GB2542923A

GB2542923A - Combined-reaction fluid turbine support structure

Info

Publication number: GB2542923A
Application number: GB1614659.9A
Authority: GB
Inventors: A Haleem Hamid
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-08-28
Filing date: 2016-08-30
Publication date: 2017-04-05
Also published as: GB201614659D0; GB201515380D0; GB2541745A

Abstract

A support structure 100 for use in an aquatic environment, such as the sea or ocean, is suitable for supporting one or more fluid turbines 140 under the water surface. The structure is composed of an elongate framework (110, figure 6) for supporting one or more turbines, with two elongate buoyant members 120 rigidly fixed to the framework and where cross members (130, figure 5) rigidly couple the buoyant members together. The buoyant members may be held below the fluid surface, which may be achieved with the use of a pump. The framework may be fixed approximately centrally along the buoyant members, and in use the buoyant members may be aligned parallel to the direction of travel of the wave front, and if present, fluid turbines may be disposed on the support structure such that their rotation axis is perpendicular to the buoyant members. One or more turbines may be arranged between the buoyant members, and the turbine installation can extend beyond the sides of the buoyant members and cross members. The turbines may be disposed on two levels, or cascaded, or may be in two or three neighbouring rows.

Description

Combined-Reaction Fluid Turbine Support Structure

Field of Invention

The invention relates to a fluid turbine support structure wherein the said support structure is held in the sea or ocean in such a manner and level of the water, that it can, on the one hand, allow the turbine (or turbines) to be at the surface of the sea, thus utilizing the power of the waves at their maximum, for power generation, while, at the same time, making use of the reduction in the movement of the waves (i.e. the “up-and-down”, and the “bobbing-and-nodding” movements), “d” metres below the surface to help stabilize the support structure.

It is in these two aspects, mainly, that the invention differs from the previous one, i.e. (EP0384757) wherein the turbines have to be positioned at the surface of the sea (or ocean) on a very high steel tower, itself supported on steel tanks floating very much lower down, where the waves are either completely dead, or close to being completely dead.

Background to the Invention:

Wave turbines, as described in Patent No. EP0384757, comprise the following components:- 1. A rotor carrying, around its circumference, a number of counterweighted swinging vanes which receive the power of the waves (or any flowing medium) irrespective of whether this power is coming from above, below, or any of its two sides. The shaft carrying the rotor is assumed to be, horizontally, at, or close to the Mean Water Level. This is affected through the buoyancy of the device. 2. A means of reaction realized by a flat surface (a plate or the flat surfaces of submerged pontoons providing the necessary buoyancy) rigidly fixed lower down at a distance sufficient for the waves to die down, or be sufficiently diminished. 3. A number of auxiliary features including: a) One-way free-wheel drive means, so that when a number of turbines are strung on the same shaft, each one of them will rotate separately when it receives the power of the waves. b) Pumps to transfer the power from the turbines to a hydraulic motor which will drive an electricity generator, and the necessary pressure pipes to affect this.

The wave turbine described in EP0384757 suffers, in addition to some other problems, from the fact that the reaction essential for obtaining power from any machine, can be realized only through the fixing of the turbine (itself at the surface) to a means of reaction very much lower down below the surface of the water where the waves are completely or nearly dead. This fixing will have to be done through the use of very heavy steel columns (or latticed lighter columns). As such, the higher will be the cost of the plant, in addition to some other problems. However, the square of the amplitude governs, to a great extent, the power obtainable from a wave utilized for power generation through the use of a wave turbine. This is shown by the following equation from “Renewable Energy Resources” by John W. Twidell, 11 New Fetter Lane, London EC4 P4EE. Also published in the USA by F.N Spon, 29 West 35th Street N.Y., N.Y. 1001. page 322, equation (12-37). Here, the power carried forward in a wave, per unit width across the wave front is expressed in the following formula:-

where, P = power p = density of water g = acceleration due to gravity, i.e. (9.8 ms"2) a = amplitude of the wave (m) (being the radius of the circular motion of the water particle) λ = wave length (m) T = period of the wave (2π/ω), ω being the angular velocity of the water particles in the wave.

