Segmented suction bucket

Abstract

A suction bucket for a seabed foundation for an offshore facility is provided. The suction bucket is arranged for being embedded into a marine sediment. The suction bucket includes a lid and a sidewall. The sidewall is segmented into a first circumferential segment and at least a second circumferential segment. The first circumferential segment is connected with the second circumferential segment. The first circumferential segment and the second circumferential segment are attached to the lid of the suction bucket. Furthermore, the first circumferential segment and the second circumferential segment each contains at least one substantially planar section. Furthermore, a method to manufacture a suction bucket for a seabed foundation for an offshore facility is also provided.

Claims

1. A suction bucket for a seabed foundation for an offshore facility, the suction bucket arranged for being embedded into a marine sediment, the suction bucket comprising: a lid and a sidewall, wherein: the sidewall is segmented into a first circumferential segment and at least a second circumferential segment; the first circumferential segment is connected with the second circumferential segment, the first circumferential segment and the second circumferential segment are attached to the lid of the suction bucket; the first circumferential segment and the second circumferential segment each contain a plurality of substantially planar sections separated from each other by an edge with an angle formed between the substantially planar sections; the first circumferential segment and the second circumferential segment comprises a flange for facilitating connection of the first circumferential segment to the second circumferential segment; and the sidewall includes a plurality of box-shaped corner elements arranged on an inner side of the sidewall.

2. The suction bucket according to claim 1, wherein: the first circumferential segment comprises a first planar section and at least a second planar section, the first planar section is separated from the second planar section by an edge, and an angle between the first planar section and the second planar section is smaller than one hundred and seventy degrees.

3. The suction bucket according to claim 2, wherein both the first planar section and the second planar section extend from a bottom of the suction bucket to the lid.

4. The suction bucket according to claim 1, wherein: the first circumferential segment comprises three, four or five planar sections, two adjacent planar sections are separated by a respective edge, and all edges are substantially parallel to each other.

5. The suction bucket according to claim 1, wherein the suction bucket comprises a substantially polygonal cross section in a plane substantially parallel to the lid.

6. The suction bucket according to claim 1, wherein a connection between the first circumferential segment and the second circumferential segment is a welded connection.

7. The suction bucket according to claim 1, wherein both the first circumferential segment and the second circumferential segment are made of steel.

8. The suction bucket according to claim 1, wherein the suction bucket further comprises a stiffening element, the stiffening element being a cross beam or a ring stiffener for increasing a stiffness of the sidewall of the suction bucket.

9. The suction bucket according to claim 1, wherein the suction bucket is reinforced by a reinforcement element which is arranged at an outside of the sidewall at a connection between the first circumferential segment and the second circumferential segment.

10. The suction bucket according to claim 9, wherein the reinforcement element is extended until a central portion above the lid of the suction bucket, where the central portion is arranged to be connected with a component of the offshore facility.

11. A method to manufacture the suction bucket for the seabed foundation for the offshore facility according to claim 1, the method comprising: providing the first circumferential segment, the second circumferential segment and the lid, connecting the first circumferential segment with the second circumferential segment such that the sidewall of the suction bucket is created, and attaching the first circumferential segment with the second circumferential segment to the lid of the suction bucket.

12. The method according to claim 11, wherein the connection between the first circumferential segment and the second circumferential segment is realized by hybrid arc welding.

13. The suction bucket according to claim 1, wherein the plurality of box-shaped corner elements are provided for every second circumferential segment of the sidewall.

14. The suction bucket according to claim 1, wherein the sidewall is cone shaped.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 shows a part of a wind turbine which is embedded into marine sediment by help of a suction bucket;

(3) FIG. 2 shows process of embedding the suction bucket into the marine sediment;

(4) FIG. 3 shows a process of embedding the suction bucket into the marine sediment;

(5) FIG. 4 shows a schematic example of a suction bucket in a perspective view;

(6) FIG. 5 shows a cross sectional view at the plane A-A′ of the exemplary suction bucket of shown in FIG. 4;

(7) FIG. 6 shows a first embodiment of a suction bucket in a perspective view;

(8) FIG. 7 shows a second embodiment of a suction bucket in a perspective view;

(9) FIG. 8 shows a first design of the segmented sidewall of the suction bucket in a perspective view;

(10) FIG. 9 shows the first design of the segmented sidewall of the suction bucket in a cross-sectional view;

(11) FIG. 10 shows a second design of the segmented sidewall of the suction bucket in a perspective view;

(12) FIG. 11 shows the second design of the segmented sidewall of the suction bucket in a cross-sectional view;

(13) FIG. 12 shows a third design of the segmented sidewall of the suction bucket in a perspective view;

(14) FIG. 13 shows the third design of the segmented sidewall of the suction bucket in a cross-sectional view;

(15) FIG. 14 shows a fourth design of the segmented sidewall of the suction bucket in a perspective view;

(16) FIG. 15 shows the fourth design of the segmented sidewall of the suction bucket in a cross-sectional view;

(17) FIG. 16 shows a fifth design of the segmented sidewall of the suction bucket in a cross sectional view;

(18) FIG. 17 shows an enlarged view of a part of the fifth design as shown in FIG. 16;

(19) FIG. 18 shows a first example of a welded connection between two adjacent circumferential segments; and

(20) FIG. 19 shows a second example of a welded connection between two adjacent circumferential segments.

