Installation method for floating structures for offshore wind power generation and floating structures for offshore wind power generation

Abstract

The present invention provides a method for installing floating structures for offshore wind power generation and a floating structure for offshore wind power generation that can improve the constructability of floating structures at sea and reduce construction costs. [Solution] The first workboat S1 transports the weight 50 to the offshore installation site, and the weight 50, to which one end of the cable 60 is connected, is lowered from the first workboat S1 and sunk to the seabed. The other end of the cable 60 is held by the fourth workboat S4, and the floating structure 1 on which the wind power generation device body 2 is mounted is towed to the installation site. The other end of the cable 60 held by the fourth workboat S4 at the installation site is pulled up towards the second floating structure 20, thereby applying tension to the cable 60, and the other end of the cable 60 is fixed to the second floating structure 20 while tension is applied to the cable 60. As a result, it is not necessary to connect the weight 50 to the floating structure 1 in advance, and the sinking of the weight 50 and the transport of the floating structure 1 can be easily carried out in separate processes.

Description

[Technical Field]

[0001] The present invention relates to a method for installing a floating structure for offshore wind power generation for installing wind power generation equipment offshore and to a floating structure for offshore wind power generation. [Background Art]

[0002] In recent years, carbon neutrality has been strongly demanded as an environmental measure, and in order to achieve this, the expansion of wind power generation using natural energy has been promoted in the power generation field. The efficiency of wind power generation depends on the size of the blades, and the efficiency is proportional to the square of the blade diameter, so it is desirable to use a wind turbine with large-diameter blades.

[0003] However, suitable land locations are limited, and the construction of large-scale wind turbines requires large-scale construction work and enormous costs, so there has been a limit to the spread of wind power generation on land.

[0004] On the other hand, there are vast suitable sites at sea, it is easy to introduce large-scale erection machinery, and it is possible to construct large-scale wind power generation equipment. However, in order to make the power generation equipment commensurate with the costs of facilities and machinery required for construction, it is necessary to construct a large-scale power generation facility with dozens of units arranged side by side, like wind farms seen in other countries.

[0005] As offshore wind power generators, floating type generators that can be installed even in deep water areas are suitable. For example, various types of floating structures with characteristics such as semi-submersible type, TLP (Tension Leg Platform) type, and spar type are known.

[0006] Of these, the TLP type utilizes the tension force generated by the buoyancy of the floating structure to secure it to the seabed by fixing a tension leg (tension mooring structure), which is formed by connecting a forcibly semi-submerged floating structure and an anchor installed on the seabed with tendons, thus ensuring stability even in deep waters (see, for example, Patent Document 1). The TLP type's foundation structure occupies a small area, making it possible to concentrate a large number of wind turbines in one location. In addition, because the cross-sectional area and distribution on the sea surface are small, and the floating structure is submerged about 10m below the sea surface, it is less susceptible to the effects of waves and storm surges, and has the advantage of reducing swaying and rotation. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2010-234965 [Overview of the project] [Problems that the invention aims to solve]

[0008] Incidentally, the construction of the aforementioned TLP-type floating structure generally involves installing a foundation on the seabed, connecting the foundation and the floating structure with tendons made of steel pipes, and then applying tension to the tendons to tension and moor the floating structure. However, the construction of such floating structures at sea is a large-scale and complex marine construction project, and in deep waters, the tension legs become very long, making it difficult to construct and increasing construction costs, thus posing a challenge to its feasibility.

[0009] Furthermore, Patent Document 1 proposes an installation method in which multiple weights that will form the seabed foundation are suspended from a floating structure by cables and towed to the installation site, and at the installation site each weight is lowered from the floating structure and sunk to the seabed. However, with such an installation method, it is necessary not only to lower the weights from the floating structure but also to apply tension to the cables and to manufacture and install a complex, specialized device on the floating structure to fix the cables to the floating structure while they are under tension. This method is not feasible for the installation of large-scale wind power generation facilities that require many such specialized devices.

