Semi-submersible floating platform for a wind turbine

Abstract

The present invention relates to a semi-submersible floating platform (1) for a wind turbine (50). The platform comprises: three columns each having an axis, the columns comprising a primary column (10 )adapted to support a wind turbine, and two secondary columns (30a, 30b) wherein each one of the three columns is connected to the other two columns by cross members (15a, 15b, 35) in a triangular arrangement. Further, the cross member between the secondary columns (35) incorporates ballast and each of the cross members (15a, 15b) connecting to the primary column incorporate buoyancy. The primary column (10) has a larger displacement than either of the two secondary columns (30a, 30b) and the cross member (35) extending between the secondary columns has a smaller displacement than the cross members (15a, 15b) connected to the primary column (10).

Description

[0001] SEMI-SUBMERSIBLE FLOATING PLATFORM FOR A WIND TURBINE

[0002] The present invention relates to a semi-submersible floating platform for a wind turbine.

[0003] Semi-submersible platforms for floating wind turbines are known, for example, from WO2016205746, EP 2789847, EP 3464893, EP2789850, WO2021032422, WO2015048147, WO2013155521 , W02012061710, US2020 / 20050, & US10202170, which are useful for understanding the invention.

[0004] Summary

[0005] The invention provides a semi-submersible floating platform for a wind turbine according to claim 1.

[0006] Optionally the columns are not all identical. For example, at least two of the columns can have non-equal parameters (e.g. dimensions, volume, diameter, cross-section, mass etc.). Optionally at least one dimension of the primary column is larger (e.g. 10-30% larger) than a corresponding dimension of one of the secondary columns. The secondary columns can be generally similar in dimensions, e.g. dimensions of the secondary columns can be within 5% or less of each other i.e. substantially equal in dimensions. Optionally the primary column has a larger diameter (typically with a larger cross section) than the secondary columns.

[0007] Providing the primary column with a greater displacement than the secondary columns typically improves the balance between the centre of mass (CoM) and the centre of buoyancy (CoB), which are typically shifted towards the primary column. The secondary columns optionally incorporate more ballast than the primary column. Optionally all of the columns incorporate at least some ballast elements to trim the platform and / or to achieve a desirable draft.

[0008] Optionally at least one of the columns (optionally at least the primary column, and optionally all of the columns) incorporates first and second sections which can have different cross- sectional dimensions (optionally diameters) optionally tapering from a lower first section to an upper second section, typically with a conical or frusto-conical outer surface which typically has a constant taper (i.e. the outer surface can form a straight line). Optionally the taper angle with respect to the axis of the column is 5-25 degrees, optionally 10-20 degrees, e.g. 14-16 degrees. This improves the distribution of size and mass of the components, reducing the mass and the span of e.g. the top slab, and helps to lower the centre of gravity of the platform. Optionally one or more of the columns has a vent, typically spaced above the column by a vent tube in communication with voids in the column.

[0009] Optionally buoyancy can be provided in buoyancy elements which can comprise voids such as cavities or chambers in the structure filled or partially filled with buoyant fluid such as a gas such as air, or can comprise solid closed cell buoyant plastics material, optionally a polystyrene such as extruded polystyrene (XPS) or expanded polystyrene (EPS).

[0010] Optionally the buoyant material has a density that is less than the density of seawater. Optionally ballast can be provided in ballast elements such as flooded compartments, or can comprise solid elements. Optionally the ballast has a density that is greater than or equal to (e.g. not less than) the density of seawater. Optionally the ballast is provided in ballast elements that are added to the structure to change the draft or balance of the platform when floating.

[0011] The two cross members connected to the primary column (hereinafter the “primary cross members”) have a larger displacement (typically having a larger cross section) than the single cross member extending between the secondary columns (hereinafter the “secondary cross member”). Increasing the displacement of the primary cross members relative to the secondary cross member typically moves the CoB towards the primary column, and away from the geometric centre of the triangular arrangement between the axes of the columns. Optionally the CoB is moved close to or typically into the same vertical axis as the CoM which is also typically closer to the primary column than to the secondary columns and is spaced away from the geometric centre of the triangular arrangement between the axes of the columns. In some examples, a larger displacement of the primary column relative to the secondary columns assists in moving the CoB towards the CoM.

