Method for constructing SPAR-type offshore wind power generation facility

Abstract

[Problem] To provide a method for constructing a spar-type offshore wind power generation facility while simply compensating shortage of crane lift height of a SEP barge equipped with a crane. [Solution] This method comprises: a first step for assembling an upper structure body 12 on a semi-submersible spud barge 46 by using a SEP barge 14 equipped with a crane, while using the semi-submersible spud barge 46 as an assembling frame 13 in a sea area of relatively calm waves, with the semi-submersible spud barge 46 being submerged or set on the seabed; a second step for lifting the assembled upper structure body 12 all at once by a large crane ship 2 and carrying the assembled upper structure body 12 to a construction place of an offshore wind power generation facility 1, after floating the assembling frame 13; a third step for holding a floating body 4 on the ocean in a standing state; and a fourth step for completing the offshore wind power generation facility 1 by connecting the upper structure body 12 to an upper part of the floating body 4 while the upper structure body 12 is lifted by the large crane ship 2.

Description

Title of Invention:  METHOD FOR CONSTRUCTING SPAR-TYPE OFFSHORE WIND POWER GENERATION FACILITY Technical Field

[0001] The present invention relates to a method for constructing a spar-type offshore wind power generation facility for stably and collectively constructing an upper structure body (a tower, a nacelle, and blades) of the offshore wind power generation facility. Background Art

[0002] Conventionally, power generation methods, such as hydroelectric power generation, thermal power generation, and nuclear power generation, have mainly been adopted, and, in recent years, wind power generation that generates electricity using natural wind has attracted attention from the viewpoints of environment and effective use of natural energy. Such wind power generation facilities include on-land installation type and water installation (mainly sea installation) type facilities, and, in the case of Japan, having mountainous terrain from coastal areas to inland areas, there are few plains in coastal areas where stable winds can be expected.  On the other hand, Japan is surrounded by sea on all four sides and thus is advantageous in that it is possible to easily obtain winds suitable for power generation at sea and, at the same time, there is little or no restriction on installation thereof. Therefore, in recent years, various types of offshore wind power generation facilities and floating body structures have been frequently proposed.

[0003] The floating structures are broadly classified into a barge-type floating body in which a floating body is floated on the water surface, a semi-submersible type floating body in which a floating body is floated in a semi-submerged state with the lower portion submerged below the water surface, and a spar-type floating body in which a floating body is floated in an upright position like a fishing float.

[0004] With regard to the spar-type floating body, the present applicant has proposed, in the following Patent Literature 1, an offshore wind power generation facility (hereinafter referred to as a spar-type offshore wind power generation facility) including a floating body, a mooring cable, a tower, and a nacelle and a plurality of windmill blades provided at the top of the tower, wherein the floating body has a spartype floating body structure including a lower concrete floating body structure (hereinafter referred to as a concrete floating body) including a plurality of concrete precast cylindrical bodies stacked on top of each other in a height direction and tightly connected to each other with a PC steel material, and an upper steel floating body structure (hereinafter referred to as a steel floating body) consecutively provided above the lower concrete floating body structure.

[0005] As a method for constructing the floating body of the spar-type offshore wind power generation facility, as shown in Fig. 22, at a shipyard, after fabricating individual steel rings, each having a weight determined by dividing the steel floating body into predetermined weight units, these individual steel rings are connected to one another by welding to complete the steel floating body. Then, after loading the steel floating body onto a barge and transporting the steel floating body by the barge to an on-site fabrication yard, the transported steel floating body is landed (unloaded) onto a quay by using a 1300-ton class large floating crane. Meanwhile, the concrete floating body is manufactured in a factory of a concrete manufacturer in a state where one ring is circumferentially divided into a plurality of parts for the convenience of truck transportation. These divided rings are transported by truck to the on-site fabrication yard and are circumferentially joined to one another in this yard. Then, the individual rings are further connected in a longitudinal direction using the PC steel material to complete the concrete floating body. Finally, the steel floating body and the concrete floating body are joined to one another using a 1300-ton class large floating crane (large crane ship) to complete the floating body. Citation List Patent Literature

[0006] Patent Literature 1: Japanese Patent No. 5274329 Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 2012-201219 Summary of Invention Technical Problem

[0007] When constructing a spar-type offshore wind power generation facility on the ocean, and when installing an upper structure body such as a tower, a nacelle, and blades while the spar-type floating body is floating on the ocean, it is desirable to perform the installation in a bay where waves are calm. However, since a draft (portion below the water surface) of the spar-type floating body is as deep as approximately 70 m or more, whereas the water depth in a bay is generally shallower than this draft, construction in a bay is difficult. Therefore, when installing a windmill facility, as shown in Fig. 23, the installation has been performed outside the bay where the water is deeper by using a large floating crane 70 (refer to Patent Literature 2).

