WO1981003358A1

WO1981003358A1 - Wave energy converting system

Info

Publication number: WO1981003358A1
Application number: PCT/GB1980/000091
Authority: WO
Inventors: E Wood
Original assignee: Sea Energy Ass Ltd; E Wood
Priority date: 1980-05-21
Filing date: 1980-05-21
Publication date: 1981-11-26
Also published as: EP0052600A1; AU5992780A; JPS57500937A; GB2089438A; NO814143L

Abstract

A device for the generation of energy from the energy in waves in a body of liquid comprises a buoyant structure (30) which is positioned in the body of liquid so as to heave up and down under the action of heave wave forces. The buoyant member is provided with a rope, cable, cord or the like (12) which extends downwards through a gland (28) to a submerged energy conversion apparatus such as a piston (22) and cylinder device (14). The lift of the buoyant member effects displacement of the piston in a submerged cylinder and from such piston movement fluid is pumped to drive a pelton wheel (38) located in a submerged air pocket (36), and the pelton wheel is connected to drive an electrical generator (43). As the buoyant member moves downwards, the piston moves downwards in the cylinder and a one-way valve arrangement (23) allows fluid to flow into the cylinder. During the upward pumping stroke of the piston, the fluid is pumped out of the cylinder and drives the pelton wheel. An accumulator (900) is coupled to the piston and cylinder to be charged when the piston and cylinder also pumps to the pelton wheel, and when the piston and cylinder moves in a pumping stroke the accumulator discharges to drive the pelton wheel. The buoyant member is biased downwards by elastic straps (300) or the like which preferably are attached to the underside of the buoyant member.

Description

WAVE ENERGY CONVERTING SYSTEM

This invention relates to energy generating systems for use in providing useful output energy (in a suitable form) from the energy in the waves in a body of liquid, more usually the sea or ocean.

There have been proposed many forms of equipment and apparatus, and schemes, for the extraction of the energy in waves in order to provide energy, such as electrical energy, in a more readily usable form, and the amount of effort which has been put into the investigation of wave energy extraction has increased considerably in recent years, in view of the world oil crisis which has been continuous since 1973/1974.

The present invention is concerned with a further proposal for wave energy extraction, and in our opinion has considerable merit in its deviation in a number of respects from the proposals which are at present attracting most favour.

Generally speaking, the known arrangements for the extraction of wave energy comprise apparatus for buoyantt support at the surface of the water, such apparatus for example, including prime movers which rock or pivot back and forth under the influence of wave forces. Energy conversion means, also provided on floating bodies, serves to convert these motions into, for example fluid under pressure, or electrical power output, which can be more readily utilised. In the preparation of designs of working arrangements on these systems, it has become clear that the apparatus in use will be subjected to extremely high forces in storm conditions. Because of this, the known proposals require to be designed to be more robust than they would otherwise have to be in order to withstand storm condition loading, and of course the need to make the structures more robust results in extremely high, and at the present time, prohibitive, capital investment as cost analysis on the various systems which have been proposed, show that the cost of wave power devices tends to be much higher, in terms of cost per unit of electricity which can be produced than from alternative and more established systems, such as nuclear power reactors. There is a need therefore to provide an effective yet relatively inexpensive wave power generator apparatus, and this is one objective of the present invention.

The present invention approaches the wave power problem in a different manner, and provides that certain operative parts of the equipment should be submerged. The part of the equipment which is deflected by the waves to provide the prime motion from which energy can be derived, is basically a buoyant structure, and is required only to bob up and down under the action of the waves .

The present invention in its most basic form comprises a buoyant structure which is for bobbing up and down in water under the influence of waves in the water and is attached by means of a cable, cord, rope or the like extending downwards to a submerged energy conversion means which is driven by said up and down movement and provides output energy in a different form.

The said energy conversion means preferably includes a piston and cylinder unit, the piston being operatively connected to the lower end of the cord, cable, rope or the like and the piston and cylinder unit is arranged to suck in water during upward movement of the buoyant member and at the same time to pump water from the cylinder into a discharge pipe arranged to jet the water onto a pelton wheel which is connected to drive an electrical generator, the generator and pelton wheel being located in an air pocket of a submerged housing. The discharge from the pelton wheel falls to a sump from which the water is sucked by the piston and cylinder unit.

