WO2009030915A1

WO2009030915A1 - Wave energy extraction apparatus

Info

Publication number: WO2009030915A1
Application number: PCT/GB2008/003001
Authority: WO
Inventors: James Milne
Original assignee: C-Wave Limited
Priority date: 2007-09-05
Filing date: 2008-09-04
Publication date: 2009-03-12
Also published as: GB0717202D0

Abstract

A wave energy extraction apparatus (1) comprises a framework (2) that is substantially immersed in water in use, walls (3) are positioned generally upright and pivotally attached at its lower end to the framework about a substantially horizontal pivotal axes (9) that extend parallel to the plane of the wall, to enable the walls to rock relative to the framework in response to the irrotational movement of water associated with waves, arcuate drive tracks (10) are fast with the wall and extend circumferentially about the pivotal axis of the respective wall, wheels (14a, 14b, 15a, 15b, 16a, 16b, 17a, 17b) are rotatably supported on the framework and engage with the tracks, pivoting of the walls causing the wheels to be driven by the track. The wheels are connected to power conversion devices (18) supported on the framework (2).

Description

WAVE ENERGY EXTRACTION APPARATUS

The present invention relates to wave energy extraction apparatus.

In our patent specification No. WO2007/072016 we have set forth a wave energy extraction device comprising a plurality of generally vertically extending plate assemblies (but which may be in a horizontal position in transit) , each plate assembly being mounted on respective generally upright arms, the lower ends of the arms of adjacent plate assemblies being pivotally attached to a basal frame, about substantially parallel, horizontally spaced-apart pivotal axes, and at least one energy absorber having direct, or indirect respective drive connections with the adjacent plate assemblies, the arrangement of the drive connections being such that relative displacement of the adjacent plate assemblies towards and/or away from each other, as accommodated by pivotal movements of one or both plate assemblies relative to the basal frame about said pivotal axes, results in operation of the energy absorber.

The present invention stems from work aimed at producing a wave energy extraction apparatus that is economic to produce and which can be arranged to be more easily serviceable.

According to one aspect of the present invention a wave energy extraction apparatus comprises a framework that is substantially immersed in water in use, at least one wall that is positioned generally upright in use and is pivotally attached at its lower end to the framework about a substantially horizontal pivotal axis that extends parallel to the plane of the wall, whereby the wall can rock relative to the framework in response to the irrotational movement of water associated with waves, at least one arcuate drive track fast with the wall and extending circumferentially about said pivotal axis, at least one wheel rotatably supported on the framework and engaging with the track, the arrangement being such that pivoting of the wall causes said wheel to be driven by the track, the wheel being connected to a power conversion device supported on the framework.

Preferably the wheel is provided with a rubber tyre.

Preferably there is a plurality of wheels driven by the track.

Preferably each wheel is urged towards the respective drive track by a respective suspension means supported on the framework.

The suspension means may be hydraulic.

Alternatively, each wheel may be provided with rubber pneumatic tyre, and the axis of each wheel is fixed to the framework, the arrangement being such that pressure in each tyre urges the tyre against the respective drive track. The width of the drive track is desirably such that there is full contact with the tyre acting upon it.

The drive track is preferably provided with upper and lower arcuate drive surfaces extending about said pivotal axis, and there are a plurality of such wheels, some wheels engaging with the upper arcuate drive surface, and other wheels engaging with the lower arcuate drive surface.

The use of upper and lower wheels can enable the forces exerted on the track to be balanced.

The wheels are desirably arranged in pairs, a first wheel of a pair engaging with the upper drive surface and being on the same radius, relative to the pivotal axis, as a second wheel of said pair engaged with the lower drive surface.

This can provide a particularly well-balanced arrangement for the forces exerted by the wheels on the track.

Preferably the wheels of each pair of wheels press against the track with substantially equal force.

When a suspension means is provided, the suspension means of some of the wheels are trailing arm suspensions, and the suspension means of the other wheels are leading arm suspensions so arranged that the suspension means overall is symmetric with respect to the forward and reverse directions of movement of the drive track.

The symmetrical arrangement of the suspension helps to provide the same response characteristics of the wheels to forward and reverse pivoting of the wall.

Each wheel may drive a respective power conversion device, and a fixed or variable ratio gearbox may be incorporated in the drive connection.

The outputs of the power conversion devices are then preferably combined.

Alternatively, such a gearbox may be arranged to combine the drives, for driving a common power conversion device.

