Wind turbine monopile installation method and apparatus

Abstract

An apparatus for, and a method of, installing a wind turbine monopile for supporting a wind 5 turbine tower, the wind turbine monopile comprising an annular wall, the annular wall defining a central axis, wherein an annular connecting flange extends radially from the annular wall. The method comprises using an anvil to strike a driving end of the wind turbine monopile thereby to transmit an impact load from the anvil to the wind turbine monopile along the central axis to drive the monopile into a substrate. The impact load is 10 focussed to a loading area defined by an area of the wind turbine monopile that is substantially within a projection of a cross sectional area of the annular wall on the driving end of the monopile.

Description

[0001] WIND TURBINE MONOPILE INSTALLATION METHOD AND APPARATUS

[0002] Technical Field

[0003] This disclosure generally relates to the construction of an offshore wind turbine having 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 provide support for mounting the wind turbine tower that is mounted on top of the wind turbine monopile.

[0007] More recent developments have proposed mounting the wind turbine tower directly to the top of the monopile. However, the requirement for the monopile to have an annular connection flange at its top end complicates the pile driving process due to the risk of causing damage to the flange.

[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, there is provided a method of installing a wind turbine monopile for supporting a wind turbine tower, the wind turbine monopile comprising an annular wall, the annular wall defining a central axis, wherein an annular connecting flange extends radially from the annular wall. The method comprises using an anvil (40) to strike a driving end of the wind turbine monopile thereby to transmit an impact load from the anvil to the wind turbine monopile along the central axis to drive the monopile into a substrate. The impact load is focussed to a loading area defined by an area of the wind turbine monopile that is substantially within a projection of a cross sectional area of the annular wall on the driving end of the monopile.

[0011] A force focussing element may be disposed between the anvil and the wind turbine monopile such that the anvil contacts the force focussing element and the force focussing element focuses the applied load from the anvil into the wind turbine monopile within the loading area.

[0012] The force focussing element may be annular.

[0013] The geometry of the force focussing element may substantially match the projection of a cross sectional area of the annular wall.

[0014] The force focussing element may be a separate component to the anvil and the monopile.

[0015] The force focussing element may be attached to the wind turbine foundation during a monopile driving operation. Alternatively, the force focussing element may be attached to the anvil during a monopile driving operation.

[0016] The force focussing element may be removed after installation of the monopile.

[0017] The wind turbine monopile may be configured such that an annular connecting flange of the wind turbine monopile is axially offset from the loading area in a direction along the central axis.

[0018] According to another aspect of the invention, there is provided an apparatus for installing a wind turbine monopile, the apparatus comprising an anvil and a wind turbine monopile. The anvil is configured to apply an impact force to the monopile for driving the monopile into a substrate, and the apparatus is configured such that the impact force is focussed to a loading area defined by an area of the wind turbine monopile that is substantially within a projection of a cross sectional area of the annular wall on the longitudinal driving end of the monopile. The apparatus may further comprise a force focussing element for focussing the impact force applied by the anvil to the loading area of the monopile.

[0019] The force focussing element may be a separate component within the apparatus.

[0020] The wind turbine monopile may further comprise an annular connection flange that extends radially from the annular wall, and wherein the wind turbine monopile is configured such that the loading area on which the impact force is focussed is defined by the annular wall of the wind turbine monopile.

[0021] Brief Description of the Drawings

[0022] 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:

[0023] Figure 1 is a view of a wind turbine and includes an inset panel illustrating a flange connection between a wind turbine tower section and a wind turbine monopile;

[0024] Figure 2 is a partial perspective view of the top of an example wind turbine monopile;

[0025] Figure 3 is a partial section view of an example monopile foundation during installation;

[0026] Figure 4 to 7 are partial section views showing a portion of various examples of monopile installation apparatus;

[0027] Figures 8A and 8B show process steps of a method of the invention. Detailed Description

[0028] In general terms, the examples discussed in this disclosure provide methods and apparatus for installing a wind turbine monopile foundation in which an impact load delivered to the monopile by an anvil is focussed to a loading area. For the purposes of this discussion, the loading area may be considered to be defined by an area of the wind turbine monopile that is substantially within a projection of a cross sectional area of the annular wall on the driving end of the monopile, as will become more apparent in the discussion that follows with reference to the accompanying drawings.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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. 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 .

[0033] 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.

[0034] 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 embodiment, 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 that a tower flange extends 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 flanges may be provided that extend radially inwardly and outwardly, thereby defining a T-shape in cross section.

[0035] 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 are integral and monolithic with the walls although in principle the flanges may be separate to the walls and welded thereto to form unitary components.

[0036] 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.

