Construction method of floating body type offshore wind power generation facility

Abstract

To provide a method which can efficiently construct a floating body type offshore wind power generation facility, in which a draft of a floating body moored at an installation object sea area is 20 m or shallower, without constructing an installation point of the floating body type offshore wind power generation facility on a quay wall.SOLUTION: A floating structure 10 is temporarily installed in a sea area whose water depth is not shallower than 8 m and not deeper than 20 m and a ring lift crane 20 is installed at a crane installation area Ca provided at the floating structure 10. Assembly components of a wind power generation device 3 are temporarily placed in a temporary placement area Ta provided at the floating structure 10. A plurality of work areas A are provided in a sea area located adjacent to the floating structure 10. The ring lift crane 20 is used to install the assembly components temporarily placed in temporary placement area Ta on a floating body 2 lying on a seat bottom SB of the work area A to assemble an assembly 9 in which the wind power generation device 3 is built on the floating body 2. In parallel with the assembly work, additional work is performed to the assembly 9 in another work area A where the assembly work is finished antecedently.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a construction method for a floating offshore wind power generation facility, and more specifically to a construction method for a floating offshore wind power generation facility that can efficiently construct a floating offshore wind power generation facility with a float draft of 20 m or less when moored in the target sea area, without the need to prepare an installation base (base port) for the floating offshore wind power generation facility on a quay. [Background technology]

[0002] Floating offshore wind power generation facilities, which have a structure in which wind power generation equipment is erected on a float moored in the sea area, are classified according to the structure of the float into spar-type, semi-submersible, TLP (tension leg platform)-type, and barge (made of steel, concrete, or hybrid) types. For example, a spar-type floating offshore wind power generation facility has a column-shaped spar-type float approximately 50 to 100 meters in height, most of which is submerged, and a wind power generation equipment is erected on this single huge spar-type float (see, for example, Patent Document 1). The draft of the spar-type float when moored in the target sea area for installation is approximately 50 to 100 meters. On the other hand, semi-submersible, TLP-type, and barge-type floating offshore wind power generation facilities other than the spar-type have a float semi-submerged and floating on the sea surface, and when moored in the target sea area for installation, the draft of the semi-submersible, TLP-type, and barge-type floats is each 20 meters or less. Specifically, for example, in a semi-submersible floating offshore wind power generation facility, a semi-submersible floater having multiple columns approximately 20m to 40m in height and connectors (so-called footing members, etc.) that connect the columns is set up in a semi-submerged state on the sea, and a wind power generation device is erected on one of the columns of the floater.

[0003] In a typical construction method for a spar-type floating offshore wind turbine, the spar-type float and the tower that make up the wind turbine are connected in an inclined position on land such as a quay, and the combined spar-type float and tower are loaded onto a semi-submersible barge in this inclined position and transported to a water area with a depth of 100 meters or more. The combined spar-type float and tower are then launched in the water area with a depth of 100 meters or more, and the ballast water in the spar-type float is adjusted to raise the combined unit from its inclined position to an upright position. The upright combined unit is then towed to the target installation area and moored in the water area with a depth of 100 meters or more. Next, a fixed crane barge is used to install a nacelle hub on top of the tower, and blades are installed on the nacelle hub, completing the erection of the spar-type floating offshore wind turbine.

[0004] The invention described in Patent Document 1 differs from general construction methods in that a bent section is provided midway through the tower and the wind turbine (nacelle hub and blades) is installed on the tower on land, but even in the invention described in Patent Document 1, the spar-type floating body (foundation) and the wind power generation equipment tower are assembled as a single unit on land.

[0005] The float and wind turbine generator that make up a floating offshore wind power generation facility are very large and heavy. Therefore, it is difficult to transport the float and tower as a single unit over long distances on land. Therefore, when assembling the float and tower assembly (unit) on land, as in the case of a typical construction method or the invention described in Patent Document 1, it is necessary to secure space on land, such as a quay, for loading the float and wind turbine generator assembly components, and to secure space for assembling the assembly and launch the assembly directly into the sea. However, in many cases, the ground at a typical quay is not strong enough to withstand the load of the assembly. Therefore, establishing an installation base for a floating offshore wind power generation facility on a quay requires large-scale construction work, such as ground improvement work to improve the bearing capacity of the quay and apron, which requires relatively high costs, labor, and time. In particular, when assembling multiple assemblies on land, it may be difficult to secure a large space on a quay as an installation base for a floating offshore wind power generation facility.

[0006] Furthermore, in a typical construction method for a spar-type floating offshore wind power facility, work is required to erect the spar-type floater and tower unit that has been laid on its side in waters with a depth of 100 meters or more. The construction method described in Patent Document 1 also requires the hinge opening / closing means to change the rear part of the tower hinge and the spar-type floater (foundation) from their laid-down state to an upright state. Therefore, the construction methods proposed so far have the problem of requiring sophisticated and complicated work at sea. As such, the construction methods proposed so far have various problems and there is room for improvement. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-202250 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a construction method for a floating offshore wind power generation facility that can efficiently construct a floating offshore wind power generation facility with a float draft of 20 m or less when moored in the target sea area, without the need to prepare an installation base for the floating offshore wind power generation facility on a quay. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides a construction method for a floating offshore wind power generation facility, which includes a float moored in a target sea area for installation and a wind power generation device erected on the float, and in which the draft from the water surface to the bottom of the float is 20m or less while the float is moored in the target sea area for installation, the construction method comprising: constructing a temporary floating structure in a sea area with a water depth of 8m to 20m, providing a crane installation area on the floating structure, in which a ring-shaped foundation frame constituting a ring lift crane and a crane main body placed on the foundation frame are installed, and a temporary storage area for temporarily storing assembly parts constituting the wind power generation device, and providing a plurality of work areas in the sea area adjacent to the floating structure for landing the float, and providing a plurality of temporary storage areas in the temporary storage area. Several sets of the assembly parts are temporarily placed, and the ring lift crane is used to install one set of the assembly parts temporarily placed in the temporary placement area onto the floating body that has been anchored on the seabed in the work area, and assembly work is performed to assemble an assembly on the floating body on which the wind power generation device is constructed, and in the work area where the assembly work has been completed, additional work including adjustment work is performed on the assembly, and in a work area different from the work area where the assembly work has been completed, the ring lift crane is used to perform the assembly work on the floating body that has been anchored on the seabed in that work area, and the assemblies that have been subjected to the additional work are sequentially transported by sea to the installation target sea area, and the assemblies are moored in the installation target sea area. [Effects of the Invention]

