A wind turbine tower structure with damper units

Abstract

A wind turbine tower structure (1) having two or more damper units (3) releasably mounted on a lower exterior part thereof is disclosed Each damper unit (3) comprises a scissor-jack damper, where a first (5a) and a second (5b) hinge connection define a first (6) and a second (8) mounting portion, respectively, and a third (5c) and a fourth (5d) hinge connection are interconnected via a damper element (10). The first mounting portion (6) of each damper unit (3) is releasably attached to a first mounting position (7) on the exterior part of the wind turbine tower structure (1) and the second mounting portion (8) of each damper unit (3) is releasably attached to a second mounting position (9, 11) on the exterior part of the wind turbine tower structure (1) or at an anchor point arranged adjacent to the wind turbine tower structure (1). Methods for transporting, storing and erecting the wind turbine tower structure (1) are also disclosed.

Description

[0001] A WIND TURBINE TOWER STRUCTURE WITH DAMPER UNITS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a wind turbine tower structure comprising one or more tower sections. The tower structure is provided with damper units providing damping of oscillations of the tower structure. The invention further relates to methods for transporting a wind turbine tower structure, storing a wind turbine tower structure or erecting a wind turbine tower, while damping oscillations of the wind turbine tower structure.

[0004] BACKGROUND OF THE INVENTION

[0005] When wind turbine tower structures, such as wind turbine towers or parts of wind turbine towers, are arranged in a vertical orientation, there is a risk that oscillations are introduced in the tower structure. Such oscillations may be referred to as 'vortex induced oscillations' or 'vortex induced vibrations'. Vortex induced vibrations is a phenomenon that may arise as the wind flows around the cylindrical tower. When the flow separates from the surface of the tower, vortices are created that changes the pressure distribution along the surface. Lift, causing a movement of the tower transverse to the flow, is developed. This movement of the tower, in turn, causes a change in the location of flow separation from the surface leading to a changed pressure distribution. This changes the lift and reverses movement of the tower. The tower will oscillate from side to side. Vortex induced vibrations will exist at certain wind speeds for a given tower.

[0006] Oscillations of a wind turbine tower structure may lead to fatigue of the wind turbine tower structure, and damping of the oscillations may therefore be required. To this end, various types of dampers have previously been applied in wind turbine towers of erected wind turbines, or in wind turbine towers or parts of wind turbine towers being transported or stored, or during erection of wind turbines. For instance, tuned mass dampers have been applied. One disadvantage of tuned mass dampers is that they need to be mounted at an upper part of the tower structure, and therefore a separate hoisting operation is required in order to install the tuned mass damper. Furthermore, tuned mass dampers are configured to dampen oscillations within a specific narrow frequency range, and therefore they have essentially no impact on oscillations outside the specified frequency range.

[0007] It has also been attempted to use other types of dampers. However, most of these are unable to provide sufficient damping of tower oscillations, or very large dampers are required in order to obtain sufficient damping.

[0008] DESCRIPTION OF THE INVENTION

[0009] It is an object of embodiments of the invention to provide a wind turbine tower structure in which oscillations can be dampened in an efficient and cost effective manner.

[0010] According to a first aspect the invention provides a wind turbine tower structure comprising one or more tower sections, the wind turbine tower structure having two or more damper units releasably mounted on a lower exterior part of the wind turbine tower structure, wherein each damper unit is or comprises a scissor-jack damper with four rigid members, each rigid member being connected to two of the other rigid members via hinge connections, where a first and a second hinge connection define a first and a second mounting portion, respectively, and a third and a fourth hinge connection are interconnected via a damper element, wherein the first mounting portion of each damper unit is releasably attached to a first mounting position on the exterior part of the wind turbine tower structure and the second mounting portion of each damper unit is releasably attached to a second mounting position on the exterior part of the wind turbine tower structure or at an anchor point arranged adjacent to the wind turbine tower structure, and wherein the first mounting positions of the respective damper units are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure.

[0011] Thus, the first aspect of the invention relates to a wind turbine tower structure comprising one or more tower sections. The wind turbine tower structure may be a complete tower structure, either forming part of an erected and / or operational wind turbine or being intended for forming part of a wind turbine to be erected. In the latter case, the wind turbine tower structure may, e.g., be arranged at a temporary storage, be under transportation, or be mounted on a foundation at a wind turbine site, and awaiting further parts of the wind turbine, such as the nacelle, the rotor, etc., being mounted on the tower, i.e. the wind turbine is, in this case, being erected.

[0012] As an alternative, the wind turbine tower structure may be a part of a wind turbine tower, e.g. a single tower section or two or more tower sections being joined to each other. In this case the wind turbine tower structure is also intended to form part of a partially completed wind turbine. Also in this case, the wind turbine tower structure may be arranged at a temporary storage, be under transportation, or be mounted on a foundation at a wind turbine site, while awaiting that one or more further tower sections are mounted on the wind turbine tower structure, so as to form the complete wind turbine tower.

