Modular fixed foundation structure for offshore wind turbines and its installation method

Abstract

Modular fixed foundation structure for offshore wind turbines and its installation method. The invention relates to a modular fixed foundation structure (2-1) for offshore wind turbines, comprising at least three identical triangular unit elements (4), each comprising a central tubular column (6), a radial tubular cross member (8) connected to a lower end of the central column at a right angle to it, and a diagonal tubular cross member (10) connected, on the one hand, to the central column above its lower end, and on the other hand, to a free end of the radial cross member at the level of anchoring means with the seabed, means for retaining from below (12) the lower ends of the central columns of the unit elements, and an upper collector (18) centered on an axis (XX) of the wind turbine mast and comprising, in an upper part, means for receiving a wind turbine mast and,in a lower part, at least three receptacles (22) each intended to receive the upper end of a central column. Figure for the abbreviation: Fig. 1.,

Description

Title of the invention: Modular fixed foundation structure for offshore wind turbine and its installation method. Technical field

[0001] The present invention relates to the general field of offshore wind turbines, i.e. those installed off the coast, and more particularly to fixed foundations for offshore wind turbines. Previous technique

[0002] An offshore wind turbine aims to harness 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 fixed wind turbines relevant to the present invention comprise a turbine generally formed by a motor with several rotating horizontal-axis blades and an electric generator coupled to the motor, the motor and generator being fixed to the upper end of a vertical mast (or pylon). The lower end of the mast is mounted on a foundation structure anchored to the seabed.

[0004] There are three main families of fixed foundation structures for wind turbines which are chosen according to the physical characteristics of the site and the nature of the seabed over a certain thickness which leads to the realization of structures of the type: monopiles (i.e. a single vertical pillar), "jacket" (i.e. in the form of a lattice), and gravity-based (i.e. using concrete or a steel caisson).

[0005] Each of these families of foundation structures has advantages and disadvantages in terms of manufacturing, installation and maintenance.

[0006] Furthermore, the wind energy market is evolving rapidly, and energy demand, and therefore the power output of wind turbines (currently in the range of 15 MW to 22 MW), is increasing. For these reasons, the design of the foundations must be easily adaptable (design, dimensions) to the power output of the wind turbine.

[0007] However, today, fixed foundations for offshore wind turbines face certain difficulties regarding their manufacture, assembly, and installation at sea. Water depth and seabed conditions also constitute limitations.

[0008] Various solutions are being studied to address these difficulties. For example, limiting underwater drilling and avoiding large-scale construction in concrete (which tends to crack), reducing the weight of foundation structures, anticipating the mass production of foundation structures, etc.

[0009] However, most fixed foundation structures (such as the one described in publication EP 2067914) were not designed for large-scale industrialization. Indeed, these structures generally consist of a large number of elements that must be assembled, which requires time and ground space. Description of the invention

[0010] The invention therefore aims to provide a fixed foundation structure for offshore wind turbines that simplifies assembly and accelerates assembly time while minimizing the space required on land.

[0011] In accordance with the invention, this objective is achieved through a modular fixed foundation structure for offshore wind turbines, comprising: - at least three identical triangular unit elements each comprising a central tubular column, a radial tubular cross member connected to a lower end of the central column at a right angle to it, and a diagonal tubular cross member connected, on the one hand, to the central column above its lower end, and on the other hand, to a free end of the radial cross member at the level of anchoring means with the seabed; - means of securing the lower ends of the central columns of the unit elements from below; and - an upper collector centered on an axis of the wind turbine mast and comprising, in an upper part, means for receiving a wind turbine mast and, in a lower part, at least three receptacles intended to receive each the upper end of a central column.

[0012] The invention is remarkable in that it is based on a modular approach for the construction of the fixed foundation structure thanks to the upper connector and the plurality of identical unit elements. The invention thus makes it possible to create a fixed foundation structure with several supports (depending on the site conditions) supporting a foundation that creates the soil-structure connection.

[0013] The fact that the unit elements of the structure are all identical greatly simplifies its assembly. Indeed, these unit elements, as well as the upper connector and the means of securing them from below, can be prefabricated in series according to the same model and quickly assembled on site. This results in simplified assembly and time savings.

