to say the least. The present invention gives us the facility of using structural cross sections which are more compatible with the flap configuration and by the use of which the bending moment problem may be solved.

There are two structural ways in which.an infinite length spine can withstand worst case wave loading; either the structure has high stiffness with the necessary strength to resist the wave loading, or the structure has low stiffness with the necessary flexibility to bend and reduce the wave loading by reducing the effective wave height.

Consider spines with the cross sections illustrated in Fig. 7.

Both these sections are relatively strong in heave and relatively flexible in surge.

Furthermore, wave loading in heave is significantly less than in surge. Hence, in heave the strength to wave loading ratio is high giving a rigid spine with minimal bending, whereas in surge the high deflection reduces the wave loading to give a flexible spine with a minimal strength requirement.

Variable stiffness spines in two dimensions may have a variety of cross sections ranging from vertical steel plates to the standard cross sections of steel work. However, the oval and box sections of Fig. 7 have the advantages of efficient use of steel, inherent buoyancy, reasonable stiffness in torque and a compatable shape to accommodate the flaps.

Fig. 8 shows two modified arrangements according to the invention. In Fig. 8(A) a simple flap 12 is hinged at the bottom of the wave side of the rectangular section spine 12. The outer face of the flap is fitted with a geometrically shaped buoyancy cross section. The second design has a right angled flap hinged beneath the spine (of similar cross-section) to give an improved weight moment to the flap.

Vertical location of the spine is maintained by the bilge ballast 1 6 to give buoyancy reserve of about 1/10th of the displacement.

To limit the distortion of the box section, vertical bulkheads and stiffeners can be added along the inside of the spine. These bulkheads, if sealed, will add to the damage stability of the device. Steel fabrication techniques seem appropriate to the construction although reinforced concrete may be used.

The purpose of the spine is to provide a reacting surface for discrete wave absorbers.

Forces along this reacting surface should tend to cancel with spine length and preferably should be associated with power loading rather than direct wave loading. Reduction of cross-sectional area reduces wave loading, but also reduces the second moment of area which determines the section strength. However, some structures meet this problem by external guys, for example as illustrated in Fig. 9.

In the case of the oval or box cross-section spine, the bending deflection in surge will generate waves on the leeward side of the apparatus. This deflection will be relatively small over the operational range of wave heights particularly with the reduction of wave loading due to impedance matching of the flap with the waves. Ideally, surge stiffness should be high over the operational range and low in survival conditions.

Fig. 9 shows the cross-section and plan of a guyed spine, the guys having controlled pretension.

The arrangement includes transverse hydraulic rams 28 which pre-tension the guy system 30 to increase appreciably the surge stiffness and hence reducing deflection. Under survival conditions the pre-tensioning can be kept either constant, irrespective of bending, or reduced to near zero to allow full bending flexibility. The need to use this technique depends entirely on the cost return in terms of energy conversion efficiency.

Consideration might also have to be given to the torsional stiffness of the spine. The torque produced by the flaps has to be balanced along the length of the spine in order to reduce pitch displacements. This torque is well within the torsional stress limits of the structural cross sections mentioned and hence torsional displacement should not figure in the efficiency of energy absorption.

The various parts of the apparatus can be manufactured in dry dock, floated out to the wave power site and the flaps clamped to the spine and connected into the secondary power system.

Maintenance would be by access into the power module compartments or by exchanging flaps for refurbishing in dock.

The apparatus according to the embodiments described with reference to Figs. 1 to 9 have the following advantages: 1. Potential wide-band high efficiency operation.

2. Survival characteristic with non-operational and non-dynamic features giving good damage stability.

3. Direct mechanical power drive in a closed environment.

4. Relatively compact and simple structure aiding constructional and assembly methods.

5. Easy access to machinery for installation, inspection, maintenance and repair purposes.

6. Close down mode of individual or all flaps for any purpose.

7. Inherent or controlled inertia and spring rate characteristics to give optimal matching to wave spectra and power system loading.

8. Limited dynamic movement of all moving parts giving efficient use of components.

9. Potential low cost device with a good output power/capital cost ratio without any expensive problem areas.

10. The device requires a relatively simple mooring system with low survival forces.

In Figure 10 there is shown a section of a buoyant spine 35 to one side of which are plate elements in the form of a number of individual flaps 36 which can move towards and away from the spine 35 in the manner indicated by arrow 37.

The flaps 36 are in fact pivoted to the lower edge of the spine as shown in Fig. 11, and are separated by means of separation plates 38.

When each flap 36 is displaced from the spine as shown in Fig. 10, there is formed a space 39 between the spine and flap, and the aggregate volume of such spaces 38 is referred to in relation to this embodiment as the "cavity".

