Semi-submersible floating structure with pendulum-type counterweight for offshore wind turbines and its installation method

Abstract

The present invention relates to a system (2) for forming anchor points for a floating body for an offshore wind turbine, the system comprising at least one housing (6) having an open bottom (8) and an open top (10), the housing being at least partially filled with solid granular material (12) that can withstand shear with the seabed (4) on which the housing is intended to be placed, and the housing further comprising at least one attachment (14) for securing a mooring line (16) of the floating body.

Description

Technical Field

[0001] The present invention relates to the general field of semi - submersible floating bodies for offshore wind turbines equipped with pendulum - type counterweights. More specifically, the present invention relates to a semi - submersible floating body in which a wind turbine support mast is fixed around the floating body and the center of gravity is corrected by a pendulum system.

Background Art

[0002] The purpose of an offshore wind turbine is to generate electricity by using wind energy with turbines and generators. There are two main types of offshore wind turbines: fixed - bottom wind turbines installed on the seabed (typically in shallow depths less than 50 m), and floating wind turbines that can be constructed on land and have the advantage of being able to be installed in areas where the seabed depth typically exceeds 50 m.

[0003] The floating - type wind turbine targeted by the present invention comprises a turbine generally formed by a motor having a rotating blade on a horizontal axis and a generator coupled to the motor, and the motor and the generator are fixed to the upper end of a vertical mast (or pylon). The lower end of the mast is attached to a floating - body support structure.

[0004] There are several main groups of floating - body support structures for offshore wind turbines, including semi - submersible floating bodies, submersible floating bodies with tension legs (tension - leg platforms (TLP)), SPAR (single - point anchor reservoir) - type floating bodies, barge - type semi - submersible floating bodies, and semi - submersible floating bodies equipped with pendulum - type counterweights.

[0005] Semi-submersible floating structures are the most widely used floating structure models today. They typically consist of a tripod-like structure made of steel or concrete, with three (or four) cylindrical sections connected by a metal structure. The stability of the structure is ensured by counterweights that allow a portion of the foundation to be submerged in water. A key characteristic of this structure is its large size and shallow draft. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] A pendulum-type semi-submersible float typically features a counterweight fixed beneath the float by a tendon. This counterweight allows for a lower center of gravity and stabilization of the assembly without requiring numerous buoyancy elements at the height of the float's free surface.

[0007] Furthermore, semi-submersible floating structures generally have a transition piece, i.e., a position for fixing the wind turbine support mast, at the geometric center of the floating structure to provide an optimized buoyancy volume. However, such mast centering often complicates access to the wind turbine and requires a large crane radius, thus necessitating a high-capacity crane for the installation of the nacelle and mast.

[0008] To significantly simplify access to wind turbines, it is known to use semi-submersible floating structures with transition pieces around the structure. However, because symmetrical compensation for weight and buoyancy is required on the opposite side of the mast to balance the weight of the wind turbine, the hull volume of such floating structures is often not well optimized.

[0009] The objective of the present invention is to propose a semi-submersible floating structure that has the advantages of a floating body having an eccentric transition piece, but without the disadvantages. [Means for solving the problem]

[0010] According to the present invention, this objective is achieved by a semi-submersible floating body equipped with a pendulum-type counterweight for offshore wind turbines. The floating structure comprises two tubular structures, each having three tubular branches forming a right triangle with horizontal, vertical, and oblique branches, assembled together by their respective vertical branches to form a pylon designed to align with the axis of a wind turbine mast, with the vertices of the tubular structures opposite the pylon spaced apart by an angle between 25° and 80°; a connecting pipe connecting the horizontal branches of the two tubular structures or the oblique branches of the two tubular structures; and a counterweight fixed to the two tubular structures by three tendons, one at the height of the pylon and the other at the height of the vertex of the tubular structure opposite the pylon, wherein the length of the tendon fixed to the pylon is greater than the lengths of the other two tendons, thereby moving the counterweight away from the axis of the wind turbine mast as needed to balance the weight of the wind turbine.

[0011] The floating body according to the present invention has a transition piece (i.e., the location where the wind turbine support mast is fixed) that is eccentric with respect to its geometric center. The geometric shape of such a floating body makes it possible to significantly simplify access to the wind turbine, in particular for its installation and maintenance.

[0012] Furthermore, while the present invention stabilizes the floating structure by lowering its center of gravity using the advantages of counterweights, it also stabilizes the floating structure by significantly correcting the center of gravity horizontally to compensate for the eccentricity of the mass of the mast and wind turbine. Therefore, the counterweights required for stability are also used to significantly correct the horizontal position of the center of gravity. Since the counterweights weigh approximately twice the weight of the mast and nacelle in water, it is not necessary to move the counterweights excessively to obtain trim corrections.

