GB2471863A - Wave powered generator responsive to wave impact - Google Patents

Abstract

A wave powered device 10 has a buoyant structure comprising a submerged hollow e.g. spherical body 12 and a stub tower 13 projecting from the hollow body 12 and extending above the surface 11 of the sea. The structure 10 is caused to roll in response to wave impact on the tower 13, and is symmetrically shaped so as to react similarly to waves from any direction. A plurality of pendulums 21 are mounted within the structure to hove relative to it as the structure rolls. Fluid e.g, hydraulic rams may be driven by the relative movement to provide pressurized fluid to drive a fluid motor which drives an electric generator.

Description

Wave Powered Generator

Technical Field of the Invention

The present invention relates to the extraction of energy from sea waves and, in particular, to the generation of electric power therefrom.

Background of the Invention

The generation of renewable energy from natural resources is the subject of increasingly intense study and development activity. Many prototype and full scale facilities have been built, employing wind, tidal and hydroelectric power. Wave energy has also been recognised as a promising potential source of renewable energy and several attempts have been made in the past decades to design and build wave energy extraction devices. Such devices harness wave motion to drive an electricity generator, the output of which may then be fed to shore via a suitable electric cable. They do not depend on tidal rise and fall but employ semi submersible slack anchored structures, whose heaving or rolling motion is converted to rotation of one or more turbines which in turn drive one or more generators.

One of the earliest such proposals, known as "Salter's Duck", is described in US patent 3928967 to S. Salter for an "Apparatus and method for extracting wave energy". This uses, as a basic component, an energy removing member (rotor), rotatably mounted on a submerged floating platform (stator). The member, shaped rather like an inverted comma, rotates like a bobbing duck as a result of impacting waves. This produces partial relative rotation between rotor and stator which causes water at high pressure to be pumped through internal manifolds to drive a power generator, not shown in any detail, which may be a turbine for generating electricity. Banks of rotors and stators may be linked together by pivot couplings to multiply the output proportionately. However, Salter's devices need to be oriented roughly orthogonally to the direction of the waves in order to work.

Another approach to wave power generation is described in a patent EP 0037408B1 for "Wave Energy Apparatus" to A. A. Wells. This shows a floating structure in the form of a quasi-spherical open topped flask which is designed to extract wave energy from both heave and from rocking movements. It has a single turbine in an upper nozzle fed by three circumferentially disposed ducts. At their lower ends, the ducts flare out around a trapped air space and open out into a shared water filled lower space. Heaving of the sea drives air in the same direction through all the ducts and pitching or rolling causes outflow of air through at least one duct and inflow through another, each flow driving the turbine in the same direction. The apparatus is therefore able to function omnidirectionally, irrespective of incident wave direction.

An alternative approach to both the Salter and Wells patents which has been proposed is to generate mechanical energy from the relative motion of a pendulum mounted in or on a floating structure and to convert this by a variety of means into electrical energy.

An early proposal is shown in Japanese patent publication 52059240A to Hitachi Shipbuilding Corporation for a wave driven generator. A number of weighted pendulums are arranged axially in line within a sealed hull and rolling of the hull as a result of wave action causes them to swing in parallel planes. The swinging pendulums drive piston and cylinder arrangements to draw air into the hull and compress it. The pressurised air is then exhausted through a turbine which drives an electric generator. Because the pendulums are in line and constrained to swing in parallel planes, the generator does not respond to waves from any direction and, like the Salter device, would need orienting to the incident wave direction.

The use of a pendulum suspended from a universal joint, so as to be able to respond to waves from any direction has been proposed in US patent 4317047 (de Almada) for "Energy Harnessing Apparatus". In this patent, a single pendulum is suspended from a universal joint at the top of a tall superstructure projecting from a buoyant base. Energy is extracted by a system of three hydraulic cylinders disposed at 120° intervals about a pendulum bar, near to the top of the superstructure. Fluid under pressure from the cylinders is used to supply an accumulator which in turn drives a hydraulic motor and electricity generator.

A later structurally similar patent application WO 2009/013766 Al to V. Catinella uses a magnetic pendulum to produce electricity by induction. Again, the pendulum is suspended from a universal joint at the top of a tall superstructure, itself supported on a floating cylindrical body, loosely anchored to the seabed. This application makes clear that the apparatus is intended for heavy sea conditions and that a massive structure, 200 metres above sea level is contemplated, presumably to enable the extraction of worthwhile large amounts of energy.