[0010] The present invention constructs a temporary floating structure in a relatively shallow sea area with a depth of 8 to 20 meters, thereby reducing the cost, labor, and time required for constructing the floating structure and making it possible to easily land the floater on the seabed in a work area adjacent to the floating structure. By installing a ring lift crane in a crane installation area on the floating structure and temporarily storing multiple sets of wind turbine assembly components in a temporary storage area, it is no longer necessary to prepare a large installation base for a floating offshore wind power generation facility, which would require an area for installing a large crane on a quay or an area for temporarily storing all of the wind turbine assembly components. Furthermore, by using a ring lift crane installed on the floating structure, which is not affected by waves, to install the wind turbine assembly components temporarily stored on the floating structure onto the floater that is landed on the seabed in the work area, assembly work can be carried out efficiently and in a very stable manner. In the work area where assembly work has been completed, additional work, including adjustment work, is performed on the assembly, and in a separate work area from the work area where assembly work has been completed, assembly work is performed using a ring lift crane on the float that has been placed on the seabed in that work area. This allows assembly work and additional work to be performed in parallel in separate locations. The assembly, after additional work, is transported by sea to the target installation area, and construction of the floating offshore wind turbine is completed simply by mooring the assembly there. Therefore, without the need to prepare a large installation base for the floating offshore wind turbine on a quay, floating offshore wind turbines with a float draft of 20 meters or less (other types of floating offshore wind turbines excluding spar types) can be efficiently constructed when moored in the target installation area. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic front view of a semi-submersible floating offshore wind power generation facility constructed in accordance with the present invention. [Figure 2] This is an explanatory diagram showing a schematic plan view of a pier constructed as a temporary floating structure in a sea area, with multiple work areas set up in the sea area adjacent to the floating structure. [Figure 3] 3 is an explanatory diagram showing a schematic side view of the floating structure of FIG. 2. FIG. [Figure 4] FIG. 3 is an explanatory diagram showing a schematic plan view of a ring-shaped foundation structure constructed by placing caissons in the sea area where a crane installation area is to be constructed during the construction process of the floating structure shown in FIG. 2. [Figure 5] 5 is an explanatory diagram illustrating a state in which an annular foundation frame constituting a ring lift crane is installed on the annular foundation structure of FIG. 4 in a plan view. [Figure 6] 6 is an explanatory diagram showing a schematic plan view of a crane body constituting a ring lift crane installed on the base frame of FIG. 5. FIG. [Figure 7] FIG. 3 is an explanatory diagram showing a schematic plan view of the sea area in which the floating structure of FIG. 2 is constructed. [Figure 8] 3 is an explanatory diagram showing a state in which a plurality of assembly parts for wind turbine generators are temporarily placed on the floating structure of FIG. 2 using a carrier ship, as viewed from above; FIG. [Figure 9] This is an explanatory diagram showing a schematic plan view of the state in which the transport ship of Figure 8 has been moved to a position away from the floating structure and the floating bodies have been landed on the seabed of each of the multiple work areas (first to fourth work areas) set up in the sea area adjacent to the floating structure. [Figure 10] This is an explanatory diagram showing a schematic side view of the state in which the tower partition members and nacelle hub, which were temporarily placed on the floating structure, have been installed on the floating body placed in the first work area of ​​Figure 9 using a ring lift crane installed on the floating structure. [Figure 11] This is an explanatory diagram showing a schematic plan view of the state in which blades are attached to a nacelle hub installed on a floating body placed in the first working area from the state shown in Figure 10, and the assembly is completed in the first working area. [Figure 12] This is an explanatory diagram showing a schematic plan view of the state in which the tower segments, nacelle hub, and blades that were temporarily placed on the floating structure have been installed on the floating body placed in the second work area from the state shown in Figure 11, and the assembly has been completed. [Figure 13]This is an explanatory diagram showing a schematic plan view of the assembly state in which the assembly, which has completed additional work in the first work area from the state shown in Figure 12, is moved from the first work area, and the tower segments, nacelle hub, and blades that were temporarily placed on the floating structure are installed on the floating body placed in the third work area, completing the assembly. [Figure 14] This is an explanatory diagram showing a schematic plan view of the assembly state in which the assembly, which has completed additional work in the second work area from the state shown in Figure 13, is moved from the second work area, a new float is placed in the first work area, and the tower partition members, nacelle hub, and blades that were temporarily placed on the floating structure are installed on the float placed in the fourth work area, completing the assembly. [Figure 15] This is an explanatory diagram showing a schematic plan view of a ring-shaped foundation structure constructed by arranging multiple steel pipe sheet piles in a ring shape in a plan view in an offshore area where a crane installation area is to be constructed during the construction of an offshore structure in another embodiment. [Figure 16] 16 is an explanatory diagram illustrating a state in which an annular foundation frame constituting a ring lift crane is installed on the annular foundation structure of FIG. 15 in a plan view. FIG. [Figure 17] This is an explanatory diagram showing a schematic plan view of a state in which multiple sets of wind power generation device assembly parts are temporarily placed on an offshore structure of yet another embodiment, and floats are each landed on the seabed of multiple work areas (first to fourth work areas) set up in the sea area adjacent to the offshore structure. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a method for constructing a floating offshore wind power generation facility will be described based on the embodiment shown in the drawings.

[0013] As illustrated in FIG. 1 , a floating offshore wind power facility 1 includes a float 2 moored in the target sea area for installation, and a wind turbine 3 erected on the float 2. In the target sea area for installation, the float 2 is moored to the seabed SB using mooring lines 7, anchors 8, etc. This construction method is a method for constructing a floating offshore wind power facility 1 in which the draft DF from the water surface to the bottom of the float 2 is 20 m or less while the float 2 is moored in the target sea area for installation. In other words, this construction method can be used for constructing floating offshore wind power facilities 1 of other types (semi-submersible, TLP, barge) except for the spar type. This construction method is particularly suitable for constructing semi-submersible floating offshore wind power facilities 1. In this construction method, the float 2 and the wind power generation device 3 are integrated into one body before being moored in the target sea area for installation as an assembly 9, and the assembly 9 in the moored state in the target sea area for installation is the floating offshore wind power generation facility 1.

[0014] This embodiment illustrates the construction of a semi-submersible floating offshore wind power generation facility 1. As illustrated in Fig. 1, a semi-submersible floater 2 is submerged in the sea to a predetermined draft DF and moored in a semi-submerged state. The wind turbine 3 has a nacelle hub 5 (a nacelle and hub integrated unit) installed on top of a tower 4 that extends vertically, and multiple blades 6 arranged radially on the nacelle hub 5. Electrical equipment such as a generator, brake equipment, and gearbox are built into the nacelle hub 5, and a power cable connected to the generator is arranged inside the tower 4.

[0015] This embodiment illustrates a wind turbine generator 3 having three blades 6 and a tower 4 made up of three divided members 4a. The number of blades 6 provided in the wind turbine generator 3, the structure of the blades 6, and the number of divided members 4a making up the tower 4 are not limited to this embodiment. For example, the blades 6 may have a structure in which multiple members are connected together, or the tower 4 may be made up of a single long member.

[0016] The longitudinal length (height) of the tower 4 is approximately 80m to 150m, and the width (thickness) of the tower 4 is approximately 5m to 15m. The weight of the tower 4 is approximately 1000t to 2000t. The longitudinal length (height) of each of the segment members 4a is approximately 25m to 50m, and the weight of each of the segment members 4a is approximately 300t to 700t. The height of the nacelle hub 5 is approximately 8m to 15m, the longitudinal length is approximately 15m to 25m, and the width is approximately 7m to 15m. The weight of the nacelle hub 5 is approximately 600t to 1000t. The longitudinal length of one blade 6 is approximately 80m to 150m, and the weight of one blade 6 is approximately 50t to 90t.

[0017] The semi-submersible float 2 has multiple pillar-shaped columns 2a extending in the vertical direction and connectors 2b (so-called footing members) that connect the columns 2a to each other. In this embodiment, the connectors 2b have a structure including a cross-shaped connector in a plan view and polygonal support sections in a plan view provided at each of the four ends of the connector, with the columns 2a erected on each of the four support sections. The lower end of a tower 4 is fixed to one of the columns 2a that constitute the semi-submersible float 2, so that the wind turbine generator 3 is erected on one column 2a. The upper end of the column 2a and the lower end of the tower 4 are joined, for example, by bolting or welding.

[0018] The float 2 is configured to be able to store (fill) ballast water inside, and the draft and attitude of the float 2 can be adjusted by adjusting the amount of stored ballast water. The semi-submersible float 2 has a length and width of approximately 60 m to 100 m in plan view, and the height of the column 2a of the semi-submersible float 2 is approximately 25 m to 50 m. Note that the structure of the float 2, specifically, in the case of a semi-submersible float 2, the shape and structure of the column 2a, the shape and structure of the connecting body 2b, the number and arrangement of the columns 2a erected on the connecting body 2b, and the position of the column 2a on which the wind turbine generator 3 is erected, are not limited to the configuration of this embodiment, and floats 2 with various other configurations can also be used. For example, when constructing a TLP-type floating offshore wind power generation facility 1, a known TLP-type float 2 is used, and when constructing a barge-type floating offshore wind power generation facility 1, a known barge-type float 2 is used.

[0019] The procedure for this construction method is explained below.

[0020] 2 and 3, a temporary underwater structure 10 is constructed in an ocean area with a water depth DW (depth from the sea surface position WL to the seabed SB) of 8 m to 20 m. In this embodiment, a pier is constructed in an ocean area as the temporary underwater structure 10, but a floating structure can also be constructed in an ocean area as the temporary underwater structure 10, for example.