DETAILED DESCRIPTION

(21) In the following, the embodiments illustrated in the accompanying drawings are described in more detail. It is to be understood that the following description is only illustrative and non-restrictive. The drawings are only schematic representations, and the elements in the drawings are not necessarily to scale with each other. Furthermore, the drawings only show a limited number of components, or parts of components, and it is to be understood that further components not shown in the drawings may be present. The components shown are selected order to facilitate the understanding of the illustrated embodiments.

(22) FIG. 1 shows a part of a wind turbine which is embedded into marine sediment 22 by help of a suction bucket 30. A wind turbine is just an example of an offshore facility for which the suction bucket according to the embodiment is suited. Other examples for offshore facilities include gas or oil rigs (i.e. offshore gas or oil platforms) or substations for offshore wind farms.

(23) In FIG. 1, a part of a tower 12 of a wind turbine is illustrated, wherein the tower 12 is not directly mounted at the seabed foundation, i.e. the suction bucket 30. Moreover, the tower 12 is attached at the suction bucket 30 via a so-called transition piece 11. At the connection between the transition piece 11 and the tower 12, a platform 13 for providing easy access for service personnel is provided. Typically, the top end of the transition piece 11 is a few meters above sea level 21 during average tidal height of the sea 20.

(24) Suctions buckets for offshore facilities are usually huge structures with a diameter of no less than seven meters. In case that the offshore facility, such as the wind turbine, rests on one single foundation (which is referred to as “monopod”, compared to e.g. tripods or other jacket support structures), the diameter may even exceed fifteen meters. Suction buckets are usually manufactured by welding steel plates together into a cylindrical form on which a top plate, which is referred to as a lid, is placed. For instance, the lid is welded on top of the cylindrical walls leaving the bottom open. The structure is so designed as to be air and water tight when placed under sea level.

(25) When installing the suction bucket it is mounted on the seabed soil facing the aperture of the bucket unit downward. When the inside of the bucket is sealed by the seabed surface, the inside water and/or air is drained forcibly using a pump, resulting in difference of hydraulic pressure between inside and outside of the bucket unit. The suction force generated by the difference of pressure is used as a press force to submerge the bucket unit onto the seabed soil.

(26) The lid itself can in principle be removed after placement of the suction bucket in the seabed as it on some designs essentially serves no other purposes than provide an air tight sealing during placement. If so after removal, the top part of the bucket can be protected by another layer such as a grout material to prevent any material inside the bucket from being flushed away by the surrounding water flow.

(27) The suction bucket can be placed at its desired location as such without being connected to any of the structures that it is supposed to support, but can advantageously be placed when pre-mounted to a structure, e.g. a wind turbine support structure.

(28) FIGS. 2 and 3 schematically show the process of embedding a suction bucket 30 into the marine sediment 22. The suction bucket 30 comprises a sidewall 32 and a lid 31. The lid 31 is closely attached to the sidewall 32 at the top of the suction bucket 30. At the bottom 34 of the suction bucket 30, the suction bucket is open therefore, the structure of the suction bucket 30 resembles an upturned bucket, which is the reason why the suction bucket 30 is also named a “suction bucket”.

(29) The lid 31 comprises an opening 311. The opening 311 is destined for providing an access to a drainage channel 42. The drainage channel is configured to enable to forcibly drain water and/or air out of the inside of the suction bucket 30, the “cavity” 33 of the suction bucket 30. This process is realized by a suitable pump 41. In practice, the pump 41 may be located at the deck of a vessel and the drainage channel 42 may extend from the opening 311 of the lid 31 to the vessel, being located near the suction bucket 30.

(30) FIGS. 4 and 5 illustrate in schematic drawings an example of a suction bucket 30 according to the embodiment of the present invention. The exemplary suction bucket 30 comprises eight circumferential segments, namely a first circumferential segment 35, a second circumferential segment 36 and six further circumferential segments. The suction bucket 30 also comprises a lid, wherein the lid is not shown in FIG. 2 for sake of clarity. All eight circumferential segments extend from the bottom 34 of the suction bucket 30 to the top. In contrast to conventional designs of the “bucket skirt”, i.e. the sidewall of a suction bucket, the sidewall is not curved, i.e. round or bent, but contains a number of planar sections. In the example shown in FIGS. 4 and 5, each of the circumferential segments, in particular the first circumferential segment 35 and the second circumferential segment 36, is configured as one flat plate. These eight flat plates are arranged in a regular manner towards each other and are connected with each other via separate connection elements 39. The connection elements are arranged inside the suction bucket 30, i.e. in the cavity 33 of the suction bucket 30.

