Wind turbine

A wind turbine is provided, including a container, a fluid which is arranged inside the container, and a damping body which is arranged inside the container, which is immersed in the fluid, and which is configured to move inside the container, wherein the fluid and the damping body are configured to damp oscillations of the wind turbine. A damper system is provided that on the one hand the fluid damps, e.g. by sloshing, and on the other hand the damping body damps by moving at least partially through the fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European application No. EP 18152074.3, having a filing date of Jan. 17, 2018, the entire contents of which are hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a wind turbine.

BACKGROUND

Modern wind turbines may comprise a tower, a nacelle which is connected to the tower, a hub which is connected to the nacelle and rotor blades which are connected to the hub. Such wind turbines may have heights of over 100 or 200 meters. Thus, e.g. due to wind loads, movements of an upper end of the tower and the nacelle may occur. This result in oscillations of the wind turbine. With increasing hub heights and/or more slender tower structures there is an increased demand to find optimal solutions for damping such tower oscillations to prevent turbine failures, as these movements result in huge loads in e.g. a yaw system, a drive train, a gearbox and/or the tower itself. However, modern wind turbines are weakly damped structures. The main damping may result from the aerodynamic forces induced by the vibrational motion of the rotor.

EP 1 855 000 A1 shows a fluid sloshing damper which includes at least one hollow body with an internal space and a fluid contained in the internal space. A hollow bulge extends outwards from a wall of the hollow body. The hollow bulge forms a bulge space which is part of the internal space.

SUMMARY

An aspect relates to an improved wind turbine.

Accordingly, a wind turbine is provided. The wind turbine comprises a container, a fluid which is arranged inside the container, and a damping body which is arranged inside the container, which is immersed in the fluid, and which is configured to move inside the container, wherein the fluid and the damping body are configured to damp oscillations of the wind turbine.

In contrast to known wind turbines, a more effective damper system is provided since on the one hand the fluid damps, e.g. by sloshing, and on the other hand the damping body damps by moving at least partially through the fluid. Damping of oscillations at the wind turbines will in general reduce the fatigue loads on the tower. This has the advantage that the necessary amount of steel in the tower may be reduced. Moreover, volume need is reduced compared to other damper systems.

The container, the fluid and the damping body may be comprised by a damper system of the wind turbine. Such a damper system should be able to provide effective damping even when the wind turbine is in a stand still operation mode and even when the wind turbine is not connected to a power source. Thus, the damper system may be operated without any energy requiring means (i.e. an electrical induced system). In particular, the damper system is a passive system. This may mean that no actuator is provided for influencing a movement of the damping body and/or fluid. Alternatively, the damper system may be provided semi-active, e.g. having an actuator configured to influence a movement of the damping body and/or fluid.

“Wind turbine” presently refers to an apparatus converting the wind's kinetic energy into rotational energy, which may again be converted into electrical energy by the apparatus. The wind turbine comprises a tower, a nacelle which is connected to an upper end of the tower, a hub which is rotatably connected to the nacelle, and rotor blades which are connected to the hub.

The damping body is a sliding element which is configured to slide inside the container for damping oscillations of the wind turbine. The damping body is a solid body. In particular, the damping body may be named damping mass. In particular, the container has an elongated shape, wherein a length of the container is at least two, three, four, five, six, seven, eight, nine or even ten times larger than a width and/or height of the container. The container comprises a solid waterproof housing which houses the damping body and the fluid. The fluid comprises oil or water.

According to an embodiment, the container and the damping body are configured such that a full rotation of the damping body inside the container is prevented.

This has the advantage that, for example, rolling friction is essentially prevented. Sliding friction has the advantage over rolling friction that more kinetic energy may be transferred into thermal energy and, thus, an increased damping effect may be achieved. A length of the damping body is larger than the height of the inner space of the container containing the damping body.

According to a further embodiment, the wind turbine further comprises a tower, wherein the container is arranged inside the tower.

It is understood that the damping body and the fluid are arranged inside the container and, thus, are arranged also inside the tower. The container is arranged at an upper or uppermost third, fourth, fifth, sixth, seventh, eighth, ninth or tenth of a height of the tower. In particular, the container is arranged at an upper end of the tower. This has the advantage that oscillations of the tower may be damped at a high oscillation amplitude.

