Connection assembly

Abstract

A connector assembly 30 for connecting ends of first and second tubular sections (fig.1, 10, 20) of a wind turbine tower or other tubular structure. The connector assembly has a connector body 40 and

Description

Technical Field The present invention relates to a connection assembly preferably for connecting first and second tubular sections and most preferably for connecting first and second tubular sections of a wind turbine tower. Background of the Invention Existing designs of onshore and offshore wind turbines with tubular steel towers are assembled in sections, which are constructed separately, and usually assembled at the installation site, typically by connecting L-shaped flanges on the ends of the sections with studs / bolts which are tensioned between the flanges in a direction parallel to the axis of the sections. This creates a tight connection between flanges during assembly of the tower structure. However, with the move to constructing larger wind turbine towers, the limitations of the traditional L-flange design become apparent. In particular, the assembly of such wind turbine towers requires the individual positioning of a large number of heavy bolts / studs (sometimes in excess of 100) by personnel whilst an upper tower section is lifted into position. As the size of the wind turbine towers increases, the weight of these studs / bolts will soon reach a point where they may not be able to be manually handled safely. This individual positioning of studs / bolts also contributes greatly to the total make-up time for assembling the wind turbine. Additionally, L-flange designs have been known to fail, with studs / nuts loosening over time, reducing the preload and subjecting the studs / nuts to large cycling stresses, thereby resulting in fatigue failure of the wind turbine tower. Furthermore, the load bearing capabilities of the L-flange design scales poorly as the size of the wind turbine tower increases. It is therefore an object of the present invention to provide an improved connector assembly design which overcomes or at least mitigates the problems described above. Summary of the Invention According to a first aspect, the invention provides a connector assembly for connecting ends of first and second tubular sections of a wind turbine tower or other tubular structure, the connector assembly comprising: a connector body; at least one clamping mechanism mounted on the connector body, the or each clamping mechanism comprising; an inner clamping member configured to engage with an inner radial surface of each tubular section and restrict relative axial movement between the tubular sections; an outer clamping member configured to engage with an outer radial surface of each tubular section and restrict relative axial movement between the tubular sections; and an actuator for driving the inner and outer clamping members in opposite directions. Optionally the connector body is annular. Optionally the connector body is configured to be removably disposed between the ends of the tubular sections. Optionally the connector body has a first axial surface and a second opposite facing axial surface. Optionally the connector body has an inner radial surface and an opposite outer radial surface. In use, the first axial surface of the connector body is arranged to engage with a free axial surface on the end of one of the tubular sections and the second surface of the connector body is arranged to engage with a free axial surface on the end of another of the tubular sections. Optionally the first and second axial surfaces of the connector body each comprise either a groove or a rib. Optionally each groove or rib is annular. Optionally each groove or rib of the connector body extends circumferentially around the connector body continuously. Optionally the connector body comprises a substantially H- shaped profile in cross section. Optionally the profile of the connector body is continuous around the connector body. In use, the groove or ribs of the connector body are configured to receive or be received by a corresponding rib or groove provided on the free axial surface of the respective tubular section. Optionally the connector body is a continuous ring. Optionally the connector assembly comprises a plurality of clamping mechanisms, optionally arranged at regular intervals (optionally equal intervals) around the connector body. Optionally the connector body comprises a through-bore, optionally passing radially through the connector body, optionally between the inner and outer radial surfaces of the connector body. Optionally the connector body comprises a through bore for each clamping mechanism. Optionally the through-bores are arranged at regular intervals (optionally equal intervals) around the connector body. Optionally the connector body is segmented, optionally into arcuate body segments. Optionally the connector body comprises at least two body segments. Optionally the connector body comprises three, four, five , six, seven or more body segments. Optionally at least one clamping mechanism is mounted on each body segment. Optionally adjacent body segments have abutting edge surfaces. Optionally means are provided for connecting abutting edge surfaces together. Optionally each body segment comprises a pin (optionally a dovetail pin) at one edge surface and a slot (optionally a dovetail slot) formed at an opposite edge surface, wherein adjacent body segments are connectable by inserting the pin of one body segment into the slot of another body segment. Alternatively said means comprise a connecting element configured to extend between the adjacent body segments and further comprises fastening elements (e.g. bolts) configured to secure the connecting element to each adjacent body segment. Optionally each adjacent body segment comprises a cavity configured to receive said means such that said means does not interfere with the connection of the first and second tubular sections. Optionally the connector body is integrally formed on the end of one of the tubular sections. Optionally the connector body has a free axial surface. In use, the free axial surface of the connector body is arranged to engage with a free axial surface on the end of the other tubular section. Optionally the free axial surface of the connector body comprises either a groove or a rib. Optionally the groove / rib is annular. Optionally the groove / rib circumferentially extends continuously around the connector body. In use, the groove or rib of the connector body is configured to receive or be received by a corresponding rib or groove provided on the free axial surface of the other tubular section. Typically by having the inner and outer clamping members engage with the corresponding surfaces of the tubular sections, the inner and outer clamping members can urge the tubular sections in opposite axial directions (i.e. together) to