Patent ID: 12202574

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth in order to provide a thorough understanding of various illustrative embodiments of the invention. It will be understood, however, to one skilled in the art, that embodiments of the invention may be practiced without some or all of these specific details. Embodiments described in the context of one of the methods or devices are analogously valid for the other methods or devices. Similarly, embodiments described in the context of a method are analogously valid for a device, and vice versa.

Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which this invention belongs.

The terms “about”, “approximately”, “substantially” must be read with reference to the context of the application as a whole, and have regard to the meaning a particular technical term qualified by such a word usually has in the field concerned. For example, it may be understood that a certain parameter, function, effect, or result can be performed or obtained within a certain tolerance, and the skilled person in the relevant technical field knows how to obtain the tolerance of such term.

The phrase “at least one of A and B” means it requires only A alone, B alone, or A and B, i.e. only one of A or B is required.

Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set.

As used herein, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. As used herein, the terms “top”, “bottom”, “left”, “right”, “side”, “vertical” and “horizontal” are used to describe relative arrangements of the elements and features. As used herein, the term “each other” denotes a reciprocal relation between two or more objects, depending on the number of objects involved.

Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, a further aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms a further aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if10and15are disclosed, then 11, 12, 13, and 14 are also disclosed.

The word “substantially” does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention.

Although each of these terms has a distinct meaning, the terms “comprising”, “consisting of” and “consisting essentially of” may be interchanged for one another throughout the instant application. The term “having” has the same meaning as “comprising” and may be replaced with either the term “consisting of” or “consisting essentially of”.

Terms such as “coupled”, “connected”, “attached”, “conjugated and “linked” are used interchangeably herein and encompass direct as well as indirect connection, attachment, linkage or conjugation unless the context clearly dictates otherwise. The coupling of two components may refer to the two components being fixed, welded, or fastened directly or indirectly, removably or non-removably.

By “polygonal”, it refers to a surface having three or more sides or a three-dimensional object having three or more side surfaces in addition to the top and bottom surfaces. Examples of polygonal shapes that may be used include triangular, quadrilateral, pentagonal, hexagonal, heptagonal, octagonal, nonagonal, decagonal and so forth.

The buoyant structure100may have an upper (first) deck8, a lower (second) deck9, and a plurality of floatable substructures coupled to and around at least one of the upper deck8and lower deck9. The upper deck8and lower deck9are coupled to each other and arranged spaced apart from each other vertically. The coupling of the upper deck8and lower deck9may be direct or indirect as explained in greater detail below. The floatable substructures are arranged spaced apart from each other and is explained in greater detail below. The intent is to achieve a robust, stable, and optimized design in terms of weight saving and better motion characteristic.

The upper deck8and lower deck9each have a channel through its deck (which are through opposing surfaces of the deck, for example from the top surface through to the bottom surface of the deck). The channels are open-ended at both ends to allow the tower1to pass through the channel and decks8,9. When deployed in the sea or other body of water, the lower deck9will be submerged in the water and water is able to flow through the channel of the lower deck9. The channels of the upper deck8and lower deck9are aligned to form a third continuous channel to receive at least a portion of a tower1of a wind turbine. Thus, the third channel is made up of the channels of the upper deck8, lower deck9and a channel between the decks8,9. The buoyant structure100may have a central axis in the vertical direction as seen when the buoyant structure is in use. The central axis may be in the middle of the third channel parallel to the longitudinal axis of the third channel and by necessity the channels of the upper deck8and lower deck9. In an embodiment, the central axis may be co-axial with the longitudinal axis of the third channel. In another embodiment, the central axis is parallel but not aligned to the longitudinal axis of the third channel in an off-centre alignment. The tower1may be coupled to the buoyant structure100by an attachment means or a fixation system that allows the tower to be secured to the buoyant structure100. As an example, during operating conditions of the buoyant structure100with the wind turbine, the tower1may be flushed with the bottom of the lower deck9. However, during installation or maintenance, the tower1may be displaced beyond (for example below) the buoyant structure100due to the lowered height of the wind turbine.