[0014] More specifically, the unit elements of the structure are easy to manufacture due to the small number of joints they have. The diameter of the tubes that compose them will vary depending on the quality of the materials used, their thickness, and the power of the wind turbine. The foundation structure is manufactured by assembling the unit elements onto the upper connector and the lower support means. This assembly can be of the non-welded type, which will allow for faster installation with less labor and fewer potential errors and defects. Conversely, the assembly can be carried out by welding, which can be a good option for saving money compared to mechanical parts, and also for making the joints watertight and improving the fatigue resistance of the structure.

[0015] In one embodiment, the anchoring means include piles installed in the seabed by drilling, driving or hammering.

[0016] In another embodiment, the anchoring means include concrete piles installed in the seabed.

[0017] In yet another embodiment, the anchoring means include suction anchors driven into the seabed.

[0018] In yet another embodiment, the anchoring means comprise a common gravity structure made of concrete or steel which is placed on the seabed.

[0019] In yet another embodiment, the anchoring means include metal piles driven into the seabed.

[0020] The structure may include a lower collector centered on the axis of a wind turbine mast and comprising means for receiving the lower end of a central column.

[0021] Depending on the anchoring depth of the structure, the upper collector can be made in two separate parts assembled together, a lower part comprising the receptacles, and an upper part ending with a transition piece comprising the means for receiving the wind turbine mast.

[0022] The diagonal cross member of the unit elements can be connected to the central column by means of a tubular fitting forming a right angle with the central column, which further facilitates the manufacture of the unit elements.

[0023] The unit elements can be regularly spaced around the axis of the wind turbine mast.

[0024] The invention also relates to a method for installing a modular fixed foundation structure as defined above, comprising: - a step of assembling the unit elements by means of holding from below by lifting each unit element and pivoting it to ensure the correct lateral positioning of the unit element; - an assembly step of the upper connector on the upper end of the central column of each unit element; - a step of connecting the central columns of the unit elements to the upper connector by welding, bonding, or mechanical assembly; and - a stage of transporting the structure by sea to its installation site.

[0025] For the installation of a fixed modular foundation structure according to claim 8, the structure without the upper part of the upper collector can be kept partially submerged by a laying vessel, then a lifting crane positions the upper part of the upper collector on the lower part of the latter before they are assembled together in dry conditions. Brief description of the drawings

[0026] [Fig.1] Fig.1 is a perspective view of a fixed foundation modular structure for an offshore wind turbine according to a first embodiment of the invention.

[0027] [Fig.2] The [Fig.2] is a top view of the fixed foundation structure of the [Fig.1].

[0028] [Fig.3] Fig.3 is a perspective view of an alternative embodiment of the fixed foundation structure according to the first embodiment of the invention.

[0029] [Fig.4] Fig.4 is a perspective view of a modular foundation structure fixed for offshore wind turbine according to a second embodiment of the invention.

[0030] [Fig.5] The [Fig.5] is a top view of the fixed foundation structure of the [Fig.4].

[0031] [Fig. 6] Fig. 6 is a perspective view of a modular foundation structure fixed for offshore wind turbine according to a third embodiment of the invention.

[0032] [Fig.7] The [Fig.7] is a top view of the fixed foundation structure of the [Fig.6].

[0033] [Fig.8] Fig.8 is a perspective view of a modular foundation structure fixed for offshore wind turbine according to a fourth embodiment of the invention.

[0034] [Fig.9] The [Fig.9] is a top view of the fixed foundation structure of the [Fig.8].

[0035] [Fig. 10] to [Fig. 14] Figures 10 to 14 show different stages of installation of a fixed foundation structure of the [Fig.1].

[0036] [Fig. 15] to [Fig. 17] Figures 15 to 17 show different stages of installation of a fixed foundation structure according to the embodiment of [Fig.3].

[0037] [Fig. 18A] to [Fig. 18G] Figures 18A to 18G show different stages of a variant of installation of the fixed foundation structure according to the embodiment of [Fig.3],

[0038] [Fig. 19] The [Fig. 19] is a perspective view of an alternative embodiment of the fixed foundation structure of the [Fig.3]. Description of the implementation methods

[0039] Figures 1 to 3 show a fixed foundation structure 2-1 (i.e., anchored to the seabed) for an offshore wind turbine according to a first embodiment of the invention. Such a structure is intended to support the mast of the offshore wind turbine.

