Method of arranging parallel wires

Abstract

To provide a parallel wire arrangement method capable of arranging a parallel wire on the sea bottom while suppressing damage.SOLUTION: And an arrangement step of arranging the parallel wire PW so as to be laid on the sea bottom SB while suppressing generation of bending compressive stress in the parallel wire PW whose one end side is connected to a foundation F fixed to the ground of the sea bottom SB.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a method for arranging parallel wires. [Background technology]

[0002] Conventionally, in order to install a structure offshore, a buoyant structure (for example, a floating foundation) is connected to tension legs fixed to the seabed. Patent Document 1 discloses connecting a floating structure and a mooring anchor installed on the bottom of the water with parallel wire strands. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Public Relations of JP 58-224884 Summary of the Invention [Problem to be solved by the invention]

[0004] When installing an offshore structure, the step of connecting the parallel wires to the seabed foundation and the step of connecting the parallel wires to the offshore structure may be performed asynchronously. In this case, the parallel wires are connected to the seabed foundation in advance and are kept in a standby state. When the parallel wires are placed on standby as described above, it is preferable to place the parallel wires lying flat on the seabed. However, if the parallel wires are simply placed hanging down on the seabed, bending and compressive forces will act on the parallel wires due to their own weight, which may cause the parallel wires to buckle and be damaged.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a method for placing parallel wires that can place the parallel wires on the seabed while minimizing damage to the parallel wires. [Means for solving the problem]

[0006] A method for arranging parallel wires according to one aspect of the present disclosure is characterized by including an arrangement step of arranging parallel wires, one end of which is connected to a foundation fixed to the ground on the seabed, so as to lay the parallel wires on the seabed while suppressing the occurrence of bending compressive stress in the parallel wires. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a parallel wire arrangement method that can arrange parallel wires on the seabed while minimizing damage to the parallel wires. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a front view of an offshore wind turbine system according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along the line II-II in FIG. [Figure 3] FIG. 2 is a perspective view showing a cross section of a parallel wire. [Figure 4] FIG. 10 is a schematic diagram showing a process of connecting one end of the parallel wire to a foundation while lifting the parallel wire with a crane. [Figure 5] FIG. 1 is a first schematic diagram showing a first arrangement step. [Figure 6] FIG. 2 is a second schematic diagram showing the first arrangement step. [Figure 7] FIG. 1 is a first schematic diagram showing the second arrangement step. [Figure 8] FIG. 2 is a second schematic diagram showing the second arrangement step. [Figure 9] FIG. 1 is a first schematic diagram showing the third arrangement step. [Figure 10] FIG. 2 is a second schematic diagram showing the third arrangement step. [Figure 11] FIG. 10 is a top view of a plurality of parallel wires laid out on the seabed in the laying step. [Figure 12] This is a view of FIG. 11 as seen from the horizontal direction. [Figure 13] FIG. 2 is a schematic diagram showing a first step of pulling up parallel wires. [Figure 14] FIG. 10 is a schematic view showing a second step of pulling up the parallel wires. [Figure 15] FIG. 1 is a schematic diagram showing the third step of pulling up the parallel wires. [Figure 16] FIG. 2 is a second schematic diagram showing the third step of pulling up the parallel wires. [Figure 17] FIG. 3 is a schematic diagram showing the third step of pulling up the parallel wires. [Figure 18] FIG. 10 is a schematic diagram showing the work of using a towing vessel to move the offshore structure closer to the second work vessel, as a first step in connecting the parallel wires and the offshore structure. [Figure 19] 18 seen from the horizontal direction. [Figure 20] FIG. 10 is a schematic diagram showing the work of aligning the offshore structure and the second working vessel as the first step in connecting the parallel wires and the offshore structure. [Figure 21] This is a view of Figure 20 as seen from the horizontal direction. [Figure 22] FIG. 10 is a schematic diagram showing a second step of connecting the parallel wires to the marine structure. [Figure 23] This is a view of Figure 22 as seen from the horizontal direction. [Figure 24] FIG. 10 is a schematic diagram showing a third step of connecting the parallel wires to the marine structure. [Figure 25] This is a view of Figure 24 as seen from the horizontal direction. [Figure 26] 10A and 10B are schematic diagrams illustrating a step of pulling up parallel wires extending in a second direction. [Figure 27] 10 is a schematic diagram showing a process of connecting parallel wires extending in a second direction to an offshore structure. FIG. [Figure 28] 10A and 10B are schematic diagrams illustrating a step of pulling up parallel wires extending in a third direction. [Figure 29] 10 is a schematic diagram showing a process of connecting parallel wires extending in a third direction to an offshore structure. FIG. [Figure 30] FIG. 1 is a schematic diagram of a process for connecting a power transmission cable to an offshore structure. [Figure 31] FIG. 1 is a schematic diagram of a process for increasing the buoyancy of an offshore structure. [Figure 32] FIG. 10 is a diagram showing the completed installation of the marine structure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a method for arranging parallel wires according to an embodiment of the present disclosure will be described with reference to the drawings. In this embodiment, the parallel wires are used to support a floating foundation on the ocean. The floating foundation is used to support an offshore wind turbine in an offshore wind turbine system. Before describing the method for arranging the parallel wires, the offshore wind turbine system according to this embodiment will be described first.

[0010] (About offshore wind turbine systems) FIG. 1 is a front view of an offshore wind turbine system 1 according to an embodiment. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. The offshore wind turbine system 1 shown in FIG. 1 includes an offshore wind turbine 10 and an offshore structure 20. The offshore wind turbine 10 is a wind turbine that is installed offshore and generates electricity using wind power. The offshore structure 20 supports the offshore wind turbine 10 on the ocean. In this embodiment, the offshore structure 20 is a floating foundation of the so-called TLP (Tension Leg Platform) type. That is, the offshore structure 20 has buoyancy, and supports the offshore wind turbine 10 on the ocean by the buoyancy. The offshore structure 20 is connected to the ground of the seabed SB via parallel wires PW.

[0011] In this embodiment, the marine structure 20 is formed, for example, in a polygonal shape when viewed from above. That is, for example, the marine structure 20 may be a square, a pentagon, or any other polygon when viewed from above. In this embodiment, the marine structure 20 is formed in a quadrangular shape when viewed from above, as shown in FIG. 2. In this embodiment, the quadrangular shape is formed by combining four box girders 21 that extend linearly. As shown in FIG. 1, in the marine structure 20, the four box girders 21 are provided in two rows in the vertical direction. The corners of the two rows of quadrangular shapes aligned in the vertical direction are connected by connecting members 22 that extend in the vertical direction. In this manner, the marine structure 20 in this embodiment is constructed. In the offshore structure 20, the offshore wind turbine 10 is placed at one of the four corners of the offshore structure 20 formed as described above.

