GB2093922A - Wave energy device - Google Patents

Abstract

The device has a hollow rigid body (10) with ports (11) each associated with a corresponding funnel (13) which terminates in an outlet (14) and an inlet (15) communicating with a respective conduit (16, 17). A flexible diaphragm (22) extending across each port (11) is oversize for its edge and, in repose, its central portion has a concave-convex cross-section. A wave impacting on the diaphragm (22) deflects it inwardly and pushes air up to the corresponding funnel (13) to the outlet (14). This air movement drives a generating device. Air is returned to the body (10) through conduit (17) and inlet (15). The shape of the diaphragm (22) maximises the displacement of air behind it and the diaphragm (22) has an optimum maintenance free life. Also disclosed is a method of making the diaphragm. <IMAGE>

Description

SPECIFICATION Wave Energy Device This invention relates to devices for extracting energy from waves or water'in seas or lakes.

There have been many types of proposal for the extraction of such energy but most rely on use of moving parts. Maintenance and replacement in the positions where such devices will be used is extremely difficult and any type of device which has no moving parts can be regarded as advantageous.

One such device is the so-called "Lancaster Flexible Bag" wherein wave energy is used to cause deflection of a flexible skin defining a closed volume. This deflection causes displacement of air in one direction or another through valve conduits and the displaced air is used to drive a generating device.

The Lancaster Flexible Bag may have a substantially rigid body with separated ports which are to be closed off by flexible diaphragms.

Various ports are joined through valves to common conduits running the length of the assembly, which may be very considerable with a large number of ports in each assembly.

The present invention is concerned with the design and method of manufacture of the flexible diaphragms which will close off these ports and which by their deflection will cause displacement of air within the ports and hence within the conduits.

The diaphragms should not be stretched flat across the ports because the deflection they would suffer upon pressure from a wave would be minimal. Rather, the diaphragms should be "oversize" for their periphery so that they can offer a maximum displacement in both directions (inwardly and outwardly over the plane(s) containing their periphery) under the action of the waves, thereby maximising the displacement of air behind them.

We have found, and are concerned in the invention to provide, a design of diaphragm and a method of making a diaphragm for this application which meets the various desiderata laid out above and provide the diaphragm with optimum maintenance-free life.

According to the invention we provide a diaphragm which is surrounded by a bead (which preferably substantially lies in a single plane) and which in at least its central portion has in repose a concave-convex cross section.

Such a diaphragm is to be sealed to a port in a wave energy device of the type mentioned and will then usually be at an angle to the vertical. The port to which it is fitted will have in order to maximise displacement of the air a taper to a narrow neck away from the diaphragm and the diaphragm will be mounted such that its concave portion in repose (concave seen from the outside of the device) is adjacent the floor of the port.

When so mounted the diaphragm may progressively roll from its lower portion towards its upper portion inwardly over the port, with progressively increasing support from the floor of the funnel behind the port.

The manufacture of such a diaphragm presents considerable difficulties. It has to be made of a material of considerable toughness and durability and must be made as far as possible free of localised stresses and wrinkles, at which tears would rapidly develop during flexion of the material. Forming the shape from unvulcanised material in a female concave mould by vacuum forming and curing is theoretically possible but presents great difficulties. The tension exerted in the material adjacent where it first enters into the cavity of the mould is liable to cause local stress, the probability of which is further increased because of the sticky and tacky nature of the unvulcanised material causes it to drag on the mould.We therefore propose in this invention to form the concave-convex diaphragm in a double convex mould the shape of one part of which is the inverse of the desired shape of one part of the diaphragm.

A proposal is to make the diaphragm from rectangularly superimposed plies of unvulcanised material in which unidirectional cords in the plies are respectively continuous from edge to edge of the diaphragm. The compound sheet so moulded may be made up of individual strips of single ply material laid in one layer side by side, with the strips of respective layers being at right angles.

The moulding is preferably achieved on the double convex mould by drawing the sheet onto the mould by marginal clamps (and also a clamp along a neutral line at the centre of the diaphragm) and by applying overall a shaped curing diaphragm by causing a vacuum between the latter and the mould.

