Semi-submersible float for offshore wind turbines and method for constructing such float

Abstract

The present invention relates to a semi-submersible floating body (2-1), in particular for offshore wind turbines, comprising four columns, including a central column (4) intended to receive a wind turbine mast (6) and at least three outer columns (8) connected to the central column by branches forming lower pontoons (10). The floating body does not have upper branches connecting the central column to the outer columns, and the outer columns and the lower pontoons are each formed by an assembly of a plurality of flat panels (81-86, 101-104) and have a polyhedral cross section. The present invention also relates to a method for constructing such a floating body.

Description

[Technical Field]

[0001] The present invention relates to the general field of semi-submersible floats used in offshore wind turbines, and more particularly to a novel semi-submersible float structure and method for constructing such a float. [Background technology]

[0002] The purpose of an offshore wind turbine is to harness wind energy to generate electricity through a turbine and generator. There are two main types of offshore wind turbines: bottom-fixed wind turbines, which are installed on the seabed (typically at shallow depths of less than 50 m), and floating wind turbines, which can be constructed on land and offer the advantage of being able to be installed in areas where the seabed depth is typically greater than 50 m.

[0003] The floating wind turbines to which the present invention relates comprise a turbine generally formed by a motor having several rotating blades with a horizontal axis and a generator coupled to the motor, the motor and the generator being fixed at the upper end of a vertical mast (or pylon), the lower end of which is attached to a floating support structure (hereinafter referred to as the float).

[0004] There are several main families of floaters for offshore wind turbines: semi-submersible floaters, submersible floaters with tension cables ("tension leg platforms" (TLPs)), SPAR (single point anchor reservoir) floaters, "barge" type semi-submersible floaters, and floaters with pendulum counterweights. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] French Patent Application Publication No. 3,064,973 Summary of the Invention [Problem to be solved by the invention]

[0006] The invention more specifically relates to semi-submersible floating bodies, i.e. steel or concrete foundations, generally in the form of a tripod with three (or four) cylindrical columns connected to each other by a metal structure. The stability of the structure is ensured by a ballast system that allows part of the foundation to be submerged. The structures are characterized by their large size and small draft.

[0007] For example, see US Pat. No. 6,299,643, which describes a semi-submersible hybrid floating structure including a central strut and three outer struts connected to the central strut by pontoon-shaped branches.

[0008] Although a relatively simple design, this hybrid floating body suffers from the drawbacks of having a relatively long assembly time and potentially high manufacturing costs. Therefore, an object of the present invention is to propose a semi-submersible floating structure that can be constructed and delivered in an extremely short period of time at low cost. [Means for solving the problem]

[0009] This object is achieved by a semi-submersible floating body, in particular for offshore wind turbines, comprising four columns, including a central column intended to receive a wind turbine mast, and at least three outer columns connected to the central column by branches forming lower pontoons, and according to the invention having no upper branches connecting the central column to the outer columns, each of the outer columns and the lower pontoons being formed by an assembly of a plurality of flat panels and having a polyhedral cross section.

[0010] The float according to the present invention is notable in that its main components (the outer struts and the lower pontoons) are assembled from multiple flat panels, making the float easier to manufacture. This feature allows for a more abundant supply chain than prior art large diameter circular struts, significantly shortening the construction and delivery time of the float (by tapping into global capacity in the shipbuilding sector).

[0011] This allows for robust and qualified floating structures that meet the site conditions and performance requirements to be provided at an attractive cost-performance ratio, and the associated risks are also reduced by the simplicity of the structure.

[0012] Preferably, the central strut is formed by an assembly of a plurality of flat panels and has a polyhedral cross section, which can further reduce the construction time and cost of the floating body.

[0013] The central post may terminate in a transition section having a downwardly flaring frusto-conical shape. Alternatively, the central support may have a downwardly flaring frusto-conical shape, the presence of which is particularly advantageous for the overall design of the wind turbine.

[0014] The outer struts may have the same height and the central strut may be of a different height than the height of the outer struts. Preferably, the central support comprises an access door to the tower, located below the interface with the tower supporting the turbine of the wind turbine, and an additional internal tower interface reinforcement, which allows an operator to enter the structure to access the equipment within the tower. Compared to the prior art, where the access door is typically located several meters above the tower interface, the position of the access door is advantageously lowered several meters to avoid the area of ​​the internal tower interface reinforcement.

[0015] Preferably, the planar panels forming the outer struts are joined together by at least one rounded strip to improve hydrodynamic behavior and reduce stress concentrations.

[0016] The planar panels forming the outer struts and lower pontoons may advantageously be reinforced with internal longitudinal and / or transverse stiffeners. The flat panels forming the outer struts and lower pontoons may also be reinforced with external longitudinal and / or transverse stiffeners. External stiffeners have the advantage over internal stiffeners of facilitating the welding operations required to install such stiffeners.

