Method for manufacturing a support structure for an offshore wind turbine, with a brace fixed inside a shell unit attached to another brace

Abstract

In the assembly of the offshore support structure (3) for a wind turbine (2), the tubular members (11, 12) are interconnected by a connection by grout injection, where the first tubular member (11) is fixed to a shell unit (17) with a cavity (20), and into the cavity (20), the end (12A) of the second tubular member (12) is inserted and fixed by grout injection. The cavity (20) is closed by a rigid inlet flange (25), and the rigid inlet flange (25) is fixed to the wall of the shell unit (17). This design converts the forces acting on the second tubular member (12) into compressive forces acting on the grout within the cavity (20).

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 also setting thereof. In particular, the present invention relates to the method according to the preamble of the independent claims, and also to an offshore support structure made by the method.

Background Art

[0002] For example, regarding an offshore support structure for supporting a wind turbine, a tetrahedral structure is advantageous in that it exhibits 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] Various principles of connection struts in support structures have been disclosed in the prior art. For example, International Publication No. WO 2022 / 008021 discloses an offshore platform for a tetrahedral wind turbine, where the end of a connection brace is inserted through an opening into a larger brace, and grout injection fills part of the larger brace. Japanese Patent Application Publication No. JP 2000-87504, and International Patent Application Publication No. WO 2013 / 156110 disclose two different, alternative approaches. In WO 2013 / 156110, a metal strut is provided with a metallic shell welded to its end, which is fixed to the outside of a metal connection pipe, for example, with an adhesive. JP 2000-87504 discloses a method for providing a tower structure offshore, where the end of a connection pipe is inserted through an opening into a larger brace, and grout injection fills part of the larger brace and the end of the pipe. To hold the grout inside the cavity, a flexible sleeve made of a rubber sealant is provided in the gap between the opening of the main member and the inserted sub-member. A sealing part, especially made of an elastomer, for closing the volume of the grout is also disclosed in US Patent Application Publication No. US 2012 / 263545, JP 2012-077533, and US Patent No. 5385432.

[0004] US Patent No. 5385432, JP 2021-77533, and JP 2000-87504 disclose the use of shear keys in grout cavities or tubular elements inserted into grout cavities to achieve axial stability. Shear keys improve the stability of the connection, but a certain transfer of load at the joint due to a certain movement by waves causes wear at the connection even with shear keys.

[0005] Therefore, there is a need to further improve the stability at the joint by such grout injection.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Summary of the Invention

Problems to be Solved by the Invention

[0007] 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 an end of a tubular segment, and the stability of the connection by grout injection is improved relatively easily. 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, as described in the following description and the scope of the claims.

[0008] In summary, in the assembly of an offshore support structure for a wind turbine, tubular members are connected at rigid connection nodes to form a three-dimensional lattice. Some or all of the connection nodes are realized as connections by grout injection, where a first tubular member has a shell unit forming a cavity into which an end of a second tubular member is inserted and fixed by grout injection. The forces and moments applied to the first tubular member by the second tubular member are mainly transmitted by compression in the grout. As an alternative to grout, injection can be done with other hardening and fixing materials.

[0009] The shell unit of the first tubular member is provided with a cavity that receives the end of the second tubular member in this cavity to form a rigid connection node. The cavity has a cavity inlet, a cavity bottom, and a cavity wall extending from the cavity inlet to the cavity bottom. The shell unit is firmly attached to the main part of the first tubular member by any relevant method applied to join the individual members. For steel members, the joint can be realized by welding. For concrete members, the joint can be realized by a combination of concrete and reinforcement. Additionally, adhesives are also an option. The shell unit can be located entirely outside the first tubular member or penetrate partially or completely inside the first tubular member.

[0010] For example, once accurately inserted and fixed therein, the longitudinal axis of the second tubular member extends at an angle in the range of 10 to 90° from the longitudinal axis of the first tubular member.

[0011] The cavity of the shell unit has a cavity opening directed towards the first end of the shell unit, which is the outer end away from the first tubular member, for inserting the second tubular member into the cavity through the cavity opening. This cavity is closed towards the second end of the shell unit to prevent grout or other fixing materials from leaking out of the cavity. After inserting the second tubular member into the cavity, the cavity opening at the first end of the shell unit is closed outwardly by a rigid inlet flange fixed to the shell unit. The inlet flange is a ring-shaped flange and extends as a collar around the first tubular member once the first tubular member is inserted into the cavity.

[0012] The closure at the second end of the cavity is achieved using a partition wall or other means for realizing a closed cavity. A part of the closure may be of a temporary nature and is realized during installation to allow the cavity to be filled without grout leakage and is then partially opened.