The power conversion devices may be electrical generators. Alternatively, the power conversion devices may be hydraulic pumps driven by the wheels, the hydraulic outputs of the pumps possibly being combined, and the combined hydraulic output of the pumps is used to drive one or more hydraulic motors mechanically driving a respective electrical generator. The combined hydraulic output may be smoothed by using one or more hydraulic accumulators connected to the high pressure line of the system, to provide a substantially constant, regulated, smoothed hydraulic supply to the motors.

Each electrical generator is desirably supported on the framework, but it could be supported on a separate structure if so desired.

Conveniently, the or each power conversion device is mounted on or in a removable module that is detachably connected to the framework.

Preferably the module is provided with overall dimensions and corner formations that are sized and positioned in accordance with ISO container specifications, to enable the module to be lifted, handled and stored by ISO container handling equipment,

Preferably the apparatus comprises a plurality of such walls, the walls being pivotally connected to a common framework that extends in a generally horizontal plane, and comprising buoyancy means so arranged as to cause the apparatus to float with the upper ends of the upright walls adjacent to the water level.

Desirably the buoyancy and any mooring are arranged such that the drive track is normally maintained above the water level.

The surface of the drive track is preferably chosen such that there is minimum slipping between the drive track and wheel/s even when wet. The buoyancy means may be provided by floats attached to, or floating sections of, the framework or floats attached to, floating sections of, or buoyancy inherent in, the walls.

Each wall is preferably provided with a plurality of such tracks, preferably one at each end of the top of the wall, but there may be one or more tracks at intermediate positions along the wall.

In a preferred embodiment the framework is of generally rectangular outline in plan and comprises four framework towers at the corners of said outline, the towers being upstanding from a bridging portion of the framework that interconnects the towers, the apparatus comprising two such walls located at opposite ends of the framework, the pivotal connections between the walls and the framework being in the form of pivots located adjacent to the bases of the towers, each wall being provided with two such tracks at opposite ends of the wall and said wheels being located adjacent the tops of the towers.

The bridging portion preferably comprises two elongate parallel longitudinal space frames which may be connected by one or more elongate transverse space frames.

The space frames may be of rectangular transverse cross-section.

Such a framework can be designed to have a degree of flexibility to accommodate unequal wave forces exerted on the apparatus.

When removable modules are provided these are conveniently mounted on the tops of the respective towers. When the wheels drive hydraulic pumps, the hydraulic pumps of one such module may be hydraulically connected to a common hydraulically-driven electrical generator conveniently housed in a further detachable module mounted on the respective tower.

The opposite ends of the drive tracks are preferably tapered whereby on excessive pivotal movement of the wall relative to the frame, the wheel or wheels disengage from the track. Such excessive movement corresponds to that produced by waves outside of the normal operating envelopes of the apparatus.

When the wheels are connected to hydraulic pumps, the hydraulic system fed thereby may incorporate one or more hydraulic accumulators to provide a smoother driving of an electrical generator at all phases of the cycle of wall movement for improved electrical grid-matching and electrical performance.

According to a second aspect of the invention we provide a method of generating power comprising positioning in water a wave energy apparatus in accordance with the first aspect of the invention with said wall generally upright, and taking power from said power conversion device on pivotal movement of said wall caused by water waves.

According to a third aspect of the invention we provide a kit of parts which when assembled provides a wave energy extraction apparatus in accordance with the first aspect of the invention.

A wave energy extraction apparatus and a modification thereof all in accordance with the invention will now be further described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a plan view of an apparatus with both walls shown in a vertical condition;

Figure 2 is a side elevation of the apparatus looking in the direction of the arrow A in Figure 1 ;

Figure 3 is an end view of the apparatus;

Figure 4 is an enlarged side elevation of the upper right hand part of Figure 2;

Figure 5 is a section on the line 5-5 of Figure 4 showing wheel assemblies and their associated hydraulic power conversion units;

Figure 6 is a hydraulic circuit diagram of a power unit of the apparatus and showing rectifier valve arrays on the outputs and inputs of the pumps, and

Figure 7 is a diagram similar to Figure 6 of a modification in accordance with the invention in which the wheel-driven pumps have internal valves, and in which hydraulic connections are provided to a similar power unit to that of Figure 6.

The apparatus 1 comprises a framework 2 of generally oblong- rectangular outline in plan pivotally supporting at the opposite ends thereof a pair of walls 3.

The walls 3 contain buoyancy chambers, and their buoyancy is arranged to be sufficient to maintain the apparatus at the depth shown in Figure 2 relative to the water surface 4. The framework 2 comprises a pair of horizontally spaced apart longitudinal elongate lattice structures 5 of square transverse cross- section, connected by two transverse lattice structures 6 of square cross- section, and the longitudinal structures 5 are connected at opposite ends thereof to respective framework towers 7, the connections being made by respective buttress frames 8. Thus the structures 5 and 6 constitute bridging frames that connect the framework towers 7. The lattice structures 5 and 6 are conveniently made from lengths of tubular steel, welded together to form a space-frame or latticework.

