WAVE ENERGY CONVERTER CELL

Abstract

A wave energy converter cell for a pressure differential converter system includes a turbine. The cell includes a cell body defining an aperture and a membrane sealing the aperture wherein the membrane has a distensible working surface extending across the aperture. The membrane may be planar and may be pre-strained over the aperture.

Claims

1-38. (canceled)

39. A wave energy converter cell for a pressure differential converter system comprising a turbine, the cell comprising a cell body defining an aperture and a membrane sealing said aperture wherein said membrane has a working surface covering said aperture and wherein said working surface is distensible such that its surface area can increase by an amount of 5% or greater.

40. A wave energy converter cell according to claim 39 wherein the working surface has a mechanical stiffness which is substantially equal and opposite to its membrane hydrostatic stiffness.

41. A wave energy converter according to claim 39 wherein the working surface of the membrane is pre-strained across the aperture in a rest configuration.

42. A wave energy converter according to claim 41 wherein the chord ratio equals about 1 such that the membrane is substantially planar across the aperture in the rest configuration.

43. A wave energy converter according to claim 39 wherein the membrane comprises a single, unitary surface which is planar across at least part of the aperture.

44. A wave energy converter according to claim 39 wherein the working surface of the membrane comprises a homogenous material.

45. A wave energy converter according to claim 39 wherein the thickness of the working surface of the membrane varies.

46. A wave energy converter according to claim 39 wherein the membrane comprises a plurality of stacked thinner membranes.

47. A wave energy converter according to claim 39 wherein the cell body comprises an internal surface which, along with the distensible working surface of the membrane defines a cell volume.

48. A wave energy converter according to claim 47 wherein the perimeter of the internal surface comprises a forward curved edge and a rearward curved edge spaced by opposing transverse linear edges wherein the forward, rearward and transverse edges are all in the same plane.

49. A wave energy converter according to claim 47 wherein the perimeter of the internal surface comprises a forward curved edge and a rearward curved edge spaced by opposing transverse edges wherein at least one of the forward and/or rearward edges are deflected above or below the plane of the opposing transverse edges and wherein the membrane is deflected and tensioned over the curved edge of the internal surface to seal the membrane to the curved edge thereby sealing the aperture.

50. A wave energy converter according to claim 39 wherein a perimeter portion of the membrane is secured to a support structure and/or wherein the perimeter portion of the membrane is thicker or thinner than the working surface of the membrane.

51. (canceled)

52. A wave energy converter according to claim 50 wherein the perimeter portion of the membrane comprises reinforcing elements.

53. A wave energy converter according to claim 50 wherein the perimeter portion of the membrane comprises a plurality of circumferentially-spaced membrane connectors.

54. A pressure differential wave energy converter system comprising at least one cell according to claim 39 and a closed power take-off system comprising a turbine.

55. A method of manufacturing a wave energy converter cell for a pressure differential converter system comprising a turbine, the cell comprising a cell body defining an aperture, the method comprising providing a membrane having a distensible working surface capable if increasing its surface area by an amount of 5% or greater and sealing the membrane over the aperture.

56. A method according to claim 55 comprising providing a substantially planar distensible membrane and sealing the substantially planar membrane over the aperture.

57. A method according to claim 55 comprising providing a membrane having a single, unitary planar surface and sealing the membrane over the aperture.

58. A method according to claim 55 comprising pre-straining the working surface of the membrane across the aperture.

59. A method of converting wave energy to electrical energy using a pressure differential converter system according to claim 54, the method comprising distending the working surface of said membrane by an amount of 5% or greater to drive an energy transfer fluid from the cell to the turbine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0117] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0118] FIG. 1 shows a first embodiment with the membrane in a rest configuration;

[0119] FIG. 2 shows the first embodiment with the membrane in a fully-deflated configuration;

[0120] FIG. 3 shows the first embodiment with the membrane in a fully-inflated configuration;

[0121] FIG. 4 shows part of the perimeter portion of the membrane; and

[0122] FIG. 5 shows a second embodiment with the membrane in a fully-inflated configuration.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES

[0123] FIGS. 1 to 3 show a cross-section through a wave energy converter cell 1. The cell 1 is for use in a pressure differential converter system having a power take-off system comprising a turbine.

[0124] The cell 1 comprises a cell body 2 having an internal concave surface 3 which provides a basin- or bowl-shaped cell body 2. The cell body 2 may be formed of stainless steel or concrete, for example, and may be treated to improve corrosion resistance from salt water.

[0125] The concave surface 3 is encircled by a perimeter/edge 4 which includes a lower forward linear edge 4a and an upper rearward linear edge 4b. Not shown are opposing curved transverse edges which space the forward and rearward edges 4a, 4b (to form an oval race track shaped edge when viewed from directly above the aperture). The forward edge 4a and rearward edge 4b are in the same plane as the transverse edges (although in other embodiments, one or both may be deflected above or below the plane of the transverse edges). The perimeter/edge 4 of the internal surface 3 defines an aperture. The aperture may be substantially circular or elliptical. The perimeter/edge 4 encircling the aperture is a rolled or curved bearing surface having a bend radius.

[0126] The cell 1 further comprises a distensible membrane 6 which has a working surface 6a which is provided across and seals the aperture defined by the perimeter/edge 4. The working surface 6a of the membrane, along with the internal concave surface 3 of the cell body 2 defines a cell volume 5. The cell volume 5 contains air as an energy transfer fluid.

[0127] FIG. 1 shows the cell 1 when the membrane 6 is in the rest configuration. This is the configuration when there is no hydrostatic pressure on the membrane 6. It is the configuration that the membrane 6 will adopt at least prior to installation of the cell subsea and with internal air pressure equal to external air pressure.