If the apparatus is considered as being arranged so as to be perpendicular to the direction, indicated by arrows 40 of the wave front of the body of liquid in which the apparatus floats, the flaps 36 will be displaced back and forth in the direction of arrow 40 by the wave forces which will be applied to the apparatus.

These forces are cyclic, and in a direction at right angles to direction 40, the wave forces continuously vary, for example shown by wave force line 41. In fact the nature of a wave front along the spine 35 in the direction of arrow 40 is such that the mean wave displacement tends to zero for infinite spine length. From a practical point of view, this also holds true for spines of a length of the order of a few crest lengths and the volume of the cavity along a finer length of spine, if sufficient, tends to be constant although the individual volumes of the said spaces 39 change constantly with the back and forth movement of the individual flaps. If reference is made to Fig.

10, it will be seen that the shape defined by the flaps 36 approximates to the wave shape 41.

In this arrangement the flaps 36 which are being displaced towards the spine 35 transmit feedback forces to other flaps which are not experiencing the same displacement forces, and such other flaps move out of phase with the flaps which are being displaced towards the spine 35.

The means for giving effect to this may be on the one hand mechanical or on the other hand hydraulic, and if reference is made to Fig. 12, in the arrangement shown the flaps are interconnected by a rope and pulley system. A rope or cable 42 extends lengthwise of the spine 35and is maintained under tension. For each flap 36 there is a group of three pulleys 43, 44 and 45 of which pulleys 43 and 45 are carried by the spine, and pulley 44 is carried by a support arm 46 connected to the flap 36 and movable therewith.

The tension in the rope 42 is held constant, for example by a winch, and with this arrangement each flap 36 in effect sees a constant spring rate with zero inertia. Thus, displacement of one flap by wave loading will be balanced by the out of phase displacement of some other flap experiencing out of phase wave loading. Power can be taken off at any of the pulleys 43, 44 and 45 by suitable hydraulic pumps which can provide impedance matching to the wave loading. Each pulley 43, 44 and 45 will rotate at a speed dictated by the rate of change of the volume of the space 1 9 of the associated flap.

In the hydraulic arrangement, shown in Fig. 1 3 and in the right hand side of Fig. 11, the cavity volume is maintained constant by connecting individual single acting rams operated by the individual flaps to common manifolds. In Fig. 13, the individual rams are indicated by numeral 46.

Displacement of one flap and its associated ram under wave force will transfer oil to another out of phase ram and will therefore cause displacement of the associated flap away from the spine and which is experiencing wave loading of a different phase. The power take-off can be from the hydraulic fluid transferred between units, and the take-off can be matched to the wave impedance to give high efficiency absorption. In the arrangement of Fig. 13, each hydraulic ram 46 is connected to two hydraulic mains 47 and 48 through one way rectifying valves 49 and 50 and by such means, a constant hydraulic flow with differential pressure can be maintained along the spine.The extraction of energy can be achieved by a hydraulic load, for example as indicated at 51 in Fig. 1 3 to provide the necessary impedance matching to the wave loading.

Referring back to Fig. 11, it is first of all to be noted that the spine 35 is provided with suitable ballasting 52 in order that it will maintain a pre determined position in the liquid in which it floats, and it will also be noticed in Fig. 11 that the individual spaces 39 are provided with a small quantity of liquid 53. This small quantity of liquid 53 can provide damping during closing of the space 39.

It is preferable in this example that the individual flaps 36 be otherwise sealed in relation to the spine to prevent ingress of the surrounding liquid. This sealing may be by the use of sliding seals and small pumps may be incorporated to keep the spaces 39 empty. In an alternative form, rolling seals may be used.

To overcome the sealing problem, an arrangement as illustrated in Fig. 14 may be used.

In the arrangement shown in Fig. 14, a continuous membrane 54 forms the flap means, and a number of support arms 53 which are individually movable define the flap sections which can move out of phase relative to other sections so that the flap 54 can take up a wave form shape as shown in Fig. 14 which can constantly vary as it comes under the influence of the wave forces applied thereto. The members 55 are individually moveable and carry the pulleys 44 as shown. The reference shown in Fig. 14 is provided with a flap section compensating means as shown in Fig.12, but it could be provided with a hydraulic system as described herein and in particular as illustrated in Fig. 13.The membrane 54 is connected to the spine at the lower end thereof and the wave loadings along the membrane 54 are absorbed by the mechanical or hydraulic system as previously described to give matched impedance for high efficiency energy absorption.

