METHOD FOR THE PARTIAL RECONSTRUCTION OF A FOUNDATION SYSTEM FOR AN OFFSHORE WIND POWER PLANT

Description

[0001] The invention lies in the field of mechanical engineering and civil engineering and can be used to a particular advantage in the repair and repowering of offshore wind turbines.

[0002] For several decades, the increasing use of renewable energies in energy supply has led to the construction of more and more wind turbines with towers and wind turbines mounted on nacelles. A significant proportion of these wind turbines have been built offshore for some years now, i.e., in shallow waters at sea. A large number of offshore wind turbines utilize so-called monopile structures, in which a steel tube is anchored in the seabed as a single pile foundation, with the steel tube supporting the wind turbine tower.

[0003] During the operational lifetime of such a system, high fatigue-inducing stresses occur due to system operation as well as wind and wave loads, placing significant strain on the supporting steel structure. Furthermore, the system's operation transmits forces into the seabed, which in some cases alter the seabed's load-bearing properties, potentially jeopardizing the stability of the supporting structure should the operating lifetime be extended. After the planned operational phase of a wind turbine, it can be dismantled, or the operating permit can be extended for a specific period. Additionally, offshore repowering allows for the installation of a more powerful wind turbine by reinforcing existing support and foundation structures.

[0004] From DE 10 2010 012094 B3 a method for the partial reconstruction of a foundation system for an offshore wind turbine is disclosed, in which, in a first preparatory step, before the first construction step, a structure of a wind turbine on a single pile is dismantled, and in which, in a first construction step, a support structure with at least one guide device, which can be slid onto a single pile in its axial direction, is slid onto the single pile founded in the seabed, and in a second construction step, the support structure is founded on the seabed.

[0005] EP 1 457 674 A2 discloses a foundation for an offshore wind turbine, wherein a central pipe is driven into the seabed at the site and a support structure is positioned over the central pipe and lowered into place. The support legs are anchored in the seabed with piles and the upper ring is positively connected to the central pipe.

[0006] From WO 2019 / 074363 A1, a foundation system with three or more suction cups installed in the seabed to act as a foundation or part thereof for supporting an offshore structure resting on the seabed is known, wherein the suction cups support a connecting body and the connecting body is designed to support a payload. WO 2019 / 074363 A1 also refers to a method for installing a suction bucket, wherein the bottom of the suction bucket penetrates the seabed and liquid is removed from the suction chamber, so that penetration is achieved by suction.

[0007] From WO 2005 / 040605 A1 a foundation for an offshore wind turbine is known, comprising a load distribution element supporting the tower of the wind turbine with nacelle and rotor and a plurality of foundation legs supporting the load distribution element, which run obliquely outwards relative to the vertical, in which the central axes of the foundation legs intersect the circular area circumscribed by the outer diameter of the tower in the plane connecting the load distribution element with the tower.

[0008] From GB 2 136 860 A, a tower structure is known with a central column, three support legs, and a base structure that can be anchored to the seabed using piles. The legs are connected at their upper ends by a sleeve. The base structure includes a central sleeve. Both sleeves can be held at the water's surface during construction so that the column can be floated into position and then encased in cement.

[0009] Against the background of the prior art, the present invention aims to create a foundation system for an offshore wind turbine that is particularly load-bearing and durable, thus enabling a long operating life for the wind turbine, and that can be created by reinforcing an existing foundation structure of a wind turbine. In this context, a foundation system is understood to be the part of the wind turbine that supports the tower with the nacelle. The foundation system therefore includes the foundation elements on the seabed as well as the supporting structure between these foundations and the tower.

[0010] The problem is solved by a method having the features of claim 1 and by a device having the features of claim 4. Examples not covered by the claims may serve to illustrate the invention.

