A floating support structure for a wind turbine system and a method for assembly

Abstract

The invention describes a floating support structure (1) for supporting an off shore wind turbine comprising a first, second and third main section (10a, 10b, 10c) each comprising a horizontal part and a vertical part (12a, b, c) directly or indirectly connected to the radial end of the horizontal part and the central ends of the horizontal parts (11a, b, c) are joined in a central region thus creating a coupling space (7) underneath the horizontal parts and between the vertical parts. The floating support structure further comprises a transition piece (15) comprising a connecting flange (16) for connecting a coupling end of the wind turbine tower (101) to the support structure. The transition piece further comprises a reinforcement body (17) welded onto the first, second and third horizontal parts.

Description

[0001] Title: A floating support structure for a wind turbine system and a method for assembly

[0002] Technical field of the invention

[0003] The invention relates to the field of off-shore wind turbines. More specifically, the invention relates to a floating support structure for supporting a wind turbine system

[0004] Background

[0005] Many different support structures have been tested and tried with various degrees of success.

[0006] For example, patent publication US 2014 / 0196654 Al discloses a floating support structure for wind turbines consisting of columns having stabilizing elements mounted to their ends. The columns have an inner volume for ballasting. Another type of support structure having the possibility of stabilization and ballasting is disclosed in patent publication US 2019 / 0061884 Al. Yet other examples of floating support structures are disclosed in patent publications US 10,518,846 B2, WO 2014 / 163501 Al and JP 2005-201194 A.

[0007] WO 2014163501 Al describes a stable floating support structure for a wind turbine comprising three stabilizing columns and a mooring system, wherein said mooring system includes at least one catenary mooring line that is connected to the semisubmersible at a point above an operational waterline thereof. Also disclosed is a method of mooring such a wind turbine carrying semi-submersible at an offshore location by means of the at least one catenary mooring line.

[0008] A common disadvantage for any of the known floating support structures of the above-mentioned type is that they are ill-suited for transport across large distances on vessels due to their bulky design and heavy weight.

[0009] To mitigate this problem N020200726 describes semi-submersible support structure, suitable for supporting a wind turbine system comprising a wind turbine tower, a windmill nacelle and wind turbine blades. The floating support structure is particularly suitable for transport as modules on heavy-lift vessels over large distances and assembly of these modules on purpose made barges close to the wind farm. The floating support structure comprises an aft main section and transverse main section joined together in a T-shape and having vertical sections at the outer ends of each main section providing buoyancy to the support structure. Although this construction is less heavy than most of the competitors, light-weight constructions is always a goal in itself because of reduced costs. In view of the above, it is an object of the invention to provide a floating support structure that solves or at least mitigates one or more of the aforementioned problems related to use of prior art solutions.

[0010] A particular object of the invention is to provide a floating support structure that may easily be produced in parts or modules, thereby facilitating long distance transport on suitable vessels such as standard Ultramax bulk vessels.

[0011] Another object of the invention is to provide parts or modules that may be assembled into a fully functional floating support structure of the above-mentioned type using purpose made barges when submerged / floating in water.

[0012] Yet another object of the invention is to provide a light-weight construction without compromising on robustness and safety.

[0013] Yet another object of the invention is to provide a floating support structure that may easily be towed from an assembly site located close to an operation site using a tugboat.

[0014] Yet another object of the invention is to provide a floating support structure that ensures sufficient robustness with respect of transfer of torque, torsion and shear forces during operation.

[0015] Yet another object of the invention is to provide a floating support structure that ensures favorable motion characteristics during operation, even in rough seas.

[0016] Yet another object of the invention is to provide a transition piece suitable for force distribution between the floating support structure 1 and the tower.

[0017] Summary of the invention

[0018] In a first aspect of the invention it is described a floating support structure for supporting a wind turbine system comprising a wind turbine tower, a wind turbine nacelle and wind turbine blades. The floating support structure comprises a first, second and third main section. Each main section comprises a horizontal part having a central end and a radial end wherein the horizontal part has a tubular shape at least in a region including the central end. Each main section further comprises a vertical part with an upper end directly or indirectly connected to the radial end of the horizontal part and oriented in a vertical plane which also includes the horizontal part. The vertical parts provide buoyancy to the floating support structure, and the central ends of the horizontal parts are joined in a central region comprising the central ends. The floating support structure further comprises a transition piece comprising a connecting flange positioned on top of the transition piece for connecting a coupling end of the wind turbine tower distal to the wind turbine nacelle vertically onto the floating support structure and a reinforcement body for joining the first, second and third central ends of each horizontal parts and providing a base for the connecting flange. A centerline LH of the horizontal parts of each main section have an angle of 120 degrees with the centerline LH of the horizontal parts of the neighboring main section.

[0019] The reinforcement body may be shaped like a tubular frustum, wherein a top side of the reinforcement body is elevated a vertical distance (DA) above a plane (P) laid on top of the horizontal parts and wherein sides of the reinforcement body extends downward and radially outward from the connection flange, at an angle a with the plane (P), to a vertical distance (DB) below the plane (P) and wherein the reinforcement body is welded onto the first , second and third horizontal parts. Preferably both on the inside and on the outside of the horizontal parts.

