Cable removal method and cable

Abstract

When disconnecting cables from equipment on a floating structure and lowering them into the sea, this design minimizes bending of the cables at their base. [Solution] The cable removal method according to the present invention comprises the steps of: attaching a buoyancy body to a cable laid in the sea and connected to equipment on a floating body; removing the end of the cable connected to the equipment from the equipment; and lowering the cable, from which the end has been removed from the equipment, into the sea until the end is separated from the floating body, wherein the buoyancy body is attached in a position where it does not touch the seabed when the end is lowered until it is separated from the floating body.

Description

Technical Field

[0004] ,

[0005] ,

[0001] The present invention relates to a cable removal method and a cable.

Background Art

[0002] As an invention of a cable laid on the seabed, there is a cable line disclosed in, for example, Patent Document 1. This cable line has an integrated mechanism that bundles at least a part of the longitudinal direction of a plurality of cable cores, and a floating portion that is laid in a floating state in water. Since each cable core can behave independently in water, when connected to a floating facility such as an offshore floating wind power generation facility, it is easy to follow the behavior of the floating facility, and it is possible to reduce the strain change associated with mechanical histories such as bending, distortion, and repeated bending.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above, and aims to suppress bending of the cable at the bottom when the cable connected to equipment on a floating body is removed and lowered into the sea. [Means for solving the problem]

[0007] The cable removal method according to the present invention comprises the steps of: attaching a buoyancy body to a cable laid in the sea and connected to equipment on a floating body; removing the end of the cable connected to the equipment from the equipment; and lowering the cable, from which the end has been removed from the equipment, into the sea until the end is separated from the floating body, wherein the buoyancy body is attached in a position that does not touch the seabed when the end is lowered until it is separated from the floating body.

[0008] In a cable removal method according to one aspect of the present invention, the cable has a bend stiffener attached near the buoyancy body, and the buoyancy body may be attached near the bend stiffener.

[0009] In a cable removal method according to one aspect of the present invention, a cable clamp may be attached to the cable at a position where the end of the cable does not touch the seabed when pulled down until it is separated from the floating body, and the buoyancy body may be attached to a rope connected to the cable clamp.

[0010] The cable according to the present invention is a cable laid in the sea and connected to equipment on a floating body, wherein a buoyancy body is attached to the end connected to the equipment at a position where it does not touch the seabed when the end is detached and pulled down until it is separated from the floating body. [Effects of the Invention]

[0011] According to the present invention, when removing a cable connected to equipment on a floating structure and lowering it into the sea, it is possible to suppress the bending of the cable at the point where it is resting on the seabed. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is an external view of an offshore platform according to an embodiment. [Figure 2] Figure 2 is a schematic diagram of the vicinity of the tower of the offshore platform according to this embodiment. [Figure 3] Figure 3 is a schematic diagram of the floating body according to the embodiment, viewed from the side. [Figure 4] Figure 4 is a schematic diagram of the inside of the junction box according to the embodiment. [Figure 5A] Figure 5A shows the power cable junction box with the door open. [Figure 5B] Figure 5B is a side view of the equipment direct connection terminal housed in the power cable junction box. [Figure 6] Figure 6 is a schematic diagram showing the inside of the junction box before the array cable is removed. [Figure 7] Figure 7 is a schematic diagram showing the state after the power lines and optical cables have been removed. [Figure 8] Figure 8 is a schematic diagram showing the state after waterproofing treatment has been applied to power lines and optical cables. [Figure 9] Figure 9 is a schematic diagram showing the array cable with buoyancy devices attached. [Figure 10] Figure 10 is a schematic diagram showing the state in which the anchoring section is lifted. [Figure 11]FIG. 11 is a schematic diagram showing a state in which a waterproof pipe and a waterproof treatment portion are housed inside a protective pipe. [Figure 12] FIG. 12 is a schematic diagram showing a state in which the protective pipe is suspended. [Figure 13] FIG. 13 is a diagram showing the result of simulation calculation of the shape of a riser cable. [Figure 14] FIG . 14 is a diagram showing the result of simulation calculation of the shape of a riser cable. [Figure 15] FIG. 15 is a diagram showing the result of simulation calculation of the shape of a riser cable. [Figure 16] FIG. 16 is a diagram showing the result of simulation calculation of the shape of a riser cable. [Figure 17] FIG. 17 is a diagram showing the result of simulation calculation of the shape of a riser cable. [Figure 18] FIG. 18 is a diagram showing the result of simulation calculation of the shape of a riser cable. [Figure 19] FIG. 19 is a diagram showing the result of simulation calculation of the shape of a riser cable. [Figure 20] FIG. 20 is a schematic diagram of a buoyancy body according to a modified example.

