System for forming anchor points for offshore wind turbine floats and method of installation

Abstract

The invention relates to a system (2) for forming an anchor point for an offshore wind turbine float, comprising at least one enclosure (6) having an open bottom (8) and an open top (10), the enclosure being at least partially filled with a solid particulate material (12) capable of withstanding shear forces with a seabed (4) on which the enclosure is intended to sit, the enclosure further comprises at least one mooring lug (14) for securing a mooring line (16) of the float.

Description

TECHNICAL FIELD

[0001] The present invention relates to the general field of offshore wind turbine floaters. More particularly, the present invention relates to an anchoring system connected to the seabed and enabling such a floater to remain in place. BACKGROUND

[0002] The purpose of offshore wind turbines is to use wind energy to produce electricity using a turbine and a generator. There are two main types of offshore wind turbines: fixed wind turbines, which are installed on the seabed, usually in shallow depths of less than 50 m, and floating wind turbines, which have the advantage of being able to be built on land and installed in areas where the seabed depth is usually more than 50 m.

[0003] Floating wind turbines generally comprise a turbine, which is usually formed of an electric motor with a plurality of rotating blades having a horizontal axis and a generator coupled to the electric motor; the electric motor and the generator are fixed to the upper end of a vertical mast (or tower), the lower end of which is mounted on a floater.

[0004] There are three main types of floaters for offshore wind turbines: semi-submersible floaters, submerged floaters with taut cables (or "Tension Leg Platforms", i.e. TLP platforms) and "SPAR" (Single Point Mooring Storage) floaters.

[0005] Currently, semi-submersible floaters and SPAR (Single Point Mooring Storage) floaters are the most widely used models of floaters. These are steel or concrete structures, usually in the form of a tripod with three interconnected columns (for semi-submersible floaters) or a single central column (for SPAR-type floaters). The structure of these floaters comprises underwater parts and a number of anchor lines, which, although not in a state of tension, must be able to withstand the drift loads of the entire assembly.

[0006] There are several techniques for installing the anchor lines of offshore wind turbine floaters: drag anchors (such as the "Delta Flipper" or "Stevpris" anchors), which are particularly suitable for anchoring catenary anchors in sedimentary soils (clay, sandy to sandy clay); anchor piles, which involve implanting metal pipes into the seabed consisting of sandy clay to silt clay by means of impact, or fixing metal pipes to rocky seabeds by means of drilling, or installing metal pipes by suction in "soft" silt clay to clay seabeds; and gravity anchors, which are placed in seabeds consisting of sedimentary soils (clay, sandy to sandy clay) and / or rock-type soils and act as a fixed point for the anchor lines, resisting loads by means of their own weight.

[0007] In floating offshore wind farm development projects, the heterogeneity of the seabed soil conditions, in which the soil type varies rapidly both in nature and in thickness, can pose risks to the mooring system and its installation, causing concerns for the developers of these projects.

[0008] For example, surface or subsoil rocky soils and / or soils with a thin layer of sediments on weathered rock do not allow the installation of a drag anchor system. However, this type of soil also poses problems if a borehole and injection of grout or installation of a pile are chosen.

[0009] Generally, these risks are related to the geotechnical profile of the soil and the seabed conditions (irregular topography, particular seabed topography, such as slopes, inclines, depressions, gullies, boulders, etc.), and concerns are raised about the possible impact on the mooring system and its installation if such situations are encountered. SUMMARY

[0010] One object of the present invention is to propose a system forming a gravity anchor point that is easy to manufacture and use and that, once in place on the seabed, is able to withstand the anchoring forces mainly relying on its own weight.

[0011] According to the invention, this object is achieved by a system forming an anchor point for a floating of an offshore wind turbine, comprising at least one cellular containment cage having an open bottom and an open top, the containment cage being at least partially filled with a solid granular material able to withstand shear forces between the seabed on which the containment cage is intended to sit and at least one mooring ear for securing a mooring line of the floating.

