Method for assembling an offshore support structure for a wind turbine

Abstract

A method of assembling braces by means of concrete-placed joints in a subsea support structure. In a subsea support structure (3) for a wind turbine (2), tubular braces (11, 12) are interconnected or connected to a tower support (8) by injection connections. The end (12A) of a corresponding brace (12) is inserted into a cavity (17) of a concrete-placed shell unit (4), which shell unit (4) is fixed to the outer surface (14) of the interconnecting braces (11) or to the outer surface of the tower support (8). The volume of the cavity (17) is generally filled with a hardening fixing material, which is grout (18), after the corresponding brace (12) has been inserted.

Description

Technical Field

[0001] The present invention relates to a method for assembling a support structure in the offshore for a wind turbine and, optionally, a method including its setting. Specifically, the present invention relates to the method according to the preamble of the independent claims.

Background Art

[0002] Regarding a structure in the offshore for supporting, for example, a wind turbine, a tetrahedral structure is advantageous in terms of high stability, while requiring only a moderate cost in terms of relative scale. An example of such a structure is disclosed in International Publication No. WO 2017 / 157399 of the International Patent Application.

[0003] In order to optimize the manufacturing method while reducing and minimizing the manufacturing cost and making the energy facility in the offshore more attractive, an unremitting effort has continued to find improvements in the manufacturing and assembly procedures.

[0004] Japanese Patent Application Laid-Open No. JP 2000-087504 discloses a method for providing a tower structure in the offshore, where the end of a connecting pipe is inserted through an opening into a larger brace, and a part of the larger brace and the end of the pipe provided with a shear key for further stability are filled with grout injection.

[0005] The fact that the grout is inserted into the entire pipe structure means consuming a large amount of grout. Furthermore, for a floating structure, filling the brace with grout reduces the buoyancy, which is not desirable. It is desirable to reduce the consumption of grout while maintaining a high level of stability and rigidity.

[0006] In the system in International Publication No. WO 2013 / 156110, which discloses a lattice tower for a wind turbine, it is used with less grout consumption. This lattice tower has tubular corner legs and tubular struts connected to these corner legs. To connect to the legs, the struts have node shells that abut against the corner legs along a partial peripheral region, whereby a plurality of node shells form a ring or a partial ring around the corner legs. The node shells are made of cast steel and the struts are welded thereto. These shells are fixed to the legs by welding, adhesives, or grout injection. Optionally, a ring flange is fixed to and around the legs, whereby the shells can rest on this ring flange for better stability.

[0007] Cast steel shells of the type disclosed in International Publication No. WO 2013 / 156110 need to be prepared in an iron smelting furnace facility, which is generally far from the construction assembly site for support structures in the offshore area. Since these shells are molded and not made of rolled iron, their production is also generally carried out at a different site from the production site of the tubular braces of the support structures in the offshore area of wind turbines, which are generally rolled and welded. Thus, such cast steel shells add the complexity of production and the transportation of the components of the structure in the offshore area to the assembly site, which runs counter to the purpose of reducing costs, assembly time, and the complexity of the production equipment of wind turbines in the offshore area. Specifically, the support structures of wind turbines in the offshore area are generally assembled near or at a port, where large pipes are interconnected to form, for example, a tetrahedral structure. The connecting pipes for the offshore structure are connected by grout injection, but it is desirable to provide an assembly method that does not have the drawbacks of the prior art. In particular, cast steel shells should be avoided as a fixing material.

[0008] It should be noted that the above two disclosures, Japanese Patent Application Laid-Open No. 2000-087504 and International Publication No. 2013 / 156110, disclose two different but common alternative approaches. In Japanese Patent Application Laid-Open No. 2000-087504, a metal strut is inserted into another metal tube in order to fix the metal strut inside a metal tube. In International Publication No. 2013 / 156110, the metal strut is provided with a metallic shell welded to its end, and this metallic shell is fixed to the outside of the metal tube.

