GB2624065A

GB2624065A - Apparatus and associated methods

Info

Publication number: GB2624065A
Application number: GB2311780.7A
Authority: GB
Inventors: Lima Roger; Kristian Johnsrud Jan
Original assignee: Aker Solutions AS
Current assignee: Aker Solutions AS
Priority date: 2023-07-31
Filing date: 2023-07-31
Publication date: 2024-05-08
Also published as: GB202311780D0

Abstract

A method of providing a buoyant concrete support structure 10 for an offshore installation, such as a wind turbine. A monolithic multicellular concrete member 11 is formed with at least five cells 14 arranged circumferentially around a central vertical longitudinal axis 20. The diameter of each cell is smaller than a diameter of a circumference along which the cells are arranged. The cells are formed as vertically-extending hollow elements with an enclosed bottom portion provided below a hollow central void 15 thereabove. The cells are formed contemporaneously such that all of the cells are integrally-formed with each other in unison to provide the seamless monolithic multicellular concrete member. The cells are coherent such that each cell shares a common wall portion 40 with an adjacent cell. A support structure formed using the method is also disclosed.

Description

APPARATUS AND ASSOCIATED METHODS

The present invention relates to a marine floating or semi-submersible support structure, particularly, but not exclusively, with or for an offshore renewable energy structure, such as a wind turbine or the like; and associated methods, such as of construction and/or installation thereof.

BACKGROUND

In various industries, such as the renewables and utilities industries, structures are often required to support the weight, and often other forces, associated with installations thereabove.

Such marine structures in offshore locations typically protrude above the sea level and are subjected to environmental conditions of tides, waves, weather, etc. Various anchoring and tethering systems have been employed for such offshore structures and installations.

Floating support structures often have pontoons for supporting associated structures, such as thereabove or alongside. Examples of support structures for offshore installations include buoyancy stabilised (semi-submersible) offshore floating wind support platforms; tension-leg offshore floating wind support platforms; and spar buoy offshore floating wind support platforms.

Floating structures can still be subjected oscillations in various directions. For example, heave, pitch and roll can all affect the orientation and stability of floating structures.

Stability and movement of the structures can be important in terms of primary functionality, such as operation of any wind turbines thereon; and also for access, maintenance, installation and durability, such as dependent upon frequencies and magnitudes of movements (e.g. harmonics, etc.).

It may be an object of one or more aspects, examples, embodiments, or claims of the present disclosure to at least mitigate or ameliorate one or more problems associated with the prior art, such as those described herein or elsewhere.

SUMMARY

According to an aspect, there is hereby disclosed a method of providing an at least partially floating support structure. The support structure may comprise a semi-submersible or floating support structure. The method may comprise deploying the support structure in a body of water such that at least a portion of the support structure may be submerged below a water line. Additionally, or alternatively, the method may comprise deploying the support structure in the body of water such that at least a portion of the support structure may protrude above the water line. Accordingly, in at least some examples, there is provided a method of deploying a support structure in the body of water such that at least a portion of the support structure protrudes above the water line and at least a portion is below the waterline. The support structure may comprise a concrete support structure.

The method may comprise providing a buoyant concrete support structure for an offshore installation. The buoyant support structure may comprise a hull. The buoyant support structure may comprise a pontoon/s. The buoyant support structure may define a buoyant or floating platform. The installation may comprise a wind turbine. The method may comprise forming a monolithic multicellular concrete member. The monolithic multicellular concrete member may comprise a plurality of cells arranged circumferentially around a central vertical longitudinal axis.

The plurality of cells may comprise at least five cells. The diameter of each cell may be smaller than a diameter of a circumference along which the cells are arranged. The circumference may pass through a centre of each cell. The plurality of cells may be arranged contiguously. The plurality of cells may be arranged contiguously to define an annular support. The annular support may be a continuous annular support.

The method may comprise forming the cells as vertically-extending hollow elements.

The method may comprise forming the cells with a hollow central void. The method may comprise forming the cells with an enclosed bottom portion. The method may comprise forming the cells with an enclosed bottom portion provided below the hollow central void thereabove.

The method may comprise forming the plurality of cells contemporaneously. The method may comprise forming the plurality of cells contemporaneously such that all of the cells are integrally-formed with each other. The method may comprise forming the monolithic multicellular concrete member seamlessly. The method may comprise forming the plurality of cells contemporaneously such that all of the cells are integrally-formed with each other in unison to provide the seamless monolithic multicellular concrete member. The plurality of cells may be coherent such that each cell shares a common wall portion with an adjacent cell.

Accordingly, in at least some examples, there is provided a method of providing a buoyant concrete support structure for an offshore installation, such as a wind turbine, the method may comprise; forming a monolithic mulficellular concrete member, the monolithic mulficellular concrete member may comprise a plurality of cells arranged circumferentially around a central vertical longitudinal axis of the member; wherein the plurality of cells may comprise at least five cells, with the diameter of each cell being smaller than a diameter of a circumference along which the cells are arranged, the plurality of cells being arranged contiguously to define an annular support; wherein the cells are formed as vertically-extending hollow elements with an enclosed bottom portion provided below a hollow central void thereabove; and wherein the method may comprise forming the plurality of cells contemporaneously such that all of the cells are integrally-formed with each other in unison to provide the seamless monolithic multicellular concrete member; and the plurality of cells are coherent such that each cell shares a common wall portion with an adjacent cell.

The method may comprise forming the member in a vertical casting process. The method may comprise using formwork and/or slip-forming. The method may comprise forming the member progressively from the bottom upwards. The method may comprise firstly forming the bottom portion of the member. The method may comprise initiating the member formation process at the bottom portion of the member. The method may comprise forming the cells progressively. The method may comprise forming the cells sequentially. The method may comprise forming the cells contemporaneously. The method may comprise forming the cells simultaneously. The method may comprise forming the cells continuously. The method may comprise forming the cells circularly concurrently, such as forming the annular support defined by the plurality of cells concurrently in a cohesive casting process, such as or like an upward extrusion process. The method may comprise providing the cells with a continuous wall thickness, at around at least a portion of the circumference and/or along vertical portions. The method may comprise providing a same cross-section as the member is formed upwardly. Alternatively, the method may comprise varying the cross-section, such as providing a taper/s as the member is formed upwardly.

The method may comprise spacing the cells at a separation from the central longitudinal axis of the structure such that the plurality of cells arranged circumferentially around the central longitudinal axis define a central space therebetween, the central space extending radially outwards from the structure's central longitudinal axis.

