EP2786013A1

EP2786013A1 - A wave energy converter with a channel feeding a whirlpool

Info

Publication number: EP2786013A1
Application number: EP12805966.4A
Authority: EP
Inventors: Patrick Joseph Duffy; Joceyln Raymond FITZSIMONS
Original assignee: Jospa Ltd
Current assignee: Jospa Ltd
Priority date: 2011-11-30
Filing date: 2012-11-29
Publication date: 2014-10-08
Also published as: EP2786012A1; WO2013079582A1; EP2786012B1; WO2013079585A1

Abstract

A wave energy converter (1) has a water inlet system (2) comprising a channel (4) having a mouth (4) to receive slugs of water and being connected (10) to a mooring to tilt in a pitching action to receive and accelerate water slugs. The water slugs are delivered to a whirlpool system (3), and this aggregates energy from said water in a vortex. The whirlpool has a cylindrical configuration with a domed lower portion. There is a turbine (36) below the whirlpool bowl (30), and the blades (270) are C-shaped, with the convex side facing the direction of travel. There is a pair of pitching buoys (12) on the channel (4). These are pivotally connected to a mooring frame (10) and are separately pivotally connected to the channel (4) by a spaced-apart pivot joint (13). This provides a buoyant fulcrum effect to achieve greater lift of the front of the channel (4).

Description

"A Wave Energy Converter with a Channel Feeding a Whirlpool" INTRODUCTION Field of the Invention

The invention relates to wave energy converters. Prior Art Discussion

Our prior published patent application nos. EP2307705 and WO2011/070559 describe wave energy converters ("WECs") having a floating tube which tracks the wave pattern to propel slugs of air and water to an energy converter such as a turbine. A rigid inlet is arranged to pitch into waves so that the slugs efficiently enter and gain momentum.

US2009/0174190 (Carter) describes a device with a central opening to receive water in a flow which drives a turbine. The turbine may be self-rectifying. US4152895 (Wirt) describes a wave- powered motor having an upwardly convex shell of large concrete construction fixed to the sea bed. Water flows over the shell and into a central conduit. An inlet may be tangential, to impart a vortex motion to the water. The mouth is very deep, down to sea bed level. It appears that the structure would need to be located close to the shore because it is on the sea bed.

The present invention is directed towards achieving improved utilization of wave energy. SUMMARY OF THE INVENTION

According to the invention, there is provided a wave energy converter comprising:

a water inlet system comprising:

a channel having a mouth to receive slugs of water and being adapted to be connected to a mooring to tilt in a pitching action to receive and accelerate water slugs;

a whirlpool linked to the water inlet system to receive slugs of water and to aggregate energy from said water in a vortex, and

a prime mover arranged to be moved by water in the whirlpool. In one embodiment, the whirlpool has a cylindrical configuration with a domed lower portion. Preferably, the wave energy converter comprises one or more check valves to prevent back- flow of water. In one embodiment, said check valve comprises a guide flap pivotally connected adjacent a whirlpool inlet. Preferably, the flap is curved to guide water in a tangential direction. Preferably, the check valve comprises at least one flap in the water inlet channel, said flap having a pivot axis across a flow path towards the whirlpool.

In one embodiment, the fins are mounted in a floor of the channel. In one embodiment, there is a plurality of said flaps arranged parallel to each other.

In one embodiment, the prime mover comprises a turbine at a lower end of the whirlpool. In one embodiment, the turbine blades are arranged to rotate about an axis which is co-axial with the whirlpool. Preferably, the blades are configured with a C shape with a convex surface facing in the direction of travel.

In one embodiment, at least some turbine blades include a flap for flexing or pivoting about a lower edge of the turbine blade to bridge a gap between the blade and a trailing blade to block back- flow. In one embodiment, there is a draft tube below the turbine blades. In one embodiment, the draft tube includes at least one flap in a side wall for flow of back- flow water. In one embodiment, the draft tube includes a check valve comprising segmented overlapping leaves arranged to block back- flow.

In one embodiment, the water inlet system channel is configured to narrow towards the trailing end.

