GB2478723A - Tuned wave energy converter uses liquid and air flow between chambers - Google Patents

Abstract

A wave energy device 1 comprises a pair of spaced-apart, fluid-tight chambers 6, 7 fluidly interconnected in a lower region by a liquid flow conduit 8, and fluidly interconnected in an upper region by an air flow conduit 11. Liquid is able to flow between the chambers due to movement of the device, and a counter flow of air 14 flows between the chambers driving a prime mover 15 such as a uni-directional e.g. Wells' turbine. Response of the device to wave movement is controlled, e.g. by air valves 16, 17, or by a water valve (24, figure 5). Response may alternatively or additionally be controlled by providing tapered chambers (figure 7) or movable or inflatable water displacers within the chambers (figures 8, 9).

Description

A WAVE ENERGY DEVICE

The present invention relates to a wave energy device, and more particularly relates to such a device configured for use in the generation of electrical energy from wave energy.

In view of concerns over the environmental effects of burning fossil-fuels in order to generate electrical power, increasing attention is being paid to so-called renewable energy sources for the generation of electrical power. One such source of energy which it has been proposed to harness for such purposes is the energy of moving waves in the sea, in lakes, or other such bodies of water. Accordingly, there have been proposed a wide range of different devices designed to convert wave energy to mechanical rotational energy, which may then be used to drive an electrical generator in order to generate electrical power.

It has been proposed previously to provide wave energy conversion devices which operate to convert wave energy into a low-pressure pneumatic energy in the form of a bi- directional air flow which may then be used to drive a uni-directional turbine such as a Wells' turbine. The turbine, in turn, drives an electrical generator. Arrangements of this type are often referred to as oscillating water column (OWC) devices, and W02008/047337A1 discloses a wave energy converter which operates on this general principle.

The wave energy converter disclosed in W02008/047337A1 is provided in the form of a floating structure which is configured to move in sympathy with oncoming waves so as to oscillate in response to the wave motion. The structure incorporates a pair of generally L-shaped water ducts which are arranged so that their longer legs are generally aligned with the direction of the oncoming waves, and open so that the waves enter the ducts. As the oncoming waves enter and progress along the ducts, the buoyant structure pitches downwardly into the water such that air is driven up the shorter leg of the L-shaped ducts and through the aforementioned uni-directiorial turbine, thereby driving the turbine and thus generating electricity. When the structure subsequently pitches upwardly, the water within the L-shaped ducts withdraws, thereby drawing air through the same turbine in the opposite direction, but again generating electricity due to the uni-directional configuration of the turbine.

US4,392,061 discloses an alternative form of wave energy device in the form of a generally buoyant vessel which is intended to be moored at sea and which may be equipped with a propulsion system in order to maintain the vessel in an orientation such that it faces into the approaching waves. In this arrangement, the vessel is described as having a hull form specifically configured to reduce pitch damping, and is also equipped with damping systems in order to adjust the degree of pitching motion.

The document proposes two damping arrangements, one comprising air-compression chambers at the bow and stern regions of the hull, and the other comprising a rapidly moving mass arranged to move out of phase with the pitching action at a point above the deck of the hull. In one configuration of this device, the hull incorporates a number of channels arranged generally longitudinally, the channels being partially filed with water. As the vessel pitches in the oncoming waves, the water contained in the channels runs back and forth along the length of the channels via turbines located in the central region of the vessel. The action of the water on the turbines is used to generate electrical power. This document also proposes an alternative configuration of vessel having a generally continuous duct arranged around the periphery of the hull, the duct being equipped with flap-gate valves arranged to direct the liquid substantially continuously around the duct, operating turbines situated at either end of the vessel in order to generate electricity.

However, previously proposed wave energy devices of the general type described above are not without problems, and there is considerable scope for improvement of such devices in several respects.

As will be appreciated, waves of different wavelengths travel at different speeds, with the fastest waves being those with the longest wavelength. As a result of this relationship between wavelength and speed, the period of a wave (and hence the excitation force of the wave) is dependent upon the wavelength and is thus not constant in a typical seaway. When several wavetrains of different wavelength are present in a seaway, the waves become separated to form groups having similar wavelengths. The velocity of a particular group of such waves is the velocity with which the variations in the shape of the wave's amplitude propagate through space. The phase velocity (or phase speed) of a wave is the rate at which the phase of the wave propagates through space, and represents the speed at which the phase of any one frequency component of the wave travels. For such a component, any given phase of the wave (for example the crest of the wave) will appear to travel at the phase velocity.

The phase speed v of a wave may be expressed as a function of the wavelength A and period T of the wave, thus: v = A/T Equation 1 The phase speed v may also be expressed in terms of the angular frequency W and wave-number k of the wave, thus: v = w/k Equation 2 From these equations it can be seen that both the period and wavelength of waves vary constantly as a wave field advances towards a stationary wave energy device. In a dispersive medium such as water the phase velocity varies with frequency and is not necessarily the same as the group velocity of a wave, which is the rate which changes in amplitude (known as the envelope of the wave) will

propagate through the wave field.

As will thus be appreciated, the wave conditions observed at the site of a stationary wave energy device are constantly changing, which means that the natural frequency of the wave device, which determines the device's response to the frequency of excitation, should ideally be capable of being easily and quickly tuned to the instant conditions so as to allow the wave energy device to respond optimally to a variety of prevalent wave conditions which change over relatively short periods of time.

The only apparent way in which the response of the arrangement proposed in US4,392,061 may be adjusted is by variation of the waterline length of the hull. As will be appreciated, the waterline length of the hull may be increased by taking on seawater as ballast, thereby increasing the displacement of the vessel. However, increasing the displacement in this manner offers little flexibility in practice and would involve a significant increase in the mass of the vessel. Taking on seawater as ballast in this manner must be carefully managed in order to avoid stability issues arising from free-surface effects attributable to the water ballast which would inevitably affect the dynamic characteristics of the arrangement.

