GB2058938A - Gyrodynamic devices for ocean wave energy conversion - Google Patents

Abstract

A rotating flywheel is mounted on a raft which is pivotally attached to a lower raft which is heavier and less buoyant. The rafts are also connected by a reciprocating piston pump. As the floats tilt due to wave action, the upper raft rotates relative to the lower raft due to precession of the flywheel, thus actuating the pump. In another embodiment the rafts are co-planar and hinged together along one edge and each carries one of a pair of contra-rotating flywheels. In a further embodiment the flywheel is formed by a tube bent to form a closed circular path which is filled with a low viscosity fluid which is driven around the closed path at a high speed. <IMAGE>

Description

SPECIFICATION Gyrodynamic devices for ocean wave energy conversion Disturbances of the surface of the sea are commonly caused by one or more wind systems acting on the water, often over a distance of two or three hundred miles. They may appear as long trains of regular waves or combinations of trains or locally modified progressions which may be called random because they have no easily recognisable pattern.

In regular waves the observer sees a rapid travel, often forty to fifty metres in a period of five to six seconds. However the water does not move far from a mean position. It circulates with a motion whose diameter is roughly equal to the difference in height from a wave crest to a wave trough.

The observed progression cannot be harnessed to produce energy but only the local fluctuations, which include change in water slope and height, pressure variations and particle circulations.

Various devices to utilise the change in water slope at or near the surface have been reported. They include hinged raft systems of considerable length driving generators through hinged arms. (These appear less favoured than heavier, shorter structures having flaps which oscillate.) The devices described herein are more compact by comparsion with the observed wave lengths. In most embodiments they tilt as the water surface tilts.

Previous types of wave energy device have been passive. Generally they have required great mass and/or high moment of inertia (against which water or loose members can move under wave action), or great size to benefit from phase variations.

They have contained no auxiliary mechanisms for the reorientation of wave response into directions where it can more easily be used.

The present devices are not passive. They depend for their performance upon the reluctance of a rapidly rotating wheel or disc to follow exactly a turning moment in a plane through the axis of rotation. It is known that, if such a moment is applied, for example by tilting the frame of a rotating gyroscope top manually, then the top must yield to force, yet it will endeavour to turn about an axis to which those of rotation and tilting are mutually at right angles.

The prototype wave energy converting device (Fig. 1), using an active component, consists therefore of a rotating mass having the dynamic behaviour of a flywheel mounted on the lighter and more buoyant of two parallel rafts. When the water surface tilts the rotating means on its raft is constrained to follow the movement. In doing so it produces a torque about an orthogonal axis. The second raft, more massive, also has a tendency to tilt with the waves since it is partially supported by the first. Yet it has no significant tendency to rotate in the transverse direction. Accordingly, on one side the first moves towards the second and on the other side, away. Energy is extracted by a crank or piston mechanism.

In a modified form (Fig. 2), two rotating masses are firmly mounted on two rafts, initially horizontal and hinged together. The masses are made to rotate in opposite directions. When a wave, coming along the line of the hinge, causes the two rafts to tilt, the active components will respond by producing a turning at the hinge and once again, energy may be extracted.

When two contra-rotating masses, mounted in gimbals, are both supported by the same raft (Fig. 3), they will respond by turning relative to each other and to the raft. Once again energy may be extracted.

Fig. 4 shows an embodiment similar to the prototype except that two contra-rotating masses are used on two parallel light rafts.

Fig. 5 shows an embodiment reminiscent of Fig. 3. Instead of being attached to a single raft, the two contra-rotating masses are attached to a submerged or partially submerged body of improved hydrodynamic shape; such bodies have evolved from immersed plates and (given something to work against) are reported to tilt more sharply with the waves than rafts, also to be more efficient. The rotating bodies provide some mass, also a stiffness whose effect resembles that of a high moment of inertia. Nevertheless it is beneficial for still further mass to be provided; this is suspended at some depth and prevents the entire device from moving idly with the sea.

The reaction of a light submerged gyrating body in a wave energy converter is such that it would prefer to go with the water. Therefore such a body can only be fully effective if it is attached to a substantial mass or supported by a high external rigidity. Accordingly in Fig.

6, an excited body near the surface, acting against a rotating mechanism at a depth, is no longer a solid plate but a buoyant structure supporting extra mass in way of the gyrating body.

An alternative form of raft is shown in Fig.

7. In this form, the raft is not inert but contains active components to retain compactness while securing maximum moment. These are contra-rotating, driven cylinders fore and aft which are acted upon by wave forces greater than those experienced by stationary cylinders. Two contra-rotating wheels may be attached to a single raft as was the case with Fig. 3, or there may be a pair as was the case with Figs. 2 and 4.