According to a further embodiment, the container may be arranged at or inside the nacelle.

According to a further embodiment, a cross-section of the damping body fills at least 30%, 40%, 50%, 60%, 70%, 80, 90, 95 or 98% of a cross-section of the container.

Thus, the inner space of the container may be used effectively. A longitudinal section of the damping body fills less than 70%, 60%, 50%, 40%, 30%, 20%, 15%, 10% or 5% of a longitudinal section of the container.

According to a further embodiment, the container comprises a sliding surface for the damping body, wherein the sliding surface has a curved shape.

Thus, the damping body is configured to slide on a curved sliding surface. The sliding surface of the container forms a sliding path for the damping body. A lowest point of the sliding path is arranged midway along the length of the container. This has the advantage that due to gravitation the damping body is forced towards a center of the container.

According to a further embodiment, a sliding surface of the damping body has a curved shape. This has the advantage that in case of a curved sliding surface of the container a larger contact area between the sliding surface of the container and the sliding surface of the damping body may be achieved.

According to a further embodiment, the damping body has a square, pentagonal, rectangular and/or trapezoidal cross-sectional shape.

This has the advantage that an adaptation of the damping body to the inner space of the container may be improved. The inner space of the container has essentially the same cross-sectional shape as the damping body.

According to a further embodiment, one of the damping body and the container comprises a recess and the other of the damping body and the container comprises a guiding element which interacts with the recess for guiding the damping body along a length of the container.

This has the advantage that a movement of the damping body inside the container is well defined and, thus, reliably reproducible over a lifetime of the wind turbine. Moreover, the contact area between the sliding surface of the container and the sliding surface of the damping body may be increased. The recess and the guiding element extend along a respective length of the damping body and/or the container. In a cross-sectional view the recess is essentially formed as a negative form of the guiding element. In particular, the guiding element has a dovetail, triangular, quadrangular or trapezoidal cross-sectional shape.

According to a further embodiment, the container comprises an end portion and the damping body comprises an end portion for fitting into the end portion of the container, wherein the container and the damping body are configured such that fluid is dammed between an end face of the damping body and an end face of the container when the end portion of the damping body fits into the end portion of the container.

This has the advantage that a soft end stop for the damping body may be realized. Thus, inelastic collisions (shocks) between the damping body and the container may be prevented. It is understood that the end face of the damping body is comprised by the end portion of the damping body and the end face of the container is comprised by the end portion of the container. The damping body comprises two of such end portions and the container comprises two of such end portions such that the soft end stop is provided at both ends of the container.

According to a further embodiment, an inner space of the container comprises a height which is constant along the length of the container.

Hence, a production of the container is simplified. The inner space has essentially a cuboid shape. Alternatively, the inner space may have a curved shape.

According to a further embodiment, the inner space of the container comprises the height which decreases along the length of the container.

The height decreases from the middle of the container towards both end faces of the container.

According to a further embodiment, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the inner space of the container is filled with the fluid.

Thus, a high damping effect may be achieved due to the fluid.

According to a further embodiment, the wind turbine further comprises a first container and a first damping body which is arranged with the fluid inside the first container, and a second container and a second damping body which is arranged with the fluid inside the second container.

The afore-mentioned container is the first container and the afore-mentioned damping body is the first damping body. A third container and a third damping body which is arranged with the fluid inside the third container is provided. In particular, a fourth container and a fourth damping body which is arranged with the fluid inside the fourth container is provided. A fifth container and a fifth damping body which is arranged with the fluid inside the fifth container is provided. In particular, a sixth container and a sixth damping body which is arranged with the fluid inside the sixth container is provided.

According to a further embodiment, the first container crosses the second container.

This has the advantage that effective damping may be provided in two directions. In particular, both the first container and the second container cross a longitudinal middle axis of the tower. Hence, the first container and the second container may be provided as long as possible since the best room use (e.g. at the inner space of the tower) may be achieved.