A particular embodiment of the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 is a section and perspective view of a diaphragm mounted in a wave energy device, Figure 2 is a perspective view of a diaphragm in its position of repose, Figure 3 shows cross sections through the diaphragm of Figure 1, Figure 4 illustrates diagrammatically the make up of the material from which the diaphragm is made, and Figure 5 is a section through a mould used in the formation of the diaphragm.

Figure 1 shows part of a wave energy device 10 in which individual ports 11 are presented in a wall 1 2 of a wave energy device which floats or is otherwise supported at the surface of a body of water.

Behind each port is a doubly tapering funnel 13 which leads to an exit 14 and an inlet 1 5 respectively fitted with one-way valves. The outlet 14 and 1 5 of each of the funnels behind respective ports 11 are joined in common through conduits 16,17 and are linked to a generating device. Each port 11 is closed off by a flexible diaphragm 20 and the present invention is concerned with the nature and method of construction of such diaphragms.

The function of each diaphragm is to be deflected by the impact or pressure of a wave upon it so as to be displaced inwardly and push air up the funnel 13 through the outlet 14 to the high pressure conduit 1 6. After use in the generating device air may be returned down the low pressure conduit 1 7 to flow into the funnel 1 3 when the diaphragm moves outwardly.

The wall 12 in which the ports 11 are situated is inclined at an angle to the vertical and the lower floor 21 of the funnel is somewhat upwardly inclined so that there is an acute angle between them, seen in cross section.

The diaphragm 20 has at least at the central portion of its length an S shaped cross section seen at 22, Figure 1 and upon inward pressure it is displaced inwardly with the lower part of the diaphragm (that which is concave into the funnel) progressively laying itself along the lower floor 21 until the diaphragm reaches the position shown in dotted lines at 23, Figure 1.

The concave-convex S shape section 22 is characteristic of the diaphragm embodying the present invention when it is in its condition of repose, which is seen in perspective in Figure 2. It can be seen that adjacent the minor edges of the diaphragm which are given the references 24, 25 the piece which forms the diaphragm is substantially planar but as the central region of its length is reached the cross section becomes increasingly concave-convex in a serpentine form.

This development is seen in Figure 3 where respective lines labelled 0--5 are sections on the lines 0--0,...55-5 of Figure 2. It will be seen that there is a neutral line 25 in the diaphragm in repose which is in the plane of its peripheral bead.

This peripheral bead will in use normally be supported planar in a wall such as 12 when it is sealed into a port 11, but some degree of non planarity in the bead when in use is permissible without affecting the principle of operation of the diaphragm.

The diaphragm seen in Figure 2 is formed from a two ply sheet of cord material. These diaphragms are envisaged to be of substantial size for example 1 5 metres in length by 7.5 metres in depth. Cord material cannot be prepared in such widths and so the composite sheet is made by laying strips with long strips 30 of single ply unidirection corded rubber material in the longitudinal direction of the diaphragm and lying crosswise perpendicularly to the direction of those cords, an underlayer of strips 31 of single ply unidirectionally corded material. The cords may be of conventional tyre cord material or may be Kevlar (Registered Trade Mark) with a specification of 78 Newtons breaking load per cord and 720 ends per metre.This composite of unvulcanised material is simply mangled to come under a modest pressure e.g. 50 p.s.i. to give it cohesion, and is then moulded and cured.

To form the concave-convex repose shape of the diaphragm it would be possible to use a concave-convex mould, but drawing the material into a concavity as conventionally done by vacuum may cause the formation of undue stress areas in the material which, in use, would generate tears and failures.

We therefore use a double convex mould, a section through the maximum curvation of which (e.g. corresponding to section 5.5 of Figure 2) is seen in Figure 5.

A suitable material for forming the shape of the mould 32 is concrete. The composite sheet formed from the strips 30 and 31 and here given the reference 33 is stretched over the double convex mould. This may be achieved by applying tension in the diagonal directions with spreading of the material on the mould and appropriate thinning or slight thickening of edge portions of it which hang down around vertical wall section 34 of the mould. The smooth transition from this section into the curvature will be noted. A bead wire or other bead reinforcement 35 may be positioned over the sheet 33 on this portion 34 and the sheet 33 turned back over it in a per se conventional manner. The dip between the two convexities 36 and 37 of the mould is equipped with a holding bar 38 which presses the sheet down into the dip which correspond to the neutral line 25.