Another problem with the types of prior art wave

energy devices proposed above, is that they rely upon the movement of large masses of water which are allowed to accelerate freely over significant distances and which can thus result in high impact loads on the structure of the arrangements, thereby necessitating heavy and expensive structural members.

Another issue of relevance to the type of arrangement proposed in US4,392,061 is that it utilises turbines which are driven by large masses of water which run freely through the duct system. Such a flow of water causes significant sloshing forces which can cause damage to the turbine rotors. In this respect, the oscillating water column principle, as employed in the arrangement of W02008/047337 is considered advantageous.

It is an object of the present invention to provide an improved wave energy device for use in the generation of electrical energy from wave energy.

According to the present invention, there is provided a wave energy device for use in the generation of electrical energy from wave energy, the device being substantially buoyant, configured to oscillate in response to wave motion, and comprising: a pair of chambers, fluidly interconnected in a lower region by a liquid-flow-conduit, fluidly interconnected in an upper region by an air-flow-conduit, and configured to receive a volume of liquid distributed between the two chambers via the liquid-flow- conduit so as to partially fill the chambers; said liquid-flow-conduit being arranged to permit the flow of said liquid back-and-forth between said chambers in response to oscillation of the device, and said air-flow-conduit being arranged to permit the counter-flow of air between said chambers under the action of said flow of liquid; the device further comprising a prime mover located in the path of said flow of air and configured to convert energy from the flow of air to mechanical energy.

Said pair of chambers are preferably spaced apart from one another.

The chambers of the device may be partially filled with water, which may be either freshwater or seawater.

However, in variants of the invention it is envisaged that other liquids may be used instead of water, thereby allowing the chosen liquid to be selected in dependence on its desired specific gravity, viscosity, or other characteristics in order to provide suitable dynamic characteristics to the wave energy device.

The prime mover preferably comprises a turbine, and may be uni-directional. As will be appreciated by those of skill in the art, a uni-directional turbine is configured for rotation in one direction regardless of the direction of the flow driving the turbine. The so-called Well's turbine is an example of a uni-directional turbine, and indeed the device of the present invention may be provided with a prime mover in the form of a Wells' turbine or similar.

Preferably, the wave energy device further comprises at least one valve provided in said air-flow-conduit, the or each said valve being adjustable so as to control said flow of air between the chambers.

Possible configurations of the wave energy device may comprise a plurality of said valves, wherein each said chamber is associated with a respective valve located between the chamber and the prime mover.

The device may comprise a fill-mechanism operable to adjust the volume of said liquid partially filling the chambers. In the event that said liquid is seawater, then the fill-mechanism may be configured to draw water from the surrounding sea in order to increase the volume of water used to partially fill the chambers, and/or to expel water from the chambers to the sea.

It is proposed that the wave energy device may comprise a flow-mechanism operable to control the flow of said liquid between the chambers.

Said flow-mechanism may be operable to adjust the flow-area of said liquid-flow-conduit.

In a preferred arrangement, the device further comprises a trim-mechanism operable to adjust the vertical position of the device's centre of gravity.

Said trim-mechanism may comprise at least one mass arranged so as to be substantially vertically moveable relative to said chambers.

Alternatively, or additionally, said trim-mechanism may comprise a plurality of moveable bodies, each said body being configured to displace the liquid partially filling a respective chamber and being arranged for movement within said chamber so as to vary the volume of said liquid displaced by the body.

Said trim-mechanism may comprise a respective inflatable element provided within each said chamber, each said inflatable element being arranged so as to at least partially lie in the liquid partially filling the respective chamber, the trim-mechanism being operable to control the degree of inflation of each said element and to thereby vary the volume of liquid within the chamber displaced by the element.

It is envisaged that in some embodiments of the wave energy device, said chambers may each have a non-constant horizontal cross-section. For example, it is envisaged that each said chamber might be substantially tapered.

It is also envisaged that a wave energy device falling within the scope of the present invention may be configured so as to comprise a plurality of said pairs of chambers.

In such an arrangement, it is preferable for said chambers to be arranged in an annular configuration relative to one another, with the two chambers of each pair being arranged diametrically opposite to one another. Such an arrangement may comprise a single said prime-mover (preferably a uni-directional turbine as indicated above) arranged to be driven by the flow of air between a) a plurality of said pairs of chambers, or b) a single said pair of chambers selected from said plurality of chambers.

So that the invention may be more readily understood, and so that further features thereof may be appreciated, embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a transverse, schematic, cross-sectional view illustrating a wave energy device in accordance with a first embodiment of the present invention; Figure 2 is a simplified illustration corresponding generally to that of Figure 1, illustrating the wave energy device in an equilibrium position and floating in substantially flat water; Figure 3 is a view corresponding generally to that of Figure 2, but illustrating the wave energy device in an alternate orientation resulting from the effect of an oncoming wave; Figure 4 is a view corresponding generally to that of Figure 3, but illustrating the wave energy device in a further position representative of the situation as the wave moves passed the device; Figure 5 is a view generally corresponding to that of Figure 1, but illustrating a second embodiment of the invention; Figure 6 is a similar view, illustrating a third embodiment of the present invention; Figure 7 illustrates a fourth embodiment of the present invention; Figure 8 illustrates a fifth embodiment of the present invention; Figure 9 illustrates a sixth embodiment of the present invention; Figure 10 illustrates a seventh embodiment of the present invention; Figure 11 illustrates a wave energy device in accordance with an eighth embodiment of the present invention, showing the device in an equilibrium position when floating in substantially flat water; Figure 12 illustrates the arrangement of Figure 11 in an alternate position resulting from the motion of an approaching wave; Figure 13 illustrates an alternative form of the arrangement illustrated in Figures 11 and 12, showing the device in an equilibrium position when floating in substantially flat water; Figure 14 illustrates the arrangement of Figure 13 in an alternate position resulting from the motion of an approaching wave; Figure 15 is a transverse cross-sectional view taken through a lower region of a wave energy device in accordance with another embodiment incorporating a plurality of chambers; and Figure 16 is a transverse cross-sectional view taken through an upper region of the device illustrated in Figure 15.

