GB2064014A

GB2064014A - Apparatus for Deriving Power From Sea Waves

Info

Publication number: GB2064014A
Application number: GB8037600A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1979-11-23
Filing date: 1980-11-24
Publication date: 1981-06-10
Also published as: GB2064014B

Abstract

A membrane 10 is arranged to lie at the water's surface and is connected by inextensible cables 17 to power generators 16, which may be hydraulic piston pumps. The generators 16 are mounted on a second membrane 15 which is anchored to the sea bed by extensible ties 19. Membrane 10 is reinforced by glass-reinforced or metal discs 11 at the points of attachment of cables 17. In a modification, membrane 10 is apertured and held firmly by cables 17; water which gushes through the apertures is used e.g. to drive a turbine. Alternatively propellors which is situated in the still water region adjacent second membrane 15 are connected to points 13 and are moved relative to the still water by membrane 10. Alternatively a hose pump may be connected between floating membrane 10 and stationary membrane 15. The membranes may be made of neoprene. <IMAGE>

Description

SPECIFICATION Apparatus for Deriving Power from Sea Waves This invention relates to apparatus for deriving power from sea waves.

It has previously been proposed to harness energy from sea waves by means of buoys which, as they rise and fall under the wave action, drive hydraulic pistons or other means for generating power and electricity. Disadvantages which exist in these systems include the high cost of manufacturing, transporting and installing the buoys which are inevitably large and relatively fragile and/or heavy. Also, buoys of a size which is effective for the production of electricity constitute a potential hazard to shipping, particularly if they drift from their moorings and they are, therefore, securely anchored to the sea bed.

It is an object of the present invention to provide an improved apparatus for deriving power from sea waves, in which the aforementioned disadvantages are at least reduced.

According to the present invention there is provided an apparatus for deriving power from sea waves comprising a buoyant member in the form of a flexible membrane arranged to lie at the water's surface and energy conversion means provided between said flexible membrane and a submerged station to derive energy from the waves during movement of the membrane relative to the submerged station.

Preferably the membrane is provided with reinforced parts which resist deformation and via which the flexible membrane may be interconnected with said energy conversion means.

The membrane may be of an elongate form and provided with one or more rows of said reinforced parts. Each of said reinforced parts may have a central node point to which energy conversion means is connected, either directly or via tie means.

The tie means may comprise cables extending from the reinforced parts of the membrane to submerged and relatively stationary energy converters such as a hydraulic piston and cylinder device or a hose pump arranged to drive an electricity generator. A hose pump may extend along and comprise the whole or only part of the length of said tie means.

The buoyant member may comprise a plurality of interconnected inflated units which may be individually or collectively flexible.

The apparatus may comprise additionally a second membrane which is arranged to lie submerged at the level of relatively still water, i.e.

water which experiences substantially less effect from waves than water at the surface. Said second membrane may support energy conversion means to which said tie means are connected.

Preferably the submerged second membrane is, in turn, connected to a submerged anchorage such as for example the sea bed or means, typically cables, extending from a ship or other structure. The connection between the second membrane and submerged anchorage preferably is not inextensible. Additional or alternative to a connection between a submerged anchorage and a second membrane, a connection may be provided between the flexible membrane and anchorage.

More than one submerged membrane may be provided, and in this case two or more of the membranes may be arranged to lie at different depths. In the case where hose pumps interconnect with said submerged membranes, the pumps connecting to membranes at different depths may be arranged to pump at different internal pressures.

A framework, typically of pressurised braces, may be provided adjacent the second membrane or interconnecting a plurality of second membranes, and the second membrane(s) may be connected to a submerged anchorage by means of said framework.

The references made herein to sea waves are not restricted to waves in ocean and tidal waters, but include also waves on inland waters and seas, and rivers, irrespective of whether they are tidal.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which Figure 1 is a fragmentary plan view showing apparatus according to the present invention in situ for deriving power from sea waves; Figure 2 is an extended section, generally on the line 1I--II of Figure 1; Figure 3 is a fragmentary plan view, part from above and part from below, showing another apparatus in accordance with the present invention for deriving power from sea waves; and Figure 4 is a section on the line A-A of Figure 3.

Referring to Figures 1 and 2, the apparatus comprises a buoyant member in the form of a flexible membrane 10 carrying a series of hexagonal sheets 1 The membrane 10 and the sheets 11 are formed of a plastics material or a synthetic rubber such as neoprene and are secured together by, for example, sewing or welding. Each hexagonal sheet 11 is reinforced by a pad-like assembly of four circular discs 12 (see Figure 2) formed of, for example, glass reinforced plastics or metal, and a node point 1 3 exists at the centre of each reinforced sheet. The membrane 10 is also provided with an air inflated tubular edge float 1 4 which extends continuously around the periphery of the membrane 10.

The membrane 11 floats on the sea water surface which is indicated generally by reference numerai 21.

