GB2045362A

GB2045362A - Wave power energy system

Info

Publication number: GB2045362A
Application number: GB8002424A
Authority: GB
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1979-01-30
Filing date: 1980-01-24
Publication date: 1980-10-29
Also published as: GB2045362B

Abstract

Leading and trailing plates 10, 12 are suspended in water normal to the direction of wave movement and are connected together at a separation of half a mean wavelength, by rods 14 which permit limited relative movement and adjustment of the separation of the plates. Plate 15 co- operates with plate 10 to form passage 16 in which the water level rises and falls. Air inducted through check valve 19 and exhausted through valve 20 drives turbines 24 and electrical generator 21. A horizontal plate 25 may be attached to plate 10 to inhibit vertical movement. <IMAGE>

Description

SPECIFICATION Wave power energy systems The present invention relates to wave power energy systems.

Amongst many ways of obtaining energy from renewable sources presently under consideration, wavepower has many attractions for countries such as the United Kingdom which have relatively long coastlines. One of the problems in extracting energy from waves arises from the fact that, to maximise the power obtainable under all wave conditions at all states of the tide, energy conversion apparatus is preferably sited some position off shore. This means that, in general, floating devices must be used, and these must in general include two portions one of which is driven to and fro by the waves, the other of which stays relatively stationary to provide an inertial reference against which the driven portion can act.

According to the present invention a wave power energy system includes a leading plate vertically suspended by floats in water normal to the direction of wave movement, a trailing plate connected parallel to and half a mean wavelength from the leading plate, and a standing wave device connected to the leading plate for converting movement of the waves forward of the leading plate into energy.

Means connecting the leading and trailing plates preferably allow for some relative vertical movement of the plates, to ease stresses, and preferably include means for varying the spacing of the plates according to the average wavelength occurring at any time.

The effect of having two plates, joined effectively rigidly, together at a spacing of half a wavelength is to reflect waves meeting the leading plate, setting up a standing wave having twice the amplitude of the incoming wave, and leaving complete calm immediately aft of the trailing plate. The horizontal wave forces on the leading and trailing plates are at all times almost equal and opposite, with the result that there is no horizontal motion during operation of the apparatus. In one method of minimising vertical movement of the leading plate a horizontal plate is secured to its base deep under water.

It will be realised that, in practice, there is considerable variation about the average wavelength under normal sea conditions, but it has been found that pressure variations on the leading and trailing plates are such that overall forces tending to induce horizontal movement are very small, and therefore the structure remains virtually stationary in the sea.

The standing wave device is preferably of the type wherein movement of waves forward of the leading plate is used to drive air through air turbines which drive an electrical generator, or to pump water to a water turbine.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing which shows an elevation, in section, of a wave power energy conversion device according to the invention.

A wave power energy system has a leading plate 10 supported in water by a float 11 separated by half a wavelength from a trailing plate 12, supported by a float 13. The plates 10, 12 are secured together by rods 14 in such a manner that a limited amount of relative motion between the plates is possible. Mounted on the leading plate 10 is a casing 1 5 which extends forward of the plate 10 and downwardly into the water, and forming with the plate 10, a passage 16 which connects, remote from the water, to two passages 17, 18, having non-return valves 19, 20 respectively. The one-way valves 1 9, 20 are of opposite sense. Mounted within the float 11, is an electrical generator 21, secured by a shaft 22 to turbines 23, 24 in the passages 1 8, 1 7 respectively.The turbines 23, 24 are designed to rotate when air passes through them in one direction, and to free-wheel when no air is passing. The arrangement of the turbines 23, 24 and non-return valves, 20, 19 respectively, is such that the turbines rotate in the same direction, one rotating when the other is freewheeling.

Horizontally secured to the base of leading plate 10 is a stabiliser plate 25, which extends an equal distance each side of the plate 10.

In operation the system is moored in the sea with the plates 10, 12 normal to the direction of wave motion. As the plates 10, 12 are half a wavelength apart the overall pressures on them will cancel out, leaving a calm area aft of plate 12, and totally reflecting waves from plate 10. This results in a standing wave having twice the amplitude 2h of the incoming wave amplitude h being set up in front of plate 10. Movement of the standing wave in the passage 1 5 causes air to be expelled from, and drawn into the passage. As illustrated, when the wave is rising in the passage 1 6 air is driven through channel 18 and non-return valve 20, driving turbine 23. As the standing wave is falling, air is drawn through the non-return valve 19 and channel 17, driving turbine 24.The turbines 23, 24 drive the generator 21 through the shaft 22, and electrical energy is led to shore through electrical cables, which for convenience are not shown. Large vertical movements of the leading plate 10 are prevented by the presence of the horizontal plate 25. In practice a plurality of turbines 23, 24 will be mounted along the length of the leading plate 10.

In a modified version of the invention the leading plate 10 (or this and the trailing plate 12) may be curved according to the law y = log cos x, where x is the horizontal and y the vertical coordinate, as illustrated by dotted line 26.