[0013] The inner end of the cavity generally has a portion widened at the end. The term "widened" needs to be understood in relation to the cross-section at the cavity inlet and will be further described in more detail below using some specific examples. The widened portion has a cross-section that extends outside the cross-section of the second tubular member, which is generally circular in cross-section, at the cavity inlet. This cross-section is perpendicular to the longitudinal axis of the second tubular member. For example, the end of the second tubular member has a widened portion such as an end flange and has a diameter larger than the diameter of the second tubular member at the cavity inlet. In other words, inside the cavity, a part of the end extends radially outward with respect to the cross-section of the cavity inlet.

[0014] However, it is not necessary to arrange the end flange in a direction transverse to the longitudinal axis of the second tubular member. Thus, for a more general definition of the reference of the widened portion, an offset is made at the cross-section of the second tubular member at the cavity inlet. This cross-section has the boundary of the outer cross-section. For example, since the second tubular member is a cylinder with a circular cross-section, the outer boundary follows a circle. At the inner end of the cavity, a widened portion, such as an end flange, is provided, which extends beyond the cross-section of the end at the cavity inlet when projected onto the plane of the cross-section at the cavity inlet. Thus, the projection of the widened portion is at least partially external to the cross-section boundary in the second tubular member at the cavity inlet.

[0015] Optionally, the width of the end increases by 2 to 40% from the cavity inlet to the widened portion. Specifically, referring to the above-mentioned projection, at the cavity inlet, the projection in the widened portion of the plane of the cross-section is 2 to 40% larger than the cross-section of the end at the cavity inlet. In this case, for a circular cross-section, the diameter of the end increases by 2 to 40% compared to the diameter of the second tubular member at the cavity inlet. This larger diameter can be achieved using a flange, using a conical widening portion, or using any other means where, for example, the extension of the cross-section that is the diameter increases.

[0016] After the end of the second tubular member is inserted into the cavity inside the shell unit through the cavity inlet, the cavity is closed by an inlet flange extending as a ring around the second tubular member and fixed to the shell unit. The inlet flange is generally made of a hard material such as steel or concrete and is firmly fixed to the shell unit after the cavity is closed using the inlet flange.

[0017] In some practical embodiments, in order to install an inlet flange around the second tubular member, the inlet flange is provided with two or more flange pieces, which are positioned on opposite sides of the second tubular member and incorporated into a single inlet flange around the second tubular member.

[0018] Advantageously, a sealing portion, such as an elastomeric gasket, seals between the flange opening in the inlet flange and the second tubular member. For example, another sealing portion, such as an elastomeric gasket, can seal between the inlet flange and the first end of the shell unit.

[0019] After the cavity is closed, a layer of grout, or other hardening injection material, is provided in the cavity of the shell unit, for example by pumping under pressure into the cavity.

[0020] Advantageously, the fixing material is fluid or semi-fluid and is, for example, a polymer or grout. It is then cured to provide a hardened and rigid injection. Grout is a preferred material because of 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.

[0021] Advantageously, the end of the second tubular member is inserted into the cavity from the closed bottom up to a certain distance. This cavity is filled with grout or other fixing material in the space of the cavity between the closed bottom and the end, maintaining the distance during and after curing. This results in the grout taking up compressive and bending forces and transmitting the forces to the cavity wall, i.e., the shell unit.

[0022] By providing a closed end at the end of the second tubular member, the flow of grout or other fixing material into the interior of the second tubular member is prevented, which minimizes the consumption of grout or other fixing material.

[0023] By curing the grout, the end of the second tubular member is firmly fixed inside the cavity.

[0024] The vertical force acting on the second tubular member is mainly transmitted to the first tubular member by the compression of the grout. The tensile force acting on the second tubular member is mainly transmitted as the compression of the grout between the widened portion and the inlet flange at the first end of the shell unit. The compressive force acting on the second tubular member is mainly transmitted as the compression of the grout between the widened portion and the closing portion at the second end of the shell unit. The lateral force acting on the second tubular member is mainly transmitted as the compression of the grout between the outside of the end and the inside of the wall in the shell unit. The bending moment acting on the second tubular member is mainly transmitted as a pair of forces realized by the compression on one side of the grout between the widened portion and the inlet flange at the first end of the shell unit, and the compression on the opposite side of the grout between the widened portion and the closing portion at the second end of the shell unit. In all cases, the shear force between the second tubular member and the shell unit in the first tubular member can contribute to the load transfer, but mainly the load is transmitted through the compression of the grout.