The diameter of the central space may be at least as large as the diameter of the surrounding individual cells that define the central space. The diameter of the central space may be at least 15 metres. In at least some examples, the diameter may be at least 20 metres. In larger examples, the diameter may be at least 25 metres. The cross-sectional area of the central space may be at least similar to the cross-sectional area of the surrounding individual cells that define the central space. The central space may comprise interstitial portions between the adjacent cells.

The method may comprise providing buoyancy by virtue of the cells. The cells may be entirely enclosed, at least when in use. The method may comprise at least partially filling one or more of the hollow central voids. The method may comprise at least partially filling one or more of the hollow central voids with ballast. The method may comprise at least partially filling one or more of the hollow central voids with fixed ballast. Additionally, or alternatively, method may comprise at least partially filling one or more of the hollow central voids with moveable ballast, such as water ballast (e.g. pumped or flowed into/out of and/or between the hollow central void/s). The method may comprise at least partially filling one or more of the hollow central voids with ballast such that the structure is balanced in use. The method may comprise at least partially filling one or more of the hollow central voids with ballast such that the structure is balanced in use, with the installation installed or mounted thereto or thereabove. The method may comprise distributing ballast across the plurality of cells.

The method may comprise distributing the ballast across the cells to balance the final installation when in use. The method may comprise distributing the ballast across the plurality of cells in varying amounts to accommodate any eccentricity or offset weight. For example, where an installation is fitted to the member, the ballast may be provided across the plurality of cells to balance the weight of the installation. The ballast may be fixed ballast, provided in advance of mounting or attachment of the installation.

Additionally, or alternatively, the ballast may be movable ballast (e.g. water ballast) provided in advance and/or after mounting or attachment of the installation. The method may comprise adapting the ballast.

The method may comprise enclosing the tops of the cells during the cell formation process. The method may comprise enclosing the tops of the cells with a deck element. The method may comprise enclosing the top of each cell with a respective deck element. Alternatively, the method may comprise enclosing the tops of a plurality of cells with a single, common deck element.

In at least some examples, the central space may define a moonpool. The moonpool may be open at the top and at the bottom, comprising a hollow central column within the member.

Alternatively, the central space may define an additional, central cell, such that the monolithic multicellular member comprises at least six cells.

The method may comprise connecting the offshore installation, such as the wind turbine, to the buoyant support structure. The method may comprise transporting the buoyant support structure to a marine deployment location. The marine deployment location may comprise the usage location of the installation, such as an offshore wind site. The method may comprise positioning the buoyant support structure. The method may comprise connecting the offshore installation to the buoyant support structure prior to positioning of the buoyant support structure at the marine deployment location.

Optionally, the method may comprise connecting the offshore installation to the buoyant support structure prior to transportation of the buoyant support structure to the marine deployment location. For example, the method may comprise connecting the offshore installation to the buoyant support structure whilst the buoyant support structure is moored at a quayside or the like. Alternatively, the method may comprise connecting the installation subsequent to transportation and optionally positioning of the buoyant support structure. For example, the buoyant support structure may be transported (e.g. towed or carried) to the marine deployment location without the installation connected thereto; with the buoyant support structure being positioned at the marine deployment location (e.g. at final usage position) and then the installation connected offshore to the buoyant support structure.

The method may comprise providing the buoyant support structure below the offshore installation. The method may comprise providing the buoyant support structure below the offshore installation such that a footprint of the offshore installation falls within a footprint of the support structure. For example, the installation may comprise a tower (e.g. tower for VVTG nacelle), with the footprint of the tower optionally falling entirely within the footprint of the support structure. In other examples, the footprint of the offshore installation may extend beyond the footprint of the support structure. The footprint may be defined by a periphery or circumference when viewed in plan view, of the buoyant support structure. In some examples, the periphery or circumference of the installation (e.g. when viewed in plan view) may fall entirely within the periphery or circumference of the support structure. In other examples, the periphery or circumference of the installation may extend beyond the periphery or circumference of the support structure. The footprints may overlap. The periphery or circumference of the installation may be entirely outside the periphery or circumference of the support structure. In at least some examples, the footprint of the offshore installation may fall within a footprint of a single cell, when installed (e.g. entirely within). The installation may comprise a tower (e.g. tower for VVTG nacelle), with the footprint of the tower optionally falling entirely within the footprint of the support structure; even within the footprint of a single cell in some examples. In other examples, the footprint of the offshore installation may overlap and/or extend beyond a footprint of a single cell, when installed.

The method may comprise forming the cells with a wall thickness between 5% and 15% of a radius of the cell.

The method may comprise providing the coating contemporaneously with the formation of the buoyant support structure. The method may comprise initiating the coating process prior to completion of the buoyant support structure formation process. The method may comprise performing the coating process during the buoyant support structure formation process.

The method may comprise performing the coating process using a same apparatus or equipment as the buoyant support structure formation process. For example, the buoyant support structure may be formed using a formation system, such as a casting system. The casting system may comprise a continuous casting system. The casting system may comprise a slipforming system. The formation system, such as the casting system, may comprise a frame or framework. The method may comprise progressively or incrementally moving the formation system during formation of the member. For example, the method may comprise progressively moving at least a portion of formation system upwards as the member is formed. The method may comprise forming the plurality of cells progressively, simultaneously. Each of the plurality of cells may be progressively formed upwards contemporaneously with the upward formation of the other, adjacent cells. The method may comprise applying the coating with or from apparatus, frames or equipment used or available for the formation process/es. For example, the coating may be applied using a frame, platform, support or other access apparatus for forming the support member. Accordingly, the method may comprise applying the coating without requiring the positioning of such apparatus, frames or equipment for applying the coating after the formation of the support member.

Accordingly, in at least some examples, the member can be provided with a coating thereon, at least on a portion/s of the member. For example, the coating may correspond to a chromatic coating for compliance with maritime regulations or guidelines on visibility of marine or offshore installations or structures. The coating may be applied or provided at portions of the member potentially visible at or above the water-line during or after deployment of the buoyant support structure. For example, a lower portion of the member may be uncoated, with the method comprising initiating the coating process once the support member has been formed to a sufficient height to define or start to define a portion/s of the member that could be sufficiently close to or above the water-line to require chromatic coating (e.g. typically yellow).

