Floating foundation for offshore wind turbines and method of construction

Abstract

A floating foundation for an offshore wind turbine, the floating foundation having a tower defining a vertical direction, the floating foundation comprising at least three vertical sections and at least two horizontal sections wherein the vertical sections and the horizontal sections are tubular members, the tubular members are arranged in an alternating manner and connected together by interpenetrating pipe joints, and wherein one of the vertical sections is arranged to receive a tower.

Description

Technical Field

[0001] The present invention relates to floating foundations, in particular for supporting offshore wind turbines, and to methods of constructing and installing such foundations and turbines. Background Art

[0002] Floating wind turbines are an excellent source of renewable energy because they can be located offshore where winds are stronger and more consistent. They show great promise for wind farms because floating wind turbines can be installed in deep waters, which significantly increases the available sea area, whereas fixed wind turbines are limited to shallow waters close to the coast.

[0003] A floating wind turbine typically has a wind turbine comprising a tower, a nacelle and blades attached to a foundation that is floating and anchored to the seabed by a catenary or a taut mooring system. Existing floating foundations can be cylindrical buoy type, wherein the foundation comprises a steel and / or concrete cylinder filled with a ballast of water and gravel to keep it upright and floating. However, these types of floating foundations are not globally suitable for large wind turbines because the draft of the foundation required to keep the foundation and wind turbine in a floating state is directly related to the size and weight of the wind turbine. This results in extreme airflow for large turbines, thereby complicating construction, transportation and installation.

[0004] Other systems use a platform construction similar to oil and gas type floating platforms. US 8471396B2 discloses one such floating wind turbine platform, which includes a floating frame including at least three columns connected to each other with horizontal main beams. The wind turbine tower is installed in the center of the three columns or above the tower support column to simplify the system construction and improve the structural strength.

[0005] EP 2387528 A2 discloses a tension-leg offshore submerged platform in a hybrid concrete-steel solution having a prestressed concrete central body, a steel peripheral structure connected to the central body by steel reinforcements and further to a foundation for such a platform.

[0006] However, floating foundations in deep waters are exposed to harsh environments of strong winds and large waves. In these environments, high forces are caused on the constituent elements of the floating foundation. Connecting elements and / or connecting elements (such as joints and / or pillars) are particularly fragile because the forces are highly concentrated in these areas. Therefore, such floating foundations require regular inspection and maintenance. A floating foundation has been proposed in the unpublished application PCT / EP2021 / 083837, which uses a continuous tubular structure with a tortuous shape. This has the particular advantage of a relatively simplified assembly process because the continuous structure does not have a closed loop in its structure that requires precise positioning and can therefore even be assembled in a floating state. The floating foundation avoids the use of joints and pillars by using a smooth curved transition. However, the design and construction of such a curved section is more complicated and less suitable for a large-volume production process.

[0007] It is desirable to provide a floating foundation suitable for large wind turbines that is capable of withstanding the harsh conditions of a deep water environment but is relatively cost effective and easy to construct, transport and install. Summary of the invention

[0008] Therefore, according to a first aspect of the present invention, there is provided a floating foundation with a tower as defined in claim 1. The floating foundation comprises at least three vertical sections and at least two horizontal sections, wherein the vertical sections and the horizontal sections are tubular members, which are arranged in an alternating manner and connected together by interpenetrating pipe joints, and wherein one of the vertical sections is arranged to receive the tower. The vertical sections include a first vertical section, a last vertical section, and an intermediate vertical section spaced apart from each other in a horizontal plane to ensure the stability of the floating foundation. In this context, the term interpenetrating pipe joint is intended to mean a joint in which a first tube passes through the front wall of a second tube and is provided with a connection to the rear wall of the second tube. A technical structural engineer will understand that this provides a significantly stronger joint than a joint connected only at an intersection line on the front wall. The term is intended to cover a joint in which a first tube terminates in a second tube and a fully interpenetrating pipe joint in which a first tube extends beyond a second tube. The term also includes joints between tubes of equal thickness and joints between those tubes where a first tube has a diameter that is smaller than a diameter of a second tube.In an embodiment, no more than two tubular members intersect at an interpenetrating tube joint.

[0009] These horizontal sections can include at least one underwater section and at least one above-water section, the at least one underwater section being configured to stay underwater when the floating foundation is in use, and the at least one above-water section being configured to stay above the water when the floating foundation is in use. The vertical sections are intended to pass through the waterline and will therefore each have an underwater portion and an above-water portion. The connection between the vertical section and the horizontal section is achieved using interpenetrating pipe joints. These joints are advantageous because they can achieve sufficient strength without the use of external supports or struts. The curved sections are difficult to manufacture because such sections require the use of double curved plates, or a plurality of smaller elements assembled together to form different sections.