[0013] Furthermore, since the floating body according to the present invention has almost no buoyancy elements on its free surface, unlike conventional floating bodies with pendulum-type counterweights, the floating body is almost permeable to swells. However, since it has a mast positioned around the floating body, like some semi-submersible floating bodies, it is very practical for installing wind turbines and for mooring the floating body when it is in the production stage.

[0014] According to one embodiment, the floating body further comprises a connector having an upper platform and a lower platform to which the respective ends of the vertical branches of two tubular structures are attached, the platforms being connected to each other by vertical tubes to increase the buoyancy of the pylon.

[0015] According to another embodiment, the vertical branches of the two tubular structures form a single component designed to receive a wind turbine mast. In yet another embodiment, the floating body further comprises a lower connector to which the lower ends of the vertical branches of two tubular structures are attached to ensure the retention and force absorption of the two tubular structures, and an upper connector to which the upper ends of the vertical branches of the two tubular structures are attached, the upper connector being designed to receive a wind turbine mast.

[0016] Preferably, the three tendons fixed to the counterweight are double-layered. Preferably, the connecting pipe is positioned to be partially submerged during the transport phase of the floating body in order to improve the stability of the floating body.

[0017] At least one of the branches of the two tubular structures may be equipped with a buoyancy element. The connecting pipe may be fixed to the branch of the two tubular structures by welding or a pin fixing system.

[0018] In one embodiment, the connecting pipe is fixed to the ends of the horizontal or oblique branches of two tubular structures on the opposite side of the pylon. In particular, the connecting pipe is fixed to the end of the oblique branch by being positioned between two vertical pipes that are attached to the end of the oblique branch of the two tubular structures.

[0019] In another embodiment, the connecting pipe is fixed to the horizontal branch or the oblique branch between the ends of the horizontal branch or the ends of the oblique branch of the two tubular structures. In this alternative embodiment, the vertices of the two tubular structures opposite the pylon are advantageously provided with pencil-shaped buoys.

[0020] An object of the present invention is also a method for installing a floating body according to the present invention, wherein the connecting pipe of the floating body is fixed to the ends of the horizontal branch sections of two tubular structures on the opposite side of the pylon. The method comprises towing the floating body to the installation site while holding a floating counterweight within a triangular area defined by the horizontal branch sections of the tubular structures and the connecting pipe, and then lowering the counterweight below the tubular structures.

[0021] In this method, the floating object can be held within the area of ​​the floating counterweight triangle by using a towline or ballast chain while being towed. Furthermore, in this method, when the counterweight is fixed below the tubular structure by a taut tendon, it is possible to offset it from the axis of the wind turbine mast and lower the center of gravity of the floating body. This offset causes the overall center of gravity to coincide horizontally with the overall thrust center, and thus makes it possible to stabilize the wind turbine vertically.

[0022] An object of the present invention is also a method for installing a floating body according to the present invention, in which a connecting pipe of the floating body is fixed to ends of horizontal branches of two tubular structures on the opposite side of the pylon. The method includes towing the floating body to its installation location, and then installing a sunken counterweight by lowering the counterweight through a triangular area defined by each horizontal branch of the tubular structure and the connecting pipe by means of a barge equipped with a crane, wherein the counterweight is pre-fixed to the two tubular structures by tendons.

[0023] In this method, during installation of the counterweight, the connecting pipe can be retracted to allow the counterweight to easily pass through the triangular area. An object of the present invention is also a method for installing a floating body according to the present invention, in which a connecting pipe of the floating body is fixed between both ends of each of horizontal branches or diagonal branches of two tubular structures. The method includes towing the floating body to its installation location, and then installing a sunken counterweight by vertically lowering the counterweight outside a triangular area defined by each horizontal branch of the tubular structure and the connecting pipe by means of a barge equipped with a crane or a winch, wherein the counterweight is pre-fixed to the two tubular structures by tendons.