[0021] As illustrated in Fig. 2, the floating structure 10 is provided with a crane installation area Ca in which a ring-shaped foundation frame 22, which constitutes the ring lift crane 20 in a plan view, and a crane main body 21 disposed on the foundation frame 22 are installed, and a temporary storage area Ta in which assembled parts, namely, the tower 4 (separate members 4a), nacelle hub 5, and blades 6, which constitute the wind turbine generator 3, are temporarily stored. In the sea area adjacent to the floating structure 10, multiple work areas A (A1 to A4) are provided for landing the floating body 2 on the bottom. In this embodiment, four work areas A1 to A4 are provided in the sea area adjacent to the floating structure 10. In Fig. 2, the imaginary boundary line between the crane installation area Ca and the temporary storage area Ta on the floating structure 10 is indicated by a dashed line, and the imaginary outer frames of each of the work areas A1 to A4 are indicated by a dashed line.

[0022] The base frame 22 that constitutes the ring lift crane 20 has rails that are annular (approximately circular) in plan view. A plurality of traveling devices that constitute the crane body 21 are arranged on the rails of the base frame 22. The ring lift crane 20 is configured so that the direction of the boom that constitutes the crane body 21 can be changed to any direction by rotating the crane body 21 along the rails of the base frame 22. In Figure 2, the outer frame of the area in which crane work can be performed by the ring lift crane 20 is shown by a two-dot chain line.

[0023] The size and maximum lifting load of the ring lift crane 20 can be determined appropriately depending on the size and weight of the floating offshore wind power facility 1 (float 2 and wind turbine 3) to be constructed, but the ring lift crane 20 is configured to be able to perform crane work on the assembled components of the wind turbine 3 temporarily placed in the temporary storage area Ta and on each work area A. The maximum lifting load of the ring lift crane 20 is preferably, for example, 1,000 to 5,000 t, more preferably 1,500 to 3,500 t, and even more preferably 2,000 to 3,000 t. The maximum height of the ring lift crane 20 (the height from the bottom of the foundation frame 22 to the tip of the boom of the crane body 21) is preferably, for example, 100 to 250 m, more preferably 120 to 230 m, and even more preferably 150 to 200 m. The maximum workable radius of the ring lift crane 20 (the distance from the center of the foundation frame 22 to the tip of the boom of the crane body 21 in a plan view) is preferably, for example, 60 m or more and 200 m or less, more preferably 80 m or more and 180 m or less, and even more preferably 100 m or more and 160 m or less.

[0024] As illustrated in Figure 2, in this embodiment, a tapered floating structure 10 is constructed in the sea area, with a width at its front end 10a (upper side of the paper in Figure 2) narrower than at its rear end 10b (lower side of the paper in Figure 2) in a plan view, and a crane installation area Ca is provided at the front end 10a of the floating structure 10, and a temporary storage area Ta is provided at the rear end 10b. More specifically, a trapezoidal floating structure 10 is constructed in the sea area in a plan view, with the shorter sides of the upper and lower bases of the trapezoid in a plan view being the front end 10a side of the floating structure 10, and the longer sides being the rear end 10b side of the floating structure 10. In other words, the relatively narrower area at the front end 10a side of the floating structure 10 is the crane installation area Ca, and the relatively wider area at the rear end 10b side of the floating structure 10 is the temporary storage area Ta.

[0025] The shape and size of the floating structure 10 in plan view can be determined appropriately depending on the size of the assembly 9 to be assembled and the size of the ring lift crane 20 to be used, but the length L1 in the fore-aft direction in plan view of the floating structure 10 should be, for example, 80 m to 200 m, more preferably 100 m to 180 m, and even more preferably 120 m to 160 m. The width (W1, W2) in the left-right direction of the floating structure 10 should be, for example, 30 m to 300 m, more preferably 40 m to 280 m, and even more preferably 50 m to 250 m. As illustrated in Figure 3, the height H from the sea surface WL to the top surface of the floating structure 10 should be, for example, 2 m to 7 m.

[0026] 2, when constructing a tapered floating structure 10 in which the width at the front end 10a where the crane installation area Ca is located is narrower than the width at the rear end 10b where the temporary storage area Ta is located, the width W1 at the front end 10a of the floating structure 10 may be, for example, 40 m to 80 m, more preferably 45 m to 75 m, and even more preferably 50 m to 70 m. The width W2 at the rear end 10b of the floating structure 10 may be, for example, 150 m to 300 m, more preferably 170 m to 280 m, and even more preferably 200 m to 250 m.

[0027] The crane installation area Ca of the floating structure 10 is large enough to accommodate the foundation frame 22 that constitutes the ring lift crane 20. Specifically, the area of ​​the crane installation area Ca is, for example, 3,000 m 2 More than 12,000m 2 The foundation structure 15, which supports the load of the ring lift crane 20 on which the foundation frame 22 is placed, is designed to be able to withstand the load when the assembly parts of the wind power generation device 3 are loaded and unloaded using the ring lift crane 20. The load capacity of the foundation structure 15 is, for example, 20 t / m 2 More than 50t / m 2 The following applies.

[0028] The temporary storage area Ta in the floating structure 10 is large enough to temporarily store multiple sets of assembly parts, i.e., the nacelle hub 5, the blades 6, and the tower 4 (divided members 4a) that make up the wind turbine generator 3. Specifically, the area of ​​the temporary storage area Ta is, for example, 5,000 m 2 More than 35,000m 2 The temporary storage area Ta is designed to be able to withstand the weight of multiple sets of assembly parts that will be temporarily stored. The load capacity of the temporary storage area Ta in the floating structure 10 is, for example, 5 t / m 2 More than 30t / m 2 The following applies.

[0029] The temporary placement area Ta may be set to have the same load capacity for the entire area, but it may also be set to have different load capacity for the area where the assembly parts of the wind turbine generator 3 are placed and the area where they are not placed. Also, it may be set to have different load capacity for each area where each assembly part of the wind turbine generator 3 is temporarily placed. Specifically, in the temporary placement area Ta, the load capacity of the area where the nacelle hub 5 is temporarily placed may be set to, for example, 5 t / m 2 More than 30t / m 2 Hereinafter, the load capacity of the area where the divided members 4a of the tower 4 are temporarily placed is, for example, 5 t / m 2 More than 30t / m 2 The load capacity of the area where the blade 6 is temporarily placed is, for example, 2 t / m 2 More than 15t / m 2 It is recommended to set it as follows.

[0030] The components used to construct the floating structure 10 are transported to the construction area of ​​the floating structure 10 using a carrier ship or the like, and the floating structure 10 is constructed in the sea area by known methods. As illustrated in FIG. 3 , when a pier is constructed as the floating structure 10, the pier is constructed using, for example, a plurality of support piles 11 driven into the seabed SB, a plurality of girders 12 spanning between the support piles 11, a plurality of deck materials 13 forming the top plate of the upper part of the pier, and a plurality of braces 14 reinforcing the connections between the support piles 11. For example, the support piles 11 are made of shaped steel such as H-shaped steel or steel pipe piles. For example, the girders 12 and the braces 14 are made of shaped steel such as H-shaped steel. For example, the deck material 13 is made of covering plate or the like.

[0031] As illustrated in FIG. 3 , in this embodiment, the foundation structure 15 of the floating structure 10, on which the foundation frame 22 of the ring lift crane 20 is installed, is composed of a reinforced concrete caisson 16. It is preferable to use a caisson 16 having a cylindrical reinforced concrete section. The caisson 16 should be sized so that the annular foundation frame 22 can be placed on the reinforced concrete section that is circular in plan view. A large number of rubble stones (paving stones) are laid on the seabed SB to form a flat foundation 18, and the caisson 16 is placed on the foundation 18. The foundation 18 can be installed arbitrarily; for example, the caisson 16 can be placed directly on the seabed SB. Taking into account subsidence and liquefaction of the seabed SB, ground improvement work can be carried out in advance below the foundation 18 as necessary to improve the bearing capacity of the seabed SB.

[0032] As shown in the example of Figure 4, when the foundation structure 15 is constructed from a caisson 16, a pier (part of the temporary storage area Ta or crane installation area Ca) that constitutes part of the offshore structure 10 adjacent to the area where the foundation structure 15 is to be constructed is first constructed in the sea area, and rubble is dumped onto the seabed SB adjacent to the pier that constitutes part of the offshore structure 10 being constructed further ahead to form a flat base 18. Then, the caisson 16 is floated off the seabed SB and transported using a tugboat or the like to the position where the foundation structure 15 will be constructed (on the base 18), and after it is set down on the seabed, the hollow portion inside the caisson 16 is filled with fill material 17, thereby installing the caisson 16 on the seabed SB (on the base 18). In this way, by first constructing a portion of the floating structure 10 adjacent to the area where the foundation structure 15 is to be constructed, winches and other equipment used to adjust the position of the caisson 16 can be placed on the previously constructed floating structure 10, and workers can also work on the floating structure 10, which is advantageous for improving the work efficiency of adjusting the position of the caisson 16.