According to a further embodiment, the first container is arranged parallel to the second container.

Thus, the damping effect in one direction may be increased. In this case the first container and the second container do not cross the longitudinal middle axis of the tower.

According to a further embodiment, the wind turbine further comprises a cable which is arranged between the first container and the second container.

The cable is comprised by a harness extending from the nacelle towards a lower end of the tower. The cable is provided for conducting electrical energy from the nacelle to an electric supply network located outside the wind turbine. The cable harness further comprises signal cables. In particular, the longitudinal middle axis of the tower extends through the cable or the cable harness. This has the advantage that the cable or the cable harness does not require much space when the nacelle rotates relative to the tower.

The embodiments and features described with reference to the first container and the first damping body apply mutatis mutandis to the second, third, fourth, fifth and/or sixth container and damping body.

Further possible implementations or alternative solutions of embodiments of the invention also encompass combinations—that are not explicitly mentioned herein—of features described above or below with regard to the embodiments. The person skilled in the art may also add individual or isolated aspects and features to the most basic form of embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1shows a wind turbine1. The wind turbine1comprises a rotor2connected to a generator (not shown) arranged inside a nacelle3. The nacelle3is arranged at the upper end of a tower4of the wind turbine1.

The rotor2comprises three wind turbine blades5. The wind turbine blades5are connected to a hub6of the wind turbine1. Rotors2of this kind may have diameters ranging from, for example, 30 to 200 meters or even more. The wind turbine blades5are subjected to high wind loads. At the same time, the wind turbine blades5need to be lightweight. For these reasons, wind turbine blades5in modern wind turbines1are manufactured from fiber-reinforced composite materials. Therein, glass fibers are generally preferred over carbon fibers for cost reasons. Oftentimes, glass fibers in the form of unidirectional fiber mats are used.

The tower4comprises a lower end7and an upper end8, wherein the lower end7is averted from the nacelle3. Further, the nacelle3is connected to the upper end8of the tower4. When the wind turbine1e.g. is subjected to high wind loads, the upper end8together with the nacelle3moves away from a neutral position which results in oscillations. Usually, an amplitude of such an oscillation is larger at the upper end8than at the lower end7. Thus, it may be useful to provide damper systems at the upper end8of the tower4or the nacelle3.

FIG. 2shows schematically a cross-section II-II of an embodiment of the tower4fromFIG. 1which intersects the upper end8(seeFIG. 1) of the tower4. In particular,FIG. 2shows a top view to the inside of the tower4. The tower4comprises a wall9which is an outermost wall of the tower4and, thus, faces an outer environment10of the wind turbine1. The wall9has a circular ring-shaped cross-section and surrounds an inner space11of the tower4. Further, a container12is provided inside the inner space11.

The container12has essentially a rectangular shape when looking from above and is, in particular rigidly, connected to the tower4(not shown). Further, the container12comprises a first end face13(or end wall) and a second end face14(or end wall) both facing the wall9and averted from each other. A length L of the container12may be at least 50%, 60%, 70%, 80%, 90%, 95% or 98% of an inner diameter D of the wall9. A fluid29(not shown) and a damping body30(also indicated as first damping body) are arranged inside the container12(see broken lines). The damping body30is immersed in the fluid29(seeFIG. 7), and is configured to move inside the container12, wherein the fluid29and the damping body30are configured to damp oscillations of the wind turbine1. The container12, the fluid29and the damping body30may be named damper system.

Further, a damping direction R1extends from the end face14towards the end face13and vice versa. The container12is elongated towards the damping direction R1. The inner space11is essentially cylindrical and has a rotational symmetry regarding a middle axis15, wherein the container12intersects the middle axis15of the inner space11.