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited by the embodiments described below. In the description of the drawings, the same or corresponding elements are appropriately given the same reference numerals. Further, it should be noted that the drawings are schematic, and the dimensional relationships of each element may be different from the actual ones. There may also be portions where the dimensional relationships and ratios between the drawings are different from each other.

[0014] Figure 1 is an external view of offshore platform 1, which generates wind power offshore. Offshore platform 1 is a tension-leg platform called a TLP (Tension Leg Platform). Offshore platform 1 consists of a floating body 11, a tower 12, a nacelle 13, a rotor 14, blades 14a, tendons 15, and a foundation 16. Offshore platform 1 is moored by a tendon 15 connecting the floating body 11, which is forcibly partially submerged, to a foundation 16 installed on the seabed, and utilizing the tension force generated by buoyancy. A nacelle 13 is provided on top of the tower 12, which is attached to the floating body 11. The nacelle 13 supports a main shaft (not shown), and a rotor 14 with blades 14a is attached to this main shaft. A generator (not shown) is housed inside the nacelle 13, and the main shaft of the rotor 14 is connected to the rotating shaft of the generator via a speed increaser. Furthermore, the nacelle 13 houses power equipment for supplying electricity generated by the generator to the array cable 2, as well as wind direction and speed meters, and computer equipment for communicating with onshore monitoring devices that monitor the offshore platform 1. The array cable 2 is laid underwater and transmits electricity generated by the generator to the substation. The structure of the array cable 2 is, for example, the same as the power cable disclosed in Japanese Patent Publication No. 2017-216170. However, the structure of the array cable 2 is not limited to the structure disclosed in Japanese Patent Publication No. 2017-216170, and may have other structures.

[0015] Figure 2 is a schematic diagram showing a plan view of the vicinity of the tower 12 of the offshore platform 1. A winch 20, multiple pulleys 21, and junction boxes 30A and 30B are installed near the tower 12, which is mounted on the floating body 11. Junction boxes 30A and 30B are rooms through which the array cable 2 and the power cable connected to the power equipment in the nacelle 13 are connected. The winch 20 is an electric winch that winds up and feeds out the wire rope 22. The wire rope 22 is fed to the top of junction boxes 30A and 30B via the pulleys 21. Note that junction boxes 30A and 30B have the same configuration, so unless it is necessary to distinguish them in the following description, they will be referred to as junction box 30.

[0016] Figure 3 is a schematic diagram of the floating body 11 viewed from the side. Below the junction boxes 30A and 30B, an I-tube 17 is provided to protect the array cable 2. The I-tube 17 is a hollow tube positioned vertically along the floating body 11, protecting the array cable 2 as it passes through the hollow section. A bend stiffener 18 restricts the bending of the array cable 2 and is attached to the lower end of the I-tube 17. The array cable 2 passes through the bend stiffener 18 and the hollow section of the I-tube 17, and its ends are fixed inside the junction boxes 30A and 30B.

[0017] Figure 4 is a schematic diagram of the inside of the junction box 30. The junction box 30 comprises a power cable junction box 31, an optical cable junction box 36, a door 33A, a ceiling door 33B, and an adapter 35. Inside the junction box 30, a retaining part 4 is provided at the end of the array cable 2. The retaining part 4 is a component for fixing the end of the array cable 2 inside the junction box 30. Beyond the retaining part 4 of the array cable 2, the optical cable 205 and the three power lines 203 of the array cable 2 are exposed.

