System and installation method for forming anchor points for floating bodies for offshore wind turbines

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 cellular 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 pad eye (14) for securing a mooring line (16) for the floating body.

Description

Technical Field

[0001] The present invention relates to the general field of floating bodies for offshore wind turbines. More specifically, the present invention relates to an anchor system that is connected to the seabed and enables such a floating body to be held in a predetermined position.

Background Art

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

[0003] A floating wind turbine generally comprises a turbine formed by a motor having a plurality of rotating blades with a horizontal axis and a generator coupled to the motor. The motor and the generator are fixed to the upper end of a vertical mast (or pylon), and the lower end of the vertical mast is attached to a floating body.

[0004] There are three main types of floating bodies for offshore wind turbines: semi-submersible floating bodies, submerged floating bodies with tension cables ("Tension Leg Platform (TLP)"), and SPAR (Single Point Anchor Reservoir) type floating bodies.

[0005] Semi-submersible and SPAR type floating bodies are currently the most widely used floating body models. These are, in most cases, tripod-shaped steel or concrete structures having three interconnected struts (in the case of semi-submersible floating bodies) or a single central strut (in the case of SPAR type floating bodies). The structure of these floating bodies comprises a submerged part and an anchor line that, although not under tension, must resist the drift of the assembly.

[0006] Several techniques exist for creating floating anchor lines for offshore wind turbines, namely, dragging anchors (e.g., "Delta Flipper" or "Stevpris" anchors) which are particularly suitable for fixing suspension lines in sedimentary soil (clay, sandy to sandy clay); anchor piles which involve driving metal tubes into the seabed by driving them in by driving them into sandy clay to silty clay soil, by drilling them into rocky seabed, or by sucking them into "soft" silty clay to clayey seabed; and gravity anchors which are placed in the seabed composed of sedimentary soil (clay, sandy to sandy clay) and / or rocky soils and function as fixed points for the anchor line, resisting with their own weight. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In projects to develop floating offshore wind farms, the heterogeneity of seabed soil conditions, where soil type changes abruptly in both properties and thickness, is a cause for concern among developers of these projects, as it can pose risks to anchor systems and their installation.

[0008] For example, drag anchor systems cannot be installed in soils with a thin layer of sediment on top of surface or subsurface bedrock and / or weathered bedrock. However, this type of soil also presents problems when options such as drilling holes and injecting mortar or installing piles are employed.

[0009] Generally, these risks are related to the geotechnical profile of the soil and the condition of the seabed (irregularities, such as slopes, inclines, depressions, cuts, and boulders), and when faced with these, concerns arise that they may hinder the anchor system and its installation.

[0010] The objective of this invention is to propose a system that is easy to manufacture and use, and which forms a gravity-type anchor point that, when placed on the seabed, resists anchoring forces primarily by its own weight. [Means for solving the problem]

[0011] According to the present invention, this objective is achieved by a system for forming anchor points for floating bodies for offshore wind turbines. The system comprises at least one cellular housing having an open bottom and an open top, the housing being at least partially filled with solid granular material capable of resisting shear with the seabed on which the housing is intended to rest, and the housing further comprises at least one pad eye for securing mooring lines for the floating body.

[0012] The anchor point forming system according to the present invention is characterized by comprising a housing that is lightweight due to its structure but becomes heavier when placed on the seabed due to being filled with solid granular material. As a result, an assembly known as a gravity anchor point is obtained, comprising the housing and the solid granular material, which is inexpensive to manufacture and easy to use, especially compared to pile anchor systems.

[0013] The housing may be cylindrical with multiple radial walls. In this case, the radial walls of the housing may be connected to each other along the axis of symmetry of the housing. Alternatively, the radial walls of the housing may be connected to an inner cylinder centered on the axis of symmetry of the housing.

[0014] The enclosure may be a polygon with multiple radial walls. In this case, these radial walls may be connected to each other along the axis of symmetry of the enclosure. Alternatively, the radial walls of the enclosure may be connected to an inner polygon centered on the axis of symmetry of the enclosure.

[0015] This system may include multiple identical storage enclosures that are connected to each other. In this case, the storage casings for the anchor system may be stacked vertically and / or arranged side by side.

[0016] The storage enclosure may consist of multiple interconnected enclosure sectors. Preferably, the bottom surface of the storage enclosure is corrugated or sawtoothed to increase the coefficient of friction between the storage enclosure and the seabed.

[0017] More preferably, the system also further comprises solid ballast material arranged around the storage enclosure. The inner surface of the housing may be roughened to reduce the risk of the system coming loose.

[0018] Another object of the present invention is a method for installing the system defined above, comprising transporting the system forming the anchor point to an installation area on a barge, and then placing the system on the seabed.