The sheet is sealed onto the mould for curing by a rubber curing diaphragm 39 which may be clamped around the extreme bottom of the mould by a ring or other clamping means 40 and underneath which vacuum is applied through duct and ports such as 41.

When the diaphragm has been cured in the conventional fashion it is taken off the mould and one of its convexities such as convexity formed of mould part 36 is readily inverted along for example dotted line 41 to give a diaphragm of the formation in repose indicated in Figures 2 and 3.

If the sheet 33 is of a material which will shrink during vulcanisation and cure, it may be preferable not to form the bead before cure but to allow the portion of the sheet overlapping the mould part 34 compensate for any shrinkage experienced in the main area of the sheet. Then, any irregularities in that edge are trimmed and a bead is formed upon it in a separate operation, again in a manner which is in itself known.

Even though the method described here will minimise the amount of wrinkles or undue stress points in the finished diaphragm it is never possible to eliminate these completely. From the point of view of containing the air pressure which is to be built up behind the diaphragms it is the cords which run vertically (in the strips 31 in this embodiment) which are of the greater importance and a preferred arrangement will be to use a high modulus cord for these strips that are more extensible and cords such as nylon for the layer which runs horizontally (strips 30). If the latter are normally held under slight tension their elasticity may be enough to accommodate any mis-match and to avoid the formation of wrinkles.

The differential in properties in the two directions can also be attained by using two piles of cord intersecting at an angle other than at right angles. For example, if the angle between the cords and each ply is 600, then the material will have three times the strength and three times the elastic modulus in the direction bisecting the smaller angle than at right angles. It has been found with the proposed shape that a satisfactory diaphragm can be built out of two such plies using angles of between 40--70 0, i.e. 20--3 to the vertical plane. The required shape is produced at the ends by stretching the material in the longitudinal direction which brings about the required reduction in perimeter.

Claims (11)

Claims

1. A wave energy device comprising a hollow rigid body having at least one port therein, and a flexible diaphragm extending across the port, the diaphragm being adapted to deflect relative to the body under the influence of a wave, so that the internal volume of the body is changed for energy generation, at least the central portion of the diaphragm being oversize for its edge and having, in repose, a concave-convex cross-section.

2. A wave energy device according to Claim 1, wherein a bead surrounds the periphery of the diaphragm, the bead being sealed to the port.

3. A wave energy device according to Claim 1 or 2, wherein the periphery of the diaphragm lies in a single plane.

4. A wave energy device according to any one of the preceding claims, wherein at least one funnel is provided in the body, corresponding to the at least one port each funnel tapering away from the corresponding port.

5. A wave energy device according to any one of the preceding claims, wherein, in use, the concave part of the diaphragm is adjacent the bottom of the body.

6. A wave energy device according to any one of the preceding claims, wherein the diaphragm is made from rectangularly superimposed plies of unvulcanised material unidirectional cords in the plies being continuous from edge to edge of the diaphragm.

7. A wave energy device according to claim 6, wherein each layer of the diaphragm comprises a plurality of individual strips of single ply material laid side by side, strips of respective layers being at right angles.

8. A wave energy device substantially as herein described with reference to and as illustrated in the accompanying drawings.

9. A method of making a diaphragm for a wave energy device according to any one of claims 1 to 8, comprising forming the diaphragm in a double convex mould, the shape of one part of which is the inverse of the desired shape of one part of the diaphragm.

10. A method according to claim 9, wherein the sheet to form the diaphragm is drawn onto the mould by marginal clamps and a clamp along a neutral line at the centre of the diaphragm.

11. A method according to claim 9 or claim 10, wherein a shaped curing diaphragm is applied onto the mould over the sheet forming the diaphragm.

1 2. A method according to claim 11 , wherein a vacuum is applied between the curing diaphragm and the mould.