[0012] Optionally each of the primary cross members can have a void such as a chamber or cavity, which can optionally contain e.g. be filled with buoyant material, such as gas, or a closed cell buoyant material which may be expandable, such as a foamed polystyrene like XPS or EPS. Other buoyant materials can of course be used. Optionally the void comprises a dry cavity.

[0013] Optionally the platform (optionally the columns and / or the cross members) can be formed from structural elements comprising a castable material, optionally concrete and optionally Light Weight Aggregate Concrete (LWAC). Optionally the platform incorporates elements of different density, typically buoyant elements, typically in the cross members, and optionally incorporated within the structural elements, e.g. in chambers or apertures within the structural elements. Typically buoyant elements can comprise materials with a lower density than the structural elements, such as XPS or EPS.

[0014] Optionally the structural elements are formed by casting or otherwise forming a castable material such as concrete or optionally LWAC around buoyant elements, such as polystyrene or other buoyant plastics elements, which can optionally fill the primary cross members.

[0015] Optionally the wind turbine tower also has first and second sections with first and second cross-sectional dimensions to provide a base with typically a larger cross-sectional dimension (e.g. diameter) than an upper section of the turbine tower supported by the base. Optionally the primary column can comprise a transition piece forming a part of the tower, and optionally permitting access to the tower.

[0016] Optionally the secondary cross member is ballasted with seawater, optionally at ambient pressure. Optionally the secondary cross member has a different cross-sectional area, for example, with a smaller width, and optionally a smaller cross-sectional area than the primary cross members. Optionally the displacement of the secondary cross member is less than the displacement of the primary cross members. This can assist in moving the CoB towards the primary column.

[0017] Optionally the primary cross members have cavities filled with a gas such as air or with another buoyant material such as a XPS or EPS. Optionally the primary cross members contain a buoyant and optionally expandable material such as XPS or EPS. Optionally the buoyant material braces the cross members and optionally fills one or more cavities within the cross members. Optionally the primary cross members have less ballast than the secondary cross member.

[0018] Optionally cavities in the cross members can incorporate braces, for example partition walls extending along a long axis of the cavity, and optionally having at least one planar section. Optionally the plane of the planar section can extend in a direction which is parallel to the axis of the column. This can reduce the required span of the slabs used for its construction, which reduces the bending moments involved. Optionally at least one of the cavities can extend parallel to a long axis of its cross member.

[0019] Optionally the cross members can have a rectilinear (e.g. rectangular) cross section, and / or can be formed from square or rectangular planar panels.

[0020] Optionally in one section (e.g. a mid-section) of at least one of the cross members the side walls of the cross members can be parallel. Optionally in another section (e.g. in an end section where the cross member connects to a column) the side walls of the cross members can be non-parallel, e.g. can diverge, optionally tapering outwards from a central axis of the cross member where they connect to the column.

[0021] Optionally the distribution of ballast and / or buoyancy in the platform is asymmetric. In some examples, the CoM is eccentric, e.g. moved towards the primary column. Optionally the CoB is also eccentric, e.g. moved towards the primary column. Optionally the asymmetric distribution of ballast and / or buoyancy in the platform moves the CoB towards alignment on a vertical axis with the CoM, and in some examples, the CoB and CoM are aligned on the same vertical axis when the platform is horizontal.

[0022] Optionally the distribution of ballast and / or buoyancy in the platform is such that more than 50% of the cross members are submerged below the water surface during normal operations; optionally the cross members are entirely submerged during normal operations. Typically the ballast arrangements submerge the cross members at least 5m below the waterline, typically between 5-10m and optionally between 10-20m, in some examples.

[0023] The invention also provides a semi-submersible floating platform according to claim 21, and a method according to claim 25.