[0020] The reinforcement body may be shaped like a tubular frustum of a right circular cone.

[0021] The reinforcement body may be shaped like a tubular frustum of a right pyramid with three or more sides.

[0022] The angle a may be between 20 and 60 degrees, more preferable between 30 and 45 degrees, most preferable 35 degrees.

[0023] The transition piece may comprise a tower can having a cylindrical shape and being welded onto the top side of the reinforcement body. The tower can is an upward extension transition piece whose main purpose is to avoid deformation caused by welding close to the connection flange positioned on top of the transition piece.

[0024] The vertical distance (DB) below plane (P) may at least be % of the diameter of the horizontal parts, more preferable at least 1 / 3 of the diameter of the horizontal parts, most preferable at least ’A of the diameter of the horizontal parts.

[0025] The vertical distance (DA) above plane (P) may at least be 1 / 5 of the diameter of the horizontal parts, more preferable at least 1 / 4 of the diameter of the horizontal parts, most preferable at least 1 / 3 of the diameter of the horizontal part.

[0026] The cross-section of the horizontal part may be circular, hexagonal, octagonal or any other polygonal shape along the entire length of the horizontal part. The cross-section of the vertical part may be circular, hexagonal, octagonal or any other polygonal shape along the entire length of the vertical part.

[0027] The horizontal parts may be indirectly connected to the respective vertical parts by means of an inclined intermediate part.

[0028] The inclined intermediate part may be oriented with an angle of 45 degree to the respective vertical part and horizontal part.

[0029] The reinforcement body may comprise a joining band positioned along each joining line between each adjacent central end of each horizontal part and a cylindrical body extending a distance above the plane P and extending downward at least through a part of the central ends. Preferably the cylindrical body extends through the entire height of the central ends.

[0030] Each horizontal part may have a radial distance to the adjacent horizontal part and being joined together by a twin bulkhead being part of the reinforcement body and comprising the joining bands and filling the gap resulting from the radial distance between adjacent horizontal parts.

[0031] The twin bulkhead may comprise three pairs of vertically positioned, parallel semicircular plate halves covering and being attached to respective halves of the central ends, wherein each pair of semicircular plate halves are attached to each other at least by means of the joining bands and a vertical central support column.

[0032] In yet an embodiment of the invention the central end of each of the horizontal parts have a surface abutting two vertical planes having a 120 degrees angle between them, wherein an intersection line between the two planes intersects a centerline (LH) of the horizontal parts, thus enabling the first, second and third central ends to form a continuous surface when joined in a horizontal plane.

[0033] The transition piece may comprise an interior frustum section extending in the interior of the horizontal parts as an extension of the frustum shaped transition piece body inside the horizontal part.

[0034] In a second aspect of the invention it is described a set of four subparts constituting a floating support structure as described above when assembled. The set of subparts comprises one central unit comprising the central ends of each horizontal part and the transition piece. The set of subparts further comprise three main sections, namely the first second and third main section (10a, b, c), minus the respective central ends 13a, b, c of each horizontal part. Preferably the central ends extends in a radial direction a distance that causes the central unit and the three main sections to have the same weight. In a third aspect of the invention it is described a method for assembly of a floating support structure as described above. The method requires a crane positioned on a quayside and a barge comprising a first second and third support structure. The purpose of the support structures is to support the respective main sections when positioned on the barge by the crane. The method comprises the following steps:

[0035] A. Positioning the central unit in a central position on the barge.

[0036] B. Positioning the first main section on the first support structure for aligning the first horizontal part with the corresponding first central end of the central unit allowing the first main section to rest on the barge in a stable position,

[0037] C. Positioning the second main section on the second support structure for aligning the second horizontal part with the corresponding second central end of the central unit allowing the second main section to rest on the barge in a stable position,

[0038] D Positioning the third horizontal part on the third support structure for aligning the third horizontal part with the corresponding third central end of the central unit allowing the third main section to rest on the barge in a stable position,

[0039] E. Welding the first, second and third main section on to the central unit in succession as they are positioned on the barge or after all three main sections have been positioned on the barge,

[0040] F. Removing the barge from underneath the floating support structure.

[0041] The first second and third main section may be allowed to rest on the barge in a stable position due to one of the following:

[0042] The point of gravity of the main sections being on the inside of the respective support structures.

[0043] If point E comprises welding the first, second and third main section to the central unit in succession as they are positioned on the barge, the point of gravity of the combined structure of the respective main section and the central unit being on the inside of the respective support structures. the first, second and third vertical parts floats in water bringing the point of gravity of the remaining structure of the main sections not floating in the water inside the respective support structures.

[0044] Step B may comprise the barge being positioned such that the first main section is orientated substantially parallel with the quay side when the first horizontal part is aligned with the corresponding first central end of the central unit during step B and wherein the barge is turned such that the first main section is directed outward form the quay side before commencing with step C. Short description of drawings

[0045] The invention will now be described in more detail by reference to the accompanying figures. The same numeral on different drawings refer to the same feature.

