OFFSHORE WIND-/WAVE-ENERGY CONVERTER

Abstract: The invention is a power plant for the exploitation of wind/wave energy on the high seas. The plant consists of a floating, self-adjusting with regards to waves, platform (1) which is anchored with hawsers (6) to a floating anchor pontoon (3), which in its turn is anchored to a swivel link on top of an anchor block (4), placed on the sea floor. The side of the platform which faces the waves is designed as a doubly curved ramp (13), on which waves are led into a shallow basin (14), which has a water level above the mean sea level determined by the surrounding prevailing height of the waves. The sea water is led back into the sea from the basin by way of turbines, which for instance run electrical generators. The platform can be equipped with curved, stiff, and thereby self-stabilising, wave reflectors (2), which deflect and focus the waves towards the ramp (13). The platform's and wave reflector's special design allow a stabile and high exploitation of wave energy for power production. The platform has a sufficiently large stability versus wave movements that it can be equipped with windmills of unusual but nevertheless known design.

Description: Offshore wind-Zwaveenergy converter. The invention concerns a plant for the exploitation of wind/wave energy on the high seas. It consists of a floating self-adjusting platform, anchored towards the waves by means of hawsers connected to a floating pon- 5 toon, which is in turn anchored to a swivel link at the top of an anchor block on the sea floor. A possible power cable can be led through the same swivel link. The plat¬ form is equipped with a ramp upon which the waves travel and spill water into a reservoir which has a variable 10 water level compared to the average sea level, and from which the sea water is led back to the sea through pipes in which power transforming machines can be installed. The platform can be equipped with wave reflectors for the deflection and focusing of waves. 15 The wave reflector is designed as a floating curved stiff, thereby self-stabilising pontoon of considerable length, compared to the width and height of any cross section, and it is equipped with means of fixing fenders ■" and hawsers to it, in such a way that it can be kept in the desired position compared to the platform. There are other known wave-driven plants of a related type such as the PCT/DK91/00329 - WO 93/09347. The Swedish company Sea Power AB has likewise developed a floating platform, where the waves travel up an inclined plane into a reservoir from where the water is led back to the sea through a turbine. ':'■ The principle in which waves are guided up a ramp is also known from a plant in Norway called TAPCHAN. This plant is the only type of large scale wave energy exploitation plant which has promised a sufficiently long lifetime with stabile power production, that there is sufficient 35 basis for a reliable estimate of the price of the elec- - tricity produced. The TAPCHAN plant is built on a rocky coast and consists primarily of a tapered channel, in which the wave energy is concentrated. When the waves travel up the narrowing and rising channel they increase in height, but are reduced in width, after which the water spills over into a reservoir whose water level is up to 3 m above average sea level. The water is led back to the sea through a conventional water power station with a Kaplan turbine which powers a 350 kW asynchronous generator. The plant has turned out to be reliable, but can obviously only produce electricity at certain wave directions. Furthermore, the electrical production at a given wave height is dependent on the tide level. The plant according to the presented invention is unusual in being an offshore wave energy converter which can be installed on all bodies of water that have a depth from approximately 10 m to more than 300 m, and which exploits the wave energy in a way, that is most alike the TAPCHAN plant, as it is able to focus wave energy and guide wave crests into a basin from which the water can be led back to the sea. As a result of this, the energy can be utili- εed in a number of low head turbines where the hydraulic pressure and flow is converted to electric power. The plant is as the Norwegian plant a relatively large and heavy construction, as the width of the platform should be more than the average wavelength on the anchorage site; a preferred example of design of the plant is therefore to make the platform in armoured concrete. To reach the necessary good economy in a renewable energy plant built according to the invention, it will be neces¬ sary for the plant to have a long lifetime and small maintenance costs - for example, a life-expectancy of 50 years can be obtained with the use of already existing materials and methods of construction. Besides the ability to resist all types of weather that can be expected in the design period for the plant, it is necessary that the plant can utilise a substantial part of the wave energy resource. This is obtained by anchoring the plant in such a way that it always sways to receive waves from the predominant direction. This means that the plant always receives the largest possible amount of wave energy in the prevalent wave climate. At the same time, the energy led to the plant's basin is maximised by adjusting the floating height of the plat¬ form. As the ramp of the platform is designed as a doubly curved surface and the wave reflectors likewise are cur¬ ved, a wave