The spacing of the members 55 will be determined by the strength of the membrane and the permissible distortion thereof and also by the prior requirements. The distortion of the membrane between the supporting members 55 can be used to advantage by allowing local contact of the membrane with the spine 35 during small-waves/small-cavity volume operation. Local damage to the membrane 54 can be isolated by either providing membrane bulk heads within the cavity or by allowing adjacent cavities to close thereby to seal off the affected area. The apparatus can be arranged to have full safe cavity closing by reducing the hydraulic pressure, allowing the membrane 54 to contact the spine, followed by the supporting members 55 finally closing the membrane under small wave loading and high liquid damping.The plan area of the apparatus can be made relatively small, and when the membrane closes against the spine, the said plan area approximates to the plan area of the spine alone. This gives the apparatus good survival characteristics. It is appreciated that the flexible membrane 54 is not technically 'pivoted' to the spine 35, but will be attached thereto in such fashion in fact to define an effective axis of pivoting.

It is possible to seal the top of the cavity provided that air can move freely along the spine.

A sealing member such as a top member which folds into the cavity can be arranged to help keep out the surrounding liquid or ejected during operation.

It is to be appreciated that the apparatus is designed to give a good energy which can be converted into a more usable form e.g. electrical energy. The means of converting the energy extracted by the apparatus can be any suitable, and can be accommodated itherwithin the spine or at a remote location. In the case of the mechanical linkage for the flaps or membrane sections, the energy provided from the flaps is in the form of reciprocating rotary energy derived from one or more of the pulleys, whilst in the case of the hydraulic system, the energy available is hydraulic fluid under pressure.

The embodiments of Figs. 10 to 1 5 possess a number of advantages of which the more important are as follows.

1. Potential high efficiency over the whole wave frequency directional spectrum.

2. Efficient continuous structure along the wave energy front giving a high capacity power system.

3. Survival characteristics with non-operational and non-dynamic features giving good damage stability.

4. Direct mechanical/hydraulic power drive with inherent natural characteristics.

5. Very compact and simple. structure aiding constructional and assembly methods.

6. Easy access to machinery for installation inspection, maintenance and repair purposes.

7. Close down mode of individual or all sections for any purpose.

8. Elimination of large or heavy moving components to give minimal loading and inertial effects. 9. Limited dynamic movement of all moving parts giving efficient use of components.

10. Inherent flexibility of spine and wave absorption components eliminates tolerance and stress concentration problems.

11. The device requires a relatively simple mooring system with low survival forces.

Referring to Fig.15, this drawing shows a section of a spine 60 of a buoyantly supportable structure which includes a plurality of wave absorbing plate elements 61 located to one side of the spine 60. The elements 61 are indicated in Fig. 1 5 as short straight lines but in fact they may be of any suitable construction. Short straight lines have been shown to indicate that the elements are in fact positionally out of phase in relation to the spine. In use, the elements 61 are moved by the waves in the body of water in which the structure is supported, in a to and fro motion as indicated by arrow 62.The phase position of each element 61 can be assumed to be the distance it is located from the lowermost edge of the spine 66 indicated in Fig. 1 5. The main wave direction of the waves in the body of liquid is indicated by the arrow 63 in Fig. 1 5. The elements 61 along the length of the spine are relatively out of phase positionally because in fact in normal circumstances the wave front which meets the structure will have waves which, relative to the length direction of the spine are out of phase. If it is assumed that the elements 61 move back and forth as indicated by arrow 62 at the same frequency, then each element will have two points of instantaneous velocity zero when it is closest to the spine 60, and when it is furthest from the spine 60.Intermediate these positions, the element 61 can be considered to have maximum velocity. For achievement of the best power conversion efficiency the movement of each element 61 should be damped in accordance with the instantaneous velocity.

Therefore, each element should experience maximum damping at maximum velocity between the said two extreme positions and minimum damping at said two extreme positions.

If it is assumed that no two elements 61 will be exactly in phase, because the wave front pattern along the length of the spine will be cyclic, then adjacent elements can be coupled hydraulically by fixed displacement pumps to provide automatic damping in accordance with instantaneous velocity. If Fig. 1 6 is now considered in detail, in conjunction with a pair of adjacent elements 61 in Fig. 1, the maximum physical displacement between each of the said elements and its neighbour of the pair will be when that element has maximum velocity or in other words is midway between the said two extreme positions.

The hydraulic system shown in Fig. 1 6 is designed to ensure that there will be maximum damping at this condition.

It is to be assumed that in Fig. 1 6 one of the elements 61 is connected to drive shaft 64, whilst the other element is connected to drive shaft 65.

To and fro movement of any element 61 effects rocking movement of drive shaft 64 or 65. Drive shaft 64 is connected to a single acting piston and cylinder device 66, whilst shaft 65 is similarly connected to a piston and cylinder device 67 which is identical in displacement to device 66.