[0017] More preferably, the outer struts are connected to each other by prestressing cables, which have the advantage of absorbing some of the out-of-plane forces, thereby reducing the stress on the structure and, consequently, its mass.

[0018] The floating body may further comprise a plurality of ribs, each extending between the center strut and one of the lower pontoons for partially transferring in-plane loads from the center strut to the lower pontoons, and such ribs may be tubular or polyhedral in shape.

[0019] The lower pontoons may be spaced apart at 120° angles from one another to form a star configuration. The present invention also relates to a method for constructing a module of a floating body as defined above, the method comprising the steps of: assembling a plurality of planar panels together to form a lower pontoon and an outer strut; assembling the lower pontoons to a central branch structure supporting the central support column; assembling an outer support strut to the lower pontoon; and assembling a central support column to the central branch structure.

[0020] The lower pontoons may be assembled to the central branch structure by welding, in which case the welds for assembling the lower pontoons to the central branch structure are advantageously externalized using external stiffeners connected by welding to facilitate attachment.

[0021] Alternatively, the lower pontoons may be assembled to the central branch structure by mechanical connectors. The lower pontoons may be assembled to the central branch structure on a floating barge at sea.

[0022] Alternatively, the lower pontoons may be assembled to a central branch structure that floats in the sea. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a perspective view of a floating body according to a first embodiment of the present invention. FIG. [Figure 2] FIG. 2 is a perspective view of a floating body according to a second embodiment of the present invention. [Figure 3] FIG. 10 is a perspective view of a floating body according to a third embodiment of the present invention. [Figure 4] FIG. 10 is a perspective view of a floating body according to a fourth embodiment of the present invention. [Figure 5] FIG. 10 is a perspective view of a floating body according to a fifth embodiment of the present invention. [Figure 6] FIG. 10 is a perspective view of a floating body according to a sixth embodiment of the present invention. [Figure 7] FIG. 10 is a perspective view of a floating body according to a seventh embodiment of the present invention. [Figure 8] FIG. 13 is a perspective view of a floating body according to an eighth embodiment of the present invention. [Figure 9] 1 shows internal stiffeners fitted to the outer struts and lower pontoons of the floating body according to the invention. [Figure 10] 1 shows external stiffeners fitted to the lower pontoons of the floating body according to the invention. [Figure 11] 1 shows different variants of the method for constructing a floating body according to the invention; [Figure 12]1 shows different variants of the method for constructing a floating body according to the invention; [Figure 13] 1 shows different variants of the method for constructing a floating body according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0024] FIG. 1 shows in perspective view a semi-submersible floating body 2-1 for an offshore wind turbine according to a first embodiment of the present invention. The floating body 2-1 comprises four struts, including a central strut 4 intended to receive a wind turbine mast 6, and three outer struts 8 connected to the central strut 4 by branches forming lower pontoons 10.

[0025] More specifically, the lower pontoons 10 and outer struts 8 are spaced apart at an angle of 120° from each other to form a star configuration. The floating body 2-1 according to the present invention is characterized in that it does not have an upper branch connecting the central strut 4 to the outer struts 8. Furthermore, at least the outer struts 8 and the lower pontoons 10 are each formed of an assembly of flat panels and have a polyhedral cross section.

[0026] Thus, in the first embodiment shown in Figure 1, each outer support 8 is made up of an assembly of six flat panels 81-86 forming a right-angled prism with a hexagonal base, and each lower pontoon 10 is made up of an assembly of four flat panels 101-104 forming a rectangular parallelepiped (only flat panels 101 and 104 are visible in Figure 1).

[0027] Naturally, the polyhedron formed by the assembly of flat panels of the outer struts and lower pontoons may be different, such as a rectangular parallelepiped, a right prism with a pentagonal base, etc. Furthermore, according to an advantageous configuration of the invention, the central support 4 is also formed by an assembly of flat panels and therefore has a polyhedral cross section.

[0028] Furthermore, in this first embodiment, the lower pontoons 10 of the floating body are each connected to the outer struts 8 on the same face thereof (i.e., to the flat panel 83 in FIG. 1). Similarly, the lower pontoons 10 are also connected to the center strut 4 on the same face thereof.

[0029] FIG. 2 shows in perspective view a semi-submersible floating body 2-2 for offshore wind turbines according to a second embodiment of the invention. This float 2-2 differs from the float of the first embodiment in that the lower pontoons 10 of the float are each connected to the outer struts 8 on their two adjacent faces (i.e., to the flat panels 83 in Figure 1).

[0030] In contrast to this, as for the first embodiment, the lower pontoons 10 are also connected to the same plane as the central column 4 . FIG. 3 shows in perspective view a semi-submersible floating body 2-3 for an offshore wind turbine according to a third embodiment of the present invention.

