Liquid damper

Abstract

A liquid damper for a wind turbine tower includes a damper housing formed from a horizontal lower annulus, a horizontal upper annulus, an essentially cylindrical outer vertical wall and an essentially cylindrical inner vertical wall, wherein the outer diameter of the damper corresponds to the interior diameter of the tower; an operational volume of liquid contained in the damper; and an arrangement of vertical ribs mounted to a vertical wall of the damper. Further provided is a method of assembling a wind turbine.

Claims

1. A liquid damper for a wind turbine tower, comprising: a damper housing formed from a horizontal lower annulus, a horizontal upper annulus, an essentially cylindrical outer vertical wall and an essentially cylindrical inner vertical wall, wherein the outer diameter of the damper corresponds to the interior diameter of the tower; an operational volume of liquid contained in the damper; and an arrangement of vertical ribs, wherein each vertical rib of the arrangement of vertical ribs is mounted to the outer vertical wall of the damper and/or the inner vertical wall of the damper, wherein at least one vertical rib of the arrangement of vertical ribs comprises an upright portion mounted to the outer vertical wall of the damper and/or the inner vertical wall of the damper, a radial portion mounted to the horizontal lower annulus of the damper and/or the horizontal upper annulus of the damper wherein a radial extension of the radial portion is greater than a radial extension of the upright portion, and a curved transition between the upright portion and the radial portion.

2. The liquid damper according to claim 1, comprising at least four ribs or at least six ribs.

3. The liquid damper according to claim 1, wherein the curved transition comprises a rounded cut-out.

4. The liquid damper according to claim 1, wherein at least one vertical rib of the arrangement of vertical ribs comprises a tube attached to an upright portion.

5. The liquid damper according to claim 1, wherein a radial extension of at least one vertical rib of the arrangement of vertical ribs is at most 50% of the interior width of the damper.

6. The liquid damper according to claim 1, comprising a plurality of bulkheads, wherein a bulkhead is shaped to partition the damper.

7. The liquid damper according to claim 1, wherein the horizontal upper annulus of the damper comprises a number of access openings.

8. The liquid damper according to claim 1, comprising a removable cover for each access opening.

9. A wind turbine comprising a tower with a height of at least 120 m; a rotor nacelle assembly with a mass of at least 700 T, installed on the tower; an aerodynamic rotor with a diameter of at least 200 m; and the liquid damper according to claim 1 installed at an upper level of the tower.

10. The wind turbine according to claim 9, wherein the outer vertical wall of the liquid damper is formed by an annular section of the wind turbine tower.

11. The wind turbine according to claim 9, comprising a plurality of dampers arranged in vertical stack.

12. The wind turbine according to claim 11, comprising a gap of at least 1.5 m between adjacent dampers.

13. A method of assembling a wind turbine, which method comprises steps of installing the liquid damper according to claim 1 in an upper level of a wind turbine tower; adjusting a configuration of the liquid damper for tower transport; placing the wind turbine tower in an upright position at an interim site; transporting the tower to an installation site; adjusting a configuration of the liquid damper for wind turbine operation; and mounting a rotor nacelle assembly onto the tower.

14. The method according to claim 13, wherein the step of installing the liquid damper in the tower comprises the steps of: A) securing an annular arrangement of ribs to the interior surface of the tower; B) assembling the damper housing by: attaching the outer perimeter of the upper annulus to the tower and attaching the inner perimeter of the upper annulus to an upper rim of the inner vertical wall; and attaching the outer perimeter of the lower annulus to the tower and attaching the inner perimeter of the lower annulus to the lower rim of the inner vertical wall; and C) filling an operational damping quantity of liquid into the damper.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 shows an exemplary embodiment of the inventive liquid damper;

(3) FIG. 2 shows an exemplary toroid damper for use in the liquid damper of FIG. 1;

(4) FIG. 3 shows an arrangement of ribs in a toroid damper of the inventive liquid damper;

(5) FIG. 4 shows an alternative way of realizing the ribs;

(6) FIG. 5 shows a further exemplary toroid damper;

(7) FIG. 6 shows further exemplary toroid dampers for use in the liquid damper of FIG. 1;

(8) FIG. 7 shows assembly stages of an embodiment of the inventive wind turbine;

(9) FIG. 8 shows assembly stages of an embodiment of the inventive wind turbine;

(10) FIG. 9 shows assembly stages of an embodiment of the inventive wind turbine;

(11) FIG. 10 illustrates a relationship for use in configuring a toroid damper of the inventive liquid damper;

(12) FIG. 11 shows a wind turbine tower equipped with a prior art liquid damper;

(13) FIG. 12 shows a wind turbine tower equipped with a prior art damper; and

(14) FIG. 13 illustrates a relationship for use in configuring the prior art damper of FIG. 12.

DETAILED DESCRIPTION

(15) FIG. 1 shows an assembly with several instances of the inventive liquid damper 1 installed in a wind turbine 2, and FIGS. 2-6 shows details of exemplary embodiments of the inventive damper.