The devices 66 and 67 discharge into a low pressure line 68 and a high pressure line 69 respectively. It might be mentioned at this stage that high pressure fluid from line 67 can be used as stated herein for the driving of a turbine for the eventual production of electrical power.

The elements 61 are connected to the shafts 64 and 65 so that when the two elements 61 are positionally in phase the cylinders of devices 66 and 67 are 1800 out of phase. The effect of this is that when the elements 61 move together in phase, the shafts 64 and 65 are driven, but the displacement of one pump 66 for example is discharged completely into the cylinder of pump 67 and vice versa and the net displacement of the pair of cylinders is zero. There will be no power output, and no damping load on the elements 67.

If there is a positional phase difference between the two elements of 1800, then the net displacement of each pair of cylinders 66 and 67 will be a maximum and the damping effect on the elements 61 will be maximum. For phase angles between zero and 1800, the total pump pair displacement will vary in accordance with the precise phase difference. It will be appreciated therefore that automatically each element will be subjected to a velocity controlled damping. For each predetermined operation, the gear ratio between the pump and the wave absorbing element will be a function of predicted sea state, element length and pump design.

The described arrangement of Figs. 1 5 and 16 gives only one form of pumping equipment. It is to be appreciated that the same principle is applicable to specially designed rotary pumps and cam or mechanism operated linear pumps such as rams and bellows.

The arrangement in Figs. 1 5 and 16 in making use of the relative phase displacement between the absorbing elements, which is for ever present, means that a simple and robust construction can be provided.

Referring now to Figs. 1 7 to 20, the apparatus illustrated is essentially theoretical and is an elongated piece of equipment, for buoyant support in the water in a direction which is the wave direction. Thus if reference is made to Fig.

17, the structure is indicated generally by numeral 20, whilst the wave direction is indicated by numeral 71. Several waves are indicated by the reference numeral 72. It will be seen that the apparatus in plan view has a shape resembling that of the hull of a long narrow ship or other vessel. The structure is made up of a number of panels 72 and 74 which are pivqtally interconnected along a common axis 75. The panels 73 and 74 generally are rectangular, except for the front panels 73A and 74A and the rear panels 73B and 74B which are triangular in order that the structure will be bow shaped at each end in order to slice into the oncoming waves in much the same manner as the bow of a ship. In a modification, the front and rear panel pairs 73A, 74A and 73B and 74B could be replaced by a solid end piece or a single plate as desired.

If reference is made to Figs. 18, 1 9 and 20, each pair of plates 73 and 74 hinged along axis 75 defines, in section, an upwardly open V-shape, and the top edges of the panel pairs are connected by fluid pressure piston and cylinder devices 76 and by compression springs 77. High and low pressure pipes from the piston and cylinder device 76 lead to and are contained in a conduit 78 which runs lengthwise of the structure, and for the sake of clarity is shown only in Fig. 18. This conduit will lead to a suitable location for the ultimate conversion of high pressure fluid to another form of energy such as electrical energy.

The operation of the apparatus is essentially simple in that as the wave height increases on the outside of each panel pair 73 and 74, for example as indicated in Fig.19, the piston and cylinder device 76 is contracted, and the compression spring 77 is compressed also as shown in Fig.19, and the piston and cylinder device 76 effects a pumping stroke delivering high pressure fluid into high pressure fluid line in conduit 78. When the wave passes the panel pair 73 and 74, the return spring 77 causes the panels once more to move to the Fig. 1 8 and also the Fig. 20 position, and the cycle repeats each time a wave passes each panel pair. The pressure fluid delivered from the respective piston and cylinder devices 76 will of course be aggregated in order to provide aggregate output energy.

The V-shape space between the panels 73 and 74 has been shown in Figs. 1 8 to 20 as being empty. In practice.this may have a liquid therein, such as sea water in order to damp the rate of pivoting together the panels 73 and 74 in much the same manner as shown in Fig. 1, and also to assist in the return of the panels to the initial position. If a quantity of water is provided between the panels 73 and 74, it may be possible to dispense with the return springs 77. The apparatus described with reference to Figs. 1 7 to 20 is theoretical in that it is also necessary from a strength point of view to have reaction means against which the panels 73 and 74 can react.

Thus, referring to Fig. 21, it will be seen that the panels 73 and 74 are pivoted to a central spine member 75A. The embodiments of Fig. 22 is similar to that shown in Fig. 21, except that the central spine member 75B is circular (which may be easier to fabricate), but in each case the spine member is required to provide the apparatus with the rigidity to prevent bending in sympathy with the wave forces.