A support element10may be optionally provided to directly couple the upper deck8and lower deck9. Examples of a support element include a rod including a plurality of rods, a lattice frame, a beam and a wall. The support element10is preferably arranged around the perimeter or edge of the bottom surface of the upper deck8and top surface of the lower deck9. It will be appreciated that the top surfaces of the upper deck8and lower deck9are relative and face in the same direction, and similarly for the bottom surfaces of the upper deck8and lower deck9. Thus, the top surface of the upper deck8is a surface facing away from the second deck while the bottom surface of the upper deck8faces the top surface of the lower deck9. Advantageously, this provides additional structural integrity and depends on the requirements of the load (e.g. the wind turbine) to be carried by the buoyant structure100. Additionally, the support element10, for example the plurality of rods improves the structural integrity of the buoyant structure and allows for a shorter span between the decks8,9and floatable substructure.

In an embodiment, the support element10is a continuous wall (for example a wall with a circular horizontal cross-section or an ellipsoidal horizontal cross-section) and the portion of the third channel between the upper deck8and lower deck9may have the wall surrounding the middle portion of the third channel, it will be appreciated that the wall will not close the two end portions to allow the tower1to be received in the channels. The wall may extend from bottom surface of the upper deck8to the top surface of the lower deck9, with the bottom surface of the upper deck8facing the top surface of the lower deck9. The wall may also be considered as a hollow cylinder with open ends. The upper deck8, lower deck9and third channel may be termed a column-less column4. Preferably, the upper deck8, lower deck9and third channel and thus the column-less column4are in the centre of the buoyant structure100.

Advantageously, the column-less column4reduces the water plane area in the centre of the buoyant structure100providing better motion characteristics while reducing the weight and material usage of the buoyant structure, in particular reducing the overall steel weight used. Further, it increases space availability for other uses and improves motion response while reducing the amount of steel used.

The floatable substructures may be coupled to at least one of the upper deck8and lower deck9, preferably both. The floatable substructures may be arranged spaced apart from one another and around the coupled deck (either or both of the upper deck8and lower deck9) and are preferably equidistant from each other. There are preferably at least three floatable substructures. The attachment of the plurality of floatable substructures to the upper deck8and/or lower deck9by the connecting elements5allows at least the upper deck8of the buoyant structure100to be above the water line21while the lower deck9may be submerged in the water when the tower1is received in the buoyant structure. It will be appreciated that in the absence of the tower1, the relative position of the decks8,9may differ depending on the dimensions. The floatable substructures may be arranged around at least one of the upper deck8and lower deck9in a radial manner and extends outwardly from the coupled deck. Thus, such radial coupling may be viewed as a hub and spoke with the decks8,9as the hub and the floatable substructures as the end of the spokes.

Each floatable substructure may comprise an elongate column2and a pontoon3. Preferably, either or both the elongate column2and pontoon3may have a polygonal horizontal cross-section. Advantageously, the polygonal horizontal cross-section of the elongate column2and pontoon3(i.e. bended radius of straight plate and vertices6) provides for ease of fabrication from the constructability point of view. The elongate column2and pontoon3may each have a polygonal horizontal cross-section with vertices6between the edges. The elongate column2and pontoon3may also be viewed as being polygonal in shape by virtue of its polygonal horizontal cross-section, and thus may be termed as a polygonal elongate column2and a polygonal pontoon3herein. The polygonal cross-section for both the elongate column2and pontoon3may have three or more edges, preferably three to ten edges. In an embodiment, the polygon has eight edges. Thus, the polygonal shapes that may be used include triangular, quadrilateral, pentagon, hexagon, heptagon, octagon, nonagon, decagon and so forth. The polygonal shape may be a regular polygon (in other words the angles of the polygon are equal and have all the sides have the same length). In an embodiment, the elongate column2has a top region and a bottom region opposite to the top region, and the pontoon3is coupled to the bottom region of the elongate column2. The top region of the elongate column2may be coupled to the upper deck8. The lower deck9may be coupled to the pontoon3. In an embodiment, the upper deck8is also coupled to the pontoon3.