[0008] For assembling the upper structure body, it has been proposed to assemble the upper structure body such as a tower, a nacelle, and blades by using a crane-equipped SEP barge in a sea area selected for being a calm sea region where waves are relatively calm, since areas outside bays where the water is deep are susceptible to the effects of wind and waves. However, with the upsizing of offshore wind power generation facilities, a situation has arisen in which a crane lift height cannot be secured with existing crane-equipped SEP barges, and a method for simply compensating the shortage of crane lift height has been desired.

[0009] On the other hand, with regard to an operation of connecting the upper structure body to the floating body floating on the ocean by using a large floating crane 70 outside a bay where the water depth is deep, there are only a few large floating cranes in Japan at present that are capable of constructing offshore wind power generation facilities, and there has been a problem that daily usage fees (charter fee) are expensive and therefore charter costs become enormous.    Accordingly, in recent years, for constructing offshore wind power generation facilities, a semi-submersible type crane equipped with a crane on a semisubmersible type floating body has been fabricated. However, since the semi-submersible type floating body has a lighter weight than a large floating crane, there is a problem in that the semi-submersible type floating body is susceptible to waves and lacks stability, and there is also a problem in that, when heavy objects such as a tower and a nacelle are suspended, the entire floating body sways and becomes unstable, which may cause difficulties in assembly work of the wind power generation facility.

[0010] Accordingly, a first problem of the present invention is to provide a method for constructing a spar-type offshore wind power generation facility while simply compensating a shortage of crane lift height of a crane-equipped SEP barge, when assembling an upper structure body such as a tower, a nacelle, and blades by using a crane-equipped SEP barge in a sea area selected for being a calm sea region where waves are relatively calm.

[0011] A second problem is to realize stable operation by suppressing swaying when a heavy object is suspended, in collectively constructing and connecting the upper structure body of the spar-type offshore wind power generation facility to the floating body by using a semi-submersible type crane. Solution to Problem

[0012] In order to solve the above-described first problem, as the present invention according to claim 1, provided is a method for constructing a spar-type offshore wind power generation facility, the method including: a first step of assembling an upper structure body of an offshore wind power generation facility, the upper structure body including a tower, a nacelle, and blades on a semi-submersible spud barge using a crane-equipped SEP barge, while using the semi-submersible spud barge as an assembly stand in a sea area selected for being a calm sea region where waves are relatively calm, in a state where the semi-submersible spud barge is submerged or set on the seabed; a second step of collectively lifting the upper structure body assembled on the assembly stand, to be transported to a construction site of the offshore wind power generation facility by a large crane ship, after floating the semi-submersible spud barge; a third step of, after assembling an entire floating body at a quay, transporting the completed floating body to the construction site of the offshore wind power generation facility by the semi-submersible spud barge, floating off the floating body on the ocean, and then attaching a mooring cable to hold the floating body in an upright position; and a fourth step of completing the offshore wind power generation facility by connecting the upper structure body to an upper portion of the floating body while the upper structure body is lifted by the large crane ship.

[0013] In the invention according to claim 1, the method includes assembling an upper structure body of an offshore wind power generation facility, the upper structure body including a tower, a nacelle, and blades on a semisubmersible spud barge using a crane-equipped SEP barge while using the semi-submersible spud barge as an assembly stand in a sea area selected for being a calm sea region where waves are relatively calm, in a state where the semi submersible spud barge is submerged or set on the seabed (first step). By using the semi-submersible spud barge as the assembly stand and completing the upper structure body in the state where the semi-submersible spud barge is submerged or set on the seabed, it becomes possible to additionally secure the lift height of the crane used for the assembly by an amount corresponding to the height at which the semi-submersible spud barge is submerged or set on the seabed, thereby making it possible to eliminate a shortage of crane lift height when assembling an ultra-large offshore wind power generation facility.

[0014] Next, after completing the assembly of the upper structure body performed on the assembly stand (semisubmersible spud barge which is submerged or set on the seabed), the submerged or set semi-submersible spud barge is floated. Then, the upper structure body is collectively lifted by the large crane ship equipped with a mobile counterweight device on a deck surface thereof and is transported to the construction site of the offshore wind power generation facility (second step).

[0015] On the other hand, after assembling an entire floating body at a quay, the completed floating body is transported to the construction site of the offshore wind power generation facility by the semi-submersible spud barge, and, the floating body is floated-off on the ocean, and a mooring cable is attached to hold the floating body in an upright position (third step). This third step is an operation performed as a process separate from the first step and the second step, and may be performed before the first step and the second step or after the first step and the second step. Alternatively, it may also be performed as a simultaneous parallel process.

[0016] The upper structure body is a considerably heavy object. However, since the semi-submersible type crane has a structure in which a mobile counterweight device is provided on a deck face, when lifting the upper structure body with the crane, the weight of the mobile counterweight device is moved to a position where swaying caused by a lifting load can be suppressed, thereby making it possible to suppress swaying of the hull and achieve stabilization.