apply a preload between the tubular sections. Typically the connector body is disposed between the inner and outer clamping members. Therefore in use, the inner clamping member is typically arranged to be disposed within the wind turbine tower or other tubular structure and the outer clamping member is typically arranged to be disposed outside of the wind turbine tower or other tubular structure. Optionally the inner and outer clamping members each comprise a first drive face and a second drive face. For each clamping member, the first and second drive faces are optionally axially spaced apart and optionally taper into the clamping member. The drive faces of the inner clamping member face radially outwards from the longitudinal axis of the connector body and the drive faces of the outer clamping member face radially inwards towards the longitudinal axis of the connector body. Optionally each drive face is sloped, typically relative to a transverse plane of the respective clamping member, optionally at an angle between 0° and 90°. Optionally said angle is between 10° and 20° or optionally between 10° and 15°. Optionally said angle is about 15°. In use, the first drive face of the inner clamping member is configured to engage with an internal flange of one of the tubular sections; the first drive face of the outer clamping member is configured to engage with an external flange of said one of the tubular sections; the second drive face of the inner clamping member is configured to engage with an internal flange of the other tubular section; and the second drive face of the outer clamping member is configured to engage with an external flange of the other tubular section. Optionally in use, each drive face is configured to engage with a shoulder of the corresponding flange. Optionally each clamping member comprises a first radial surface and an opposite second radial surface. Optionally in use, the first radial surface of each clamping member faces radially inwards relative to a longitudinal axis of the connector body and the second radial surface of each clamping member faces radially outwards relative to the longitudinal axis of the connector body. Optionally the inner clamping member and the outer clamping member each comprise a recess the outer ends of which are defined by the respective drive faces of the clamping members. Optionally the recess of the inner clamping member is formed on the second radial surface of the inner clamping member and the recess of the outer clamping member is formed on the first radial surface of the outer clamping member. Optionally each clamping member has a substantially C-shaped profile in cross section. Optionally each first drive face is arranged to be in axial alignment with each other and each second drive face is arranged to be in axial alignment with each other. In use, the recess of the inner clamping member is configured to receive the inner shoulders of each tubular section and the recess of the outer clamping member is configured to receive the outer shoulders of each tubular section. Optionally the inner and outer clamping members each comprise a through-bore, optionally passing radially through the inner and outer clamping members, optionally between respective inner and outer radial surfaces. Optionally the through-bores of the inner and outer clamping member are arranged to be in axial alignment with the respective through-bore on the connector body. Optionally an end of the through-bore of the outer clamping member is counterbored. Optionally the inner clamping member is a locking dog and the outer clamping member is a locking dog. Optionally the actuator is suitable for driving the inner and outer clamping members in opposite radial directions. Optionally the actuator connects the inner and outer clamping members, optionally by passing through the connector body. Optionally the actuator passes through the respective through-bore of the connector body, and optionally the through-bore of the inner clamping member, and optionally through the through-bore of the outer clamping member. Optionally the actuator comprises a fastener such as a threaded stud / bolt and nut arrangement. Optionally a head of the stud / bolt is provided at the outer radial surface of the outer clamping member, optionally within the counterbore of the through-bore of the outer clamping member. Optionally the nut is provided at an inward radial facing surface of the inner clamping member. Optionally the actuator is configured to be operational from within the wind turbine tower or other tubular structure. Optionally the actuator is a common driver, configured to drive both the inner and outer clamping members. Optionally the or each clamping mechanism comprises a biasing mechanism configured to urge the inner and outer clamping members away from each other, typically radially away from each other. Optionally the biasing mechanism comprises a biasing element (e.g. a spring such as a coil spring, a flat or leaf spring or any other suitable spring / spring-like component) connected between (and optionally partially embedded within) the connector body and one of the inner or outer clamping members. Optionally the biasing mechanism comprises a second biasing element connected between (and optionally partially embedded within) the connector body and the other of the inner or outer clamping members. According to a second aspect the invention provides a wind turbine tower or other tubular structure comprising: first and second tubular sections; a connector assembly according to the first aspect of the invention; and wherein the connector assembly is positioned between the ends of the first and second tubular sections. Optionally an internal flange is formed on the inner radial surface of each tubular section and an external flange is formed on the outer radial surface of each tubular section. Optionally for each tubular section, internal and external flanges are in axial alignment. Optionally each flange is arranged adjacent to but spaced from the end of the respective tubular section. Optionally each flange is annular. Optionally each flange is formed by a shoulder, optionally configured to engage with a corresponding drive face of the clamping members. Optionally for each tubular section, the shoulders of each flange face in diverging directions. Optionally in use, the shoulders of one of the tubular sections and the shoulders of the other tubular section face in opposite axial directions. In use, the connector body is optionally configured to be radially flush with the internal and external flanges. Optionally each shoulder is set at an angle (typically relative to a transverse plane of the tubular section) corresponding to the angle of its respective drive faces. Optionally longitudinal axes of the clamping members and the connector body are mutually parallel. According to a third aspect, the invention also provides a method of assembling a wind turbine tower or other tubular structure, the method comprising: providing a wind turbine tower or other tubular structure according to the second aspect of the invention; positioning the connector assembly between the ends of the tubular sections; operating the actuator to drive the inner clamping member into engagement with the inner radial surface of the tubular sections and the outer clamping member into engagement with the outer radial surface of the tubular sections such that relative axial movement between the tubular sections is restricted. 