[0025] Since the allowable compressive stress of the grout can be more than 10 times greater than the allowable shear stress of the grout, considering safety and stability criteria, as known in conventional grout injection connections, the force transmission is mainly as the compression of the grout rather than the shear of the grout, which enables better utilization of the grout. As a result, it is possible to achieve the connection by relying on a smaller surface and using less grout than in conventional grout injection connections for load transfer.

[0026] The firm encapsulation of the grout or other fixing material in the cavity by the inlet flange prevents the deterioration of the grout. In particular, when an elastomeric sealant is used between the flange opening of the inlet flange and the second tubular member, and between the inlet flange and the first end of the shell unit, the ingress of water into the joint by grout injection is minimized and the outflow of the grout is prevented. As a result, the bondability of the joint by grout injection will be maintained even if the grout is damaged or crushed.

[0027] This is in contrast to the cylindrical end in the prior art cavity that is not covered by a rigid inlet flange and whose connection by grout injection cannot guarantee a rigid connection over time even if it has shear keys. The present invention provides a simple solution to the severe problems that occur during long-term use, such as cracks and breakage of the grout inside the cavity. The additional rigidity obtained by the present system and method prolongs the stability and usefulness of the support platform in such offshore situations.

[0028] It is important to emphasize that the present invention is based on converting force into compression of the grout, fixing the brace against the force, and transmitting the force from the grout to the shell unit. This results in higher strength than the prior art even when the connection node does not have shear keys.

[0029] As is apparent from the above, by firmly fixing the rigid inlet flange to the shell unit, the force from the injection material that will be cured later is transmitted to the shell unit. It also prevents the movement of the end part coming out of the cavity due to the tensile force acting along its longitudinal axis on the second tubular member.

[0030] Regarding assembly, a first set in N first tubular braces, where N = 3, 4, 5, or 6 for example, and a second set in N second tubular braces are provided in addition to the tower support used to support the tower of the wind turbine. These components are then incorporated into the support structure.

[0031] This assembly method is particularly useful for support structures in offshore situations involving wind turbines, but the generality of the method is not excluded from being used as a support structure for other types of offshore platforms, such as more general types of floating platforms.

[0032] In some embodiments, for each pair of one of the first braces and one of the second braces, the second end in the first brace is connected at a first node connection to a first portion of the tower support, and the second end in the second tubular brace is connected at a second node connection to a second portion of the tower support. Further, the first end in the second brace is connected at a third node connection to the first brace. When the support structure is oriented for operation and the tower of the wind turbine is in the vertical direction, the second node connection is above the first node connection. Thus, the tower support, the first brace, and the second brace form a triangle in a vertical plane. Due to the vertical triangular shape in the combination of the tower support, the radial braces, and the second brace, the second brace is also referred to as a diagonal brace. The N pairs of braces are optionally directed outward from the tower support in various directions around the vertical central axis of the tower support in a horizontal plane. For this reason, the first brace is also referred to as a radial brace.

[0033] 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 a floating structure 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 reason, as an option, the following extended embodiments are useful.

[0034] In this extended embodiment, a third set in the N third braces, which are generally tubular braces, is provided to interconnect the first braces by the third braces. The above-described method with a shell unit as a connector 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.

[0035] 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 brace forms a diagonal. 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 brace has its first ends at the tower support extending out of, for example, the lower plane of the square face in the third brace. Further, although not necessarily required, these braces are of equal length, and for the N = 4 assembly, one or two of the first braces may be longer than the remaining two such that the third brace deviates from a square and instead forms a rectangle.

[0036] 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 also form the sides of the triangle and are thus called side braces. The first brace generally extends radially from the tower support to each of one of the corners of the triangle and is thus also generally called a radial brace. 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 brace has its first ends at the tower support extending out below or above the horizontal plane of the triangle in 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 still, the tower support may not be at the center of the triangle. For example, the tower support is provided on or near one of the sides of the triangle.

[0037] Optionally, the interconnection of the first brace by the third brace includes interconnecting the ends of the first brace by the third brace. However, this is not necessarily required since the connection can be offset from the ends.

[0038] For the case of N = 3, the assembly can have 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.

[0039] 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 a corner of the support structure, or along the side of a triangle between two nodes.

[0040] 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.

[0041] 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 flooded to adjust the buoyancy. In the most common cases, the braces are straight.

[0042] As an example, the braces can optionally have a diameter in the range of 1 - 6 meters and can be as long as over 50 meters for the larger ones. The brace ends are optionally inserted into their respective cavities at a distance of 3 - 5 meters.

[0043] Optionally, the tower support itself is tubular, for example cylindrical or conical, or a combination of them in adjacent sections of a tubular support structure.

