WO2024256782A1 - Semi-submersible float for an offshore wind turbine - Google Patents

Abstract

The invention relates to a semi-submersible float (2) for an offshore wind turbine, comprising at least three vertical columns (4, 6), one of which is intended to receive a wind turbine mast, the vertical columns being connected together by pontoons (8) each formed by a plurality of planar panels (81 to 84) which are assembled together at edges (10) extending longitudinally between two columns, the edges of the pontoons being rounded and connected at each of their longitudinal ends to a column via a transition piece (12).

Description

Description

Title of the invention: Semi-submersible float for offshore wind turbine

Technical Domain

[0001] The present invention relates to the general field of semi-submersible floats used for offshore wind turbines. It relates more specifically to a novel semi-submersible float architecture.

Previous technique

[0002] An offshore wind turbine aims to use wind energy to produce 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 depth of the seabed 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 the generator being fixed to an upper end of a vertical mast (or pylon). The lower end of the mast is in turn mounted on a floating support structure (hereinafter called a float).

[0004]There are several main families of floats 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 floats with a pendulum counterweight.

[0005] The invention relates more specifically to semi-submersible floats, i.e. steel or concrete foundations which are generally presented under the tripod shape with three (or four) cylindrical columns connected to each other by metal structures. The stability of the structure is ensured by a ballasting system that allows part of the foundation to be submerged. This structure is characterized by its large size and reduced draft.

[0006] For example, reference may be made to publication FR 3,064,973 which describes a semi-submersible hybrid float structure comprising a central column and three external columns connected to the central column by pontoon-shaped branches.

[0007]This type of hybrid float has the advantage of being of simple design. However, such a construction has a significant weight which is strongly influenced by fatigue.

Disclosure of the invention

[0008)11 There is therefore a need to be able to have a semi-submersible float whose weight is optimized while respecting the fatigue criteria.

[0009]This aim is achieved by means of a semi-submersible float for an offshore wind turbine, comprising at least three vertical columns, one of which is intended to receive a wind turbine mast, the vertical columns being connected to each other by pontoons each formed by a plurality of flat panels which are assembled together at edges extending longitudinally between two columns, and in which, in accordance with the invention, the edges of the pontoons are rounded and are connected at each of their longitudinal ends to a column by means of a transition piece.

[0010] The float according to the invention is remarkable in that the edges of the pontoons are not sharp (i.e. at right angles) but are rounded, which makes it possible to limit the stress concentrations and thus to significantly improve the fatigue behavior of these areas. Compared to right angles, this characteristic allows the float to meet the fatigue criteria while reducing its weight. As for the transition piece, it makes it possible to limit the stresses in the area of the connection between the pontoons and the columns of the float. [0011] Furthermore, the invention makes it possible to improve the manufacturability of the pontoons by eliminating the continuity of the transverse stiffeners from one face of the pontoon to another. The invention also makes it possible to improve the hydrodynamic behavior of the float by eliminating the undesirable effects linked to the sharp edges of the prior art.

[0012] Preferably, the rounded edges of the pontoons have a quarter circle geometry with a radius between 100 and 1500 mm.

[0013] Also preferably, the rounded edges of the pontoons have a thickness identical to that of the adjacent flat panels.

[0014] The transition piece may have an end that is rounded to connect to the longitudinal end of a rounded edge and an opposite end that forms a right angle.

[0015] The transition part may be a part obtained by one of the following techniques: forging, casting, shaping by bending under a press, and additive manufacturing changing from a triangular shape on one side to a rounded shape on its opposite side.

[0016] Preferably, each flat panel is provided on an internal face with two or three longitudinal main stiffeners and a plurality of transverse secondary stiffeners. This feature makes it possible to reduce the weight of the float and to facilitate its manufacture.

[0017] In this case, the main stiffeners of each flat panel are preferably regularly spaced from each other by means of vertical partitions delimiting ballast zones.

[0018]According to one embodiment, the float comprises four vertical columns including a central column (4) which is intended to receive the wind turbine mast, and three external columns are connected to the central column by lower pontoons.

[0019] In this embodiment, the outer columns may each be formed by an assembly of flat panels. Alternatively, the outer columns may each have a substantially cylindrical shape. [0020]Still in this embodiment, the float may further comprise at least one walkway between an upper end of an outer column and the central column. Such a walkway makes it possible to facilitate access to the float (by helicopter for example) or to have a second access point for a maintenance vessel.

[0021]Still in this embodiment, the central column may have a truncated cone shape or a cylindrical shape.

[0022]According to an advantageous arrangement of the invention, the float comprises inside each pontoon and/or each external column a ballast zone which can be adjusted to correct the trim of the float and improve the hydrodynamic behavior of the float.

Brief description of the drawings

[0023] [Fig. 1] Figure 1 shows in perspective a semi-submersible float according to the invention.

[0024] [Fig. 2] Figure 2 is a sectional view along II-II of Figure 1.

[0025] [Fig. 3] Figure 3 shows the stiffeners inside a pontoon of the float of Figure 1.

Description of the embodiments

[0026] Figure 1 shows in perspective a semi-submersible float 2 for an offshore wind turbine according to a first embodiment of the invention.

[0027] In this embodiment, the float 2 comprises four vertical columns including a central column 4 intended to receive a wind turbine mast (not shown in FIG. 1), and three external columns 6 which are connected to the central column 4 by branches forming lower pontoons 8.

[0028] More specifically, the lower pontoons 8 and the outer columns 6 are angularly spaced from each other by 120° to form a star structure. [0029] Of course, it is possible to envisage that the vertical columns of the float are connected to each other by upper pontoons and/or lower pontoons.

