Floating offshore support structure, in particular for offshore wind turbines, assembly method and use thereof, and precursor frame structure - Patents.com

Abstract

Each of the vertices (3) of the polygonal frame (19) of the floating offshore support structure (1) is provided with a tubular sleeve segment (12C). The tubular connecting members (15) are inserted through the sleeve segments (12C) and secured to the sleeve segments (12C) by filling the gaps between them with portions (16C) of an injectable casting material (16), such as grout, which is then allowed to harden. The buoyancy modules (2) are then secured to the connecting members (15).

Description

[Technical field]

[0001] The present invention relates to a floating offshore support structure, in particular a floating offshore support structure for an offshore wind turbine, its assembly method and use, and a precursor frame structure. [Background technology]

[0002] Some types of support structures for offshore wind turbines consist of monopiles or columns inserted into the sand on the seabed. Typical connections between the monopile and the wind turbine tower, or between columns embedded in the seabed and the tower's support frame, consist of grouted connections between vertically arranged coaxial tubular members, with shear keys to provide long-term mechanical stability after the grout has hardened. The frame is often a welded structure with multiple tubes arranged in a grid pattern, assembled and welded onshore and then transported to the offshore location.

[0003] As an alternative to offshore wind turbines mounted on the seabed, floating support structures are provided, often consisting of a roughly tetrahedral frame with buoyancy modules at three nodes and the wind turbine tower located on top of a central support. An example is shown in US Pat. No. 5,399,323 to Stiesdal, where the tetrahedral frame is assembled and welded on land and then transported to the offshore location.

[0004] However, assembly of the final floating support structure using buoyancy tanks is difficult due to the large size, weight, and complexity of the tanks, and it is therefore desirable to find a useful method for such assembly.

[0005] Patent Document 2 describes an assembled UHPC tube-box combination floating structure, which includes three kinds of prefabricated parts, namely, UHPC tube, UHPC box, and UHPC sleeve, and is formed by joining, welding, and bonding. Based on the assembled UHPC tube-box, marine operation platforms, marine net cages, shallow water floating bridges, underwater sightseeing platforms, marine leisure platforms, etc. can be further constructed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2017 / 157399 [Patent Document 2] China Utility Model No. 212354345 Specification Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object to provide improvements in the art, in particular to provide alternative and improved constructions and assembly methods for floating offshore support structures, in particular for floating offshore support structures for wind turbines. These and other objects are solved by the floating offshore support structure, its assembly method and use, and the precursor frame structure, as described below. [Means for solving the problem]

[0008] In contrast to fixing the buoyancy modules to the support frame by welding or bolting as traditionally used in the art, the attachment provided by the present invention is based on cast, in particular grouted, connections, which facilitate assembly and result in a long-lasting connection even under harsh offshore conditions. The casting method for attaching the buoyancy modules to the offshore frame, in particular the use of fine-grained grout between horizontally aligned coaxial tubular members at the apexes of the polygonal frame structure, deviates from traditional fastening methods in the field, even though grouted connections are commonly known for vertical offshore structures.

[0009] A particular advantage achieved by the present invention is the reduced requirement for frequent inspections compared to all-steel connections such as the bolted and welded solutions mentioned above. The advantages of this method are particularly relevant for floating offshore wind turbines in deep sea areas.

[0010] The floating offshore support structure comprises a plurality of interconnected tubes forming a rigid frame with vertices arranged as a polygon (e.g., a triangle having three vertices) in a horizontal plane. After fabrication of the precursor frame structure, a buoyancy module is attached to the frame at each of the vertices.

[0011] As an example, the precursor frame structure may include a rigid frame having a plurality of rigidly interconnected tubes forming a tetrahedral structure with three vertices arranged as a triangle in a horizontal plane, and a support member configured to support a tower of a wind turbine as part of the tetrahedral structure.

[0012] Each of the apexes of the frame is provided with a sleeve segment (preferably a tubular sleeve segment) into which a connecting member (preferably a tubular connecting member) is inserted. The connecting member is fixed to the sleeve segment by filling the gap between the sleeve segment and the connecting member with a portion of an injectable casting material, which is then allowed to harden. Upon hardening, the connecting member is rigidly fixed to the sleeve segment. A buoyancy module is then ready to be attached to each of the apex connecting members.