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. 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. 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. 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. 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. Brief Description of the Figures In the accompanying drawings: Figure 1 shows a perspective view of a tubular structure comprising a connector assembly connecting first and second tubular sections; Figure 2 shows a perspective view of the connector assembly of Figure 1; Figure 3 shows an exploded cross sectional view of a clamping mechanism of the connector assembly of Figure 1; Figure 4 shows cross section views of ends of the first and second tubular sections of Figure 1; Figures 5-10 show sequential cross sectional views of a method of assembling the tubular structure of Figure 1; Figure 6a shows a detailed view of section A of Figure 6 Figure 7a shows a detailed view of section B of Figure 7; Figure 9a shows a detailed view of section C of Figure 9; Figure 10a shows a detailed view of section D of Figure 10; Figure 11 shows a plan view of a first modification to the connector assembly of Figure 1; Figure 12 shows a perspective view of a connector body segment of the connector assembly of Figure 11; Figure 13 shows a detailed view of section E of Fig. 11; Figure 14 shows a cross-sectional view of a second modification to the connector assembly of Figure 1; and Figure 14a shows a detailed view of section F of Figure 14. Detailed Description of the Figures Referring now to the drawings, Figure 1 shows a tubular structure 1 assembled from a first tubular section 10, a second tubular section 20 and a selectively removable connector assembly 30 configured to connect ends of the first and second tubular sections 10, 20. The tubular structure 1 is typically at least a part of an onshore or offshore wind turbine tower. Alternatively, the tubular structure may be any other tubular structure with tubular sections for which the connector assembly 30 is suitable. The tubular structure 1 may comprise more than two sections, with a suitably configured connector assembly 30 connecting each set of adjacent tubular sections. As seen in Figure 2, the connector assembly 30 comprises a connector body 40 carrying a plurality of clamping mechanisms 50. Figure 3 shows an exploded cross sectional view of the connector assembly 30, with only one clamping mechanism 50 being shown for clarity purposes. The connector body 40 has a seamless toroidal form with a substantially H-shaped profile in cross section. The connector body 40 comprises a first axial surface 41 and an opposite second axial surface 42. The connector body 40 further comprises an inner radial surface 43 and an opposite outer radial surface 44. The edges between the axial surfaces 41,42 and the radial surfaces 43, 44 are chamfered. An annular groove 45, 46 is formed on each axial surface 41, 42 of the connector body 40. Each groove 45, 46 extends axially into the connector body 40 and has equal axial depths to each other. Each groove 45, 46 is shallow relative to the axial height of the connector body 40. In the example illustrated in Figure 3, the axial depth of the grooves 45, 46 is substantially equal to an eighth of the axial height of the connector body 40. In other examples, the axial depth of the grooves 45, 46 may be greater or less than an eighth of the axial height of the connector body 40. The grooves 45, 46 have an equal radial widths to each other. Each groove extends radially across a majority of the radial thickness of the connector body 40. In the example illustrated in Figure 3, the radial width of the grooves 45, 46 is substantially equal to half of the radial thickness of the connector body 40. In other examples, the radial width of the grooves may be greater or less than half of the radial thickness of the connector body 40. Each annular groove 45, 46 is centrally positioned between the inner and outer radial surfaces 43, 44 of the connector body 40. Each annular groove 45, 46, circumferentially extends around the connector body 40 seamlessly. Mouth edges of each groove 45, 46 which open onto the axial surfaces 41,42 are chamfered while base edges of each groove 45, 46 within the connector body 40 are filleted. A plurality of through-bores 47 are provided on the connector body 40 arranged in an equispaced array around the connector body 40. Each through-bore 47 passes through the connector body 40 between the inner and outer radial surfaces 43, 44. Each through-bore 47 on the connector body 40 has a substantially circular crosssection and extends continuously in a direction perpendicular to the longitudinal axis of the connector body 40. The diameter of each through-bore 47 is wide relative to the axial height of the connector body 40. In the illustrated example of Figure 3, each through-bore 47 provided on the connector body 40 has a diameter substantially equal to a third the axial height of the connector body. In other examples, the diameter of each through-bore 47 provided on the connector body 40 may be greater or less than a third of the axial height of the connector body 40. Each through bore 47 on the connector body 40 is positioned at an axial centre between the first axial surface 41 and the second axial surface 42. One though-bore 47 is provided on the connector body 40 for every clamping mechanism 50 the connector assembly 30 carries. Each clamping mechanism 50 comprises an inner clamping member 60 and an outer clamping member 70. Each clamping member 60, 70 has a substantially cuboidal form and a substantially C-shaped profile in cross-section. Each clamping member 60, 70 comprises a first axial surface 61, 71 and an opposite second axial surface 62, 72. Each clamping member 60, 70 comprises a first radial surface 63, 73 and an opposite second radial surface 64, 74. The cuboidal form of each clamping member 60, 70 is completed by first and second circumferential surfaces (not shown). Each clamping member 60, 70 comprises substantially equal dimensions, in particular equal axial heights, radial thicknesses, and circumferential widths. For each clamping member 60, 70, the edges between the axial surfaces 61, 62, 71, 72, and the radial surfaces 63, 64, 73, 74 are chamfered. A recess 65, 75 is formed on the second radial surface 