[0046] Fig. 1 shows a perspective view of an embodiment of the floating support structure with a wind turbine mounted.

[0047] Fig. 2 shows a perspective view of an embodiment of the transition piece.

[0048] Fig. 3 shows a cross-section of an embodiment of the transition piece and a main section including interior parts of the transition piece.

[0049] Fig. 4 shows an embodiment of the main section including an inclined intermediate part.

[0050] Fig. 5a-c shows an embodiment of the central unit comprising the central ends of the horizontal sections and the transition piece in a top view, a perspective view and a side view respectively.

[0051] Fig. 6a and b shows two different shapes of the transition piece.

[0052] Fig. 7 show a transition piece comprising an elevation structure and horizontal parts with an octagonal cross-section.

[0053] Fig. 8 a and b shows a side view and top view respectively of a cargo vessel carrying parts constituting a floating support structure according to the invention.

[0054] Fig. 9a-d illustrates an embodiment of the method of assembling the floating support structure by a quay side using a barge.

[0055] Fig. 10a and 10b shows an embodiment of the coupling space from above and from the side respectively.

[0056] Fig. 11 shows an embodiment of a purpose made service vessel before entering into the coupling space of the floating support structure.

[0057] Fig. 12 shows a horizontal sectional view of an embodiment of the support structure having a cylindrical body as part of the reinforcement structure

[0058] Fig. 13 shows a more detailed view of the reinforcement body

[0059] Fig. 14 shows the embodiment of fig. 12 and 13 from above.

[0060] Fig. 15 shows the joining bands with upper and lower joining plates.

[0061] Fig. 16 shows an octagonal embodiment of the central unit. Fig. 17 shows an octagonal embodiment of the joining band.

[0062] Fig. 18 shows an embodiment of the twin bulkheads.

[0063] Fig. 19 shows another embodiment of the twin bulkheads.

[0064] Detailed description

[0065] In the following a floating support structure 1 for supporting an offshore wind turbine system is described as seen in fig. 1. The wind turbine system comprises a wind turbine tower 101, a wind turbine nacelle 102 and wind turbine blades 103. The floating support structure 1 comprises a first, second and third main section 10a, 10b, 10c. In an embodiment, the three main sections are similar to each other and positioned equidistant from each other as seen in fig. 1 and fig. 5a.

[0066] Fig. 3 and 4 shows that each first, second and third main section 10a, b, c comprises a first, second and third horizontal part 1 la, b, c and a first, second and third vertical part 12a, b, c respectively. Each horizontal part I la, b, c has a respective first, second and third central end 13a, b, c and respective first, second and third radial end 14a, b, c, wherein the horizontal parts I la, b, c has a tubular shape at least in a region including the central ends 13a, b, c. The horizontal parts and the central ends can have a round, oval or polygonal cross-section. For simplicity we will hereinafter not use ‘first, second and third’ with respect to the main sections, horizontal parts and the vertical parts. The vertical parts 12a, b, c are, directly or indirectly connected to the respective radial end 14a, b, c of the respective horizontal parts 1 la, b, c and are oriented in a vertical plane in common with the respective horizontal part I la, b, c. The vertical parts 12a, b, c provide buoyancy to the floating support structure 1, and the central ends of the horizontal parts 1 la, b, c are joined in a central region of the floating support structure. Preferably, the central ends 13a, b, c are joined together by welding although bolting is conceivable.

[0067] The horizontal parts 1 la, b, c are connected to an upper region of the vertical parts 12a, b, c to form a coupling space 7 free of any kind of structural obstacles underneath the horizontal parts I la, b, c and between the vertical parts 12a, b, c as illustrated in fig. 10a and b. The coupling space 7 enables the structure to be assembled on a purpose made barge 26 and also allows a purpose made service vessel 9 to attach itself to the floating support structure 1 by positioning an aft coupling section 5 of the service vessel 9 into the coupling space 7 and elevate vessel contact means 6 to attach the vessel contact means 6 to support structure contact means 8 located on the support structure as seen in fig. 11. The support structure contact means 8 can be a strengthened section 36 of the horizontal parts 1 la, b, c or a structure that can interact with the vessel contact means. The coupling process comprises elevating the aft coupling section 5 of the service vessel to lift a portion of the vertical parts 12a, b, c out of the water and thus transferring some of the weight of the support structure to the service vessel 9 in order to make the service vessel and the support structure act as one structure in the waves. Due to the symmetry of the main parts 10a, b, c of the support structure, three coupling spaces are available, which the service vessel 9 may choose from to achieve optimal position according to weather and waves. This provides increased flexibility and will increase the weather window in which safe operation is possible.