The piston and cylinder unit preferably is adapted to extend vertically in use and is attached to the housing, which rests on the sea bed, through a high-pressure flexible pipe joint, through which the water is drawn by the piston and cylinder unit and also^' through a pipe in which the water is pumped to the pelton wheel. The said water is pumped in a closed loop and in fact is a 95% - 5% water lubrican emulsion; any suitable liquid, such as oil, may be used. The piston of the said unit may be connected to the suspension rope, said rope passing through a gland sleeve at the top of the cylinder. A rubber or other flexible sleeve may surround the rope between the said gland sleeve and the buoyant member to seal same from the surrounding sea water. The said sleeve may be elastic so as also to serve as a means of applying a tension force to the underside of the buoyant member to urge same in a downwards direction. There may be a leakage path to ensure that any leakage of emulsion through the gland sleeve is returned to the pump, and there will be no loss of emulsion.

The flexible pipe joint will allow the piston and cylinder unit to tilt relative to the housing to which it is attached. This is desirable in that the buoyant member should preferably be capable of some lateral movement as it comes under the influence of the waves.

The said housing may be grouted to the sea bed and the air (or other gas) pocket which houses the pelton wheel and electrical generator may be accessible in conventional fashion through a suitable trap door. The pocket may suitably be filled with an inert gas such as helium or nitrogen.

Also according to the invention there is provided an apparatus for use in converting wave energy into a more readily usable form comprising a buoyant structure which is for moving up and down in water under the influence of waves in the water against the action of resiliently stretchable pretensioning means set or adapted to be set so that when the apparatus is in position in the water the buoyant structure is pretensioned in a downward direction making the displacement of the buoyant structure greater than it is when the buoyant structure is free floating, the apparatus including a^' submerged energy conversion means which is operatively coupled to the buoyant structure, to be driven by said up and down movement to provide output energy in a different form.

Further, the invention provides apparatus for use in converting wave energy into a more readily usable form comprising a buoyant structure which is for moving up or down in water under the influence of waves in the water, an energy conversion means comprising a piston and cylinder device operatively coupled to the buoyant structure to be driven as a pump by the buoyant structure as it moves up and down, a rotary drive member of a type which is driven by pressure fluid discharged from the pump, and an accummulator which is charged from the pump and is adapted to discharge and contribute to the driving of said rotary member.

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V*ϊ; -τ The arrangements described have a number of advantages, not the least of which is that the cost of the equipment has been kept to a minimum. Also, the only part of the equipment which will experience storm conditions is the buoyant member (or members) and if the upward limit of travel of such member is limited, or the back pressure against which the buoyant member is working is too high, it will not lift, and in any case in use the apparatus will be set so that the waves will tend to pass over the buoyant structure, and in this respect the buoyant member is to a certain extent self-surviving.

The buoyant member may be of any construction suitable to give the required buoyancy, but we envisage that it will be in the form of a large disc horse shoe member or wholly or mainly of buoyant material, such as polystyrene foam, and there may be additional elastic tie ropes connecting the underside of the buoyant member to the submerged apparatus, to stabilize the buoyant member in use and to urge the buoyant member downwards. Finally, the buoyant member may have a keel means in order that it might be presented automatically in the best manner to the oncoming wave front.

When a number of buoyant members are used in a field, they may be interlinked by chains, ropes or the like at the water surface in order to positionally fix the said buoyant members one relative to another.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:-

Fig. 1 is a diagrammatic perspective view of apparatus according to a first embodiment of the invention;

Fig. 2 is a sectional elevation of the apparatus shown in Fig. 1, to an enlarged scale;

Fig. 3 is a diagrammatic perspective view of apparatus according to a second embodiment of the invention.

Fig. 4 is a sectional elevation of the apparatus shown in Fig. 3, to an enlarged scale;

Fig. 4a is a hydraulic circuit diagram showing the hydraulic inter connection of the components of the apparatus of Fig. 4;

Fig. 5 shows diagrammatically how the apparatus of Figs. 3 and .. .la^"put to sea; and

Fig. 6 shows a graph illustrating pressure and displacement curves typical of curves which might be obtained from the apparatus of Figs. 1 to 4.