[0033] As shown in FIG. 5, a pier is then constructed for the remaining area of ​​the floating structure 10 (part of the crane installation area Ca) outside the foundation structure 15 constructed using the caissons 16, and a foundation frame 22 constituting the ring lift crane 20 is installed on the foundation structure 15. At this time, the annular foundation frame 22 is placed on the annular reinforced concrete part of the caissons 16. As shown in FIG. 6, the crane body 21 constituting the ring lift crane 20 is then installed on the foundation frame 22. The crane body 21 may be transported pre-assembled by a transport ship 40, or the components of the crane body 21 may be transported by the transport ship 40 and the crane body 21 may be assembled on the floating structure 10.

[0034] When the foundation structure 15 is constructed using a caisson 16, for example, before constructing the pier that constitutes the offshore structure 10, rubble can first be dumped onto the seabed SB to form a flat base 18, and after installing the caisson 16 on the seabed SB (on the base 18), the pier that constitutes the part of the offshore structure 10 other than the foundation structure 15 can be constructed in the sea area.

[0035] As illustrated in FIG. 7 , the offshore structure 10 is preferably constructed in a calm sea area where the impact of waves is minimal. Preferably, the offshore structure 10 is constructed in a sea area behind a breakwater 50 installed in a bay or the like. The "sea area behind the breakwater 50" here refers to a sea area where the impact of waves is reduced by the breakwater 50. By utilizing idle waters other than the shipping route and avoiding anchorages as much as possible, port activities using existing quays are not affected and coexistence with previous users is possible. Alternatively, the offshore structure 10 may be constructed in the target sea area where the floating offshore wind power generation facility 1 will be installed, or in a sea area close to a quay 60 where assembly components for the wind turbine 3 will be loaded onto a carrier ship. In this embodiment, the offshore structure 10 is constructed in a sea area away from the quay 60. However, for example, the offshore structure 10 could also be constructed adjacent to the quay 60, so that it is continuous with the quay 60.

[0036] When the floating structure 10 is constructed in an area of ​​the sea away from the quay 60, as in this embodiment, the floating structure 10 is designed to allow a carrier ship that transports assembly parts for the wind turbine generator 3 to dock. As equipment used to moor the carrier ship to the floating structure 10, temporary mooring equipment and temporary protection equipment should be provided near the floating structure 10. Note that the mooring equipment and protection equipment are omitted from the drawings.

[0037] The floating structure 10 may be constructed in an ocean area with a water depth of 8 m to 20 m and may be configured to support the multiple assemblies that make up the wind turbine generator 3 and the ring lift crane 20, and the shape and structure of the floating structure 10 are not limited to the configuration exemplified in this embodiment. For example, the floating structure 10 may be constructed in a polygonal shape such as a square in plan view, or in other planar shapes such as a T-shape or an L-shape. There are no particular limitations on the method of constructing the floating structure 10 in an ocean area.

[0038] For example, when a floating structure is constructed in the sea area as the floating structure 10, mooring equipment that serves as the base of the floating structure is installed in the sea area using piles or the like. After that, a float (barge) that forms the upper part of the floating structure is fixed to the mooring equipment that is fixed to the seabed SB, thereby constructing the floating structure as the floating structure 10. For example, the foundation structure 15 of the floating structure 10 on which the foundation frame 22 of the ring lift crane 20 is installed can be constructed using a caisson 16 or the like, and other areas of the floating structure 10 can be constructed as floating structures.

[0039] As illustrated in FIG. 8 , after the floating structure 10 is constructed in a sea area, multiple sets of assembly parts (separate members 4a of the tower 4, the nacelle hub 5, and the blades 6) that make up the wind turbine generator 3 are temporarily placed in a temporary storage area Ta of the floating structure 10. In this embodiment, the temporary storage area Ta of the floating structure 10 is configured to be able to temporarily store four sets of assembly parts of the wind turbine generator 3. When the floating structure 10 is constructed in a sea area away from a quay 60, the assembly parts of the wind turbine generator 3 are transported over the sea by a carrier ship 40 (specifically, for example, a LOLO ship) equipped with a crane, and when the carrier ship 40 is docked at the floating structure 10, the assembly parts loaded on the carrier ship 40 are unloaded into the temporary storage area Ta of the floating structure 10 using the crane 41 and ring lift crane 20 mounted on the carrier ship 40. It is preferable to transport the assembly parts of the wind power generation device 3 by sea to the floating structure 10, but if the floating structure 10 is constructed in an ocean area close to or adjacent to the quay 60, the assembly parts of the wind power generation device 3 can be transported overland to the quay 60, and then the assembly parts can be moved from the quay 60 to a temporary storage area Ta on the floating structure 10 using a ring lift crane 20 installed on the floating structure 10 or a crane deployed on the quay 60, for temporary storage.

[0040] 8 illustrates an example in which a carrier ship 40 is docked in the sea area on both the left and right sides of the underwater structure 10, but the position and direction in which the carrier ship 40 is docked in relation to the underwater structure 10, and the number of carrier ships 40 that are docked in relation to the underwater structure 10, are not particularly limited. For example, the carrier ship 40 may be docked in the sea area on the rear end 10b side of the underwater structure 10.

[0041] In this embodiment, in addition to the assembly parts of the wind turbine generator 3, a mobile crane 30, a work platform 31 (SPMT: multi-axle platform) equipped with a raising device 32, and a tower lift hoist 33 are arranged on the floating structure 10. Also arranged on the floating structure 10 are a horizontal placement frame that supports the divided members 4a of the tower 4 in a laid-down position, and a vertical placement frame that holds the divided members 4a in an upright position. The vertical placement frame is configured to temporarily place a total of 12 divided members 4a that make up four sets of towers 4 in an upright position.

[0042] The transport vessel 40 carries the divided members 4a of the tower 4 in a laid-down state. When loading and unloading the divided members 4a of the tower 4 from the transport vessel 40 onto the floating structure 10, the divided members 4a are first lifted in a laid-down state by a crane 41 mounted on the transport vessel 40 and placed in a laid-down state on a horizontal placement platform arranged on the floating structure 10. A tower lift hoisting device 33 is then used as a hoisting device for the crane 41 mounted on the transport vessel 40 or a mobile crane 30 arranged on the floating structure, and the tower lift hoisting device 33 is connected to the upper end of the divided member 4a. A work platform 31 carrying an erection device 32 is then moved to the vicinity of the lower end of the laid-down divided member 4a, and the lower part of the divided member 4a is held by the holding portion of the erection device 32. The work platform 31 may be operated by a human operator or may be remotely controlled by a remote controller.

[0043] Next, the upper end of the divided member 4a is lifted by the crane 41 or the crane 30 via the tower lift hoisting device 33 toward above the erection device 32, and the lower end of the divided member 4a is rotated using the erection device 32 as a guide, thereby erecting the divided member 4a. Then, the crane 41 or the crane 30 moves the erected divided member 4a above the vertical installation stand, and inserts the divided member 4a in an erect state into an insertion hole provided in the vertical installation stand.

[0044] In this embodiment, four sets of mounts that support the nacelle hub 5 are arranged on the floating structure 10, and a nacelle hub 5 is placed on each of the mounts. In addition, mounts that are structured to be able to mount multiple blades 6 that are laid on their side and spaced apart from one another are provided on the floating structure 10, and multiple blades 6 are arranged vertically. In this embodiment, three sets of mounts that can each accommodate four blades 6 arranged vertically are arranged on the floating structure 10.

[0045] In this embodiment, the blades 6 temporarily placed on the floating structure 10 do not protrude from the floating structure 10, but it is also possible for some of the temporarily placed blades 6 to protrude from the floating structure 10. In other words, the floating structure 10 may be large enough that some of the blades 6 protrude. Because the nacelle hub 5 and the divided members 4a are relatively heavy, it is preferable to temporarily place them without stacking them one on top of the other. Because the blades 6 are large in size and relatively light, it is preferable to temporarily place multiple blades 6 lined up one on top of the other.

