Floating foundation for offshore wind turbines and construction method

Abstract

A floating foundation for an offshore windmill having a tower defining a vertical direction, the floating foundation including at least three vertical members and at least two horizontal members, the vertical members and the horizontal members being tubular members, arranged alternately and integrally connected by mutually penetrating tube joints, and one of the vertical members being arranged to receive the tower.

Description

Detailed Description of the Invention

[0001] [Field of the Invention]

[0001] The present invention relates in particular to a floating foundation for supporting an offshore windmill, and a method for constructing and installing such a foundation and a windmill.

[0002] [Background Art]

[0002] Floating windmills are excellent renewable energy sources because they can be installed on the ocean where the wind is stronger and more stable. They show the potential to greatly develop wind power generation, because floating windmills can be installed in deeper waters, so unlike fixed windmills that are limited to shallow waters near the coast, the available sea area is greatly expanded.

[0003]

[0003] A floating windmill generally has a windmill including a tower, a nacelle, and blades, which are located on the ocean and are attached to a foundation fixed to the seabed by a catenary or taut mooring system. Existing floating foundations can be of the spar buoy type, in which case the foundation includes cylinders made of steel and / or concrete filled with ballast water and gravel and is kept upright and floating. However, such types of floating foundations are not entirely suitable for large windmills, because the draft of the foundation required to keep the foundation and the windmill afloat is directly related to the size and weight of the windmill. As a result, extreme drafts occur for large windmills, making construction, transportation, and installation complicated.

[0004]

[0004] In other systems, platform construction such as an oil and gas field type floating platform is used. U.S. Patent No. 8471396B2 discloses one such floating windmill platform, which includes a floating frame, which includes at least three columns, which are interconnected by horizontal main beams. The windmill tower is attached at the center of the three columns or above the columns of the tower to simplify the construction of the system and improve the structural strength.

[0005] In European Patent No. 2387528 A2, a tension moored offshore diving platform as a concrete-steel hybrid type is disclosed, including a central body made of concrete with reinforcing iron wires and a peripheral structure made of steel connected to the central body and further to the base for such a platform through steel stiffeners.

[0006] However, floating foundations in deep waters are exposed to severe environments such as strong winds and large waves. In such environments, strong forces are generated on the components of the floating foundation. Coupling and / or connecting elements such as joints and / or struts are particularly vulnerable because the forces strongly concentrate in these areas. Therefore, such floating foundations require regular inspection and maintenance work. In unpublished PCT / EP2021 / 083837, a floating foundation using a meandering continuous tubular structure was proposed. This is particularly advantageous in that the assembly process is relatively simplified, because the continuous structure has no closed rings that require precise positioning within the structure and can therefore be assembled even in a floating state. In this floating foundation, joints and struts are not required by using smooth curved transition parts. However, such curved parts are more complex in design and construction and are not suitable for mass production processes.

[0007] It would be desirable to provide a floating foundation that is resilient to the severe conditions of the deep water environment, is relatively cost-effective, and is suitable for large wind turbines that are easy to construct, transport, and install.

[0008] [Summary of the Invention]

[0008] Thus, according to a first aspect of the present invention, there is provided a floating foundation having a tower as defined in claim 1. This floating foundation includes at least three vertical members and at least two horizontal members, the vertical and horizontal members being tubular members, arranged alternately and integrally connected by means of mutually penetrating tube joints, and one of the vertical members being arranged to receive the tower. The vertical members include a first, a final, and intermediate vertical members spaced apart from each other in a horizontal plane, thereby ensuring the stability of the floating foundation. For the purposes of the present application, the term mutually penetrating tube joint shall refer to a joint in which a first tube penetrates the front wall of a second tube and a connection with its rear wall is provided. A skilled structural engineer will appreciate that this provides a joint that is significantly stronger than one simply connected by an intersection line on the front wall. This term shall include joints in which the first tube terminates within the second tube and fully mutually penetrating tube joints in which the first tube extends beyond the second tube. This term shall also include joints between tubes of equal thickness and joints where the first tube is of smaller diameter than the second tube. In certain embodiments, no more than two tubular members intersect at the mutually penetrating tube joints.