According to an aspect, there is provided an at least partially floating support structure. The support structure may comprise a semi-submersible or floating support structure. In use, when deployed, at least a portion of the support structure may be submerged below a water line. Additionally, or alternatively, in use, when deployed, at least a portion of the support structure may protrude above the water line. Accordingly, in at least some examples, there is provided a support structure with at least a portion above the water line and at least a portion below the waterline, when deployed. In some examples an entirety of the support structure may be submerged below the waterline, in use. The entire support structure may be submerged, with the support structure defining a fully submerged hull/s. The support structure may comprise a deep-floater or a spar. An upper body or support may extend above the support structure. The upper body or support may be smaller relative to the support structure therebelow. The upper body or support may extend to surface/topsides. The upper body or support may also comprise a plurality of cells. The cells of the upper body or support may be smaller, relative to those of the fully-submerged support structure therebelow (e.g. of smaller diameter and/or axial/vertical extent). The upper body or support may at least partially protrude above the waterline.

Accordingly, there may be provided a buoyant concrete support structure for an offshore installation. The offshore installation may comprise a wind turbine. The buoyant support structure may comprise a monolithic multicellular concrete member.

The monolithic multicellular concrete member may comprise a plurality of cells arranged circumferentially around a central vertical longitudinal axis of the member.

The plurality of cells may comprise at least five cells. The cells may be vertically-extending hollow elements. The cells may comprise an enclosed bottom portion provided below the hollow central void thereabove. The plurality of cells may be provided as a monolithic structure or member. The plurality of cells may be integrally-formed with each other. The plurality of cells may be integrally-formed with each other in unison to provide a seamless monolithic multicellular concrete member. The plurality of cells may be coherent such that each cell shares a common wall portion with an adjacent cell.

Accordingly, in at least some examples, there is provided a buoyant concrete support structure for an offshore installation, such as a wind turbine, the support structure comprising; a monolithic multicellular concrete member, the monolithic multicellular concrete member comprising a plurality of cells arranged circumferentially around a central vertical longitudinal axis of the member; wherein the plurality of cells comprises at least five cells, with the diameter of each cell being smaller than a diameter of a circumference along which the cells are arranged, the plurality of cells being arranged contiguously to define an annular support; wherein the cells are vertically-extending hollow elements with an enclosed bottom portion provided below a hollow central void thereabove; and wherein the plurality of cells are integrally-formed with each other in unison to provide a seamless monolithic multicellular concrete member; and the plurality of cells are coherent such that each cell shares a common wall portion with an adjacent cell.

Each cell may comprise a hollow cell. Each cell may define a chamber therewithin.

Each cell may be closed or enclosed at its bottom or lower end. Each cell may be permanently closed or enclosed at its bottom or lower end. Each cell may be sealably closed or enclosed at its bottom or lower end. Each cell may comprise a bucket. The/each cell may be vertically oriented. For example, each cell may comprise a longitudinal axis, such as associated with a longitudinal shape of the cell, such as a prismatic shape; and the longitudinal axis may be vertically oriented.

The plurality of cells may be arranged around a central point or axis. The central axis may be a vertical axis. The plurality of cells may be peripherally or circumferentially arranged, such as along or around a periphery or circumference. The circle, along which the plurality of cells is circumferentially arranged, may pass through a centre of each cell. The diameter of each cell may be smaller than a diameter of a circumference or circular path along which the cells are arranged. The circumference may pass through a centre of each cell. The plurality of cells may be arranged contiguously. The plurality of cells may be annularly arranged. The plurality of cells may be arranged contiguously to define an annular support. The annular support defined by the plurality of cells may be a continuous annular support. The annular support may comprise a lobed annular support. The lobes of the lobed annular support may be defined by portions of the constituent cells, such as an outer circumference or periphery of the constituent cells.

Each cell may comprise an annular wall extending from the bottom to the top. At least one of the cells may be a cylindrical structure configured to support a tower. The tower may be arranged off-center of the buoyant or floating structure. The support structure may comprise a column or post for mounting the tower thereon or thereto. At least part of the height of the column or post may be accommodated within the height of the buoyant support member. In at least some examples, the part of the height of the column or post is received within a single cell of the buoyant support member.

Alternatively, instead of an intermediate or connecting column/post, at least part of the height of the tower may be accommodated within the height of the buoyant support member (e.g. directly therewithin). In at least some examples, the part of the height of the tower is received within a single cell of the buoyant support member.

The cell may comprise a cylindrical profile. The cell may comprise a vertically-oriented cylinder with a central longitudinal axis of the cylinder being vertically oriented. The cylinder may comprise a hollow cylinder. The cylinder may comprise an open central portion for accommodating buoyancy and/or ballast material therein.

The cell may comprise a thin-walled element. For example, the wall thickness of the wall defining the cylinder may comprise a thickness of at least an order of magnitude less than a radius of the cylinder. The cell may be formed of or from concrete. The method may comprise prefabricating the cells at a location remote from the location for installation or deployment.

The plurality of cells may each define a pocket or compartment within the member, such that a plurality of pockets or compartments are provided in the monolithic support member.

The cells may be dimensioned to each only comprise a diameter considerably smaller than that of the annular support region defined by the plurality of cells. The plurality of cells may be laterally arranged to define the annular support region. The plurality of cells may be non-concentrically arranged. The center of each cell may be non-coincident with the other cells. The plurality of cells may be arranged around a common centrepoint, such as corresponding to a vertical, central longitudinal axis of the installation when installed. The plurality of cells may be distributed, such as evenly distributed, around the centrepoint. The plurality of cells may be arranged in an annular pattern centered on the longitudinal axis of the installation, the annular pattern defining the annular support region. When formed, the plurality of cells may be horizontally laterally arranged. The plurality of cells may be horizontally spaced from each other.

The plurality of cells may all comprise a similar height; and/or a similar depth when installed. In at least some examples, the bottoms of all the cells may be on a same horizontal plane as each other. The respective tops of all the cells may be on a same horizontal plane as each other. The tops of the plurality of cells may define the horizontal plane of a deck level of the structure.

The plurality of cells formed in the support member may all comprise a similar type. For example, each of the plurality of cells may comprise one or more same or similar properties and/or configuration/s, such as of shape/s and/or dimension/s. The support member may comprise a plurality of similarly-proportioned cells, regularly arranged about a central longitudinal, vertical axis for the support member.

The shared common wall portion may extend along an arc or a chord of the cell's perimeter or circumference. The common wall portion may lie on the circle along which the plurality of cells is circumferentially arranged. The shared common wall portion may define a secant or chord of the cell's perimeter. The shared common wall portion may extend along or through an arc or chord of each of the two cells common to the shared wall portion. The length of the common wall portion may comprise a percentage portion of the circumference or perimeter of the total cell wall. The length of the common wall portion may comprise a percentage portion of the circumference or perimeter of each associated total cell wall. The percentage may be between 5% and 20%. The percentage may be around 10%. The common wall portion may extend through an arc or angle of the cell of between around 20° and around 60°. The common wall portion may extend through an arc or angle of the cell of around 45°. The two common wall portions of each cell may be separated by an arc of the cell of between around 1000 to around 160°. The/each common wall portion may comprise a linear or flat wall portion.