[0012] The system forming an anchor point according to the invention is characterized in that it comprises a containment cage which, because of its structure, is light in weight but which, when placed on the seabed, is made heavier by the solid granular material with which it is filled. The end product is an assembly comprising the containment cage and its solid granular material, called a gravity anchor point, which is inexpensive to manufacture and simpler to use, in particular compared to a pile anchor system.

[0013] The containment cage can have a cylindrical structure with a plurality of radial walls. In this case, the radial walls of the containment cage can be connected together at the symmetry axis of the containment cage. Alternatively, the radial walls of the containment cage can be connected to an inner cylinder centered on the symmetry axis of the containment cage.

[0014] The containment cage can have a polygonal shape with a plurality of radial walls. In this case, the radial walls can be connected together at the symmetry axis of the containment cage. Alternatively, the radial walls of the containment cage can be connected to an inner polygon centered on the symmetry axis of the containment cage.

[0015] The system can comprise a plurality of identical containment cages connected to each other.

[0016] In this case, the containment casings of the mooring system can be stacked on top of each other and / or placed side by side.

[0017] The containment casings can be composed of a plurality of mutually connected containment casing portions.

[0018] Preferably, the lower surface of the containment casing is corrugated or serrated to increase the coefficient of friction between the containment casing and the seabed material.

[0019] Even more preferably, the system further comprises a solid ballast material arranged around the containment casing.

[0020] The inner surface of the containment casing can be roughened to reduce the risk of the system coming loose.

[0021] Another object of the application is a method of installing a system as defined above, the method comprising transporting the system forming an anchorage point by barge to the installation area, then depositing it on the seabed.

[0022] Alternatively, the method for installing a system as defined above can comprise towing the system forming an anchorage point at sea to the installation area, the system forming an anchorage point being equipped with temporary buoyancy means, then depositing the system on the seabed by emptying the gas in the buoyancy means and / or injecting seawater into them. BRIEF DESCRIPTION OF DRAWINGS

[0023] [ Figure 1 ] Figure 1 is a cross-sectional view of a system forming an anchorage point in situ according to the application.

[0024] [ Figure 2 ] Figure 2 shows Figure 1 a perspective view of the system shown.

[0025] [ Figure 3A ] and Figure 3B Figure 3A and Figure 3B shows a perspective view of a system according to another alternative embodiment of the application.

[0026] [ Figure 4A ] and Figure 4B Figure 4A and Figure 4B shows a polygonal-shaped system according to other alternative embodiments of the application.

[0027] [ Figure 5A ] and Figure 5B Figure 5A and Figure 5B shows a polygonal-shaped system according to still other alternative embodiments of the application. ​​​

[0028] [ Figure 6A ] and Figure 6B Figure 6A and Figure 6B A cylindrical system according to further alternative embodiments of the application is shown.

[0029] [ Figure 7A ] and Figure 7B Figure 7A and Figure 7B A system according to further alternative embodiments of the application is shown.

[0030] [ Figure 8A ] and Figure 8B Figure 8A and Figure 8B A system according to further alternative embodiments of the application is shown.

[0031] [ Figure 9 ] Figure 9 is a cross-sectional in-situ view of a system according to the application, surrounded by a solid particulate material.

[0032] [ Figure 10 ] Figure 10 is a cross-sectional in-situ view of a system according to yet further alternative embodiments of the application. DETAILED DESCRIPTION

[0033] The present application relates to a system forming a gravity anchor having the function of keeping an offshore wind turbine floater, such as a semi-submersible floater or a SPAR type floater, in place, due to a heavier mass that is kept in place on the seabed and / or due to friction forces generated on the seabed.

[0034] Figure 1 An example of such a system 2 forming a gravity anchor in-situ, i.e. placed on a seabed 4, is shown.

