Wind turbine tower support arrangement

Abstract

A tower support arrangement comprises a wind turbine base tower section that is joinable to an offshore foundation, such as a monopile. An annular foundation wall has an axis (X), and a foundation flange disposed at an end of the foundation wall. The foundation flange is substantially orthogonal to the foundation wall. A first end face portion of the foundation wall disposed at the upper end of the foundation is substantially orthogonal to the axis (X).A second end face portion of the foundation flange is downwardly inclined. The base tower section comprises: an annular tower wall and a tower flange that is configured to be joinable to the foundation flange, wherein the tower flange has a first end face portion and wherein the tower wall has a second end face portion. The base tower section and the offshore foundation are configured such that a clearance (C) is defined between i) the first end face portion (62) of the tower flange (48) and the second end face portion (64) of the tower wall (46), and ii) the first end face portion (54) of the foundation wall (50) and second end face portion (56) of the foundation flange (52). Advantageously, the presence of the clearance channel provides tolerance to ovalities between the tower flange and the foundation flange that could otherwise lead to stress concentrations at the joined surfaces.

Description

[0001] WIND TURBINE TOWER SUPPORT ARRANGEMENT

[0002] Technical Field

[0003] The present disclosure generally relates to the arrangement of a wind turbine tower on a flanged support, for example an offshore foundation such as a monopile.

[0004] Background

[0005] The current trend is for wind turbines to be designed ever larger to capture more energy from the wind. Wind turbine towers therefore need to be higher and constructed more strongly to accommodate the required operational loads of larger wind turbine generators. Offshore installation is preferred for larger wind turbines due there being fewer restrictions for locating wind turbines in an offshore location, and for the more consistent wind conditions.

[0006] Typically, offshore wind turbines are mounted on a suitable foundation such as a monopile, a gravity-based foundation, a tripod foundation or a jacket foundation. As is known in the art for monopile foundations, it is conventional for a monopile to be driven into the seabed to the required depth, following which a transition piece is mounted to the top of the wind turbine monopile. The transition piece provides support for mounting the wind turbine tower that is mounted on top of it.

[0007] More recent developments have proposed mounting the wind turbine tower directly to the top of the monopile. However, this approach presents challenges relating to the mounting arrangement between the flanged interconnection between the top of the monopile and the base of the wind turbine tower.

[0008] It is against this background that the examples of the invention have been devised.

[0009] Summary of the Invention

[0010] According to an aspect of the invention, a wind turbine tower support arrangement comprising an annular connection interface is provided. The arrangement comprises a wind turbine base tower section and an offshore foundation, such as a monopile. The wind turbine base tower section is joinable to the offshore foundation, wherein the offshore foundation comprises: an annular foundation wall having a central axis, and a foundation flange disposed at an end of the foundation wall. The foundation flange is substantially orthogonal to the foundation wall. A first end face portion of the foundation wall that is disposed at the upper end of the foundation is substantially orthogonal to the central axis (X) and may comprise a loading area that is substantially within a projection of a cross sectional area of the annular foundation wall. A second end face portion of the foundation flange is downwardly inclined. Moreover, the base tower section comprises: an annular tower wall and a tower flange that is configured to be joinable to the foundation flange, wherein the tower flange has a first end face portion and wherein the tower wall has a second end face portion. The base tower section and the offshore foundation are configured such that a clearance (C) is defined between i) the first end face portion of the tower flange and the second end face portion of the tower wall, and ii) the first end face portion of the foundation wall and second end face portion of the foundation flange.

[0011] The foundation may be any suitable sort of foundation, but more particularly may be a monopile in an offshore installation.

[0012] Advantageously, the presence of the clearance provides tolerance to ovalities between the tower flange and the foundation flange that could otherwise lead to stress concentrations at the joined surfaces.

[0013] In one example, the first end face portion provided by the foundation wall and the second end face portion provided by the foundation flange are configured to define an annular transition edge therebetween. In this example, the clearance (C) is provided at the annular transition edge of the foundation and is defined by a clearance channel provided at an intersection between the first end face portion of the tower flange and the second end face portion of the tower wall.

[0014] In one example, a first end face portion of the tower flange is downwardly inclined so as to correspond generally with the shape of the second end face portion of the foundation flange. The angles of inclination may be configured so as to control the contact between the end face portions of the tower flange and the foundation flange as they are brought into contact with one another during an installation process. In particular, the first end face portion of the tower flange may be is downwardly inclined at a shallower angle (for example between around 0.5 to 5 degrees, or preferably between 1 and 3 degrees) compared to an inclination angle of the second end face portion of the foundation flange so that the first end face portion of the tower flange and the second end face portion of the foundation flange diverge in a radial direction towards ends of the respective tower flange and foundation flange. This configuration is believed to provide a more predictable and controlled contact between the flanges.