Brief Description of the Drawings

[0024] [Figure 1] A perspective view of a floating body according to an embodiment of the present invention. [Figure 2] A perspective view of a floating body according to another embodiment of the present invention. [Figure 3] A perspective view of a floating body according to another embodiment of the present invention. [Figure 4] An embodiment of a method for installing a floating body according to the present invention is shown, in which a connecting pipe is fixed to ends of horizontal branches of two tubular structures on the opposite side of the pylon. [Figure 5] A modification of an embodiment of a method for installing a floating body according to the present invention is shown. [Figure 6]Another modified embodiment of the method for installing a floating body according to the present invention is shown. [Figure 7] This describes one embodiment of a method for installing a floating body according to the present invention, in which a connecting pipe is fixed between the respective ends of the horizontal branches of two tubular structures. [Figure 8] This is a perspective view of a floating object according to one embodiment of the present invention. [Modes for carrying out the invention]

[0025] Figure 1 is a perspective view of a semi-submersible floating body 2a having a pendulum-type counterweight for an offshore wind turbine according to a first embodiment of the present invention. The floating body 2a according to the present invention comprises two identical tubular structures 4, each of which comprises three tubular branches forming a right triangle, namely a horizontal branch 6, a vertical branch 8, and an oblique branch 10.

[0026] The two tubular structures 4 are assembled together by their respective vertical branches 8 to form a pylon designed to align with the vertical axis XX of the wind turbine mast 12.

[0027] Furthermore, the soms of the two tubular structures 4 on the opposite side of the pylon are spaced apart by an angle between 25° and 80°, preferably about 40°.

[0028] The floating body 2a according to the present invention also includes a connecting pipe 14 that connects the oblique branch portions 10 of the two tubular structures 4 to each other. Alternatively, the connecting pipe may connect the horizontal branch portions 6 to each other.

[0029] Furthermore, the connecting pipe 14 may be fixed to the end of the oblique branch portion 10 (or horizontal branch portion) of the two tubular structures on the opposite side of the pylon (in the embodiments shown in Figures 1 to 6), or it may be fixed to the horizontal branch portion 6 (or oblique branch portion) between the ends of each of the horizontal branch portions 6 (or oblique branch portions) of the two tubular structures (in the embodiment shown in Figure 7).

[0030] The connecting pipe 14 may be fixed to the branch of the tubular structure to which it is connected by welding or by a pin fixing system (or pins and holes). In such a pin fixing system, the pad eyes are fabricated in advance, but the holes for the pad eyes for passing the fixing pins are drilled during the assembly of the connecting pipe.

[0031] This connecting pipe 14 not only allows the two tubular structures 4 to be connected to each other, but also functions as a stabilizing float when the float's counterweight has not yet been suspended from the tubular structure (typically during the towing phase of the float).

[0032] The floating body 2a according to the present invention also comprises a counterweight 16 fixed to two tubular structures 4 by three tendons, on the one hand fixed at the height (niveau) of the pylon by a first tendon 18-1, and on the other hand fixed at the height (niveau) of the apex opposite the pylon by two other tendons 18-2.

[0033] Considering the eccentricity of the wind turbine mast 12 relative to the center of gravity of the two tubular structures 4, the counterweight 16 needs to be moved away from the axis XX of the wind turbine mast in order to balance the weight of the wind turbine and ensure the stability of the floating structure. For this purpose, the length of the first tendon 18-1 fixed to the pylon is provided to be longer than the lengths of the other two tendons 18-2.

[0034] Furthermore, in this first embodiment of the present invention, the floating body 2a further comprises a lower connector 20 to which the lower ends of the respective vertical branches 8 of the two tubular structures 4 are attached, and an upper connector 22 to which the upper ends of these vertical branches are attached.

[0035] These lower connectors 20 and upper connectors 22 have the function of holding the tubular structure together and ensuring force absorption. In addition, the upper connector 22 is also designed to receive the mast 12 of the wind turbine.

[0036] Figure 2 is a perspective view of a semi-submersible floating body 2b having a pendulum-type counterweight for an offshore wind turbine, according to a second embodiment of the present invention. The floating body 2b in this embodiment differs from the one described above, particularly in that it is assembled together with the tubular structure 4.

[0037] In fact, in this second embodiment, the vertical branches of the two tubular structures form a single component 24 designed to receive the mast 12 of the wind turbine at its top.

[0038] Figure 3 is a perspective view of a semi-submersible floating body 2c having a pendulum-type counterweight for an offshore wind turbine according to a third embodiment of the present invention. This third embodiment of the floating body 2c differs from the one described above in that the tubular structure 4 is assembled together with it.

[0039] The floating body 2c according to this embodiment further comprises a connector 26 formed from an upper platform 28 to which the upper ends of the vertical branches 8 of the two tubular structures are fixed, and a lower platform 30 to which the lower ends of the vertical branches of the two tubular structures are fixed.