Although onmidirectional in operation, the structures described in both these patent publications would appear to be both unstable and subject to immense bending stresses in storm conditions.

A further universal joint "Pendulum Generator" is also described in patent application W02002061277 Al to F Jauregui Carro in which one or more arms at the end of the pendulum push against and drive so-called "energy transformers" These arms are arranged circumferentially about the pendulum so that energy is produced whatever the plane of the pendulum swing. The pendulum is mounted, via a support frame, on a floating element which sways under the action of waves. The energy transformers convert the mechanical energy derived from the waves into electrical energy. This is more compact in appearance than the two preceding proposals but is described in only limited detail. It is not clear how much energy a device of this nature could produce.

Finally, it is noted that deep water vessels known as FPSOs (Floating production, storage and offloading) which are employed in the offshore oil extraction industry also have to withstand severe weather conditions at sea. Stresses caused by movement under extreme weather conditions can cause a great deal of damage to the FPSO itself and to any subsea connections, as the FPSO strains against its moorings. A known solution to this problem is the use of internal turret systems about which the body of the vessel can rotate and which are connected to slack mooring chains. Cabling and piping can then be fed out through the turret without being damaged by the motion of the vessel

Disclosure of the Invention

The various prior art proposals fail to show a wave power generator which is onmidirectional, extremely robust and which can produce large amounts of energy.

Accordingly the present invention provides a wave powered device for generating electric power from sea waves comprising: a buoyant structure comprising a hollow body and a stub tower projecting from the hollow body, the buoyant structure being arranged to float with the hollow body submerged and with the tower projecting upwardly from the hollow body above the surface of the sea to a sufficient extent, to a sufficient extent as to cause the structure to roll in response to wave impact on the tower, the structure being symmetrically shaped so as to react substantially identically to waves from any direction; a plurality of pendulums mounted internally within the structure and being relatively inclinable thereto in any direction when the structure rolls; a plurality of fluid ram means each coupled between the interior of the structure and a respective pendulum in an arrangement such that, when the structure rolls, each ram means is driven to produce fluid under pressure irrespective of the direction of the roll; and electricity generating means within the structure for producing electricity at an output thereof and comprising a fluid motor, arranged to be driven by said fluid under pressure, and an electromagnetic generator, coupled to said motor.

The symmetrical nature of the structure consisting of hollow body and tower combined with its relatively low height, similar to that of the largest expected waves, provides a very robust external structure, capable of withstanding the roughest conditions. The height can be kept relatively low compared to the single pendulum prior art, without compromising energy extraction, by the use of multiple pendulums. Energy can be extracted whatever the direction of the seas by virtue of the pendulum mounting, allowing the relative inclination of the pendulum and buoyant structure to be in any direction.

The tendency of the pendulums will be to keep vertical, while the buoyant structure rolls about them. However, it will be realised that this will be altered by the damping effect of the ram action and also by the fact that pendulums at different positions within the floating structure will also be subject to quite extensive translational movements the further they are away from the centre of rotation of the structure.

Preferably, the hollow body and stub tower are round. Specifically, it is preferred that the hollow body be substantially spherical and the tower be cylindrical in form, the axis of the cylinder passing through the centre of the hollow body. This may be the most robust structure for strength and hydrodynamic efficiency to handle waves from any direction but it will be realised that, within reason, any regular polygonal sectional shape for both floating body and tower will also produce substantially identical movements, whatever the direction of the sea.

Also preferably, each pendulum comprises a weighted shaft suspended by means of a universal joint, such as a ball and socket joint or a gimbal. However, other shapes of pendulum may be satisfactory with or without added weights.

In one preferred implementation, each of the ram means should include at least two rams disposed at different non-aligned circumferential positions about their respective pendulum so that a component of the roll motion will affect one or other of the rams irrespective of the plane of roll. Specifically, a balanced arrangement in which each of the ram means includes four such rams disposed at 900 intervals about their respective pendulum or three rams disposed at 120° is preferred.

Although at least two rams are necessary for an omnidirectional response when the rams are disposed about the pendulum, an alternative implementation can be envisaged in which a single ram attached by universal joints to the lower end of the pendulum and the deck surface below would also exhibit an omnidirectional response and produce pressurized fluid whatever the direction of roll by bending in the same direction as the relative displacement of the pendulum.

