STRUCTURES FOR OFFSHORE INSTALLATIONS

Abstract

A structure for mounting offshore installations such as wind turbines or oil and gas platforms. The structure comprises a base, a top piece, and a lattice structure connecting the base to the top piece. The sub-components of the structure can be pre-assembled prior to installation to facilitate ease of construction, or they may be transported to a pre-determined location and assembled on site.

Claims

1. An offshore structure comprising a base having one or more scour protection mattresses, each scour protection mattress comprising a series of portions which are attached together by attachment means.

2. The offshore structure according to claim 1, wherein the portions are concrete portions.

3. The offshore structure according to claim 2, wherein the portions are substantially cylindrical.

4. The offshore structure according to claim 1, wherein each scour protection mattress is integrally formed with the base.

5. The offshore structure according to claim 1, wherein the attachment means are cables.

6. The offshore structure according to claim 5, wherein the cables are polypropylene cables.

7. The offshore structure according to claim 1, wherein the attachment means form an attachment mechanism for attaching the scour protection mattress to the base.

8. The offshore structure according to claim 1, wherein the portions are substantially cylindrical.

9. A method of installing an offshore structure comprising a base having one or more scour protection mattresses, each scour protection mattress comprising a series of portions which are attached together by attachment means, the method comprising the steps of: storing each scour protection mattress in a curled or rolled up configuration during a base transportation and installation process; and after positioning the base on the seabed, releasing each scour protection mattress such that the portions unfold down onto the seabed.

10. The method according to claim 9, wherein in the curled or rolled up configuration prior to deployment, the centre of mass of each scour protection mattress remains outside a pivot point of connection to the base such that, when released, each scour protection mattress will unfold and deploy around the base under its own weight.

Description

DRAWINGS

[0044] Specific embodiments of the invention are now described by way of example and with reference to the accompanying drawings in which like numerals are used to indicate like parts and where:

[0045] FIG. 1 shows a structure according to the present invention installed with a wind turbine;

[0046] FIG. 2 shows the three main sub-components of the invention of FIG. 1;

[0047] FIG. 3 shows a base and a load-transferring lattice of FIG. 2;

[0048] FIG. 4 shows the base of FIG. 2;

[0049] FIG. 5 shows the underside of the base of FIG. 4;

[0050] FIG. 6 shows a cross-section through the line A-A of the base of FIG. 4;

[0051] FIG. 7 shows an alternative view of FIG. 6 additionally comprising a pre-cast shim;

[0052] FIG. 8 shows the base of FIG. 4 additionally comprising integrated scour protection mattresses;

[0053] FIG. 9 shows the load-transferring lattice of FIG. 2;

[0054] FIG. 10 shows a basal ring of the load-transferring lattice of FIG. 9;

[0055] FIG. 11 shows a foot node of the load-transferring lattice of FIG. 9;

[0056] FIG. 12 shows the top ring of the load-transferring lattice of FIG. 9;

[0057] FIG. 13 shows a top node of the load-transferring lattice of FIG. 9;

[0058] FIG. 14 shows the top node of FIG. 13 viewed from below;

[0059] FIG. 15 shows the top piece of FIG. 2;

[0060] FIG. 16 shows a cross-section through the line B-B of the top piece of FIG. 15;

[0061] FIG. 17 shows an alternative view of the top piece of FIG. 2;

[0062] FIG. 18 shows a cross-section through the line C-C of the top piece of FIG. 17;

[0063] FIG. 19 shows the top piece of FIG. 15 viewed from below; and

[0064] FIG. 20 shows a structure of the present invention mounted on a seabed.

SPECIFIC EMBODIMENTS OF THE INVENTION

[0065] Referring now to the drawings, FIG. 1 shows a structure 1 (or gravity jacket foundation) according to the present invention for mounting an offshore installation thereon, e.g. a wind turbine 2.

[0066] The sub-components of the structure 1 are shown in more detail in FIG. 2 and include a base 4 (or gravity slab), a load-transferring lattice 6 (or hyperboloid jacket), and a top piece 8 (or gravity transition piece).

[0067] The base 4 sits on the seabed SB (FIG. 20) and acts as a load spreader, managing the pressure exerted on the seabed by the structure 1. The lattice 6 reduces the hydrodynamic forces experienced by the structure 1 and transfers the forces impacted by the installation (e.g., the wind turbine 2) through the wave zone to the seabed. The top piece 8 acts as the principle mass for the structure 1. It stresses the struts of the lattice 6 and contributes to good frequency characteristics. The sub-components combine to reduce loads induced through hydrodynamics on the structure 1, while remaining a stiff, massive structure with good frequency characteristics. The design is capable of accommodating a wide range of different types of wind turbine 2 (and other installations) and reduces the forces applied to the seabed thereby avoiding the need for seabed preparation. The structure 1 can significantly reduce offshore construction times by avoiding the need for piling and seabed preparation.