[0035] According to the present application, the system 2 comprises at least one cellular containment vessel 6 having an open bottom 8 and an equally open top 10. The containment vessel 6 can be made of pre-stressed or non-pre-stressed concrete and / or steel.

[0036] Furthermore, the containment vessel 6 is at least partially filled with a solid particulate material 12, which is capable of withstanding shear forces between the containment vessel and the seabed 4 on which it is intended to be seated. The solid particulate material 12 can consist of large rock particulate material.

[0037] The containment vessel 6 further comprises at least one mooring ear 14 for securing a floater mooring line 16.

[0038] ​​​The system 2 according to the application is thus constituted by the shearing resistance of the combined system of the containment hood 6 and of the volume of solid granular material 12 and by the supporting mooring resistance.

[0039] It should be noted that the volume of solid granular material 12 chosen is defined according to the anchoring strength required.

[0040] It should also be noted that the volume of solid granular material 12 used by the system according to the application is located inside, outside and below the containment hood 6.

[0041] It should also be noted that the containment hood of the system according to the application can take different forms.

[0042] Thus, in the embodiment illustrated in Figure 2 the containment hood 6-1 of the system is in a cylindrical structure and has a plurality of radial walls 18 which are connected together at the axis of symmetry X-X of the containment hood.

[0043] More particularly, in the embodiment illustrated in Figure 2 there are six radial walls 18 which are regularly angularly spaced from each other.

[0044] In the embodiments illustrated in Figure 3A and Figure 3B the containment hood 6-2 of the system is in a cylindrical structure and has a plurality of radial walls 18 which are connected to an internal cylinder 20 centred on the axis of symmetry X-X of the containment hood.

[0045] In the embodiments illustrated in Figure 4A and Figure 4B the containment hoods 6-3 and 6-4 of the anchoring system are each in a polygonal shape (here a hexagon) and have a plurality of radial walls 22.

[0046] In the embodiment illustrated in Figure 4A the radial walls 22 are connected to an internal polygon (here a hexagon) centred on the axis of symmetry X-X of the containment hood 6-3.

[0047] In the embodiment illustrated in Figure 4B the radial walls 22 are connected together at the axis of symmetry X-X of the containment hood 6-4.

[0048] Furthermore, regardless of the geometry of the containment hood, the system according to the application can comprise a plurality of identical containment hoods connected to each other.

[0049] Thus, in the embodiment illustrated in Figure 5A the system 2a comprises two containment hoods 6-3 as described in Figure 4A stacked on each other along their axis of symmetry X-X.

[0050] Similarly, in Figure 5B the illustrated embodiment, the system 2b comprises six caps 6-3 as described above, stacked one on top of the other along their symmetry axis X-X. Figure 4A Furthermore, the caps are arranged side by side in three pairs formed in this way.

[0051] In Figure 6A the illustrated embodiment, the system 2c comprises three caps 6-2 as described above, stacked one on top of the other along their symmetry axis X-X. Figure 3A

[0052] In Figure 6B the illustrated embodiment, the system 2d comprises nine caps, each formed by a cap 6-2 as described above. Here, the caps are stacked in a three-by-three manner along their symmetry axis X-X, and the three groups of three caps thus formed are arranged side by side. Figure 3A

[0053] In Figure 7A and Figure 7B the illustrated embodiments, the cap is composed of a plurality of mutually connected cap portions.

[0054] In Figure 7A the example illustrated, the cap 6-5 has a cylindrical structure and is composed of five identical sector-shaped portions 26. In Figure 7B the example illustrated, the cap 6-6 has a star-shaped structure and is composed of four identical sector-shaped portions 28.

[0055] In particular, according to Figure 8A the advantageous arrangement illustrated, the lower surface 30 of the cap 6-7 of the system forming the anchor point has a sawtooth in order to increase the coefficient of friction between the cap and the seabed material.

[0056] Likewise, in order to increase the coefficient of friction between the cap and the seabed material, the lower surface 32 of the cap 6-8 of the system can alternatively be corrugated (see Figure 8B ).