[0009]

[0009] The horizontal members may include at least one underwater member configured to remain underwater during use of the floating foundation and at least one above-water member configured to remain above water during use of the floating foundation. The vertical members are intended to extend above the waterline and thus each has an underwater portion and an above-water portion. The connection between the vertical and horizontal members is achieved using mutually penetrating tube joints. These joints are advantageous as they can achieve the appropriate strength without using external braces or struts. Curved sections are difficult to manufacture as they require the use of double-curved plates or a plurality of smaller elements that are integrally combined to form such sections.

[0010]

[0010] To assist in the following description, the following directions are used throughout this application. The direction parallel to the tower of the windmill is the vertical direction. The plane orthogonal to the vertical direction is the horizontal plane. When the floating foundation is floating, the horizontal plane is defined by the water surface. The above-water member remains out of contact with the water surface during use, and the underwater member remains submerged during use. Only the vertical member that passes through the water surface and connects the underwater member to the above-water member when the floating foundation is floating. It should be understood that the exact depth at which the foundation floats depends on the weight of the windmill and the presence of ballast within the foundation, and that some portions of the underwater member may extend above the waterline under certain conditions and vice versa.

[0011]

[0011] It should be noted that the floating foundation according to the present invention can be substantially hollow. However, this does not imply that the floating foundation cannot include a plurality of internal chambers or compartments. In fact, in many instances, it will be apparent from this disclosure that the internal space of the floating foundation needs to be partitioned in order for the floating foundation to function properly.

[0012]

[0012] In one embodiment, the floating foundation can be arranged to define a meandering path extending from a proximal end to a distal end. The proximal end can be arranged to remain above water during use of the floating foundation, while the distal end can be arranged to remain underwater during use of the floating foundation. The first vertical member can be positioned at the proximal end of the floating foundation. The intermediate vertical member can be positioned between the horizontal underwater member and the horizontal above-water member. The final vertical member can be positioned at the distal end of the floating foundation. For the purposes of this application, the word "meandering" should be understood to mean, in the broadest sense, "not extending linearly but changing direction". Therefore, meandering can be interpreted, by way of example, as being serpentine, zigzag, curved, twisted, bent, etc.

[0013] [

[0013] ] The three vertical members are spaced apart from each other to form a stable base. The base is stable in the case where a system including a floating foundation and a windmill can somehow return to the equilibrium position when displaced from the equilibrium position under the influence of external forces such as waves and / or wind. In other words, the system must have sufficient hydrodynamic-mechanical stability to resist the tilting moments of strong winds, strong currents, and high waves. Generally, for this, the vertical members need to be sufficiently spaced apart from each other, and the center of buoyancy needs to be away from each of them. Also, the superstructure needs to be large enough so as not to sink under the maximum possible force or moment that may act on the windmill. In an embodiment, the vertical members can be spaced apart from each other by at least 40 m or at least 60 m, and even more than 100 m when measured from center to center. Preferably, the distance between the vertical members is about 85 m.

[0014] [

[0014] ] Any of the vertical members can be arranged to receive the tower. The tower can be connected to the floating foundation by one or more of the following connecting means. That is, the use of welding, bolts, flanges, couplers, sleeves, slip joint connections, and / or the like. In an embodiment, a part of the tower and a part of each vertical member can overlap. For the sake of clarity, it is noted that in this regard, the tower is considered to start above the waterline, and the vertical members of the floating foundation cross the waterline. Nevertheless, towers connected to the floating foundation underwater beyond the waterline are not excluded. In such a case, the base of the tower can form the vertical member. Preferably, the tower is connected to the middle vertical member, and as a result, a hydraulically stable structure is obtained. Nevertheless, the tower can also be connected to the first or final vertical member, which is advantageous because the installation process can be carried out more smoothly as will be described later. The hydraulics of such a structure can be further improved by the use of heave plates and / or ballast tanks.

[0015]

[0015] According to another embodiment, the distance between consecutive vertical members in the horizontal plane is equal. The transition regions are spaced at equal intervals. Preferably, the vertical members form the vertices of an equilateral triangle in the horizontal plane. This symmetrical configuration provides optimal stability to the base of the floating foundation. This is particularly suitable for foundations that are directionally constrained in their position. Other configurations and different numbers of vertical members are possible, and it should be understood that a minimum of three is required for stability. In particular, for a foundation moored to rotate with the wind direction, it may be advantageous to arrange the vertical members differently.

