Online monitoring system for liquid hydrogen superconducting mixed transportation composite pipeline based on optical fiber sensing

Abstract

The invention discloses an on-line monitoring system for a liquid hydrogen superconducting mixed transportation composite material pipeline based on optical fiber sensing, and aims to solve the problem that multi-parameter monitoring such as temperature, strain and leakage cannot be performed on the liquid hydrogen superconducting composite material pipeline in an extremely low-temperature environment in real time in the prior art. The sensing optical fibers are arranged on all layers of the liquid hydrogen superconducting pipeline, the running state of the liquid hydrogen superconducting pipeline in the low-temperature environment can be monitored and mastered online in real time, long-distance continuous monitoring is achieved, and the running safety and reliability of the liquid hydrogen superconducting pipeline are greatly improved. Compared with the prior art, the system has the beneficial effects that the system adapts to a low-temperature environment, multi-parameter synchronous monitoring is realized, and long-distance distributed continuous monitoring is realized. The monitoring system comprises a liquid hydrogen superconducting pipeline, a sensing optical fiber network, a distributed optical fiber sensing demodulation and processing unit, a state evaluation and early warning unit, a man-machine interaction and data storage unit and other key parts.

Description

Technical Field

[0001] This invention relates to the field of cryogenic fluid transport technology, and in particular to an online monitoring system for liquid hydrogen superconducting mixed transport composite pipelines based on fiber optic sensing. Background Technology

[0002] With the large-scale application of clean energy sources such as hydrogen and natural gas, and the rapid development of modern chemical industries, the deployment of various transmission pipelines under extreme low-temperature and high-pressure conditions is becoming increasingly widespread. Liquid hydrogen superconducting transmission pipelines represent a paradigm shift in energy transmission, physically integrating hydrogen energy carriers with superconducting power transmission to overcome geographical limitations and efficiency bottlenecks in the large-scale application of clean energy. The medium, liquid hydrogen (-253℃), places stringent requirements on the pipeline's sealing integrity, material permeability, and structural stability; any minute leak or deformation could trigger a major safety accident.

[0003] Therefore, real-time online monitoring of multiple parameters of liquid hydrogen superconducting pipelines in a low-temperature environment simulating actual working conditions has become a core technological requirement for ensuring the safety of energy transmission.

[0004] Currently, most online monitoring systems for liquid hydrogen superducting pipelines are used for monitoring single parameters such as temperature, lacking multi-parameter fusion monitoring techniques. Existing monitoring technologies typically suffer from the following problems: Poor adaptability to temperature and electromagnetic fields: Most existing monitoring systems' electrical sensors cannot operate stably for long periods in low-temperature environments such as liquefied hydrogen pipelines and electromagnetic field environments such as superconducting systems, resulting in inaccurate monitoring results or even failure to monitor.

[0005] Limitations of monitoring parameters: Traditional monitoring systems can usually only monitor a single parameter, such as temperature or strain, and lack the technical means to integrate and monitor multiple parameters, making it difficult to fully reflect the pipeline's operating status.

[0006] Distributed monitoring is challenging: long-distance pipelines, ranging from tens to hundreds of kilometers, require densely deployed sensors, resulting in high costs, complex installation, and difficult maintenance. Existing point sensors, such as thermocouples, strain gauges, and point hydrogen sensors, have limited monitoring coverage and blind spots; data acquisition and processing may be delayed, failing to meet the need for rapid early warning; and traditional electrical sensors may be interfered with by superconducting magnetic fields.

[0007] Therefore, there is an urgent need for a comprehensive monitoring system specifically designed for the extreme low temperature and high risk special scenario of liquid hydrogen superconducting pipelines, capable of real-time online monitoring of multiple parameters such as temperature, strain, and leakage, in order to improve the safety and reliability of energy transmission. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides an online monitoring system for liquid hydrogen superconducting hybrid composite pipelines based on fiber optic sensing. This system can monitor multiple parameters, including temperature, strain, and leakage, in real time under the special conditions of liquid hydrogen superconducting pipelines. Through innovative design, this invention solves the problems of existing technologies, such as inability to adapt to low-temperature environments, limited monitoring parameters, and difficulties in distributed monitoring. It can operate stably for extended periods in low-temperature environments, enabling multi-parameter fusion monitoring and comprehensive understanding of the pipeline's operational status. Furthermore, distributed fiber optic sensing offers high spatial resolution and real-time performance, high sensitivity and accuracy, and is inherently safe, passive, electricity-free, and resistant to electromagnetic interference. It allows for long-distance continuous monitoring, significantly improving the safety and reliability of liquid hydrogen superconducting pipeline operations.

