Method for reducing vortex excitation vibration in multiple riser tubes, multiple riser tube system for reducing vortex excitation vibration, and phase-changing joint and asymmetrical arrangement bracket for multiple riser tube system.

Abstract

To provide a reduction method of vortex-induced vibration (VIV: Vortex-Induced Vibration) reducing the vortex-induced vibration generated in a raiser installed underwater.SOLUTION: A reduction method of vortex-induced vibration generated by a water flow in a plurality of raisers 22 arranged underwater is to reduce the vortex-induced vibration generated in the plurality of raisers 22 by a water flow through cancellation by arranging positions of the plurality of raisers 22 to be different positions, or to reduce the vortex-induced vibration generated in the plurality of raisers 22 by suppressing influence of vortex generated in the plurality of raisers 22 by a water flow.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for reducing vortex-induced vibration (VIV) of multiple riser pipes, a multiple riser pipe system for reducing vortex-induced vibration, a phase change joint for a multiple riser pipe system, and an asymmetric arrangement bracket.

Background Art

[0002] In offshore drilling and offshore production, riser pipes are used to transport fluids between equipment on the seabed and on the sea surface. Due to the influence of ocean currents and the like, Karman vortices are generated on the downstream side of the riser pipe. When the frequency of the Karman vortices approximately matches the natural vibration frequency of the riser pipe, vortex-induced vibration is induced, and the vortex-induced vibration may occur in a direction perpendicular to the flow of the riser pipe, causing fatigue and damage.

[0003] Therefore, an anti-vibration device for a subsea riser pipe is disclosed in which a flag-shaped flow rectifying device is rotatably and slidably fitted around the outer periphery of the subsea riser pipe (Patent Document 1). In addition, a configuration is disclosed in which strakes or fairings that reduce fluid resistance are provided so as to surround the riser pipe continuously extended vertically from a work vessel on the sea surface side toward the seabed side and follow changes in ocean currents (Patent Documents 2 to 4). The strake suppresses the generation of vortex-induced vibration by attaching a spiral-shaped device around the riser pipe and dispersing the phase of the vortex release position in the longitudinal direction. The fairing suppresses vortex release and reduces the generation of vortex-induced vibration by attaching a device having an airfoil cross-sectional shape around the riser pipe.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] In the future, it is anticipated that riser systems combining multiple riser tubes will be used more frequently in mineral resource development and other applications. However, when strakes or fairings are installed on riser tubes to suppress vortex excitation, the installation of these strakes or fairings is done manually, one by one, which presents a significant technical challenge as it requires a considerable amount of time. [Means for solving the problem]

[0006] The method for reducing vortex excitation vibration in a plurality of riser tubes according to claim 1 is a method for reducing vortex excitation vibration generated by the water flow in a plurality of riser tubes installed in water, characterized in that the arrangement of the plurality of riser tubes is different from that of the plurality of riser tubes to cancel out and reduce the vortex excitation vibration generated in the plurality of riser tubes by the water flow, or the effect of vortices generated in the plurality of riser tubes by the water flow is suppressed to reduce the vortex excitation vibration generated in the plurality of riser tubes.

[0007] Here, it is preferable to use a riser tube set in which a plurality of riser tubes are set together, and to arrange them differently from one another so that the riser tube set and other adjacent riser tube sets are twisted together, thereby creating different phases for each riser tube set and canceling out and reducing the vortex-excited vibrations generated in the riser tubes.

[0008] Furthermore, when differentiating the phase for each riser tube set, it is preferable to change it continuously by the same angle.

[0009] Furthermore, it is preferable that the aforementioned identical angle is an angle obtained by dividing 360° by an integer of 3 or more.

[0010] In this case, it is preferable to suppress the vortices that cause the vortex excitation vibrations generated in the riser tubes by arranging the relative positions of the multiple riser tubes asymmetrically in a plane perpendicular to the longitudinal direction.

[0011] Furthermore, it is preferable that the asymmetrically arranged positions of the riser tubes are such that one riser tube is located in the wake region of the vortex generated in the riser tube by the flow.

[0012] Furthermore, it is preferable to determine the optimal arrangement of the relative positions of the multiple riser tubes in advance through simulation.