[0010] To aid further description, the following directions are used throughout this application. The direction parallel to the tower of the wind turbine is the vertical direction. The plane perpendicular to the vertical direction is the horizontal plane. The horizontal plane is defined by the water surface when the floating foundation floats. The above-water sections are kept away from the water surface during use, while the underwater sections remain submerged during use. Only the vertical sections pass through the water surface and link the underwater sections to the above-water sections when the floating foundation floats. It should be understood that the exact depth at which the foundation floats will depend on the weight of the turbine and the presence of ballast within the foundation, and that parts of the underwater sections may extend above the waterline under certain conditions, and vice versa.

[0011] It should be noted that the floating foundation according to the present invention can be substantially hollow. However, this does not mean that the floating foundation cannot include multiple interior chambers or compartments. In fact, in many cases, for the correct operation of the floating foundation, the interior space of the floating foundation must be divided, as will be apparent from this disclosure.

[0012] In an embodiment, the floating foundation may be arranged to define a tortuous path extending from a proximal end to a distal end. The proximal end may be arranged to stay above water when the floating foundation is in use, and the distal end may be arranged to stay underwater when the floating foundation is in use. A first vertical section may be located at the proximal end of the floating foundation. An intermediate vertical section may be located between a horizontal underwater section and a horizontal above water section. A final vertical section may be located at the distal end of the floating foundation. In this context, the word "tortuous" should be understood in the broadest sense to mean "changing direction, rather than extending linearly". Thus, tortuous may be interpreted as meandering, zigzagging, bending, twisting, turning, to name just a few.

[0013] The three vertical sections are spaced apart from each other to form a stable base. If the system including the floating foundation and the wind turbine manages to return to the equilibrium position when it is displaced from its equilibrium position under the influence of external forces (such as waves and / or wind), the base is stable. In other words, the system must have sufficient hydrodynamic stability to offset the heeling moment of strong winds, currents and waves. Typically, this will require that the vertical sections are sufficiently spaced apart from each other so that the floating center is kept at a distance from each of the vertical sections. It will also be required that the size of the above-water section is sufficient not to be submerged by the maximum possible force or moment acting on the wind turbine. In an embodiment, the vertical sections can be spaced apart from each other by at least 40m or at least 60m or even greater than 100m in a center-to-center measurement. Preferably, the distance between the vertical sections is about 85m.

[0014] Any of these vertical sections may be arranged to receive a tower. The tower may be connected to the floating foundation by connection means, such as one or more of the following: welding, using bolts, flanges, couplers, sleeves, sliding joint connections, and / or the like. In an embodiment, a portion of the tower and a portion of the corresponding vertical section may overlap. For the avoidance of doubt, in this context, the tower is considered to start above the waterline and the vertical section of the floating foundation passes through the waterline. However, it is not intended to exclude a tower that passes through the waterline and is connected to an underwater floating foundation. In this case, the base of the tower may form a vertical section. Preferably, the tower is connected to an intermediate vertical section, which creates a hydrodynamically stable structure. Nevertheless, the tower may be connected to the first vertical section or the last vertical section, which is advantageous because the installation process may be carried out in a smoother manner, as will be discussed below. The hydrodynamics of this structure may be further improved by using a heave plate and / or a ballast tank.

[0015] According to another embodiment, the distances between successive vertical segments in the horizontal plane are equal. The transition regions are equidistantly spaced. Preferably, the vertical segments form the nodes of an equilateral triangle in the horizontal plane. Such a symmetrical configuration provides optimized stability for the base of the floating foundation. This is particularly suitable for foundations that are tethered in place in a direction. It will be appreciated that other configurations and different numbers of vertical segments are also possible, with a minimum of three vertical segments for stability. In particular, foundations that are tethered to rotate with the wind direction may benefit from a different distribution of vertical segments.

[0016] The sections of the floating foundation are preferably linear. The linear shape of these sections is advantageous because it is easiest to produce and assemble. The length of these horizontal sections can be selected to provide sufficient vertical section spacing for the floating foundation when the wind turbine is attached to the floating foundation and thus provide the required stability. This length will depend on the parameters of the wind turbine and the parameters of the floating foundation. The length of the vertical sections will depend on other factors of the design (especially the expected wave height) to ensure that the above-water sections remain above water.

[0017] In addition, the use of straight underwater sections can be beneficial to limit the draft of the floating foundation. In a preferred embodiment, the draft of the loaded foundation can be less than 30m or even less than 20m, and preferably about 24m. It can be ballasted to a deeper operating position subsequently. Under unloading conditions, before installing the tower, for a foundation with sufficient capacity for a wind turbine greater than 10MW, the draft may be less than 10m or less than 8m and as small as 6m. Such shallow draft allows easy repositioning and / or movement in nearshore waters. When the foundation is stranded on shore or in shallow waters, one or more straight sections can also provide a stable base.