[0009] U.S. Patent No. 4,245,928 discloses another grout connection for a structure in the offshore where piles are driven into the seabed and braces are fixed to these piles to provide stability. The braces are connected to the piles at the joints and fixed using cement. International Publication No. 2011 / 147472 discloses a segmented jacket structure, particularly for the foundation of a wind turbine facility, which comprises lattice segments interconnected by joints including tubular modules adhered by grout material.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0011] The object of the present invention is to improve the prior art. Specifically, it is an object to provide an improved construction method for a platform in the offshore for a wind turbine, which is particularly a tubular structure, optionally a tetrahedral structure. Further, it is an object to provide a construction method for a platform in the offshore for a wind turbine, in which a connection by grout injection is provided at the end of a tubular segment, enabling assembly and minimization of grout consumption in a relatively simple manner. Another object is to have greater flexibility with respect to the connection by grout injection, particularly without the need to transport a cast iron shell. One or more of these objects, as well as other advantages, are achieved by a method of assembling and optionally setting a support structure in the offshore for a wind turbine, such as in the following description and the scope of the claims.

Means for Solving the Problems

[0012] In summary, in the assembly of a support structure in the offshore for a wind turbine, tubular braces are interconnected or connected to a tower support by connection by injection. The ends of the corresponding braces are inserted into the cavities of a shell unit cast with concrete. The shell unit cast with concrete is fixed to the outer surface of the interconnected braces or to the outer surface of the tower support. The volume of the cavity is generally filled with a hardening fixing material, which is grout, after inserting the corresponding braces.

[0013] In contrast to the above-mentioned International Publication No. 2013 / 156110, these shells are in-situ concrete, not cast steel. This has the great advantage that the shells can be manufactured near the site where the structure in the offshore is assembled. Thus, not only the material cost is reduced, but also the manufacturing and transportation costs are reduced.

[0014] Additionally, concrete placement is simpler to set up and can be easily changed not only with respect to the number of units produced but also with respect to dimensions, which is an advantage when assembling structures of different sizes. Specifically, the formwork for placement can be easily adjusted for the changing dimensions of the tower support and braces.

[0015] Therefore, the preparation of the shell by concrete placement is significantly more flexible and adjustable than a steel-cast shell.

[0016] The combination with a concrete shell is more useful because the grout injection connection, especially since the grout adheres well to the concrete surface of the shell unit.

[0017] As a further additional advantage, the concrete placement can be adjusted to extend outside the shell unit so that reinforcing profiled steel can more easily bond to adjacent surfaces such as the outer surfaces of the braces or tower supports and adjacent shell units.

[0018] Another advantage of concrete placement is the prestressing of the placed shell units by means of reinforcing profiled steel extending through the placed concrete. These advantages are not realized when providing steel-cast shell units.

[0019] It should also be noted that the weight of the concrete shell unit is lighter than that of cast iron, which is advantageous for floating support structures, especially when considering that the shell unit has dimensions of several meters.

[0020] Generally, using a concrete shell with openings into which braces are inserted and fixed by grout injection provides several advantages not disclosed or predicted in the prior art.

[0021] Details will be described below.

[0022] For the assembly, a first set of N first tubular braces, where, for example, N = 3, 4, 5, or 6, and a second set of N second tubular braces are provided in addition to a tower support that is to be used to support the tower of a wind turbine. These components are then incorporated into the support structure.

[0023] This assembly method is particularly useful for support structures in the offshore for offshore wind turbines, but the generality of the method does not exclude it from being used as a support structure for other types of offshore platforms, such as more general types of floating platforms.

