GB2044843A - Wave energy device - Google Patents

Abstract

A pump for generating energy from wave motion has a tube 2 in the form of a bellows or equivalent which is capable of pumping water via inlet and outlet valves 5, 6 as its volume changes due to interaction with wave motion. The tube is adapted to retain a substantially linear axial orientation during its extension and contraction. <IMAGE>

Description

SPECIFICATION Wave energy device The present invention relates to wave energy devices and more particularly relates to pumps for operating wave energy devices.

Wave motion has long been regarded as a potential source for power generation and a number of suggestions have been proposed for the extraction of this power. Amongst these suggestions are our UK patent application no. 30057/78 (Serial No. 2007314) which discloses a device actuated by wave motion comprising one or more liquid wave actuated pumps, each pump comprising a surface float or raft which conforms to the changes in liquid surface level during the passage of waves, a resilient tube suspended from the float, which tube is capable of changing volume when extended or contracted, and having inlet and outlet unidirectional valves and a means to maintain the lower end of the tube at a substantially constant level below the surface of the liquid.

It has been found that the structure of bellows pumps used in small scale liquid wave actuated pumps are often not suitable for larger scale applications. Thus, although the encased spiral spring bellows construction is suitable for small wave pumps, for larger pumps the higher pumping forces require greater spiral wire diameters which are increasingly difficult to encase and in addition the resultant spring bellows tend to have a poor fatigue life.

The present invention is directed towards the construction of bellows having improved stability to distortion when delivering fluid at pressure and having an improved fatigue life.

Thus, according to the present invention there is provided a pump suitable for wave energy generation, the pump comprising a tube capable of changing volume when extended or contracted in length relative to its ends by wave motion and having inlet and outlet unidirectional valves, the tube having means for maintaining it in a substantially linear exial orientation during extension and contraction.

The tube may be adapted to tend to maintain itself in a substantially linear orientation the following preferred ways.

In a first preferred embodiment, the tube comprises a cylindrical bellows having springs connected internally or externally to the bellows, the spring being symmetrically arranged around the bellows to cause uniform contraction when the applied extending forces are removed. The spring may comprise a plurality of springs connected in series and across individual segments of the bellows. Strops may be used to limit the extension of the springs to a pre-determined maximum extension.

In a second preferred embodiment, the tube comprises a plurality of stacked co-axial hollow rings, each ring comprising a resilient filling, for example, containing a pressurised gas, each ring being joined around its circumference to its neighbour.

In a third preferred embodiment, the tube comprises a pair of bellows one within the other and having substantially co-axial longitudinal axes, the bellows being rigidly connected to each other at short intervals along their lenths, the inner bellows containing air or gas at reduced pressure and the annulus between the bellows comprising a passageway for liquid flow.

In a fourth preferred embodiment, the tube comprises a plurality of cylinders arranged along their longitudinal axes, the adjacent cylinders being of different diameters, the cylinders being joined end to end by means of an annular resilient seal. Most preferably the cylinders have a wedge shaped profile and have alternate larger and smaller diameters.

In a fifth preferred embodiment the tube comprises a plurality of tyre-like segments, each segment containing a number of Ushaped leaf springs encased in a polymeric material, e.g. rubber. The tyre like segments are joined together via spacers at their beads.

In use of the device, relative motion of the surface float or raft and the lower end of the tube causes liquid to be pumped into the tube through an inlet valve when the tube volume increase and through an outlet valve when the tube volume decreases. The resultant water flow may, then for example, be passed through a turbine or the like to produce electricity.

Each pumping bellows may hang below a float and have a reaction plate or inertial container at or hung below its lower end.

Where the capacity of one pump is insufficient a plurality of pumps may be arranged in an array to pump more liquid. The bellows may be arranged in groups between floats and reaction plates (or inertial containers) so that any relative motion between them causes fluid pumping and energy capture. For high energy capture, each float is arranged to couple with six pump tubes arranged as two sets of three orthogonal axes with different origins so that the six possible degrees of freedom of movement of the float are coupled with the pumps. In practice less pumps may be used with reduced efficiency but less complexity and cost.

Pumps may be mounted vertically below floats connected to a reaction plate and also horizontally between floats.

Alternatively an array may consist of floats each with three pumps mounted orthogonally to one another, the pumps being connected to the pumps of neighbouring floats via reaction plates or inertial containers. A float with three pumps mounted orthogonally may be con nected to a single large reaction plate.

An array of pumps may extend as a line across the surface of the fluid or as a raft in both dimensions across the surface. Where the pump units are arranged in a line each may be subjected to similar wave conditions.