[0015] Further optional features of the aspects of the invention are set out herein and in the dependent claims.

[0016] Brief Description of the Drawings

[0017] So that it may be more fully understood, the invention will now be described, by way of example only, with reference to the following drawings, in which like features are assigned like reference numerals, and in which:

[0018] Figure 1 is a view of a wind turbine installation in an offshore setting and which shows, in an inset panel, a conventional flanged connection between a wind turbine foundation and a base tower section of the wind turbine;

[0019] Figure 2 is an example of a flanged connection suitable for use in a wind turbine support arrangement between a wind turbine foundation and a base tower section of a wind turbine, in which the flanged connection is spaced apart and not joined, whereas Figure 3 shows the flanged connection of Figure 2 but with the foundation and the base tower section brought closer together for mounting purposes so that the detail of the mating faces can be appreciated more fully;

[0020] Figure 4 is a view of the flanged connection in Figure 2, but showing the parts of the flanged connection joined together by an array of mechanical fasteners such as bolts, as is conventional;

[0021] Figure 5 is a view like that in Figure 4, but which illustrates an alternative scheme.

[0022] Detailed Description

[0023] To provide context for the invention, Figure 1 shows a typical horizontal axis wind turbine 2, that includes a nacelle 4, mounted on top of a tower 6, which supports a front facing rotor 8 comprising a plurality of coplanar blades 10. Although not shown in Figure 1 , the rotor 8 is connected to a powertrain housed within the nacelle. The powertrain comprises components required to convert rotation of the rotor into electricity, including a generator, a transmission system and a controller, although these components are not shown in Figure 1 or described in detail for brevity. Although a horizontal-axis wind turbine is shown in Figure 1 , which is a common configuration of wind turbine, it should be noted that the invention may be applicable to other wind turbine configurations.

[0024] Typically, the tower 6 may be made from steel, particularly in an offshore setting like that shown in Figure 1. The tower 6 may be formed from several separate sections, joined together at suitable flanged connections as is known in the art. Note that the tower may comprise more than two tower sections, for example between three and ten tower sections.

[0025] As has been mentioned, the wind turbine 2 shown in Figure 1 is in an offshore setting and is therefore provided with a foundation 12 suitable for this purpose. The foundation 12 in this case is a monopile 14. Other offshore foundations are known such as jackets, tripods, gravity-based and pontoon foundations.

[0026] The monopile 14 is embedded in the seabed 15 in a known manner and extends upwardly through the water 18 to provide a stable mounting platform for the wind turbine 2. Typically, a wind turbine 2 will be connected to a transition piece (not shown) which is connected to the top of the monopile. However, in Figure 1 the wind turbine 2 is shown connected directly to the upper end of the monopile 14.

[0027] The base of the tower 6 and the top of the monopile 14 are connected together by way of a flanged connection or ‘coupling’ 20. Here, the tower 6 is not shown in sections, but it is envisaged that the base of the tower 6 would be constituted by a base tower section on which other tower sections are mounted. Therefore, references in this disclosure to ‘base tower section’ should be understood to mean a separate and distinct base section of the tower, but also cover a base of a single piece tower. In this respect, the ‘base section’ of the tower 6 is labelled as ‘16’ in Figure 1 .

[0028] A portion of the flanged connection 20 between the base tower section 16 and the monopile 14 is shown in the inset panel in Figure 1.

[0029] The base tower section 16 comprises an annular tower wall 22 and a tower flange 24. The tower flange 24 extends away from the tower wall 22 in a radial direction. In this example, the tower flange 24 extends in a radially inwards direction, towards a central axis X of the base tower section 16. It is also possible for a tower flange to extend radially outwardly. In both cases, it will be appreciated that the flange and the tower wall define an L-shape in cross section. It is also possible that tower flanges may be provided that extend radially inwardly and outwardly, thereby defining a T-shape in cross section.

[0030] The monopile 14 also comprises an annular monopile wall 26 and a monopile flange 28. Like the tower flange 24, the monopile flange 28 extends away radially from the monopile wall 26. As illustrated, the flanges 24,28 are integral and monolithic with the walls 22,26 although in principle the flanges may be separate to the walls and welded thereto to form unitary components.