[0013] The wind turbine tower structure has two or more damper units releasably mounted on a lower exterior part of the wind turbine tower structure. Thus, oscillations of the wind turbine tower structure can be dampened by means of the damper units. This will be described in further detail below.

[0014] In the present context the term 'releasably mounted' should be interpreted to mean that the damper units can be easily removed from the wind turbine tower structure, without structurally affecting the wind turbine tower structure.

[0015] Accordingly, the damper units are not permanently mounted on the wind turbine tower structure, but can be mounted thereon with the purpose of dampening oscillations under specific circumstances. This will be described in further detail below. In the present context the term 'lower exterior part of the wind turbine tower structure' should be interpreted to mean a part of the wind turbine tower structure which is close to an end being supported by a support structure, such as a foundation, a tower stand, the ground, etc., while the wind turbine tower structure is arranged in a vertical or upright orientation, and on the outside of the wind turbine tower structure rather than inside a space enclosed by the tower structure. Positioning the damper units in this manner allows them to be easily mounted on the wind turbine tower structure, without requiring a separate hoisting process. Thus, the damper units can be mounted on and removed from the wind turbine tower structure in an easy and cost effective manner.

[0016] Since at least two damper units are mounted on the wind turbine tower structure, it is possible to dampen oscillations in multiple directions. This is particularly useful when the oscillations are caused by impact from the wind, because the direction of such oscillations depend on the wind direction, which is inherently subject to change.

[0017] Each damper unit is or comprises a scissor-jack damper, i.e. a damper operating in accordance with a scissor principle. Thus, the scissor-jack damper comprises four rigid members, each rigid member being connected to two of the other rigid members via hinge connections. Thus, the four rigid members form a rhombic structure where the corners of the rhombic shape are formed by the hinge connections interconnecting the respective rigid members. The hinge connections allow the rigid members to pivot relative to each other, thus changing the shape of the rhombic structure.

[0018] A first and a second hinge connection define a first and a second mounting portion, respectively. Accordingly, the damper unit can be attached to relevant structures via two positions, defined by the first and second mounting portions. Thus, the connecting points between the damper unit and relevant structures coincide with two of the hinge connections, and thus points where two of the rigid members can pivot relative to each other.

[0019] A third and a fourth hinge connection are interconnected via a damper element.

[0020] When the rigid members pivot relative to each other, thus changing the shape of the rhombic structure, the third and fourth hinge connections are moved towards or away from each other, thereby affecting the damper element interconnecting the third and fourth hinge connections. For instance, the first and second hinge connections may be arranged diagonally relative to each other, and the third and fourth hinge connections may be arranged diagonally relative to each other.

[0021] The first mounting portion of each damper unit is releasably attached to a first mounting position on the exterior part of the wind turbine tower structure. Furthermore, the second mounting portion of each damper unit is releasably attached to a second mounting position on the exterior part of the wind turbine tower structure or at an anchor point arranged adjacent to the wind turbine tower structure.

[0022] The first and second mounting positions of a given damper unit, as defined above, are such that, when oscillations occur in the wind turbine tower structure, the distance between the first and second mounting positions will change. This, in turn, changes the shape of the rhombic structure of the scissor- jack damper of the damper unit, thus affecting the damper element interconnecting the third and fourth hinge connections. This results in damping of the oscillations in the wind turbine tower structure. The scissor-jack damper ensures that the relative movement between the third and fourth hinge connections caused by the oscillations of the wind turbine tower structure are leveraged, thus resulting in a relatively large stroke of the damper element interconnecting the third and fourth hinge connections. Accordingly, effective damping of oscillations in the wind turbine tower structure is obtained using low cost damper elements of a manageable size.

[0023] The first mounting positions of the respective damper units are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure. Accordingly, the respective damper units extend from the wind turbine tower structure in different directions, and they are, thus, able to handle oscillations in various directions. The wind turbine tower structure may have three or more damper units releasably mounted on the lower exterior part of the wind turbine tower structure. This allows the damper units to handle oscillations in multiple directions.

[0024] For instance, the wind turbine tower structure may have exactly three, or a multiple of three, damper units mounted thereon. Alternatively, any other suitable number of damper units could be mounted on the wind turbine tower structure, such as two damper units or four or more damper units.

[0025] In the case that the wind turbine tower structure has two damper units mounted thereon, the first mounting positions of the two damper units may preferably be displaced relative to each other along the circumferential direction by a distance differing from 180°, e.g. by 90°, thus allowing the damper units to handle oscillations of the wind turbine tower structure in different directions.