[0013] The multiple riser tube system according to claim 8 is a multiple riser tube system for reducing vortex excitation vibrations caused by water flow in a plurality of riser tubes installed in water, and preferably comprises a plurality of riser tubes and arrangement changing means for canceling out and reducing vortex excitation vibrations generated in the plurality of riser tubes by the water flow, or for suppressing the effect of vortices generated in the plurality of riser tubes by the water flow.

[0014] Here, it is preferable that the arrangement changing means has a phase changing joint that connects each of the riser tube sets with a different phase by changing the arrangement so that the multiple riser tube sets, each consisting of multiple riser tubes as a single group, are twisted together.

[0015] Furthermore, it is preferable that the phases of multiple riser tube sets are continuously changed by the same angle using the same phase-changing joint.

[0016] Furthermore, it is preferable that the same angle of the phase-changing joint is an angle obtained by dividing 360° by an integer of 3 or more.

[0017] Here, it is preferable that the arrangement changing means has an asymmetric arrangement bracket that arranges the relative positions of the plurality of riser tubes asymmetrically in a plane perpendicular to the longitudinal direction and maintains the asymmetric arrangement of the plurality of riser tubes.

[0018] Furthermore, the relative positions of the multiple riser tubes in the asymmetrically arranged bracket are preferably such that the distance between them is such that other riser tubes are located in the wake region of the vortex generated in the riser tube by the flow.

[0019] Furthermore, it is preferable that the distance between the relative positions of the multiple riser tubes of the asymmetrically arranged bracket is the distance determined in advance by simulation to find the optimal relative position of the multiple riser tubes.

[0020] The phase-changing joint for a multiple riser tube system according to claim 15 is a phase-changing joint used in a multiple riser tube system for reducing vortex-excited vibrations, characterized in that it has a connection portion corresponding to a plurality of riser tube sets and a shape that changes a predetermined phase.

[0021] The asymmetrical arrangement bracket for a multiple riser tube system according to claim 16 is an asymmetrical arrangement bracket used in a multiple riser tube system for reducing vortex-excited vibration, characterized in that it comprises a set of multiple types of asymmetrical arrangement brackets having different dimensions for the distance between them in order to arrange the multiple riser tubes to be targeted asymmetrically. [Effects of the Invention]

[0022] The method for reducing the vortex-induced vibration of a plurality of riser pipes according to claim 1 is a method for reducing the vortex-induced vibration caused by the water flow of a plurality of riser pipes provided in water. By making the arrangements of the plurality of said riser pipes different from each other, the vortex-induced vibrations generated in the plurality of said riser pipes by said water flow are offset and reduced, or the influence of the vortices generated by the plurality of said riser pipes on the water flow is suppressed to reduce the vortex-induced vibration generated in the plurality of said riser pipes, whereby vortex-induced vibration (VIV) can be suppressed without providing strakes or fairings on the riser pipes. Thereby, the time taken for the installation of the riser pipes can be shortened and the cost can be reduced.

[0023] Here, by using a riser pipe set with a plurality of said riser pipes as one set and making the arrangements different from each other such that the other riser pipe sets adjacent to said riser pipe set are in a mutually twisted state, different phases are obtained for each riser pipe set, whereby the vortex-induced vibration generated in the riser pipes can be offset and reduced.

[0024] Also, when making the phases different for each riser pipe set, by continuously changing at the same angle, vortices shifted at the same angle are generated to more effectively offset and reduce the vortex-induced vibration generated in the riser pipes.

[0025] Also, by setting the same angle as the angle obtained by dividing 360° by an integer of 3 or more, vortices shifted at an appropriate angle are generated to more effectively offset and reduce the vortex-induced vibration generated in the riser pipes.

[0026] Here, by arranging the relative positions of the plurality of said riser pipes asymmetrically on a plane perpendicular to the longitudinal direction of the plurality of said riser pipes, the vortices causing the vortex-induced vibration generated in the riser pipes can be suppressed.

[0027] Furthermore, the asymmetrical arrangement of the riser tubes, where each riser tube is positioned in the wake region of the vortex generated in the riser tube by the flow, suppresses the influence of vortices generated in the riser tube by the water flow and reduces vortex excitation vibrations generated in multiple riser tubes.

[0028] Furthermore, by pre-determining the optimal relative positions of the multiple riser tubes through simulation, it is possible to design a multiple riser tube system that can suppress vortex excitation without actually constructing a multiple riser tube system.