[0017] Finally, the offshore wind power generation facility is completed by connecting the upper structure body to an upper portion of the floating body while the upper structure body is lifted by the large crane ship (fourth step).

[0018] As the invention according to claim 2, provided is the method for constructing the spar-type offshore wind power generation facility according to claim 1, wherein the floating body is a spar-type floating body comprising a concrete floating body formed by stacking a plurality of concrete rings in multiple stages and tightly connecting the respective concrete rings by a PC steel material to integrate the concrete rings with one another, and a steel floating body consecutively provided above the concrete floating body, or the floating body is a spar-type floating body comprising a concrete floating body formed by stacking a plurality of concrete rings in multiple stages and tightly connecting the respective concrete rings by the PC steel material to integrate the concrete rings with one another.

[0019] The invention according to claim 2 as described above specifically defines the structure of the floating body. Specifically, the floating body may be a spar-type floating body comprising a concrete floating body formed by stacking a plurality of concrete rings in multiple stages and tightly connecting the respective concrete rings by a PC steel material to integrate the concrete rings with one another, and a steel floating body consecutively provided above the concrete floating body, or may be a spar-type floating body comprising a concrete floating body formed by stacking a plurality of concrete rings in multiple stages and tightly connecting the respective concrete rings by the PC steel material to integrate the concrete rings with one another.

[0020] As the invention according to claim 3, provided is the method for constructing the spar-type offshore wind power generation facility according to claim 1, wherein, on the semi-submersible spud barge used as the assembly stand, a waterproof partition wall is installed around the tower in order to prevent water ingress into the tower.

[0021] The invention according to claim 3 described above is configured so that a waterproof partition wall is installed around the tower in order to prevent water ingress into the tower. Since various electrical equipment may be disposed in advance inside the tower, the waterproof partition wall is provided around the tower in order to prevent water ingress in advance.

[0022] In order to solve the above-described second problem, as the invention according to claim 4, provided is the method for constructing the spar-type offshore wind power generation facility according to claim 1, wherein a semisubmersible type crane ship equipped with a mobile counterweight device on a deck face is used as the large crane ship.

[0023] The invention according to claim 4 as described above is configured to use a semi-submersible type crane ship equipped with a mobile counterweight device on a deck surface, as the large crane ship. Since the semi-submersible type crane is equipped with the mobile counterweight device, it becomes possible to suppress swaying particularly when a heavy object is suspended and to stably perform work.

[0024] As the invention according to claim 5, provided is the method for constructing the spar-type offshore wind power generation facility according to claim 4, wherein the mobile counterweight device is configured to be movable in any direction by providing a traveling unit on a lower surface of a weight, winches are disposed at four or three corners, or at front and rear portions across the weight, wires paid out from the winches are connected to the weight, and then the winches are operated, thereby controlling the movement of the weight to a predetermined position.

[0025] The invention according to claim 5 as described above specifically defines the structure of the mobile counterweight device. Specifically, a device can be preferably adopted, in which the mobile counterweight device is configured to be movable in any direction by providing a traveling unit on a lower surface of a weight, winches are disposed at appropriate positions, and then the winches are operated, thereby controlling the movement of the weight to a predetermined position. Advantageous Effects of Invention

[0026] As described in detail above, according to the present invention, it is possible to construct a spar-type offshore wind power generation facility while simply compensating a shortage of crane lift height of a crane-equipped SEP barge, when assembling an upper structure body such as a tower, a nacelle, and blades using the crane-equipped SEP barge in a sea area selected for being a calm sea region where waves are relatively calm.

[0027] Moreover, it is possible to realize stable operation by suppressing swaying when a heavy object is suspended, in collectively constructing and connecting the upper structure body of the spar-type offshore wind power generation facility to the floating body by using a semi-submersible type crane. Brief Description of Drawings

