WIND TURBINE OFFSHORE SUPPORT STRUCTURE

Abstract

Semi-submersible offshore support structure for a wind turbine comprising three semi-submersible columns that are connected to each other by a connection structure, wherein the connection structure defines three sides of the support structure, wherein the support structure further comprises a wind turbine receiving element for receiving a wind turbine tower, wherein the wind turbine receiving element is positioned on a side of the support structure between two semi-submersible columns.

Claims

1. A semi-submersible offshore support structure for a wind turbine comprising three semi-submersible columns that are connected to each other by a connection structure, wherein the connection structure defines three outer sides of the support structure, wherein the support structure further comprises a wind turbine receiving element for receiving a wind turbine tower, wherein the wind turbine receiving element is positioned on one of the outer sides of the support structure formed by the connection structure, in between two semi-submersible columns.

2. The semi-submersible offshore support structure according to claim 1, wherein a lower end of the wind turbine receiving element extends to the same level as a lower end of the semi-submersible columns.

3. The semi-submersible offshore support structure according to claim 1, wherein the wind turbine receiving element is positioned in the middle in between two semi-submersible columns.

4. The semi-submersible offshore support structure according to claim 1, wherein the wind turbine receiving element is integrated to the connection structure.

5. The semi-submersible offshore support structure according to claim 1, wherein the connection structure between the semi-submersible columns is provided by a truss connection structure.

6. The semi-submersible offshore support structure according to claim 5, wherein the truss structure comprises upper braces and lower braces, connecting adjacent columns, wherein the upper braces connect upper ends of the columns, and wherein the lower braces connect lower ends of the adjacent columns.

7. The semi-submersible offshore support structure according to claim 5, wherein the truss structure further comprises upper braces and lower braces that connect the upper end of the wind turbine receiving element with an upper end of a column and that connect the lower end of the wind turbine receiving element with a lower end of a column respectively.

8. The semi-submersible offshore support structure according to claim 5, wherein the truss structure further comprises oblique braces.

9. The semi-submersible offshore support structure according to claim 5, wherein the upper braces and/or the lower braces of the truss structure are arranged in a T-shaped configuration.

10. The semi-submersible offshore support structure according to claim 1, wherein the columns and/or the wind turbine receiving element at a lower end thereof are provided with a damper element for dampening movement of the associated column or wind turbine receiving element induced by environmental motions such as wave motions or wind motions.

11. The semi-submersible offshore support structure according to claim 1, wherein an upper end of the semi-submersible columns are provided with a mooring connection for connecting with a mooring system, which mooring system is configured to connect the support structure to a seabed.

12. The semi-submersible offshore support structure according to claim 1, wherein the wind turbine receiving element further comprises a cable guide.

13. The semi-submersible offshore support structure according to claim 1, wherein the wind turbine receiving element has about the same height as the semi-submersible columns.

14. The semi-submersible offshore support structure according to claim 1, wherein the wind turbine receiving element is provided with engagement elements for engaging with a wind turbine tower, such as a flange for a bolt connection with the wind turbine tower, or a recess in which a lower part of the wind turbine tower is insertable.

15. The semi-submersible offshore support structure according to claim 1, wherein the semi-submersible columns comprise a passive ballast system.

16. A semi-submersible offshore support system comprising the semi-submersible offshore support structure according to claim 1 and a wind turbine mounted to the wind turbine receiving element.

17. A semi-submersible offshore support system comprising the semi-submersible offshore support structure according to claim 1, and a mooring system connected to the support structure.

18. The semi-submersible offshore support system according to claim 17, further comprising a wind turbine mounted to the wind turbine receiving element.

19. A method for installing an offshore wind turbine, the method comprising: Providing the semi-submersible offshore support structure according to claim 1; Launching the support structure in a water, typically a harbor water; Mounting at least a wind turbine tower of a wind turbine to the wind turbine receiving element of the support structure; Tugging the support structure with wind turbine tower towards installation location offshore; Mooring the support structure; Connecting electrical cables to the support structure to establish electrical connection.

20. An offshore wind turbine mounted to a wind turbine support structure according to claim 1.

21. A wind turbine farm comprising a number of wind turbine support systems according to claim 18.

22. An assembly of a tug boat and the wind turbine support structure according to claim 1.

23. An assembly of a tug boat and the support system according to claim 16, said support system being connected to the tug boat.

Description

[0030] These and other aspects will further be elucidated with reference to the drawing comprising figures of exemplary embodiments. In the drawing shows:

[0031] FIG. 1 a perspective view of a support structure;

[0032] FIG. 2 a perspective view of a support structure with a wind turbine mounted thereon;

[0033] FIG. 3 a front view of a support structure with a wind turbine mounted thereon, in a floating condition.