[0012] Hereinafter, in this embodiment, as shown in Figure 2, when viewing the offshore structure 20 from above, the side corresponding to the edge extending clockwise from the diagonal corner at which the offshore wind turbine 10 is located will be referred to as the first side 10Sa, and the other side faces will be referred to as the second side 10Sb, third side 10Sc, and fourth side 10Sd, respectively, in a clockwise direction. 2, when viewed from above, the direction from the center of the offshore structure 20 toward the first side surface 10Sa is referred to as the first direction D1. When viewed from above, the direction from the center of the offshore structure 20 toward the second side surface 10Sb is referred to as the second direction D2. When viewed from above, the direction from the center of the offshore structure 20 toward the third side surface 10Sc is referred to as the third direction D3. When viewed from above, the direction from the center of the offshore structure 20 toward the fourth side surface 10Sd is referred to as the fourth direction D4.

[0013] The parallel wires PW are provided at each of the four corners of the offshore structure 20. For example, one parallel wire PW may be provided at each of the four corners of the offshore structure 20, or two parallel wires PW may be provided at each of the four corners, or three or more parallel wires PW may be provided at each of the four corners of the offshore structure 20. In this embodiment, two parallel wires PW are provided at each of the four corners as shown in FIG. 2. That is, in this embodiment, eight parallel wires PW are provided for one offshore structure 20. This prevents the position and angle of the offshore structure 20 from being shifted due to the force of waves, etc.

[0014] One end of the parallel wire PW is connected to a foundation F fixed to the ground of the seabed SB, and the other end is connected to the offshore structure 20. Tension acts on the parallel wire PW due to the buoyancy of the offshore structure 20. The offshore structure 20 is fixed on the ocean as the buoyancy of the offshore structure 20 and the tension of the parallel wire PW are balanced. The parallel wires PW in this embodiment have a strength sufficient to withstand the tension caused by the buoyancy of the marine structure 20. In other words, the parallel wires PW have sufficient strength to support the marine structure 20 against a force in the tensile direction.

[0015] (Parallel wire placement) In this embodiment, the marine structure 20 and the parallel wires PW are connected by connecting one end of the parallel wires PW, the other end of which is fixed to the foundation F in advance, to the marine structure 20. Here, in order to be able to arbitrarily determine the timing of manufacturing and transporting the marine structure 20, it is preferable that the parallel wires PW be kept on standby with one end connected to the foundation F in advance. When the parallel wires PW with one end connected to the foundation F are kept on standby, the parallel wires PW are arranged so as to lie on the seabed SB. Then, after the marine structure 20 has been transported, the parallel wires PW are pulled up from the seabed SB and connected to the marine structure 20.

[0016] FIG. 3 is a perspective view showing a cross section of the parallel wire PW. In this embodiment, the parallel wire PW is formed by bundling a plurality of strands PWs in parallel and covering them with a covering material PWc, as shown in FIG. 3 . When a bending compressive force is applied to such a parallel wire PW, a compressive force acts on some of the strands PWs included in the parallel wire PW, and a tensile force acts on some of the other strands PWs. As a result, in one parallel wire PW, the strand PWs to which the compressive force acts may buckle. In this embodiment, when one of the strands PWs buckles, it may be said that the parallel wire PW has buckled. For example, when one of the strands PWs is deformed laterally due to compression, it may be determined that one of the strands PWs has buckled. When a parallel wire PW with one end connected to a foundation F is laid flat on the seabed SB, if the parallel wire PW is placed on the seabed SB in a manner that it is simply hanging down from an upright position, a bending compressive force will act on the parallel wire PW due to its own weight, causing the parallel wire PW to buckle and become damaged.

[0017] For this reason, when laying the parallel wires PW on the seabed SB as described above, it is preferable to prevent bending and compressive force from acting on the parallel wires PW. That is, for example, when laying the parallel wires PW, one end of which is connected to the foundation F, on the seabed SB, it is preferable to maintain a state in which tension is acting on the parallel wires PW. In order to achieve the above, the method for arranging the parallel wires PW according to this embodiment includes the following steps: That is, the method for arranging the parallel wires PW according to this embodiment includes a basic connection step, an arrangement step, and a connection step.

[0018] (Foundation connection process) The base connecting step is a step of connecting one end of the parallel wire PW to the base F. FIG. 4 is a schematic diagram showing a process of connecting one end of the parallel wire PW to a foundation F while lifting the parallel wire PW with a crane CL. In the foundation connection process, for example, a first work vessel OS1 (work vessel) shown in Fig. 4 is used. In this embodiment, it is preferable that work by the first work vessel OS1 is carried out while measuring the position of the first work vessel OS1 with a GPS device (not shown). The first work vessel OS1 is equipped with a crane CL for hoisting the parallel wires PW, as shown in Fig. 4. Any vessel equipped with a crane CL, such as an SEP or a floating crane, may be used for the first work vessel OS1. Furthermore, when the foundation connecting step is performed, it is preferable that the first work vessel OS1 be connected to the anchor wire AW.

[0019] Before the placement process is performed, one end of the parallel wire PW is connected to a foundation F that has been fixed to the ground of the seabed SB. As shown in FIG. 4, the connection of one end of the parallel wire PW to the foundation F is performed with the other end of the parallel wire PW hoisted by the crane CL of the first work vessel OS1. The crane wire CW provided on the crane CL and the parallel wire PW are connected via a hoisting wire HW. It is preferable to use a hoisting wire HW that has lower bending rigidity (more flexible) than the parallel wire PW, for example.

[0020] In this embodiment, various underwater tasks, including connecting one end of the parallel wires PW to the foundation F, are preferably performed by an underwater robot ROV, for example, as shown in Fig. 4. The underwater robot ROV is a so-called unmanned submersible (remotely operated vehicle).

[0021] (Placement process) The placing step is a step of placing the parallel wires PW so that they lie on the seabed SB while suppressing the occurrence of bending compressive stress in the parallel wires PW, one end of which is connected to a foundation F fixed to the ground of the seabed SB. In this embodiment, in the placing step, the parallel wires PW are placed so that they lie on the seabed SB while maintaining tension acting on the parallel wires PW.

[0022] FIG. 5 is a first schematic diagram illustrating the first arrangement step. FIG. 6 is a second schematic diagram illustrating the first arrangement step. In the placement process, the first work vessel OS1 is equipped with, in addition to the crane CL, a first rope-shaped body R1 connected to the other end of the parallel wire PW, and a first winch W1 (winch) for winding up the first rope-shaped body R1, as shown in Figures 5 and 6. The first rope-like body R1 preferably has a lower bending rigidity (more flexible) than the parallel wires PW, for example. The first rope-like body R1 preferably has a bending rigidity equivalent to that of the suspension wires HW. The first winch W1 preferably has a function of managing, for example, the winding amount and payout amount of the first rope R1 and the tension acting on the first rope R1. The first work vessel OS1 may be equipped with the first rope R1 and the first winch W1 at the time of the foundation connection process. Furthermore, when the placing step is performed, the first work vessel OS1 is preferably connected to the anchor wire AW. The procedure of the work carried out by the first work vessel OS1 during the placement process will be described below. That is, the arrangement step includes the following first to third arrangement steps.