[0044] The present invention will be described in more detail with reference to the drawings.

Brief Description of the Drawings

[0045]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0046] FIG. 1 shows the facility 1 of the wind turbine in the offing. The facility 1 includes a wind turbine 2 and a support structure 3 in the offing to which the wind turbine 2 is attached for operation and supported under the conditions in the offing. The wind turbine 2 includes a rotor 5, a tower 7, and a nacelle 6 that connects the rotor 5 to the tower 7. 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.

[0047] The support structure 3 in the offshore area is exemplified as a bottom support structure with legs 14 embedded in the seabed 13 below the sea surface 4. Such a type of support structure 3 in the offshore area is used in shallow waters. Generally, for deeper waters, a floating structure such as a semi-submersible structure is used, which involves mooring lines and buoyancy tanks that keep the structure 3 floating while being half-submerged in the water. In such cases, the buoyancy tanks are attached to the joints 9 of the structure 3 instead of the legs 14, unless the tubular structure itself provides sufficient 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.

[0048] The illustrated structure 3 has a tetrahedral shape with a central tower support 8. From the first lower part of the tower support 8, the first braces 11 extend mainly radially outward in different radial directions at 120° intervals. Therefore, these first braces 11 are also called radial braces 11, and this term is used hereinafter for simplicity. From the second upper part of the tower support 8, the second braces 12 extend to the first radial braces 11, whereby the tower support 8 forms a flat and vertically oriented triangle with each set of one first brace 11 and one second brace 12. The second braces 12 are also called diagonal braces 12. This is due to the triangular shape formed by combining the tower support 8, the radial braces 11, and the diagonal braces 12, and this term is used hereinafter for simplicity. The triangular base for the tetrahedron is formed by each set of side braces 10 and two radial braces 11. The side braces 10 are interconnected to the radial braces 11 for enhanced stability.

[0049] Each of the radial braces 11 is connected at its second end 11B to the first lower part of the tower support 8 at the first rigid connection node 29A, and each of the diagonal braces 12 is connected at its second end 12B to the second upper part of the tower support 8 at the second rigid connection node 29B. The first end 12A of each of the diagonal braces 12 is connected to one of the radial braces 11 at the third rigid connection node 29C, which is generally at or near the first end 11A of the corresponding radial brace 11.

[0050] The tower support 8 is exemplified as a support column, but may have other shapes than those shown. As shown, the tower support 8 extends above the water surface 4, which is also a feature of the floating support structure.

[0051] As will be exemplified in more detail later, the connection between the braces 10, 11, 12 and the tower support 8 is a connection by injection, such as by grout injection. The ends 11A, 11B, 12B of the braces 11, 12 are housed in cavities of another brace and / or cavities of the tower support 8, which are then generally filled with a fixed injection material, which is generally grout, and then cured to provide a firmly fixed connection.

[0052] An example of the connection by injection between the diagonal brace 12 and the radial brace 11 will be described in more detail with reference to the following corresponding example. However, a similar connection can be used to fix the second ends 11B, 12B of the braces 11, 12 to the tower support 8.

[0053] Although the system has been exemplified as a triangular, particularly tetrahedral structure, it is also applicable to other polygonal structures having, for example, 4, 5, or 6 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 complete the structure as shown in FIG. 1 and improve rigidity.

[0054] Figure 2 is a perspective view of a coaxial arrangement in which a first end of a tubular diagonal brace 12 is inserted into a cavity in a shell unit 17 welded to a tubular radial brace 11 along a weld line 16. This cavity does not extend into the radial brace 11. After the end of the diagonal brace 12 is inserted into the shell unit 17, grout or other hardening fixing material is injected into the cavity space between the end of the diagonal brace 12 and the inner wall of the shell unit 17. Before injecting the fixing material, the cavity space is optionally closed with an elastomeric gasket by an inlet flange 24 extending around the diagonal brace 12 to prevent the fixing material from leaking out of the cavity of the shell unit 17. Providing a small injection opening is sufficient to fill the cavity with the fixing material. Such an injection opening can be provided in the inlet flange 24 or the elastomeric gasket.

[0055] In some practical embodiments, in order to install the inlet flange 24 around the second tubular member, the inlet flange 24 is provided with two or more flange pieces. They are positioned on both sides of the second tubular member 12 and incorporated into a single inlet flange 24 around the second tubular member 12.

[0056] The inlet flange 24 is fixed to the shell unit 17 so that the axial tensile force acting on the radial brace 12 is transmitted to the inlet flange 24 and further to the shell unit 17. Furthermore, as will be described in more detail below, grout or other injection material mainly receives compressive force inside the cavity in the load situation between the braces 11, 12. The inlet flange 24 provides additional stability for the diagonal brace 12 in the tubular shell unit 17.