[0026] In the case that the wind turbine tower structure has at least three damper units mounted thereon, the first mounting positions of the respective damper units may be substantially evenly distributed in the circumferential direction along the exterior part of the wind turbine tower structure. According to this embodiment, substantially equal or uniform damping of oscillations in the wind turbine tower structure is obtained, regardless of the direction of the oscillations.

[0027] For instance, in the case that the wind turbine tower structure has exactly three damper units mounted thereon, the first mounting positions of the respective damper units may be arranged with a mutual distance therebetween of approximately 120°.

[0028] The wind turbine tower structure may be mounted on a temporary support structure, and the second mounting position of each damper unit may be an anchor point formed on the temporary support structure. In the present context the term 'temporary support structure' should be interpreted to mean a structure which supports the wind turbine tower structure when it is in a vertical or upright orientation, but which is not supposed to form a permanent support structure for a wind turbine which the wind turbine tower structure forms part of or is supposed to form part of. The temporary support structure may, e.g., be a wind turbine tower storage stand, a seagoing vessel, or any other suitable kind of temporary support structure.

[0029] According to this embodiment, the wind turbine tower structure is not arranged at its final end destination, such as being part of a fully erected wind turbine, but is rather arranged at a temporary position, such as at a manufacturing site, a storage site, or on a transport vessel or vehicle. The wind turbine tower structure is supported by the temporary support structure, and it is preferably arranged in a vertical or upright orientation.

[0030] The damper units are, according to this embodiment, connected to the wind turbine tower structure with the first mounting portions being attached to the lower exterior part of the wind turbine tower structure and the second mounting portions being attached to the temporary support structure, via the respective anchor points. This positions the two connecting points of a given damper unit on two different structures, i.e. the wind turbine tower structure and the temporary support structure, respectively. Accordingly, when oscillations are occurring in the wind turbine tower structure, this can be expected to cause relatively large changes in the distance between the first mounting portion and the second mounting portion, and hence between the first and second hinge connections. This, in turn, causes large changes in the distance between the third and fourth hinge connections, and hence in a large stroke of the damper element interconnecting the third and fourth hinge connections. Thus, efficient damping of oscillations of the wind turbine tower structure can be expected.

[0031] Furthermore, arranging the second mounting positions on the temporary support structure positions these at a distance from the wind turbine tower structure, along a radial direction defined by the wind turbine tower structure. This also contributes to providing large changes in the distance between the first and second hinge connections, and a corresponding large stroke of the damper elements of the damper units.

[0032] It is an advantage that the damper units are releasably mounted on the wind turbine tower structure when the wind turbine tower structure is mounted on a temporary support structure, because the wind turbine tower structure will eventually be dismounted from the temporary support structure in order to be mounted on a permanent support structure, such as a wind turbine foundation. In order to allow for this, the damper unit must be detached from the wind turbine tower structure and / or the temporary support structure. Thus, according to this embodiment, damping of oscillations of the wind turbine tower structure is provided during temporary situations, such as storage or transport of the wind turbine tower structure, and when the temporary situation ends, the damper units can easily be removed. It is also an advantage that the damper units are mounted on the lower exterior part of the wind turbine tower structure, because this allows for easy and cost effective mounting and dismounting of the damper units.

[0033] As an alternative, the wind turbine tower structure may be mounted on an offshore wind turbine tower foundation, and the second mounting position of each damper unit may be an anchor point formed on a transition piece mounted on or forming part of the offshore foundation. This is similar to the embodiment described above, in the sense that the second mounting positions are arranged on different structure than the wind turbine tower structure, and at a distance from the wind turbine tower structure. The remarks set forth above in this regard are therefore equally applicable here.

[0034] However, according to this embodiment, the wind turbine tower structure is mounted on a permanent support structure, in the form of the offshore wind turbine tower foundation. The transition piece forms a suitable structure for attaching the second mounting portions of the damper units.

[0035] As an alternative, the wind turbine tower structure may be mounted on an onshore wind turbine tower foundation. In this case the second mounting portions of the damper units may be connected to second mounting positions formed on the onshore wind turbine tower foundation or on separate structures arranged in or on the ground adjacent to the onshore wind turbine tower foundation. In the case that the second mounting positions of the damper units are formed on a temporary support structure or a part of an offshore or onshore wind turbine tower foundation, each damper unit may extend between the first mounting position and the second mounting position along a direction defining an acute angle relative to an axial direction defined by the wind turbine tower structure.

[0036] According to this embodiment, a line interconnecting the first and second mounting positions, and thus the first and second hinge connections, of a given damper unit, intersects a line along the axial direction defined by the wind turbine tower structure, e.g. represented by a centre axis of the wind turbine tower structure, in such a manner that an acute angle is formed between the two lines. This can, e.g., be obtained by arranging the second mounting positions at a distance from the wind turbine tower structure, at a level corresponding to a lowermost end of the wind turbine tower structure, while arranging the first mounting positions on the exterior part of the wind turbine tower structure at a level being at a distance from the lowermost end of the wind turbine tower structure.