[0040] Furthermore, the connector platforms 28 and 30 are connected to each other by the vertical tube 32, which allows for increased buoyancy of the pylon. Regardless of the embodiment, the three tendons 18-1, 18-2 fixed to the counterweight 16 are advantageously doubled to enhance safety in the event of failure of one of the tendons.

[0041] In addition, at least one of the two tubular structures of the floating body according to the present invention is advantageously provided with a buoyancy element. Thus, in the embodiments of Figures 2 and 3, each horizontal branch 6 of the two tubular structures of the floating bodies 2b and 2c is provided with a (buoy-type) buoyancy element 34. These buoyancy elements may enclose the horizontal branch or be fixed around it, as shown in Figure 4.

[0042] In relation to Figure 4, one embodiment of a method for installing the floating body 2a according to the first embodiment of the present invention will be described. The installation method involves towing the floating body 2a to its installation location while maintaining the counterweight 16 in a floating state within a triangular area Z defined by the two horizontal branches 6 of the tubular structure and the connecting pipe 14.

[0043] This allows the counterweight 16 to float within the float 2a with a significant margin. This large margin is necessary to prevent the counterweight from contacting the float during towing.

[0044] During the towing of the floating object, the floating counterweight can be held within this triangular area by using a towline or ballast chain (not shown in Figure 4).

[0045] Therefore, it is possible to connect tendons 18-1 and 18-2 to the floating body and counterweight 16 in a protected location such as a harbor, then tow the floating body to its installation location, and then lower the counterweight below the floating body by ballasting the counterweight.

[0046] When fixed beneath the floating body, the counterweight 16 is displaced from the axis XX of the wind turbine mast 12, lowering the center of gravity of the floating body. This displacement causes the overall center of gravity to coincide horizontally with the overall thrust center, thus enabling vertical stabilization of the wind turbine.

[0047] In relation to Figure 5, another embodiment of the method for installing the floating body 2a will be described. In this alternative embodiment, a floating body 2a without a counterweight is towed to its installation site. The counterweight 16 is transported in parallel by a barge 36. The counterweight 16 is not necessarily floating.

[0048] Upon reaching the floating structure installation area, the counterweights 16, which are in a submerged state and pre-fixed to the two tubular structures by tendons 18-1 and 18-2, are moved by a crane 38 attached to the barge 36 over the connecting pipe 14, and then descend through the triangular area defined by the two horizontal branches 6 of the tubular structure and the connecting pipe.

[0049] In one modified embodiment shown in Figure 6, the connecting pipe is retracted during the installation of the counterweight 16 so that the counterweight 16 can easily pass through the triangular area. In relation to Figure 7, another embodiment of the method for installing a floating body according to the present invention will be described.

[0050] In this embodiment, the connecting pipe 14 of the floating body 2d is fixed between the ends of the horizontal branches 6 of the two tubular structures 4. This particular arrangement of the connecting pipe has the advantage that the counterweight 16 of the floating body can descend outside (but not inside) the triangular area defined by the two horizontal branches of the tubular structure and the connecting pipe.

[0051] Therefore, this installation method provides the installation of a counterweight 16 (in a submerged state) by a barge 36 equipped with a simple winch 40 (or crane) by towing the floating body to its installation location and then vertically lowering the counterweight outside a triangular area Z defined by the horizontal branches and connecting pipes of the tubular structure.

[0052] Before descent, the counterweight 16 is secured to the two tubular structures of the floating body by tendons 18-1 and 18-2. Furthermore, to improve the stability of the floating structure while it is being towed, advantageously, pencil-shaped buoys 42 are provided at the apex of the two tubular structures 4 on the opposite side of the pylon.

[0053] Figure 8 shows a perspective view of a semi-submersible floating body 2e having a pendulum-type counterweight for an offshore wind turbine, according to yet another embodiment of the present invention. This embodiment differs from the embodiment described in relation to Figure 1 in that the connecting pipe 14 that connects the respective oblique branch portions 10 of the two tubular structures to each other is positioned between two vertical pipes 44 attached to the ends of the oblique branch portions. An additional vertical clamping system (not shown) allows the connecting pipe 14 to be secured to the oblique branch portions 10.

[0054] These vertical tubes 44 simplify the fixing of the connecting tubes 14 and significantly improve the stability of the floating body during the towing phase.

