In another preferred form, particularly suited for applications of the kind described herein, in which the working fluid is a gas such as air, the reversal of the blade pitching is by means responsive to a pressure transducer disposed to detect the point of reversal of the gas flow. It will therefore be appreciated that most prior art turbines suited to this type of application are often quite complex in design and usually have severe limitations in relation to operating conditions and/or efficiencies. Some later prior art devices have attempted to overcome this problem by effectively installing two monoplane Wells turbines in series resulting in a bi-plane turbine.
These prior art turbines also usually rely on a low revving high mass construction in order to ensure smooth continuous rotation under periodically reversing driving air flows of the kind contemplated. In the second case most prior art turbines are designed for constant velocity rotation in response to fluid flow in one direction only, and as such are unable to operate continuously in response to the reversing fluid flow conditions present in wave powered applications of the kind discussed above. Desirably, the above discussed maximum included angle is adjustable and further can preferably be reversed in synchronization with the reversing fluid flow, to thereby optimize the angle of attack for the fluid flow in both directions. It should be noted that the mechanism for adjusting the blade pitch is preferably configured such that the pitch can be automatically reversed in synchronization with he reversing fluid flow through the rotor, so that the angle of attack is optimized in both directions.
30 and −30 and is reversible to correspond with the reversing fluid flow. Disposed at or closely adjacent the plan location 42 circumscribing the harnessing region is an air compression chamber 43. The chamber has a generally submerged water inlet 44 and is sized such that on admission of the periodically oscillating waves a volume of air 45 is thereby displaced to generate a correspondingly periodic reversing air flow. In use, the incoming waves are focused so as to magnify the periodic vertical peak to trough displacement of the waves adjacent the location 42. In this manner, a reciprocating body or column of water oscillates within the air compression chamber 43 via the water inlet 44, thereby acting like a piston on the volume of air 45 thereabove. More particularly, the invention relates to wave powered energy extraction systems and the components thereof, in which the oscillating ocean wave motion is used to displace a volume of air to drive a wind operated turbine connected to an electrical generator.
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While this modified system solves the stalling problem, it does so at a penalty to the overall efficiency. If the energy is initially scattered due to a very choppy and irregular incoming wave, then some energy will be scattered away from the focus or foci 9 and 10. The loss of energy due to this or to any of the above-mentioned conditions can be lessened by choosing the focal length appropriately, so that the waves do not have time or the space in which to vary greatly within the parabolic domain. Dolor de espalda tensional . DISCLOSURE OF THE INVENTION According to a first aspect of the invention there is provided a plane wave focusing and amplifying structure, said structure comprising an open sided bay bounded by a generally upright wall, the wall being configured at its inner periphery to define in plan section from the bay opening two converging arms of generally part parabolic curvature, wherein the axes of symmetry of each said paraboli from which the arms are derived are parallel and the arms are joined adjacent their converging ends to form a shared apex, said wall being oriented to admit an advancing wave front in a direction generally parallel to said axes of symmetry, so that upon reflection from the wall the wave converges to an energy harnessing region near the apex at or adjacent the focus of each of said paraboli, thereby amplifying the vertical displacement of the wave at that region.
Once the section of the plane wave enters the domain of the parabola, the sea bottom should ideally be reasonably flat or planar across the axis of the parabola or paraboli, so as not to disturb the wave direction, and of sufficient depth or otherwise configured to prevent the wave crests from breaking prior to entering the harnessing region as they grow due to non-linear effects. Desirably, the air compression chamber is configured to converge from the water inlet toward the air outlet so as to accelerate the air flow. This is because it sacrifices the first set of blades by allowing them to correspondingly stall and shut down, the second set of blades then continuing operation at a reduced pace and efficiency. This is due to the total air flow rate having now been decreased and smoothed out by the stalling and interruption of the air flow by the first turbine.