[0031] The annular tower wall 22 and tower flange 24 are configured to define a flat underside surface 30. Likewise, the annular monopile wall 26 and the monopile flange 28 are configured to define a flat upper surface 32. The two surfaces 30,32 are therefore shaped to complement one another for when they are joined.

[0032] The surfaces 30,32 are configured to mate together when the base tower section 16 is mounted on the monopile 14. A circular array of mechanical fasteners in the form of bolts 34 extends circumferentially about the flanged connection 20 and serves to join together the tower flange 24 and the monopile flange 28. The mechanical fasteners are headed- bolts 34 that are T-shaped in cross section thereby defining an upper bolt head that is integral to a respective shank. Respective nuts are secured on the shanks of the bolts and tightened suitably to join the flanged connection 20. In principle the diameter of the tower 6 may be any size, but the examples of the invention are envisaged to be most suited to large-diameter tower sections in which the ‘bolt circle diameter’ or BCD of the bolts is in excess of 3m, for example between 3m and 10m, and more preferably between 3.5m and 8m.

[0033] It is also customary to turn the mechanical fasteners upside down, so the bolt heads are below the tower flange and the nuts are above the tower flange. Also, the mechanical fasteners may instead be in the form of stud bolts having no fixed heads but first and second removable nuts, as would be well understood by the skilled person. Alternatively, the mechanical fasteners may take the form of rivets. At this point it should be noted that the flanged connection 20 in Figure 1 is conventional in the sense that it is a known approach to configure mating flange faces in a flanged connection between a wind turbine tower and a foundation on which the tower is to be mounted in a flat and horizontal configuration. However, as tower diameters get larger, and as wind turbine equipment gets heavier, this imposes challenges on the mechanical interface between the flanges.

[0034] This disclosure will now focus on a wind turbine support arrangement that it apt to substitute for the flanged connection 20 shown in Figure 1 and described above.

[0035] Referring now to Figure 2, there is shown a wind turbine support arrangement 40 embodying an example of the invention. As in Figure 1 , the wind turbine support arrangement 40 of Figure 2 includes an annular base tower section 42 and a foundation 44 which may be in the form of a monopile as discussed above.

[0036] The base tower section 42 includes an annular wall 46 and a tower flange 48. The tower flange 48 extends in a radial direction with resect to the annular wall 46 in the direction of the tower axis X. The tower flange 48 is transverse to the annular wall 46 and in this example generally perpendicular to the annular wall 46. Note that the tower axis X is shown in a representative position in Figure 2 albeit that position may not be in the centre of the tower.

[0037] Note that the tower wall 46 and the tower flange 48 are shown as a single piece in Figure 2, but the parts may be separate components which are welded together.

[0038] The foundation 44 includes an annular foundation wall 50 which extends about the central axis X. A foundation flange 52 extends from the annular foundation wall 50 in a radially inward direction, towards the axis X. in the same way as the tower flange, the foundation flange 52 is generally transverse to the foundation wall 50 and, in this example, is perpendicular to it.

[0039] The foundation 44 and the base tower section 42 define a flanged connection 54 where they join together. The flanged connection 54 is shown as completed in Figure 3, but is shown as incomplete in Figures 2 and 3, wherein the base tower section 42 and the foundation 44 are not joined. Apertures or ‘bolt holes’ 51 ,53 are provided in the foundation flange 52 and the tower flange 48, respectively, in a manner conventional with connection flanges of wind turbine tower installations.

[0040] It will be appreciated that the foundation 44 and the base tower section 42 are configured so that their mating faces compliment each other in such as way so as to reduce stress concentrations in use.

[0041] To this end, it will be apparent that an upper end of the annular foundation 44 includes a first end face portion 54. The first end face portion 54 is substantially orthogonal to the axis X and comprises a loading area or region ‘A’. The loading region A is substantially within a projection of a cross sectional area of the annular foundation wall 50. The cross-sectional area is shown in Figure 2 as ‘A’.

[0042] The upper face of the annular foundation 44 also comprises a second end face portion 56 that is provided by the foundation flange 52. Here, the second end face portion 56 is downwardly inclined such that an annular transition edge 58 is defined between the two upper surface portions 54,56. It will be appreciated, therefore, that the foundation flange 52 has an inwardly dished form, in a radially inwards direction, when considered from the transition edge 58. Note that the underside surface 60 of the foundation flange 52 is orthogonal to the foundation wall 50 and, thus, to the axis X.

[0043] The somewhat ‘dished’ form of the foundation flange 52 is complemented by the underside surface of the base tower section as will now be described.