[0023] (1st placement process) The first arrangement step is a step of connecting the first rope-like body R1 to the other end of the parallel wire PW. That is, for example, first, one end of the parallel wire PW is connected to the foundation F of the seabed SB, and then the other end of the parallel wire PW is pulled upward by a crane CL as shown in Fig. 4. This causes tension to act on the parallel wire PW. Next, as shown in Fig. 5, the first work vessel OS1 is moved away from the foundation F to which one end of the parallel wire PW is connected. In the example shown in Fig. 5, the first work vessel OS1 is moved in the first direction D1. This causes the parallel wire PW to tilt while maintaining a state in which tension is applied. Then, the first rope-like body R1 is let out from the first winch W1 and connected to the other end of the parallel wires PW. More specifically, the first rope-like body R1 is connected to the hanging wire HW connected to the other end of the parallel wires PW, thereby connecting the other end of the parallel wires PW to the first rope-like body R1.

[0024] After the connection between the parallel wires PW and the first rope-like body R1 is completed, the first rope-like body R1 is wound up by the first winch W1 while the other end of the parallel wires PW is pulled upward by the crane CL. This eliminates slack in the first rope-like body R1, allowing the first rope-like body R1 to apply tension to the parallel wires PW. After that, the crane wire CW is loosened. Then, as shown in FIG. 6, the crane wire CW is detached from the parallel wires PW. This allows the parallel wires PW to be laid on the seabed SB during the placement process by pulling the other end of the parallel wires PW with the first winch W1 possessed by the first work vessel OS1, while maintaining the tension acting on the parallel wires PW.

[0025] (Second placement process) FIG. 7 is a first schematic diagram illustrating the second arrangement step. FIG. 8 is a second schematic diagram illustrating the second arrangement step. The second arrangement step is a step of laying down the parallel wires PW. In the second arrangement step, the parallel wires PW are laid down while maintaining the tension acting on the parallel wires PW.

[0026] That is, first, with the parallel wire PW connected to the first rope-like body R1, as shown in Figure 7, the first work boat OS1 is moved in the first direction D1 so as to move further away from the foundation F to which one end of the parallel wire PW is connected. The movement of the first work vessel OS1 in the second placement step is carried out while the first winch W1 pays out the first rope R1. That is, in the second placement step, the first work vessel OS1 moves away from the foundation F while the first winch W1 pays out the first rope R1 connected to the other end of the parallel wires PW. This allows the parallel wires PW to be placed so that they lie on the seabed SB while maintaining the tension acting on them as the first work vessel OS1 moves away from the foundation F.

[0027] As the first work vessel OS1 continues to move as described above, the parallel wires PW gradually tilt. Eventually, the parallel wires PW become aligned in a substantially horizontal direction, as shown in Fig. 8. In this embodiment, the substantially horizontal direction refers to a direction within a range of about ±10° with respect to the horizontal direction at the construction site of the offshore wind turbine system 1. After the parallel wires PW are aligned in a substantially horizontal direction, the process proceeds to the third arrangement step.

[0028] (Third placement process) FIG. 9 is a first schematic diagram illustrating the third arrangement step. FIG. 10 is a second schematic diagram illustrating the third arrangement step. The third placement step is a step of landing the parallel wires PW on the seabed SB. In the third placement step, after the parallel wires PW are aligned in a substantially horizontal direction in the second placement step, the first work vessel OS1 approaches the foundation F, thereby landing the parallel wires PW so that they lie flat on the seabed SB. That is, first, after the parallel wires PW are aligned in a substantially horizontal direction by the second placement step, the first work vessel OS1 is moved closer to the foundation F without winding or unwinding the first rope-like body R1 with the first winch W1. That is, the first work vessel OS1, which has been moved away from the foundation F, is moved back in its original direction. This causes the parallel wires PW to land on the seabed SB, as shown in FIG. 9. After the parallel wires PW reach the seabed SB, the first winch W1 reels in the first rope-like body R1, positioning the first work vessel OS1 directly above the connection between the first rope-like body R1 and the lifting wire HW, as shown in Figure 10. The underwater robot ROV then releases the connection between the first rope-like body R1 and the lifting wire HW.

[0029] FIG. 11 is a top view of a plurality of parallel wires PW laid out on the seabed SB in the laying step. FIG. 12 is a view of FIG. 11 viewed from the horizontal direction. In the placement process, the parallel wires PW are placed so as to lie on the seabed SB through the above-mentioned processes. The parallel wires PW wait in the state placed so as to lie on the seabed SB through the placement process until the offshore structure 20 arrives. That is, after the offshore structure 20 is transported to the installation location of the parallel wires PW, the parallel wires PW are pulled up from the seabed SB. Then, the other end of the parallel wires PW is connected to the offshore structure 20. In this way, the offshore structure 20 is installed on the ocean.

[0030] As described above, in this embodiment, eight parallel wires PW are provided for one offshore structure 20. Therefore, when one offshore structure 20 is placed on the ocean, the above-described placement process is performed eight times, so that eight parallel wires PW are placed lying on the seabed SB. At this time, the directions in which the eight parallel wires PW extend are as follows, as shown in FIGS. 11 and 12, for example. In FIG. 11, the first side surface 10Sa, the second side surface 10Sb, and the third side surface 10Sc after the offshore structure 20 has been installed are each shown by imaginary lines. Of the four parallel wires PW corresponding to both ends of the first side face 10Sa, one wire from each end of the first side face 10Sa (two wires in total) are arranged to extend in the first direction D1. Of the four parallel wires PW corresponding to both ends of the second side face 10Sb, one of the two wires that also correspond to the ends of the first side face 10Sa and one of the two wires that do not correspond to the ends of the first side face 10Sa (also correspond to the ends of the third side face 10Sc) (two wires in total) are arranged to extend in the second direction D2. Of the four parallel wires PW corresponding to both ends of the third side surface 10Sc, one of the two that also correspond to the ends of the second side surface 10Sb, and one of the two that do not correspond to the ends of the second side surface 10Sb (also correspond to the ends of the fourth side surface 10Sd) (two in total) are arranged to extend in the third direction D3. Of the four parallel wires PW corresponding to both ends of the fourth side surface 10Sd, one of the two that also correspond to the ends of the third side surface 10Sc and one of the two that also correspond to the ends of the first side surface 10Sa (two in total) are arranged to extend in the fourth direction D4. It is preferable that a buoy B be connected to the suspension wires HW connected to the parallel wires PW arranged as described above, for example, as shown in Fig. 12. It is preferable that the buoy B be attached to the suspension wires HW after the arrangement step is completed, for example. The direction in which the parallel wires PW laid on the seabed SB extend is not limited to the above, and may be determined in any direction as appropriate depending on the ship used in the placement process and the procedure for carrying out the placement process.