Below the membrane 10, which is either inherently buoyant or formed with foam fill or air spaces to produce buoyancy, is a submerged second membrane 15 of similar form and dimensions but not buoyant. The membrane 15 carries power generators 1 6 such as hydraulic piston and cylinder devices, and individual ties 1 7 in the form of inextensible cables extend from the node points 1 3 to these generators. Further ties 19, which may be elastic, extend down to the sea bed where they are anchored at points 20.

The size of the membranes 10 and 15 and the depth of membrane 15 is selected dependent on factors such as sea conditions and power requirements, but typical dimensions are a breadth of about 20 metres and a length of about 1 kilometre.

In use of the apparatus, wave movements cause the upper membrane 10 to undulate and the distributed force of rising water is carried through sheets 11 and the reinforcing discs 1 2 to the node points 1 3 which also rise and fall. As indicated in Figure 2, the membrane 10 and sheets 11 are flexible and the reinforcing discs are also flexible, albeit to a lesser degree, to allow the membrane to follow the contour of the waves and facilitate the passage of the waves below the unrestrained edges of the membrane. It is also found that the continuous edge float 14 resists the passage of surface water and acts to increase the buoyancy of the membrane 10.

The lower membrane 1 5 is submerged at a depth which is preferably greater than half the wave length which is generally expected in the area where the apparatus is sited, and at this depth there should be relatively still water. Thus, the node points 13 will move up and down in relation to and thereby drive the power generators 1 6 by means of the ties 1 7 which are drawn back downwards by weights (not shown) or other suitable means. It is preferred that the submerged membrane 15 is more rigid than the upper membrane 10, to minimise deformation by any water movement which does occur at that depth, and it is to be noted that the presence of the lower membrane 1 5 may reduce the required number of ties 19 to the sea bed.A further advantage of providing a submerged second membrane is that, if sea waves of a size greater than expected occur, the submerged membrane will tend also to flex and so accommodate, at least in part, any abnormally large movements of the upper membrane 10.

The hydraulic power which is generated by the devices 16 is either transferred through pipes along the sea bed or along one of the membranes to a central electricity generating station, or could be employed to induce a rotational movement to generate electricity for example at each node point 13.

In a modified form of the aforedescribed apparatus the upper membrane 10 is apertured at the node points and held firmly by means of the substantially inextensible upper cables 1 7. With this arrangement sea water will gush through the node openings as the sea rises and the gushing water can be employed, for example, to power turbines. In this embodiment, smaller or flapcontrolled apertures provided with valve means may be provided to allow the return of water as the sea falls.

In a further modified form, means such as propellors are attached by substantially inextensible ties to the node points 1 3 at approximately the level of the submerged membranes shown in Figure 2. In this case, the rise of the node points 13 will draw the propellors upwardly through relatively still water thus rotating the propellors to produce power. In yet a further modified form, hydraulic power is generated by the elongation and contraction of a set of flexible straps interconnected with a flexible, generally tubular envelope so that a greater volume of water is enclosed in their contracted state than in their stretched state.

As an alternative to being anchored to the sea bed, the membranes may be tethered to and possibly towed by a ship in which the electrical generator is mounted. This embodiment is particularly suited to deep-sea locations.

In a further modification, cross cables may also be provided to restrain unwanted lateral movement of the node points 13.

In a further embodiment of the invention (illustrated in Figures 3 and 4) apparatus comprises a series of inflated units 30 interconnected with one another along adjacent edges 31. The units are formed from flexible membranes of plastics material or synthetic rubber, and preferably the lower parts 30a which are subject to the greatest strain, are of stouter material than the sides and upper parts 30b. Each hexagonal unit 30 is formed with a central drainage outlet 32 which opens to a non-return valve 33 and also extends downwardly to provide a connection with the central (node) point of the lower membrane 30a.

Around the periphery of the buoyant member is an inflated edge float 34 which is connected to the outer units 30 by lower and upper membranes 34a and 34b.

Extending from the central (node) point of each unit 30 is a hose pump 35 closed at its upper end.

The lower end of each hose pump is connected to a submerged station 36 which will hereinafter be described. Hose pumps are already known (see for example the specification of U.K. Patent Application No. 2,002,052) and consist of lengths of flexible and elastic tubing which, when extended, reduce in internal volume and, when they retract, expand in internal volume; thus, as the tubing is stretched and released, water can be pumped out and in of at least one end.

The submerged station 36 comprises a weighted membrane 37 which is anchored to the sea bed by ties 38 connected to the membrane through skirts 39, and a structural support, such as a series of pressurised braces 40 which extend between feed pipes 41. The feed pipes 41 connect with the hose pumps 35 through oneway valves 42, and the feed pipes lead to one or more turbines (not shown).

In use of the apparatus, as the buoyant units 30 rise and fall, the hose pumps 35 stretch and retract to pump water through the valves 33 and the feed pipes 41 to power the turbines. Any water which passes over the edge float 34 will drain off through the outlets 32 and non-return valves 33.