[0018] As mentioned above, the floating foundation comprises interpenetrating pipe joints. The interpenetrating pipe joints are arranged to interconnect the vertical sections with the horizontal sections. The interpenetrating pipe joints (or more precisely the connections between the sections forming the interpenetrating pipe joints) can be fixed by one or more of the following: welding, using bolts, flanges, couplers, sleeves, and / or the like. Welding is the most preferred option. Preferably, for each interpenetrating pipe joint, one end of the horizontal section completely passes through the vertical section and is welded on both the inlet side and the outlet side.

[0019] In an embodiment, the horizontal segments all have the same constant first diameter and the vertical segments all have the same constant second diameter. The first diameter may be greater than the second diameter, or the two diameters may be the same. In a preferred embodiment, the first diameter of the horizontal segment is smaller than the second diameter of the vertical segment. This allows the horizontal segment to pass through the vertical segment, leaving at least a portion of the wall of the vertical segment intact. In an embodiment, the central axis of the horizontal segment and the central axis of the vertical segment may coincide.

[0020] Preferably, the sections of the floating foundation have a circular cross section. However, it should be noted that the sections may also be triangular, rectangular, octagonal, or any other suitable cross section. In the case of a circular cross section, the diameter of each section of the floating foundation may be in the range between 7.5m and 15m, and more preferably in the range between 9m and 12m. The second diameter may be in the range between 10m and 15m, preferably about 12m, and the third diameter may be in the range between 7.5m and 12m, preferably about 9m.

[0021] The floating foundation can be made of a plurality of short tubular elements. The tubular elements are interconnected and configured to form different sections of the floating foundation, such as horizontal sections and vertical sections. These tubular elements can be interconnected using connection means, such as one or more of the following: welding, using bolts, flanges, couplers, sleeves, and / or the like. Welding is the most preferred option. The tubular element can have the shape of a hollow cylinder or a pipe section. The wall of the tubular element must be thick enough to withstand the force caused by waves and wind, and when the tubular element is interconnected to form the floating foundation, it supports the weight of the wind turbine. It is advantageous to use tubular elements to form the floating foundation, because compared with the different sections of the floating foundation, these elements have smaller sizes and are therefore easier to mass produce. The elements exposed to greater stress can be equipped with thicker walls, or the entire floating foundation can be manufactured to have a constant wall thickness. In a preferred embodiment, the thickness of the wall of the floating foundation is between 10mm and 100mm, preferably between 20mm and 70mm.

[0022] In one embodiment, the wall thickness of different sections of the floating foundation is constant. However, different sections of the floating foundation may have different thicknesses relative to each other. The wall thickness of the above-water section may be less than the wall thickness of the underwater section. For example, the wall thickness of the above-water section may be 75% or less of the wall thickness of the underwater section. In this way, the total weight and material costs of the floating foundation may be optimized. In addition, the thickness of the wall around the interpenetrating pipe joint, more particularly around the fixed connection of the interpenetrating pipe joint, may be in the range between 110% and 140%, preferably about 120%, of the wall thickness of the underwater section and / or the above-water section.

[0023] According to an embodiment, each of these tubular elements includes an inner surface, and at least one ring frame can be attached to the inner surface. The ring frame is connected to the inner surface by welding or similar means. The ring frame is preferably in the form of a flat flange, which is constructed to surround the inner surface and strengthen the tubular element to prevent buckling or collapse. However, other forms, such as T-shaped, angled strips, etc., can also be foreseen. This allows the thickness of the tubular element to be reduced, thereby achieving a lighter floating foundation with improved buoyancy characteristics. Surprisingly, it has been found that by using this ring frame at every 2m to 10m and preferably every 3m of the length of the section, the required total wall thickness can be reduced to 1 / 3, and the weight of the floating foundation can be reduced accordingly. Some of these ring frames can completely block the interior of the floating foundation as a sealed or open diaphragm. The thickness of the ring frame can correspond to 25% to 100% of the wall thickness and is preferably in the range of 10mm and 50mm. The radial extent of the ring frame may be between 5% and 30% of the diameter of the tubular element or between 5 cm and 100 cm and preferably between 20 cm and 50 cm.

[0024] The tubular elements can be manufactured and assembled using conventional monopile construction techniques and can be manufactured off-site in a dedicated manufacturing facility. The use of a ring frame can also ensure that the tubular elements maintain their shape during production and assembly. In this sense, it also allows the use of thinner materials, as otherwise thicker plates would be required to maintain sufficient accuracy during manufacturing.