To accommodate changes in level of points on the pendulum when inclined with respect to the structure and changes of lateral alignment of rams in the multi-ram case upon extension or contraction, it is preferable that each ram means is coupled to the interior of the buoyant structure and to its respective pendulum by means of universal joints.

One preferred way of mounting, which avoids any problems from any tendency of the pendulum to twist or rotate is that each pendulum comprises a hub rotatable on bearings about a pendulum shaft, each ram means being coupled to its respective pendulum via the hub.

Alternatively, the hub may be fixed directly to the pendulum and the pendulum suspended via a Hooke's or Cardan coupling, so preventing it from rotating.

The hub arrangement could also be modified to make the centres of pivoting of each ram coupling coincident with the pendulum axis. However, this alternative might require connection of the rams at different levels.

To extract the greatest energy from the relative motion of pendulum and buoyant structure, it is preferable that the rams be double acting. However, it is also possible to employ rams which work in one direction, such as on extension, only.

To prevent over-travel and impact damage in extreme conditions, it is preferred that the apparatus includes a limit means coupled to each pendulum, for example at its free end for limiting the relative movement of the pendulum and the floating structure.

It is preferred that both the limit means and the ram means contact the pendulum at different points and in a preferred form the floating structure has a plurality of decks, each pendulum extending between three adjacent decks such that it is suspended from one deck, passes through a hole in an intermediate deck and extends towards a lowest deck of the three, each ram means being coupled to the intermediate deck and the limit means being mounted on the lowest deck.

To maximise the energy available within the minimum volume, it is also a preferred feature that each pendulum and its associated rams form a unit within the floating structure and that multiple pluralities of said units are disposed between respective different sets of adjacent decks within the floating structure. This enables the units to be distributed as widely as possible throughout the available volume.

It is also preferred that each ram means is comprised of hydraulic rams, the device further including an accumulator for accumulating hydraulic fluid under pressure from the ram means associated with all or some of the plurality of pendulums, and the fluid motor is arranged to be driven by hydraulic fluid under pressure from the accumulator, the electromagnetic generator being connected to be driven by the hydraulic motor so as to generate electricity.

Although the apparatus can in theory function with a gaseous fluid, such as air, it is advantageous that a hydraulic fluid be employed as the pressures are more manageable.

Preferably, the apparatus includes a swivel linkage about which the buoyant structure is mounted for rotation, the linkage being attachable to an external slack mooring system. The swivel linkage preferably comprises a cylinder internal to the structure, including bearings to permit relative rotation of linkage and structure, and a slip ring arrangement for connecting the output of the electromagnetic generator to an external electric output cable while permitting relative rotation between the generator output and the external output cable. If this were not used, there would be stresses caused by the floating structure rotating about the anchor system, causing the cable to twist about the mooring system anchor chains.

Brief Description of the Drawings

The invention will now be described by way of example only with reference to preferred embodiments thereof as illustrated in the accompanying drawings in which: Figure 1 is a schematic side section through a wave powered device for generating electric power according to the present invention; Figures 2A and B are partial cross sections through a pendulum energy extraction unit forming part of a wave powered device, such as that of Figure 1, under different sea conditions; Figure 3A is a sectional plan view taken on the line A-A of Figure 2A; Figure 3B is a sectional plan view taken on the line B-B of Figure 2A and also showing a pendulum weight in dash-dot line; Figure 4 is detail of a hub assembly used in the unit of Figures 2 and 3; Figure 5A is a plan view similar to Figure 3A illustrating an orthogonal displacement of the pendulum and rams of the energy extraction unit of Figures 2A and B under roll conditions; Figure 5B is a plan view similar to Figure 3B illustrating the corresponding displacement of the travel limiting devices of the energy extraction unit shown in Figures 2A and B; Figure 6A is a schematic version of Figure 3A showing an example of an alternative twisting displacement of the pendulum and rams of the energy extraction unit of Figures 2A and B under roll conditions; Figure 6B is a schematic version of Figure 3B illustrating the corresponding displacement of the travel limiting devices of the energy extraction unit shown in Figures 2A and B; Figure 7 is a schematic diagram illustrating the main energy production and power generation sequence of a wave powered device for generating electricity, such as that of Figures 1 to 4, according to the present invention; Figure 8 shows an arrangement of shared generating units, accumulators and transformers on one of the decks of the wave powered device of Figure 1; Figure 9 shows one possible arrangement of energy extraction units on a deck within the widest part of the spherical body portion of the device of Figure 1; Figure 10 shows one possible arrangement of energy extraction units on a deck within a narrower part of the spherical body portion of the device of Figure 1; and Figure 11 shows a possible arrangement of energy extraction units on a deck within a tower portion of the device of Figure 1.

