MONOPILE AND WIND TURBINE STRUCTURE

Abstract

A monopile comprising a body (1) having a hollow interior, a toe (9) at a distal end for insertion into a soil (19) during monopile installation, and a proximal end region (2) for supporting a structure (7), such as a wind turbine tower, once the monopile has been installed. The body (1) further comprises a door aperture (12) provided in the body (1) for accessing the interior of the body (1). The door aperture (12) is configured to receive a door assembly (6,18) once the monopile (1) has been installed.

Claims

1-18. (canceled)

19. A monopile, comprising: a body having a hollow interior, a toe at a distal end for insertion into a soil during monopile installation, and a proximal end region for supporting a wind turbine tower once the monopile has been installed; and a door aperture provided in the body for accessing the interior of the body and for receiving a door assembly once the monopile has been installed.

20. The monopile according to claim 19, further comprising one or more reinforcement formations for axially reinforcing the body adjacent to the door aperture.

21. The monopile according to claim 20, wherein the one or more reinforcement formations comprise one or more struts longitudinally aligned with the body.

22. The monopile according to claim 20, wherein the reinforcement formations are at least the same height as the height of the door aperture.

23. The monopile according to claim 20, wherein the one or more reinforcement formations comprise two reinforcement formations located either side of the door aperture.

24. The monopile according to claim 23, wherein the reinforcement formations are located at least 100 mm from the door aperture.

25. The monopile according to claim 20, wherein the one or more reinforcement formations are provided on the interior of the body.

26. The monopile according to claim 25, wherein the one or more reinforcement formations project radially inward from the body's interior surface.

27. The monopile according to claim 20, wherein the one or more reinforcement formations comprise tapered ends for tapering between the body's surface and a radially projected section.

28. The monopile according to claim 20, wherein the one or more reinforcement formations comprise a T-beam cross-section.

29. The monopile according to claim 20, wherein the one or more reinforcement formations are welded to the body.

30. The monopile according to claim 20, wherein the body comprises a plurality of connected tubular sections, and one of said tubular sections comprises the door aperture formed therein.

31. The monopile according to claim 20, wherein the one or more reinforcement formations are configured to not substantially alter the lateral stiffness of the body adjacent to the door aperture.

32. A wind turbine structure comprising: a monopile according to claim 19; and a wind turbine tower mounted to the monopile and comprising a rotor blade assembly, a generator housed within a nacelle, and a tower support supporting the rotor blade assembly and nacelle in an elevated position above the monopile.

33. A method of installing a monopile, comprising the steps of: inserting a monopile according to claim 19 into a soil; and driving the monopile to a required installation depth.

34. The method of installing a monopile according to claim 33, further comprising the step of installing a door assembly into the door aperture once the monopile has been driven to the required installation depth.

35. The method of installing a monopile according to claim 33, further comprising installing a platform at the same level as the door aperture.

Description

[0024] An illustrative embodiment of the present invention will now be described with reference to the accompanying drawings, in which:

[0025] FIG. 1 shows a conventional wind turbine structure comprising a monopile and a transition piece supporting a wind turbine tower;

[0026] FIG. 2 shows a conventional TP-less wind turbine structure comprising a monopile directly supporting a wind turbine tower;

[0027] FIG. 3 shows a sectioned isomeric view of a section of monopile body according to an illustrative embodiment of the present invention;

[0028] FIG. 4 shows the monopile according to the illustrative embodiment during installation;

[0029] FIG. 5 shows a horizontal cross sectional view of a section of the monopile according to the illustrative embodiment, with the door assembly fitted; and

[0030] FIG. 6 shows the monopile according to the illustrative embodiment, once installed.

[0031] FIGS. 3 to 6 show a monopile 1 according to an illustrative embodiment of the present invention. Advantageously, the monopile 1 is provided with a door aperture 12 into which a door assembly 6,18 can be subsequently fitted after the monopile has been installed.

[0032] The monopile 1 is constructed from a plurality of sections that may be connected together onshore to form a hollow tube shaped body for insertion into a soil. In other embodiments, the monopile body 1 may further comprise one or more conical sections. FIG. 3 shows a sectioned isomeric view of one section of the monopile body 1 containing the door aperture 12. As with other sections, the section of monopile body 1 shown in FIG. 3 is formed from a plate of steel that has been bent in a bending machine comprising a plurality of rollers. The ends of the bent plate are then joined to form an annulus with the curved wall defining a circular cross section. In this section, a door aperture 12 is provided that forms an opening through the wall of the body 1.