[0028] [Fig. 1] Fig. 1 is an overall view of a spar-type offshore wind power generation facility 1. [Fig. 2] Fig. 2 is a longitudinal sectional view of a floating body 4. [Fig. 3] Fig. 3 shows a precast cylindrical body 15, in which Fig. 3(A) is a longitudinal sectional view, Fig. 3(B) is a plan view (view taken in the direction of arrows B-B), and Fig. 3(C) is a bottom view (view taken in the direction of arrows C-C). [Fig. 4] Fig. 4 is a schematic diagram showing tight connection between precast cylindrical bodies 15 (Figs. 4(A) and 4(B)). [Fig. 5] Fig. 5 is an enlarged longitudinal sectional view showing a boundary portion between a concrete floating body 4A and a steel floating body 4B. [Fig. 6] Fig. 6 shows a semi-submersible type crane 2 according to the present invention, in which Fig. 6(A) is a side view, and Fig. 6(B) is a plan view thereof. [Fig. 7] Fig. 7 is a plan view showing another example of a mobile counterweight device 3. [Fig. 8] Fig. 8 is a plan view showing yet another example of the mobile counterweight device 3. [Fig. 9] Fig. 9 shows a construction procedure (Part 1) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 10] Fig. 10 shows a construction procedure (Part 2) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 11] Fig. 11 shows a construction procedure (Part 3) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 12] Fig. 12 shows a construction procedure (Part 4) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 13] Fig. 13 shows a construction procedure (Part 5) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 14] Fig. 14 shows a construction procedure (Part 6) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 15] Fig. 15 shows a construction procedure (Part 7) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 16] Fig. 16 shows a construction procedure (Part 8) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 17] Fig. 17 shows a construction procedure (Part 9) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 18] Fig. 18 shows a construction procedure (Part 10) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 19] Fig. 19 shows a construction procedure (Part 11) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 20] Fig. 20 shows a construction procedure (Part 12) of the spar-type offshore wind power generation facility 1 according to the present invention. [Fig. 21] Fig. 21 is an assembly schematic diagram of an upper structure body 12 showing a modified example of an assembly stand 13. [Fig. 22]   Fig. 22 is a flow chart showing a conventional floating body construction method. [Fig. 23]   Fig. 23 is a schematic diagram of collectively construction by a large floating crane 70 disclosed in Patent Literature 2. Description of Embodiments

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0030] [Hybrid Spar-Type Offshore Wind Power Generation Facility 1] First, a spar-type offshore wind power generation facility 1 to which the present invention is applied will be described in detail on the basis of Figs. 1 to 5.

[0031] The spar-type offshore wind power generation facility 1 is, as shown in detail in Fig. 1, composed of a spar-type cylindrical floating body 4, a mooring cable 10, a tower 6, and a windmill 7 including a nacelle 8 and a plurality of blades 9, 9 ... provided at a top portion of the tower 6.

[0032] The floating body 4, as shown in Fig. 2, includes a concrete floating body 4A formed by stacking a plurality of concrete precast cylindrical bodies 15,  15 . in a height direction and tightly connecting and integrating the respective precast cylindrical bodies 15,  15 . with one another by a PC steel material 19, and a steel floating body 4B consecutively provided above the concrete floating body 4A.

[0033] Ballast materials such as water, gravel, fine aggregates or coarse aggregates, metal particles, or the like can be introduced into or discharged from a hollow portion of the floating body 4, thereby making it possible to adjust buoyancy (draft). The introduction / discharge of the ballast materials can be realized by adopting a fluid transportation method previously proposed by the present applicant in Japanese Patent Application Laid-Open Publication No. 2012-201217.

[0034] The concrete floating body 4A is composed of concrete precast cylindrical bodies 15, 15 .. As shown in Fig. 3, the precast cylindrical bodies 15 are circular cylindrical precast members having the same cross section in an axial direction fabricated by using the same formwork for each member, or hollow precast members manufactured by centrifugal molding.

[0035] In a wall surface, in addition to reinforcing bars 20, sheaths 21,  21 ... for inserting the PC steel materials 19 therethrough at appropriate intervals in a circumferential direction are embedded. At lower end portions of the sheaths 21, 21 ., sheath diameter expansion portions 21a are formed so as to allow couplers for connecting the PC steel materials 19 to each other to be inserted therein, and at upper portions thereof, boxed-out portions 22 for fitting fixing anchor plates therein are formed. Moreover, a plurality of lifting fittings 23 are provided on the upper surface.

[0036] As shown in Fig. 4(A), for tightly connecting the precast cylindrical bodies 15 to one another, when the precast cylindrical bodies 15, 15 are stacked on top of each other while inserting the PC steel materials 19,  19 . extending upward from the lower precast cylindrical body 15 through the sheaths 21, 21 ., an anchor plate 24 is fitted into the boxed-out portion 22, and tensile force is introduced into the PC steel material 19 by an anchor member 25 to integrate the precast cylindrical bodies 15, 15 with one another. In addition, a grout material is injected into the sheath 21 through a grout injection hole 27. Note that the hole 24a formed in the anchor plate 24 is a grout injection confirmation hole, and filling of the grout material is completed when the grout material is discharged from the confirmation hole.

[0037] Next, as shown in Fig. 4(B), when a coupler 26 is screwed onto a protruding portion of the PC steel material 19 and the PC steel materials 19, 19 ... on the upper side are connected to one another, the precast cylindrical body 15 to become the tier above is stacked while inserting the PC steel materials 19, 19 . into the sheaths 21, 21 ., thus the precast cylindrical bodies 15 are stacked in a height direction by sequentially repeating the procedure for anchoring the PC steel material 19 in the above-described manner. In this case, an adhesive 28 such as an epoxy resinbased adhesive or a sealing material is applied to the joint surface between the lower precast cylindrical body 15 and the upper precast cylindrical body 15 in order to ensure water-tightness and bonding of mating surfaces.