[0029] The multiple riser tube system according to claim 8 is a multiple riser tube system for reducing vortex-induced vibrations caused by the water flow of multiple riser tubes installed in water, and comprises multiple riser tubes and arrangement changing means for changing the arrangement of the riser tubes to cancel out and reduce vortex-induced vibrations generated in the multiple riser tubes by the water flow, or to suppress the effect of vortices generated in the multiple riser tubes by the water flow, thereby suppressing vortex-induced vibrations (VIV) without providing strakes or fairings on the riser tubes. This reduces the time required for the installation of riser tubes and reduces costs.

[0030] Here, the arrangement changing means has a phase changing joint that connects each riser tube set with a different phase by changing the arrangement such that multiple riser tube sets, each consisting of multiple riser tubes as a single unit, are twisted together, thereby canceling out and reducing the vortex-excited vibrations generated in the riser tubes.

[0031] Furthermore, by using the same phase-changing joint, the phases of multiple riser tube sets are continuously changed by the same angle and connected, thereby generating vortices shifted by the same angle, and more effectively canceling out and reducing vortex-excited vibrations generated in the riser tubes.

[0032] Furthermore, by having the same angle of the phase-changing joint be an angle obtained by dividing 360° by an integer of 3 or more, it is possible to generate vortices shifted to an appropriate angle, thereby more effectively canceling out and reducing vortex-excited vibrations generated in the riser tube.

[0033] Here, the arrangement changing means has an asymmetric arrangement bracket that arranges the relative positions of the plurality of riser tubes asymmetrically in a plane perpendicular to the longitudinal direction of the plurality of riser tubes and maintains the asymmetric arrangement of the plurality of riser tubes, thereby suppressing the vortices that cause the vortex excitation vibrations generated in the riser tubes.

[0034] Furthermore, the relative positions of the multiple riser tubes in the asymmetrically arranged bracket are such that the distance between them is such that other riser tubes are located in the wake region of the vortex generated in the riser tube by the flow. This suppresses the influence of vortices generated by the riser tubes due to the water flow and reduces vortex excitation vibrations generated in the multiple riser tubes.

[0035] Furthermore, by setting the distance between the relative positions of the multiple riser tubes in the asymmetrically arranged bracket to a distance determined in advance by simulation to find the optimal relative position of the multiple riser tubes, it is possible to design a multiple riser tube system that can suppress vortex excitation vibrations in advance without actually constructing a multiple riser tube system.

[0036] The phase-changing joint for a multiple riser tube system according to claim 15 is a phase-changing joint used in a multiple riser tube system that reduces vortex-excited vibrations, and has a connection portion corresponding to a plurality of riser tube sets and a shape that changes a predetermined phase, so that a plurality of riser tube sets, each consisting of a plurality of riser tubes as a single unit, can be rearranged so that they are twisted together, thereby canceling out and reducing vortex-excited vibrations generated in the riser tubes.

[0037] The asymmetrical arrangement bracket for a multiple riser tube system according to claim 16 is an asymmetrical arrangement bracket used in a multiple riser tube system for reducing vortex excitation vibration, and comprises a set of multiple types of asymmetrical arrangement brackets having dimensions that result in different distances to arrange the target multiple riser tubes asymmetrically, thereby more effectively canceling and reducing vortex excitation vibration generated in the riser tubes. [Brief explanation of the drawing]

[0038] [Figure 1] This figure shows the configuration of the multiple riser tube system in the first embodiment. [Figure 2] This figure shows the configuration of multiple riser tubes in the first embodiment. [Figure 3] This figure shows the configuration of the riser tube set in the first embodiment. [Figure 4] This figure shows the configuration of the phase transformation joint in the first embodiment. [Figure 5] This figure shows the vortex discharge by multiple riser tubes in the first embodiment. [Figure 6] This figure shows the configuration of the multiple riser tube system in the second embodiment. [Figure 7] This figure shows the configuration of multiple riser tubes in the second embodiment. [Figure 8] This figure shows an example of an asymmetrical arrangement of riser tubes in the second embodiment. [Figure 9] This figure shows the vortex discharge by multiple riser tubes in the second embodiment. [Figure 10] This is a conceptual diagram illustrating the process of vortex discharge using multiple riser tubes. [Figure 11] This is a conceptual diagram of vortex discharge when the water flow angle in multiple riser tubes is changed from 0° to 315° in the second embodiment. [Figure 12] This is a conceptual diagram of vortex discharge when the water flow angle in multiple riser tubes is set to 0° in the second embodiment. [Figure 13] This is a conceptual diagram of vortex discharge when the water flow angle in the multiple riser tubes is set to 45° in the second embodiment. [Figure 14] This is a conceptual diagram of vortex discharge when the water flow angle in multiple riser tubes is set to 90° in the second embodiment. [Figure 15] This is a conceptual diagram of vortex discharge when the water flow angle in the multiple riser tubes is set to 135° in the second embodiment. [Figure 16] This is a conceptual diagram of vortex discharge when the water flow angle in multiple riser tubes is set to 180° in the second embodiment. [Figure 17] This is a conceptual diagram of vortex discharge when the water flow angle in the multiple riser tubes is set to 225° in the second embodiment. [Figure 18] This is a conceptual diagram of vortex discharge when the water flow angle in the multiple riser tubes is set to 270° in the second embodiment. [Figure 19] This is a conceptual diagram of vortex discharge when the water flow angle in the multiple riser tubes is set to 315° in the second embodiment. [Modes for carrying out the invention]

