WO2017025718A1

WO2017025718A1 - Resonant pneumatic wave compressor

Info

Publication number: WO2017025718A1
Application number: PCT/GB2016/052382
Authority: WO
Inventors: Norman West Bellamy; Neil Michael Bellamy; Robert Ian Smith
Original assignee: Norman West Bellamy; Neil Michael Bellamy; Robert Ian Smith
Priority date: 2015-08-07
Filing date: 2016-08-03
Publication date: 2017-02-16

Abstract

There is provided a first wave energy converter, operating as a long attenuator, for extracting energy from sea waves comprising a floating flexible power hose, suction coupled to the wave surface. The power hose is buckled by an internal tensioned spinal cord into a resonant waveform that couples with the wave surface to extract energy from the incident waves. The spinal cord drives a skeleton reinforced diaphragm that pumps atmospheric air along the hose at the propagation velocity of waves. The air flow is unidirectional and the air pressure increases at every change of curvature along the flexible hose to produce compressed air. This compressed air is delivered by pipe to land where it can be converted to electricity or used as energy storage. There is provided a second wave energy converter, operating as a long attenuator, for extracting energy from sea waves comprising a floating flexible hose, suction coupled to the wave surface, that transfers energy to an internal buckled elastic spine, tuned to the wave frequency, which drives skeleton reinforced diaphragm seals that pump atmospheric air at the propagation velocity of waves. The air flow is unidirectional and the air pressure increases along the flexible hose to produce compressed air for delivery by pipe to land where it can be converted to electricity or used as energy storage.

Description

RESONANT PNEUMATIC WAVE COMPRESSOR

This invention relates to apparatus for extracting energy from sea waves. Ocean waves are created by wind passing over extensive stretches of sea. Because wind is originally derived from solar energy, waves may be considered to be stored form of renewable energy. With the effects of climate change and the depletion of fossil fuels, the availability of this immense energy source should help to meet the future energy needs of mankind.

Energy of sea waves off the Atlantic coast of the UK averages over 70 kW per metre in deep water and dissipates down to typically 20kW per metre at the shoreline. Storm conditions can produced megawatts of power per metre and are very destructive particularly in the shoreline surf zone. The engineering challenge to harness this energy is enormous and there have been numerous attempts to find an economical solution to harvest the significant amount of energy available.

The conversion of wave energy to a useful form of energy to serve mankind, such as electricity, has been seriously studied for a number of decades. As a result, numerous patents have been filed covering wide-ranging ideas for wave energy converters that would exploit this vast energy resource. Despite the ingenuity of many of these ideas, none have proved to be a commercial success and only a few have been demonstrated in trials at full scale. The overriding problem has been engineering costs of extracting energy from sea waves due to the harsh environment and the diffuse nature of the resource. A truly practical and economic solution to the problem has yet to be found.

The nature of sea waves presents enormous engineering challenges that designers have found difficulty to resolve. In particular, sea waves are generally random in height, period and direction and have instantaneous power levels varying from zero to peak every half cycle. A typical Atlantic wave energy site may have an average power level of 50kW/m peaking up to a disruptive 10MW/m in storm conditions. Surviving and harnessing power in this vast range of power variations is the major challenge for designers of wave energy converters. A common solution is to locate the wave energy converters on the shoreline where operating and maintenance costs are significantly less than at sea. Shoreline devices, normally oscillating water columns (OWCs) have been demonstrated many times but with disappointing results, normally due to the significantly reduced shoreline energy available. Some devices have the primary capture equipment at sea, or on the sea bed, where energy levels are high and then pipe hydraulic fluid or high pressure water ashore where the fluid power is converted to electricity. None of these ideas have proved successful probably because many of the devices do not generate enough power to pay for the big and heavy structures.

Designs for floating offshore wave energy converters are very varied and have the benefit of higher incident wave powers than shore based units. However, most of these devices have major structural and machinery cost centres and have not proved to be economic. Attempts have also been made to reduce the size of these device structures by using self- reaction techniques, such as hinged raft devices, but the resulting mechanical complication has added other costs. Energy capture with membrane air bags combine with pneumatic power conversion has reduced structural and machinery costs but not sufficient to make a real impact on the cost of energy delivered.

The designs for wave energy converters fall generally into six groups; attenuator, terminator, point absorber, shoreline structures, overtopping reservoirs and submerged seabed devices. Attenuators are currently seen as the promising devices and generally consist of a long floating device, normally flexible, which operates normal to the wave front and effectively rides the waves. Motion along its length can be restrained to produce energy normally as hydraulic power from movement at hinges between raft sections. Attenuators experience lower forces than terminators which is claimed to increase survivability. Long attenuators can benefit from energy diffraction which effectively increases the capture width since energy is drawn in from the sides.

Many attenuator designs of wave energy converters are self-reacting and consist of hinged raft structures, such as the recent UK Pelamis, that bridge up to about one wavelength in the wave direction and use hydraulics to extract energy from the relative movement of neighbouring segments. Onboard conversion to electricity includes hydraulic accumulators to smooth the pulsing power before driving the generators that feed electricity through subsea cables to land. These devices use mass and buoyancy to lever across the hinges to drive the hydraulic power take-off. Both mass and buoyancy are expensive to provide at sea and often result in large raft structures and associated heavy duty hinges.

Wave power as a renewable source of energy is an attractive idea but its development has been held back by the potential high costs of current devices designed to convert the energy and deliver it to land. Recent assessments of the realistic costs of electricity produced by current 'front runner' wave power devices indicates that energy produced is nearly five times as expensive as from fossil fuel sources. Clearly, a more radical approach needs to be taken to reduce device costs and improve energy capture efficiency.

The two major cost centres for most devices are the structure, and mechanical and electrical equipment (M&E). The need for large structures at sea can be drastically reduced by using self-reacting principles with flexible membrane construction and locating M&E on land where costs are much lower. This would avoid the expensive mass at sea that adds cost at every stage of manufacture, deployment and operation. Furthermore, the majority of devices capture power at wave orbital velocities at around 1 m/s whereas surface wave propagation phase velocities are around 15m/s in the North Atlantic. Capturing this unidirectional high velocity wave power by pneumatic means gives a significant advantage in terms of energy capacity and provides the opportunity to transfer power to land by compressed air rather than by electricity.