[0031] Before proceeding to the connection process described next, it is preferable to set up a temporary anchor TA for mooring the marine structure 20 transported to the installation site, as shown in Fig. 12. The temporary anchor TA is set up, for example, by a towing vessel TB that transports the marine structure 20 on the ocean. The temporary anchor TA is set up before the marine structure 20 is transported by the towing vessel TB. By providing the temporary anchors TA, it is preferable that the temporary anchors TA can maintain the position of the marine structure 20 when performing the connection step. Note that the temporary anchors TA are preferably installed at locations far enough away from the parallel wires PW that they do not interfere with the pulling up of the parallel wires PW in the connection step, for example.

[0032] Anchor lines AL of a length necessary to maintain the position of the marine structure 20 on the sea are connected to the temporary anchors TA. The anchor lines AL are made of, for example, steel wire. It is preferable that the number of temporary anchors TA and anchor lines AL to be installed be determined after appropriate consideration.

[0033] (Connection process) The connecting step is a step of connecting the other end of the parallel wire PW to the offshore structure 20. That is, in the connecting step, first, the parallel wire PW that has been arranged so as to be laid on the seabed SB in the arranging step is pulled up. Then, the other end of the parallel wire PW is connected to the offshore structure 20. In the connecting step, similar to the arranging step, the other end of the parallel wire PW is connected to the offshore offshore structure 20 while suppressing the occurrence of bending compressive stress in the parallel wire PW. That is, in the connecting step, the other end of the parallel wire PW is connected to the offshore offshore structure 20 while maintaining the tension acting on the parallel wire PW.

[0034] FIG. 13 is a schematic diagram showing a first step of pulling up the parallel wires PW. FIG. 14 is a schematic diagram showing a second step of pulling up the parallel wires PW. In the connection process, for example, the second work vessel OS2 (work vessel) shown in Figures 13 and 14 is used. In this embodiment, it is preferable that the work by the second work vessel OS2 is carried out while measuring the position of the second work vessel OS2 with a GPS device (not shown). Note that the following work carried out by the second work vessel OS2 may also be carried out by the first work vessel OS1. In this case, the first work vessel OS1 may be equipped with the various components described below as being equipped on the second work vessel OS2. The second work vessel OS2 is equipped with a second rope-like body R2 for pulling up the parallel wires PW laid on the seabed SB, and a second winch W2 (winch) for winding up the second rope-like body R2. The second winch W2 preferably has the function of managing, for example, the winding amount and payout amount of the second rope-like body R2, and the tension acting on the second rope-like body R2. Any vessel, such as an SEP or a floating crane, may be used for the second work vessel OS2 as long as it has the above-mentioned configurations.

[0035] During the connecting step, it is preferable to connect a buoy B to the anchor line AL as shown in Fig. 13. In this way, when the temporary anchor TA is installed, the buoy B floats on the sea surface. The buoy B can hold the upper end of the anchor line AL on the sea surface. This makes it easier to connect the marine structure 20 and the anchor line AL.

[0036] Furthermore, when connecting the marine structure 20 and the parallel wires PW, that is, when the marine structure 20 is held by the temporary anchors TA, it is preferable to provide ballast water inside the marine structure 20. This preferably makes the marine structure 20 submerged in water more than in its installed state, making it easier to connect the marine structure 20 and the parallel wires PW.

[0037] Furthermore, depending on the size of the second work vessel OS2, multiple parallel wires PW laid on the seabed SB may be pulled up simultaneously. In this case, the second work vessel OS2 may be equipped with multiple second rope-like bodies R2 and multiple second winches W2. In this embodiment, the second work vessel OS2 is equipped with, for example, four combinations of second rope-like bodies R2 and second winches W2. The procedure of the work carried out by the second work vessel OS2 during the connection process will be described below.

[0038] (Parallel wire pulling process) First, the parallel wires PW are pulled up by the second work vessel OS2. The pulling up of the parallel wires PW is carried out in the following first to third steps.

[0039] (First step: pulling up the parallel wires) As a first step in pulling up the parallel wires PW, the second work vessel OS2 is positioned directly above the hoisting wires HW connected to the other ends of the parallel wires PW, as shown in Figure 13. The position of the hoisting wires HW is confirmed, for example, by an underwater robot ROV. In this embodiment, first, the second work vessel OS2 is positioned directly above the hoisting wire HW connected to the other end of the parallel wire PW arranged to extend in the first direction D1. Note that when the first step is performed, it is preferable that the buoy B be removed.

[0040] (Second process: pulling up the parallel wires) In the second step of pulling up the parallel wires PW, first, the second rope-shaped body R2 is let out from the second work vessel OS2 toward the seabed SB. Then, as shown in Figure 14, the underwater robot ROV connects the second rope-shaped body R2 to the lifting wires HW. In this way, by connecting the parallel wires PW and the second rope-like body R2 via the hanging wire HW, the parallel wires PW can be pulled up by winding up the second rope-like body R2.

[0041] (The third step is to pull up the parallel wires) FIG. 15 is a first schematic diagram showing the third step of pulling up the parallel wire PW. FIG. 16 is a second schematic diagram showing the third step of pulling up the parallel wire PW. FIG. 17 is a third schematic diagram showing the third step of pulling up the parallel wire PW. In the third step of pulling up the parallel wire PW, the second rope-shaped body R2 is wound up. This pulls up the parallel wire PW from the seabed SB. While the parallel wire PW is being pulled up from the seabed SB, tension is applied to the parallel wire PW to prevent bending compressive stress from occurring in the parallel wire PW. To make it easier to apply tension to the parallel wires PW, in the third step, before starting to reel in the second rope-like body R2 with the second winch W2, the second work vessel OS2 is moved away from the foundation F to which one end of the parallel wires PW is connected, as shown in FIG. 15. In the example shown in FIG. 15, the second work vessel OS2 is moved in the first direction D1. This allows the second rope-like body R2 to apply tension to the parallel wires PW without reeling in the second rope-like body R2. Furthermore, by moving the second work vessel OS2 in this manner, the parallel wires PW are moved away from the seabed SB before starting to reel in the second rope-like body R2. After the parallel wires PW have been separated from the seabed SB as described above, the second winch W2 begins to wind up the second rope-shaped body R2. Then, as shown in Figures 16 and 17, as the parallel wires PW are pulled up, the second work vessel OS2 is moved closer to the foundation F to which one end of the parallel wires PW is connected. In this way, in the connecting process, the parallel wires PW are pulled up while maintaining the tension acting on the parallel wires PW. In the connecting step, as described above, the second winch W2 of the work vessel winds up the second rope-shaped body R2 connected to the other end of the parallel wire PW, thereby pulling up the parallel wire PW while maintaining the tension acting on the parallel wire PW. Then, the other end of the parallel wire PW is connected to the marine structure 20 by a step described later.