[0025] The tubular elements may be joined together, for example by welding, to form respective underwater sections, above-water sections, vertical sections and / or interpenetrating pipe joint sections. Preferably, the different sections of the floating foundation are produced and partially assembled at one location (such as a factory or yard near a port or pier, etc.), and then moved to another location (such as a port or pier) or to a nearshore or offshore location for final assembly to form the floating foundation.

[0026] The installation of the wind turbine can be done near shore or even at sea. Near shore installation is preferred because it significantly reduces the cost and installation time. In addition, near shore installation in shallow waters allows easy inspection and commissioning of the system. This is different from fixed foundations or girders that need to be installed at sea, i.e., in deep waters at the project location. Alternatively, the wind turbine can be installed offshore, where the wind turbine can be connected to a floating foundation using a heavy lift construction vessel.

[0027] The interior of the floating foundation is substantially hollow and may also be in open communication with the interior of the tower. The interior may be partitioned by walls of the respective sections. However, for various reasons, it may be desirable to additionally divide each section into a plurality of separate interior chambers that are hermetically sealed relative to one another. To achieve this, some of the ring frames may extend completely across the inner diameter to form partitions that are used to define the separate interior chambers.

[0028] According to an embodiment, at least one of the inner chambers is configured to receive a certain amount of water to operate as a ballast tank, thereby allowing the foundation to be ballasted with water during commissioning to achieve an optimal draft for stable operation. The floating foundation can be ballasted with seawater equivalent to more than the combined weight of the foundation and the turbine. This will more than double the draft. It will be understood that the ballast should be distributed between the inner chambers and / or different sections of the floating foundation to maintain the stability of the floating foundation when in use.

[0029] The ballast system may be passive, meaning that the ballast water quantity and position remains the same during the operational life of the unit. The inflow of water into the different sections and chambers of the foundation may be controlled by sea valves.

[0030] Alternatively, the inner chamber may be provided in combination with an active ballast system which may be used to compensate for the static tilt caused by the turbine thrust and which may include pumps, valves and control equipment. In this way, the buoyancy of the floating foundation may be adjusted, for example in response to wind loads. This is particularly relevant for smaller systems where wave heights and maximum load conditions may otherwise exceed the limits of a "static" ballast.

[0031] The ballast system may be based on moving ballast between chambers in a closed system, which is the preferred solution, or may be by means of inflow and outflow to the sea.

[0032] According to an embodiment, the floating foundation may have at least four inner chambers or ballast tanks. The number and configuration of the inner chambers do not necessarily depend on the type of ballast system. Preferably, the floating foundation comprises at least seven inner chambers, wherein the underwater section comprises at least four inner chambers. The inner chambers belonging to different sections are closed by watertight partitions. However, the inner chambers belonging to the same section may be interconnected, for example by valves, pipes and / or similar flow control devices.

[0033] According to an embodiment, the last vertical section is arranged to end underwater and is preferably provided with a heave plate. The last vertical section may be arranged at the distal end of the floating foundation. The heave plate may be in the form of a large and heavy disc or body made of steel or other suitable material. The weight of the heave plate is arranged to control the center of gravity of the floating foundation and improve its stability while limiting the overall draft, especially during assembly.

[0034] The floating foundation may be made largely of steel. However, other materials may also be present, such as one or more of the following: iron, concrete, fiberglass, resin, plastic, copper, aluminum, etc.

[0035] The floating foundation is preferably configured to support a wind turbine (including tower, nacelle and blades) with a power output in the range of 2 MW to more than 15 MW and a weight of more than 1000 t or even more than 9000 t. The length of the horizontal section in the horizontal plane may be in the range between 60m and 120m, preferably about 100m. The length of the vertical section may be in the range between 30m and 70m, preferably in the range between 35m and 60m, and most preferably about 40m. The weight of the floating foundation when the ballast tanks are empty may be in the range between 2500t and 9000t.

[0036] According to an embodiment, the floating foundation is secured to the seabed by a catenary or a tensioned or semi-tensioned system. The exact form of the mooring system will depend on various factors, including the depth and nature of the seabed. A semi-tensioned mooring system may be preferred for water depths less than 200m. A catenary system may be preferred for water depths above 200m.

[0037] In an embodiment, the floating foundation consists of three vertical members and two horizontal members. It should be understood that this does not exclude the presence of the mentioned heave plates or further non-structural elements such as ladders, cradles, platforms or the like.

[0038] The present invention further contemplates a floating foundation wherein the interconnected segments define a non-branched, meandering body. The body may have no forks or forks above the waterline, or may have no forks or forks at all, having only a proximal end and a distal end. In an embodiment, the distal end is a submerged segment.