[0016]

[0016] The compartments of the floating foundation are preferably linear. The linear shape of the members is advantageous because manufacturing and assembly are easier. The length of the horizontal members can be selected to provide sufficient spacing between the vertical members and thus the stability required for the floating foundation when the wind turbine is attached to it. This length depends on the parameters of the wind turbine as well as on the parameters of the floating foundation. The length of the vertical members also depends on other elements of the design, in particular on the expected wave height to ensure that the above-water members remain above water.

[0017]

[0017] In addition, the use of straight underwater members can be advantageous in limiting the draft of the floating foundation. In a preferred embodiment, the draft of the load-bearing foundation can be less than 30 m, or even less than 20 m, preferably about 24 m. Thereafter, ballast can be injected to reach deeper operating positions. In the unloaded state, i.e., before the tower is installed, the draft of the foundation with sufficient capacity for wind turbines exceeding 10 MW is less than 10 m or less than 8 m and can be as small as 6 m. Such a shallow draft facilitates transfer and movement in coastal waters. One or more straight portions can provide a stable base even when the foundation is on land or installed in shallow waters.

[0018] As described above, the floating foundation includes intrusion tubes joints. The intrusion tubes joints are arranged to interconnect the vertical members and the horizontal members. The connection of the intrusion tubes joints, or more precisely, the connection between the members forming the intrusion tubes joints, can be fixed by one or more of the following: namely, welding, bolts, flanges, couplings, use of sleeves, and / or the like. Welding is the most preferred option. Preferably, for each intrusion tubes joint, the end of the horizontal member penetrates completely through the vertical member and is welded on both the inlet side and the outlet side.

[0019]

[0019] In certain embodiments, all of the horizontal members have the same constant first diameter, and all of the vertical members have the same constant second diameter. The first diameter may be larger than the second diameter, or both diameters may be the same. In a preferred embodiment, the first diameter of the horizontal members is smaller than the second diameter of the vertical members. Thereby, the horizontal members can penetrate through the vertical members, whereby at least a portion of the wall of the vertical members remains intact. In certain embodiments, the central axes of the horizontal and vertical members may coincide.

[0020]

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

[0021]

[0021] The floating foundation can be manufactured from a plurality of short tubular elements. The tubular elements are interconnected and configured to form different members of the floating foundation, such as horizontal and vertical members. The tubular elements can be interconnected using connection means, such as one or more of the following: namely, welding, bolts, flanges, couplers, use of sleeves, and / or the like. Welding is the most preferred option. The tubular elements can have the shape of a hollow cylinder or pipe member. The walls of the tubular elements must have a thickness sufficient to withstand the forces caused by waves and wind when the tubular elements are interconnected to form the floating foundation, and also to support the weight of the wind turbine. Forming the floating foundation using tubular elements is advantageous because these elements are small compared to other members of the floating foundation and as a result, are easy to produce continuously. Elements that are subject to greater stress can be provided with thicker walls, or the entire floating foundation can be manufactured with a constant wall thickness. In a preferred embodiment, the wall thickness of the floating foundation is from 10 mm to 100 mm, preferably from 20 mm to 70 mm.

[0022]

[0022] In one embodiment, the wall thickness of different members of the floating foundation is constant. However, different members of the floating foundation may have different thicknesses relative to each other. The wall of the above-water member may be smaller than the wall thickness of the underwater member. For example, the wall thickness of the above-water member can be 75% or less of the wall thickness of the underwater member. In this way, the total weight and material cost of the floating foundation can be optimized. Furthermore, the wall thickness around the mutually penetrating tube joint, more specifically around the fixed connection of the mutually penetrating tube joint, can be in the range of 110% to 140%, preferably 120% of the wall thickness of the underwater member and / or the above-water member.