Onboard pneumatic power conversion is a preferred option for many wave energy converters because it offers the most flexible solutions, particularly where oscillating water columns (OWCs) are involved. However, OWCs generate reversing air flow that has proved difficult to convert efficiently to electricity through self-rectifying turbines due to the wide dynamic range of the incident wave power. Direct generation of unidirectional air flow is difficult and therefore rare in wave energy converters despite the fact it would offer major advantages in terms of efficiency and equipment costs. Most pneumatic devices use air power at low pressure but one family of devices claim to produce air at high pressure, that is, compressed air. If a wave power converter produced compressed air, say at 6 bars or above, then it becomes a practical and cost effective proposition to pipe the compressed air power to land for final conversion to electricity. This is an attractive solution in that all mechanical and electrical equipment is on land where equipment, operating and maintenance costs are much lower.

A number of inventors have proposed, and filed for patents, wave energy converters that use the influence of wave propagation on a flexible floating pneumatic hose to extract energy and produce compressed air. In one method, air pockets and water slugs are injected into a floating flexible pipe and trapped by gravity to match the velocity of the crests and troughs, respectively, of the incident wave. In theory, the output air pressure in a pipe will be equivalent to the cumulative differential pressure of all the water heads created by the water slugs. These attenuators are simple and have few moving parts at sea and would be very competitive if the concept was not flawed. The basic concept can be easily demonstrated in the laboratory by using coils of a pipe wrapped around a drum to simulate sequences of waves and then turning the drum to create cumulative air pressure. Unfortunately, actual wave velocities at sea are too high to pump water along a practical sized pipe and, in such cases, nearly all the energy generated within the pipe is loss through water friction and turbulence. Therefore, these devices are not practical using water slugs but the general concept is attractive and underpins this patent application.

The invention featured in our Patent GB2475049A and related Patent GB2010002028 describes a flexible pneumatic hose floating as a surface following attenuator and constructed from reinforced membrane materials. It has the potential to produce significant amounts of air power at low cost when air is driven along the hose at wave velocity. Typical average Atlantic waves are 4m high with energy periods of 10s, and wavelengths of 150m, and have wave velocities of 15m/s (nearly 40mph). Each wave travelling along the flexible hose increases the air pressure within the hose and for a long hose, with multiple wavelengths along its length, a cumulative high pressure is produced. In the given sea state, a hose, 1 m in diameter and km in length, which delivers compressed air at say 6 bar, through a 1km pipe, has the potential output of several megawatts.

However, extracting large amounts of power from the surface of the waves will exert high vertical forces on the hose that have to be resisted by the buoyancy and mass of the hose. The hose buoyancy is generally adequate to deal with the downward forces but the very low mass of a membrane hose will be insufficient to prevent the hose lifting from the wave surface. The solution is to provide the hose with fins along its length that define an adequate suction area to hold the hose in firm contact with the wave surface. By this means, atmospheric pressure will provide the necessary downward force removing the need for mass in the form of expensive ballast. The hose may have to be reinforced near the bow where the air pressure is low. A flexible hose filled with air can be constrained to follow a wave surface by virtue of its buoyancy and surface suction and will be able to extract wave energy if it is self-reacting in some way. If the mass and stiffness of the hose are designed to be low, the natural bending frequency is inherently too high to achieve the efficiency benefits of a fully resonant system. Therefore, to extract energy from typical sea waves requires an alternative reaction member, preferable tuned to the predominant wave frequency, which resists the flexing motion of the hose in the vertical plane. It is known that a long elastic beam, or spine, under axial compression will buckle at a particular wavelength and this can be tuned by adjusting its stiffness (El, where E, is Young's modulus and I, is the second moment of area of the section) or by adjusting its axial compression force. Such a spine can be conveniently fitted inside the flexible hose and compressed by a constant axial force applied at the ends of the hose. The hose itself is therefore kept in axial tension and its internal diameter limits the lateral excursions of the compressed spine, which, in turn, promotes multiple buckling wavelengths that can be tuned to the target wave climate. When the hose is subjected to incident waves, the buckling wavelengths will tune with wave frequency and the crests and troughs of the spine motion will lock with the crests and troughs of the hose motion producing a travelling wave in the spine. The spine motion is, in effect, driven by the wave curvature. If the spine is tuned to the wave frequency, it will resonate with the incident wave excitation and amplify the power capture. The captured wave energy is induced into the spine as elastic strain energy and this energy will flow along the spine as flexural waves. These spine waves are used to drive internal diaphragm seals at wave velocity along the inside of the hose to produce air power. This system has featured in the two previous patents mentioned and is effective over a broad band of wave periods and enables efficient energy capture.

An alternative configuration to the above is to use a buckled hose, fitted with high stiffness flanges, under compression provided by an internal spinal cord in tension. This arrangement would enable a more resonant response to wave motion but would require a modified design of the internal power take off mechanism. Such a stiffened hose, or power hose, has to match its internal tension to the equivalent beam stiffness of the power hose in order to tune the natural bending frequency of the device to that of the driving waves. When correctly tuned the device should exhibit extremely high dynamic magnification and high power capture.

According to a first aspect of the invention, there is provided a wave energy converter for extracting energy from sea waves, the converter comprising a flexible air filled power hose, in surface contact with an incident wave surface in the general direction of wave propagation, whose coupled wave energy is transferred as strain energy into the power hose, that is under buckling compression by a tensioned internal spinal cord, that in turn, drives a series of diaphragm inverting seals inside the power hose at the velocity of wave propagation and thereby sequentially pumps atmospheric air to a high pressure for conversion to electricity as a source of energy.

In embodiments of the invention, a tensioned internal spinal cord may drive a diaphragm, located between two side hinges fitted with a series of bearings and reinforced with internal skeleton ribs, are progressively switched through a transition phase between the two stable sealing states by the wave induced action of the spinal cord.