[0039] The invention further relates to a floating wind turbine having a tower and a floating foundation as described above or below. The tower can be connected to a first vertical section of the floating foundation or preferably to an intermediate vertical section. In particular, the tower can be aligned with the floating foundation, so the floating foundation should preferably be oriented vertically at this position. The cross section of the tower can correspond to the cross section of the floating foundation at the connection location, so that the tower can be considered as an extension of the elongated floating foundation.

[0040] The tower may be connected to the floating foundation by any suitable means as detailed above, including flanged or welded connections. Welded connections using field joint techniques may be preferred as this requires less manufacturing accuracy to the surfaces to be joined. Another alternative is a sleeve joint.

[0041] According to another aspect of the present invention, there is provided a method for constructing a floating foundation for a wind turbine. The method comprises the following steps: a. Providing a first annular foot and a second annular foot, each annular foot having a recessed portion of a first diameter on the upper side, the first foot and the second foot having a second diameter; b. providing a first horizontal section having a first end and an intermediate end, the first horizontal section being tubular and having a diameter corresponding to the first diameter, c. placing the first horizontal section onto the first annular foot and the second annular foot such that the first horizontal section is aligned with the corresponding recess, wherein the first end and the intermediate end extend beyond the corresponding foot, d. providing a first vertical section and an intermediate vertical section, the first vertical section and the intermediate vertical section are tubular and have a second diameter, and a recess having a first diameter is provided on the respective lower sides of the first vertical section and the intermediate vertical section, e. placing the first vertical section and the intermediate vertical section onto the first horizontal section, aligning with the first annular leg and the intermediate annular leg, respectively, and welding all elements together to form the first intermediate interpenetrating pipe joint and the lower intermediate interpenetrating pipe joint, f. Providing at least the second horizontal section and the last vertical section with further interpenetrating pipe joints.

[0042] It will be appreciated that other sequences of assembly steps may be envisaged, in particular the interpenetrating pipe joint may be constructed first and subsequently connected to the remainder of the respective horizontal and vertical sections. Alternatively, the horizontal sections may be inserted through openings provided in the vertical sections.

[0043] In an embodiment, at least method steps a to c take place on shore, and at least method step f takes place with the first horizontal section floating.

[0044] The tubular elements may comprise ring frames. These ring frames may be connected by welding. In addition, the sections of the floating foundation may also be assembled by welding.

[0045] The build can be performed a single unit at a time, or multiple units can be batched together in a production line.

[0046] In another embodiment, tubular elements are interconnected on shore at a first location to form segments of a floating foundation. The horizontal segments and vertical segments are then assembled together at a second location, such as a quayside, a levee, or an offshore location. In this context, a quayside is understood to be a location where different segments of a floating foundation can be lifted into the water using one or more lifting devices, such as heavy cranes, floating crane vessels, jacking systems, and / or launching barges.

[0047] Therefore, a distinction is made between the assembly of sections carried out by connecting tubular elements together at least partially in a production environment and in a sheltered assembly location (such as a port, a bay or a fjord). Advantageously, these sections can be transported to a quayside, where these sections can be assembled floatingly at a shallow water location or even on a ground. The quayside can be arranged to have a storage area and an assembly area. The storage area can be used to stack a plurality of different sections of a floating foundation. These sections can be moved from the storage area to the assembly area next to the storage area by a self-propelled modular transporter (onshore) or a barge (floating). The assembly area can include a lifting device for unloading and / or lifting the sections of the floating foundation into the water. These sections can be partially assembled on shore and partially assembled when floating. In particular, the underwater horizontal section can be connected to two vertical sections on shore and can be launched into a floating position, and the horizontal section on water can be assembled to link the underwater sections together in a floating manner.

[0048] To keep the segments afloat during assembly, lift bags may be attached to the sides of the segments and / or the interior chamber may be ballasted with water.

[0049] Unlike dry dock assembly, floating assembly does not require a large assembly area because the sections can be easily moved / rotated by winches, barges, carriers, ships or the like during the assembly process. After assembly, the floating foundation can be towed away by a towing device (such as a ship or barge) to clean the assembly area for the next assembly. This significantly reduces assembly time, allows flexibility during mass production, and allows large-scale assembly of floating foundations at a relatively small assembly area.

[0050] In one embodiment, the method comprises the steps of preparing an intermediate vertical section for receiving a wind turbine tower, and optionally connecting the wind turbine tower to the intermediate vertical section. This step may also occur at or adjacent to the second position. Preferably, the tower of the wind turbine is installed above the water surface. If this occurs near the shore, the completed wind turbine can then be towed to the offshore location, and the foundation ballasted and anchored. In an alternative, a floating foundation can be towed to the offshore location, and the tower and wind turbine installed at sea. The shallow draft of the unballasted floating foundation makes navigation in nearshore waters easy. The cable of the wind turbine preferably passes through the tower and leaves the interior near the height of the boarding deck level of the above-water section. The cable can leave the foundation via a J-tube. This structure allows easy installation of the export cable and avoids penetration of the permanently submerged hull.