[0010] The present invention has been made in view of the above-mentioned problems, and its objective is to provide a method for installing a floating structure for offshore wind power generation and a floating structure for offshore wind power generation that can improve the constructability of floating structures at sea and reduce construction costs. [Means for solving the problem]

[0011] To achieve the above objective, the present invention provides a method for installing a floating structure for offshore wind power generation, which includes a first floating body on which the wind power generation device is mounted and a plurality of second floating bodies arranged around the first floating body, and installing the floating structure on the sea by connecting the second floating bodies to a sinker sunk to the seabed with a cable and applying tension to the cable. In this method, the sinker is transported to the offshore installation site by a workboat, the sinker to which one end of the cable is connected is lowered from the workboat and sunk to the seabed, and the other end of the cable is held by the workboat, the floating structure on which the wind power generation device is mounted is towed to the installation site, and the other end of the cable held by the workboat at the installation site is pulled up to the second floating body side to apply tension to the cable, and the other end of the cable is fixed to the second floating body side while the cable is under tension.

[0012] Furthermore, in order to achieve the above objective, the present invention provides an offshore wind power generation floating structure that is installed on the sea by connecting the second floating bodies and sinkers submerged in the seabed with cables and applying tension to the cables, wherein one end of the cable is connected to the sinkers and the other end is pulled up toward the second floating body so that it is fixed toward the second floating body while under tension.

[0013] As a result, tension is applied to the cable by pulling the other end of the cable towards the second floating body, and the other end of the cable is fixed to the second floating body while under tension. Therefore, it is not necessary to attach the counterweight to the floating structure in advance, and the sinking of the counterweight and the transport of the floating structure can be carried out as separate processes. [Effects of the Invention]

[0014] According to the present invention, the sinking of the weights and the transport of the floating structure can be carried out in separate processes, thereby improving constructability and reducing construction costs even in the construction of large-scale offshore wind power generation facilities. [Brief explanation of the drawing]

[0015] [Figure 1] Front view of a floating structure for offshore wind power generation showing one embodiment of the present invention. [Figure 2] Side view of a floating structure for offshore wind power generation. [Figure 3] Plan view of a floating structure for offshore wind power generation [Figure 4] Bottom side perspective view of the guide device [Figure 5] Bottom view of the guide device [Figure 6] Perspective view of the weight [Figure 7] Side cross-sectional view of the weight [Figure 8] Base view of the weight [Figure 9] Front cross-sectional view of the fixing device [Figure 10] A-A cross-sectional view taken from the direction of the ship [Figure 11] Side cross-sectional view of the fixing device [Figure 12] Side view of the weight installation device [Figure 13] Plan view of the weight installation device [Figure 14] Plan view of the first work vessel with the weight installation device installed thereon [Figure 15] Side view illustrating the operation of the weight installation device [Figure 16] Side view illustrating the operation of the weight installation device [Figure 17] Side view illustrating the operation of the weight installation device [Figure 18] Side view illustrating the operation of the weight installation device [Figure 19] Schematic side view illustrating the weight conveying step [Figure 20] Schematic side view illustrating the weight conveying step [Figure 21] Schematic side view illustrating the weight conveying step [Figure 22] Schematic side view illustrating the weight installation step [Figure 23] Schematic side view illustrating the weight installation step [Figure 24] Schematic side view illustrating the weight installation step [Figure 25] Schematic side view illustrating the weight installation step [Figure 26] Schematic side view illustrating the weight installation step [Figure 27] Side cross-sectional view of the weight illustrating the weight installation step [Figure 28] Side cross-sectional view of the weight illustrating the weight installation step [Figure 29] Schematic plan view illustrating the cable holding step [Figure 30] Partial side view illustrating the cable holding step [Figure 31] Partial side view illustrating the cable holding step [Figure 32] Schematic side view illustrating the weight installation step [Figure 33] Schematic side view illustrating the floating structure conveying step [Figure 34] Schematic side view illustrating the floating structure conveying step [Figure 35] Schematic side view showing the transport process of a floating structure. [Figure 36] A schematic side view showing the installation process of the wind turbine unit onto a floating structure. [Figure 37] Schematic plan showing the transport process for floating structures. [Figure 38] Schematic plan view showing the cable connection process to a floating structure. [Figure 39] Schematic side view showing the cable connection process to a floating structure. [Figure 40] Schematic side view showing the cable connection process to a floating structure. [Figure 41] A schematic side cross-sectional view of a cylindrical member illustrating the cable connection process to a floating structure. [Figure 42] Schematic side view showing the cable connection process to a floating structure. [Figure 43] A schematic side cross-sectional view of a cylindrical member illustrating the cable connection process to a floating structure. [Figure 44] A schematic side cross-sectional view of a cylindrical member illustrating the cable connection process to a floating structure. [Figure 45] Schematic side view showing the cable connection process to a floating structure. [Figure 46] A schematic side cross-sectional view of a cylindrical member illustrating the cable connection process to a floating structure. [Modes for carrying out the invention]

[0016] Figures 1 to 46 show one embodiment of the present invention, illustrating an installation method for installing a wind power generation device body 2 mounted on a floating structure 1 offshore.