In the arrangement of Fig. 23, panels 74 are provided on only one side of a robust spine member, but the principle of operation is as described in relation to Figs. 1 7 to 20.

The apparatus as described in this specification has the advantage that it lies in a direction to slice through the waves. That is to say the bow end splits the water meeting the apparatus to cause it to travel along the sides of the apparatus in much the same manner as a ship cuts through the water, and therefore there is no long spine which lies transverse to the wave direction and is subjected to heavy bending movements.

The apparatus described with reference to Figs.

21,22 or 23 may have its ends 78 and 79 anchored by anchor ropes but it is also conveivable that only the forward end will be anchored, and the apparatus will be allowed to swing about its forward anchorage in order to align automatically with the wave direction. This may prove to be of advantage in some cases.

Furthermore, the spine may be in a numbar of hingedly inter-connected sections so that the respective sections can tilt relative to their neighbours, to relieve excess bending stressing of the spine.

It may be necessary to provide sealing arrangements between respective pairs of panels 73 and 74 as described earlier herein and such sealing arrangements may be provided by rubber or the like gaiters.

Figs. 24, 25 and 26 show some modifications of arrangements which operate in essence similar to the arrangements described with reference to Figs. 21 to 23. In each of Figs. 24,25 and 26, the spine is represented by numeral 90, whilst the plate elements are represented by numeral 91.

The plate elements are provided to each side of the spine 90, and the various pivot axes are indicated by 92. In each of Figs. 24 and 25, the spine element is spear headed in cross-section, with a cut-off flatened base regions, and in the arrangement of Fig. 24, the plate elements 91 to opposite side of the pivot axis 92 are integral, the pivot axis 92 being at the top of the spine, whilst in Figs. 25 and 26, the separate elements 91 are hinged to the lower edges of the spine.

The embodiments of Figs. 24, 25 and 26 operate as described in relation to Figs. 1 7 to 23, but it will be noticed that each of the spines 90 is provided with a high pressure manifold 93 and a low pressure manifold 94. The apparatus in the case of each of Figs. 24 to 26 is adapted to pump air in a manner which will be described in more detail hereinafter when the arrangement of Fig.

29 is described, but it is sufficient to say at the present time that for each inward movement of plate element towards the spine 90, air is pumped into the high pressure manifold 93, whilst during the return movement of the plate element 91 to an outwardly disposed position, low pressure air is supplied from the low pressure manifold 94.

The high pressure air is delivered to a suitable energy conversion means, such as an air turbine, for converting the pressure energy in the high pressure air into mechanical motion. Air exhausted from such mechanical conversion is returned to the low pressure manifold.

Fig. 27 shows an arrangement of a long spine pointing into the wave direction 95, the spine being indicated by 90. A plurality of plate elements 91 are shown as arranged side by side lengthwise of the spine element 90. The plate elements 91 down each side of the spine are shown respectively displaced different distances from the spine 90, as this is in fact what will occur as the waves travel down the sides of the spine. In other words, at any instant in time some of the plate elements 91 will be displaced inwardly relative to the spine, whilst others on the same side, will be displaced outwardly relative to the spine, depending upon the wavelength of the waves travelling down the spine. The apparatus draws energy from the waves as they pass down the length of the spine, and the device will also absorb energy of waves which by refraction fall on the spine in a sidewise direction.As a practical example, the length of the spine may be in the order of 200 to 500 metres, although it is not intended that such exemplary length should necessarily mean that the spine may not be longer or shorter. There are certain advantages in arranging the spine to face the wave direction as shown in Fig. 27, and these advantages include that surge forces on the spine can be substantially eliminated, heave forces are likely to be lower and mooring can be made much simpler.

Referring now to Fig. 28, this Figure shows diagrammatically an arrangement wherein the spine 90 as illustrated in Fig. 27, is in fact in the form of a vessel hull, with the plate elements 91 being mounted on pivot axes 92 on each side of the hull 90. This however would be self-propelled, and therefore could adapt itself to the nearest and best wave fields for extracting energy from waves.

One suggestion for converting the energy extracted by the plate elements would be to provide on-board absorbers to convert the wave energy via electricity to some energy vector such as hydrogen, by means of electrolysis, and to store the product in tanks. When such tanks are full, the vessel could then return to port, unload its stored energy and then return to the wave fields.

Instead of the vessel returning energy to port, it could be in fact a floating process plant, the energy to drive the plant being extracted by the plate elements 91. An example of such floating plant could be an amonia or chlorine production plant, the amonia or chlorine being delivered to port in due course.

The energy extraction means could be as described in relation to Fig. 29.