[0051] In an embodiment, the method further comprises the step of arranging a heave plate to the lower end of the last vertical section. The heave plate improves the motion behavior of the foundation by decoupling the heave and pitch motions of the foundation when the foundation is floating. Furthermore, the heave plate limits the draft of the foundation by compensating for the submerged volume of the underwater section, thereby allowing the foundation to be assembled and the wind turbine to be installed at a shallow draft.

[0052] Additional advantages of the disclosed invention will become apparent hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present invention will now be discussed in more detail with reference to the accompanying drawings, in which:

[0054] Figure 1 A floating wind turbine device is depicted in perspective;

[0055] Figure 2 Depicted in side elevation Figure 1 equipment;

[0056] Figure 3 Depicted in plan view Figure 2 equipment;

[0057] Figure 4 Depicted in exploded view Figures 1 to 3 Sections of floating foundations;

[0058] Figure 5 Depicted Figure 2 an enlarged portion of the interpenetrating pipe joint marked V in FIG. 1 ; and

[0059] Figure 6 Depicted is the assembly process of the floating foundation. DETAILED DESCRIPTION

[0060] The present invention will be explained in more detail below with reference to the accompanying drawings, in which a number of illustrative embodiments of the present invention are shown. The accompanying drawings are intended for illustrative purposes only and are not intended to limit the inventive concept, which will encompass all modifications, equivalents and alternatives falling within the scope of the present invention. The scope of the present invention is limited only by the limitations presented in the appended claims.

[0061] Figure 1A first embodiment of a floating wind turbine device 1 according to the invention is shown in a perspective view. The device 1 comprises a wind turbine 2 having a tower 4, a nacelle 6 and blades 8. The wind turbine is mounted on a floating foundation 10 comprising an elongated hollow body 12 having three vertical sections 24 and two horizontal sections 11. The floating foundation 10 is unmanned but can be accessed by service personnel. The elongated hollow body 12 has a proximal end 26 located above the water surface S when in use, and a distal end 28 equipped with a heave plate 30. The device 1 is held in place by a mooring line 15. The wind turbine 2 shown has a rated capacity of 15 MW and a weight of 2400 t. The height of the nacelle 6 above the waterline is about 150 m, and the blade length is about 110 m. The following description of the floating foundation 10 is based on a turbine of this specification. However, the skilled person will appreciate that the dimensions of the floating foundation 10 will vary depending on the size of the turbine.

[0062] Figure 2 The side elevation view shows the installed state Figure 1 The invention relates to a device 1 which floats on a body of water having a surface S. The horizontal section comprises an underwater section 14 and an above-water section 18. The horizontal section 11 is in a tubular shape with closed ends. The vertical sections 24A, 24B, 24C pass through a splash zone at the water surface S. Figure 2 It is also shown that the interior of the elongated hollow body 12 is divided into eight inner chambers 31A, 31B, 31C, 31D, 31E, 31F, 31G, 31H. The inner chambers 31B, 31C, 31D, 31E, 31H are ballasted with seawater. The inner chambers are separated by watertight partitions.

[0063] Figure 3 Shown in plan view Figure 2 1, showing the position of vertical sections 24A, 24B, 24C in the horizontal plane. The first vertical section 24A is located at the proximal end 26, the last vertical section 24C is located at the distal end 28, and the wind turbine 2 is connected to the middle vertical section 24B, which is located between the above-water section 18 and the underwater section 14. As can be seen, in the embodiment shown, these vertical sections are located at the corners of an equilateral triangle. The underwater section 14 and the above-water section 18 form two sides of the triangle. In this case, the length of the corresponding side is calculated to be 85m at the center line CL of the elongated hollow body 12. The deck 23 extends along the above-water section 18 and extends circumferentially around the vertical sections 24A, 24B, 24C at the same height as the above-water section 18. The interior of the above-water section 18 can be entered from the deck 23 via an inspection hole (not shown) to perform inspection and maintenance of the floating foundation 10. Inspection and maintenance of the tower 4 may be performed via a waterproof door (not shown) located on the intermediate vertical section 24B.

