Electrical Power Generator

Abstract

An electrical power generator comprises a capturing element (1) attached to a base (1000) in correspondence with a first end (11) thereof. The capturing element is located in a fluid and configured such that, when the fluid moves, the capturing element generates vortices in the fluid which produce an oscillating movement of the capturing element (1). The capturing element (1) has a cross section with a characteristic dimension, which decreases from a first longitudinal position (11A) located closer to the first end (11) than to a second end (12) until a second longitudinal position (12A) located closer to the second end (12) than the first longitudinal position (11A).

Claims

1. An electrical power generator comprising: a capturing element having an elongated shape, the capturing element extending in a longitudinal direction between a first end of the capturing element and a second end of the capturing element, wherein the capturing element has a length between the first end and the second end, the capturing element being configured to be attached to a base and submerged in a fluid with the first end closer to the base than the second end, the capturing element being configured such that, when the fluid moves, the capturing element generates vortices in the fluid so that an oscillating lift force is generated on the capturing element, which produces an oscillating movement of the capturing element; and a subsystem for converting the oscillating movement of the capturing element into electrical energy; wherein the capturing element has a cross section with a characteristic dimension, wherein the characteristic dimension decreases from a first longitudinal position located closer to the first end than to the second end until a second longitudinal position located closer to the second end than the first longitudinal position.

2. The electrical power generator according to claim 1, wherein the distance between the first longitudinal position and the second longitudinal position is greater than 30% of the length of the capturing element, such as greater than 80% of the length of the capturing element, such as 100% of the length of the capturing element.

3. The electrical power generator according to claim 1, wherein the distance between the first longitudinal position and the first end is less than 10% of the length of the capturing element.

4. The electrical power generator according to claim 1, wherein the capturing element has a substantially circular cross section, so that the cross section has a diameter, the characteristic dimension being the diameter.

5. The electrical power generator according to claim 1, wherein the capturing element has a cross section with a shape substantially as a regular polygon, with or without rounded vertices, wherein the characteristic dimension is the diameter of a circle which has the same surface area as the cross section of the capturing element.

6. The electrical power generator according to claim 1, wherein the capturing element comprises, between a cover point and the second end, a first portion wherein the decrease rate is either constant or increases in the direction from the first end towards the second end, and a second portion, which is closer to the second end than the first portion, wherein the decrease rate is either constant and lower than the decrease rate at the first portion; or decreases in the direction from the first end towards the second end.

7. The electrical power generator according to claim 6, wherein the first portion has a frustoconical shape, the cross section being substantially circular and the decrease rate being constant, and the second portion has a frustoconical or conical shape, the cross section being substantially circular and the decrease rate being constant but lower than the decrease rate in the first portion.

8. The electrical power generator according to claim 6, wherein the first portion is convex towards the exterior and the second portion is concave towards the exterior.

9. The electrical power generator according to claim 1, wherein the capturing element is at least partially hollow, and the subsystem is at least partially housed inside the capturing element.

10. The electrical power generator according to claim 9, wherein the subsystem is completely housed within the capturing element.

11. The electrical power generator according to claim 9, wherein the subsystem is placed at a distance of more than 0.05 times the length of the capturing element from the first end, such as at a distance of more than 0.3 times the length of the capturing element or more than 0.4 times the length of the capturing element from the first end, and optionally at a distance of at least 0.1 times the length of the capturing element from the second end, such as at a distance of more than 0.2 times the length of the capturing element or more than 0.3 times the length of the capturing element from the second end.

12. The electrical power generator according to claim 9, wherein the subsystem comprises at least one first subsystem component and at least one second subsystem component arranged for the production of electrical power by movement of the first subsystem component in relation to the second subsystem component, wherein the first subsystem component is attached to the capturing element (1) and the second subsystem component is attached to a subsystem support, so that the oscillating movement of the capturing element produces an oscillating movement of the first subsystem component in relation to the second subsystem component.

13. The electrical power generator according to claim 12, wherein at least one of the first subsystem component and the second subsystem component comprises at least one magnet, and wherein at least another one of the first subsystem component and the second subsystem component comprises at least one coil, arranged so that the oscillating movement of the first subsystem component in relation to the second subsystem component generates an electromotive force in the at least one coil by relative displacement between the at least one magnet and the at least one coil.

14. The electrical power generator according to claim 13, wherein the at least one coil comprises two coils arranged in a common plane and surrounding an axis of the capturing element, one of the coils being external to the other one of the coils, the two coils being connected in series so that when current circulates in a clockwise direction through one of the coils, current circulates in a counter-clockwise direction through the other one of the coils, and vice-versa.

15. The electrical power generator according to claim 9, wherein the subsystem comprises at least one annular magnet or at least one annular coil arranged in a plane perpendicular to a longitudinal axis of the capturing element, wherein said annular magnet or annular coil is asymmetrically positioned in relation to the longitudinal axis.

16. The electrical power generator according to claim 9, comprising means for generating a magnetic field that produces a magnetic repulsion force between the capturing element and a subsystem support, which varies with the oscillating movement of the capturing element and which has a maximum value that increases when the amplitude of the oscillating movement of the capturing element increases.

17. The electrical power generator of claim 16, wherein the means for generating a magnetic field comprises at least one first magnet associated to the capturing element and at least one second magnet associated to the subsystem support, said at least one first magnet and said at least one second magnet being arranged in such a way that they repel each other and in such a way that when the oscillating movement of the capturing element takes place, the distance between the at least one first magnet and the at least one second magnet varies according to the oscillating movement.

18. The electrical power generator according to claim 16, wherein the capturing element is arranged so that the amplitude of the oscillating movement increases with the velocity of the fluid, at least within a certain range of velocities, wherein the repulsion force between the, at least one, first magnet and the, at least one, second magnet is inversely proportional to the square of the distance between the first magnet and the second magnet, and wherein, when the speed of the fluid increases, the amplitude of the oscillating movement tends to increase, whereby the magnets tend to get closer during a part of maximum approach of each oscillation cycle, whereby the maximum repulsion force produced between the, at least one, first magnet and the, at least one, second magnet in each oscillation cycle increases accordingly, whereby the increase of the repulsion force increases the resonance frequency of the capturing element, whereby the structure of the generator contributes to an automatic increase in the resonance frequency of the capturing element when the speed of the fluid increases, and vice-versa.