[0037] 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 are placed circumferentially about the flanged connection 20 and extend axially to join together the tower flange 24 and the monopile flange 28. The mechanical fasteners are headed-bolts that are T-shaped in cross section thereby defining an upper bolt head that is integral to shank. Respective nuts are secured on shank of the bolts and tightened suitably to join the flanged connection. In principle the diameter of the tower 6 may be any size, but the invention is envisaged to be most suited to large-diameter tower sections in which the ‘bolt circle diameter’ or BCD of the fasteners is in excess of 3m, for example between 3m and 10m, and more preferably between 8m and 10m.

[0038] It is also customary to turn the mechanical fasteners upside down, so the bolt heads are below the lower annular connecting flange portion and the nuts are above the upper annular connecting 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.

[0039] At this point it should be noted that the monopile 14 shown in Figure 1 is conventional in a sense that it represents a known design of monopile 14 or use in supporting a wind turbine tower 6. However, as tower diameters get larger, and as wind turbine equipment gets heavier, this drives a requirement for larger and sturdier monopiles 14 to transfer a corresponding increased load to the ground, seabed or substrate 15 in which the monopile 14 is installed. Increasing the size of the monopiles 14 also increases the force requirements for their installation into the substrate 15. This increase in installation force poses a risk of deformation to a driving end 36 of the monopile 14, in particular a connecting flange 28 of the monopile 14. Plastic deformation or damage to the driving end 36 of the monopile 14 could prevent the base tower section 16 from being assembled to the monopile 14, thus rendering the monopile 14 useless. This problem is compounded by the difficult process of onsite repair, removal or digging up of the useless damaged monopile 14 from the substrate 15 after installation, wasting valuable time and resources.

[0040] This disclosure will now focus on apparatus for installing wind turbine monopile 14, and a wind turbine monopile 14, as such, that is better suited to resist higher installation load requirements.

[0041] Referring now to Figure 2, there is shown a partial perspective view of an upper or ‘driving’ end 36 of a monopile 14. In this particular example, a force focussing element 38 is operable to transfer installation loads delivered by an anvil 40 to the driving end 36 of the monopile 14.

[0042] In this example, such a force focussing element 38 may be a geometric feature of the monopile 14 or it may be an additional component detachably attached to the monopile 14. Where the force focussing element 38 is detachably attached to the monopile 14, there are many possibilities by which the force focussing element 38 may be detachably attached to the monopile 14. For example, the force focussing element 38 may be attached to the monopile 14 by a number of nuts and bolts forming a bolted joint. Such a bolted joint may use the existing holes provided in the monopile flange 28. Alternatively, the bolted joint may use holes provided in the monopile flange 28 for the purpose of attaching the force focussing element 38. In another example, the force focussing element 38 may be clamped to the monopile flange 28.

[0043] In either case, the force focussing element 38 is an annular structure that corresponds to the geometry of the annular wall 26 of the monopile 14. In other words, the geometry of the force focussing element 38 substantially matches the projection of a cross sectional area of the annular wall 26 on the driving end 36 of the monopile 14. The width T1 of the force focussing element 38 in the radial direction may be thicker than the radial width T2 of the annular wall 26, for example, 1.2 times the width. Alternatively, the radial width T1 of the force focussing element 38 may be thinner than the radial width T2 of the annular wall 26, for example 0.8 times the width. Expressed another way, the radial width T1 of the force focussing element 38 is envisaged to be around 80% to 120% of the radial width T2 of the annular wall 26 of the monopile immediately below the force focussing element 38.

[0044] The monopile 14 comprises a load application area, hereinafter referred to as a loading area 42, that is annular in shape and corresponds with a projection of a cross sectional area of an annular wall 26 of the monopile on the uppermost face 32 of the monopile 14 as it is being installed in the substrate 15. The role of the force focussing element 38 is to receive the installation load from the anvil 40 and direct the load to a loading area 42 of the monopile 14.

[0045] Figure 3 shows the force focussing element 38 as a separate component detachably attached to the monopile 14. In this example, the end of the force focussing element 38 that contacts the monopile 14, only makes contact in the load application area of the monopile 14.

[0046] Figure 3 also shows the anvil 40 moving in the direction of arrow A to strike the driving end transferred from the anvil 40 to the annular wall 26 of the monopile 14 which drives the monopile 14 into the substrate 15 along the central axis X of the monopile 14.

[0047] Imparting the impact load on the cantilever of the connecting flange 28 would introduce a bending moment into the connecting flange 28. The force applied to the monopile 14 during installation is likely sufficient to impart a bending moment that could plastically deform the connecting flange 28. It is therefore necessary to reduce this risk of plastic deformation by avoiding the application of monopile installation force to the connecting flange 28 altogether. Applying the installation force to the load application area ensures that the force is directed around the connecting flange 28 and into the annual wall 26, rather than through the connecting flange 28. However, it is possible for an outboard portion of the connecting flange 28 to be loaded without the connecting flange sustaining damage as the bending moment imparted would be relatively small. For example, a loaded portion of the connecting flange 28 may be equivalent to 20% of the radial width T2 of the annular wall 26 of the monopile 14.