In a two dimensional surface raft at right angles to the wave fron the pumps nearest to the approaching waves will be subjected to the full wave action while thos further from this edge will be subjected to progressively attenuated waves. An array of pumps may be connected by a system of manifolds to collect the water pumps from the outlet valves. In normal wind driven sea waves the intermittent water flow from each unit of any array of pumps will be added in the manifold system to provide a more steady flow at the manifold outlet.

When extended from its normal free length, the tubing exerts a restoring force to regain its original length. The changes in length of the tube caused by wave motion result in a change in the enclosed volume of the tube as in a concertina. Preferably, the change in volume of the resilient tube causes unidirectional liquid flow by drawing liquid through the inlet non return valve system while the volume of the tube increases and expelling the liquid through a second non return valve system into, for example, a manifold while the volume decreases.

Supplementary valves may be used between the inlet and outlet valves if desired, for example, to minimise back flow. The tube must have sufficient structural strength to maintain the change in its volume associated with its change of length caused by the waves while subjected to the fluctuating pressures associated with the pumping of the fluid.

If the device is operated in shallow water, i.e. the wavelength of the longest waves in which the device is required to operate is greater than twice the water depth, it is preferable to attach the lower end of the pump tube to an anchoring system on the sea bed to provide the vertical restraint to the buoyancy forces. In deeper water the reaction system is preferably a plate or mesh which is suspended from the pumping tube sufficiently far below the surface to be largely unaffected by surface waves. The plate or mesh has a large hydraulic impedance to provide a restraint against the surface buoyancy and has sufficient weight to return the plate to is position in still water against the upward forces exerted by the pump tube when operating in waves. Alternatively the pump tube may be used horizontally as disclosed in UK patent application No. 29006/78 or in an inclined position.

The subsurface plate or mesh (reaction plate) is preferably fitted with inflatable chambers which may be filled with air during launching and towing to the site of operation to reduce the draught of the system. Subsequent flooding of the chambers allows the subsurface plate to sink to the desired operating level.

The structure is provided with suitable means for towing and positioning, e.g. cables and ropes, and also for anchorage purposes.

Anchoring may be made by use of ropes or wires, e.g. nylon or chains to a buoy or directly to sea bed anchors. The anchor cables may be connected to the surface float, reaction plate or inertial container or to an intermediate position but attachment at the lowest point will be subject to least movement and will provide a resilient connection to the float. This may enhance the system's ability to survive severe weather conditions.

The construction of the device is determined by the operating wave conditions and the type of fluid flow required.

Preferably the surface floats should have sufficient excess buoyancy above that required to float in still water so that they just remain at the surface during the passage of the maximum wave crest anticipated while extending the pumping tube by about half the height of the largest waves. The restoring force of the tube when returning to its normal contracted length then determines the maximum pressure pumped by each unit. For a given set of wave conditions the tubes may be chosen to pump a small volume at relatively high pressure or high volume at low pressure or some intermediate combination.

The devices may be used for various water pumping operations, e.g. for inflation of wave calming booms or pumping sea water for trace element extraction plants.

The device may be used to pump the fluid in which the waves occur, or, by the provision of manifolds to both the inlet and the outlet valves to pump a different liquid or gas in a closed circuit.

For sea water operation the materials of construction should be resistant to corrosion and marine fouling.

The invention will now be described by way of example only.

Figure 1 shows a vertical section through a wave energy device comprising a vertical resilient tube pump.

Figures 2 to 7 illustrate vertical cross sections of resilient tube pumps according to the invention.

In Fig. 1, a surface float of foam plastic 1 supports a steel spiral wound plastic coated bellows tube 2 to which the subsurface plate 3 is attached. When a wave crest causes the float to rise, the subsurface plate, which is in still water, resists the upward motion causing the bellows to extend. The result increase in volume is accompanied by the flow of water through a coarse filter 4 and a non-return inlet rubber flap valve 5. As the crest passes and a trough approaches, the restoring force in the extended bellows causes contraction and expulsion of water through the outlet valve 6.

In use of the device, an incident liquid wave causes the float 1 to move in sympathy.

The subsurface mesh plate 3, because of its inherent inertial and hydraulic resistance, remains at substantially the same liquid height and thus the relative movement between the raft 1 and the anchoring plate 3 causes alternate compression and extension of tubes 2 as the incident wave passes. Thus, when a particular float 1 rises when a wave crest approaches, the associated inlet flap valve 5 opens as water is drawn through the filter 4 into the tube 2. When the float 1 falls with an approaching wave through the restoring force of the extended tube 2 forces water out of the outlet valve 6 into a manifold (not shown).