[0057] In Figure 9 another advantageous arrangement illustrated, the system forming the anchor point also comprises a solid granular material 38 arranged around the cap 6. This solid granular material 38 can be the same as the material used to (at least partially) fill the cap of the system.

[0058] The presence of the solid granular material 38 around the cap has the advantage of increasing the lateral resistance of the vertical cellular structure to the approximately horizontal traction force.

[0059] According to Figure 10 ​​In a further advantageous arrangement, the containment hood 6 of the system forming an anchor point comprises on its inner surface 40 a roughness which can reduce the risk of detachment of the system from the solid particulate material 12.

[0060] The method for installing a system forming an anchor point as defined above can be as follows. The initial step involves transporting the system to the installation area by barge. The system is then deposited on the seabed.

[0061] Another method for installing a system forming an anchor point as defined above can be as follows. The initial step involves towing the system at sea to its installation area. To do this, the system will be equipped with temporary buoyancy means, for example floats.

[0062] Once the system has reached the installation area, the system (more particularly its containment hood) is deposited on the seabed by emptying the gas in the buoyancy means and / or injecting seawater into them, then the solid particulate material is deposited to at least partially fill the interior of the containment hood.

Claims

1. A system (2) for forming an anchor point for a floating object of an offshore wind turbine, the system comprising at least one cellular containment vessel (6; 6-1 to 6-9) having an open bottom (8) and an open top (10), the containment vessel being at least partially filled with a solid particulate material (12) capable of withstanding shear forces between the seabed (4) on which the containment vessel is intended to sit, the containment vessel further comprising at least one mooring ear (14) for securing a mooring line (16) of the floating object.

2. The system according to claim 1, wherein the containment vessel (6-1, 6-2) is in the form of a cylindrical structure having a plurality of radial walls (18).

3. The system according to claim 2, wherein the radial walls (18) of the containment vessel are connected together at a symmetry axis (X-X) of the containment vessel (6-1).

4. The system according to claim 2, wherein the radial walls (18) of the containment vessel are connected to an inner cylinder (20) centered on a symmetry axis (X-X) of the containment vessel (6-2).

5. The system according to claim 1, wherein the containment vessel (6-3, 6-4) is in the form of a polygonal shape having a plurality of radial walls (22).

6. The system according to claim 5, wherein the radial walls (12) of the containment vessel are connected together at a symmetry axis (X-X) of the containment vessel (6-4).

7. The system according to claim 5, wherein the radial walls (22) of the containment vessel are connected to an inner polygon centered on a symmetry axis (X-X) of the containment vessel (6-3).

8. The system according to any one of claims 1 to 7, comprising a plurality of identical containment vessels connected to each other.

9. The system according to claim 8, wherein the containment vessels are stacked on top of each other.

10. The system according to claim 8 or claim 9, wherein the containment vessels are placed side by side.

11. The system according to any one of claims 1 to 10, wherein the containment vessel (6-5) is composed of a plurality of containment vessel portions (26) assembled together.

12. The system according to any one of claims 1 to 11, wherein a lower surface (30, 32) of the containment vessel (6-7, 6-8) is corrugated or serrated.

13. The system according to any one of claims 1 to 12, further comprising a solid particulate material (38) disposed around the containment vessel (6).

14. The system according to any one of claims 1 to 13, wherein an inner surface (40) of the containment vessel has a roughness to reduce the risk of the system coming loose.

15. A method for installing a system according to any one of claims 1 to 14, the method comprising transporting the system forming an anchor point to an installation area by barge, and then depositing it on the seabed.

16. A method for installing a system according to any one of claims 1 to 14, the method comprising towing the system forming an anchor point to an installation area at sea, the system forming the anchor point being equipped with temporary buoyancy means, and then depositing the system on the seabed by emptying the buoyancy means of gas and / or injecting seawater into it.

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