Method for monitoring the buried state of submarine cables, system for monitoring the buried state of submarine cables, and computer program for monitoring the buried state of submarine cables

Abstract

This provides a technical improvement that solves or mitigates at least some of the problems of the prior art. [Solution] The present invention provides a method for monitoring the buried state of a submarine cable, characterized in that it causes one or more computer processors to perform the following steps: a temperature information acquisition step to acquire temperature information inside the submarine cable using at least two optical fibers laid inside the submarine cable; a temperature gradient calculation step to calculate a temperature gradient inside the submarine cable from the temperature information acquired in the temperature information acquisition step; a thermal diffusivity calculation step to calculate the thermal diffusivity around the submarine cable from the temperature gradient calculated in the temperature gradient calculation step; and a status detection step to detect the buried state of the submarine cable based on the thermal diffusivity calculated in the thermal diffusivity calculation step.

Description

Technical Field

[0001] The present disclosure relates to a method for monitoring the buried state of a submarine cable, a system for monitoring the buried state of a submarine cable, and a computer program for monitoring the buried state of a submarine cable.

Background Art

[0002] Normally, submarine cables are buried at a predetermined depth on the seabed for the purpose of preventing damage, but there is a problem that the buried situation changes due to external factors such as natural disasters, ocean currents, and fishing activities (such as dropping anchors and bottom trawling nets).

[0003] Conventionally, as a method for monitoring the buried situation of submarine cables, visual inspections by divers or remotely operated unmanned submersibles (ROVs: Remotely Operated Vehicle) have been common. In recent years, however, as disclosed in Patent Document 1, a technique for estimating the coating height of a submarine cable from the temporal changes in the temperature measured by an optical fiber installed in the submarine cable and the current flowing through the submarine cable has been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, Patent Document 1 does not disclose in detail an algorithm for estimating the coating height of a submarine cable, and its practicality is low.

[0006] Therefore, an object of the present invention is to provide a technical improvement that solves or alleviates at least some of the problems of the above-described conventional techniques.

[0007] Specifically, the objective is to provide a method for monitoring the buried state of submarine cables, a system for monitoring the buried state of submarine cables, and a computer program for monitoring the buried state of submarine cables that can monitor the buried state of submarine cables more effectively and with higher accuracy. [Means for solving the problem]

[0008] The present invention provides a method for monitoring the buried state of a submarine cable, characterized in that it causes one or more computer processors to perform the following steps: a temperature information acquisition step to acquire temperature information inside the submarine cable using at least two optical fibers laid inside the submarine cable; a temperature gradient calculation step to calculate a temperature gradient inside the submarine cable from the temperature information acquired in the temperature information acquisition step; a thermal diffusivity calculation step to calculate the thermal diffusivity around the submarine cable from the temperature gradient calculated in the temperature gradient calculation step; and a status detection step to detect the buried state of the submarine cable based on the thermal diffusivity calculated in the thermal diffusivity calculation step.

[0009] In the temperature information acquisition step, temperature information including the temperatures at at least two points in the cross-section of the submarine cable is acquired using at least two optical fibers. In the temperature gradient calculation step, the radial temperature gradient of the submarine cable can be calculated from the temperature difference between the at least two points acquired in the temperature information acquisition step.

[0010] When the power flowing through the submarine cable is constant, the thermal diffusivity can be calculated using a formula in which the distance from the center of the submarine cable to the point where temperature information was acquired in the temperature information acquisition step, the temperature gradient calculated in the temperature gradient calculation step, and the amount of heat generated from the submarine cable are variables.

[0011] When the power flowing through a submarine cable changes, the thermal diffusivity can be calculated at least at a predetermined time using a formula in which the distance from the center of the submarine cable to the point where temperature information was acquired in the temperature information acquisition step, the temperature gradient calculated in the temperature gradient calculation step, the amount of heat generated from the submarine cable, and time are variables.

[0012] In the situation detection step, based on the thermal diffusivity calculated in the thermal diffusivity calculation step, it can be determined whether the environment around the submarine cable consists only of seawater or a mixture of seawater and sand.

[0013] The two optical fibers can consist of a first optical fiber extending linearly in the longitudinal direction from the center of the submarine cable at a radial position r1, and a second optical fiber extending linearly in the longitudinal direction from the center of the submarine cable at a radial position r2.

[0014] The two optical fibers can consist of a first optical fiber extending linearly or spirally in the longitudinal direction at a radial position r1 from the center of the submarine cable, and a second optical fiber extending spirally in the longitudinal direction at a radial position r2 from the center of the submarine cable.

[0015] In the temperature information acquisition step, a distributed temperature measurement system including optical fibers can be used to acquire a temperature profile over approximately the entire length of the submarine cable.

[0016] In the temperature gradient calculation step, the radial temperature gradient over approximately the entire length of the submarine cable can be calculated from the temperature profile obtained in the temperature information acquisition step.