The wave turbine has been introduced for the purpose of harvesting the huge amounts of energy available in offshore ocean (and sea) waves all over the globe. As such, and in order to be generally acceptable, the following points had to be taken into consideration:- 1. It has to be able to operate in any sea or ocean waves irrespective of the depth of the water in which, and by which, it is going to be operated, except very shallow water areas, or times when “tsunamis” are blowing, by which it can be destroyed. However, it suffers from some shortcomings. 2. The awkwardness of the above-described structure, insofar as it represents a hazard to sea life in the form of sea mammals or swarms of smaller sea creatures, or submarines, where the damage can be mutual. 3. The fact that the horizontal surfaces of the buoyancy tanks carrying the whole structure and providing, at the same time, the required reaction, can, at certain times, say when the waves are lower than usual, chop off part of the amplitude (and hence the energy) for which the turbine is being used. 4. Mobility (or immobility) has a great bearing on the cost of operation of any structure which may have to be shifted during its working life (for maintenance or modification)

in addition to the saving realized by simply towing such a structure from the dock where it has been assembled, instead of having to assemble it at the site where it is going to operate.

There is a need to improve the performance of wave turbines. There is a need to improve the effectiveness of harnessing energy from the waves of the sea or ocean. Furthermore, there is a need to improve the versatility of wave turbines so that the wave turbines can adapt to their marine environment.

It is an object of some aspects of the present invention to attempt to overcome at least one of the above or other identified problems.

It is a further object of the present invention to provide a fluid turbine support structure that provides improved stability and is capable of utilizing more than one source of reaction simultaneously. Further, it is an aim to provide better structural support to wave turbines at or close to the surface of the water, taking into account the costs and other aspects of doing that.

The purpose of this invention is to produce a wave energy generating device having two sources of reaction, namely: (1) the first source, is by utilizing the difference in phases between the waves, through the use of a long rigid buoyant body made up of two long rigid buoyant bodies, latticed together by steel sections, designated, for short, as a “Rigid Frame” as a supporting structure for the turbines, and designed according to the calculations of Figures 9 to 28, at the end of this paper. (2) keeping in mind the drawbacks of supporting the wave turbine or turbines at, or very close to the surface, on a support structure itself carried on very long columns, i.e. a tower, itself carried on steel tanks situated quite a considerable distance below the surface of the sea, thus depending, for a reaction, on the cessation, or near cessation of the waves at that depth, as in Patent EP0384757, with all the problems associated with that, or, alternatively, on a support structure situated at the surface of the sea utilizing the contradiction between the two types of wave motion (namely the “up-and-down” movement, and the “bobbing-and-nodding” movement), to dampen the waves, the other alternative will be through placing the support structure a few metres, (hereinafter referred to as “d” metres) below the surface of the sea, thus creating a “combined-Reaction” wave turbine.

As a result of this arrangement, the wave turbine will receive the waves at their strongest to drive them, while the support structure will receive the waves at a weaker state for it to oppose (i.e. much less “up-and-down” movement, and much less “bobbing-and-nodding” movement for it to oppose). The “gain” is, therefore, clear, especially when taking into account the fact that the drop in the height of waves, as we go down, follows an exponential, and not a straight line, relationship, (see reference; “Renewable Energy Resources” by John W. Twidell and Antony D. Weir, chapters 12 (Wave Energy), Section 12.2 (Wave Motion), point (4),page 314).

Summary of the Invention

According to the present invention, there is provided a fluid turbine combined-reaction support structure for use in an aquatic environment and an array of fluid turbine combined support structures for use in an aquatic environment, as the sea or ocean, as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims and the description which follows.

