Offshore Wind Turbine Foundation

Abstract

Offshore structure that is provided with a supporting system with one, two, three or more suction buckets (1) to be installed in the seabed, which buckets are fastened to the rest of the foundation system and with a star-shaped, seen in top view, connector body (6) of reinforced mineral cement concrete with the same number of external corners as there are suction buckets, which external corners are formed by the radial outwardly extending arms which provide the star shape and with a single vertical central column (5) placed centrally between the suction buckets, seen in top view, formed by a single tube and made of e.g. thin-walled steel, which carries the gondola of the windmill at its top, the gondola with the rotor blades at least 20 meters above the local water level.

Claims

1. (canceled)

2. (canceled)

3. (canceled)

4. (canceled)

5. (canceled)

6. (canceled)

7. (canceled)

8. (canceled)

9. (canceled)

10. (canceled)

11. An offshore structure that is provided with a supporting system with one, two, three, or more suction buckets to be installed in a seabed, wherein the suction buckets are fastened to the rest of a foundation system, wherein the offshore structure comprises a star-shaped connector body of reinforced mineral cement concrete with the same number of external corners as there are suction buckets, wherein external corners are formed by arms that extend radially outward and provide the star shape, wherein a floor or roof of the star-shaped connector body is level with a top bulkhead of a suction bucket, and wherein the top bulkhead of the suction bucket is provided by reinforced mineral cement concrete and simultaneously provides the floor or roof, respectively, of the star-shaped connector body.

12. The offshore structure according to claim 11, wherein the top bulkhead of the suction bucket and the floor or roof of the star-shaped connector body are integrated parts.

13. The offshore structure according to claim 11, wherein a single vertical central column is placed centrally between the suction buckets, seen in top view, and wherein the single vertical central column is formed by a single tube, which is configured to carry a gondola of a windmill at its top such that the gondola has rotor blades at least 20 meters above a local water level.

14. The offshore structure according to claim 13, where, if completely installed: the single vertical central column, the star-shaped connector body, and the suction buckets are rigidly mounted so that all loads (including vertical and horizontal loads), bending moments, and torsion are transmitted from the single vertical central column to the suction buckets via the star-shaped connector body; an attachment of the single vertical central column to the star-shaped connector body or of the star-shaped connector body to the suction buckets is arranged as a beam of which a single longitudinal end is fixedly wedged so that the single vertical central column extends vertically upwards from the star-shaped connector body; each suction bucket extends vertically downwards from the star-shaped connector body, as a cantilever beam, in other words the single vertical central column is above the connector body; or each suction bucket is below the star-shaped connector body, free from structures that transfer mechanical loads from the single vertical central column onto the seabed.

15. The offshore structure according to claim 13, wherein the foundation system: extends less than 15 meters above a local seabed; and is located completely below the highest point of the star-shaped connector body, and wherein, only in an area downwards from the highest point of the star-shaped connector body are there any structures that: (i) extend from the star-shaped connector body; (ii) are attached to the single vertical central column; and (iii) transfer any load from the single vertical central column to the seabed.

16. The offshore structure according to claim 11, wherein the floor or roof of the star-shaped connector body completely covers a space enclosed by an outer circumference of an axial wall of the suction bucket and also extends outside the outer circumference at all radial locations.

17. The offshore structure according to claim 11, wherein the floor or the roof of the star-shaped connector body provides a gas-tight, oversized, uninterrupted cover of an axial wall of the suction bucket.

18. The offshore structure according to claim 11, wherein the star-shaped connector body comprises: a floor plate and a roof plate, wherein the floor plate and the roof plate are mutually opposite and spaced; and two web plates, wherein the two web plates are mutually opposite, spaced, and bridge the floor and roof plate such that these four plates provide a box shaped structure that extends horizontally.

19. The offshore structure according to claim 18, wherein the offshore structure is configured to allow a mast to pass through a roof plate or to end above the roof plate.

20. The offshore structure according to claim 11, wherein the star-shaped connector body comprises: a floor plate and a roof plate, wherein the floor plate and the roof plate are mutually opposite and spaced; and two web plates, wherein the two web plates are mutually opposite, spaced, and bridge the floor and roof plate, and wherein a thickness of at least one of the floor plate, the roof plate, and the web plate is between 5 times and 30 times a thickness of an axial wall of the suction bucket.

