GB2200694A - Harnessing power from waves - Google Patents

Abstract

A wave oscillating structure has a variable centre of gravity and thereby a variable period of roll to make more efficient use of the random mixture of waves encountered in ordinary conditions. Apparatus suitable for connection to wave-powered generators to achieve this effect comprises secondary 1 and primary 2 containers partially filled with a reactive liquid 1b, 2a. Flow of the liquid is controlled by valves (100, Fig. 8) to make use of the 'free surface' effect in varying the centre of gravity. The structure may be used as or in buoys, ships, bulk carriers, tankers and other vessels or purpose built to harness power. <IMAGE>

Description

TITLE Wave Osclllatlng Structure This invention is concerned with a wave oscillating structure. More specifically the invention is ,concerned with wave-powered generators which oscillate in response to wave- motion. The invention provides an improved generator and a structure capable of oscillation being either connected to wave-powered generating means or capable of subsequent connection to such means.

For an example of one form of wave-powered generator which may be used in conjunction with the present invention, the reader is referred to my prior United Kingdom Patent No. 1551848.

This known form ofwave-powered generator is constructed in the form of a container divided into four chambers, between opposite pairs of which air is caused to move by wave motion, the moving air driving e.g. a turbine, to generate electricity.

Wave powered generators of the aforementioned type may suffer from the disadvantage of a fixed centre of gravity and thereby a non-variable oscillation period.

Surprisingly it has now been found that wave-powered generators with a variable roll period can take better advantage of prevailing random or mixed wave conditions.

In whatever location a wave-powered generator is installed, it is statistically unlikely that all waves acting thereon will be of ideal amplitude and frequency because of the random nature of such waves.

I have now discovered that better advantage may be taken of prevailing wave conditions by devising wavepowered generators equipped with a variable centre of gravity and thus a variable roll period. This can provide a more efficient means of using wave energy for conversion into e.g. electricity.

It is from a consideration of the drawbacks of known wave-powered generators that has led to the development of the present invention. The invention provides suitable means for carrying this finding into effect. The present invention may be regarded as an improvement for assisting synchronisation of the natural period of oscillation of wave generators with the forced periods of oscillation of ambient waves by providing a structure with a variable or apparently variable centre of gravity and consequently changing the natural roll periods of such wave-powered generators. The variability in centre of gravity may be regarded as "self-adjusting" as may become clearer from a description of a preferred embodiment.

The present invention is based broadly on the "free surface effect" already known within the technical field of naval architecture. The free surface effect arises from free (unrestrained) surfaces of liquid anywhere in a floating vessel, such as a ship, for example a tank partly filled with water, fuel or other liquid. When the vessel heels to one side, the surface bf the liquid in the tank retains its natural orientation in relation to the sea but in relation to the vessel its geometry changes. This results in a weight transfer and consequently a virtual rise in the centre of gravity of the- vessel bringing with it a change in roll period.

According to a first aspect of the invention there is provided a wave-powered generator responsive to wave motion for generating power and capable of floating in water, the generator being constructed or adapted to have a variable roll period. Such a generator may be provided with means for varying its actual or apparent centre of gravity.

According to a second aspect of the invention there is provided means suitable for attachment to a wave powered generator to provide that generator with a variable roll period, the means comprising a wave oscillating structure including a primary and a secondary container, each of which can be partially filled with liquid, the primary container located within an area bounded by the secondary container and spaced therefrom, the primary and/or secondary container divided into at least two compartments between which liquid can flow, the primary container capable of liquid communication with the secondary container in one region at the base of said primary container and in a further region remote from its base, means provided which can restrict flow of liquid away from the base of the secondary container and further means provided which can restrict or prevent backs low of liquid from the secondary to the primary container at the said further region.

The invention may thus be seen as employing a compound free surface effect in a manner creating a selfadjusting centre of gravity. By adjustment or finetuning of the variable factors involved, it should be possible to match the structure's period of roll to that of any dominant wave in a wave-train or other wavesystem. The arrangement of structure may be of any useful shape from plain angular to, for example, ideal spherical. An embodiment of the invention is described below with reference to a structure of ideal spherical shape. The structure according to the invention may be adapted to take the form of a buoy or vessel, for example ships, bulk carriers, tankers and the like.It should be noted that whilst the free surface effect is largely disadvantageous in conventional naval architecture the present invention unexpectedly turns that effect to advantage in improving the efficiency and response of wave-powered generators in terms of energy conversion.

In order that the invention may be illustrated and readily carried into effect, an embodiment'thereof will now be described by way of example only and with reference to the accompanying drawings, in which; Figure 1 is an elevation of a wave oscillating structure showing the internal arrangement and space for a generator, Figure 2 is a plan view of Figure 1 in section along A-A, Figures 3 to 6 illustrate a form of valve for the apertures in the primary container, Figure 7 is a partial view of Figure 1 in which the liquids are level, Figure 8 is an enlarged detail of Figure 7 showing valve location and operation, Figure 9 represents one complete oscillation of the structure and forces diagram, and Figure 10 represents one wave and 24 relative positions of the structure thereon.