[0018] Door 33A is a door for workers to enter and exit the inside of the junction box 30 and is located on the side of the junction box 30. Ceiling door 33B is located on the ceiling of the junction box 30 and opens and closes an opening in the ceiling. The optical cable junction box 36 connects the optical cable 205 to the optical cable connected to the computer equipment inside the nacelle 13 using connectors. The adapter 35 is a component shaped like a hollow cylinder with a flange cut in half. The adapter 35 is positioned around the upper end of the I-tube 17. The adapter 35 is installed between the anchoring part 4 and the floor of the junction box 30 and supports the anchoring part 4 at its upper end, through which the array cable 2 passes.

[0019] The power cable connection box 31 is a box that houses equipment direct connection terminals that connect the power line 203 to the section cable 131 connected to the power equipment in the nacelle 13. The section cable 131 is an example of equipment according to the present invention. Figure 5A shows the power cable connection box 31 in an open state, and Figure 5B is a side view of the equipment direct connection terminals housed in the power cable connection box 31. Equipment direct connection terminals 5A are provided at the end of the power line 203, and equipment direct connection terminals 5B are provided at the end of the section cable 131 connected to the power equipment in the nacelle 13. Equipment direct connection terminals 5A and 5B are housed in the power cable connection box 31 while connected to each other and are supported inside the power cable connection box 31 by brackets 34. Cable cleat 32A supports the three section cables 131, and cable cleat 32B supports the three power lines 203.

[0020] Next, we will explain how to remove the array cable 2 from the offshore platform 1 when servicing the offshore platform 1. Figure 6 is a schematic diagram showing the inside of the junction box 30A before the array cable 2 is removed. In the state before the array cable 2 is removed from the offshore platform 1, the end of the array cable 2 is secured inside the junction box 30A by the anchoring part 4, the power line 203 is connected to the section cable 131 at the power cable junction box 31, and the optical cable 205 is connected to the optical cable junction box 36.

[0021] First, the worker disconnects the power line 203 from the power cable junction box 31 and the optical cable 205 from the optical cable junction box 36. Figure 7 is a schematic diagram showing the state after the power line 203 and optical cable 205 have been disconnected. The worker disconnects the equipment direct connection terminal 5A inside the power cable junction box 31 from the equipment direct connection terminal 5B, exposing the stress cone 57 and terminal 53 attached to the end of the power line 203.

[0022] Next, the workers waterproof the ends of the power line 203 and the optical cable 205. Figure 8 is a schematic diagram showing the state after waterproofing the ends of the power line 203 and the optical cable 205. Specifically, the workers insert the stress cone 57 and terminal 53 into the waterproof pipe 61 and insert the end of the optical cable 205 into the waterproof pipe 63. The waterproof pipes 61 and 63 are hollow cylinders with one end closed and are made of, for example, metal. To prevent seawater from entering the inside of the waterproof pipe 61, the workers waterproof the opening of the waterproof pipe 61 into which the stress cone 57 and terminal 53 are inserted to form a waterproof section 62, and to prevent seawater from entering the inside of the waterproof pipe 63, they waterproof the opening of the waterproof pipe 63 into which the end of the optical cable 205 is inserted to form a waterproof section 64.

[0023] Next, the diver DV attaches the buoyancy body 3 to the array cable 2. Figure 9 is a schematic diagram showing the state in which the buoyancy body 3 is attached to the array cable 2. The buoyancy body 3 is, for example, a cylindrical buoy, and is attached to the array cable 2 by sandwiching the array cable 2 with one half of the buoyancy body 3 and the other half. The attachment position of the buoyancy body 3 is preferably near the bend stiffener 18. This position near the bend stiffener 18 is an example of a position where the buoyancy body 3 does not touch the seabed when the end of the array cable 2 is removed and pulled down until it is away from the buoyancy body 11.

[0024] Next, the worker lifts the anchoring section 4 and removes the adapter 35. Figure 10 is a schematic diagram showing the state after the adapter 35 has been removed and the anchoring section 4 has been lifted. Inside the connection box 30A, the worker attaches the lifting beam 23 to the wire rope 22 and connects the lifting beam 23 and the eye bolt 44 with the suspension rope 24. The worker also removes the bolts that secure the anchoring section 4 to the adapter 35 to remove the adapter 35 from the anchoring section 4, and drives the winch 20 to lift the anchoring section 4.