[0023]

[0023] According to an embodiment, each of the 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 the like. The ring frame is preferably in the form of a flat flange configured to abut against the inner surface, reinforcing the tubular element against buckling and crushing. However, other shapes such as T-shaped steel, angle steel, and the like are also conceivable. This enables the thinning of the tubular element, and as a result, a lighter floating foundation with better floating characteristics can be obtained. Surprisingly, it has been found that by using such ring frames every 2 m to 10 m, preferably every 3 m along the length of the member, the overall wall thickness required can be reduced to one-third, and the weight of the floating foundation can also be correspondingly reduced. Some of the ring frames can be completely closed as sealed or open partitions inside the floating foundation. The thickness of the ring frame can correspond to 25% to 100% of the wall thickness, preferably in the range of 10 mm to 50 mm. The radial range of the ring frame can be 5% to 30% of the diameter of the tubular element, i.e., 5 cm to 100 cm, preferably 20 cm to 50 cm.

[0024]

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

[0025]

[0025] The tubular elements can be joined to each other, for example, by welding or the like, to form each of the underwater member, the above-water member, the vertical member, and / or the mutually penetrating tube joint member. Preferably, the different members of the floating foundation are manufactured and partially assembled at one location such as a factory or yard near a bay or a port, and then moved to other locations such as a bay or a port, or an inshore or offshore location for final assembly to form the floating foundation.

[0026]

[0026] The installation of the wind turbine can be carried out on the shore or even offshore. Installation on the shore is preferred because it can significantly reduce costs and shorten the installation time. Furthermore, installation in the shallow waters along the shore facilitates the inspection and commissioning of the system. This is different from fixed foundations or spar that need to be installed at sea, i.e., at the project site in deep waters. Alternatively, the wind turbine can be installed offshore, in which case the wind turbine can be connected to the floating foundation using a large foundation construction vessel.

[0027]

[0027] The interior of the floating foundation is substantially hollow and may be in open communication with the interior of the tower. The interior may be divided by the walls of the respective members. However, for various reasons, it may be preferable to further divide each member into a plurality of internal chambers, which are sealed with respect to each other. To achieve this, several ring frames can extend across the inner diameter to form partitions used to define another internal chamber.

[0028]

[0028] According to an embodiment, at least one internal chamber is configured to receive a certain amount of water and operate as a ballast tank, stabilizing the foundation with water during commissioning and achieving an optimal draft for stable operation. The floating foundation can be stabilized with seawater equal to a weight exceeding the total weight of the foundation and the wind turbine. As a result, the draft is more than doubled. It should be understood that the ballast should be distributed between the internal chambers and / or between different members of the floating foundation to maintain the stability of the floating foundation during use.

[0029]

[0029] The ballast system can also be passive, which means that the amount and position of the ballast water remain the same during the operating life of the unit. The inflow of water into different members and chambers of the foundation can be controlled by seawater valves.

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

[0031]

[0031] The ballast system can be based on moving ballast between internal chambers in a closed system as a preferred solution or can be due to inflow and outflow from the sea.

[0032]

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

[0033]

[0033] According to an embodiment, the final vertical member is arranged to end underwater, and preferably a heave plate is provided. The final vertical member can be arranged at the tip of the floating foundation. The heave plate can be in the form of a large disk or mass 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, especially to limit the overall draft during assembly.

[0034]

[0034] The floating foundation can be mostly made of steel. However, other materials can also be present, which are, for example, one or more of the following, namely iron, concrete, glass fiber, resin, plastic, copper, aluminum, etc.

[0035]

[0035] The floating foundation is preferably configured to support a wind turbine including a tower, a nacelle, and blades, with an output of more than 2 MW to over 15 MW and a weight of 1000 t, or even more than 9000 t. The length of the horizontal member in the horizontal plane can range from 60 m to 120 m, preferably about 100 m. The length of the vertical member can range from 30 m to 70 m, preferably from 35 m to 60 m, and most preferably about 40 m. The weight of the floating foundation with the ballast tank empty can range from 2500 t to 9000 t.

[0036]

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

[0037]

[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 other non-structural elements such as the aforementioned heave plates, ladders, gantries, platforms, etc.

[0038]

[0038] The present invention further contemplates a floating foundation in which interconnected members define a bulkhead body without branches. This body may have no branches or branch points above the waterline, or no branches or branch points at all, and may have only a base end and a tip end. In an embodiment, the tip end is a submerged member.

[0039]

[0039] The present invention further relates to a wind turbine having a tower and the aforementioned or hereinafter described floating foundation. The tower can be connected to the first vertical member of the floating foundation, or preferably to an intermediate vertical member. In particular, the tower can be aligned with the floating foundation, and for this reason, it should preferably be oriented vertically at this position. The cross-section of the tower can correspond to that of the floating foundation at the connection position, and as a result, the tower can be considered an extension of the elongated floating foundation.