According to an exemplary embodiment, a combined-reaction support structure is composed of two elongate buoyant members, having cross members arranged to couple the two elongate buoyant members. An elongate framework is arranged to support the fluid turbine, wherein the fluid turbine is arranged to be buoyantly held in close proximity to the surface of the fluid. Therefore, the two elongate buoyant members are rigidly fixed together to form one body and improve stability over a single elongate buoyant member, because a single member is likely to easily topple or roll over onto one of its sides due to the forces incurred when carrying various equipment. Each elongate buoyant member is, by definition, buoyant. The buoyancy may be altered when a change of the level of Rigid Frame is required, by having a small in-built space within each elongate buoyant member. This in-built space may be symmetrically placed across the line dividing the length of each elongate buoyant member in two, while a suitable buoyancy pump can be placed (inside or outside) of each elongate buoyant member, so that the fluid turbine can be maintained in close proximity to the surface of the fluid, the latter being water of the sea or ocean. Manipulation of the level of the fluid turbine is controlled by the combined-reaction support structure.

The elongate buoyant member may be an elongate body (i.e a very long body, especially when compared with its cross-sectional area). The elongate buoyant member may be an elongate hollow member, such as a tube. The elongate buoyant member may have a circular or square cross-sectional area, or may have a cross-sectional area shaped like a regular polygon.

The term “fluid turbine”, or “wave turbine” may be used to define a complete energy generating plant. This would include a combined-reaction support structure, one (or more than one) fluid (or wave) turbine depending on size (including blades, shaft, bearings...etc, electricity generating sets, pumps, hydraulic motors, etc). However, the term may be used to mean only the fluid turbine itself (i.e. composed of shaft, blades, bearings...etc).

Preferably, the fluid turbine has a generator to convert the rotational energy into electrical energy. Further, the fluid turbine has a pump-operated hydraulic motor. The combined-reaction support structure, (C.-R.S.S. for short), may therefore have a top structure or housing that houses the various components such as, the generator, pump, and hydraulic motor. This housing may be rigidly fixed to the C.-R.S.S. via the elongate framework. Therefore, the C.-R.S.S. may be provided as one structure with several parts interconnected. Alternatively, the housing may be rigidly fixed to the cross members which extend between the two elongate buoyant members. The top structure housing the generator, pump, and hydraulic motor, facilitates access to these items for operational and maintenance purposes, by putting them immediately above the surface of the water. A cross beam, or stout steel structure extending across the space between the two elongate buoyant members (at their mid-points) may also be provided for this job.

Preferably, the elongate framework is a lattice-type structure in order to help the rigidity of the R.F, whilst allowing the C.-R.S.S. to be lightweight.

Preferably, the buoyancy pumps maintain the R.F. at a predetermined distance below the mean level of the fluid surface, which may be the mean water level of the ocean or sea. The advantage of submersing the R.F. is to stabilise the C.-R.S.S. The wave-energy at the lower level, (“d” metres below the surface) reduces exponentially (see Reference on a previous page) as the depth increases, but the stability increases. This allows the fluid turbine to maximise the energy at the surface of the water where the turbines are located.

Preferably, the elongate buoyant members comprising the R.F extend outwardly from the elongate framework. The elongate framework may be positioned at a central or midpoint along the length of the R.F. This helps to improve the stability of the fluid turbine. Further, the R.F may be substantially parallel to the mean water level. This helps to more easily control the buoyancy. The length of the R.F may be far greater than the length of the elongate framework. This improves the stability of the C.-R.S.S. and helps to counteract the various multi-directional forces of the waves, which could be present if the elongate buoyant members forming the R.F. were too much apart.

Preferably, the axis of rotation of the fluid turbine is substantially perpendicular to the longitudinal axis of the R.F., so that in use, the direction of the wave propagation extends along the longitudinal axis of each elongate buoyant member. This allows “the up-and-down” and the “bobbing-and-nodding” movements by the waves to provide the reaction essential for the generation of energy, so that the fluid turbine converts the maximum amount of wave energy into mechanical, and subsequently into electrical energy. In other words, the two elongate buoyant members constituting the R.F. provide the turbines with a support which is stationary (or substantially so), in a medium which is not stationary.