The plurality of cells may be conjoined. Each cell may be conjoined with an adjacent cell. Each cell may share a common wall-portion with an adjacent cell. Each cell may be conjoined with two adjacent cells. Each cell may be conjoined with two adjacent cells: the two adjacent cells being on opposite lateral sides. Each cell may be conjoined with an adjacent lateral cell on a left side and another adjacent lateral cell on a right side.

Each cell may comprise two shared wall portions. Each cell may comprise two shared wall portions such that the total percentage of the circumference or perimeter of each individual cell defined by common walls may be twice that of an individual common wall. For example, the total percentage of the circumference or perimeter of each individual cell defined by common walls may be between 10% and 40%. The two respective common wall portions of each cell may be opposed, such as diametrically opposed.

The cells may each comprise a wall thickness of between 5% and 15% of a radius of the cell. The cell wall thickness may comprise at least 0,3 metres. The wall thickness of the common wall portions may be thicker than non-shared wall portions of the cells. The common wall portion may comprise a thickness twice that of non-shared wall portion/s. The common wall portion may comprise a thickness of at least 0,5 metres.

In at least some examples, the cell/s may be open at the top. The cell/s may be open at the top upon completion of the support member formation process. The monolithic concrete support member may comprise open-topped cells. At least after completion of the casting process, the cells may be open at their upper ends, the upper ends being below the installation when installed. The concrete support member may comprise open-topped cells as an interim component during the construction of the buoyant support structure.

In at least some examples, the cell/s may be closed at the top. The cell/s may comprise a cup-shape, at least as formed from concrete. The method may comprise enclosing the cells subsequent to the concrete formation step of forming the multicellular monolithic concrete support member. The cell may comprise a top cover. Accordingly, the cells may be enclosed at an upper end. The upper end may be below the installation when installed, such as below the tower or at least WIG. Each cell may be enclosed at an upper end by a respective end wall. Alternatively, the plurality of cells may be enclosed at their respective upper ends by a common end wall. The common end wall may comprise a circular or ring-shaped end wall; or an annular end wall formed of a plurality of conjoined circular or cylindrical walls corresponding in number and arrangement to the plurality of cells therebelow. The common end wall may be configured to correlate to the arrangement of the cells. For example, the common end wall may define or circumscribe a footprint or circle within which the cells are circumscribed. The end wall may comprise or define a deck/s. The end wall may comprise a metal end wall, such as a steel sheet. Alternatively the end wall may comprise a concrete component, such as a reinforced concrete slab.

The method may comprise enclosing the cell prior to installation of the cell. The method may comprise enclosing the cell prior to transportation of the cell to the location for deployment. The method may comprise enclosing the cell/s by placing the end wall/s or a top cover/s over the upper end of the cell/s. The method may comprise attaching the end wall/s or top cover/s to the cell/s.

The plurality of cells for forming a single installation support structure may all comprise a similar type. For example, each of the plurality of cells may comprise a similar configuration/s, such as dimension/s and/or a presence of a top cover/s. In at least some examples, the structure comprises a plurality of similarly-proportioned cells, regularly arranged about a central longitudinal, vertical axis of the support structure.

The cells may be spaced at a separation from the central longitudinal axis of the structure. The cells may be spaced at a separation from the central longitudinal axis of the structure such that the plurality of cells are arranged circumferentially around the central longitudinal axis. The cells may be spaced at a separation from the central longitudinal axis of the structure such that the plurality of cells are arranged circumferentially around the central longitudinal axis to define a central space therebetween. The central space may extend radially outwards from the structure's central longitudinal axis. A diameter of the central space may be at least as large as a diameter of the surrounding individual cells that define the central space. The diameter of the central space may be at least 15 metres. A cross-sectional area of the central space may be at least similar to a cross-sectional area of a surrounding individual cell that defines the central space. The cross-sectional area may be a horizontal planar cross-sectional area, such as when viewed in plan view.

The plurality of cells may be annularly arranged so as to define a central space or volume therebetween. The central volume or space may comprise an open space. The structure may comprise a central volume or space. The central volume or space may be arranged at/around the central vertical axis of the structure. The central volume or space may be defined by the plurality of cells therearound.

The central volume or space may comprise a moonpool. The central volume or space may comprise an opening. The central volume or space may comprise an opening at the top, at least during one or more phases of construction or installation. The central volume or space may comprise an opening at the bottom, at least during one or more phases of construction or installation. In at least some examples, the central volume may comprise an opening at the top and at the bottom, at least during one or more phases of construction or installation. The central volume or space may be permanently open at the top and/or the bottom. The central volume or space may define the moonpool.

Alternatively, the central volume or space may be closed or enclosed. The central volume or space may define an additional, central cell. The central space may define an additional, central cell such that the monolithic mulficellular member comprises at least six cells.

The support structure may comprise apparatus or devices within one or more of the cell/s and/or within the central volume or space. For example, a pull-tube/s may be provided within the central volume or space. The pull-tube may run along or outside a cell wall, such as mounted thereto or supported thereby. The pull-tube may be at least partially provided or housed in a pilaster, such as described in Applicant's UK patent application 2305918.1, the contents of which are incorporated herein by reference.

The plurality of cells may be enclosed at their tops by a deck element/s. The plurality of cells may be enclosed at their tops by a deck element/s, except for a single cell of the plurality. The exceptional single cell of the plurality may be configured to receive a portion of a column or post within its central void. The inner diameter of the single cell may be large enough to receive an outer diameter of the column or post therewithin. The inner diameter of the single cell may be larger than an outer diameter of the column/post. The single cell may be shaped and dimensioned to receive a portion, such as a length, of the column/post therewithin. The column/post may extend into the cell. The column/post may extend upwardly from the cell and protrude therefrom. The column/post may be configured to receive the tower. The column/post may provide an intermediate connection between the support member and the tower. The column/post may comprise an interface for attaching the tower. The interface may comprise a flange, such as for fastening the tower thereto. A vertical length of the post/column may overlap with a vertical length of the buoyant support structure, such as a vertical length of a cell of the buoyant support member. The post/column may be connected to the support member, such as by fastener/s. The post/column may comprise a metal post/column, such as a hollow steel pipe or tube.