The draft of the vessel would of course need to be adequate to accommodate the required depth of absorbing plate element. It may be necessary to ballast the vessel in a variable manner to lower it to the required depth for energy absorption, and to raise it for travelling or plate element maintenance.

The utilisation of a vessel provided with pivoting plate elements overcomes a number of problems which exist with positionally fixed energy extraction devices. These problems are as follows:- (a) Wave Directionality Waves do not always come from the same direction. If devices are placed in fixed arrays they will only have 100% of the energy presented to the array when the mean wave direction is perpendicular to the line of the array. When the mean wave direction is not perpendicular the available capture width is reduced. Present estimates indicate that 35% of the annually available energy could be lost as a result of directionality.

(b) Energy Quantity and Distribution Recent results from a wave measuring buoy off South Uist indicate that the available wave energy off the Hebrides is approximately half of what had been assumed from the wave measurements made by "Station India" further out in the Atlantic Ocean. Also the distribution of energy within the wave spectra in terms of wave heights and periods is less advantageous to the present conceptions of absorbing devices than had previously been assumed.

(c) Device Reliability Wave absorbing devices have to work in an extremely hostile environment, and there are long periods, particularly in winter, when access to the device for even minor repairs and adjustments is impossible. Periods of "down-time" must therefore be inevitable. A recent system analysis of this problem indicates a serious effect on the overall load-factor due to device down-time.

(d) Cable Reliability Floating devices need flexible cables to transmit the generated electricity. The present proposal for an installation for Scotland is to run flexible A.C. cables from the devices to a number of fixed platforms where the power from several devices would be concentrated, converted to D.C.

electricity and transmitted to short via sea-bed D.C. cables. Transmission lines would then run, via underwater D.C. cable to Skye, across Skye and to the mainland by A.C. overhead lines, and by overhead lines to the nearest high voltage access to the Grid at Perth.

The reliability of sea-bed cables is not ideal, repair time is retricted by weather changes, and a factor therefore has to be introduced to allow for cable downtime.

Also, the various processes of conversion to D.C. and back to A.C. together with various stages of voltage transformation, lead to energy losses.

(e) Transmission Cost The cost of the transmission system outlined above is high in comparision with conventional systems. When a reduced load factor due to the influences outlined in (a) to (d) above is applied, the cost of transmission alone exceeds the existing cost of electricity generated for the Grid.

The overall load factor resulting from combining the effects of the above influences amounts to approximately 20% for most devices; i.e. for every 1 KW of mean annual output delivered to Perth, 5 KW of generating capacity is required off the Hebrides.

The advantages of utilising a self-propelled vessel with energy extraction flap elements are that: (a) The directional problem is eliminated and the vessel could position and align itself in the optimum attitude for the wave climate.

(b) The vessel could sail to the best wave climate, and absorption capacity would therefore be better utilised.

(c) Running repairs could be carried out at sea and major maintenance could be carried out in port. The vessel down-time due to weather conditions could therefore be reduced or eliminated.

(d) Cables and moorings, transmission lines and wasteful energy conversion and transforming processes could be eliminated.

Although a floating vessel as described has particular advantage, it is to be stressed that the present invention has much wider application, even although in some circumstances the power generation system will have disadvantages not present when one utilises a self-propelled floating vessel.

The use of fluid has been described herein for conversion of the wave energy into more usable form. It is within the overall scope of this invention to use any form of fluid, liquid or gas, and initial work which we have carried out has been concentrated on the use of liquid usually-oil, water or oil/water mixtures.

For several known devices, a hydraulic system is the only practical method suitable to the device.

We have discovered that hydraulic systems can place limitations on wave energy devices.

These are mainly: (a) It is proving extremely difficult to design at reasonable cost, the necessary mechanical power trains to drive the primary hydraulic pumps or rams.

(b) The transmission fluid, if it consists of or contains oil, is a pollutant and therefore likely to be unacceptable in view of the risk of leakage.

(c) Large numbers of pumps, valves, controls appear to be required since it is not possible, using current technology, to design single components large enough to generate the power required. This creates problems of maintenance and reliability of the total system.

(d) Unless very high pressures are used, with the consequent requirement of close engineering tolerances and shorter working life, the turbines and alternators driven by hydraulic systems tend to be relatively slow-speed-and therefore large, heavy and expensive.

In contrast to the above disadvantages, the use of air, particularly low-pressure air has a number of attractions as the transmission fluid; (a) It is non-polluting.

(b) It is available "in situ".

(c) Being a lighter medium it is more easily accelerated to high speeds. High turbine speeds-and therefore smaller, cheaper turbines and alternators are possible.

(d) There are fewer moving parts in the system.