[0011] The foundation system created according to the invention achieves a high load-bearing capacity by combining a monopile, i.e., a single support tube or, in short, a single pile, anchored in a pile foundation on the seabed, with a support structure that is also anchored on the seabed. The support structure is slid onto the monopile, so that the monopile serves as a guide for the support structure during the construction of the foundation system. Thus, the relative position between the monopile and the support structure can be ensured by the guide before the support structure is anchored on the seabed.

[0012] It is therefore intended that the support structure can be mechanically guided along the monopile as it is slid onto it. The support structure can, for example, have a ring-shaped element that is slid over the monopile and can slide along the monopile in its axial direction. Alternatively, the support structure can also have a guide tube that can be slid over the monopile for this purpose.

[0013] A guide tube slid onto the monopile can, in its installed state, project upwards beyond the monopile and support the tower of a wind turbine. In this case, the weight of the wind turbine would be primarily borne by the support structure. However, the monopile can also be so firmly connected to the guide tube that it partially absorbs the forces transmitted vertically through the guide tube, i.e., the weight of the wind turbine, and transfers them into the foundation. The guide tube can have a horizontal platform and / or a flange at its upper end, to which a wind turbine tower can be attached.

[0014] If the monopile does not absorb vertical forces, it can in any case support the support structure in the case of lateral, horizontally acting forces and tilting moments acting on the wind turbine.

[0015] The monopile can also be directly connected to a platform to which the guide tube or, more generally, the support structure is connected, or to a flange of the guide tube, and then, for example, absorb forces and / or weight forces acting horizontally on the wind turbine via the platform or flange.

[0016] The monopile can, for example, protrude through an opening in such a platform or flange and be fixed in the opening. This allows the coupling of the guide tube to the monopile to be adapted to different foundation levels of the support structure and the monopile.

[0017] The monopile can remain movable in the guide tube in its longitudinal direction, so that it only absorbs lateral forces from the support structure.

[0018] Ultimately, the monopile can also extend upwards beyond the guide tube / support structure and bear the vertical forces of the wind turbine on its own, by supporting the wind turbine tower alone. In this case, the support structure supports the monopile against lateral loads.

[0019] The support structure is founded on the seabed using one or more suction buckets (suction cylinders) by generating a fluid flow through them. Suction buckets are a well-established method for founding support structures on the seabed. For example, the support structure used here can have one, two, three, or four legs, each with a suction bucket at its end. Upon being placed on the seabed, these buckets initially form a bell shape. Fluid, particularly any seawater that has seeped in, can then be drawn upwards through valves in each suction bucket. Simultaneously, fluid is drawn in where the suction buckets are in contact with the seabed, causing them to become embedded in the seabed.A control device that regulates the pumping capacity at each suction bucket allows the overall inclination of the support structure to be controlled, thus creating vertical penetration into the seabed. The guidance of the support structure by the monopile proves to be very advantageous in this foundation method.

[0020] In a further step, it is planned that after the support structure is installed on the seabed, it will be mechanically connected to the monopile, in particular by force-fit, material-fit, and / or form-fit connection, specifically by grouting a gap between the outer circumferential surface of the monopile and a guide tube of the support structure surrounding it. This connection of the support structure to the monopile, in addition to its guiding function during installation, achieves a load distribution of the wind turbine loads to be borne later between the support structure and the monopile. Various types of connection are conceivable, which can be designed to be stiffer or less stiff depending on the requirements.

[0021] If, for example, the majority of the load is to be absorbed by the support structure and only be supported by the monopile under extreme loads, a relatively elastic connection between the monopile and the support structure can be used. If the load is to be distributed essentially evenly between the support structure and the monopile, a more rigid connection between the two elements is advisable.

[0022] An advantageous implementation of the connection can be achieved by grouting the gap between the monopile and a guide tube of the support structure. This grouting can be done with a potting compound such as a plastic or cement. Other materials are also conceivable. A connection can also be made using clamping devices between the support structure and the monopile. Welding or bonding are also possible joining methods.