The lower end of each tower 7 is pivotally connected at 9 to the bottom of the respective wall 3, the axes of the pivots 9 extending transversely of the frame 1 , and in the mid-plane of the respective wall 3.

The configuration of the frame 2 maintains the lattice structures 5 and 6 at depth, whereas the walls 3 are fully exposed to the irrotational water movement associated with waves.

The framework 2 will normally be moored in position by mooring lines, not shown.

The typical size of the framework 2 is 80m long x 40m wide.

The walls 3 at their opposite ends fixedly carry arcuate drive tracks 10, each in the form of a curved flat bar of uniform thickness but having tapered ends 11 , the bars projecting horizontally outwards from the upper ends of the respective wall.

The drive tracks define upper and lower part-cylindrical, elongate drive surfaces 12 and 13 respectively that extend circumferentially about the axis of pivot 9 of the associated wall. As shown in Figure 5, each drive track 10 is engaged by eight wheels 14a, 14b, 15a, 15b, 16a, 16b, 17a, 17b rotatably carried by the body 19 of a modular power conversion unit 18.

The wheels, 14a, 14b, 15a, 15b, 16a, 16b, 17a, 17b, are mechanically connected to respective hydraulic pumps as will be further described below.

The wheels are independently supported from the body 19 on trailing or leading arm hydraulic suspensions 25 which bias the individual wheels towards the corresponding drive surfaces 12, 13.

The wheels are arranged in four pairs 14a and 14b, 15a and 15b, 16a and 16b, 17a and 17b, the rotational axes of the wheels of each pair being arranged on a common radius with respect to the pivotal axis of the associated wall 3, whereby each pair of wheels exerts a pinching action on the drive track 10.

The number of trailing arm suspensions 25 is made equal to the number of leading arm suspensions 25 to provide equal characteristics for the forward and reverse pivoting of the associated wall 3.

The wheels are each provided with a pair of rubber tyres, and the material of the track surfaces 12, 13 is chosen so as to provide a strong frictional grip between the wheels and the track even when subject to water. The drive tracks 10 are made sufficiently wide to accommodate the full available contact area of the tyres.

Each wheel 14a, 14b, 15a, 15b, 16a, 16b, 17a, 17b is connected to the drive shaft of a respective hydraulic pump 18' housed within body 19. The pump can be a standard rotary hydraulic pump or may be a variable pump, such as an Artemis™ unit, allowing full control, and the hydraulic outputs of the pumps are combined to provide a common hydraulic output which is used to drive one or more common electrical generators located in a respectively adjacent generator unit 20. One or more hydraulic accumulators is provided to smooth the hydraulic input to the electrical generator. The hydraulic accumulators may be housed in unit 18 or unit 20, or elsewhere.

The units 18 and 20 shown have all external dimensions and all locating/attachment points in accordance with the 20ft ISO freight container specifications, to permit the units 18 and 20 to be handled, stacked and transported as can an ISO freight container. In a modification, not shown, the 40ft ISO container specification is used.

The arcuate working length of each track surface 12, 13, which is the distance between regions 21 in Figure 4, is chosen to be sufficient to accommodate the extent of the pivotal movement of the wall 3 relative to the framework 2 produced by waves in the normal operating envelope of the apparatus in the selected location of the apparatus, and to retain the full engagement of all of the wheels with the track surfaces in such conditions.

The tapered ends 11 of the drive tracks 10 enable the walls under extreme wave conditions to pivot beyond their normal pivotal range, by permitting the tracks to disengage from the wheels, in a progressive manner for each pair of wheels as the pair of wheels, such as 14a and 14b, encounter the tapered end. Thus, under extreme conditions, the walls are permitted to pivot into a substantially horizontal position. When the severe wave conditions abate, the buoyancy of the walls will cause them to pivot back towards a normal condition, and the tapered ends will progressively cause the tracks to re-engage in turn with the pairs of wheels, urging them apart against their suspension biasing.

The arrangement of the wheels in pairs and with the wheels of each pair arranged on a common radius of the wall pivot can help to ensure that the torque is shared between pumps, reducing the torque requirements of each pump and traction and wear of each tyre.

The pairs of wheels are preferably substantially angularly equally spaced- apart about the wall pivot.