[0024] For each pair of one of the first braces and one of the second braces, the second end in the first brace is connected to a first part of the tower support at a first connection, and the second end in the second tubular brace is connected to a second part of the tower support at a second connection. Further, the first end in the second brace is connected to the first brace at a third connection. When the support structure is oriented for operation and the tower of the wind turbine is in a vertical orientation, the second connection is above the first connection. Thus, the tower support, the first brace, and the second brace form a triangle in a vertical plane. Due to the triangular shape in the combination of the tower support, the radial brace, and the second brace, the second brace is also referred to as a diagonal brace. The N pairs of braces are directed outward from the tower support in various directions around the vertical central axis of the tower support. For this reason, the first brace is also referred to as a radial brace.

[0025] The shell unit comprises a base having a first side and a second side, and a cavity extending from the first side of the base. This cavity has a cavity inside the cavity. The second side is fixed to the outer surface of the tower support or the brace.

[0026] In the following, various specific embodiments are presented, where injection-based connections, such as grout injection, are used for the interconnection between the brace and the tower support.

[0027] In a first embodiment, the method includes providing, on a second side of the shell unit, a curvature corresponding to the curvature on the outer surface of the tower support, and attaching the second side to the outer surface of the tower support by a first hardening and fixing material, such as an adhesive, but generally grout. Next, the first connection is brought about by inserting a second end of the first brace into the cavity of the shell, and filling the cavity of the shell around the second end of the first brace with a second hardening and fixing material, such as an adhesive, but generally grout, to provide a firm fixation between the first brace and the shell unit and solidify the fixing material.

[0028] In a second embodiment, the method includes providing, on a second side of the shell unit, a curvature corresponding to the curvature on the outer surface of the tower support, and attaching the second side to the outer surface of the tower support by a first hardening and fixing material, such as an adhesive, but generally grout. Next, the second connection is brought about by inserting a second end of the second brace into the cavity of the shell, and filling the cavity of the shell around the second end of the second brace with a second hardening and fixing material, such as an adhesive, but generally grout, to provide a firm fixation between the second brace and the shell unit and solidify the fixing material.

[0029] In a third embodiment, the method includes providing, on a second side of the shell unit, a curvature corresponding to the curvature on the outer surface of the first brace; and attaching the second side to the outer surface of the first brace with a first hardening fixing material, such as an adhesive, but generally grout. Next, the third connection is provided by inserting a first end of the second brace into the cavity of the shell, and filling the cavity of the shell around the first end of the second brace with a second hardening fixing material, such as an adhesive, but generally grout, to provide a firm fixation between the second brace and the shell unit and solidify the fixing material.

[0030] In some other embodiments, two or all three of the above three embodiments are combined.

[0031] Generally, a support flange, such as a ring flange, is fixed to the outer surface, for example by welding, to support the shell unit on the outer surface. The shell unit is positioned relative to this flange to support the shell unit at its ends. For example, two support flanges are provided at both ends of the shell unit, thereby fixing and supporting the shell unit therebetween.

[0032] Optionally, while positioning the shell unit on the outer surface, a steel wire is clamped around the shell unit and the brace or tower unit to hold and tension the shell unit towards the outer surface.

[0033] Advantageously, a protrusion that rests on the outer surface is provided on a second side at the base of the shell unit, while a fixing material, generally grout, creates a distance to the outer surface between the protrusions such that the fixing material can flow between the protrusions between the outer surface and the second side of the base.

[0034] The fixing material is a fluid or semi-fluid, such as a polymer or grout. It is then cured to provide a solidified and firm injection. Grout is a preferred material due to its high rigidity and effective period in salt water. In the following, grout is exemplified as the injection material, but can be replaced by other injection materials if more appropriate or useful.

[0035] Advantageously, the outer surface below the shell unit has no openings to prevent the first and second cured fixing materials from flowing through the outer surface. This improves the control of where the fixing material is precisely provided and particularly prevents the excessive use of the injection material, which is grout in particular. For the same purpose, optionally, the connection at the end of the brace is provided with a closed end.