Referring firstly to Figures 1 and 2 of the drawings, the wave oscillating structure la broadly includes a secondary container 1 in the form of a closed sphere, the sphere being closed to external air or. liquid but capable of communication as defined above, with an internally located primary container 2. The said primary container can be approximately hemispherical in shape. The primary and/or secondary container can be suitably connected to a wave powered generator 60 which may convert wave energy into electricity through a turbine 70. The connection would be rigid and secure so that the generator rollswwith the structure as one combined unit. Such a generator could be as per my United Kingdom Patent 1551848. The liquids in the primary and secondary containers work in conjunction, and together they provide the driving medium for the Wave Powered Generator, with the liquid in the secondary container effecting the variable delays necessary to cope with waves of different dimensions.

For the sake of simplicity and clarity the primary container 2 is illustrated merely as a container and is described accordingly. The primary container is spaced from the base of the secondary container 1 whereby the space continues up to the uppermost edge of the primary container 2.

In this embodiment both primary and secondary containers are divided into four compartments, the secondary container compartments being designated 6, 7, 8 and 9, and the primary container compartments being designated 10, 11, 12 and 13. Liquid may flow between these compartments underneath the respective partitions 3 which-should-extend into the secondary container. Since any two diagonally opposed compartments for a pair, i.e.

6/10 - 8/12, and 7/11 - 9/13, and are loosely speaking self contained systems, there must be no liquid or gaseous communication between any pair of compartments with any other pair of compartments above the base of the partitions. Below that base there is free liquid communication between all compartments. The primary container 2 has a perforated base 5 or holes of small diameter- allowing for liquid communication between the primary and secondary containers in one region at the base.

In a further region 6a of the primary container remote from the base, liquid communication between containers is permitted under certain conditions. The upper region of the primary container is provided with a plurality of apertures 80 or portholes" and each such aperture is associated with a one-way valve such as counterbalanced pivotable valves. The valves illustrated and shown at region 6a are on the exterior surface of the primary container and allow liquid to flow out of the primary into secondary container but restrict backs low thereof.

A flow retarding member 4 in the form of a perforated membrane is located within the interior of the secondary container and spaced from the base thereof. The perforations are designed to retard or restrict flow of liquid away from and back to the base of the said secondary container when the structure is oriented towards maximum displacement. A ballast weight Ba is added to the lowermost point of the secondary container, which may assist the apparatus in response to wave inputs. Although not shown a ballast could be located within the structure preferably so as to avoid interference with flow of liquid thereon.

The contained reactive operating liquids are respectively 2a in the primary container and 1b in the secondary container. The structure may float at a water line designated WL. When the structure encounters wave motion the liquid 2a in the primary container, being unrestricted, moves smoothly in the same direction; but the liquid ib in the secondary container is restricted in two places by the perforated membrane 4. However, a certain amount of liquid passes through the perforated base 5 of the primary container from the secondary to the said primary container. This is in accordance with accepted laws of hydrostatics. Simultaneously the valves (fitted to each aperture per Figure 8) begin to open partly under liquid pressure from within the primary container and partly due to their own weight.

Consequently liquid flows into the secondary container inducing a levelling-out process.

The levelling-out process continues until the end of rolling motion towards the right, when the respective liquids 1b and 2a have again regained their initial and common level. By way of explanation, the free surface effect produced by the liquid 2a in the primary container was supplemented by a further and retarded free-surface effect of liquid 1b in the primary container. This process will be repeated during return movement and can continue for as long as waves are present to move the structure. For an approximation of the difference of water levels in primary and secondary containers, reference is made to views a to y in Figures 9 and 10.

Variation in roll period is actually achieved by the waves themselves; the longer and higher they are (lower frequency, greater amplitude), the greater the deflection of the structure by the wave and the greater also the angle' of inclination whereby more liquid is being transferred via the valves at 6a from the primary into the secondary container. That in turn means greater retardation, higher centre of gravity and slower period of roll. The system can therefore be self-regulating.

Referring to Figures 3 to 6, these respectively illustrate internal, external, side and plan views of one type of one-way valve. A planar body 100 is secured to a flange-20 and connected at their lowermost ends to fulcrum means 30. The external face of the flange has a limit stop 40 and the internal face has a counterpoise 50 for closing the valve and sealing the aperture(s). The limit stop could vary by plus or minus 150 from the 900 shown with respect to said external surface.

The valve as shown in Figures 5 and 8 operates in the following manner. Referring to Figures 7 and 8 the vessel has completed a half oscillation from the Figure 7 equilibrium to the Figure 8 position, i.e. moving to the right and is now executing the second half of that period of oscillation to the left, with the water in the Drimarv container free to move, but the water in the secondarv container restricted in its movement by the retarder membranes (which is the intention).The drawing shows the moment when the vessel, still moving to the left, passes the normal position, and hydrostatic pressure begins to build up on the inside of the valves, which, at a certain calculated value start to open and allow water from the primary container to overflow into the secondary container, where the water level rises until a common level is reached and hydrostatic pressure is equalised, when the valve, aided by its counterpoise, closes. Should the water in the primary container rise above the tops of the valves, the same hydrostatic principle must still apply, which tends to level out the two bodies of water, and so the valves open and close accordingly. As the end of the oscillating period is reached and the vessel begins a new cycle and swings to the right again, the water in the primarv container is once more free to move, while the flow of that in the secondarv container is again restricted by the retarder membranes, and so the whole process is repeated cycle after cycle.