Referring to Figs. 1 and 2 of the drawings, the device comprises a buoyant member 10 which may be in the shape of a flat pad of horseshoe configuration in plan, and the pad is connected by means of a rope or cable 12 to piston and cylinder unit 14 connected to a housing 15 on the sea bed. The housing 15 is of relatively massive weight to form an anchorage for the remainder of the apparatus and additionally is grouted to the sea bed as shown at 17 and also by grout pipe 19.

The piston and cylinder device 14 comprises a long cylinder 16 disposed in upright position, and the bottom end is connected by means of a high pressure flexible pipe joint 18 to the housing 15. Inside the cylinder 16 is a piston 22 which cc-operates with a bob weight 23 to define a one way valve arrangement as will be explained. The piston 22 is a hollow sleeve through which the cable 12 passes as shown, and the lower end of the cylinder 16 connects with a suction pipe 26. At the top of the piston is a PTFE slide and guide gland 28 in which the- cable 12 is received, and the gland 28 is also shown as being provided with an outlet 30 leading to a gland leakage return pipe 32 which leads to the lower interior of cylinder 16. The top end of the interior of cylinder 16 leads to a discharge pipe 34, which leads through joint 18 and a gas filled pocket 36 to a pelton wheel 38 also located in pocket 36. The bore of the gland 28 may be lined with a snap-in plastic lining sleeve, and the bore of the sleeve may be provided with grooves or rifling so that it will be lubricated by the fluid which leaks through the gland during operation. It is to be noted that the gland 28 is of significant length for the effective sliding and guiding of the rope 12.

The apparatus is provided with an elasticated sleeve 40 which extends, from the underside of the member 10 to the gland outlet 30. The elasticated sleeve 40 is - essentially a constant rate spring. It serves to return the buoyant member to a medial position after passage of the wave, and provide an extremely simple means for retaining the buoyant member in position. The sleeve also serves as a means of keeping the fluid which is pumped by piston 22 out of contact with the surrounding sea. The apparatus may additionally have elasticated straps arranged to apply tension to the underside of the buoyant member. The straps could be anchored to the sea bed or to the housing 15 or to another fixed location as desired. It may be that the straps could be replaced by tension springs such springs should be of a material to withstand sea water corrosion.

When the device is in use, the buoyant member 10 rises as shown by arrow 38 stretching the elastic sleeve 40 and the straps when it experiences a buoyancy force from a wave, and during this operation bob 23 seats on the underside of piston 22 and fluid above the piston 22 is pumped through the discharge pipe 34 at high pressure. At the same time, make up fluid is drawn into the lower part of the cylinder 16 through suction pipe 26. Any fluid which leaks past 5 gland 28 is returned via return pipe to the suction side of piston 22.

The high pressure fluid delivered by pipe 34 impinges on the pelton wheel 38 which is driven thereby, the discharge

10 from the wheel falling to a sump 41 with which the suction pipe 26 communicates to enable fluid to be drawing therefrom and of which the fluid level is shown at 42. It will be noted that the fluid travels in a closed path and is isolated from the surrounding sea water, which

15 therefore need not be used as the medium for driving the pelton wheel 38, and in fact an emulsion of 95% water 5% lubricant is preferably used for this purpose.

The pelton wheel 38 is connected to drive an electrical

20. generator 43 and electrical power is drawn therefrom by cable 45, to any suitable location, along with the output of other similar apparatus as may be used in any installation.

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25 The housing 15 defines the gas filled pocket 36 by having a conventional U-shaped gas trap 39 herein. The gas trap link has an emergency exit cover 44,the top of the other limb of the trap 39 being closed by a removable cover 47, which has a shackle 49 for connection to the generator and

30 pelton wheel assembly, so that such assembly can be raised from the trap after being uncoupled from its operative position shown, lowered onto a trolley 50 and moved to a position directly under the shackle 49.

