Essentially the gas, being free to move between two or more similar devices remains under constant pressure, as required by the depth below the surface International Application WO 95/17555 as described, and its subsequent developments is a heavily engineered device, one that will not readily flex with the lateral movements of water as found below waves, it is not independent of the seabed and is not independent of tidal changes in mean sea level The base or centre of the device is fixed in its position with respect to the seabed A common problem with existing devices designed to harvest significant amounts of energy from the sea is their complexity and cost They are predominantly large structures, with rigid components, placed in a harsh environment There is little use of well-proven components Most devices proposed are very demanding in terms of engineering design, deployment and maintenance Other known devices which are used in the marine environment, although not designed for the conversion of wave energy to usable power, include that described in FR-A-2 488 339; which is designed to pump fluids from the sea-bed AMENDED SHEET Object of the Invention It is an object of this present invention to provide an improved device for extracting energy from sea waves or a swell in a body of liquid.
7, the variable buoyancy 6 is exerting a tension Ti; towards the surface, on Printed from Mimosa WO 99/28623 PCT/IE98/00101 the hydraulic actuator 8 This device is also suitable for reacting against a lever or pump type mechanism within a tank or process vessel Figure 2b shows the situation when the surface 5 is not flat, equivalent to the 5 occurrence of waves on a water surface The device 1 is now under a crest 10 of a wave As a result, the height of water column h2 is greater than hi The effect of this is the exertion of more pressure on the quantity of gas 7 According to Boyle’s Law pressure times volume (PV) is constant for constant temperature or, under conditions that will most probably favour adiabatic change, PV is constant where gamma tends towards 1 4 10 for air Hence, as the pressure has increased, the volume of gas 7 within the variable buoyancy 6 contracts.
Dolor De Muelas
The size of this resource has been estimated to be 219 gigawatts along the coats of the European Union, or more than 180 terawatt hours each year. Research and development into wave energy converters (WECs) over the past twenty-five years, plus the knowledge and practical experience gained from the off-shore 5 oil and gas industries, has now reached a stage where robust and effective wave energy converters with installed capacities of one megawatt and greater are being developed The wave energy resource may be split into three broad categories, based on where the energy from waves may be recovered 10 1 in the open sea, i e offshore 2 on or close to the shore line, i e on-shore or inshore 3 outside the normal area of breaking waves but not in the deep ocean, i e near shore A fourth category, not generally considered in the context of wave energy 15 converters, but which may be of relevance to this present invention, is waves or surges in a liquid contained in vessels and tanks The very large number of devices and concepts proposed to date has been classified and described in summary form for the Engineering Committee on Oceanic 20 Resources by the Working Group on Wave Energy Conversion (ECOR draft report, April 1998) This follows a similar classification based on the intended location, i e offshore, near shore to off-shore, and on-shore Wave Energy Converters (WECs) may also be classified in different ways 25 according to their operating principle and the ways in which they react with waves In terms of practical application, only a very few types of device are presently, or in the recent past have been, in use or under test in European waters By way of illustration, two different but overlapping classes will be briefly 30 commented on the Oscillating Water Column (OWC) devices and Point Absorbers, the latter being the relevant class in the present context Printed from Mimosa WO 99/28623 PCT/IE98/00101 3 OWC devices are typically those where the wave is confined in a vertical tube or a larger chamber and, as it surges back and forth, drives air through a power conversion device Megawatt-scale OWC devices are now at an advanced stage of development One such device, being built in a rocky gully on the western shore of Pico in the Azores, 5 is a reinforced concrete chamber partly open at one side to the waves, and with two turbines above and behind through which the confined air is forced These are specially developed Wells turbines (one with variable blade pitch) and on the whole would seem to be the best-developed and perfected conversion system available today It is, however, unlikely that any one such installation will have an installed capacity greater than two 10 megawatts and the number of suitable sites has to be extremely limited Point absorbers may react against the seabed (therefore