64 of the inner clamping member 60 and the first radial surface 73 of the outer clamping member 70. Each recess 65, 75 extends radially into its clamping member 60, 70. Each recess 65, 75 tapers into its respective clamping member 60, 70 and is formed by a first drive face 66, 76, a second drive face 67, 77 and an intermediate surface 68, 78 positioned between the first and second drive faces 66, 67, 76, 77. Each drive face 66, 67, 76, 77 forms an axial end of its respective recess 65, 75 and is sloped such that for each clamping member 60, 70, the first drive face 66, 76 and the second drive face 67, 77 are converging as the recess 65, 75 extends into the clamping member 60, 70. In the example illustrated in Figure 3, each drive face 66, 67, 76, 77 is sloped at an angle of around 15° with respect to the transverse plane. In other examples, this angle may be between 10° and 15°; or between 10° and 20°; or between 0° and 90° non-inclusive. Each intermediate face 68, 78 forms a base of the respective recess 65, 75 and faces in a direction perpendicular to the longitudinal axis of its respective clamping member 60, 70. Each recess 65, 75 is shallow relative to a radial thickness of its clamping member 60, 70. In the example illustrated in Figure 3, the radial depth of each recess 65, 75 is substantially a fifth of the radial thickness of its respective clamping member 60, 70. In other examples, the radial depth of each recess 65, 75 may be greater of less than a fifth of the radial thickness of the corresponding clamping member 60, 70. In the example illustrated in Figure 3, the axial height of each recess 65, 75 is substantially three fifths of the axial height of its respective clamping member 60, 70. In other examples, the axial height of each recess 65, 75 may be greater or less than three fifths of the overall axial height of its respective clamping member 60, 70. Additionally, each recess 65, 75 is positioned at an axial centre between the first axial surface 61, 71 and the second axial surface 62, 72. Each recess 65, 75 extends continuously between the circumferential surfaces of its respective clamping member 60, 70 in a direction perpendicular to the first and second radial surfaces 63, 64, 73, 74 of the corresponding clamping member 60, 70. A through-bore 69, 79 is provided on each clamping member 60, 70. Each through-bore 69, 79 passes radially through its respective clamping member 60, 70 between its first and second radial surfaces 63, 64, 73, 74. Each through-bore 69, 79 has a substantially circular cross-section and extends in a direction perpendicular to the longitudinal axis of the clamping member 60, 70. The through-bore 79 of the outer clamping member 70 comprises a substantially square counterbore 79a at the second radial surface 74 of the outer clamping member 70. The diameter of the through-bores 69, 79 provided on the clamping members are narrow relative to the axial height of the clamping members 60, 70. In the illustrated example of Figure 3, the diameter of the through-bores 69, 79 provided on the inner and outer clamping members 60, 70 is substantially equal to that of the through-bores 47 provided on the connector body 40. In this case, that is substantially a seventh of the axial height of the inner and outer clamping members 60, 70. In other examples, the diameter of each through-bore 69, 79 provided on the inner and outer clamping members 60, 70 is greater or less than the a seventh of the axial height of the inner and outer clamping members 60, 70. For each clamping member 60, 70, the through-bore 69. 79 is provided centrally on its respective radial surfaces 63, 64, 73, 74. The height of the counterbore 79a is narrow relative to the axial height of the outer clamping member 70 while the width of the counterbore 79a extends along a majority of the circumferential width of the outer clamping member 70. In other examples, the height and width of the counterbore 79a may be greater or lesser than what is shown in Figure 3. Each clamping mechanism 50 further comprises an actuator 80. In the illustrated example of Figure 3, the actuator 80 is a fastener 80. As seen in Figure 3, the fastener 80 comprises a threaded bolt 81 and a nut 82. The bolt 81 comprises an elongated shaft 83 and a head 84. The shaft 83 has a free end to which it extends to from the head 84. The shaft also has a circular cross section and is configured to be received within the through-bores 47, 69, 79 provided on the connector body 40, the inner clamping member 60 and the outer clamping member 70. The head 84, has a rectangular or square cross section and has a width greater than the diameter of the shaft 83 and is configured to be received within the counterbore 79a of the outer clamping member 70. In use, unwanted relative rotation between the bolt 81 and the outer clamping member 70 is restricted by the straight edges of the head 84 of the bolt 81 and the counterbore 79a. In other examples, the head 84 may have any other shape (circular or non-circular) that compliments the shape of the counterbore 79a. In other examples the length of the shaft 83 may be divided into two sections (not shown), each with different cross sectional shapes. The sections will typically be integrally formed. The first section extending from the head 84 towards a point along the length of the shaft 83, may have a non-circular cross section (e.g. substantially square / rectangular) and the second section, extending from the end of the first section remote from the head to the free end of the shaft 83, may have a circular cross section. In such examples, the through-bores 47, 69, 79 provided on the connector body 40, the inner clamping member 60 and the outer clamping member 70 also have non-circular cross sections matching that of the first section of the shaft 83. The first section has a length such that it in use it can be received within each of the through-bores 47, 69, 79 with the straight edges of the second section of the shaft 83 and the through-bores 47, 69, 79 restricts unwanted relative rotation between the bolt 81, the connector body 40, the inner clamping member 60 and the outer clamping member 70. In other examples, the bolt 81 may be a stud. Figure 4 shows cross-sectional views of the ends of the first and second tubular sections 10, 20 configured to be connected by the connector assembly 30. Each tubular section 10, 20 has a seamless tubular form. Each tubular section 10, 20 comprises an abutment surface 11, 21 on its axial end. Each tubular section 10, 20 comprises an inner radial surface 12, 22 and an opposite outer radial surface 13, 23. The ends of each tubular section 10, 20 have a substantially cross shaped profile in cross-section, with a region of increased radial thickness in the profile in crosssection adjacent to but spaced from the axial end of the tubular section 10, 20. Said regions allow for the tubular sections 10, 20 to be connected