[0036] Several useful embodiments are identified below. In these embodiments, the shell unit comprises a reinforcing steel element embedded in the concrete of the shell unit, and this steel element extends from the concrete of the shell unit at the edge of the base. When assembling a plurality of shell units around a tower support or brace, these steel elements are used as connecting elements. In such a case, the method comprises providing another shell unit with a steel element extending from the concrete at the edge of the base in another shell unit, and, for another shell unit adjacent to the shell unit, fixing the steel elements extending from the shell unit and the other shell unit in an overlapping region in an overlapping and meshing manner. This overlapping region is then filled with a third cured fixing material, which is generally grout, and cured to fix the edges at the base of the shell unit and the other shell unit to each other.

[0037] Alternatively, a shell unit comprises a first interlocking part, and another shell unit comprises a second interlocking part, which are counterparts of the interlocking parts. Next, another shell unit is fixed to an adjacent shell unit, and the first and second interlocking parts are connected to form an interlocking part. Optionally, a third hardening and fixing material, generally grout, is filled into this interlocking part and solidified to fix the interlocking part.

[0038] For a subsea fixed support structure, a robust frame structure with a tower support and N first braces and N second braces is generally sufficient for long-term stability. For floating structures such as a tension leg platform (TLP) for a wind turbine tower, or a semi-submersible platform, it is desirable to provide additional stability. For this purpose, as an option, the following extended embodiments are useful.

[0039] In this extended embodiment, a third set in the N third braces, generally tubular braces, is provided to interconnect the first braces by the third braces. The above-described method with shell units as connectors is advantageously also used for the third braces. However, in principle, the third braces can also be connected to the first braces by welding or by connection to corresponding brackets.

[0040] For example, for N = 4, the first brace forms an intersection with the tower support at the center, and the third brace stabilizes the intersection on the plane formed by this intersection. Generally, the third set of braces for N = 4 forms a square, where the first braces together form the diagonals. The first and third braces are, optionally, in a single plane. However, this is not necessarily required. For example, the third brace forms a square in one plane, and the first braces extend such that their first ends at the tower support extend outside the lower plane of the square formed by, for example, the third brace. Further, although not necessarily required, these braces are of equal length, and one or two of the first braces may be longer than the remaining two such that the assembly of the third braces for N = 4 deviates from a square and instead forms a rectangle.

[0041] Another typical preferred example is N = 3, where the third brace forms a triangle, and optionally, the tower is at the center of this triangle. These third braces form the sides of the triangle and are thus also called side braces. The first braces generally radiate from the tower support to each of one of the corners of the triangle and are thus generally also called radial braces. Further, in this case, the first and third braces are, optionally, in a single horizontal plane. However, this is not necessarily required. For example, the third brace forms a triangle in one plane, and the first braces extend the first ends at the tower support outside the lower or upper plane of the horizontal plane of the triangle formed by, for example, the third brace. Further, the triangle does not necessarily have to be an equilateral triangle, so the braces do not necessarily have to form an equilateral triangle of equal length. Further, the tower support does not have to be at the center of the triangle. For example, the tower support may be provided on or near one of the sides of the triangle.

[0042] Optionally, the interconnection of the first braces by the third brace includes interconnecting the ends of the first braces by the third brace. However, this is not necessarily required as the connection can be offset from the ends.

[0043] For the case of N = 3, the assembly can result in a tetrahedral structure optionally formed as a regular tetrahedron by the first, second, and third braces. In this case, the first brace is a radial brace and extends radially from the tower support. Since the third brace forms the side of a triangle, it is a side brace. Since the second brace extends obliquely from the first brace to the tower support, it is a diagonal brace. Each second brace forms a vertical triangle together with the first brace and the tower support.

[0044] For example, the column support is placed at the center of the tetrahedral structure. Alternatively, it can be off-center, or the tower support can be provided at the corner of the upper structure, or along the side of the triangle between two nodes.

[0045] Once the support structure in the offshore area is generally assembled on the shore or on land, the wind turbine is attached to the top of this structure. This assembly is then generally towed by a ship to the final offshore point and then fixed to the seabed, for example while floating the structure. As mentioned, the example is a TLP, which is generally a semi-submersible floating in the sea. They float half-submerged from the sea surface.