[0068] As shown in fig. 5a - c and fig. 12- 15, the floating support structure further comprises a transition piece 15. The transition piece 15 comprises a connecting flange 16 and a reinforcement body 17. The connecting flange 16 is adapted for connecting a coupling end of the wind turbine tower 101 distal to the wind turbine nacelle 102 vertically onto the floating support structure 1. The connecting flange 16 can be positioned on a top side 29 of the reinforcement body 17. In an embodiment the reinforcement body 17 is shaped like a tubular frustum. In an embodiment, the connecting flange is located some distance above the reinforcement body 17. In such an embodiment the transition piece 15 comprises a tower can 23 shaped like a cylinder or slightly coned cylinder having the connection flange 16 on top as seen in fig. 7. Fig. 5c shows the floating support structure 15 from the side in a direction from where the third main section would have been. The purpose of the transition piece 15 is to increase stiffness and reduce fatigue in the central region of the floating support structure. As illustrated in fig. 5c the connecting flange 16 is elevated a vertical distance (DA) above a plane (P) laid on top of the horizontal parts I la, b, c. Sides of the reinforcement body 17 extends downward and radially outward from the connection flange, at an angle a with the plane (P), to a vertical distance (DB) below the plane (P). The reinforcement body is fastened onto the first, second and third horizontal parts I la, b, c. Preferably both on the inside and on the outside of the horizontal parts I la, b, c. In one embodiment, brackets are added between the reinforcement body 17 and the horizontal parts I la, b and c.

[0069] In an embodiment shown in fig. 14 and 15 the reinforcement body 17 comprises three reinforcement bands 31 covering joining lines 33 (see fig. 5a and 5b) where the central ends of adjacent horizontal parts meet and are joined together. The joining bands 31 may be attached at the top and bottom to an upper and lower joining plate 34a, b. The reinforcement body 17 further comprises a cylindrical body 32 extending a distance above the plane P, and going downward through at least parts of the central ends 13 a, b, c. The cylindrical body may be having the connection flange 16 on its top. The cylindrical body can be cut to fit on top side of the central ends 13a, b, c and then continue inside the central ends at least part of the distance to the bottom side of the central ends as indicated in fig. 12 and 13. The central ends 13a, b, c are joined together at the center of the support structure. There are endless numbers of ways to make the central ends meet in a continuous manner (continuous meaning without gaps). A functional way of doing it is indicated in fig. 5a as seen from above and comprises cutting each central end along two vertical planes having a 120 degree angle between them and let a centerline LH of each central end of horizontal part divide the 120 degree angle in two equal parts. The central ends 13a, b, c can be joined directly with the reinforcement bands 31 attached outside of the joining lines 33 that arises. Or the central ends can be moved radially outward and joined by a twin bulkhead 41being part of the reinforcement body 17 and comprising the reinforcement bands 33, and filling the gap resulting from moving the central ends 13a, b, c outwards as indicated in fig. 13. Preferably, a plurality of strengthening plates 38 are welded on to the intersections between the cylindrical body 32 and the central ends 13a, b, c and between the cylindrical body and the joining bands 31 as indicated in fig. 14.

[0070] In an embodiment shown in fig. 18 the twin bulkhead 41 comprises three pairs of vertically positioned parallel semicircular plate halves 42, wherein each pair of semicircular plate halves has an angel of 120 degrees to the adjacent pair of semicircular plate halves 42 as seen in fig. 18 and 19. The semicircular plate halves are strengthened with vertical ribs 40 and horizontal ribs 39. Each semicircular plate halves 42 covers and are welded onto the respective halves of the central ends 13a, b, c. The twin bulkhead 41 may further comprise a central vertical support column 43 comprising three vertical plates 37 welded on to each other and on to vertical joining lines of respective adjacent semicircular plate halves 42 providing the central support column 43 with a triangular cross-section.

[0071] In an embodiment shown in fig. 19 the principle is the same as in fig. 18, but the central support column 43 is larger with a hexagonal cross-section. The three pairs of semicircular plate halves 42 are fitted with an intermediate section 44 having an angle of 150 degrees with each of two adjacent semicircular plate halves. The central ends 13a, b, c must be reshaped accordingly. The hexagonal shape of the central support column 43 is created by three vertical plates 37 positioned between adjacent corners of respective semicircular shaped plates and respective intermediate sections 44 and the three intermediate sections 44 themselves.

[0072] As mentioned previously the support structure is designed to be able to be coupled to a purpose made service vessel 9. Preferably, the horizontal parts I la, b, c and vertical parts 12a, b, c are fitted with strengthened sections 36 as indicated in fig.

[0073] 12, where the support vessel 9 may interact with the horizontal parts either because of wave action or poor handling of the service vessel 9. Extra strength may also be needed due to gravitational forces acting differently on the horizontal parts I la, b, c when the vertical parts 12a, b, c are partly lifted out of the water.