[0024] The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect can typically be combined alone or together with other features in different aspects of the invention. Any subject matter described in this specification can be combined with any other subject matter in the specification to form a novel combination. Various aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, each example herein should be understood to have broad application, and is meant to illustrate one possible way of carrying out the invention, without intending to suggest that the scope of this disclosure, including the claims, is limited to that example. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. In particular, unless otherwise stated, dimensions and numerical values included herein are presented as examples illustrating one possible aspect of the claimed subject matter, without limiting the disclosure to the particular dimensions or values recited. All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa.

[0025] Language such as "including", "comprising", "having", "containing", or "involving" and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Thus, throughout the specification and claims unless the context requires otherwise, the word “comprise” or variations thereof such as “comprises” or “comprising” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0026] Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

[0027] In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of’, "consisting", "selected from the group of consisting of”, “including”, or "is" preceding the recitation of the composition, element or group of elements and vice versa. In this disclosure, the words “typically” or “optionally” are to be understood as being intended to indicate optional or non-essential features of the invention which are present in certain examples but which can be omitted in others without departing from the scope of the invention.

[0028] References to directional and positional descriptions such as upper and lower and directions e.g. “up”, “down” etc. are to be interpreted by a skilled reader in the context of the examples described to refer to the orientation of features shown in the drawings, and are not to be interpreted as limiting the invention to the literal interpretation of the term, but instead should be as understood by the skilled addressee.

[0029] Brief Description Of The Drawings

[0030] In the accompanying drawings:

[0031] Figure 1 shows a side view of a semi-submersible floating platform for supporting a wind turbine according to a first example;

[0032] Figure 2 shows a schematic perspective view of the platform in Fig 1 illustrating a mooring arrangement;

[0033] Figure 3 shows a schematic perspective view of the platform in Fig 1 ;

[0034] Figure 4 shows a schematic perspective cutaway view showing the internal arrangement of a cross member of the Fig 1 platform;

[0035] Figure 5 shows a schematic perspective view of a semi-submersible floating platform for supporting a wind turbine according to a second example;

[0036] Figures 6 & 7 show schematic perspective cutaway views showing the internal arrangement of cross members of the Fig 5 platform;

[0037] Figure 8 shows a schematic perspective view of the platform in Fig 5; Figures 9 &10 shows schematic views from below the platform in Fig 5;

[0038] Referring now to the drawings, a semi-submersible floating platform 1 for supporting a wind turbine has three columns comprising a primary column 10, and two secondary columns 30a, 30b, each of which has an axis. The column axes are mutually parallel. Each one of the three columns 10, 30a, 30b is interconnected to its two adjacent columns by at least one cross member 15a, 15b & 35, in a triangular arrangement. The axes of the columns in this example are optionally arranged on the vertices of an equilateral triangle. The arrangement of the turbine 50 on the primary column at one of the vertices is therefore eccentric, leading to the Centre of Mass (CoM) being closer to the axis of the primary column than to the axis of the secondary columns. The columns are typically not all identical; in this example, the secondary columns 30a, 30b are substantially identical, but the primary column 10 is different. In this example, the primary column is adapted to support a wind turbine 50 having a wind turbine tower 51. The tower 51 is typically coaxially arranged on the primary column 10, and can optionally have different dimensions along its axis, e.g. a larger diameter lower section below a relatively smaller diameter upper section. In this example, the tower 51 is tapered.

[0039] Optionally each of the columns 10, 30a, 30b has a vent, typically spaced from the upper surface of the column on a vent tube, which permits fluid communication between the vent opening at the top of the tube and a void within the column. The vent tube maintains the vent openings above the anticipated waterline in high sea states, avoiding water ingress into the void.