[0017] The submarine cable embedding state monitoring system in the present disclosure includes a temperature information acquisition unit that acquires temperature information in the submarine cable, obtained using at least two optical fibers laid in the submarine cable; a temperature gradient calculation unit that calculates the temperature gradient in the submarine cable from the temperature information acquired by the temperature information acquisition unit; a heat diffusion rate calculation unit that calculates the heat diffusion rate around the submarine cable from the temperature gradient calculated by the temperature gradient calculation unit; and a situation detection unit that detects the embedding situation of the submarine cable based on the heat diffusion rate calculated by the heat diffusion rate calculation unit.

[0018] The computer program for monitoring the embedding state of the submarine cable of the present invention causes one or more computer processors to implement a temperature information acquisition function for acquiring temperature information in the submarine cable, obtained using at least two optical fibers laid in the submarine cable; a temperature gradient calculation function for calculating the temperature gradient in the submarine cable from the temperature information acquired by the temperature information acquisition function; a heat diffusion rate calculation function for calculating the heat diffusion rate around the submarine cable from the temperature gradient calculated by the temperature gradient calculation function; and a situation detection function for detecting the embedding situation of the submarine cable based on the heat diffusion rate calculated by the heat diffusion rate calculation function.

Effect of the Invention

[0019] According to the present invention, it is possible to provide a technical improvement that solves or alleviates at least some of the problems of the above-described prior art.

[0020] Specifically, it is possible to provide a method for monitoring the embedding state of a submarine cable, a submarine cable embedding state monitoring system, and a computer program for monitoring the embedding state of a submarine cable that can more effectively and accurately monitor the embedding state of the submarine cable.

Brief Description of the Drawings

[0021] [Figure 1] It is a conceptual diagram showing an example of an image of the submarine cable embedding state monitoring system of the present disclosure. [Figure 2]It is a conceptual diagram showing an image of an installation example of a facility including the submarine cable of the present disclosure. [Figure 3] It is a configuration diagram showing an example of the hardware configuration of the buried state monitoring system for the submarine cable of the present disclosure. [Figure 4] It is a configuration diagram showing an example of the functional configuration of the buried state monitoring system for the submarine cable of the present disclosure. [Figure 5] It is an image diagram showing an example of the arrangement configuration of the optical fiber in the submarine cable. [Figure 6] It is an image diagram showing another example of the arrangement configuration of the optical fiber in the submarine cable. [Figure 7] It is an image diagram showing another example of the arrangement configuration of the optical fiber in the submarine cable. [Figure 8] It is a flowchart showing an example of the flow of the buried state monitoring method of the submarine cable in the buried state monitoring system of the submarine cable of the present disclosure. [Figure 9] It is a circuit configuration diagram showing an example of the circuit configuration for realizing the computer program for monitoring the buried state of the submarine cable executed in the buried state monitoring system of the submarine cable of the present disclosure.

Embodiments for Carrying Out the Invention

[0022] First, an example of an embodiment of the buried state monitoring system for the submarine cable disclosed in this specification will be described with reference to the drawings.

[0023] The buried state monitoring system 1000 for the submarine cable in the embodiment of the present disclosure can be provided with one or more information processing devices 100 having one or more computer processors, as shown as an example in FIG. 1. Such an information processing device 100 can be a real device that can be connected to other various devices via a network, or a virtual server device on the cloud. A detailed description of the information processing device 100 will be given later.

[0024] Furthermore, in the example shown in Figure 1, an acquisition device 200 for acquiring data from various sensors that can be connected to the system 1000 is also shown. However, this acquisition device 200 can be an external device to the system 1000, or the information processing device 100 and the acquisition device 200 can be provided as a single device within the system 1000.

[0025] Figure 2 shows an image of the actual arrangement and connection state when the submarine cable is a submarine power cable for offshore power generation. As shown in Figure 2, as an example, the submarine power cable (submarine transmission line) 10 is mainly configured to connect offshore wind turbines 20 and land-based facilities (landing stations) including substations 30. In addition to the submarine power cable 10, a submarine communication cable 11 is also shown in Figure 2.

[0026] The acquisition device 200 described above is installed at the landing station located on the coast and is connected to a sensor (optical fiber described later) installed on a submarine cable, enabling it to acquire data from that sensor.

[0027] <Hardware Configuration> Here, the hardware configuration will be described using Figure 3. The information processing device 100 includes a processor 101, memory 102, storage 103, input / output interface (input / output I / F) 104, and communication interface (communication I / F) 105. Each component is interconnected via bus B.

[0028] The third information processing device 300 can realize the functions and methods described in this embodiment through the cooperation of the processor 101, memory 102, storage 103, input / output I / F 104, and communication I / F 105.