[0046] In this embodiment, the assembly parts of the wind turbine generator 3 are temporarily stored together by type, but the arrangement of each assembly part temporarily stored on the floating structure 10 is not particularly limited. For example, each assembly part constituting each wind turbine generator 3 can be temporarily stored together. Generally, the nacelle hub 5 is the heaviest of the assembly parts of the wind turbine generator 3, so it is recommended that the nacelle hub 5 be temporarily stored in a position closest to the ring lift crane 20, where it can be easily and stably handled by the ring lift crane 20. The segmented member 4a, which is the next heaviest, should also be temporarily stored in a position relatively close to the ring lift crane 20. The blades 6 are relatively light, so they should be temporarily stored in a position relatively far from the ring lift crane 20. Note that there are also cases where the tower 4, in which the segmented members 4a are pre-assembled together, is suspended.

[0047] After the assembly parts of the wind turbine generator 3 have been temporarily placed on the temporary storage area Ta of the floating structure 10, the carrier ship 40 is moved away from the floating structure 10. Thereafter, as illustrated in Fig. 9, the floating body 2 is transported by sea and the floating body 2 is successively brought to a state of being settled on the seabed SB of each of the work areas A (A1 to A4) provided in the sea area adjacent to the floating structure 10. For example, when the carrier ship 40 is brought to a berth in a position that does not interfere with the work area A, the work of temporarily placing the assembly parts of the wind turbine generator 3 on the temporary storage area Ta and the work of bringing the floating body 2 to a state of being settled on the seabed SB of the work area A can be carried out in parallel.

[0048] As illustrated in Figure 9, in this embodiment, two work areas A (A1, A4) are provided in the sea area ahead of the floating structure 10, and one work area A (A2, A3) is provided in each of the sea areas on either side of the floating structure 10 (crane installation area Ca). More specifically, a first work area A1 is provided in the sea area on the right side in front of the floating structure 10, and a fourth work area A4 is provided in the sea area on the left side in front of the floating structure 10. A second work area A2 is provided in the sea area on the left side of the floating structure 10 (crane installation area Ca), and a third work area A3 is provided in the sea area on the right side.

[0049] It is preferable to install buoys or the like in the sea area to visualize the extent of each work area A (A1 to A4). Note that it is sufficient for the workers and managers involved in the construction to understand the extent and boundaries of each work area A, and it is not essential to visualize the extent of each work area A in the sea area.

[0050] During marine transportation, the float 2 is floated on the sea with a relatively small amount of ballast water stored therein, and is towed to the vicinity of the floating structure 10 using a tugboat or the like. After the float 2 is moved to the work area A, ballast water is poured into the float 2, causing it to gradually sink and its bottom to land on the seabed SB. If the ground of the seabed SB where the float 2 will land is not flat, it is advisable to level or cure the ground of the seabed SB before placing the float 2 near the floating structure 10. Preferably, sandbags, filter units, or the like are placed on the seabed SB where the float 2 will land to form a flat mound on which the float 2 will land, and the float 2 is then landed on top of that mound. In each work area A, the floating body 2 is preferably arranged so that the column 2a on which the wind turbine generator 3 is erected faces the floating structure 10 (crane installation area Ca).

[0051] In this construction method, the floating structure 10 is constructed in a sea area with a water depth DW of 8 m or more and 20 m or less, so that the semi-submersible floating body 2, the TLP floating body 2, and the barge floating body 2 can be towed to the work area A near the floating structure 10. Furthermore, because the water depth DW is 8 m or more and 20 m or less, each type of floating body 2 can be easily landed on the seabed SB, and assembly components for the wind turbine generator 3 can be installed on the floating body 2 once it has landed on the seabed SB. In other words, in sea areas with a water depth DW of less than 8 m, the water depth DW is too shallow, making it difficult to tow the floating body 2 near the floating structure 10. In sea areas with a water depth DW of more than 20 m, the water depth DW is too deep, making it difficult to install assembly components for the wind turbine generator 3 on the floating body 2 once it has landed on the seabed SB.

[0052] After the float 2 is landed on the seabed SB of the work area A, as illustrated in Figures 10 and 11, a ring lift crane 20 installed on the offshore structure 10 is used to install a set of assembly parts on the float 2 that has been landed on the seabed SB of the work area A, and assembly work is performed to assemble an assembly 9 on which a wind power generation device 3 is constructed on the float 2.

[0053] In this embodiment, first, a set of assembly parts is sequentially installed on the floating body 2 that has been seated on the seabed SB in the first working area A1, thereby assembling the assembly 9. Specifically, first, using a ring lift crane 20, the divided members 4a that form the base of the tower 4 that has been temporarily placed on the floating structure 10 are installed on one of the columns 2a of the floating body 2. It is also possible to install the tower 4, which has been pre-assembled with the divided members 4a, on one of the columns 2a of the floating body 2.

[0054] Since the divided member 4a is temporarily placed upright on the vertical installation frame, the hoisting device of the ring lift crane 20 is connected to the upper end of the upright divided member 4a, and the upright divided member 4a is lifted above the vertical installation frame. Then, the ring lift crane 20 is used to move the upright divided member 4a above one of the columns 2a of the floating body 2, so that the lower end of the divided member 4a is placed on the column 2a. The lower end of the divided member 4a is then fixed to the upper end of the one of the columns 2a of the floating body 2 by bolting, welding, or the like. After that, the hoisting device of the ring lift crane 20 is released from the upper end of the divided member 4a.

[0055] Next, similarly, using the ring lift crane 20, the divided member 4a constituting the middle part of the tower 4 temporarily placed on the floating structure 10 is connected onto the divided member 4a constituting the base part of the tower 4. Thereafter, similarly, using the ring lift crane 20, the divided member 4a constituting the upper end part of the tower 4 temporarily placed on the floating structure 10 is connected onto the divided member 4a constituting the middle part of the tower 4, thereby erecting the tower 4 on the column 2a.

[0056] Next, the ring lift crane 20 is used to install the nacelle hub 5, which has been temporarily placed on the floating structure 10, on top of the tower 4. After that, the ring lift crane 20 is used to attach each of the three blades 6, which have been temporarily placed on the floating structure 10, to the nacelle hub 5. By performing the above operations, the assembly work of the assembly 9 is completed in the first work area A1, as shown in FIG. 11.

[0057] 12, additional work including adjustment work is performed on the assembly 9 in the work area A (first work area A1) where the assembly work has been completed, and in a work area A (second work area A2) different from the work area A (first work area A1) where the assembly work has been completed, similar assembly work is performed using the ring lift crane 20 on the float 2 that has been anchored to the seabed SB in that work area A (second work area A2). While the ring lift crane 20 is being used to perform assembly work on the float 2 in the different work area A (second work area A2), additional work can be performed on the assembly 9 in the work area A (first work area A1) where the assembly work has been completed in advance.

[0058] The additional work is preparatory work performed on the assembly 9 before it is transported to the sea area where it will be installed, and specifically includes pre-commissioning work. Pre-commissioning work is work such as setting up, testing, and adjusting the electrical equipment of the assembly 9. In this embodiment, the additional work is performed on the assembly 9 after assembly work has been completed in work area A, where the assembly work has already been completed. The additional work on the assembly 9 after assembly work may be performed, for example, by moving the assembly 9 outside work area A and performing it in waters outside work area A.

[0059] In the work area A (first work area A1) where the pre-assembly work has been completed, pre-commissioning work is then performed as additional work on the assembly 9. Then, after it has been confirmed in the pre-commissioning work that there are no abnormalities in the wind turbine generator 3, the assembly 9 is gradually raised from the seabed SB by reducing the amount of ballast water stored in the floating body 2. Then, while the assembly 9 is floating on the sea, it is transported by sea to the target installation area using a tugboat or the like. As illustrated in FIG. 13 , in this embodiment, before the assembly work is performed in the third work area A3, additional work (pre-commissioning work) is completed in the first work area A1, and the assembly 9 after the additional work is completed is moved out of the first work area A1.

[0060] As shown in Figure 1, the assembly 9 after the additional work is completed is transported by sea to the target sea area for installation, where the assembly 9 (float 2) is moored to the seabed SB using mooring lines 7, anchors 8, etc. After that, a submarine cable is connected to the wind turbine 3, and a final operational check (so-called final commissioning) of the floating offshore wind power facility 1 is carried out. With this, the construction of the floating offshore wind power facility 1 is completed.