Brief Description of the Drawings

Fora better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying figures of in which:

Figure 1 shows a chart from “Renewable Energy Resources” by John W. Twidell;

Figure 2 shows the “bobbing and nodding” forces using odd numbered frame lengths;

Figure 3 shows the “bobbing and nodding” forces using even numbered frame lengths;

Figure 4 shows an elevation of a combined-reaction support structure (G = generator; X = Hydraulic Motors; M.W.L = Mean Water Level);

Figure 5 shows a plan of a combined-reaction support structure;

Figure 6 shows a side view of a combined-reaction support structure (M.W.L = Mean Water Level);

Figure 7 shows a summary of the total discrepancies between the up-and-down forces;

Figure 8 shows a summary of the discrepancies between the anti-clockwise and clockwise moments;

Figures 9 to 12 show the calculation of the up-and-down forces (cases 1 to 16); and

Figures 13 to 28 show the calculation of the bobbing and nodding forces (cases 1 to 16). Detailed Description of the Invention

The search to overcome the above-mentioned problems with the prior art led to the alteration of the source of the reaction (or part thereof) namely, by utilizing the difference in phase between the waves i.e. by reacting one wave (or part thereof) against another. For this purpose, a long rigid structure of uniform construction, extending in the direction of the principal wave propagation is required. Uniformity here means that all the immersed surfaces of (or on) the structure are evenly distributed over its whole length.

As such the “Rigid Frame AB” has to be:- a) Capable of allowing the turbines mounted on it to directly access the waves by which they are meant to operate, without dampening them. b) Sufficiently long so that it will extend over the length of the operational wavelength. The relation between the length of the frame and that of the operational wavelength is treated and illustrated in Figures 9 to 28. They are also summarized in Figures 7 and 8. However, it is pertinent at this juncture, to clearly state that the whole length of the Rigid Frame cannot, simply, be utilized to accommodate turbines on it as will be explained. c) Moored in such a way so that it can move freely in the vertical, but not in the horizontal plane (except when it is intentionally realigned with the direction of the principal wave propagation due to a change in the operational wavelength as explained later).

Theoretical Analysis

Figure 1 has been taken from page 315 of “Renewable Energy Resources” by John W. Twidell, but with the wave surfaces depicted in straight lines instead of curves for ease of execution.

Resultant forces on surface particles:

Notations (Figure 1): M.W.L. = Mean (Static) Water Level m = mass of an element of water ω = angular velocity of the water particles in radians per second g = acceleration due to gravity = 9.8 ms'2 a = amplitude of the wave.

From the same reference mentioned above (page 315, Figure 12.4), “Resultant forces on surface particle”, are as follows:- “A particle at the top of a crest, position Pi, is thrown upwards by the centrifugal force mau>2. A moment later, the particle is dropping, and the position in the crest is taken by a neighbouring particle rotating with a delayed phase. At P2, a particle is at the average water level, and the surface orientates perpendicular to the resultant force F. At the trough P3, the downward force is maximum. At P4, the particle has almost completed a full cycle of its motion”.

The horizontal components (maio2) of the forces “F” acting at the intersection points P2 and P4 at the Static Water Level, and later on in this paper named “Intersections 1 and 2”, will be neglected in the calculations. They act against each other, as well as they act along the length (and not the height) of the proposed rigid frame. As such, they are redundant and have no effect on the reaction provided by the latter.

The force at Pi which is equal to (mg - mau2) will, throughout this report, be referred to as “y”. Similarly, the force at P3, which is equal to “mg + mau2” will be represented by “x”.

Conditions for stability of the “Rigid Frame”

The proposed “Rigid Frame AB”, the length of which is assumed to be extending -incompliantly - in the direction of the principal wave propagation will be, due to the action of the waves, subjected - at the same time - to two types of motion, namely:- 1) An overall purely up-and-down movement of the whole frame relative to the “Mean Water Level”, which movement, if it extends beyond a certain limit, will neutralize or seriously affect the operation of the turbines mounted on it. 2) An alternate, oscillatory, up-and-down movement of the two ends “A” and “B” of the frame about a vertical line (or plane) passing through its centre, i.e. a rocking movement which will negatively affect the operation of the turbines mounted on it, especially those nearer the ends AB, if any; this becomes all the more true when the turbines are fixed “d” metres above the back of the R.F.