The buoyant or floating support structure may comprise an at least partially submerged buoyant or floating structure. For example, the structure may comprise a positive buoyancy, but be positioned subsea, such as using tension, tethers, anchors and/or gravity supports (e.g. GBS) or the like. The floating structure may be selected from: semisubmersible; spar, tension-leg platform (TLP); and/or barge.

The structure may comprise a coating. The structure may comprise a coating over at least a portion of its surface. The structure may comprise the coating over an upper portion/s of its surface. The structure may comprise the coating over surface/s that may potentially be close to, at, or above the water-line, in use. The coating may comprise a pigment. The coating may comprise a paint. The coating may comprise a full-surface coating. The coating may comply with one or more regulations, such as national, local and/or international regulations or guidelines, such as for maritime safety.

The support member may comprise the coating. The support member may comprise an enhanced bonding with the coating. The support member may comprise a transition phase, layer or portion between the concrete and the coating. The transition phase, layer or portion may be associated with an enhanced bonding of the coating to the concrete (e.g. in comparison to an alternative without the transition phase, layer or portion). The transition phase, layer or portion may be associated with an application of the coating to the concrete before any intermediate layer has formed on the concrete.

The transition phase, layer or portion may comprise the coating and the concrete.

The installation may comprise a tower. The tower may be a single tower. The installation may comprise a single tower, the single tower extending upwards from the floating support structure therebleow. In at least some examples, the tower is positioned off-centre. The tower may be positioned off-centre, laterally-spaced from the central longitudinal vertical axis of the support structure. Particularly where a central moonpool is provided, the tower may be positioned off-centre, at a radial separation form the central vertical axis of the buoyant support structure, at or on the annular support region defined by the buoyant support member. Alternatively, the tower may be centrally-positioned, such as on and aligned with the buoyant support structure's central vertical axis.

The tower may be positioned directly above a single cell. The tower may be dimensioned and configured to be directly supported on a single cell therebelow. The tower may comprise at least a portion with a shape/s and dimension/s corresponding to a portion of the cell therebelow. The tower may be connected to the cell therebelow. The tower may be fixedly connected to the cell therebelow. The tower, when connected, may effectively form an upwardly-extending extension of the cell therebelow. The tower may comprise a portion with a circular cross-section with a dimension associated with or corresponding to a circular cross-section of the cell therebelow. The tower may be attached to the cell therebelow via the post-column located in the cell.

Alternatively, a vertical length of the tower may overlap with a vertical length of the buoyant support structure, such as a vertical length of a cell of the buoyant support member. For example, the tower or a portion thereof may be received in the cell, without use of an intermediate post/column.

According to at least some examples, there is provided a method of installing a buoyant support structure, the method comprising: installing the buoyant structure at a position to be below the offshore installation, such as the wind turbine tower/nacelle, the buoyant support structure providing a platform upon which to support the wind turbine tower/nacelle when installed; and installing the buoyant support structure to define at least an annular support region for the wind turbine tower/nacelle; and installing the wind turbine tower/nacelle above the buoyant support structure with the annular support region there below.

The method may comprise installing the structure at a marine location. The structure may comprise an offshore structure. The method may comprise installing the structure at an offshore location. The method may comprise installing the structure to be at least partially buoyant once installed. The method may comprise installing the structure to be floating once installed.

The method may comprise providing the structure below the installation such that the installation falls within a footprint, such as a periphery or circumference when viewed in plan view, of the buoyant support structure when installed; and wherein a central axis of the installation is vertically aligned with an axis of the buoyant support structure when installed. The axis may comprise the central vertical axis of the buoyant support structure. Additionally, or alternatively, the axis may comprise a central vertical axis of a single cell of the buoyant support structure.

The method may comprise transporting the installation and structure as a combined pre-assembled unit to the location for installing. Alternatively, the method may comprise assembling the structure and installation at or adjacent the deployment location during installing. The method may comprise connecting the structure to the installation.

According to an aspect there is provided a method of performing an operation. The operation may comprise a method of installing a structure. According to an aspect, there is provided a system for performing the method.

In at least some examples, there is provided a method of providing a support structure. The method may comprise providing a buoyant support structure. The method may comprise providing a floating support structure.

According to an aspect, there is provided a method of coating a floating support structure. The method may comprise providing the coating during the formation of the support member. The method may comprise commencing provision of the coating of the support structure prior to the completion of the formation process of the support member. For example, the method may comprise slip-forming or otherwise casting the concrete support member, with the coating being applied to portions of the concrete support member prior to completion of the formation of the concrete support member The coating may be applied to the concrete whilst fresh. The coating may be applied to the concrete before the concrete is set.

The structure may comprise the coating over at least a portion of its surface. The structure may comprise the coating over an upper portion's of its surface. The structure may comprise the coating over surface's that may potentially be close to, at, or above the water-line, in use. The coating may comprise a pigment. The coating may comprise a paint. The coating may comprise a full-surface coating. The coating may comply with one or more regulations, such as national, local and/or international regulations or guidelines, such as for maritime safety.

The method may comprise applying the coating to the concrete before any outer or intermediate layer has formed on the concrete, such as associated with fully-set concrete. The method may comprise applying the coating without allowing formation of any barrier intermediate the concrete and the coating. The support member may comprise the coating. The support member may comprise an enhanced bonding with the coating. The support member may comprise a transition phase, layer or portion between the concrete and the coating. The transition phase, layer or portion may be associated with an enhanced bonding of the coating to the concrete (e.g. in comparison to an alternative without the transition phase, layer or portion). The transition phase, layer or portion may be associated with an application of the coating to the concrete before any intermediate layer has formed on the concrete. The transition phase, layer or portion may comprise the coating and the concrete.

According to an aspect there is provided a system comprising the apparatus of any other aspect, example, embodiment or claim. The apparatus may comprise the structure or a component thereof, such as a support/cell, of any other aspect, claims, embodiment or example.

According to an aspect, there is provided an offshore or marine installation system. The installation system may comprise the installation and the structure of any other aspect, example, claim or embodiment.

According to an aspect, there is provided a method of using the apparatus, such as the buoyant support structure or portion/s thereof, according to an aspect, claim, embodiment or example of this disclosure.

The steps of the methods described herein may be in any order.

According to an aspect of, there is provided an apparatus configured to perform a method according to an aspect, claim, embodiment or example of this disclosure.