[0017] The power generation device body 2 comprises a tower 3 erected on the floating structure 1, a nacelle 4 located at the upper end of the tower 3, and blades 5 attached to the nacelle 4. By rotating the blades 5 with wind power, the electricity generated by the generator in the nacelle 4 is transmitted to the outside.

[0018] The floating structure 1 of this embodiment comprises a first floating body 10 that supports the tower 3, three second floating bodies 20 arranged around the first floating body 10 at intervals from each other, a connecting member 30 that connects each second floating body 20 to the first floating body 10, a cylindrical member 40 that penetrates each second floating body 20 vertically, a plurality of weights 50 that are sunk to the seabed, a cable 60 that connects each cylindrical member 40 to the weights 50, a fixing device 70 that fixes the cable 60 inside the cylindrical member 40, and a work platform 80 provided on the upper end side of each cylindrical member 40, and is installed on the sea surface in a semi-submerged state by applying tension to each cable 60.

[0019] The first floating body 10 consists of a cylindrical member with its lower surface closed, and a tower 3 is attached to its upper end.

[0020] Each second floating body 20 is made of a cylindrical member with a smaller height dimension than the first floating body 10, and its upper and lower surfaces are closed. Each second floating body 20 is positioned at the vertices of an equilateral triangle centered on the first floating body 10, and its lower surface is positioned at the same height as the lower surface of the first floating body 10.

[0021] Each connecting member 30 consists of an upper member 31 extending from the outer peripheral surface of the upper end of the second floating body 20 to the outer peripheral surface of the first floating body 10, a lower member 32 extending from the outer peripheral surface of the lower end of the second floating body 20 to the outer peripheral surface of the first floating body 10, and a truss member 33 positioned between the upper member 31 and the lower member 32. The upper member 31 and the lower member 32 are positioned parallel to each other with a vertical gap between them.

[0022] Each cylindrical member 40 is formed such that its upper end extends to the same height as the upper end of the first floating body 10, and its lower end protrudes slightly downward from the lower surface of the second floating body 10, with both its upper and lower ends being open. A guide device 41 for inserting a cable 60 is provided at the lower end of each cylindrical member 40. As shown in Figures 4 and 5, the guide device 41 comprises a plurality of intersecting guide rollers 41a, and each cable 60 is inserted between two guide rollers 41a positioned above each other with horizontal spacing between them, and between three guide rollers 41a positioned below each other with horizontal spacing between them. Each guide roller 41a is rotatably supported at both ends by a plurality of support plates 41b, and each support plate 41b is joined to a circular fixing plate 41c fixed to the lower end of the cylindrical member 40. The fixing plate 41c is provided with a circular hole 41d for inserting each cable 60.

[0023] Each weight 50, as shown in Figures 6 to 8, is equipped with a cubic weight body 51, which is formed by filling the inside of a box-shaped steel material with concrete. Hollow sections 52 are formed in the weight body 51, opening at the top and bottom of the weight body 51, and the inner surface of the hollow section 52 is formed in a conical shape that widens from the top end to the bottom end. An outlet 52a is provided at the top end of the hollow section 52 to discharge seawater from inside the hollow section 52 to the outside. Connecting pieces 53 extending upward are provided on both sides of the weight body 51, and holes 53a for connecting the lower ends of the cables 60 are provided in the connecting pieces 53. In this embodiment, the weight 50, formed by joining three weight bodies 51 in the width direction, is connected to each cylindrical member 40, and two cables 60 are connected to each weight 50.

[0024] Each cable 60 consists of, for example, multiple strands of steel wire, and two cables are arranged in each cylindrical member 40. A socket 61 for fixing the cable 60 to the cylindrical member 40 is provided at the upper end of the cable 60, and the socket 61 is formed by a cylindrical member having a larger outer diameter than the cable 60. In addition, a suspension device 62, such as a suspension ring, can be attached to the end of the socket 61.

[0025] As shown in Figures 9 to 11, each fixing device 70 consists of a pair of locking members 71 that engage with the socket 61 of the cable 60 from above, a pair of support members 72 that support each locking member 71 from below, and a fixing member 73 that can fix the support members 72 within the cylindrical member 40 at any position in the vertical direction, and is arranged inside the cylindrical member 40.