[0046] To optimize the strength and duration of the grout connection, shear keys are advantageously used at the insertion part of the brace.

[0047] The first and second braces are tubular, and generally the third brace is also tubular. Optionally, these tubular braces have a volume with positive buoyancy. Optionally, this volume can be filled with water to adjust the buoyancy. In the most common cases, the braces are straight.

[0048] As an example, the braces can optionally have a diameter in the range of 1 to 6 meters and can be as long as over 50 meters in the larger ones. The brace ends are optionally inserted into their respective cavities at a distance of 3 to 5 meters.

[0049] Optionally, the tower support itself is tubular, for example cylindrical, or conical, or a combination thereof in adjacent sections of a tubular support structure.

[0050] The present invention will be described in more detail with reference to the drawings.

Brief Description of the Drawings

[0051]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 2D

Figure 2E

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0052] FIG. 1 illustrates a facility 1 for a wind turbine in the offing. The facility 1 includes a wind turbine 2 and an offshore support structure 3 to which the wind turbine 2 is attached for operation and supported under offshore conditions. The wind turbine 2 includes a rotor 5, a tower 7, and a nacelle 6 that connects the rotor 5 to the tower 7.

[0053] The offshore support structure 3 includes a tower support 8 on which the tower 7 of the wind turbine 2 is mounted. It should be noted that the wind turbine 2 is not to scale with the support structure 3 and is shown at a small scale for ease of illustration.

[0054] The support structure 3 in the offshore area is exemplified as a tetrahedral floating structure with a buoyancy tank 22. The floating tank 22 is mounted in pairs on the lattice structure at the nodes of this tetrahedral structure. During operation, at least a part of the buoyancy tank 22 is in the sea. Alternatively, when used especially in shallow water, the structure can be a bottom plate foundation.

[0055] Generally, for deeper waters, a floating structure such as a semi-submersible structure is used, which involves a mooring line and a buoyancy tank 22 that keeps the structure 3 floating while being half-submerged in the water. The tubular lattice structure itself provides additional buoyancy. Alternatively, the structure 3 can be a tension leg platform (TLP) with a fully submerged floating support structure. The floating support structure 3 is held in place by mooring lines fixed to the seabed 13.

[0056] The illustrated structure 3 is tetrahedral in shape and has a tower support 8 attached at the middle of one of the sides of the horizontal triangle of the tetrahedron. From the first lower part of the tower support 8, the first braces 11 extend radially outward in different radial directions. Therefore, these first braces 11 are also called radial braces. From the second upper part of the tower support 8, the second braces 12 extend to the first braces 11, whereby the tower support 8 forms a flat triangle with each set of one first brace 11 and one second brace 12. The second brace 12 is also called a diagonal brace. This is because of the triangular shape formed by combining the tower support 8, the radial braces 11, and the second braces 12. The triangular base for the tetrahedron is formed by each set of side braces 10 and two radial braces 11. The side braces 10 interconnect with the radial braces 11.

[0057] In each of the diagonal braces 12, the first end 12A generally connects to one of the radial braces 11 at or near the first end 11A of the corresponding radial brace 11. The radial braces 11 connect at their second ends 11B to the first lower part of the tower structure 8, and the diagonal braces 12 connect at their second ends 12B to the second upper part of the tower structure 8.

[0058] The tower support 8 is exemplified as a support column, but may have other shapes than those shown.

[0059] As will be illustrated in more detail later, the connection portions of the braces 10, 11, 12 and the tower support 8 can be injection connections, such as connections by grout injection. Thus, the ends 10A, 10B, 12A, 12b in the side braces 10 or the diagonal braces 12 are received in the cavities of the shell of the shell unit 4 fixed to the surface of the radial brace 11, or the end 11B of the radial brace 11 is received in the cavity of the shell of the shell unit 4 fixed to the surface of the tower support 8. The ends 10A, 10B, 11B, 12A, 12b of the braces 10, 11, 12 in this shell cavity are generally fixed to the shell unit 4 by a fixing material which is grout, and it is cured after the insertion of the ends to provide a firmly fixed connection by the shell unit 4.