[0064] Figure 4 Shown in exploded view Figures 1 to 3 10. The elongated hollow body 12 can be considered as five segments. The underwater segment 14 has a first end 16 and a second end 13. The diameter of the first end 16 of the underwater segment 14 is smaller than the diameter of the first vertical segment 24A and is configured to pass through a first pair of holes 33A, 33B on the surface of the first vertical segment 24A defining a first through hole 33. Similarly, the intermediate vertical segment 24B has a second pair of holes 35A, 35B defining a second through hole 35, which is configured to receive the second end 13 of the underwater segment 14. The intermediate vertical segment 24B has a third pair of holes 37A, 37B defining a third through hole 37, which is configured to receive the first end 17 of the above-water segment 18, and the last vertical segment 24C has a fourth pair of holes 39A, 39B defining a fourth through hole 39, which is used to receive the second end 19 of the above-water segment 18. The middle vertical section 24B has an opening 41 for receiving the tower 4 of the wind turbine 2. Each hole is formed by connecting a recessed annular leg 43A, 43B, 43C, 43D to a recessed end 42A, 42B, 42C, 42D of the vertical section 24A, 24B, 24C using a weld line 45A, 45B, 45C, 45D. The recessed area of ​​the recessed end 42A, 42B, 42C, 42D and the recessed annular leg 43A, 43B, 43C, 43D each define a semicircle arranged to form a first through hole 33, a second through hole 35, a third through hole 37 and a fourth through hole 39 when the elements are connected by the weld lines 45A, 45B, 45C, 45D.

[0065] Figure 5 Shown Figure 2 Detail of the interpenetrating pipe joint marked as V in FIG. 1 , showing the interior space 58 of the floating foundation 10. The middle vertical section 24B and the underwater section 14 and other sections of the floating foundation are formed by a steel wall 56 having a thickness d and defining the interior space 58. Ring frames 54 are welded on the inner surface 62 of the wall 56 to strengthen the section. The sections further include bulkheads 52 that divide the interior space 58 of the floating foundation 10 into different compartments. The second end 13 of the underwater section 14 extends through the second through hole 35 and beyond the middle section 24B to form an interpenetrating pipe joint. The diameter Dt of the second end and the diameter Dh of the second through hole are designed to form a tight fit, and the interpenetrating pipe joint is fixed by welding the two sections together around the second pair of holes 35A, 35B.

[0066] Figure 6The assembly steps of the floating foundation 10 are shown. In step 1, the first recessed annular leg 43A and the second recessed annular leg 43B are placed at a distance from each other. In step 2, the underwater section 14 is positioned on top of the first recessed annular leg and the second recessed annular leg so that the first end 16 and the second end 13 of the underwater section 14 are placed on the recessed areas of the leg 43A and the leg 43B, respectively, and are connected by the first weld line 49A and the second weld line 49B to form the first structure 102. In step 3, the first vertical section 24A and the second vertical section 24B are placed on the first structure 102. The first vertical section 24A has a first recessed end 42A, which is placed on the first annular leg 43A and the first end 16 of the underwater section 14 to completely enclose the first end 16 of the underwater section 14. The same process is repeated with the intermediate vertical section 24B at the second end 13 of the underwater section 14. The first vertical section 24A and the second vertical section 24B are connected to the first structure 102 by the third weld line 45A and the fourth weld line 45B to form the second structure 103. The first three process steps are performed at the onshore location, and then the second structure 103 is launched into the floating position together with the last vertical section 24C placed away from the second structure. The last vertical section 24C has a heave plate 30 connected thereto to ballast the floating foundation during assembly and use. By appropriate ballasting and the use of lifting bags, the corresponding second structure 103 and the last vertical section 24C can be stably floated at the correct height. In step 5, the above-water section 18 is positioned on the intermediate vertical section 24B and the last vertical section 24C. The middle vertical section 24B and the last vertical section 24C have a third and fourth recessed ends 42C, 42D, and the first and second ends 17, 19 of the above-water section 18 are placed on the third and fourth recessed ends. The above-water section 18 is connected to the rest of the structure by the fifth and sixth weld lines 49C, 49D to form the third structure 105. Finally, at step 6, the third and fourth recessed caps 43C, 43D are placed on the ends 17, 19 of the above-water section 18, thereby being enclosed by the third and fourth recessed ends 42C, 42D. The elements are connected by the seventh and eighth weld lines 45C, 45D to form the floating foundation 10.

[0067] Due to its simple conception, the floating foundation according to the invention is fully scalable and adaptable to wind turbines of different sizes. Depending on the needs of the user and the environmental conditions at the project location, the floating foundation can be provided with an active ballast system or a passive ballast system. Exemplary properties of different embodiments of the floating foundation according to the invention are shown in Table 1. Turbine Wave (Hs) Outfitting Center distance, typical diameter Basic weight 9.5MW 6.5m initiative 65m, 9.3m 2500t 9.5MW 6.5m passive 84m, 12m 3900t 9.5MW 11m initiative 65m, 9.3m Under development 9.5MW 11m passive 84m, 12m 4900t 15MW 6.5m initiative 84m, 12m 4700t 15MW 6.5m passive 105m, 15m 7600t 15MW 11m initiative 84m, 12m 5200t 15MW 11m passive 105m, 15m 9000t Table 1

[0068] The floating foundation according to the present invention can be mass produced efficiently because many elements are identical. Further, the sections can be easily stored and moved for final assembly. Final assembly can be performed near shore and / or in a floating state with a minimum number of welds or other types of connections. The minimum draft of the floating foundation can be only 8m, while the operating draft of the floating foundation can be about 24m.