[0039] [First Embodiment] The multiple riser pipe system 100 in the first embodiment, as shown in Figure 1, consists of an offshore facility 10 installed in the water, a riser assembly device (derrick) 12, a submersible pump 14, a transfer pipe 16, a drilling unit 18, and multiple riser pipes 20. Multiple riser pipes are used in oil and gas development to separate the transported materials, such as a pipe for injecting seawater into the seabed (oil reservoir) and a pipe for lifting oil and gas to the offshore facility. In mineral resource development, multiple pipes are used as pipes for lifting ore and seawater to the offshore facility and pipes for returning unwanted seawater to the seabed. As these examples show, multiple pipes are used depending on the transported materials and applications.

[0040] The offshore facility 10 is a structure that floats on the water surface to extract resources such as ore. The offshore facility 10 is equipped with a riser assembly device (derrick) 12 for suspending multiple riser pipes 20 to near the seabed. The riser assembly device (derrick) 12 is used to assemble the multiple riser pipes 20 and to support the multiple riser pipes 20 installed underwater.

[0041] The submersible pump 14 is a pump for transporting resources from the seabed to the surface. For example, in the development of mineral resources, the submersible pump 14 is used to transport ore and multiphase fluids such as seawater from the seabed to the offshore facility 10. The transfer pipe 16 is a pipe that connects the submersible pump 14 and the drilling unit 18 in the development of mineral resources on the seabed. The transfer pipe 16 is also a pipe that connects multiple riser pipes 20 and the offshore facility 10 in the development of fluids such as petroleum.

[0042] The drilling unit 18 is a device for collecting ore from the seabed. The drilling unit 18 sends the collected ore as a slurry to multiple riser pipes 20 via a transfer pipe 16 and a submersible pump 14. In this embodiment, a drilling unit 18 is provided for collecting ore from the seabed, but any device for drilling, collecting, etc., from underwater or seabed resources may be used, for example, an excavator or dredger for drilling the seabed.

[0043] The multiple riser pipe 20 is a long underwater pipe formed by combining multiple riser pipes for transporting resources such as ore extracted from the seabed to the offshore facility 10 on the water surface. In this embodiment, an example of extracting ore using the multiple riser pipe 20 is shown, but it can also be used to transport other resources such as oil, gas, and deep-sea water.

[0044] Figure 2 shows the configuration of the multiple riser tube 20. The multiple riser tube 20 includes a riser tube set 20a which is a combination of multiple riser tubes, and is configured by combining the riser tube set 20a with a phase conversion joint 20b. In this embodiment, an example is shown in which a riser tube set 20a consisting of three riser tubes is applied. However, the number of riser tubes that make up the riser tube set 20a is not limited to three, but can be two or more.

[0045] As shown in Figure 3, the riser pipe set 20a is a component formed by combining multiple riser pipes 22 at predetermined intervals using spacers 24. The diameter of the riser pipes 22 is approximately 4 inches to 22 inches (approximately 101.6 mm to approximately 559 mm). The length of a single riser pipe 22 is approximately 50 feet to 90 feet (approximately 15.24 m to approximately 27.432 m). However, the size of the riser pipes 22 is not limited to these and may be appropriately changed depending on the type of resource to be collected, the environment in which the multiple riser pipe system 100 is installed, the water depth at which the resource is collected, etc. The configuration of the multiple riser pipe system 100 in this embodiment can be applied to riser pipes 22 of all sizes. The ends of the riser pipe set 20a are connectors 20c for connecting to the phase conversion joint 20b.