In further embodiments of the invention, the internal skeleton ribs may sequentially rotate through nearly 180 degrees in bearings, from a crest position in sealing contact with the hose, to a trough position in opposite sealing contact with the hose, thereby defining a sequence of travelling air pockets or air passages.

In calm or small seas, the power hose may buckle into sinusoidal waveforms, determined by the tension in the spinal cord, to create stationary sequential air pockets defined by each point of zero curvature, when subjected to zero air pressure.

In active sea waves with no air power being extracted, the compressed power hose may buckle into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined at each point of zero curvature of the power hose, when subjected to zero air pressure.

In active sea waves with air power being extracted, the compressed power hose may buckle into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined by a phase lag from each point of zero curvature of the power hose, when subjected to air pressure determined by the external load.

The bow unit may consist of a rigid section that supports a projecting sleeve within the power hose, in order to initiate the travelling wave motion and to enclose the fixed end of the spinal cord.

The stern unit may consist of a rigid section that supports a projecting sleeve to terminate the travelling wave motion and to accommodate an adjustable end mechanism for the spinal cord in order to adjust the tension in the spinal cord.

In this new embodiment of the invention, the power hose is kept in axial compression by the tensioned spinal cord and the hose buckles into a waveform that couples with the incident sea waves. The internal diameter of the power hose limits the lateral excursions of the tensioned spinal cord by internal contact at the crest and trough positions. These points of contact effectively seal the upper and lower air passages in the hose enabling air to be progressively compressed along the power hose. This travelling wave motion in the hose pumps the pressurised air along the device to produce compressed air at the stern of the device. If the power hose is tuned to the wave frequency, it will resonate with the incident wave excitation and amplify the power capture. The output air pressure, and therefore compressed air power, increases with the length of the power hose and is expected to achieve 6 bar, and megawatts of power, for a 1 km long, 1m diameter (nominal), flexible power hose device. The device components can be manufactured from flexible materials to allow it to follow wave surface profiles with minimum resistance. The flexible power hose and associated fins use rubber membrane material reinforced with high tenacity fibre cords oriented to give the desired flexibility characteristics. The diaphragm has a composite structure of a plastic or metal spring skeleton, covered in rubber material to give good sealing qualities. The spinal cord is a flexible material in the form of a webbing belt made from a high strength polymer fibre or a carbon fibre composite.

The bow unit of the device, with its air inlet, has a rigid structural section to terminate the power hose and enable the heave motion at the bow to initiate the spine travelling wave motion that propagates along the hose. It is fitted with a means of anchoring the end of tensioned spinal cord. Mooring forces for attenuators are relatively low and the bow is moored to maintain position offshore.

The stern unit of the device has a rigid structural section to terminate the power hose and the spinal cord. The end of the spinal cord is attached to a screw mechanism in the stern unit to enable the cord to be tensioned. The stern unit also enables the heave motion at the stern to terminate the travelling wave motion that propagates along the hose and thereby prevent reflections. One method is to use a short rigid sleeve projecting into the flexible hose to restrict the hose deflection in order to terminate the travelling wave. The compressed air output at the stern is fed to the seabed by a riser pipe of the type used in the oil/gas industry. The stern mooring is slack moored to limit stern movement.

The power hoses are in close contact with sea water and the air will be kept at near constant temperature throughout the compression process. This efficient isothermal cycle means that the internal energy is removed from the system as heat at the same rate that it is added by the mechanical work of compression. The compressed air power from farms of power hoses at sea can be fed ashore for conversion to electrical power. The onshore conversion can be carried out by a modified gas turbine plant with its air compressor replaced by the compressed air from the power hoses. The heat produced by the fuel combustion enables recuperation for the expansion cooling that takes place due to air expansion. In conventional gas turbines, 2/3rd of the fuel gas used is required to compress the intake air and 1/3rd used to generate electrical power. Replacing the compressor unit with compressed air from the wave energy farm enables all the shaft power produced by the gas turbine to drive the electrical generator. Note that overall efficiencies of gas turbine generators can achieve 60% whereas this modified gas turbine should significantly exceed this figure.

Using fossil fuel in an energy conversion process is not acceptable in a renewable energy system. Also, fuel gas is unlikely to be available at wave energy sites and piping gas to site would be expensive. An alternative arrangement, that avoids using fossil fuel, is to heat the compressed air input using electrical power from the electrical generator. This reduces the electrical power available to feed to the grid by 1/3rd but eliminates the need for another fuel source of the same magnitude. This power conversion system is a practical solution for large scale wave energy farms that produce compressed air power of lOOMW or more. The availability of compressed air from wave energy converters at sea leads to the real possibility of compressed air storage. The power hoses can be designed to deliver compressed air at 6 bar, that is a pressure that could be efficiently contained on the seabed at 60m depth. This convenient form of compressed air energy storage (CAES) enables renewable wave energy to be supplied according to demand rather than dictated by supply.

To summarise, the hose is closely-coupled to the wave surface to absorb and transfer wave energy to the hose structure in the form of elastic strain energy that propagates as a matching resonant wave along the device at wave velocity. The captured strain energy in the power hose is then converted to compressed air flow in the hose by a mechanism that progressively increases the air pressure within the hose. The overall advantage of the device is the competitive low energy cost that results from using compliant materials to build a tuned self-reacting energy capture system that produces compressed air at wave velocity for transmission to land before final M&E conversion to electricity.

In embodiments of the invention, the converter may comprise a flexible hose, in surface contact with an incident wave surface in the general direction of wave propagation, whose coupled wave energy is transferred to an internal spine reaction member, that is under bucking compression, in the form of elastic strain energy that, in turn, drives a series of diaphragm inverting seals inside the hose at the velocity of wave propagation and thereby sequentially pumps atmospheric air to a high pressure for conversion to electricity as a source of energy. In further embodiments of the invention, an internal spine driving diaphragm inverting seals, located between two side hinges fitted with a series of bearings and reinforced with internal skeleton ribs, may be progressively switched through a transition phase between the two stable sealing states by the wave induced action of the spine reaction member.