[0042] (Process of connecting parallel wires to marine structures) After the parallel wires PW are pulled up by the second work vessel OS2, the pulled-up parallel wires PW are connected to the offshore structure 20. When connecting the parallel wires PW to the offshore structure 20, it is preferable that the second work vessel OS2 is connected to the anchor wire AW and its position is fixed. The connection of the parallel wires PW to the offshore structure 20 is performed by steps 1 to 3 described below.

[0043] (First step: connecting the parallel wire to the marine structure) FIG. 18 is a schematic diagram showing the work of bringing the marine structure 20 closer to the second work vessel OS2 by the towing vessel TB as the first step of connecting the parallel wires PW and the marine structure 20. FIG. 19 is a view of FIG. 18 viewed from the horizontal direction. FIG. 20 is a schematic diagram showing the work of aligning the offshore structure 20 with the second work vessel OS2 as the first step in connecting the parallel wires PW and the offshore structure 20. As shown in FIG. FIG. 21 is a view of FIG. 20 viewed from the horizontal direction. In the first step of connecting the parallel wires PW and the marine structure 20, the marine structure 20 is brought close to the pulled-up parallel wires PW. The marine structure 20 is transported to the installation site at any timing during the step of pulling up the parallel wires PW. The marine structure 20 is connected to the temporary anchor TA via the anchor line AL when the first step of connecting the parallel wires PW and the marine structure 20 is performed. In the first step, after the parallel wires PW are pulled up, the marine structure 20 connected to the temporary anchor TA is moved by the towing vessel TB, as shown in Figures 18 and 19. This moves the marine structure 20 to a position where precise alignment of the parallel wires PW and the marine structure 20 is possible. The marine structure 20 is connected to a towing line TW provided on the towing vessel TB, and is moved on the sea by the towing vessel TB pulling the towing line TW. After the movement in the first step is completed, the tow rope TW is removed from the marine structure 20. Then, before connecting the parallel wires PW to the marine structure 20, the marine structure 20 and the second work vessel OS2 are connected by a mooring rope MR, as shown in Figures 20 and 21. This preferably temporarily holds the marine structure 20 and the second work vessel OS2 in place.

[0044] (Second step: connecting the parallel wire to the marine structure) FIG. 22 is a schematic diagram showing a second step of connecting the parallel wires PW and the marine structure 20. As shown in FIG. FIG. 23 is a view of FIG. 22 viewed from the horizontal direction. As a second step in connecting the parallel wires PW and the offshore structure 20, the parallel wires PW are aligned with the offshore structure 20. Specifically, the other ends of the parallel wires PW are pulled toward the offshore structure 20 to align the parallel wires PW with the offshore structure 20. At this time, as shown in Figures 22 and 23, the offshore structure 20 is held by the anchor line AL, thereby preventing the offshore structure 20 from colliding with the second work vessel OS2. In the second step of connecting the parallel wires PW and the marine structure 20, one of the following two examples is appropriately selected and applied.

[0045] (First example of the second step of connecting the parallel wire to the marine structure) In a first example of the second step of connecting the parallel wires PW to the offshore structure 20, a third rope-like body R3 is used in addition to the second rope-like body R2, as shown in FIG. 23 . The third rope-like body R3 has a configuration similar to that of the second rope-like body R2 and is used to support the second rope-like body R2. The third rope-like body R3 is connected to the other end of the parallel wires PW. More specifically, the third rope-like body R3 is connected to the other end of the parallel wires PW via a suspension wire HW. When connecting the parallel wires PW to the offshore structure 20 according to the first example, a suspension wire HW is provided in advance at the other end of the parallel wires PW to connect the third rope-like body R3. Then, the suspension wire HW provided at the other end of the parallel wires PW and the third rope-like body R3 are connected, for example, by an underwater robot (ROV) after the parallel wires PW are pulled up from the seabed (SB) as described above. Hereinafter, the connection between the parallel wires PW and the third rope-like body R3 via the suspension wires HW will simply be referred to as the connection between the parallel wires PW and the third rope-like body R3.

[0046] When the second step according to the first example is performed, first, the second rope-like body R2 is engaged with the marine structure 20. For this purpose, it is preferable that the marine structure 20 be provided with a first engagement portion E1 that enables engagement with the second rope-like body R2. The first engagement portion E1 is, for example, a ring-shaped member. A plurality of first engagement portions E1 are provided in the vertical direction. Engagement of the first engagement portion E1 with the second rope-like body R2 means that the second rope-like body R2 is inserted into the first engagement portion E1. Next, the third rope R3 is connected to the parallel wire PW without engaging with any other components. The third rope R3 connected to the other end of the parallel wire PW in this manner is wound up by the third winch W3 (winch) provided on the second work vessel OS2. After the third rope R3 is connected to the other end of the parallel wire PW, the second rope R2 and the third rope R3 are wound up. As the second rope R2 is wound up by the second winch W2, the other end of the parallel wire PW to which the second rope R2 is connected naturally approaches the offshore structure 20. As the third rope R3 is wound up by the third winch W3, it can assist the second rope R2 in pulling the other end of the parallel wire PW and the offshore structure 20 together. That is, in the first example, in addition to the second winch W2 winding up the second rope-like body R2 connected to the other end of the parallel wire PW, the third winch W3 winds up the third rope-like body R3 connected to the other end of the parallel wire PW, thereby pulling the other end of the parallel wire PW toward the marine structure 20 while maintaining the tension acting on the parallel wire PW.

[0047] (Second example of the second step of connecting the parallel wire to the marine structure) The second example of the second step of connecting the parallel wires PW to the offshore structure 20 differs from the first example in that the third rope-like body R3 is not used. That is, in the second step of the second example, the second winch W2 winds up the second rope-like body R2, thereby pulling the other end of the parallel wires PW to the offshore structure 20 and connecting it.

[0048] (The third step is to connect the parallel wires to the marine structure.) FIG. 24 is a schematic diagram showing a third step of connecting the parallel wires PW and the marine structure 20. As shown in FIG. FIG. 25 is a view of FIG. 24 viewed from the horizontal direction. As a third step of connecting the parallel wires PW to the offshore structure 20, as shown in FIGS. 24 and 25 , the other ends of the pulled-up parallel wires PW are connected to the offshore structure 20. The other ends of the parallel wires PW are engaged with, for example, second engagement portions E2 provided on the offshore structure 20. The second engagement portions E2 are formed, for example, in a U-shape or an L-shape. As a result, the other ends of the parallel wires PW are connected to the offshore structure 20 by hooking the other ends of the parallel wires PW onto the second engagement portions E2. For this reason, it is preferable that the other ends of the parallel wires PW be formed, for example, in a hook shape so that they can be engaged with the second engagement portions E2. The other ends of the parallel wires PW are engaged with the second engagement portion E2 by, for example, an underwater robot ROV.