35 Of course by so locating the pelton wheel and generator assembly in a gas space, maintenance and repair can be carried out on the assembly in situ. As each wave passes, the buoyant member 10 falls as indicated by arrow 46, bob 23 falls away from the piston 22 which freely descends in the cylinder 16 under gravity, the tension forces in sleeve 40 assisting the fall of the buoyant member 10, and during such descent fluid in the lower half of the cylinder passes through the piston 22 into the upper half of the cylinder ready to be pumped into the pipe 34 at higher pressure when the buoy 10 is once more lifted by a wave. During the up and down movement of member 10, the flexible rope, cable or the like, which may for example be Parafil (registered trade mark), cable, slides effectively in the gland 28, and the grooves or rifling therein make for the effective lubrication of the gland by the fluid being pumped.

The stroke of the piston 22 in normal wave conditions (which in practice prevail for 80% of the time), will be of the order of 3 or 4 metres, but the piston and cylinder unit 16/22 is designed so that the piston 22 can in fact move as much as 30 metres along the cylinder 16, to take account of storm conditions. If, in storm conditions, the pressure in the pipe 34 becomes so high that the piston 22 cannot pump any more fluid against such pressure, the buoyant member 10 is simply prevented from moving upwards, and the storm condition wave will pass over the top of the buoyant member, and in this respect the system is self-surviving, which is of course a considerable advantage.

It will normally be the case that there will be a plurality of the devices each as shown in Fig. 1, but coupled electrically to provide a common, aggregated ouput.

Referring now to Figs, 3, 4 and 5, the second embodiment of the invention is shown in these figures, and Fig. 3 is a view similar to Fig. 1 and in the view will be seen the buoyant structure 100, the piston and cylinder assembly 102 and an anchorage base 104. The piston and cylinder assembly 102 and the buoyant structure 100 are connected by elastic straps 300 and an elastic sleeve 400, which is similar to the sleeve 40 shown in Figs. 1 and 2.

Referring in more detail to Fig. 4, reference numeral 200 indicates a universal joint connecting buoyant structure 100 and the top end of the sleeve 400. The flexible rope, cable or the like 500, similar to cable 12 of the Fig. 2 embodiment is connected to a piston bob 180 which is surrounded by a sleeve 170, these constructional elements performing the same function as the elements 22 and 23 shown in Fig. 2. It is to be noted that it is preferable to make the bob 180 of greater mass than the sleeve 170 so that when the bob 180 falls under gravity, it will travel in advance of the free falling sleeve 170, allowing these two elements to perform the one-way function already described.

Reference numeral 600 represents a one-way valve at the lower end of the sleeve 400, whilst 700 represents a gland which receives and guides the cable 500 in the same fashion as described with reference to Fig. 2.

A high pressure fluid discharge passage leads from the top of the piston cylinder assembly 102 through a one-way valve 300, and the said passage then leads to a pressure accummulator 900 which includes a piston 101, and the intake and discharge of fluid to and from the accummulator are controlled by a valve 110. The high pressure discharge pipe also branches to a helium filled chamber containing a pelton wheel assembly 150 and an electrical generator 120. The high pressure liquid is in fact directed to a jet control valve of the pelton wheel assembly to control the jetting of liquid from the high pressure discharge passage on to the pelton wheel blades to drive same. The helium chamber liquid level is controlled by means of float control valve 160, and a helium bottle 130 is coupled to the float control valve to ensure the supply of helium to the chamber when the liquid level in the chamber reaches a predetermined value.

The bottom of the helium chamber is hydraulically ^"coupled to a flexible storage bag 190, which is kept in upright condition by means of a float 210, such bag serving as a reservoir for the fluid which forms the hydraulic circuit of the apparatus.

The piston cylinder assembly, the helium chamber and the accummulator 900 and flexible bag 190 in fact form an assembly which is coupled to the base 104 (which would be on the sea bed) by means of a rubber universal joint 220.

Fig. 5 in fact shows how the apparatus may be put to sea.