[0074] The purpose of the transition piece 15 is to increase stiffness and reduce fatigue in the central region of the floating support structure. Preferably, a central axis A, indicated in fig 5b, of the floating support structure 1 goes through a common intersection of the three centerlines LH of the respective horizontal sections I la, b, c (and central ends) and the central axis A is centrally positioned in the reinforcement body 17 as indicated in fig. 5a and 5b. Because of the central position of the tower 101 and the peripheral position of the buoyant vertical parts 12a, b, c, and since the support structure do not have any structural support between the three main sections 10a, b, c except from in the central region, the transition piece 15 must absorb a lot of forces . However, if this problem is solved, a very light weight construction is achieved in terms of capacity pr. ton of steel.

[0075] In an embodiment, shown in fig. 6b, the reinforcement body 17 is shaped like a tubular frustum of a right circular cone. In another embodiment, shown in fig. 6a, the reinforcement body 17 is shaped like a tubular frustum of a right pyramid with three or more sides. Fig. 6a shows an embodiment with six sides. This corresponds with a cut-out for each main section being done in every second side constituting the frustum as indicated in the figure.

[0076] Preferably, the angle a between the plane P and the side(s) of the frustum is between 20 and 60 degrees, more preferable between 30 and 45 degrees, most preferable 35 degrees.

[0077] The vertical distance (DB) of the extension of the reinforcements structure below plane (P) is, preferably, at least A of the diameter of the horizontal parts 1 la, b, c, more preferable at least 1 / 3 of the diameter of the horizontal parts I la, b, c, most preferable at least ’A of the diameter of the horizontal parts 1 la, b, c. In a particular advantageous embodiment, the transition piece extends down to the altitude of a centerline LH of the horizontal part 1 la, b, c. This is equivalent to the extension of the reinforcements structure below plane (P) being ’A of the diameter of the horizontal parts I la, b, c.

[0078] In an embodiment of the floating support structure the vertical distance (DA) of the connecting flange 16 above plane (P) is at least 1 / 5 of the diameter of the horizontal parts I la, b, c, more preferable at least 1 / 4 of the diameter of the horizontal parts 1 la, b, c, most preferable at least 1 / 3 of the diameter of the horizontal parts 1 la, b, c. The elevation of the connecting flange 16 above the plane P causes the frustum of the reinforcement body 17 to extend further outward on the horizontal parts 1 la, b, c thus making the central region of the floating support structure stiffer. The reinforcement body 17 must at least extend further outward than the welding joining the three central ends 13a, b, c of the horizontal parts 1 la, b, c. In a preferable embodiment a lower rim of the reinforcement body 17 has a diameter, which is 1,5 - 3 times the diameter of the horizontal sections, more preferable substantially 2 times the diameter of the horizontal sections I la, b, c.

[0079] The cross section of the horizontal parts and the vertical parts 12a, b, c can have many shapes, but in a preferred embodiment the cross-section of the horizontal parts 1 la, b, c and / or the vertical parts 12a, b, c is circular along their entire lengths. In theory, parts of the horizontal section could comprise a framework or a truss system instead of a tubular structure.

[0080] In an advantageous embodiment the horizontal parts I la, b, c are indirectly connected to the respective vertical parts 12a, b, c by means of an inclined intermediate part 18a, b, c. A direct 90 degree connection will produce more fatigue problems and also add to the combined length of the horizontal and vertical parts.

[0081] In an optimal embodiment shown in fig. 3 and 4 the inclined intermediate part 18 is oriented with an angle of 45 degree to the respective vertical part 12a, b, c and horizontal part I la, b, c.

[0082] In a preferred embodiment shown in fig 5c the centerline LH of the horizontal parts 1 la, b, c of each main section 10a, b, c have an angle of 120 degrees with the centerline LH of the horizontal parts (I la, b, c) of the neighboring main section (10a, b, c). This will provide a floating support structure which is mirror symmetric around a vertical plane going through the centerline LH of any one of the horizontal parts I la, b, c.

[0083] In order to join the three main sections a lot of possibilities will be available for the skilled person. However, in a preferred embodiment illustrated in fig 5a the central end 13a, b, c of each of the horizontal parts 1 la, b, c are cut in such a way that the cut surface would abut two vertical planes having a 120 degrees angle between them, and being symmetrically positioned around the centerline LH of the horizontal parts, wherein an intersection line between the two planes intersects the centerline (LH) of the horizontal parts 13a, b, c, thus enabling the central ends 13a, b, c to form a continuous surface when joined. We assume that the angle between the centerline LH and the two vertical planes are 60 degrees when seen in a horizontal plane.

[0084] In order to integrate the central ends 13a, b, c and the transition piece 15, semicircular cut-outs of an interior frustum section 20, as seen in fig. 6a and 6b, can be executed on the reinforcement body 17. Thus, the main part of the reinforcement body can be lifted on top of the three central ends for welding and the interior frustum section 20 can be positioned on the inside of the central end for welding. The transition piece 15 may further comprise a frustum extension 21 connecting the lower part of the interior frustum section 20 to the lower parts of the horizontal part 1 la, b, c. If the shape of the reinforcement body 17 is a cone, this could be done by the frustum section 21 being a cut-out of a cylindrical shape with a diameter similar to the lower part of the reinforcement body 17 as indicated in fig. 3 and 5c. If the shape of the reinforcement body is a frustum pyramid this could be done by using one or more plates.