Optionally, the top surface of the upper deck8is flush with the top surface15of the floatable structure which may be the top surface15of the elongate column2. The top surfaces of the upper deck8and floatable structure or elongate column2are arranged substantially along the same plane and may be termed a deck plane22. A top surface of the connecting element5coupling the upper deck8and floatable structure or elongate column2may also be flush with the deck plane22. Optionally, the bottom surface of the lower deck9is flush with the bottom surface of the floatable structure which may be the pontoon3. The bottom surfaces of the floatable structure or pontoon3and lower deck9are arranged substantially along the same plane and may be termed a keel plane24. Further, the bottom surface of the connecting element5coupling the lower deck9and floatable surface or pontoon3may also be flush with the keel plane. Preferably, the top surfaces of the pontoon3, lower deck9and connecting element5are also on the same pontoon deck plane23.

The polygonal elongate column2and pontoon3have been shaped such that there is a significant reduction in the amount of construction workload resulting in mass production at the same time improving fatigue life. The amount of material wastage has also been significantly reduced.

Another advantageous feature of the embodiments is the option to have an eccentric column centre for the floatable substructure instead of concentric to further enhance the stability performance. This makes the embodiments easily scalable from a benign to a harsh environment, and from a lower megawatt (MW) to a higher megawatt turbine installation. In a concentric column arrangement, the elongate column2is coupled to a substantially centre region of the pontoon3(for example, proximal to or at the centre of the pontoon). In an eccentric arrangement, the elongate column2is coupled to a substantially off-centre region of the pontoon3(for example, proximal to an edge or between the edge and centre of the pontoon3).

A plurality of connecting elements5(i.e. an inter-connecting structure) may be provided to couple the floatable substructures to the upper deck8and/or lower deck9. The connecting elements5may also indirectly couple the upper deck8to the lower deck9as evident in one of the embodiments described herein. Examples of connecting elements include a rod and a beam. The connecting element5may be used to couple the upper deck8to a top region of the elongate column2, with the bottom region of the elongate column2attached to the pontoon3. The connecting element5may be used to couple the lower deck9to the pontoon3. A diagonal connecting element5may also be used to couple the upper deck8to the pontoon3.

The upper deck8and lower deck9may be coupled together directly by the support element10or indirectly by the connecting elements5and struts11as will be evident from the figures and description herein.

FIG.1Ashows a perspective view of an embodiment of the buoyant structure100with a wind turbine received in the buoyant structure100, in particular received in the channels of the buoyant structure100.FIG.2Ashows a top plan view of the embodiment inFIG.1Awithout the tower. InFIG.1A, the upper deck8has a channel passing from the top to the bottom surface of the upper deck8and may be viewed as a first channel, i.e. a hole through the upper deck8that forms the channel of the upper deck8. Similarly, the lower deck9has a channel passing from the top to the bottom surface of the lower deck9and may be viewed as a second channel. The channels of the upper deck8and lower deck9are aligned to receive a tower1(may also be called a mast) of a wind turbine. The channels of the upper deck8and lower deck9along with the intervening space between the upper deck8and lower deck9may be viewed as forming a third channel. The upper deck8, lower deck9and channels may also be termed a “column-less” centre column4as the centre portion is hollow to receive the tower1. The channels may be viewed more clearly without the tower1in another embodiment shown inFIG.3A. It would be appreciated that the upper deck8and lower deck9may be identical or non-identical in size, shape, and cross-section. For example, the upper deck8may be thicker than the lower deck9as more equipment may need to be installed on the upper deck8. In addition, a central axis of the buoyant structure100may be present in the middle and parallel and co-axial (or coincident) with the longitudinal axis of the third channel12(and also the channels of the upper deck8and lower deck9).

InFIG.1A, the support element10comprises three rods (or pillars)10each located at the intersection of the connecting element5and decks8,9. The upper deck8may be coupled to the elongate column2by a connecting element5, for example a beam or a bar, and the lower deck8may be similarly coupled to the pontoon3.