[0009] The technical solution of this invention, an online monitoring system for liquid hydrogen superconducting mixed-material pipelines based on fiber optic sensing, includes: Fiber Optic Sensing Network: A sensing network is formed by spirally winding sensing fibers around the outer wall of the liquid hydrogen superconducting channel to be measured, enabling distributed data acquisition of the liquid hydrogen superconducting channel. Distributed fiber optic sensing demodulation and processing unit: used to process the collected distributed data to obtain multi-parameter data; Status assessment and early warning unit: performs multi-level decision-making based on the calculated multi-parameter data; executes different levels of response measures and different levels of early warning according to the type of parameter anomaly; Human-computer interaction data storage unit: Constructs a visual 3D holographic interactive platform and stores the data; the stored data supports historical data analysis and multi-terminal access.

[0010] Preferably, the liquid hydrogen superconducting pipeline is provided with, from the inside out, a first liquid hydrogen delivery pipeline, a first superconducting cable layer, a first electrical insulation layer, a second superconducting cable layer, a second liquid hydrogen delivery pipeline, a second electrical insulation layer, an electrical shielding layer, an outer protective layer, a vacuum insulation layer, and an outer protective layer. The first liquid hydrogen transport pipeline is used for liquid hydrogen transport and simultaneously cools the first superconducting cable layer; the first superconducting cable layer is used for electrical energy transport; and the first electrical insulation layer is used for electrical insulation between the first and second superconducting cable layers. The second superconducting cable layer is used for power transmission; the second liquid hydrogen transport pipeline is used for liquid hydrogen transport and also cools the second superconducting layer; the second electrical insulation layer is used for electrical insulation of the entire liquid hydrogen superconducting pipeline. Electrical shielding layer, used to provide electrical shielding for the entire liquid hydrogen superconducting pipeline; The vacuum insulation layer is used to provide insulation for the entire liquid hydrogen superconducting pipeline. The outer protective layer includes both inner and outer sides, which are used to create an installation space for the vacuum insulation layer; Preferably, the second liquid hydrogen transmission pipeline is provided with a number of non-metallic support frames arranged radially along the energy transmission pipeline, and the vacuum insulation layer is provided with a number of metallic support frames arranged radially along the energy transmission pipeline.

[0011] Preferably, the sensing optical fiber is spirally wound with temperature monitoring optical fiber on the outer wall of the liquid hydrogen transportation pipeline, and strain monitoring optical fiber is axially pasted on the superconducting cable layer, and mechanical vibration monitoring optical fiber is circumferentially surrounded by the outer protective layer.

[0012] Preferably, the temperature monitoring optical fiber is spirally wound around the outer wall of the liquid hydrogen transportation pipeline with a pitch of 20mm, and fixed with low-temperature curing epoxy resin by dispensing. It is mechanically reinforced with titanium alloy clamps at every 200mm intervals.

[0013] Preferably, strain monitoring optical fibers are axially bonded to the superconducting cable layer, with three optical fibers arranged at 120° intervals around the circumference of the pipe. The fibers are bonded after being pre-stretched by 0.1% strain to eliminate installation slack, and a low-temperature adhesive containing nano-alumina filler is used.

[0014] Preferably, the mechanical vibration monitoring optical fiber is arranged around the outer protective layer in the circumferential direction, and is deployed about 50mm vertically in the upper and lower and left and right directions of the pipe.

[0015] Preferably, the distributed optical fiber sensing demodulation and processing unit includes a BOTDA module and a Φ-OTDR module; wherein, the BOTDA module emits laser light into the sensing fiber and uses stimulated Brillouin scattering radio frequency shift to synchronously calculate temperature and strain; the Φ-OTDR module detects Rayleigh scattering phase changes and captures mechanical vibration and liquid hydrogen leakage acoustic patterns.