19. The electrical power generator according to claim 16, wherein the means for generating a magnetic field are placed at a distance of more than 0.05 times the length of the capturing element from the first end, such as at a distance of more than 0.3 times the length of the capturing element, from the first end, and optionally at a distance of at least 0.1 times the length of the capturing element from the second end, such as at a distance of more than 0.2 times the length of the capturing element or more than 0.3 times the length of the capturing element below the second end.

20. The electrical power generator according to claim 1, further comprising a support element which comprises a first attaching point and a second attaching point, wherein: the first attaching point is a point of the support element where the electrical power generator is intended to be attached to the base; the second attaching point is a point of the support element where the support element is attached to the capturing element.

21. The electrical power generator according to claim 20, wherein the capturing element is at least partially hollow, and the subsystem is at least partially housed inside the capturing element, further comprising means for generating a magnetic field that produces a magnetic repulsion force between the capturing element and a subsystem support, which varies with the oscillating movement of the capturing element and which has a maximum value that increases when the amplitude of the oscillating movement of the capturing element increases, wherein the means for generating a magnetic field comprises at least one first magnet associated to the capturing element and at least one second magnet associated to the subsystem support, said at least one first magnet and said at least one second magnet being arranged in such a way that they repel each other and in such a way that when the oscillating movement of the capturing element takes place, the distance between the at least one first magnet and the at least one second magnet varies according to the oscillating movement, wherein at least one magnet forming part of the means for generating a magnetic field which produces a magnetic repulsion force between the capturing element and the support element, also forms part of the subsystem for converting the oscillating movement of the capturing element into electrical energy.

22. The electrical power generator according to claim 20, wherein the capturing element is configured to be attached to the base via a support element arranged to be repetitively deformed by the oscillating movement of the capturing element, wherein the support element extends into the capturing element, and wherein a subsystem support supporting at least part of the subsystem likewise extends into the capturing element.

23. The electrical power generator according to claim 20, wherein the support element is a rod member extending from the base and into the capturing element, and wherein the subsystem support extends into the capturing element to a position axially beyond the rod member.

24. The electrical power generator according to claim 20, suitable for being submerged in an airflow with a speed profile given by Hellmann's law, the size of the characteristic dimension being defined by the following formula: $\frac{D\left(y\right)}{d}={\left(1+\frac{y}{y_0}\right)}^{}.Math.g\left(y\right)-k_1.Math.\frac{y}{H}$ wherein y.sub.0 is the distance between the first attaching point and the first end; is the Hellmann's law coefficient, comprised between 0.05 and 0.3; d is the value of the characteristic dimension at the first end of the capturing element; y is the coordinate measured from the first end of the capturing element, in the direction towards the second end of the capturing element; D(y) is the size of the characteristic dimension of the cross section of the capturing element; g(y) is a sigmoid function; H is the length of the capturing element; and k.sub.1 is a constant value depending on the oscillation amplitude of the capturing element.

25. The electrical power generator according to claim 24, wherein is comprised between 0.05 and 0.18, y.sub.0 is comprised between 0.2 and 2 metres, H is comprised between 2 and 5 times y.sub.0 and k.sub.1 is comprised between 0.325 and 0.5.

26. The electrical power generator according to claim 24, wherein $g\left(y\right)=\frac{1}{1+e^{-}}$ $\mathrm{wherein}$ $=\frac{\frac{2.Math.K}{p}.Math.\left(H-y\right)}{H-L/2}-K$ K>4, and p<0.3.

27. The electrical power generator according to claim 10, wherein the subsystem comprises: a plurality of coils comprising at least three coils arranged side by side in a plane perpendicular to a longitudinal axis of the capturing element and preferably substantially symmetrically in relation to said longitudinal axis; and at least one pair of magnets arranged to produce a magnetic field; the coils and the magnets being arranged so that the oscillating movement of the capturing element produces a relative movement between the at least one pair of magnets and the coils so as to generate an electromotive force in the coils.

28. The electrical power generator according to claim 27, wherein the coils are attached to a subsystem support structure and wherein the pair of magnets are attached to the capturing element so as to oscillate with the capturing element.

29. The electrical power generator according to claim 27, further comprising additional magnets arranged in such a way that the additional magnets and the at least one pair of magnets repel each other and in such a way that when the oscillating movement of the capturing element takes place, the distance between the additional magnets and the at least one pair of magnets varies according to the oscillating movement.

30. The electrical power generator according to claim 27, wherein the plurality of coils consists of three coils situated around the longitudinal axis and having their axial centre portions spaced by approximately 120 degrees from the axial centre portions of the adjacent coils.

31. An electrical power generator comprising: a capturing element having an elongated shape, the capturing element extending in a longitudinal direction between a first end of the capturing element and a second end of the capturing element, the capturing element being configured to be attached to a base and submerged in a fluid with the first end closer to the base than the second end, the capturing element being configured such that, when the fluid moves, the capturing element generates vortices in the fluid so that an oscillating lift force is generated on the capturing element, which produces an oscillating movement of the capturing element; and a subsystem for converting the oscillating movement of the capturing element into electrical energy, the subsystem being at least partially housed inside the capturing element; wherein the subsystem comprises: a plurality of coils comprising at least three coils arranged side by side in a plane perpendicular to a longitudinal axis of the capturing element and preferably substantially symmetrically in relation to said longitudinal axis, and at least one pair of magnets arranged to produce a magnetic field; the coils and the magnets being arranged so that the oscillating movement of the capturing element produces a relative movement between the at least one pair of magnets and the coils so as to generate an electromotive force in the coils.

32. The electrical power generator according to claim 31, wherein the subsystem is completely housed within the capturing element.

33. The electrical power generator according to claim 31, wherein the capturing element has a length between the first end and the second end, wherein the subsystem is placed at a distance of more than 0.05 times the length of the capturing element from the first end, such as at a distance of more than 0.3 times the length of the capturing element or more than 0.4 times the length of the capturing element from the first end, and optionally at a distance of at least 0.1 times the length of the capturing element from the second end, such as at a distance of more than 0.2 times the length of the capturing element or more than 0.3 times the length of the capturing element from the second end.