Referring now in more detail to Figure 1, there is illustrated a wave energy device 1 in accordance with the present invention. The device comprises a hull structure 2 and is configured so as to be substantially buoyant and thus able to float on, or at least in the region of, the surface 3 of a body of water 4 such as a sea, ocean or estuary. The hull 2 may be shaped so as to take any convenient form, and it is envisaged that the actual shape of the hull used in practical embodiments of the invention will be selected in dependence upon local conditions such as prevalent wind, wave, tidal conditions or the like.

It is intended for the wave energy device 1 of the present invention to be provided in a fixed position in use within a significantly sized body of water 4 so as to be acted upon by the motion of waves travelling across the body of water, and due to the buoyant nature of the device it is thus configured to oscillate in response to the wave motion in a manner which will be described in more detail below.

In order to anchor the wave energy device 1 in a suitable fixed position within the body of water 4, the hull 2 is provided with a fixing arrangement, illustrated generally at 5, which is configured for releasable engagement with a mooring tether such as, for example, a generally conventional catenary-type mooring arrangement.

However, it should be appreciated that any suitable mooring or anchoring arrangement could be used to secure the wave energy device 1 within the body of water 4. For example, in situations where it is desired to position the wave energy device 4 in very deep water, a catenary-type mooring arrangement may be undesirable for a number of reasons including, but not limited to, the significant mass required in a cateneray mooring arrangement of sufficient length, and the repetitive flexing of the components of the cateneray mooring system on or near the seabed which reduces service life of the system. In such installations, it is therefore envisaged that the cateneray mooring arrangement may be supplemented with a taut-leg mooring system in a known manner.

Within the floating structure of the hull 2, there is provided a pair of spaced-apart tanks or chambers 6, 7. In the particular arrangement illustrated in Figure 1, the chamber located on the port side of the device is denoted by reference number 6, whilst the chamber located on the starboard side of the device is identified by reference number 7. The two chambers are substantially fluid-tight, and indeed in a preferred embodiment are substantially hermetically sealed.

A liquid-flow conduit in the form of a duct 8 is provided and which serves to fluidly interconnect the two chambers 6, 7 in their lower regions. As will be noted, each chamber 6, 7 has a respective flow port 9, 10 at its lower end, and the liquid flow duct 8 is arranged so as to be connected at each end to a respective said flow port 9, 10. As illustrated in Figure 1, the two chambers 6, 7 are partially filled with a drive liquid L, the liquid being distributed between the two chambers via the interconnecting flow duct 8. As will be appreciated, Figure 1 illustrates the wave energy device 1 in an equilibrium position adopted when the device is allowed to float in substantially flat water, and in this orientation it will be noted that the drive liquid L is distributed substantially equally between the two chambers 6, 7.

It is envisaged that in most installations in which the wave energy device 1 is anchored at sea, seawater will be used as the drive liquid L. In such arrangements, it is envisaged that the device may optionally be provided with a fill-mechanism operable to adjust the volume of the seawater contained within and distributed between the two chambers 6, 7. For example, it is envisaged that such a fill-mechanism may be configured so as to draw additional drive liquid L from the body of seawater 4 and to expel surplus drive liquid L from the chambers and interconnecting flow duct into the body of seawater 4.

Nevertheless, it is to be appreciated that variants of the invention are also envisaged in which freshwater may be used as the drive liquid L, in which case it is envisaged that the above-mentioned fill-mechanism will not be appropriate. Furthermore, it is also possible for other liquids to be used in place of seawater or freshwater as the drive liquid L, and it is envisaged that the actual drive liquid L used in any particular installation will be selected according to its physical properties such as specific density, viscosity or the like, in order to provide desired dynamic characteristics to the wave energy device.

The two spaced-apart chambers 6, 7 are also fluidly interconnected in their upper regions by an additional flow duct 11 which, as will become apparent, serves as an airflow conduit between the two chambers. The airflow conduit 11 is thus connected between respective vent apertures 12, 13 formed in the upper ends of the two chambers 6, 7. The two chambers 6, 7 and their interconnecting lower and upper ducts 8, 11 thus forms a substantially closed system which is partially filled with the drive liquid L, such that the remaining volume of the system is taken up by air 14.

A prime mover 15 is located within the airflow duct 11, at a position between the two chambers 6, 7 so as to thus be located in the path of air flowing in either direction along the flow duct 11 from one chamber to the other. In this regard, it is to be appreciated that the term "prime mover" is used herein to refer to a device by which a natural source of energy (in this case airflow) is converted into mechanical power. In this regard, it is envisaged that favoured embodiments of the present invention will incorporate a prime mover 15 in the form of a uni-directional turbine such as a Wells' turbine. As will be apparent to those of skill in the art, a uni-directional turbine is a turbine which is configured to rotate in the same direction even if the driving fluid flow should change direction. Such turbines are commonly used in the general field of oscillating-water-column wave energy arrangements and so need not be described in further detail here.

In addition to the prime mover 15, the airflow duct 11 is also optionally provided with a pair of flow-control valves 16, 17. In a particular arrangement illustrated in Figure 1, the flow control valves 16, 17 are provided on opposite sides of the prime mover 15 and, as such, each flow-control valve is associated with a respective chamber 6, 7.