[0046] The phase-shifting joint 20b is a component that connects two riser pipe sets 20a. The end of the phase-shifting joint 20b is a connector 20c for connecting to the riser pipe set 20a. As shown in Figure 4, the phase-shifting joint 20b is a means for changing the arrangement of riser pipe sets 20a, having a shape such that the angles in the direction in which the riser pipes 22 are aligned are different at both ends. The phase-shifting joint 20b has a shape such that, for example, at least some of the riser pipes 22 are twisted to change the angle (phase) in which the riser pipes 22 are aligned at both ends, so that the distance between the multiple riser pipes 22 remains unchanged at one end (side D in the figure) and the other end (side E in the figure).

[0047] Multiple riser pipes 20 are formed by connecting riser pipe sets 20a using phase conversion joints 20b. Therefore, as shown in cross-sections AA, BB, and CC in Figure 2, the angle (phase) of the direction in which the multiple riser pipes 22 constituting the riser pipe set 20a are aligned is changed at each point where they are connected by the phase conversion joints 20b.

[0048] Specifically, for example, it is preferable to provide a phase conversion joint 20b for each riser pipe set 20a to make the angle (phase) between adjacent riser pipe sets 20a different. In this case, it is preferable to change the angle continuously by the same angle for each riser pipe set 20a. For example, the angle (phase) is changed every 50 to 90 feet (approximately 15.24 m to approximately 27.432 m), which is the length of a typical riser pipe 22, along the extension direction of the multiple riser pipes 20. The angle (phase) changed by one phase conversion joint 20b is preferably an angle obtained by dividing 360° by an integer of 3 or more. For example, it is preferable to change the angle (phase) by one phase conversion joint 20b in the range of 30° to 120°. However, the angle (phase) to be changed may be changed according to the conditions of the environment in which the multiple riser pipe system 100 is applied. Also, the angle (phase) between adjacent riser pipe sets 20a does not have to be the same angle. For example, if the water flow distribution in the depth direction of a body of water differs significantly between the upper and lower layers, the angle (phase) between adjacent riser pipe sets 20a may be changed from the same angle. Note that using the same angle has the advantage of allowing the same phase conversion joint 20b to be used.

[0049] In this embodiment, the phase-shifting joint 20b is configured such that the angle between the direction in which the riser pipes 22 are aligned on the D side (D cross-section) and the direction in which the riser pipes 22 are aligned on the E side (E cross-section) is 45°. Therefore, each time a phase-shifting joint 20b is installed, the angle (phase) of the riser pipe set 20a is changed to 0°, 45°, 90°, 135°, etc. However, this angle is not limited to 45°.

[0050] Figure 5 shows the release of vortices when a water flow is applied to multiple riser tubes 20. Vortices are generated in the multiple riser tubes 20 downstream of the water flow. In this embodiment, the arrangement of the multiple riser tubes 20 is made different from each other so that riser tube set 20a and adjacent riser tube sets 20a are twisted to each other. This changes the direction in which the riser tubes 22 are aligned at different angles (phases) for each riser tube set 20a, thereby changing the direction in which the vortices generated by the water flow are released. This makes it possible to cancel out and reduce the vortex excitation (VIV) generated in the multiple riser tubes 20.

[0051] [Second Embodiment] The multiple riser pipe system 200 in the second embodiment, as shown in Figure 6, is composed of an offshore facility 10, a riser assembly device (derrick) 12, a submersible pump 14, a transfer pipe 16, a drilling unit 18, and multiple riser pipes 30. Here, the configuration excluding the multiple riser pipes 30 is the same as that of the multiple riser pipe system 100 in the first embodiment, so a description is omitted.

[0052] The multiple riser pipes 30 are long underwater pipes consisting of riser pipes for transporting resources such as ore extracted from the seabed to the offshore facility 10 on the water surface. In this embodiment, an example of extracting ore using the multiple riser pipes 30 is shown, but they can also be used to transport other resources such as oil, gas, and seawater.

[0053] Figure 7 shows the configuration of the multiple riser pipe 30. The multiple riser pipe 30 is composed of a combination of multiple riser pipes 30a. In this embodiment, a multiple riser pipe 30 composed of three riser pipes 30a is shown as an example. However, the number of riser pipes 30a is not limited to three, but can be three or more. The multiple riser pipe 30 is composed of a combination of riser pipes 30a and asymmetrical arrangement brackets 30b.