[0038] The steel floating body 4B is composed of a steel cylindrical body 17 relatively located on a lower side and a steel cylindrical body 18 relatively located on an upper side. A lower portion of the lower steel cylindrical body 17 has the same outer diameter dimension as the precast cylindrical body 15, and the lower steel cylindrical body 17 is connected to the precast cylindrical body 15 by bolts, welding, or the like (bolt fastening is shown in the illustrated example), as shown in Fig. 5. An upper portion of the steel cylindrical body 17 has a truncated conical shape with a gradually narrowed diameter.

[0039] The upper steel cylindrical body 18 is a cylindrical body having an outer diameter dimension continuous with an upper outer diameter of the lower steel cylindrical body 17, and is connected to the lower steel cylindrical body 17 by bolts, welding, or the like (bolt fastening is shown in the illustrated example).  These steel cylindrical bodies 17, 18 are composed of a plurality of steel rings each having a predetermined weight, and the respective steel rings are integrated by being circumferentially welded.

[0040] On the other hand, the tower 6 is composed of steel material, concrete, or prestressed reinforced concrete (PRC), but it is preferable to use one manufactured of steel material so as to reduce the total weight.   The outer diameter of the tower 6 and the outer diameter of the upper steel cylindrical body 18 substantially coincide with each other, and the outer shape is continuous in the vertical direction without any step or the like.

[0041] As shown in Fig. 1, a mooring point P of a mooring cable 10 to the floating body 4 is set at a position below the sea surface and higher than the center of gravity G of the floating body 4. Accordingly, it becomes possible to prevent ships and vessels from coming into contact with the mooring cable 10.   Moreover, since a resisting moment centered on the center of gravity G of the floating body 4 is generated at the mooring point P so as to suppress excessive tilting of the floating body 4, it becomes possible to appropriately maintain a tilted posture state of the tower 6.

[0042] Meanwhile, the nacelle 8 is a device equipped with a generator for converting rotation of the windmill 7 into electricity, a controller capable of automatically changing the angle of the blades 9, and the like.

[0043] [Regarding Semi-Submersible Type Crane 2] Before describing in detail, a method for constructing the spar-type offshore wind power generation facility 1, the semi-submersible type crane 2 used in the construction method will be described in detail on the basis of Figs. 6 to 8.

[0044] As shown in Fig. 6, the semi-submersible type crane 2 includes a crane 5 on a deck surface of a semi-submersible type floating body 11 configured to include a plurality of columns 31, 31 ... serving as buoyant bodies and connecting members 33, 33 . connecting the plurality of columns 31, 31 . to one another.

[0045] The semi-submersible type floating body 11 includes the plurality of columns, three columns 31,  31 . in the illustrated example, serving as buoyant bodies. Each of these columns 31 is a cylindrical hollow structure, and a floating body base portion 30 of the semi-submersible type floating body 11 is configured by arranging these columns 31, 31 ... at, for example, vertex points of a polygon in a plan view and then connecting the respective columns 1031, 31 . to one another by connecting members 33, 33 ..

[0046] A deck main body 38 is provided on an upper surface of the floating body base portion 30, and an extended deck portion 37 is provided continuously from the deck main body 38 so as to extend in a cantilever manner toward one end side. Moreover, a mobile counterweight deck portion 39 is provided on the opposite side of the extended deck portion 37 across the deck main body 38. A frame structure 34 is disposed in a cantilever manner on a lower surface side of the extended deck portion 37 so as to provide structural reinforcement. Similarly, frame structures 35, 36 are disposed in a cantilever manner on the lower surface side of the mobile counterweight deck portion 39 so as to provide structural reinforcement. The deck main body 38 has a shape in which its width gradually decreases toward the left side in the drawing, and the extended deck portion 37 has a shape extending in a bar-like manner from a distal end side edge of the deck main body 38 and serves as a bow side. The mobile counterweight deck portion 39 is a space provided to secure a moving range of the weight and serves as a stern side. Note that the deck main body 38 and the mobile counterweight deck portion 39 have a stepped structure since the decks have an overlapping margin, but they may be formed on the same plane.

[0047] The crane 5 is provided on an upper surface of the deck main body 38 of the semi-submersible type floating body 11, corresponding to a position closer to the extended deck portion 37. The installation position of the crane 5 is directly above the column 31, so that a load from the crane 5 is directly transmitted to the column 31. As the crane 5, a fixed type crane is preferable, but a mobile crane can be mounted on the deck main body 38 depending on the situation. In any case, it is necessary to have a lifting capacity and a lift height capable of erecting the tower 6, the nacelle 8, and the blades 9 of the offshore wind power generation facility. Moreover, when a tower crane is adopted, it becomes easily possible to secure a desired lift height by a self-elevating structure.

[0048] A tower gripping device 40 for fixing the tower of the offshore wind power generation facility integrally with the semi-submersible type crane 2 is provided at a tip end portion of the extended deck portion 37. The tower gripping device 40 has an openable and closable gripper mechanism.