[0034] It is to be noted that the figures are given by way of exemplary examples and are not limiting to the disclosure. The drawings may not be to scale. Corresponding elements are designated with corresponding reference signs.

[0035] FIG. 1 shows a perspective view of a semi-submersible offshore wind turbine support structure 1. The support structure 1 comprises three semi-submersible stabilizing columns 2. Here, the columns are embodied as tubular shaped legs 2, but a polygonal shaped cross-section of such a leg may also be possible. The columns 2 are positioned with respect to each other to form a triangular shaped structure. The columns 2 are connected to each other by means of a connection structure 4, here a truss connection structure 4. The truss structure 4 comprises braces 5 that connect to each other to form the truss structure connecting the columns 2. The connection structure 4 connects two adjacent columns 2, and thus defines a side 6 of the triangular configuration of the structure. Thus, the connection structure 4 defines three sides 6a, 6b, 6c, each between two associated ones of the columns 2a, 2b, 2c, thus forming the outer sides 6a, 6b, 6c of the support structure 1. The three sides 6a, 6b, 6c of the triangular configuration can be equally long, or, alternatively, one of the sides may have a different length. Here, the sides 6a, 6b, 6c form the sides of the triangular shaped configuration, with the columns 2a, 2b, 2c positioned at the corners of the triangular configuration. Here, two of the columns 2a, 2b, 2c are connected to each other by two parallel longitudinally extending braces 5a, 5b, and two oblique braces 5c. The longitudinally extending braces 5a, 5b can be said to be mainly horizontally oriented. Other configurations of the braces 5 forming the truss structure 4 are of course possible. The truss structure 4 is shown schematically in these figures, so the exact connection of a brace or bar to a column may differ in practice. Instead of a truss structure 4 an alternative connection between the columns 2 can be provided as well, e.g. a flat plated structure.

[0036] The truss structure 4 comprises upper braces 5a longitudinally extending between upper ends 201a, 201b, 201c, 701 of the columns 2a, 2b, 2c, and of the wind turbine receiving element 7. The truss structure 4 further comprises lower braces 5b connecting lower ends 202a, 202b, 202c, 702 of the columns 2a, 2b, 2c, of the wind turbine receiving element 7. The upper braces 5a and lower braces 5b provide for an optimal support to the columns 2a, 2b, 2c, and to the wind turbine receiving element 7, by connecting to the columns and receiving element at an upper end 201a, 201b, 201c, 701 thereof and at a lower end 202a, 202b, 202c, 702 thereof. As such, the wind turbine receiving element is supported by three upper braces 5a, and three lower braces 5b, both arranged in a T-shaped configuration, with respect to each other. The upper braces 5a and the lower braces 5b connect each of the three columns 2a, 2b, 2c and the wind turbine receiving element 7 with each other. The wind turbine receiving element 7 is mounted to the connection structure, here truss structure 4. In particular, the wind turbine receiving element 7 is positioned in the middle between two adjacent semi-submersible columns 2b, 2c that are connected by the connection structure 4. As such, the wind turbine receiving element 7 forms part of the connection structure 4. The wind turbine receiving element 7 is advantageously integrated to the connection structure 4 connecting two adjacent semi-submersible columns 2b, 2c, in particular in the middle in between the two adjacent semi-submersible columns. The support structure 1 has a triangular shape, with on each corner a semi-submersible column 2a, 2b, 2c and the outer sides of the triangular shape formed by the connection structure 4 connecting the corners, namely the columns, of the triangular shape. On one of the sides of the triangular shape, being an outer side of the support structure 1, the wind turbine receiving element is provided, preferably in the middle of the said side in between the two adjacent semi-submersible columns that are connected by the said side of the support structure. The wind turbine receiving element is mounted to or forms part of the connection structure, defining the outer sides of the triangular shaped support structure, preferably is integrated to the connection structure.

