Pendulum counterweight semi-submersible floater for offshore wind turbine and method of installing same

Abstract

The invention relates to a system (2) forming an anchor point for floaters of offshore wind turbines, comprising at least one containment enclosure (6) having an open bottom (8) and an open top (10), the containment enclosure being at least partially filled with a solid granular material (12) capable of withstanding shear with the seabed (4) on which the containment enclosure is intended to rest, the containment enclosure further comprising at least one attachment (14) for securing a mooring line (16) of the floater.

Description

Description Title of the invention: Semi-submersible float with pendulum counterweight for offshore wind turbine and its installation method Technical Field

[0001] The present invention relates to the general field of semi-submersible floats equipped with a pendulum counterweight for offshore wind turbines. More specifically, it relates to a semi-submersible float whose wind turbine support mast is fixed to the periphery of the float, the center of gravity being corrected by a pendulum system. Prior art

[0002] An offshore wind turbine uses wind energy to generate electricity using a turbine and an electric generator. There are two main types of offshore wind turbines: fixed wind turbines, which are installed on the seabed (at shallow depths, typically less than 50m), and floating wind turbines, which offer the advantage of being able to be built on land and installed in areas where the seabed depth typically exceeds 50m.

[0003] The floating wind turbines to which the present invention relates comprise a turbine generally formed by a motor with several horizontal-axis rotating blades and an electric generator coupled to the motor, the motor and generator being fixed to an upper end of a vertical mast (or pylon). The lower end of the mast is mounted on a floating support structure.

[0004] There are several main families of floating support structures for offshore wind turbines: semi-submersible floats, submerged floats with tensioned cables (or "TLP" platforms for "Tension-Leg Platform" in English), "SPAR" type floats (for "Single Point Anchor Reservoir"), semi-submersible floats of the “barge” type, and semi-submersible floats with a pendulum counterweight.

[0005] Semi-submersible floats are the most common float design currently available. They consist of a steel or concrete foundation that generally takes the form of a tripod with three (or four) cylindrical columns connected to each other by metal structures. The stability of the structure is ensured by a counterweight that allows part of the foundation to be submerged. This structure is characterized by its large size and reduced draft.

[0006] Semi-submersible pendulum floats typically include a counterweight that is immobilized under the float by tendons. This counterweight lowers the center of gravity to stabilize the assembly without the need for numerous buoyancy elements at the free surface of the float.

[0007] Furthermore, semi-submersible floats usually have their transition piece, i.e. the place where the wind turbine support mast is attached, at the geometric center of the float in order to provide an optimized buoyancy volume. However, such centering of the mast often makes access to the wind turbine complicated and requires large capacity cranes for the installation of the nacelle and the mast due to the large radius of the crane required.

[0008] It is known to use semi-submersible floats with their transition piece on the periphery of the structure in order to greatly simplify access to the wind turbine. However, the hull volume of such floats is most often less well optimized because it is necessary to have symmetrical compensation in weight and buoyancy on the side opposite the mast to balance the weight of the wind turbine. Statement of the invention

[0009] The object of the invention is to propose a semi-submersible float structure which has the advantages of floats with an eccentric transition piece without having their disadvantages.

[0010] According to the invention, this aim is achieved by means of a semi-submersible float with pendulum counterweight for an offshore wind turbine, comprising: two tubular structures which each comprise three tubular branches forming a right triangle with a horizontal branch, a vertical branch and a diagonal branch, the tubular structures being assembled together by their respective vertical branch to form a pylon intended to be aligned with an axis of a mast of the wind turbine, the respective tops of the tubular structures which are opposite the pylon being spaced from each other by an angle of between 25° and 80°; - a connecting tube connecting the horizontal branches or the diagonal branches of the two tubular structures; and - a counterweight fixed by three tendons to the two tubular structures, on the one hand at the level of the pylon, and on the other hand at the level of their summits opposite the pylon, the length of the tendon fixed to the pylon being greater than the length of the other two tendons so as, in situation, to move the counterweight away from the axis of the wind turbine mast to counterbalance the weight of the wind turbine.

[0011] The float according to the invention has a transition piece (i.e. the place where the wind turbine support mast is fixed) which is eccentric relative to its geometric center. Such a geometry of the float makes it possible to greatly simplify access to the wind turbine, in particular for its installation and maintenance.