[0049] A mobile counterweight device 3 is provided on an upper surface of the mobile counterweight deck portion 39. As shown in Fig. 6(B), for example, the mobile counterweight device 3 is a device configured to move the weight 42 in any direction by providing a traveling unit on a lower surface of the weight 42, and to control the movement of the weight 42 to a predetermined position by disposing winches 41A to 41D at four corners, respectively, connecting wires 43a to 43d paid out from the winches 41A to 41D to respective corner portions of the weight 42, and operating the winches 41A to 41D. The mobile counterweight device 3 is configured so that the weight 42 can be moved to any position within a plane in the X and Y directions in a plan view. It is preferable that control of each winch 41A to 41D is performed by cooperative control under computer control (not shown).

[0050] The weight 42 has a box-shaped structure as shown in the drawing, and the weight can be adjusted by introducing ballast materials such as slag aggregates into the inside thereof or, when the weight is insufficient, by introducing a combination of steel materials or the like therewith.

[0051] As for the winches 41, as shown in Fig. 7, winches 41A to 41C may be disposed respectively at three corners in three directions corresponding to the vertexes of a substantially equilateral triangle, wires 43a to 43c paid out from the winches 41A to 41C may be respectively connected to the weight 42, and then the winches 41A to 41C may be operated, thereby controlling the movement of weight 42 to a predetermined position. Alternatively, as simply shown in Fig. 8, winches 41A and 41B may be disposed at front and rear portions across the weight 42, wires 43a and 43b paid out from the winches 41A and 41B may be connected to the weight 42, and then the winches 41A and 41B may be operated, thereby controlling the movement of weight 42 to a predetermined position in the Y direction. In this case, it is preferable to provide movement guides 44, 44 on both sides of the weight 42 so that the weight 42 can move only in the Y direction.

[0052] As shown in Fig. 6, it is preferable to provide fin stabilizers 32,  32 on a submerged portion of the semi submersible type floating body 11 so as to enhance stability against waves.

[0053] [Construction Method of Spar-Type Offshore Wind Power Generation Facility 1] Next, a method for constructing the spar-type offshore wind power generation facility 1 using the semi-submersible type crane 2 will be described in detail on the basis of Figs. 9 to 21.

[0054] <First Step> As shown in Fig. 9, in a quay yard, when the crane-equipped SEP barge 14 is berthed at the quay, the towers 6, 6 ., the nacelle 8, and the blades 9,  9 ... are loaded onto the SEP barge 14 by using a crane 45. The crane-equipped SEP barge 14 is provided with vertically extending elevatable leg columns (hereinafter also referred to as "elevating legs") at three or four locations of the barge, and is equipped with a hydraulic jack system for driving the elevating legs to move upward and downward, wherein the barge portion can be lifted to a state above the sea surface by lowering the elevating legs downward, supporting lower ends thereof on the seabed and then continuing to drive the elevating legs downward, and the crane 45 is integrally provided on the barge, thereby making it possible to load and unload cargo onto and from the barge.

[0055] Next, as shown in Fig. 10, an assembly stand 13 is provided in a sea area selected for being a calm sea region where waves are relatively calm. This assembly stand 13 is a stand for assembling the upper structure body 12 of the offshore wind power generation facility 1 including the tower 6, the nacelle 8, and the blades 9. The semi-submersible spud barge 46 is used as the assembly stand 13. This semisubmersible spud barge 46 is a barge capable of adjusting its draft to a semi-submerged state by adjusting ballast water, and is provided with vertically extending elevatable leg columns (elevating legs) at three or four locations of the barge. As shown in Fig. 10, the semi-submersible spud barge 46 is configured to be capable of stably holding the barge by bringing the elevating legs into contact with the seabed.

[0056] In the assembly, first, as shown in Fig. 10, the tower 6 is assembled in multiple stages from a lower side on the assembly stand 13 (the semi-submersible spud barge 46) by using the crane-equipped SEP barge 14.  The number of stages is set so that the height of the tower is greater than the water depth.  Once a predetermined number of stages of tower 6 (two stages in the illustrated example) have been assembled, the barge portion of the assembly stand 13 (the semisubmersible spud barge 46) is lowered so that the assembly stand 13 is in a state of being submerged or set on the seabed. In the illustrated example (Fig. 11), the barge portion is in a state of being set on the seabed. In this state, the top end of the assembled two-stage tower 6 is positioned above the water surface.    Subsequently, the remaining stages of the tower 6 are assembled, and the nacelle 8 and the blades 9 are assembled in this order, thereby completing the upper structure body 12.