[0029] The processor 101 executes functions and / or methods realized by code or instructions contained in a program stored in the storage 103. The processor 101 may include, for example, a central processing unit (CPU), an MPU (Micro Processing Unit), a GPU (Graphics Processing Unit), a microprocessor, a processor core, a multiprocessor, an ASIC (Application-Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), etc., and may realize each process disclosed in each embodiment by logic circuits (hardware) or dedicated circuits formed on an integrated circuit (IC (Integrated Circuit) chip, LSI (Large Scale Integration)), etc. Furthermore, these circuits may be realized by one or more integrated circuits, and the multiple processes shown in each embodiment may be realized by a single integrated circuit. In addition, LSIs may be referred to as VLSI, Super LSI, Ultra LSI, etc., depending on the degree of integration.

[0030] Memory 102 temporarily stores the program loaded from storage 103 and provides a workspace for the processor 101. Various data generated while the processor 101 is executing the program are also temporarily stored in memory 102. Memory 102 includes, for example, RAM (Random Access Memory) and ROM (Read Only Memory).

[0031] Storage 103 stores programs. Storage 103 includes, for example, an HDD (Hard Disk Drive), an SSD (Solid State Drive), flash memory, etc.

[0032] The communication interface 105 is implemented as hardware such as a network adapter, communication software, or a combination thereof, and transmits and receives various types of data over the network. This communication may be performed via wired or wireless connection, and any communication protocol may be used as long as communication between the two devices is possible. The communication interface 105 communicates with other information processing devices over the network. The communication interface 105 transmits various types of data to other information processing devices according to instructions from the processor 101. The communication interface 105 also receives various types of data transmitted from other information processing devices and transmits them to the processor 101.

[0033] The input / output interface 104 includes an input device for inputting various operations to the information processing device 100, and an output device for outputting processing results processed by the information processing device 100. The input / output interface 104 may have the input device and output device integrated, or they may be separated into an input device and an output device.

[0034] The input device is implemented by any or a combination of any type of device capable of receiving input from a user and transmitting the information related to said input to the processor 101. The input device includes, for example, hardware keys such as touch panels, touch displays, and keyboards, pointing devices such as mice, cameras (for image-based operation input), and microphones (for voice-based operation input).

[0035] The input device, or operating unit, can be one that is appropriate for the type of information processing device 100. Examples of operating units include a touch panel integrated with a display, operation buttons provided on the casing of the user terminal, a keyboard, a mouse, or a controller operated by the user's hand.

[0036] The output device outputs the processing results processed by the processor 101. The output device includes, for example, a touch panel, a speaker, etc.

[0037] The functions realized by the components described herein may be implemented in a circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (a Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to realize the described functions. A processor includes transistors and other circuits and is considered a circuitry or processing circuitry. A processor may be a programmed processor that executes a program stored in memory.

[0038] In this specification, circuitry, unit, and means are hardware programmed to perform or execute the functions described herein. Such hardware may be any hardware disclosed herein, or any hardware known to be programmed to perform or execute the functions described herein.

[0039] If the hardware is a processor that is considered to be a type of circuitry, then the circuitry, means, or unit is a combination of hardware and software used to constitute the hardware and / or processor.

[0040] Furthermore, other information processing devices in this disclosure can also be configured with a hardware configuration similar to that shown in Figure 3, unless otherwise noted.

[0041] Next, with reference to the drawings, one embodiment of the functional configuration of the submarine cable burial status monitoring system described herein will be explained.

[0042] The submarine cable burial status monitoring system in this disclosure comprises at least an information processing device 100, as shown in Figure 1.

[0043] Furthermore, the submarine cable burial status monitoring system 1000 in this disclosure is characterized by comprising a temperature information acquisition unit 110, a temperature gradient calculation unit 120, a thermal diffusivity calculation unit 130, and a status detection unit 140, as shown as an example in Figure 4.

[0044] The temperature information acquisition unit 110 acquires temperature information inside the submarine cable 10, which is obtained using at least two optical fibers laid inside the submarine cable 10.

[0045] Figure 5 shows an example of a cross-sectional image of a submarine cable 10. The submarine cable 10 can be configured with a central conductor 13 for power transmission at its center, a first optical fiber 14 at a position r1 from the center, and a second optical fiber 15 at a position r2 from the center.

[0046] In other words, the two optical fibers described above can consist of a first optical fiber 14 that extends linearly in the longitudinal direction from the center of the submarine cable 10 at a radial position r1, and a second optical fiber 15 that extends linearly in the longitudinal direction from the center of the submarine cable 10 at a radial position r2.

[0047] The temperature information acquisition unit 110 can acquire temperature information, including the temperatures at at least two points in the cross-section of the submarine cable 10, obtained using the at least two optical fibers 14 and 15, by using a known distributed temperature sensing (DTS) technology. Details of this DTS technology will be described later.