In particular, a further container16(also indicated as second container) is provided. The fluid29(not shown) and a damping body30′ (also indicated as second damping body) are arranged inside the container16(see broken lines). The damping body30′ is immersed in the fluid29, and is configured to move inside the container16, wherein the fluid29and the damping body30′ are configured to damp oscillations of the wind turbine1. The container12and the container16may be identical, wherein a damping direction R2of the container16is essentially perpendicular to the damping direction R1. Thus, the tower4may be damped in two directions R1, R2perpendicular to each other. In particular, the containers12,16are placed above one another optionally with a distance in between in vertical direction Z which also is a longitudinal direction of the tower4(seeFIG. 1) but turned 90° relative to one another. The containers12,16are placed as close to the nacelle3(seeFIG. 1), i.e. at topmost possible point in the upper end8of the tower4. Alternatively, the containers12,16may be placed within the nacelle3. The containers12,16may be provided as pair of containers12,16.

FIG. 3shows schematically the cross-section II-II fromFIG. 1of a further embodiment of the tower4. Two pairs of containers12,16,17,18may be placed of one another at the upper end8, in particular on top, of the tower4, and each pair may be twisted relative to one another. An angle α between the damping direction R1of container12and a damping direction R3of container17may be between 30 and 60°, in particular 45°. An angle β between the damping direction R2of container16and a damping direction R4of container18may be between 30 and 60°, in particular 45°. For example, all containers12,16,17,18are intersected by the middle axis15.

Several of such pairs of containers12,16,17,18may be placed of one another at the upper end8, in particular on top, of the tower4, and each pair may be twisted relative to one another. This has the advantage that effective damping in a plurality of directions may be ensured.

FIG. 4shows schematically the cross-section II-II fromFIG. 1of a further embodiment of the tower4. In contrast toFIG. 3, the containers12,16are arranged parallel to each other forming a gap G1in between. This means that damping directions R1, R2are essentially parallel to each other. The containers12,16are arranged in the same horizontal plane E which is essentially perpendicular the middle axis15(seeFIG. 2). Further, containers17,18are in particular also arranged parallel to each other and underneath containers12,16. In particular, a gap G2is arranged between the containers17,18. The damping directions R1, R2are arranged perpendicular to the damping directions R3, R4. The middle axis15is arranged between the containers12,16and between the containers17,18such that a central hollow space19is provided between the containers12,16,17,18.

Cables20,21,22,23,24extend through the central hollow space19along the middle axis15. In particular, a central cable24intersects the middle axis15. This has the advantage that a center of the tower4is not blocked. Thus, the cables20,21,22,23,24have an ideal location in case of a rotation of the nacelle3relative to the tower4(yaw movement). At least one essentially free hanging cable20,21,22,23,24is provided which may freely twist caused by yaw movement of the nacelle3. A lift area25may be provided at a radially outer boundary area of the inner space11. Alternatively, the lift area25may be provided along the middle axis15, wherein the lift area extends through the central hollow space19. In particular, a ladder area26is provided inside the inner space11at the wall9.

The containers12,16,17,18are placed in a fixed position, e.g. resting on support such as a platform or support beams (not shown) connected to the tower4. In particular, in an alternative embodiment such support could also be designed to be movable, i.e. able to turn (0-360 deg.) in order to optimize the damping effect in accordance with a given prevailing (but changing) wind direction. The movement may be directly related to the yaw movement of the nacelle3, or work independently. The latter is in particular useful when the yaw function of the nacelle3is damaged. Optimal damping is crucial especially at high wind speeds if the nacelle3is not facing towards the wind (for an upwind turbine).

The containers12,16have for example the same distance to the middle axis15(seeFIG. 2) and thus are balanced regarding a center of the tower4when locking from above. Also, the containers17,18have for example the same distance to the middle axis15(seeFIG. 2) and thus are balanced regarding the center of the tower4.

FIG. 5shows schematically the cross-section II-II fromFIG. 1of a further embodiment of the tower4. In contrast toFIG. 4, the containers12,16,17,18protrude from the wall9towards the outer environment10of the wind turbine1. Further, the length L of the container12,16,17,18is larger than the inner diameter D of the wall9. Thus, the containers12,16,17,18extends out of an outer skirt of the tower4

Alternatively, the containers12,16,17,18may in principle also be attached to an outer skirt of the tower4, i.e. one or more individual containers12,16,17,18or pairs of containers12,16,17,18may be placed at various locations around the tower4.