[0057] Note that similar arrangements and connections can be made between the tower support 8 and the diagonal brace 12, and / or between the tower support 8 and the diagonal brace. Similar arrangements can also be made between the radial brace 11 and the side brace 10, or between any type of brace and the buoyancy tank of the floating foundation in the offshore area.

[0058] Figure 3 shows a schematic cross-section of the diagonal brace 12, the end 12A of which is inserted into the cavity 20 of the shell unit 17 through the first end 17A of the shell unit 17. The shell unit 17 is made of steel, and its second end 17B is fixed to the surface of the radial brace 11, which is also made of steel, by welding 16.

[0059] In the embodiment illustrated in Figure 3, the shell unit 17 extends only outward from the radial brace 11 and does not extend into the internal volume of the radial brace 11. This has several advantages in that the radial brace 11 does not require holes for the cavities and the cavity 20 is provided only in the shell unit 17 on the surface of the radial brace 11.

[0060] To determine the amount of grout or other fixing material for the connection, the cavity 20 is closed by an end wall 18 at its bottom. Without this end wall 18, the grout would fill the entire internal volume in the shell unit 17 but would not enter the radial brace 11. This is because the shell unit 17 is provided only outside the radial brace 11 and the radial brace 11 has no openings within the surface area defined by the weld line 16.

[0061] After inserting the first end 12A of the diagonal brace 12 into the cavity 20 inside the shell unit 17 through the cavity inlet 20B, the cavity 20 is closed by an inlet flange 24, which is fixed to the shell unit 17, for example, by a bayonet connection or a bolt connection.

[0062] After closing the cavity 20, an injection material, generally grout, is inserted into the volume of the cavity 20 between the inner wall 20A of the shell unit 17 and the outer wall at the first end 12A of the diagonal brace 12, and then the injection material is solidified to firmly fix the diagonal brace 12 in the shell unit 17.

[0063] The end 12A of the diagonal brace 12 is closed by a closed end flange 19. The end flange 19 has a diameter larger than the diameter of the end 12A of the diagonal brace 12 at the cavity inlet 20B. As shown, the end flange 19 also has a diameter larger than the diameter of the opening passing through the inlet flange 24.

[0064] In the following, the action of the force will be described with respect to the grout, but other injection materials can also be used.

[0065] The tensile force acting on the diagonal brace 12 is transmitted to the shell unit 17, and thus to the radial brace 11, mainly by the compression of the grout between the end flange 19 and the inlet flange 24. The compressive force acting on the diagonal brace 12 is mainly transmitted by the compression of the grout between the end flange 19 and the end wall 18. The lateral force acting on the diagonal brace 12 is mainly transmitted as the compression of the grout between the composite region of the outer side at the end 12A of the diagonal brace 12 and the end flange 19, and the inner side 20A of the shell unit 17 forming the cavity 20. The bending moment acting on the diagonal brace 12 is mainly transmitted as a pair of forces realized by the compression of the grout on one side between the end flange 19 and the inlet flange 24, and by the compression of the grout on the other side between the end flange 19 and the end wall 18. In all cases, the shear force between the end 12A of the diagonal brace 12, the end flange 19, and the inner side 20A of the shell unit 17 forming the cavity 20 can contribute to the load transfer, but the load is mainly transmitted through the compression of the grout.

[0066] It is important to understand that such transmission of force and moment is different from the prior art. In the conventional connection by grout injection, the force is transmitted by shear. Attempts have been made to improve the shear force by adding shear keys. However, the force is transmitted as shear inside the grout. In contrast, in this system, the force is transmitted by compression. It is proposed that this joint will function even if a low-friction surface such as a surface coated with grease is provided on the surface. Even when using a shear key, the strength of the grout is significantly greater in compression than in friction. Unreinforced grout can transmit compression up to 60 - 80 MPa, while, as known in prior art systems, it is not normally assumed to transmit shear greater than 1 - 2 MPa. Therefore, by utilizing the compression of the grout, a smaller assembly can be made, while having a greater strength than the prior art grout injection connection when including a shear key. For these reasons, the grout injection connection described herein also does not require a shear key and generally no shear key is provided.