21. The offshore structure according to claim 20, wherein the top bulkhead of a suction bucket comprises a downward-directed flange, and wherein the downward-directed flange overlaps with and is fastened to a top part of an axial wall of the suction bucket to provide: (i) a load transfer between the star-shaped connector body and the suction bucket or (ii) a gas-tight connection of the top bulkhead to the axial wall of the suction bucket, which is usable to generate a vacuum within the suction bucket that sucks the suction bucket into a sea bottom.

22. The offshore structure according to claim 21, wherein the downward-directed flange is configured to extend completely around the axial wall of the suction bucket, and wherein the downward-directed flange: is made of concrete; is cast against the axial wall of the suction bucket; is integrated into the top bulkhead; encloses the axial wall of the suction bucket internally and externally; or is sandwiched between a flange pair.

23. The offshore according to claim 21, further comprising: anchor elements configured to penetrate the axial wall of the suction bucket and the downward-directed flange to increase a loading capacity; a sealing element of neoprene or other elastomeric material applied in a joint between the axial wall of the suction bucket and the top bulkhead, wherein the sealing element improves the gas-tight connection; prestressed tendons of steel embedded internally into the roof plate, the floor plate, or the web plates, wherein a cross-sectional diameter of the prestressed tendons is between 25 mm and 60 mm; a tendon built-up of multiple strands, each with a cross-sectional area of between 100 mm.sup.2 and 200 mm.sup.2; a connector body having, arranged in a central area, a first connection area that is prepared and arranged to connect a wind turbine mast to the connector body; or a connector body having, at a distal end of each arm, a second connection area that is prepared and arranged to connect a suction bucket to the connector body.

24. A star-shaped connector body for use in the offshore structure according to claim 11.

Description

[0037] The invention is further illustrated by way of non-limiting, presently preferred embodiments providing the best way of carrying out the invention and shown in the drawings, showing:

[0038] FIG. 1A-C a first example of a connector body from three different angles; FIG. 2-4 a perspective view of a second, third and fourth example of a connector body, respectively; FIG. 5A-C a perspective view, of exploded type, of three alternative ways of mounting the monopole to the supporting system; FIG. 6-8 in side view the three main phases during a possible manner of installing the offshore wind energy installation; FIG. 9 a double slip joint in section from the side; FIG. 10-11 the cross section A-A and B-B of a modification of the FIG. 2 connector body, fabricated from reinforced mineral cement concrete; FIG. 12-23 a further embodiment in different views, wherein the connector body is fabricated from reinforced mineral cement concrete.

[0039] FIG. 1 shows three suction buckets, on top of it a star shaped connector body having three arms, each radially outward converging, and there above a single upright tube providing a mast. The lower part of the mast has a conical shape.

[0040] FIG. 2 shows three suction buckets, there above a triangular shaped connector body and there above a prismatic mast. The water level 100 is also illustrated. FIG. 3 shows four suction buckets, a star shaped connector body having four arms and above it a prismatic mast. FIG. 4 shows a star shaped connector body having three arms and a prismatic mast. At the radially outer end of each of its three (FIG. 4) or four (FIG. 3) arms, or at each of its three corners (FIG. 2), the connector body is mounted to a suction bucket 1.

[0041] In FIG. 5A the lower end of the mast penetrates the connector body. In FIG. 5B the lower end of the mast penetrates a from the connector body upwards projecting coupling tube. In FIG. 5C the coupling tube penetrates the lower end of the mast. In all three cases the slip joint can be applied.

[0042] According to FIG. 6, the suction buckets and connector body provide a sub assembly separate from the mast. This subassembly was sailed to its final offshore location and there the suction buckets were penetrated into the sea bed. After that part of the lower part of the mast (e.g. the monopole) was added (FIG. 7) and after that the upper part of the mast (e.g. tower) was added (FIG. 8). The relative location of the water line during tow (WLtow) and if the installation of the structure at the final offshore destination is completed (WLfinal) and of the sea bottom (ML) are indicated.

[0043] Different from FIG. 6-8, an alternative manner of installation is to sail the subassembly shown in FIG. 7 (buckets, connector body 6 and monopole 5 mutually assembled at a remote location) to the final offshore location and install it there, after which the payload (e.g. tower+wind turbine) is added.

[0044] FIG. 9 shows an inner tube, e.g. the monopole, and an outer tube, e.g. the wall of the central hole of the connector body to receive the monopole. Each tube is provided with two axially spaced conical rings, providing two pairs of each an inner ring of the inner tube and an outer ring of the outer tube. Due to the downward directed force Fv, oriented according to the gravity force, the radially inward directed clamping forces are generated (only shown for the upper pair).