[0040] The primary column 10 has a conical upper section that tapers radially inward between a lower section of the primary column 10 at the base of the primary column 10, and an upper section of the primary column 10 connecting to the tower 51. The lower section of the primary column 10 is larger (e.g. in diameter and mass) than the upper section. Optionally more than one tapered section is provided as best seen in Fig 3. The tapered sections can optionally each have a straight taper, optionally with different angles between adjacent sections, such that the diameter of the primary column 10 reduces with height in a non-linear manner. The reduction in diameter with height maintains a lower centre of gravity for the primary column 10. Typically the taper angle is around 15°. In contrast, the secondary columns 30a, 30b in this example are typically cylindrical with straight sides having generally constant diameter. In this example, the secondary columns 30a, 30b are substantially identical.

[0041] The lower section of the primary column 10 in this example has a larger diameter than the secondary columns 30a, b, allowing the primary column 10 a greater mass than the secondary columns 30a, 30b, and a greater displacement. This improves the balance between the platform’s centre of mass (CoM) and the centre of buoyancy (CoB), which are both shifted towards the primary column 10, e.g. by between 1-3m from the geometric centre of the triangle formed by the axes of the columns. Typically the mass of the primary column is between 105%-130% of the mass of one of the secondary columns 15a, 15b.

[0042] The bottom panels of the cross members 15a, 15b & 35 are typically planar sheets of cast material, all arranged in the same plane, at the base of the columns, so that the keel of the platform is on one plane, typically occupied by the bases of the columns and the bottoms of the cross members. When the platform is level, the cross members 15a,b, 35 are all submerged, typically having a draft of around 10-20m. The cross members 15a, b, 35 are typically formed with generally rectangular cross sections, typically with flat and mutually parallel bottom and top panels, all of which are typically submerged when the keel is level. The sides of the primary cross members 15a, b, 35 are typically tapered radially outward towards the diameter of the column bases, typically to match the diameter of the column bases.

[0043] The columns and the cross members in the platform 1 in this example are formed from a castable material such as concrete and optionally by light weight aggregate concrete (LWAC).

[0044] In this example, the primary cross members 15a, 15b connecting to the primary column 10 are substantially identical but the secondary cross member 35 connecting between the secondary columns 30a, 30b is different.

[0045] The primary cross members 15a, 15b have a larger dimension with a larger cross section (typically creating a larger displacement) than the secondary cross member 35. Each of the primary cross members 15a, 15b in this example has an internal void 16 which can optionally be filled with buoyant material, such as gas (air in this example). The internal void 16 in this example is optionally divided (e.g. equally divided) by a brace formed by an internal wall 17 which extends along the void 16 along an axis of the primary cross members 15a, 15b. At least one of the walls, in this case, the lower wall of the primary cross members 15a, 15b, is formed by casting or otherwise forming LWAC around buoyancy elements 18, which comprise blocks or strips of low density buoyant material e.g. expanded polystyrene or similar. Optionally the upper wall can be similarly formed, and optionally all walls in the cross members. Optionally the void can be filled with a different buoyant material, e.g. a closed cell foamed polystyrene material such as XPS or EPS, which can optionally provide additional bracing. Optionally the secondary cross member 35 can be similarly formed. The primary cross members 15a, 15b are typically dry internally, having no fluid ballast, but they can optionally have some (usually minimal) ballast for trimming purposes and for achieving a necessary draft for the platform 1. In this example, the primary cross members 15a, 15b incorporate solid buoyancy elements comprising foamed polystyrene blocks of XPS or EPS which are incorporated within voids set in parallel arrays in a common plane. The voids are typically formed by casting the LWAC around the blocks during construction of the cross member. In this example, the secondary cross member 35 is ballasted with seawater, optionally at ambient pressure and optionally at the same pressure as the seawater outside the platform. In this example, the secondary cross member 35 has a different cross sectional area, for example, with a smaller lateral width perpendicular to the main axis of the secondary cross member 35 which allows a smaller cross-sectional area than the primary cross members 15a, 15n.

[0046] In this example, the ballast distribution is eccentric as the secondary cross member 35 incorporates more ballast than the primary cross members 15a, 15b, which typically lack any additional ballast added to affect the draft or balance or to move the CoM when floating. The secondary columns typically incorporate some ballast to trim the platform and / or to achieve a desirable draft.

