Positioning device and system for extracting energy from a waterflow

Abstract

A positioning device positions a central longitudinal axis AE of an elongate body 1 at a desired angle relative to a water flow in a first direction DI. The elongate body 1 is connected at a first en

Description

Title: Positioning device and system for extracting energy from a waterflow Field of invention The invention relates to exploitation of hydrodynamic forces, more precisely to use the force of moving water acting on a positioning device to position an elongated body, which the positioning device is attached to, in a desired position or angle. Background Renewable energy extracted from the flow of water has been used by humans for several hundreds of years. This application is directed towards extracting energy from tidal currents or water flowing in a river. The inventor has developed a helical screw that has shown increased efficiency relative to the throughflow area compared to other rotors. The helical screw is dependent on having a certain angle relative to the flow of water. If the helical screw is designed as described in EP3120014 Bl the efficiency of the helical screw will increase due to the flow of water causing a rotational force in the same direction on both sides of an axis around which the helical screw is turning. The velocity of water flows both in rivers and tidal currents is higher closer to the surface. Therefore, it is an advantage to install the helical screw close to the surface. In particular this is an advantage when considering that the extractable energy is proportional to the third power of the water velocity. However, placing the helical screw in the region of the water mass that is close to the surface, may result in the operation of the helical screw being affected by waves and weather. For example, a working angle of the helical screw may be mechanically restricted compared to a floating vessel, but the floating vessel may be affected by wind and waves, and this may result in large loads on the helical screw and stability issues. It is desirable to avoid unnecessary large loads and instability while maintaining a good working angle for extracting energy from the water masses. It is an object of the invention to solve the problem of positioning the helical screw at an optimal angle relative to the water flow in all conditions. It is an object of the invention to achieve moment equilibrium around the pivoting axis P at the desired angle aopt using the hydrodynamic properties as well as buoyancy / weight, where the hydrodynamic properties is the major controlling factor. It is an object of the invention to develop a positioning device without any moving parts, so called ‘passive dynamic control’, that will hold any elongated body, for instance the mentioned helical screw, at a desired angle relative to a water flow into which the elongated object is immersed. It is also an object of the invention to achieve the desired angle at a velocity range of the water flow that is as large as possible. Summary of the invention In an aspect of the invention there is provided a positioning device for positioning a first central longitudinal axis AE of an elongated body at a desired angle aopt relative to a water flow in a first direction DI. The elongated body is connected at a proximal end at a pivot point P and is pivotable about the pivot point P in a plane parallel with the first direction DI. The positioning device comprises a foil shaped body and fastening means for fastening the foil shaped body to the elongated body. The foil shaped body is configured for mounting to the elongated body. The foil shaped body has a second central longitudinal axis AF, a concave side and a convex side, wherein the concave side and the convex side curve from a first edge to a second edge. The positioning device comprises fastening means configured for fastening the foil shaped body to a distal end of the elongated body such that the second central longitudinal axis AF is substantially at a right angle to both the first central longitudinal axis AE of the elongated body 1 and the first direction DI of the waterflow when the positioning device is in a working state. The concave side of the positioning device is facing the elongated body. The fastening means 13 may position the first and second central longitudinal axis, AE and AF for intersection with the first central longitudinal axis AE when the foil shaped body 4 is fastened to the elongated body 1. The foil shaped body may have a two-way configuration that may be symmetric around a plane including the second central longitudinal axis AF and a line perpendicular to the second central longitudinal axis AF, and the fastening means is configured to position a line L intersecting the first edge and the second edge perpendicularly to the first central longitudinal axis AE when the foil shaped body is fastened to the elongated body. The longest distance between L and the concave side is within the interval 0,2 and 0,5Cl, where Cl is the distance between the first and second edge. The foil shaped body may have a one-way configuration, wherein the fastening means is configured to position the line L from the first edge to the second edge at an angle P with the first central longitudinal axis AE which is within the interval [aopt, aopt + 20 degrees], and the longest distance between L and the concave side may be within the interval 0,0 and O,25C1. An angle between the first central longitudinal axis AE and a tangent T of the concave side at the first edge facing the waterflow may be equal to the desired angle aopt + / -10 degrees, more preferable + / -5 degrees. The foil shaped body may comprising a side wall on each side of the foil shaped body, where each side wall covers an area from the straight line L between the first edge and the second edge and extends towards