Detailed Description of the Invention

Figure 1 shows the basic components of a wave powered generator device designed for the harsh environments such as may be found in deeper ocean waters and sometimes also in near offshore locations. To operate in such environments requires a massive and robust structure 10 comparable in size to a merchant ship, drilling platform or so-called FPSO (floating production storage and offloading) vessel. Such a structure must be of sufficiently robust design as to maintain integrity and reliability for a typical design life of 20-30 years.

The structure 10 is buoyant and designed to float in sea water at a depth indicated by the mean sea level (equivalent to calm conditions) illustrated by waves 11. The structure is a sealed one comprising a hollow spherical body 12 and a cylindrical stub tower 13. The tower 13 is attached to the body 12 and, when the structure is floating with the body 12 submerged as shown, the tower projects upwardly above the sea surface through the wave splash zone, being the region lying between the troughs and crests of the waves. The correct level of buoyancy is achieved by means of a ballast chamber 14, surrounding all but the top of the structure. For maximum efficiency, the tower will be designed to project to a height of the same order of magnitude as the crests of the waves, which will of course depend on intended location and prevailing weather conditions. Typically, the magnitude of the highest waves expected would be around 15 to 20 metres. On top of the tower is a helideck 15 to enable access by a maintenance crew. The purpose of the tower 13 is to act as a wave energy catcher which will react to incident waves from any direction thereby causing the spherical body 12 to roll.

Internally, the buoyant structure is divided into multiple decks 16, labelled conventionally A to Z, A' and B', at a standard inter deck spacing of four metres. The whole structure is rotatable about an internal cylindrical turret 17 on bearings 18. The device is anchored by a slack mooring system, illustrated schematically by two anchor chains 19, attaching the lower end of the turret to anchor blocks, such as 23, on the sea bed. In practice four or more such chains would be required. The device is free to rise and fall and to move laterally within a restricted floating area up to the limit of the anchor chains. The turret system allows the device to rotate about its moorings without excessive torsional strains on the anchor chains and is a well known feature of FPSO vessels. The device therefore is free to move and predominantly roll in two of its six possible degrees of freedom although, as mentioned, it is anticipated to have minimal heave and rotation on its axis.

Since the turret only rotates around a vertical axis, the drag of the anchor lines will tend to work against rotation of the device about horizontal axes. However, such an anchoring system is desirable for operation in very heavy seas at some distance from shore. The mass of the device and the characteristics of the deep ocean waves will still cause the device to roll and it will settle at a frequency determined by its mass and shape and the power and size of the waves.

A large number of energy extraction units 20 are disposed within the buoyant structure such that each unit spans three adjacent decks 16. A few of these units 20 are illustrated schematically between G, H and I decks, between M, N and 0 decks and also between Y, Z and A -decks. At the heart of each of the energy extraction units is a weighted pendulum like device 21 suspended from a universal joint 22. Rolling of the spherical body 12 caused by waves incident on the tower 13 causes relative motion between the structure 10 and the pendulums, with the pendulums tending to retain their vertical position. The resultant displacement drives hydraulic rams (not shown in Figure 1), connected to the pendulums, to produce pressurized fluid which, in turn, drives an internal combined hydraulic motor and electricity generation system 24, located on 0 deck, the operation of which will be further explained below. The electricity so produced is fed to a conventional slip ring arrangement 25, set into the top of the turret and led out by a cable 26, which may, if desired, be linked to one of the anchor chains, to a junction box 82 of a seabed distribution system.

One of the pendulum energy extraction units 20 is shown in more detail in Figures 2, 3 and 4. A pendulum 21 is formed by a weight 29 mounted near the end of a shaft 30. The shaft is suspended from an upper one of three decks 16 by a ball and socket joint 22, the ball having a stub extension clamped to shaft 30, as shown. The ball and socket joint 22 allows relative movement in any direction of inclination between the pendulum and the buoyant structure 10, of which the decks 16 are part. The shaft 30 passes through a hole 31 in an intermediate deck. It will be appreciated that, in this arrangement, the tendency of the pendulum will be to remain stationary as the buoyant structure 10 rolls in the waves, rather than to swing as a conventional pendulum. In any case, the hole 31 is sufficiently large to accommodate the expected range of inclination.