[0057] The reason why the upper structure body 12 is completed in a state where the assembly stand 13 (the semi-submersible spud barge 46) is submerged or set on the seabed is as a countermeasure to eliminate a shortage of crane lift height of the crane-equipped SEP barge 14. In the future, 20 MW class offshore wind power generation facilities are planned, and, as a countermeasure for when a shortage of crane lift height of the crane-equipped SEP barge 14 is a concern, it becomes possible to secure additional lift height of the crane used for the assembly by an amount corresponding to the height at which the assembly stand 13 (the semisubmersible spud barge 46) is submerged or set on the seabed, thereby making it possible to eliminate a shortage of crane lift height when assembling an ultra-large offshore wind power generation facility.

[0058] <Second Step> Next, in the second step, as shown in Fig. 13, the assembly stand 13 (the semi-submersible spud barge 46) is raised so that the entire upper structure body 12 is exposed in the air.    Then, the semi-submersible type crane 2 described above is brought alongside the assembly stand 13 (the semi-submersible spud barge 46), and the assembled upper structure body 12 is suspended by the crane 5. At this time, the lower end of the tower 6 is held by the tower gripping device 40, thereby preventing the upper structure body 12 from swaying as much as possible. Moreover, since the upper structure body 12 is a considerably heavy object, the weight 42 of the mobile counterweight device 3 is moved toward the rear side in order to horizontally stabilize the hull that has swayed toward the front side due to this suspension load.

[0059] Once the upper structure body 12 is suspended by the semi-submersible type crane 2, as shown in Fig. 14, the semisubmersible type crane 2 is transported to a construction site of the spar-type offshore wind power generation facility 1 by a towing vessel 47.

[0060] <Third Step> The third step is an operation performed as a process separate from the first step and the second step, and may be performed before the first step and the second step or after the first step and the second step. Alternatively, it may also be performed as a simultaneous parallel process.

[0061] The third step is an operational process in which, after the entire floating body 4 is assembled at the quay, the completed floating body 4 is transported to the construction site of the spar-type offshore wind power generation facility 1 by the semi-submersible spud barge 46, and, once the floating body 4 is floated off on the ocean, a mooring cable is attached to hold the floating body 4 in an upright position.

[0062] Specifically, first, the floating body 4 is completed in the quay yard. As a method for constructing the floating body, it is possible to preferably adopt the method according to the invention disclosed in Japanese Patent Application Laid-Open Publication No. 2018-173011 proposed by the present applicant.

[0063] As shown in Fig. 15, in the floating body construction method, a steel ring connecting yard A, a concrete ring fabricating yard B, and a concrete ring connecting yard C are defined and provided in the quay yard.

[0064] In the steel ring connecting yard A, a first gantry crane 50 is provided so as to be moveable in a predetermined direction, rotating-function-equipped stands 52,  52 ... are installed at appropriate intervals in the traveling direction of the first gantry crane, and a mobile tent 56 movable in the traveling direction of the first gantry crane is provided. In the concrete ring fabricating yard B, a mobile tent 57 is provided, and a complete set of concrete ring manufacturing facilities is installed. In the concrete ring connecting yard C, a second gantry crane 55 is provided so as to be movable in a predetermined direction, and a mobile tent 58 movable in the traveling direction of the second gantry crane is provided.

[0065] The floating body construction method of the spar-type offshore wind power generation facility includes: a first process of sequentially installing the steel rings 51, 51 . on the rotating-function-equipped stands 52, 52 . by using the first gantry crane 50, covering the surroundings with the mobile tent 56 as necessary, and circumferentially welding and connecting the steel rings 51,  51  . while rotating the steel rings 51, 51 . around an axis, thereby completing the steel floating body 53B; and a second process of, once the steel floating body 53B is moved to the concrete ring connecting yard C and installed at a predetermined position, transporting the concrete rings 54 fabricated in the concrete ring fabricating yard B to the concrete ring connecting yard C in sequence, covering the surroundings with the mobile tent 58 as necessary, and continuously connecting the concrete rings 54 to the steel floating body 53Bby using the second gantry crane 55 and tightly connecting and integrating the concrete rings 54 by PC steel material, thereby completing the floating body 53.

[0066] When the floating body 4 is completed in this manner, as shown in Fig. 16, at the quay, the floating body 4 is moved and loaded onto the semi-submersible spud barge 46 in a sideways state (roll-on). The semi-submersible spud barge 46 is a barge capable of adjusting its draft to a semisubmerged state by adjusting ballast water, and, after rollon (loading) the cargo onto the barge while adjusting the ballast, the cargo can be floated off (floating and launching) by bringing the barge into a semi-submerged state by adjusting the ballast water offshore. Accordingly, once the floating body 4 is transported to the construction site, it becomes possible to float off and launch the floating body 4 onto the ocean in a semi-submerged state without using a crane.

[0067] Once the semi-submersible spud barge 46 is towed by the towing vessel 47 and transported to the construction site of the spar-type offshore wind power generation facility 1, as shown in Fig. 17, the floating body 4 is launched and floated off onto the ocean (roll-off) by bringing the semisubmersible spud barge 46 into a semi-submerged state. Then, the floating body 4 is erected by injecting ballast water into the floating body 4, thereby bringing the floating body 4 into an upright position.