[0045] The connector 6 body typically comprises a floor plate and a roof plate, mutually opposite and spaced, and two web plates, mutually opposite and spaced and bridging the floor and roof plate, such that these four plates provide a box shaped structure, extending horizontally. The monopole 5 e.g. passes through the roof plate (viz. FIG. 5A) or ends above the roof plate (viz. FIG. 5B or 5C). The floor plate and/or the roof plate preferably comprise a central section and at least three arm sections extending radially outward from the central section, to provide a star shaped plate.

[0046] Preferably, the thickness of at least one of the floor plate, roof plate and web plate, is at least 5 or 10 and/or less then 20 or 30 times the thickness of the axial wall of the suction bucket.

[0047] FIG. 10-11 show ballast tanks 11 integrated within the connector body 6. Different from the FIG. 2 embodiment, the roof of the connector body 6 is level with the top of the suction buckets 1.

[0048] FIG. 12-21 show a further embodiment of the connector body. The floor of the connector body is level with the top of the suction bucket. Importantly, the top bulkhead of the suction bucket is provided by reinforced mineral cement concrete and simultaneously provides the floor of the connector body, thus the top bulkhead and the floor are integrated parts. As an alternative, e.g. based on the FIG. 10-12 embodiment, the top bulkhead of the suction bucket and the roof of the connector body could be integrated parts.

[0049] The floor (and thus the top bulkhead) completely covers the space enclosed by the outer circumference of the axial wall of the suction bucket and also extends outside said outer circumference at all radial locations. Thus, the floor (or the roof in case of the alternative embodiment) provides an gas tight oversized uninterrupted cover of the axial wall of the suction bucket.

[0050] As FIGS. 15, 17, 18 and 20 show, the top bulkhead is provided with a downward directed flange 2 (length e.g. at least 10 centimetre) overlapping with and fastened to the top part of the axial wall 1 (i.e. the cylindrical wall) of the suction bucket, for load transfer between the connector body and the suction bucket and/or for a gas tight connection of the top bulkhead to the axial wall of the suction bucket, required to be able to generate a vacuum within the suction bucket to suck the bucket into the sea bottom. Preferably, this flange 2, extending completely around the axial wall of the suction bucket, is one or more of: made of concrete; cast against the axial wall of the suction bucket; integral part of the top bulkhead; encloses the axial wall of the suction bucket internally and externally (e.g. the axial wall of the suction bucket is embedded in the flange (viz. FIG. 15), or is sandwiched between a flange pair (viz. FIG. 20). Preferably, anchor elements 3 penetrate the axial wall of the suction bucket and the flange, to increase the loading capacity.

[0051] Preferably, a sealing element 4, e.g. of neoprene or other elastomeric material, is applied in the joint between the axial wall of the suction bucket and the top bulkhead, to improve the gas tight connection.

[0052] FIG. 16-18 show the cross sections indicated in FIG. 15. Prestressing tendons, preferably of steel, are embedded internally of each of the roof plate, floor plate and web plates. Preferred tendon cross section diameter: at least 25 or 30 and/or less than 50 or 60 millimetre. Preferably, a tendon is build up of multiple strands, e.g. et least four and/or less than fourty, each with a cross section of at least 100 or 140 and/or less than 200 or 150 square millimetre.

[0053] FIG. 19-20 show design details of the connection between the mast and the connector body, and of the connection between the connector body 6 and the suction bucket 1, respectively. The connector body has, preferably arranged in the central area, a first connection area that is prepared and arranged to connect a wind turbine mast 5 to the connector body. The connector body has, preferably at the distal end of each arm, a second connection area that is prepared and arranged to connect a suction bucket to the connector body.

[0054] FIG. 21-23 show design alternatives for the tendons.

[0055] The invention is not limited to the above described and in the drawings illustrated embodiments. E.g. the marine structure can have a different number of suction buckets. The drawing, the specification and claims contain many features in combination. The skilled person will consider these also individually and combine them to further embodiments. Features of different in here disclosed embodiments can in different manners be combined and different aspects of some features are regarded mutually exchangeable. All described or in the drawing disclosed features provide as such or in arbitrary combination the subject matter of the invention, also independent from their arrangement in the claims or their referral.