In still further embodiments of the invention, the internal skeleton ribs may sequentially rotate through nearly 180 degrees in bearings, from a crest position in sealing contact with the hose, to a trough position in opposite sealing contact with the hose, thereby defining sequence of travelling air pockets or air passages.

In calm seas, the spine may buckle into sinusoidal waveforms, determined by spine compression, to create sequential air pockets defined by each point of zero curvature, when subjected to zero air pressure.

In active sea waves with no air power being extracted, the compressed spine may buckle into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined by each point of zero curvature, when subjected to zero air pressure.

In active sea waves with air power being extracted, the compressed spine may buckle into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined by each point of curvature near to maximum, when subjected to air pressure determined by the external load.

The bow unit may consist of a rigid section that supports a projecting sleeve enclosing the end of the spine member, that initiates the travelling wave motion.

The stern unit may consist of a rigid section, that supports the end of the spine member by a pivotal bearing, that terminates the travelling wave motion.

To avoid the wear problems of sliding seals, the diaphragm strip acts as a rolling seal between the top and bottom internal surfaces of the flexible hose. The diaphragm is made of a series of transverse strips, to facilitate 3D profiling, that are designed to buckle between hinges along both edges to the horizontal axis within the flexible hose. This built- in transverse compression strain in the diaphragm enables it to be stable in two distinct shapes that can seal on either, the upper or, the lower, internal surfaces of the hose. This bi-stable action of the spine-diaphragm within the hose defines air passages above or below the diaphragm according to the particular stable state. The diaphragm is made of a reinforced composite material, with both elastic and spring characteristics, and is profiled to provide a pressure air seal within the hose. By making the spine integral with the diaphragm, the spine can drive the diaphragm upwards during the crest of the wave into one state and downwards during the trough of the wave into the alternative inverted state. The transition between stable states will take place near the points of inflexion of the wave in the form of an inverting seal action of the diaphragm that pumps the air along the hose. Each crest in the wave train increases the pressure at each inverting seal and pumps air along the top passages within the hose. Simultaneously, the troughs pump air in the lower passages to add to the air flow. The output air pressure, and therefore compressed air power, increases with the length of the hose and is expected to achieve 6 bar, and megawatts of power, for a 1 km long, 1m diameter, flexible hose device.

A major benefit of the integral spine-diaphragm arrangement is the enhanced stiffness given to the spine by the added diaphragm section that substantially increases the second moment of inertial of the total section during the crest and trough profiles. Furthermore, the stiffness at the transition section between crest and trough sections is reduced to the natural spine stiffness which enables a rapid transition every half wavelength. This inherent characteristic of spine-diaphragm stiffness allows practical spine sections to be used to give the required overall stiffness to tune to practical wavelengths. A further benefit of this stiffness characteristic of the spine-diaphragm section is the reduction of the spine stiffness when the device is coiled as a layflat section. This is very useful feature for manufacturing, transport and deployment purposes.

The device components can be manufactured from flexible materials to allow it to follow wave surface profiles with minimum resistance. The flexible hose and associated fins use rubber membrane material reinforced with high tenacity fibre cords oriented to give the desired flexibility characteristics. The diaphragm has a composite structure of a plastic or metal spring skeleton, covered in rubber material to give good sealing qualities, and edged with a corded bead. The spine rectangular beam section can be made from spring steel, polycarbonate or a fibre-resin composite. A tubular spine of fibre reinforced materials, pressurised with air or water, would enable the spine stiffness to be controlled for tuning purposes. The use of an inflatable spine has the advantage that the device is flexible when the tube is deflated and can be easily rolled up for manufacture, transport and deployment. The bow unit of the device, with its air inlet, has a rigid structural section to enable the heave motion at the bow to lever the bending moment that initiates the spine travelling wave motion that propagates along the hose. It is fitted with a means of compressing the spine by about 1 to 5% of its length to produce the required buckling effect. A short rigid sleeve, projecting into the flexible hose to restrict the spine deflection, helps to initiate the travelling wave. Mooring forces for attenuators are relatively low and the bow is moored to maintain position offshore.

The stern unit of the device, with its compressed air riser pipe to the seabed, also has a rigid structural section to support the spine termination guides. The spine termination has to match the wave propagation characteristics to ensure spine waves terminated effectively and do not generate reflections. One method is to use a short rigid sleeve projecting into the flexible hose to restrict the spine deflection in order to terminate the travelling wave. The stern mooring is slack moored to limit stern movement.

To summarise, the hose is closely-coupled to the wave surface to absorb and transfer wave energy to the spine structure in the form of elastic strain energy that propagates as a matching resonant wave along the spine at wave velocity. The captured spine energy is then transferred to air flow in the hose by progressively increasing the air pressure. The overall advantage of the device is the competitive low energy cost that results from using compliant materials to build a tuned self-reacting energy capture system that produces compressed air at wave velocity for transmission to land before final M&E conversion to electricity.

According to a second aspect of the invention, there is provided a wave energy converter for extracting energy from sea waves, the converter comprising a flexible hose, in surface contact with an incident wave surface in the general direction of wave propagation, whose coupled wave energy is transferred to an internal spine reaction member, that is under bucking compression, in the form of elastic strain energy that, in turn, drives a series of diaphragm inverting seals inside the hose at the velocity of wave propagation and thereby sequentially pumps atmospheric air to a high pressure for conversion to electricity as a source of energy.

In embodiments of the invention, an internal spine driving diaphragm inverting seals, located between two side hinges fitted with a series of bearings and reinforced with internal skeleton ribs, may be progressively switched through a transition phase between the two stable sealing states by the wave induced action of the spine reaction member.

In further embodiments of the invention, the internal skeleton ribs may sequentially rotate through nearly 180 degrees in bearings, from a crest position in sealing contact with the hose, to a trough position in opposite sealing contact with the hose, thereby defining sequence of travelling air pockets or air passages.

The features of the wave energy converter of the second aspect of the invention and its embodiments share the same technical effects and advantages as the corresponding features of the wave energy converter of the first aspect of the invention and its embodiments.