As illustrated, the inflated units 30 are completely sealed but, in a modified form, may be continuously pressurised by, for example, one or more hose pumps (such as 35) arranged to draw air from the atmosphere above the apparatus.

In a further modification, the buoyant member may consist of a pressurised tubular structure, the pressurised tubes being interconnected by suitable membranes.

In yet a further modification, to provide a relatively small amount of power, the apparatus may comprise a single buoyant unit such as 30 with its individual hose pump 35, the lower end of which may be anchored directly to the sea bed possibly through a suitable tie. In constructions such as this the submerged membrane or station may not be required.

The weighted membrane 37 may consist of two layers, the lower layer being a load-carrying (perforated) scrim and the upper layer being formed with flexible flaps. This arrangement will resist upward movement of the station 36 when the buoyant member (units 30) rises, but the flaps will deflect to allow through-flow of water when the station returns downwards under gravity, so that the output of the hose pumps 35 will be increased.

In a development of the invention, the feed pipes 41 may lead to a reverse osmosis device or to another alternative apparatus which is hydraulically powered.

In a further development, the units 30 may be formed of transparent upper membranes 30b and dark-coloured lower membranes 30a. With this arrangement, limited quantities of salt water admitted into the units 30 may evaporate, condense as fresh water on the angled inner surfaces of the upper membranes and collect in annular troughs (not shown) around the drainage outlets 32; thus, a form of water-distillation plant can be incorporated in the apparatus.

Although specific mention has been made of energy converters which derive energy from the sea waves as a means of providing a source of energy, it is to be understood that the energy converters may be employed alternatively to serve as energy dissipators where it is required only to dampen wave movements and not provide an energy source.

The apparatus according to the present invention is of simple construction, and the membranes may be assembled at least partly on site. Also, due to the flexible nature of the membranes, the danger to shipping is greatly reduced, although it is still desirable to mark the position of the apparatus.

Claims

1. Apparatus for deriving power from sea waves comprising a buoyant member in the form of a flexible membrane arranged to lie at the water's surface and energy conversion means provided between said flexible membrane and a submerged station to derive energy from the waves during movement of the membrane relative to the submerged station.

2. Apparatus according to claim 1, wherein the flexible membrane is provided with reinforced parts which resist deformation and via which the flexible membrane is interconnected with said energy conversion means.

3. Apparatus according to claim 1 or claim 2 comprising a second membrane arranged to lie at the level of relatively still water and to serve as a submerged station.

4. Apparatus according to claim 3, wherein the second membrane is more rigid than the flexible membrane of the buoyant member.

5. Apparatus according to claim 3 or claim 4, wherein said second membrane supports energy conversion means.

6. Apparatus according to any one of claims 3 to 5, wherein the second membrane is secured to a submerged anchorage by an extensible means.

7. Apparatus according to any one of claims 3 to 6 and comprising a plurality of second membranes arranged to lie at different levels.

8. Apparatus according to any one of claims 3 to 7, wherein the submerged station comprises a structural support.

9. Apparatus according to claim 8, wherein said structural support comprises a series of pressurised braces.

1 0. Apparatus according to any one of the preceding claims, wherein energy conversion means is provided between the flexible membrane of the buoyant member and a submerged anchorage.

11. Apparatus according to any one of the preceding claims, wherein the flexible membrane of the buoyant member comprises a plurality of interconnected inflated units.

12. Apparatus according to claim 11, wherein said units are individually flexible.

1 3. Apparatus according to claim 11, wherein the inflated units are collectively flexible.

14. Apparatus according to any one of the preceding claims, wherein the buoyant member comprises a substantially continuous edge float extending around the periphery of the flexible membrane.

1 5. Apparatus according to any one of the preceding claims, wherein the flexible membrane is of elongate shape comprising at least one row of reinforced parts which resist deformation.

16. Apparatus according to any one of the preceding claims, wherein the flexible membrane of the buoyant member is provided with apertures for the flow of water therethrough.

1 7. Apparatus according to claim 16, wherein energy conversion means is provided to derive energy from water flowing through said apertures.

1 8. Apparatus according to claim 16 or claim 1 7, wherein at least some of said apertures are provided with valve means arranged to permit water to drain from an upper surface of the buoyant member.

19. Apparatus according to any one of the preceding claims, wherein the energy conversion means comprises a flexible reinforced tubular memberthe internal volume of which reduces on elongation of the member.

20. Apparatus according to any one of claims 1 to 18, wherein the energy conversion means comprises a hydraulic piston and cylinder device.

21. Apparatus for deriving power from sea waves comprising a buoyant member in the form of a flexible membrane arranged to lie at the water's surface, a second membrane arranged to lie at the level of normally still water, substantially inextensible tie means interconnecting said buoyant member and second membrane, and energy conversion means movable substantially in unison with the second membrane to derive energy from the waves in consequence of said waves causing relative movement of the buoyant member and submerged second membrane.

22. Apparatus for deriving power from sea waves constructed and arranged substantially as hereinbefore described with reference to the accompanying ewings.