[0047] In a modified example of a platform 101 shown in Figs 5-10, similar features are shown as previously described with reference to the platform 1. Because of the similarity between the platforms 1 and 101 , the same features are provided with the reference numbers but increased by 100. The skilled reader will understand that the same features do not require the same depth of explanation for the platform 101 for features common to the platform 1 . As previously described in relation to the platform 1 , the platform 101 has three columns comprising a primary column 110 and two secondary columns 130a, 130b which are generally similar to one another, and primary and secondary cross members 115a, 115b, and 135 having similar features to the columns 10, 30a, 30b previously described. Some or all of the cross members 115a, 115b and 135 can optionally incorporate internal bracing members 117, and can optionally comprise buoyancy elements 118. The cross members 115a, 115b, 135 can all incorporate tapered end sections like the cross members 15, 25, and the primary cross members 115 connecting to the primary column 110 typically have a larger dimension and optionally larger displacement than the secondary cross member 35 as described for the primary and secondary cross members 15a, 15b and 35. All of the columns 110, 130a, 130b can optionally have conical sections like the column 10. As best shown in Figs 8-10, and as in the first example, the column 110 has a larger dimension (e.g. diameter) than the columns 130a, 130b, and the cross members 115a, 115b each have a larger dimension (e.g. diameter) than the cross member 135. Optionally the secondary columns 130a, 130b incorporate more ballast than the primary column 110, but optionally all of the columns incorporate some ballast to achieve a desirable draft.

[0048] Because the primary column supports the mass of the tower and nacelle of the wind turbine, the natural CoM 145 of the platform in use without considering any added buoyancy is typically closer to the primary column 110 than to the secondary columns 130a, 130b, as best shown in the Fig 10, and is spaced away from the geometric centre of the triangle 140 formed by the axes of the three columns 110, 130a,b. Typically the added ballast in the platform is asymmetrically distributed away from the primary column 110, for example, towards the centre of the secondary cross member 135, resulting in the CoM 145 moving slightly away from the primary column 110 and back towards the geometric centre of the triangle 140 and the secondary cross member 135, but typically still remaining spaced away from the geometric centre of the triangle 140, by around 1-3m, as typically shown in Fig 10. Typically added buoyancy (e.g. in the primary cross members) also has a asymmetric distribution but in the opposite direction, which results in the CoB moving towards the primary column 110 and away from the geometric centre of the triangle 140, typically into the same vertical axis as the CoM 145, as shown in Fig 10.