[0068] FIGS. 4 to 7 show a base 4 cast from concrete and having three mating interfaces 10 for mounting the lattice 6 onto the base 4. Each mating interface 10 is located at an apex of the base 4 and has tapered sides 12 to simplify the installation processes through reducing the positional tolerance required to locate the lattice 6. The base 4 includes an aperture 14 extending from an upper surface 16 of the base 4 through to a lower surface 18 of the base 4. The base 4 includes six tapering surfaces 20, each surface 20 extending upwards from a lower surface 18 of the base 4 towards the aperture 14.

[0069] In this example, the mating interfaces 10 on the base 4 are shown as female connecting parts but male connecting parts (or a mixture of male and female connecting parts) could also be provided. FIG. 7 shows an additional pre-cast weighted shim 22 that can be introduced into a female mating interface 10 to permit any deviations in the level of the structure 1 to be rectified on the seabed. In an alternative arrangement where the mating interface 10 of the base 4 includes male connecting parts, a pre-cast weighted tubular or substantially conical sleeve (not shown) can be used for a similar purpose.

[0070] FIG. 8 shows how scour protection mattresses 24 can be attached to an outer edge of the base 4. Seven mattresses 24 are shown in FIG. 8 and are each formed from a series of tubular concrete sections 26 which are connected and held together by polypropylene cables. A single mattress 24 is shown tied up in a curled or rolled up position prior to deployment. The remaining mattresses 24 are all shown in the deployed position. Once the base 4 has been mounted at its preferred location, the mattresses 24 are untied and the concrete portions are allowed to unfold onto the seabed under the natural weight of the concrete sections themselves.

[0071] FIGS. 9 to 14 show the main sub-components of the lattice 6, in particular a basal ring 28, a top ring 30, and three pairs of struts 32 extending substantially vertically between the basal ring 28 and the top ring 30. The struts 32 are cast from concrete as hollow tubular members.

[0072] The basal ring 28 includes three base nodes 34 and three base struts 36 as can be seen in FIG. 10. Each base node 34 includes a pair of protrusions 60 for receiving an end of a respective base strut 36 such that adjacent base nodes 34 are connected together by a base strut 36. Each base node 34 also includes a pair of protrusions 62 for receiving a lower end of a respective substantially vertically extending strut 32. The base nodes 34 and base struts 36 are cast from concrete, the latter being formed as hollow tubular members. Cables can be routed through the hollow interior of the vertically extending struts 32 and through cable ducts that are formed in the base nodes 34. FIG. 3 shows how the lattice 6 is mounted onto the base 4 with the base nodes 34 of the basal ring 28 located in the mating interfaces 10.

[0073] The top ring 30 includes the six top nodes 38 and six top struts 40. Each top node 38 includes a pair of protrusions 64 for receiving an end of a respective top strut 40 such that adjacent top nodes are connected together by a top strut 40. Each top node 38 also includes a protrusion 66 for receiving an upper end of a substantially vertically extending strut 32. The top nodes 38 and top struts 40 are cast from concrete, the latter being formed as hollow tubular members. Cables can be routed through cable ducts that are formed in the top nodes 38. Each top node 38 includes an opening 42 to rout cables into the top piece 8.

[0074] The components of the basal ring 28 and top ring 30, as well as the substantially vertical struts 32 may be secured together through the use of industrial adhesives, mechanical mechanisms, such as locking pins, or other suitable means. The sub-components that comprise the structure 1 may incorporate load, or lifting, points such that the structure 1 may be conveniently secured to a crane, winch or other such device, for the deployment of it.

[0075] It will be readily appreciated that other designs of lattice 6 can be utilised. Also, the lattice 6 can have any suitable number of substantially vertically extending struts 32, nodes 34, 38 etc. as required for the overall design requirements of the structure 1.

[0076] FIGS. 15 to 19 show the top piece 8 which is cast from concrete. The top piece 8 has an upper surface 44 and a lower surface 46 and has sloping exterior walls 48 connecting the upper surface 44 to the bottom surface 46. A central recess 50 is located in the middle of the upper surface 44 to receive a mounting part of an installation such as a wind turbine 2. Mating interfaces 52 on the lower surface 46 provide a connection between the top piece 8 and the top ring 30 (or more particular, the top nodes 40) of the lattice 6. Empty regions or chambers within the top piece 8 define ballast tanks 54 which are also partially defined by internal walls 56 of the top piece. Openings 58 located at the mating interfaces 52 are in register with the opening 42 in each top node 38 to facilitate cable routing into the top piece 8.

[0077] In use, a structure 1 according to the present invention may be assembled prior to installation at a location, or the sub-components (i.e., the base 4, the lattice 6, and the top piece 8) may be transferred separately to the location and the structure 1 assembled on site. FIG. 20 shows a side view of a structure 1 of the present invention in use mounted on the seabed SB showing the structure 1 and how the sub-components are positioned in relation to the waterline WL.