[0049] Through the above-described arranging step and connecting step, the four parallel wires PW arranged to extend in the first direction D1 are connected to the marine structure 20. At this time, the marine structure 20 is held by the four parallel wires PW and the anchor line AL, as shown in Figures 24 and 25. Therefore, the position of the marine structure 20 is temporarily fixed by the above-mentioned placing step and connecting step.

[0050] FIG. 26 is a schematic diagram showing a step of pulling up the parallel wires PW extending in the second direction D2. FIG. 27 is a schematic diagram showing a process of connecting the parallel wires PW extending in the second direction D2 to the marine structure 20. FIG. 28 is a schematic diagram showing a step of pulling up the parallel wires PW extending in the third direction D3. FIG. 29 is a schematic diagram showing a process of connecting the parallel wires PW extending in the third direction D3 to the marine structure 20. After the four parallel wires PW are connected to the offshore structure 20 as described above, the remaining parallel wires PW are connected to the offshore structure 20. That is, after the four parallel wires PW are connected to the offshore structure 20, three parallel wires PW arranged to extend in the second direction D2 are connected to the offshore structure 20. Then, two parallel wires PW arranged to extend in the third direction D3 are connected to the offshore structure 20. That is, first, as shown in Fig. 26, the second work vessel OS2 is positioned directly above the hoisting wires HW connected to the other ends of the parallel wires PW arranged to extend in the second direction D2. Then, as shown in Fig. 27, the parallel wires PW are pulled up and connected to the second side surface 10Sb. The anchor line AL connected to the marine structure 20 is removed from the marine structure 20 after the above process is completed. Thereafter, as shown in Fig. 28, the second work vessel OS2 is positioned directly above the lifting wires HW connected to the other ends of the parallel wires PW arranged to extend in the third direction D3. Then, as shown in Fig. 29, the parallel wires PW are pulled up and connected to the third side surface 10Sc. Similarly, the second work vessel OS2 is positioned directly above the lifting wires HW connected to the other ends of the parallel wires PW arranged to extend in the fourth direction D4, and the parallel wires PW are then pulled up and connected to the fourth side surface 10Sd. The parallel wires PW are pulled up and connected to the marine structure 20 in accordance with the above-described steps. Through the above steps, the parallel wires PW and the marine structure 20 are connected to each other.

[0051] FIG. 30 is a schematic diagram of a process for connecting the power transmission cable EW to the marine structure 20. FIG. 31 is a schematic diagram of a process for increasing the buoyancy of the marine structure 20. FIG. 32 shows the marine structure 20 after installation is completed. After the parallel wires PW and the offshore structure 20 have been connected, the power transmission cable EW is connected to the offshore structure 20 as shown in Fig. 30. The power transmission cable EW is connected to the offshore wind turbine 10 which is connected to the offshore structure 20. This makes it possible to transmit electricity generated by the offshore wind turbine 10 to the outside. Then, a pump (not shown) mounted on the marine structure 20 discharges ballast water from inside the marine structure 20. This increases the buoyancy of the marine structure 20. Then, tension is applied to the parallel wires PW of the marine structure 20. As a result, as shown in FIG. 31 , the buoyancy of the marine structure 20 and the tension of the parallel wires PW are balanced, thereby fixing the marine structure 20 on the ocean. Through the above steps, the offshore structure 20 is installed on the ocean, as shown in Figure 32. After that, the offshore wind turbine 10 (not shown in Figure 32) is installed on the offshore structure 20, and the offshore wind turbine system 1 is constructed.

[0052] As described above, according to the parallel wire PW placement method of this embodiment, in the placement step, the parallel wire PW is placed so as to lie on the seabed SB while suppressing the occurrence of bending compressive stress in the parallel wire PW, one end of which is connected to the foundation F fixed to the ground of the seabed SB. This makes it possible to suppress bending and damage to the parallel wire PW when placing the parallel wire PW on the seabed SB. Furthermore, by placing the parallel wire PW so as to lie on the seabed SB, the parallel wire PW can be made to wait on the seabed SB with one end of the parallel wire PW connected to the foundation F. Therefore, the timing for connecting the other end of the parallel wire PW to the offshore structure 20 can be determined arbitrarily. This makes it easier to connect the offshore structure 20 to the seabed SB using the parallel wire PW.

[0053] In the placing step, the parallel wires PW are placed so as to lie on the seabed SB while maintaining tension acting on the parallel wires PW. This makes it easier to maintain the stretched state of the parallel wires PW when placing the parallel wires PW so as to lie on the seabed SB. This makes it possible to more reliably prevent the parallel wires PW from being bent and damaged.

[0054] In the placement step, the other end of the parallel wire PW is pulled by the first winch W1 of the work vessel, thereby maintaining tension on the parallel wire PW and placing the parallel wire PW so that it lies on the seabed SB. This makes it easier to more reliably maintain the stretched state of the parallel wire PW when placing the parallel wire PW so that it lies on the seabed SB. Therefore, it is possible to more reliably prevent the parallel wire PW from being bent and damaged.

[0055] Furthermore, in the placement step, the first work vessel OS1 moves away from the foundation F while the first winch W1 pays out the first rope-like body R1 connected to the other end of the parallel wire PW, thereby placing the parallel wire PW so that it is laid on the seabed SB while maintaining the tension acting on the parallel wire PW. In this way, the first work vessel OS1 moves away from the foundation F to which one end of the parallel wire PW is connected, so that tension can be applied to the parallel wire PW by the movement of the first work vessel OS1. Furthermore, the first work vessel OS1 moves while the first winch W1 pays out the first rope-like body R1 connected to the other end of the parallel wire PW, so that as the first work vessel OS1 moves away from the foundation F, the parallel wire PW can be laid down while maintaining the tension acting on the parallel wire PW. This more reliably prevents the parallel wire PW from being bent and damaged.

[0056] Furthermore, in the placement process, after the parallel wires PW are aligned in a substantially horizontal direction, the first work vessel OS1 approaches the foundation F, thereby causing the parallel wires PW to land so that they lie flat on the seabed SB. This allows the parallel wires PW to land on the seabed SB while maintaining tension on the parallel wires PW. That is, compared to, for example, when the parallel wires PW are landed by separating the first rope-shaped body R1 from the parallel wires PW, it is possible to prevent the parallel wires PW from being subjected to impact. Therefore, it is possible to more reliably prevent the parallel wires PW from being bent and damaged. Furthermore, it is possible to prevent the first work vessel OS1 from moving away from the foundation F more than necessary. Therefore, the work of placing the parallel wires PW on the seabed SB can be performed efficiently.