Preferred embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings in which:

Figure 1 is a sectional elevational side view of the wave energy converter at sea as disclosed in our British Patent No. GB2475049A (original document);

Figure 2 is a plan view of the wave energy converter farm showing four units, as shown in Figure 1 , feeding compressed air to a power conversion plant located on land;

Figure 3 is a perspective elevational view of a section of the wave energy converter shown in Figure 1 ; Figure 4 is a sectional elevation side view of a new embodiment of the invention shown in Figure 1 , showing a section of the flexible hose with an internal spinal cord without tension when the device is floating on a calm sea;

Figure 5 is a sectional elevational side view of a new embodiment of the invention shown in Figure 1 , showing a section of the flexible power hose with an internal spinal cord under tension when the device is subjected to small sea waves;

Figure 6 is a sectional elevational side view, with cross sections, of a new embodiment of the invention, showing part of the flexible power hose with an internal spinal cord under increased tension and driving a diaphragm inverting seal when the device is subjected to larger sea waves;

Figure 7 is a view of cross sections of a new embodiment of the invention showing the three configurations taken by the spinal cord and diaphragm in a flexible power hose as the waves propagate along the hose;

Figure 8 is a view of the cross section, elevations and plan of the new embodiment of the invention showing the skeleton structure of the power hose comprising a rib structure driven by the spinal cord;

Figure 9 is a view of the elevation of the new embodiment of the invention showing the skeleton structure of the power hose when operating without air pressure load, and under air pressure load, when the device is subjected to larger sea waves;

Figure 10 is a sectional elevational side view of a new embodiment of the invention showing the bow and stern sections of the power hose;

Figure 11 is a sectional elevational side view of the wave energy converter at sea as disclosed in our British Patent No. GB2475049A (original document);

Figure 12 is a plan view of the wave energy converter farm showing four units, as shown in Figure 11 , feeding compressed air to a power conversion plant located on land;

Figure 13 is a perspective elevational view of a section of the wave energy converter shown in Figure 11 ;

Figure 14 is a sectional elevation side view of the wave energy converter, shown in Figure 11 , showing part of the flexible hose with an internal reactive spine when the device is floating on a calm sea;

Figure 15 is a sectional elevational side view of the wave energy converter, shown in Figure 11 , showing part of the flexible hose with an internal reactive spine when the device is subjected to sea waves;

Figure 16 is a sectional elevational side view, with cross sections, of the wave energy converter, shown in Figure 11 , showing part of the flexible hose with an internal reactive spine driving a diaphragm inverting seal when the device is subject to sea waves; Figure 17 is a view of cross sections of a new embodiment of the invention showing the three configurations taken by the spine-diaphragm in a flexible elastic hose as the waves propagate along the power hose;

Figure 18 is a cross section, local plan, elevation and full plan of a new embodiment of the invention showing the skeleton of the power hose comprising a rib structure driven by the spine;

Figure 19 is an elevation of the new embodiment of the invention showing the skeleton of the power hose when operating with no load and full load air pressures; and Figure 20 is a sectional elevational side view of a new embodiment of the invention showing the bow and stern sections of the power hose.

The following section describes an embodiment of the invention, with reference to Figures 1 to 10. Figure 1 shows a device for extracting and converting the energy of waves in a body of liquid, typically the sea or ocean. The complete floating device 10 is normally many wavelengths longer than the shortened representation and is called a Power Hose. The device 10 floats on the body of water and contours to the wave surface 11. The device is designed to function as an attenuator with the bow 12 moored 19 to face the wave front and the stern 13 moored 19 in the wave propagation direction 14. The device draws air from the atmosphere at inlet 15 and air flows along the length of the device 10, where it is pressurised, to produce compressed air at the stern 13 that is fed through the output riser pipe 6 to the seabed and then to land through pipe 17 or to seabed storage through pipe 18. To accommodate the compressibility of air, the device 10 is shown as decreasing in diameter along its length. The moorings 19 align the device to function as an attenuator.

Figure 2 shows a wave farm of four devices 10 drawing air from the atmosphere 12 and feeding compressed air 16 to land for conversion to electrical power in the shore based plant 20. The devices are slack moored 19 at the bow 12 and at the stem 13 to maintain position.

Figure 3 shows a perspective view of a section of the device consisting of a buoyant flexible hose 25, fitted with stiff flanges 44 and flexible side fins 26, that floats on the water surface. The fins 26 are flexible enough to create a suction area in contact with the water surface 27 that is sufficient to hold down the device in operational sea states. The suction waterline

27 is defined by the fins 26 and the flexible power hose 25 floats on the higher waterline

28 caused by the loss of air, due to wave action, that creates lower air pressure beneath the device. During wave action, the fins 26 allow air to escape causing the edges of the fins to sink, due to suction, thereby preventing inlet of air.

Figure 4 shows a section of the flexible power hose 25, fitted with an internal spinal cord 30, without tension, floating on a calm water surface 11. The flexible power hose can be buckled into a waveform by applying a constant axial tension force 31 to the ends of the spinal cord.

Figure 5 shows the same section of the power hose as in Figure 4 but with applied tension 31 in the spinal cord 30 and with the device subjected to waves 11 equal in height to the hose diameter. The flexible hose 25 is buckled to match the waves and the tensioned spinal cord just touches the internal surface of the flexible hose and air is driven along the hose, if the air pressure is low. Contact between spinal cord 30 and flexible hose 25 takes place at the wave crest 32 and the wave trough 33 sections and this propagates the buckled wave along the inside of the power hose 25 at wave velocity.

Figure 6 shows the same section as in Figure 5 but with higher tension in the spinal cord and with larger waves. The flexible hose 25 is buckled to match the waves and the tensioned spinal cord 30 makes pressure contacts with the internal surface of the flexible hose and air under pressure is driven along the hose. The tensioned spinal cord 30 has to bend around each point of contact and thereby applies a contact force proportional to the tension force in the spinal cord. This creates an upper air passage 41 at the crest section of the power hose and a lower air passage 40 at the trough section of the power hose. The three cross sections 36, 37, 38, show the different configurations taken by the spinal cord 30 - rib 47 structure as the wave propagates along the power hose. These three cross sections are described in detail in the following Figure 7.