[0023] It is also conceivable that a first material or body made of a first material can be inserted into the gap between the guide tube and the monopile in certain areas, with the material or body completely filling the gap in these areas. In other areas, the gap can be only partially filled by inserting a second material or body made of the second material, leaving a residual gap. The first material is chosen to be softer / more compliant / more elastic than the second material. This creates dynamic damping, resulting in weak coupling between the monopile and the support structure at small deflections and stronger coupling at larger deflections.

[0024] In particular, harder bodies made of the second substance / material can be embedded in a cast layer made of the first material.

[0025] The inventive method also provides that, in a first preparatory step prior to the first assembly step, the structure of a wind turbine on the monopile is dismantled. In this case, the method for producing a foundation system is linked to the prior dismantling of an existing wind turbine and constitutes part of a method for refurbishing or repairing and partially reconstructing a wind turbine.

[0026] The invention relates, in addition to a method of the type mentioned above, to a foundation device for an offshore wind turbine comprising a monopile founded in the seabed by means of a pile foundation, and a support structure slid onto the monopile, which is founded independently of the monopile in the seabed. A guide device is movable relative to the monopile within a limited range without a connection, and a rigid connection between the monopile and the guide device is ensured from a certain deflection onward by means of spacers arranged on the inner circumference of the guide device or on the outer circumference of the monopile, which partially bridge the gap between the monopile and the guide device. The support structure can be mechanically connected to the monopile. The support structure is founded in the seabed by means of one or more support legs that abut the seabed.The ends of the support legs or feet are anchored in the seabed using suction basins. In a variant not covered by the claims, the ends of the support legs or feet of the support structure can, for example, be individually anchored in the seabed using pile foundations. Other methods of anchoring individual feet of the support structure to the seabed are also conceivable.

[0027] As mentioned above, it can therefore be provided that the support structure has at least one guide tube whose inner diameter is larger than the outer diameter of the monopile, and that the space between the monopile and the guide tube is at least partially filled with a cast material.

[0028] The connection between the support structure and the monopile can be achieved not only by potting but also by a bolted connection. For example, the monopile and a guide tube of the support structure can be bolted together at several points around their circumference using radially extending screws. Driving clamping elements into the space between a guide tube of the support structure and the monopile is another conceivable connection method.

[0029] It is also possible to insert stop elements into the gap between the monopile and a guide tube, which only partially bridge the gap, so that the monopile and the guide tube can be moved freely against each other by a certain amount and are connected during further movement.

[0030] Furthermore, the support structure may also include at least one guide tube whose inner diameter is larger than the outer diameter of the monopile, and the guide tube may be positively attached to the monopile by one or more clamping elements, whereby the clamping elements, in particular, bridge the gap between the monopile and the guide tube or reduce the diameter of the guide tube. Thus, for example, a clamp is conceivable that reduces the diameter of the guide tube sufficiently to allow it to be clamped onto the monopile.

[0031] An example not covered by the claims and presented here for illustrative purposes relates to a support structure for the foundation system of a wind turbine, comprising at least one guide device that can be slid onto a monopile in its axial direction, and one or more support legs connected to the guide device, which are arranged radially outside the monopile with respect to the axial direction of the support structure, which corresponds to the axial direction of the monopile after assembly, wherein the support legs in particular have suction buckets or are each prepared for pile foundations. The support structure can thus be designed, for example, as a bipod, a tripod, or a quadripod.

[0032] The tower of the wind turbine to be installed can, for example, be placed directly onto the support structure and supported by it. Alternatively, the support structure can be braced against the monopile. However, it is also conceivable that the wind turbine tower is placed on the monopile, and the monopile, in turn, is braced against the support structure.