[0037] Arranging the damper units in this manner results in relatively large changes in the distance between the first and second hinge connections, in response to oscillations of the wind turbine tower structure, and hence to corresponding large changes in the distance between the third and fourth hinge connections, leading to a large stroke of the damper elements interconnecting the third and fourth hinge connections. Accordingly, efficient damping with low cost damper units of a manageable size is obtained.

[0038] As an alternative to arranging the second mounting positions on a structure adjacent to the wind turbine tower structure, the second mounting position of each damper unit may be arranged on the exterior part of the wind turbine tower structure, where the second mounting positions may be displaced relative to the respective first mounting positions in an axial direction defined by the wind turbine tower structure along the exterior part of the wind turbine tower structure. According to this embodiment, the first mounting positions as well as the second mounting positions are formed on the exterior part of the wind turbine tower structure, but at different levels along the axial direction defined by the wind turbine tower structure, i.e. at different vertical levels. One advantage of this is that it is not necessary to rely on external structures, such as temporary support structures, foundations, anchor blocks, etc., in order to mount the damper units on the wind turbine tower structure. Thus, the damper units can be mounted on the wind turbine tower structure in an easy and simple manner.

[0039] Arranging the first and second mounting positions at different axial or vertical levels ensures that oscillations of the wind turbine tower structure results in changes in the distance between the first and second mounting portions, and thus the first and second hinge connections, of the respective damper units, thus resulting in damping of the oscillations by means of the damper element interconnecting the third and fourth hinge connections.

[0040] The hinge connections of the damper units may each comprise a revolute joint. In the present context the term 'revolute joint' should be interpreted to mean a kinematic pair with one degree of freedom, which constrains the motion of two bodies to pure rotation about a common axis. Such a joint is very suitable for use in a scissor-jack structure, because it restricts the mutual movements of the rigid members to movements within a plane, and therefore the correspondence between the changes in the distance between the first and second hinge connections, on the one hand, and the impact on the damper element interconnecting the third and fourth hinge connections, on the other hand, is very well defined. This results in reliable and accurate damping of oscillations of the wind turbine tower structure.

[0041] The wind turbine tower structure may be a wind turbine tower or part of a wind turbine tower. This has already been described in detail above.

[0042] According to a second aspect, the invention provides a method for transporting a wind turbine tower structure comprising one or more tower sections in a vertical orientation, the method comprising the steps of: arranging the wind turbine tower structure in the vertical orientation,

[0043] - providing two or more damper units, each damper unit being or comprising a scissor-jack damper with four rigid members, each rigid member being connected to two of the other rigid members via hinge connections, where a first and a second hinge connection define a first and a second mounting portion, respectively, and a third and a fourth hinge connection are interconnected via a damper element,

[0044] - mounting each of the two or more damper units on the wind turbine tower structure by attaching the first mounting portion to a first mounting position on a lower exterior part of the wind turbine tower structure and attaching the second mounting portion to a second mounting position on the exterior part of the wind turbine tower structure or at an anchor point arranged adjacent to the wind turbine tower structure, wherein the first mounting positions of the respective damper units are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure,

[0045] - damping oscillations of the wind turbine tower structure by means of the two or more damper units, and

[0046] - at a later point in time, detaching the two or more damper units from the wind turbine tower structure.

[0047] Thus, the method according to the second aspect of the invention is a method for transporting a wind turbine tower structure. The wind turbine tower structure could, e.g., be a wind turbine tower structure according to the first aspect of the invention, and the remarks set forth above with reference to the first aspect of the invention are therefore equally applicable here.

[0048] In the method according to the second aspect of the invention, the one or more tower sections forming the wind turbine tower structure are initially arranged in a vertical orientation, i.e. in an upright orientation. For instance, the wind turbine tower structure may be mounted on a suitable transport vessel, such as a seagoing vessel or a vehicle, e.g. by means of a suitable support structure.

[0049] Furthermore, two or more damper units of the kind described above with reference to the first aspect of the invention are provided. Thus, the damper units are or comprise scissor-jack dampers with four rigid members connected to each other via hinge connections, and with a damper element interconnecting two of the hinge connections. This has already been described in detail above.

[0050] Next, each of the two or more damper units are mounted on the wind turbine tower structure. This is done by, for each damper unit, attaching a first mounting portion, defined by a first hinge connection, to a first mounting position on a lower exterior part of the wind turbine tower structure and attaching a second mounting portion, defined by a second hinge connection, to a second mounting position. The second mounting position is formed on the exterior part of the wind turbine tower structure or at an anchor point arranged adjacent to the wind turbine tower structure. Furthermore, the first mounting positions of the respective damper units are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure. This has already been described in detail above with reference to the first aspect of the invention.