The manifold, which is itself flexible, collects water from all the pump units and passes it to a turbine unit (not shown) which floats in the protected water at the back of the array away from the incident waves. The turbine then discharges the water back into the sea. Water flow is the result of many pumps all operating out of phase and storing water in the turbine tube.

Fig. 2 shows a part of a pump formed from a cylindrical bellows 7 having springs 8 mounted on support projections 9 extended to the bellows 7, the projections 9 being attached between bellows segments. Alternatively the springs may be internal to the bellows. Liquid flow occurs through passageway 1 0. This type of pumps is designed to work at pressure between ambient and high positive pressures and will expel liquid at pressure on the contraction stroke.

Fig. 3 shows part of a pump formed from a number of stacked gas inflated or rubber filled rings 11. Flexing of the rings 11 causes liquid flow through the central passageway 1 2.

Fig. 4 shows part of a pump having a bellows 1 3 through the central passageway of which liquid may flow. External springs 1 4 tend to compress the bellows 13, water pumping occurring on the suction stroke of bellows movement caused by wave action.

The pressure reduction possible in this form is limited by the initial ambient pressure. Pump tubes of this form located deep below the surface of the sea may be operated over a greater pressure range than the pumps of Fig.

3 due to the higher ambient pressures.

Fig. 5 shows part of a pump in which a pair of bellows 15, 1 6 are joined one within the other, the annulus 1 7 between the bellows 15, 1 6 acting as a liquid flow passageway and the inside of bellows 1 5 being pressurised with gas to provide a semi rigid backbone to the pump.

Fig. 6(a) shows part of a pump having rigid preferably metal tubes 1 8 being sealingly connected to tubes 1 9 of different diameter to form an extended tube, the connection from tube to tube being of resilient rubber springs 20. The rubber is bonded to both tubes by a rubber/metal bond 21. The rubber springs 20 include an element of compressive resistance to limit movement under extreme loading. This may be achieved by use of partial end stops of tapered or conical sections of collars with rubber interleaving (Figs. 6(c) and 6(d). Alternatively the rubber can be in compression only in which case it is bonded only to the horizontal sections of the bent over tubes (Fig. 6(b).

Fig. 7 shows part of a pump in which the resilience of the bellows results from Ushaped springs incorporated in a tyre-like construction so that the sidewalls are sprung.

Movements of the beads of the bellows elements away from their rest position will result in a powerful self-restoring force. The springs are preferably encased in the rubber or plastics material of the bellows to provide corrosion resistance. The ends of the U-shaped springs at the bead are drilled or shaped to permit connection between a stack of the (tyre-like) units to form a spring bellows.

Combinations of these construction methods may be used to form composite pumps whick act on both the extension and contraction parts of the wave actuated cycle.

Claims (11)

1. A pump suitable for wave energy generation comprising a tube capable of changing volume when extended or contracted in length relative to its ends by wave motion and having inlet and outlet uni-directional valves, the tube having means for maintaining it in a substantially linear axial orientation during extension and contraction.

2. A pump according to claim 1 in which the tube comprises a cyulindrical bellows having springs connected internally or externally to the bellows, the springs being symmetrically arranged around the bellows to cause uniform contraction when the applied extending forces are removed.

3. A pump according to claim 2 in which the springs comprise a plurality of springs connected in series and across individual segments of the bellows.

4. A pump according to claim 1 in which the tube comprises a plurality of stacked coaxial hollow rings, each comprising a resilient filling each ring being joined around its circumference to its neighbour.

5. A pump according to claim 4 in which the resilient filling is a pressurised gas.

6. A pump according to claim 1 in which the tube comprises a pair of bellows one within the other and having substantially coaxial longitudinal axes, the bellows being rigidly connected to each other at short intervals along their lengths, the inner bellows containing air or gas at reduced pressure and the annulus between the bellows comprising a passageway for liquid flow.

7. A pump according to claim 1 in which the tube comprises a plurality of cylinders arranged along their longitudinal axes, the adjacent cylinders being of different diameters, the cylinders being joined end to end by means of an annular resilient seal.

8. A pump according to claim 7 in which the cylinders have alternate larger and smaller diameters.

9. A pump according to claim 1 in which the tube comprises a plurality of tyre-like segments, each segment containing a number of U-shaped leaf springs encased in a plastics material.

10. A pump according to claim 9 in which the plastics material is rubber.

11. Pumps as hereinbefore described with reference to Figs. 1 to 7 of the accompanying drawings.