FIG. 6shows a schematic perspective view of a plurality of containers12,16,17,18,27,28and the central cable24located between the containers12,16,17,18,27,28. In contrast toFIG. 4, a further pair of containers27,28is provided underneath the containers17,18. The containers2728are arranged parallel to the containers12,16. For example, the containers17,18are stacked on the containers27,28and the containers12,16are stacked on the containers17,18. Moreover, further pairs of containers (not shown) may be stacked on the containers12,16. Each container12,16,17,18,27,28is provided as a damper system.

FIG. 7shows a longitudinal section VII-VII fromFIG. 4of the container12. As shown inFIG. 4the fluid29and the damping body30are arranged inside the container12. The damping body30is immersed in the fluid29, and is configured to move inside the container12, wherein the fluid29and the damping body30are configured to damp oscillations of the wind turbine1. In particular, the container12and the damping body30are configured such that a full rotation of the damping body30inside the container12is prevented. Thus, rolling friction is essentially prevented. Sliding friction has the advantage over rolling friction that more kinetic energy may be transferred into thermal energy when comparing the same moving path35of the damping body30. In particular, the moving path35extends essentially from the end face13to the end face14and vice versa. A length A of the damping body30is larger than the height H of an inner space31of the container12containing the damping body30.

The container12comprises a floor face37(or floor wall) having a sliding surface32for the damping body30, wherein the sliding surface32has a curved shape. The sliding surface32is concave when looking from above such that the damping body30is arranged inside a potential well. As shown inFIG. 7the damping body30is arranged at the lowest point34of the sliding surface32which may be seen as position of rest for the damping body30. Gravitation G forces the damping body30towards this rest position which is arranged midway between the end face13and the end face14and thus is a center position of the container12. Further, a ceiling face36(or ceiling wall) of the container12may also have a curved shape. The ceiling face36is concave when looking from above. The ceiling face36is arranged opposite to the floor face37. In some circumstances, the ceiling face36may also be a sliding surface interacting with the sliding body30. The inner space31is surrounded by the end faces13,14, the floor face37, the ceiling face36and side walls57,58(seeFIG. 16).

In particular, the inner space31may have a curved shape. A sliding surface33of the damping body30may have a curved shape. In particular, the damping body30is provided with a curved bottom face38comprising the sliding surface33. Thus, in case of a curved sliding surface32a larger contact area between the sliding surface32and the sliding surface33of the damping body30may be achieved.

At least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or even more of the inner space31of the container12is filled with the fluid29. A damping effect may be achieved when the damping body30moves through the fluid29while displacing the fluid29. Further, the fluid29itself sloshes e.g. against the end faces13,14and thus provides a further damping effect. Optionally, further damping may be achieved by sliding of the sliding surface33of the damping body30on the sliding surface32of the container12.

Alternatively, the damping body30may float on the fluid29(seeFIG. 8) such that the sliding surface33is in some instances not or permanently not in contact with the sliding surface32or the floor face37. Thus, essentially no sliding friction would occur between the sliding surfaces32,33. In particular, the longitudinal section of the damping body30may be arch-shaped. The damping body30and the container12may have a similar curvature as to provide a smooth sliding motion from one end face13to the other end face14when the wind turbine1is oscillating.

The damping body30is capable to move, in particular to slide, within the container12from the end face13to the end face14in counteractive response to the tower oscillations. The moving path35of the damping body30is dictated by the shape and length L of the container12which may be fully filled with the fluid29(e.g. after the damping body30has been placed) or only partly filled with fluid29. When the wind turbine1oscillates, i.e. moves in one direction away from its initial position, the damping body30and the fluid29will move opposite to this direction. As wind directions obviously change and the container12for example is placed in a fixed and locked position, it is advantageous to use at least two or more of these containers12,16,17,18,27,28(seeFIG. 2toFIG. 6). When arranging containers12,16,17,18,27,28perpendicular to one another, it is possible to cover an optimal damper system irrespectively of the wind direction (and thus the tower oscillation direction).

FIG. 8shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. In contrast toFIG. 7, the longitudinal section of the damping body30is essentially rectangular. Moreover, the ceiling face36and the floor face37are essentially flat. The inner space31of the container12comprises the height H which is constant along the length L of the container12. A longitudinal section of the inner space31is rectangular.

