Modular fixed-foundation structure for offshore wind turbine and method for installing same

Abstract

The invention relates to a modular fixed-foundation structure (2-1) for an offshore wind turbine, comprising: at least three identical individual elements (4) of triangular shape, each comprising a central tubular column (6), a radial tubular crosspiece (8) connected to a lower end of the central column forming a right angle with same, and a diagonal tubular crosspiece (10) connected to the central column above the lower end thereof, as well as to a free end of the radial crosspiece at means for anchoring to the seabed; means for holding the lower ends of the central columns of the individual elements by the bottom (12); and an upper clamp (18) centred on an axis (X-X) of the mast of the wind turbine and comprising, in an upper portion, means (20) for receiving a wind turbine mast and, in a lower portion, at least three receptacles (22) intended to each receive the upper end of one central column.

Description

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 located 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 turbines, which are installed on the seabed (typically at shallow depths of less than 50 meters), and floating turbines, which offer the advantage of being able to be built on land and installed in areas where the seabed depth typically exceeds 50 meters.

[0003] The fixed wind turbines covered by 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 shape 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, with energy demand and therefore the power output of wind turbines (currently in the range of 15MW to 22MW) increasing. For these reasons, the foundation design must be easily adaptable (design, dimensions) to the turbine's power output.

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

[0008] Various solutions are being studied to address these difficulties. For example, consideration is being given to limiting underwater drilling, avoiding large concrete constructions (which tend 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. This is because these structures typically consist of a large number of components that require assembly, which is time-consuming and requires significant 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] According to the invention, this goal 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 one side, to the central column above its lower end, and on the other hand at a free end of the radial crossbeam 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 creating the fixed foundation structure using the upper connector and a 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 establishes the soil-structure connection.

[0013] The fact that all the structural components are identical greatly simplifies assembly. Indeed, these components, as well as the upper connector and the lower support elements, can be prefabricated in series according to the same model and quickly assembled on site. This results in simplified assembly and significant time savings.

[0014] More specifically, the unit elements of the structure are easy to manufacture due to their small number of joints. The diameter of the tubes that compose them will vary depending on the quality of the materials used, their thickness, and the power output of the wind turbine. The foundation structure is manufactured by assembling the unit elements onto the upper connector and the lower support brackets. This assembly can be of the non-welded type, allowing 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, while also ensuring watertight joints and improving the structure's fatigue resistance.

[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 include 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 including 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 pieces 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 via 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 fixed modular 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] Figure 1 is a perspective view of a modular fixed foundation structure for an offshore wind turbine according to a first embodiment of the invention.

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

[0028] [Fig. 3] Figure 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] Figure 4 is a perspective view of a modular fixed foundation structure for an offshore wind turbine according to a second embodiment of the invention.

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

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

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

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

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

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

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

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

[0039] Figures 1 to 3 show a fixed foundation structure (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] Structure 2-1 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 connected to a lower end of the central column 6 at a right angle to it, and a diagonal tubular cross member 10 connected, on one side, to the central column 6 above its lower end, and on the other side to a free end of the radial crossbeam 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 mechanical assembly (e.g. bolting).

[0042] 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 of 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 equipped with three centering guides 12b, each designed 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 at their respective end points to form a point.

[0045] Of course, other methods can be used to secure the central columns of the unit elements from below. For example, these methods could include a clamp securing the central columns to a vertical guide.

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

[0047] 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. This could, for example, consist of 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 Figure 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 to 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 figure 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 receiving means 20 of the wind turbine mast.

[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, we will now describe a 2-2 fixed foundation structure for an offshore wind turbine according to a second embodiment of the invention.

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

[0059] In this second embodiment, the means of anchoring the structure 2-2 to the seabed include concrete piles 28 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.

[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, we will now describe a fixed foundation structure 2-3 of an offshore wind turbine according to a third embodiment of the invention.

[0062] This 2-3 structure differs from previous implementations 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] Suction anchors, as is well known, are in the form of a large-diameter pile with a closed upper end. Their operating principle is as follows: a vacuum is created inside the anchor (via pumps) to overcome the resistance to penetration offered by the seabed. Once the anchor has penetrated the seabed to the desired depth, the pumps are disconnected and brought to the surface.

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

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

[0067] In this fourth embodiment, the means of 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 take 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 crossbeam opposite the central column and which are driven into the seabed.

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

[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 Figure 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] For example, one could refer 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 apply to the mass production of fixed foundation structures according to the present invention.

[0074] According to a first step illustrated by Figure 11, 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 Figure 12, the unit elements 4 are assembled one after the other on the lower manifold 12. For this purpose, each unit element is lifted (using a crane or a lifting gantry) to vertically insert the lower end of its central column 6 onto a centering guide 12b of the lower manifold 12.

[0076] The ring 14 is also positioned and fixed onto 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 Figure 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 into the seabed. The structure 2-1 is then lowered by the crane to allow the piles 24 to be positioned in the boreholes 36 (Figure 14).

[0078] Figures 15 to 17 show another example of installation applied to the fixed foundation structure 2-1' described in connection with Figure 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 drilled into the seabed (Figure 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 (figure 16) and inserted into the lower part 18a of the upper collector before being fixed to it by welding, gluing or mechanical assembly (figure 17).

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

[0082] In this variant embodiment, a laying vessel 38 is used. As shown in Figure 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 (figure 18B).

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

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

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

[0087] In connection with Figure 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 of the structure described in connection with Figure 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 unit elements by creating right-angle connections between two tubular elements.

Claims

Demands

1. Modular (2-1 to 2-4) fixed foundation structure for 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 securing from below (12) the lower ends of the central columns of the unit elements; and - an upper collector (18; 18') centered on an axis (XX) of the wind turbine mast and comprising, in an upper part, means for receiving (20) 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) 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, in which 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 with a transition piece (18b) comprising the means for receiving the wind turbine mast.

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

10. Structure according to any one of claims 1 to 9, in which 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 holding from below (12) 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 (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, bonding, or mechanical assembly; and - a stage 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 kept partially submerged by a laying vessel (38), 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 in dry conditions.

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