[0061] After that, following a similar work procedure, as illustrated in Figure 13, in the second work area A2 where assembly work has been completed, additional work including adjustment work is performed on the assembly 9, and similar assembly work is performed using the ring lift crane 20 on the float 2 which has been anchored on the seabed SB in the third work area A3.

[0062] 14, the assembly 9, for which the additional work has been completed in the second work area A2, is raised from the seabed SB, transported by sea to the target installation area, and moored in the target installation area. In this embodiment, before the assembly work is performed in the fourth work area A4, the additional work (pre-commissioning work) is completed in the second work area A2, and the assembly 9 for which the additional work has been completed is moved outside the second work area A2.

[0063] After that, following a similar work procedure, additional work including adjustment work is carried out on the assembly body 9 in the third work area A3 where assembly work has been completed, and similar assembly work is carried out on the float body 2 which has been anchored on the seabed SB in the fourth work area A4 using the ring lift crane 20.

[0064] 14, when continuing the assembly work of the assembly body 9, a new floater 2 transported by sea to the first working area A1 is landed on the seabed SB. It is preferable to transport the floater 2 by sea to the first working area A1 and have the floater 2 land on the seabed in the first working area A1 before the assembly work is completed in the fourth working area A4. In this case, it is also preferable to transport the assembly parts of the wind turbine generator 3 to the floating structure 10 by a carrier ship 40 or the like and replenish the assembly parts of the wind turbine generator 3 in the temporary storage area Ta before the assembly work is completed in the fourth working area A4.

[0065] Thereafter, using the same work procedure, additional work including adjustment work is performed on the assembly 9 in the fourth work area A4 where the assembly work has been completed, and the ring lift crane 20 is used to similarly perform assembly work on the floater 2 that has been anchored to the seabed SB in the first work area A1. Then, the assembly 9 for which the additional work has been completed in the fourth work area A4 is raised from the seabed SB and transported by sea to the target installation area, where the assembly 9 is moored. Then, by the time the assembly work in the first work area A1 is completed, it is advisable to transport the floater 2 by sea to the second work area A2 and leave the floater 2 anchored in the second work area A2.

[0066] In this way, by simultaneously carrying out the work of temporarily placing the assembly parts of the wind power generation device 3 in the temporary storage area Ta of the floating structure 10, the assembly work, the addition work, and the work of transporting the assembly 9 after the addition work has been completed by sea to the sea area where it will be installed and mooring it, it is possible to construct a large number of floating offshore wind power generation facilities 1 in parallel.

[0067] After the use of the offshore structure 10 as a manufacturing base has ended, the offshore structure 10 can be removed from the sea area, or it can remain in the sea area as a base for performing maintenance on the floating offshore wind power facility 1 (assembly 9). When the offshore structure 10 is left as a maintenance base, the assembly 9 to be maintained is transported to the offshore structure 10 and landed on the seabed SB in work area A. Then, maintenance of the assembly 9 is performed using a ring lift crane 20. When the offshore structure 10 is removed from the sea area, the ring lift crane 20 is removed, and then the pier that constitutes the offshore structure 10 is dismantled and removed. Then, holes in the seabed SB where the support piles 11 that constituted the pier were inserted are backfilled, restoring the seabed SB to its state before the construction of the offshore structure 10. Finally, the caissons 16 that constitute the foundation structure 15 are removed. In this way, the floating structure 10, which can be set up and removed in a temporary form, can be moved to a different location and reinstalled and removed many times in a relatively short period of time.

[0068] As described above, this construction method makes it possible to construct multiple floating offshore wind power facilities 1 in parallel, each with a floater 2 having a draft of 20 m or less when moored in the target sea area, and can be adopted for constructing other types of floating offshore wind power facilities 1 except for the spar type. With this construction method, a temporary floating structure 10 is constructed in a relatively shallow sea area with a water depth DW of 8 m or more and 20 m or less, so the cost, labor, and time required to construct the floating structure 10 are relatively low, and the floating structure 2 can be easily landed in a work area A set up in the sea area adjacent to the floating structure 10.

[0069] When constructing a pier as the offshore structure 10, the length of the support piles 11 driven into the seabed SB is relatively short because the sea area is relatively shallow, and the cost, labor, and time required to construct the pier are relatively low. When constructing a floating structure as the offshore structure 10, the work of fixing the mooring equipment that constitutes the floating structure to the seabed SB can also be done relatively easily because the sea area is relatively shallow, and the cost, labor, and time required to construct the floating structure are relatively low.

[0070] Furthermore, with this construction method, the ring lift crane 20 is installed in the crane installation area Ca provided on the offshore structure 10, and multiple sets of assembly parts for the wind turbine 3 are temporarily stored in the temporary storage area Ta. This eliminates the need to prepare a vast installation base for the floating offshore wind power facility 1, which would include an area on the quay 60 for installing a large crane and an area for temporarily storing all of the assembly parts for the wind turbine 3. In other words, if an installation base for the floating offshore wind power facility 1 were to be prepared on the quay 60, large-scale construction work such as ground improvement work to improve the bearing capacity of the quay 60 would be required, which would require relatively large costs, labor, and time. However, with this construction method, such large-scale construction work on the quay 60 is not necessary, and there is no need to secure large spaces in front of and behind the quay 60. This construction method also has the advantage of making it easier to secure an installation site for the offshore structure 10 within the port area, since the offshore structure 10 is constructed in a sea area with a relatively shallow water depth DW.

[0071] Furthermore, in this construction method, a ring lift crane 20 installed on the floating structure 10, which is not affected by waves, is used to install the assembly parts of the wind power generation device 3, which are temporarily placed on the floating structure 10, onto the floating body 2 that is anchored to the seabed SB in the work area A, allowing the assembly work of the assembly 9 to be carried out efficiently in a very stable state.

[0072] In addition, multiple work areas A are set up in the sea area adjacent to the floating structure 10, and in the work area A where assembly work has been completed, additional work including adjustment work is carried out on the assembly body 9, and in a work area A other than the work area A where assembly work has been completed, assembly work is carried out using a ring lift crane 20 on the floating body 2 that has been anchored to the seabed SB in that work area A, so that assembly work and additional work can be carried out in parallel in different locations.

[0073] Generally, additional work takes several weeks. For example, if additional work on an assembly 9 that has already been assembled is to be carried out in a location other than work area A, a location for the assembly 9 must be secured, and the work of floating the assembly 9 and moving it to another location also requires time and effort. In contrast, with this construction method, additional work on the assembly 9 that has already been assembled can be continued in work area A near the floating structure 10, while assembly work on another assembly 9 can be carried out in parallel in another work area A.

[0074] Because the sea area where the floating offshore wind turbines 1 are to be installed is a windy area, the period in which the working environment is calm and suitable for construction in the installation area is limited to a relatively short period of several months. Therefore, if the construction of the floating offshore wind turbines 1 is not completed during a period when the working environment is relatively calm, construction will be halted until a suitable period for construction the following year. Therefore, in order to construct a large number of floating offshore wind turbines 1 within this limited short period, it is important to efficiently perform the assembly work and addition work of the assemblies 9 in a short period of time. In this regard, this construction method can significantly shorten the cycle time for sequentially constructing a large number of floating offshore wind turbines 1, making it extremely advantageous for efficiently constructing a large number of floating offshore wind turbines 1 in a short period of time.

[0075] After the additional work is completed, the assembly 9 is transported by sea to the target sea area for installation, and construction of the floating offshore wind power facility 1 is completed simply by mooring the assembly 9 in the target sea area. This construction method does not require complicated and advanced work to be performed in the target sea area for installation. Therefore, this construction method makes it possible to efficiently construct a floating offshore wind power facility 1 with a float 2 having a draft of 20 m or less when moored in the target sea area, without having to prepare an installation base for the floating offshore wind power facility 1 on a quay 60.

[0076] Furthermore, this construction method is extremely useful for those skilled in the art because, after the use of the offshore structure 10 as a manufacturing base has ended, the offshore structure 10 can be left in the sea area as a base for performing maintenance on the floating offshore wind power facility 1 (assembly 9). When removing the offshore structure 10, the sea area is relatively shallow, so the offshore structure 10 can be removed relatively easily. The work of restoring the state of the seabed SB to the state before the construction of the offshore structure 10 can also be performed relatively easily.