[0048] Furthermore, the temperature information acquisition unit 110 may acquire the temperature information via the acquisition device 200 described above.

[0049] The temperature gradient calculation unit 120 calculates the temperature gradient within the submarine cable 10 from the temperature information acquired by the temperature information acquisition unit 110.

[0050] Specifically, the temperature gradient calculation unit 120 can calculate the radial temperature gradient of the submarine cable 10 from the temperature difference between at least two points obtained by the temperature information acquisition unit 110. Details of the method for calculating this temperature gradient will be described later.

[0051] The thermal diffusivity calculation unit 130 calculates the thermal diffusivity around the submarine cable 10 from the temperature gradient calculated by the temperature gradient calculation unit 120.

[0052] For example, if the power flowing through the submarine cable 10 is constant, the thermal diffusivity can be calculated using a formula in which the distance from the center of the submarine cable 10 to the point where temperature information is acquired by the temperature information acquisition unit 110, the temperature gradient calculated by the temperature gradient calculation unit 120, and the amount of heat generated from the submarine cable 10 are variables. Details of this method for calculating thermal diffusivity will be described later.

[0053] As another example, when the power flowing through the submarine cable 10 changes, the thermal diffusivity can be calculated using a formula in which the distance from the center of the submarine cable 10 to the point where temperature information is acquired by the temperature information acquisition unit 110 at a predetermined time, the temperature gradient calculated by the temperature gradient calculation unit 120, the amount of heat generated from the submarine cable 10, and time are variables. Details of this method for calculating thermal diffusivity will be described later.

[0054] The status detection unit 140 detects the burial status of the submarine cable 10 based on the thermal diffusivity calculated by the thermal diffusivity calculation unit 130.

[0055] For example, the situation detection unit 140 can determine, based on the thermal diffusivity calculated by the thermal diffusivity calculation unit 130, whether the environment around the submarine cable 10 consists only of seawater or a mixture of seawater and sand.

[0056] Seawater and sand have different thermal conductivity. Seawater has high thermal conductivity, so when a power cable is in contact with seawater, heat is efficiently dissipated from the cable surface. On the other hand, sand has relatively low thermal conductivity, so when a cable is buried in sand, heat diffusion is slower, and the temperature of the cable surface tends to rise. This difference can be used to determine whether the environment surrounding the cable is seawater or sand. Details of this determination method will be described later.

[0057] The above configuration provides a technical improvement that solves or mitigates at least some of the problems of the prior art described above.

[0058] Specifically, the above configuration makes it possible to monitor the buried state of submarine cables with greater feasibility, effectiveness, and high accuracy compared to conventional remote monitoring of the buried state of submarine cables, which is less feasible.

[0059] Furthermore, with this system 1000, a temperature profile can be obtained over approximately the entire length of the submarine cable 10 using at least two optical fibers 14 and 15 as described above, and the burial status of the submarine cable 10 can be detected over approximately the entire length of the submarine cable 10 using these profiles.

[0060] Next, we will explain specific application examples of the system 1000 described above. The following disclosure, as above, pertains to the submarine power cable 10 shown in Figure 2.

[0061] According to this disclosure, it will be possible to remotely identify whether the submarine power cable 10 is buried (i.e., whether the cable is covered with sand) or exposed above the seabed.

[0062] In this disclosure, as shown as an example in Figure 5, two optical fibers for temperature sensing are embedded within the submarine power cable 10, and the temperature difference between them is used to monitor the buried state.

[0063] In other words, this disclosure utilizes the temperature gradient within the submarine power cable 10 to detect and monitor changes in its buried state and external environment.

[0064] This disclosure utilizes a distributed temperature sensing (DTS) system, including optical fibers laid within the submarine cable 10, to diagnose the buried condition of the submarine power cable 10 by monitoring temperature fluctuations along the submarine power cable 10 in real time.

[0065] DTS technology is a technique that uses optical fibers to acquire a temperature profile along the entire length of a cable. By analyzing Raman scattering within the optical fiber, it enables highly accurate measurement of temperature changes on a meter-by-meter scale.

[0066] This technology allows for the rapid detection of situations where the submarine cable 10 experiences temperature fluctuations due to the surrounding environment (sand, seawater), such as when the submarine cable is exposed to the seabed or becomes covered again by sediment.

[0067] In particular, abnormal overheating or cooling of the submarine cable 10 suggests changes in the burial depth or surrounding geological changes, so it is useful to detect problems early and carry out appropriate maintenance.

[0068] Furthermore, utilizing a distributed temperature sensing (DTS) system, including optical fibers laid within the submarine cable 10, offers advantages in terms of safety and cost compared to conventional visual inspections by ROVs or divers.

[0069] Furthermore, the use of a distributed temperature sensing (DTS) system, including optical fibers laid within the submarine cable 10, is particularly useful because it allows for real-time remote monitoring of the submarine cable 10 during its operation, enabling preventative maintenance and rapid response in the event of an anomaly, thereby ensuring the stability of the power supply.