[0085] In order to provide a flexible mounting and transport of the floating support structure 1 it can be produced in four parts almost anywhere in the world, stacked onto a carrier vessel 30, for instance an ordinary bulk carrier as seen in fig. 8a and b and assembled on a site near the final working position of the floating support structure 1. The symmetry of the floating support structure 1 also enables an advantageous division of the support structure 1 into a set of subparts comprising four subparts of fairly similar weight, thus reducing the maximum lifting capacity needed when assembling the floating support structure. The set of subparts may comprise a first second and third subpart respectively comprising the first second and third main section 10a, b, c, minus the respective central ends 13a, b, c of each horizontal part 1 la, b, c. The set of four subparts may further comprise a fourth subpart comprising a central unit 24 comprising the central ends 13a, b, c of each horizontal part I la, b, c and the transition piece 15.

[0086] Figure 4 shows an anchor line connection 22 above sea level and fig. 12 shows an anchor connection 22 below sea level. Preferably, the anchor line connection 22 is below sea level. This feature reduces total length of anchor line 35 and therefor total weight while also avoiding the exposed wave region near the water surface. Preferably, the anchor line 35 is made of a slightly elastic plastic material.

[0087] With reference to fig. 9 a-d a method for assembling the floating support structure is also described. In order to carry out the method a barge 26 of suitable size is needed. Preferably the barge provides equal buoyancy under all the main sections 10a, b, c and is provided with a first second and third support structure 27a, b, c to support the horizontal parts 12a, b, c of the main sections 10a, b, c. One shape that will accomplish this is a substantially square shape as seen in fig. 9a-d.

[0088] Furthermore, a lifting device 28 is needed, preferably a crane 28 mounted on a quay side 25 to lift the central unit 24 and the three main sections 10a, b, c into a correct position on the barge 26. We will assume that the central unit 24 and the main sections 10a, b, c are all stored on the quay side 29. We will also assume that when writing first second or third main sections 10a, b, c, we will not include the central ends 13a, b, c, because those are connected to the central unit 24 The method will comprise the following steps:

[0089] A. Positioning the central unit 24 in a central position on the barge 26 as indicated in fig. 9a. The central ends of the central unit 24 should be directed towards the respective first, second and third support structure 27a, b, c. The dotted rectangles in fig. 9a show alternative or additional positions of the first second and third support structures 27a, b, c to obtain a configuration where the point of gravity of the main sections 10a, b, c are on the inside of the first, second or third support structure 27a, b, c when in a correct position for welding.

[0090] B. As indicated in fig. 9b, positioning the first main section 10a on a first support structure 27a for aligning the first horizontal part with the corresponding first central end 13a of the central unit 24 while the first vertical part 12a floats in water and welding the first central end 13a and the first horizontal part I la together. If needed the crane may hold the main section in position while welding is done.

[0091] C. As indicated in fig. 9c, positioning the second main section 10b on a second support structure 27b for aligning the second horizontal part 1 lb with the corresponding second central end 13b of the central unit 24 while the second vertical part 12b floats in water and welding the second central end 13b and the second horizontal part 1 lb together.

[0092] D As indicated in fig. 9d, positioning the third horizontal part 11c on a third support structure 27c for aligning the third horizontal part 11c with the corresponding third central end 13c of the central unit 24 while the third vertical part 12c floats in water and welding the third central end 13c and the third horizontal part 11c together.

[0093] E. Removing the barge from underneath the floating support structure 1.

[0094] Obviously, the lifting can be done with the barge 26 in one position only. However, the distance from the crane to the main section 10a pointing away from the quay side 25 as seen in fig. 9c and d, will put high demands on the reach of the crane.

[0095] In order to reduce the needed capacity in terms of reach of the crane, the barge can be turned 90-120 degrees between step B and C and / or step C and D as indicated in fig. 9 a-d. In this manner the reach of the crane can be reduced to roughly half the needed reach when positioning the main section 10a, b, c positioned on the opposite side of the barge 26 relative to the crane 28. Preferably, the barge is turned between step B and C only, because then there is less mass to move and the reduction of reach achieved because of the second turning is minimal. In a preferred embodiment the barge is equipped with thrusters and / or propellers to be able to conduct the turning operation without using tugboats. This translates into step B comprising the barge being positioned such that the first main section 10a is orientated parallel with the quay side 25 when aligned with the first horizontal part I la during step B as seen in fig. 9b. Fig. 9c illustrates that the barge has been turned such that the first main section 10a is directed outward form the quay side 25 before commencing with step C and positioning the second main section 10b on the barge. Fig 9 d shows the third main section 10c being hoisted in position for mounting. In such an embodiment we assume that the first main section 10a is parallel with a centerline of the barge 26 and that the second and third main section 9b, c is positioned at an angle of 120 degrees with said centerline at each respective side.