[0012] Furthermore, the invention uses the advantages of the counterweight to stabilize the float by lowering its center of gravity, but also by strongly modifying the center of gravity in the horizontal direction to compensate for the eccentricity of the masses of the mast and the wind turbine. Thus, the counterweight necessary for stability is also used to strongly correct the horizontal position of the center of gravity. Since the counterweight is about twice as heavy underwater as the weight of the mast and nacelle, it is not necessary to shift the counterweight too much to obtain a trim correction.

[0013] Furthermore, the float according to the invention has few buoyancy elements on the free surface like traditional pendulum counterweight floats, which makes the float almost transparent to the swell, but with a mast which is located at the periphery of the float like some semi-submersibles, which is very practical for installing the wind turbine and for mooring the float when it is in the production phase.

[0014] According to one embodiment, the float further comprises a connector comprising an upper platform and a lower platform on which the respective ends of the vertical branches of the two tubular structures are mounted, the platforms being connected to each other by a vertical tube in order to increase the buoyancy of the pylon.

[0015] According to another embodiment, the vertical branches of the two tubular structures form a single piece which is intended to receive the mast of the wind turbine.

[0016] According to yet another embodiment, the float further comprises a lower connector on which are mounted the lower ends of the vertical branches of the two tubular structures in order to ensure their maintenance and a transfer of forces, and an upper connector on which are mounted the upper ends of the vertical branches of the two tubular structures, the upper connector being intended to receive the mast of the wind turbine.

[0017] Preferably, the three tendons attached to the counterweight are doubled.

[0018] Preferably also, the connection tube is positioned so that it is half submerged during the transport phase of the float in order to improve its stability.

[0019] At least one of the branches of the two tubular structures can be provided with flotation elements.

[0020] The connecting tube can be fixed to the branches of the two tubular structures by welding or by a pin fixing system.

[0021] In one embodiment, the connecting tube is attached to the ends of the horizontal branches or diagonal branches of the two tubular structures that are opposite the pylon.

[0022] In particular, the connecting tube can be fixed to the ends of the diagonal branches of the two tubular structures by being positioned between two vertical tubes mounted at the ends of the diagonal branches.

[0023] In another embodiment, the connecting tube is attached to the horizontal legs or diagonal legs of the two tubular structures between their respective ends.

[0024] In this other embodiment, the tops of the two tubular structures which are opposite the pylon are advantageously provided with pencil-type flotation buoys.

[0025] The invention also relates to a method of installing a float according to the invention, the connection tube of which is fixed to the ends of the horizontal branches of the two tubular structures which are opposite the pylon, the method comprising towing the float to its installation site while keeping the counterweight floating in the triangular-shaped area delimited by horizontal branches of the tubular structures and by the connection tube, then lowering the counterweight under the tubular structures.

[0026] In this method, while towing the float, the floating counterweight can be kept in the triangular shaped area with the help of towing lines or ballast chains.

[0027] Still in this process, when immobilized under the tubular structures by the tensioned tendons, the counterweight can be misaligned from the axis of the wind turbine mast and lower the center of gravity of the float, this misalignment making it possible to obtain an overall center of gravity centered horizontally on the overall center of thrust, thus making it possible to stabilize the wind turbine vertically.

[0028] The invention also relates to a method of installing a float according to the invention, the connection tube of which is fixed to the ends of the horizontal branches of the two tubular structures which are opposite the pylon, the method comprising towing the float to its installation site, followed by the installation of the sinking counterweight by a barge equipped with a crane by lowering the counterweight through the triangular-shaped area delimited by the respective horizontal branches of the tubular structures and by the connection tube, the counterweight being previously fixed to the two tubular structures by the tendons.

[0029] In this method, the connecting tube can be retracted when installing the counterweight in order to facilitate its passage through the triangular-shaped area.

[0030] The invention also relates to a method of installing a float according to the invention, the connecting tube of which is fixed to the horizontal branches or to the diagonal branches of the two tubular structures between their respective ends, the method comprising towing the float to its installation site, followed by installing the sinking counterweight by a barge equipped with a crane or a winch by vertically lowering the counterweight outside a triangular-shaped area delimited by the respective horizontal branches of the tubular structures and by the connecting tube, the counterweight being previously fixed to the two tubular structures by the tendons. Brief description of the drawings

[0031] [Fig. 1] Figure 1 is a perspective view of a float according to one embodiment of the invention.

[0032] [Fig. 2] Figure 2 is a perspective view of a float according to another embodiment of the invention.

[0033] [Fig. 3] Figure 3 is a perspective view of a float according to yet another embodiment of the invention.

