Offshore Wind Turbines with Floating Platforms

Abstract

An offshore wind turbine system comprising a wind turbine (8) in combination with a floating platform (1). The platform (1) comprises three buoyancy modules (6) at the corners (5A, 5B, 5C) of a triangular configuration. A tower (2) is midway between two buoyancy modules (6) located at the ends of the base of the triangle and is eccentrically located near the base (3).

Description

[Technical field]

[0001] The present invention relates to a floating platform for a wind turbine, in particular to a wind turbine and a floating structure as disclosed in the preambles of the independent claims. [Background technology]

[0002] For floating platforms for offshore wind turbines, triangular shapes are often preferred due to their relatively high degree of rigidity compared to the size and therefore also the required material, which is considerable for large wind turbines. An example is given in International Patent Application WO2017 / 157399.

[0003] In a triangular floating platform, each corner of the triangle is usually equipped with one or more vertical buoyancy columns, and the wind turbine tower is usually located at the center of the triangle. However, for large wind turbine towers, this arrangement implies challenges for assembly, since the assembly crane has to reach from the periphery of the platform to the center of the platform, which can be up to 35 m or more.

[0004] In some configurations of triangular floating platforms, it has been preferred to place the wind turbine above one of the corners, as this is easily reachable by a crane. However, the corner location has been found to be suboptimal, as the weight of the turbine added to one corner must be compensated for by adding a similar weight to the other two corners. A 2000 ton turbine at one corner would result in the need to add 1000 tonnes of ballast to each of the other two corners. This significant addition of balancing ballast usually results in an undesirable draft, which often exceeds 12m. A draft of no more than 8m would be preferred, as this would significantly expand the number of ports available to floating offshore wind installations.

[0005] It is an object of the present invention to disclose a triangular floating offshore wind platform configuration that significantly reduces the crane reach required for turbine installation while at the same time maintaining a moderate draft. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International patent application WO2017 / 157399 Summary of the Invention

[0007] It is an object of the present invention to provide improvements in the art, and in particular to provide an improved arrangement for a floating offshore platform. This object and further advantages are achieved by the systems and methods described hereinafter and in the claims.

[0008] In summary, the object is achieved with an offshore wind turbine system comprising a wind turbine in combination with a floating platform, the platform comprising three buoyancy modules at the corners of a triangular configuration, the tower being midway or approximately midway between two buoyancy modules located at the ends of the base of the triangle and eccentrically located near the base.

[0009] The term "buoyancy module" is used for an element that provides buoyancy and / or stability to a platform. For example, a buoyancy module may be a buoyancy tank or may comprise a number of buoyancy tanks attached to one another. What a buoyancy module comprises or is a vertical or near-vertical cylinder, a group of two or more vertical or near-vertical cylinders, or other configuration of related vertical or near-vertical vessels, optionally located at the corners of a triangular configuration, and capable of providing buoyancy and / or stability to the platform.

[0010] Compared to the prior art where the tower is supported at the center of a triangular configuration, the presented structure significantly reduces the outreach of the crane used to install the wind turbine on the platform.

[0011] Compared to the prior art where the tower is supported at the corners in a triangular configuration, the proposed structure requires less ballast to counterbalance the weight of the turbine load since two buoyancy modules are used to support the wind turbine instead of one. This reduces the operational depth at which the turbine is installed. For example, the installation of an offshore wind turbine with a power rating of 15 MW would normally require a water depth of around 12 m for the corner location of the wind turbine, whereas the proposed structure requires a depth of only around 8 m, as can be seen, with two corner buoyancy modules, one at each end of the base, supporting the tower.

[0012] It is pointed out that this typically implies that some ballast to balance the platform, for example of the order of one third to two thirds of the weight of the wind turbine, is provided in a third buoyancy module.

[0013] More specifically, the offshore platform comprises tower supports, e.g. tower support columns, that support the tower of the wind turbine, the tower supporting the wind rotor. The platform comprises three buoyancy modules. For example, each module comprises a group of buoyancy members, e.g. two, three or more groups of buoyancy members, such as buoyancy tanks. The buoyancy modules are lighter than water and provide buoyancy to the platform when submerged. The three modules are arranged in a triangular configuration at the corners of an isosceles triangle, the isosceles triangle having a base and two equal length sides extending from the two base angles at the ends of the base and meeting at an apex angle of the triangle. The isosceles triangle is optionally an equilateral triangle with three equal length sides.