InFIGS.1A and2A, the embodiment has three floatable substructures each connected to the upper deck8and lower deck9. The third channel12(which is formed by the channels of the upper deck8, lower deck9and channel between the decks8,9) contains the central axis of the buoyant structure100along its longitudinal side or long side, and also preferably passes through the centroid of the deck plane and keel plane. The three floatable substructures may be arranged equidistant from each other such that each floatable substructure may be viewed as an end of an equilateral triangle. The embodiment further contains thee support elements10each placed proximal to the intersection of the connecting element5and upper and lower decks8,9.

InFIGS.1A and2A, the elongate column2and pontoon3each has a polygonal horizontal cross-section with vertices6between the edges, in particular a octagonal horizontal cross-section. The elongate column2and pontoon3may also be viewed as being polygonal (specifically an octagon) in shape by virtue of its polygonal horizontal cross-section. In the embodiment, the elongate column2is coupled at a substantially centre region of the pontoon3(as indicated by the dashed lines) as most clearly seen inFIG.2Awith a substantially uniform spacing7between the edge of the elongate column2and pontoon3. The placement of the elongate column in the substantially centre region of the pontoon3may be termed a concentric arrangement.

The tower1may be coupled to the buoyant structure100by an attachment means or a fixation system that allows the tower to be secured to the buoyant structure100. As an example, during operating conditions of the buoyant structure100with the wind turbine, the tower1may be flushed with the bottom of the lower deck9(i.e. flushed with the keel plane as explained below and shown inFIG.3B). However, during installation or maintenance, the tower1may be displaced beyond (for example below) the buoyant structure100due to the lowered height of the wind turbine.

FIGS.1B and2Bshow a perspective view and top plan view of another embodiment of the buoyant structure100. The difference between this embodiment and that shown inFIGS.1A and2Ais that the elongate column2is coupled to the pontoon3at a substantially off-centre region or proximal to an edge on the pontoon as may be seen inFIGS.1B and2B. Thus, the spacing7between the edge of the elongate column2and edge of the pontoon3is not uniform. In an embodiment, the spacing7is larger at the side of the elongate column2facing the connecting element5as shown inFIG.2B. The other features of the upper deck8, lower deck9, connecting elements5and support element10are the same as that described forFIG.1A. It may be seen inFIG.2Bthat the elongate column2is located mostly in one of the quadrants indicated by the dashed lines and the central longitudinal and vertical axis of the elongate column2is no longer co-axial with the centre of the pontoon3. This is termed an eccentric arrangement. The placement of the elongate column2at a substantially off-centre region may be termed an eccentric arrangement. Advantageously, the eccentric elongate column2and pontoon3arrangement enhance the stability performance of the buoyant structure100. The different available arrangements of elongate column2on the pontoon3makes the embodiments easily scalable from a benign to a harsh environment, and from a lower megawatt to a higher megawatt turbine installation. Hence, the placement of the elongate column2may be adjusted according to the operating location of the buoyant structure100.

FIG.3Ashows a perspective view of an embodiment similar to the embodiment inFIG.1Ain the absence of the tower1. The embodiment inFIG.3Ahas additional struts11between the upper deck8and pontoon3to couple them together. The strut11may couple to the bottom region of the elongate column2or the pontoon3either alone or in combination.

FIG.3Bshows a side cross-section view of the embodiment inFIG.3Awith a tower received in the third channel12. It may be seen that when the tower1is received in the buoyant structure100, the buoyant structure100is partially submerged with the lower deck9below the water line21and immersed in the water, while the upper deck8is above the water line21and equipment and personnel may be located. In the embodiments shown inFIGS.1A,1B, and3A, the top surface15of the elongate column2(and by necessity the floatable structure), top surface of the connecting element5between the top region of the elongate column and the upper deck8, and top surface of the upper deck8are substantially on the same deck plane22. The bottom surface of the pontoon3(and by necessity the floatable structure), bottom surface of the connecting element5between the pontoon3and the lower deck9, and bottom surface of the lower deck9are substantially on the same keel plane24. Further, the top surface13of the pontoon3, top surface of the connecting element5between the pontoon3and the lower deck9, and top surface of the lower deck9are substantially on the same pontoon deck plane23.