FIG. 9shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. In contrast toFIG. 8, the damping body30comprises a curved bottom face38. The bottom face38is convex when looking from below. Moreover, the container12comprises a curved floor face37. Further, the inner space31of the container12comprises the height H which is not constant along the length L of the container12. The height H decreases from the lowest point34of the container12towards both end faces13,14.

FIG. 10shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. In contrast toFIG. 9, the ceiling face36has a curved shape. The ceiling face36is concave when looking from above.

FIG. 11shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. In contrast toFIG. 10, the inner space31of the container12comprises the height H which is constant along the length L of the container12. Further, a top face39of the damping body30has a curved shape. The top face39is concave when looking from above.

FIG. 12shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. In contrast toFIG. 11, the ceiling face36comprises a flat portion40arranged at one side (right-side) of the ceiling face36and a flat portion41arranged the other side (left-side) of the ceiling face36. A height H1of the inner space31at the flat portion40decreases towards the end face13. A height H2of the inner space31at the flat portion41decreases towards the end face14. The height H of the inner space31between the flat portions40,41may be essentially constant.

The heights H1, H2of the container12vary, in particular such that the height gradually decreases towards the end faces13,14. Thus, cross-sectional areas of the container12gradually decrease towards the end faces13,14. This has the advantage that when the wind turbine1moves in one direction the damping body30and liquid29move in a counteractive direction such that the damping body29pushes parts of the liquid29in front of it creating a liquid “buffer zone” at the respective end face13,14.

The liquid “buffer zone” will slow and stop the damping body30as it moves towards the end face13,14. In particular, the damping body30is so designed that it essentially matches the container cross-section but remain free moving so as to enable the damping body30to push towards the liquid29without too much liquid29simply just flowing across the damping body30since this reduces the “buffer zone” effect.

Alternatively, or additionally, an end-stop or breaking mechanism (not shown) at both end faces13,14may be provided for preventing the damping body30from damaging the end faces13,14of the container12because great force may occur due to collisions between the damping body30and the end faces13,14. Such end-stops may comprise compressible material, e.g. a rubber material, or high friction material placed at any side of the container12.

FIG. 13shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. In contrast toFIG. 12, the damping body30is shown at a position which is near to the end face13while moving towards the end face13(see broken arrow44). Further, the ceiling face36comprises a curved portion42instead of the flat portion40and a curved portion43instead of flat portion41. Furthermore, the top face39of the damping body30is essentially flat. Moreover, the damping body30has an essentially trapezoidal longitudinal section, wherein the bottom face38is curved. The damping body30comprises end faces45,46which are averted from each other. Further, an end face45of the damping body30faces the end face13of the container12. Furthermore, an end face46of the damping body30faces the end face14of the container12. As shown inFIG. 13, when the damping body30moves towards the end face13, fluid29is dammed between an end face45of the damping body30and the end face13of the container12e.g. forming a fluid front.

Furthermore, a fluid flow47flows contrary to the movement (see arrow44) of the damping body30between the bottom face38and the floor face37causing an increase of fluid friction and thus an increased damping effect. Moreover, a fluid flow48may flow contrary to the movement (see arrow44) of the damping body30between the top face39and the ceiling face36causing an increase of fluid friction and thus an increased damping effect. This effect may also occur between side walls57,58(seeFIG. 16) of the container12and side faces55,56(seeFIG. 16) of the damping body30.

In particular, any air caught between the fluid front and damping body30would also contribute to this counter active effect towards the movement (see arrow44).

FIG. 14shows detail view XIV fromFIG. 13of a further embodiment of the container12. In contrast toFIG. 13, the container12comprises an end portion49and the damping body30comprises an end portion50for fitting into the end portion49of the container12, wherein the container12and the damping body30are configured such that fluid29is dammed between the end face45of the damping body30and the end face13of the container12when the end portion50of the damping body30fits into the end portion49of the container12.