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A transducer 48 may be positioned within the air outlet 46 to detect a change in the gas flow. There may also be losses due to interfering wave reflection from coastal structures located adjacent the parabolic bay and irregularities in the sea bed. In other preferred forms, the air compression chamber outlet and/or the shrouding and/or stators associated with the turbine, may include guide vanes to optimize the direction of air flow into and/or out of the turbine. Others include various means to alter the formation of the sea bed to controllably disrupt the wave propagation, so as to thereby maximize the wave amplitude at a predetermined location. These parameters include the aspect ratio of the blades (chord ratio), the chord length of the blade, the solidity of the turbine (effectively a blade length to hub diameter ratio), the number of blades, and the maximum angle through which the blades can turn to the air flow (ie.
One example that has been proposed as suitable to one particular application has a blade chord ratio of 18%, a chord length of 0.4 m, a hub diameter 1.2 meters, a blade length of 0.45 m, a total of 12 blades and a maximum included angle between the chordal plane of the blades and the hub axis of 30°. The preferred blade profile comprises two merged front half portions of a standard NACA 65-418 aerofoil. The original Wells turbine was of a monoplane axial fan type structure having radially extending blades of an aerofoil section that are generally symmetrical about the chord line, where the blades are fixed with their planes of zero lift normal to the axis of the rotor. FIELD OF THE INVENTION The present invention relates in general to systems for harnessing and converting the energy from ocean waves to more useable energy forms such as electric power.
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This is defined as the energy harnessing region shown generally at 12 which in FIG. The general aim will be to optimize local conditions to maximize the wave magnification, ideally without the waves breaking prior to entering the harnessing region. In the preferred form, the system utilizes the parabolic wave focusing device of the first aspect of the invention and the unidirectional turbine of the second aspect of the invention. Sintomas dolor muscular . The potential of a wave focusing device of this kind is significant, computer simulations indicating that 24% more energy flows into the parabolic domain than exists in a non focused wave of a length corresponding to the opening width of the parabola. It should be noted that there are a few conditions which need to be met so as to achieve maximal energy focusing with the generally parabolic or part parabolic wave focusing and amplifying structure described above.
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7 and 8. In this embodiment, each of the blades 23 are connected to the central hub 21 by means of a central spigot 28 or the like which, by means of some appropriate internal mechanism, facilitates rotation of the blade to thereby vary its pitch. In this manner it is possible while the turbine is rotating at high speed, to vary the inclination of the blades relative to the axis of the rotor by means of the gear mechanism described. The sleeve 29 of the central spigot 28 of the blade 23 has at its end a smaller bevel gear 34 which engages the annular bevel gear 33. A similar arrangement is provided for each blade. However, it is appreciated that in reality there will be losses that will prevent the maximum theoretical energy levels from being obtained. BACKGROUND OF THE INVENTION Concerns regarding the limited resources of traditional combustible hydrocarbon fuel sources and the damaging emissions resulting from their use, has prompted considerable research into sustainable non-polluting energy sources such as waves, wind, tidal, geothermal and solar.
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6 has the chordal plane of each of the blades straightly aligned with or parallel to the central hub axis 22, that is at an included angle of 0°. In this manner, air flow entering the turbine from either axial direction will have the same angle of incidence with the rotor blades 23 and effect the same resultant rotation of the rotor as marked. This is not generally a major concern providing the wave focusing structure is correctly oriented at installation, as waves at the coast do not vary their angle of incidence greatly due to the approach bathometry. For example, one such system utilizes oscillating floating paddles, the motion of which is converted directly or indirectly to electrical power. Preliminary investigations have indicated that for one particular application a depth at the bay opening of approximately 6 meters should be sufficient in most but the biggest of surf conditions.
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It is an object of the present invention to provide a wave energy extracting system and/or one or more of the components thereof, which overcomes or at least ameliorates one or more of the above discussed disadvantages of the prior art, or at least offers a useful alternative thereto. In the first case, most of the prior art wave focusing devices have relied on planar reflection of the wave front and/or channelling of the wave front through a narrowed opening such that the vertical displacement or amplitude of the wave is magnified.
As wave lengths are typically 35 to 105 meters, this translates to a focal length of about 5 to 15 meters. As the rate of rotation of the blades is unable, with its blade configuration, to increase correspondingly to counter this increased airflow, the angle of attack of the airflow to the blades increases beyond the stalling angle and the turbine shuts down. In order to address this problem, a second variable pitch embodiment of the invention has been proposed as illustrated in FIGS.