[0069] The present invention can be implemented in other specific forms without departing from the essential characteristics of the present invention. The described embodiments should be considered as only illustrative and non-restrictive in all aspects for the present invention. Therefore, the scope of the present invention is indicated by the appended claims rather than by the previous description. It is obvious to those skilled in the art that replacement and equivalent embodiments of the present invention can be envisioned and put into practice. In addition, without departing from the essential scope of the present invention, many modifications can be made to adapt specific configurations or materials to the teachings of the present invention.

[0070] All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. A floating foundation for an offshore wind turbine, the floating foundation having a tower defining a vertical direction, the floating foundation comprising at least: a first vertical section, a last vertical section, and an intermediate vertical section; and at least two horizontal sections, wherein The vertical sections and the horizontal sections are tubular members arranged in an alternating manner and connected together by interpenetrating pipe joints, and wherein one of the vertical sections is arranged to receive the tower.

2. The floating foundation according to claim 1, characterized in that: The intermediate vertical section is arranged to receive the tower.

3. The floating foundation according to claim 1 or 2, characterized in that: The horizontal section includes at least one underwater section and at least one above-water section.

4. A floating foundation according to any one of the preceding claims, characterised in that The horizontal sections have a constant first diameter and the vertical sections all have a constant second diameter, and the first diameter of the horizontal sections is preferably smaller than the second diameter of the vertical sections.

5. A floating foundation according to any one of the preceding claims, characterised in that The vertical segments are equidistantly spaced apart and, optionally, wherein the vertical segments form nodes of an equilateral triangle in a horizontal plane.

6. A floating foundation according to any one of the preceding claims, characterised in that For each interpenetrating pipe joint, the ends of the horizontal section completely pass through the vertical section and are welded on both the inlet and outlet sides.

7. A floating foundation according to any one of the preceding claims, characterised in that The floating foundation consists of three vertical members and two horizontal members.

8. A floating foundation according to any one of the preceding claims, characterised in that Each segment of the floating foundation further includes a plurality of ring frames attached to the inner surface and extending radially inwardly.

9. A floating foundation according to any one of the preceding claims, characterised in that Each section of the floating foundation has a circular outer cross-section having a diameter ranging between 7.5m and 15m and more preferably between 9m and 12m.

10. A floating foundation according to any one of the preceding claims, characterised in that The last vertical section is arranged to end underwater and is preferably provided with a heave plate.

11. A floating foundation according to any one of the preceding claims, characterised in that The interior of the floating foundation is substantially hollow and includes a plurality of separate ballast tanks.

12. A floating foundation according to any one of the preceding claims, characterised in that The floating foundation is made of steel and is configured to support a wind turbine having a total weight greater than 1000 t.

13. A floating wind turbine having a tower and a floating foundation according to any one of the preceding claims.

14. A method for constructing a floating foundation for an offshore wind turbine, wherein: The method comprises the following steps: Step a: providing a first annular support foot and an intermediate annular support foot, wherein the upper side of each annular support foot has a recess of a first diameter, and the first annular support foot and the intermediate annular support foot have a second diameter; Step b: providing a first horizontal section having a first end and an intermediate end, the first horizontal section being tubular and having a diameter corresponding to the first diameter, Step c: placing the first horizontal section onto the first annular foot and the intermediate annular foot so that the first horizontal section is aligned with the corresponding recess, wherein the first end and the intermediate end extend beyond the corresponding foot, Step d: providing a first vertical section and an intermediate vertical section, the first vertical section and the intermediate vertical section being tubular and having the second diameter, and providing a recess having the first diameter on the respective lower sides of the first vertical section and the intermediate vertical section, Step e: placing the first vertical section and the middle vertical section onto the first horizontal section, aligning with the first annular leg and the middle annular leg respectively, and welding all elements together to form a first middle interpenetrating pipe joint and a lower middle interpenetrating pipe joint, Step f: Providing at least the second horizontal section and the last vertical section with further interpenetrating pipe joints.

15. The method according to claim 14, characterized in that At least steps a to c occur on shore, and at least step f occurs with the first horizontal section floating.

16. The method according to claim 14 or claim 15, characterized in that The method further comprises providing a heave plate to a lower end of the last vertical section.

17. The method according to any one of claims 14 to 16, characterized in that The method further includes preparing the intermediate vertical section for receiving a wind turbine tower, and optionally connecting a wind turbine tower to the intermediate vertical section.

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