FIG.4shows a perspective view of a similar embodiment to that inFIG.3A. The difference between the two embodiments is that inFIG.4the support element10is a lattice frame10rather than the three rods in the embodiment inFIG.3A. The lattice frame10generally comprises a network of rods including a plurality of vertical rods, horizontal rods and diagonal rods. InFIG.4, the lattice frame10comprises three vertical rods with a plurality of horizontal and diagonal rods between the three vertical rods. However, any appropriate lattice frame may be used as the support element10.

FIG.5shows a perspective of a similar embodiment to that inFIG.3Abut viewed from the bottom (or pontoon3side). In the embodiment inFIG.5, the support element10comprises the three vertical rods (as inFIG.3A) and additionally a circular wall coupling the upper deck8and lower deck9. The wall surrounds the middle portion of the third channel12between the upper deck8and lower deck9. The wall and channel may be viewed as a hollow cylindrical shell with both ends open to receive the tower1.

FIGS.6A and6Bshows a comparison of two embodiments without and with the support element10respectively.FIG.6Bshows the embodiment inFIG.3Afrom a different perspective. In bothFIGS.6A and6B, the darker lower portion of the buoyant structure illustrates the water line due to the operating draft. In other words, the darker regions of the buoyant structure100may be submerged in the water at the operating draft. InFIG.6A, the embodiment does not have a support element10to couple the upper deck8and lower deck9directly. The upper deck8and lower deck9are instead coupled indirectly by the connecting elements5. InFIG.6A, the connecting elements5comprises three beams5between the upper deck8and the top region of the elongate columns2, three beams5between the lower deck and the pontoons3, and three diagonal struts between the upper deck8and the pontoons3(or alternatively the lower region of the elongate column2). The additional support element10(for example three vertical rods as shown inFIG.6B) in the embodiment inFIG.6Bmay improves the structural integrity of the buoyant structure100compared to the embodiment inFIG.6Aand leads to a shorter span (and connecting element5) between the decks8,9and floatable substructure (e.g. upper deck8and elongate column2, and lower deck9and the pontoon3). Advantageously, this reduces the amount of material needed and reduces the weight of the buoyant structure.

FIG.7shows a perspective view of an embodiment with a floatable substructure having a quadrilateral shaped (in other words a quadrilateral horizontal cross-section) elongate column2and pontoon3, specifically a trapezoidal shaped elongate column2and a substantially square or rectangular shaped pontoon3. The elongate column2has a trapezoidal horizontal cross-section when viewed from the top. Preferably, the top portion of the elongate column2that couples to the upper deck8is larger than the bottom portion of the elongate column2that sits on the pontoon3. In the embodiment shown inFIG.7, the trapezoidal shaped cross section has one pair of parallel sides with the shorter side of the trapezoid being coupled to the connecting element5and faces the centre of the buoyant structure100. The longer side of the parallel sides faces outwards of the buoyant structure100. The pontoon3may have a rectangular horizontal cross-section which includes a square horizontal cross-section, or may other polygonal cross-section as described herein. The connecting elements5of the embodiment inFIG.7couple the upper deck8to the elongate column2and the lower deck9to the pontoon3, other configurations as described herein may be used as well. In addition, struts11couple the upper deck8to the pontoon3. The support element10may be a circular wall coupling the upper deck8and lower deck9and may be viewed as a hollow cylindrical shell with both ends open to receive the tower1.

FIG.8shows a perspective view of the buoyant structure100with the wind turbine and a mooring system. The buoyant structure100may contain a plurality of anchoring points for mooring the buoyant system, preferably at least three anchoring points. The anchoring points may be located on the top region of the elongate column2. An example mooring system may be a cost-effective three-line14concept with a spread catenary mooring design. A drag anchor was used for the embodiment, but other types of anchor may also be used. A fairlead connection may be used at the deck of the buoyant structure100to enhance stability against wind-induced overturning moment. As may be seen inFIG.8the force of the wind load acts on the wind turbine and the force of the station-keeping mooring load acts on the buoyant structure100and creates a moment arm.