Moreover, the end portion49comprises a contact surface51and the end portion50comprises a contact surface52, wherein the contact surface52is configured to touch the contact surface51for defining an end position of the damping body30inside the container12. In particular, the end portion49forms essentially a negative form of the end portion50. The contact surfaces51,52are arranged essentially perpendicular to the floor face37and/or the bottom face38.

The end portion50is shaped such that it essentially does not touch any surface of the end portion49apart from the floor face37, the contact surface51and for example side walls57,58(seeFIG. 16). This design may in the end position prevent the damping body30from getting stuck between the ceiling face36and floor face37of the container12.

FIG. 15shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. The container12is a closed structure for keeping the fluid29inside the inner space31. However, the container12may comprise an opening53at the ceiling face36for placing the fluid29and the damping body30, in particular from above, inside the container12. Moreover, this opening53may be used for service purposes. Further, a cap54may be provided for closing the opening53.

The container material could be any material, e.g. a metal casing or made of a composite material or the like. The damping body30is a durable high-density material, e.g. a metal such as iron or lead. A heavy damping body30is provided to get a better damping effect. In particular, the damping body30is easily grinded or polished to provide a smooth sliding surface33to ease the sliding movement. The damping body30comprises an outer coating or cover material for achieving a reduced friction such as Teflon or other polymeric material.

In an alternative embodiment, the damping body30is placed on (e.g. a plate) or within a box (e.g. a casing) that may provide a low friction contact point between the container12and damping body30. Further, the materials should be chosen as not to deteriorate or erode over time under the influence of the fluid29in the container12because the sliding movement may increase such effects. The fluid is e.g. an oil which may prevent the damping body30from getting in contact with the container12to a great extend upon its sliding movement.

In particular, the damping body30may be a solid structure provided as one piece element, but can also be made of separate elements stacked next or on top of one another and joined together to form one structure.

In particular, the fluid29may be water optionally comprising a number of different agents e.g. salts. The agent is sodium chloride because it is environmentally harmless and because the solubility of sodium chloride in water hardly changes with the temperature so that crystallization will not occur in the container12. Sodium chloride both lowers the freezing temperature of the water and increases the density.

The agent is zinc chloride and/or ferrous sulphate and/or ferrous nitrate having a cost advantage. Further, the agent may by glycerol. As fluid29oils may be used. Examples of such oils could be a mineral, animal or vegetable oil. Such oil fulfills at least one of the following properties:

i) higher density than water,

v) of a viscosity that,a) provides a free-flowing fluid29mass with a relatively quick response to the oscillations,b) allows the damping body30to slide easily—even at low temperatures, orc) sufficiently high to effectively contribute to the “buffer zone” effect and assist in slowing down the damping body30(end-stop effect).

The container12is placed on a platform or support beams designated to be attached to the tower4or the nacelle3. The time of placement can be done after a given tower4has been placed on a wind turbine foundation (on- or off-shore), but pre-assembled in that section before the tower4is installed.

FIG. 16shows a cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12, wherein the container12and the damping body30are intersected. The container12has an elongated shape, wherein a length L of the container12is at least two, three, four, five, six, seven, eight, nine or even ten times larger than a width W and/or height V of the container12. In particular, a cross-section of the damping body30fills at least 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 98% of a cross-section of the container12. The damping body30comprises side faces55,56which are averted from each other and arranged essentially perpendicular to the top face39and/or the bottom face38. Further, the container12comprises a side wall57facing the side face55and a side wall58facing the side face56. The damping body30has essentially a rectangular cross-sectional shape. The container12has essentially a rectangular cross-sectional shape.

FIG. 17shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 16, both the damping body30and the container12have a quadratic cross-sectional shape.

FIG. 18shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 16, the bottom face38and the floor face37are roof shaped. The damping body30has a pentagonal cross-sectional shape.

FIG. 19shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 16, the bottom face38is convex when looking from below and the floor face37is concave when looking from above.

FIG. 20shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 16, the side faces55,56are concave when looking thereon. Further, side walls57,58are convex when looking from the inner space31.

FIG. 21shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 16, the bottom face38and the top face39are convex when looking thereon. Further, the ceiling face36and floor face37are concave when looking from the inner space31.