[0013] Possible pouring materials are cement-based pouring materials such as grouts containing very fine sand or other filler materials but usually no stone. Sand-free grouts are good candidates for this purpose. Alternative pouring materials are long-term weathering hardening polymers.

[0014] Advantageously, in order to provide a strong mechanical connection between the buoyancy module and the connecting member, the sleeve segment has an inner wall provided with a shear key and / or the connecting member has an outer wall provided with another shear key, with casting material being provided in the gap between the shear key and the other shear key in order to secure the sleeve and the connecting member against mutual movement by the hardened casting material. The shear key is particularly useful in case of shrinkage of the casting material during hardening.

[0015] In a practical embodiment, the connecting member is longer than the sleeve segment and has a first free portion extending a distance from a first end of the sleeve segment, and the buoyancy module is attached to the sleeve segment by incorporating the free portion of the connecting member into another sleeve segment which is attached to the buoyancy module. Similar to fastening the connecting member to the sleeve segment of the frame, the tubular sleeve segment is fastened to the free portion of the connecting member by filling the gap between them with another portion of injectable casting material and then curing.

[0016] In the case where the buoyant module comprises a plurality of buoyant members, the connecting member comprises a first free portion and a second free portion extending a distance from one of the two opposite ends of the sleeve segment. In this case, the first buoyant member with the first further sleeve segment attached thereto is attached to the first free portion by incorporating the first free portion into the first further sleeve segment. Similarly, the second buoyant member with the second further sleeve segment attached thereto is attached to the second free portion by incorporating the second free portion into the second further sleeve segment. Another portion of the injectable casting material is filled into the void and allowed to harden between the further sleeve segment and the free portion.

[0017] Where each buoyant module has three or more buoyant members, it is also possible for more than one buoyant member to be attached to each of the free portions of the connecting member.

[0018] Advantageously, each sleeve segment has an inner wall provided with a shear key to provide a strong mechanical connection between the buoyant member and the connecting member, and each free portion to which the sleeve segment is attached has an outer wall provided with another shear key, and casting material is provided between the shear key and the other shear key to secure each sleeve segment and the connecting member against relative movement by hardened casting material.

[0019] If the viscosity of the casting material is relatively low, it is advantageous to seal the gap between the connecting member and the sleeve segment with seals at both ends of the sleeve segment to prevent the casting material from escaping from the gap during filling. This is particularly useful when the coaxial arrangement has a horizontal longitudinal axis. Similarly, seals can be used to ensure proper filling of other gaps between the connecting member and another segment with the casting material.

[0020] For example, the seal may be an inflatable torus that is placed around the connecting members and inflated prior to filling the respective voids with casting material. Expansion of the torus around the connecting members and inside the sleeve segments assists in centering and coaxial alignment of the connecting members inside the segments, as well as coaxial alignment of the connecting members with other segments when the buoyancy module is attached to the precursor frame structure.

[0021] A triangular arrangement of buoyancy modules is often used in offshore wind turbines. A useful precursor frame structure comprises a rigid frame having a plurality of rigidly interconnected tubes forming a tetrahedral structure with three vertices arranged as a triangle in a horizontal plane, and a support member configured to support the tower of the wind turbine as part of the tetrahedral structure. Each of the vertices comprises a sleeve segment and a connecting member extending through the sleeve segment. As described in more detail above, the connecting member is secured to the sleeve segment by an injectable but hardened casting material in the gap between the tubular sleeve segment and the connecting member. The connecting member is coaxially aligned with the sleeve segment in the horizontal plane. The connecting member is longer than the sleeve segment, so that the connecting member has a free portion that extends a distance from the end of the sleeve segment (typically both ends of the sleeve segment). Each free portion is configured to secure a buoyancy module. However, to facilitate transportation and storage, the precursor frame structure does not have a buoyancy module attached to the vertices until the precursor is ready to be transported to an offshore location. At that stage, buoyancy modules are attached to the free parts of the three connecting members, as already explained above.

[0022] If the vertices are arranged in a non-triangular polygon, four or more buoyancy modules are provided, one of which is attached corresponding to each of the four or more vertices.