[0016] Preferably, the BOTDA module operates according to the following steps: A high-frequency pulsed pump light is injected into one end of the optical fiber under test, and a low-frequency continuous probe light is injected into the other end. By changing the frequency of continuous light, the Brillouin gain values ​​at different frequencies are obtained, and the Brillouin gain spectrum at a certain point in the optical fiber is obtained. By using Lorentz curve fitting to calculate the Brillouin frequency shift at various locations in an optical fiber, distributed sensing of temperature or strain along the entire optical fiber can be achieved.

[0017] Preferably, the Φ-OTDR module operates according to the following steps: Using a narrow-linewidth laser as the light source, scattered light within the same pulse width interferes with each other; Demodulate the Rayleigh scattered light to obtain vibration information along the optical fiber; The vibration location is identified and located by using the difference between the backscattered Rayleigh signals of two adjacent cycles; The amplitude difference method is used to analyze the changes in the amplitude of the optical signal before and after vibration under different conditions, so as to identify and locate the pipeline leak.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: 1. Existing technologies struggle to simultaneously meet the stringent requirements of extremely low temperatures, strong electromagnetic interference, and potential flammability and explosion risks associated with liquid hydrogen superconducting pipelines. This invention, based on distributed fiber optic sensing technology, deploys a network of sensing fibers to acquire real-time, online multi-dimensional key parameters such as temperature and strain along the entire pipeline. Its spatial resolution reaches meter-level or even centimeter-level, offering high measurement accuracy. Furthermore, the sensing fibers themselves are completely passive, inherently safe, and resistant to strong electromagnetic interference, perfectly overcoming the deployment difficulties and reliability bottlenecks of traditional electrical sensors in liquid hydrogen superconducting environments.

[0019] 2. Traditional monitoring methods have limited coverage, complex wiring, are susceptible to interference, and are difficult to maintain. This invention provides fully distributed, blind-spot-free continuous monitoring data, enabling early and high-precision location of minute leaks and safety hazards caused by abnormal temperature or vibration characteristics, structural deformation such as bending, or abnormal strain due to settlement. This comprehensive situational awareness capability, combined with a multi-parameter fusion and multi-level decision-making mechanism, allows maintenance personnel to proactively warn, accurately locate faults, and assess structural health, greatly reducing the risk of safety accidents and production interruptions caused by leaks, calving, or structural failures. Simultaneously, the use of fiber optic sensors replaces a large number of point sensors, simplifying the system structure and reducing installation complexity and long-term maintenance costs.

[0020] 3. This invention provides strong support for the intelligent and efficient operation of liquid hydrogen superconducting pipelines, while also supporting more accurate fault diagnosis and life prediction, greatly improving the safety and reliability of liquid hydrogen superconducting pipeline operation, and providing a key data foundation, thus having significant engineering application value. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the cross-sectional structure of the liquid hydrogen superconducting channel in this invention; Figure 2 This is a structural diagram of the online monitoring system for liquid hydrogen superconducting mixed transport composite pipeline based on fiber optic sensing in this invention; Figure 3 This is a flowchart of the multi-parameter fusion decision module in this invention; Figure 4 This is a front view of the temperature monitoring optical fiber spirally wound around the outer wall of the liquid hydrogen superconducting channel in this invention; Figure 5 This is a side view of the strain monitoring fiber axially bonded to the superconducting cable layer in this invention; Figure 6 This is a front view of the mechanical vibration monitoring optical fiber circumferentially surrounding the outer protective layer in this invention; Figure 7 This is a side view of the mechanical vibration monitoring optical fiber circumferentially surrounding the outer protective layer in this invention; Figure 8 The figure shows the simulation results of the liquid hydrogen superconducting channel based on MATLAB in this invention.