[0048] Implementing the force focussing element 38 as a separate component to the anvil 40 or the monopile 14 provides opportunity for the design of the force focussing element 38 to be sacrificial. For example, a material of the force focussing element 38 may be purposefully less resilient than a material of either or both the anvil 40 and the monopile 14 such that any deformation is incurred in the sacrificial force focussing element 38 instead of the anvil 40 or the monopile 14. This mitigates risk of damaging the monopile 14 during installation by ensuring that the cheaper load application element 38 will sustain damage before the monopile 14 does.

[0049] For example, the skilled person would appreciate that a typical material for the monopile 14 is steel, for example S355 or S420 in accordance with EN 10025: 2004. whereas a typical material for the anvil 40 is likely to be harder and / or more resilient. It is envisaged that the force focussing element may be made from the same material as the monopile 14 or the anvil 40, or a material with hardness and / or resilience between the two.

[0050] Moving on to Figure 4, the force focussing element 38 is shown as a geometric feature of the monopile 14. Here, it is shown as an annular axial protrusion from the driving end 36 of the monopile 14. The axial protrusion may be implemented as a continuation of the annular wall 26. In this case, the connecting flange 28 shown in Figure 3 is attached to the monopile 14 in a position below or underflush to an upper end of the annular wall 26. In other words, the annular connecting flange 26 of the monopile 14 is axially offset from the loading area in a direction along the central axis X, for example, an inward or downward direction.

[0051] In being attached to the monopile 14, it is envisaged that the flange 28 is either a separate component that is somehow fixed to the monopile, particularly through a suitable welding process so that the flange 28 is a non-removable part of the monopile 14 or, alternatively, that the flange 28 defines part of a monolithic component with the monopile 14.

[0052] This solution of incorporating the force focussing element 38 as a geometrical feature of the monopile 14 represents a cost-effective solution as there are minimal additional components required during installation of the monopile 14.

[0053] Figure 5 shows an embodiment wherein the force focussing element 38 comprises a combination of two features; a force focussing element 38’ which is a geometric feature of the monopile 14 and a force focussing element 38” being a separate force focussing component. This approach brings the functional benefits of both of the approaches described above and in Figures 2 and 3, but likely at an additional implementation cost. It is worth noting that the radial width T3 of the force focussing component 38” is thicker than the radial width T1 of the force focussing geometric feature 38’ included in the geometry of the monopile 14 in this example. In this example the radial width T1 of the force focussing geometric feature 38’ is substantially the equal to the radial width T2 of the annular wall 26 of the monopile 14. This is not intended to be limiting, in fact, the radial width T3 of the force focussing component 38” may be the equal to or thinner than the radial width T1 of the force focussing geometric feature 38’ included in the geometry of the monopile 14.

[0054] Moving on, Figure 6 shows an alternative embodiment of the invention wherein the force focussing element 38 is either a geometric feature of, or a separate component detachably attached to, the anvil 40. In this embodiment, the functional principle is the same in that the force focussing element 38 is operable to transfer installation loads delivered by the anvil 40 to the loading area 42 of the of the monopile 14.

[0055] The force focussing element 38 may be specific to the monopile 14 being installed, for example, the geometry of the force focussing element 38 may substantially match the projection of a cross sectional area of the annular wall 26 of the monopile 14 being installed. With this in mind, the anvil 40 may be configured to be compatible with multiple types of force focussing element 38 such that the anvil 40 remains a common component with the ability to install multiple types of monopile 14. It is envisaged that the force focussing element 38 would attach to the anvil 40 in a corresponding manner to how the force focussing element 38 attaches to the monopile 14 as described above, for example, with bolted joints or clamps (not shown).

[0056] Figure 7 shows an alternative example to that shown in Figure 5 wherein the force focussing element 38 comprises a combination of a geometric feature 38’ of the monopile 14 and a separate component 38”. The difference between these approaches is that in Figure 6, the force focussing component 38” is detachably attached to the anvil 40 instead of the monopile 14 as shown in Figure 5. The benefit of fitting the force focussing component 38” to the anvil 40 is an increase in installation efficiency when installing multiple monopiles 14 of the same type at a jobsite, as there is no need to disassemble and reassemble the force focussing component 38” when moving from one monopile 14 to another.