mowing towards the plant will arrive to the platform in such a way that a relative long amount of time will pass from when a crest hits the central part of the plant until the last part of the reflected wave reaches the wave catcher elements farthest away. The re¬ sult of this is, that the forces acting on the construc¬ tion parts are reduced and that the plant's movement on the sea is dampened, by which the efficiency in the ex¬ ploitation of wave energy increases. Before a wave crest reaches the plant's ramp, the energy has been significantly concentrated by reflection from the wave reflectors. When the concentrated wave hits the ramp, a substantial part of the wave energy is converted from a mixture of potential and kinetic energy to pure potential energy as part of the wave crest spills over into the plant's basin. During the process of conversion, there are energy losses that manifest themselves in the following ways: Wave movements of a certain size continues to exist to the rear of the plant. There is a certain reflection from the ramp and finally there is a certain amount of wave breakage along the wave reflectors and on the platform itself. The efficiency in the converting process is greatly dependent on the height of the waves, as all of the losses of efficiency mentioned above will increase in proportion to the height of the waves. However, the doubly curved design of the ramp in connection with its variable height over the average sea level results in a energy conversion that has a high degree of efficiency in all wave heights up to the significant wave height for which the plant is designed to produce maximum power. In wave heights that exceed the design height the plant will have a constant power production, which means that its efficiency of cause decreases greatly in large waves. In large waves the floating height of the platform will be at its maximum value, as the amount of water in the ballast tanks is kept on the minimum level in such weather conditions. Thus the stabilising effect of the surrounding masses of water as well as the weight of the platform itself are at its minimum in harsh weather con¬ ditions. The result of this is, that the plant starts to ride the waves to a substantial degree - that is to fol¬ low the motion of the surface - on the high and thereby relative long waves. The energy loss due to the deflection of the wave energy by means of a wave reflector will be the lowest possible when the wave reflector is lying still in the water and when the waves hit the reflector at a relatively acute angle. At the same time with regards to the construction economy, it is important that the forces on the wave reflector's moorings and on the wave reflector itself become relatively small in comparison to the forces that can be seen on the moorings of ships, barges and other floating constructions such as pontoon-bridges. These qualities are obtained because the wave reflector in a horizontal plane is part of a conic section. Fur- thermore, its front is vertical and of a rising height over the water line in the direction in which the waves predominantly move along the wave reflector, when it is anchored properly, whilst the rear side is made with a chamfered edge. The wave reflector is furthermore equip- ped with stabilisers in the form of a keelsheet supported by shored up sheets, which mean that movement of the wave reflector caused by waves hitting the front of the re¬ flector in the prevailing direction of movement will be damped to a high degree on the grounds of the hydrodyna- mical added masses of water, acting transversally as well as alongside the wave reflector. The height of the wave reflector over the water line as well as the maximal floating height of the platform it¬ self should be adapted to the wave climate in which the plant is designed. This means that in the case of wave heights above the design value, the wave reflectors will be flooded. This effect and the above described riding of the platform when the wave lengths are large mean that the forces that act upon the anchoring system do not rise significantly when the wave heights exceed the wave height where the plant reaches its maximum effect. The plant is designed in such a way, that the platform can be brought to float at a level so low, that the top parts will be at sea level. The wave reflectors can be rotated around the points of fixture on the platform and be brought in a position such that the wave energy in¬ stead of concentrating towards the platform, will spread away from it. Such a lowering of the platform with a simultaneous rotation of the wave reflectors can be used when parts of the machinery on the platform are failing and in extreme weather conditions. When undertaking main¬ tenance on the plant, the platform is raised to the highest floating position, and if necessary, the wave reflectors are rotated to minimise the plants movements upon the sea. A preferred design of the plant according to the inven¬ tion is characterised by the contour lines of the ramp and/or the curves with the largest drop towards a hori¬ zontal plane being parts of conic sections. As an example there are, with regards to strength as well as practical construction work, substantial advantages to gain in de¬ signing the ramp in such a way that the horizontal curves are concentric circle sections, and that the curves with the largest drop are parts of ellipsoids. Furthermore a very effective conversion of the waves' kinetic energy to potential energy is hereby