[0060] The fact that there are no holes drilled in the surface 14 of the radial brace 11 or the tower support 8 and no openings at the locations where the shell unit 4 is fixed to the surface is advantageous for the method as described in this specification. This is because it is simpler compared to prior art methods where the diagonal brace 12 extends through an opening into the radial brace 11 and into the cavity inside the radial brace 11 that it receives. It also significantly reduces grout consumption.

[0061] Although the system has been illustrated as a triangular, particularly tetrahedral structure, it is also applicable to other polygonal structures having, for example, four, five, or six radial braces 11 and a corresponding number of diagonal braces 12. As a general option, side braces 10 are connected to the radial braces 11 to improve rigidity in order to complete a structure as shown in FIG. 1.

[0062] Figures 2A - 2E show an exemplary assembly method in which the shell unit 4 is attached to the radial brace 11 and the ends of the diagonal braces 12 are inserted into the shell cavities 17 within the shell unit. Instead of the radial brace 11, the shell unit 4 is attached to the tower support 8 as shown in FIG. 1 according to a similar principle.

[0063] The shown section of the radial brace 11 in FIG. 2A has an unperforated surface 14 between two circular support flanges 13, which are generally fixed to the brace 11 by welding, and between which the shell unit 4 is generally attached to the radial brace 11 by grout injection. The two flanges 13 have a distance corresponding to the length of the base 4B of the shell unit 4 such that the shell unit 4 is provided therebetween, and optionally, any small gap space between the shell unit 4 and the support flange 13 is filled by filling it with a fixing material, generally grout.

[0064] The shell unit 4 is in - situ concrete. This is a more advantageous method than using castings for the shell unit as disclosed in the prior art. The prior art is a much more expensive solution and does not have the same advantages as those in a manufacturing facility near the assembly site. Concrete placement is relatively simple, and considering that the shell unit has dimensions of several meters, the material cost is significantly lower than that of cast iron. Another advantage is that in the case of in - situ concrete, the weight of the shell unit 4 is significantly reduced, which is advantageous for floating support structures.

[0065] In FIG. 2B, the shell unit 4 is in the process of being attached to the radial brace 11 and is generally raised and lowered using a crane. The shell unit 4 includes a cavity portion 4A with a cavity and a base 4B. The base 4B abuts against the surface 14 of the radial brace 11, and the shell unit 4 is fixed to the radial brace 11 by grout or other types of contact bonding agents such as adhesives.

[0066] As shown in FIG. 2C, four shell units 4 are arranged around the radial brace 11 such that they extend throughout the periphery of the radial brace 11. In this exemplary case, only the inner three of the shell units 4 are used to connect to the other braces 10, 12 by inserting them into the corresponding shell units 4. However, in other configurations such as, for example, N = 4, the four shell units 4 are optionally used to connect four radial braces and / or diagonal braces to the tower.

[0067] The shell unit 4 can be configured from edge to edge. However, as shown, a gap space is provided between the edges of the shell unit 4. Into this gap space, the steel profiled bar 15 extends in an overlapping configuration from both of two adjacent edges in the shell unit 4. Once the shell unit 4 is arranged around the radial brace 11, this overlapping region 20 and the gap space are sealed and fixed by meshing the steel profiled bar 15 within a filling material for fixation, which is generally grout.

[0068] Once the shell unit 4 is arranged around the radial brace 11, the ends of the diagonal brace 12 and the ends of the side brace 10 are inserted into the cavity 17 of the shell as shown in FIG. 2D, and the remaining gap space between the cavity 17 of the shell and the inserted braces 10, 12 is filled with a fixing material 18, which is generally grout, as shown in FIG. 2E.