It is drawn by means of a floating vessel 225, with the assembly of piston and cylinder, helium chamber, accummulator and big 190 carried by the buoyant structure

100 as shown in Fig. 5, until the desired location at sea is reached. Then the said assembly is dropped through the buoyant structure 100 and the elasticated straps 300 are connected to the underside of the buoyant structure 100 thereby to create a pretensioning effect by loading the buoyant structure against the natural buoyancy forces of the water, such loading being designed so that in use the buoyant structure 100 will exhibit a higher buoyancy than its natural free floating buoyancy, and preferably so that the buoyant structure 100 will be positioned so as to lie slightly under the water surface during operation to enable the buoyant structure 100 to experience the best heave forces for best efficiency as related to wave theory which suggests that waves are defined by particles of water which execute orbital movements, and the diameters of the orbits decrease exponentially in a direction downwards into the body of the water from the surface thereof.

The operation of the apparatus illustrated in Fig. 4 is most usefully described in relation to the hydraulic circuit of Fig. 4a. When the apparatus is positioned with the straps 300 at the desired tension, the buoyant structure 100 will immediately commence oscillation under the influences of waves in the sea, and this osciallation will effect pumping of . the fluid in the circuit from piston and cylinder assembly 102 through the one-way valve 800 and, depending upon conditions and requirements, the output of the piston 102 will be charged either into the accummulator 900, or on to the pelton wheel 150, or both. If the pelton wheel is driven there will be power output from the generator 120. In the initial stages, the piston 102 will draw its supply of fluid from the flexible bag 190.

As the accummulator 900 receives fluid from the pumping action from piston 102, so the accummulator will become charged and the float 101 thereof will rise. As the accummulator is otherwise sealed, so the internal pressure will increase. The apparatus reaches a condition in which, with each pumping stroke of piston 102, there is a jet of fluid impinged upon the pelton wheel blades to drive the pelton wheel 150, and also a charge of fluid into the accummulator 900. On the return stroke, the accummulator delivers fluid under the pressure of the accummulator as a jet onto the pelton wheel 150, so that there is continuity of driving of same. As the fluid impinges upon the pelton wheel blades giving up its pressure, it falls to the bottom of the helium chamber and is drawn therefrom by the piston 102, and so the cycle repeats. If there is an excess of pressure in the supply line, a relief valve 155 opens allowing discharge of the pressure fluid into the helium chamber without in fact impinging the pelton wheel blades. It has been found that if the pressure in the system increases, for example if the energy in the waves becomes excessive, then the buoyant structure 100 tends to be drawn deeper into the water and the stroke of the piston 102 becomes shorter, and in this respect the system is self-preserving, because in the event of excessive waves, the buoyant structure will tend to pull downwards.

It is to be mentioned that the flexible tension cable 12 in Fig. 1, and 500 in Fig. 4 is a smooth surfaced member, and it may be a coated wire rope , smooth wire rope , or parafil rope, and in fact it is the weight of the piston which pulls the cable back through the gland at the top of the cylinder.

The design of the piston, in relation to the Fig. 4 embodiment, is a significant novelty, in that there is a balance of the mass between the sleeve 170 and the piston bob 180, as related to the area which is swept by piston movement. If the sleeve provides more pressure due to its mass than the bob, then the bob tends to be forced up through the holes in the sleeve during the descending movement, and in fact there is a blockage of the descent of the combined piston. Both the sleeve and bob therefore have to be reasonably balanced to ensure maximum flow through of fluid when the sleeve and piston separate during the free fall of the bob and sleeve.

By providing that in each case a significant part of the apparatus is located submerged, that part of the apparatus need not be designed for storm or survival conditions and by connecting the buoyant member to that part of the apparatus by means of a rope, cable, chain or the like, in storm conditions, the buoyant member can simply move with the wave forces it experiences.

It is to be appreciated that the above describes two forms of apparatus when in the in-use condition, as their operation is best understood when it is in use, but it is also appreciated that this invention extends to each apparatus in its various components when produced on land and for transportation to a position of use which may be twelve or more miles from the coast line.

It is doubtless that other structural and design modifications may present themselves to persons skilled in the art, and it is intended that such modifications be included within the scope of the present invention.

Referring briefly to Fig. 6, the graph A shown therein is a typical time-displacement graph illustrating a typical buoyant member movement in a normal sea. It will be noted that all amplitude excursions are not equal. The graphs B are pressure verses time graphs illustrating pressure energy availabe at the respective strokes of the buoyant member.