Figure 7 shows three detailed cross sections, Figures 7a, 7b and 7c, representing the locations of cross sections 36, 37 and 38 shown in Figure 6. These cross sections show the complete diaphragm 35 which consists of a flexible rubber sleeve, reinforced by the internal skeleton comprising of a spinal cord 30 and rib 47 structure, located by the bearing/hinge 39 to the longitudinal flanges 44 along the neutral axis of the hose. The reinforced diaphragm effectively forms a series rolling seals on the inside of the hose to compress air from the bow intake to the stern outlet. The integral spinal cord 30, enclosed along the centreline of the diaphragm 35, provides the means of forcing the diaphragm from a stable position at the trough of the hose 36 (Figure 7a) to the opposite stable position at the crest of the hose 38 (Figure 7c); and vice versa. Between the two stable states, near the points of inflexion, is the transition zone 37 (Figure 7b) where the spinal cord forces the transit of the diaphragm against the air pressure. The transition zones define the air passages that are in the form of pockets of air at the crest 41 and trough 40 that are driven by the incident wave along the power hose.

Figure 8 shows details of the internal structural configuration of the diaphragm 35 that enables air compression within the power hose. It includes a skeleton structure, driven by the spinal cord motion, to support the flexible rubber diaphragm in its sealing ability and to enable the diaphragm transition between crest and trough configurations.

Figure 8a shows a cross section the internal skeleton structure of the power hose where the spinal cord 30, drives a series of ribs 47 whose ends are located in bearings 51 along the inside of the flanges 44. The ribs 47 are split in the centre 50 to enable the spine to drive the rib motion during transitions between crest and trough positions.

Figure 8b shows a side elevation of the transit path 33 of the spinal cord 30 and ribs 47 about the bearings 51 located in flanges 44. This transit is driven by spinal cord as it moves (less than 180 degrees) from its crest to trough positions and vice versa. Figure 8c shows an elevation of the power hose 25 internal structure at the point where the transition takes place from crest to trough when the wave is equal in height to the diameter of the power hose. During the transition, the tensioned spinal cord 30 rotates the ribs 47 about their bearings 51 located in the flange 44, from the crest position that defines the air passage 41 , to the trough position that defines the air passage 40. Air is pumped along the hose if there is no resistance to the flow of air. At this point of transition, any resistance to air flow will cause reverse leakage at the sealing points resulting in the stalling of the air flow.

Figure 8d shows the plan of the action described in Figure 8c and illustrates the more positive sealing action of the spinal cord 30 driving the ribs 47 in line contact with the internal surface of the power hose 25. During transition, the rib spacing 48, 49 varies slightly and creates a strain in the enclosing rubber diaphragm that results in significant bistable action. This bistable action provides substantial stiffening support to the spine between transitions thereby increasing the performance in high energy seas.

Figure 9a shows an elevation of the power hose 25 internal structure at the point where the transition takes place from crest to trough when the waves are significantly higher than the diameter of the power hose. These sea waves pump air along the power hose but no air power is being extracted because there is no resistance to the air flow. In these conditions, the spinal cord - diaphragm transition is shown to take place at the point of zero curvature.

Figure 9b shows an elevation of the power hose 25 internal structure at the point where the transition takes place from crest to trough when the waves are significantly higher than the diameter of the power hose. These sea waves pump air along the power hose and air power is being extracted because there is resistance to the air flow that creates air pressure. In these operational conditions, the load causes a phase lag the spinal cord - diaphragm transition towards a point where the curvature is near maximum.

Figure 10a shows the bow section 12 of the power hose 0 that is designed to initiate the travelling wave propagation along the hose. The end of the spinal cord 30 is fixed to the bow end and centrally located by a guide 55 along the power hose to enable the spinal cord to swing from the crest to trough positions. Atmospheric air is drawn into the inlet pipe 15 by suction pressure generated by the first diaphragm 35 seals. The air flow divides every half wavelength between the upper air passage 41 , and lower air passage 40, that are defined and separated by the diaphragm 35. The primary mooring 19 is attached to the bow 12 to maintain the device in an attenuator configuration.

Figure 10b shows the stern section 13 of the device 10 where the compressed air is fed down a riser 16 to the seabed for transmission to land 17 or storage 18. The end of the spinal cord 30 is guided into the stern unit by guide 55 to provide a matched termination for the energy in the power hose 10. The end of the spinal cord 30 is terminated by a screw mechanism 56 to control the tension in the spinal cord 30. Note that the diameter of the power hose is tapered which makes the diameter of the stern section less than that of the bow section in order to accommodate for the compression of the air flow. The secondary mooring 19 is attached to the stern 13 to limit the excursion of the device.

The following section describes a further embodiment of the invention, with reference to Figures 11 to 20.

Figure 11 shows a device for extracting and converting the energy of waves in a body of liquid, typically the sea or ocean. The complete device 10 is normally many wavelengths longer than the shortened representation. The device 10 floats on the body of water and contours to the wave surface 11. The device is designed to function as an attenuator with the bow 12 moored 19 to face the wave front and the stern 13 moored 19 in the wave propagation direction 14. The device draws air from the atmosphere at inlet 15 and air flows along the length of the device 10, where it is pressurised, to produce compressed air at the stern 13 that is fed through the output riser pipe 16 to the seabed and then to land through pipe 17 or to seabed storage through pipe 18. To accommodate the compressibility of air, the device 10 is shown as decreasing in diameter along its length. The moorings 19 align the device to function as an attenuator.

Figure 12 shows a wave farm of four devices 10 drawing air from the atmosphere 12 and feeding compressed air 16 to land for conversion to electrical power in the shore based plant 20. The devices are slack moored 19 at the bow 12 and at the stern 3 to maintain position.

Figure 13 shows a perspective view of a section of the device consisting of a buoyant flexible hose 25, fitted with flexible side fins 26, that floats on the water surface. The fins 26 are flexible enough to create a suction area in contact with the water surface 27 that is sufficient to hold down the device in operational sea states. The suction waterline 27 is defined by the fins 26 and the flexible hose 25 floats on the higher waterline 28 caused by the loss of air, due to wave action, that creates lower air pressure beneath the device. During wave action, the fins 26 allow air to escape causing the edges of the fins to sink, due to suction, thereby preventing inlet of air.