[0040]

[0040] The tower can be connected to the floating foundation by any suitable means already described in detail, including flange connection or welded connection. Welded connection using on-site joining methods may be preferred as the manufacture of the surfaces to be joined need not be so precise. Another alternative is the sleeve joint.

[0041]

[0041] According to another aspect of the invention, a method of constructing a floating foundation for a windmill is provided. The method comprises a. providing a first and a second annular foot each having an upper surface with a recess of a first diameter, the first and second feet having a second diameter; b. providing a first horizontal member having a first end and an intermediate end, the first horizontal member being tubular and having a diameter corresponding to the first diameter; c. installing the first horizontal member on the first and second annular feet such that it aligns with the respective recesses and the first and intermediate ends extend beyond the respective feet; d. providing first and intermediate vertical members that are tubular, have a second diameter, and have recesses of the first diameter provided in their respective lower surfaces; e. installing the first and intermediate vertical members on the first horizontal member, aligning them with the first and intermediate annular feet respectively, and welding all the elements together to form first and lower intermediate nested tube joints; f. providing at least a second horizontal member and a final vertical member with another nested tube joint; and includes.

[0042]

[0042] It is understood that other orders of the assembly steps may also be envisaged, in particular by first manufacturing the nested tube joints and then connecting them to the remaining respective horizontal and vertical members. Alternatively, the horizontal members can be inserted into openings provided in the vertical members.

[0043]

[0043] In one embodiment, at least method steps a. to c. are performed on land, and at least method step f. is performed with the first horizontal member floating.

[0044]

[0044] The tubular element may include a ring frame. The ring frame may be connected by welding. In addition, the members of the floating body foundation may also be connected by welding.

[0045]

[0045] The construction may be carried out one unit at a time, or multiple units can be continuously produced in the form of a production line.

[0046]

[0046] In another embodiment, the tubular elements are interconnected at a first onshore location to form the members of the floating body foundation. The horizontal and vertical members are then assembled integrally at a second location such as around a quay, a jetty, or an offshore location. In this regard, the area around the quay is to be understood as a location from where various members of the floating body foundation can be lifted and lowered into the water using one or more lifting means such as a heavy lift crane, a floating crane ship, a jacking system, and / or a launching barge.

[0047]

[0047] Thus, the integral connection of tubular elements, which is carried out at least partially in a production environment, is distinguished from the assembly of members carried out in a sheltered assembly location such as a port, bay, fjord, etc. As an advantage, these members can be transported to the vicinity of the quay, where they can be assembled in a floating state in shallow water or even on land. The vicinity of the quay can be arranged to have a storage area and an assembly area. The storage area can be used to stack a plurality of different members of the floating foundation. The members can be moved from the storage area to the assembly area adjacent to the storage area by a self-propelled modular transport device (on land) or a barge (at sea). The assembly area can include lifting means for lowering and / or lifting the members of the floating foundation into and out of the water. Some of the members can be assembled on land and some can be assembled in a floating state. In particular, the horizontal member in the water is connected to two vertical members on land and lowered into a floating position, and the horizontal member on the water is assembled in a floating state and joined integrally with the member in the water.

[0048]

[0048] In order to keep the members in a floating state during assembly, lifting bags can be attached to the sides of the members and / or the internal chambers can be stabilized with water.

[0049]

[0049] Different from the assembly in a dry dock, a large-scale assembly area is not required for the assembly in a floating state, because the members can be easily moved / rotated by a winch, barge, carrier, ship, or the like during the assembly process. After assembly, the floating foundation is towed out of the assembly area by a towing means such as a ship or a barge for the next assembly. This significantly shortens the assembly time, thereby obtaining flexibility during continuous production and enabling mass assembly of the floating foundation in a relatively small assembly area.