Turning now to consider Figures 2 to 4, operation of the above-described wave energy device 1 will be described.

Figure 2 shows in schematic form, a wave energy device 1 of the general configuration described above lying in an equilibrium position in the situation where the device is floating in flat water 4, and in this position it will be appreciated that the drive liquid L is distributed evenly between the two chambers 6, 7 via the interconnecting liquid flow duct 8.

As an advancing water wave approaches the device 1, and moves beneath the device 1, the device is moved to the alternate position illustrated schematically in Figure 3, where the advancing wave slope is denoted by reference number 18. As the wave passes beneath the device 1, the device 1 becomes tilted out of its substantially horizontal equilibrium position as it attempts to conform to the profile of the advancing wave slope 18. The tilting motion imparted to the device 1 is thus effective to shift the distribution of drive liquid L between the two chambers 6, 7. Figure 3 illustrates the situation in which the device 1 has been tilted such that the starboard chamber 7 moves to a position generally below the level of the port chamber 6, and thus the drive liquid L flows from the higher port chamber 6 so as to run into the lower starboard chamber 7 meaning that the starboard chamber 7, at least temporarily, holds a higher proportion of the fixed volume of drive liquid L than the higher port chamber 6. This shift in the fixed volume of drive liquid L is thus effective to displace the balancing and fixed volume of air 14 in the opposite direction, as indicated schematically by arrows 19, meaning that the air 14 is caused to flow from the lower starboard chamber 7, to the higher port chamber 6 via the interconnecting airflow duct 11. This flow of air is thus directed through the uni-directional turbine 15, thereby driving the turbine. When the turbine is connected to and arranged to drive an electric generator, the flow of air denoted by the arrows 19 is thus effective to generate electricity as a result of the wave motion acting upon the wave energy device 1.

Figure 4 illustrates the subsequent orientation of the wave energy device as the wave moves beneath and away from the device. Figure 4 thus illustrates the device 1 having been tilted in the opposite sense as it floats on the back face 20 of the wave. As will be appreciated, in this tilted orientation, the two chambers 6, 7 have swapped relative vertical positions, such that the port chamber 6 has become located below the level of the starboard chamber 7. This shift in the relative vertical positions of the two chambers is thus effective to reverse the imbalance in the distribution of the drive liquid L between the two chambers such that the drive liquid L flows from the higher starboard chamber 7, via the interconnecting liquid flow duct 8, into the lower port chamber 6. In this orientation, the lower port chamber 6 thus holds a higher proportion of the fixed volume of liquid L than the higher Figure 7 illustrates an arrangement in which the chambers 6, 7 are configured so as to have a non-uniform transverse cross-section. In the particular arrangement illustrated in Figure 7, the two chambers 6, 7 are configured so as to have a transverse cross-section of a tapering nature, the chambers narrowing from a widest transverse dimension at their top regions to a narrowest transverse dimension at their narrowest regions. As will thus be appreciated, during oscillation of the wave energy device 1 of this arrangement, as the drive liquid L initially fills the lower part of the chamber located on the downside of the hull 2, it will do so by relatively rapidly increasing in depth within the chamber, with the rate of increase in depth reducing as the chamber becomes more full. By careful selection of the variation in dimension of the chambers 6, 7 along their heights, the dynamic characteristics of the wave energy device 1 can be optimised to the prevalent conditions of a given seaway.

It should be appreciated, however, that the chambers 6, 7 could alternatively, or additionally, be configured also to have a varying cross-section in a substantially vertical plane as well as in a substantially horizontal plane as illustrated in Figure 7.

Figure 8 illustrates a further embodiment of the present invention in which each chamber 6, 7 contains a moveable displacement body 32. Each displacement body is arranged so as to be moveable in a vertical direction under the action of a respective hydraulic actuator 33 and is configured so as to have a density which is significantly lower than the density of the drive liquid L. For example, the bodies 32 may be configured so as to be substantially hollow, or made out of cork or foam. In the particular arrangement illustrated in Figure 8, each displacement body 32 is generally conical in shape, being narrower at the starboard chamber 7. This shift in the balance of the drive liquid between the two chambers is thus effective to displace the fixed volume of air 14 in the opposite direction to that illustrated in Figure 2, as denoted by the arrows 21 in Figure 4. This flow of air 21, which of course again passes through the airflow duct 11 is thus also effective to drive the turbine 15, and due to the uni-directional nature of the turbine 15 it rotates in the same direction under the action of the airflow 21 as it does under the action of the airflow 19, and is thus again able to drive a connected electrical generator.

As will be appreciated, as successive waves advance towards and pass beneath the wave energy device 1 described above, the device will effectively oscillate between the positions illustrated in Figures 3 and 4, with the fixed volume of water alternately shifting between the two chambers and thereby alternately driving the flow of air in each direction 19, 21, and driving the turbine 15 always in the same direction. As will also be appreciated, the arrangement is configured such that the turbine 15 is driven by a flow of air through the turbine rather than the flow of liquid through the turbine. As such, the arrangement of the present invention is perceived to offer significant advantages over the aforementioned prior art arrangement in which a uni-directional turbine is arranged to be driven by a sloshing volume of liquid having considerable mass and hence exerting potentially damaging impact forces on the turbine.

By selectively adjusting the flow control valves 16, 17 the rate at which the fixed volume of air 14 is allowed to flow through the turbine 15 may be controlled. As will be appreciated, due to the fixed nature of the fluid system comprising the two chambers 6, 7 and the two interconnecting flow ducts 8, 11, by restricting the flow of air through the flow control valves 16, 17 and the turbine 15 in this manner, the shifting flow of the drive liquid L between the two chambers 6, 7 is effectively slowed, with the result that the oscillating motion of the wave energy device 1 may thus be damped which can be advantageous in particularly rough seas.