Within the scope of this disclosure it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION

An embodiment of the present disclosure will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 shows three examples of support structures for offshore installations: Figure la shows a buoyancy stabilised (semi-submersible) offshore floating wind support platform 3; Figure lb shows a tension-leg offshore floating wind support platform 5; and Figure lc shows a spar buoy offshore floating wind support platform 7; Figure 2 shows an example of a method according to the present disclosure; Figure 3 shows a plan view of a portion of an example of a buoyant support structure according to the present disclosure; Figure 4 shows a side cross-sectional view of the example of Figure 3; Figure 5 shows a series of schematic views during the construction of the example of Figure 3, sequentially showing the progression of formation; Figure 6 shows a schematic view of the example of Figure 3; Figure 7 shows a schematic view of the example of Figure 3 with an exemplary installation of a wind turbine completed thereon; Figure 8 shows a detail schematic view of a portion of the example shown in Figure 7; Figure 9 a detail cross-sectional view of a portion of the example shown in Figure 8; Figure 10 shows another detail schematic view of a portion of the example shown in Figure 7; Figure 11 shows a plan view of a portion of another example of a buoyant support structure according to the present disclosure; and Figure 12 shows a side cross-sectional view of the buoyant support structure of Figure 11.

DETAILED DESCRIPTION

Referring firstly to Figure 1, there is shown three examples of support structures for offshore installations, such as a wind turbine. Figure la shows a buoyancy stabilised (semi-submersible) offshore floating wind support platform 3. Figure lb shows a tension-leg offshore floating wind support platform 5. Figure lc shows a spar buoy offshore floating wind support platform 7. Atop each of these support structures is a single tower with a nacelle connected to the turbine blades.

Referring now to Figure 2, there is depicted an example diagram of a method 2 according to the present disclosure. Firstly, cell formation is initiated in a first step 4. In at least some examples, the cell formation is initiated by forming a base portion, such as a base plate. Accordingly, in at least some examples the cells are enclosed at their bottoms during or upon formation. Thereafter the cells are extended upwards in a continuation 4 of the cell formation process. Ultimately, cell formation is completed 8 so as to form the monolithic cell structure.

Referring now to Figure 3, there is shown a plan view of an example of a buoyant support structure 10. The support structure 10 is also shown in partial cross-section in Figure 4. It will be appreciated that the buoyant support structure 10 is formed following the method shown in Figure 2.

One example of a neutral draft line 12, indicative of a possible water level is shown for illustrative purposes. Accordingly, it will be appreciated that the structure 10 is a buoyant structure, with a portion floating above the water level and a portion submerged below the water.

As clearly visible in the view of Figure 3, the support member 11 of the structure 10 here is formed from a plurality of conjoined cells 14. The conjoined cells 14 form a continuous annular support. As shown here, the support member 11 is a hull with the plurality of cells 14. Here, there are twelve cells 14 of concrete cylinders forming a global ring 16 with an open moonpool 20 in its center 18. As shown here, a single cell 14a directly supports a post 70 for the tower rotor nacelle assembly 72 (see e.g. Figure 7), off-centre on the structure 10.

As shown here, the base of the support member 11 is defined by a global ring slab 22 of reinforced concrete, integrally-formed with the cells 14. The global ring slab 22 forms an outer damping plate 24 and an inner damping plate 26, with the slab 22 extending both radially outwards and inwards relative to the cells 14. The damping plates 24, 26 are configured to reduce motions. In particular, the inner ring 26 dampens heave motion; whilst the outer ring 24 dampens pitch motion. Excluding viscous effects, the inner damping plate 26 brings the heave motion and moonpool wave action out of phase. The support member 11 is configured to avoid natural frequency matches, such as between components and heave or pitch motions.

Here, the cells 14 are all enclosed at their tops by watertight decks 28. The decks 28 in this example are connected to form a global ring.

Figure 4 shows a side cross-sectional view of the example of Figure 3. As shown here, the cells 14 are formed with a wall thickness between 5% and 15% of a radius of the cell 14. The cross-section of Figure 4 clearly shows the ballast 31. Ballast 31 is used for trimming of the eccentric weight of the post 70 (and RNA and tower 72).

Figure 5 shows a series of schematic views during the construction of the example structure 10 of Figure 3, sequentially showing the progression of formation. The method comprises forming the member 11 in a vertical casting process, using formwork and/or slip-forming, progressively from the bottom upwards. The method comprises firstly forming the bottom portion of the member 11, as shown in the leftmost view of Figure 5, the method comprising initiating the member 11 formation process 2 at the bottom portion of the member 11. Here, the first portion of the support member 11 that is formed is the global ring slab 22 of reinforced concrete.

The formation of the support member 11 involves constructing the member 11, including substructures (e.g. base slab 22, cell walls 14), with a combination of formwork system and slipform techniques (first five views from the left of Figure 5) As shown in the fifth view from the left of Figure 5, the method also involves installing outfitting and post 70 tensioning. All equipment can be pre-commissioned.

Accordingly, the method provides a buoyant concrete support structure 10 for an offshore installation, such as with a wind turbine 72. As shown in Figure 5, the method comprises forming a monolithic multicellular concrete member 11. The monolithic multicellular concrete member 11 comprises the plurality of cells 14 arranged circumferentially around the central vertical longitudinal axis 20.

The diameter of each cell 14 is smaller than a diameter of a circumference along which the cells 14 are arranged, with the circumference passing through a centre of each cell 14. The plurality of cells 14 is arranged contiguously to define a continuous annular support. The method comprises forming the cells 14 as vertically-extending hollow elements, with a hollow central void 15. The method comprises forming the cells 14 with an enclosed bottom portion 17 below the hollow central void 15 thereabove.

The method comprises forming the plurality of cells 14 contemporaneously such that all of the cells 14 are integrally-formed with each other, as shown in the sequential progression of the formation of the support structure 10 as shown progressively from the leftmost view of Figure 5 to the rightmost view. Here, the method comprises forming the monolithic multicellular concrete member 11 seamlessly. The plurality of cells 14 are formed contemporaneously such that all of the cells 14 are integrally-formed with each other in unison to provide the seamless monolithic mulficellular concrete member 11. The plurality of cells 14 is coherent such that each cell 14 shares a common wall portion 40 with an adjacent cell 14.

As also visible in Figure 3, the method comprises spacing the cells 14 at a separation from the central longitudinal axis 20 of the structure 10 such that the plurality of cells 14 are arranged circumferentially around the central longitudinal axis 20. The cells 14 define a central space 21 therebetween, the central space 21 extending radially outwards from the structure's central longitudinal axis 20.