[0096] As an alternative to welding each main section 10a, b, c on to the central unit in succession as they are position on the barge, all the main sections may be welded on to the central unit after all the main sections have been positioned on the barge. This is possible if the point of gravity of the main sections are positioned inside the respective support structures 27a, b, c. By ‘inside’ we mean closer to the central region of the barge than the support structures. In such a configuration the vertical parts will rest in a stable position on the barge and do not need to float in the water to obtain a stable position for the main sections. Obviously if the main section is welded on to the central unit their combined point of gravity will be inside the support structure 27a, b, c. A stable position for the main section may also be obtained by allowing the vertical part 12a, b, c to float at least partly in the water thus allowing the point of gravity of the remaining part of the main section not floating in water to be inside the support structure. Instead of letting the vertical part 12a, b, c float in water in may also be held by a crane on the barge or some other structure.

[0097] References

[0098] 1 Floating support structure

[0099] 5 Aft coupling section

[0100] 6 Vessel contact means

[0101] 7 Coupling space

[0102] 8 Support structure contact means

[0103] 9 Service vessel

[0104] 10a First main section

[0105] 10b Second main section

[0106] 10c Third main section

[0107] I la First Horizontal part

[0108] 11b Second horizontal part

[0109] 11c Third horizontal part

[0110] 12a First vertical part

[0111] 12b Second vertical part

[0112] 12c Third vertical part

[0113] 13a First central end

[0114] 13b Second central end

[0115] 13c Third central end

[0116] 14a First radial end

[0117] 14b Second radial end

[0118] 14c Third radial end

[0119] 15 Transition piece

[0120] 16 Connecting flange

[0121] 17 Reinforcement body

[0122] 18a, b, c first second and third inclined intermediate part

[0123] 19 Wave damper

[0124] 20 Interior frustum section of transition piece

[0125] 21 Interior frustum extension

[0126] 22 Anchor line connection

[0127] 23 Tower can

[0128] 24 Central unit

[0129] 25 Quay side

[0130] 26 Barge

[0131] 27 Support structure

[0132] 27a First support structure

[0133] 27b Second support structure

[0134] 27c Third support structure

[0135] 28 Lifting device / crane

[0136] 29 Top side of reinforcement body

[0137] 30 Carrier vessel 31 Joining band

[0138] 32 Cylindrical body

[0139] 33 Joining lines

[0140] 34a, b Upper and Lower joining plate

[0141] 35 Anchor line

[0142] 36 Strengthened section

[0143] 37 Vertical plate

[0144] 38 Strengthening plates

[0145] 39 Horizontal ribs

[0146] 40 Vertical ribs

[0147] 41 Twin bulkhead

[0148] 42 Semicircular plate halves

[0149] 43 Central support column

[0150] 44 Intermediate section

[0151] 101 Wind turbine tower

[0152] 102 wind turbine nacelle

[0153] 103 Wind turbine blades

[0154] P Plane laid on top of horizontal parts

[0155] DA Vertical distance of connection flange 16 above the plane P

[0156] DB Vertical distance of extension of reinforcement body below the plane P

[0157] LH Central line of Horizontal parts I la, b, c

[0158] A Vertical central axis of floating support structure

Claims

CLAIMS1. A floating support structure (1) for supporting a wind turbine system comprising a wind turbine tower (101), a wind turbine nacelle (102) and wind turbine blades (103), wherein the floating support structure (1) comprises: a first, second and third main section (10a, 10b, 10c) each comprising: a horizontal part (1 la, b, c) having a central end 13a, b, c) and a radial end (14a, b, c), wherein the horizontal part has a tubular shape at least in a region including the central end (13a, b, c) a vertical part (12a, b, c) with an upper end directly or indirectly connected to the radial end (14a, b, c) of the horizontal part (1 la, b, c) and oriented in a vertical plane in common with the horizontal part (1 la, b, c), wherein the vertical parts (12a, b, c) provide buoyancy to the floating support structure (1), and the central ends of the horizontal parts (I la, b, c) are joined in a central region comprising the central ends (13a, b, c), a transition piece (15) comprising: a connecting flange (16) positioned on top of the transition piece (15) for connecting a coupling end of the wind turbine tower (101) distal to the wind turbine nacelle (102) vertically onto the floating support structure (1), a reinforcement body (17) for joining the first, second and third horizontal parts (1 la, b, c) and providing a base for the connecting flange 16, and wherein a centerline (LH) of the horizontal parts (I la, b, c) of each main section (10a, b, c) have an angle of 120 degrees with the centerline (LH) of the horizontal parts (I la, b, c) of the neighboring main sections (10a, b, c).

2. The floating support structure according to claim 1, wherein the reinforcement body (17) is shaped like a tubular frustum, wherein a top side (29) of the reinforcement body (17) is elevated a vertical distance (DA) above a plane (P) laid on top of the horizontal parts (I la, b, c) and wherein sides of the reinforcement body (17) extends downward and radially outward from the connection flange, at an angle a with the plane (P), to a vertical distance (DB) below the plane (P) and wherein the reinforcement body is welded onto the respective horizontal parts (I la, b, c).