[0044] As is also seen in Figure 2, the base tower section 42 has a lower or underside surface that provides a first end face portion 62 and a second end face portion 64. The first end face portion 62 of the base tower section 42 is provided at the tower flange 48, whereas the second end face portion 64 is provided at the tower wall 46. As can be seen, there is not a sharp intersecting line dividing the first end face portion 62 and the second end face portion 64 as there is for the foundation 44. Instead, the first end face portion 62 and the second end face portion 64 of the base tower section 42 are separated by a clearance channel 66 that is provided at an intersection between the end face portions 62,64.

[0045] The clearance channel 66, the first end face portion 62 and the second end face portion 64 are configured so that, when the base tower section 42 is joined to the foundation 44, the clearance channel 66 defines a clearance ‘C’ with the annular transition edge 58 of the foundation 44. Because of the presence of the clearance channel 66, it will be noted that the width of the second end face portion 64 of the tower wall 46 is less than the radial width of the first end face portion 54 of the foundation wall 50. More particularly, the width ‘W of the second end face portion 64 of the tower wall 46 may be between 60% and 90% of the width of the first end face portion 54 of the foundation wall 50.

[0046] The clearance channel 66 is configured in the illustrated example as an annular groove that is formed, for example by a suitable machining process, at the intersection between the first end face portion 62 and the second end face portion 64. In this example the clearance channel 66 extends the entire way round the underside surface of the base tower section 42.

[0047] In this example, the clearance channel 66 has a generally semi-circular cross section, although that is not essential. For example, the channel 66 may be elliptical in form or any other form, for example it may have a rectilinear cross section, as long as it defines sufficient clearance around the transition edge on the upper face of the annular foundation. Expressed another way, the clearance channel 66 resembles a cut-out or carved-out groove defined in the underside of the base tower section positioned between the underside of the tower wall and the underside of the tower flange. Note that the clearance is marked on Figure 4 by reference ‘C’.

[0048] A particular advantage of the clearance channel 66 is that it provides tolerance to ovalities and other dimensional tolerances in the foundation flange 52 and the tower flange 48. For example the annular transition edge 58 may not be precisely circular and this radial tolerance can be absorbed by the clearance channel 66. As wind turbine tower diameters increase in size, the precision with which the circular towers are manufactured become more challenging to achieve. Therefore, some ovalities may be introduced into the circular forms and geometrical changes can be introduced in the event that the upper face of the flange requires machining. The stress concentrations that can be generated by tower ovalities and other dimensional inaccuracies are mitigated by the clearance channel 66.

[0049] As will be appreciated from Figure 2, both the foundation flange 52 and the tower flange 48 are configured so that their mating surfaces are inclined with respect to the horizontal, as illustrated in the Figure. Also, it is to be noted that the angles of inclination of the mating surfaces are not equal. This means that when the base tower section 42 is lowered into contact with the foundation 44 during an installation process, a gap will be formed between the mating surfaces which enlarges in the radially inward direction. This can be appreciated in Figure 2 by the marked angles. Here, the first end face portion 62 of the tower flange 48 defines an angle 01 with the horizontal plane H.

[0050] Similarly, the second end face portion 56 of the foundation flange 52 defines an angle 02 with the horizontal plane H. It will be appreciated at this point that the horizontal plane H is a theoretical horizontal plane, based on the assumed vertical orientation of the tower. Here, the plane H is perpendicular to the axis X.

[0051] Although the angles 01 and 02 may be the same, in one example the angles may be different. In particular the angle 02 may be greater than the angle 01. The extent of difference may be between 0.5 degrees and 5 degrees, more particularly between 1 degree and 3 degrees. The difference in angle can be appreciated at angle 03. Preferably the difference angle 03 should be configured to provide a gap at the ends of the flanges 48,52 of between 0.5mm and 10mm, and optionally between 1mm and 5mm. This example is provided on the bases if a flange with a radial width of between about 250mm to about 600mm.

[0052] This can be seen more clearly from Figure 3, which shows the base tower section 42 being lowered onto the foundation 42. The difference angle 03 is seen clearly in Figure 3, as is the gap, ‘G’ between the radial inner ends of the foundation flange 52 and the tower flange 48.

[0053] A benefit of this is to control the face-to-face contact between the flanges 48,52 as the two flanges are mated together. In this respect, once the foundation flange 52 and the tower flange 48 are installed with connection bolts, tensioning of the connection bolts serves to deform the tower flange slightly so as to remove the gap G so that the first end face portion 62 of the tower flange 52 is urged into contact with the second end face portion 56 of the foundation flange 52. This is shown in Figure 4, which shows a bolt 34 extending through the two flanges 48,52. The bolt 34 is suitable tensioned to force closure of the gap G, which is not shown on Figure 4, but which is shown in Figure 3.