[0025] Next, the worker places the waterproof pipes 61 and 63 and the waterproof sections 62 and 64 inside the protective pipe 71 and secures the protective pipe 71 to the anchoring section 4 with bolts. Figure 11 is a schematic diagram showing the state in which the waterproof pipes 61 and 63 and the waterproof sections 62 and 64 are placed inside the protective pipe 71. In this operation, a temporary support stand 25, which is split in half, is placed between the anchoring section 4 and the I-tube 17, and the suspension beam 23 is lowered to place the anchoring section 4 on the temporary support stand 25. The worker then attaches the protective pipe 71 to the anchoring section 4, which is placed on the temporary support stand 25, with bolts.

[0026] The protective tube 71 is a hollow cylindrical shape with both ends open in the longitudinal direction and is made of metal. The protective tube 71 is equipped with an eye bolt 73. The protective tube 71 is designed to sink under its own weight when it is thrown into the sea. The protective tube 71 may also be made of resin or a cylindrical metal mesh. The protective tube 71 has a flange formed on one end and is open on the other end. The one end of the protective tube 71, into which the waterproof pipe 61, waterproof section 62, waterproof pipe 63, and waterproof section 64 are inserted, has its flange fixed to the anchoring section 4 with a bolt. The other open end of the protective tube 71 is closed by attaching a metal cover 72 with a bolt. The eye bolt 73 is provided at the end of the protective tube 71 on the side where the cover 72 is attached, and the wire rope 22 is tied to it.

[0027] Next, the worker reconnects the wire rope 22 from the suspension beam 23 to the eyebolt 73 to suspend the protective tube 71, and removes the temporary support stand 25. Figure 12 is a schematic diagram showing the protective tube 71 in a suspended state. Here, the outer diameter of the protective tube 71 and the outer diameter of the anchoring part 4 are smaller than the inner diameter of the I-tube 17, so the protective tube 71 can be lowered onto the I-tube 17.

[0028] Next, the worker operates the winch 20 to lower the protective tube 71 and the array cable 2 until the protective tube 71 emerges from the lower end of the I-tube 17 into the sea. When lowering the protective tube 71 and the array cable 2, for example, the bend stiffener 18 is removed before lowering. When lowering the protective tube 71 and the array cable 2, the protective tube 71 may pass over the bend stiffener 18.

[0029] If the buoyancy body 3 is not attached to the array cable 2, as the array cable 2 descends below the floating body 11 and the length of the array cable 2 in the sea increases, the bending radius of the array cable 2 at the seabed may decrease, potentially becoming smaller than the allowable bending radius.

[0030] On the other hand, in this embodiment, a buoyancy body 3 is attached to the array cable 2, and when the array cable 2 is being lowered, the buoyancy of the buoyancy body 3 acts on the array cable 2 while it is submerged in water. As the array cable 2 descends, in addition to the elasticity of the array cable 2, a force acts on the array cable 2 from the buoyancy body 3 toward the water surface. As a result, the buoyancy body 3 descends to a position further away from the initial bottom-settling position where the array cable 2 began to descend, thereby preventing the bending radius of the array cable 2 from decreasing on the seabed.

[0031] The inventors performed simulation calculations to determine the effect of the buoyancy body 3 on the bending radius of the array cable 2. In these simulation calculations, the mass of the array cable 2 was set to 40.61 [kg / m], the underwater weight of the array cable 2 to 0.237 [kN / m], and the outer diameter of the array cable 2 to 0.1429 [m]. The maximum curvature near the bottom, the minimum bending radius near the bottom, and the curvature reduction rate near the bottom were calculated. Table 1 shows the calculation results for the maximum curvature near the bottom, Table 2 shows the calculation results for the minimum bending radius near the bottom, and Table 3 shows the calculation results for the curvature reduction rate near the bottom. The curvature reduction rate is the value obtained by dividing the maximum curvature with the buoyancy body 3 by the maximum curvature without the buoyancy body 3.

[0032] [Table 1]

[0033] [Table 2]

[0034] [Table 3]

[0035] As shown in Tables 1-3, when the buoyancy body 3 is attached to the array cable 2, as the absolute value of the underwater weight of the buoyancy body 3 increases, that is, as the buoyancy of the buoyancy body 3 increases, the maximum curvature near the bottom when the array cable 2 is pulled down becomes smaller, the minimum bending radius increases, and the reduction rate of curvature decreases.