[0037] The wind turbine receiving element 7 is connected to its two adjacent columns 2b, 2c respectively via upper braces 5a, and via lower braces 5b. The wind turbine receiving element 7 is also connected to its opposite semi-submersible column 2a via an upper brace 5a and via a lower brace 5b. As such, the wind turbine receiving element 7 is connected via upper braces 5a, and via lower braces 5b each arranged in a T-shaped configuration. Additionally, the columns 2a and 2c are connected via an upper brace 5a and via a lower brace 5b as well. Also, the columns 2a and 2b are connected via an upper brace 5a and via a lower brace 5b as well. Further, between the columns 2c and 2a, and/or between columns 2b and 2a, oblique braces 5c are provided, here two oblique braces 5c are shown, but in another configuration more oblique braces, or only a single oblique brace, or no oblique brace can be possible, as e.g. shown in FIG. 2. Between the adjacent column 2c and the wind turbine receiving element 7, there is also an oblique brace 5c provided. Between the adjacent column 2b and the wind turbine receiving element 7, there is also an oblique brace 5c provided. Further, between the wind turbine receiving element 7 and the opposite column 2a, there are, in this example, two oblique braces 5c provided. It is to be understood that the configuration of oblique braces may differ. Advantageously, the upper brace and lower brace connecting the wind turbine receiving element 7 and the opposite column 2a are arranged in a vertical plane, which plane provides for a symmetry plane of the support structure 1.

[0038] Further, the truss structure 4 comprises oblique braces 5c that can connect a lower end 702 of the wind turbine receiving element 7 with an upper end 201c of the adjacent column 2c, as well as an oblique brace 5c that can connect a lower end 702 of the wind turbine receiving element 7 with an upper end 201b of the adjacent column 2b. The support structure 1 is arranged to hold and support a wind turbine in harsh offshore conditions. To receive the wind turbine, or at least the wind turbine tower, the support structure 1 is provided with a wind turbine receiving element 7. The wind turbine receiving element 7 is positioned between two of the columns 2a, 2b, 2c. In particular, the wind turbine receiving element 7 is positioned on a side 6 of the support structure 1. Advantageously, the wind turbine receiving element 7 is positioned in the middle between two columns 2b, 2c, to be understood that the distance L1 between the wind turbine receiving element 7 and one connected column 2 is the same as the distance L2 between the wind turbine receiving element 7 and the other connected column 2. The weight of the wind turbine, to be positioned onto the wind turbine receiving element 7, can then be equally distributed over the two adjacent columns 2. The wind turbine receiving element 7 is here embodied as a tubular column as well, but may have also other shapes or configurations. The wind turbine receiving element 7 has approximately the same diameter or outer dimensions as a lower end 212 of the wind turbine tower. There is no further structure provided to enclose the wind turbine receiving element, contrary to the conventional arrangement wherein the wind turbine receiving element is arranged inside a column of the support structure. The wind turbine receiving element 7 is about as high as the stabilizing columns 2a, 2b, 2c and is preferably integrated to the truss structure 4, thereby providing an efficient, effective and a rather low weight, thus less costs, support structure for a wind turbine.

[0039] The wind turbine receiving element adds to the buoyancy of the support structure and can be connected by the braces of the truss structure, and, as such, be integrated in the connection structure 4. The wind turbine receiving element 7 is arranged as a column, tubular or polygonal, but does not have ballast capacity, so typically will be smaller in diameter than the semi-submersible columns 2a, 2b, 2c each having ballast capacity. The beneficial positioning of the wind turbine receiving element halfway in between two columns 2, provides for compact overall dimensions, a lower steel weight, a lower fatigue sensitivity, and a lower harbor draft. Also, an active ballast system may be omitted, and a passive ballast system may suffice. However, should one wish to implement an active ballast system, this is possible as well.

[0040] All the columns, 2a, 2b, 2c and the wind turbine receiving element 7 are provided with a damper element 8 at a lower end 202a, 202b, 202c. The damper element 8 is here embodied as a damper box 8, a closed, in this example cylindrically shaped box having a diameter that is larger than the diameter of the column to which it is connected. Instead of a damper box, a damper element comprising plates may be provided as well. By providing a damper box 8, the motion characteristics of the support structure 1 can be beneficially influenced. The damper element 8 can dampen the movement of the support structure due to environmentally induced motions such as wind induced motions and/or wave induced motions. Also, the damper boxes 8 can be sized such that movement characteristics such as roll, heave or pitch periods can be optimized. Advantageously, the wind turbine receiving element 7 is provided with a damper box 8 as well, thus adding to the favorable motion characteristics.

[0041] The columns 2a, 2b, 2c are each provided with a ballast tank inside the columns. The ballast tanks, not shown in the figures, form part of a passive ballast system of the support structure. The wind turbine receiving element has the same diameter as the wind turbine tower, or at least as the lower part of the wind turbine tower, it does not have a ballast tank. A passive ballast system may suffice because the support structure is sufficiently stable to limit tilt angles and/or due to the advantageous connection of the mooring system at the upper ends of the columns reducing the overturning moment. The damper boxes 8 provide for buoyancy, added mass and damping, thus adding to beneficial motion characteristics of the support structure. Also, a low harbor draft can be achieved, and, additional temporary buoyancy devices can be omitted during the stay of the support structure in the harbor prior to the mounting of the wind turbine on the support structure. Also, very little counter-ballast is needed due to the positioning of the wind turbine receiving element in between two columns 2, and a passive ballast system suffices.