(31) The suction bucket 30 can thus be described as having a cylindrical shape with a polygonal cross section, as can be well discerned in FIG. 5, which is a cross section in the plane A-A′ of the suction bucket 30.

(32) FIG. 6 shows a first embodiment of a suction bucket 30 in a perspective view. The suction bucket 30 again comprises a plurality of circumferential segments, all of them extending from the bottom 34 of the suction bucket 30 to its top. At the top, a lid 31 is welded onto the circumferential segments which build the sidewall 32 of the suction bucket 30. The suction bucket 30 has a slightly coned shape, which means that the diameter of the suction bucket 30 at the bottom 34 is slightly smaller than at the top.

(33) FIG. 6 also shows reinforcement elements 37 arranged at the lid 31 for stabilizing the entire structure. The reinforcement elements 37 extend from the sidewall 32 to a central portion above the lid 31, wherein the central portion is prepared to receive a supporting element for supporting an offshore facility. In case of a wind turbine, the supporting element could e.g. be realized as a transition piece.

(34) FIG. 7 shows a second embodiment of a suction bucket 30 in a perspective view. The suction bucket 30 comprises a plurality of circumferential segments, all of them extending from the bottom 34 of the suction bucket 30 to its top. At the top, a lid is foreseen, but has been omitted in FIG. 7 in order to show a part of the cavity 33 of the suction bucket 30. The sidewall 32 of the suction bucket contains sixteen circumferential segments. Each circumferential segment comprises three planar sections. In addition, each circumferential segment comprises flanges at both ends (not visible in FIG. 7) for facilitating connection of adjacent circumferential segments with each other.

(35) The embodiment disclosed in FIG. 7 also comprises a plurality of cross-beams, which act as stiffening elements 38 for the suction bucket. The cross-beams extend from the sidewall to a central portion of the suction bucket 30. Again, the central portion is prepared to receive a supporting element for supporting an offshore facility.

(36) Another specific feature of the suction bucket 30 according to this embodiment are the reinforcement elements 37 which aim to reinforce the structure of the suction bucket 30. The reinforcement elements 37 are realized as T-bars. They extend from the central portion above the lid along the sidewall down to the bottom 34 of the suction bucket 30. Note that one reinforcement element 37 is provided for every second circumferential segment. Thus, in total, there are provided eight T-bars for further reinforcing and stiffening the structure of the suction bucket 30.

(37) FIGS. 8-15 show different design proposals for a sidewall 31 of a suction bucket 30. The proposals differ in the number, arrangement and design of the individual circumferential segments which together constitute the sidewall. FIGS. 8, 10, 12 and 14 illustrate perspective views of the different embodiments; FIGS. 9, 11, 13 and 15 show an enlarged view of a part of a cross-sectional view of the associated embodiment.

(38) In general, some designs are based on a plate-to-plate connection (optionally with a sealing in between), others rely on a connection joint wherein a separate structure, e.g. a T-beam, a simple (flat) plate or a box-like beam (in the form of a, hollow, tube), is placed in between the plates, or combinations thereof. The mentioned separate structure, which is also referred to as “connection element”, between each plate or every pair (or higher e.g. triple pair) of plates is to be provided as long as the distribution between these separate structures and plates follow an identical pattern around the full circumference of the suction bucket. The box-beam may comprise 4, 5, 6 or more sides, and thus represent a tube when placed along the circumferential segments.

(39) Further, each plate may advantageously comprise one or more bends out- or inwards, as seen from the inside of the suction bucket rather than being a plain flat surface. The bends point outwards, as this has proven to further strengthen the overall suction bucket structure and minimize an overall buckling of the bucket during placement in the seabed. In this respect, buckling is understood as an instability of a structure often observed at thin walled structures due to compressive stresses in the structure.

(40) The width (and height) of the plates can be matched to provide a certain diameter of the suction bucket, or the number of plates per suction bucket can be modified to the desired diameter. In the disclosed examples, the designs for mono-buckets are typically of an outer diameter of fifteen to twenty meters and ten meters in height, whereas the other suction buckets are designed for jacket support structures and are of a diameter of seven to twelve meters and exemplarily eight meters in height.