achieved, as the run-up to the reservoir only causes minor breaking and reflection of the waves for all wave heights because the water meets a slope with an evenly decreasing inclination as it travels up the ramp to the basin. Another preferred design is characterised by the ramp being constructed by joining together a relatively large number of exactly identical sections. Each of which is designed as a single curved surface. In this way, the horizontal curves can be sections of regular polygons whose circumscribed/inscribed circles have the same centre, whereby a rational and simple production of the ramp can be obtained. By designing the platform in such a way that the ballast tanks are divided into cells by means of bulkheads and ribs and by using perforated plates as bottom plates in the ballast tanks, the possibility of adjusting the floating level of the platform by changing the air pres¬ sure in the ballast tanks exists, as the water can float freely through the holes in the bottom-plates. This leads t ι furthermore to an increase in the strength and stiffness of the construction, and dampening the movement of the plant on the sea, partly because the water in the tanks only has limited freedom of movement in a horizontal direction - partly because the force that acts on the platform's bottom plate and the variation of this as a result of varying pressure generated by the waves is diminished. Due to the fact that the pressure in the air-filled sections of the ballast tanks under normal conditions will be higher than the atmospheric pressure, there will be a reduction of the resulting forces acting on the parts of the platform which are directly in con¬ tact with the waves. To secure the plant's platform against sinking if the air pressure in the ballast tanks should be lost, the ballast tanks could be equipped with buoyancy material in such a volume and with such a placement that the platform would lie so deep in the water that the top of the side pon¬ toons would just be visible and in a horizontal position. It would be appropriate, that the plant's anchor block and the anchor pontoon are equipped with detectors for registration of heights, frequencies and speeds of the incoming waves. With the proper automation for adjusting the air pressure in the ballast tanks and the number in use and/or the effect of the power converting machines on the platform, the efficiency of the plant could hereby be optimised with regards to the actual wave climate. It should be noticed, that such an adjustment of the plant's operating parameters neither could or should happen so fast that there would be significant changes over a single wave period. Since waves often travel in groups, which move at a significantly lower speed than the waves themselves, it would however be practically possible to change the operating parameters significantly within a period corresponding to the frequency of the wave groups. It should be mentioned that a rather common time-distance between wave groups is approximately 1 minute. The effect of such automation is primarily that it ensures there al¬ ways will be water in the platform's basin. Thus there will only be minor fluctuations in the power production and a higher efficiency of the plant. The strategy for the regulation is as follows: A relatively large amount of water will be retained in the basin when only small wave trains are registered to be heading towards the ramp. Besides ensuring the basin against a complete emptying, this will also contribute to a lowering of the platform's floating height, which in turn will increase the water supply to the basin. When on the other hand, a large group of waves approach the ramp, an increased turbine capacity is brought into action prior to this, leading to a nearly empty basin and a raising of the platform. It is hereby ensured that the basin will not overflow and thus that the increased wave power effect can be fully used. The production of the wave power plant can be increased substantially by using wave reflectors. It is therefore an appropriate design, that the platform's side pontoons, on the side turning against the incoming waves, are equipped with a fender arrangement consisting of one or more vertical braces for almost the entire height of the pontoon. A fender element of an elastic material is mounted around the brace in such a way that a wave re- flector can be fixed to the pontoon. The fixed wave reflector can maintain a constant floating height without causing an exchange of vertical forces with the platform despite the floating height of the platform being vari¬ able. Another preferred design of the plant according to the invention is characterised by being supplied with machin¬ ery for the variable positioning of two wave reflectors. The wave reflectors can be moved by varying the draw in the hawsers connecting the wave reflectors, for example by changing the draw in one or more wires which are lead out through the ramp in the platform's middle and fas¬ tened to the middle of the connecting hawsers. At the same time this is done, the hawsers which prevent the wave reflectors from moving towards each other as a re¬ sult of wave forces moving contrary to the predominant wave direction on the wave reflectors rear side are loosened. A preferred design of the wave power plant's platform ac¬ cording to the invention is characterised by the place¬ ment of windmills of type where the rotors are suspended in a so-called free yaw/tilt suspension. This means that, compared