Surrounding the pendulum 21 at 900 displacement from each other (best seen in Figure 3A) are four hydraulic rams 32. In a calm sea, with no rolling of the buoyant structure 10, the relative position of the components will be as illustrated in Figure 2A. The pendulum hangs vertically through the centre of hole 31 and is equidistant from the rams 32. In rougher conditions, the structure 10 rolls and inclines relative to the pendulum, as illustrated in Figure 2B.

Relative displacement of the pendulum and buoyant structure is resisted by the four hydraulic rams 32, mounted on the intermediate deck of the three. Hydraulic fluid is supplied to and exhausted from each ram by means of two flexible hydraulic lines 33, portions of which are shown in outline in Figure 3A. One line supplies unpressurized fluid to opposite ends of the ram -10 -through one way inlet valves on induction and pressurized fluid is supplied through one way outlet valves to the other line, on compression. The ram cylinders are connected via a rod 34 and ball joint 35 to a post 36 in the form of a short I-beam fixed to the deck. The ram pistons 37 are connected by connecting rods 38 to further ball joints 39 fixed to a hub 40, clamped about the shaft 30. The ball joints 35 and 39 allow the rams to tilt in the vertical plane as the structure rolls.

The hub 40 is formed of two half rings terminating in abutting flanges 43 which are bolted together to clamp the hub onto a bearing 41. The purpose of the bearing structure is to permit some rotation of the pendulum on its suspending ball joint 22 to occur without producing torsional or other strains between the pendulum and the ram couplings. The bearing is supported partially by a collar or flange 42 formed on the shaft 30, as also shown in the detail of Figure 4.

The pendulums 21 are thus suspended in a manner which allows their relative inclination to the buoyant structure 10 to be in any direction. The analogy with a swinging pendulum is that it would be free to swing in any plane within the complete 360° of possible orientations. Because, as best illustrated in Figure 3A, there are four rams 32 at different circumferential positions about the pendulum 21, the resulting inclination of the structure to the pendulum, whatever the direction of roll, will result in work being done on at least two of the rams to produce hydraulic fluid under pressure. The device 10 is thus responsive to incident waves from any direction. Furthermore, because of the symmetrical structure of spherical body 12 and cylindrical tower 13, the response is the same for an identical wave, whatever its angle of incidence.

To complete the description of the device 10, with special reference also to Figures 2A, 2B and 3B, it will be noted that the pendulum shaft 30 has an extension 50, below the weight 29. The extension includes a collar 51, bearing 52 and hub 53, similar to that on the main shaft 30. The hub 53 is connected by ball joints 54 and rods 55 to four respective travel limiting devices 56 disposed at 90° intervals about the shaft extension 50. A suitable device 56 is a commercially available limit stop known as a sway brace, such as is used to limit piping movement in hurricane or earthquake conditions. Internally, each sway brace has a pressure plate 57 entrapping a heavy duty spring 58 within the body of the brace. Externally the braces 56 are connected via a further rod 59 and ball joint 60 to a fixture 61 on the lowest deck 16 of the unit. The braces function to prevent the pendulum 21 exceeding its permitted range of inclination, expected to be around 10°, which could cause the pistons of rams 32 to strike the ends of their cylinders or, dependent on the particular dimensions, could cause the pendulum -11 -shaft 30 to strike the edges of hole 31 on the intermediate deck. The spring characteristics of the braces 56 are such as to provide little resistance until the design limits of travel are approached, after which the resistance increases gradually to a maximum.

It will be realised that although the pendulums, if unconstrained, would remain in a vertical orientation while the buoyant structure rolls about them, in practice, the limiting effect of both the energy producing rams and, if engaged, the travel limiters will result in some movement of the pendulums. Pendulum movement may also be caused by the translational movement of the pendulum suspension points located away from the centre of rotation of the structure 10.

The basic relative motion of the pendulum, rams and travel limiting devices in rolling conditions will now be described, with reference to Figures 5 and 6. These are based on Figure 3 which shows the position of the major drive components in a state of rest. In this state, the four rams 32a to 32d are all orthogonal to each other and equidistant from the central axis of the pendulum shaft 30.