The ability of the Rigid Frame to provide the reaction required to produce power from the waves will be affected by these two types of movement compared with the magnitude (height) of the available waves.

The “Results of the Analysis” shown later (see Figures 7 and 8) are based on the following:- a) Selecting a particular wavelength for the design of the “Frame”. This will, most probably, be the longest, most prevalent wave available in the proposed site. Selecting various proposed lengths for the frame, and relating these to the wavelength, and checking the degree of stability of the frame according to the results shown therein. b) When calculating the “rocking” forces acting on the frame referred to in 2) above, the force passing through the centre line (or plane) of the frame will not be taken into consideration. The same forces, however, will be taken into consideration when calculating the purely “up-and-down” forces acting on the frame (referred to in 1) above) as shown in Figures 9 to 12. 3) It must be noted here, however, that the length of the waves moving in the direction of the principal wave propagation, and according to which the length of the frame is selected and designed, cannot be guaranteed to remain the same over an unlimited period of time, but may increase or decrease. To meet this situation, a, what may be called, “variable length” frame is proposed. Very briefly, this is done, for the situation where the design wave, i.e. the wave on which the design of the frame is based (possibly or preferably being of the longest duration in the site), through making the frame AB slightly longer than the one actually required (i.e. “3b” meters, see Figure 7, where the discrepancy is zero). The longer frame, now designated “AB” is placed and anchored at an angle “Θ” to the direction of the principal wave propagation, so that AB’ cos Θ = AB. The fixing has to be done in such a way that the “effective length” of the frame remains the same.

By “effective length” is meant the length of the frame that would result in a zero (or nearest to zero) discrepancy between the up-and-down forces acting on the frame such as in Cases 3, 7, 11 and 15 (of Figure 7). Fixing of the frame has to be arranged in such a way that it can be swayed, horizontally, according to the angle Θ. This, of course, is different from the situation where the waves in the direction of the principal wave propagation themselves change direction and not length. In the latter situation, the frame is simply swayed into the new direction.

Swaying of the frame, by the way, does not negatively affect the operation of the wave turbines. These are universal machines which operate by the power of the waves, as long as their shafts remain (in the water) horizontal or nearest to horizontal.

Explanation of the Drawings

The wave selected for the development of the frame AB will be represented by a straight line “4b” metres long (b being any suitable arbitrary number, say 25 metres for North Atlantic waves). The multiple 4 is selected simply because a wave can be represented by four salient points, namely: “top of crest”, “bottom of trough”, and two points “1” and “2” being the intersections of the surface of the wave with the “Mean Water Level” (see Figure 1). For such a wave, a number of frame lengths, each of which is called a “Case”, are selected and treated to check their stability. Each one of these “Cases” is individually considered four times i.e. when each wave engages the beginning of the frame (point A) either by its “Crest”, “Intersection 1”, “Trough”, or “Intersection 2”. Each one of these treatments is called a “State”.

To find out the length of the frame capable of providing the stability needed to produce the required reaction, the behaviour of the frame will be analysed under the influence of the force of the wave. To do this, two types of checking are carried out, namely:- 1. The first is by adding up all the forces acting on the whole frame to find out whether it will be subjected to any purely “up-and-down” forces. 2. The second is by calculating the same forces acting on the frame, except those passing through its central line (or point) and then calculating the “Clockwise and the Anti-clockwise” moments to which each side of it is subjected.

The results of these two types of checking are shown in the following pages together with special graphs indicating the various lengths of frames being checked, and the corresponding moments acting on them (Figures 2 and 3).

In order for this type of frame to serve the purpose for which it is meant, it has to> (i) be strengthened by latticing to avoid the use of very heavy steel sections. (ii) have sufficient buoyancy so that the equipment and structures mounted on it will remain at the intended level i.e. at or close to the M.W.L (i.e. Mean Water Level).

Results of the Analysis a) The purely “Uo-and-Down” Forces:-

The detailed calculations for all the Cases of the purely “up-and-down” forces are shown in a separate Figures 9 to 12 attached at the end of this paper. However, Figure 7 summarizes the results of this exercise.