[0054] The diameter of the riser pipe 30a is approximately 4 inches to 22 inches (approximately 101.6 mm to 559 mm). The length of one riser pipe 30a is approximately 50 feet to 90 feet (approximately 15.24 m to 27.432 m). However, the size of the riser pipe 30a is not limited to these values ​​and may be appropriately changed depending on the type of resource to be collected, the environment in which the multiple riser pipe system 200 is installed, the water depth at which the resource is collected, etc. The configuration of the multiple riser pipe system 200 in this embodiment can be applied to riser pipes 30a of all sizes. The ends of the riser pipes 30a are equipped with connectors 30c for connecting to other riser pipes 30a.

[0055] The asymmetrical arrangement bracket 30b is a component for maintaining the arrangement of multiple riser tubes 30a. The asymmetrical arrangement bracket 30b has a structure in which annular members through which riser tubes 30a pass are connected to each other. By passing the riser tubes 30a through the annular members of the asymmetrical arrangement bracket 30b, multiple riser tubes 30a are arranged such that their relative positions are asymmetrical in a plane perpendicular to the longitudinal direction of the riser tubes 30a. Here, asymmetric means that the arrangement is not point-symmetric with respect to any point included in the plane perpendicular to the longitudinal direction of the riser tubes 30a, and is not line-symmetric with respect to any line. In this case, it is preferable that the relative positions of the multiple riser tubes 30a in the asymmetrically arranged state be such that one riser tube 30a is located in the wake region of a vortex generated in the riser tube 30a by the fluid flow when the multiple riser tubes 30 are placed in a fluid.

[0056] Figure 8 shows an example of an arrangement of multiple riser pipes 30 using three riser pipes 22. Figure 8 is a view from a direction perpendicular to the longitudinal direction of the riser pipe 30a (the AA cross-sectional direction shown in Figure 7). Taking the central riser pipe 30a as the reference, if the outer diameter OD1 of the central riser pipe 30a is the same as the outer diameters OD2 and OD3 of the other riser pipes 30a, then, as shown in Figure 8, the hydrodynamic interaction becomes large when the distances from the central riser pipe 30a to the other riser pipes 30a are within the range of 2 × (OD1 + OD2) and 2 × (OD1 + OD3), respectively. In other words, it is preferable that the distance between two adjacent riser pipes 30a be within twice the sum of the outer diameters of the outer diameters of one riser pipe 30a and the other riser pipe 30a.

[0057] Multiple riser pipes 30 are formed by connecting riser pipes 30a, which are arranged asymmetrically by asymmetrical arrangement brackets 30b, in the longitudinal direction (from the water surface to the bottom). The riser pipes 30a can be connected by connecting connectors 30c to each other.

[0058] Furthermore, in order to arrange the multiple riser pipes 30a asymmetrically, several types of asymmetrical arrangement brackets 30b with varying distances between the riser pipes 30a may be used. In this case, the connectors 30c at the ends of the riser pipes 30a can be connected using bent connecting pipes or flexible pipes.

[0059] Figure 9 shows the release of vortices when a water flow is applied to multiple riser tubes 30. Vortices are generated in the multiple riser tubes 30 downstream of the water flow. Figure 10 shows vortex excitation occurring in a single riser tube 30a. At time t1 (left figure), the first vortex is generated downstream of the riser tube 30a. The region where the vortex is generated (shown in light gray in the figure) becomes a low-pressure region, and due to the influence of this low-pressure region, a resultant force with the water flow is generated in the riser tube 30a. As time progresses, at time t2 (right figure), a second vortex is generated at a different position downstream of the riser tube 30a. In this state as well, the region where the vortex is generated becomes a low-pressure region, and a resultant force is generated in the riser tube 30a. In this way, as time progresses, resultant forces are generated in the riser tube 30a in different directions, and the riser tube 30a vibrates in a direction perpendicular to the water flow. This type of vibration is called vortex-induced vibration (VIV) and affects the fatigue and other durability of riser tube 30a.

[0060] Figure 11 is a conceptual diagram showing the expected vortex generation state when water flow is applied to multiple riser tubes 30 at various angles in this embodiment. In Figure 11, the vortex generation state is shown at 45° intervals from 0° (Rotation 0°) to 315° (Rotation 315°).