[0057] The arrangement method according to the present disclosure further includes a connecting step. In the connecting step, one end of the parallel wire PW connected to the foundation F is connected to the other end of the parallel wire PW on the offshore offshore structure 20 while suppressing the occurrence of bending compressive stress in the parallel wire PW. This makes it possible to moor the offshore offshore structure 20 while suppressing the parallel wire PW from being bent and damaged when connected to the offshore offshore structure 20.

[0058] In the connecting step, the tension acting on the parallel wire PW is maintained while the other end of the parallel wire PW is connected to the offshore structure 20. This makes it possible to moor the offshore structure 20 while more reliably preventing the parallel wire PW from being bent and damaged when the parallel wire PW is connected to the offshore structure 20.

[0059] In the connecting step, the parallel wire PW is pulled up while maintaining the tension acting on the parallel wire PW, which makes it possible to prevent the parallel wire PW from being bent and damaged when the parallel wire PW laid on the seabed SB is pulled up.

[0060] In the connecting step, the second winch W2 of the second work vessel OS2 reels in the second rope-shaped body R2 connected to the other end of the parallel wire PW, thereby pulling up the parallel wire PW while maintaining the tension acting on the parallel wire PW and connecting the other end to the offshore structure 20. This makes it easier to maintain the stretched state of the parallel wire PW when pulling up the parallel wire PW that is laid on the seabed SB. This makes it possible to more reliably prevent the parallel wire PW from being bent and damaged.

[0061] Furthermore, in the connecting step, the second winch W2 possessed by the second work vessel OS2 winds up the second rope-like body R2, thereby pulling the other end of the parallel wire PW to the offshore structure 20 and connecting it. This allows the other end of the parallel wire PW to be efficiently moved toward the offshore structure 20. Furthermore, the other end of the parallel wire PW can be easily aligned with the offshore structure 20. Therefore, the work of connecting the other end of the parallel wire PW to the offshore structure 20 can be efficiently performed.

[0062] Furthermore, in the connecting step, the third winch W3 of the second work vessel OS2 takes up the third rope-shaped body R3 connected to the other end of the parallel wire PW, thereby pulling and connecting the other end of the parallel wire PW to the offshore structure 20 while maintaining the tension acting on the parallel wire PW. This makes it easier to maintain the stretched state of the parallel wire PW when moving the other end of the parallel wire PW toward the offshore structure 20. Therefore, it is possible to more reliably prevent the parallel wire PW from being bent and damaged.

[0063] The technical scope of the present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure. For example, the method for arranging the parallel wires PW according to this embodiment may be applied to the construction of any structure using the parallel wires PW. That is, the method for arranging the parallel wires PW according to this embodiment may be used for the construction of structures other than floating structures. Furthermore, the parallel wires PW are not limited to those having the above-mentioned structure, and those having any structure may be appropriately selected and used. Furthermore, in the above-described arrangement step, the first work vessel OS1 is moved while the first winch W1 is letting out the first rope-like body R1, but this is not a limitation. For example, the arrangement step may be performed by hooking the first rope-like body R1 onto a bollard (not shown) provided on the first work vessel OS1 to apply tension to the parallel wires PW, and then unwinding the first rope-like body R1 as the first work vessel OS1 moves.

[0064] In addition, within the scope of the present disclosure, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modified examples may be combined as appropriate.

[0065] (Addendum) The method for arranging parallel wires according to the embodiment can be understood, for example, as follows. <1> An offshore wind turbine system according to one aspect of the present disclosure is characterized by including an arrangement process of arranging parallel wires, one end of which is connected to a foundation fixed to the ground on the seabed, so that the parallel wires are laid flat on the seabed while suppressing the generation of bending compressive stress in the parallel wires.

[0066] According to the placement method of the present disclosure, in the placement step, the parallel wires, one end of which is connected to a foundation fixed to the seabed, are placed so as to lie flat on the seabed while suppressing the occurrence of bending compressive stress in the parallel wires. This makes it possible to suppress bending and damage to the parallel wires when placing them on the seabed. Furthermore, by placing the parallel wires so as to lie flat on the seabed, the parallel wires can be left waiting on the seabed while one end of the parallel wire remains connected to the foundation. This makes it possible to arbitrarily determine the timing for connecting the other end of the parallel wire to the offshore structure. This makes it easier to connect the offshore structure to the seabed using the parallel wires.

[0067] <2> the above <1> In the parallel wire arrangement method according to the above, a configuration may be adopted in which, in the arrangement step, the parallel wires are arranged so as to lie on the seabed while maintaining tension acting on the parallel wires.

[0068] In the disposing step, the parallel wires are disposed so as to lie on the seabed while maintaining tension acting on the parallel wires. This makes it easier to maintain the parallel wires in a stretched state when disposing the parallel wires so as to lie on the seabed. This makes it possible to more reliably prevent the parallel wires from being bent and damaged.

[0069] <3> the above <2> In the parallel wire placement method according to the above, a configuration may be adopted in which, in the placement step, the parallel wires are placed so as to lie on the seabed while maintaining the tension by pulling the other ends of the parallel wires with a winch carried by a work vessel.

[0070] In the placement step, the other ends of the parallel wires are pulled by a winch on the work vessel, thereby maintaining tension on the parallel wires and placing the parallel wires so that they lie flat on the seabed. This makes it easier to more reliably maintain the stretched state of the parallel wires when placing them so that they lie flat on the seabed. This makes it even more reliably possible to prevent the parallel wires from being bent and damaged.

[0071] <4> the above <3> In the parallel wire placement method according to the above, a configuration may be adopted in which, in the placement step, the winch unwinds the first rope-like body connected to the other end while the work vessel moves away from the foundation, thereby placing the parallel wires so that they lie flat on the seabed while maintaining the tension.

[0072] Furthermore, in the placement step, the work vessel moves away from the foundation while the winch pays out the first rope-like member connected to the other end of the parallel wires, thereby placing the parallel wires so that they are laid on the seabed while maintaining the tension acting on them. In this way, the work vessel moves away from the foundation to which one end of the parallel wires is connected, so that tension can be applied to the parallel wires by the movement of the work vessel. Furthermore, the work vessel moves while the winch pays out the first rope-like member connected to the other end of the parallel wires, so that the parallel wires can be laid down as the work vessel moves away from the foundation while maintaining the tension acting on them. This makes it possible to more reliably prevent the parallel wires from being bent and damaged.

[0073] <5> the above <3> or <4> In the parallel wire placement method according to the above, a configuration may be adopted in which, in the placement step, after the parallel wires are aligned in a substantially horizontal direction, the work vessel approaches the foundation, causing the parallel wires to land so as to lie flat on the seabed.