The diameter of the central space 21 is at least as large as the diameter of the surrounding individual cells 14 that define the central space 21. As shown here, the diameter of the central space 21 is at least 15 metres. In other examples, the diameter is at least 20 metres or at least 25 metres. The cross-sectional area of the central space 21 is at least similar to the cross-sectional area of the surrounding individual cells 14 that define the central space. As shown in Figure 3, the example here has a larger cross-sectional area of the central space 21 than the cross-sectional area of any individual surrounding cell 14. The central space 21 shown here comprises interstitial portions between the adjacent cells 14. As visible in Figure 3, the global ring slab 22 of reinforced concrete has an inner damping plate 26 than extends further radially inward than the cells 14, protruding into the central space 21.

The method comprises providing buoyancy by virtue of the cells 14, with the cells 14 being entirely enclosed, at least when in use. As shown in Figure 4, one or more of the hollow central voids 15 of the cells 14 is at least partially filled. The method comprises at least partially filling one or more of the hollow central voids 15 with fixed ballast 31. That is to say that the ballast 31 is permanent in the cell 14. The ballast 31 here is provided in advance of mounting or attachment of the installation 72. It will be appreciated that each cell 14 can comprise a different amount or level of ballast 31 and/or buoyancy. As shown in Figure 4, the cell 14 diametrically opposite the single cell 14a associated with the post 70 and the tower 72 comprises ballast 31 to compensate for a weight of the tower 72 such that the structure is balanced in use. It will be appreciated that the ballast 31 is distributed across the plurality of cells 14, such as with varying amounts of ballast 31 around the structure 10 with off-centre tower 72 to balance the structure 10. The method comprises distributing the ballast across the cells 14 to balance the final installation when in use. The method comprises distributing the ballast 31 across the plurality of cells 14 in varying amounts to accommodate any eccentricity or offset weight, such as associated with the off-center tower 72. For example, it will be appreciated that the single cell 14a housing the post 70 and associated with the tower 72 does not include any ballast here, with the post 70 and the tower 72 already providing additional weight on the single cell 14a.

It will be appreciated from Figure 5 that the buoyant support structure 10 is formed using a formation system, which is a combined formwork and slipforming system in this example. The method involves progressively or incrementally moving the formation system during formation of the member. Here, the method comprises progressively moving at least a portion of formation system upwards as the member is formed, from left to right as shown in Figure 5. Each of the plurality of cells 14 is progressively formed upwards contemporaneously with the upward formation of the other, adjacent cells 14-as shown in the sequential time-lapse views of the formation of a single support member 11 from left to right in Figure 5.

As also shown in Figure 5, from the fourth view (fourth from left), a coating 50 is applied to the support member 11 during its formation. The coating 50 is applied with or from apparatus, frames or equipment used or available for the formation process/es.

For example, the coating can be applied using a frame, platform, support or other access apparatus (not shown, for clarity) for forming the support member 11. Accordingly, the coating can be applied without requiring the positioning of such apparatus, frames or equipment for applying the coating 50 after the formation of the support member 11.

As shown in the views towards the right-hand side of Figure 5, the support member 11 is provided with the coating 50 on portions of the member. Here, the coating 50 is a chromatic coating (e.g. paint) for compliance with maritime regulations or guidelines on visibility of marine or offshore installations or structures 10. The coating 50 is applied here at portions of the member 11 that are potentially visible below, at or above the water-line 12 during or after deployment of the buoyant support structure 11. As shown in the three leftmost views of Figure 5, a lower portion of the member 11 can be left uncoated. As shown here, the coating process is only initiated once the support member has been formed to a sufficient height to define or start to define a portion/s of the member 11 that could be sufficiently close to, at or above the water-line 12 to require chromatic coating 50 (e.g. typically yellow). It will also be appreciated that the coating 50 can comprise other properties or benefits in addition or as an alternative to chromatic -such as for anti-corrosion, anti-fouling or other purposes. It will also be appreciated that a plurality of coatings can be applied. For example, a protective coating can be applied to an entirety of the support member 11 (e.g. to all concrete surfaces, both externally and internally within the cells) and a chromatic coating 50 can be applied only to portions where required. The method here comprises applying the coating 50 to the concrete before any outer barrier or intermediate layer has formed on the concrete, such as associated with fully-set concrete. Accordingly, the support member 11 has an enhanced bonding with the coating 50 (e.g. in comparison to a bonding of a coating applied subsequent to formation and setting of the concrete).

It will be appreciated that the schematic view of the support structure 10 shown in Figure 6, with the indicative waterline 12 has omitted the coating 50 for clarity of viewing the individual cells 14. Here, it can be appreciated that the moonpool 20 is open at the top and at the bottom, comprising a hollow central column within the member 11.

Figure 7 shows a schematic view of the example of Figure 3 with an exemplary installation of a wind turbine completed thereon. It will be appreciated that the buoyant support structure 10 has been transported to and positioned at a marine deployment location. The offshore installation, here the wind turbine 72, has been attached to the buoyant support structure 10. It will be appreciated that the tower 72 can be mounted to the support structure 10 after both have been transported separately to the deployment location; or prior to transportation of the buoyant support structure 10 to the marine deployment location. Here, when installing is to start, the support structure 10 is skidded to a submersible barge and sea launched. The support structure 10 is towed to a turbine integration location and wind turbine 72 is installed. 1A/hen the wind turbine 72 has been installed, the structure 10 is towed to a commissioning installation stations and made ready for offshore tow and installing at the deployment location.

Figure 8 shows a detail schematic view of a portion of the support structure 11. Here, two of the three mooring brackets 90 are shown on the base 22. It will be appreciated that at least portions of the mooring brackets can be integrally-formed with the base 22, such as during the concrete casting or slipforming process. Additionally, or alternatively the mooring brackets 90 can be attached to the support member 11, typically by fastening to the base 22. As shown in the detail cross-sectional view of Figure 9, locating the mooring brackets 90 on the base 22, at or towards the bottom of the support structure 10, allows the mooring lines 92 to be attached at lowermost points of the structure 10, thereby providing maximum stability of the mooring lines 92.

Figure 10 shows another detail schematic view of a portion of the buoyant support structure 10. Here, it can be seen that the support structure 10 has apparatus or devices within the central volume or space 20. For example, a pull-tube 88 is provided within the central volume or space 20. The pull-tube 88 runs along a cell wall, mounted thereto. In other examples (not shown), the pull-tube can be at least partially provided or housed in a pilaster. The pull-tube 88 here terminates at the base slab 22, with a bell-opening aligned with an indent in the inner damping plate 26.