[0034] [Fig. 4] Figure 4 illustrates an implementation of a method of installing the float according to the invention, the connection tube of which is fixed to the ends of the horizontal branches of the two tubular structures which are opposite the pylon.

[0035] Fig. 5] Figure 5 illustrates an alternative implementation of the method of installing the float according to the invention.

[0036] Fig. 6] Figure 6 illustrates another variant of implementation of the method of installing the float according to the invention.

[0037] Fig. 7] Figure 7 illustrates an implementation of the method of installing the float according to the invention, the connection tube of which is fixed between the respective ends of the horizontal branches of the two tubular structures.

[0038] [Fig. 8] Figure 8 is a perspective view of a float according to yet another embodiment of the invention. Description of the embodiments

[0039] Figure 1 shows in perspective a semi-submersible float 2a with pendulum counterweight for an offshore wind turbine according to a first embodiment of the invention.

[0040] The float 2a according to the invention comprises two identical tubular structures 4 which each comprise three tubular branches forming a right triangle, namely: a horizontal branch 6, a vertical branch 8, and a diagonal branch 10.

[0041] The two tubular structures 4 are assembled to each other by their respective vertical branch 8 to form a pylon intended to be aligned with a vertical axis XX of the mast 12 of the wind turbine.

[0042] In addition, the respective tops of the two tubular structures 4 which are opposite the pylon are spaced from each other by an angle α of between 25° and 80°, and preferably of the order of 40°.

[0043] The float 2a according to the invention also comprises a connecting tube 14 which connects the respective diagonal branches 10 of the two tubular structures 4 to each other. Alternatively, the connecting tube could connect the horizontal branches 6 to each other.

[0044] Furthermore, the connection tube 14 can be fixed to the ends of the diagonal branches 10 (or the horizontal branches) of the two tubular structures which are opposite the pylon (case of the embodiments of figures 1 to 6) or be fixed to the horizontal branches 6 (or to the diagonal branches) of the two tubular structures between their respective ends (case of the embodiment of figure 7).

[0045] The connection tube 14 can be fixed to the branches of the tubular structures that it connects by welding or by a pin and hole fixing system. With such a pin fixing system, the pins (or "padeye" in English) are prefabricated but their drilling to pass the fixing pins is carried out during the assembly of the connection tube.

[0046] This connection tube 14 allows both the two tubular structures 4 to be connected to each other, but it also plays the role of a stabilizing float when the counterweight of the float is not yet suspended from the tubular structures (typically during the towing phases of the float).

[0047] The float 2a according to the invention also comprises a counterweight 16 which is fixed by three tendons to the two tubular structures 4: on the one hand at the level of the pylon by a first tendon 18-1, and on the other hand at the level of their summits opposite the pylon by two other tendons 18-2.

[0048] Given the eccentricity of the wind turbine mast 12 relative to the center of gravity of the two tubular structures 4, it is necessary to move the counterweight 16 away from the axis XX of the wind turbine mast to counterbalance the weight of the wind turbine and thus ensure stability of the float. For this purpose, it is provided that the length of the first tendon 18-1 fixed to the pylon is greater than the length of the other two tendons 18-2.

[0049] Furthermore, in this first embodiment of the invention, the float 2a further comprises a lower connector 20 on which the lower ends of the respective vertical branches 8 of the two tubular structures 4 are mounted, as well as an upper connector 22 on which the upper ends of these vertical branches are mounted.

[0050] These lower 20 and upper 22 connectors have the function of ensuring the maintenance of the tubular structures between them, as well as a recovery of forces. In addition, the upper connector 22 is also intended to receive the mast 12 of the wind turbine.

[0051] Figure 2 shows in perspective a semi-submersible float 2b with pendulum counterweight for offshore wind turbine according to a second embodiment of the invention.

[0052] The float 2b according to this embodiment is distinguished from that previously described in particular by the assembly of the tubular structures 4 between them.

[0053] Indeed, in this second embodiment, the respective vertical branches of the two tubular structures form a single piece 24 which is intended to receive in its upper part the mast 12 of the wind turbine.

[0054] Figure 3 shows in perspective a semi-submersible float 2c with pendulum counterweight for offshore wind turbine according to a third embodiment of the invention.

[0055] The float 2c according to this third embodiment is distinguished from those previously described by the assembly of the tubular structures 4 between them.

[0056] The float 2c according to this embodiment further comprises a connector 26 formed of an upper platform 28 on which the upper ends of the vertical branches 8 of the two tubular structures are fixed and a lower platform 30 on which the lower ends of the vertical branches of the two tubular structures are fixed.