[0033] The support structure may also include a guide tube, in particular with a sealing device designed to at least partially seal an annular gap between the guide tube and the monopile, thus enabling the gap to be filled with a bonding material. Since the bonding between the guide tube of the support structure and the monopile is to take place below sea level after installation, it is advantageous to integrate a sealing device into the support structure that at least partially seals the gap between the support structure and the monopile during the casting process, preventing the casting material from leaking out on at least one side during insertion.The support structure can also have several sealing lips, each sliding along the monopile and thus creating a closed annular space between the sealing lips, which can be grouted after the support structure is anchored to the seabed. A valve for filling the annular space with a grout material can then be provided at at least one sealing lip or at another point on the support structure, for example, on the circumference of the guide tube.

[0034] The invention is shown below with reference to exemplary embodiments in figures of a drawing and subsequently explained. Fig. 1 An offshore wind turbine founded by means of a monopile, and a ship with a crane; Fig. 2 Schematic representation of the monopiles remaining after the dismantling of the existing wind turbine; Fig. 3 The placement of a support structure onto a monopile using a ship crane; Fig. 4 The placement of a support structure on the seabed; Fig. 5 The installation of a support structure on the seabed using suction buckets; Fig. 6 The placement of a wind turbine tower onto a support structure; Fig. 7 An enlarged view of a foundationed support structure; Fig. 8 An offshore wind turbine with a monopile and a support structure in a front view; Fig. 9 A top view of a system according to Figure 8Fig. 10 a support structure of another type with two feet, wherein the support structure is pushed onto a monopile, Fig. 11 a wind turbine with a support structure as shown in Figure 10 in a front view, Fig. 12 the system made of Figure 11 In a side view, Fig. 13 the foundation structure consisting of a monopile and two feet of a support structure from above, Fig. 14 a view of the wind turbine from the Figures 11 and 12 Views from above, Figs. 15, 16, 17, 18, each similar to those in the Figures 10, 12 , 13 and 14 The views shown are for a support structure with four feet, Fig. 19 shows various connection structures of a monopile and a guide tube in cross-section, and Fig. 20 shows a guide tube with a sealing lip, pushed onto a monopile, before potting.

[0035] In Figure 1A schematic representation shows an offshore wind turbine with a nacelle 1 attached to a tower 2. The tower 2 is supported by a monopile 9 that protrudes from the seawater 5. A submerged part 4 of the monopile transitions into a part that extends into the seabed 6.

[0036] Work on the offshore wind turbine is carried out from a ship 7, which can also be erected like a platform and which has a crane 8.

[0037] During the dismantling of the wind turbine, tower 2 and nacelle 1 can be removed using crane 8 by separating tower 2 from monopile 9 by flame cutting or machining. Figure 2It is shown that the crane 8 of the ship 7 places the parts of the wind turbine to be replaced on the ship and that, depending on the type of repair, the remaining part 9, 9' of the monopile ends either below the waterline of the seawater or above the waterline.

[0038] The Figure 3 Figure 3 shows a crane ship 7 mounted on stilts with a crane 8, a support structure 10 being mounted on the crane ship 7. In the right part of Figure 3, a support structure 10' is shown, which has a central guide tube 12 and which is lowered onto the monopile 9 in such a way that the guide tube 12 is pushed onto the monopile 9.

[0039] In Figure 4 The procedure is shown in the process step in which the support structure 10' rests on the seabed 6.

[0040] In Figure 5The figure shows that the individual suction buckets 11, 13, of which the depicted support structure has four, are connected to a pump on board the ship 7 by means of a suction line 14. Fluid is pumped out of the upper end of the suction buckets via the suction line 14, so that fluid flows in at the point of contact between the suction buckets and the seabed, causing the suction buckets to sink into the seabed as a result of the fluid transport and thus anchoring the support structure 10' in the seabed.

[0041] Ship 7 is equipped with a control system that regulates the intensity with which liquid is extracted from the individual suction buckets, enabling the 10' support structure to be lowered vertically into the seabed. The suction intensity can be understood as either pressure regulation during the extraction process or regulation of extraction times, if liquid is extracted from the individual suction buckets at intervals.

[0042] The in the Figures 3 to 6 The depicted support structure is shown in slightly more detail in the Figures 15 to 18 depicted.