FIG.9shows a side cross section view of the buoyant structure100deployed in a body of water. An installation vessel200or maintenance vessel200may be used to install the wind turbine or to perform maintenance work on the buoyant structure100and wind turbine.

The buoyant structure100may be provided with a jacking module configured to raise and lower the tower1through the first channel, second channel and third channel12. The jacking module may be used to lower the tower during maintenance and provides for a reduced installation and maintenance height. This reduces the work at height risk and the expected operating expenses (OPEX). Further, the jacking module reduces the dependency on a large crane capacity installation vessel and thus can lead to greater cost savings and efficiencies. As an example, the jacking module may be a portable unit that may be deployed with the buoyant structure100during installation or maintenance work. An interface structure or platform may be provided on the upper deck8to allow the jacking module to be securely used with the buoyant structure100. Alternatively, the jacking module may be integrally built with the buoyant structure100, for example on the upper deck8.

An example of wind turbine that may be used is the GE Haliade X wind turbine with a capacity of 12 to 14 MW as shown in Table 1.

TABLE 1Characteristics of a wind turbine that maybe used with the buoyant structure 100CharacteristicSpecification ValueRotor diameter (m)220 (Annotation 2 on the right)Blade length (m)107Swept area (m2)38,000Cut-in wind speed (m/s)3.5Cut-out wind speed (m/s)28

FIGS.10A and10Bcompares the motion characteristics of two embodiments of the buoyant structure100and other systems.FIG.10Ashows the heave response amplitude operator (RAO) over time (period).FIG.10Bshows the pitch response amplitude operator (RAO) over time. The RAO data for the buoyant structure100may be obtained from the aqwa software. The RAOs are obtained based on a buoyant structure100for a 12 MW wind turbine at moderate environmental conditions. The RAO data for the existing buoyant structures were obtained from the public domain but may have be based on different turbine power settings.

Lines56and59show the heave performance of the embodiment of the buoyant structure shown inFIGS.7and1Arespectively compared to other systems, and it may be observed that the embodiments of the buoyant structure100described provides better motion characteristics than existing systems. The heave and pitch characteristics may depend in part on the environmental conditions where the buoyant structure100is deployed. This results in the wind turbine assembly of the buoyant structure100and wind turbine having higher operability as the wind turbine assembly may be able to withstand harsher conditions than existing systems.

All wind turbines and their assembly have a maximum pitch and/or heave angle under which it can operates. If the sea conditions are harsh and the wind turbine assembly exceed the maximum angle, the wind turbine stops operating. By having better heave and pitch characteristics than existing systems, the buoyant structures100descried herein are able to operate under harsher conditions and maximise the operating time of the wind turbine.

TABLE 2Steek weight comparison between buoyantstructure 100 and existing systemsBuoyantstructuredescribedUnitshereinSystem ASystem BSystem CPowerMW125510Draftm202013.222FreeboardM11.5121811Hull steelmt3500 (NTE)208426603213weightMast steelmt477270270540weightTotal steelmt3900 (NTE)235429303753weightSteel weight/MT/<375471586375MWMW

Table 2 above shows a comparison of the buoyant structure100and existing systems (or installations). As the other systems are catered for a different Wind Turbine Capacity, the steel weight/MW for each system provides a fairer comparison of the respective weights of the various systems. It may be observed from Table 2 that the embodiments of the buoyant structure100have a not to exceed (NTE) total steel weight of 3900 mt and the steel weight/MW of the embodiments of the buoyant structure100are lower comparing to the other existing systems.

FIG.11shows different ballast systems that may be used with the shaded regions indicating the ballast component. In an embodiment, sea water is used as the ballast without any other active ballast system. The open-ended channel in the lower deck9allows sea water to flow through. The embodiment meets intact stability as per Det Norske Veritas (DNV) requirements and damage stability as per mobile offshore drilling unit (MODU) requirements. In another embodiment, a fix ballast with different ballast content may be used with an increase metacentric height (GM) of about 1.88 m and as shown inFIG.11. For example, concrete or barite may be used as the fixed ballast content. The ballast system may be located at and/or within pontoon3and/or elongate column2.