[0050]

[0050] In one embodiment, the method includes preparing an intermediate vertical member to receive a wind turbine, and optionally connecting a wind turbine tower to the intermediate vertical member. This step may be performed at or near the second location. Preferably, the wind turbine is installed above the waterline. If this is done along the shore, the completed wind turbine can then be towed to an offshore location where the foundation can be ballasted and fixed. Alternatively, a floating foundation can be towed to an offshore location and the tower and wind turbine can be installed offshore. The shallow draft of the unballasted floating foundation facilitates navigation in coastal waters. The electrical cable of the wind turbine is preferably routed inside the tower and exits from the inside at about the height of the working deck level of the superstructure. The cable can exit the foundation through a J-tube. This structure facilitates the installation of the export cable and avoids permanently submerged floating penetrations.

[0051]

[0051] In certain embodiments, the method further includes providing a heave plate at the lower end of the final vertical member. The heave plate improves the rocking motion of the foundation by decoupling the heave and the pitch motion of the floating foundation. Further, the heave plate limits the draft of the foundation by compensating for the submerged volume of the underwater member, thereby enabling the assembly of the foundation and the installation of the wind turbine in shallow water.

[0052]

[0052] Other advantages of the disclosed invention will become apparent hereinafter.

[0053]

[0053] The present invention will be described in more detail hereinafter with reference to the accompanying drawings.

Brief Description of the Drawings

[0054]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0055] [Description of Embodiment]

[0060] The present invention will be described in more detail below with reference to the drawings in which exemplary embodiments thereof are shown. The drawings are for illustrative purposes only and do not limit the inventive concept covering any improvements, equivalents, and alternatives within the scope of the present invention. The scope of the present invention is limited only by the definitions set forth in the appended claims.

[0056]

[0061] FIG. 1 shows a first embodiment of a floating wind power facility 1 according to the present invention in a perspective view. The facility 1 includes a wind turbine 2 having a tower 4, a nacelle 6, and blades 8. The wind turbine is mounted on a floating foundation 10, which includes an elongated hollow body 12 having three vertical members 24 and two horizontal members 11. The floating foundation 10 is unmanned, but a passage for service personnel may be provided. The elongated hollow body 12 has a base end 26 above the water surface S and a tip end 28 provided with a heave plate 30 during use. The facility 1 is held in place by a mooring cable 15. The wind turbine 2 shown in the figure has a rated output of 15 MW and a weight of 2400 t. The height above the waterline of the nacelle 6 is about 150 m, and the blade length is about 110 m. The following description of the floating foundation 10 is based on a wind turbine of this scale. However, those skilled in the art will understand that the dimensions of the floating foundation 10 will vary depending on the size of the wind turbine.

[0057]

[0062] Figure 2 shows a side view of the installed facility 1 of FIG. 1 floating on a water area having a surface S. The horizontal member includes a submerged member 14 and a superstructure member 18. The horizontal member 11 has a tubular shape with both ends closed. The vertical members 24A, B, and C pass through the splash zone at the water surface S. FIG. 2 further shows that the interior of the elongated hollow body 12 is partitioned into eight internal chambers 31A, B, C, D, E, F, G, and H. Seawater ballast is injected into the internal chambers 31B, C, D, E, and H. The internal chambers are separated by watertight partitions.

[0058]

[0063] Figure 3 shows a plan view of the facility 1 of FIG. 2, illustrating the positions of the vertical members 24A, B, and C in the horizontal plane. The first vertical member 24A is at the base end 26, the final vertical member 24C is at the tip end 28, and the windmill 2 is connected to the intermediate vertical member 24B between the superstructure member 18 and the submerged member 14. As can be seen from the figure, in the illustrated embodiment, these vertical members are positioned at the vertices of an equilateral triangle. The submerged member 14 and the superstructure member 18 form two sides of the triangle. In this case, the length of each side is 85 m calculated along the center line CL of the elongated hollow body 12. The deck 23 extends circumferentially around the vertical members 24A, B, and C along the superstructure member 18 and at the same height as the superstructure member 18. Inside the superstructure member 18, it is possible to enter from the deck 23 through a manhole (not shown) to perform inspections and maintenance of the floating foundation 10. Inspections and maintenance of the tower 4 can be carried out through a watertight door (not shown) on the intermediate vertical member 24B.