FIG. 22shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 16, the bottom face38is convex when looking thereon. Further, floor face37is concave when looking from the inner space31. The top face39has a triangular cavity in the cross-sectional view. Further, the ceiling face36is adapted to the top face39.

FIG. 23shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 16, the damping body30comprises a recess59at the bottom face38and the container12comprises a guiding element60at the floor face37which interacts with, in particular protrudes in, the recess59for guiding the damping body30along the length L of the container12. The guiding element60has a trapezoidal cross-sectional shape. The bottom face38is adapted to the guiding element60.

FIG. 24shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 23, two of such guiding elements60at the floor face37and two of such recesses59at the bottom face38are provided, wherein the guiding elements60have a triangular cross-sectional shape.

FIG. 25shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 24, three of such guiding elements60and three of such recesses59are provided. The guiding elements60are provided at the side walls57,58and the floor face37. The recesses59are provided at side faces55,56and the bottom face38.

FIG. 26shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 24, the top face39is concave when looking from above and the bottom face38is convex when looking from below. Further, the ceiling face36and the floor face37are adapted respectively.

FIG. 27shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 23, four of such guiding elements60and four of such recesses59are provided. The guiding elements60are provided at the side walls57,58and two guiding elements60are provided at the floor face37. The corresponding recesses59are provided at the side faces55,56and the bottom face38. The guiding elements60and the recesses59are rounded.

FIG. 28shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 23, the guiding element60is dovetail shaped, wherein the recess59is adapted thereto.

FIG. 29shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 20each side wall57,58comprises a guiding element60and each side face55,56comprises a corresponding recess59.

The guiding elements60may be named rail system which extend along the length L of the container (in total or in part). The function may be to guide the damping body30during sliding within the container12. The guiding elements60may also be characterized as sidewall protection means and/or sliding pads for the damping body30. Such guiding elements60may be placed along the inner space31of the container12at any side, and would thus prevent the damping body30from scraping against the walls. Such guiding elements60may be provided separately from the container12or may be formed inside the container12as integral part thereof. The guiding elements60are exchangeable in part or in total.

FIG. 30shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 16, the damping body30and the container12have a circular cross-sectional shape. Moreover, four guiding elements60are dispersed along a circumference of the container12touching the damping body30. The guiding elements60taper towards the damping body30.

FIG. 31shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 27, the ceiling face36comprises a further guiding element60. Moreover, recesses59are not provided at the damping body30.

FIG. 32shows the cross-sectional view XVI-XVI fromFIG. 7of a further embodiment of the container12. In contrast toFIG. 16, the bottom face38is concave when looking from below and the floor face37is convex when looking from above.

FIG. 33shows the longitudinal section VII -VII fromFIG. 4of a further embodiment of the container12. The container12further comprises a compensation container61. The compensation container61is connected to the container12by means of two ducts62,63. A first duct62is connected to the container12close to the first end face13. A second duct63is connected to the container12close to the second end face14. Each duct62,63comprises a valve64,65. The valves64,65control the flow speed of the fluid29and thereby the damping body30. The damping body30can be immersed in the fluid29completely or only partly.

FIG. 34shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. The container12according toFIG. 34differs from the container12according toFIG. 33in that it does not have a compensation container61but only one duct66with a valve67. The duct66is connected to the container12both close to the first end face13and to the second end face14thereof.

FIG. 35shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. The container12according toFIG. 35differs from the container12according toFIG. 34in that there is not only provided one damping body30but more than one, for example three. The damping bodies30are in the form of rollers or cylinders and can rotate inside the container12. The fluid29can be controlled by one or more valves67.

FIG. 36shows the longitudinal section VII-VII fromFIG. 4of a further embodiment of the container12. The container12according toFIG. 36differs from the container12according toFIG. 35in that there is provided a separate end-stop-valve68which is connected to the ceiling face36by means of a duct69.

It is understood that all features described regarding the container12, the damping body30and the fluid29also apply mutatis mutandis to the containers16,17,18,19,27,28.