[0022] Reference numerals: 1. First liquid hydrogen transport pipeline; 2. First superconducting cable layer; 3. First electrical insulation layer; 4. Second superconducting cable layer; 5. Second liquid hydrogen transport pipeline; 6. Second electrical insulation layer; 7. Electrical shielding layer; 8. Vacuum insulation layer; 9. Outer protective layer; 10. Liquid hydrogen superconducting pipeline; 11. Sensor fiber optic network; 12. Distributed fiber optic sensing demodulation and processing unit; 13. Status assessment and early warning unit; 14. Human-machine interaction and data storage unit; 15. BOTDA module; 16. Φ-OTDR module; 17. Multi-parameter fusion decision module; 18. Non-metallic support frame; 19. Metallic support frame; 20. Sensor fiber optic cable. Detailed Implementation

[0023] To enhance understanding of the present invention, we will now describe it in further detail with reference to the accompanying drawings. These embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention. Example

[0024] like Figure 2 As shown, this embodiment proposes an online monitoring system for liquid hydrogen superconducting mixed transport composite pipelines based on optical fiber sensing, including a sensing optical fiber network 11, a distributed optical fiber sensing demodulation and processing unit 12, a status assessment and early warning unit 13, and a human-computer interaction and data storage unit 14.

[0025] The cross-sectional structure of the liquid hydrogen superconducting channel 10 of the present invention is as follows: Figure 1 As shown, the system includes a first liquid hydrogen transport pipeline 1 for liquid hydrogen transmission and cooling of a first superconducting cable layer; a first superconducting cable layer 2 for electrical energy transmission; a first electrical insulation layer 3 for electrical insulation between the first superconducting cable layer 2 and the second superconducting cable layer 4; a second superconducting cable layer 4 for electrical energy transmission; a second liquid hydrogen transport pipeline 5 for liquid hydrogen transmission and cooling of the second superconducting layer; a second electrical insulation layer 6 for electrical insulation of the entire liquid hydrogen superconducting pipeline; an electrical shielding layer 7 for electrical shielding of the entire liquid hydrogen superconducting pipeline; a vacuum insulation layer 8 for providing insulation for the entire liquid hydrogen superconducting pipeline; and an outer protective layer 9. The second liquid hydrogen transport pipeline 5 contains several non-metallic support frames 18 arranged radially along the energy transmission pipeline, and the vacuum insulation layer 8 contains several metallic support frames 19 arranged radially along the energy transmission pipeline.

[0026] Among them, the first liquid hydrogen transport pipeline 1 and the second liquid hydrogen transport pipeline 5 are both made of carbon fiber composite material; the first superconducting cable layer 2 and the second superconducting cable layer 4 are both made of superconducting tape MgB2; the first electrical insulation layer 3 and the second electrical insulation layer 6 are both made of polypropylene laminated paper; the electrical shielding layer 7 is made of superconducting tape Bi2223; the vacuum insulation layer 8 is made of coaxial double-layer stainless steel corrugated pipe, with a vacuum drawn between the two layers of stainless steel corrugated pipe and multiple layers of radiation-proof metal foil embedded; the outer protective layer 9 is the outermost stainless steel corrugated pipe.

[0027] Fiber optic sensor network 11 deployment Figure 3 As shown, a temperature monitoring optical fiber is spirally wound around the outer wall of the liquid hydrogen transportation pipeline with a pitch of 20 mm. It is fixed using low-temperature curing epoxy resin dispensing, and mechanically reinforced with titanium alloy clamps at 200 mm intervals. Figure 4 As shown, strain monitoring optical fibers are axially bonded to the superconducting cable layer. Three optical fibers are arranged at 120° intervals around the circumference of the pipe, pre-stretched with a 0.1% strain before bonding to eliminate installation slack, and a low-temperature adhesive containing nano-alumina filler is used. Figure 5 and Figure 6 As shown, optical fibers for monitoring mechanical vibration are arranged around the outer protective layer, and are deployed at approximately 50mm vertically along the pipe at the top and bottom and left and right positions, namely the 12 o'clock, 6 o'clock, 9 o'clock, and 3 o'clock positions.