In one embodiment, the water inlet system comprises buoys attached to the water inlet channel. Preferably, there is at least one stabilization buoy on a water guide forwardly of the mouth, and at least another stabilization buoy at the trailing end of the water inlet channel. In one embodiment, at least one pitching buoy is adapted to be connected to a mooring at a first pivot joint and is connected to the channel at a spaced-apart pivot joint. In one embodiment, there is a pair of laterally spaced pitching buoys, one on each side of the channel. Preferably, the pitching buoy is narrower facing the channel mouth, there being increasing cross-sectional area with distance from the mouth. In one embodiment, the wave energy converter comprises a frame for attachment to a mooring, and wherein the frame is attached to a pitching buoy, and the buoy is pivotally attached to the water inlet channel at a spaced-apart pivot joint.

In one embodiment, the water inlet channel comprises a top wall and comprises spikes on said top wall to deter seals.

In one embodiment, the channel has a top wall, and water inlet channel comprises a fish and debris outlet in the top wall or a side wall. In one embodiment, the water inlet channel is connected to the whirlpool by a flexible joint allowing relative sliding motion. In one embodiment, the flexible joint comprises pivot joints and a flexible liner.

In one embodiment the wave energy converter further comprises a plurality of fins (206) mounted on the water inlet channel, said fins being directed rearwards and downwards. Preferably, there is a plurality of pairs of fins, one fin of each pair being each side of the channel.

According to another aspect, the invention provides a wave energy converter comprising a floating buoy, a first joint attaching the buoy to a mooring line, and a second joint attaching to a prime mover for force transfer, said first and second joints being spaced-apart so that as mooring tension increases buoy displacement increases, providing a greater upward prime mover force.

In one embodiment, the buoy is attached to a water inlet channel, so that said upward force is a channel lifting force.

In one embodiment, the second joint is connected to a submerged prime mover to apply upward force to the prime mover.

In one embodiment, the second joint is linked with a floating element which is linked with at least one other element by a coupler which has a prime mover converting mutual rotation of the elements to useful energy

DETAILED DESCRIPTION OF THE INVENTION

Brief Description of the Drawings The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: -

Fig. 1 is a perspective view of a WEC of one embodiment, in which there is a water inlet capturing slugs of water from wave crests and delivering them to a turbine system having a vortex whirlpool feeding turbine blades; Figs. 2 and 3 show a check valve of the inlet system;

Figs. 4 and 5 are front and rear perspective views of an alternative WEC, in which buoys on the water inlet body pivot in a different manner; Fig. 6 is a side view of a further WEC, having fixed fins to enhance pitching motion to increase kinetic energy in the inlet;

Fig. 7 is a diagrammatic side view of the turbine system; Fig. 8 is a perspective view of the turbine of the WECs, and Fig. 9 is a detailed side view of a blade of the turbine;

Fig. 10 is a cut-away side view of another turbine system; Figs. 11 and 12 are diagrammatic side views showing WECs in which a buoyant fulcrum mechanism of the WECs of Figs. 1 to 10 is also utilised;

Figs. 13 and 14 are diagrammatic side views of a further WEC of the invention using the same principle; and

Figs. 15 and 16 are side views showing further WECs using the buoyant fulcrum mechanism.

Description of the Embodiments Referring to Fig. 1 a WEC 1 of the invention comprises a water inlet system 2 and a turbine system 3. The water inlet system 2 comprises a rigid channel, in this embodiment a hollow body 4 of generally rectangular cross-sectional configuration, tapered to reduce in cross-sectional area from a mouth 5 towards an outlet connected to the turbine system 3. The outlet comprises an opening 25 into the turbine system 3, before which there is a joint 26 which allows both bending (due to pivot axes) and sliding relative movement (due to a telescopic flexible liner).

At a leading end where water enters, the inlet system 2 comprises curved guide plates 6 having small buoys 7 for added stability. The guide plates 6 guide water from the crests of waves into the mouth 5.

The body 4 is retained by an A-frame 10 which is connected by a pivot joint 11 to a pair of lateral buoys 12 on either side of the body 4. The pivot joint 11 is below the body 4. The buoys 12 are connected to the body 4 by a pivot joint 13 across the top of the body 4. This arrangement allows mutual rotation between the buoys 12 and the body 4 and between the buoys 12 and the frame 10.