[0054] The skilled person will appreciate that various modifications may be made to the examples that have been described in this disclosure so far, without departing from the invention as defined by the claims. Some variants have already been mentioned. A further variant is shown in Figure 5. It should be noted that the wind turbine support arrangement 40 shown in Figure 5 is substantially the same as that shown in Figure 4. Therefore, the same reference numerals will be used to refer to common parts, components and features, where appropriate, and this discussion will focus on the difference for the sake of brevity.

[0055] Firstly, it will be noticed that in the example of Figure 5, the clearance (C) between the mating faces of the foundation 44 and the base tower section 42 is not provided by the ‘cut-out’ like form of the clearance channel 66. Instead the clearance C is provided by a chamfered region 76 of the foundation that, in effect, blunts the previously defined transition edge that was provided between the end face portion 54 of the foundation wall 50 and the end face portion 56 of the foundation flange 52. It is believed that this measure may provided similar advantages to the previously illustrated examples.

Claims

Claims1. A wind turbine support arrangement (40), comprising a wind turbine base tower section (42) and an offshore foundation (44), such as a monopile, wherein the wind turbine base tower section (42) is joinable to the offshore foundation (44), wherein the offshore foundation (44) comprises: an annular foundation wall (50) having a central axis (X); a foundation flange (52) disposed at an end of the foundation wall (50) wherein the foundation flange (52) is substantially orthogonal to the foundation wall (50); wherein a first end face portion (54) of the foundation wall (50) disposed at the upper end of the foundation (44) is substantially orthogonal to the central axis (X) and wherein a second end face portion (56) of the foundation flange (52) is downwardly inclined; and wherein the base tower section (42) comprises: an annular tower wall (46) and a tower flange (48) that is configured to be joinable to the foundation flange (52), wherein the tower flange (48) has a first end face portion (62) and wherein the tower wall (46) has a second end face portion (64); wherein the base tower section (42) and the offshore foundation (44) are configured such that a clearance (C) is defined between i) the first end face portion (62) of the tower flange (48) and the second end face portion (64) of the tower wall (46), and ii) the first end face portion (54) of the foundation wall (50) and second end face portion (56) of the foundation flange (52).

2. The wind turbine support arrangement of Claim 1 , wherein the first end face portion (54) provided by the foundation wall (50) and the second end face portion (56) provided by the foundation flange (56) are configured to define an annular transition edge (58) therebetween, and wherein the clearance (C) is provided at the annular transition edge (58) of the foundation (44) and is defined by a clearance channel (66) provided at an intersection between the first end face portion (62) of the tower flange (48) and the second end face portion (64) of the tower wall (46).

3. The wind turbine support arrangement of Claims 1 or 2, wherein the foundation (44) is a monopile.

4. The wind turbine support of any one of the preceding claims, wherein a first end face portion (62) of the tower flange (48) is downwardly inclined so as to correspond generally with the shape of the second end face portion (56) of the foundation flange (52).

5. The wind turbine support of Claim 4, wherein the first end face portion (62) of the tower flange (48) is downwardly inclined at a shallower angle (01) compared to an inclination angle (02) of the second end face portion (56) of the foundation flange (52) so that the first end face portion (62) of the tower flange (48) and the second end face portion (56) of the foundation flange (52) diverge in a radial direction towards ends of the respective tower flange (48) and foundation flange (52).

6. The wind turbine support arrangement of Claim 5, wherein an angular difference (02) between the second end face portion (56) of the foundation flange (52) and the second end face portion (56) of the foundation flange (52) is between 0.5 to 5 degrees.

7. The wind turbine support arrangement of Claims 5 or 6, wherein the radial direction is a radially inwards direction towards the axis (X) of the foundation (44).

8. The wind turbine support arrangement of any one of the preceding claims, when dependent on Claim 2, wherein the clearance channel (66) is configured such that the second end face portion (64) of the annual tower wall (46) has a width (W) in the radial direction that is at least 60% of and less than 90% of a radial width of the end face of the foundation wall (50).

9. The wind turbine support arrangement of any one of the preceding claims, when dependent on Claim 2, wherein the clearance channel (66) is configured such that the second end face portion (64) of the annual tower wall (46) has a width (W) in the radial direction that is at least 70% of and less than 80% of a radial width of the end face of the annular foundation wall.

Images