Non-limiting conditions of where the buoyant structure100may be used include a wind speed of approximately 44 m/s, a significant wave height of up to and approximately 10.9 m, and a peak period range of approximately 9 to 16 seconds. The buoyant structure100may be modified as described above to suit the operating conditions of the environment to be operated in.

The embodiments of the buoyant structure100described herein provide several technical advantages compared to existing systems. The embodiments have higher operability compared to existing systems with maximised power generation and excellent motion characteristics like heave, pitch and drift. The embodiments have a robust hull design that meets industry stability requirements including damage stability and have a lower vertical centre of gravity (VCG). The embodiments have a significant hull weight reduction with a lower weight per power (MT per MW) value (or ratio) than existing systems. The embodiments possess improved structural strength and fatigue life with an estimated 25 years of lifespan. The embodiments have improved constructability with a simplified and construction friendly hull form with bended radius reducing the welding requirements. The embodiments are amenable to be scaled to meet increasing turbine capacity, for example by using a concentric or eccentric elongate column2arrangement on the pontoon3in the floatable substructure. It is expected that cost savings may be higher for larger wind turbines. In addition, no active ballast system is required, but may be provided if required depending on the environmental conditions. The embodiments have an improved weather envelope for operation, installation, and maintenance (OIM).

Various embodiments of the buoyant structure100may provide:1. A buoyant structure100to cater for a tower1of a wind turbine.2. A buoyant structure100with a polygonal column2with three or more sides and with regular or irregular shapes.3. A buoyant structure100with Polygonal pontoon3with three or more sides and with regular or irregular shapes.4. A buoyant structure100with a column-less centre column4with a reduced water plane area for better motion characteristics and weight savings.5. A buoyant structure100with a column-less centre column4with increased space availability.6. A buoyant structure100with improved design fatigue life at vertices (6) of the polygon7. A buoyant structure100with eccentric or concentric pontoon3and elongate column2arrangements.8. A buoyant structure with Inter-connecting structures5including but not limited to top, bottom, vertical and diagonal structures and bracing.

In an embodiment there is provided a floating offshore buoyant structure100comprising:a column4configured to receive at least portion of a tower1of a wind turbine, wherein the column4has an open top end for the at least portion of the tower1to enter through, and an open bottom end opposite to the open top end, the open bottom end configured to allow water to flow through, thereby provide a column-less column4; anda plurality of floatable substructures arranged and coupled in a radial manner, extending outwardly from a central axis of the buoyant structure100, each floatable substructure having a top end and a bottom end opposite to the top end,wherein the column4is coupled to at least one of the plurality of floatable substructures such that the open top end of the column and top ends of the plurality of floatable substructures are arranged substantially along a same deck plane22, and the open bottom end of the column and bottom ends of the plurality of floatable substructures are arranged substantially along a same keel plane24.

Preferably, each of the plurality of floatable substructures comprises an elongate column2having a polygonal horizontal cross-section.

Preferably, each of the plurality of floatable substructures comprises a pontoon3having a polygonal horizontal cross-section.

Preferably, each of the plurality of floatable substructures comprises an elongate column2having a polygonal horizontal cross-section; and a pontoon3having a polygonal horizontal cross-section, wherein the elongate column2extends upwardly from the pontoon3.

Preferably, the column-less column4comprises a column-less center column4arranged along the central axis of the buoyant structure100.

Preferably, the column-less column4comprises a plurality of supports10extending between the open top end of and the open bottom end, the plurality of supports10arranged space apart from one another along a peripheral circumference of the column-less column4. More preferably, the plurality of supports10forms a lattice frame10.

Preferably, the column-less column4comprises a wall10extending between the open top end of the column and the open bottom end of the column4, the wall10arranged surrounding a peripheral circumference of the column-less column4.

Preferably, the buoyant structure100further comprising a jacking module disposed along the deck plane21, wherein the jacking module is configured to raise and lower the tower1through the column4.

Preferably, the buoyant structure100further comprising a plurality of anchoring points for mooring the buoyant structure100.

Preferably, the plurality of floatable substructures is coupled radially and extending outwardly from the central axis of the buoyant structure by inter-connecting structures.