Two flywheels, or even one, of, say, ship's stabiliser type, have been seen in the above embodiments to provide a cognate means of wave energy conversion when mounted in such a way that the supporting structure(s) respond(s) to the wave motion.

In each case the rotation is provided from an independent circuit, powered initially by a separate supply or by a passive, wave-actuated auxiliary mechanism and subsequently from the output of the present devices.

There are illustrated in the subsequent figures alternative rotating and counter-rotating systems in each of which a torus forms a part of each raft and the rotating mass is a fast-moving liquid. It is possible for two such systems of large size to lie closely in a vertical plane (Fig. 8) since the amplitude of wave particle movement is much greater near the surface than at a depth and an illusion of tilting is created.

To the pair of tori shown in Fig. 8 may be attached a plate which improves the capture of the energy of movement at the surface.

However, in the preferred system the separate driving plate has given way to plate(s) which may be regarded as extender(s) to the torus areas.

The liquid flowing in a torus is unlikely to be water though it could be driven by a propeller powered by the waves. It is necessary at high speeds to employ not only cascades (to minimise secondary flow) but also some liquid with a substantially iower viscosity than water. Pentane and liquid ammonia have less than one quarter of the viscosity of water and about two thirds of its mass. However the very high static pressure of liquid carbon dioxide can be tolerated because of its very low viscosity (less than one fourteenth that of water), provided the dynamic problem of structural strength can be resolved.

With each torus visualised as of 30 metres external diameter and 3 metres bore the strength must be adequate for a pressure of 60 atmospheres in the static condition. At high pipe velocities of the order of 200-250 metres per second there is a very substantial centrifugal force, more than twice the static pressure. Accordingly it is necessary to construct each torus in cardioid form, peripherally strengthened by that same steel which is to provide extra exposed area for the capture of wave energy (Fig. 9).

This procedure introduces a minor disadvantage that each extension of exposed area on the two systems (units, members) forming a pair will be in the same direction. This could lead to shielding of one by the other and it is necessary to ensure adequate separation of the pair or to arrange for a small difference in diameter. Only by a great dissimilarity could one torus lie inside the other.

The creation and maintenance of the liquid velocity in each torus is a novel feature. It is possible to accelerate water in a torus by a bladed propeller or similar. In the system described it will be achieved in a different way. However, either form of creation tends to make each torus spin and it is necessary to ensure that the two tori exert a mutual restraint during production of opposite rotations about the mutual axis.

The described means of creating and maintaining the velocity of the liquid contents is intended for use with carbon dioxide, though it could be used for liquids like ethane or acetylene or ammonia if they were not regarded as too viscous for the present purpose.

If one or more electric heaters is placed in a duct or ducts having one completely open end and pointing (Fig. 10) in a circumferential direction, then each can create a driving force which may be continually renewed by the introduction of fresh, cool liquid. At start-up, an injector is provided for this purpose. The heat generated in the system is dissipated in the sea. It is desirable that there should be a small content of ambient gas, whether carbon dioxide or not, as a buffer against sea temperature drift and evaporation at the liquid thermodynamic duct(s).

Fig. 11 differs from Fig. 8 only in that the tori are horizontal and more easily recognisable as a pair of inter-dependent rafts.

Claims (8)

CLAIMS The features of these devices, with the claims for them and for variations upon them, are as follows:

1. They differ from the majority of wave energy converters by the presence of an active component and in particular of an active, rotating component driven by a small auxiliary device. There may also be present an injector, driven from the same auxiliary power source, to assist in the provision and maintenance of rotation. Control of raft separation and the proportion of effective pistons may conveniently be powered from the same auxiliary source.

2. The devices rely upon the well known principles of the gyroscope and gyrostat in which a torque in a plane on the rotational axis will provide a torque at right angles.

3. The devices may use the rotating mass as a stabiliser, against which an external moment may act to provide power, or may require the rotating mass in its resisted motion to provide power from the derived torque, acting against a moment of inertia.

4. The devices may use two contra-rotating masses, not to double the forces or the torque but to double the available stroke. In the case of the rotating liquid, counter-rotation minimises the tendency to spin, especially at start-up.

5. The use of a liquid lighter than water improves buoyancy and tends to support a steel container (and external mechanism) which is heavier than water.

6. Acceleration and maintenance of veloc ity are by liquid thermodynamic duct (lithodyd).

7. Separation control is by automatic interference with power extraction, during that part of the cycle where little work is being done per inch movement of the compensated mechanism.

8. The centrifugal stress created by the very high rotational speed of a liquid having about three-quarters of the density of water is taken care of by a cardioid cross section in the torus and some steel is used for strengthening, which would otherwise have performed no useful function but to provide extra exposed area.