[0074] Furthermore, in the placement process, after the parallel wires are aligned in a substantially horizontal direction, the work vessel approaches the foundation, causing the parallel wires to land so that they lie flat on the seabed. This allows the parallel wires to land on the seabed while maintaining tension on the parallel wires. That is, compared to, for example, when the parallel wires are landed by separating the first rope-shaped body from the parallel wires, it is possible to prevent the parallel wires from being subjected to impact. Therefore, it is possible to more reliably prevent the parallel wires from being bent and damaged. Furthermore, it is possible to prevent the work vessel from moving away from the foundation more than necessary. Therefore, the work of placing the parallel wires on the seabed can be performed efficiently.

[0075] <6> the above <1> from <5> In the parallel wire arrangement method according to any one of the above aspects, a configuration may be adopted that further includes a connecting step of connecting the other ends of the parallel wires to an offshore marine structure while suppressing the occurrence of bending compressive stress in the parallel wires.

[0076] The arrangement method according to the present disclosure further includes a connecting step in which one end of each of the parallel wires connected to the foundation is connected to the offshore offshore structure while preventing the parallel wires from being subjected to bending compressive stress. This allows the offshore structure to be moored offshore while preventing the parallel wires from being bent and damaged when connected to the offshore offshore structure.

[0077] <7> the above <6> In the parallel wire arrangement method according to the above aspect, a configuration may be adopted in which, in the connecting step, the other ends of the parallel wires are connected to the marine structure while maintaining tension acting on the parallel wires.

[0078] In the connecting step, the other ends of the parallel wires are connected to the offshore structure while maintaining tension on the parallel wires, thereby more reliably preventing the parallel wires from being bent and damaged when connected to the offshore structure, and mooring the offshore structure.

[0079] <8> the above <7> In the parallel wire arrangement method according to the above aspect, a configuration may be adopted in which, in the connecting step, the parallel wires are pulled up while maintaining the tension.

[0080] In the connecting step, the parallel wires are pulled up while maintaining tension on the parallel wires, which makes it possible to prevent the parallel wires from being bent and damaged when the parallel wires are pulled up while laid on the seabed.

[0081] <9> the above <7> or <8> In the parallel wire arrangement method according to the above, a configuration may be adopted in which, in the connection step, a winch carried by a work vessel winds up the second rope-shaped body connected to the other end, thereby pulling up the parallel wire while maintaining the tension and connecting the other end to the marine structure.

[0082] In the connecting step, a winch on the work vessel reels in the second rope-shaped member connected to the other end of the parallel wire, thereby maintaining tension on the parallel wire while pulling it up and connecting the other end to the marine structure. This makes it easier to maintain the parallel wire in a stretched state when pulling up the parallel wire that has been laid on the seabed. This more reliably prevents the parallel wire from being bent and damaged.

[0083] <10> the above <9> In the parallel wire arrangement method according to the above, a configuration may be adopted in which the winch winds up the second rope-like body in the connecting step, thereby pulling the other end to the marine structure and connecting it.

[0084] In the connecting step, a winch on the work vessel winds up the second rope-like body, thereby pulling the other end of the parallel wire to the offshore structure and connecting it. This allows the other end of the parallel wire to be efficiently moved toward the offshore structure. Also, the other end of the parallel wire can be easily aligned with the offshore structure. Therefore, the work of connecting the other end of the parallel wire to the offshore structure can be efficiently performed.

[0085] <11> the above <9> or <10> In the parallel wire arrangement method according to the present invention, a configuration may be adopted in which, in the connection step, the winch winds up the third rope-like body connected to the other end, thereby pulling and connecting the other end to the marine structure while maintaining the tension.

[0086] In the connecting step, a winch on the work vessel winds up the third rope-shaped body connected to the other end of the parallel wire, thereby maintaining tension on the parallel wire and pulling the other end of the parallel wire to the offshore structure for connection. This makes it easier to maintain the stretched state of the parallel wire when the other end of the parallel wire is moved toward the offshore structure. This more reliably prevents the parallel wire from being bent and damaged. [Explanation of symbols]

[0087] 1 Offshore wind turbine system 10 Offshore wind turbines 10Sa 1st side 10Sb 2nd side 10Sc 3rd aspect 20 Marine structures 21 Box girder 22 Connecting member AL Anchor Line AW Anchor Wire B Buoy CL Crane CW Crane Wire D1 1st direction D2 2nd direction D3 Third direction D4 4th direction E1 1st engagement part E2 Second engagement part EW power transmission cable F Basics Hardware Wire MR Mooring Rope OS1 No. 1 Workboat OS2 No. 2 Workboat PW Parallel wire PWc coating material PWs strand R1 First plexiform body R2 Second rod-like body R3 Third plexus ROV Underwater Robot SB Undersea TA Temporary Anchor TB Towing Vessel TW tow rope W1 No. 1 winch W2 No. 2 winch W3 3rd winch

Claims

1. an arrangement step of arranging parallel wires, one ends of which are connected to a foundation fixed to the ground of the seabed, so as to lay the parallel wires on the seabed while suppressing the occurrence of bending compressive stress in the parallel wires; A parallel wire arrangement method comprising:

2. In the placing step, the parallel wires are placed so as to lie on the seabed while maintaining tension acting on the parallel wires.

2. The parallel wire arrangement method according to claim 1, wherein:

3. In the placing step, the parallel wires are placed so as to lie on the seabed while maintaining the tension by pulling the other end of the parallel wires with a winch provided on the work vessel.

3. The parallel wire arrangement method according to claim 2.

4. In the placing step, the work vessel moves away from the foundation while the winch pays out the first rope connected to the other end side, thereby placing the parallel wires so as to lay them on the seabed while maintaining the tension.

4. The parallel wire arrangement method according to claim 3.

5. 5. The parallel wire arrangement method according to claim 4, wherein, in the arrangement step, after the parallel wires are aligned in a substantially horizontal direction, the work vessel approaches the foundation, thereby causing the parallel wires to land so as to lie on the seabed.

6. a connecting step of connecting the other end of the parallel wire to an offshore marine structure while suppressing the occurrence of bending compressive stress in the parallel wire; The parallel wire arrangement method according to any one of claims 1 to 5, further comprising:

7. In the connecting step, the other end side is connected to the marine structure while maintaining tension acting on the parallel wires.

7. The parallel wire arrangement method according to claim 6.

8. In the connecting step, the parallel wires are pulled up while maintaining the tension.

8. The parallel wire arrangement method according to claim 7.

9. In the connecting step, a winch on a work vessel winds up the second rope-shaped body connected to the other end, thereby pulling up the parallel wires while maintaining the tension, and connecting the other end to the marine structure.

9. The parallel wire arrangement method according to claim 8.

10. In the connecting step, the winch winds up the second rope-like body, thereby pulling the other end side to the marine structure and connecting it. The parallel wire arrangement method according to claim 9 .

11. In the connecting step, the winch winds up the third rope connected to the other end side, thereby pulling and connecting the other end side to the marine structure while maintaining the tension. The parallel wire arrangement method according to claim 9 .

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