[0028] The distributed fiber optic sensing demodulation and processing unit 12 includes a BOTDA module (Brillouin Optical Time Domain Analysis) 15 and a Φ-OTDR module (Phase-Sensitive Optical Time Domain Reflectometer) 16. BOTDA module 15 is a dual-end injection system that injects a high-frequency pulsed pump light into one end of the fiber under test and a lower-frequency continuous probe light into the other end. Both lights have frequencies on the order of approximately 193 THz (corresponding to a wavelength of 1550 nanometers), but the key is the frequency difference between them, which typically ranges from 10 GHz to 11 GHz. When the frequency difference between these two beams falls within the Brillouin frequency shift range of the fiber, stimulated Brillouin scattering occurs, causing energy to transfer from the higher-frequency pulsed pump light to the lower-frequency continuous probe light, resulting in maximum gain for the continuous light. By changing the frequency of the continuous light, Brillouin gain values ​​at different frequencies can be obtained, thus yielding the Brillouin gain spectrum at a specific point in the fiber. Subsequently, Lorentz curve fitting can be used to calculate the Brillouin frequency shift at various locations within the fiber, enabling distributed sensing of temperature or strain along the entire fiber. The Φ-OTDR module 16 uses a narrow-linewidth laser as its light source, causing scattered light within the same pulse width to interfere with each other. The system obtains vibration information along the optical fiber by demodulating this backscattered Rayleigh light. When there is a slight disturbance in the external environment, it changes the refractive index of the optical fiber at that location, causing a change in the optical path length and thus altering the optical phase. Since the interference result is sensitive to the optical phase, this changes the amplitude of the backscattered Rayleigh light. Therefore, the vibration location can be identified and located by the difference between the backscattered Rayleigh signals between two adjacent cycles. Subsequently, the vibration signal can be used to monitor pipeline leaks. When a pipeline leaks or suffers human damage, the amplitude difference method can be used to analyze the changes in the amplitude of the optical signal before and after vibration under different circumstances. This allows for timely identification and location of pipeline leaks and provides early warning of actions that may threaten pipeline safety.

[0029] After processing the monitored multiple parameters, the status assessment and early warning unit 13 responds by executing the multi-parameter fusion decision module 17 to conduct a risk assessment, take response actions, and issue tiered early warnings. (See Table 1 and...) Figure 2 As shown, when any single parameter is slightly abnormal, a log is recorded without warning; when any single parameter is significantly abnormal, maintenance personnel are notified (Level 1 warning); when any two parameters are abnormal, pipeline flow is limited, pipeline pressure is reduced and stabilized, and maintenance personnel are remotely notified (Level 2 warning); when multiple parameters are abnormal together, the fire protection system is activated, and valves are shut off in an emergency (Level 3 warning). Built-in fatigue life model and vacuum deterioration entropy value warning enable tiered control from logging without warning to three levels of emergency response warnings. It has a low false alarm rate for leaks and provides early fault diagnosis and predictive maintenance support. The anomaly levels and parameter definitions for multi-parameter fusion decision-making are shown in Table 1 below. Table 1. Definition of Anomaly Level and Parameter Range for Multi-Parameter Fusion Decision Module The human-computer interaction and data storage unit 14 constructs a three-dimensional holographic interaction platform, and the visualization engine renders the pipeline temperature / strain cloud map in real time, accurately locating the leak point with an error of <0.5m; the data is stored in a time-series database and object storage in layers; it supports multi-terminal access, and ensures system security through encryption and access control. The disaster recovery architecture ensures RTO <1min, ensuring system security and the traceability of historical data, forming a monitoring closed-loop management hub.

[0030] The BOTDA module operates by following these steps: Step 1: Inject a high-frequency pulsed pump light into one end of the fiber under test, and inject a low-frequency continuous probe light into the other end.

[0031] Step 2: Change the frequency of the continuous light to obtain the Brillouin gain value at different frequencies, and then obtain the Brillouin gain spectrum at a certain point in the optical fiber.

[0032] Step 3: Calculate the Brillouin frequency shift at each location of the optical fiber using Lorentz curve fitting to achieve distributed sensing of temperature or strain along the entire optical fiber.

[0033] The relationship between Brillouin frequency shift and temperature and strain is as follows:

[0034] In the formula: Represents the Young's modulus of an optical fiber; Indicates Poisson's ratio; Indicates the density of the fiber core; This is expressed as the wavelength of the pump light in a vacuum; This represents the refractive index of the optical fiber. The temperature of the optical fiber itself. or strain When it changes, its refractive index It will change under the influence of the elasto-optical effect and the thermo-optical effect, thus making The parameters change. Therefore, these parameters can be expressed as follows: .

[0035] Brillouin frequency shift variation in sensing fiber and its temperature change and the amount of strain change Under certain conditions, it can be expressed as:

[0036] In the formula: Indicates the initial reference temperature; Indicates the initial reference strain; This represents the temperature coefficient of the optical fiber; This represents the strain coefficient of the optical fiber.