[0031] This float 2-3 differs from the float of the second embodiment in that the flat panels 81-86 forming the outer struts 8 are joined together by rounded strips 12 so as to improve their hydrodynamic behavior and reduce stress concentrations.

[0032] Additionally, it should be noted that in each of the embodiments of Figures 1-3, the central support 4 terminates (at its upper end) at a transition 14 with the wind turbine mast 6, which has a cylindrical shape.

[0033] Other shapes are also contemplated. Thus, in the fourth embodiment shown in Figure 4, the semi-submersible floating body 2-4 differs from that of the second embodiment in that the transition 14' between the central column 4 and the wind turbine mast 6 has a frusto-conical shape that widens downwards so as to limit the height of the transition area between the central column and the wind turbine mast.

[0034] In the fifth embodiment shown in FIG. 5, the central strut 4 of the semi-submersible floating body 2-5 has a downwardly widening truncated cone shape. In the sixth embodiment shown in FIG. 6, the central strut 4 of the semi-submersible floating body 2-6 has a cylindrical shape.

[0035] FIG. 7 shows in perspective view a semi-submersible floating body 2-7 for offshore wind turbines according to a seventh embodiment of the present invention. The float 2-7 differs from the float of the second embodiment in that it further comprises ribs 16. Each of the ribs 16 extends between the center strut 4 and one of the lower pontoons 10 to partially transfer in-plane loads from the center strut to the lower pontoons.

[0036] The presence of these ribs 16 therefore makes it possible to reduce the height of the lower pontoon 10. In addition, the draft of the float during operation can be reduced, so that less reinforcement is required to resist submergence pressure.

[0037] These ribs 16 may have a tubular shape, as shown in Figure 7. Alternatively, they may have a polyhedral shape. FIG. 8 shows in perspective view a semi-submersible floating body 2-8 for offshore wind turbines according to an eighth embodiment of the present invention.

[0038] The float 2-8 differs from the float of the second embodiment in that the outer struts 8 are connected to each other by prestressing cables 18. More specifically, these prestressing cables 18 are fixed to the planar panels of the outer struts. The presence of these cables allows the width of the lower pontoons 10 to be reduced due to the out-of-plane moment loads transmitted to the cables.

[0039] This results in a reduction in the weight of the float, which allows for less structural reinforcement as it reduces wave sensitivity and therefore loads, and also reduces the installation time of the float as the dimensions of the lower pontoon connections are reduced.

[0040] The prestress loads of the cables 18 are defined so that they remain in tension throughout the life of the floating body. Of course, it is possible to envisage a floating body having both ribs as shown in FIG. 7 and prestressing cables as shown in FIG.

[0041] According to an advantageous configuration, particularly shown in FIG. 9, the outer struts 8 of the floating body according to the invention can be reinforced by longitudinal inner stiffeners 20a and / or transverse inner stiffeners 20b. Similarly, the lower pontoons 10 of the floating body may be reinforced by longitudinal inner stiffeners 22a and / or transverse inner stiffeners 22b.

[0042] Alternatively or additionally, the outer struts 8 of the floating body according to the invention may be reinforced by external longitudinal stiffeners and / or external transverse stiffeners. Similarly, as shown in FIG. 10, the lower pontoons 10 of the floating body may be reinforced by external longitudinal stiffeners 24a and / or external transverse stiffeners 24b.

[0043] Preferably, as shown in Figures 1 to 8, the outer struts 8 of the floating body have the same height, and the central strut 4 has a height different from that of the outer struts. Advantageously, as shown in Figure 1, the central support 4 of the floating body according to the invention is provided with an access door 28 to the tower, located below the interface with the tower supporting the turbine of the wind turbine, and with an internal additional reinforcement at the interface with the tower. This new position of the door allows for a lower external platform and a shorter access ladder from the support vessel for maintenance personnel.

[0044] A method for constructing a module of a floating body according to the invention will now be described with reference to Figures 11 to 13. Generally, this method involves assembling planar panels together to form lower pontoons and outer struts. The lower pontoons thus formed are then assembled to a central branch structure that supports the central strut. Similarly, the outer struts thus formed are assembled to the lower branches. Finally, the central strut can be assembled to the central branch structure.

[0045] Different variations may be shown. Thus, in the variant shown in Figure 11, four blocks are assembled together, namely three identical outer blocks B each constituted by the assembly of an outer strut 8 to a lower pontoon 10, and a central block C formed by the assembly of a central strut 4 to a central branch structure 30 supporting the central strut.

[0046] The three outer blocks B are then assembled by welding to the central block C. This variant avoids welding in fatigue sensitive areas. To limit fatigue stresses in the welds, the central branch structure 30 is sized to space the weld areas of the central strut.