As the structure 10 rolls, the weight of the pendulum will act to try to keep the pendulum vertical which will drive the double acting rams 32. Figure 5A is an illustration of this situation with the relative displacement of the pendulum to the rams being to the left, as drawn. It can be seen from the position of the pistons that the rams 32a and 32c compress and extend the most and that they stay diametrically in line. Rams 32b and 32b are skewed to non-radial lines and extend only slightly. In this example all four rams contribute fluid under pressure to the generator system, with the greatest contribution being from rams 32a and 32c.

Figure SB shows the similar displacement of the four travel limiting devices, labelled 56a -56d.

It is also possible that the hub 40 may twist under roll action, as shown in Figure 6A, so that all four rams 32a -32d are somewhat skewed and the work done is distributed differently between them. It will be noted however, that the combination of ball joint attachments and freely rotatable hub can accommodate the movement without strain.

Figure 6B shows the similar displacement of the four travel limiting devices 56a-56d.

The cross-hatched areas 65 shown in Figures 5 and 6 represent the maximum limits of movement or footprint of the pendulum weight 29, the rams 32 and the braces 56 on the decks for all possible directions of roll.

-12 -The operational sequence of electricity generation by the device illustrated in Figures 1 to 4 is illustrated in Figure 7. Some details have been simplified and shown only schematically in order to assist explanation. Where possible, however, identical reference numerals to those used in earlier figures are employed.

In Figure 7, four energy extraction units 20 are shown, the leftmost being expanded to show the principal components, namely a pendulum like device 21 comprising a weight 29 on a shaft 30 suspended from a universal joint (not shown) fixedly mounted on the structure 10. As explained in more detail above, rolling motion of the structure in the waves causes the inertial mass of the pendulum to drive a number of hydraulic rams 32 coupled to the pendulum shaft.

The rams are supplied with hydraulic fluid from a reservoir 70 via check valves. As each ram and the pendulum move relative to each other, fluid is drawn into one end of the ram cylinder by movement of pistons 37 and expelled from the other end. The expelled fluid under pressure exits via check valve 71 to form one of a number of hydraulic ram feeds 72 from other units to an accumulator tank 73.

The accumulator tank feeds pressurized fluid through pipes 74 to a hydraulic motor 75.

The pressurized fluid causes a turbine in the motor to drive an output shaft to a gearbox 78. The gearbox steps up the rate of rotation sufficiently to drive an electromagnetic generator (alternator) 79.

A cable 80 from the generator feeds three phase alternating current to a transformer 81, the output of which is supplied to the brushes 83 of a slip ring arrangement 25 within a rotatable internal turret (not shown) such as 17 in Figure 1. A subsea output cable 26 connects the rings of the slip ring connector to a sea bed junction box 82, from where it can be fed to the main on-shore supply grid.

Figure 8 shows how a number of accumulators, such as 73, reservoirs, such as 70, and transformers, such as 81, might be arranged on one of the decks of the buoyant structure 10 together with generating units 85, which could contain the hydraulic motors 75 and electromagnetic generators 79. In Figure 1, these would correspond to the unit 24 on 0 deck.

Figure 9 shows one possible layout for energy extraction units 20 on the widest decks, such as decks G, II and I, within spherical body 12 surrounding the turret 17 and separated from it by an access passage 90. Rather than showing the actual units, instead their footprints 65 are shown as it is these which determine the necessary spacing.

-13 -An arrangement for narrower portions of spherical body 12, such as M, N and 0 decks, is shown in Figure 10.

Figure 11 shows how it would also be possible to locate some energy extraction units 20 within the decks of tower 13 such as Y, Z and A' decks, for example.

As previously pointed out, it will be realised from Figures 9 to 11, as well as from Figure 1, that the further away the units are positioned from the centre of rotation, the more translational movement they will be subjected to, causing corresponding movement of the pendulum suspension points. This must also be taken into account in considering component strength and limit stop design.

It would be possible to locate multiple devices 10 in arrays in any given selected sea area and concentrate the produced energy at one onshore location. It may also be possible to utilise redundant fixed rig platforms as electrical gathering stations. It may be an added advantage that multiple unit placements could result in reducing coastal erosion in problem areas.

The potential for energy extraction from the sea is important to today's drive for lower carbon emissions. The object of the described device is to enable the extraction of greater energy than current schemes, by building larger units and placing multiple arrays further offshore where wave energy and therefore potential power extraction are greatest. However this does not rule out optimal deepwater locations near to shore for this device on a smaller scale and with higher placement frequency per array.

In summary some of the main potential advantages of this device are: * Operation from a free unpolluted power source without producing carbon emissions.