[0051] Once the two or more damper units have been mounted on the wind turbine tower structure, oscillations of the wind turbine tower structure are dampened by means of the two or more damper units, essentially in the manner described above with reference to the first aspect of the invention. Thus, oscillations in the wind turbine tower structure causes changes in the distance between the first and second hinge connections of the respective damper units, causing a change in the rhombic structure defined by the rigid members, and thus a change in the distance between the third and fourth hinge connections, leading to an impact on the damper element interconnecting the third and fourth hinge connections and providing damping. This has already been described in detail above with reference to the first aspect of the invention. Thus, oscillations of the wind turbine tower structure are dampened while the wind turbine tower structure is being transported, e.g. between a manufacturing location, a storage location and / or a final operating site.

[0052] At a later point in time, the two or more damper units are detached from the wind turbine tower structure. This could, e.g., be when the transport of the wind turbine tower structure has been completed. Accordingly, the damper units may be particularly designed for handling oscillations expected to occur during transport of the wind turbine tower structure, and once transport has been completed, the damper units have served their purpose and can be removed, and possibly replaced with other dampers being designed for handling expected oscillations during the next phase, e.g. during erection of and / or operation of a wind turbine comprising the wind turbine tower structure.

[0053] According to a third aspect, the invention provides a method for storing a wind turbine tower structure comprising one or more tower sections in a vertical orientation, the method comprising the steps of:

[0054] - arranging the wind turbine tower structure in the vertical orientation,

[0055] - providing two or more damper units, each damper unit being or comprising a scissor-jack damper with four rigid members, each rigid member being connected to two of the other rigid members via hinge connections, where a first and a second hinge connection define a first and a second mounting portion, respectively, and a third and a fourth hinge connection are interconnected via a damper element,

[0056] - mounting each of the two or more damper units on the wind turbine tower structure by attaching the first mounting portion to a first mounting position on a lower exterior part of the wind turbine tower structure and attaching the second mounting portion to a second mounting position on the exterior part of the wind turbine tower structure or at an anchor point arranged adjacent to the wind turbine tower structure, wherein the first mounting positions of the respective damper units are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure,

[0057] - damping oscillations of the wind turbine tower structure by means of the two or more damper units, and

[0058] - at a later point in time, detaching the two or more damper units from the wind turbine tower structure.

[0059] The method according to the third aspect of the invention is very similar to the method according to the second aspect of the invention, and it will therefore not be described in detail here.

[0060] However, the method according to the third aspect of the invention is a method for storing a wind turbine tower structure, rather than a method for transporting a wind turbine tower structure. For instance, the wind turbine tower structure may be stored at a manufacturing location or at an intermediate storage location, for instance at a harbour while awaiting shipping to an offshore wind turbine site.

[0061] Thus, when arranging the wind turbine tower structure in the vertical orientation, this may include mounting the wind turbine tower structure on a temporary support structure, such as a wind turbine tower stand.

[0062] Furthermore, in the method according to the third aspect of the invention, the dampening of oscillations of the wind turbine tower structure takes place while the wind turbine tower structure is being stored, and the damper units may be removed when the wind turbine tower structure is no longer to be stored, e.g. immediately prior to transferring the wind turbine tower structure to a suitable transport vessel. Thus, the damper units may be designed for handling oscillations expected to occur during storage of the wind turbine tower structure.

[0063] According to a fourth aspect, the invention provides a method for erecting a wind turbine tower structure comprising one or more tower sections, the method comprising the steps of: arranging the wind turbine tower structure in a vertical orientation,

[0064] - providing two or more damper units, each damper unit being or comprising a scissor-jack damper with four rigid members, each rigid member being connected to two of the other rigid members via hinge connections, where a first and a second hinge connection define a first and a second mounting portion, respectively, and a third and a fourth hinge connection are interconnected via a damper element,

[0065] - mounting each of the two or more damper units on the wind turbine tower structure by attaching the first mounting portion to a first mounting position on a lower exterior part of the wind turbine tower structure and attaching the second mounting portion to a second mounting position on the exterior part of the wind turbine tower structure or at an anchor point arranged adjacent to the wind turbine tower structure, wherein the first mounting positions of the respective damper units are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure,

[0066] - damping oscillations of the wind turbine tower structure by means of the two or more damper units, and

[0067] - at a later point in time, detaching the two or more damper units from the wind turbine tower structure.

[0068] The method according to the fourth aspect of the invention is very similar to the methods according to the second and third aspects of the invention, and it will therefore not be described in detail here.