[0070] As described above, the invention disclosed herein provides a system for monitoring the buried state of a submarine cable 10 with high accuracy and in real time based on the measurement of a temperature gradient, thereby contributing to the sound operation and maintenance of the submarine cable 10.

[0071] Here, we will explain in detail the method for deriving the temperature equations observed in each optical fiber 14 and 15 for the following cases 1 and 2 under the conditions shown in Figure 5.

[0072] (Case 1) When a certain amount of power is flowing through the cable The conditions are as follows: • Radius R of the cylinder • There is a heater (central conductor) of negligible thickness in the center. • Determine the temperature distribution at time t. • Thermal conductivity is k, density is ρ, and specific heat is C p Let's assume

[0073] The general formula for temperature distribution is as follows: TIFF2026092185000002.tif2637 Here, α is the thermal diffusivity.

[0074] The boundary conditions are as follows: A heat source exists at r=0 (the central point). The device is in contact with the external environment at r=R, and heat transfer occurs due to external seawater or a mixture of seawater and sand.

[0075] Then, the temperature distribution T1(r) in the case of seawater only is TIFF2026092185000003.tif1349 Here, T0 is the ambient temperature and Q is the output of the heat source due to power.

[0076] The temperatures at locations r1 and r2 where the fiber optic cable is located are expressed as follows: TIFF2026092185000004.tif2851

[0077] As a result, the temperature difference between optical fibers is The result is TIFF2026092185000005.tif1751, and the temperature difference when a power cable is exposed is determined by the amount of heat generated Q (proportional to the amount of energy) and the thermal conductivity k.

[0078] Similarly, the temperature distribution T2(r) for a mixture of seawater and sand is as follows: TIFF2026092185000006.tif1550

[0079] The temperature at positions r1 and r2 where the optical fibers are located, and the temperature difference between the optical fibers, are expressed as follows: TIFF2026092185000007.tif4050

[0080] From the results, T 1a , T 1b Similarly, the temperature difference between optical fibers is determined by the amount of heat generated Q (which is proportional to the amount of electrical energy) and the thermal conductivity k' of the mixture of seawater and sand.

[0081] As the heat generation Q is known from the electrical energy, the thermal conductivity k is as follows. TIFF2026092185000008.tif1739

[0082] This formula allows us to determine the thermal diffusivity α around a power cable in a steady state and detect whether it is exposed. For example, if the calculated thermal diffusivity α exceeds a predetermined threshold, it can be determined that the power cable is exposed, and if the calculated thermal diffusivity α is below the predetermined threshold, it can be determined that the power cable is not exposed.

[0083] (Case 2) When the power flowing through the cable changes over time The heat conduction equation when the amount of electrical energy changes over time is as follows: TIFF2026092185000009.tif2873

[0084] Solving this for T(r,t) gives TIFF2026092185000010.tif20105 Here, T0 is the ambient temperature (seawater temperature), Q is the heat output from the heater, k is the thermal conductivity of the material, J0 is the 0th-order Bessel function, λ0 is a constant (depending on environmental conditions), A n These are the coefficients of the Fourier series.

[0085] When the surrounding area is seawater, the temperature T at positions r1 and r2 where the optical fibers are located is... 1a (t), T 1b (t) is as follows: TIFF2026092185000011.tif45143

[0086] Similarly, the case of a mixture of seawater and sand is as follows: TIFF2026092185000012.tif3097 Here, k' is the thermal conductivity of the mixture of seawater and sand, α'=k' / ρ'c' is the new thermal diffusivity, B n These are the coefficients of the Fourier series.

[0087] Similar to the steady state, the temperature difference is as follows: TIFF2026092185000013.tif12105

[0088] This equation includes a time-independent steady term and a time-dependent transient term.

[0089] In other words, the steady term is The filename is TIFF2026092185000014.tif1733, and the non-stationary term is The filename is TIFF2026092185000015.tif1891.

[0090] Here, let the non-stationary term be f(t). TIFF2026092185000016.tif1783

[0091] Solving for the thermal diffusivity α, TIFF2026092185000017.tif1686TIFF2026092185000018.tif4092TIFF2026092185000019.tif4190

[0092] This result indicates that the thermal diffusivity α of seawater alone, or a mixture of seawater and sand, can be determined from two temperature measurements.

[0093] Therefore, even when the amount of power is changing, that is, in a non-steady state, the conditions around the cable can be estimated. Note that non-steady states can occur due to load fluctuations such as power adjustments.

[0094] Figure 6 shows another example of the submarine cable 10 shown in Figure 5, in which the submarine cable 10 consists of a first optical fiber 14 extending linearly in the longitudinal direction at a radial position r1 from the center of the submarine cable 10, and a second optical fiber 15 extending spirally in the longitudinal direction at a radial position r2 from the center of the submarine cable. Note that the central conductor (power conductor) is omitted.