[0023] For example, the buoyant member is a buoyant post.

[0024] A typical diameter of the connecting member is in the range of 1 to 10 meters, optionally 2 to 6 meters.

[0025] Typically, the segments have a diameter 5 to 20% larger than that of the connecting members to provide a large enough air gap to create strength in the poured connection, especially when shear keys are used.

[0026] For example, the floating support structure may include columns configured to support a load, such as a wind turbine, from which a number of braces (eg, three) radiate out to the apexes of a polygonal frame.

[0027] Embodiments and further details of the invention are explained below with reference to the figures. [Brief description of the drawings]

[0028] [Figure 1] 1 shows a floating support structure including several vertices. [Figure 2A] FIG. 2 shows a view of the structure of FIG. 1 taken in section through a buoyancy module. [Figure 2B] The cross section is shown in more detail. [Diagram 3] FIG. 13 shows a close-up cross-section of a connection at the apex of the precursor framework structure. [Figure 4] 13 shows an enlarged cross-section of the connection at the apex after attachment of the buoyant member. [Diagram 5] 1 shows a floating support structure for supporting a wind turbine. [Figure 6] Shows the shear keys in the connections. [Figure 7] Show the seal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] 1 shows an exemplary embodiment of a floating support structure 1, typically for offshore use. The support structure 1 comprises three buoyancy modules 2, one module 2 at each of three corner nodes 3 of a frame 19. The frame 19 is illustrated as having three corner nodes 3. Alternatively, the frame 19 has four or more nodes 3 arranged in a polygonal shape. The frame 19 is typically made of hollow steel tubes 4, 6, 9 that help the buoyancy modules 2 increase the total buoyancy of the support structure 1.

[0030] Each buoyancy module 2 is illustrated as comprising a pair of two buoyancy members 2A, 2B. Alternatively, each module 2 comprises only one or more than two buoyancy members. The buoyancy members 2A, 2B are typically air-filled buoyancy tanks. In the following, they are illustrated as cylinders, but may be other shapes.

[0031] The frame 19 comprises three main braces 4, each of which extends from a support element 6, exemplified as a column, to only one of the nodes 3. An end 5 of each of the main braces 4 is fixed to the buoyancy module 2 by a connection 11. In this embodiment, two buoyant members 2A, 2B are symmetrically arranged on either side of a corresponding end 5 of the main brace 4. The connection 11 extends horizontally through both the buoyant members 2A, 2B and through the end 5 of one of the main braces 4.

[0032] The support structure 1 is useful for supporting an offshore wind turbine, as shown in Figure 5, where the support elements 6 support the tower of a wind turbine 21. In the exemplary support structure 1 of Figure 1, a platform 20 is shown which can have different sizes and can also be used when a wind turbine 21 is supported by the structure 1, as shown in Figure 5.

[0033] The support element 6 may be located centrally between the buoyancy modules 2. However, this is not required and the example of Figure 1 shows an eccentric support element 6.

[0034] At the lower end 7 of each buoyant member 2A, 2B, exemplified as a buoyant pillar, a damping plate 8 is provided which extends transversely to the longitudinal axis X1 through the buoyant members 2A, 2B.

[0035] The frame 19 further comprises several support braces 9, 10 to increase the stiffness between the support elements 6 and the buoyancy modules 2. A tetrahedral frame structure is shown. The tetrahedron formed is not a regular tetrahedron because the strut 6 is not at the centre.

[0036] The connections 11 connecting the buoyant members 2A, 2B to one of the main braces 4 are tubular and will be described in more detail below.

[0037] Figure 2A shows the floating support structure of Figure 1, with the connecting part 11 and the buoyant members 2A, 2B cut vertically in cross section to show the internal structure of the connecting part 11. The part indicated by the dotted rectangle is shown in enlarged form in Figure 2B.