[0057] Furthermore, the platforms 28, 30 of the connector are connected to each other by a vertical tube 32 making it possible to increase the buoyancy of the pylon.

[0058] Whatever the embodiment, the three tendons 18-1, 18-2 fixed to the counterweight 16 are advantageously doubled in order to increase safety if one of the tendons gives way.

[0059] In addition, at least one of the branches of the two tubular structures of the float according to the invention is advantageously provided with flotation elements. Thus, in the embodiments of Figures 2 and 3, the respective horizontal branches 6 of the two tubular structures of the float 2b, 2c are each provided with flotation elements 34 (of the buoy type). These flotation elements can envelop the horizontal branch or be fixed on its periphery as shown in Figure 4.

[0060] In connection with Figure 4, a mode of implementation of a method of installing the float 2a according to the first embodiment of the invention will be described.

[0061] The installation method consists of towing the float 2a to its installation site while maintaining the counterweight 16 in a floating state in a triangular-shaped zone Z delimited by the two horizontal branches 6 of the tubular structures and by the connection tube 14.

[0062] Thus, the counterweight 16 can float inside the float 2a with a large margin. This large margin is necessary to prevent the counterweight from touching the float during towing.

[0063] During towing of the float, the floating counterweight can be held in this triangular shaped area using towing lines or ballast chains (not shown in Figure 4).

[0064] It is thus possible to connect the tendons 18-1, 18-2 to the float and the counterweight 16 in a sheltered location, such as a port, then to tow the float to its installation site, then lower the counterweight under the float by ballasting it.

[0065] When immobilized under the float, the counterweight 16 is misaligned from the axis XX of the mast 12 of the wind turbine and lowers the center of gravity of the float, this misalignment making it possible to obtain a centered overall center of gravity horizontally on the overall center of thrust, thus stabilizing the wind turbine vertically.

[0066] In connection with Figure 5, another method of implementing the method of installing the float 2a will be described.

[0067] In this other embodiment, the float 2a without its counterweight is towed to its installation site. The counterweight 16 is transported in parallel on a barge 36. It is not necessarily floating.

[0068] Once it has reached the float installation area, the counterweight 16, in a flowing state and previously fixed to the two tubular structures by the tendons 18-1, 18-2, is lowered by a crane 38 mounted on the barge 36 by passing it over the connection tube 14 and then through the triangular-shaped area delimited by the two horizontal branches 6 of the tubular structures and by the connection tube.

[0069] In an alternative embodiment shown in Figure 6, the connection tube is retracted during installation of the counterweight 16 so as to facilitate the passage of the latter through the triangular-shaped area.

[0070] In connection with Figure 7, another embodiment of the method of installing the float according to the invention will be described.

[0071] In this embodiment, the connection tube 14 of the float 2d is fixed to the horizontal branches 6 of the two tubular structures 4 between their respective ends.

[0072] This particular arrangement of the connecting tube has the advantage that the counterweight 16 of the float can be lowered outside (and not inside) the triangular-shaped area delimited by the two horizontal branches of the tubular structures and by the connecting tube.

[0073] Thus, this installation method provides for towing the float to its installation site, followed by installation of the counterweight 16 (in a sinking state) by a barge 36 equipped with a simple winch 40 (or a crane) by vertically lowering the counterweight outside the zone Z of shape triangular delimited by the horizontal branches of the tubular structures and by the connecting tube.

[0074] Prior to its descent, the counterweight 16 is fixed to the two tubular structures of the float by the tendons 18-1, 18-2.

[0075] Furthermore, in order to improve the stability of the float when it is towed, the tops of the two tubular structures 4 which are opposite the pylon are advantageously provided with pencil-type flotation buoys 42.

[0076] Figure 8 shows in perspective a 2nd semi-submersible float with pendulum counterweight for offshore wind turbine according to yet another embodiment of the invention.

[0077] This embodiment differs from that described in connection with FIG. 1 in that the connecting tube 14 which connects the respective diagonal branches 10 of the two tubular structures to each other is positioned between two vertical tubes 44 mounted at the ends of the diagonal branches. An additional vertical clamping system (not shown) makes it possible to fix the connecting tube 14 to the diagonal branches 10.

[0078] These vertical tubes 44 make it possible to simplify the fixing of the connection tube 14 and to significantly increase the stability of the float during towing.