3. Floating support structure according to claim 2, wherein the reinforcement body (17) is shaped like a tubular frustum of a right circular cone or like a tubular frustum of a right pyramid with three or more sides.

4. Floating support structure according to any of the claims 2 - 3, wherein the angle a is between 20 and 60 degrees, more preferable between 30 and 45 degrees, most preferable 35 degrees, the vertical distance (DB) below plane (P) is at least i of the diameter of the horizontal parts (I la, b, c), and the vertical distance (DA) above plane (P) is at least 1 / 3 of the diameter of the horizontal parts (I la, b, c).

5. Floating support structure according to claim 1, wherein the reinforcement body (17) comprises a reinforcement band (31) positioned along each joining line (33) between each adjacent central end (13a, b, c) of each horizontal part (I la, b, c) and a cylindrical body (32) extending a distance above the plane P and extending downward at least through parts of the central ends.

6. Floating support structure according to claim 5, wherein each central end (13a, b, c) of the horizontal parts (1 la, b, c) have a radial distance to the adjacent central end (13a, b, c) and is joined together by a twin bulkhead (41) being part of the reinforcement body (17) and comprising the joining bands (31) and filling the gap resulting from the radial distance between adjacent central ends (13a, b, c).

7. Floating support structure according to claim 6, wherein the twin bulkhead (41) comprises three pairs of vertically positioned parallel semicircular plate halves (42) covering and being attached to respective halves of the central ends (13a, b, c), wherein each pair of semicircular plate halves (42) are attached to each other at least by means of the joining bands (31) and a vertical central support column (43).

8. Floating support structure according to any of the preceding claims, wherein the cross-sections of the horizontal parts (1 la, b, c) and the vertical parts (12a, b, c) are circular along the entire length of the horizontal parts (I la, b, c) and vertical parts (12a, b, c).

9. Floating support structure according to any of the preceding claims, wherein the horizontal parts (I la, b, c) are indirectly connected to the respective vertical parts (12a, b, c) by means of an inclined intermediate part (18a, b, c).

10. Floating support structure according to claim 9, wherein the inclined intermediate part (18a, b, c) is oriented with an angle of 45 degree to the respective vertical part (12a, b, c) and horizontal part (11 a, b, c).

11. Floating support structure according to any of the preceding claims, wherein the central end (13a, b, c) of each of the horizontal parts (1 la, b, c) have an end surface abutting two vertical planes having a 120 degrees angle between them, and being symmetrically positioned around a centerline (LH) of the respective horizontal part (13a, b, c), thus enabling the first, second and thirdcentral ends (13a, b, c) to form a continuous surface when joined in a horizontal plane.

12. A set of four subparts constituting a floating support structure according to any of the claims 1-11, the set of subparts comprising: a central unit (24) comprising the central ends 13a, b, c of each horizontal part (I la, b, c) and the transition piece (15), the first second and third main section (10a, b, c), minus the respective central ends 13a, b, c of each horizontal part (I la, b, c).

13. Method for assembly of a Floating support structure (1) according to claim 12, wherein the method requires a crane (28) positioned on a quayside (25) and a barge (26) comprising a first second and third support structure (27a, b, c), wherein the method comprises the following steps:A. Positioning the central unit (24) in a central position on the barge (26).B. Positioning the first main section (10a) on the first support structure (27a) for aligning the first horizontal part (I la) with the corresponding first central end (13a) of the central unit (24) allowing the first main section to rest on the barge in a stable position,C. Positioning the second main section (10b) on the second support structure (27b) for aligning the second horizontal part (1 lb) with the corresponding second central end (13b) of the central unit (24) allowing the second main section to rest on the barge in a stable position,D Positioning the third horizontal part (11c) on the third support structure (27c) for aligning the third horizontal part (11c) with the corresponding third central end (13 c) of the central unit (24) allowing the third main section to rest on the barge in a stable position,E. Welding the first, second and third main section to the central unit (24) in succession as they are positioned on the barge or after all three main sections have been positioned on the barge,F. Removing the barge (26) from underneath the floating support structure (1).

14. Method according to claim 13 wherein the first second and third main section (10a, b, c) is allowed to rest on the barge in a stable position due to one of the following:the point of gravity of the main sections (10a, b, c) being on the inside of the respective support structures (27a, b, c), if point E comprises welding the first, second and third main section to the central unit (24) in succession as they are positioned on the barge, the point of gravity of the combined structure of the respective main section and the central unit being on the inside of the respective support structures (27a, b, c) the first, second and third vertical parts (12a, b, c) floats in water bringing the point of gravity of the remaining structure of the main sections not floating in the water inside the respective support structures (27a, b, c).

15. Method according to claim 13, wherein step B comprises the barge (26) being positioned such that the first main section (10a) is orientated substantially parallel with the quay side (25) when the first horizontal part (1 la) is aligned with the corresponding first central end (13a) of the central unit (24) during step B and wherein the barge is turned such that the first main section is directed outward form the quay side (25) before commencing with step C.

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