The link between a mooring rope (not shown) and the body 4 is therefore:

mooring frame 10,

pivot joint 11,

buoys 12,

pivot joint 13, and

body 4. The top wall of the body 4 has spikes 20 to deter seals from forming a colony. Also, there is a fish outlet 21 having grid bars which are arranged to pivot down to a limited extent to provide a small opening for fish to escape while not significantly affecting the overall flow of water along the inlet system 2. At the trailing end of the body 4 there is a pair of lateral buoys 22 for trailing- end buoyancy for stabilisation close to the turbine system 3.

Referring to Figs. 2 and 3 the portion of the body 4 between the joint 25 and the turbine system has a check valve formed by flaps 27. These pivot up with water back-flow, thus minimising the extent of back-flow from the turbine system 3 into the body 4. Referring to Figs. 4 and 5 an alternative WEC, 40, is illustrated. This is similar to the WEC 1, except that in this case there is a water inlet system 41 having a pair of generally rectangular buoys 45 and a frame 47 for connection to a mooring rope on one side and to the top of the buoys 45 by a pivot joint 46 at the other. The buoys 45 are connected to the body 4 by a pivot joint 48 below the body 4. As in the WEC 1 the buoyancy 45 can move relative to the main body 4, providing a "buoyant fulcrum" effect, described in more detail below.

In both of the WECs 1 and 40 the mooring frame is pivotally connected to the buoys, which are in turn separately pivoting on the hollow body, the pivot axes being spaced-apart. In the WEC 1 the frame-buoy axis is below, whereas in the WEC 40 it is above. In another embodiment the buoys may be connected as shown in Figs. 4 and 5, but may be triangular in shape as illustrated in Fig. 1.

In the WEC 40, the end of the water inlet body 4 also has flaps 27 which are free to pivot upwardly under the action of water back- flow. They therefore act as a very effective check valve to prevent back- flow into the water inlet system 4, as for the WEC 1.

Referring to Fig. 6 a WEC 200 has a water inlet 201 with a hollow body 203 and buoys 204 linked to a mooring line frame 205. The frame 205 is linked by a pivot joint 205(a) to the buoys 204, and the buoys 204 are linked to the body 203 by a pivot joint 204(a). The inlet 201 is linked with the turbine system 3. The WEC 200 is similar in principle to those described above, however in this case there are three pairs of fixed fins 206 along the length of the inlet 201. The fins 206 provide the effect of lifting the leading end up more as a wave approaches and of lifting the trailing end up more as the wave leaves the trailing end. This provides an enhanced movement to help propel slugs of water into the turbine system 202. This action arises from the circular motion of water in waves. At a crest the clockwise water motion pushes upwardly against the leading fins 206 while the trailing fins 206 are pushed down.

For all of the WECs 1, 40, and 200 referring to Fig. 7 the turbine system 3 comprises a whirlpool or vortex bowl 30 with an inlet pivoting guide 31 for deflecting water around the wall in a tangential or centrifugal manner while preventing or at least reducing back-flow. A turbine 36, shown in detail in Figs. 8 and 9, is mounted at the bottom of the bowl 30, and there are four buoys 37 equally spaced around the bowl 30. There is a draft tube 35 below the bowl 30 and the turbine 36. Referring to Figs. 8 and 9 the turbine 36 comprises a generator with a bearing 272, a vertical shaft 271 , and blades 270. These have a C-shape, with the convex side facing in the direction of rotation. The whirlpool 30 is configured so that the water impinges at an angle to horizontal as illustrated by the arrow U_rel, for maximum efficiency.

There is a flap 273 attached to the lower edge of each turbine blade 270. This acts to prevent back- flow of water, the lower edge of the trailing blade acting as a stop to movement of the flaps 273. The flaps 273 dip down in accordance with the flow without imposing a significant restriction in normal conditions, and so do not affect turbine operation. The flaps 273 are not necessary, but do help in scenarios where back- flow might be a problem.

Referring to Fig. 10 back- flow prevention may be achieved by providing a turbine system 300 with a segmented check valve 304. The turbine system 300 has a whirlpool bowl 301, turbine blades 302, and a draft tube 303. The segmented check valve 304 is mounted at the lower end of the draft tube 303. Its blades are arranged to block upward flow due to their overlapping segmented configuration.