(16) In FIG. 1, several dampers 1 are installed at the upper level of a wind turbine tower 20, but it shall be understood that the wind turbine tower may be equipped with a single instance of the inventive damper 1. The tower 20 supports an RNA 21, 22 comprising an aerodynamic rotor 22 and a nacelle 21, which houses the generator and various other components. The mass of the RNA 21, 22 can be in the order of 700 t, the rotor diameter 22D can be in the order of 220 m or more, and the height of the tower 20 can be in the order of 100 m or more.

(17) Each of the toroid dampers 1 can be comparatively flat and favourably straightforward to manufacture and to install, but together the dampers can contain a large quantity of liquid.

(18) The toroid dampers 1 (four are shown here) are arranged in a vertical configuration or stack, with a gap G between adjacent dampers 1. Each toroid damper 1 comprises a housing formed from a horizontal lower annulus 10B or base-plate, a horizontal upper annulus 10T or top-plate, a cylindrical outer vertical wall 10W1 and a cylindrical inner vertical wall 10W2. The central openings of the dampers 1 align as shown, to accommodate export power cables as well as other components such as an access ladder, power cables for auxiliaries, etc. For the sake of clarity, these components are not shown in the diagram.

(19) The outer diameter 10D of each toroid damper 1 corresponds to the interior width of the tower 20, so that each damper 10 is a full-size damper or FSD. Each toroid damper 1 comprises an operational volume of liquid L, for example the dampers 1 each contain the same quantity of liquid.

(20) FIG. 2 shows an exemplary toroid damper 1 for use in the assembly of FIG. 1. The diagram shows the base-plate 10B, the top-plate 10T, and the vertical cylindrical walls 10W2. The top plate 10T has various access openings IOTA, and lids or covers are shown in place over the openings IOTA. A cover 10TC can be moved aside to access the damper interior, as shown here, for example for inspection purposes. The damper 1 can comprise several ribs 10R that serve to minimize stress concentrations.

(21) In an assembly procedure, the base-plate 10B and top-plate 10T are welded into place, for example these may be welded to a tower section can before assembling that tower section as explained above. A suitable number of outer wall ribs 10R are secured to the outer damper wall 10W1, a suitable number of inner wall ribs 10R are secured to an inner vertical wall 10W2 which is then welded to the inner perimeters of the top-plate and bottom-plate.

(22) Alternatively, each horizontal annulus 10T, 10B and the inner wall 10W2 may be provided in the form of sections, and these sections are assembled inside the tower by welding them together. The damper can be assembled sideways, i.e. starting at one side of the tower wall, damper sections are progressively welded together, moving across the width of the tower, until the damper housing is complete. The assembly of a damper 1 can be carried out during manufacture of the tower 20.

(23) FIG. 3 shows an outer wall rib 10R in more detail. Each rib 10R has an upright portion 10RV and radial extensions 10RH, with a curved transition 10Rarc, 10Rcut-out between the upright 10RV and each radial extension 10RH. For example, as shown here, each radial extension 10RH can segue into the upright portion 10RV over a quarter circle 10Rarc. In this exemplary embodiment, the upright portion 10RV comprises rounded cut-outs 10Rcut-out, shaped to reduce or minimize stresses in the rib 10R arising from tower deformations during oscillation of the tower 20. This embodiment is particularly effective in the case of a toroid damper 1 whose outer wall 10W1 is welded to the tower wall, since tower deformations are directly transferred to the damper structure.

(24) As described above, the ribs 10R can reduce or eliminate the rotational liquid modes which might develop when the tower oscillations comprise a side-to-side component and also a fore-aft component. By effectively suppressing any such rotational mode of the damper liquid, the ribs 10R ensure consistently favourable damping performance. As shown here, the inner ribs and outer ribs can be provided in a staggered arrangement.

(25) A further advantage of the ribs is that they contribute to the stiffness of the damper, i.e. the ribs can prevent or minimize deflections and buckling. In one embodiment of the invention, a damper rib can be stamped or laser cut from a sheet of steel, for example.

(26) FIG. 4 shows an alternative way of realizing the ribs 10R. Here, each rib 10R of a toroid damper 1 comprises an upright 10RV and a tubular element TORT connected to the upright 10RV. The tubular elements have the effect of optimising the motion of the liquid in the damper, even if the tower is oscillating in both fore-aft and side-to-side directions. The beneficial effect of the ribs in disrupting the fluid flow, particularly if a rotational mode develops, can be augmented by adding surface irregularities to the tubular elements, for example an arrangement of radial fins extending along the outer surface of each tubular element.

(27) FIG. 5 shows a further exemplary toroid damper 1. Here, the liquid damper 1 comprises an arrangement of bulkheads 11 to partition the interior cavity of the damper 1. The top-plate 10T of the damper 1 has radial openings to allow the bulkheads 11 to be lowered into the damper interior.