Figure 14 shows a section of the flexible hose 25, fitted with an internal spine 30, floating on a calm water surface 11. The spine is buckled into a waveform by a constant axial compression force 31 causing it take a wave shape limited in amplitude by the internal dimensions of the flexible hose 25. Without incident waves, the spine waveform is stationary.

Figure 15 shows the same section as in Figure 14 but with the device subjected to waves 11 propagating along the length of the device. The buckling of the spine 30 is significantly increased in amplitude and illustrates the physical coupling mechanism from external water wave 1 to internal spine wave 30. Pressure contact between spine 30 and flexible hose 25 takes place at the wave crest 32 and the wave trough 33 sections and this propagates the buckled wave in the spine 30 along the inside of the hose at wave velocity. When the strain energy of the buckled spine wave is in tune with the incident wave, the power transferred from wave to the spine, in the form of elastic strain energy, is maximised. Figure 16 shows the same section as in Figure 15 but with the spine 30 integral with a diaphragm sealing strip 35. The edges of the diaphragm strip are located within the flexible hose 25 by longitudinal flexible hinges 39 within the horizontal diameter of the hose that also seals the air passages 40, 41. The three cross sections 36, 37, 38, show the different configurations taken by the diaphragm 35 as the wave propagates along the device. In the crest section 36 of the wave, the spine forces the diaphragm seal 35 to the top of the hose creating a lower air passage 40, whilst in the trough section 38 the diaphragm seal is forced to the bottom of the hose creating an upper air passage 41. The diaphragm inverting transition 37 near each point of inflexion moves along the hose and pumps air along the hose passages at wave velocity. To achieve the three cross section configurations for the diaphragm strip, as described above, requires special properties and construction techniques.

Figure 17 is a new embodiment of the device showing the individual cross sections, Figures 17a, 17b and 17c, for three configurations taken by the diaphragm 35 as the wave propagates along the hose 25. The diaphragm 35 consists of a flexible rubber sleeve internally reinforced by an internal metallic skeleton, hinged 39 to the longitudinal flange stiffeners 44 along the neutral axis of the hose. The reinforced diaphragm effectively forms a series rolling seals on the inside of the hose to compress air from the bow intake to the stern outlet. The integral spine 30, enclosed along the centreline of the diaphragm 35, provides a means of forcing the diaphragm from a stable position at the crest of the hose 36 to the opposite stable position at the trough of the hose 38; and vice versa. Between the two stable states, near the points of inflexion, is the transition zone 37 where the spine forces the transit of the diaphragm against the air pressure 45. The transition zones define the air passages that are in the form of pockets of air at the crest 40 and trough 41 that are driven by the incident wave along the hose.

Figure 18 shows a new internal configuration of the power hose that significantly improves the performance of the air compression within the power hose. It includes a skeleton structure, driven by the spine motion, to support the flexible rubber diaphragm in its sealing ability and to enable the diaphragm transition between crest and trough configurations.

Figure 18a shows a cross section, plan and elevation of a new internal skeleton structure of the power hose where the spine 30 drives a series of ribs 47 whose ends are located in bearings 51 along the inside of the flanges 44. The ribs are split in the centre 50 to enable the spine to drive the rib motion during transitions between crest and trough positions. The elevation shows the transit path 52 of the ribs 47 about the bearing 51 in flange 44. Figure 18b shows an elevation of the power hose 25 internal structure at the point where the transition takes place from crest to trough on a calm sea. During the transition, the compressed spine 30 rotates the ribs 47 about the bearings 51 located in the flange 44, from the crest position that defines the air passage 41 , to the trough position that defines the air passage 40.

Figure 8c shows the plan of the action described in Figure 18b and illustrates the positive sealing action of the ribs 47 in line contact with the internal surface of the power hose 25. During transition, the rib spacing 48, 49 varies slightly and creates a strain in the enclosing rubber diaphragm that results in significant bistable action. This bistable action provides substantial stiffening support to the spine between transitions thereby increasing the performance in high energy seas. Figure 19a shows the same elevation as Figure 18b where the device is driven by sea waves but no power is being extracted. The spine - diaphragm transition is shown to take place at the point of zero curvature.

Figure 19b also shows the same elevation as Figure 18b where the device is driven by sea waves but with power being extracted. The spine - diaphragm transition is shown to take place at the point where the curvature is near maximum.

Figure 20a shows the bow section 12 of the device 10 where atmospheric air is drawn into the inlet pipe 15 by suction pressure generated by the first diaphragm seals 35. The air flow divides between the upper air passage 41 , and lower air passage 40, that are defined and separated by the diaphragm 35. The end of the spine 30 is centrally located by guides 55 and is under a constant compressive end force 31 provided by mechanical means. This end restraint is designed to initiate the travelling wave propagation in the spine. The primary mooring 19 is attached to the bow 12 to maintain the device in an attenuator configuration.

Figure 20b shows the stern section 13 of the device 10 where the compressed air is fed down a riser 16 to the seabed for transmission to land 17 or storage 18. The end of the spine 30 is terminated by a pivot or rocker mechanism 56 within the stern unit. Again, this end restraint has to be designed to match the wave propagation characteristics of the spine and needs to be non-reflective to provide a matched termination of the spine wave. The secondary mooring 19 is attached to the stern 13 to limit the excursion of the device. Note that the diameter of the power hose is tapered which makes the diameter of the stern section less than that of the bow section in order to accommodate for the compression of the air flow. It will be appreciated that the above-described embodiments of the invention may be used in combination, that is to say one or more features of the wave energy converter of the embodiment of the invention described with reference to Figures 1 to 10 may be used in combination with one or more features of the wave energy converter of the embodiment of the invention described with reference to Figures 11 to 20.

Claims

1. A wave energy converter for extracting energy from sea waves, the converter comprising a flexible air filled power hose, in surface contact with an incident wave surface in the general direction of wave propagation, whose coupled wave energy is transferred as strain energy into the power hose, that is under buckling compression by a tensioned internal spinal cord, that in turn, drives a series of diaphragm inverting seals inside the power hose at the velocity of wave propagation and thereby sequentially pumps atmospheric air to a high pressure for conversion to electricity as a source of energy.