In addition to or instead of the above, flaps 310 may be mounted in the wall of the draft tube 303. Because there is naturally a vacuum in the draft tube 303 the flaps 310 are normally closed. However, if back- flow occurs the water will push out the flaps 310 and exit the draft tube 103.

The water inlet system body 4 may be referred to as a "chuter" as it acts as a chute to propel with momentum slugs of water into the turbine system 3. The pivoting buoys 12 or 45 or 204 provide a "buoyant fulcrum" which is the centre of buoyancy axis through the buoys. The mooring tension is a force acting on one side of a "see-saw" and on the opposite side of the buoyant fulcrum is attached the 'working load'. The tension in the mooring increases with an oncoming wave because the buoys are pushed up and in front of the wave. This causes the body 4 to tend to move away in front of the wave so that the buoyant fulcrum tends to rotate through about 10° to 40°, thus lifting the heavy load of the chuter 4 higher than it would if the buoyancy was attached rigidly to the chuter body. Accompanying this upward exertion lifting the chuter, the buoyancy 12 or 45 or 204 rotates to sink more deeply, hence displacing more water. This beneficial effect is achieved because the frame is pivotally connected to the buoys, which are separately pivotally connected to the body 4. The inlet system 2 or 41 or 201 feeds a vortex within the whirlpool 30, which has a diameter of about 10m in one embodiment. Also, the whirlpool has a hemispherical bottom to allow some pitching to occur without wasting much energy. The flaps 27 and 31 prevent water run-back when water is not entering. The whirlpool 30 provides a vortex as an energy storage flywheel. Analogous to the flywheel of a single-cylinder engine, it provides intermittent power strokes but continuous rotational power output.

The inlet system 2 or 40 or 201 gives a stream of highly energetic slugs of water (for example over 100 tonnes of water/slug, and traveling at about 50km/hr with a slug hitch of about 95). The whirlpool 30 stores the energy of the slugs and subsequently releases it slowly without substantial losses. The vortex maintains the maximum velocity possible and by the configuration of the turbine blades as illustrated the water is diverted downwards, thus forcing the water out of the vortex and through the turbine. In the above conditions an output of 0.5MW would be achieved on average.

Near the walls of the bowl 30 the water level will be above the outside water level while in the centre it will be slightly lower. The curved blades 270 are about 30° from horizontal at the top and catch the rotating water (arrow U_rel) and divert it downwards. The blades 270 are curved so that as the water travels downward, the absolute (not with respect to the blades 270) direction becomes more vertical and downward so the water is traveling vertically downward (arrow (Uexit) as it leaves the blades, with almost no rotational component. The blades 270 have therefore scooped the water and diverted it downwards so that the overall level in the bowl falls to a lower level. Occasionally, while not desirable, all of the water within the vortex could be at a lower level than the outside water with this approach.

At their lower ends the blades 270 are backward angled and so direct the vortex water seamlessly from nearly horizontal rotation and eject it downwards with little swirl. This vertical kinetic energy is then recovered in the draft tube 35 in the normal way with turbines. The draft tube slows the water velocity, creating suction at the bottom of the runner and a greater pressure differential ΔΡ in the turbine system 3. The flaps are flexible enough not to affect down flow of water. They only come into effect when pushed up by back- flow. Advantageously, the WECs 1 and 40 and 200 make use of the varying force in the mooring line. The force and the distance through which the force acts impart energy. As referred to above this movement is achieved by pivotally attaching one end of the buoyancy to the load (i.e. weight of chuter filled with water) and at a distance, the other side of the buoyancy centre the mooring line is attached. Thus there is a 'couple' acting around the buoyancy. When a wave approaches the inlet body it tends to move away in front of the wave thus tightening the slack mooring. As the buoyancy pulls more forcibly it rotates, sinking the buoyancy deeper and lifting the heavy load (which is the chuter). As illustrated, the buoyancy of the WEC 1 has a substantially triangular shape. This is because the slope at the front meets the oncoming wave and is pushed up somewhat.