Claims

CLAIMS1 A semi-submersible floating platform for a wind turbine, comprising: three columns each having an axis, the columns comprising a primary column adapted to support a wind turbine, and two secondary columns, wherein each one of the three columns is connected to the other two columns by cross members in a triangular arrangement; wherein the cross member between the secondary columns incorporates ballast; wherein each of the cross members connecting to the primary column incorporate buoyancy; wherein the primary column has a larger displacement than either of the two secondary columns, and wherein the cross member extending between the secondary columns has a smaller displacement than the cross members connected to the primary column.2 A platform as claimed in claim 1 wherein the primary column has a larger crosssection than either of the two secondary columns.3 A platform as claimed in claim 1 or claim 2, wherein the primary column has different cross-sectional dimensions at different locations along its axis.4 A platform as claimed in claim 3, wherein the primary column has an axial section with a conical or frusto-conical outer surface having a constant inward taper.5 A platform as claimed in any one of claims 1-4 wherein one or more of the columns has a vent, typically spaced above the column by a vent tube in communication with a void in the column.6 A platform as claimed in any one of claims 1-5, wherein the cross members connecting to the primary column each comprise a void containing a buoyant material.7 A platform as claimed in claim 6, wherein the buoyant material is a solid buoyant material.8 A platform as claimed in claim 7 wherein the void comprises a dry cavity filled with a buoyant material.9 A platform as claimed in any one of claims 1-8 including a brace between opposite inner surfaces of a void in one of the cross members.10 A platform as claimed in any one of claims 1-9, wherein the cross member extending between the secondary columns is ballasted with seawater.11 A platform as claimed in any preceding claim, wherein the cross member extending between the secondary columns has a smaller cross-sectional area than the cross members connected to the primary column.12 A platform as claimed in any one of claims 1-11 , wherein the cross members have a rectilinear cross section.13 A platform as claimed in any one of claims 1-12, wherein the distribution of ballast in the platform is asymmetric.14 A platform as claimed in any preceding claim, wherein the distribution of buoyancy in the platform is asymmetric.15 A platform as claimed in any one of claims 1-14, wherein the distribution of added ballast moves the centre of mass away from the primary column and wherein the distribution of added buoyancy moves the centre of buoyancy towards the primary column.16 A platform as claimed in any one of claims 1-15, wherein the centre of mass and the centre of buoyancy are both closer to the axis of the primary column than to the axes of the secondary columns.17 A platform as claimed in any one of claims 1-16, wherein the distribution of ballast and / or buoyancy in the platform entirely submerges the cross members when the platform is floating and horizontal.18 A platform as claimed in any one of claims 1-17, wherein the columns and / or the cross members are formed from a castable material.19 A platform as claimed in claim 18, wherein the castable material comprises one of concrete and light weight aggregate concrete.20 A platform as claimed in any one of claims 1-19, wherein the cross members comprise solid buoyancy elements comprising foamed polystyrene blocks incorporatedwithin arrays of parallel voids set in a common plane within walls formed from castable material.21 A semi-submersible floating platform for a wind turbine, comprising: three columns each having an axis, the columns comprising a primary column adapted to support a wind turbine, and two secondary columns, wherein each one of the three columns is connected to the other two columns by cross members in a triangular arrangement; wherein the cross member between the secondary columns incorporates ballast; wherein each of the cross members connecting to the primary column incorporate buoyancy, the buoyancy in each of the primary cross members comprising a dry cavity; wherein the primary column has a lower section and an upper section; wherein the lower section of the primary column has a larger cross-section than either of the two secondary columns; wherein the primary column has a conical or frusto-conical outer surface, whereby the upper section has a smaller diameter than the lower section; wherein the cross members connected to the primary column have a larger displacement than the cross member extending between the secondary columns; wherein the cross members connected to the primary column comprise solid buoyancy elements comprising foamed polystyrene blocks incorporated within arrays of parallel voids set in a common plane within walls formed from castable material; the cross members comprising a brace between opposite inner surfaces of a void in one of the cross members; wherein the distribution of ballast and / or buoyancy in the platform is asymmetric; wherein the centre of mass and the centre of buoyancy are both closer to the axis of the primary column than to the axes of the secondary columns. wherein the columns and / or the cross members are formed from a castable material comprising one of concrete and light weight aggregate concrete.22 A platform as claimed in claim 21 , wherein the conical or frusto-conical outer surface of the primary column has a constant taper between the lower section and the upper section.23 A platform as claimed in claim 22, wherein the cavities in the primary cross members are filled with buoyancy elements comprising closed cell foamed plastics material.24 A platform as claimed in any one of claims 21-23, wherein the distribution of added ballast moves the centre of mass away from the primary column and wherein the distribution of added buoyancy moves the centre of buoyancy towards the primary column.25 A method of balancing a semi-submersible floating platform supporting a wind turbine, the floating platform comprising: three columns each having an axis, the columns comprising a primary column adapted to support the wind turbine, and two secondary columns, wherein each one of the three columns is connected to the other two columns by cross members in a triangular arrangement; wherein the primary column has a larger displacement than either of the two secondary columns, wherein the method includes controlling balance of the platform by: incorporating ballast in the cross member between the secondary columns; incorporating buoyancy in each of the cross members connecting to the primary column; and providing the cross member extending between the secondary columns with a smaller displacement than the cross members connected to the primary column. 26 A method of generating power comprising balancing a semi-submersible floating platform as claimed in claim while operating the wind turbine on the platform.

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