[0030] Furthermore, at least the pontoons formed by a plurality of flat panels which are assembled together. More precisely, in the embodiment of FIG. 1, each lower pontoon 8 is constituted by the assembly of four flat panels 8i to ₈₄ forming a rectangular parallelepiped (only the flat panels 8i and ₈₄ are visible in FIG. 1).

[0031] Of course, it is possible to envisage that the number of flat panels forming each pontoon is different (for example five, six, etc.).

[0032]According to the invention, the flat panels of each pontoon are assembled together at edges 10 which extend longitudinally between two columns and which are rounded by connecting at each of their longitudinal ends to a column by means of a transition piece 12.

[0033] More precisely, as shown in FIG. 2, the edges 10 of the pontoons have a quarter-circle geometry with a radius of between 100 and 1500 mm.

[0034] The rounded edges 10 of the pontoons are connected at each of their two longitudinal ends to a vertical column of the float by means of a transition piece 12 making it possible to change from a quarter-circle shape to a right-angle shape.

[0035]For this purpose, as shown in the magnifying glass of FIG. 1, the transition piece 12 has an end 12a which is rounded to connect to the longitudinal end of a rounded edge 10 and an opposite end 12b which forms a right angle.

[0036]This transition part 12 is a part which can be obtained by one of the following techniques: forging, casting, shaping by folding under a press, and additive manufacturing going from a triangular shape on one side, to a rounded shape on its opposite side. [0037] Furthermore, the rounded edges 10 of the pontoons 8 may have a thickness which is identical or different to that of the adjacent flat panels.

[0038] According to an advantageous arrangement shown in FIG. 3, each flat panel 8i to ₈₄ constituting the pontoons 8 is provided, on an internal face, with two or three longitudinal main stiffeners 14 and a plurality of transverse secondary stiffeners 16.

[0039] Thus, in the embodiment of FIG. 3, each flat panel 8i to ₈₄ is provided with three longitudinal main stiffeners 14 regularly spaced from each other and a plurality of transverse secondary stiffeners 16.

[0040] Furthermore, the main stiffeners 14 of each flat panel are advantageously spaced from each other by means of vertical partitions 18 delimiting ballast zones.

[0041] Thus, inside each pontoon and/or each external column, at least one ballast zone is provided which can be adjusted to correct the trim of the float and improve its hydrodynamic behavior.

[0042] It will be noted that in the embodiment of FIG. 1, the outer columns 6 of the float 2 each have a substantially cylindrical shape. Of course, the invention also applies to floats whose outer columns are each formed by an assembly of flat panels in order to have a polyhedron shape (reference may be made to patent application FR 23 01328 filed on February 13, 2023 by the Applicant).

[0043] It will also be noted in the embodiment of FIG. 1, the central column 4 of the float 2 receiving the wind turbine mast has a truncated cone shape widening downwards. Of course, the invention also applies to floats whose central column has a cylindrical shape.

[0044] It will also be noted that the float can advantageously further comprise at least one walkway (not forming part of the primary structure of the float and not shown in the figures) between an upper end of an external column and the central column in order to facilitate access to the float (for example helicopter for example) or to have a second access point for a maintenance vessel.

Claims

Claims [Claim 1] Semi-submersible float (2) for an offshore wind turbine, comprising four vertical columns including a central column (4) which is intended to receive the wind turbine mast, and three external columns (6) which are connected to the central column by lower pontoons (8) each formed by a plurality of flat panels (8i to 8 ₄ ) which are assembled together at edges (10) extending longitudinally between two columns, characterized in that the edges (10) of the pontoons are rounded, connected at each of their longitudinal ends to a column by means of a transition piece (12), and have a thickness identical to that of the adjacent flat panels. [Claim 2] Float according to claim 1, characterized in that the rounded edges (10) of the pontoons (8) have a quarter-circle geometry with a radius between 100 and 1500 mm. [Claim 3] Float according to one of claims 1 and 2, characterized in that the transition piece (12) has an end (12a) which is rounded to connect to the longitudinal end of a rounded edge (10) and an opposite end (12b) which forms a right angle. [Claim 4] Float according to claim 3, characterized in that the transition piece (12) is a piece obtained by one of the following techniques: forging, molding, shaping by folding under a press, and additive manufacturing changing from a triangular shape on one side to a rounded shape on its opposite side. [Claim 5] Float according to any one of claims 1 to 4, characterized in that each flat panel (8i to ₈₄ ) of the pontoons (8) is provided on an internal face with two or three longitudinal main stiffeners (14) and a plurality of transverse secondary stiffeners (16). [Claim 6] Float according to claim 5, characterized in that the main stiffeners (14) of each flat panel are regularly spaced from each other by means of vertical partitions (18) delimiting ballast areas. [Claim 7] Float according to claim 6, characterized in that the outer columns (6) are each formed by an assembly of flat panels. [Claim 8] Float according to claim 6, characterized in that the outer columns (6) each have a substantially cylindrical shape. [Claim 9] Float according to any one of claims 6 to 8, characterized in that it further comprises at least one walkway between an upper end of an outer column (6) and the central column (4). [Claim 10] Float according to any one of claims 6 to 9, characterized in that the central column (4) has a truncated cone shape. [Claim 11] Float according to any one of claims 6 to 9, characterized in that the central column (4) has a cylindrical shape. [Claim 12] Float according to any one of claims 6 to 11, characterized in that it comprises inside each pontoon (8) and/or each external column (6) a ballast zone which can be adjusted to correct the trim of the float and improve the hydrodynamic behavior of the float.