[0037] The Φ-OTDR module operates in the following steps: Step 1: Using a narrow linewidth laser as the light source, make the scattered light within the same pulse width interfere with each other.

[0038] Step 2: Demodulate the backscattered Rayleigh light to obtain vibration information along the optical fiber.

[0039] Step 3: Use the difference between the backscattered Rayleigh signals of two adjacent cycles to identify and locate the vibration location.

[0040] Step 4: Use the amplitude difference method to analyze the changes in the amplitude of the optical signal before and after vibration under different conditions, identify and locate pipeline leaks in a timely manner, and provide early warnings for behaviors that may threaten pipeline safety.

[0041] When there is no external disturbance, the optical signal detected at the input end of the sensing fiber is as shown in the following formula:

[0042] In the formula: Indicates the amplitude of the scattered light; This represents the time required for the scattered light to return to the incident end; This indicates the first segment of the sensing fiber. One scattering point; This indicates the total number of scattering points in this segment of the sensing fiber; Represents the frequency of the pulsed light. (Rectangular function) As shown below:

[0043] Therefore, the formula for the power of backscattered Rayleigh light is:

[0044] In the formula: It represents the sum of the backscattered Rayleigh light power generated at different scattering points in the optical fiber, and is independent of the vibration, temperature and frequency of the light source of the optical fiber; This represents the result of the coherent superposition of Rayleigh scattered light from different scattering points. The phase difference between two scattering points can be expressed as: ,in This represents the distance between two scattering points. Due to the interference term... It is about The function of refractive index, and the refractive index Depending on the vibration of the optical fiber, the Φ-OTDR can achieve the sensing of minute disturbances.

[0045] For example, MATLAB can be used to simulate and test liquid hydrogen superconducting pipelines. Taking the BOTDA module as an example, the temperature parameter characteristics obtained from the calculated and identified signals are as follows: Figure 8 As shown, the abnormal temperature location was detected at 24.9 meters, with an abnormal temperature of 16.7K. According to the multi-parameter fusion decision module 17, ΔT = 3-5K was found, indicating a significant single-parameter anomaly. The maintenance personnel were notified, and a level one warning was issued. Finally, the possible causes were analyzed: liquid hydrogen leaked at 24.9 meters in the pipeline, causing local insulation failure.

[0046] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. An optical fiber sensing based on-line monitoring system for liquid hydrogen superconducting hybrid composite pipeline, characterized in that, The application relates to a liquid hydrogen superconducting pipeline monitoring system. The application comprises the following: A sensing optical fiber network: a sensing network is formed by spirally winding sensing optical fibers outside the outer wall of a liquid hydrogen superconducting pipeline to be measured, and distributed data acquisition of the liquid hydrogen superconducting pipeline is performed; A distributed optical fiber sensing demodulation and processing unit: used for demodulating the collected distributed data to obtain multi-parameter data; A state evaluation and early warning unit: multi-level decision is made by fusing the multi-parameter data after demodulation; Different levels of response measures and different levels of early warning are performed according to the type of parameter abnormality; 2. The liquid hydrogen superconducting mixed transport composite pipeline online monitoring system based on optical fiber sensing according to claim 1, characterized in that, A man-machine interactive data storage unit: a visual three-dimensional holographic interactive platform is constructed, and data is stored; the stored data supports historical data analysis and multi-terminal access. The liquid hydrogen superconducting pipeline comprises, from inside to outside, a first liquid hydrogen conveying pipeline, a first superconducting cable layer, a first electrical insulation layer, a second superconducting cable layer, a second liquid hydrogen conveying pipeline, a second electrical insulation layer, an electrical shielding layer, an outer protective layer, a vacuum heat insulation layer and an outer protective layer. The first liquid hydrogen conveying pipeline is used for liquid hydrogen transmission and simultaneously cools the first superconducting cable layer; the first superconducting cable layer is used for electric energy transmission; the first electrical insulation layer is used for electrical insulation between the first superconducting cable layer and the second superconducting cable layer; The second superconducting cable layer is used for electric energy transmission; the second liquid hydrogen conveying pipeline is used for liquid hydrogen transmission and simultaneously cools the second superconducting layer; the second electrical insulation layer is used for electrical insulation of the whole liquid hydrogen superconducting pipeline; The electrical shielding layer is used for electrical shielding of the whole liquid hydrogen superconducting pipeline; The vacuum heat insulation layer is used for providing heat insulation for the whole liquid hydrogen superconducting pipeline; 3. The liquid hydrogen superconducting mixed transport composite pipeline online monitoring system based on optical fiber sensing according to claim 2, characterized in that, The outer protective layer comprises inner and outer sides and is used for forming an installation space for the vacuum heat insulation layer.