[0059]

[0064] Figure 4 shows an exploded view of the members of the floating foundation 10 of FIGS. 1 to 3. The long hollow body 12 can be considered as five members. The underwater member 14 has a first end portion 16 and a second end portion 13. The diameter of the first end portion 16 of the underwater member 14 is smaller than the diameter of the first vertical member 24A and passes through the first pair of holes 33A, B on the surface of the first vertical member 24A that define the first through hole 33. Similarly, the intermediate vertical member 24B has a second pair of holes 35A, B that define a second through hole 35 configured to receive the second end portion 13 of the underwater member 14. The intermediate vertical member 24B has a third pair of holes 37A, B that define a third through hole 37 configured to receive the first end portion 17 of the upper water member 18, and the final vertical member 24C has a fourth pair of holes 39A, B that define a fourth through hole 39 for receiving the second end portion 19 of the upper water member 18. The intermediate vertical member 24B has an opening 41 for receiving the tower 4 of the windmill 2. Each hole is formed by connecting the recessed annular feet 43A, B, C, D to the recessed end portions 42A, B, C, D of the vertical members 24A, B, C using welding lines 45A, B, C, D. The recessed regions of the recessed end portions 42A, B, C, D and the recessed annular feet 43A, B, C, D each define a semi-circle and are arranged to form the first through hole 33, the second through hole 35, the third through hole 37, and the fourth through hole 39 when the elements are connected by the welding lines 45A, B, C, D.

[0060]

[0065] Figure 5 shows the details of the intrusion tube joint indicated by V in Figure 2, showing the internal space 58 of the floating foundation 10. In addition to the intermediate vertical member 24B and the underwater member 14, the other members of the floating foundation are formed from a steel wall 56 with a thickness d that defines the internal space 58. A ring frame 54 is welded onto the inner surface 62 of the wall 56 to reinforce this member. These members further include a partition wall 52, which divides the internal space 58 of the floating foundation 10 into different compartments. The second end portion 13 of the underwater member 14 extends through the second through hole 35 and beyond the intermediate member 24B to form an intrusion tube joint. The diameter Dt of the second end portion and the diameter Dh of the second through hole are designed to be in an interference fit state, and the intrusion tube joint is fixed by welding two members to each other around the second pair of holes 35A, B.

[0061]

[0066] Figure 6 shows the assembly steps of the floating body foundation 10. In step 1, the first concave annular foot 43A and the second concave annular foot 43B are installed spaced apart from each other. In step 2, the underwater member 14 is positioned thereon, and the first end portion 16 and the second end portion 13 of the underwater member 14 are respectively placed on the concave regions of the feet 43A and 43B, 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 member 24A and the second vertical member 24B are placed on the first structure 102. The first vertical member 24A has a first concave end portion 42A, which is placed on the first annular foot 43A and the first end portion 16 of the underwater member 14 and completely surrounds the first end portion 16 of the underwater member 14. The same process is repeated for the intermediate vertical member 24B at the second end portion 13 of the underwater member 14. The first vertical member 24A and the second vertical member 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 carried out at an onshore location, and then the second structure 103 is advanced to a floating position together with the final vertical member 24C installed separately therefrom. The final vertical member 24C has a heave plate 30 connected thereto to stabilize the floating body foundation during assembly and use. Each of the second structure 103 and the final vertical member 24C can be stably floated at the correct height by appropriate ballast injection and the use of lifting bags. In step 5, the upper water member 18 is positioned on the intermediate vertical member 24B and the final vertical member 24C. The intermediate vertical member 24B and the final vertical member 24C have a third concave end portion 42C and a fourth concave end portion 42C, and the first and second end portions 17, 19 of the upper water member 18 are placed thereon. The upper water member 18 is connected to the rest of the structure by the fifth and sixth weld lines 49C, D to form the third structure 105. Finally, in step 6, the third and fourth concave caps 43C, D are placed on the end portions 17, 19 of the upper water member 18, which are thus surrounded by the third and fourth concave end portions 42C, D. These elements are connected by the seventh and eighth weld lines 45C, D to form the floating body foundation 10.

[0062]

[0067] From this simple concept, the floating foundation according to the present invention can be freely expanded and contracted and is suitable for wind turbines of various sizes. An active ballast system or a passive ballast system can be provided for the floating foundation according to the needs of the user and the environmental conditions at the project site. Exemplary features of different embodiments of the floating foundation according to the present invention are shown in Table 1.