to the tower, the rotor has freedom of movement within certain limits. The power transforming machinery, such as a gearshift, electrical generator, or a mill- driven water-pump with exit to the platform's basin is placed in the side pontoons. This way the static as well as the dynamic forces acting on the tower will be small. Since there normally only exists a small difference be¬ tween the wind direction and the dominant wave direction, and since the plant moves in such fashion that the plant's symmetry axis lies in a direction between the prevailing wind and wave directions, there is no need for an actual yawing ability of the rotor/nacelle. The rotor's axis will not be able to completely follow the platform's movements on account of the gyroeffects. For this reason, there will have to be a large distance between the rotor planes and the tower. A suitable wind¬ mill type could be a dual-bladed mill with fixed but flexible wings (i.e. stall-regulated), which without an actual gearbox run the propeller in a directly linked propeller-pump, which in its turn lifts the sea water into the plants basin. The mill will be able to function with variable rotations and can this way achieve a high degree of efficiency. During storms, the wings will be stowed in a horizontal position and there will therefore be no risk of direct wave influences in spite of the relatively small tower height. The placement of windmills will also have a sta¬ bilising effect on the plant's movements on the waves. Windmills lifting water into the plants basin will gener¬ ate steadier water stream to the power generating machin¬ ery and thereby will also cause a better utilisation of the installed machinery. The increase in power production resulting from windmill placement on the plant can be calculated to approximately 1/3. The invention will be further explained in the following, with reference to the drawing showing a preferred embodi¬ ment of the invention where: Fig. 1 shows the general plant with windmills in plane and elevation, respectively. Fig. 2 is a vertical section in the symmetry plane of the plant, section I-I at fig. 1. i > Fig. 3 is a vertical section near the middle of the platform next to a turbine/generator. The plat¬ form is shown in its highest floating position, 13 Fig. 4 is a vertical section near the middle of the platform. The platform is shown in its middle floating position. Fig. 5 is a vertical section in a wave reflector, 70 section II-II at fig. 1. Fig. 6 is a vertical section in a wave reflector, section III-III at fig. 1. ^ Fig. 7 is a plane section of the platform next to a side-pontoon. Fig. 8 is a vertical section in a side-pontoon, section IV-IV at fig. 7. 30 Fig. 9 shows the general plant without windmills in plane and elevation respectively - a wave reflection pattern is marked, and 35 Fig. 10 shows the general plant with windmills in plane and in 3 spatial inclined top views, respectively. Fig. 1 shows the plant according to the general inven¬ tion. Fig. 1A is a top view of the plant and fig. IB is a direct front view of the plant. The plant is in this example provided with two windmills 11 and two wave re- flectors 2. The central part of the wave power plant is a floating platform, which is mainly made of concrete and which is marked 1. The platform and wave reflectors are connected to a floating anchor pontoon 3. The anchor pon¬ toon is a closed body, possibly made of steel, which is filled with a buoyant material and is thereby unsinkable. The anchor pontoon is anchored to the top of the anchor block 4 by means of a chain 5 or an oblique steel pole. The anchor block is a concrete construction, that is secured to the sea floor in all conditions of weather either by a large net weight or by piling. The anchor can also be designed as a suction-anchor, which has the advantage, among other things, that it is easy to move the plant to another anchorage, if this should be neces¬ sary. The top of the anchor block 4 can rotate freely around a vertical axis, which means, that the wave power plant is self-adjusting in accordance to the prevailing wave directions. If the plant is connected with pipes 12 or leads 12 to other installations or to the coast, these are as shown in figs. 1 or 2. The pipes/leads 12 lead from the platform 1 to the anchor pontoon 3 and from here by the anchor chain 5 to the top of the anchor block. Further pipe/lead connections run by a revolving link through the anchor block to the sea floor, where the pipe/lead 12 is sheltered under the sea floor. Fig. 2 illustrates that the anchor system allows for a certain degree of limited movement of the platform in a direction away from the anchor block. This is because the anchor pontoon 3 is pulled deeper into the water. This arrangement greatly enhances the anchor system's elasticity, which in turn strongly reduces the maximum strain on the anchor system as a whole. The platform 1 is, as shown at figs. 3 and 4, equipped with a ramp 13, by which waves are lead into a shallow basin 14. The basin however, has a large volume, as it is enclosed by the ramp 13, a vertical wall near the back of the platform and the two vertical walls at the side pontoons 18 of the platform. The volume of the basin is proportionate to the wave conditions at the anchoring place, so in the majority of the time, the basin is large enough to receive the entire wave flow without ever draining completely. From the basin 14, which has a sloping bottom, the water flow is lead back to the sea, for instance by