4. The liquid hydrogen superconducting mixed transport composite pipeline online monitoring system based on optical fiber sensing according to claim 2 or 3, characterized in that, The second liquid hydrogen conveying pipeline is provided with a plurality of non-metallic support frames arranged along the radial direction of the energy transmission pipeline, and the vacuum heat insulation layer is provided with a plurality of metal support frames arranged along the radial direction of the energy transmission pipeline.

5. The liquid hydrogen superconducting mixed transport composite pipeline online monitoring system based on optical fiber sensing according to claim 4, characterized in that, The sensing optical fibers are spirally wound on the outer wall of the liquid hydrogen conveying pipeline to monitor temperature, and are axially pasted on the superconducting cable layer to monitor strain, and are circumferentially wrapped on the outer protective layer to monitor mechanical vibration.

6. The liquid hydrogen superconducting mixed transport composite pipeline online monitoring system based on optical fiber sensing according to claim 4, characterized in that, The temperature monitoring optical fibers are spirally wound on the outer wall of the liquid hydrogen conveying pipeline with a pitch of 20 mm, are fixed by using low-temperature curing epoxy resin dispensing, and are mechanically reinforced by using titanium alloy clamps every 200 mm.

7. The liquid hydrogen superconducting mixed transport composite pipeline online monitoring system based on optical fiber sensing according to claim 4, characterized in that, The strain monitoring optical fibers are axially pasted on the superconducting cable layer, three optical fibers are arranged at intervals of 120 degrees in the circumferential direction of the pipeline, are pasted after being pre-stretched by 0.1 percent, are used for eliminating installation slack, and are fixed by using low-temperature adhesive containing nano-aluminum oxide fillers.

8. The liquid hydrogen superconducting mixed transport composite pipeline online monitoring system based on optical fiber sensing according to claim 1, characterized in that, The mechanical vibration monitoring optical fibers are circumferentially wrapped on the outer protective layer, and are arranged on the upper and lower positions and the left and right positions of the pipeline in the vertical direction of the pipeline.

9. The liquid hydrogen superconducting mixed transport composite pipeline online monitoring system based on optical fiber sensing according to claim 8, characterized in that, The distributed optical fiber sensing demodulation and processing unit comprises a BOTDA module and a Phi-OTDR module; the BOTDA module emits laser to the sensing optical fibers, and simultaneously demodulates temperature and strain by using stimulated Brillouin scattering frequency shift; the Phi-OTDR module detects Rayleigh scattering phase change, captures mechanical vibration and liquid hydrogen leakage sound marks. The BOTDA module operates according to the following steps: High-frequency pulse pump light is injected into one end of the optical fiber to be measured, and low-frequency continuous probe light is injected into the other end. The frequency of the continuous light is changed to obtain the Brillouin gain values at different frequencies, and thus the Brillouin gain spectrum of a certain point of the optical fiber is obtained; The Brillouin frequency shift of the optical fiber at each position is calculated by using a Lorentz curve fitting, so that the distributed sensing of the temperature or strain of the optical fiber is realized.

10. The liquid hydrogen superconducting hybrid pipeline on-line monitoring system based on fiber-optic sensing according to claim 8, wherein, The Φ-OTDR module operates according to the following steps: A narrow-linewidth laser is used as a light source, so that the scattered light in the same pulse width interferes with each other; The back Rayleigh scattering light is demodulated to obtain vibration information of the optical fiber along the line; The difference between the adjacent two period back Rayleigh scattering signals is used to identify and locate the vibration position; The amplitude difference method is used to analyze the change of the light signal amplitude before and after the vibration under different conditions, so as to identify and locate the pipeline leakage position.

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