[0036] Figures 13 to 19 show the results of simulation calculations of the shape of the array cable 2. Specifically, Figure 13 shows the state of the array cable 2 before lowering begins. Figures 14 and 15 show the state of the array cable 2 when it is lowered with the underwater weight of the buoyancy body 3 set to -1.3 [kN]. Figures 16 and 17 show the state of the array cable 2 when it is lowered with the underwater weight of the buoyancy body 3 set to -1.5 [kN]. Figures 18 and 19 show the state of the array cable 2 when it is lowered without the buoyancy body 3 attached.

[0037] As shown in Figures 14 to 17, when the buoyancy body 3 is attached to the array cable 2 and the array cable 2 is pulled down, the bending radius of the array cable 2 is larger compared to when the buoyancy body 3 is not attached to the array cable 2, as shown in Figures 18 and 19. Furthermore, comparing Figures 14 and 15 with Figures 16 and 17, it can be seen that increasing the absolute value of the underwater weight of the buoyancy body 3, that is, increasing the buoyancy of the buoyancy body 3, increases the bending radius of the array cable 2.

[0038] [Differentiation] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above and can be implemented in various other forms. For example, the present invention may be implemented by modifying the embodiments described above as follows. The embodiments described above and the following modifications may be combined with each other. The present invention is also included in configurations that appropriately combine the components of each embodiment and each modification described above. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, broader embodiments of the present invention are not limited to the embodiments and modifications described above, and various modifications are possible.

[0039] The buoyancy body 3 attached to the array cable 2 is not limited to a cylindrical shape, but may have other shapes. Figure 20 is a schematic diagram showing a modified example of the buoyancy body 3. The cable clamp 6 is attached to the array cable 2 near the bend stiffener 18. A rope 7 of a predetermined length is attached to the cable clamp 6. The buoyancy body 3A is a spherical buoy and is attached to the rope 7. Even with this buoyancy body 3A, the buoyancy of the buoyancy body 3A acts on the underwater array cable 2, preventing the bending radius of the array cable 2 from decreasing on the seabed when the array cable 2 is detached from the offshore platform 1 and lowered.

[0040] The positions in which the buoyancy bodies 3 and 3A are attached to the array cable 2 are not limited to the vicinity of the bend stiffener 18, but may be other positions. For example, the buoyancy bodies 3 and 3A may be attached to the array cable 2 in a position where they do not touch the seabed while the array cable 2 is being pulled down and the protective tube 71 is being brought out from the lower end of the I-tube 17.

[0041] In this embodiment, the buoyancy body 3 is attached to the array cable 2 after the power lines 203 are removed from the power cable connection box 31 and the optical cable 205 is removed from the optical cable connection box 36. However, the buoyancy body 3 may be attached to the array cable 2 first, and then the power lines 203 are removed from the power cable connection box 31 and the optical cable 205 is removed from the optical cable connection box 36.

[0042] In this embodiment, one buoyancy body 3 is attached to the array cable 2, but multiple buoyancy bodies 3 may be attached to the array cable 2. [Explanation of symbols]

[0043] 1. Offshore platform 2 Array Cables 3, 3A buoyant body 11 Floating bodies 17 I-tube 18 Bend Stiffener

Claims

1. The process of attaching buoyancy devices to cables laid in the sea and connected to equipment on a floating structure, The steps include: removing the end of the cable that is connected to the equipment from the equipment; The process of lowering the cable, whose end has been removed from the equipment, into the sea until the end is separated from the floating body, Equipped with, The buoyancy body is attached in a position where it does not touch the seabed when pulled down until its end is separated from the floating body. How to remove the cable.

2. The cable has a bend stiffener attached near the floating body. The buoyancy body is attached near the bend stiffener. The cable removal method according to claim 1.

3. The cable is fitted with a cable clamp at a position where it does not touch the seabed when the end is pulled down until it is separated from the floating body, and the buoyancy body is attached to a rope connected to the cable clamp. The cable removal method according to claim 1.

4. A cable laid in the sea and connected to equipment on a floating body, wherein a buoyancy body is attached to the end of the cable connected to the equipment at a position where it does not touch the seabed when the end is detached and pulled down until it is separated from the floating body.

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