[0033] Two reinforcement struts 13 are provided on the interior surface of the body 1, either side of the door aperture 12 to axially reinforce the body 1 adjacent to the door aperture 12. The reinforcement struts 13 are provided as steel T-beams, with a flange 16 connected to the interior surface of the body 1 by a solid radially projecting web piece 14. As such, each reinforcement strut 13 effectively forms an I-beam arrangement, with the interior surface of the body 1 functioning as the opposing flange to the reinforcement strut's flange 16. With this arrangement, a a formation is provided which projects radially inward from the interior surface of the body 1, and extends longitudinally down the body 1, parallel with the longitudinal axis of the door aperture 12. The reinforcement struts 13 extend beyond the boundary of the door aperture 12 at the top and bottom. In this respect, in these regions, each end of the reinforcement struts 13 are provided with a tapered section of the web 14, tapering between the projected flange 16 and the interior surface of the body 1. This thereby provides a gradual change in axial stiffness to avoid stress concentrations. In this embodiment, the reinforcement formations are spaced 250 mm from the sides of door aperture 12. In this respect, in embodiments, this spacing is preferably within the range of 100-400 mm, and most preferably between 200-300 mm to allow space for the door assembly to be fitted. In particular, this allows the door frame to connect to both the interior and exterior surfaces of the body 1, either side of the door aperture 12.

[0034] The reinforcement struts 13 provide axial reinforcement at the sides of the door aperture 12, but importantly do not significantly alter the lateral stiffness of the associated section of the body 1 as a whole. Firstly, this prevents deformations that might otherwise be caused by localised distortions in stiffness response as an impact wave propagates through the body material during pile driving. For example, if the door aperture 12 were stiffened by a flange around its periphery, the lateral stiffness response would be different as the shear wave passes through the sections of body containing the top, sides and bottom of the aperture. This could deform the body around the aperture 12. Secondly, as the lateral stiffness of this section of the body 1 is substantially the same other sections, it also substantially mirrors their response under the cyclic lateral loads applied during subsequent operation of the wind turbine. This mitigates the risk of fatigue failure.

[0035] FIG. 4 shows the monopile 1 during installation. The distal end of the monopile 1 comprises a toe 9 that is inserted into the soil 19 of the seabed under its own weight. Once inserted, the monopile 1 is then pile driven into the soil 19 by using a hammer (not shown) to apply impacts in the insertion direction I to the head 17 at the proximal end region 2 of the body 1. During each hammer impact, the impact force is transmitted axially down the body 1 to the toe 9, driving it further into the soil 19. Whilst this impact force generates a pressure wave that propagates down through the body's wall, the force is sufficiently high to also manifest as a shear wave that forces the body 1 to elastically displace laterally as the wave is transmitted there through. Advantageously, the reinforcement formations are configured to mitigate the effects of these impact loads, which have different technical considerations to an applied static compressive load.

[0036] In this connection, as the impact waves propagate through the section of the pile comprising the door aperture 12, the reinforcement struts 13 act to axially reinforce the body 1 to prevent excessive deformation of the door aperture 12. That is, the axial alignment of the struts 13 not only acts to transmit the pressure wave around the door aperture 12, but they resist any lateral displacement of the door caused by the shear wave. As such, the presence of the door aperture 12 does not reduce the overall axial stiffness of the monopile as a whole, allowing it to be driven to the required installation depth without the integrity of the structure being compromised.

[0037] Once the monopile 1 has been installed to the required depth, a door assembly may then be fitted to the door aperture 12. FIG. 5 shows a horizontal cross sectional view of the door aperture 12 once the door assembly 6,18 has been fitted. The door assembly 6,18 comprises a frame section 18 that is fitted into the door aperture 12 and engages around both the opposing interior and exterior surfaces of the body 1. This provides a secure fixing for the frame's hinges to pivotably support the door 6. Importantly, as the door assembly 6,18 is fitted after installing the monopile, it is not subjected to the impact forces applied during pile driving. As such, damage to the hinges and other moveable components of the door assembly 6,18 are avoided. At the same time, it is possible to accommodate minor deformation to the door aperture 12 by tolerances within the mounting of the door frame 18.

[0038] FIG. 6 shows the monopile according to the illustrative embodiment once installed and fitted with the wind turbine tower. The door assembly 6,18 and the secondary steel structures of the platform 5 and ladder 4 have also been fitted. As shown, with the door 6 provided in the monopile body, the platform 5 can be located at the same level as the door way. The platform may also be located at a lower position on the monopile, closer to the water level 8, but still nevertheless clear of the any waves in the water. Therefore, steps and additional beam exchange system are no longer required to access the door 6. At the same time, the lower platform 5 allows much simpler access from a boat landing via a short ladder 4.

[0039] As with other TP-less monopiles, the monopile 1 shown in FIG. 6 allows significant advantages in terms of speed of installation. For example, by avoiding having to wait for the transition piece to be installed and the mounting to set, the idle time of the heavy lift equipment required to install the monopile and the turbine tower is minimised. As this heavy lift equipment is typically rented, such a time saving translates to a considerable overall cost saving. At the same time, less steel is required by avoiding the need for an overlapping transition piece. It also frees up space on the transportation ship, and hence allows further cost savings here.

[0040] It will be understood that the embodiment illustrated above shows an application of the invention only for the purposes of illustration. In practice the invention may be applied to many different configurations, the detailed embodiments being straightforward for those skilled in the art to implement.

[0041] For example, although in the above illustrative embodiment the reinforcement formations are provided in an I-beam configuration, it will be understood that other configurations are also possible.