to each other by the connector assembly 30. For each tubular section 10, 20, said region of increased radial thickness defines a internal flange 14, 24 extending from the inner radial surface 12, 22 and an external flange 15, 25 extending from the outer radial surface 13, 23. Said region has a radial thickness substantially equal to the radial thickness of the connector body 40. For each tubular section 10, 20, the internal flange 14, 24 and the external flange 15, 25 are axially aligned. Each flange 14, 15, 24, 25 has a sloped shoulder 16, 17, 26, 27 facing axially away from the end of its respective tubular section 10, 20. For each tubular section 10, 20, the shoulders 16, 17, 26, 27 diverge towards the end of the tubular section 10, 20. Each shoulder 16, 17, 26, 27 is sloped at an angle relative to a transverse plane of its tubular section 10, 20 matching the angle of the sloped drive faces 66, 67, 76, 77 of the clamping members 60, 70. In the example illustrated in Figure 4, the angle of the shoulders 16, 17, 26, 27 is around 15°. In other examples, the angle of the shoulders 16, 17, 26, 27 is between 10°-20° or between 10°-15°. An annular rib 18, 28 is defined on the abutment surface 11, 21 of each tubular section 10, 20. Each rib 18, 28 extends axially away from its abutment surface 11, 21. Each rib 18, 28 is dimensioned such that they are receivable with the grooves 45, 46 of the connector body 40, with the axial height of each rib 18, 28 being substantially equal to the axial depth of the grooves 45, 46 and the radial width of each rib 18, 28 being substantially equal to the radial width of the grooves 45, 46. Each rib 18, 28 is positioned centrally between the inner and outer radial surfaces 12, 13, 22, 23 of its tubular section 10, 20. Each rib 18, 28 circumferentially extends around its tubular section 10, 20 seamlessly. Base edges of each rib 18, 28 proximate to the flanges 14, 15, 24, 25 are filleted while extending edges of each rib 18, 28 distal from the flanges 14, 15, 24, 25 are chamfered. A method of assembling the tubular structure 1 of Figure 1 is sequentially shown in Figures 5-10, as described below. Starting with Figure 5, which shows an installed first tubular section 10. The first tubular section 10 is typically connected to a base (not shown) or to a lower adjacent tubular section (not shown) of the tubular structure 1. The first tubular section 10 is arranged such that its abutment surface 11 is facing upwards and the shoulders 16, 17 of its flanges 14, 15 are facing downwards. Figures 6 shows an assembled connector assembly 30 that has been lifted above the first tubular section 10. Figure 6a shows a detailed view of section A of Figure 6, with only one clamping mechanism 50 being shown for clarity. The inner clamping member 60 of each clamping mechanism 50 is disposed within the toroidal connector body 40 and the outer clamping member 70 of each clamping mechanism 50 is disposed outside of the toroidal connector body 40. The longitudinal axes of the connector body 40, each inner clamping member 60 and each outer clamping member 70 are arranged mutually parallel, with the first axial surfaces 41, 61, 71 of the connector body 40, the inner clamping members 60 and the outer clamping members 70 facing upwards and the second axial surfaces 42, 62, 72 of the connector body 40, the inner clamping members 60 and the outer clamping members 70 facing downwards. The first radial surfaces 43, 63, 73 of the connector body 40, the inner clamping members 60 and the outer clamping members 70 face radially inwards relative to the longitudinal axis of the connector body 40 and the outer radial surfaces 44, 64, 74 of the connector body 40, the inner clamping members 60 and the outer clamping members 70 face radially outwards relative to the longitudinal axis of the connector body 40. For each clamping member 50, the bolt 81 passes through the respective through-bore 47 on the connector body 40 and the through-bores 69, 79 on the respective clamping members 60, 70 when they are axially aligned, with the head 84 of the bolt 81 received within the counterbore 79a of the outer clamping member 70. This brings the inner clamping member 60 and outer clamping member 70 into axial alignment. In particular, the first drive faces 66, 76 of each clamping member 60, 70 are axially aligned and the second drive faces 67, 77 of each clamping member 60, 70 are axially aligned. The nut 82 is provided on the free end of the shaft 83 of the bolt 81 and at the first radial surface 63 of the inner clamping member 60. For each clamping mechanism 50, the inner and outer clamping members 60, 70 are radially moveable relative to each other through operation of the actuator 80. Torquing the nut 82 drives the inner and outer clamping members 60, 70 together in opposite radial directions while loosening the nut 82 allows the inner and outer clamping members 60, 70 to be radially separated. Figures 6 and 6a show the clamping mechanisms 50 in an open configuration, in which the inner and outer clamping members 60, 70 of each clamping mechanism 50 are radially separated such that the flanges 14, 15 of the first tubular section 10 can be received between the second radial surface 64 of the inner clamping member 60 and the first radial surface 73 of the outer clamping member 70. The chamfered edge between the first radial surface 64 and first axial surface 61 of the inner clamping member 60 and the chamfered edge between the first radial surface 73 and the first axial surface of the outer clamping member 70 may guide the connector assembly 30 into position as it is lowered on to the first tubular section 10. Figure 7 shows the assembled connector assembly 30, with the clamping mechanisms 50 in their open configuration, lowered on to the first tubular section 10. As best seen in Figure 7a, which is a detailed view of section B of Figure 7 again only showing one clamping mechanism 50, the abutment surface 11 of the first tubular section 10 is engaged with the first axial surface 41 of the connector body 40. In particular, the rib 18 of the first tubular section 10 is received within the groove 45 of the first axial surface 41 of the connector body 40. This brings the first tubular section 10 and the connector body 40 into co-axial alignment and restricts relative radial movement between the first tubular section 10 and the connector body 40. For each clamping mechanism 50, the first drive faces 66, 76 of the clamping members 60, 70 are axially aligned with the shoulder 16, 17 of the flanges 14, 15 of the first tubular section 10. Figure 8 shows the second tubular section 20 lifted above the connector assembly 30. The second tubular section 20 is arranged such that its abutment surface 21 is facing downwards and the shoulders 26, 27 of its flanges 24, 25 are facing upwards. The connector assembly 30 remains in its open configuration, allowing the flanges 