[0042] The columns 2 having a height H extending between an upper side 10 of the support structure 1 and a lower side 9 of the support structure 1. The wind turbine receiving element 7 has about the same height H, extending between the lower side 9 of the support structure 1 and the upper side 10 of the support structure 1. As such, the column of the wind turbine receiving element 7 may add to the buoyancy and the motion characteristics of the support structure. The wind turbine receiving element 7 may be provided with engagement elements 11 for engaging to a lower end of a wind turbine tower. The engagement element 11 can be a ring shaped flange for bolted connection with a corresponding ring shaped flange of the wind turbine tower.

[0043] In FIG. 1, it further can be seen that the upper end 701 of the wind turbine receiving element further is provided with an outwardly extending flange 711. The outwardly extending flange 711 typically is provided for connecting the upper braces 5a, and for providing a walking deck.

[0044] FIG. 2 shows a support structure 1 with a wind turbine 20 is mounted onto the wind turbine receiving element 7. The wind turbine 20 comprises a wind turbine tower 21, a nacelle 22 and blades 23. The weight of this wind turbine 20 is carried by the support structure 1, but, is, in particular distributed over the adjacent columns 2b, 2c, due to the beneficial positioning of the wind turbine receiving element 7 in between the two columns, in particular in the middle of the two columns.

[0045] FIG. 3 shows a front view of a support system comprising the support structure 1 and the wind turbine 20 mounted to the support structure 1, in particular to the wind turbine receiving element 7. At an upper end of the columns 2, a mooring connection 25 is provided to which a mooring line 26 can be connected. The mooring system 26 typically comprises one or more mooring lines 26 per column, that are at one end connected to the upper end, typically a top deck 29 of the columns 2, and at an other end connected to the sea bottom. The mooring system 26 connects the floating support structure 1 to the sea bottom, while allowing, limited, movement of the support structure 1 due to waves and/or wind. By connecting the mooring lines at the top deck 29 of the columns, the distance between the sea bed and the mooring connection point 25 is increased. For relatively shallow water, between about 40 to about 100 m water depth, a lighter mooring system may be possible. The top deck connection of the mooring lines reduces the stiffness of the mooring system, which may result in lower loads in the mooring lines. Also, by connecting the mooring lines 26 at the top deck 29 of the columns, the overturning moment due to the environmental loads, the wind turbine loads and/or mooring loads is minimized, thereby the overall dimensions of the support system may remain compact. The wind load on the wind turbine causes a load and an overturning moment, but due to the higher connection of the mooring lines, the lever between the wind load and the counteracting load from the mooring system is reduced. The water line level WL is indicatively provided, showing that the support structure 1, when floating, is semi-submersible. Part of the structure 1 is below the water line WL, and part of the structure 1 is above the water line WL. Further, in FIG. 3, a boat landing 300 mounted to the wind turbine receiving element 7 is shown, as well as a crane 301 provided on the flange 711 of the wind turbine receiving element 7. By providing the boat landing 300 to the wind turbine receiving element 7, the boat landing is farther away from the columns 2, and thus, from the mooring lines 26, which may allow for a safer approach of a vessel to the support structure. Alternatively, the boat landing, and preferably crane, can be provided to one of the columns.

[0046] The wind turbine receiving element 7 may further be provided with cable entries 12a for allowing cables 12 to enter the support structure 1. The cable entry 12a can be provided as a cable guide that can at least partly be received inside of the wind turbine receiving element 7. Alternatively, the cable entry 12a may be provided as a cable guide, not shown here, that may be connected at an outside of the receiving element 7. The cable entry at the wind turbine receiving element 7 may provide for an efficient cable, in particular electrical cable, pull-in operation. Also, the hanging-off arrangement of the electric cables 12, once connected, is more efficient as well, as well as less interference with mooring lines 26 may occur.

[0047] It will be appreciated that many variants of the first and second cooperating elements are possible. Some of those variants are described above.

[0048] For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the claims and disclosure may include embodiments having combinations of all or some of the features described. It may be understood that the embodiments shown have the same or similar components, apart from where they are described as being different.

[0049] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word comprising does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words a and an shall not be construed as limited to only one, but instead are used to mean at least one, and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to an advantage. Many variants will be apparent to the person skilled in the art as long as they are comprised within the scope of the invention defined in the following claims.