[0068] As shown in Fig. 18, it is desirable to attach mooring cables 10,  10 ... to the floating body 4 brought into an upright position, thereby ensuring stability of the floating body 4.

[0069] <Fourth Step> In the fourth step, as shown in Figs. 19 and 20, the spar-type offshore wind power generation facility 1 is completed by connecting the upper structure body 12 to an upper portion of the floating body 4 while the upper structure body 12 is kept in a lifted state by the semisubmersible type crane 2.

[0070] [Other Embodiments] (1) In the first step, the lower end portion of the tower 6 is submerged in water, but various electrical equipment may be disposed in advance in the lower end portion of the tower 6. Therefore, in such a case, as shown in Fig. 21, it is also possible to provide a waterproof partition wall 48 surrounding the lower end of the tower 6 so as to prevent water ingress.

[0071] (2) The above-described embodiment is directed to a spar-type floating body in which the floating body 4 comprises the concrete floating body 4A and the steel floating body 4B consecutively provided above the concrete floating body 4A. However, even in the case of a spar-type floating body in which the floating body 4 comprises only the concrete floating body 4A formed by stacking a plurality of concrete rings 15, 15 ... in multiple stages and tightly connecting the respective concrete rings 15, 15 . by the PC steel material 19 to integrate the concrete rings 15, 15 . with one another, it is possible to construct the floating body 4 using the same procedure. Naturally, the same applies to other floating body structures.

[0072] (3) In the above-described embodiment, the semisubmersible type crane 2 is used as the large crane ship for collectively constructing the upper structure body 12 of the spar-type offshore wind power generation facility 1. However, instead of this example, it is also possible to use an ordinary large floating crane ship, a large floating crane ship provided with the mobile counterweight device 3, or the like. Reference Signs List

[0073] 1: Spar-type offshore wind power generation facility; 2:  Semi-submersible type crane; 3:  Mobile counterweight device; 4: Floating body; 4A: Concrete floating body; 4B: Steel floating body; 5, 45: Crane; 6: Tower; 7: Windmill; 8: Nacelle; 9: Blade; 10: Mooring cable; 12: Upper structure body; 13: Assembly stand (semi-submersible spud barge 46); 14: Crane-equipped SEP barge; 15, 16: Precast cylindrical body (concrete ring); 19:  PC steel material; 46:  Semi- submersible spud barge; and 48: Waterproof partition wall.

Claims

A method for constructing a spar-type offshore wind power generation facility, the method comprising:a first step of assembling an upper structure body of an offshore wind power generation facility, the upper structure body including a tower, a nacelle, and blades on a semi-submersible spud barge using a crane-equipped SEP barge, while using the semi-submersible spud barge as an assembly stand in a sea area selected for being a calm sea region where waves are relatively calm, in a state where the semi-submersible spud barge is submerged or set on a seabed;a second step of collectively lifting the upper structure body assembled on the assembly stand after floating the semi-submersible spud barge, and transporting the upper structure body to a construction site of the offshore wind power generation facility by a large crane ship;a third step of, after assembling an entire floating body at a quay, transporting the completed floating body to the construction site of the offshore wind power generation facility by the semi-submersible spud barge, floating off the floating body on the ocean, and then attaching a mooring cable to hold the floating body in an upright position; anda fourth step of completing the offshore wind power generation facility by connecting the upper structure body to an upper portion of the floating body while the upper structure body is lifted by the large crane ship.The method for constructing the spar-type offshore wind power generation facility according to claim 1, wherein the floating body is a spar-type floating body comprising a concrete floating body formed by stacking a plurality of concrete rings in multiple stages and tightly connecting therespective concrete rings by a PC steel material to integrate the concrete rings with one another, and a steel floatingbody consecutively provided above the concrete floating body,or a spar-type floating body comprising a concrete floating body formed by stacking a plurality of concrete rings in multiple stages and tightly connecting the respective concrete rings by the PC steel material to integrate the concrete rings with one another.

3. The method for constructing the spar-type offshore wind power generation facility according to claim 1, wherein, in the semi-submersible spud barge used as the assembly stand, a waterproof partition wall is installed around the tower in order to prevent water ingress into the tower.

4. The method for constructing the spar-type offshore wind power generation facility according to claim 1, wherein a semi-submersible type crane ship equipped with a mobile counterweight device on a deck face is used as the large crane ship.The method for constructing the spar-type offshore wind power generation facility according to claim 4, wherein the mobile counterweight device is configured to be movable in any direction by providing a traveling unit on a lower surface of a weight, winches are disposed respectively at four or three corners, or at front and rear portions across the weight, wires paid out from the winch are connected to the weight, and then the winches are operated, thereby controlling the movement of the weight to a predetermined position.

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