Figure 9 represents one complete oscillation of a structure in the form of Wave-Powered Generating Buoy, showing 24 successive positions arranged in a circle and designated a to y running anti-clockwise in the direction of the arrows.

Figure 10 shows a representative wave and those 24 relative positions of the Buoy thereon.

Figure 9 includes a forces diagram. Two positions are shown.

Position a = the Buoy at rest; Position g = the Buoy at an extended inclination to the right.

Position a 0 = Centre, also Metacentre ("fulcrum"); xB = Centre of Buoyancy; xGl = Centre of Gravity of the total rigid structure; xG2a = Centre of Gravity of liquid in the primary container; xG3a = Centre of Gravity of liquid in the secondary container (1).

Position g = xG2a has become +G2b, and xG3a has - become +Gsb (compare with diagram ffi on the circle where the respective Centres of gravity of the contained liquids are decidedly off centre).

The '+" sign is used to indicate the relative shifts of position of xG2a and xG3a to their new positions at +G2b and +G b.

These two Centres of Gravity can be regarded as "separate and mobile", i.e. shifting their position constantly during wave action.

Taking two water masses to be equal in weight (for the sake of convenience), we now connect +G2b and +Gsb with a line, on which we then mark their common centre.

xB (the Centre of Buoyancy) remains in its former at position. But xG1 is nowf+G1a. Drawing a line from "+G2b/+G3b common centre" to +G1a and marking on that line the position where the two centres balance (if the

total weight of the contained liquid represents one third of the total operative weight of the Buoy, then the division should be made one third along the line from +Gia), we get (Gib). Next we extend (Gib) vertically to where it intersects with the centre-line of the rigid structure, i.e. at Gib, we arrive at the true Centre of Gravity of the complete Wave-Powered Generating Buoy as of that moment.The distance from Gib to Z is the

righting couple, which, as can be seen, has/substantiall reduced, because the Centre of Gravity of the total structure has been effectively raised.

In conclusion - because of the "separateness and mobility" of xG2a and xG3a- the true Centre of Gravity of the complete Wave Powered Generating Buoy is constantly changing while wave action continues.

It will be convenient for the valves to be constructed to begin closing as soon as the return movement is initiated to trap the liquid in the secondary container. A structure according to this invention may advantageously be designed to react to a "minimum length/height" wave. As noted above, the structure may be useful as or in buoys, ships, bulk carriers, tankers and other vessels or purpose-built to extract useful power from the waves in an expedient manner.

Claims (14)

1. A wave powered generator responsive to wave motion for generating power and capable of floating on water, the generator being constructed or adapted to have a variable roll period.

2. A generator as claimed in Claim 1 which includes means capable of varying the centre of gravity of the generator.

3. Means suitable for attachment to or incorporation within a wave powered generator so as to provide that generator with a variable roll period, the means comprising a wave oscillating structure including a primary and a secondary container, each of which can be partially filled with liquid, the primary container located within an area bounded by the secondary container and spaced therefrom, the primary and/or secondary container divided into at least two compartments between which liquid can flow, the primary container capable of liquid communication with the secondary container in one region at the base of said primary container and in a further region remote from its base, means provided which can restrict flow of liquid away from the base of the secondary container and further means provided which can restrict or prevent backs low of liquid from the secondary to the primary containertat the said further region.

4. Means as claimed in Claim 3 in which the primary and secondary containers are partially filled with liquid.

5. Means as claimed in Claim 3 or 4, in which the means for restricting flow of liquid away from said base comprise perforations or other small diameter apertures in said base.

6. Means as claimed in any one of Claims 3 to 5 in which the further region is an upper part of the primary container which comprises a series of apertures.

7. Means as claimed in Claim 6 in which the apertures are provided with valves to allow outflow but restrict or prevent backs low of liquid from the secondary to the primary container, the valves preferably being counterbalanced and capable of pivoting to open and close said apertures.

8. Means as claimed in any one of Claims 3 to 7 in which the-primary container is hemispherical.

9. Means as claimed in any one of Claims 3 to 8 when connected to a wave-powered generator.

10. Means as claimed in Claim 9 wherein the generator is of a type as disclosed and claimed in U.K.'Patent 1551848.

11. Means as claimed in Claim 9 or 10 in the form of a vessel or buoy.

12. Means suitable for attachment to a wave powered generator substantially as herein described with reference to and as illustrated in any one of Figures 1, 2, 7 or 8 or the accompanying drawings.

13. A wave powered generator as claimed in any one of Claims 1, 2 or 9 to 12 substantially as herein described.

14. A wave powered generator as claimed in Claim 13 substantially as illustrated in Figures 1 and 2, 7, 8 or 9 of the accompanying drawings.