For all the cases, the same graphs already used for calculating the “bobbing and nodding” forces (i.e. moments), can be used for calculating the “Up-and-Down” forces after discounting the centre line.

The purpose of the above-mentioned exercise is to see if there is a vertical repetitive oscillatory (up-and-down) force, and how much of it, to which the frame is subjected. A vertical constant force (purely up or down) does not pose any problem, since it can be taken care of through increasing or decreasing the buoyancy.

The results of the exercise, as shown in Figure 7, prove that the up-and-down forces are either equal, as in Cases 3, 7, 11 and 15, or that the difference being (2macjj2) at its maximum, is negligible when compared with the total force which, in all cases, is a multiple of g (acceleration due to gravity) plus or minus. b) The “bobbing and nodding” ends of the frame

The detailed calculations of the above forces are shown in a separate Figures 13 to 28, at the end of this paper. Figure 8, summarizing these results is shown by diagrams depicting these figures.

Briefly, these results indicate the following:- 1) If the frame is equal to, or shorter than “1b”, it is unstable, and cannot be used for obtaining a reaction. In fact, it can flounder. This is so, in spite of the fact that the discrepancy between the anti-clockwise and the clockwise moments for it, is minimal, being (Vimau)2, referred to as z/2). 2) For the 16 frames, where lengths are increasing in increments of “b” metres each time, the discrepancy between the anti-clockwise and the clockwise moments increases according to a certain pattern except for the frames of Cases 1,5, 9 and 13 where discrepancy is constant, and always equal to bz/2. As such, the discrepancy is smaller than in all other cases. Consequently, these particular frames (except that of Case (1) already referred to in (1) above) may seem to be the most suited for obtaining a reaction for the turbines mounted on them. However, and notwithstanding the aforementioned fact, this should not automatically lead to the belief, in cases where numerous turbines are needed to be fixed on the frame (to generate more energy), that extension of such fixing (in the direction of the wave propagation) can be carried out without limitations. This is so because, each wave once passing through a turbine, loses some, or possibly most of, its energy (depending on the efficiency of the latter). Moreover, such fixing will, seriously, interfere with the “bobbing and nodding” results (referred to above) and, consequently, on the operation of the R.F. Hence, the only way to increase the energy extractable from the waves using the proposed device, will be through increasing the number of turbines fixed on the R.F. breadthwise, i.e. along the wave front, and not along the direction of the principal wave propagation. As such, the reasonable space (which extends along the wave front and at right angles to the principal wave propagation) is extremely critical, since it is along it, and possibly along very small extensions of it on both sides of the R.F., that more turbines (or protruding parts of turbines) can be installed. Consequently, harvesting more energy from any area of the sea or ocean, using the proposed device, will mainly be through installing numerous (R.F.s) in the particular area, each one of them moored independently, and keeping a reasonable space between each R.F. and the other.

Conclusions: A Combined-Reaction support structure

Reference the comments made at the beginning of this paper highlighting some disadvantages of using the “diminishing amplitude” of waves as a sole reaction in the turbine of Patent No. EP0384757. But before deciding on which other type of reaction to adopt, or add, it is better to first clarify certain points pertaining to the nature of the energy which the intended turbines are intended to capture, and economically:- a) The R.F. as presented is supposed to be at the surface of the sea. Now, any lowering of the source of reaction below the surface of the sea, leads to an exponential reduction of the amplitude of the motion of the particles of water (same reference, page 1), leading, in turn, to a reduction of both the forces acting on the R.F., i.e. the “up-and-down”, and the “bobbing-and-nodding” forces, (i.e. the moments). b) The energy of the waves, however, is maximum nearer the surface of the sea, and diminishes as we go deeper and deeper, until it dies down. As such, installation of turbines cannot, if they are to be most economically productive, be at any place lower than that of the surface of the sea. c) As is seen from the “bobbing-and-nodding” (Figure 7), it is only the central point of line AB (representing the R.F.) which is stable. All its other points (including those which, from the point of view of the “up-and-down” angle, are stable, such as those of Cases 3, 7, 11 and 15 etc. of Figure 7) are, in a gradually increasing manner as we approach its two ends A & B, unstable. As such, it is only the central point, and possibly some points very close to it, on both sides, which can be used for installing turbines requiring a reaction, as well as for connecting the R.F. to the mooring facility. d) In addition to what is mentioned in b) above, and as has already been mentioned earlier (the “bobbing-and-nodding” ends of the frame subsection), the energy of the waves will, mainly, be harvested by the earlier turbines which come earlier in the course of the line interrupting the direction of the principal wave propagation.