conventional Kaplan type turbines and/or the Ossberger crosεflow type. The turbines are for in¬ stance able to draw ordinary asynchronous electric gene¬ rators. A stabile power production from the plant is achieved by using a larger number of turbines (10 for instance) coupled with correct regulation of the opera¬ tion of these turbines, as shown in fig. 1. This is due to fact that the pressure of the water above the turbines can only vary in short periods according to the water depth in the shallow basin 14, which means few wave periods. The constant filling of the basin 14 under different weather conditions is achieved by varying the floating height of the platform in accordance with the relevant wave heights. At wave heights which are equal to or lar¬ ger than the designed value, the platform and thereby the basin 14 lies at the highest level, as shown at fig. 3. At lower wave heights, the platform lies lower, as shown at fig. 4. It is possible to lower the platform so much that waves with heights down to approximately 0,5 m can be used for power production. This is because at low wave heights crossflow turbines, which can achieve a good efficiency even at low hydraulic heads (0,75m) can be utilised. As shown at fig. 3 and 4, the wave crests for all wave 5 heights up to the designed heights, will hit the ramp 13 rather high up, i.e. in the zone where the buoyancy mate¬ rial 21 is shown under the ramp. The ramp's inclination is so small here, that wave reflection becomes negligib¬ le. The front of the plant is shaped in such a fashion 0 that it allows the conversion of the wave's kinetic ener¬ gy to potential energy to occur with small loss of energy as breaking and friction against the ramp is minimised. Because a wave breaks when the wave height reaches a cer¬ tain water depth, the enhanced curve of the ramp's lower ! 5 part causes the waves running up against the platform to meet a very abrupt slope at first and therefore will only break in a modest degree, before hitting the upper part of the ramp. This is shown at fig. 3 and 4. In the preferred embodiment the ramp is made of concrete consisting of 19 identical shells, which have the shape of an ellipse in a cross section analysis. The concrete elements are held together with steel cables and are clasped to the parts already in place. A high quality of /3 concrete is used, so that the lifetime expectancy is at least 50 years, without major maintenance costs. The shape of a wave reflector 2 is seen in the background in figs. 3 and 4. It floats at a constant height above the mean sea level, which is marked with an "H" in the two figures. The platform's floating height is variable, as the cavities 15 work as ballast tanks and they are emptied through holes in the bottom plates 19. Only a few holes are shown in the figures, but the bottom plates 35 are made with a large number of holes, for reasons of strength and weight. Therefore constructively they will be characterised as an open rib deck with crossing ribs or a closely perforated plate. The bottom plate is especially strongly perforated in the front part of the bottom plate i.e. the area under the ramp. The result is that the increasing pressure which appears under the bottom plate when a wave runs up against the platform, causes a relatively small lifting force at the front part of the platform, because pressure is relieved as water is pressed up through the holes in the bottom plate to the ballast tanks. Therefore the perforation of the bottom plates results in a considerable reduction of the verti¬ cal load on the platform, which in turn results in the reduction of the platform's movements on the sea. No. 16 shows a complete cavity for the full extent of the ramp. No. 17 is one of the 9 pieces of transverse concrete bulkheads from the embodiment and no. 20 is a concrete- rib shown longitudinally. The ribs are cast to the con¬ crete-bulkheads and both ribs and bulkhead are cast to the bottom plates. The result is a very strong and stiff construction and that the ballast tanks are divided into smaller chambers, which decrease the movement of the bal¬ last water and thereby making the platform float more steady. The buoyancy material 21 can for instance be polystyrene foam, which does not have a propped up effect on the platform's carrying parts, or a light porous con¬ crete, which is also able to interact constructively with the bottom of the basin 14. The volume and placement of buoyancy material have to be such that the platform is just able to float and to keep its mainly horizontal position, if the air pressure in the ballast tanks should be lost. The floating height is varied by changing the air pressure in the ballast tanks, in that the pressure is at its maximum when the floating- height (and thereby the forces from the waves) is high. It is therefore obvious that emptying the ballast tanks by means of air pressure instead of the traditional way by pumping water, leads to a considerable reduction of the strain on the part of the construction which is most exposed to the waves, such as the ramp 13 and the basin's bottom 14. Two large holes in the wall between the side-pontoon 18 and the basin 14 are seen in fig. 4.. These holes only exist if wind mills are placed on the pontoons, as the holes are outlets from the wind driven propeller pumps, which lift water up into the basin 14 and thereby increase the effect of the plant's turbines with approximately 1/3 in this preferred embodiment of the invention. Fig. 5 and 6 show a cross