34. The electrical power generator according to claim 31, wherein the capturing element is configured to be attached to the base via a support element arranged to be repetitively deformed by the oscillating movement of the capturing element, wherein the support element extends into the capturing element, and wherein a subsystem support supporting at least part of the subsystem likewise extends into the capturing element.

35. The electrical power generator according to claim 31, further comprising additional magnets arranged in such a way that the additional magnets and the at least one pair of magnets repel each other, and in such a way that when the oscillating movement of the capturing element takes place, the distance between the additional magnets and the at least one pair of magnets varies according to the oscillating movement.

36. The electrical power generator according to claim 1, wherein the capturing element is shaped for generation of von Karman vortices in a substantially synchronised manner along the capturing element.

37. A method of producing electrical power with an electrical power generator according to claim 1, comprising the step of subjecting the capturing element to a moving fluid such that the capturing element is caused to oscillate due to von Karman vortices induced in the fluid by the capturing element, whereby the von Karman vortices are generated in a substantially synchronized manner along the capturing element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0129] To complement the description and with the object of helping to a better understanding of the features of the invention, in accordance with examples of practical embodiments of the same, a set of drawings is attached as an integral part of the description, which by way of illustration and without limitation represent the following:

[0130] FIGS. 1A and 1B are a schematic elevational view and a cross sectional view, respectively, of an electrical power generator according to an embodiment of the invention.

[0131] FIG. 2 shows the effect of a laminar airflow passing across a capturing element of the electrical power generator according to this embodiment of the invention.

[0132] FIG. 3 shows the effect of the oscillation of the capturing element of the electrical power generator according to this embodiment of the invention.

[0133] FIGS. 4A and 4B schematically illustrate the effect on the wind in correspondence with a top portion of an electrical power generator as known in the prior art and of an electrical power generator according to an embodiment of the invention, respectively.

[0134] FIGS. 5A and 5B show a schematic distribution of the centres of the vortices in an electrical power generator as known in the art and according to an embodiment of the invention, respectively.

[0135] FIGS. 6A, 6B and 6C are schematic elevational and cross sectional views of the capturing element according to three different embodiments of an electrical power generator according to the invention.

[0136] FIGS. 7A and 7B show the top views of capturing elements of two different embodiments of electrical power generators according to the invention.

[0137] FIGS. 8A-8E are schematic cross sectional views (FIGS. 8A and 8E) and schematic top views (FIGS. 8B-8D), respectively, of a portion of a subsystem for converting oscillating movement into electrical power in accordance with different embodiments of the invention.

[0138] FIGS. 9A and 9B illustrate two simplified models of the behaviour of the capturing element without any tuning system (FIG. 9A) and with a tuning system (FIG. 9B), respectively.

[0139] FIG. 10 represents the evolution against displacement (x) of the spring force (F.sub.k) and of the magnetic repulsion force (F.sub.b).

[0140] FIG. 11 represents the variation over time of the amplitude (displacement x) and frequency (oscillation along the time axis t) of a device without tuning (I) and a tuned device (II) (movement with magnetic repulsion) when subjected to the action of an instantaneous force in the initial instant.

[0141] FIGS. 12A-12E are views analogous to the ones of FIGS. 8A-8E, but of an alternative arrangement of coil and magnets.

[0142] FIGS. 13A and 13B schematically illustrate the oscillatory movement of the capturing element in two different embodiments or modes of operation of the invention.

[0143] FIG. 13C schematically illustrates the arrangement of the coil in relation to the longitudinal axis of the generator in accordance with an alternative embodiment of the invention.

[0144] FIGS. 14A and 14B are a schematic elevational view and a cross sectional view, respectively, of a portion of another embodiment of the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0145] FIG. 1A shows, schematically, an electrical power generator according to one possible embodiment of the invention. The generator comprises a capturing element 1 in the shape of vertically arranged pole (that is, a pole having a longitudinal axis 2000 arranged vertically) with a first end 11 (the bottom end of the capturing element 1 when arranged as shown in FIG. 1) and a second end 12 (the top end of the capturing element 1 when arranged as shown in FIG. 1). The height or length H of the capturing element 1 is the distance between its first end 11 and its second end 12. In this embodiment, the capturing element 1 has a circular cross section, which is often advantageous in that it allows the generator to operate in the same way independently of the direction of the wind.

[0146] The generator further comprises a subsystem support 2 for supporting part of a subsystem for converting the oscillating movement of the capturing element 1 into electrical power, which will be described below. In this embodiment, the subsystem support 2 comprises a generally cylindrical housing 21 extending coaxially with the longitudinal axis 2000 of the capturing element 1 (when the capturing element is in its neutral position). The generator further comprises a support element that supports the capturing element, in this case, a support element in the form of a rod member 5 arranged within generally cylindrical housing 21 of the subsystem support 2. The rod member 5 is anchored to the base 1000, corresponding to a first attaching point 51. Also the subsystem support 2 is attached to the base 1000. From there, the subsystem support 2 comprises a first section extending upwards surrounding the rod member 5, defining a space 200 between the rod member 5 and the cylindrical housing 21 within which the rod member 5 can oscillate laterally. Towards the top, the generally cylindrical housing 21 of the subsystem support 2 terminates in three separate axially extending legs or sections 26 that extend axially further into the capturing element 1. There, the support element 2 terminates in a platform 27 provided with an axially projecting member 23 arranged for supporting part of a subsystem 3 for converting the oscillating movement of the capturing element 1 into electrical power. This subsystem 3 comprises a first subsystem component 31 with magnets arranged so that during the oscillatory movement the magnets are displaced in relation to a second subsystem component 32 comprising one or more coils. The first subsystem component is attached to the capturing element 1, and the second subsystem component 32 is supported by the subsystem support 2, on the platform 27. In this embodiment, additional magnets 42 are provided for the purpose of tuning the natural frequency of oscillation of the capturing element 1, as explained above. Also these magnets 42 are placed on the axially projecting member 23. It may be preferred to use a material of low magnetic permeability for the axially projecting member 23 to prevent, at least to a certain extent, the magnetic field of the magnets 42 to be directed through this projecting member 23, which could result in a loss of efficiency of the magnets in terms of their contribution to the tuning of the natural frequency of oscillation of the capturing element 1.