[0038] The connection 11 comprises a segmented cylindrical tubular sleeve 12 having three sleeve segments, namely a first sleeve segment 12A fixed (typically welded) to the first buoyant column 2A, a second sleeve segment 12B fixed to the second buoyant column 2B, and a third central sleeve segment 12C fixed to the end 5 of the corresponding main brace 4. A connecting member, shown here as a cylindrical connecting member 15, extends through all three axially aligned sleeve segments 12A, 12B, 12C. The outer diameter of the cylindrical connecting member 15 is smaller than the inner diameter of the tubular sleeve 12, so that a space is formed in which the grout material 16 is filled. Three portions 16A, 16B, 16C of the grout material 16 are provided, one portion for each of the segments 12A, 12B, 12C.

[0039] 3 shows the assembly step of the support structure 1. The end 5 of the main brace 4 is provided with its sleeve segment 12C, and the cylindrical connecting member 15 is fixed inside the sleeve segment 12C by a corresponding portion 16C of casting material, in particular grout material 16. The connecting member 15 is longer than the sleeve segment 12C, so that the free portions 15A, 15B extend outside both ends 18 of the sleeve segment 12C.

[0040] The grout material 16 has a relatively low viscosity and may be provided without sand or stones. To fill the space between the sleeve segment 12C and the connecting member 15, a seal is used, an example of which is shown in FIG. 7, which is placed around the connecting member 15 to fill the space in the void at the end 18 of the sleeve segment 12C. For example, such a seal may be an inflatable torus-shaped tube, which in principle is equivalent to an inflatable tire tube, only much larger, for example in the range of 2 to 6 meters in diameter.

[0041] 3, the sleeve segment 12C and the connecting member 15 are horizontally coaxially aligned. At this stage of construction, the unfinished support structure can be transported as a precursor to the final assembly site, where the buoyancy modules 2 are fixed to the free portions 15A, 15B of the connecting member 15.

[0042] In Figure 4 such a seal space 17 can be seen between adjacent portions 16B, 16C of grout material 16. A toroidal seal 23 useful at end 18 within such a space 17 is shown in Figure 7.

[0043] The cylindrical connecting members 15 are fixed to the ends 5 of the main brace 4, which simplifies their assembly with the buoyant members 2A, 2B. They are pressed from both ends to the first and second ends 15A, 15B of the already fixed connecting member 15 by the further sleeve segments 12A, 12B. After positioning and adjusting the orientation of the buoyant members 2A, 2B with respect to the main brace 4 at the ends 5 of which the third segment 12C is located, the corresponding portions 16A, 16B of grout material are filled in the gaps between the connecting members and the respective segments 12A, 12B. Alternatively, the first buoyant member 2A is positioned and adjusted to the first end 15A of the connecting member, after which grout is filled and hardened in the gaps between the first further sleeve segment 12A and the connecting member 15 to fix the first buoyant member 2A to the connecting member 15, after which the second buoyant member 12B is attached in a similar step.

[0044] The seals provided in the spaces 17 are usually left behind and corresponding seals are provided at both ends of the sleeve 12 when the casting material (particularly grout material) is pumped into the gaps between the corresponding other segments 12B, 12C and the connecting member 15. After hardening, all three segments 12A, 12B, 12C are rigidly fixed to the connecting member 15.

[0045] Typically, the cylindrical connecting member 15 is a hollow tube, advantageously a steel tube. When the ends of the hollow cylindrical connecting member 15 are clamped, the internal void provides additional buoyancy.

[0046] Typically, the grout material 16 itself does not provide sufficient rotational and axial stability between the sleeve 12 and the connecting member 15. However, a high degree of stability is achieved by using shear keys provided on the outside of the connecting member 15 and on the inside of the segments 12A, 12B, 12C of the sleeve 12. This is illustrated in FIG. 6, which is a simplified cross-sectional view to explain the principle. For example, a first shear key 22A extending along the inside of the sleeve 12, partially or entirely around the connecting member 15, secures the connection against axial displacement from the segments 12A, 12B, 12C of the sleeve 12 relative to the connecting member 15. A second shear key 22B extending axially of the connecting member 15 on the outside of the connecting member 15 and inside the sleeve 12 secures the connection 11 against rotational forces. Usually, the shear keys are bent or straight metal profiles, welded to the steel surfaces of the corresponding components, optionally forming a shear key grid.

[0047] FIG. 7 shows a seal 23 that fits into a gap 24 between the connecting member 15 and the sleeve 12, particularly at the end 18 of the sleeve segment 12C within the space 17 as shown in FIG.