[0069] FIG. 3 shows a perspective side view in order to better represent the radial brace 12 inside the cavity 17 of the shell. It is confirmed that the brace 12 with the end flange 16 extends into the cavity 17 of the shell only up to the position where the end flange 16 contacts the outer surface 14 of the radial brace 11 without holes. The end flange 16 assists the axial stability of the diagonal brace 11 fixed inside the cavity 17 of the shell when the radial brace 12 receives an axial force.

[0070] Optionally, as an alternative to or as an additional means to the end flange 16, the inserted braces 10, 12 are provided with shear keys. As another option, the inside of the cavity 17 of the shell has a profiled surface and, after filling the cavity 17 with a hardened filling material, generally grout, it adheres axially and / or tangentially for better axial and / or rotational gripping force between the inserted braces 10, 12 and the shell unit 4.

[0071] FIG. 4 shows an embodiment in which the base 4B is located between two support flanges 13 and has a protrusion 25. The protrusion 25 is for maintaining the distance to the outer surface 14 and providing a volume 21 into which grout or other fluid fixing material can be inserted to fix the shell unit 4 to the surface 14. Further shown as an option is the use of a band clamp 26 of the brace 11 or the tower unit 8 to hold the unit 4 that surrounds the shell unit and still presses against the outer surface 14.

[0072] FIG. 5 shows an alternative to the meshing steel profiles 15. In the illustrated embodiment, corresponding male part 19A and receiving female part 19B of the interlocking part 19 are provided at the edge of the shell unit. This interlocking part has the advantage of maintaining the shell unit in a predetermined radial position once the shell unit 4 surrounds the corresponding brace 11 or tower support 4. Other known interlocking principles are also possible as alternatives.

Claims

Claim 1 A method of assembling a support structure (3) offshore for a wind turbine (2), comprising: providing a tower support (8) for holding a wind turbine tower (7); providing N first braces (11) and N second braces (12), where N is at least 3, and each brace (11, 12) has a first end (11A, 12A) and a second end (11B, 12B); for each pair of one of the first braces (11) and one of the second braces (12), at a first connection (24A), connecting the second end (11B) of the first brace (11) to a first portion of the tower support (8); at a second connection (24B), connecting the second end (12B) of the second tubular brace (12) to a second portion of the tower support (8); and at a third connection (24C), connecting the first end (12A) of the second brace (12) to the first brace (11), wherein the second portion of the tower support (8) and the second connection (24B) are above the first portion of the tower support (8) and the first connection (24A) when the support structure (3) is oriented for operation offshore, and the combination of the tower support (8), the first brace (11), and the second brace (12) forms a triangle in a vertical plane, and the N pairs of braces (11, 12) are radially outwardly directed from the tower support (8) in different directions around the vertical central axis (23) of the tower support (8); comprising: wherein the method further comprises: providing a shell unit (4) of in-situ concrete, the shell unit (4) having a base (4B) with a first side and a second side, and a cavity (4A) extending from the first side of the base (4B), the cavity (4A) having an inner cavity (17); the method further comprises the following A, B, and C, namely: A, wherein the method provides the second side of the shell unit (4) with a curvature corresponding to the curvature at the outer surface (14) of the tower support part (8), attaches the second side to the outer side (14) of the tower support part (8) by means of a first hardening and fixing material (18), and inserts the second end (11B) of the first brace (11) into the cavity (17) of the shell to provide the first connection part (24A), fills the cavity (17) of the shell around the second end (11B) of the first brace (11) with a second hardening and fixing material (18), solidifies the fixing material (18), and provides a firm fixation between the first brace (11) and the shell unit (4). B, wherein the method provides the second side of the shell unit (4) with a curvature corresponding to the curvature at the outer surface (14) of the tower support part (8), attaches the second side to the outer surface (14) of the tower support part (8) by means of a first hardening and fixing material (18), and inserts the second end (12B) of the second brace (12) into the cavity (17) of the shell to provide the second connection part (24B), fills the cavity (17) of the shell around the second end (12B) of the second brace (12) with a second hardening and fixing material (18), solidifies the fixing material (18), and provides a firm fixation between the second brace (11) and the shell unit (4). C, wherein the method provides the second side of the shell unit (4) with a curvature corresponding to the curvature at the outer surface (14) of the first brace (11), attaches the second side to the outer surface (14) of the first brace (11) by means of a first hardening and fixing material (18), and inserts the first end (12A) of the second brace (12) into the cavity (17) of the shell to provide the third connection part (24C), fills the cavity (17) of the shell around the first end (12A) of the second brace (12) with a second hardening and fixing material (18), solidifies the fixing material (18), and provides a firm fixation between the second brace (11) and the shell unit (4). further comprising at least one of the above. A method, characterized by...