[0147] The rod member 5 is elastic. The term elastic does not exclude the possibility of using a relatively rigid rod member 5, but merely implies that the rod member should have enough capability of bending/inclining sideways to allow for causing an oscillating movement of the capturing element 1 in relation to the base 1000, that is, an oscillating movement according to which the capturing element 1 is inclined first to one side and then to the other, etc.

[0148] The capturing element 1 is attached to the rod member 5 by means of two substantially disc-shaped members 24, 25, which are arranged to attach the capturing element 1 to the rod member 5 as schematically shown in FIGS. 1A and 1B. The disc-shaped members 24, 25 are fixed to the rod member 5, which passes through a centre opening present in the disc-shaped members 24, 25. Each disc-shaped member 24, 25 further comprises three larger openings 28 radially spaced from the centre of the disc-shaped member. As shown in FIGS. 1A and 1B, the legs or axial extensions 26 of the subsystem support 2 extend through these openings 28, which are large enough to allow the disc-shaped member to oscillate with the rod 5 without interfering with the legs 26. In this way, the subsystem support 2 ends above the upper axial end of the rod member 5, so that the equipment or subsystem 3 for converting the oscillatory movement of the capturing element into electrical power and also the equipment for tuning the natural frequency of oscillation can be placed above the rod member 5, without any risk of interfering with it during oscillation.

[0149] As shown in FIG. 2, when the laminar flow 3001 of the wind impacts against the elongated pole-shaped capturing element 1, it produces a series of vortices 3002 that occur alternately on one side and on the other side of the capturing element 1 and with a constant distance 3003 between the successive vortices on each side of the capturing element 1. Therefore, a substantially constant drag force 3004 in the direction of the wind and a lift force 3005 substantially perpendicular to the general direction of the wind and to the direction of the drag force are produced on the capturing element 1. This lift force 3005 switches sign periodically, with a frequency that corresponds to the onset of the vortices, and this force causes the oscillation of the capturing element 1, towards one side and towards the other side. In this embodiment of the invention, the capturing element 1 has a circular cross section.

[0150] The capturing element 1 shown in FIG. 1 features a cross section with a diameter D that decreases with height from the first end 11 (corresponding to a first longitudinal position 11A) to the second end 12 (corresponding to a second longitudinal position 12A), for the reasons explained above. The decrease rate is substantially constant during most of the distance from the first end 11 to the second end 12, more specifically, between the first end 11 and a position referred to herein as the cover point 13, where the decrease rate increases. Thus, between the first end 11 and the cover point 13, in this embodiment the outer side of the cross section of the capturing element is substantially straight or, if curved, features a very large curvature radius.

[0151] As schematically illustrated in FIG. 1A, the subsystem 3 is placed under the axial centre portion of the capturing element 1 but still relatively close to it. There, the diameter is relatively large and the amplitude of the oscillation is not so big so as to cause physical interference between the moving parts associated to the capturing element and the parts placed on the subsystem support. Thus, a balance exists between the need for space to accommodate the subsystem, the desire the place the subsystem and the tuning magnets at a substantial distance from the base so as to take advantage of the lever effect, and the desire for a substantial amplitude of oscillation to enhance energy production.

[0152] As explained above, it has been found that an abrupt termination of the capturing element at the top end thereof may generate additional vortices that disturb the vortices that cause the oscillatory movement. It has been found that it is advantageous to provide a top portion of the capturing element where the diameter decreases towards the second end in a way that reduces or minimizes this disturbance. More specifically, as from the cover point 13, the capturing element features a first portion 121 where the diameter is decreasing in the direction from the first end 11 to the second end 12 at a higher rate than before the cover point, that is, from the cover point the decrease rate increases in the direction from the first end 11 to the second end 12 in correspondence with this first portion 121 of the capturing element. This first portion 121 is followed by a second portion 122, which is in turn a portion where the diameter is also decreasing in the direction from the first end 11 to the second end 12, but with the decrease rate decreasing in the direction from the first end 11 to the second end 12. Thus, and differently from many prior art arrangements discussed above, the diameter does not decrease with a constant or increasing decrease rate all throughout the axial extension from the cover point to the second end, but features at least one point where the decrease rate decreases. This has been found to improve the efficiency of the generator in terms of its capacity of capturing energy from the wind.

[0153] In some embodiments, the capturing element 1 does not have a circular cross section, but a cross section with a different shape, for instance, the shape of a polygon with rounded edges. Accordingly, the relations and formulae discussed herein are still valid for these embodiments, but replacing the word diameter by the expression characteristic dimension, which is the diameter of a circle with the same surface area as the cross section of these embodiments.

[0154] In the embodiment shown in FIG. 1, the capturing element 1 further comprises a skirt 6, which is a hollow part of the capturing element 1 which surrounds the subsystem support 2 and the rod member 5 below the position where the capturing element is fixed to the rod member 5. This skirt 6 is thus the piece of the capturing element 1 comprised between the second attaching point 52 of the rod member 5 (that is, in this embodiment, the point where the lowest disc-shaped element 25 attaches the capturing element 1 to the rod member 5) and the first end 11 of the capturing element 1. In this embodiment, the distance between the second attaching point 52 of the rod member 5 and the first end 11 of the capturing element 1 is substantially equal to the distance between the first end 11 of the capturing element 1 and the first attaching point 51 of the rod member 5. In some embodiments, a cover member (not shown in FIG. 1) having, for example, a substantially cylindrical shape can be arranged surrounding the subsystem support 2 between the skirt 6 and the surface on which the generator is mounted, for example, to improve the appearance of the generator. In other embodiments, the skirt 6 can extend further towards the base so as to conceal the subsystem support 2.

[0155] FIG. 3 shows the capturing element of the embodiment of FIGS. 1A and 1B in two different positions, an equilibrium position and a maximum amplitude position. X(y) represents the amplitude of this oscillatory movement with respect to the y coordinate, which is measured from the first end 11 of the capturing element 1.