2. A wave energy converter according to Claim 1 , wherein a tensioned internal spinal cord drives a diaphragm, located between two side hinges fitted with a series of bearings and reinforced with internal skeleton ribs, are progressively switched through a transition phase between the two stable sealing states by the wave induced action of the spinal cord.

3. A wave energy converter according to Claim 1 or Claim 2, wherein the internal skeleton ribs sequentially rotate through nearly 180 degrees in bearings, from a crest position in sealing contact with the hose, to a trough position in opposite sealing contact with the hose, thereby defining a sequence of travelling air pockets or air passages.

4. A wave energy converter according to any one of the preceding claims, wherein in calm or small seas, the power hose buckles into sinusoidal waveforms, determined by the tension in the spinal cord, to create stationary sequential air pockets defined by each point of zero curvature, when subjected to zero air pressure.

5. A wave energy converter according to any one of the preceding claims, wherein in active sea waves with no air power being extracted, the compressed power hose buckles into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined at each point of zero curvature of the power hose, when subjected to zero air pressure.

6. A wave energy converter according to any one of the preceding claims, wherein in active sea waves with air power being extracted, the compressed power hose buckles into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined by a phase lag from each point of zero curvature of the power hose, when subjected to air pressure determined by the external load.

7. A wave energy converter according to any one of the preceding claims, wherein the bow unit consists of a rigid section that supports a projecting sleeve within the power hose, in order to initiate the travelling wave motion and to enclose the fixed end of the spinal cord.

8. A wave energy converter according to any one of the preceding claims, wherein the stern unit consists of a rigid section that supports a projecting sleeve to terminate the travelling wave motion and to accommodate an adjustable end mechanism for the spinal cord in order to adjust the tension in the spinal cord.

9. A wave energy converter according to any one of the preceding claims, wherein the converter comprises a flexible hose, in surface contact with an incident wave surface in the general direction of wave propagation, whose coupled wave energy is transferred to an internal spine reaction member, that is under bucking compression, in the form of elastic strain energy that, in turn, drives a series of diaphragm inverting seals inside the hose at the velocity of wave propagation and thereby sequentially pumps atmospheric air to a high pressure for conversion to electricity as a source of energy.

10. A wave energy converter according to Claim 9, wherein an internal spine driving diaphragm inverting seals, located between two side hinges fitted with a series of bearings and reinforced with internal skeleton ribs, are progressively switched through a transition phase between the two stable sealing states by the wave induced action of the spine reaction member.

11. A wave energy converter according to Claim 9 or Claim 10, wherein the internal skeleton ribs sequentially rotate through nearly 180 degrees in bearings, from a crest position in sealing contact with the hose, to a trough position in opposite sealing contact with the hose, thereby defining sequence of travelling air pockets or air passages.

12. A wave energy converter according to any one of Claims 9 to 11 , wherein in calm seas, the spine buckles into sinusoidal waveforms, determined by spine compression, to create sequential air pockets defined by each point of zero curvature, when subjected to zero air pressure.

13. A wave energy converter according to any one of Claims 9 to 12, wherein in active sea waves with no air power being extracted, the compressed spine buckles into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined by each point of zero curvature, when subjected to zero air pressure.

14. A wave energy converter according to any one of Claims 9 to 13, wherein in active sea waves with air power being extracted, the compressed spine buckles into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined by each point of curvature near to maximum, when subjected to air pressure determined by the external load.

15. A wave energy converter according to any one of Claims 9 to 14, wherein the bow unit consists of a rigid section that supports a projecting sleeve enclosing the end of the spine member, that initiates the travelling wave motion.

16. A wave energy converter according to any one of Claims 9 to 15, wherein the stern unit consists of a rigid section, that supports the end of the spine member by a pivotal bearing, that terminates the travelling wave motion.

17. A wave energy converter for extracting energy from sea waves, the converter comprising a flexible hose, in surface contact with an incident wave surface in the general direction of wave propagation, whose coupled wave energy is transferred to an internal spine reaction member, that is under bucking compression, in the form of elastic strain energy that, in turn, drives a series of diaphragm inverting seals inside the hose at the velocity of wave propagation and thereby sequentially pumps atmospheric air to a high pressure for conversion to electricity as a source of energy.

18. A wave energy converter according to Claim 17, wherein an internal spine driving diaphragm inverting seals, located between two side hinges fitted with a series of bearings and reinforced with internal skeleton ribs, are progressively switched through a transition phase between the two stable sealing states by the wave induced action of the spine reaction member.

19. A wave energy converter according to Claim 17 or Claim 8, wherein the internal skeleton ribs sequentially rotate through nearly 180 degrees in bearings, from a crest position in sealing contact with the hose, to a trough position in opposite sealing contact with the hose, thereby defining sequence of travelling air pockets or air passages.

20. A wave energy converter according to any one of Claims 17 to 19, wherein in calm seas, the spine buckles into sinusoidal waveforms, determined by spine compression, to create sequential air pockets defined by each point of zero curvature, when subjected to zero air pressure.

21. A wave energy converter according to any one of Claims 17 to 20, wherein in active sea waves with no air power being extracted, the compressed spine buckles into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined by each point of zero curvature, when subjected to zero air pressure.

22. A wave energy converter according to any one of Claims 17 to 21 , wherein in active sea waves with air power being extracted, the compressed spine buckles into sinusoidal waveforms to match and couple with the wave profiles, to create sequential travelling air pockets defined by each point of curvature near to maximum, when subjected to air pressure determined by the external load.

23. A wave energy converter according to any one of Claims 17 to 22, wherein the bow unit consists of a rigid section that supports a projecting sleeve enclosing the end of the spine member, that initiates the travelling wave motion.

24. A wave energy converter according to any one of Claims 17 to 23, wherein the stern unit consists of a rigid section, that supports the end of the spine member by a pivotal bearing, that terminates the travelling wave motion.