Referring now to Figure 5, there is illustrated an alternative embodiment of the present invention in which the wave device 1 is provided with a flow-mechanism 22 which is operable to control the rate of flow of the drive liquid L between the two chambers 6, 7. In the particular arrangement illustrated, the flow-mechanism 22 comprises a linear actuator 23, such as a hydraulic ram, which is arranged so as to adopt a position located generally between the two chambers 6, 7 and which is configured to move a shutter element 24 in a substantially vertical direction. As illustrated in Figure 5, the shutter element 24 is fixed to the lower end of a piston rod 25 forming part of the linear actuator 23, and is initially housed within a recess 26. Under the action of the actuator 23, the shutter element 24 may be moved from its initial position illustrated generally in Figure 5 in which substantially unrestricted flow is permitted through the liquid flow duct 8, beneath the shutter, to a lower position in which the shutter element 24 at least partially blocks the liquid flow duct 8, thereby restricting the flow of the drive liquid L through the liquid flow duct 8. As will thus be appreciated, by adjusting the position of the shutter element 24 across the liquid flow duct 8, the maximum flow rate of the drive liquid L between the two chambers 6, 7 can be controlled, thereby supplementing or replacing the function of the flow control valves 16, 17 provided in the airflow duct 11.

Figure 6 illustrates a wave energy device in accordance with the present invention in which an external frame structure is mounted to the hull 2 of the device and which carries a plurality of external floatation members 28. The flotation members 28 are substantially buoyant in water and thus serve to supplement the buoyancy contribution of the hull structure 2.

As will be seen from Figure 6, the frame structure 27 is configured such that the flotation members 28 are spaced outwardly from the hull structure 2 in the manner of outriggers. Furthermore, it is to be noted that the preferred frame configuration is adjustable in the sense of comprising a plurality of individual frame members pivotally connected to one another and to the hull structure 2 and the flotation members 28. The frame 27 further comprises a number of hydraulic actuators 30, each of which is pivotally connected at an inboard end to the hull structure 2 via a respective pivotal connection 31 and which is pivotally connected at its outboard end either to a respective frame member 29 or to a flotation member 28.

Via actuation of the hydraulic actuators 30, such that the effective length of the actuators is adjusted, the configuration of the frame structure 27 may be adjusted, thereby moving the flotation members 28 in a vertical and/or horizontal sense relative to the illustrated equilibrium position of the hull structure 2. By adjusting the positions of the flotation members 28 relative to the hull structure 2, the waterplane moment and vertical centre of buoyancy of the wave energy device 1 as a whole may be adjusted in order to optimise the dynamic characteristics of the wave energy device to a particular sea state and/or wave characteristics without necessitating an increase in the overall mass, and hence displacement of the system.

bottom than at the top. However, it is to be appreciated that the illustrated conical bodies can be replaced with bodies of other convenient shapes.

Figure 8 shows the port-side displacement body 32 in a generally upper position in which only the relatively small volume of the lower pointed region 34 of the body enters the drive liquid L within the chamber (in the equilibrium position of the device 1 illustrated) . The starboard-side displacement body 32, on the other hand, is illustrated in a lower position in which it has been moved downwardly into the volume of drive liquid L located within the starboard chamber 7, thereby displacing a significant volume of the drive liquid such that substantially the entire volume of the displacement body 32 has become submerged. It should be appreciated, however that the two bodies 32 are only shown in different positions to one another in figure 8 for the purposes of illustration, and in practice the two bodies will usually both be moved in synchronism so as to remain substantially level with one another relative to the transverse axis of the device. As will thus be appreciated, by simultaneously moving both of the displacement bodies 32 between the two positions illustrated in Figure 8, the vertical centre of gravity of the drive liquid L within the chambers 6, 7 can be adjusted. Because the density of the displacement bodies 32 is significantly less than the density of the drive liquid, the upwards movement of the mass of the drive liquid more than compensates for the downwards movement of the mass of the displacement bodies, with the result that the position of the vertical centre of gravity of the wave energy device 1 as a whole is moved upwardly as the displacement bodies move downwardly without necessitating the take-on or discharge of any additional ballast. In other words, the vertical centre of gravity of the device 1 can be adjusted through movement of the displacement bodies 32 without the need to increase the overall mass and hence displacement of the device.

It should be appreciated, however, that although the particular arrangement illustrated in Figure 8 is shown to incorporate displacement bodies 32 of varying cross-sectional shape and dimension, the bodies could, in alternative arrangements, be configured so as to have substantially uniform cross-sectional shape.

Figure 9 illustrates an embodiment of the present invention incorporating an alternative trim mechanism to that described above and illustrated in Figure 8. In the arrangement of Figure 9, the moving displacement bodies 32 have been replaced by substantially fixed inflatable elements 36, each of which is again provided within a respective chamber 6, 7. Each inflatable element 36, has a gas inlet aperture 37 provided at its uppermost end, and each gas inlet aperture is fluidly connected to a respective gas flow duct 38. The gas flow ducts 38 are provided in fluid communication with a source of inflating gas such as a compressor 39.

Figure 9 shows the port-side inflatable element 36 in a substantially un-inflated condition and it will be seen that in this position the lower end of the un-inflated element extends into the volume of drive liquid L lying within the port-side chamber 6 when the wave energy device 1 adopts its equilibrium position as illustrated. On the other hand, Figure 9 shows the starboard-side inflatable element 36 in an inflated condition in which it has been supplied with a flow of inflating gas from the compressor 39, via the gas flow duct 38 and the gas inlet aperture 37 such that the inflated element has effectively increased in volume. As will be appreciated, the resultant increase in volume is effective to displace the volume of drive liquid L located within the chamber 7, thereby effectively increasing the depth of the liquid within the chamber, and hence moving its centre of gravity vertically upwardly.