Figure 11 shows a plan view of a portion of another example of a buoyant support structure 110 according to the present disclosure. The buoyant support structure 110 shown in Figure 11 is generally similar to that shown in Figure 3, with like features referenced by like numerals, incremented by 100. Accordingly, the buoyant support structure 110 comprises a plurality of cells 114 arranged around a common central longitudinal axis 118. For conciseness, definitions of all like features are not duplicated in this description. Here, the central space 120 defines an additional, central cell 114, such that the monolithic multicellular member 111 here comprises seven cells 114. It will be appreciated than in another example (not shown) there may be provided a total of five cells 114 arranged around the central cell 114.

Figure 12 shows a side cross-sectional view of the buoyant support structure 110 of Figure 11. Here, it is clearly shown that the installation 172 can be centrally-mounted, aligned with the central longitudinal axis 118 of the structure 110. Here, no intermediate post/column is provided, with the installation 172 directly connected and fastened to the support structure 110. It will also be appreciated that the base slab 122 here can be open or closed, with the structure 110 here not necessarily comprising a moonpool.

It will be appreciated that the relative proportions of the cells shown are shown to scale with the relative proportions of the hulls, towers, etc. in all directions (e.g. x, y and z).

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims, including with equivalence.

Claims

CLAIMSA method of providing a buoyant concrete support structure for an offshore installation, such as a wind turbine, the method comprising; forming a monolithic multicellular concrete member, the monolithic multicellular concrete member comprising a plurality of cells arranged circumferentially around a central vertical longitudinal axis; wherein the plurality of cells comprises at least five cells, with a diameter of each cell being smaller than a diameter of a circumference along which the cells are arranged, the plurality of cells being arranged contiguously to define an annular support; wherein the cells are formed as vertically-extending hollow elements with an enclosed bottom portion provided below a hollow central void thereabove; and wherein the method comprises forming the plurality of cells contemporaneously such that all of the cells are integrally-formed with each other in unison to provide the seamless monolithic multicellular concrete member; and the plurality of cells are coherent such that each cell shares a common wall portion with an adjacent cell.
2. The method of claim 1, wherein the method comprises forming the member in a vertical casting process, such as using formwork and/or slip-forming.
3. The method of claim 1 or 2, wherein the method comprises spacing the cells at a separation from the central longitudinal axis of the structure such that the plurality of cells arranged circumferentially around the central longitudinal axis define a central space therebetween, the central space extending radially outwards from the structure's central longitudinal axis.
4. The method of claim 4, wherein a diameter of the central space is at least as large as the diameters of the surrounding individual cells that define the central space.
5. The method of claim 5, wherein the diameter of the central space is at least 15 metres. 35 6.
The method of any preceding claim, wherein the method comprises applying a coating, such as a paint, to the monolithic multicellular concrete member during the formation of thereof, the coating being applied using at least a portion of a formation system, such as an access and/or support frame thereof.
The method of any preceding claim, wherein the method comprises providing buoyancy by virtue of the cells, the cells being entirely enclosed at least when in use.
8. The method of any preceding claim, wherein the method comprises at least partially filling one or more of the hollow central voids with ballast, particularly fixed ballast, such that the structure is balanced in use with the installation installed or mounted thereto or thereabove.
9. The method of any preceding claim, wherein the method comprises enclosing the tops of the cells with a deck element.
10. The method of any preceding claim, wherein the cells are formed with a wall thickness between 5% and 15% of a radius of the cell.
11. The method of any preceding claim, wherein the method comprises connecting the offshore installation, such as the wind turbine, thereto; transporting the buoyant support structure to a marine deployment location; and positioning the buoyant support structure.
12. The method of claim 11, wherein the method comprises connecting the offshore installation to the buoyant support structure prior to positioning of the buoyant support structure, optionally prior to transportation of the buoyant support structure to the marine deployment location.
13. The method of any preceding claim, wherein the method comprises connecting the installation, such as a wind turbine generator tower, to a cell of the buoyant support structure.
14. The method of claim 13, wherein the method comprises inserting or housing at least a portion of the tower within the cell.
15. The method of any preceding claim, wherein the method comprises connecting the installation subsequent to positioning of the buoyant support structure.
16. A buoyant concrete support structure for an offshore installation, such as a wind turbine, the support structure comprising; a monolithic multicellular concrete member, the monolithic multicellular concrete member comprising a plurality of cells arranged circumferentially around a central vertical longitudinal axis of the member; wherein the plurality of cells comprises at least five cells, with the diameter of each cell being smaller than a diameter of a circumference along which the cells are arranged, the plurality of cells being arranged contiguously to define an annular support; wherein the cells are vertically-extending hollow elements with an enclosed bottom portion provided below a hollow central void thereabove; and wherein the plurality of cells are integrally-formed with each other in unison to provide a seamless monolithic multicellular concrete member; and the plurality of cells are coherent such that each cell shares a common wall portion with an adjacent cell.
17. The buoyant concrete support structure of claim 16, wherein the circumference, about which the plurality of cells is arranged, passes through a centre of each cell and the annular support defined by the plurality of cells is continuous.
18. The buoyant concrete support structure of claim 16 or 17, wherein the cells comprise a wall thickness of between 5% and 15% of a radius of the cell.
19. The buoyant concrete support structure of any of claims 16 to 18, wherein the cells are spaced at a separation from the central longitudinal axis of the structure such that the plurality of cells arranged circumferentially around the central longitudinal axis define a central space therebetween, the central space extending radially outwards from the structure's central longitudinal axis.
20. The buoyant concrete support structure of claim 19, wherein a diameter of the central space is at least as large as a diameter of the surrounding individual cells that define the central space.
21. The buoyant concrete support structure of claim 20, wherein the wherein the diameter of the central space is at least 15 metres.
22. The buoyant concrete support structure of any of claims 19 to 21, wherein a cross-sectional area of the central space is at least similar to a cross-sectional area of a surrounding individual cell that defines the central space.
23. The buoyant concrete support structure of any of claims 19 to 22, wherein the central space defines a moonpool.
24. The buoyant concrete support structure of any of claims 19 to 22, wherein the central space defines an additional, central cell, such that the monolithic multicellular member comprises at least six cells.
25. The buoyant concrete support structure of any of claims 16 to 24, wherein the plurality of cells are enclosed at their tops by a deck element/s, except for a single cell of the plurality that is configured to receive a portion of a tower within its central void, the inner diameter of the cell being large enough to receive an outer diameter of the tower therewithin.