Claims

1. A semi-submersible floating body (2a to 2d) equipped with a pendulum-type counterweight for offshore wind turbines, Two tubular structures (4) each having three tubular branches forming a right triangle, each having a horizontal branch (6), a vertical branch (8), and an oblique branch (10), wherein the tubular structures are assembled together by their respective vertical branches (8) to form a pylon designed to align with the axis (X-X) of a wind turbine mast (12), and the vertices of the tubular structures on opposite sides of the pylon are spaced apart by an angle (α) between 25° and 80°, and A connecting pipe (14) connects the horizontal branches or the oblique branches of the two tubular structures (4), A floating body comprising a counterweight (16) fixed to the two tubular structures by three tendons, on one side at the height of the pylon and on the other side at the height of the apex of the tubular structure opposite to the pylon, wherein the length of the tendon (18-1) fixed to the pylon is greater than the lengths of the other two tendons (18-2), thereby, depending on the situation, moving the counterweight away from the axis of the wind turbine mast to balance the weight of the wind turbine.

2. The floating body (2c) according to claim 1, further comprising a connector (26) having an upper platform (28) and a lower platform (30) to which the respective ends of the vertical branch portions (8) of the two tubular structures (4) are attached, wherein the platforms are connected to each other by vertical tubes (32) to increase the buoyancy of the pylon.

3. The floating body (2b) according to claim 1, wherein the vertical branch portions (8) of the two tubular structures (4) form a single component (24) designed to receive the wind turbine mast (12).

4. The floating body (2a) according to claim 1, further comprising: a lower connector (20) to which the lower ends of the vertical branches (8) of the two tubular structures (4) are attached to ensure the holding and force absorption of the two tubular structures (4); and an upper connector (22) to which the upper ends of the vertical branches of the two tubular structures are attached, wherein the upper connector is designed to receive the wind turbine mast (12).

5. The floating body according to any one of claims 1 to 4, wherein the three tendons (18-1, 18-2) fixed to the counterweight (16) are doubled.

6. The floating body according to any one of claims 1 to 5, wherein the connecting pipe (14) is arranged to be partially submerged during the transport stage of the floating body in order to improve the stability of the floating body.

7. The floating body according to any one of claims 1 to 6, wherein at least one of the branches of the two tubular structures is provided with a buoyancy element.

8. The floating body according to any one of claims 1 to 7, wherein the connecting pipe (14) is fixed to the branch portion of the two tubular structures by welding or a pin fixing system.

9. The floating body according to any one of claims 1 to 8, wherein the connecting pipe (14) is fixed to the end of the horizontal branch (6) or the oblique branch (10) of the two tubular structures on the opposite side of the pylon.

10. The floating body (2e) according to claim 9, wherein the connecting pipe (14) is fixed to the end of the oblique branch portion (10) by being positioned between two vertical pipes (44) attached to the end of the oblique branch portion (10) of the two tubular structures.

11. The floating body according to any one of claims 1 to 8, wherein the connecting pipe (14) is fixed to the horizontal branch portion (6) or the oblique branch portion (10) between the ends of the horizontal branch portion (6) or the ends of the oblique branch portion (10) of the two tubular structures.

12. The floating body according to claim 11, characterized in that a pencil-shaped buoy (42) is provided at the vertices of the two tubular structures on the opposite side of the pylon.

13. A method for installing the floating body according to claim 9 or 10, comprising: towing the floating body to an installation location while holding the floating counterweight within a triangular area defined by the horizontal branch of the tubular structure and the connecting pipe; and then lowering the counterweight below the tubular structure.

14. The method according to claim 13, characterized in that the floating counterweight is held within the triangular area using a towing line or ballast chain while the floating body is being towed.

15. The method according to claim 13 or 14, wherein when the counterweight is fixed below the tubular structure, it is offset from the axis of the wind turbine mast, lowering the center of gravity of the floating body, and this offset causes the overall center of gravity to coincide horizontally with the overall thrust center, thereby enabling the wind turbine to be stabilized vertically.

16. A method for installing a floating body according to claim 9 or 10, comprising: towing the floating body to a location for installation; and then installing the submerged counterweight by lowering it through a triangular area defined by the respective horizontal branches of the tubular structure and the connecting pipe using a barge equipped with a crane, wherein the counterweight is pre-secured to the two tubular structures by tendons.

17. The method according to claim 16, wherein, during the installation of the counterweight, the connecting pipe is retracted so that the counterweight can easily pass through the triangular area.

18. A method for installing a floating body according to claim 11 or 12, comprising: towing the floating body to a location for installation; and then installing the submerged counterweight by vertically lowering the counterweight outside a triangular area defined by the respective horizontal branches of the tubular structure and the connecting pipe using a barge equipped with a crane or winch, wherein the counterweight is pre-secured to the two tubular structures by tendons.

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