Thus, the inflatable element 36 can be selectively inflated and deflated via the compressor 39 and an associated venting arrangement so that the vertical position of the centre of gravity of the entire wave energy device 1 can be controlled, thereby adjusting the dynamic characteristics of the device without increasing the overall mass and hence displacement of the device.

Figure 10 illustrates an alternative form of trim-mechanism which is again operable to control the vertical position of the device's centre of gravity. In this arrangement, the trim-mechanism comprises a mass 40 of substantially fixed shape and dimension, which may preferably take the form of a lead weight or the like. The mass 40 is positioned generally between the two chambers 6, 7 and is arranged for movement in a substantially vertical direction within the hull 2. In the arrangement illustrated, the mass 40 is arranged to move along a centrally located lead screw 41 which extends through the mass 40 via a central, internally threaded bore formed in the mass 40, the lead screw-being threadedly engaged with the bore. The lead screw 41 is arranged for rotation about its longitudinal axis via a motor or gearbox arrangement 42, and the periphery of the mass 40 may be supported and guided via a number of guide slides 43 extending generally vertically around the periphery of the mass 40.

Upon actuation of the motor 42, the lead screw 41 is thus caused to rotate, with rotation in one direction being effective to move the mass 40 downwardly within the hull 2, and rotation in the opposite direction being effective to move the mass 40 upwardly. Movement of the mass 40 is thus effective to adjust the vertical position of the centre of gravity of the wave energy device 1, thereby adjusting its trim and dynamic characteristics without necessitating an overall increase in the weight of the device and hence the volume of water 4 which it will displace. It should be appreciated however, that in variants of this embodiment, the lead screw arrangement could be replaced with an alternative actuation mechanism to move the mass 40 up and down. For example, hydraulic or pneumatic actuators could be used.

Turning now to consider Figures 11 and 12, there is illustrated an alternative embodiment of the wave energy device 1 of the present invention. In this arrangement, the volume of air 14 which serves to drive the turbine 15 is isolated from the volume of drive liquid L via a pair of flexible and deformable bladders 44. As illustrated, each bladder 44 has a bellows-type configuration comprising a plurality of zig-zag folds. Each bladder 44 is closed by an end face 45 at its lower end and is closed at its upper end by virtue of being substantially sealingly connected to the upper wall 46 of the respective chamber 6, 7 so as to extend around the respective vent aperture 12, 13.

Figure 11 illustrates the wave energy device 1 in its equilibrium position which is adopted when the device 1 is permitted to float in flat water 4. In this condition, the volume of drive liquid L is distributed substantially equally between the two chambers 6, 7 and so the volume of air 14 within the system is also distributed substantially equally between the two chambers 6, 7. The result of this equal distribution of the air 14 between the two chambers is that both bladders 44 adopt a generally identical configuration such that each has the same effective vertical length. However, Figure 12 illustrates the wave energy device 1 in a tilted position under the action of an advancing wave face 18 such that the starboard chamber 7 has moved to a position in which it is located generally below the level of the port chamber 6. In the same manner as described above, this orientation of the device is effective to drain drive liquid L from the port chamber 6 so that it moves, via the interconnecting liquid flow duct 8, into the starboard chamber 7 so as to fill the starboard chamber to a greater degree. This movement of the liquid is thus effective to reduce the air space above the drive liquid L within the lower chamber 7, thus compressing the bladder 44 located within that chamber. As will be appreciated, this is effective to drive a flow of air through the turbine 15 in the manner described above and into the interior volume of the bladder located in the upper chamber 6, thereby expanding the bladder as illustrated.

Isolation of the drive liquid L from the air 14 within the closed tank system, in a broadly similar manner to that described above and illustrated in figures 11 and 12, can alternatively be achieved by replacing the bladders 44 with substantially free-running pistons 47 such as in the manner illustrated generally in Figures 13 and 14. The particular arrangement illustrated in Figures 13 and 14 comprises a substantially vertical shaft 48 mounted within each chamber 6, 7, the shafts 48 extending downwardly from, and rigidly secured to, the upper walls 46 of the respective chambers 6, 7. A respective buoyant piston 47 slidably engages each shaft via a close-fitting central bore so as to be moveable in a sliding manner up and down the shaft under the action of the drive liquid L. Each piston is sized and configured so as to be a close sliding fit within the chambers, and thus forms a seal against the sidewall of the respective chamber 6,7 in order to isolate the drive fluid from the air.

Figure 13 illustrates the wave energy device 1 in its equilibrium position which is adopted when the device 1 is permitted to float in flat water 4. In this condition, the volume of drive liquid L is distributed substantially equally between the two chambers 6, 7 and so the two pistons each float on the drive liquid so as to be level with one another. In contrast, Figure 12 illustrates the wave energy device 1 in a tilted position under the action of an advancing wave face 18 such that the starboard chamber 7 has moved to a position in which it is located below the level of the port chamber 6. In the same manner as described above, this orientation of the device is effective to drain drive liquid L from the port chamber 6 so that it moves, via the interconnecting liquid flow duct 8, into the starboard chamber 7 thereby filling the starboard chamber to a greater degree. This movement of the liquid is thus effective to cause the port-side piston, which floats on the surface of the drive liquid contained within the port chamber 6, to move downwardly along its shaft 48 whilst simultaneously driving the starboard-side piston, which floats on the surface of the drive liquid contained within the starboard chamber 7, upwardly along its shaft. As will be appreciated, this upwards movement of the starboard-side piston is effective to drive a flow of air through the turbine 15 in the general manner described above, and into the space defined within the port chamber 6 above its piston 47.