[0156] The known formula for the calculation of the frequency of the appearance of new vortices may be used in a point where the oscillation of the capturing element is almost zero. In some particular embodiments, the first end of the capturing element is made coincident indeed with this point, as taught by WO-2016/055370-A2, to maximize energy capture efficiency. Thus, the following formulae are based on the presumption that the first end of the capturing element is a point where oscillation is almost zero.

[0157] At the first end 11 of the capturing element 1, the characteristic dimension is referred to as d, and estimated wind speed is referred to as v.sub.1. As a consequence, at this wind speed, the frequency of appearance of new vortices in correspondence with the first end 11 will be

[00011]$f=\frac{\mathrm{St}.Math.v_1}{d}$

[0158] If this frequency is calculated at a generic point of the capturing element, and if it is imposed as a design criterion that this frequency is to be equal along the whole capturing element, this would lead to the following expression

[00012]$\frac{\mathrm{St}.Math.v_1}{d}=\frac{\mathrm{St}.Math.v\left(y\right)}{\left(y\right)}$

[0159] wherein v(y) is the wind speed at a generic point located to a distance y from the first end, and (y) is the equivalent characteristic dimension of the capturing element at this point.

[0160] Without being bound by theory, this equivalent characteristic dimension may be expressed as a function of the characteristic dimension D(y) of the capturing element at this point when it does not move, and a contribution due to oscillation, in the following way:

(y)=D(y)+2.Math.k.sub.0.Math.X(y)

wherein k.sub.0 is an experimental constant which relates the influence of the amplitude of the movement X(y) on the value of the equivalent characteristic dimension (y).

[0161] However, as the amplitude of the movement may be expressed as a linear function of the coordinate y, the equivalent characteristic dimension (y) may be expressed in the following way:

[00013]$\left(y\right)=D\left(y\right)+k_1.Math.\frac{y}{H}.Math.d$

[0162] wherein k.sub.1 is constant for each generator, and depends on the linear relation between the amplitude of the oscillation X(y) and the coordinate y.

[0163] If we introduce the expression of (y) into the first equation, the shape of the characteristic dimension of the capturing element will be given by the following non-dimensional expression:

[00014]$\frac{D\left(y\right)}{d}=\frac{v\left(y\right)}{v_1}-k_1.Math.\frac{y}{H}$

[0164] This expression shows two terms with opposed signs. Depending on the expression used for the estimation of v(y), D(y) will grow or decrease along the length of the capturing element. However, for standard values, it may be shown that there is a first longitudinal position closer to the first end than to the second end where the characteristic dimension is greater than at a second longitudinal position located closer to the second end than the first longitudinal position.

[0165] For example, if we use the Hellmann's exponential law for wind speed

[00015]$\frac{v\left(y\right)}{v_1}=\frac{v\left(y\right)}{v_1}.Math.\frac{v_{10}}{v_{10}}=\frac{v\left(y\right)}{v_{10}}.Math.\frac{v_{10}}{v_1}={\left(\frac{y+y_0}{10}\right)}^{}.Math.{\left(\frac{10}{0+y_0}\right)}^{}={\left(\frac{y}{y_0}+1\right)}^{}$

[0166] where y.sub.0 is the distance between the first end of the capturing element and the first attaching point of the support element.

[0167] Accordingly, the following expression of the characteristic dimension is obtained:

[00016]$\frac{D\left(y\right)}{d}={\left(\frac{y}{y_0}+1\right)}^{}-k_1.Math.\frac{y}{H}$

[0168] If usual values, such as =0.15, y.sub.0=0.35 metres. H=1 metre and k.sub.1=0.45 are used, the expression of

[00017]$\frac{D\left(y\right)}{d}$

decreases with y from y=0 to y=H, so the first longitudinal position coincides with the first end and the second longitudinal position coincides with the second end, as shown in previous figures.

[0169] FIGS. 4A and 4B show a schematic comparison between the generation of vortices in correspondence with the upper end of a prior art capturing element 1 (FIG. 4A) and the generation of vortices in correspondence with the upper end of a capturing element 1 in accordance with an embodiment of the invention (FIG. 4B).

[0170] More specifically, FIG. 4A schematically illustrates the effect of wind blowing against a capturing element as known in the art. A representation of the density of these upper vortices and the axial extension e1 of the capturing element 1 affected by these upper vortices is shown in this figure.

[0171] FIG. 4B schematically illustrates the effect of wind blowing against a capturing element of an electrical power generator according to an embodiment of the invention. A representation of the density of these upper vortices and the axial extension e2 of the capturing element 1 affected by these upper vortices is shown in this figure. It can be observed how less upper vortices are formed and how the axial extension e2 of the capturing element 1 affected by them (FIG. 3B) is much smaller than the axial extension e1 affected by such vortices in the case of the prior art capturing element 1 (FIG. 3A), due to the design of the upper zone of the capturing element 1.

[0172] FIGS. 5A and 5B show the capturing elements of FIGS. 4A and 4B but instead of illustrating density of the upper vortices and their region of influence, a schematic distribution of the centres of the vortices along the capturing element is shown. Since vortices extend along the whole length of the capturing element, the line joining the centres of said vortices may be represented as a continuous line. As it may be seen in these figures, this line is not a straight line.

[0173] FIG. 5A shows a schematic distribution of the centres of the vortices in an electrical power generator with a capturing element as known in the art, which is severely affected by the upper vortices generated in the upper zone of the capturing element 1, the density of which is shown in FIG. 4A. These upper vortices affect the normal operation of the generator, causing a delay in the aerodynamic scenario in the upper zone. The result is that the centres of the vortices in this upper zone are also delayed with respect to the rest of the centres of the vortices. This delay causes that the energy which is absorbed by the electrical power generator is lower, and this reduction in the absorption of energy takes place in the zone where in theory, the available energy is at its maximum. As a consequence, the performance of this electrical power generator is sub-optimal.