section of a wave reflector. In the preferred embodiment two of such reflectors are moored and anchored to the plant's platform 1. Both wave reflectors are marked "2", as these are identical, and in planal view are mirror-images of one another. The wave reflectors, which are also shown at all the other figures of the preferred embodiment, are predo-minately made of steel. The wave reflectors are of a size that allow them to be built in most shipyard docks. Several reflectors can be built simultaneously in a dock of normal propor¬ tions. The wave reflector is a closed construction welded by plane steel plates 23 of the same type as used in ship construction. The width of the wave reflector is the same everywhere, marked with a "B" on the figures, while the height above the water line is smoothly rising from the side directed towards the waves, marked with "axH", to the height "H" in the opposite end. It appears from the figures that the essential parts of the construction are identical for the entire length of the wave reflector, facilitating a rational production of these. Steel bulk- head supports are placed at regular intervals in the cavity 28, which is also shown with openings that access the inner parts for inspection and maintenance. The side from which the waves are reflected, is vertical from the section under the water line to the top, while the back is only vertical from slightly under the water line until meeting an oblique surface from the top of the wave re¬ flector. This geometry grants a good stiffness/strength to the cross section and the oblique cut reduces the influence from any waves which may hit the wave reflector from behind. The keelsheet 25 gives the wave reflector great stabi- lity in case of the wave reflector moving sideways by adding a large hydrodynamic mass of water to the wave reflectors. The keelsheet is propped up by means of transverse steel ribs 24, placed against the inner steel bulkhead. In this way, greater stability against movement lengthwise is also achieved by the addition of a hydro- dynamically added mass. The wave reflector is to obtain great stability provided with ballast 26 in varied quantities, as seen in the cross section. The ballast can for instance be concrete. The wave reflector achieves extra stability against rolling on the waves, because it is curved, seen from the horizontal plane, as shown in figs. 1 and 9. In the preferred embodiment a constant curve of the wave reflec- tors is used, which has certain production-technical advantages. Alternatively, the wave reflectors can be made as para- bella-curves of a type and placement, so that, in prin- ciple, the reflected waves are focused near the middle and the top of the ramp, resulting in the reflecting waves not crossing each other. A wave reflector designed in this fashion will resemble the shown circle-curved shaped wave reflector, apart from the parabella-curved wave reflector will have a smaller curve at the tip and a larger curve near the platform. This means that the para¬ bella-curved wave reflector has certain advantages with regards to strength vis-a-vis the circle-curved wave reflector. The wave reflectors are supplied with means for securing a fender arrangement 7 as shown in figs. 7 and 8. The wave reflectors are also anchored by means of transverse hawsers, which connect the two wave reflectors. Finally, the wave reflectors are secured to the anchor pontoon 4 with hawsers, as shown in fig. 1A. The wave reflector in the preferred embodiment is supplied with a arm 8 which is fixed to the exterior of the reflector near the fender arrangement. The arm is connected with two hawsers to a motor-driven capstan, which in turn, is placed in the platform's side pontoon 18. These capstans ensure the wave reflectors do not move against each other in case of transverse waves, hitting the wave reflector from behind. At the same time, the capstans ensure that the transverse hawsers between the wave reflectors are held constantly tight, resulting in a substantial lowering of the maximum draw of the hawsers and thereby also of the forces acting on of the wave reflector. It is possible to change the draw of the connecting haw¬ sers 6 by means of a supplementary capstan, revolving the wave reflector around the fender arrangement as the draw in the hawsers 9 is changed simultaneously. As shown in fig. 1A it is by utilising the supplementary capstan possible to turn the wave reflector to such a de- gree that the opening to the waves becomes less than one fifth of the entire opening. This is done by pulling cer¬ tain wires, which are lead through a hole in the middle of the ramp and along the central anchor hawser to the centre of the connecting hawsers. After a maximum turn of the wave reflector, its position will be as marked with a dot-and-dash shape in the figure. The fender arrangement 7 consists of a pipe-shaped fender element, which is mounted on a wave reflector by means of a vertical steel brace. The fender element is made of an elastic material, and is a special version of the ordi- nary rubber pipe fender. The side pontoon 18 of the platform is supplied with a vertical steel brace, which is lead through the fender element and covers almost the entire height of the pontoon, as shown in fig. 8. The floating height of the platform can in this way freely be varied without influencing the wave reflectors. Fig. 9 illustrates the elevated front of the wave power plant, identical to fig. IB - the only difference is the absence of windmills on