(e) The "pumps" can be large, comparatively simple, cheap and few in number.

The disadvantage of low pressure air systems is that turbine efficiency is lower than that of hydraulic machines. However, it is thought that considerable improvements can be made comparatively easily in this field of technology. it could also be said that the simplicity of the air system, and its consequent improved reliability, would more than compensate for the lower efficiency when compared with hydraulic systems.

The present invention is readily adaptable to a pneumatic power take-off system.

It is merely necessary to create and maintain an air pump cavity between the hinged plate and the spine. The movement of the plate relative to the spine will then cause a pumping action to take place.

Various methods can be used to control and harness the pressurised air. Figure 29 shows one such method. Referring to Fig. 29, provided in spine 100 are two air ducts 101 and 102 respectively carrying high pressure air and low pressure air (the terms "high" and "low" in this instance are relative only). The high pressure duct 101 carries air from a number of plate elements 103 to a centrally placed turbine/generator. The turbine passes the spent air into the low pressure duct 102 which then returns it to the claims for re-pressurising.

The ingress and discharge of air to and from the clams is controlled by valves 104 and 105. In the simplest mode of operation the valve 104 from the plate 103 into the high pressure duct 107 opens when the pressure of a wave on the plate 107 exceeds that in the duct 107 and closes when the pressure in the duct 101 exceeds that in the pump cavity 106 between spine 100 and plate 103. Similarly the low pressure valve 105 opens when the pressure in the low pressure duct exceeds that in the cavity 105 and closes when the cavity pressure exceeds the duct 102 pressure. More complex control of the valves is possible if required, e.g. to improve the velocity response of the plate to individual waves, to restrict or cushion extreme movements in large waves, or to seal off individual plates in the event of the pressure bags 107 which defines cavity 106 becoming seriously punctured.

In the calm water condition and with no pressure in the air ducts 101 and 107 the natural position of the plates is the "closed" condition i.e.

tight against the spine 100. The first stage in actuating the apparatus is therefore, to pressurise the system to a given "ambient" pressure so that the plates 103 open out to the desired mean position such that the ambient air pressure is balancing the external water pressure. The smaller the bag or bellows 107 relative to the external head of water, the higher the required ambient pressure will be. It is an additional advantage of the arrangement that the ambient pressure of the air-and hence the density of the air used-can be optimised by choosing the correct air bag dimensions.

When the plates commence to operate in response to the waves differential pressures will be created in the air ducts and the turbine will be driven.

One further advantage of the system is that it is "fail safe", i.e. in the event of loss of air pressure the clams will automatically close and be held against the spine by the external water pressure.

Fig. 30 shows in elevation similar to Fig. 29, an alternative means for the conversion of the wave energy into electrical energy. In Fig. 30 the spine is indicated by numeral 110 and it will be seen that it is of the same configuration as the spine illustrated in Fig. 29, except that there is only a single air duct 112. Between the spine 112 and each plate element 114 there is a flexible bag or bellows 116, which communicates through its own communication passage 1 16, with the duct 112. In the passage 11 6 is arranged a self rectifying air turbine 11 8, the shaft 120 of which is coupled to an electrical generator 122.The self rectifying air turbine operates to drive the shaft 120 inner directionally regardless of whether or not air is being forced out of the bag 11 6 as the flap 114 moves towards the spine or when air is moving in the opposite direction by being drawn from the air duct 112 when the plate element 114 moves away from the spine 110. Such self rectifying turbines are not in common use, but are at present under development. One such self rectifying turbine has been designed by Professor Wells of Queens University, Belfast.

As the plate element 114 moves back and forth relative to the spine 110, so air is alternately driven along the passage 11 6A as the bag 1 6 is collapsed by the plate element moving towards the spine 110, and as the plate element pivots away from the spine 110, the air is drawn back through the passage 11 6A.

This method of converting the wave energy has the advantage that it achieves velocity proportional damping of the movement of the plate element. The track input to the electrical generator is proportional to the velocity of the rotor, provided that there is a resistive load, and as each plate element is coupled to its own generator 1 22.

In a cam water condition with no pressure in the duct 112, the natural position of the plate element is the closed position, i.e. lying against the spine. Therefore, the first stage in actuating the apparatus is to pressurise the system to give an ambient pressure in the bag so that the plate element opens out to the desired mean position, the ambient air pressure then balancing the external water pressure. When a wave moves against the plate element, the pressure in the bag 11 6 will increase and air will flow through the main turbine to the main duct 113, and the turbine will be driven. As the wave recedes, the plate element will move outwards, the pressure and the cavity following below the pressure in the main duct, so that air will flow back into the cavity and the turbine, by virtue of its self rectifying operation, will again be driven.