[0067] Figure 4 shows the bayonet fixing principle of the inlet flange 24 through which the diagonal brace 12 extends. Figure 4A shows a perspective view, and Figure 4B shows a plan view looking radially from inside the cavity 20 towards the brace 12. The fixing principle is similar to bayonet locking. The shell unit 17 has an inlet plate 23 at its inlet, which has a centrally extending opening in three opening slots 25 offset from each other by 120°. Correspondingly, the inlet flange 24 has three radially extending protrusions 26 offset from each other by 120°, which fit into the slots 25. Once the protrusions 26 are inserted into the slots 25, their depth is deeper than the thickness of the inlet flange 24. Axial rotation of the inlet flange 24 will move the protrusions 26 behind the edge 28 of the inlet plate 23, whereby the inlet flange 24 is locked to the inlet plate 23 of the shell unit 17. A small gap 27 in the radial direction is advantageous for facilitating rotation. Note that different numbers of slots and protrusions other than three can be used.

[0068] Figure 5 shows another embodiment of the joint in a side cross-section of the diagonal brace 12 with its end 12A inserted into the cavity 20 of the shell unit 17. The shell unit 17 is made of steel, and its second end 17B is fixed to the surface 11D of the radial brace 11, also made of steel, by a weld line 16.

[0069] In the exemplary embodiment of FIG. 5, the end 12A of the diagonal brace 12 has a conical portion 12D inside the cavity 20, which is larger than the diameter D of the diagonal brace 12 at the inlet 20B of the cavity 20 and larger than the diameter 24B of the throughput opening 24A in the inlet flange 24, providing the diameter of the end 12A of the diagonal brace 12 inside the cavity 20. The end 12A of the diagonal brace 12 is closed by a closed end flange 19 to prevent grout from entering the internal volume of the diagonal brace 12. Different from the embodiment shown in FIG. 3, the end wall 18 is not provided, and the cavity 20 is bounded by the surface 11D on the wall of the radial brace 11. Thus, when the cavity 20 is filled with grout, the grout extends to the surface 11D of the radial brace 11 defined by the weld line 16.

[0070] After inserting the first end 12A of the diagonal brace 12 into the cavity 20 inside the shell unit 17 through the cavity inlet 20B, the cavity 20 is closed by the inlet flange 24, and the inlet flange 24 is fixed to the shell unit 17 by bolt connection. To facilitate the connection, the shell unit 17 is provided with an inlet plate 23, which is generally welded to the first end 17A of the shell unit 17, and the inlet flange 24 is fixed to the inlet plate 23 by bolts (not shown). However, other fixing means other than bolts are also possible.

[0071] After closing the cavity 20, an injection material, generally grout, is inserted into the volume of the cavity 20 between the inner wall 20A of the shell unit 17 and the outer wall at the first end 12A of the diagonal brace 12, and then the injection material is solidified to firmly fix the diagonal brace 12 in the shell unit 17.

[0072] As shown, there is a small gap 29 between the diagonal brace 12 and the inlet flange 24. This gap is generally closed by a gasket extending around the diagonal brace 12 at the location of the inlet flange 24.

[0073] The tensile force acting on the diagonal brace 12 is mainly transmitted to the shell unit 17, and thus to the radial brace 11, by the compression of the grout between the inner side of the shell unit 17 at the end 12A, the inlet flange 24, and the portion between the inlet flange 24 and the end flange 19. The compressive force acting on the diagonal brace 12 is mainly transmitted by the compression of the grout between the end flange 19 and the outer side of the radial brace 11. The lateral force acting on the diagonal brace 12 is mainly transmitted as the compression of the grout between the composite region of the outer side at the end 12A of the diagonal brace 12 and the end flange 19, and the inner side 20A of the shell unit 17 forming the cavity 20. The bending moment acting on the diagonal brace 12 is mainly transmitted as a pair of forces realized by the compression on one side of the grout between the end flange 19 and the inlet flange 24, and the compression on the other side of the grout between the end flange 19 and the outer side 11D of the radial brace 11. In all cases, the shear force between the end 12A of the diagonal brace 11, the end flange 19, and the inner side of the shell unit 17 forming the cavity 20 can contribute to the load transfer, but the load is mainly transmitted through the compression of the grout.

[0074] Advantageously, the extension of the end flange 19 in the radial direction, which is perpendicular to the central axis 22 of the diagonal brace 12, is less than the cavity cross-section, thereby providing a gap space 21 between the edge of the end flange 19 and the inner wall 20A of the shell unit 17. The gap space 21 will completely embed the end 12A including the end flange 19 in the grout or other hardening and fixing material. The forces acting on the grout or other hardening and fixing material are thus distributed in other directions, distributing the load in two or more directions.