[0026] Each locking member 71 has a hole 71a through which the socket 61 can be inserted, and is arranged apart from each other in the radial direction of the cylindrical member 40. The locking member 71 locks the socket 61 by interposing a pair of half-circular fixing plates 71b and a pair of height adjustment plates 71c, each having an inner diameter equal to the outer diameter of the cable 60, between the lower end of the socket 61 and the upper surface of the locking member 71. In this case, by changing the number of height adjustment plates 71c, the thickness dimensions of the fixing plates 71b and height adjustment plates 71c can be adjusted according to the vertical position of the socket 61.

[0027] Each support member 72 is positioned at a 90° angle from each locking member 71, and spaced apart from each other in the radial direction of the cylindrical member 40, with each cable 60 passing through the spaces between the support members 72. The support members 72 are connected to each other by connecting plates 72a.

[0028] The fixing member 73 is provided so as to extend vertically along the inner surface of the cylindrical member 40, and is provided at four locations around the cylindrical member 40 so as to fix both ends of each support member 72 to the cylindrical member 40. In this case, each support member 72 is fixed to any position in the vertical direction of the fixing member 73 by bolts and nuts (not shown) via a fixing plate 73a, and the support member 72, fixing member 73, and fixing plate 73a are each provided with numerous holes 74 for bolt insertion at equal intervals in the vertical direction.

[0029] The work platform 80 is provided from the upper end of each cylindrical member 40 to the first floating body 10, and allows for the installation of equipment and other items to be used in the floating structure installation process described later.

[0030] Furthermore, in this embodiment, when sinking the weight 50 to the seabed, the weight installation device 90 shown in Figures 12 and 13 is used.

[0031] This weight-setting device 90 comprises a device body 91 extending in the front-rear direction, a winding drum 92 on which the cable 60 is wound, a pair of left and right bearing parts 93 that rotatably support the winding drum 92, a first hydraulic jack 94 for rotating the winding drum 92, and a second hydraulic jack 95 for restricting the rotation of the winding drum 92, and is installed on the first workboat S1, which will be described later.

[0032] The main body of the device 91 comprises a pair of left and right base members 91a arranged at a distance from each other in the width direction, and a base plate 91b provided across the upper surface of each base member 91a. A winding drum 92, bearings 93, a first hydraulic jack 94, and a second hydraulic jack 95 are arranged on the base plate 91b. The front end of each base member 91a extends forward of the base plate 91b, and guide rollers 91c for guiding the cable 60 unwound from the winding drum 92 are provided across each base member 91a.

[0033] The winding drum 92 is provided with disc-shaped flange portions 92a at both axial ends, and each flange portion 92a has a plurality of engagement holes 92b that engage with the first hydraulic jack 94, provided at equal intervals in the circumferential direction of the winding drum 92. The engagement holes 92b are elongated holes that are long in the circumferential direction of the winding drum 92, and a portion of them is cut out so that the first hydraulic jack 94 can be engaged and disengaged.

[0034] Each bearing portion 93 is provided at a distance from each other in the axial direction of the winding drum 92 and is positioned axially inward of each flange portion 92a of the winding drum 92.

[0035] The first hydraulic jacks 94 are provided in pairs on each side of the flange portion 92a of the winding drum 92, and a cylindrical engaging portion 94b provided at the tip of the drive rod 94a is formed to engage with the engaging hole 92b of the winding drum 92. In this case, the base end of the first hydraulic jack 94 is rotatably supported on the base plate 91b, and it rotates with the base end as a pivot point by an auxiliary jack 94c provided on the base plate 91b.

[0036] The second hydraulic jack 95, like the first hydraulic jack 94, is provided in pairs on each side of the flange portion 92a of the winding drum 92, and a cylindrical engaging portion 95b provided at the tip of the drive rod 95a is formed to engage with the engaging hole 92b of the winding drum 92. In this case, the base end of the first hydraulic jack 95 is rotatably supported on the base plate 91b, and it rotates with the base end as a pivot point by an auxiliary jack 95c provided on the base plate 91b.

[0037] As shown in Figure 14, the weight-setting device 90 configured as described above is installed on the first workboat S1, which is made up of a barge, and the weight 50 is suspended from the cable 60 of the winding drum 92. In this case, two weight-setting devices 90 are installed on one side of the first workboat S1, and one weight-setting device 90 is installed on the other side of the first workboat S1. Each weight-setting device 90 on one side is positioned at a distance equal to the distance between the second floating bodies 20 of the floating structure 1 in the longitudinal direction of the first workboat S1, and the weight-setting device 90 on the other side is positioned midway between each weight-setting device 90 on one side.