Claims

1. Apparatus for use in. converting wave energy into a more readily usable form comprising a buoyant structure which is for bobbing up and down in water under the influence of waves in the water and is attached by means of a cable, cord, rope or the like extending downwards to a submerged energy conversion means which is driven by said up and down movement and provides output energy in a different form.

2. Apparatus according to claim 1, wherin the said energy conversion means comprises a piston and cylinder unit, the piston being attached to the lower end of the cord, cable, rope or the like and the piston cylinder unit is arranged to suck in fluid and during upward movement of the buoyant member, and at the same time to pump fluid from the cylinder into a discharge pipe arranged to jet the fluid onto a pelton wheel which is connected to drive an electrical generator, the generator and pelton wheel being located in an air pocket of a submerged housing.

3. Apparatus according to claim 2, wherein the discharge from the pelton wheel is arranged to fall to a sump in the housing from which fluid is sucked by the piston and cylinder unit.

4. Apparatus according to claim 2 or 3, wherein the piston and cylinder unit is adapted to extend vertically in use and is attached to the housing, which rests on the sea bed, through a high-pressure flexible pipe joint.

5. Apparatus according to claim 4, wherein the piston and cylinder is adapted to draw in fluid through the flexible pipe joint and is adapted to discharge high pressure fluid to the pelton wheel through a pipe housing through said joints.

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6. Apparatus according to any one of the preceding claims 2 to 5, wherein the piston of said piston and cylinder unit is operatively connected to the buoyant member by means of a rope or cable which passes through a gland sleeve at the top of the cylinder.

7. Apparatus according to claim- 6, wherein a rubber or other flexible sleeve surrounds the rope or cable between the gland sleeve and the buoyant member to seal same from the surrounding sea water.

8. Apparatus according to claim 7, wherein said sleeve is elastic so as also to serve as a means of applying a tension force to the underside of the buoyant member to urge same in a downwards direction.

9. Apparatus according to claim 8, provided claim 8 depends back to claim 3, wherein there is a leakage path from the interior of said sleeve back to the sump to ensure that any leakage of fluid through the gland sleeve is returned to the sump.

10. Apparatus according to any preceding claim wherein the buoyant member is a flat disc of horse-shoe shape.

11. Apparatus according to any preceding claim, wherein there are elastic tie ropes pretensioning the buoyant member to the submerged means.

12. Apparatus according to any preceding claim, wherein said buoyant member has a keel in order that the member will be best presented to the oncoming waves.

13. Apparatus for use in converting wave energy into a more readily usable form comprising a buoyant structure which is for moving up and down in water under the influence of waves in the water against the action of resiliently stretchable pretensioning means set or adapted to be set so that when the apparatus is in position in the water the buoyant structure is pretensioned in a downward direction makintg the displacement of the buoyant structure greater than it is when the buoyant structure is free floating, the apparatus including a submerged energy conversion means which is operatively coupled to the buoyant structure to be driven by said up and down movement to provide output energy in a different form.

14. Apparatus according to claim 13, wherein the pretensioning means comprises resiliently stretchable straps having their top ends anchored to the buoyant structure and the lower ends anchored fixed at positions restrained from moving up and down with the buoyant- structure.

15. Apparatus for use in converting wave energy into a more readily usable form comprising a buoyant structure which is for moving up or down in water under the influence of waves in the water, an energy conversion means, comprising a piston- and cylinder device operatively coupled to the buoyant structure to be driven as a pump by the buoyant structure as it moves up and down, a rotary drive member of a type which is driven by pressure fluid discharged from the pump, and an accummulator which is charged from the pump and is adapted to discharge and contribute to the driving of said rotary member.

16. Apparatus according to claim 15, including a flexible, sealed reservoir containing the fluid which is pumped by the pump, the reservoir being coupled to the pump so that the pump draws fluid from said reservoir during pumping.

17. Apparatus according to claims 15 or 16 wherein the accummulator and pump are formed in an assembly which is connected by means of a universal joint to a structur for standing on or anchorage to the sea bed.

18. Apparatus according to claim 15 to 17 wherein ther is a pressure relief valve associated with the pump t limit the maximum delivery pressure of the pump.

19. Apparatus according to any preceding claim, wherei the underside of the buoyant structure is downwardl convex.