[0069] However, the method according to the fourth aspect of the invention is a method for erecting a wind turbine tower structure, e.g. as part of erecting a wind turbine. Thus, in the method according to the fourth aspect of the invention, oscillations of the wind turbine tower structure are dampened during erection of the wind turbine tower structure, rather than during storage or transport of the wind turbine tower structure. Thus, when arranging the wind turbine tower structure in a vertical orientation, this may include mounting the wind turbine tower structure on a permanent support structure, such as an offshore or onshore wind turbine tower foundation. The damper units may be detached from the wind turbine tower structure when a specified part of the erecting process of the wind turbine has been completed.

[0070] Accordingly, the damper units may be designed particularly for handling oscillations of the wind turbine tower structure expected to occur during a specified part of the erecting process of the wind turbine.

[0071] The method according to the fourth aspect of the invention may further comprise the step of mounting a nacelle on the wind turbine tower structure, and the step of detaching the two or more damper units from the wind turbine tower structure may be performed after the nacelle has been mounted on the wind turbine tower structure. This could, e.g., include detaching the damper units after the nacelle has been mounted on the wind turbine tower structure, but before the rotor is mounted on the nacelle, or detaching the damper units after the wind turbine has been fully erected.

[0072] Mounting a nacelle on top of a wind turbine tower significantly changes the properties of the structure, including the expected behaviour with regard to oscillations of the wind turbine tower structure. It therefore makes sense to detach the damper units from the wind turbine tower structure after the nacelle has been mounted on the wind turbine tower structure, and possibly replace the damper units with other damper units being designed for the next phase, e.g. completion of the erecting process or operation of the wind turbine.

[0073] As an alternative, the damper units may be detached from the wind turbine tower structure when the wind turbine tower has been completed, but before the nacelle is mounted on the wind turbine tower structure.

[0074] In the methods according to the second, third or fourth aspects of the invention, the step of arranging the wind turbine tower structure in the vertical orientation may comprise mounting the wind turbine tower structure on a temporary support structure, and the second mounting position of each damper unit may be an anchor point formed on the temporary support structure. This has already been described in detail above with reference to the first aspect of the invention.

[0075] BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The invention will now be described in further detail with reference to the accompanying drawings in which

[0077] Fig. 1 is a side view of a wind turbine tower structure according to a first embodiment of the invention,

[0078] Fig. 2 is a top view of the wind turbine tower structure of Fig. 1, and

[0079] Fig. 3 is a side view of a wind turbine tower structure according to a second embodiment of the invention.

[0080] DETAILED DESCRIPTION OF THE DRAWINGS

[0081] Fig. 1 is a side view of a portion of a wind turbine structure 1 according to a first embodiment of the invention. More particular, only the lower part of the wind turbine tower structure 1, and not the entire width thereof, is shown.

[0082] The wind turbine tower structure 1 is mounted on a support structure 2, which could be in the form of a temporary support structure, such as a wind turbine tower stand, or in the form of a permanent support structure, such as an offshore or onshore wind turbine foundation. Furthermore, the wind turbine tower structure 1 is arranged in a vertical, or upright, orientation.

[0083] The wind turbine tower structure is provided with two or more damper units 3, one of which is shown. The damper unit 3 is in the form of a scissor-jack damper with four rigid elements 4 connected to each other via hinge connections 5 in such a manner that a rhombic structure is formed. Mutual pivotal movements of neighbouring rigid members 4, via the respective hinge connections 5, cause the shape of the rhombic structure to change. A first hinge connection 5a defines a first mounting portion 6 of the damper unit 3. The first mounting portion 6 is releasably attached to first mounting position 7 on an exterior part of the wind turbine tower structure 1, at a distance from the bottom of the wind turbine tower structure 1, i.e. from the part of the wind turbine tower structure 1 being connected to the support structure 2.

[0084] A second hinge connection 5b defines a second mounting portion 8 of the damper unit 3. The second mounting portion 8 is releasably attached to a second mounting position 9 at an anchor point formed on the support structure 2, at a distance from the outer wall of the wind turbine tower structure 1.

[0085] A third hinge connection 5c and a fourth hinge connection 5d are interconnected via a damper element 10.

[0086] When oscillations occur in the wind turbine tower structure 1, this causes relative movement of the first mounting position 7 and the second mounting position 9, and thus between the first mounting portion 6 and the second mounting portion 8 of the damper unit 3. This, in turn, causes a change in the distance between the first hinge connection 5a and the second hinge connection 5b of the damper unit 3, defining the first mounting portion 6 and the second mounting portion 8, respectively. This change in distance between the first hinge connection 5a and the second hinge connection 5b changes the shape of the rhombic structure defined by the damper unit 3, thus changing the distance between the third hinge connection 5c and the fourth hinge connection 5d. The change in distance between the third hinge connection 5c and the fourth hinge connection 5d affects the damper element 10 interconnecting the third hinge connection 5c and the fourth hinge connection 5d, thus causing damping of the oscillations of the wind turbine tower structure 1.