[0019] Alternatively, a method for installing the system as defined above may include towing a system that forms an anchor point and is equipped with a temporary buoyancy device to the installation area in the sea, and then placing the system on the seabed by contracting the buoyancy device and / or filling the buoyancy device with seawater. [Brief explanation of the drawing]

[0020] [Figure 1] This is a cross-sectional view of the field system for forming anchor points according to the present invention. [Figure 2] Figure 1 shows a perspective view of the system. [Figure 3A] A perspective view of the system according to an alternative embodiment of the present invention is shown. [Figure 3B] A perspective view of the system according to an alternative embodiment of the present invention is shown. [Figure 4A] This shows a polygonal system according to another alternative embodiment of the present invention. [Figure 4B] Shows a polygonal system according to another alternative embodiment of the present invention. [Figure 5A] Shows a polygonal system according to yet another alternative embodiment of the present invention. [Figure 5B] Shows a polygonal system according to yet another alternative embodiment of the present invention. [Figure 6A] Shows a cylindrical system according to yet another alternative embodiment of the present invention. [Figure 6B] Shows a cylindrical system according to yet another alternative embodiment of the present invention. [Figure 7A] Shows a system according to yet another alternative embodiment of the present invention. [Figure 7B] Shows a system according to yet another alternative embodiment of the present invention. [Figure 8A] Shows a system according to yet another alternative embodiment of the present invention. [Figure 8B] Shows a system according to yet another alternative embodiment of the present invention. [Figure 9] Is a cross-sectional view of the system according to the present invention surrounded by solid granular material. [Figure 10] Is a cross-sectional view of the system according to yet another alternative embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention relates to a system for forming a gravity anchor point. This gravity anchor point has a function of holding a floating body (for example, a semi-submersible or SPAR type floating body) for an offshore wind turbine at a predetermined position by its heavy mass staying at a predetermined position on the seabed and / or the frictional force generated on the seabed.

[0022] FIG. 1 shows an example of a system 2 that forms a gravity anchor point in situ, that is, is arranged on the seabed 4. According to the present invention, the system 2 comprises at least one cellular storage enclosure 6 having an open bottom 8 and an open top 10. The storage enclosure 6 may be made of prestressed or unprestressed concrete and / or steel.

[0023] In addition, the storage casing 6 is at least partially filled with solid granular material 12 that can withstand shearing with the seabed 4 on which the storage casing is intended to rest. The solid granular material 12 may be large rocky granules.

[0024] The storage housing 6 also includes at least one pad eye 14 for securing the floating mooring line 16. Therefore, the system 2 according to the present invention consists of mooring resistance by shear and contact using a system that combines a certain volume of solid granular material 12 with a storage housing 6.

[0025] It should be noted that the volume (surface area and height) of the selected solid granules 12 is determined according to the required fixing strength. It should also be noted that the volume of the solid granular material 12 used by the system according to the present invention is located inside, outside, and below the storage enclosure 6.

[0026] It should also be noted that the housing for the system according to the present invention may take on different forms. Therefore, in the embodiment shown in Figure 2, the system housing 6-1 has a cylindrical shape with a plurality of radial walls 18 connected to each other along the axis of symmetry XX of the housing.

[0027] More specifically, in the embodiment shown in Figure 2, there are six radial walls 18 arranged at a constant angular interval from each other. In the embodiments shown in Figures 3A and 3B, the system housing 6-2 is cylindrical and has a plurality of radial walls 18 connected to an inner cylinder 20 centered on the axis of symmetry XX of the housing.

[0028] In the embodiments shown in Figures 4A and 4B, the storage housings 6-3 and 6-4 of the anchor point system each have a polygonal shape (here, a hexagon) with multiple radial walls 22.

[0029] In the embodiment shown in Figure 4A, these radial walls 22 are connected to an inner polygon (here, a hexagon) centered on the axis of symmetry XX of the storage housing 6-3. In the embodiment shown in Figure 4B, these radial walls 22 are joined to each other along the axis of symmetry XX of the storage housing 6-4.

[0030] Furthermore, regardless of the geometric shape of the storage enclosure, the system according to the present invention can comprise a plurality of identical storage enclosures connected to one another. Therefore, in the embodiment shown in Figure 5A, the system 2a comprises two storage housings 6-3 as described in relation to Figure 4A, and the two storage housings are stacked vertically along their axis of symmetry XX.

[0031] Similarly, in the embodiment shown in Figure 5B, system 2b comprises six storage housings 6-3 as described with respect to Figure 4A. In addition, the storage housings are stacked two at a time along their XX axis of symmetry, and the three pairs of storage housings thus formed are arranged side by side.

[0032] In the embodiment shown in Figure 6A, the system 2c comprises three storage housings 6-2 as described in relation to Figure 3A, the three storage housings being stacked vertically along their axis of symmetry XX.