[0038] The operation of the weight-setting device 90 will now be explained with reference to Figures 15 to 18.

[0039] First, as shown in Figure 15, the engagement portion 94b of the first hydraulic jack 94 is engaged with the engagement portion 92b of the winding drum 92, and then the engagement portion 95b of the second hydraulic jack 95 is released from the engagement portion 92b of the winding drum 92. At this time, the winding drum 92 will attempt to rotate in the unwinding direction due to the load of the weight 50 applied to the cable 60, but the rotation of the winding drum 92 is restricted by the engagement with the first hydraulic jack 94.

[0040] Next, as shown in Figure 16, the drive rod 94a of the first hydraulic jack 94 is extended, and the winding drum 92 is rotated by a predetermined angle (one unit interval of the engagement holes 92a) in the unwinding direction, thereby unwinding the cable 60 from the winding drum 92 to a predetermined length.

[0041] Next, as shown in Figure 17, the engagement portion 95b of the second hydraulic jack 95 is engaged with the engagement portion 92b of the winding drum 92, and then the engagement between the engagement portion 94b of the first hydraulic jack 94 and the engagement portion 92b of the winding drum 92 is released. At this time, the winding drum 92 will attempt to rotate in the unwinding direction due to the load of the weight 50, but the rotation of the winding drum 92 is restricted by the engagement with the second hydraulic jack 95.

[0042] Next, as shown in Figure 18, the drive rod 94a of the first hydraulic jack 94 is retracted, and the engaging portion 94b of the first hydraulic jack 94 is engaged with the engagement hole 92b on the opposite side of the winding direction of the winding drum 92. Then, by repeating the operations shown in Figures 15 to 18, the cable 60 is unwound from the winding drum 92 in predetermined lengths.

[0043] Next, the installation method for the floating structure for offshore wind power generation according to this embodiment will be described with reference to Figures 19 to 46. Note that the types of work vessels S1 to S6 shown below are examples, and other types of work vessels with equivalent functions can be used.

[0044] First, as shown in Figure 19, the second workboat S2, which consists of a floating crane, lifts the weights 50 from the harbor or factory quay and transfers them to the weight installation devices 90 of the first workboat S1. Then, as shown in Figures 20 and 21, the third workboat S3, which consists of a tugboat, tows the first workboat S1 towards the installation site at sea.

[0045] Next, after arriving at the installation site for the wind power generation equipment, as shown in Figure 22, the first workboat S1 unwinds the cable 60 using each weight installation device 90, and simultaneously lowers each weight 50 connected to one end of the cable 60 to a predetermined height H1 (for example, 10m) from the seabed. Next, as shown in Figure 23, the two weights 50 on one side of the first workboat S1 are lowered to the seabed using the weight installation device 90 and then, as shown in Figure 24, the first workboat S1 is moved to the sinking position of the weight 50 on the other side of the first workboat S1, and the weight 50 on the other side of the first workboat S1 is lowered to the seabed using the weight installation device 90 and then settles.

[0046] Specifically, as shown in Figure 25, the distance L1 between the two weights 50 on one side of the first workboat S1 is equal to the distance between the second floating bodies 20 of the floating structure 1. However, the distance L2 between the weights 50 on one side of the first workboat S1 and the weights 50 on the other side is shorter than L1. Therefore, as shown in Figure 26, the first workboat S1 is moved by the third workboat S until the distance from the sinking position of the weights 50 on one side of the first workboat S1 to the weights 50 on the other side equals L1. After that, the weights 50 on the other side are sunk, so that the sinking position of each weight 50 is equal to the installation position of each second floating body 20.

[0047] At that time, as shown in Figures 27 and 28, when the weight 50 settles on the seabed, the weight 50 sinks into the mud of the seabed due to its own weight, and mud enters the hollow section 52 from the lower surface of the weight body 51. The amount of seawater in the hollow section 52 that has entered is then discharged to the outside through the discharge port 52a. As a result, the buoyancy of the weight 50 by the amount it has sunk into the mud decreases, and the resistance to the pull-out load from the cable 60 increases due to the so-called suction effect. In this case, a check valve may be provided at the discharge port 52a to prevent seawater from entering the hollow section 52 from the outside.