The mechanical pivot joints of the buoys described above could be replaced by flexibility of a rubber connection which allows the pivoting action to happen. This would reduce or avoid exposure of metal to the sea, thus reducing corrosion and consequent maintenance.

Referring to Fig. 11 a WEC 400 has an eye 401 for connection to a prime mover, a mooring eye 402, and a mooring 403. Due to the buoyant fulcrum effect the prime mover eye 401 moves upwardly with an oncoming wave (in right-hand diagram) thereby moving a prime mover, not shown. The latter may be an element of any of a wide range of other types of WEC that would benefit from extra lift at wave crests. Referring to Fig. 12 a WEC 410 comprises a buoy having an eye 411 tied to a mooring rope and a lower eye 412 linked with a prime mover, not shown. This operates on the same principle. Figs. 13 and 14 show an alternative WEC, 450, making use of this principle. In this case the WEC 450 has a buoy 451 of generally triangular shape in side view. It has an eye 452 linked by a rope 453 to a piston 454 which is a prime mover for power generation. There is a trailing eye tied to a mooring rope 455. Referring to Fig. 15 a WEC 500 comprises a buoy 501 linked to a prime mover system 502 having a piston 503 in a cylinder 504. The linkage mechanism comprises a link 510 at its top end and to a lever arm 51 1 at its lower end. One end of the lever arm 51 1 is connected to a mooring 512, and the other end to a connecting rod 515 for the piston 503. This arrangement utilizes the tension in the mooring 512 as a part of a mechanism providing a useful force. With an oncoming wave the mooring tension increases and the buoy 501 sinks (right hand diagram), thereby adding to the force applied via the rod 515 to the piston 503. Referring to Fig. 16 a WEC 600 has attenuator elements 601 which are inter- linked by hydraulic piston pumps to provide power based on their mutual angles. These angles are amplified by virtue of the fact that separate buoys are attached. Each buoy has two pivot axes, one (603) linked to the mooring 604 and the other (605) linked to the element 601. They therefore benefit from the buoyant fulcrum effect described above.

It will be appreciated that the invention provides for improved wave energy conversion. There is enhanced pitching action of the water inlet body due to the arrangement of the buoys, mooring, and inlet channel. Feeding slugs directly into a whirlpool allows the overall WEC to be very compact, and achieves smooth operation of the turbine. Also, the WEC is very light in comparison to previous proposals, providing a very high power-to -weight ratio. Also, it has few wearing parts.

Further, the mooring system is very simple. Advantageously, the WECs take advantage of the mooring forces, allowing them to make a very valuable power contribution. On the other hand, the conventional approach heretofore was to isolate the WEC from the mooring forces.

The invention is not limited to the embodiments described but may be varied in construction and detail. For example the turbine system may be linked with a flexible tube fed by a chuter. Also, the inlet system channel may be U-shaped rather than fully enclosed as a hollow body.

Claims

A wave energy converter (1) comprising:

a water inlet system (2) comprising:

a channel (4) having a mouth (5) to receive slugs of water and being adapted to be connected to a mooring (10) to tilt in a pitching action to receive and accelerate water slugs;

a whirlpool (3) linked to the water inlet system to receive slugs of water and to aggregate energy from said water in a vortex, and

a prime mover (36) arranged to be moved by water in the whirlpool.

A wave energy converter as claimed in claim 1, wherein the whirlpool (30) has a cylindrical configuration with a domed lower portion.

A wave energy converter as claimed in claims 1 or 2, wherein the wave energy converter comprises one or more check valves (27, 31) to prevent back- flow of water.

A wave energy converter as claimed in claim 3, wherein said check valve comprises a guide flap (31) pivotally connected adjacent a whirlpool inlet.

A wave energy converter as claimed in claim 4, wherein the flap (31) is curved to guide water in a tangential direction.

A wave energy converter as claimed in any of claims 3 to 5, wherein the check valve comprises at least one flap (27) in the water inlet channel, said flap having a pivot axis across a flow path towards the whirlpool.

A wave energy converter as claimed in claim 6, wherein the flaps (27) are mounted in a floor of the channel.

A wave energy converter as claimed in claims 6 or 7 wherein there is a plurality of said flaps (27) arranged parallel to each other.