Figures 15 and 16 illustrate another arrangement in accordance with the present invention, in transverse cross-section; Figure 15 representing a section taken at the level of the lower liquid-flow ducts 8, and Figure 16 representing a section taken at the level of the upper air-flow ducts 11. In this arrangement, the device 1 incorporates a hull 2 of generally circular form within which there are provided a plurality of chambers 6, 7 arranged in an annular array. As will be noted, each chamber 6 on the port side of the hull is paired with a diametrically opposing chamber 7 on the starboard-side, thus effectively forming a pair of spaced-apart chambers in a similar manner to the embodiments described previously.

Each pair of chambers is interconnected by lower liquid-flow ducts 8 and upper air-flow ducts 11, as described in more detail below. This annular distribution of chambers, arranged in diametrically-opposing pairs, allows the wave energy device 1 to operate in the general manner described above regardless of its orientation relative to the direction of oncoming waves. Thus for any given wave direction there will be at least one opposing pair of chambers 6, 7 which are at least approximately aligned with the direction along which the advancing waves are moving, with the result that that aligned pair of chambers will experience the greatest relative change in vertical height as the device 1 oscillates under the action of the waves.

Should the direction of the advancing waves subsequently change, another pair of opposing chambers may become more closely aligned with the approaching direction of the waves, thus becoming the dominant pair of chambers experiencing the greatest relative change in vertical positions and thus contributing most to driving the turbine 15.

With particular reference to Figure 15, it can be seen that each chamber 6, 7 is connected at its lower end to a centrally located flow-chamber 49 via a respective liquid flow duct 8, the liquid flow ducts 8 being arranged substantially radially around the flow-chamber. All of the chambers 6,7 are this provided in fluid communication with the central flow-chamber 49. Under the action of waves moving in the direction indicated by the arrow in Figure 15, the pair of chambers denoted 6b, 7b will represent the dominant pair of chambers and will thus oscillate with the greatest relative amplitude. However, the other two pairs of chambers 6a, 7a and 6c, 7c will also oscillate, albeit with a lower amplitude than the dominant pair 6b, 7b. The volume of liquid thus flowing into and out of the dominant chambers 6b, 7b will thus be greater than the volume of liquid flowing into and out of the other chambers as the hull 2 oscillates in the wave system. The central flow-chamber, and the radial array of flow ducts 8 permits appropriate distribution of the oscillating volume of liquid L between the chambers.

Turning now to consider Figures 16 and 17, it can be seen that the manner in which the upper regions of the chambers are interconnected with one another and the turbine 15 is rather more complicated. Each chamber 6, 7 is connected at its upper end to a centrally located plenum housing 50 via a respective air flow duct 11, the air flow ducts 11 again being arranged substantially radially.

Figure 17 illustrates the plenum housing 50 and its connection to the air ducts 11 in more detail. As will be noted, in the particular configuration illustrated, the plenum housing 50 has a generally hexagonal configuration and is oriented so as to present a respective side face towards each of the six chambers arranged around the hull 2 (Figure 17 actually illustrating the chamber with two side faces removed in order to show the internal features of the chamber) . It should be appreciated, however, that in other embodiments using more or fewer chambers, the plenum housing may take alternative polygonal forms accordingly.

For example, an arrangement comprising eight chambers may use a plenum housing of octagonal form. Nevertheless, it is to be noted that the plenum chamber 50 does not need to be polygonal in form, and could instead be substantially circular.

The plenum chamber 50 is internally divided into two plenum chambers 51, 52, by a horizontal dividing wall 53.

The dividing wall 53 is provided with a central aperture through which a cylindrical turbine shroud 54 extends.

The turbine shroud is open-ended and is orientated such that its central axis 55 is substantially vertical. The uni-directional turbine 15 is mounted for rotation about a substantially vertical shaft 56 and is received as a close fit within the turbine shroud 54 for rotation therein. As can be seen in Figure 17, the upper end of the turbine shroud 54 is spaced below the level of the top face of the plenum housing, whilst the lower end of the turbine shroud is spaced above the bottom face of the plenum housing. In this manner, each end of the turbine 15 is exposed to any flow of air occurring within a respective plenum chamber 51, 52.

At its inner end, each air duct 11 is fluidly connected to both plenum chambers 51, 52 by a respective manifold 57. Each manifold defines an upper arm 58 connecting the air duct 11 to the upper plenum chamber 51 via an upper selector valve 59, and a lower arm 60 connecting the air duct 11 to the lower plenum chamber 52 via a lower selector valve 61.

During operation of the device, the positions of the upper and lower selector valves 59, 61 are set so that the chambers 6 located closest to the oncoming waves are fluidly connected with only one of the plenum chambers, and so that the chambers 7 located furthest from the oncoming waves are fluidly connected only to the other plenum chamber. For example, in the illustrated example in which the waves are shown advancing from the left of Figure 16, the upper valves 59 associated with each of the port-side chambers 6 may be closed, whilst the corresponding lower valves 61 are opened, thereby connecting the port-side chambers 6 to the lower plenum chamber 52 and isolating the port-side chambers 6 from the upper plenum chamber 51.

Similarly, the lower valves 61 associated with the starboard side chambers 7 would thus be closed, and the corresponding upper valves 59 opened, so as to connect the starboard side chambers 7 to the upper plenum chamber 51 and to isolate them from the lower plenum 52. In this manner, the port side chambers 6 and the starboard side chambers 7 are provided in fluid communication via the turbine 15. Thus, as the port side of the hull 2 rises, the air 14 within the closed system of chambers is driven out of the lower starboard side chambers (with the largest volume flowing out of the chamber 7b due to its lower level relative to the chambers 7a and 7c), into the upper plenum 51, through the turbine 15 (thereby driving the turbine), and into the lower plenum 52 from where the air is then distributed between the port side chambers 6. As the device is subsequently rolled in the opposite sense as the wave passes, the air is driven in the opposite direction passing through the turbine from the lower plenum 52 to the upper plenum 51, again driving the turbine and hence rotating the shaft 56 in the same direction due to the uni-directional nature of the turbine.