a respective end of the foil shaped body. If the waterflow is coming from the first direction DI, the first edge is a leading edge and the second edge is a trailing edge. If the waterflow is coming from a direction D2 opposite to the first direction DI the second edge will be the leading edge and the first edge will be the trailing edge. A cross section of the foil shaped body may be described by a portion of a first circle with radius RI representing the convex side and a portion of a second circle with radius R2 representing the concave side, where the circle with radius RI represents a larger portion of a circle than the circle with radius R2, wherein the portions having chords of same length Cl. The two intersection points of the circles have a chord of length Cl drawn between them. The perpendicular distance between the surface of the concave side 8 at the second central longitudinal axis AF and a line between the first and second edge 6, 7, also called the leading and trailing edge, may be between O*C1 and 0.5*Cl. A cross section of the foil shaped body may be described by a portion of a circle with radius RI representing the convex side and a circle with radius R2 larger than RI representing the concave side, and both having chords of length Cl. The positioning device may comprise a first support foil mounted on the convex side at a distance from the first edge, wherein the first support foil has a concave side that has a constant distance from the convex side of the foil shaped body and a convex side described by a portion of a circle bigger than the concave side, wherein both portions of circles are cut out by chords of same lengths less than Cl / 2. The convex side may also be described by a portion of a circle bigger than the portion of a circle describing the concave side, wherein both portions of circles are cut out by chords of same lengths less than Cl / 2, preferably equal to Cl / 3. The positioning device may comprise a second support foil mounted on the convex side at a distance from the second edge wherein the second support foil has a concave side that has a constant distance from the convex side of the foil shaped body and a convex side described by a portion of a circle bigger than the concave side, wherein both portions of circles are cut out by chords of same lengths less than Cl / 2. The convex side may also be described by a portion of a circle bigger than the portion of a circle describing the concave side, wherein both portions of circles are cut out by chords of same lengths, wherein the mentioned lengths are less than Cl / 2, for instance Cl / 3. The thickness of the foil shaped body 4 may be 0,125 X Cl at the second central longitudinal centerline AF. A sector spanned by the concave side of the foil shaped body on each side of the longitudinal centerline may be substantially equal to the desired angle aopt. In a second aspect, there is provided a system for extracting energy from a water flow. The system comprises the mentioned positioning device and the elongated body. The elongated body comprises one or more axles parallel with the central longitudinal axis AE and a helical screw mounted on each of the one or more axles for extracting energy from the waterflow. The positioning device is fastened to distal ends of the one or more axles while allowing the one or more axles to rotate around its rotational axis. The invention may be held in place by the one or more shafts or together with a separate holding structure. The system comprises a holding structure to which proximal ends of the axles are coupled, and wherein the rotation of the helical screw is transferred to an energy converter. The energy converter of the system may comprise an electrical generator 12. The at least one helical screw may comprise a first helical screw and a second helical screw arranged to counterrotate. The holding structure may comprise a floating vessel rotatably connected to a single point mooring. The holding structure may comprise a concrete slab positioned on a subsea surface with fixtures for connecting to the elongated body. Short description of the drawings To facilitate the understanding of the invention, we have attached some figures where the same reference number refers to the same feature in the various figures. Fig. 1 shows a side view of helical screw with a positioning device hung from a vessel. Fig. 2 shows a helical screw with a positioning device coupled to a subsea holding structure. Fig. 3 shows a helical screw with a positioning device hung from a floating holding structure. Fig. 4 shows a first foil shaped body configured to handle currents from two opposite directions. Fig. 5 shows a foil shaped body configured to handle currents from one direction. Fig. 6a and b show a wing shaped body configured to handle currents in one direction. Fig 7 shows a side view of a foil shaped body having support foils mounted on the convex side. Fig. 8 show two perspective views of an embodiment of a position device. Fig. 9 shows the positioning device of fig. 8 having side plates mounted. Fig. 10 shows top view of a positioning device. Fig. 11 show a sectional view of the positioning device of fig. 7 and 8 with exemplary measurements. Fig. 12 shows a top view of a system including a positioning device for extracting energy from a flow of water. Detailed description There is provided a positioning device 100 for positioning a first central longitudinal axis AE of an elongated body 1 at a desired angle aopt relative to a water flow in a first direction DI as illustrated in fig. 1 and 2. The positioning device 100 is a fixed body with no moving parts made of materials able to remain submerged in water for longer periods of time. The elongated body 1 is connected at a proximal end at a pivot point P shown in fig. 1, 2 and 3 and is pivotable about the pivot point P, preferable in a plane