necessarily sited near-shore), or be floating and self-reacting Theoretical analysis has greatly increased our understanding of point absorbers Point absorbers are usually axi-symmetric about a vertical axis, and by definition their dimensions are small with respect to the wavelength of the predominant wave The devices usually operate in a vertical mode, often referred to as ‘heave’ As such they are capable of absorbing energy arising from changes in the surface level rather than from 20 forward motion of breaking seas The theoretical limit for the energy that can be absorbed by an isolated, heaving, axi-symmetrical device has been shown to depend on the wavelength of the incident waves rather than the cross section of the device, i e from the wavelength divided by 2n Thus the wavelength is a critically important criterion, resulting in the attraction of locating the point absorber devices well outside the region of 25 breaking waves, and where they will be open to long wavelength ocean swell or ‘heave’ A point absorber device may react against the inherent inertia of one of its components, or against the bottom of the sea Thus, point absorbers may be deployed near-shore in contact with the sea-bed or, in the case of self-reacting devices, near-shore or off-shore Small-scale practical point absorbers such as fog horns and navigation buoys, both of which may incorporate OWCs, have been in use for decades Typically these have a power of a few hundred watts Printed from Mimosa One new point absorber device, now claimed to be capable of generating of the order of a megawatt, is described in International Application WO 95/17555 This is based on the buoyancy variations of a submerged, partly air filled, rigid vessel open at the bottom Initially the device is floating with neutral buoyancy at a certain depth If a wave passes above it the pressure around this vessel increases and water will flow into the vessel, displacing the air or gas inside (which is free to flow to a large reservoir or to similar devices linked by pipelines), decreasing the air volume in it and hence its buoyancy.
A lack of practical solutions or reasonable prospects of efficient and robust technologies, plus declining oil prices, led to a general disenchantment. Background Quest for economic sources of renewable energy The oil crisis in the early 1970’s was the impetus for much of the pioneering work into wave energy conversion. Summary of the invention Accordingly the invention provides: a wave energy conversion apparatus for harnessing energy from wave motion on the surface of a body of liquid comprising: 10 at least one buoyant member of variable buoyancy for holding a substantially constant mass of gas in an at least partially submerged position in the body of liquid such that as the volume of the substantially constant mass of gas changes with changes of pressure on said buoyant member caused by wave motion a change in buoyancy of the variable buoyant member results; and a conversion means for converting said change in buoyancy of the buoyant member to an energy output device.
- Problemas en algún órgano
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- Aplicación de cremas antiinflamatorias a base de árnica
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The term “wave motion” as used herein refers to both waves on a surface of a liquid and swell in a body of a liquid. The height I12 is equivalent to the height of the wave crest 10 plus any downward movement of the variable buoyancy 6 Both components of h2 act so as to increase the pressure on the elastic member 6 and cause a reduction in volume of the elastic member According to Archimedes’ Principle, as the volume of the elastic member 15 6 decreases and less liquid is displaced, the upthrust corresponding to the mass of water displaced will be lessened The change in buoyancy, caused by the reduction in volume of the variable buoyancy 6, results in less tension T2 being exerted on the hydraulic actuator 8 Figure 2c shows an equivalent situation for when the device 1 is under a trough 11 of a wave The height h3 is less than hi, such that less pressure is being exerted on the gas 7, with a resultant increase in the volume of the elastic member 6 In a similar manner to that described with relation to Figure 2b, hi is made up of two components, the depth of the trough 11 and the upward movement of the variable buoyancy 6 The increase in 25 buoyancy of the elastic member 6 results in more tension T3 being exerted on the actuator 8 The movement of the variable buoyancy 6, which results from using a flexible balloon type arrangement, under the crest and trough adds a dynamic effect to the static 30 effect caused by the passage of the passing wave The change in tension in the cable 9, arising from differing conditions illustrated Printed from Mimosa WO 99/28623 PCT/IE98/00101 11 in Figures 2b and 2c, is passed to the hydraulic actuator 8, displacing hydraulic fluid (not shown), which in turn powers a motor-generator set (not shown).