[0061] Figure 12 shows the temporal change in vortex generation when a water flow is applied at an angle of 0° to a multi-riser tube 30, which is formed by combining three riser tubes 30a in an asymmetrical position. As shown in the figure, when multiple riser tubes 30a are placed close together to satisfy the above distance condition, a different flow field is created due to hydrodynamic mutual interference compared to the case of a single riser tube 30a. That is, at time t1 (left figure), vortices are generated in opposite phases for each of the riser tubes 30a. Furthermore, at time t2 (right figure), a smaller low-pressure region is generated compared to the case of a single riser tube 30a. Here, if the forces generated in each of the riser tubes 30a are added together to find the resultant force, the resultant force in the direction perpendicular to the water flow is canceled out to some extent, and the vibrations occurring in the entire multi-riser tube 30 are reduced.

[0062] Figure 13 shows the temporal change in vortex generation when a water flow is applied to multiple riser tubes 30 at a 45° angle. Similar to the case with a 0° angle, vortices are generated in opposite phases in each riser tube 30a, and the resultant force perpendicular to the water flow cancels out, becoming smaller compared to the case with a single riser tube 30a.

[0063] Figures 14 to 19 show the temporal changes in vortex generation when water flow is applied to multiple riser tubes 30 at angles of 90°, 135°, 180°, 225°, 270°, and 315°, respectively. At these angles, as with angles 0° and 45°, vortices are generated in opposite phases in each riser tube 30a, and the resultant force perpendicular to the water flow cancels out, becoming smaller than in the case of a single riser tube 30a. Therefore, the vortex excitation vibration (VIV) generated in the multiple riser tubes 30 is also small at all angles.

[0064] Furthermore, as described above, the degree to which the resultant force perpendicular to the water flow on the multiple riser pipes 30 cancels out and the degree to which vortex-induced vibration (VIV) is reduced varies depending on the strength of the water flow and the distance and arrangement of the riser pipes 30a. Therefore, it is preferable to analyze the optimal distance and arrangement of the riser pipes 30a in advance by simulation to accurately determine the optimal conditions for installing the multiple riser pipe system 200.

[0065] As described above, in the multiple riser tube system 200 of this embodiment, by arranging three or more riser tubes 30a asymmetrically in the multiple riser tubes 30, the influence of vortices generated in the multiple riser tubes 30 by the water flow can be suppressed, thereby reducing vortex excitation (VIV). [Industrial applicability]

[0066] The present invention provides a method for reducing vortex excitation vibration in multiple riser tubes using riser tubes placed in a fluid, a multiple riser tube system for reducing vortex excitation vibration, and a phase-changing joint and an asymmetrically arranged bracket wire for the multiple riser tube system. The scope of application of the present invention is not limited to linear structures including riser tubes in water such as oceans and lakes, but can also be used to reduce vortex excitation vibration (VIV) in linear structures in gases such as outdoor poles and power lines in the air. When applied to linear structures in gases, terms related to water such as "in water" in the claims shall be interpreted as being replaced with "gas". [Explanation of Symbols]

[0067] 10 Offshore facilities, 12 Riser assembly equipment (derrick), 14 Submersible pump, 16 Transfer pipe, 18 Drilling unit, 20 Multiple riser pipes, 20a Riser pipe set, 20b Phase conversion joint, 20c Connector, 22 Riser pipe, 24 Spacer, 30 Multiple riser pipes, 30a (30a-1, 30a-2, 30a-3) Riser pipe, 30b Asymmetrical placement bracket, 30c Connector, 32 Riser pipe, 100, 200 Multiple riser pipe system.

Claims

1. A method for reducing vortex-induced vibrations caused by the water flow in multiple riser tubes installed in water, A method for reducing vortex excitation vibration in multiple riser tubes, characterized by canceling out and reducing vortex excitation vibration generated in the multiple riser tubes by the water flow by arranging the multiple riser tubes in different positions, or by suppressing the effect of vortices generated in the multiple riser tubes by the water flow to reduce vortex excitation vibration generated in the multiple riser tubes.

2. A method for reducing vortex excitation vibration of multiple riser tubes according to claim 1, A method for reducing vortex excitation vibrations of multiple riser tubes, characterized by using a riser tube set in which a plurality of riser tubes are arranged as a single unit, and by arranging the riser tube set and other adjacent riser tube sets differently from each other so that they are twisted together, thereby creating different phases for each riser tube set, and canceling out and reducing the vortex excitation vibrations generated in the riser tubes.

