DYNAMIC VIBRATION ABSORBER

Abstract

A dynamic vibration absorber includes a frame configured for mounting to a moveable structure; a flywheel mounted on a first shaft; and a first converter adapted to convert a linear displacement of the frame into rotation of the first shaft; including a rotary damper mounted on a second shaft; and a second converter adapted to convert a rotational velocity of the first shaft into a rotational velocity of the second shaft.

Claims

1. A dynamic vibration absorber comprising a frame configured for mounting to a moveable structure; a flywheel mounted on a first shaft; a first converter adapted to convert a linear displacement of the frame into rotation of the first shaft; a rotary damper mounted on a second shaft; and a second converter adapted to convert a rotational velocity of the first shaft into a rotational velocity of the second shaft.

2. The dynamic vibration absorber according to claim 1, wherein the first converter comprises a rack and pinion assembly, comprising a linear gear mounted to the frame and a pinion arranged about the first shaft.

3. The dynamic vibration absorber according to claim 2, wherein the linear gear is arranged essentially in the direction of linear displacement of the frame.

4. The dynamic vibration absorber according to claim 1, wherein the second converter comprises an arrangement of intermeshing circular gears, with a first circular gear mounted on the first shaft and a second circular gear mounted on the second shaft.

5. The dynamic vibration absorber according to claim 4, wherein the gear ratio of the second converter results in conversion of the rotational speed of the first shaft into a higher rotational speed of the second shaft.

6. The dynamic vibration absorber according to claim 1, wherein the rotary damper is realized as a continuous rotation dashpot.

7. The dynamic vibration absorber according to claim 1, wherein the second converter is realized in the interior of the rotary damper.

8. A wind turbine rotor blade comprising a root portion for mounting to the hub of a wind turbine; an airfoil portion; and at least one dynamic vibration absorber according to claim 1 mounted to the rotor blade.

9. The wind turbine rotor blade according to claim 8, comprising a dynamic vibration absorber installed at a distance of at least 85% of the rotor blade length, or at a distance of at least 90% of the rotor blade length.

10. The wind turbine rotor blade according to claim 8, comprising a flap-wise dynamic vibration absorber arranged such that the direction of linear displacement of the frame is essentially perpendicular to the chord plane of the rotor blade.

11. The wind turbine rotor blade according to claim 10, wherein a flap-wise dynamic vibration absorber is configured to suppress flap-wise oscillations with a frequency in the order of 0.5-5 Hz.

12. The wind turbine rotor blade according to claim 8, comprising an edge-wise dynamic vibration absorber arranged such that the direction of linear displacement of the frame is essentially parallel to an airfoil chord line of the rotor blade.

13. The wind turbine rotor blade according to claim 12, wherein an edge-wise dynamic vibration absorber is configured to suppress edge-wise oscillations with a frequency in the order of 0.5-5 Hz.

14. A wind turbine comprising a number of rotor blades according to claim 8.

15. A dynamic vibration absorber comprising a frame configured for mounting to a moveable structure, a flywheel mounted on a first shaft, a first translation means adapted to convert a linear displacement of the frame into rotation of the first shaft; wherein a rotary damper mounted on a second shaft, and a second translation means adapted to convert a rotational velocity of the first shaft into a rotational velocity of the second shaft.

Description

BRIEF DESCRIPTION

[0026] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0027] FIG. 1 shows an embodiment of the inventive damper;

[0028] FIG. 2 shows an exploded view of the damper of FIG. 1;

[0029] FIG. 3 shows a wind turbine with rotor blades equipped with various instances of the inventive damper;

[0030] FIG. 4 shows a wind turbine with rotor blades equipped with the inventive damper;

[0031] FIG. 5 illustrates an advantage of the inventive damper; and

[0032] FIG. 6 shows a conventional damper.

DETAILED DESCRIPTION

[0033] FIG. 1 and FIG. 2 show an embodiment of the inventive damper 1. The damper 1 comprises a frame 10 for mounting to a structure that requires damping. A carriage 100 encloses a flywheel 11. The flywheel 11 is mounted on an axle or shaft 110, which terminates at one end in a pinion 14 of a first transmission system T1. The pinion 14 can travel along a rack or linear gear 13 arranged along one planar surface of the frame 10. When the damper 1 is displaced up or down as indicated by the double-ended arrow on the left-hand side, this first transmission system T1 converts a linear displacement of the first shaft 110 into rotation of the flywheel 11. The carriage 100 with the first shaft 110 and flywheel 11 can move back and forth in the direction D shown.