1. A wave power energy system which includes a leading plate vertically suspended by floats in water normal to the direction of wave movement, a trailing plate connected parallel to and half a mean wavelength from the leading plate, and a standing wave device connected to the leading

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Wave power energy systems The present invention relates to wave power energy systems. Amongst many ways of obtaining energy from renewable sources presently under consideration, wavepower has many attractions for countries such as the United Kingdom which have relatively long coastlines. One of the problems in extracting energy from waves arises from the fact that, to maximise the power obtainable under all wave conditions at all states of the tide, energy conversion apparatus is preferably sited some position off shore. This means that, in general, floating devices must be used, and these must in general include two portions one of which is driven to and fro by the waves, the other of which stays relatively stationary to provide an inertial reference against which the driven portion can act. According to the present invention a wave power energy system includes a leading plate vertically suspended by floats in water normal to the direction of wave movement, a trailing plate connected parallel to and half a mean wavelength from the leading plate, and a standing wave device connected to the leading plate for converting movement of the waves forward of the leading plate into energy. Means connecting the leading and trailing plates preferably allow for some relative vertical movement of the plates, to ease stresses, and preferably include means for varying the spacing of the plates according to the average wavelength occurring at any time. The effect of having two plates, joined effectively rigidly, together at a spacing of half a wavelength is to reflect waves meeting the leading plate, setting up a standing wave having twice the amplitude of the incoming wave, and leaving complete calm immediately aft of the trailing plate. The horizontal wave forces on the leading and trailing plates are at all times almost equal and opposite, with the result that there is no horizontal motion during operation of the apparatus. In one method of minimising vertical movement of the leading plate a horizontal plate is secured to its base deep under water. It will be realised that, in practice, there is considerable variation about the average wavelength under normal sea conditions, but it has been found that pressure variations on the leading and trailing plates are such that overall forces tending to induce horizontal movement are very small, and therefore the structure remains virtually stationary in the sea. The standing wave device is preferably of the type wherein movement of waves forward of the leading plate is used to drive air through air turbines which drive an electrical generator, or to pump water to a water turbine. One embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing which shows an elevation, in section, of a wave power energy conversion device according to the invention. A wave power energy system has a leading plate 10 supported in water by a float 11 separated by half a wavelength from a trailing plate 12, supported by a float 13. The plates 10, 12 are secured together by rods 14 in such a manner that a limited amount of relative motion between the plates is possible. Mounted on the leading plate 10 is a casing 1 5 which extends forward of the plate 10 and downwardly into the water, and forming with the plate 10, a passage 16 which connects, remote from the water, to two passages 17, 18, having non-return valves 19, 20 respectively. The one-way valves 1 9, 20 are of opposite sense. Mounted within the float 11, is an electrical generator 21, secured by a shaft 22 to turbines 23, 24 in the passages 1 8, 1 7 respectively.The turbines 23, 24 are designed to rotate when air passes through them in one direction, and to free-wheel when no air is passing. The arrangement of the turbines 23, 24 and non-return valves, 20, 19 respectively, is such that the turbines rotate in the same direction, one rotating when the other is freewheeling. Horizontally secured to the base of leading plate 10 is a stabiliser plate 25, which extends an equal distance each side of the plate 10. In operation the system is moored in the sea with the plates 10, 12 normal to the direction of wave motion. As the plates 10, 12 are half a wavelength apart the overall pressures on them will cancel out, leaving a calm area aft of plate 12, and totally reflecting waves from plate 10. This results in a standing wave having twice the amplitude 2h of the incoming wave amplitude h being set up in front of plate 10. Movement of the standing wave in the passage 1 5 causes air to be expelled from, and drawn into the passage. As illustrated, when the wave is rising in the passage 1 6 air is driven through channel 18 and non-return valve 20, driving turbine 23. As the standing wave is falling, air is drawn through the non-return valve 19 and channel 17, driving turbine 24.The turbines 23, 24 drive the generator 21 through the shaft 22, and electrical energy is led to shore through electrical cables, which for convenience are not shown. Large vertical movements of the leading plate 10 are prevented by the presence of the horizontal plate 25. In practice a plurality of turbines 23, 24 will be mounted along the length of the leading plate 10. In a modified version of the invention the leading plate 10 (or this and the trailing plate 12) may be curved according to the law y = log cos x, where x is the horizontal and y the vertical coordinate, as illustrated by dotted line 26. CLAIMS

1. A wave power energy system which includes a leading plate vertically suspended by floats in water normal to the direction of wave movement, a trailing plate connected parallel to and half a mean wavelength from the leading plate, and a standing wave device connected to the leading plate for converting movement of the waves forward of the leading plate into energy.

2. A wave power energy system as claimed in Claim 1 wherein the standing wave device is of the type wherein movement of waves forward of the leading plate is used to drive air through air turbines.

3. A wave power energy system as claimed in Claim 2 wherein the air turbines drive an electrical generator.

4. A wave power energy system as claimed in Claim 1 wherein movement of waves forward of the leading plate is used to pump water to a water turbine.

5. A wave power energy sustem as claimed in any one of Claims 1 to 4 wherein the means connecting the leading and trailing plates allows for some relative vertical movement of the plates.

6. A wave power energy system as claimed in any one of Claims 1 to 5 wherein the means connecting the leading and trailing plates includes means for varying the spacing of the plates.

7. A wave power energy system as claimed in any one of Claims 1 to 6 including a horizontal plate secured to the lower end of the leading vertical plate.

8. A wave power energy system which is constructed substantially as herein described with reference to the accompanying drawing.