The use of a plurality of sets of drive wheels also increases redundancy, thereby improving the potential reliability of the power take off system.

Figure 6 shows the hydraulic circuit of one set of the units 18 and 20 mounted on one of the towers 7 of the apparatus of Figures 1 to 3. It will be appreciated that the apparatus has four such circuits, one for each corner of the apparatus.

The individual wheel and pump combination have been labelled P₁ , P₂ P₃... in Figure 6. The output and input of each pump, in the case of a directional pump, are connected to a high pressure rail 30 and a low pressure rail 31 by respective one-way valve arrays Ri , R₂, R₃, ... , the valve arrays being arranged in a analogous manner to diodes in an electrical rectifier array.

The high pressure line 30 is connected to a plurality of hydraulic motors Ml , M2, M3.... which each drive a respective electrical generator Gen 1 , Gen 2, Gen 3, A plurality of accumulators Accl , Acc2, Acc3, are connected to the high pressure line 30 in order to smooth out undulations in the pressure generated by the units P₁ , P₂ P₃, due to the cyclic pivotal movement of the associated wall 3.

The electrical outputs of the generators Gen 1 , Gen 2, Gen 3 are combined.

The units P₁, P₂ P₃ can be controlled in different ways according to the type of the unit by a controller Ctllr in response to a pressure sensor Psens and in response to monitoring signals from the motors M₁ , M₂, M₃, .... and from the generators Gen 1 , Gen 2 , Gen 3,

A reservoir Res is connected to the lower pressure rail 31.

Figure 7 shows a modification of the circuit of Figure 6 in which provision is made at 40, 41 to interconnect the low and high pressure rails of two or more units 18. The pumps P₁ , P₂ P₃ in this case are some sort of variable displacement, radial piston pump. Such pumps are of a design which requires them to have their own internal valves which, either automatically or under the discipline of a control system, ensure that regardless of the direction of rotation of the drive wheel, fluid is always pumped from the low pressure side of the pump to the high pressure side. An example of a suitable pump is an Artemis™ multiple radial piston pump with high speed intelligent valve control.

Principal energy extraction is expected to be from the differential motion of the walls 3 relative to each other due to their location in different wave phase positions. In these circumstances the framework is used to realise this relative motion in that "plol ⁼⁼ r (.ΔX_Walll ~ ΔXbasc/ and P_p,_o2 = f(- (Δx_{w a},_I2- Δx_basJ) so Ppioi + Ppιo2 ⁼ f(Δx_{Λ al] 1}- Δx_base- Δx»_an2 + Δ x_bas_e)

or P_tolal = f(Δx_wa]ll- Δx_wall2)

In practice it is envisaged that common mode (in phase) wall movement will be used to supplement energy conversion in wave conditions where prevailing wavelengths dictate that wall spacing is not correct to cause differential movement, and under these circumstances the inertia of the framework and its mooring to the seabed or lake bed will supply the reactive force necessary for power extraction.

Each power unit 18, 19 is desirably controllable independently of the other units 18, 19 to allow tailoring of the braking (power extracting) force. By virtue of this feature the device wide control system has the ability to optimise power output in different wave climates and also to mitigate out of line forces in the framework caused by mixed or offline seas.

It is envisaged that such force control will for instance be sufficient to allow the use of a framework that is not necessarily rigid in all degrees of freedom - ie one that is free to 'parallelogram' and twist with geometry sensors feeding back into the control system and resistive force imbalances introduced between different units in order to resist the tendency of the framework to undergo these motions.

Such freedoms have the capacity to introduce significant structural cost savings and potential performance benefits.

Claims

1. A wave energy extraction apparatus (1) comprising a framework (2) that is substantially immersed in water in use, at least one wall (3) that is positioned generally upright in use and is pivotally attached at its lower end to the framework about a substantially horizontal pivotal axis (9) that extends parallel to the plane of the wall, whereby the wall can rock relative to the framework in response to the irrotational movement of water associated with waves, at least one arcuate drive track (10) fast with the wall and extending circumferentially about said pivotal axis, at least one wheel (14a, 14b, 15a, 15b, 16a, 16b, 17a, 17b) rotatably supported on the framework and engaging with the track, the arrangement being such that pivoting of the wall causes said wheel to be driven by the track, the wheel being connected to a power conversion device (18) supported on the framework (2) .

2. Apparatus as claimed in claim 1 comprising a plurality of such walls (3) horizontally spaced apart, the walls being pivotally connected to a common framework (2) that extends in a generally horizontal plane, each wall carrying at least one such drive track engaged by at least one such wheel rotatably supported on the framework.