Claims

1. A method for assembling a floating offshore support structure (1), wherein the floating offshore support structure (1) comprises a plurality of interconnected pipes (4, 6, 9, 10) forming a rigid frame (19) having vertices (3) arranged as a polygon in a horizontal plane, the method including the step of attaching a buoyancy module (2) to each of the vertices (3) of the frame (19), the method including the step of providing a sleeve segment (12C) at each of the vertices (3) of the frame (19), the step of inserting a connecting member (15) through the sleeve segment (12C), filling a void (24) between the sleeve segment (12C) and the connecting member (15) with a pourable placement material (16), optionally a grout portion (16C), and curing the portion (16C) to fix the connecting member (15) to the sleeve segment (12C), and the step of fixing the buoyancy module (2) to each of the connecting members (15). A method characterized by including the above steps.

2. The connecting member (15) is longer than the sleeve segment (12C) and has a first free portion (15A) extending a distance from a first end (18) of the sleeve segment (12C), the method including, after the step of fixing the connecting member (15) to the sleeve segment (12C) by curing the portion (16C), taking the first free portion (15A) of the connecting member (15) into another sleeve segment (12A) attached to the buoyancy module (2), filling another void between the another sleeve segment (12A) and the first free portion of the connecting member (15) with another portion (16A) of the pourable placement material (16), and curing the another portion (16A) to fix the buoyancy module (2) to the free portion (15A), thereby attaching the buoyancy module (2) to the first free portion (15A), the method according to Claim 1.

3. The connecting member (15) comprises a second free portion (15B) extending a distance from a second end (18) of the sleeve segment (12C), the buoyancy module (2) comprising a second buoyancy member (2B) to which a second different sleeve (12B) is attached. The method according to claim 2 includes the steps of fixing the connecting member (15) to the sleeve segment (12C) by curing the portion (16C), and attaching the first buoyancy member (2A) to the first free portion (15A) by incorporating the first free portion (15A) into a first another sleeve segment (12A). After that, the second free portion (15B) is incorporated into a second another sleeve segment (12B), and another portion (16A, 16B) of the pourable placing material (16) is filled into the gap (24) between the another sleeve segment (12A, 12B) and the free portion (15A, 15B), and by curing the another portion (16A, 16B), attaching the second buoyancy member (2B) to the second free portion (15B).

4. The sleeve segment (12C) has an inner wall provided with shear keys (22A, 22B), the connecting member (15) has an outer wall provided with other shear keys (22A, 22B), the placing material (16) is provided in the gap (24) between the shear keys and the other shear keys (22A, 22B), and the cured placing material (16) fixes the sleeve (12) and the connecting member (15) so as not to move relative to each other. The method according to any one of claims 1 to 3.

5. One or more of the sleeve segment (12C), the first another sleeve segment (12A), and / or the second another sleeve segment (12B) has an inner wall provided with shear keys (22A, 22B), The connecting member (15) has an outer wall provided with other shear keys (22A, 22B), The placing material (16) is provided in the gap (24) between the shear keys and the other shear keys (22A, 22B), and the cured placing material (16) fixes any of the sleeve segments (12A, 12B, 12C) and the connecting member (15) so as not to move relative to each other. The method according to claim 2 or 3.

6. The method is The method according to any one of claims 1 to 3, including the step of sealing the gap (24) between the connection member (15) and the sleeve segment (12C) with seals (23) at both ends (18) of the sleeve segment (12C) to prevent the placing material (16) from leaking from the gap during filling.

7. The method comprises: the step of sealing the gap (24) between the connection member (15) and the sleeve segment (12C) with seals (23) at both ends (18) of the sleeve segment (12C) to prevent the placing material (16) from leaking from the gap during filling; the step of maintaining the seals at both ends (18) of the sleeve segment (12C) after the hardening of the placing material; and the step of using at least one of the seals as a seal for another placing material when attaching the buoyancy module (2) to the connection member (15). The method according to claim 2 or 3.