24, 25 of the second tubular section 20 to be received between the second radial surface 64 of the inner clamping member 60 and the first radial surface 73 of the outer clamping member 70. The chamfered edge between the second radial surface 64 and second axial surface 62 of the inner clamping member 60 and the chamfered edge between the first radial surface 73 and the second axial surface 72 of the outer clamping member 70 may guide the second tubular section 20 into position as it is lowered on to the connector assembly 30. Figure 9 shows the second tubular section 20 lowered on to the connector assembly 30, with the connector assembly 30 in its open configuration. As best seen in Figure 9a, which is a detailed view of section C of Figure 9 again only showing one clamping mechanism 50, the abutment surface 21 of the second tubular section 20 is engaged with the second axial surface 42 of the connector body 40. In particular, the rib 28 of the second tubular section is received within the groove 46 of the second axial surface 42 of the connector body 40. This brings the second tubular section 20 into co-axial alignment with the connector body 40 and consequently the first tubular section 10. This also restricts relative radial movement between the second tubular section 20 and the connector body 40 and consequently the first tubular section 10. For each clamping mechanism 50, the second drive faces 67, 77 of the clamping members 60, 70 are axially aligned with the shoulders 26, 27 of the flanges 24, 25 of the second tubular section 20. Following the positioning of the second tubular section 20, the nut 82 of each clamping mechanism 50 is torqued. As the bolt passes through both the inner and outer clamping members and the connector body, torquing of the nut 82 drives each set of inner and outer clamping members 60, 70 together in opposite radial directions as is shown in Figure 10 and Figure 10a which is a detailed view of section D of Figure 10 again only showing one clamping mechanism 50. As each nut 82 is torqued, the clamping members 60, 70 move towards the connector body 40 and tubular sections 10, 20, the internal flanges 14, 24 are held within the recess 65 of inner clamping member 60 and the external flanges 15, 25 are held within the recess 75 of the outer clamping member 70. In particular: the first drive face 66 of the inner clamping member 60 engages the shoulder 16 of the first tubular section’s 10 internal flange 14, the first drive face 76 of the outer clamping member 70 engages the shoulder 17 of the first tubular section’s 10 external flange 15; the second drive face 67 of the inner clamping member 60 engages the shoulder 26 of the second tubular section’s 20 internal flange 24; and the second drive face 77 of the outer clamping member 70 engages the shoulder 27 of the second tubular section’s 20 external flange 25. This arrangement and the slope of each shoulder 16, 17, 26, 27, 66, 67, 76, 77 pulls the tubular sections 10, 20 axially together, applying a preload between the tubular sections 10, 20. The extent of this preload is dependent on the angle of the shoulders 16, 17, 26, 27 and drive faces 66, 67, 76, 77 as well as the radial forces applied to the actuator 80. As the angle of the shoulders 16, 17, 26, 27 and drive faces 66, 67, 76, 77 decreases, the extent of the preload from a given radial force from the actuator 80 increases. However, this increases the degree of stress experienced by each clamping member 60, 70 while in use. This is typically compensated for by increasing the radial thickness of the clamping members 60, 70, in turn increasing the overall weight of the clamping mechanism 50. Alternatively, as the angle of the shoulders 16, 17, 26, 27 and drive faces 66, 67, 76, 77 increases, the extent of the preload for a given radial force decreases, thereby decreasing the stress experienced by the clamping members 60, 70 allowing for thinner clamping members 60, 70 to be used. However, in such cases, the connector assembly 30 will require a greater number of clamping mechanisms 50 in order to drive enough total preload between the tubular sections 10, 20. Therefore, when choosing the angle of the shoulders 16, 17, 26, 27 and the drive faces 66, 67, 76, 77, a balance between the weight of each clamping mechanism 50 and the overall number of clamping mechanisms 50 in the connector assembly 30 should be considered. The nuts 82 of each clamping mechanism 50 may be torqued in a sequence following the circumference of the connector assembly 30. More preferably, the nuts 82 of each clamping mechanism 50 may be torqued in a sequence as shown in Figure H.1 of the American Petroleum Institute Specification 6A, 21st Edition or a sequence similar thereto depending on the number of nuts to be torqued. In such sequences, nuts are typically divided into sets. Each set consists of a first nut, a second nut angularly positioned around 180° from the first nut (with respect to the longitudinal axis of the connector body 40), a third nut positioned around 90° from the first nut and a fourth nut angularly positioned 180° from the third nut. The first to fourth nuts of a first set are torqued in sequence to a first torque level (e.g. around 50 to 60% of the desired final torque). Then, a second set with its first nut approximately 45° from the first nut of the first set, i.e. approximately mid-way between the first and third nuts of the first set is torqued in sequence to the first level. Afterwards, third and fourth sets with first nuts approximately 27.5° from the first nuts of the first and second sets respectively are torqued in sequence to the first level. Each new set of four nuts has a first nut that is positioned approximately mid-way between two previously torqued nuts. As further sets of nuts are torqued, the angle from which each first nut is relative to that of an already torqued set is approximately halved. This sequence is continued until all nuts 82 of the connector assembly have been torqued to the first level and then repeated with further increasing torque levels until each nut is fully torqued (e.g. a second level is around 90% of the desired torque and a third level may be 100% of the desired torque). Once the nut 82 of each clamping mechanism 50 has been fully torqued, the tubular sections 10, 20 are effectively clamped together and cannot be axially separated. From this point, assembly of the tubular structure 1 is complete or a further tubular section (not shown) is then installed to the other end (not shown) of the second tubular structure using a suitably configured connector assembly 30. The arrangement described above advantageously reduces the need to handle loose bolts 81 and nuts 82 during installation of the tubular structure 1. All the components of the connector assembly 30 can be pre-assembled in a dedicated facility, meaning that fewer individual components need to be carried up the tubular