the platform in fig. 9. A plan of the wave power plant is shown above the elevated front, but the entire anchoring system is left out to facilitate the illustration of the pattern of wave reflection. The lines 30 indicate the crests on idealised straight waves, which run against the plant at the ideal direc- tion, parallel to the plant's symmetry axis. The dotted lines are radii from a point 33 to a wave reflector 2, whose sides create a section of a circular-ring with centre in point 33. The arrows 32 indicate the direc¬ tion in which the waves move. The arrow points indicate where the wave crests hit a wave reflector and where the same wave crests hit 1/3 and 2/3 respectively of the wave period later. In the case of an ideal reflection, the direction of the reflected waves is found by mirroring the entrance direction in the respective circle radius, since the entry angle and the exit angle are identical. The direction in which the reflected waves move, is marked by the lines 32. The arrow points indicate where the reflected waves reach the front of the ramp of the platform. The reflected crests 32 are seen clearest by the right wave reflector. It can be seen that the crest that has just reached the ramp is crossed by a reflected crest from the former wave that reached the ramp. The cross point is marked with a circle. The wave reflection pattern indicates that a wave reflec¬ tor with a constant curve causes the reflected waves to cross each other. In this way, local crests arise which are essentially higher than the undisturbed wave heights. In reality, however, the reflected energy will be dissi¬ pated to a certain degree through non-linear wave inter¬ action between incoming and reflected waves. Never the less, the reflection pattern gives a good picture of how the waves move. It is furthermore clear, that none of the reflected waves are able to cross the symmetry axis of the plant. In this way, interaction between the reflected waves from the two wave reflectors is avoided, with lower strain on the platform's front as a result. The dimensions of the wave power plant in the preferred embodiment are selected proportionate to the illustrated prevailing wave length in such a fashion that there are direct or reflected wave crests constantly going up the ramp. The undisturbed waves hit the middle of the ramp first, while the reflected waves hit the ramp near the side pontoons and from here move obliquely up the ramp towards the middle of the plant. A steady stream of sea water into the basin is therefore achieved on account of the curved shape of the ramp and the wave reflectors. At the same time this increases the stability of the platform against the rolling of the waves to be signi¬ ficantly larger than that of barges, pontoon bridges and the like, which also lie across the waves and have the same width as the platform. A high degree of stability of the platform also gives a proportionate high degree of efficiency in the use of wave energy. This is why the proportions of the plant must be adapted to the local wave climate. The preferred embodiment estimates an opening width of approximately 160 meters between the wave reflectors and a maximum water pressure for the turbines of approximate- ly 4 meter. Such a plant fits the wave climate existing in several positions in the Danish part of the North Sea. Fig. 10 shows the entire plant with wave reflectors and wind mills. The type of windmill illustrated here has the wings placed in front of the tower, but the mills can as well be the down-wind type, i.e. a type with a self- stabilising rotor placed behind the tower, as seen from the wind's direction. A windmill of the down-wind type has a rotor plane placed further back on the ramp of the platform, reducing the risk of spray on the wings. In the spatial drawings, all construction lines are shown, i.e. the "hidden lines" have not been removed. When figs. 5 and 6 are compared, it becomes obvious that the wave reflectors are supplied with a large amount of shored up sheets which in conjunction with the keelsheet 25 results in the great stability of the wave reflectors against movements caused by wave action mentioned before. The wave reflectors according to the invention are also able to increase the energy production of other types of wave power plants, if these are able to utilize a focused wave field. Such plants can achieve a much better pro¬ fitability, especially if two mirrored reflectors which reciprocally are connected with hawsers or tension bars are used, according to the preferred embodiment of the invention. This is due to the fact, that the caught wave energy is doubled compared to what can be achieved with one wave reflector, while a major part of the forces caused by the waves in such an arrangement of two wave reflectors is counteracted by draws in the connecting hawsers, whereby the draws in the actual mooring system are far from being doubled. This makes a much better relation between energy production and capital cost pos- sible, as the cost of the mooring system for all types of floating wave power plants accounts for a considerable part of the plant's total price. The wave reflectors according to the invention can fur¬ thermore be used profitably instead of using ordinary breakwaters, for instance to protect harbour entrances or jetties with rather great depths of water, as the wave reflectors also when used with fixed anchorings lead to steady and rather small draws in the anchor system. By using such wave reflectors, the investment will become much smaller than can normally be achieved with known floating constructions, which consequently not often are used as breakwaters. 15 75 30