[0174] FIG. 5B, on the contrary, shows a schematic illustration of the centres of the vortices in an electrical power generator according to the embodiment of the invention shown in FIG. 4B, which is much less affected by the upper vortices than the generator of FIG. 5A, since, as shown in FIG. 4B compared with FIG. 4A, the density and extension of these upper vortices is much lower in the case of the capturing element of FIG. 4B. The result is that the aforementioned delay of the centres of the vortices affects a much smaller length of the capturing element, and therefore the distribution of the centres of the vortices is more similar to a straight line than in the previous case, and consequently more energy may be absorbed by the capturing element 1 in this zone. This makes the performance of this generator be better than the performance of the generator with the capturing element shown in FIG. 5A.

[0175] As explained above, this is achieved by terminating the capturing element in a way that differs from the flat-cut or flat-dome-shaped termination known in the art, that is, a termination similar to the one of a base-ball bat. Instead, the present invention involves at least one change from a higher to a lower decrease rate, for example, as in the illustrated embodiment, by transition from a convex portion 121 (where the longitudinal cross section of the capturing element is convex towards the exterior) to a concave portion 122 (see FIG. 1A).

[0176] FIGS. 6A, 6B and 6C show three different embodiments of electrical power generators according to the invention with their upper ends designed to enhance performance based on the principles discussed above. In the first two embodiments, shown in FIGS. 6A and 6B, the first portion 121 is convex and the second portion 122 is concave, as seen from the exterior of the capturing element 1. However, in FIG. 6B, the distance between the cover point 13 and the second end is smaller than in the case of FIG. 6A. FIG. 6C shows a capturing element where the first portion 121 corresponds to a frustoconical section and the second portion 122 corresponds to another frustoconical section, but with a decrease rate (which in this case it is the apex angle) lower than the one of the frustoconical section of the first portion 121.

[0177] FIGS. 7A and 7B show the top views of capturing elements 1 of two different embodiments of electrical power generators according to the invention. These top views may be combined with all the previously illustrated embodiments, such as with the three different capturing elements shown in FIGS. 6A to 6C.

[0178] FIG. 7A shows a capturing element with a circular cross section.

[0179] FIG. 7B shows a capturing element with cross section that has the shape of a regular pentagon with rounded vertices. As this cross section is not circular, a graphic representation of the characteristic dimension Ic is also shown. A virtual circumference 13v of a circle which has the same area as the cross section of the capturing element 1 is represented in this figure, the area of this cross section depending on its side Lp and apothem a. The diameter of this virtual circumference is deemed to be the characteristic dimension Ic of the cross section of the capturing element 1.

[0180] FIG. 8A schematically illustrates a portion of a subsystem for converting the movement of the capturing element 1 into electrical power. The subsystem comprises two coils 321 and 322 interconnected so that when current flows in one direction (such as clockwise) in one of the coils, it flows in the opposite direction in the other coil. The coils are attached to the subsystem support 2 and, more specifically, to a projecting member 23. Electrical conducting wires 350 are arranged for conducting the generated current away from the coils.

[0181] On the other hand, annular magnets 311 (for example, each formed by a plurality of individual magnets arranged one after the other in a ring) are provided above and below the coils. In this case, both annular magnets 311 have their N pole (black) directed upwards and their S pole (white) directed downwards. A magnetic field is established between the upper and the lower annular magnet, and when the capturing element oscillates, the magnets will move in relation to the fixed coils, so that the coils will be subjected to a varying magnetic field. As easily understood from FIG. 8A, the electromotive force induced in the outermost coil 321 when the capturing element 1 inclines in one direction will be opposed to the electromotive force induced in the innermost coil 322 at the same time, but due to the way in which the coils are interconnected (as discussed above; cf. also FIG. 8C), the generated current will correspond to the sum of the electromotive forces induced in the two coils. FIGS. 8B and 8D schematically illustrate the distribution of the magnets of FIG. 8A, and FIG. 8C schematically illustrates the arrangement of the coils. FIG. 8E schematically illustrates an alternative arrangement in which ferromagnetic material 360 has been added to conduct the field lines in a suitable manner.

[0182] Additionally, further annular magnets 41 are provided on the fixed subsystem support, namely, on the projection 23. As understood from FIG. 8A, due to their orientation, there is a repulsive force between these magnets 41 and the magnets 311 attached to the capturing element, and this repulsive force increases when the magnets approach each other during the oscillating movement, as explained above. Thus, these magnets can serve to constitute a passive system for adaptation of the natural frequency of oscillation of the capturing element to the wind speed, as explained above. More specifically, when the capturing element 1 oscillates in relation to the base, a portion of the annular magnet 311 mounted on the capturing element approaches a portion of the annular magnet 41 mounted on the subsystem support 2, while on the diametrically opposite side of the capturing element, a portion of the magnet 311 moves away from the corresponding portion of the magnet 41. The repulsion force between the magnets 311 and 41 is inversely proportional to the square of the distance between the magnets 311 and 41. When the wind increases, the amplitude of the oscillatory movement of the capturing element tends to increase, whereby the magnets 311 and 41 tend to get closer and closer during the part of maximum approach of each oscillation cycle and therefore, the maximum repulsion force produced between the magnets 311 and 41 in each oscillation cycle increases accordingly. The increase of this repulsion force increases the resonance frequency of the structure. In this way, the very structure of the generator of FIG. 8A, with its magnets 311 and 41, contributes to an automatic increase in the resonance frequency of the capturing element 1 when the wind speed increases and vice versa. In this way, by properly selecting and arranging the magnets 311 and 41, something that can be done by trial and error tests and/or by computer simulations, the automatic adjustment of the natural oscillation frequency of the capturing element to wind speed can be achieved, such that it is always tuned with the frequency of appearance of vortices, thereby achieving a good uptake of energy from the movement of the fluid. In other words, a function of the magnets 311 and 41 may be to obtain the automatic tuning between the natural oscillation frequency of the capturing element and the frequency of appearance of vortices.

[0183] For example, both the capturing element 1 and the subsystem support 2 are provided with magnets, for example, in the shape of magnetic rings or sets of individual magnets arranged in the shape of a ring, arranged coaxially and in such a way that the magnets tend to repel each other. Thereby, the oscillating movement of the capturing element is not only influenced by the vortices but also by the magnetic forces, so that the natural oscillation frequency of the capturing element increases as the amplitude of oscillation increases.