[0040] The structure 2-1 here comprises three identical triangular unit elements 4. Each of these unit elements 4 consists of a central tubular column 6 (aligned parallel to an axis XX of the wind turbine mast), a radial tubular cross member 8 which is connected to a lower end of the central column 6 at a right angle to it, and a diagonal tubular cross member 10 which is connected, on the one hand, to the central column 6 above its lower end, and on the other hand, to a free end of the radial cross member 8 at the level of anchoring means on the seabed.

[0041] Typically, the unit elements 4 are made from steel tubes which are joined together by welding or by mechanical assembly (e.g. bolting).

[0042] The structure 2-1 also includes means for holding together the lower ends of the central columns 6 of the different unit elements 4.

[0043] In the first embodiment shown in figures 1 to 3, these means for retaining the central columns from below are in the form of a lower collector (or "clamp") 12.

[0044] As shown more precisely in Figures 10 and 11, this lower collector 12 is in the form of a plate 12a provided with three centering guides 12b, each intended to facilitate the assembly of a corresponding end of a central column. For example, these centering guides 12b are each formed by two plates positioned in a cross shape and beveled in their respective end portions to form a point.

[0045] Of course, it is possible to provide other means of securing the central columns of the unit elements from below. For example, these means could be a clamp tightening the central columns onto a vertical guide.

[0046] Furthermore, these means for securing the central columns from below can be associated with a ring 14 equipped with rings 16 that engage with each central column 6, this ring 14 allowing the alignment of the central columns to be maintained with each other. Once in position, the rings are bolted and / or welded to the central columns.

[0047] The structure 2-1 further includes an upper collector 18 which is centered on the axis XX of the wind turbine mast. This upper collector 18 includes, in an upper part, means for receiving a wind turbine mast 20 and, in a lower part, receptacles 22 each intended to receive the upper end of a central column 6.

[0048] Preferably, the receptacles 22 of the upper connector 18 each have a centering guide (not shown in the figures) to facilitate the assembly of a corresponding end of the central column. For example, these could be plates positioned in a cross shape and beveled at their respective ends to form a point.

[0049] Once fitted inside these receptacles 22 of the upper connector, the central columns 6 are fixed to this connector, by welding, by gluing or by mechanical assembly.

[0050] Furthermore, the means for receiving the wind turbine mast are in the form of a ring 20 into which the lower end of the wind turbine mast is fitted before being fixed (by welding for example).

[0051] In this first embodiment, as shown in [Fig.2], it should be noted that the unit elements 4 are regularly spaced around the axis XX of the wind turbine mast (at the same angle a of 120°).

[0052] Still in this first embodiment, the means of anchoring the structure 2-1 on the seabed include piles 24 which extend vertically downwards from the end of each radial cross member 8 opposite the central column 6 and which are installed in the seabed 26 by drilling, driving or hammering.

[0053] The structure 2-1 shown in figures 1 and 2 is typically intended to be anchored on a seabed 26 located at a depth P of approximately 60m.

[0054] According to a variant of this first embodiment illustrated by [Fig.3], the structure 2-1' is typically intended to be anchored on a seabed located at a greater depth P', on the order of 75m (and can go up to about 100m).

[0055] For this purpose, the upper collector 18' of this structure 2-1' is made in two separate pieces assembled together, namely a lower part 18a comprising the receptacles 22, and an upper part 18b ending with a transition piece comprising the means for receiving the wind turbine mast 20.

[0056] Thus, by varying the height of the upper part 18b according to the anchoring depth of the structure, it is possible to adapt to the installation requirements of the wind turbine.

[0057] In connection with Figures 4 and 5, a 2-2 fixed foundation structure for an offshore wind turbine will now be described according to a second embodiment of the invention.

[0058] This structure 2-2 differs from that of the first embodiment by its means of anchoring to the seabed.

[0059] In this second embodiment, the means for anchoring the structure 2-2 to the seabed comprise concrete piles 28 which extend vertically towards the bottom from the end of each radial crossbeam 8 opposite the central column 6 and which are installed in the seabed 26.

[0060] For example, each unit element 4 can be associated with two concrete piles 28 which extend vertically downwards from the end of each radial cross member 8.

[0061] In connection with Figures 6 and 7, a fixed foundation structure 2-3 of an offshore wind turbine will now be described according to a third embodiment of the invention.