[0095] With this configuration, even if the temperature gradient becomes directional, such as when a portion of the submarine power cable is exposed, the buried state of the submarine cable can be monitored with high accuracy. Specifically, in the example shown in Figure 5, if a portion of the submarine cable, for example the upper half, is exposed, if the second optical fiber is on the upper side, it will be determined to be exposed, and if it is on the lower side, it will be determined to be buried, which may result in (radial) directionality. However, in the example shown in Figure 6, this problem can be solved.

[0096] As yet another example, the submarine cable may consist of a first optical fiber extending spirally in the longitudinal direction at a radial position r1 from the center of the submarine cable, and a second optical fiber extending spirally in the longitudinal direction at a radial position r2 from the center of the submarine cable.

[0097] With this configuration, the buried state of the submarine cable can be monitored with higher accuracy compared to the example shown in Figure 6. Specifically, in the example shown in Figure 6, the inner cable is offset from the center of the submarine power cable, so the magnitude of (r2-r1) varies depending on the longitudinal position, which may cause errors. However, in this configuration, the distance from the center (r2-r1) is constant regardless of the longitudinal position of the cable, thus solving the above problem.

[0098] Furthermore, in order to more clearly measure the temperature difference between each optical fiber, it is preferable that the first optical fiber 14 is positioned further inward (with a smaller distance r1 from the center), and the second optical fiber 15 is positioned further outward (with a larger distance r2 from the center).

[0099] Furthermore, as shown in Figure 7 as an example, the second optical fiber 15 can also be configured to be placed in the outer sheath of the submarine cable, for example, in the outer sheath of a steel wire (armored steel wire).

[0100] While the submarine power cable exemplified in Figure 5 is a single-core cable, Figure 7 shows an example of its application to a three-phase integrated cable with three conductors 13.

[0101] The outline of the present invention, as disclosed above, is described herein. (1) Monitoring of buried conditions by acquiring real-time and wide-range temperature profiles. Conventional methods for monitoring the condition of buried submarine cables mainly involved visual inspections by ROVs and divers, requiring regular maintenance. However, frequent inspections posed a significant burden in terms of cost and safety.

[0102] This disclosure describes how DTS technology can be used to lay optical fibers within a cable and monitor the temperature gradient along its entire length in real time, enabling immediate response when an anomaly occurs.

[0103] Furthermore, because it covers the entire submarine cable, it allows for real-time monitoring of changes in a wide area compared to conventional localized monitoring methods.

[0104] (2) Estimation of burial depth and detection of environmental changes using temperature fluctuations Conventional technologies required expensive acoustic or magnetic sensors to determine the physical location and burial depth of cables.

[0105] The present invention, as disclosed here, employs a technique that estimates variations in burial depth and the presence or absence of exposure by utilizing the influence of the surrounding environment on temperature. This eliminates the need for physical sensors and allows for highly accurate monitoring of the burial status solely through temperature measurement using optical fibers.

[0106] Thus, detecting environmental changes indirectly from temperature fluctuations is a different approach from conventional methods.

[0107] (3) Improvement of the accuracy and speed of anomaly detection using DTS technology The DTS technology employed in the invention described herein enables temperature detection with far greater accuracy than conventional inspection methods.

[0108] When submarine power cables are buried in sand, heat cannot be adequately dissipated, which can cause the cable's surface temperature to become abnormally high. DTS fibers can immediately detect this abnormal heat generation, helping to pinpoint the location of the problem in the submarine cable. Furthermore, by analyzing the temperature distribution of the submarine power cable, it is possible to assess how much the portion buried in sand affects the overall temperature of the cable.

[0109] Furthermore, because it can detect temperature fluctuations in increments of several meters, it can quickly detect even partial exposure of power cables that are buried underground. In addition, by analyzing the temperature data, the location of the anomaly can be accurately identified, improving the efficiency of inspections and repairs.

[0110] Thus, according to this disclosure, highly accurate and rapid anomaly detection can be achieved.

[0111] (4) Cost reduction and improved safety Traditional cable monitoring methods, which involve the use of ROVs or divers, are costly and raise safety concerns during operation.

[0112] According to the invention disclosed herein, DTS technology using optical fibers enables remote monitoring without the need for expensive equipment, thus significantly contributing to cost reduction and improved safety. This is also an advantage compared to conventional technology.

[0113] Next, an example of a method for monitoring the buried state of submarine cables disclosed in this specification will be described.

[0114] The method for monitoring the buried state of a submarine cable in this disclosure is, as an example, the method for monitoring the buried state of a submarine cable in the submarine cable buried state monitoring system 1000 shown in Figure 1. The submarine cable buried state monitoring system 1000 comprises at least an information processing device 100.