[0128] The chord length of the membrane in the rest configuration shown in FIG. 1 is about 1 i.e. the length of the (working surface 6a) of the membrane 6 between the lower forward edge 4a and upper rearward edge 4b is substantially the same as the straight-line distance between the lower forward edge 4a and upper rearward edge 4b. In effect, this means that the working surface 6a of the membrane 6 is substantially planar across the aperture.

[0129] This significantly reduces manufacturing complexity and costs of the membrane 6 as a planar membrane can be easily cast/moulded.

[0130] The membrane 6 is formed of a unitary piece of natural rubber having a homogenous distribution of carbon black. There are no joins and no fibrous/mesh reinforcements, at least not in the working surface 6a of the membrane 6. It may have a Shore A Hardness of around 60.

[0131] In alternative embodiments (not shown here), the membrane 6 may be formed of a series of stacked thinner membranes.

[0132] The membrane 6 further comprises a perimeter portion 6b which circumscribes the working surface 6a of the membrane 6.

[0133] The thickness of the membrane 6 varies. It is thicker in both a central portion 14 of the working surface 6a and in the outermost regions of the perimeter portion 6b. The thickness of the membrane in the un-thickened portions may be around 50 mm.

[0134] The perimeter portion 6b has a scalloped edge 7 (as shown in FIG. 4) which is reinforced with a perimeter rope 8. The scalloped edge 7 comprises reinforcing elements 9 which are embedded within the rubber forming the perimeter portion 6b. Eyelets 16 are provided at the peaks 7a of the scalloped edge 7 and rope tethers 10 secure the perimeter portion 6b to clamps 11 provided on a skirt 12 which depends from the perimeter/edge 4. The skirt 12 (which is also formed of stainless steel and is formed integrally with the rest of the cell body 2) comprises perforations 13 to reduce the weight of the cell body 2.

[0135] Once in position on the cell body 2, the membrane 6 is pre-strained by applying a tensile force in the plane of the membrane 6. The tensile force is applied using the rope tethers 10 to stretch the working surface 6a and perimeter portion 6b of the membrane 6. A pre-strain of around 10-50% may be applied.

[0136] The perimeter portion 6b of the membrane 6 is deflected and tensioned over the curved bearing surface 4 of the internal surface 3 to seal the membrane 6 to the curved bearing surface 4 thereby sealing the aperture. The membrane 6 is tensioned to conform to the curved bearing surface 4 of the internal surface 3. By deflecting the membrane around a curved bearing surface, the bending stress in the membrane 6 reduced because it is limited by the curve of the curved bearing surface 4.

[0137] By forming the seal by tensioning the membrane 6 over the curved bearing surface 4, a “one-sided seal” is provided i.e. an outer surface 6c of the membrane 6 in the region of the seal is exposed.

[0138] The cell volume 5 is variable by distension of the working surface 6a of the membrane 6 away from the internal surface 3 (in an inflation stroke) to a fully-inflated configuration caused by a decrease in hydrostatic pressure resulting from a wave trough (shown in FIG. 2) and towards the internal surface 3 (in a deflation stroke) to a fully-deflated configuration caused by an increase in hydrostatic pressure resulting from a wave peak (shown in FIG. 3). During a deflation stroke, air from the cell volume 5 is forced out of the cell volume through an outlet (not shown) comprising a one-way valve in the internal concave surface 3. The flow of air causes rotation of the turbine and generation of electrical energy. During an inflation stroke, the cell volume 5 is replenished with air through an inlet (not shown) comprising a one-way valve in the internal concave surface 3. Where the turbine is a bidirectional turbine, the return flow of air also causes rotation of the turbine and generation of electrical energy.

[0139] A complete operation stroke/cycle of the membrane 6 comprises a complete inflation and deflation stroke e.g. from the fully-inflated configuration (FIG. 3) to the fully-deflated configuration (FIG. 2). The surface area and chord length ratio are both greater in both of the fully-inflated and fully-deflated configurations than in the rest configuration. They are also greater in all intermediate positions between the fully-inflated and fully-deflated configurations.

[0140] This means that the membrane 6 is constantly under strain during both the inflation stroke and the deflation stroke. Given that the membrane 6 is also pre-strained in the rest configuration, it can be seen that the membrane 6 is constantly under strain during the entire operational cycle. This means that creasing and buckling in the membrane 6 are eliminated thus eliminating bending stresses in the membrane 6.

[0141] Furthermore, by using a distensible membrane 6, the PV stiffness becomes dependent not only on the hydrostatic stiffness but also on the mechanical stiffness of the membrane 6. The mechanical stiffness (which is attributable in part to the elastomeric nature of the distensible rubber membrane) can be used to off-set the hydrostatic stiffness. The mechanical stiffness may be equal and opposite to the membrane hydrostatic stiffness (as previously defined herein).

[0142] The pre-straining of the membrane 6 increases the minimum strain in the membrane 6 and improves the fatigue life of the membrane by preventing the undesirable cycling between positive and negative strain the during an operational cycle (i.e. during the inflation and deflation strokes).

[0143] In the embodiment shown in FIGS. 1 to 3, damage to the membrane 6 by over inflation is avoided by allowing venting of the energy transfer fluid (air) through the seal between the membrane 6 and the curved bearing surface 4 (thus breaking the seal) during excessive wave conditions.

[0144] In a second embodiment shown in the fully-inflated configuration in FIG. 5, the cell 1 further comprises a meshed, domed cage 15 that defines the inflation limit of the membrane 6. The cage 15 extends from the cell body away from the aperture. In this way, during any excessive inflation, the working surface 6a of the membrane 6 will abut an inner surface (e.g. a concave inner surface) of the cage 15 thus preventing further distension.

[0145] It will be understood that the disclosure is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.