structure 1 when it is being assembled vertically. This removes or reduces heavy lifting by personnel when making up the connection. It also removes activities from the critical path of the tubular structure’s 1 assembly, with these removed activities being completed in the dedicated facility. Pre-assembly of the connector assembly 30 also advantageously offers a reduced make-up time compared to a traditional L-flange design. Advantages in relation to providing a stronger connection able to achieve higher loading and improved fatigue performance also arise from this arrangement. Whilst the example above describes a connector body 40 formed as a seamless toroid, Figures 11-13 show a first modification to the previously described tubular structure 1 of Figure 1, in which the connector body 140 is segmented into a plurality of arcuate connector body segments 140s. In the example illustrated in Figure 11, the connector body 140 comprises seven body segments 140s. Other examples may have the connector body 140 comprising less or more than seven body segments 140s. In the example illustrated in Figure 12, each body segment 140s carries ten clamping mechanisms 50. However, other examples may have each body segment 140s carrying more or less than ten clamping mechanisms 50. Abutting edges surfaces 140e of adjacent body segments 140s (see Figure 13, which is a detailed view of section E of Figure 11) may be connected via a connection means which may include a connecting element (not shown) arranged to extend across the adjacent body segments 140s and fastening elements such as bolts (not shown) arranged to secure the connecting element to each of the adjacent body segments 140s. In examples including such connection means, each body segment 140s may comprise a cavity (not shown) arranged to receive the connection means such that said connection means does not interfere with the connection between the first and second tubular sections 10, 20. Alternatively, the connection means may comprise each body segment 140s having a dovetail pin (not shown) provided at one abutting edge surface 140e and a dovetail slot (not shown) provided at the opposite abutting edge surface 140e such that adjacent body segments 140s are connectable via a dovetail joint (not shown). Tubular structures comprising a segmented connector body 140 comprise largely similar components and are assembled in the same way as the previously described tubular structure 1 of Figure 1, except in that assembly of such tubular structures comprises the additional step of assembling the body segments 140s to make up the toroidal connector body 140. Tubular structures comprising a segmented connector body 140 enjoy the same advantages as the previously described tubular structure 1 of Figure 1. They also enjoy additional advantages over the tubular structure of Figure 1, as segmented connector bodies 140 may be more easily manufacturable, transportable, and storable than seamless connector bodies 40. Furthermore, the body segments 140s advantageously allow for easier assembly of the connector assembly as each clamping mechanism 50 may be assembled on each body segment 140s that are then connected to form the fully assembled connector assembly. Furthermore, Figures 14 and 14a show a second modification to the previously described tubular structure 1 of Figure 1, in which the connector body 240 is integrally formed on the end of one of the tubular sections. In the example illustrated in Figure 14 and 14a, the connector body 240 is formed on the end of the first (i.e. lower) tubular section 210. Other examples may have the connector body formed on the end of the second (i.e. upper) tubular section. As best seen in Figure 14a (which is a detailed view of section F of Figure 14), the connector body 240 comprises only one annular groove 246 disposed on the free axial surface 241 of the connector body 240. Tubular structures comprising an integrally formed connector body 240, are assembled in much the same way as the previously described tubular structure 1 of Figure 1, except in that the first tubular section 210 with the integrally formed connector body 240 is positioned and a standard tubular section as described in the first example is then installed over the integrally formed connector body 240. Tubular structures comprising an integrally formed connector body 240 enjoy the same advantages as the previously described tubular structure of Figure 1. They also enjoy the further advantage of requiring less tooling, as only one groove 246 and one rib 28 need to be manufactured. They are also likely to require less time in installation as the connector body is integral with one of the tubular sections so will not require separate transportation and installation. Whilst the invention has been described above in relation to the accompanying drawings, it is envisaged that the skilled person may consider some additional features to be useful in some circumstances. For example, it may be advantageous to ensure that the clamping mechanisms 50 remain in their open configuration during the positioning steps of the disclosed tubular structure 1 assembly method (e.g. shown in Figures 7 and 9). In this case, each clamping mechanism 50 may comprise a biasing mechanism (not shown) that urges the inner and outer clamping members 60, 70 apart. Such a biasing mechanism may comprise a plurality of biasing elements (not shown) such as coil springs, flat springs or any other suitable spring / spring-like component). Each biasing element may be connected between the connector body 40 and one of the inner or outer clamping members 60, 70. Typically, each biasing element will be connected to either the inner or outer radial surface 43, 44 of the connector body 40. Biasing elements connected to the inner radial surface 43 of the connector body will be connected to the second radial surface 64 of the inner clamping member 60, typically on the intermediate surface 68 of the inner clamping member 60. Likewise, biasing elements connected to the outer radial surface 43 of the connector body 40 will be connected to the first radial surface 73 of the outer clamping member 70, typically on the intermediate surface 78 of the outer clamping member 70. Each connection may be made by embedding the ends of the biasing elements within the connector body 40 and the inner / outer clamping member 60, 70. Each fastener 80 may further comprise an anti-back off mechanism (not shown) configured to restrict / prevent loosening of the nut 82 over time once the tubular structure 1 is assembled. Such mechanisms may include having the nut 82 be a locknut configured to selectively restrict rotation of the nut 82 about the shaft 83. 5 Additionally, each clamping mechanism 50 may have an imbedded strain gauge (not shown) such that the tension provided by each fastener 80 can be monitored over the lifetime of the assembled tubular structure 1. 10