Claims: C L A I M S 1. Plant for exploiting wind/wave energy on the high seas consisting of a floating, self-adjusting with regards to wave movement, platform (1) anchored with hawsers connected to a floating anchor pontoon (3), which in its turn is moored to a swivel link at the top of an anchor block (4) on the sea floor through which a pipe or power cable (12) possibly can be led; a ramp (13), said ramp on which waves can travel and spill over into a basin (14) which has a variable water level relative to the mean sea level and from which the water once again is led back to the sea through pipes in which power trans¬ forming machinery (10) can be installed, said plant characterised by the ramp (13) having a doubly curved surface with a property such that all curves produced by cutting the surface of the ramp with horizontal planes, have a convex form with respect to the direction of the incoming waves, and that curves produced by cutting the surface of the ramp with vertical planes through the anchor pontoon (3) are downwards hollow. 2. Plant according to claim 1, characterised by the horizontal curves of the ramp (13) and/or the curves of the largest fall on the ramp are parts of conic sections. 3. Plant according to claim 1, characterised by the ramp (13) being constructed by joining together a rela¬ tively large number of sections each of which designed as single curved surfaces. 4. Plant according to claim 1, characterised by the ballast tanks (15) being divided in cells by means of bulkheads (17) and ribs (20), and by the bottom plates (19) in the platform's ballast tanks (15) being per- forated whereby the floating height of the platform can be regulated by changing the air pressure in the ballast tanks. 5. Plant according to claim 1, characterised by the ballast tanks being equipped with buoyancy material (21) with such a volume and in such a placement, that the platform with atmospheric pressure in the ballast tanks (15) lies so deep in the water, that the top of the side 0 pontoons (18) are just visible and lies horizontally. 6. Plant according to claim 1, characterised by the anchor block (4) and/or the anchor pontoon (3) being equipped with detectors for recording of heights, fre- 5 quencies and speed of the incoming waves and a corre¬ sponding automation for adjusting the air pressure in the ballast tanks and the numbers and/or effects of the power converting machines in operation on the platform whereby the efficiency of the plant can be optimised with respect 0 to the actual wave climate. 7. Plant according to claim 1, characterised by the side pontoons (18) on the side facing the incoming waves being equipped with a fender arrangement consisting of a 5 vertical brace in almost the entire height of the pontoon (7), around which a fender element of an elastic material is mounted in such a way that a wave reflector (2) can be secured to the pontoon without giving rise to exchanging of vertical forces with the platform at any floating Ϊ height of the platform. 8. Plant according to claim 1, characterised by the side pontoons (18) being equipped with machinery for a variable positioning of the two wave reflectors (2), 5 which is obtained by varying the pull in the hawsers (6) connecting the wave reflectors and at the same time the pull in the hawsers (9), which by means of moment-arms (8) on the wave reflectors prevent the wave reflectors from moving uncontrollably against each other as a result of forces acting on the rear side of the wave reflectors due to waves moving in another direction than the pre¬ vailing wave direction. 9. Plant according to claim 1, characterised by there being placed on top of the side-pontoons (18) two wind¬ mills (11) of a type with the rotor suspended cardanic i.e. with free yaw/tilt allowing the rotor to move freely within certain limits with regards to the windmill tower, and where the power-converting machinery like gearbox, generator or a mill-driven water pump with outlet (22) to the basin (14) on the platform is placed inside the side pontoons (18), thus making the static as well as the dynamic influence of forces on the tower small. 10. Wave reflector (2) for deflection and focusing of waves designed as a floating stiff, curved and thereby self-stabilising pontoon of considerable length with regards to the width and height of any cross section and being equipped with means for fixing to fenders (7) and hawsers (6,9), characterised by the wave reflector in a horizontal plane is a part of a conic section, said wave reflector's front is vertical and of an ever increasing height over the water line in the direction the waves predominantly move along the reflector, when this is appropriately anchored, while the rear section (23) is made with a chamfered edge, and that said wave reflector is equipped with stabilisers in form of a keelsheet (25) supported by shore up sheets (24), which means that move¬ ments of the wave reflector caused by waves hitting the front of the reflector in the prevailing direction of movement will be damped to a high degree thanks to the hydrodynamically added masses of water acting transver- sally as well as alongside the wave reflector.

Inventors: FRIIS-MADSEN ERIK, FRIIS-MADSEN, ERIK
Applicants: FRIIS MADSEN ERIK, FRIIS-MADSEN, ERIK
Application year: 1995
Main classification: F03B13
IPC codes: F03B13, F03D9