[0048] Next, as shown in Figure 29, three fourth workboats S4, each consisting of a small barge, are positioned around the first workboat S1 for each weight-setting device 90, and the other end of the cable 60 is detached from each weight-setting device 90 and held by each fourth workboat S4. At this time, the other end of the cable 60 is lifted from the weight-setting device 90 by a fifth workboat S5, which consists of an anchor-handling vessel, and is engaged with a temporary holding member 63 provided on the fourth workboat S4, as shown in Figures 30 and 31, thereby holding the other end of the cable 60 by the fourth workboat S4. The temporary holding members 63 are provided at both ends of the fourth workboat S4 and are designed to hold the two cables 60 connected to one weight 50. As a result, as shown in Figure 32, the cables 60 connected to each weight 50 are held in place by each fourth workboat S4.

[0049] Furthermore, as shown in Figure 33, the floating structure 1 manufactured at the factory is lowered onto the water from the harbor or factory quay by a second workboat S2, and as shown in Figures 34 and 35, the floating structure 1 is towed by multiple third workboats S3 to a work facility S6 consisting of a SEP vessel (self-elevating barge), as shown in Figure 36. At the work facility S6, the wind power generation unit 2 is lifted and the tower 2 is joined to the first floating body 10 of the floating structure 1 to install the wind power generation unit 2 on the floating structure 1. At this time, ballast water is injected into each second floating body 20 to adjust the buoyancy of each second floating body 20.

[0050] Next, as shown in Figure 37, the floating structure 1 on which the wind power generation device body 2 is mounted is towed by multiple third work vessels S3 to the installation site offshore, as shown in Figure 38. At the installation site, as described above, each weight 50, held by the fourth work vessel S4 via the cable 60, is sunk, and the floating structure 1 is positioned so that each second floating body 20 is located above the sunk position of each weight 50, as shown in Figure 39.

[0051] Furthermore, at the upper end of each cylindrical member 40 of the floating structure 1, a hoisting device 100 is installed for pulling the other end of the cable 60 into the cylindrical member 40, and a tensioning device 110 is installed for applying tension to the cable 60 by further pulling up the cable 60 that has been pulled into the cylindrical member 40.

[0052] The hoisting device 100 consists of a well-known electric winch for winding up the rope 101, and the rope 101 extends outwards from the lower end of the cylindrical member 40 through the inside of the cylindrical member 40 and is connected to the other end of the cable 60.

[0053] The tension-applying device 110 consists of a well-known strand jack that continuously feeds out the strand 111 by repeatedly gripping and releasing it, by moving one of a pair of upper and lower clamping mechanisms capable of gripping a strand 111 made of steel wire up and down using a hydraulic device, and the lower end of the strand 111 is connected to a socket 61 of the cable 60 via a suspension device 62.

[0054] Next, the other end of each cable 60, which has been held in place by each of the fourth workboats S4 at the installation site, is pulled up into the cylindrical member 40 of each of the second floating bodies 20, tension is applied to each cable 60, and each cable 60 is fixed to each cylindrical member 40 while under tension. This process is performed simultaneously in the cylindrical member 40 of each of the second floating bodies 20 as follows.

[0055] First, as shown in Figure 40, the rope 101 of the hoisting device 100 is connected to the other end of the cable 60, and as shown in Figure 41, the rope 101 is wound up by the hoisting device 100 to pull the cable 60 into the cylindrical member 40 without any slack. At this time, at the lower end of the cylindrical member 40, the rope 101 and the cable 60 are smoothly guided into the cylindrical member 40 by the guide rollers 41a of the guide device 41.

[0056] Next, as shown in Figure 42, the strand 111 of the tensioning device 110 is connected to the socket 61 of the cable 60 that has been pulled up into the cylindrical member 40, and as shown in Figure 43, the cable 60 is switched from the rope 101 to the strand 111.

[0057] Next, as shown in Figure 44, tension is applied to the cable 60 by pulling up the strand 111 with the tension-applying device 110. At this time, as the tensioned cable 60 is pulled up, the second floating body 20 sinks as shown in Figure 45, and tension is applied to the cable 60 by the tension-applying device 110 until the second floating body 20 is submerged to a predetermined depth H2 (for example, 10m) from the water surface.

[0058] Subsequently, as shown in Figure 46, the cable 60 is secured inside the cylindrical member 40 by the fixing device 70 while tension is applied to the cable 60, and the strand 111 of the tensioning device 110 is removed from the cable 60, thereby completing the installation of the floating structure 1 supporting the wind turbine body 2.