Claims

1. A connector assembly for connecting ends of first and second tubular sections of a wind turbine tower or other tubular structure, the connector assembly comprising:a connector body;at least one clamping mechanism mounted on the connector body, the or each clamping mechanism comprising;an inner clamping member configured to engage with an inner radial surface of each tubular section and restrict relative axial movement between the tubular sections;an outer clamping member configured to engage with an outer radial surface of each tubular sections and restrict relative axial movement between the tubular sections; andan actuator for driving the inner and outer clamping members in opposite directions.

2. The connector assembly of claim 1:wherein the connector body is configured to be removably disposed between the ends of the tubular sections.

3. The connector assembly of claim 2:wherein the connector body has a first axial surface and second opposite facing axial surface;wherein the first and second axial surfaces of the connector body each comprise either a groove or a rib.

4. The connector assembly of any of claims 1-3: wherein the connector body is a continuous ring.

5. The connector assembly of any of claims 1-3:wherein the connector body is segmented into arcuate body segments; and wherein the connector body comprises at least two body segments.

6. The connector assembly of claim 5:wherein means are provided for connecting abutting edge surfaces of adjacent body segments together.

7. The connector assembly of claim 1:wherein the connector body is integrally formed on the end of one of the tubular sections.

8. The connector assembly of claim 7:wherein the connector body has a free axial surface; andwherein the free axial surface comprises a groove or a rib.

9. The connector assembly of any of claims 1-8:wherein the inner and outer clamping members each comprise first and second drive faces facing in converging directions.

10. The connector assembly of claim 9:wherein each drive face is sloped relative to a transverse plane of the respective clamping member.

11. The connector assembly of claim 10:wherein each drive face is sloped at an angle between 0° and 90°.

12. The connector assembly of claim 11:wherein each drive face is sloped at an angle between 10° and 20°.

13. The connector assembly of claim 12:wherein each drive face is sloped at an angle of 15°.

14. The connector assembly of any of claims 9-13:wherein each first drive face is in axial alignment and each second drive face is in axial alignment.

15. The connector assembly of any of claims 9-14:wherein the inner and outer clamping members each comprise a recess formed by their respective drive faces.

16. The connector assembly of any preceding claim: wherein the actuator connects the inner and outer clamping members.

17. The connector assembly of any preceding claim: wherein the actuator comprises a fastener.

18. The connector assembly of claim 17: wherein the actuator comprises a threaded stud / bolt and nut arrangement.

19. The connector assembly of any preceding claim: wherein the actuator is configured to be operational from within the wind turbine tower or other tubular structure.

20. The connector assembly of any preceding claim comprising: a plurality of clamping mechanisms arranged at regular intervals around the connector body.

21. A wind turbine tower or other tubular structure comprising: first and second tubular sections;a connector assembly according to any of claims 1-20; and wherein the connector assembly is positioned between ends of the first and second tubular sections.

22. The wind turbine tower or other tubular structure of claim 21:wherein an internal flange is formed on the inner radial surface of each tubular section; andwherein an external flange is formed on the outer radial surface of each tubular section.

23. The wind turbine tower or other tubular structure of claim 21 or claim 22: wherein each flange is formed by a shoulder;wherein for each tubular section, the shoulders of each flange face in diverging directions.

24. The wind turbine tower or other tubular structure of claim 23 comprising: a connector assembly according to any of claims 9-15; and wherein each shoulder is set at an angle corresponding to the angle of a respective drive face.

525. A method of assembling a wind turbine tower or other tubular structure comprising:providing a wind turbine tower or other tubular structure according to any of claims 20-24;10 positioning the connector assembly between the ends of the tubular sections;andoperating the actuator to drive the inner clamping member engagement with the inner radial surface of the tubular sections and the outer clamping member into engagement with the outer radial surface of the tubular sections such that relative 15 axial movement between the tubular sections is restricted.

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