3. A method for reducing vortex excitation vibration of multiple riser tubes according to claim 2, A method for reducing vortex excitation vibration in multiple riser tubes, characterized in that the phase of each riser tube set is changed continuously by the same angle.

4. A method for reducing vortex excitation vibration of multiple riser tubes according to claim 3, A method for reducing vortex-induced vibrations in multiple riser tubes, characterized in that the aforementioned identical angle is an angle obtained by dividing 360° by an integer of 3 or more.

5. A method for reducing vortex excitation vibration of multiple riser tubes according to claim 1, A method for reducing vortex excitation vibration in multiple riser tubes, characterized by arranging the relative positions of the multiple riser tubes asymmetrically in a plane perpendicular to the longitudinal direction of the multiple riser tubes, thereby suppressing vortices that cause vortex excitation vibration generated in the riser tubes.

6. A method for reducing vortex excitation vibration of multiple riser tubes according to claim 5, A method for reducing vortex excitation vibration of multiple riser tubes, characterized in that the asymmetrically arranged relative positions of the riser tubes are such that each riser tube is located in the wake region of the vortex generated in the riser tube by the flow.

7. A method for reducing vortex excitation vibration of multiple riser tubes according to claim 5 or 6, A method for reducing vortex-excited vibrations in multiple riser tubes, characterized by determining the optimal arrangement of the relative positions of the multiple riser tubes in advance through simulation.

8. A multiple riser tube system for reducing vortex-induced vibrations caused by the water flow of multiple riser tubes installed in water, Multiple riser tubes, A multiple riser tube system for reducing vortex excitation vibration, characterized by comprising arrangement changing means for altering the arrangement of the riser tubes to cancel out and reduce vortex excitation vibration generated in the multiple riser tubes by the water flow, or to suppress the influence of vortices generated in the multiple riser tubes by the water flow.

9. A multiple riser tube system for reducing vortex-excited vibrations according to claim 8, The arrangement changing means is characterized by having a phase changing joint that connects each riser tube set with a different phase by changing the arrangement so that each riser tube set, which is a set of multiple riser tubes, is twisted to one another.

10. A multiple riser tube system for reducing vortex-excited vibrations according to claim 9, A multiple riser tube system for reducing vortex-excited vibrations, characterized in that the phases of multiple riser tube sets are continuously changed by the same angle and connected using the same phase-changing joint.

11. A multiple riser tube system for reducing vortex-excited vibration according to claim 10, A multiple riser tube system for reducing vortex-excited vibrations, characterized in that the same angle of the phase-changing joint is an angle obtained by dividing 360° by an integer of 3 or more.

12. A multiple riser tube system for reducing vortex-excited vibrations according to claim 8, A multiple riser tube system for reducing vortex-excited vibrations, characterized in that the arrangement changing means has an asymmetric arrangement bracket that arranges the relative positions of the multiple riser tubes asymmetrically in a plane perpendicular to the longitudinal direction of the multiple riser tubes and maintains the asymmetric arrangement of the multiple riser tubes.

13. A multiple riser tube system for reducing vortex-excited vibrations according to claim 12, A multiple riser tube system for reducing vortex excitation, characterized in that the relative positions of the multiple riser tubes of the asymmetrically arranged bracket are the distance at which other riser tubes are located in the wake region of a vortex generated in one of the riser tubes by the flow.

14. A multiple riser tube system for reducing vortex-excited vibration according to claim 13, A multiple riser tube system for reducing vortex-excited vibrations, characterized in that the distance relating to the relative positions of the multiple riser tubes of the asymmetrically arranged bracket is a distance determined in advance by simulation to find the optimal arrangement of the relative positions of the multiple riser tubes.

15. A phase-changing joint for use in a multiple riser tube system for reducing vortex-excited vibration according to any one of claims 9 to 11, A phase-changing joint for a multiple riser tube system, characterized by having a connection part corresponding to multiple riser tube sets and a shape that changes a predetermined phase.

16. The asymmetrical arrangement bracket used in a multiple riser tube system for reducing vortex-excited vibration according to claim 13 or claim 14, An asymmetrical arrangement bracket for a multiple riser pipe system, characterized by comprising a set of multiple types of asymmetrical arrangement brackets having dimensions that result in different distances between the multiple riser pipes to be arranged asymmetrically.

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