[0115] The method for monitoring the buried state of a submarine cable in this disclosure is characterized by causing one or more computer processors to perform a temperature information acquisition step S110, a temperature gradient calculation step S120, a thermal diffusivity calculation step S130, and a status detection step S140, as shown as an example in Figure 8.

[0116] In the temperature information acquisition step S110, temperature information within the submarine cable is acquired using at least two optical fibers laid within the submarine cable. This temperature information acquisition step S110 can be performed by the temperature information acquisition unit 110 described above.

[0117] In the temperature gradient calculation step S120, the temperature gradient within the submarine cable is calculated from the temperature information acquired in the temperature information acquisition step S110. This temperature gradient calculation step S120 can be performed by the temperature gradient calculation unit 120 described above.

[0118] In the thermal diffusivity calculation step S130, the thermal diffusivity around the submarine cable is calculated from the temperature gradient calculated in the temperature gradient calculation step S120. This thermal diffusivity calculation step S130 can be performed by the thermal diffusivity calculation unit 130 described above.

[0119] In the status detection step S140, the burial status of the submarine cable is detected based on the thermal diffusivity calculated in the thermal diffusivity calculation step S130. This status detection step S140 can be performed by the status detection unit 140 described above.

[0120] The above configuration provides a technical improvement that solves or mitigates at least some of the problems of the prior art described above.

[0121] Specifically, the above configuration makes it possible to monitor the buried state of submarine cables with greater feasibility, effectiveness, and high accuracy compared to conventional remote monitoring of the buried state of submarine cables, which is less feasible.

[0122] Finally, an example of a computer program for monitoring the buried state of submarine cables disclosed herein will be described with reference to the drawings.

[0123] The computer program for monitoring the buried state of submarine cables in this disclosure is, as an example, the computer program for monitoring the buried state of submarine cables in the submarine cable buried state monitoring system 1000 shown in Figure 1. The submarine cable buried state monitoring system 1000 comprises at least an information processing device 100.

[0124] The computer program for monitoring the buried state of submarine cables in this disclosure is characterized by implementing a temperature information acquisition function, a temperature gradient calculation function, a thermal diffusivity calculation function, and a status detection function on one or more computer processors.

[0125] The temperature information acquisition function acquires temperature information within the submarine cable using at least two optical fibers laid inside the cable.

[0126] The temperature gradient calculation function calculates the temperature gradient within the submarine cable from the temperature information obtained by the temperature information acquisition function.

[0127] The thermal diffusivity calculation function calculates the thermal diffusivity around the submarine cable from the temperature gradient calculated by the temperature gradient calculation function.

[0128] The status detection function detects the burial status of submarine cables based on the thermal diffusivity calculated by the thermal diffusivity calculation function.

[0129] The above functions can be realized by the temperature information acquisition circuit 1110, temperature gradient calculation circuit 1120, thermal diffusivity calculation circuit 1130, and status detection circuit 1140 shown in Figure 9. The temperature information acquisition circuit 1110, temperature gradient calculation circuit 1120, thermal diffusivity calculation circuit 1130, and status detection circuit 1140 are realized by the temperature information acquisition unit 110, temperature gradient calculation unit 120, thermal diffusivity calculation unit 130, and status detection unit 140 described above, respectively. Details of each unit are as described above.

[0130] The above configuration provides a technical improvement that solves or mitigates at least some of the problems of the prior art described above.

[0131] Specifically, the above configuration makes it possible to monitor the buried state of submarine cables with greater feasibility, effectiveness, and high accuracy compared to conventional remote monitoring of the buried state of submarine cables, which is less feasible.

[0132] Furthermore, in order to function as an information processing device according to the above-described embodiment, an information processing device such as a computer or a mobile phone can be suitably used. Such an information processing device can be realized by storing a program describing the processing content that realizes each function of the information processing device according to the embodiment in the storage unit of the information processing device, and having the CPU of the information processing device read and execute the program.

[0133] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0134] Furthermore, the methods described in the embodiments can be distributed by storing the program, which can be executed by a computer, on recording media such as magnetic disks (floppy disks, hard disks, etc.), optical disks (CD-ROMs, DVDs, MOs, etc.), and semiconductor memory (ROMs, RAMs, flash memory, etc.), and by transmitting them via communication media. The program stored on the media also includes a configuration program that configures the software means (including not only the executable program but also tables and data structures) to be executed by the computer. The computer implementing this device reads the program recorded on the recording media and, if necessary, constructs the software means using the configuration program, and executes the above-described process by controlling its operation with this software means. The recording media referred to in this specification are not limited to those for distribution, but also include storage media such as magnetic disks and semiconductor memory provided inside the computer or in devices connected via a network. The storage unit may function as, for example, main memory, auxiliary memory, or cache memory. [Explanation of Symbols]