[0062] This structure 2-3 differs from previous embodiments by its means of anchoring to the seabed.

[0063] In this third embodiment, the means for anchoring the structure 2-3 to the seabed include suction anchors 30 which are fixed to the end of each radial cross member 8 opposite the central column 6 and which are driven into the seabed 26.

[0064] As is known, suction anchors 30 are in the form of a large-diameter stack with a closed upper end. Their operating principle is as follows: a vacuum is created inside the anchor (by means of pumps) to overcome the resistance to penetration offered by the seabed. When the anchor has penetrated the seabed to the desired depth, the pumps are disconnected and raised to the surface.

[0065] In connection with Figures 8 and 9, a fixed foundation structure 2-4 of an offshore wind turbine will now be described according to a fourth embodiment of the invention.

[0066] This structure 2-4 differs from previous embodiments by its means of anchoring to the seabed.

[0067] In this fourth embodiment, the means for anchoring the structure 2-4 to the seabed include a common gravity structure 32 made of concrete or steel which is placed on the seabed 26.

[0068] More specifically, the end of each radial cross member 8 opposite the central column 6 has means of attachment 34 to the common gravity structure 32.

[0069] In yet another embodiment of the fixed foundation structure according to the invention (not shown in the figures), the means of anchoring the structure to the seabed are in the form of metal piles (working in compression / tension) and / or tie rods (i.e., sealed and pre-tensioned metal bars) which extend vertically downwards from the end of each radial cross member opposite the central column and which are driven into the seabed.

[0070] In connection with Figures 10 to 14, a first example of the installation of a fixed foundation structure according to the invention will now be described.

[0071] In this example, the fixed foundation structure corresponds to that of the first embodiment (figures 1 and 2), it being understood that the same installation method also applies to the other embodiments of the structure previously described.

[0072] As shown in [Fig. 10], the various elements of the unassembled structure (namely the unit elements 4, the collectors 12, 18, the ring 14 and the piles 24) are prepared and stored at an assembly site.

[0073] Reference may be made, for example, to patent application FR2302023 filed on March 3, 2023, which describes a method for the mass production of offshore wind turbine floats on a limited production area and which could be applied to the mass production of fixed foundation structures according to the present invention.

[0074] According to a first step illustrated by [Fig.1 1], the piles 24 are assembled on each unit element 4. Positioning supports (not shown in the figures) can advantageously be arranged on the assembly site around the lower collector 12 at the precise locations where the unit elements must be angularly positioned.

[0075] As shown in [Fig. 12], the unit elements 4 are assembled one after the other on the lower collector 12. For this purpose, each unit element is lifted (using a crane or a lifting gantry) to vertically introduce the lower end of its central column 6 onto a centering guide 12b of the lower collector 12.

[0076] The ring 14 is also positioned and fixed on the central columns of the unit elements. The upper collector 18 is then lifted to allow the upper ends of the central columns 6 to be inserted into each of the receptacles 22, and then the upper collector is fixed by welding, gluing or mechanical assembly.

[0077] As shown in [Fig. 13], the assembled structure 2-1 is then transported to its offshore installation site. Using a crane, the structure is positioned over the boreholes 36 drilled in the seabed. The structure 2-1 is then lowered by the crane to allow the piles 24 to be positioned in the boreholes 36 ([Fig. 14]).

[0078] Figures 15 to 17 show another example of installation applied to the fixed foundation structure 2-1' described in connection with [Fig.3].

[0079] In this other installation example, the entire structure is assembled except for the upper part 18b of the upper manifold 18' which remains on board the laying vessel.

[0080] Using a crane, the structure is lifted (by the lower part 18a of the upper collector 18') and positioned above the boreholes 36 made in the seabed ([Fig. 15]). Once the piles 24 are at least partially positioned in the boreholes 36, the upper part 18b of the upper collector 18' is then lifted by the crane ([Fig. 16]) and inserted into the lower part 18a of the upper collector before being fixed to it by welding, gluing or mechanical assembly ([Fig. 17]).

[0081] Figures 18A to 18G illustrate an alternative installation of the fixed foundation structure 2-1' described in connection with [Fig.3].

[0082] In this variant of the embodiment, a laying vessel 38 is used. As shown in [Fig. 18A], this laying vessel 38 notably supports a lifting crane 40 and has at its bow a clamp 42 for holding the fixed foundation structure 2-1' to be installed.