[0034] The other end of the primary shaft 110 drives a second transmission system T2 comprising intermeshed gears 17, 18 as illustrated in FIG. 2. The first gear 17 is turned by the first shaft 110 (turned by the rack and pinion 14), and the second gear 18 turns a second shaft 120 which in turn causes a rotary damper 12 to rotate. In this exemplary embodiment, the gear ratio of the second transmission system T2 is in the order of 3:1, so that the second shaft 120 turns at about three times the rate of the first shaft 110. Here, the rotary damper 12 can be a continuous rotation dashpot or similar. In this embodiment, the secondary shaft is essentially parallel to the primary shaft, but it shall be understood that the transmission shafts can have any suitable orientation (parallel, orthogonal) with respect to the frame and to each other.

[0035] FIGS. 3 and 4 show a wind turbine 2 with rotor blades 20 equipped with various instances of the inventive damper 1. The diagrams indicated possible positions of the damper 1 in the interior of the rotor blades 20. In FIG. 3, each rotor blade 20 has a flap-wise DVA 1 installed in an outboard region as shown to suppress flap-wise vibrations, as well as an edge-wise DVA 1 installed further inboard as shown to suppress edge-wise vibrations. Each edge-wise damper 1 is mounted so that the linear gear 13 of its first transmission system T1 is essentially parallel to the chord line of the airfoil at the mounting position. Each flap-wise damper 1 is mounted so that the linear gear 13 of its first transmission system T1 is essentially perpendicular to the chord plane at the mounting position. In FIG. 4, each rotor blade 20 has two edge-wise DVAs 1 installed as shown to suppress edge-wise vibrations. Of course, these embodiments are merely exemplary, and the skilled person will understand that any suitable number of dampers 1 can be chosen to suppress edge-wise and/or flap-wise oscillations. The number of dampers 1 and the configuration of the damper(s) 1 can be chosen on the basis of rotor blade parameters such as length, mass etc., and also under consideration of the wind parameters relevant to that wind turbine.

[0036] FIG. 5 illustrates the concept underlying the inventive DVA. The curve 50 shows the relationship between percentage mass reduction MR of the dashpot (Y-axis) against gear ratio GR of the second translation means 12 (dimensionless, X-axis). In the diagram, a gear ratio of 1:1 represents the mass of a comparable conventional art damper that would comprise a dashpot mounted on a primary shaft, without any further damping means. The curve 50 corresponds to a constant damping level, i.e. the damping is the same at any point along the curve. Of course, there can be multiple such curves for multiple damping levels. For a particular wind turbine rotor blade, the geometry and mass of the rotor blade will allow the designer to compute the necessary level of damping required in order to suppress classical flutter, for example, and the designer can also determine the desired position along the rotor blade length for an intended DVA.

[0037] The diagram shows that, for a standard gear train with a gear ratio in the order of 10:1, the mass of the dashpot in an embodiment of the inventive DVA can be very favourably reduced by up to 90% compared to the mass of a comparable damping element in a conventional art DVA. An even higher gear ratio (and a correspondingly lower dashpot mass) may be achieved with an alternative translation means such as a planetary gearset (at the expense of increased complexity).

[0038] With one or more embodiments of such a customized compact and lightweight damper, a wind turbine rotor blade can achieve a higher flutter speed, i.e. the rotational velocity at which the aeroelastic rotor system becomes unstable. The aerodynamic rotor must not turn faster than this speed when the rotor blades experience edge-wise vibration, otherwise damage to the rotor blades may result. Thus, increasing flutter speed allows for a greater operational range of the rotor.

[0039] In the case of the conventional art rotor blade, e.g. a rotor blade equipped with a conventional art passive damper or without any kind of passive damper, the edge-wise oscillations of the rotor blade must be reduced by lowering the rotor speed. Here, the flutter speed is lower than for the rotor blades equipped with the inventive damper. The lower flutter speed leads to reduced output power and reduced earnings.

[0040] FIG. 6 shows a conventional art DVA 6. Here also, the basic structure comprises a frame 60, a single damping elementin this case a flywheel 61mounted on a shaft 610, which terminates at one end in a pinion 64 of a transmission system. The pinion 64 travels along a linear gear 63 arranged along a planar surface of the frame 60. The transmission system converts a displacement of the frame 60 (and therefore the shaft 610) into rotation of the flywheel 61. To achieve the damping effect of the inventive DVA shown in FIGS. 1 and 2 above, the conventional art DVA 6 must be larger overall to accommodate a significantly more massive flywheel. However, as explained with FIG. 5 above, the increased mass and dimensions add to the overall weight of the rotor blade and also prohibit installation of the conventional art damper in the flatter and more confined airfoil in the outboard region of the rotor blade.

[0041] Although embodiments of the present invention has been disclosed in the form of exemplary embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of embodiments of the invention. For example, instead of arranging the inventive DVA inside the rotor blade as described above, an embodiment of the inventive DVA may be only partially enclosed by the rotor blade, or may even be mounted at the exterior of the rotor blade. Furthermore, the number of transmission shafts is not limited to two, and in a further embodiment, the dashpot could be arranged on a tertiary shaft structure.

[0042] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.