In view of the points shown above (a, b, c and d), and in the search for a means to increase the possibility of extracting more energy through the use of the R.F., the following arrangement is proposed:- 1. Creating a “compound structure” (see Figure 3 - diagrammatic at the end of this report) where the turbines are positioned at the surface of the sea (see section titled “The bobbing and nodding ends of the frame”), by fixing them on an elongate framework, itself mounted on the R.F. the latter being positioned “d” metres below the surface of the sea. In this way, the turbines will be more stable than when the R.F. itself is positioned at the surface. This is so, because lowering the level of the R.F “d” metres leads to a reduction of the angular velocity “ω” of the particles of water, and subsequently, to a reduction of the height of the waves. As such, the “bobbing and nodding” of the R.F. will be reduced. It is actually from these two facts that this invention derives its name, i.e. “Combined-Reaction”. As such, both the “up-and-down”, and the “bobbing-and-nodding” movements of the R.F. will be reduced. The level of the R.F. can be manipulated, when required, by pumping sea water in or out of the ballast tanks by special pumps mounted midway in, or on, each one of the two elongate buoyant members forming the Rigid Frame. 2. Making the most of the R.F. economically, by utilizing the space in between the two elongate buoyant members (and possibly slightly extending that space) on both the outer sides of the R.F. - (see Figures 4 to 6) and installing the maximum number of turbines (depending on the size) on the line dividing the R.F. in two across its length. Also, the possibility of installing the turbines in two or three neighbouring rows along the wave front can be considered. 3. Depending on the sizes (i.e. diameters) of the turbines, the possibility of installing these on two levels (i.e. one above the other) can be considered with, maybe, some cascading.

The industrial application of the invention will be readily appreciated from the description herein:-

Figure 4 shows an elevation of a combined-reaction support structure i.e. Rigid Frame 100 that is arranged to support a fluid turbine 140. The R.F. 100 is comprised of two long rigid buoyant members 120 each of which may be herein referred to as an elongate buoyant member (E.B.M). Each E.B.M is tubular, and may be circular or rectangular in cross section. The frame supporting the turbine (or turbines) plus the top structure (housing the generator, pump and hydraulic motor) is rigidly fixed to the R.F. AB. The fluid turbine 140 is shown with a generator, “G”, a pump, and hydraulic motor (X). A centre line is shown which crosses the axis of the fluid turbine 140, and through the centre of the combined-reaction support structure 100 (C.-R.S.S). The C.-R.S.S 100 is shown with an elongate framework 110. The elongate framework 110 is shown with multiple slim members that are rigidly fixed to both of the elongate buoyant members 120 at or very close to the centre line C.L. The elongate buoyant members 120 extend from A to B in a direction of wave propagation 150. Each one of the two elongate buoyant members 120 contains buoyancy chambers which may comprise pumps in fluid communication with each elongate buoyant member 120, and the water. The buoyancy of the C.-R.S.S is preferably controlled by the elongate buoyant members 120, by pumping water into or out of the buoyancy chambers (by pumps fixed inside or on the back of) the elongate buoyant members 120, so that a predetermined difference “d” to the mean water level (M.W.L) can be maintained. The C.-R.S.S 100, in particular each elongate buoyant member 120, is aligned with the direction of principal wave propagation 150. Also, the length of each elongate buoyant member 120 is far greater than the length of the elongate framework 110 in order to improve stability.