It will be appreciated that various features of some embodiments described herein can be utilised in other embodiments.

The reader is directed to the possibility that in order to construct any particular form of apparatus in accordance with the invention, any feature of any embodiment may be selected for use, where suitable, in any'other embodiment.

The present invention it is to be noted envisages the utilisation of apparatus which is for buoyant support by the body of liquid, as opposed to an apparatus which is for permanent fixture to the sea bed.

By such means, the difficulty of providing substantial support structures, and the limitation that the apparatus can only be used in relatively shallow water, are avoided.

Claims (1)

1. Claims

   1. Buoyantly supportable apparatus for use in the generation of energy from wave motions of a body of liquid in or on which the apparatus floats, said apparatus comprising a reaction element, and a displaceable plate element operatively connected to the reaction element for back and forth movement to react against the reaction element when the plate element comes under the influence of waves in the body of liquid, and including means for extracting wave energy in another and more readily usable form by virtue of the relative movement between the reaction element and the plate element.

   2. Apparatus according to Claim 1 wherein the plate element is of a flexible nature.

   3. Apparatus according to Claim 1 or 2 wherein the plate element is pivotally connected to the reactor element.

   4.-Apparatus according to Claim 1,2 or 3 wherein the reaction element is part of an elongated spine and there is a plurality of said plate elements disposed along at least one side of said spine when the apparatus is to be used in the position parallel or at an acute angle to the wave front from which the energy is to be extracted.

   5. Apparatus according to Claim 4, wherein there are plate elements arranged side by side along each side of the spine adapting the apparatus for use in the position at right angles to the wave front from which energy is to be extracted.

   6. Apparatus according to Claim 4 or 5, wherein said means for extracting wave energy comprises air pumps, and of which said plate elements form piston means, the spine embodying a high pressure manifold and a low pressure manifold into which air is pumped by the movement of plate elements, and from which air is extracted by movement of the plate elements respectively, appropriate energy being derived by expanding the high pressure air delivered to said manifold.

   7. Apparatus according to Claim 6, wherein there is means defining a pumping cavity between the spine and each plate element, such means being in the form of flexible sealing elements.

   8. Apparatus according to any preceding Claim, wherein between the plate element and the reaction element there may be a region for containment of a quantity of liquid which will act as a variable damping means on the swinging movement of the plate element.

   9. Apparatus according to Claim 4 or 5 or any preceding claim when dependent upon Claim 4 or 5, wherein the plate elements along the length of the spine are such as to be capable of complying with instantaneous wave displacement along the length of the spine, so that different plate elements on the spine can move out of phase and there is coupling means inter-connecting said plate elements so that when wave forces push some plate elements towards the spine other plate elements which the wave forces are out of phase are forced away from the spine.

   10. Apparatus according to Claim 9, wherein the coupling means comprises a tensioned cord, cable or the like extending lengthwise of the spine and trained round groups of three pulleys, one group for each plate element, two pulleys for each group being carried by the spine and the third being displaceable in synchronism with the associated plate element.

   11. Apparatus according to Claim 9, wherein the coupling means comprises, for each plate element, a hydraulic ram, the rams being connected to a common high pressure coupling means.

   12. Apparatus according to any one of Claims 4 toll, wherein each of said plate elements is connected to damping means, the damping effect of which is varied depending upon the degree by which the element is positionally out of phase relative to an adjacent plate element.

   12. Apparatus according to Claim 12 wherein pairs of plate elements are hydraulically coupled by similar fixed displacement hydraulic piston and cylinder devices coupled through check valves so that when the two plate elements of the pair are positionally in phase, the piston and cylinder devices are out of phase so that one discharges displacement into the other and there is no damping, but if the adjacent plate elements become out of positional phase by 1800, the damping is a maximum, said devices being arranged to discharge their contents into a high pressure main.

   14. Apparatus according to any preceding claim, wherein the reaction element or spine is relatively massive in inertia in comparison to the individual plate elements.

   1 5. Apparatus according to any preceding Claim, wherein the reaction element or spine is ballasted towards the lower region thereof, in order that it will take up a pre-determined attitude when buoyantly supported in the body of water.

   1 6. Apparatus according to any preceding claim, wherein the spine is of greater crosssectional dimension in one dimension and in the other, and is adapted to take up the position in the body of liquid such that the longer cross-sectional dimension will be upright.

   1 7. Apparatus according to any preceding claim, wherein the reaction element or spine is in the form of a vessel hull, and the whole apparatus is self-propelled.

   1 8. Buoyantly supportable apparatus substantially as any of the embodiments hereinbefore described with reference to the accompanying drawings.