[0075] Figure 6 shows a side view of the joint in another embodiment. The end 12A of the diagonal brace 12 is inserted into the cavity 20 of the shell unit 17 through the cavity inlet 20B. The shell unit 17 is made of steel and penetrates through the wall of the radial brace 11 and into the internal volume of the radial brace 11, which is also made of steel. The shell unit 17 is fixed to the outer side 11D of the wall of the radial brace 11 by the weld line 16. By the penetration of the wall of the radial brace 11, the range in which the shell unit 17 extends outside the periphery of the radial brace 11 is reduced, which can be an advantage during transportation without compromising mechanical stability. The function of the joint shown in Figure 6 is similar to the function of the joint shown in Figure 5 in other respects.

[0076] Figure 7 shows a modified version of Figure 5, where the flange 19 is tilted at an angle different from the vertical version of Figure 4. For the sake of similarity with Figure 4, some of the reference numerals are omitted for clarity However, they apply equally. The grout compression effect described above is also realized in this embodiment. For further clarity, note the following. The end 12A of the diagonal brace 12 has a first cross-section 34 in the plane 32 of the cross-section, which is oriented perpendicular to the longitudinal axis 22 and is located at the cavity inlet 20B. This first cross-section 34 is composed of an inner circle and an outer circle. This is because the diagonal brace 12 has a cylindrical wall. The outer circle in the first cross-section 34 provides the outer cross-section boundary 36 of this first cross-section 34. The flange 19 is the widened part of the end 12A, and its projection on the plane 32 of the cross-section (see the line 31 and arrow 35 of the example) extends outside the cross-section boundary 36 in the first cross-section 34 of the diagonal brace 12 at the cavity inlet 20B. Due to this lateral extension of the projections 31, 35 of the flange 19 beyond the first cross-section 34 at the cavity inlet 20B, when a force acts on the diagonal brace 12, a similar rationale applies to the compression of the grout, the transmission of the force from the flange 19 to the grout, and the transmission of the force from the grout to the shell unit 17 through the flange inlet 24.

[0077] Note that the connection by grout injection in the above figure is exemplified as the connection between the diagonal brace 12 and the radial brace 11. However, the same principle applies to the connection between the tower support 8 having the shell unit 17 with cavities and the second ends 12B, 11B of the diagonal brace 12 or the radial brace 11 inserted into such cavities. This also applies to the connection between the radial brace 11 and the tower support 8, the connection between the radial brace 11 and the side brace 10, the connection between any type of brace and the buoyancy tank of the floating support structure in the offshore for a wind turbine, or any other type of joint related to the bottom-fixed or floating support structure in the offshore for a wind turbine.

Claims

1. A method for constructing a support structure in the offshore for supporting a wind turbine, including connecting tubular members (8, 11, 12) at rigid connection nodes (29A, 29B, 29C) to form a three-dimensional lattice, The method includes providing a first tubular member (8, 11) and a second tubular member (12) of the tubular members (8, 11, 12), the first tubular member (8, 11) having both ends and, between the both ends, a tubular wall with an inner side and an opposite outer side (11D), the first tubular member (11) being provided with a cavity (20), the cavity (20) receiving ends (12A, 12B) of the second tubular member (12) therein to form one of the rigid connection nodes (29A, 29B, 29C), the cavity (20) having a cavity inlet (20B) and a closed cavity bottom (18), and a cavity wall (20A) extending from the cavity inlet (20B) to the cavity bottom (18), The method includes inserting ends (12A, 12B) of the second tubular member (12) into the cavity (20) through the cavity inlet (20B), closing the cavity (20), providing a layer of a curable injection material in the closed cavity (20) between the ends (12A, 12B), the cavity wall (20A), and the closed cavity bottom (18), and curing the injection material to firmly fix the ends (12A, 12B) of the second tubular member (8, 11) inside the cavity (20), The second tubular member (12) has a first lateral cross-section (34) at the cavity inlet (20B), with a longitudinal axis (22) and an outer cross-section boundary (36) in a plane (32) of a cross-section oriented perpendicular to the longitudinal axis (22), An expanded portion (19) is provided at the end (12A) inside the cavity (20), whereby a projection on the plane (32) of the cross-section extends beyond a first cross-section (34) outside the cross-section boundary (36), wherein the method, provides the cavity (20) as part of a shell unit (17) firmly attached to the first tubular member (11), provides an inlet flange (24) made of a rigid material and having a flange opening (24A), Disposing a rigid inlet flange (24) with the flange opening (24A) around the second tubular member (12), and Closing the cavity (20) with the inlet flange (24) before inserting the injection material into the cavity (20), and then transmitting a force from the cured injection material through the inlet flange (24) to the shell unit (17), and firmly fixing the rigid inlet flange (24) to the shell unit (17) to prevent the ends (12A, 12B) from moving out of the cavity (20) due to a tensile force along the longitudinal axis (22). A method, characterized by the above. **Claim 2** The method according to claim 1, including inserting the ends (12A, 12B) of the second tubular member (12) into the cavity (24) to a certain distance from the closed bottom (18), and filling the space of the cavity (20) between the closed bottom (18) and the ends (12A, 12B) with an injection material. **Claim 3** The method according to claim 1 or 2, including inserting the ends (12A, 12B) of the second tubular member (12) into the cavity (20) using an enlarged portion (19), such as an end flange (19), and positioning the enlarged portion (19) with a gap space (21) on the wall (20A) of the cavity (20) to prevent the enlarged portion (19) from contacting the wall (20A), and maintaining the gap space (21) between the enlarged portion (19) and the wall (20A) of the cavity (20) by filling the gap space (21) with the injection material as well. **Claim 4** The method according to any one of claims 1 to 3, including providing the enlarged portion (19) as a circular end flange (19) having a diameter larger than that of the second tubular member (12) at the cavity inlet (20B). **Claim 5** The method according to any one of claims 1 to 4, including providing an elastomeric gasket on the inlet flange (24) to seal the flange opening with respect to the second tubular member (12). **Claim 6** The method according to any one of claims 1 to 5, including fixing the shell unit (17) to the first tubular member by welding along the weld line (16) on the first tubular member (11). **Claim 7** Providing the weld line (16) as a closed curved portion surrounding the region outside the first tubular member (11), the first tubular member (11) being continuous in the region surrounded by the weld line (16), the method according to claim 6, comprising providing.