[0077] Constructing the floating structure 10 in an ocean area inside the breakwater 50 allows the floating structure 10 to be constructed in an ocean area less affected by waves, which is advantageous for reducing the labor required to construct the floating structure 10. Furthermore, this reduces the risk of water pressure due to waves acting on the floating body 2 while it is attached to the seabed SB or the tower 4 installed on the floating body 2, which is advantageous for reducing the load on the floating body 2 and the tower 4. Note that with this construction method, the floating structure 10 can also be constructed in calm ocean areas less affected by waves, for example, in an ocean area outside the breakwater 50 or in an ocean area where no breakwater 50 is installed.

[0078] The shape of the floating structure 10 in plan view and the number of work areas A to be provided for the floating structure 10 can be determined appropriately depending on the number of floating offshore wind power facilities 1 to be constructed and the construction period, but providing four or more work areas A in the sea area adjacent to the floating structure 10 is advantageous for efficiently constructing a large number of floating offshore wind power facilities 1. If a new floater 2 is set down on the seabed SB of the work area A where the assembly 9 has been transported by sea to the target sea area for installation, multiple assemblies 9 can be assembled in one work area A, allowing a large number of floating offshore wind power facilities 1 to be constructed very efficiently. In particular, replenishing assembly parts in the temporary storage area Ta before starting assembly work on the newly settled floater 2 is advantageous for efficiently constructing a large number of floating offshore wind power facilities 1.

[0079] As in this embodiment, when the floating structure 10 is configured to have a tapered shape in which the width W1 at the front end 10a is narrower than the width W2 at the rear end 10b in a plan view, and a crane installation area Ca is provided at the front end 10a of the floating structure 10 and a temporary storage area Ta is provided at the rear end 10b of the floating structure 10, it is possible to provide a large temporary storage area Ta at the rear end 10b of the floating structure 10, while facilitating the provision of multiple work areas A near the crane installation area Ca. This is advantageous for efficiently constructing multiple floating offshore wind power generation facilities 1. In addition, the distance between each work area A and the ring lift crane 20 can be shortened, which is also advantageous for stable assembly work using the ring lift crane 20.

[0080] In particular, as in this embodiment, by constructing an underwater structure 10 that is trapezoidal in plan view in the sea area, with the shorter sides of the upper and lower bases of the trapezoid in plan view being located at the front end 10a of the underwater structure 10 and the longer sides being located at the rear end 10b of the underwater structure 10, the underwater structure 10 can have a simple shape, yet a large temporary storage area Ta can be secured at the rear end 10b of the underwater structure 10, and multiple work areas A can be set up near the crane installation area Ca.

[0081] Furthermore, by configuring two work areas A in the sea area in front of the crane installation area Ca and one work area A in each of the sea areas on either side of the crane installation area Ca, four work areas A can be set up near the crane installation area Ca, and the distance between the ring lift crane 20 and each work area A and the distance between the ring lift crane 20 and the temporary storage area Ta can be set within a range that allows the ring lift crane 20 to perform work stably.

[0082] Furthermore, of the first to fourth work areas A1 to A4 where assembly work is carried out sequentially, the work area A on one side, left or right, located in the sea area in front of the crane installation area Ca is designated as the first work area A1, and the work area A on the other side, left or right, of the crane installation area Ca is designated as the second work area A2. Then, the work area A on the other side, left or right, located in the sea area in front of the crane installation area Ca is designated as the third work area A3, and the work area A on the other side, left or right, of the crane installation area Ca is designated as the fourth work area A4. By carrying out assembly work sequentially in the first to fourth work areas A1 to A4, it is possible to efficiently construct a large number of floating offshore wind turbines 1 while preventing the blades 6 of the assemblies 9 from interfering with each other when assembly work is carried out in each work area A. In other words, when assembly work and additional work are carried out in parallel in adjacent work areas A, there is a possibility that the blades 6 of the assemblies 9 installed in each work area A may interfere with each other. However, by using the configuration described above, such interference between the blades 6 can be reliably avoided, making it possible to carry out assembly work and additional work more safely.

[0083] In this embodiment, the case where one side is the right side and the other side is the left side has been exemplified, but the same effect can be achieved, for example, if one side is the left side and the other side is the right side. Furthermore, for example, the work area A provided in the sea area on one side of the crane installation area Ca is designated as the first work area A1, and the work area A provided in the sea area in front of the crane installation area Ca on the other side is designated as the second work area A2. The same effect can also be achieved if the work area A provided in the sea area on the other side of the crane installation area Ca is designated as the third work area A3, and the work area A provided in the sea area in front of the crane installation area Ca on the other side is designated as the fourth work area A4.

[0084] The number of work areas A provided for the floating structure 10 is not particularly limited as long as it is two or more. However, the number of work areas A provided for the floating structure 10 is preferably three, and more preferably four. Providing three or more work areas A for the floating structure 10 allows the assembly work, the addition work, and the work of landing a new floater 2 on the seabed SB to be performed in parallel in separate locations, which is advantageous for efficiently constructing a large number of floating offshore wind power facilities 1. Furthermore, providing five or more work areas A for the floating structure 10 makes it difficult to shorten the distance between each work area A and the temporary storage area Ta relative to the ring lift crane 20. However, by limiting the number of work areas A to four or less, the distance between each work area A and the temporary storage area Ta relative to the ring lift crane 20 can be relatively short. This is therefore advantageous for stable assembly work using the ring lift crane 20.

[0085] In this embodiment, when assembling the assembly 9 in each work area A, the orientation of the wind turbine generator 3 relative to the float 2 is exemplified as being the correct orientation for mooring in the sea area where the assembly is to be installed. However, because the blades 6 of the wind turbine generator 3 are huge, if the wind turbine generator 3 is assembled in the correct orientation, the blades 6 may interfere with work in other work areas A. In such a case, the orientation of the tower 4 relative to the float 2 or the orientation of the nacelle hub 5 relative to the tower 4 may be shifted from the correct orientation so that the blades 6 of the wind turbine generator 3 do not interfere with work in other work areas A. In that case, the orientation of the tower 4 relative to the float 2 or the orientation of the nacelle hub 5 relative to the tower 4 may be corrected to the correct orientation after the assembly 9 is moved outside the work area A or after the assembly 9 is moved to the sea area where the assembly is to be installed.

[0086] As in this embodiment, if a vertical placement stand for holding the divided members 4a of the tower 4 in an upright position is provided in the temporary placement area Ta and the divided members 4a are temporarily placed in an upright position, the work of installing the divided members 4a on the floating body 2 using a ring lift crane 20 can be carried out very stably and efficiently. Furthermore, if a work platform 31 equipped with an erection device 32 and a tower lift hoisting device 33 are used, the work of changing the divided members 4a from a laid-down position to an upright position can be carried out very stably and efficiently.

[0087] In this construction method, for example, the erection device 32 may be configured to be moved by a crane 30 or the like, without being mounted on the work platform 31. Furthermore, the erection device 32 and the tower lift hoisting device 33 may be used as desired, and the work of temporarily placing the divided member 4a may also be performed by a different method that does not use the erection device 32 or the tower lift hoisting device 33.

[0088] As in this embodiment, in the work of constructing the floating structure 10, a caisson 16 that is circular in plan view is placed in the sea area where the crane installation area Ca is to be constructed to construct the ring-shaped foundation structure 15, and the foundation frame 22 that constitutes the ring lift crane 20 is installed on the foundation structure 15, thereby enabling the foundation structure 15 and the foundation frame 22 to be constructed easily and efficiently. In particular, if the ring-shaped foundation frame 22 is placed on the ring-shaped reinforced concrete portion of the caisson 16, the foundation frame 22 is stably supported by the reinforced concrete portion of the caisson 16, allowing the construction of a very stable foundation structure 15 and foundation frame 22.

[0089] The foundation structure 15 on which the foundation frame 22 of the ring lift crane 20 is installed may also be configured as in another embodiment illustrated in FIGS. 15 and 16, for example.