[0033] In the embodiment shown in Figure 6B, the system 2d comprises nine storage enclosures, each formed by a storage enclosure 6-2 as described in relation to Figure 3A. Here, the storage enclosures are stacked in groups of three along their XX axis of symmetry, and these three sets of triplets of storage enclosures are arranged side by side.

[0034] In the embodiments shown in Figures 7A and 7B, the storage enclosure is composed of a plurality of interconnected storage enclosure sectors. In the example shown in Figure 7A, the storage enclosure 6-5 is cylindrical and consists of five identical angular sectors 26. In the example shown in Figure 7B, the storage enclosure 6-6 is star-shaped and consists of an assembly of four identical angular sectors 28.

[0035] In particular, according to the advantageous configuration shown in Figure 8A, the bottom surface 30 of the storage housing 6-7 of the system forming the anchor point has a serrated edge to increase the coefficient of friction between the storage housing and the seabed.

[0036] To reiterate, the bottom surface 32 of the system's housing casing 6-8 may be corrugated as an alternative to increase the coefficient of friction between the housing casing and the seabed (see Figure 8B). In the further advantageous configuration shown in Figure 9, the system forming the anchor point further comprises solid granules 38 arranged around the housing 6. These solid granules 38 may be the same as those used to fill (at least partially) the housing of the system.

[0037] The presence of solid granular material 38 around the storage enclosure has the advantage of increasing the lateral resistance of the vertical cell-like structure to quasi-horizontal tensile forces. According to yet another advantageous configuration shown in Figure 10, the housing 6 of the system forming the anchor point has a rough surface on its inner surface 40 which can reduce the risk of the system detaching from the solid granules 12.

[0038] The method for installing the system that forms the anchor point as defined above may be as follows: The first step involves transporting the system to the installation area on a barge. The system is then placed on the seabed.

[0039] Another method for installing the system that forms the anchor point as defined above may be as follows: The first step involves towing the system to the installation area in the sea. For this purpose, the system may be fitted with a temporary buoyancy device, such as a buoy.

[0040] Upon arrival at the installation area, the system, more specifically its containment casing, is positioned on the seabed by retracting the buoyancy device and / or filling it with seawater, and then solid granular material is arranged to at least partially fill the interior of the containment casing.

Claims

1. A system (2) for forming anchor points for a floating body for an offshore wind turbine, comprising at least one cellular housing (6; 6-1 to 6-9) having an open bottom (8) and an open top (10), wherein the housing is at least partially filled with solid granular material (12) capable of resisting shear with the seabed (4) on which the housing is intended to be placed, and the housing further comprises at least one pad eye (14) for securing a mooring line (16) of the floating body.

2. The system according to claim 1, wherein the storage housing (6-1, 6-2) is cylindrical and has a plurality of radial walls (18).

3. The system according to claim 2, wherein the radial walls (18) of the storage housing are connected to each other along the axis of symmetry (X-X) of the storage housing (6-1).

4. The system according to claim 2, wherein the radial wall (18) of the storage housing is connected to an inner cylinder (20) centered on the axis of symmetry (X-X) of the storage housing (6-2).

5. The system according to claim 1, wherein the storage enclosure (6-3, 6-4) has a polygonal shape with a plurality of radial walls (22).

6. The system according to claim 5, wherein the radial walls (12) of the storage housing are connected to each other along the axis of symmetry (X-X) of the storage housing (6-4).

7. The system according to claim 5, wherein the radial wall (22) of the storage housing is connected to an inner polygon centered on the axis of symmetry (X-X) of the storage housing (6-3).

8. The system according to any one of claims 1 to 7, comprising a plurality of identical storage enclosures connected to one another.

9. The storage enclosures are stacked vertically, according to claim 8.

10. The storage enclosures are arranged side by side, as in the system according to claim 8 or 9.

11. The system according to any one of claims 1 to 10, wherein the storage enclosure (6-5) is composed of an assembly of a plurality of enclosure sectors (26) assembled together.

12. The system according to any one of claims 1 to 11, wherein the bottom surfaces (30, 32) of the storage enclosure (6-7, 6-8) are corrugated or sawtooth-shaped.

13. The system according to any one of claims 1 to 12, further comprising solid granular material (38) arranged around the storage enclosure (6).

14. The system according to any one of claims 1 to 13, wherein the inner surface (40) of the storage enclosure is provided with a rough surface to reduce the risk of the system coming loose.

15. A method for installing the system according to any one of claims 1 to 14, comprising: transporting the system, which forms an anchor point, to an installation area on a barge; and then placing the system on the seabed.

16. A method for installing the system according to any one of claims 1 to 14, comprising towing the system, which forms an anchor point and is equipped with a temporary buoyancy device, to an installation area in the sea, and then placing the system on the seabed by contracting the buoyancy device and / or filling the buoyancy device with seawater.

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