parallel with the first direction DI. However, examples of the positioning device with movements outside the mentioned plane are also conceivable. The flow in the first direction would typically be flows found in a river or at a site exposed to tidal waterflows. In tidal regions the flow patterns can usually be ordered in two opposite directions, but substantial deviations can be found. On such sites positioning device with a more flexible directionality should be applied. The positioning of the elongated body lisa balancing act between the force of the flowing water acting on the elongated body, the forces from the positional device 100 directing the flowing water by means of its shape and the gravitation and buoyancy acting on the combined structure. The combined forces achieve a moment equilibrium around the pivoting axis P at the desired angle aopt using the hydrodynamic properties of the positioning device 100 as well as buoyancy / weight, where the hydrodynamic properties is the major controlling factor. The size of the positioning device is driven by the same moment equilibrium. The positioning device 100 comprises a foil shaped body 4 for mounting to the elongated body 1. By foil shaped we mean a shape that is curved in the same direction on both sides as can be seen in fig 4, 5 and 6. The foil shaped body has a second central longitudinal axis AF as indicated in fig. 7 and 9. The foil shaped body 4 has a concave side 8 and a convex side 9, wherein the concave side 8 and the convex side 9 curve from a first edge 6 to a second edge 7. A positioning device 100, as described herein, may be a positioning device that responds to a waterflow in one direction as seen in fig. 5 and a set of positioning device that responds to waterflows in two opposite directions as seen in fig. 4. The positioning device further comprises fastening means 13 for fastening the foil shaped body 4 to a distal end 5 of the elongated body 1 such that the second central longitudinal axis AF is substantially at a right angle to both the first central longitudinal axis AE of the elongated body 1 and the first direction DI when the positioning device is mounted on the elongated body 1 in a working position. The concave side 8 of the foil shaped body 4 is facing the elongated body 1. Figure 4 and 7-9 show two-way examples of the positioning device 100 that responds likewise to waterflows in two opposite directions. When the waterflow is coming from a first direction, the first edge 6 is a leading edge and the second edge 7 is a trailing edge if the water flow comes from a second opposite direction the second edge 7 is the leading edge and the first edge is the trailing edge. The foil shaped body 4 is symmetric around a plane including the second central longitudinal axis AF and a line parallel with the central longitudinal axis AE when the foil shaped body is mounted. The fastening means 13 is configured for positioning the first central longitudinal axis AE of the elongated body and second central longitudinal axis, AF of the positioning device 100 such that their axes intersects at a right angle when the foil shaped body is in a working position, as indicated in fig. 8. Preferably, the positioning device is also symmetric around a plane containing the two central longitudinal axes, AE and AF as best seen in fig.7. In other words, as shown in fig. 4, a line L intersecting the first edge 6 and the second edge 7 is at a right angle with the first central longitudinal axis AE of the elongated body 1. If so, the positioning device will respond likewise to a waterflow in an opposite direction D2 as to a waterflow in the first direction DI as illustrated in fig. 2. Fig. 8 shows positioning device wherein the foil shaped body 4 comprises a side wall 10a, 10b on each side covering an area from a straight line between the first edge 6 and the second edge 7 and towards respective end sides Ila, 1 lb of the foil shaped body 4 shown in fig. 7. The effect of the side walls Ila, 1 lb is that the water flowing past the positioning device do not flow over the side walls 10a and 10b, but is to a larger degree forced along the curvature of the foil shaped body 4 and thus avoiding water particles to move from the pressure side to the suction side, increasing the directional forces and reducing drag caused by the positioning device 100 acting on the elongated body 1. In the positioning device shown in fig. 9 a cross section of the foil shaped body 4 is described by a portion of a circle with radius RI representing the convex side 9 and a portion of a circle with radius R2 smaller than RI representing the concave side 8. Both portions of a circle are cut off by chords of length Cl, which will enable the two portions to form a sickle shape, also called a crescent shape. This relation between the convex and the concave side also implies that the concave side is made up of a smaller portion of a circle than the convex side. In fig. 7-9 the positioning device comprises a first support foil 14 mounted on the convex side at a distance from the first edge 6 having substantially the same distance between the convex side of the foil shaped body 4 and the concave side of the first support foil 14. In other words, the concave side of the support foil 14 is equidistant from the convex side 9 of the foil shaped body 4. The first support foil 14 has a cross section described by a concave side curved as a circle with radius RI and a convex side curved as a circle with a bigger portion of a circle with radius smaller than RI. Both portions of a circle are cut off by chords of length smaller than Cl / 2. A well-functioning length of the support foil 14 in the direction of the water current (DI) is Cl / 3 as shown in fig. 11. Different lengths are possible, varying between Cl / 10 - Cl / 2. As seen in fig. 7-9 the positioning device may further comprise a second