8. The method comprises: the step of providing the seal (23) as an inflatable torus; the step of arranging the seal (23) around the connection member (15) in a sealing position; and the step of inflating the seal before placing to seal around the connection member (15) and prevent the placing material from flowing out from one or more gaps (24). The method according to claim 6.

9. The method according to any one of claims 1 to 3, including the step of coaxially aligning the sleeve segment (12C) and the connection member (15) in a horizontal plane.

10. A floating offshore support structure (1), wherein the floating offshore support structure (1) comprises a plurality of interconnected tubes (4, 6, 9, 10) forming a rigid frame (19) having vertices (3) arranged as a polygon in a horizontal plane; a buoyancy module (2) is attached to each of the vertices (3) of the frame (19); a tubular sleeve segment (12C) is provided at each of the vertices (3) of the frame (19), and a tubular connection member (15) extending through the sleeve segment (12C) is inserted therein. The tubular connecting member (15) is fixed to the sleeve segment (12C) by a portion (16C) of the cast material (16) that can be injected but has hardened within the gap (24) between the tubular sleeve segment (12C) and the tubular connecting member (15). A floating offshore support structure (1) in which a buoyancy module (2) is fixed to each of the connecting members (15).

11. The connecting member (15) is longer than the sleeve segment (12C) and has a first free portion (15A) and a second free portion (15B), and each of the first free portion (15A) and the second free portion (15B) extends by a distance from one of the ends (18) on two opposite sides of the sleeve segment (12C). The buoyancy module (2) includes a first buoyancy member (2A) to which a first different tubular sleeve (12A) is attached, and a second buoyancy member (2B) to which a second different tubular sleeve (12B) is attached. The first buoyancy member (2A) is attached to the first free portion (15A) by taking the first free portion (15A) into a first different sleeve segment (12A), and the second buoyancy member (2B) is attached to the second free portion (15B) by taking the second free portion (15B) into a second different sleeve segment (12B). Another portion (16A, 16B) of the cast material (16) that can be injected but has hardened is provided in the gap (24) between the different tubular sleeve segments (12A, 12B) and the free portions (15A, 15B). Each sleeve segment (12A, 12B, 12C) has an inner wall provided with shear keys (22A, 22B), and the tubular connecting member (15) has an outer wall provided with other shear keys (22A, 22B). The cast material (16) is provided in the gap (24) between the shear keys and the other shear keys (22A, 22B), and the hardened cast material (16) fixes the sleeve segments (12A, 12B, 12C) and the tubular connecting member (15) so as not to move relative to each other. The structure according to Claim 10.

12. An offshore wind turbine system comprising a wind turbine (21) and the floating offshore support structure (1) according to Claim 10 or 11.

13. Use of the method according to any one of claims 1 to 3 for an offshore support structure supporting a wind turbine (21).

14. A precursor frame structure for an offshore wind turbine, The precursor frame structure includes a rigid frame (19) comprising a plurality of rigidly interconnected tubes (4, 6, 9, 10) forming a rigid tetrahedral structure having three vertices arranged in a triangle in a horizontal plane, and a support member (6) configured to support a tower of a wind turbine (21) as part of the tetrahedral structure, Each of the vertices (3) comprises a sleeve segment (12C) and a connecting member (15) extending through the sleeve segment (12C), The connecting member (15) is fixed to the sleeve segment (12C) by a cured casting material (16) within a gap (24) between the sleeve segment (12C) and the connecting member (15), The connecting member (15) is aligned coaxially with the sleeve segment (12C) in a horizontal plane, The connecting member (15) is longer than the sleeve segment (12C) and has a free portion (15A) extending a distance from an end (18) of the sleeve segment (12C), and a buoyancy module (2) is fixed to the free portion (15A), There is no buoyancy module (2) at the vertices (3) of the precursor frame structure, The free portions (15A, 15B) of the three connecting members (15) are configured and dimensioned for attaching a buoyancy module (2), the precursor frame structure.

15. The connecting member (15) has a first free portion (15A) and a second free portion (15B), and each of the first free portion (15A) and the second free portion (15B) extends a distance from one of the ends (18) on two opposite sides of the sleeve segment (12C) for fixing a buoyancy member (2A, 2B) to each of the free portions (15A, 15B), the precursor frame structure according to claim 14.

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