[0083] The structure 2-1' except for the upper part 18b of the upper collector is lifted using the lifting crane 40 to be moved and partially submerged below sea level M with the lower part 18a of the upper collector which is inserted into the clamp 42 of the laying vessel ([Fig.18B]).

[0084] The structure 2-1' is thus kept partly submerged by the lower part 18a of the upper collector ([Fig.18C]).

[0085] As shown in [Fig.18D] and [Fig.18E], the upper parts 18b of the upper collectors are conveyed and unloaded onto the laying vessel 38 where they are stored.

[0086] The lifting crane 40 then grasps one of these upper parts 18b ([Fig. 18F]) to assemble it onto the lower part 18a of the upper collector of the structure 2-1' held by the clamp 42 ([Fig. 18G]). Once assembled, the upper part can be fixed (out of the water) to the lower part by welding, gluing, or mechanical assembly.

[0087] In connection with [Fig. 19], we will now describe a variant of the realization of the fixed foundation structures according to the embodiments previously described.

[0088] In this variant embodiment of the structure described in connection with [Fig.3], the diagonal cross member 10 of each unit element 4 of the structure 2-1” is connected to the central column 6 by means of a tubular fitting 44 forming a right angle with the central column 6.

[0089] The presence of such a tubular fitting 44 makes it easier to manufacture the unit elements by making right-angle connections between two tubular elements.

Claims

Demands

1. Modular (2-1 to 2-4) fixed foundation structure for an offshore wind turbine, comprising: - at least three identical triangular unit elements (4), each comprising a central tubular column (6), a radial tubular cross member (8) connected to a lower end of the central column at a right angle to it, and a diagonal tubular cross member (10) connected, on the one hand, to the central column above its lower end, and on the other hand, to a free end of the radial cross member at the level of anchoring means with the seabed; - means for retaining from below (12) the lower ends of the central columns of the unit elements; and - an upper collector (18;18') centered on an axis (X-X) of the wind turbine mast and comprising, in an upper part, means for receiving a wind turbine mast and, in a lower part, at least three receptacles (22) intended to receive each the upper end of a central column.;

2. Structure (2-1; 2-1') according to claim 1, wherein the anchoring means comprise piles (24) installed in the seabed (26) by drilling, driving or hammering.

3. Structure (2-2) according to claim 1, wherein the anchoring means comprise concrete piles (28) installed in the seabed (26).

4. Structure (2-3) according to claim 1, wherein the anchoring means comprise suction anchors (30) driven into the seabed (26).

5. Structure (2-4) according to claim 1, wherein the anchoring means comprise a common gravity structure (32) made of concrete or steel which is placed on the seabed (26).

6. Structure according to claim 1, wherein the anchoring means comprise metal piles driven into the seabed.

7. Structure according to any one of claims 1 to 6, comprising a lower collector (12) centered on the axis of a wind turbine mast and comprising receiving means (12b) for the lower end of a central column (6).

8. Structure according to any one of claims 1 to 7, wherein the upper collector (18') is made in two separate pieces assembled together, a lower part (18a) comprising the receptacles (22), and an upper part ending in a transition piece (18b) comprising the receiving means (20) for the wind turbine mast.

9. Structure according to any one of claims 1 to 8, wherein the diagonal cross member (10) of the unit elements (4) is connected to the central column (6) via a tubular fitting (44) forming a right angle with the central column.

10. Structure according to any one of claims 1 to 9, wherein the unit elements (4) are regularly spaced around the axis (XX) of the wind turbine mast.

11. A method for installing a fixed modular foundation structure according to any one of claims 1 to 10, comprising successively: - a step of assembling the unit elements (4) by means of the bottom support (12) by lifting each unit element and pivoting it to ensure the correct lateral positioning of the unit element; - a step of assembling the upper connector (18) on the upper end of the central column (6) of each unit element; - a step of connecting the central columns of the unit elements to the upper connector by welding, by gluing or by mechanical assembly; and - a step of transporting the structure by sea to its installation site.

12. A method according to claim 11 for installing a fixed modular foundation structure according to claim 8, wherein the structure without the upper part (18b) of the upper collector (18') is held partially submerged by a laying vessel (38), and then a lifting crane (40) positions the upper part of the upper collector on the lower part (18a) of it before they are assembled together dry.

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