[0014] In some embodiments, the central axis of the tower is equidistant to the base angle and is located on the base. Alternatively, the central axis of the tower is located inside or outside the triangle at a distance from the base. Advantageously, the distance is within the range of 0 to 15% of the length L of the base, for example 0 to 15% of the length L of the base.

[0015] For example, the tower lies on a line extending from the apex through the center of the base.

[0016] A typical location for the central axis of the tower is the center of the base, but slight deviations from equidistant to the corners of the base are possible, for example within 2% to 10%, such as 2% to 5%.

[0017] A 10% deviation from the equidistant configuration would imply that the distance to one base corner is 0.55L and the distance to the other base corner is 0.45L, with each distance from the tower centerline to the base corner being reduced or enlarged by 10% of L / 2.

[0018] Typically, however, the deviation is smaller, rather in the range of 2% to 5%. Small amounts of asymmetry can be advantageous in that they may reduce natural frequency problems while maintaining the required load and bearing capacity.

[0019] In some practical embodiments, the platform comprises a support structure of rigid tubular members, in particular braces, connecting the buoyancy modules with the tower support. A convenient and useful configuration is a tetrahedral or approximately tetrahedral configuration.

[0020] For example, the support structure may comprise a bracing arrangement in which each buoyant member is connected to the tower support by a support brace connecting the buoyant member to the base of the tower support and an additional brace connecting the buoyant module to an upper portion, e.g., the top, of the tower support. Advantageously, the buoyant modules may be connected to each other by secondary braces. The bracing arrangement may generally form a tetrahedral shape.

[0021] For example, a method of tower installation includes positioning a floating platform adjacent to a quay, with a tower support, such as a tower support column, located separately from the buoyancy modules and with a base located adjacent to the quay and with the centerline of the tower at or near the center of the base at a location on or adjacent to the base. The tower and nacelle and rotor are then installed on the tower support of the floating platform. Following installation, the floating platform may be towed to a final location offshore. This arrangement allows for installation of the wind turbine directly on the floating platform while it is in port, without the need for excessive crane reach, even in relatively shallow ports adjacent to the quay. Two buoyancy modules, e.g., buoyancy tanks, support the weight of the wind turbine, while a third buoyancy module, e.g., buoyancy tanks, provide counterweight and stability. The third buoyancy member is at a significant distance and does not require a significant amount of ballast. The overall arrangement even makes it possible to place large loads on large floating platforms in ports where depth limitations would otherwise be imposed.

[0022] As an example, a 15 MW wind turbine may be installed on the disclosed floating platform docked in a port with a depth of 8 m or less. Advantageously, the draft during installation or floating of any buoyant member may be less than 8 m. Also, the draft during installation of the third buoyant member may be less than 8 m, less than 6 m, or less than 4 m.

[0023] Embodiments of the invention are illustrated in the drawings. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 illustrates the triangular construction principle of a floating platform for wind turbines. [Diagram 2]FIG. 1 shows a wind turbine on a floating platform. [Diagram 3] FIG. 3 is a top view of the floating platform of FIG. 2. [Figure 4] FIG. 13 illustrates an alternative embodiment. [Diagram 5] FIG. 13 illustrates a further alternative embodiment. [Figure 6] FIG. 1 shows a floating platform in use at high seas in a) calm water, b) low waves, and c) when exposed to high waves. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Figure 1 is a schematic diagram illustrating the principle of a triangular platform 1 and the location of a wind turbine tower 2 on the platform 1. At the corners 5A, 5B, 5C, buoyancy modules 6 are provided, which are dimensioned to provide sufficient buoyancy to hold the platform 1 with its wind turbines on the surface of the water on which the offshore platform 1 floats.

[0026] A reference triangle 9 used to describe the triangular shape of the platform 1 as well as the position of the tower 2 extends from the centre of a single buoyancy module 6 .

[0027] However, in a typical practical application, the buoyancy module 6 at each corner 5A, 5B, 5C is not a single member, but rather a group of buoyancy members, such as tanks, and the centre of the buoyancy module 6 must be constructed as a centre for multiple buoyancy members, for example as a centre between two buoyancy members in a buoyancy pair.

[0028] In the present example, triangle 9 is an isosceles triangle having a base 3 and two equal length sides 4A, 4B that meet at an apex angle 5A. However, triangle 9 could also be an equilateral triangle.