support foil 15 mounted on the convex side at a distance from the second edge 7 and in parallel with the foil shaped body 4, wherein the second support foil 14 has a cross section described by a concave side curved as a circle with radius RI and a convex side curved as a circle with a bigger portion of a circle with radius smaller than RI. Both portions of a circle are cut off by chords of length smaller than Cl / 2. A well-functioning length in the direction of the waterflow (DI) may be Cl / 3 as shown in fig. 11 or a different length, varying between Cl / 10 - Cl / 2. Furthermore, with reference to fig. 11, the thickness of the foil shaped body 4 may be 0,125 X Cl at the second central longitudinal centerline AF. Furthermore, a sector spanned by the concave side of the foil shaped body on each side of the longitudinal centerline may be substantially equal to the desired angle aopt. The invention also describes a system for converting energy from a waterflow using the positioning device 100 as described, in particular generating electricity by using a generator 12 is a natural choice of energy conversion. The system comprises the positioning device 100 and a first elongated body wherein the positioning device is mounted on the elongated body 1. The elongated body comprises one or more axles 2 parallel with the central longitudinal axis AE of the elongated body, and the one or more axles each has a rotating helical screw 3 mounted thereon for extracting energy from the waterflow with the first central longitudinal axis AE at a desired angle aopt with the waterflow. In fig. 1 and 12 two axles 2 and corresponding helical screws 3 is hung from a floating vessel 16 by means of a rotational coupling 17 at the pivot point P that enables the two axles 2 to pivot around the pivot axis AP in a vertical plane parallel with a longitudinal direction of the floating vessel 16 as illustrated in fig. 12 The pivot axis AP and the first central longitudinal axis AE are preferably at a right angle to each other. The floating vessel is preferably moored on a single point mooring 18 in one end of the floating vessel and the two axles and corresponding screws at the other. This configuration will enable the helical screw 3 to be positioned and moveable in a plane parallel with the flow direction indicated with an arrow in fig. 12 The advantage with this configuration is that free rotation around the single point mooring 18 and free rotation around the pivot axis AP causes no unnecessary loads on the system. The only force of any magnitude is a pull in the direction of the two axles acting at a right angle to the pivot axis AP on the rotational coupling 17. At the same time the correct angle is efficiently upheld because the forces from the positioning device 100 is applied at the end of the helical screw. Although the drag caused by the positioning device 100 is substantial, this causes no negative effect on the efficiency of the helical screw 3 because the drag and associated turbulence is taking place downstream of the helical screw 3. Furthermore, a positive effect of the drag is that it tends to stabilize the helical screw 3 against vibrations and oscillations. The downwards force at the stern of the floating vessel 16 originated at the positioning device 100 also increases directional stability of the floating vessel due to reduction of forward pitch in the floating vessel 16. Some oscillations originating from the helical screws are unavoidable. By mounting two counterrotating helical screws beside each other and connect them to a common positioning device 100 as seen in fig. 12 the oscillations are substantially reduced. Where the one or more helical screw is only tilted one way to obtain the desired angle such as can be seen in fig. 1 and 12it is conceivable with a non-symmetric positioning device as shown in fig. 5, 6a and 6b. In particular, a wing shaped body 19 shown in fig, 6a and 6b would function reasonably well. The wing shaped body 19 is fixedly mounted on the one or more axles 3 with a suction side, similar to the convex side 8 of the foil shaped body, pointing downward. In other words, the wing shaped body 19 is mounted upside down as compared to the wings of an airplane. Preferably the central longitudinal axis AE of the helical screws are directed substantially through the balancing point of the combined force from the wing shape to avoid loads acting on connection means between the axle 3 and the wing shaped body. Fig. 5 show the one-way configuration with an angle P between the line L from the leading edge to the trailing edge of the foil shaped body / wing shaped body and the first central longitudinal axis AE should be within an interval [aopt, aopt + 25 degrees]. In the two-way configuration the corresponding angle should be 90 degrees + / - 10 degrees, more preferable + / - 5 degrees. Figure 2 shows the system comprising a fixed body 20 to which the axle 3 is mounted. This avoids to a large degree the problems of exposure to wind and waves and resulting unwanted movements but will receive less energy due to lower water velocities. Furthermore, there is a problem with access to generators which is mounted below the surface. References 1 Elongated body 2 Axle 3 Helical screw 4 Foil shaped body 5 Distal end of elongated body 6 First edge of foil shaped body 7 Second edge of foiled shaped body 8 Concave side of foil shaped body 9 Convex side of foil shaped body 10a and 10b First and second side surface on each side of foil shaped body Ila and 1 lb First and second end of foil shaped body 12 Generator / energy converter 13 Fastening means / fastening flanges 14 First support foil 15 Second support foil 16 Floating vessel 17 Rotational coupling 18 Single point mooring 19 Wing shaped body 20 Holding structure 21 Concrete slab 100 Positioning device

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