8. The method according to any one of claims 1 to 7, comprising fixing the longitudinal axis (22) of the second tubular member (12) at an angle in the range of 10 to 90° from the longitudinal axis of the first tubular member (11).

9. The method comprises providing a tower support (8) for supporting the 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), connecting the second end (11B) of the first brace (11) to a first rigid connection (24A) to a first portion of the tower support (8); connecting the second end (12B) of the second tubular brace (12) to a second rigid connection (24B) to a second portion of the tower support (8); and connecting the first end (12A) of the second brace (12) to the first brace (11) by a third rigid connection (24C), wherein the second portion of the tower support (8) and the second rigid connection (24B) are above the first portion of the tower support (8) and the first rigid connection (24A) when the tower support structure (3) is oriented for offshore operation, the tower support (8), the first brace (11), and the second brace (12) form a triangle in a vertical plane, and with respect to the vertical central axis (23) of the tower support (8), the N pairs of braces (11, 12) are radially outward from the tower support (8) in different directions around the vertical central axis (23), connecting. including wherein the method is the following A, B, and C, namely As A, the tower support part (8) constitutes the first tubular member and is welded to the shell unit (17). The first brace (11) constitutes the second tubular member. The second end (11B) of the first brace (11) constitutes the end of the second tubular member. Here, the method includes inserting the second end (11B) of the first brace (11) into the cavity (20) of the shell unit (17) and fixing it therein using an injection material to form the first rigid connection part (24A). As B, the tower support part (8) constitutes the first tubular member and is welded to the shell unit (17). The second brace (12) constitutes the second tubular member. The second end (12B) of the second brace (12) constitutes the end of the second tubular member. Here, the method includes inserting the second end (12B) of the second brace (12) into the cavity (20) of the shell unit (17) and fixing it therein using an injection material to form the second rigid connection part (24B). As C, the first brace (11) forms the first tubular member and is welded to the shell unit (17). The second brace (12) constitutes the second tubular member. The first end (12A) of the second brace (12) constitutes the end of the second tubular member. Here, the method includes inserting the first end (12A) of the second brace (12) into the cavity (20) of the shell unit (17) and fixing it therein using an injection material to form the third rigid connection part (24C). The method according to any one of claims 1 to 8, including at least one of the above.

10. Providing a third set of N third braces (10) and interconnecting the first braces (11) by the third braces (10) to improve the rigidity between the first braces (11), the method according to claim 9.

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

12. The method according to claim 11, comprising forming a tetrahedral structure by the first brace (11), the second brace (12), and the third brace (10).

13. The method according to any one of claims 1 to 12, comprising assembling a support structure (3) in the offshore area on the shore or on land, providing a wind turbine (2) at the top of the support structure (3), moving the support structure (33) to the final offshore point after assembly, and fixing the support structure (3) to the seabed (13), optionally providing a buoyancy tank (22) in the support structure, and setting the support structure (3) as a floating structure.

14. An offshore support structure provided by the method according to any one of claims 1 to 13.

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