[0087] Due to the scissor-jack structure of the damper unit 3, a large stroke of the damper element 10 can be obtained using low cost damper elements 10 of manageable size

[0088] Fig. 2 is a top view of the wind turbine tower structure 1 of Fig. 1. It can be seen that the wind turbine tower structure 1 comprises three damper units 3, attached to respective first mounting positions 7 on the exterior part of the wind turbine tower structure 1. The first mounting positions 7 are distributed evenly on the exterior part of the wind turbine tower structure 1 in a circumferential direction. Thus, the first mounting positions 7 are displaced relative to each other with approximately 120° between neighbouring mounting positions 7.

[0089] Applying three damper units 3 and arranging them as illustrated in Fig. 2 allows for efficient damping of oscillations of the wind turbine tower structure 1 along any direction.

[0090] Fig. 3 is a side view of a wind turbine tower structure 1 according to a second embodiment of the invention. Only the lower part of the wind turbine tower structure 1 is shown. Similarly to the wind turbine tower structure 1 illustrated in Figs. 1 and 2, the wind turbine tower structure 1 of Fig. 3 is mounted on a support structure 2, which could be in the form of a temporary or a permanent support structure 2.

[0091] Furthermore, the wind turbine tower structure 1 of Fig. 3 is provided with two or more damper units 3, one of which is shown, of the kind described above with reference to Fig. 1. However, in the embodiment illustrated in Fig. 3, the second mounting portion 8 defined by the second hinge connection 5b is releasably attached to a second mounting position 11 on the exterior part of the wind turbine tower structure 1. The second mounting position 11 is arranged at a lower position of the wind turbine tower structure 1 than the first mounting position 7, i.e. closer to the part of the wind turbine tower structure 1 being connected to the support structure 2.

[0092] The damper unit 3 illustrated in Fig. 3 operates essentially as described above with reference to Fig. 1, thus providing efficient damping of oscillations of the wind turbine tower structure 1 at low cost and without the need for bulky damper units 3.

[0093] The wind turbine tower structure 1 of Fig. 3 may, e.g., be provided with three damper units 3 arranged essentially as illustrated in Fig. 2.

Claims

CLAIMS1. A wind turbine tower structure (1) comprising one or more tower sections, the wind turbine tower structure (1) having two or more damper units (3) releasably mounted on a lower exterior part of the wind turbine tower structure (1), wherein each damper unit (3) is or comprises a scissor-jack damper with four rigid members (4), each rigid member (4) being connected to two of the other rigid members (4) via hinge connections (5), where a first (5a) and a second (5b) hinge connection define a first (6) and a second (8) mounting portion, respectively, and a third (5c) and a fourth (5d) hinge connection are interconnected via a damper element (10), wherein the first mounting portion (6) of each damper unit (3) is releasably attached to a first mounting position (7) on the exterior part of the wind turbine tower structure (1) and the second mounting portion (8) of each damper unit (3) is releasably attached to a second mounting position (9, 11) on the exterior part of the wind turbine tower structure (1) or at an anchor point arranged adjacent to the wind turbine tower structure (1), and wherein the first mounting positions (7) of the respective damper units (3) are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure (1).

2. A wind turbine tower structure (1) according to claim 1, wherein the wind turbine tower structure (1) has three or more damper units (3) releasably mounted on the lower exterior part of the wind turbine tower structure (1).

3. A wind turbine tower structure (1) according to claim 2, wherein the first mounting positions (7) of the respective damper units (3) are substantially evenly distributed in the circumferential direction along the exterior part of the wind turbine tower structure (1).

4. A wind turbine tower structure (1) according to any of the preceding claims, wherein the wind turbine tower structure (1) is mounted on a temporary supportstructure (2), and wherein the second mounting position (9) of each damper unit (3) is an anchor point formed on the temporary support structure (2).

5. A wind turbine tower structure (1) according to any of claims 1-3, wherein the wind turbine tower structure (1) is mounted on an offshore wind turbine tower foundation (2), and wherein the second mounting position (9) of each damper unit (3) is an anchor point formed on a transition piece mounted on or forming part of the offshore foundation (2).

6. A wind turbine tower structure (1) according to claim 4 or 5, wherein each damper unit (3) extends between the first mounting position (7) and the second mounting position (9, 11) along a direction defining an acute angle relative to an axial direction defined by the wind turbine tower structure (1).