[0029] The tower 2 is located on an imaginary line 7 that extends from the apex angle 5A through the center of the base 3. For example, the line 7 follows a tubular support brace that is part of the support structure of the platform 1.

[0030] Typically, the tower 2 is placed with its centre 2A located in the middle of the base 3. However, in some embodiments, the centre of the tower 2 is outside the triangle 9 and is displaced from the base 3 by a distance X1, which is indicated by reference numeral 2'. This configuration has the advantage of being closer to the crane that mounts the tower 2 on the platform, especially when the buoyancy modules cover a large diameter.

[0031] As will be shown in more detail below, this can be advantageous when the buoyancy modules 6 are arranged in more complex configurations than shown in Figure 1. For example, X1 may be in the range of 0-15% of the base length L, potentially 0-10% of the length L.

[0032] Alternatively, the tower 2 is optionally located inside the triangle and displaced a distance X2 from the base 3 towards the centre of the triangle 9. This is indicated by the reference numeral 2″. For example, X2 may be in the range of 0-15% of the length L of the base, potentially 0-10% of the length L. This has the advantage that the weight of the wind tower is more loaded onto the buoyancy module 6 at the apex angle 5A, thus lowering the required depth of the platform during installation.

[0033] In most cases, the tower centerline 2A is equidistant to the base angles 5B, 5C, but in some cases, a slight deviation 20 from such an equidistant configuration may be desirable to cancel resonant frequencies. Such a slight deviation 20 will typically be less than 5% of L, and typically not exceed 10% of L.

[0034] FIG. 2 shows an example of a floating platform 1 configured to support a wind turbine 8. The platform 1 is configured with a tower support in the form of a power support column 10 supporting a wind turbine tower 2. Three buoyancy modules 6 in the form of pairs of buoyant members 6A, such as tanks, provide buoyancy and stability. The buoyant members 6A are arranged at the corners 5A, 5B, 5C of a planar triangle 9. Each of the buoyant members 6A is provided at its lower end with a heave plate 16 for damping vertical movements at sea. The heave plates 16 lie in a reference plane 17 that is parallel to the reference triangle 9 and perpendicular to the centerline 2A of the cylindrical tower 2. Optionally, the heave plates 16 are foldable for convenience when maneuvering in a harbor.

[0035] The platform 1 achieves stability by a tubular structure comprising a first support brace 12A extending from the most distal buoyancy module 6 at the apex angle 5A to the tower support column 10, and two further support braces 12B extending from the tower support column 10 to each of the other two buoyancy modules 6 at the base corners 5B, 5C, possibly combined into a single further support brace. Further stability is achieved by additional braces 13A and 13B extending from the two further support braces 12B to the first support brace adjacent the buoyancy module 6 at the most distal apex angle 5A relative to the tower support column 10. The additional braces 13A, 13B together with the two further support braces 12B form a planar triangle. As illustrated, this planar triangle is in the same plane as the reference triangle 9.

[0036] A stabilizing brace 15 extends from the top of the support tower support column 10 to each of the support braces 12A, 12B at the location of the buoyancy module 6 to provide a rigid structure to the platform 1. The shape roughly resembles a tetrahedron.

[0037] A work platform 14 surrounds the tower 2 and is typically fastened to the tower 2 .

[0038] A support tower support column 10 is mounted on base 3 with its centerline 2A halfway between the buoyant members 6 and supports the wind turbine tower 2. This is shown in more detail in Figure 3, a top view.

[0039] While Figures 2 and 3 showed the tower located on the base 3, Figure 4 shows a further embodiment of the floating platform 1 corresponding to the one indicated with reference number 2' in Figure 1, i.e. the position of the tower is outside the reference triangle and offset by a certain distance, for example corresponding to less than 15% of the length of the base 3. Two further support braces 12B are not parallel to the base 3 but form an angle with it.

[0040] By comparison, in the embodiment of Figures 2 and 3, the combination of the first support brace 12A and the further support brace 12B is T-shaped, whereas the embodiment of Figure 4 resembles an arrow shape.

[0041] FIG. 5 shows an embodiment of a floating platform 1 corresponding to that shown with reference number 2″ in FIG. 1, i.e. the tower position is inside the reference triangle 9 and offset towards the inside of the reference triangle 9 by a certain distance, corresponding for example to less than 15% of the length of the base side 3.