(41) FIG. 8 shows a perspective view of the first design of a segmented sidewall of a suction bucket. The sidewall 32 contains thirty-three identical circumferential segments, wherein a first circumferential segment is connected to a second one; the second one is connected to the first one and a third one; the third one is connected to the second one and a fourth one; and further on. All circumferential segments are arranged and prepared to be attached to a lid of the suction bucket.

(42) FIG. 9 shows an enlarged cross-sectional view of the first circumferential segment 35. The first circumferential segment 35 contains a first planar section 351 and a second planar section 352. Both planar sections 351, 352 extend from the bottom of the suction bucket to the lid (which is not visible in FIGS. 8 and 9). The first planar section 351 is arranged in an angle 357 of smaller than one hundred and seventy degrees with the second planar section 352. In other words, both planar sections 351, 352 are bent outwards. This has the technical effect of strengthening the structure and increasing the load bearing capacity of the suction bucket. As a consequence, the risk of buckling of the structure of the suction bucket, in particular of the sidewall, is reduced. This is particularly advantageous during the process of driving the suction bucket into the marine sediment, as relatively high forces apply on the structure of the suction bucket during the period.

(43) The first planar section 351 and the second planar section 352 are separated by an edge 356. At the opposite end of the planar sections, a flange 358 is provided, respectively. The function of the flange 358 is to facilitate connection of the first circumferential segment with adjacent segments. In the view shown in FIG. 9, the flange 358 adjacent to the second planar section 352 is connected with a flange 361 of the second circumferential segment 36, for instance.

(44) FIGS. 10 and 11 show a second design of a segmented sidewall. The overall structure is similar to the first design, therefore only the most relevant differences will be discussed below.

(45) The flanges 358 of the first circumferential segment 351 comprise a second bend such that a C-shape of the two end sections of the first circumferential segment 351 is created. Obviously, all circumferential segments are designed with this type of flanges.

(46) FIGS. 12 and 13, which illustrate a third design option for the segmented sidewall of a suction bucket, show box-shaped corner elements 301 which are provided for every second circumferential segment. These box-shaped corner elements 301 are another way to increase the stability of the structure without allowing an excessively high material consumption.

(47) Finally, FIGS. 14 and 15 show a design option with a reinforcement element 37 with a T-shape. These reinforcement elements 37 are arranged between the flanges 358, 361 of adjacent circumferential segments 35, 36. In addition, the reinforcement elements comprise one part, which is present at the outside of the suction bucket, i.e. which stands out from the sidewall. The reinforcement elements 37 disclosed in FIGS. 14 and 15 may well be designed such that they extend until a central portion above the lid, as e.g. shown in FIG. 7.

(48) FIGS. 16 and 17 show a fifth design of a segmented sidewall of a suction bucket. Again, the individual segments are designed and arranged such that they form a polygon in cross-sectional view. In other words, the sidewall has the characteristics of a closed loop composed by a plurality of straight lines.

(49) The example of FIG. 16 comprises twelve circumferential segments, namely the first circumferential segment 35, the second circumferential segment 36 and ten further circumferential segments. All circumferential segments are equal in size and shape, having an overall width 302. Each circumferential segment comprises three planar sections and two flanges. The planar sections are separated or sub-divided from each other by edges. The edges are oriented substantially parallel to each other.

(50) FIG. 17 is an enlarged view of the encircled section of FIG. 16, showing the first circumferential segment 35 in detail. It can be seen that the first circumferential segment 35 comprises a first planar section 351, a second planar section 352 and a third planar section 353. Each planar section is adjacent to an edge 356.

(51) Furthermore, the planar sections are “bent outwards” for increasing the structural stability of the suction bucket sidewall. In particular, the angle 357 between the first planar section 351 and the second planar section 352 is, in the exemplarily design of FIGS. 16 and 17, one hundred and fifty degrees. To give further dimensions, the diameter of the entire suction bucket is around six meter the individual circumferential segments are approximately 1.5 meters.

(52) Although depending on how the plates to be joined are designed, two overlapping flanges can be welded together in full length in just a few turns. Accordingly, the welded connection point(s) are placed within the suction bucket skirt, i.e. within the cavity delimited by the sidewall, along one flange side which provides sufficient bonding between the plates. Optionally the plates can be welded on both sides and even on the outside joint. This method is especially advantageous when a “tube” is placed between the plates, as welding within the hollow tube is rather difficult if not impossible.

(53) FIG. 18 shows an example of two overlapping flanges 358, 361 which are welded at (necessary) welding points 51 and optionally at additionally welding points 52.

(54) Similarly, FIG. 19 shows an example of two overlapping flanges 358, 361, in between which a reinforcement member 37, designed as a T-bar, is inserted. Again, (necessary) welding points 51 and (optionally) additional welding points 52 are illustrated.

(55) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(56) For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.