* Minimal moving parts.

* The use of existing technologies.

* Robust shape and profile to eliminate/minimise wave impact damage and maintain safe operation and reliability.

* Totally symmetrical design to ensure a totally onmi-directional source wave application.

* Unmanned operation but accessible for routine maintenance (Helipad etc).

* No external fittings/turbines hence reducing external drag and consequently increasing roll efficiency.

* Potential reduction in coastal erosion.

* Can be easily floated to other locations if required unlike fixed devices.

-14 -The floating device moves with the applied wave loads damping impact reactions as compared to other static devices, establishing its own natural frequency of operation.

Other fixed static devices cannot accommodate such impacts and with some this has resulted in structural damage and even failure.

It should be noted that the embodiment of the invention has been described above purely by way of example and that many modifications and developments may be made thereto within the scope of the present invention.

Claims (16)

1. -15 -Claims 1. A wave powered device for generating electric power from sea waves comprising: a buoyant structure comprising a hollow body and a stub tower projecting from the hollow body, the buoyant structure being arranged to float with the hollow body submerged and with the tower projecting upwardly from the hollow body above the surface of the sea to a sufficient extent as to cause the structure to roll in response to wave impact on the tower, the structure being symmetrically shaped so as to react substantially identically to waves from any direction; a plurality of pendulums mounted internally within the structure and being relatively inclinable thereto in any direction when the structure rolls; a plurality of fluid ram means each coupled between the interior of the structure and a respective pendulum in an arrangement such that, when the structure rolls, each ram means is driven to produce fluid under pressure irrespective of the direction of the roll; and electricity generating means within the structure for producing electricity at an output thereof and comprising a fluid motor, arranged to be driven by said fluid under pressure, and an electromagnetic generator, coupled to said motor.
2. 2. A device as claimed in claim 1 in which the hollow body and stub tower are round.
3. 3. A device as claimed in claim 2 in which the hollow body is substantially spherical and the tower is cylindrical in form, the axis of the cylinder passing through the centre of the hollow body.
4. 4. A device as claimed in any preceding claim in which each pendulum comprises a weighted shaft suspended by means of a universal joint.
5. 5. A device as claimed in claim 4 in which the universal joint is a ball and socket joint.
6. 6. A device as claimed in any preceding claim in which each of the ram means includes at least two rams disposed at different circumferential positions about their respective pendulum.
7. 7. A device as claimed in claim 6 in which each of the ram means includes four such rams disposed at 90° intervals about their respective pendulum.

   -16 -
8. 8. A device as claimed in any preceding claim in which each ram means is coupled to the interior of the buoyant structure and to its respective pendulum by means of universal joints.
9. 9. A device as claimed in any preceding claim in which each pendulum comprises a hub rotatable on bearings about a pendulum shaft, each ram means being coupled to its respective pendulum via the hub.
10. 10. A device as claimed in any preceding claim in which each ram means comprises at least one double acting ram.
11. 11. A device as claimed in any preceding claim including limit means coupled to each pendulum for limiting the relative movement of the pendulum and the floating structure.
12. 12. A device as claimed in claim 11 in which the floating structure has a plurality of decks, each pendulum extending between three adjacent decks such that it is suspended from one deck, passes through a hole in an intermediate deck and extends towards a lowest deck of the three, each ram means being coupled to the intermediate deck and the limit means being mounted on the lowest deck.
13. 13. A device as claimed in any preceding claim in which each pendulum and its associated ram means form a unit within the floating structure and in which multiple pluralities of said units are disposed at different respective levels within the floating structure.
14. 14. A device as claimed in any preceding claim in which each ram means is comprised of hydraulic rams, the device further including an accumulator for accumulating hydraulic fluid under pressure from the ram means associated with all or some of the plurality of pendulums, and the fluid motor being arranged to be driven by hydraulic fluid under pressure from the accumulator, the electromagnetic generator being connected to be driven by the hydraulic motor so as to generate electricity.
15. 15. A device as claimed in any preceding claim further including a swivel linkage about which the floating structure is mounted for rotation, the linkage being attachable to an external slack mooring system, the swivel linkage comprising a cylinder internal to the structure including bearings to permit relative rotation of linkage and structure, the device further including a slip -17 -ring arrangement for connecting the output of the electromagnetic generator to an external electric output cable while permitting relative rotation between the generator output and the external output cable.
16. 16. A wave powered device for generating electric power from sea waves substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.