[0063]

Table 1

[0064]

[0068] Since many elements of the floating foundation according to the present invention are the same, it can be efficiently mass-produced. Furthermore, the members can be easily stored and transported to the final assembly. The final assembly can be carried out on the coast and / or at sea with a minimum number of welds or other types of connections. The minimum draft of the floating foundation can be only 8 m, and the operating draft of the floating foundation can be about 24 m.

[0065]

[0069] The present invention can also be implemented in other specific forms without departing from its essential features. The foregoing embodiments are to be considered in all respects as illustrative and not restrictive of the inventive concept. The scope of the present invention is, therefore, indicated by the appended claims rather than by the foregoing description. It will be apparent to those skilled in the art that alternative and equivalent embodiments of the present invention can be contemplated and implemented. In addition, many improvements can be made to adapt a particular configuration or material to the teachings of the present invention without departing from its essential scope.

[0066]

[0070] All changes that fall within the meaning and scope of the equivalence of the claims are intended to be embraced within that scope.

Claims

1. A floating foundation for an offshore wind turbine having a tower defining a vertical direction, comprising at least one first vertical member, one final vertical member, and one intermediate vertical member, and at least two horizontal members, wherein the vertical members and the horizontal members are tubular members, arranged alternately and integrally connected by means of mutually penetrating tube joints, and one of the vertical members is arranged to receive the tower.

2. The floating foundation according to claim 1, wherein the intermediate vertical member is arranged to receive the tower.

3. The floating foundation according to claim 1 or 2, wherein the horizontal member includes at least one underwater member and at least one above-water member.

4. The floating foundation according to any one of claims 1 to 3, wherein the horizontal member has a constant first diameter, all of the vertical members have a constant second diameter, and the first diameter of the horizontal member is preferably smaller than the second diameter of the vertical member.

5. The floating foundation according to any one of claims 1 to 4, wherein the vertical members are spaced apart at equal intervals, and optionally, the vertical members form the vertices of an equilateral triangle in a horizontal plane.

6. For each mutually penetrating tube joint, the ends of the horizontal member pass completely through the vertical member and are welded on both the inlet side and the outlet side. The floating foundation according to any one of claims 1 to 5.

7. The floating foundation according to any one of claims 1 to 6, comprising three vertical members and two horizontal members.

8. Each member of the floating foundation further includes a plurality of ring frames attached to the inner surface and extending radially inward. The floating foundation according to any one of claims 1 to 7.

9. Each member of the floating foundation has a circular outer cross-section with a diameter in the range of 7.5 m to 15 m, more preferably 9 m to 12 m. The floating foundation according to any one of claims 1 to 8.

10. The final vertical member is arranged to end underwater, and preferably a heave plate is provided. The floating foundation according to any one of claims 1 to 9.

11. The interior of the floating foundation is substantially hollow and includes a plurality of separated ballast tanks. The floating foundation according to any one of claims 1 to 10.

12. The floating foundation according to any one of claims 1 to 11, which is made of steel and is configured to support a wind turbine with a total weight exceeding 1000 t.

13. A floating wind turbine having a tower and a floating foundation according to any one of claims 1 to 12.

14. A method for constructing a floating foundation for an offshore wind turbine, comprising: a. providing first and intermediate annular feet each having an upper surface with a recess of a first diameter, the first and second feet having a second diameter; b. providing a first horizontal member having a first end and an intermediate end, the first horizontal member being tubular and having a diameter corresponding to the first diameter; c. installing the first horizontal member on the first and second annular feet such that it is aligned with the respective recesses and the first and intermediate ends extend beyond the respective feet; d. providing first and intermediate vertical members that are tubular, have a second diameter, and have recesses of the first diameter provided on their respective lower surfaces; e. installing the first and intermediate vertical members on the first horizontal member, aligning them with the first and intermediate annular feet respectively, and welding all elements together to form first and lower intermediate interpenetrating tube joints; f. providing at least a second horizontal member and a final vertical member with another interpenetrating tube joint. A method including the above steps.

15. The method according to claim 14, wherein at least steps a. to c. are performed on land and at least step f. is performed with the first horizontal member floating.

16. The method according to claim 14 or claim 15, further comprising providing a heel plate at the lower end of the final vertical member.

17. The method according to any one of claims 14 to 16, further comprising preparing the intermediate vertical member to receive a wind turbine tower and optionally connecting the wind turbine tower to the intermediate vertical member.

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