7. A wind turbine tower structure (1) according to any of claims 1-3, wherein the second mounting position (11) of each damper unit (3) is arranged on the exterior part of the wind turbine tower structure (1), and where the second mounting positions (11) are displaced relative to the respective first mounting positions (7) in an axial direction defined by the wind turbine tower structure (1) along the exterior part of the wind turbine tower structure (1).

8. A wind turbine tower structure (1) according to any of the preceding claims, wherein the hinge connections (5) of the damper units (3) each comprises a revolute joint.

9. A wind turbine tower structure (1) according to any of the preceding claims, wherein the wind turbine tower structure (1) is a wind turbine tower or part of a wind turbine tower.

10. A method for transporting a wind turbine tower structure (1) comprising one or more tower sections in a vertical orientation, the method comprising the steps of: arranging the wind turbine tower structure (1) in the vertical orientation,- providing two or more damper units (3), each damper unit (3) being or comprising a scissor-jack damper with four rigid members (4), each rigid member (4) being connected to two of the other rigid members (4) via hinge connections (5), where a first (5a) and a second (5b) hinge connection define a first (6) and a second (8) mounting portion, respectively, and a third (5c) and a fourth (5d) hinge connection are interconnected via a damper element (10),- mounting each of the two or more damper units (3) on the wind turbine tower structure (1) by attaching the first mounting portion (6) to a first mounting position (7) on a lower exterior part of the wind turbine tower structure (1) and attaching the second mounting portion (8) to a second mounting position (9, 11) on the exterior part of the wind turbine tower structure (1) or at an anchor point arranged adjacent to the wind turbine tower structure (1), wherein the first mounting positions (7) of the respective damper units (3) are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure (1),- damping oscillations of the wind turbine tower structure (1) by means of the two or more damper units (3), and- at a later point in time, detaching the two or more damper units (3) from the wind turbine tower structure (1).

11. A method for storing a wind turbine tower structure (1) comprising one or more tower sections in a vertical orientation, the method comprising the steps of:- arranging the wind turbine tower structure (1) in the vertical orientation,- providing two or more damper units (3), each damper unit (3) being or comprising a scissor-jack damper with four rigid members (4), each rigid member (4) being connected to two of the other rigid members (4) via hinge connections (5), where a first (5a) and a second (5b) hingeconnection define a first (6) and a second (8) mounting portion, respectively, and a third (5c) and a fourth (5d) hinge connection are interconnected via a damper element (10),- mounting each of the two or more damper units (3) on the wind turbine tower structure (1) by attaching the first mounting portion (6) to a first mounting position (7) on a lower exterior part of the wind turbine tower structure (1) and attaching the second mounting portion (8) to a second mounting position (9, 11) on the exterior part of the wind turbine tower structure (1) or at an anchor point arranged adjacent to the wind turbine tower structure (1), wherein the first mounting positions (7) of the respective damper units (3) are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure (1),- damping oscillations of the wind turbine tower structure (1) by means of the two or more damper units (3), and- at a later point in time, detaching the two or more damper units (3) from the wind turbine tower structure (1).

12. A method for erecting a wind turbine tower structure (1) comprising one or more tower sections, the method comprising the steps of:- arranging the wind turbine tower structure (1) in a vertical orientation,- providing two or more damper units (3), each damper unit (3) being or comprising a scissor-jack damper with four rigid members (4), each rigid member (4) being connected to two of the other rigid members (4) via hinge connections (5), where a first (5a) and a second (5b) hinge connection define a first (6) and a second (8) mounting portion, respectively, and a third (5c) and a fourth (5d) hinge connection are interconnected via a damper element (10),- mounting each of the two or more damper units (3) on the wind turbine tower structure (1) by attaching the first mounting portion (6) to a first mounting position (7) on a lower exterior part of the wind turbine tower structure (1) and attaching the second mounting portion (8) to a second mounting position (9, 11) on the exterior part of the wind turbine tower structure (1) or at an anchor point arranged adjacent to the wind turbine tower structure (1), wherein the first mounting positions (7) of the respective damper units (3) are displaced relative to each other in a circumferential direction along the exterior part of the wind turbine tower structure (1),- damping oscillations of the wind turbine tower structure (1) by means of the two or more damper units (3), and- at a later point in time, detaching the two or more damper units (3) from the wind turbine tower structure (1).

13. A method according to claim 12, further comprising the step of mounting a nacelle on the wind turbine tower structure (1), wherein the step of detaching the two or more damper units (3) from the wind turbine tower structure (1) is performed after the nacelle has been mounted on the wind turbine tower structure (1).

14. A method according to any of claims 10-13, wherein the step of arranging the wind turbine tower structure (1) in the vertical orientation comprises mounting the wind turbine tower structure (1) on a temporary support structure (2), and wherein the second mounting position (9) of each damper unit (3) is an anchor point formed on the temporary support structure (2).

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