[0184] As follows from what has been explained above, the subsystem support and the part of the subsystem that is arranged on it has a function corresponding to that of the stator of a non-conventional alternator designed to produce energy without the use of any bearing or reduction gearbox and that can produce power regardless of the direction in which the rod 5 is flexed. A large number of rows of coils and magnets such as those of FIGS. 8A-8E can be provided, whereby the magnets 41 contribute both to the production of power and to the auto-tuning of the generator to wind speed. FIGS. 9A and 9B illustrate schematically the behaviour of a capturing element without any tuning system (FIG. 9A) and the behaviour of a capturing element with the tuning system according to a possible embodiment of the invention (FIG. 9B).

[0185] The object of the tuning mechanism is to modify the natural oscillation frequency of the equipment according to the speed of the fluid. When the device has no tuning system its movement can be modelled as the one of a damped simple harmonic oscillator (a) (FIG. 9A):

m.Math.{umlaut over (x)}+c.Math.{dot over (x)}+k.Math.x=0a)

[0186] where m is its mass, c is the damping constant including the structural damping of the device itself, other losses and the mechanical energy converted into electrical energy and k is the elasticity constant of the elastic rod. In this case, the natural oscillation frequency of the equipment is:

[00018]$\begin{array}{cc}{w}_0=\sqrt{\frac{k}{m}}& b)\end{array}$

[0187] When, given the generation of vortices, the capturing element is affected by the sinusoidal force F with maximum value F.sub.0 (proportional to the square of the frequency if the value of the lift coefficient is considered constant), a delay in and frequency w=2.Math..Math.f(w[rad/s], f[Hz]), the movement can be modelled as the one of a forced damped harmonic oscillator:

m.Math.{umlaut over (x)}+c.Math.{dot over (x)}+k.Math.x=F=F.sub.0.Math.cos(wt+)c)

[0188] When the frequency w coincides with the natural frequency of the equipment w.sub.0, the latter enters in resonance and experiences a remarkable increase in its ability to absorb energy from the fluid.

[0189] As the frequency w is proportional to the speed of the fluid, in principle, given that the device has only one natural oscillation frequency (in the first oscillation mode), there will only be one single speed at which the device would work. However, the profit that can be obtained by for example a wind power generator is related to the number of hours/year during which the generator is running, producing electrical power. As explained above, there is a small range of wind speeds (the aerodynamic phenomenon of lock-in) in which an equipment based on the Karman vortices can maintain its resonance, but this is far smaller than desirable for a reasonably competitive generator.

[0190] In order to be able to increase this range of wind speeds, a tuning mechanism can be incorporated that modifies the oscillation frequency of the device. Thus, the capturing element will oscillate at greater frequency in the presence of higher wind speed, or in other words, in the presence of an increase in the frequency of appearance of vortices.

[0191] The arrangement of FIG. 9B differs from that of FIG. 9A by the addition of two pairs of magnets in repulsion mode. The movement of this model can be described by the following expression:

[00019]$\begin{array}{cc}m.Math.\stackrel{\mathrm{.Math.}}{x}+c.Math.\stackrel{.}{x}+k.Math.x+\frac{b}{{\left(d-x\right)}^2}-\frac{b}{{\left(d+x\right)}^2}=F& d)\end{array}$

[0192] where b would include (the Coulomb law for magnetism), the inverse of the magnetic permeability and the product of the magnetic masses, d is the distance at rest between each pair of magnets.

[0193] As shown in FIG. 10, the evolution with the displacement x of the spring force F.sub.k produced on the mass by deformation of the rod and the joint force produced by the two pairs of magnets F.sub.b are very different. As it can be seen and as already mentioned, as the mass (the capturing element) moves, near its neutral position of zero bending the spring force is predominant against the magnetic forces. As the displacement increases, its influence begins to equalise and in high displacements, the predominant force is of magnetic origin.

[0194] This has several implications.

[0195] The kinetic energy of the oscillating capturing element when it passes through its neutral position of zero bending depends in both cases on the square of its mass and its speed. Not so with the stored potential energy when its displacement is maximum. In the case represented in FIG. 9A, the potential energy is only elastic potential energy and in the case represented in FIG. 9B, the potential energy will have both an elastic and a magnetic nature with the difference that the potential energy of magnetic origin increases with the cube of the displacement and not with the square. As shown in FIG. 10, in comparison with the damped simple harmonic movement (I) for large displacements, the trajectory of the movement with magnetic repulsion (II) suffers an increase in its frequency of oscillation. With small displacements (on the right side of the graph), where almost all the potential energy is accumulated by the elastic rod, both trajectories have a very similar size period. FIG. 11 schematically illustrates the variation over time of the amplitude (displacement x) and frequency (oscillation along the time axis t) of a device without tuning (I) and a tuned device (II) (movement with magnetic repulsion) when subjected to the action of an instantaneous force in the initial instant.

[0196] FIGS. 12A-12D are views analogous to the views of FIGS. 8A-8D, but of an embodiment featuring an alternative arrangement of magnets and coils. Here, the subsystem for converting the movement into electrical power comprises, at the illustrated level of the system, one coil 323. This coil is arranged between two annular magnets (in other embodiments, there can be more coils per level, and the subsystem can comprise multiple levels of coils 323 and magnets 312). In this embodiment, and differently from the arrangement of FIGS. 8A-8D, the annular magnets are arranged with their N pole and S pole arranged radially outwards or inwards, rather than up/down. It is clear from FIG. 12A how the oscillating movement will displace the magnets 312 radially, thereby inducing an electromotive force into the coil 323. Also in this embodiment magnets 42 are provided for auto-tuning the natural frequency of oscillation of the capturing element. In this case, these magnets 42 are likewise oriented with the N pole and S pole radially rather than vertically.

[0197] Regarding the annular magnets, such as magnets 42, in some embodiments these magnets are formed by several individual magnets arranged in a ring, but in other embodiments these magnets consist of a single ring-shaped magnet. In such cases, it has been found that it may be cheaper to obtain ring-shaped magnets with the N and S poles oriented in the axial direction (as in annular magnet 41 of FIG. 8A) rather than in the radial direction (as in the case of magnet 42 of FIG. 12A). Thus, in order to reduce the costs involved, one possibility can be to obtain a magnet with a radially oriented S (or N) pole by positioning one magnet with axially arranged poles on top of another one, as schematically illustrated in FIG. 12E.