[0059] As described above, the floating structure 1 installed on the ocean is connected to each counterweight 50 sunk to the seabed via cables 60, and is tension-moored by the balance between the tension of the cables 60 and the buoyancy. This provides sufficient prestress to maintain tension against the horizontal force generated in the wind turbine body 2, making it possible to always stably support even large wind turbines. In addition, since the multiple second floating bodies 20 arranged around the semi-submerged first floating body 10 are submerged below the water surface, there is also the advantage that it is less susceptible to the effects of waves and storm surges.

[0060] As described above, according to this embodiment, the counterweight 50 is transported to the offshore installation site by the first workboat S1, the counterweight 50 with one end of the cable 60 connected to it is lowered from the first workboat S1 and sunk to the seabed, the other end of the cable 60 is held by the fourth workboat S4, and the floating structure 1 on which the wind power generation device body 2 is mounted is towed to the installation site, the other end of the cable 60 held by the fourth workboat S4 at the installation site is pulled up toward the second floating structure 20 to apply tension to the cable 60, and the other end of the cable 60 is fixed toward the second floating structure 20 while tension is applied to the cable 60. Therefore, it is not necessary to connect the counterweight 50 to the floating structure 1 in advance, and the sinking of the counterweight 50 and the transport of the floating structure 1 can be easily carried out as separate processes. As a result, even in the construction of large-scale offshore wind power generation facilities, constructability can be improved and construction costs can be reduced.

[0061] Furthermore, since the other end of the cable 60 is pulled up into a cylindrical member 40 that penetrates each second floating body 20 vertically, and the other end of the cable 60 is fixed to the cylindrical member 40 while tension is applied to the cable 60, even if the second floating body 20 is submerged below the water surface, the cylindrical member 40 can remain protruding above the water surface. As a result, the pulling up and fixing of the cable 60 can be performed using the cylindrical member 40 above the water surface, making it easier to tension and moor the floating structure 1.

[0062] In this case, a rope 101 extending outward from the lower end of the cylindrical member 40 is connected to the other end of the cable 60 held by the fourth workboat S4 at the installation site, and the other end of the cable 60 is positioned inside the cylindrical member 40 by pulling the rope 101 into the cylindrical member 40. Then, the other end of the cable 60 is reconnected from the rope 101 to the tension-applying device 110, and tension is applied to the cable 60 by pulling it up with the tension-applying device 110. As a result, the cable 60, which does not require tension application, can be easily and quickly pulled in by the hoisting device 100, and the amount of cable 60 that the tension-applying device 110 has to lift can be reduced. This makes the entire tensioning and mooring operation more efficient, and by using, for example, an electric winch for the hoisting device 100 and a strand jack for the tension-applying device 110, the tensioning and mooring operation can be performed with general-purpose equipment without the need to manufacture specialized equipment, thereby improving the efficiency and cost of construction.

[0063] Furthermore, since the other end of the cable 60, which is pulled up into the cylindrical member 40 and tensioned, is fixed by a fixing device 70 that can be fixed at any position in the vertical direction of the cylindrical member 40, the fixing position of the cable 60 can be adjusted to any height according to the tension, making the fixing work of the cable 60 easy and accurate.

[0064] Furthermore, a weight setting device 90 equipped with a winding drum 92 on which the cable 40 is wound is installed on the first workboat S1, and the winding drum 92 is rotated by a predetermined rotation angle using first and second hydraulic jacks 94 and 95 that engage with the winding drum 92, thereby unwinding the cable 60 from the winding drum 92, and the weight 50 connected to the cable 60 is lowered from the first workboat S1. As a result, the cable 60 can be unwound from the winding drum 92 while the weight 50 is alternately supported by the first and second hydraulic jacks 94 and 95, and even a heavy weight 50 can be reliably lowered.

[0065] Furthermore, the weight 50 has hollow sections 51a opening on the upper and lower surfaces of the weight body 51, respectively. The weight 50 is sunk to the seabed with the weight of the weight 50 causing seabed mud to enter the hollow sections 51a. As a result, the suction effect of the hollow sections 51a provides resistance to being pulled out of the weight 50, thereby increasing the anchoring effect of the weight 50.

[0066] In this case, since the hollow portion 51a is formed in a conical shape with its inner surface widening from the upper end to the lower end, the lower surface of the weight body 51 can be formed such that the area other than the hollow portion 51a is small, thereby increasing the amount that the weight body 51 sinks into the seabed and further increasing the pull-out resistance.