Claims

Claims 1. Semi-submersible float (2a to 2d) with pendulum counterweight for offshore wind turbine, comprising: - two tubular structures (4) which each comprise three tubular branches forming a right triangle with a horizontal branch (6), a vertical branch (8) and a diagonal branch (10), the tubular structures being assembled together by their respective vertical branch (8) to form a pylon intended to be aligned with an axis (XX) of a mast (12) of the wind turbine, the respective tops of the tubular structures which are opposite the pylon being spaced from each other by an angle (a) of between 25° and 80°; - a connecting tube (14) connecting the horizontal branches or the diagonal branches of the two tubular structures (4); and - a counterweight (16) fixed by three tendons to the two tubular structures, on the one hand at the level of the pylon, and on the other hand at the level of their summits opposite the pylon, the length of the tendon (18-1) fixed to the pylon being greater than the length of the other two tendons (18-2) so as, in situation, to move the counterweight away from the axis of the mast of the wind turbine to counterbalance the weight of the wind turbine.

2. Float (2c) according to claim 1, further comprising a connector (26) comprising an upper platform (28) and a lower platform (30) on which are mounted the respective ends of the vertical branches (8) of the two tubular structures (4), the platforms being connected to each other by a vertical tube (32) in order to increase the buoyancy of the pylon.

3. Float (2b) according to claim 1, in which the vertical branches (8) of the two tubular structures (4) form a single piece (24) which is intended to receive the mast (12) of the wind turbine.

4. Float (2a) according to claim 1, further comprising a lower connector (20) on which are mounted the lower ends of the vertical branches (8) of the two tubular structures (4) in order to ensure their maintenance and a recovery of forces, and an upper connector (22) on which are mounted the upper ends of the vertical branches of the two tubular structures, the upper connector being intended to receive the mast (12) of the wind turbine.

5. Float according to any one of claims 1 to 4, in which the three tendons (18-1, 18-2) fixed to the counterweight (16) are doubled.

6. Float according to any one of claims 1 to 5, in which the connection tube (14) is positioned so that it is half submerged during the transport phase of the float in order to improve its stability.

7. Float according to any one of claims 1 to 6, in which at least one of the branches of the two tubular structures is provided with flotation elements.

8. Float according to any one of claims 1 to 7, in which the connecting tube (14) is fixed to the branches of the two tubular structures by welding or by a pin fixing system.

9. Float according to any one of claims 1 to 8, wherein the connecting tube (14) is fixed to the ends of the horizontal branches (6) or the diagonal branches (10) of the two tubular structures which are opposite the pylon.

10. Float (2e) according to claim 9, wherein the connecting tube (14) is fixed to the ends of the diagonal branches (10) of the two tubular structures by being positioned between two vertical tubes (44) mounted at the ends of the diagonal branches.

11. A float according to any one of claims 1 to 8, wherein the connecting tube (14) is fixed to the horizontal branches (6) or to the diagonal branches (10) of the two tubular structures between their respective ends.

12. Float according to claim 11, in which the tops of the two tubular structures which are opposite the pylon are provided with pencil-type flotation buoys (42).

13. Method of installing a float according to one of claims 9 and 10, comprising towing the float to its installation site while keeping the floating counterweight in a triangular-shaped area delimited by the horizontal branches of the tubular structures and by the connection tube, then lowering the counterweight under the tubular structures.

14. A method according to claim 13, wherein, during towing of the float, the floating counterweight is maintained in the triangular-shaped area using towing lines or ballast chains.

15. Method according to one of claims 13 and 14, in which, when immobilized under the tubular structures, the counterweight is misaligned from the axis of the wind turbine mast and lowers the center of gravity of the float, this misalignment making it possible to obtain an overall center of gravity centered horizontally on the overall center of thrust, thus making it possible to stabilize the wind turbine vertically.

16. A method of installing a float according to one of claims 9 and 10, comprising towing the float to its installation site, followed by installing the sinking counterweight by a barge equipped with a crane by lowering the counterweight through a triangular-shaped area delimited by the respective horizontal branches of the tubular structures and by the tube connection, the counterweight being previously fixed to the two tubular structures by the tendons.

17. Method according to claim 16, in which the connecting tube is retracted during the installation of the counterweight in order to facilitate the passage of the latter through the triangular-shaped area.

18. A method of installing a float according to one of claims 11 and 12, comprising towing the float to its installation site, followed by installing the sinking counterweight by a barge equipped with a crane or a winch by vertically lowering the counterweight outside a triangular-shaped area delimited by the respective horizontal branches of the tubular structures and by the connecting tube, the counterweight being previously fixed to the two tubular structures by the tendons.

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