[0198] Theoretically, when the fluid moves in a constant direction, such as when the wind blows constantly in one direction, the projection of the oscillatory movement of the capturing element on the horizontal plane is linear, as shown in FIG. 13A. However, it has been observed that sometimes, and apparently especially when a magnetic auto-tuning arrangement as explained above is used, the capturing element will oscillate but not only in one vertical plane, but in an apparently randomized way, as schematically illustrated in FIG. 13B. That is, the movement when projected onto the horizontal plane is not only linear, but has also a rotational component.

[0199] Although it may be desirable to prevent the capturing element from oscillating as per FIG. 13B, it has been found that also in this kind of oscillation mode energy can be extracted from the movement. However, it has been found that in such cases and in order to optimise the extraction of electrical power when using coils arranged in the horizontal plane as per FIGS. 8A-8E or 12A-12D, it may be advantageous to arrange the coils so that their centres do not coincide with the longitudinal axis 2000 of the generator. This kind of arrangement is schematically illustrated in FIG. 13C, where the coil 323 is asymmetrically arranged in relation to the projection 23, that is, in relation to the longitudinal axis 2000 of the generator. Also, two further coils 323 and 323, arranged in other horizontal planes than the coil 323, are schematically suggested in FIG. 13C. These coils are axially displaced in relation to the coil 323, that is, they correspond to different levels of the subsystem for converting movement into electrical power. The centres of the coils 323 and 323 are also radially displaced in relation to the projection 23. The three coils 323, 323 and 323 are offset in different radial directions, with an angular spacing of 120, as schematically illustrated in FIG. 13C.

[0200] On the other hand, for example as an alternative to the approach suggested above, a controlled injection or extraction of energy into/out of the subsystem(s) 3 for converting the oscillating movement of the capturing element into electrical energy can be used to keep the oscillation of the capturing element substantially in one vertical plane, that is, to prevent oscillation as per FIG. 13B.

[0201] FIGS. 14A and 14B illustrate an alternative embodiment in which the subsystem comprises a plurality of coils 324 supported by the subsystem support 2, the coils being arranged substantially in the same plane and side by side, preferably symmetrically in relation to the longitudinal axis 2000, for example, as shown in FIG. 14B where three coils 324 are distributed symmetrically (at an angular spacing of 120 degrees) around the axis 2000. One or more pairs of magnets 313 are arranged to establish a magnetic field so that the relative movement between magnets and coils generates an electromotive force in the coils. In this embodiment, the magnets are attached to the capturing element and the coils are arranged on the subsystem support 2. This arrangement with a plurality of coils arranged side by side (rather than concentrically) around the longitudinal axis 2000 has been found to be efficient for converting the oscillating movement into electrical energy, for example, when the oscillation is not strictly limited to one vertical plane, which can often be the case when, as explained above, there is an interaction between magnets. Also in this embodiment, magnets 43 for tuning the natural frequency of oscillation of the capturing element are provided, that interact with the magnets 313 creating a repulsion force. The principles for this tuning have been described above.

[0202] In the embodiment of FIG. 14A, the capturing element 1 is attached to the rod member 5 by an interconnecting member 25 featuring through holes for the legs 26 of the subsystem support 2, as explained above, so that the capturing element can sway and oscillate without any interference with the subsystem support 2, through which the rod member 5 extends. In what regards the pair of magnets 313, one member of the pair is attached over the coils 324 by a bridge member 29 attached to the capturing element 5, whereas the other member of the pair of magnets 313 is attached to the end of the rod member 5 and, thus, indirectly attached to the capturing element. This allows the capturing element including the components physically attached to it to be implemented with a relatively low weight, which favours the amplitude of oscillation and a substantial lock-in range.

[0203] In the illustrated embodiment, the tuning magnets 43 comprise two annular magnets 43 placed on the subsystem support 2, on two axially opposite sides of the coils 324, facing the respective member of the pair of magnets 313 so as to provide the tuning of the natural frequency of oscillation according to the principles explained above.

[0204] In this text, the term subsystem in the expression subsystem for converting the oscillating movement of the capturing element into electrical energy or similar should not be interpreted in any limited sense. In the field of conventional wind turbines, the expression generator is frequently used for the part of the overall wind turbine that converts the mechanical or kinetic energy into electrical energy. In the present document, the term generator is used to denote the global system including the capturing element, that is, the part that interacts with the primary energy source, for example, the wind, to capture energy. In order to avoid confusion, the term generator has thus not been used for the subsystem for converting the oscillating movement of the capturing element into electrical energy. However, this subsystem can obviously be regarded as a generator, as it generates electrical energy. Also, the generator can comprise more than one subsystem for converting movement into electrical energy. If there are more than one subsystem, not all of the subsystems have to be arranged as described above.

[0205] In this text, the term magnet generally refers to a permanent magnet, although whenever appropriate also electromagnets may be used, as readily understood by the person skilled in the art.

[0206] In this text, the term annular when applied to magnets does not require that the magnet in question be a completely annular magnet made up of one single annular element. Rather, the term annular refers to the general configuration of the magnet, but not to its constitution. That is, an annular magnet in the context of the present document can be made up of a plurality of individual magnets, substantially arranged in a circle, with or without space between the individual magnets. The space can be substantial, as long as it does not deprive the set of magnets in question from forming a general circular configuration. The person skilled in the art will use components considering aspects such as cost of the components and cost of their installation. The same applies to references to a magnet shaped as a ring.

[0207] In this text, terms as above, below, vertical, horizontal, etc., generally refer to a situation in which the elongated capturing element is arranged with its first end below its second end, that is, generally, with a longitudinal axis of the capturing element extending vertically. However, this should not be interpreted to imply that the capturing element must always be arranged in this way. In some implementations, other orientations of the capturing element are possible.

[0208] In this text, the term comprises and its derivations (such as comprising, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0209] The invention is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.