[0043] Figure 15 Figure 1 shows in a perspective view the so-called mono-tetrabucket in the form of a support structure with a guide tube 12, which is arranged centrally between four support legs 15, 16, each of which supports a suction bucket 11, 13 at its lower end.

[0044] In Figure 16Figure 6 shows a mono-tetrabucket after installation on the seabed, with the suction buckets 11 and 13 completely submerged in the seabed and the guide tube 12 placed over a monopile 9. A wind turbine tower 2 and a nacelle 1 with rotor blades are mounted on the support structure 10'.

[0045] The support structure 10' and a wind turbine with such a support structure are shown in a top view in Figure 17 and together with a mounted wind turbine in Figure 18As shown, a support leg 15, 16 is attached to the guide tube 12 on each of four sides of the support structure 10', with a suction bucket 11, 13 attached to the lower end of each support leg 15, 16. The individual support legs 15, 16 are rigidly connected to the guide tube 12 at one or more points. A truss-like support structure can also be provided to brace the legs 15, 16 against the guide tube 12.

[0046] In Figure 17It is evident that the guide tube 12 is positioned symmetrically in the center between the support legs 15, 16. The guide tube 12, or the monopile located within it after installation, will later support the wind turbine tower. A symmetrical distribution of the legs 15, 16 and suction buckets around the guide tube 12 ensures equally good support under loads from all directions. However, the guide tube 12 can be offset from the center point between the support legs 15, 16 if it is foreseeable that significantly stronger loads will act on the wind turbine from one direction than from the other directions.

[0047] Instead of the guide tube 12, another structure can be chosen that allows the support structure 10, 10', 10", 10' to be supported on a monopile. Such a structure can, for example, have several ring-shaped elements spaced apart from each other in the vertical direction. Another alternative can be any type of guide rail.

[0048] The Figures 7, 8 and 9 The supporting structure consists of a mono-tribucket 10" with a central guide tube 12 and three support legs 15', 16'. As with the supporting structure described in the preceding figures, each of the support legs 15', 16' carries a suction bucket at its lower end.

[0049] The anchoring of the support structure 10" to the seabed, as well as the anchoring of the support structure 10', can be achieved not only by suction buckets but also by pile foundations for the individual feet / lower ends of the support legs 15, 15', 16, 16'. All other known methods for anchoring to the seabed are also conceivable for the individual support legs.

[0050] In Figure 7 The figure shows the state in which the support structure 10" is pushed over a monopile 9 and is already founded in the seabed 6.

[0051] Figure 8 Figure 1 shows a front view of the wind turbine, with a tower 2 already mounted on the guide tube 12. The tower 2 in turn supports a nacelle 1 with rotor blades.

[0052] Figure 9 shows the structure made of Figure 8in a top view, so that the three legs 15', 16' of the tributary are clearly visible. These legs form a support for the supporting structure, which complements the supporting effect of the monopile 9.

[0053] In the Figures 10, 11, 12 A support structure 10‴ in the form of a mono-dibucket is shown in each case. This support structure has a central guide tube 12 or other guide element, which is supported on the seabed by means of two support legs 15", 16". As in the other embodiments described above, the support legs 15", 16" are each anchored to the seabed by means of suction buckets. The support structure 10‴ is designed such that, after being anchored in the seabed, it protrudes from the water, i.e., extends above the sea surface.

[0054] In Figure 11 The image shows a front view of a wind turbine supported by a mono-dibucket, and in Figure 12A side view is shown, clearly demonstrating that the support legs 15", 16" are arranged asymmetrically relative to the guide tube 12, such that they extend from the guide tube and the tower 2 subsequently mounted on it essentially in the direction from which the highest load acts on the wind turbine during operation. In this embodiment, the support structure 10‴ is substantially supported by the monopile 9 on which it is mounted. At least in this case, a rigid connection between the monopile and the guide tube 12, or between the monopile and the support structure 10‴, is advantageous.