[0042] Figures 6A, 6B and 6C show the turbine 8 on the platform 1 in three different situations with respect to waves. Figure 6A shows calm seas. Due to the weight of the wind turbine 8, optionally of the order of 2000 tonnes (2,000,000 kg), the two buoyancy modules 6' adjacent to the tower 2 and supporting its weight are deeper in the water than the buoyancy modules 6" which are further away to the tower 2. The increasing tilt of the tower 2 due to increasing wind, shown in the order of Figures 6A, 6B and 6C, pushes this distal buoyancy module 6" out of the water, so that the weight of the buoyancy module 6" as well as the weight of the part of the platform above the surface increases stability. The extent to which this distal buoyancy module 6" and part of the platform 1 are pushed out of the water depends on the wind relative to the wind turbine. However, the combination of the adjacent buoyant module 6' being pushed further down and the distal buoyant module 6" being pushed out of the water has a stabilising effect during wave action on the platform 1 and wind push on the wind turbine 8. The platform is anchored to the seabed 19 by cables 18A, 18B.

Claims

1. An offshore wind turbine system comprising a wind turbine (8) in combination with a floating platform (1), said platform (1) comprising a tower support (10) supporting a tower (2) of said wind turbine (8), said tower (2) supporting a wind rotor, said platform (1) comprising three buoyancy modules (6) providing buoyancy to said platform (1) when in water, said three buoyancy modules (6) being arranged in a triangular configuration forming an isosceles triangle (9), optionally 1. A system in which the buoyancy modules (6) are generally arranged at the corners (5A, 5B, 5C) of an equilateral triangle (9), said triangle (9) having a base (3) and two equal length sides (4A, 4B) extending from two base angles (5B, 5C) at the ends of said base (3) and meeting at an apex angle (5A) of said triangle (9), said platform (1) comprising a support structure of braces (12A, 12B, 13A, 13B, 15) rigidly connecting said buoyancy modules (6) to said tower support (10) in an approximately tetrahedral configuration, The central axis of the tower (2) is On the base (3) or at a distance (X1, X2) from the base (3) that is within a range of 0 to 15% of the length L of the base (3), Equidistant to said base angles (5B, 5C) or deviating from such equidistant configuration by less than 10% of L A system characterized in that

2. 2. The system according to claim 1, wherein the central axis (2A) of the tower (2) is located outside the triangle (9).

3. 2. The system according to claim 1, wherein the central axis (2A) of the tower (2) is located inside the triangle (9).

4. said platform (1) comprising a support structure of braces (12A, 12B, 13A, 13B, 15) rigidly connecting said buoyancy module (6) to said tower support (10); The support structure comprises: a first support brace (12A) connecting the tower support (10) to the buoyancy module (6) at the apex angle (5A); a further support brace (12B) rigidly connecting each of the buoyancy modules (6) of the base corners (5B, 5C) to the tower support (10); additional braces (13A) and (13B) extending from opposite sides of the first support brace (12B) towards the buoyancy modules (6) at the base corners (5B, 5C) and forming a triangular configuration with one or more of the further support braces (12B); The planar arrangement of the braces (12A, 12B, 13A, 13B) is provided, 2. The system of claim 1, wherein the support structure further comprises a stabilizing brace (15) outside the plane of the planar arrangement (12A, 12B, 13A, 13B), the stabilizing brace (15) connecting the tower support (10) with the three buoyancy modules (6).

5. 5. The system of claim 4, wherein the first support brace (12A) and one or more further support braces (12B) are connected to the base of the tower support (10) and the stabilizing brace (15) is connected to an upper portion of the tower support (10).

6. 2. The system according to claim 1, wherein the buoyancy modules (6) are dimensioned such that for a wind turbine having a weight of 2,000,000 kg, the buoyancy modules (6) are dimensioned such that they reach down into the water to a depth of 8 m or less when the platform (1) is provided with a ballast at the apex angle (5A) having a weight in the range of 30-50% of the weight of the wind turbine.

7. 2. The system of claim 1, wherein the central axis (2A) is located at a distance (X1, X2) from the base (3) that is within a range of 0-10% of the length L of the base (3) and is offset from the equidistant configuration by less than 5% of L.

8. 2. The system according to claim 1, wherein the central axis of the tower (2) is equidistant to the base angles (5B, 5C).

9. The system of claim 1 , wherein the buoyancy module (6) comprises a plurality of buoyancy tanks.

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