[0067] The embodiments described above are examples of the present invention, and the present invention is not limited to those described in these embodiments. [Explanation of Symbols]

[0068] 1...Floating structure, 2...Wind turbine main body, 10...First floating body, 20...Second floating body, 30...Connecting member, 40...Cylindrical member, 50...Weight, 60...Cable, 70...Fixing device, 80...Working platform, 90...Weight installation device, 100...Hoisting device, 110...Tensioning device.

Claims

1. In a method for installing an offshore wind power generation floating structure, the floating structure comprises a first floating body on which the wind power generation device is mounted, and a plurality of second floating bodies arranged around the first floating body, which is then placed at an offshore installation site, and the second floating bodies are connected to counterweights submerged on the seabed by cables, and tension is applied to the cables to install the floating structure on the sea. The aforementioned weights are transported to the installation location at sea by a work vessel. A weight to which one end of the aforementioned cable is attached is lowered from a workboat and sunk to the seabed, while the other end of the cable is held by the workboat. The floating structure on which the wind power generation device body is mounted is towed to the installation site. By pulling the other end of the cable, which was being held on the workboat at the installation site, towards the second floating body, tension is applied to the cable. With tension applied to the cable, the other end of the cable is fixed to the second floating body. A method for installing a floating structure for offshore wind power generation, characterized by the following features.

2. The other end of the cable is pulled up into a cylindrical member provided so as to penetrate vertically through each of the second floats, and the other end of the cable is fixed to the cylindrical member while tension is applied to the cable. The method for installing a floating structure for offshore wind power generation according to feature 1.

3. A rope extending from the lower end of the cylindrical member is connected to the other end of the cable held by the workboat at the installation site. After pulling the rope into the cylindrical member and positioning the other end of the cable inside the cylindrical member, The other end of the cable is reconnected from the rope to a tension-applying device installed on a cylindrical member, The cable is pulled up by a tension-applying device to apply tension, and the other end of the cable is then fixed to a cylindrical member. The method for installing a floating structure for offshore wind power generation according to feature 2.

4. The other end of the cable, which has been pulled up into the cylindrical member and subjected to tension, is fixed at any position in the vertical direction of the cylindrical member by a fixing device. The method for installing a floating structure for offshore wind power generation according to feature 2.

5. The winding drum on which the cable is wound is installed on the workboat, and the winding drum is rotated by a hydraulic jack engaged with the winding drum at predetermined rotational angles to unwind the cable from the winding drum, thereby lowering the weight connected to the cable from the workboat. The method for installing a floating structure for offshore wind power generation according to feature 1.

6. As the aforementioned weight, a weight having hollow sections with openings on the upper and lower surfaces of the weight body is used. The weight is sunk to the seabed while the weight itself causes the mud from the seabed to enter the hollow section. The method for installing a floating structure for offshore wind power generation according to feature 5.

7. A weight is used in which the inner surface of the hollow portion is formed in a conical shape that widens from the upper end to the lower end. The method for installing a floating structure for offshore wind power generation according to feature 6.

8. An offshore wind power generation floating structure comprises a first floating body on which the wind power generation device is mounted, and a plurality of second floating bodies arranged around the first floating body, wherein the second floating bodies are connected to counterweights submerged on the seabed by cables, and tension is applied to the cables to install the structure on the sea. The cable is connected at one end to the weight and fixed to the second floating body by being pulled up towards the second floating body, thereby applying tension to it. A floating structure for offshore wind power generation characterized by the following features.

9. Each of the aforementioned second floating bodies is provided with a cylindrical member that penetrates it vertically, The cable is pulled up at one end within the cylindrical member, and the other end is fixed to the cylindrical member while tension is applied. The floating structure for offshore wind power generation according to feature 8.

10. The device includes a fixing device that can secure the other end of the cable, which is under tension within the cylindrical member, at any position in the vertical direction of the cylindrical member. The floating structure for offshore wind power generation according to feature 8.

11. The aforementioned weight has hollow sections opening on the upper and lower surfaces of the weight body, and is sunk to the seabed with its own weight causing seabed mud to enter the hollow sections. The floating structure for offshore wind power generation according to feature 8.

12. The hollow portion is formed in a conical shape, with its inner surface widening from the upper end to the lower end. The floating structure for offshore wind power generation according to feature 11.

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