[0055] In Figure 13 The supporting structure 10‴ is shown together with the monopile 9 in a top view. From Figure 13It becomes clear that in this setup, the monopile 9 and the feet / suction buckets 11', 13' are distributed at the corners of an isosceles or even equilateral triangle. Furthermore, it is evident from Figure 13 It is evident that the support legs 15", 16" can also be connected to each other by struts 17.

[0056] In Figure 14 is a wind turbine setup on a mono-dibucket, as seen in Figure 13 The image is shown from above.

[0057] In Figure 19 The enlarged view shows a cross-sectional view of the connection between a guide tube 12 and a monopile 9. On the right side of the dashed line 19, the variant of a full encapsulation between the monopile 9 and the guide tube 12, for example using cement, is shown.

[0058] On the left side of the dashed line 19, a variant is shown in which the guide tube 12 is movable relative to the monopile 9 within certain limits and without a connection, and in which a rigid connection between the monopile 9 and the guide tube 12 is ensured from a certain deflection. This is achieved by arranging spacers 20 on the inner circumference of the guide tube 12 or on the outer circumference of the monopile 9, which partially bridge the gap between the monopile and the guide tube. As a further alternative, the spacers 20 can also be embedded in a casting material between the guide tube and the monopile, which consists of a material that is more flexible than the material of the spacers 20.

[0059] The inventive method as well as the inventive foundation system facilitates and improves the construction, repair and repowering of offshore wind turbines with regard to their foundation systems.

Claims

1. A method to partially rebuild a foundation system (9, 10,10', 10', 10") with a monopile (9, 9') for an offshore wind turbine (1,2), in which prior to the first construction step, a wind turbine erected on the monopile (9, 9') is dismantled in a first preparatory step, and in which a support structure (10, 10', 10', 10‴) with at least one guide device (12) that can be pushed onto a monopile (9, 9') in its axial direction, as well as one or more support legs (15, 15', 16, 16') being connected to the guide device is erected on the monopile (9, 9') which is founded in the seabed (6) in a first construction step, , and in a second construction step, the support structure (10, 10', 10", 10") is founded in the seabed (6) by suction cylinders by generating a fluid flow through the suction cylinders (11, 11', 13, 13'), whereby spacer elements (20) are preferably arranged on the inner circumference of the guide device (12) or on the outer circumference of the monopile (9, 9'), which partially bridge the distance between the monopile and the guide device.

2. A method according to claim 1, characterised in that the support structure is mechanically guided on the monopile (9, 9') when pushed onto it.

3. A method according to one of claims 1 or 2, characterised in that, after the support structure (10,10', 10", 10") has been founded in the seabed (6), it is mechanically connected to the monopile (9, 9'), in particular via a force-fit and / or material-fit and / or form-fit connection, furthermore in particular by filling an intermediate space between the outer circumferential surface of the monopile (9, 9') and a guide tube (12) of the support structure that surrounds it.

4. A partially newly constructed foundation device for an offshore wind turbine (1,2) with a monopile (9, 9') that is founded in the seabed (6) via a pile foundation, as well as a support structure (10, 10', 10', 10‴) comprising one or more support legs (15, 15', 16, 16") comprising at least one guide device (12), the support structure (10, 10', 10", 10‴) being grounded into the seabed independently of the monopile via one or more suction cylinders (11, 11', 13, 13') at the ends of the support legs, the guide device (12) being movable relative to the monopile in a limited manner without a connection and a rigid connection between the monopile and the guide device is ensured from a certain deflection, spacers (20) being arranged preferably on the inner circumference of the guide device (12) or on the outer circumference of the monopile (9, 9'), which partially bridge the distance between the monopile and the guide device.

5. Foundation device according to claim 4, characterised in that the support structure (10, 10', 10", 10") has at least one guide tube (12) whose internal diameter is larger than the external diameter of the monopile (9, 9'), and that the intermediate space between the monopile and the guide tube is at least partially filled with a casting material.