3. Apparatus as claimed in claim 2 in which the framework (2) is of generally rectangular outline in plan and comprises four framework towers (7) at the corners of said outline, the towers being upstanding from a bridging portion (5, 6) of the framework that interconnects the towers, the apparatus comprising two such walls located at opposite ends of the framework, the pivotal connections between the walls and the framework being in the form of pivots (9) located adjacent to the base of the towers, each wall being provided with two such tracks (10) at opposite ends of the wall and said wheels being located adjacent the tops of the towers (7) .

4. Apparatus as claimed in claim 3 in which the bridging portion comprises two elongate parallel longitudinal space frames (5) .

5. Apparatus as claimed in claim 4 in which the longitudinal space frames (5) are connected by at least one transverse space frame (6) .

6. Apparatus as claimed in claimed in any one of claims 1 to 5 in which the wheel is provided with a rubber tyre.

7. Apparatus as claimed in any one of the preceding claims in which each wheel is urged towards the respective drive track by a respective suspension means (25) supported on the. framework.

8. Apparatus as claimed in claim 6 in which the rubber tyres are pneumatic tyres, and the axis of each wheel is fixed to the framework, the arrangement being such that pressure in each tyre urges the tyre against the respective drive track.

9. Apparatus as claimed in any one of the preceding claims in which each drive track has upper and lower arcuate drive surfaces extending about the pivotal axis of the associated wall, and in which there are a plurality of such wheels engaging with the respective track, some wheels (14a, 15a, 16a, 17a) engaging with the upper arcuate drive surface (12) , and other wheels (14b, 15b, 16b, 17b) engaging with the lower arcuate drive surface (13) .

10. Apparatus as claimed in claim 9 in which the wheels are arranged in pairs (14a, 14b; 15a, 15b; 16a, 16b; 17a, 17b) , a first wheel (14a) of a pair engaging with the upper drive surface and being on the same radius, relative to the pivotal axis of the associated wall, as a second wheel (14b) of said pair engaged with the lower drive surface.

11. Apparatus as claimed in claim 9 as appended to claim 7 in which the suspension means (25) of some of the wheels (14a, 14b, 16a, 16b) are trailing arm suspensions, and the suspension means (25) of the other wheels (15a, 15b, 17a, 17b) are leading arm suspensions so arranged that the suspension means overall is symmetric with respect to the forward and reverse directions of movement of the drive track.

12. Apparatus as claimed in any one of the preceding claims in which there is a plurality of such wheels and each wheel drives a respective power conversion device (P₁ , P₂, P₁) , and the outputs of at least some of the power conversion devices are combined.

13. Apparatus as claimed in claim 12 in which the power conversion devices are hydraulic pumps (P₁ , P₂, P₃) driven by the wheels, the hydraulic outputs of at least some of the pumps being combined, and the combined hydraulic output being used to drive at least one common electrical generator (Gen 1 , Gen 2, Gen 3) .

14. Apparatus as claimed in claim 13 in which the electrical generator is supported on the framework.

15. Apparatus as claimed in any one of the claims 1 to 11 in which there is a plurality of such wheels and each wheel drives a respective power conversion device in the form of a hydraulic pump (P₁ , P₂, P,) connected by a hydraulic circuit (30, 31) to hydraulic motors (M₁ , M₂, M₃) mechanically coupled to respective electrical generators (Gen 1 , Gen 2, Gen 3) .

16. Apparatus as claimed in any one of the preceding claims in which the or each power conversion device is mounted on or in a removable module (20) that is detachably connected to the framework, and the module has external dimensions and all locating points in accordance with an ISO container specification, to enable the module to be lifted by ISO container handling equipment.

17. Apparatus as claimed in any one of the preceding claims in which the apparatus comprises buoyancy means so arranged as to cause the apparatus to float with the upper end of each wall adjacent to the water level. r

18. Apparatus as claimed in claim 17 in which the buoyancy is arranged such that the drive track is normally maintained above the water level.

19. Apparatus as claimed in claim 17 or 18 in which the buoyancy means is provided by hollow portions of the walls.

20. Apparatus as claimed in any one of the preceding claims in which the opposite ends (21) of the drive tracks are tapered whereby on excessive pivotal movement of the associated wall relative to the frame, the wheel or wheels disengage from the track (10) .

21. A method of generating power comprising positioning in water a wave energy apparatus as claimed in any one of the preceding claims with said wall (13) generally upright, and taking power from said power conversion device on pivotal movement of said wall caused by water waves.

22. A kit of parts which when assembled provides a wave energy extraction apparatus as claimed in any one of claims 1 to 20.