(28) FIG. 6 shows a further exemplary toroid damper 1 comprising bulkheads 11. Here, each bulkhead 11 is hinged to the base-plate 10B of the damper 1. Initially, the bulkheads 11 are in a vertical position for the assembly and transport stages of the wind turbine tower 20. Each bulkhead may be secured to the top plate, for example by a suitable fastener. Once the tower is ready to receive the RNA, the fasteners are released, and the bulkheads 11 are allowed to tilt sideways, coming to rest on the bottom plate 10B. The bulkheads 11 remain in this position permanently.

(29) FIGS. 7-9 show assembly stages of an embodiment of the inventive wind turbine. In FIG. 7, a tower 20 at a quay-side location S0 is being prepared for transport. A liquid damper 1 as described above has been installed at the upper level of the tower 20 and the toroid dampers 10 have been filled with liquid according to the desired damping of tower oscillations during operation of the planned wind turbine.

(30) In FIG. 8, the tower 20 is shown during transport by marine vessel to the installation site Si. The enlarged view shows that bulkheads 11 have been lowered into the dampers 10 to achieve damping at the higher tower oscillations expected in the absence of the wind turbine's RNA.

(31) In FIG. 9, the tower 20 has been mounted onto a transition piece 20P at the installation site, and the RNA 21, 22a nacelle 21 and aerodynamic rotor 22has been installed at the top of the tower. In preparation for this stage of assembly, the bulkheads 11 have been raised from the dampers 10 which are now no longer partitioned, so that the liquid damper 1 can achieve the desired damping of the lower-frequency tower oscillations during normal operation of the wind turbine 2. Bulkheads 11 as described in FIG. 5 above can be removed, since they are no longer required during the remaining lifetime of the wind turbine. The bulkheads 11 can be stored in the tower, or they may be re-deployed in the transport of further towers.

(32) FIG. 10 illustrates a relationship for use in configuring a liquid damper 1 described above. It is known that the natural frequency f.sub.10 of a toroid damper is expressed as

(33) $\begin{array}{cc}{f}_{10}=\frac{\sqrt{\left(\frac{g}{R}.Math..Math.\tanh \left(\frac{h}{R}\right)\right)}}{2}& \left(1\right)\end{array}$
where g is the standard gravity value, R is the outer radius of the damper, h is the height of the liquid in the damper, and is a coefficient that is a function of the ratio of inner toroid radius to outer toroid radius. The diagram shows the graph of coefficient (Y-axis, dimensionless) against radius ratio r/R (X-axis, dimensionless). For the inventive damper 1, the larger radius R 1 can be the same as the tower interior radius, i.e. half the tower inner diameter 20D. Working backwards, i.e. knowing the desired damper frequency f.sub.10 (the tower's natural frequency), R (the tower interior diameter) and g, values of h and can be chosen that will satisfy equation (1) while maximizing the volume of liquid in the damper.

(34) FIG. 11 shows a wind turbine tower 20 equipped with a prior art liquid damper 41. Here, the damper 41 is realised as a single toroid or torus arranged in the upper level of the tower. The interior of the toroid damper 41 contains the desired quantity of liquid to achieve the desired degree of damping. However, as explained above, the tower may exhibit both fore-aft and side-to-side oscillations. The liquid in this prior art damper 41 may then follow a circular path about the damper interior instead of moving in the necessary back and forth manner. As a result, the prior art damper 41 fails to counteract the tower oscillations, i.e. the damping effect is essentially absent. Fatigue damage to the tower may result. A further drawback of the known toroid damper 41 is its inability to dampen the higher frequency oscillations in the transport and installation phases prior to mounting the RNA on the tower.

(35) FIG. 12 shows a wind turbine tower equipped with a different type of prior art liquid damper 42. Here, the damper 42 comprises multiple stacks of disc-shaped dampers 420, each stack arranged in a secondary containment bucket, with two such stacks arranged side by side on a platform in the upper level of the tower 20. Each disc-shaped damper is raised to the upper tower level during installation. The need to be able to manoeuvre a damper disc within the confines of the tower interior effectively determines the maximum practicable diameter of about 2.25 m. Even with two such stacks of damper discs with the maximum practicable diameter, a satisfactory damping effect cannot be achieved for a wind turbine with a very large rotor diameter and a correspondingly low tower frequency under 0.14 Hz.

(36) FIG. 13 illustrates a further limitation of the prior art liquid damper of FIG. 12. The diagram shows a graph of liquid level h (Y-axis, mm) against tower frequency f (X-axis, Hz) and demonstrates that a very low tower frequency such as 0.15 Hz or lower is associated with a non-practicable low liquid level in each damper disc. The very low liquid height requires an unreasonably high number of damper discs in order to arrive at the total necessary mass of damper liquid, so that this type of damper is not practicable for towers with very low natural oscillation frequencies.

(37) The dynamics of a wind turbine with a very large rotor diameter in the order of 200 m are such that the tower has a very low natural frequency, but the necessary damping cannot be achieved with the prior art damper 41 of FIG. 11 or the prior art damper 42 of FIG. 12.

(38) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(39) 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.