[0047] In the variant shown in Figure 12, three blocks are assembled together: two identical outer blocks B, each constituted by the assembly of outer struts 8 to lower pontoons 10, and a main block D formed by the assembly of a central strut 4 to a central branch structure 32 comprising the lower pontoons and the outer struts.

[0048] The two outer blocks B are then assembled to the main block D by welding. Compared to the previous one, this variant makes it possible to limit the number of connections and therefore shorten the duration of the final assembly stage. It also avoids welding in fatigue-sensitive areas.

[0049] In the variant shown in Figure 13, only two blocks are assembled together: an outer block B constituted by assembling outer struts 8 on lower pontoons 10, and a main block D' formed by assembling a central strut 4 on a central branch structure 34, comprising two lower pontoons on each of which an outer strut is assembled.

[0050] The outer block B is assembled to the main block D' by welding. Compared to the previous one, this variant makes it possible to further limit the number of connections. It also avoids welding in fatigue-sensitive areas.

[0051] It should be noted that the welds for assembling the lower pontoons of the outer blocks onto these different central branch structures may be externalized by using external stiffeners. It should be noted that the lower pontoons of the outer blocks may be assembled to these various central branch structures using mechanical connectors instead of welding.

[0052] Likewise, these assemblies can be carried out at sea on a floating barge or while floating at sea.

Claims

1. A semi-submersible floating body (2-1 to 2-8) in particular for offshore wind turbines, said floating body comprising four columns including a central column (4) intended to receive a wind turbine mast (6) and at least three outer columns (8) connected to said central column by branches forming lower pontoons (10), said columns having no upper branches connecting said central column to said outer columns, said outer columns and said lower pontoons each being fitted with a plurality of flat panels (8 １ ~8 ６ , 10 １ ~10 ４ ) and has a polyhedral cross section, and the plurality of flat panels (8) forming the outer support (8) １ ~8 ６ ) are connected together by at least one rounded strip (12) so as to improve their hydrodynamic behavior and reduce stress concentrations.

2. 2. A floating body according to claim 1, characterized in that the central strut (4) has a downwardly widening truncated cone shape.

3. A floating body (2-4) according to claim 1 or 2, characterized in that the central strut (4) terminates in a transition section (14') having a downwardly widening truncated cone shape.

4. 2. A floating body according to claim 1, characterized in that the central strut (4) has a downwardly widening truncated cone shape.

5. A floating body according to any one of claims 1 to 4, characterized in that the outer struts (8) have the same height and the central strut (4) has a height different from that of the outer struts.

6. 6. The floating body according to any one of claims 1 to 5, characterized in that the central mast (4) comprises an access door (28) to a tower supporting a turbine of the wind turbine, located below the interface with the tower, and an internal additional reinforcement of the interface with the tower.

7. 7. A floating body according to any one of claims 1 to 6, characterized in that the planar panels forming the outer struts (8) and the lower pontoons (10) are reinforced by longitudinal internal stiffeners (20a, 22a) and / or transverse internal stiffeners (20b, 22b).

8. 8. A floating body according to any one of claims 1 to 7, characterized in that the planar panels forming the outer struts (8) and the lower pontoons (10) are reinforced by external longitudinal stiffeners (24a) and / or external transverse stiffeners (24b).

9. A floating body (2-6) according to any one of claims 1 to 8, characterized in that the outer struts (8) are connected to each other by prestressing cables (18).

10. 10. The floating body (2-5) according to any one of claims 1 to 9, characterized in that the floating body (2-5) further comprises a plurality of ribs (16), each of which extends between the central strut (4) and one of the lower pontoons (10) for partially transferring in-plane loads from the central strut to the lower pontoons.

11. A floating body according to claim 10, characterized in that the ribs (16) have a tubular or polyhedral shape.

12. A floating body according to any one of claims 1 to 11, characterized in that the lower pontoons (10) are spaced apart from each other at an angle of 120° to form a star configuration.

13. A method for constructing a module of a floating body according to any one of claims 1 to 12, comprising the steps of: assembling together a plurality of planar panels to form said lower pontoons (10) and said outer struts (4); assembling the lower pontoons to a central branch structure (30-34) that supports the central strut; Assembling the outer strut to the lower pontoon; and assembling said central strut (4) to said central branch structure.

14. 14. The method of claim 13, wherein the lower pontoons are assembled to the central branch structure by welding.

15. 15. The method of claim 14, wherein the welds for assembling the lower pontoons to the central branch structure are externally applied by using external stiffeners connected by welding.

16. 14. The method of claim 13, wherein the lower pontoons are assembled to the central branch structure by mechanical connectors.

17. A method according to any one of claims 13 to 15, characterized in that the lower pontoons are assembled to the central branch structure on a floating barge at sea.

18. A method according to any one of claims 13 to 15, characterized in that the lower pontoons are assembled to the central branch structure floating in the sea.

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