[0135] 1000 Submarine Cable Buried Status Monitoring System 100 Information Processing Devices 200 Acquisition device 10 Submarine power cables 11 Submarine power transmission lines 12 Submarine communication cables 20 Offshore wind turbines 30 Substations 40 Offshore Substations and Observation Towers 50 Operation monitoring facilities 60 Power system 13. Central conductor 14. The first optical fiber 15. The second optical fiber

Claims

1. One or more computer processors, A temperature information acquisition step involves acquiring temperature information within the submarine cable using at least two optical fibers laid within the submarine cable, A temperature gradient calculation step, which calculates the temperature gradient within the submarine cable from the temperature information acquired in the temperature information acquisition step, A thermal diffusivity calculation step, which calculates the thermal diffusivity around the submarine cable from the temperature gradient calculated in the above temperature gradient calculation step, A situation detection step in which the burial status of the submarine cable is detected based on the thermal diffusivity calculated in the thermal diffusivity calculation step, A method for monitoring the buried state of submarine cables, which enables the following:

2. In the temperature information acquisition step, temperature information is acquired using the at least two optical fibers, including the temperatures at at least two points in the cross-section of the submarine cable. The method for monitoring the buried state of a submarine cable according to claim 1, characterized in that the temperature gradient calculation step calculates the radial temperature gradient of the submarine cable from the temperature difference of at least two points obtained in the temperature information acquisition step.

3. If the power flowing through the aforementioned submarine cable is constant, The method for monitoring the buried state of a submarine cable according to claim 1, characterized in that the thermal diffusivity is calculated using a formula in which the distance from the center of the submarine cable to the point where the temperature information was acquired in the temperature information acquisition step, the temperature gradient calculated in the temperature gradient calculation step, and the amount of heat generated from the submarine cable are variables.

4. When the power flowing through the aforementioned submarine cable changes, The method for monitoring the buried state of a submarine cable according to claim 1, characterized in that the thermal diffusivity is calculated at least at a predetermined time using a formula in which the distance from the center of the submarine cable to the point where the temperature information was acquired in the temperature information acquisition step, the temperature gradient calculated in the temperature gradient calculation step, the amount of heat generated from the submarine cable, and time are variables.

5. The method for monitoring the buried state of a submarine cable according to claim 1, characterized in that the condition detection step determines, based on the thermal diffusivity calculated in the thermal diffusivity calculation step, whether the environment around the submarine cable consists only of seawater or a mixture of seawater and sand.

6. The two optical fibers mentioned above are From the center of the aforementioned submarine cable, in the radial direction r １ A first optical fiber extending linearly in the longitudinal direction at the position, From the center of the submarine cable, in the radial direction r ２ A second optical fiber extends linearly in the longitudinal direction at the position and A method for monitoring the buried state of a submarine cable according to claim 1, characterized by comprising the above.

7. The two optical fibers mentioned above are From the center of the aforementioned submarine cable, in the radial direction r １ A first optical fiber extending linearly or spirally in the longitudinal direction at the position, From the center of the aforementioned submarine cable, in the radial direction r ２ A second optical fiber extends spirally in the longitudinal direction at the position and A method for monitoring the buried state of a submarine cable according to claim 1, characterized by comprising the above.

8. The method for monitoring the buried state of a submarine cable according to claim 1, characterized in that, in the step of acquiring temperature information, a temperature profile is acquired over substantially the entire length of the submarine cable using a distributed temperature measurement system including the optical fiber.

9. The method for monitoring the buried state of a submarine cable according to claim 1, characterized in that the temperature gradient calculation step calculates a radial temperature gradient over substantially the entire length of the submarine cable from the temperature profile obtained in the temperature information acquisition step.

10. A temperature information acquisition unit that acquires temperature information inside the submarine cable using at least two optical fibers laid inside the submarine cable, A temperature gradient calculation unit calculates the temperature gradient within the submarine cable from the temperature information acquired by the temperature information acquisition unit, A thermal diffusivity calculation unit calculates the thermal diffusivity around the submarine cable from the temperature gradient calculated by the temperature gradient calculation unit, A condition detection unit detects the buried state of the submarine cable based on the thermal diffusivity calculated by the thermal diffusivity calculation unit. A system for monitoring the buried status of submarine cables.

11. One or more computer processors, A temperature information acquisition function that acquires temperature information within the submarine cable using at least two optical fibers laid within the submarine cable, A temperature gradient calculation function that calculates the temperature gradient within the submarine cable from the temperature information acquired by the aforementioned temperature information acquisition function, A thermal diffusivity calculation function calculates the thermal diffusivity around the submarine cable from the temperature gradient calculated by the aforementioned temperature gradient calculation function, Based on the thermal diffusivity calculated by the thermal diffusivity calculation function, a status detection function is used to detect the burial status of the submarine cable. A computer program for monitoring the buried state of submarine cables, which makes this possible.

Images