[0090] As illustrated in Figure 15, in this embodiment, the foundation 15 of the floating structure 10 on which the foundation frame 22 of the ring lift crane 20 is installed is composed of a plurality of steel pipe sheet piles 19 arranged in a ring shape in a plan view. In this embodiment, a pier constituting the portion of the floating structure 10 other than the foundation 15 is constructed with the area in which the plurality of steel pipe sheet piles 19 are arranged in a ring shape in a plan view left hollow, and then the plurality of steel pipe sheet piles 19 are arranged in a ring shape in a plan view in the hollow part of the pier to construct the ring-shaped foundation 15. Then, as illustrated in Figure 16, the foundation frame 22 constituting the ring lift crane 20 is installed on the foundation 15.

[0091] Each steel pipe sheet pile 19 is driven into the seabed SB using a hydraulic hammer, a vibro hammer, or the like. By connecting the joints of adjacent steel pipe sheet piles 19, a ring-shaped foundation structure 15 can be constructed in which multiple steel pipe sheet piles 19 are integrated. In this embodiment, the inner area of ​​the ring-shaped foundation structure 15 is filled with filler material 17, but it is also possible to configure the structure without filling with filler material 17. In this embodiment, the upper part of each steel pipe sheet pile 19 is closed with a top cover, but it is also possible to fill with filler material, for example, in the upper part of the inner space inside the steel pipe sheet pile 19. When the foundation structure 15 is configured with multiple steel pipe sheet piles 19, ground improvement of the seabed SB is not required.

[0092] As in this embodiment, by constructing a ring-shaped foundation structure 15 by arranging a plurality of steel pipe sheet piles 19 in a ring shape in a plan view and installing a foundation frame 22 constituting a ring lift crane 20 on the foundation structure 15, the foundation structure 15 and the foundation frame 22 can be constructed easily and efficiently. In particular, by placing the ring-shaped foundation frame 22 on the steel pipe sheet piles 19 arranged in a ring shape, the foundation frame 22 is stably supported by the plurality of steel pipe sheet piles 19, and therefore a very stable foundation structure 15 and foundation frame 22 can be constructed.

[0093] The floating structure 10 can also be configured, for example, as shown in Fig. 17. In this embodiment, a crane installation area Ca having a relatively narrow width W1 and a rectangular shape in plan view is provided at the forward end 10a of the floating structure 10, and a temporary storage area Ta having a relatively wide width W2 and a rectangular shape in plan view is provided at the aft end 10b of the floating structure 10. Two work areas A (A1, A4) are provided in the sea area forward of the crane installation area Ca, and one work area A (A2, A3) is provided in each of the sea areas on either side of the crane installation area Ca.

[0094] In this embodiment, the floating structure 10 also has a tapered shape in a plan view in the sea area, with a width W1 at the front end 10a narrower than a width W2 at the rear end 10b. A crane installation area Ca is provided at the front end 10a of the floating structure 10, and a temporary storage area Ta is provided at the rear end 10b of the floating structure 10. Two work areas A are provided in the sea area forward of the crane installation area Ca, with one work area A provided in each sea area on either side of the crane installation area Ca. Therefore, the floating structure 10 of this embodiment can achieve substantially the same effects as the floating structure 10 of the above-mentioned embodiment, which has a trapezoidal shape in a plan view. In the above-mentioned embodiment and this embodiment, preferred shapes in a plan view of the floating structure 10 are exemplified, but the shape in a plan view of the floating structure 10 is not limited to the exemplified embodiment and can be other shapes, such as a triangular or rectangular shape in a plan view.

[0095] When the floating structure 10 is constructed as a floating structure, for example, the assembly parts of the wind turbine generator 3 are placed in advance on a float that forms the top plate of the floating structure, and the float with the assembly parts placed on it is towed to the construction area where the floating structure 10 is to be constructed. The float with the assembly parts of the wind turbine generator 3 temporarily placed on it can then be fixed on mooring equipment that is fixed to the seabed SB in the construction area. This eliminates the need to transport the assembly parts of the wind turbine generator 3 by a carrier ship 40 or the like after the floating structure 10 is constructed, allowing the floating offshore wind power facility 1 to be constructed very efficiently. Note that when the floating structure 10 is constructed as a floating structure, the assembly parts of the wind turbine generator 3 can be transported by a carrier ship 40 or the like after the floating structure is constructed in the sea area, and the assembly parts can be temporarily placed on the floating structure, just as when the floating structure 10 is constructed as a pier.

[0096] The above example illustrates the construction of a semi-submersible floating offshore wind power facility 1, but the same construction method and effects can be achieved when constructing a TLP-type floating offshore wind power facility 1 or a barge-type floating offshore wind power facility 1. This construction method can also be used when constructing multiple types of floating offshore wind power facilities 1 in parallel. [Explanation of symbols]

[0097] 1. Floating offshore wind power generation facilities 2 Floating body 2a Column 2b Concatenation 3. Wind power generation equipment 4. Tower 4a Divided member 5 Nacelle hub 6 blades 7 Mooring line 8. Anchor 9 Assembly 10 Floating structures 10a front end 10b rear end 11 Support pile 12 Girder material 13 Deck materials 14 braces 15 Basic structure 16 Caisson 17 Filling material 18 Foundation 19 Steel pipe sheet pile 20 Ring Lift Crane 21 Crane body 22 Foundation frame 30 Crane (placed on floating structures) 31 Work trolley 32 Standing device 33 Tower lift sling 40 Carrier 41 Crane (mounted on a carrier) 50 Breakwater 60 Quay SB Undersea A, A1~A4 (1st~4th) working areas Ca Crane installation area Ta provisional region WL sea level position

Claims

1. A construction method for a floating offshore wind power generation facility comprising a float moored in a target sea area for installation and a wind power generation device erected on the float, wherein the draft from the water surface to the bottom end of the float is 20 m or less when the float is moored in the target sea area, Construct a temporary floating structure in the sea area with a water depth of 8m to 20m. a crane installation area in which a ring-shaped foundation frame that constitutes a ring lift crane in a plan view and a crane body that is placed on the foundation frame are installed on the floating structure; and a temporary storage area in which assembly parts that constitute the wind power generation device are temporarily stored, and a plurality of work areas in which the floating body is to be landed on the bottom are provided in the sea area adjacent to the floating structure; a plurality of sets of the assembly parts are temporarily placed in the temporary placement area; using the ring lift crane to install the set of assembly parts that are temporarily placed in the temporary placement area onto the floating body that has been landed on the seabed in the work area, and perform assembly work to assemble an assembly in which the wind power generation device is constructed on the floating body; In the work area where the assembly work has been completed, additional work including adjustment work is performed on the assembly, and in a work area different from the work area where the assembly work has been completed, the assembly work is performed using the ring lift crane on the floating body that has been landed on the seabed in that work area, A construction method for a floating offshore wind power facility, characterized in that the assemblies after the additional work are completed are sequentially transported by sea to the target sea area for installation, and the assemblies are moored in the target sea area for installation.

2. The construction method for a floating offshore wind power facility according to claim 1, wherein a pier or a floating structure is constructed as the above-water structure.

3. 3. A construction method for a floating offshore wind power facility according to claim 1 or 2, wherein the floating structure has a tapered shape in which the width at its front end is narrower than the width at its rear end in a plan view, the crane installation area is provided at the front end side of the floating structure, and the temporary storage area is provided at the rear end side of the floating structure.

4. 4. The construction method for a floating offshore wind power facility according to claim 3, wherein two work areas are provided in the sea area in front of the crane installation area, and one work area is provided in each of the sea areas on either side of the crane installation area.

5. 3. A construction method for a floating offshore wind power facility according to claim 1 or 2, wherein the work of constructing the floating structure comprises constructing a ring-shaped foundation structure by placing a caisson that is annular in plan view in the sea area where the crane installation area is to be constructed, and then installing the foundation frame on top of the foundation structure.

6. 3. The construction method for a floating offshore wind power facility according to claim 1 or 2, wherein the work of constructing the floating structure comprises constructing a circular foundation structure by arranging a plurality of steel pipe sheet piles in a circular shape in plan view in the sea area where the crane installation area is to be constructed, and then installing the foundation frame on the foundation structure.

7. 3. The construction method for a floating offshore wind power facility according to claim 1 or 2, wherein, while the assembly work is being performed on the float in the other work area by the ring lift crane, the additional work on the assembly is performed in parallel in the work area where the assembly work has been completed in advance.

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