[0057] The inventive concept also embraces a method of installation of a monopile 14 for supporting a wind turbine tower 6 as illustrated in Figure 8. The method comprises striking an anvil 40 against a driving end 36 of the wind turbine monopile 14 in the direction of arrow A wherein the monopile 14 is positioned vertically at the install location, with the driving end 36 facing upwards. Next, an impact load from the anvil 40 is transmitted to the driving end 36 of the wind turbine monopile 14 along the central axis X to drive the monopile 14 into the substrate 15 in the direction of arrow B. The impact load is focussed to a loading area 42 defined by an area of the wind turbine monopile 14 that is substantially within a projection of a cross sectional area of the annular wall 26 on the driving end of the monopile 14 such that the load is transferred to the annular wall 26 of the monopile 14. This action is repeated until the monopile 14 has been sufficiently installed in the substrate 15. An installation depth will be known by the skilled person and will vary from one application to another.

[0058] The method may further comprise introducing the force focussing element 38 in between the anvil 40 and the monopile 14, such that the load applied by the anvil 40 is transferred to the force focussing element 38 before being transferred to the monopile 14 at the loading area 42. As explained above, it will be appreciated that the force focussing element 38 may be a feature of the monopile 14, the anvil 40, a separate component detachably attached to either the anvil 40 or the monopile 14, or a combination of these features during installation.

[0059] Where the force focussing component 38 is, at least in part, a separate component, detachably attached to the monopile 14, the force focussing component 38 is removed from the monopile 14 after installation of the monopile 14 in the substrate 15.

[0060] In the above discussion, various alternative examples to the illustrated embodiments have been mentioned. Other variants and examples would be apparent to the skilled person.

Claims

Claims1. A method of installing a wind turbine monopile (14) for supporting a wind turbine tower (6), the wind turbine monopile (14) comprising an annular wall (26), the annular wall (26) defining a central axis (X), wherein an annular connecting flange (28) extends radially from the annular wall (26), the method comprising: using an anvil (40) to strike a driving end (36) of the wind turbine monopile (14) thereby to transmit an impact load from the anvil (40) to the wind turbine monopile (14) along the central axis (X) to drive the monopile (14) into a substrate (15); wherein the impact load is focussed to a loading area (42) defined by an area of the wind turbine monopile (14) that is substantially within a projection of a cross sectional area of the annular wall (26) on the driving end (36) of the monopile (14).

2. The method of Claim 1 , wherein a force focussing element (38) is disposed between the anvil (40) and the wind turbine monopile (14) such that the anvil (40) contacts the force focussing element (38) and the force focussing element (38) focuses the applied load from the anvil (40) into the wind turbine monopile (14) within the loading area (42).

3. The method of Claim 2, wherein the force focussing element (38) is annular.

4. The method of Claim 2 or Claim 3, wherein the geometry of the force focussing element (38) substantially matches the projection of a cross sectional area of the annular wall (26).

5. The method on any preceding claim, wherein the force focussing element (38”) is a separate component to the monopile (14) and the anvil (40).

6. The method of Claim 5, wherein the force focussing element (38’) is attached to the monopile (14) during a monopile driving operation.

7. The method of Claim 5, wherein the force focussing element (38’) is attached to the anvil (40) during a monopile driving operation.

8. The method of any of Claims 5 to 7, wherein the force focussing element (38’) is removed after installation of the monopile (14).

9. The method of any preceding claim, wherein the impact load is focussed to a loading area (42) defined by an area of the wind turbine monopile (14) that is substantially within a projection of a cross sectional area of the annular wall (26) on the driving end (36) of the monopile (14), by configuring the wind turbine monopile (14) such that the annular connecting flange (28) of the wind turbine monopile (14) is axially offset from the loading area (42) in a direction along the central axis (X).

10. An apparatus for installing a wind turbine monopile (14), the apparatus comprising: an anvil (40); and a wind turbine monopile (14); wherein the anvil (40) is configured to apply an impact force to the monopile (14) for driving the monopile (14) into a substrate (15), and wherein the apparatus is configured such that the impact force is focussed to a loading area (42) defined by an area of the wind turbine monopile (14) that is substantially within a projection of a cross sectional area of the annular wall (26) on the driving end (36) of the monopile (14).

11. The apparatus of Claim 10, further comprising a force focussing element (38) for focussing the impact force applied by the anvil (40) to the loading area (42) of the monopile (14).

12. The apparatus of Claim 11 , wherein the force focussing element (38’) is a separate component to the monopile (14) and the anvil (40).

13. The apparatus of any of Claims 10 to 12, wherein the wind turbine monopile (14) further comprises an annular connection flange (28) that extends radially from the annular wall (26), and wherein the wind turbine monopile (14) is configured such that the loading area (42) on which the impact force is focussed is defined by the annular wall (26) of the wind turbine monopile (14).

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