2. Providing the outer surface (14) under the Schur unit (4) without an opening, and preventing the first and second fixing materials (18) from flowing through the outer surface (14), the method according to claim 1.

3. Providing a protrusion on the second side of the base (4B), and positioning the shell unit (4) relative to the outer surface using the protrusions resting on the outer surface (14) for flowing the first fixing material between the protrusions, the method according to claim 1 or 2.

4. The shell unit (4) comprises a reinforcing steel element (15) embedded in the concrete of the shell unit (4), the steel element (15) extending from the concrete of the shell unit (4) at the edge of the base (4B), the method comprising providing another shell unit (4) with a steel element (15) extending from the concrete of the other shell unit (4) at the edge of its base (4B), and fixing the shell unit (4) to the adjacent other shell unit (4) using the meshing overlap in the overlapping region of the steel elements (15) extending from the shell unit (4) and the other shell unit (4), filling the overlapping region with a third curable fixing material (18), and curing the third curable fixing material (18) to fix the shell unit (4) and the other shell unit (4) to each other, the method according to any one of claims 1 to 3.

5. The shell unit (4) comprises a first interlocking part (19A), the method comprising providing another shell unit (4) with a second interlocking part (19B), the first and second interlocking parts being counterparts of the interlocking part (19), the method comprising fixing the other shell unit (4) to the adjacent shell unit (4) to interlock the first and second interlocking parts (19A, 19B), filling the interlocking part with a third curable fixing material (18), and curing the third curable fixing material (18) to fix the interlocking part, the method according to any one of claims 1 to 4.

6. At least one of the first, second, and third curable fixing materials (18) is grout, the method according to claim 4 or 5.

7. Providing a support flange (13), such as a ring flange, fixed to the outer surface (14), and positioning the shell unit (4) relative to the flange (13) in order to support the shell unit (4) at its end, the method according to any one of claims 1 to 6.

8. Providing a third set of N third braces (10) and interconnecting the first braces (11) by means of the third braces (10) in order to increase the rigidity between the first braces (11), the interconnecting including fixing another shell unit (4) to the surface (14) of the first braces (11) adjacent to the shell unit (4) and fixing each of the third braces (10) in the cavity (17) of the other shell unit (4), the method according to any one of claims 1 to 7.

9. The method according to claim 8, wherein N is 3 and the third braces (10) form a triangular structure.

10. The method according to claim 9, including forming a tetrahedral structure by means of the first braces (11), the second braces (12), and the third braces (10).

11. The method according to any one of claims 1 to 10, including arranging the shell unit (4) and the other shell unit (4) side by side on the first braces (11) or the tower support (8) to form a ring around the first braces (11) or the tower support (8).

12. Assembling the support structure (3) offshore on the shore or on land, providing a wind turbine (2) at the top of the support structure (3), after assembly, moving the support structure (33) to the offshore destination, and fixing the support structure (3) to the seabed (13), the method according to any one of claims 1 to 11.

13. The method according to claim 12, including providing a buoyancy tank (22) on the support structure (3) and setting the support structure (3) as a floating structure.

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