9. A wave energy converter as claimed in any preceding claim, wherein the prime mover comprises a turbine (36) at a lower end of the whirlpool (30).

10. A wave energy converter as claimed in claim 9, wherein the turbine blades (270) are arranged to rotate about an axis which is co-axial with the whirlpool (30).

11. A wave energy converter as claimed in claim 10, wherein the blades (270) are configured with a C shape with a convex surface facing in the direction of travel. 12. A wave energy converter as claimed in claim 11 , wherein at least some turbine blades (270) include a flap (273) for flexing or pivoting about a lower edge of the turbine blade to bridge a gap between the blade and a trailing blade to block back- flow.

13. A wave energy converter as claimed in any of claims 9 to 12, wherein there is a draft tube (36) below the turbine blades.

14. A wave energy converter as claimed in claim 13, wherein the draft tube includes at least one flap (310) in a side wall for flow of back- flow water. 15. A wave energy converter as claimed in claims 13 or 14, wherein the draft tube includes a check valve comprising segmented overlapping leaves (304) arranged to block back-flow.

16. A wave energy converter as claimed in any preceding claim, wherein the water inlet system channel (4) is configured to narrow towards the trailing end.

17. A wave energy converter as claimed in any preceding claim, wherein the water inlet system comprises buoys (12, 45, 204) attached to the water inlet channel.

18. A wave energy converter as claimed in claim 17, wherein there is at least one stabilization buoy (7)on a water guide forwardly of the mouth, and at least another stabilization buoy (22) at the trailing end of the water inlet channel. A wave energy converter as claimed in claims 17 or 18, wherein at least one pitching buoy (12, 45, 204) is adapted to be connected to a mooring at a first pivot joint (11, 46, 205(a)) and is connected to the channel at a spaced-apart pivot joint (13, 48, 204(a)).

A wave energy converter as claimed in claim 19, wherein there is a pair of laterally spaced pitching buoys (12, 45, 204), one on each side of the channel.

A wave energy converter as claimed in claims 19 or 20, wherein the pitching buoy (12) is narrower facing the channel mouth, there being increasing cross-sectional area with distance from the mouth.

A wave energy converter as claimed in claims 19 or 20 or 21, wherein the wave energy converter comprises a frame (10, 47, 205) for attachment to a mooring, and wherein the frame is attached to a pitching buoy (12, 45, 204), and the buoy is pivotally attached to the water inlet channel at a spaced-apart pivot joint (13, 48, 204(a)).

A wave energy converter as claimed in any preceding claim, wherein the water inlet channel comprises a top wall and comprises spikes (20) on said top wall to deter seals.

A wave energy converter as claimed in any preceding claim, wherein the channel has a top wall, and water inlet channel comprises a fish and debris outlet (21) in the top wall or a side wall.

A wave energy converter as claimed in any preceding claim, wherein the water inlet channel is connected to the whirlpool by a flexible joint (26) allowing relative sliding motion.

A wave energy converter as claimed in claim 25, wherein the flexible joint (26) comprises pivot joints and a flexible liner.

A wave energy converter as claimed in any preceding claim, further comprising a plurality of fins (206) mounted on the water inlet channel, said fins being directed rearwards and downwards. A wave energy converter as claimed in claim 27, wherein there is a plurality of pairs of fins, one fin of each pair being each side of the channel.

A wave energy converter comprising a floating buoy (400, 451), a first joint (402) attaching the buoy to a mooring line (403), and a second joint (401) attaching to a prime mover for force transfer, said first and second joints being spaced-apart so that as mooring tension increases buoy displacement increases, providing a greater upward prime mover force.

A wave energy converter as claimed in claim 29, wherein the buoy (12, 45, 204) is attached to a water inlet channel (4, 203), so that said upward force is a channel lifting force.

A wave energy converter as claimed in claim 29, wherein the second joint is connected to a submerged prime mover (454, 504) to apply upward force to the prime mover.

A wave energy converter as claimed in claim 29, wherein the second joint (605) is linked with a floating element which is linked with at least one other element by a coupler which has a prime mover converting mutual rotation of the elements (601) to useful energy.