Figure 5 shows a plan view of the C.-R.S.S 100 shown in Figure 4. The fluid turbine 140 (or-at that, any suitable number of fluid turbines), can be arranged in the space between the two elongate buoyant members 120, or arranged to extend partly, or fully, beyond the side of each elongate buoyant member 120. Elongate cross members 130 are shown (in the form of a lattice structure) that are arranged to couple the two elongate buoyant members 120. A top structure 132, which may be a housing is also shown, above the mean water level, to house various other components such as the generator, pump, and hydraulic motor. By providing two elongate buoyant members 120, the R.F. is more stable, thus avoiding simply rolling over or turning up-side-down when in use. Each elongate buoyant member 120 is arranged in parallel leaving a region there between. The region or space is then bridged by the cross-members to provide a strong and stable rigid frame.

It is anticipated that two elongate buoyant members 120 are adequate to provide suitable stability for the wave turbines 140. Increasing the number beyond two in any one Rigid Frame 100, in an effort to create a broader (and consequently larger) R.F. 100 may lead, unnecessarily, to problems of another type, such as:- 1) Risk of presence of variations in the characteristics of the wave, along the wave front (thus leading to a disturbance in the application of the figures of Figure 7 (“Total discrepancies between the ‘up-and-down’ forces”), and Figure 8 (“Discrepancies between the Anti-clockwise and the Clockwise moments”); 2) Difficulty of being manoeuvred, and 3) representing a hazard to other sea-users. The overall dimensions (length, and, more particularly, breadth, and depth) have always better not to exceed those of an ocean-going ship. Harvesting more energy from the sea can always be realized by increasing the number of independent units (Rigid Frames) in the area without any rigid connection between them, or between any other object, which itself is rigidly fixed to any other object, at that.

Although preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made without departing from the scope of the invention as defined in the claims.

Figures 9 to 28 show the calculations of the “up-and-down” forces as summarised in Figure 7 and the “bobbing-and-nodding” forces as summarised in Figure 8.

Claims

1. A combined-reaction support structure for use with a fluid turbine, or a number of fluid turbines, the combined-reaction support structure comprising:- an elongate framework arranged to support the fluid turbine or turbines; two elongate buoyant members rigidly fixed to the elongate framework; and cross members arranged to rigidly couple the two elongate buoyant members (the resulting body to be called “Rigid Frame”) wherein the fluid turbine is arranged to be buoyantly held inside the fluid in close proximity to the surface of the fluid.

2. The combined-reaction support structure of claim 1, wherein the elongate buoyant members are maintained below the surface of the fluid at a predetermined distance.

3. The combined-reaction support structure of claim 2, wherein the fluid is the water of the sea or ocean.

4. The combined-reaction support structure of any preceding claim, wherein the elongate framework is rigidly fixed at a substantially central location along the elongate buoyant members.

5. The combined-reaction support structure of any preceding claim wherein the axis of rotation of the fluid turbine (or turbines) is substantially perpendicular to the longitudinal axis of each elongate buoyant member so that, in use, the direction of wave propagation extends along this latter axis.

6. The combined-reaction support structure of any preceding claim, wherein a pump is provided that is in fluid communication with each elongate buoyant member, wherein the pump is arranged to control the buoyancy of the combined-reaction support structure such that the fluid turbine is maintained in close proximity to the surface of the fluid.

7. The combined-reaction support structure (C.-R.S.S) of any preceding claim, wherein the at least one fluid turbine is arranged on the elongate framework in the space between the two elongate buoyant members.

8. The C.-R.S.S of any preceding claim, where, more than one fluid turbine can be installed on the elongate framework in the space between the two elongate buoyant members.

9. The C.-R.S.S of any preceding claim, wherein fluid turbine installation on the elongate framework can extend for a short distance beyond the outer sides of the R.F.

10. The C.-R.S.S of any proceeding claim, wherein the (C.-R.S.S) has a plurality of fluid turbines where the fluid turbines are arranged on two levels.

11. The C.-R.S.S of claim 10, wherein the fluid turbines are cascaded.

12. The C.-R.S.S of any preceding claim wherein a number of fluid turbines can be installed on the elongate framework (in two or three neighbouring rows) along the line of the wave front, in the space between the two elongate buoyant members, and possibly extending for a short distance beyond the outer sides of the R.F.