As will be appreciated, as the direction of travel of the waves changes, the selector valves 59, 61 are opened and closed as appropriate so as to ensure that the chambers located closest to the oncoming waves are grouped together in communication with one of the plenum chambers, and the chambers located furthest from the oncoming waves are grouped together in communication with the other plenum chamber.

Whilst the embodiment illustrated in figures 15 to 17 has been described above as being operable so as effectively to divide the chambers into two groups, with all chambers 6, 7 contributing at least some degree to driving the turbine, it is envisaged that a similar arrangement could alternatively be operated such that only the dominant pair of chambers 6b, 7b are operable at any one time. For example, the volume of air driven through the turbine could be limited by closing all of the selector valves associated with the other chambers 6a, 6c, 7a, and 7c thereby isolating those chambers from the plenum arrangement, whilst leaving only the dominant pair of chambers connected to respective plenum chambers 51, 52.

Whilst the invention has been described above with reference to several particular embodiments, it is to be appreciated that various modifications could be made, without departing from the scope of the invention. For example, it is envisaged that the arrangement of Figures 15 to 17 could be modified so as to arrange the turbine 15 for rotation about a substantially horizontal axis. In such an arrangement, it is envisaged that the two plenum chambers would be arranged in side-by-side relation to one another rather than in a vertical arrangement as described above.

For the avoidance of doubt, it is to be noted that the terms "vertical" and "horizontal" as used herein, are to be interpreted in relation to the equilibrium position of the wave energy device when the device is floating in substantially flat water.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure.

Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

Claims (19)

1. CLAIMS1. A wave energy device (1) for use in the generation of electrical energy from wave energy, the device being substantially buoyant, configured to oscillate in response to wave motion, and comprising: a pair of chambers (6, 7) fluidly interconnected in a lower region by a liquid-flow-conduit (8), fluidly interconnected in an upper region by an air-flow-conduit (11), and configured to receive a volume of liquid (L) distributed between the two chambers via the liquid-flow-conduit (8) so as to partially fill the chambers; said liquid-flow-conduit (8) being arranged to permit the flow of said liquid (L) back-and-forth between said chambers (6, 7) in response to oscillation of the device (1), and said air-flow-conduit (11) being arranged to permit the counter-flow of air (14) between said chambers (6, 7) under the action of said flow of liquid (L) ; the device further comprising a prime mover (15) located in the path of said flow of air (14) and configured to convert energy from the flow of air to mechanical energy, wherein the device comprises a mechanism which is actuable to allow controlled adjustment of the response of the device to wave motion.
2. 2. A device according to claim 1, wherein said pair of chambers (6, 7) are spaced apart from one another.
3. 3. A device according to claim 1 or claim 2, wherein said prime mover (15) comprises a turbine.
4. 4. A device according to any preceding claim, wherein said prime mover (15) is unidirectional.
5. 5. A device according to any preceding claim, comprising at least one valve (16, 17) provided in said air-flow-conduit (11), the or each said valve (16, 17) being adjustable so as to control said flow of air (14) between the chambers (6, 7)
6. 6. A device according to claim 5, comprising a plurality of said valves (16, 17), wherein each said chamber (6, 7) is associated with a respective valve (16, 17) located between the chamber and the prime mover (15)
7. 7. A device according to any preceding claim, having a fill-mechanism operable to adjust the volume of said liquid (L) partially filling the chambers (6, 7)
8. 8. A device according to any preceding claim comprising a flow-mechanism (23, 25) operable to control the flow of said liquid (L) between the chambers (6, 7)
9. 9. A device according to claim 8, wherein said flow-mechanism is operable to adjust the flow-area of said liquid-flow-conduit (8)
10. 10. A device according to any preceding claim, comprising a trim-mechanism operable to adjust the vertical position of the device's centre of gravity.
11. 11. A device according to claim 10, wherein the trim-mechanism comprises at least one mass (40), the or each mass (40) being substantially vertically moveable relative to said chambers (6, 7)
12. 12. A device according to claim 10 or claim 11, wherein said trim-mechanism comprises a plurality of moveable bodies (32), each said body being configured to displace the liquid (L) partially filling a respective chamber (6, 7) and being arranged for movement within said chamber (6, 7) so as to vary the volume of said liquid (L) displaced by the body.
13. 13. A device according to any one of claims 10 to 12, wherein said trim-mechanism comprises a respective inflatable element (36) provided within each said chamber (6, 7), each said inflatable element (36) being arranged so as to at least partially lie in the liquid (L) partially filling the respective chamber, the trim-mechanism being operable to control the degree of inflation of each said element (36) and to thereby vary the volume of liquid (L) within the chamber displaced by the element.
14. 14. A device according to any preceding claim, wherein said chambers (6, 7) each have a non-constant horizontal cross-section.
15. 15. A device according to claim 14, wherein each said chamber (6, 7) is substantially tapered.
16. 16. A device according to any preceding claim comprising a plurality of said pairs of chambers (6, 7)
17. 17. A device according to claim 16, wherein said chambers (6,7) are provided in a substantially annular array, the two chambers (6a, 7a; 6b, 7b; 6c, 7c) of each pair being substantially diametrically opposite to one another.
18. 18. A device according to claim 16 or claim 17 comprising a single said prime-mover (15) arranged to be driven by the flow of air between a) a plurality of said pairs of chambers, or b) a single said pair of chambers selected from said plurality of chambers.
19. 19. A device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.