A device and method for monitoring flow and leaks in a liquid pipeline based on fiber optic sensing

Abstract

The application belongs to the technical field of distributed optical fiber sensing, and particularly relates to a liquid pipeline flow and leakage monitoring device and method based on optical fiber sensing. The device comprises a scattering enhancement detection system, a scanning laser, a second optical fiber coupler, an optical fiber ring, an optical fiber wavelength division multiplexer, an optical fiber grating strain sensor, a fourth photoelectric detector, a data acquisition unit, a data processing unit and a scattering enhancement optical fiber. The second optical fiber coupler, the optical fiber wavelength division multiplexer and the data acquisition unit are connected with the scattering enhancement detection system. The scanning laser, the second optical fiber coupler and the optical fiber ring are sequentially connected. The optical fiber ring, the optical fiber wavelength division multiplexer, the fourth photoelectric detector, the data acquisition unit and the data processing unit are sequentially connected. The device and method provided by the application can realize accurate measurement of pipeline flow and real-time monitoring of pipeline leakage.

Description

Technical Field

[0001] This invention belongs to the field of distributed optical fiber sensing technology, specifically relating to a device and method for monitoring flow and leakage in liquid pipelines based on optical fiber sensing. Background Technology

[0002] Fiber-optic distributed acoustic sensor (DAS) technology has been widely used in exploration, security, and structural health monitoring over the past decade due to its numerous advantages, including non-invasiveness, long testing distance, and immunity to electromagnetic interference. Traditional DAS systems use single-mode fiber as the sensing unit. However, due to issues in fiber fabrication processes, the refractive index distribution within single-mode fiber is uneven, leading to random interference between scattered signals and resulting in coherent fading. Coherent fading severely impacts the testing performance of DAS systems, specifically manifesting as very low signal amplitude at fading points, making phase demodulation difficult and hindering effective signal extraction. Scatter-enhanced fibers, by periodically etching gratings onto the fiber core, can effectively increase the intensity of reflected signals. Scatter-enhanced DAS systems can effectively solve the coherent fading problem and improve DAS system performance.

[0003] Accurate flow monitoring is crucial for liquid transportation via pipelines, ensuring both safety and efficiency. Leaks during pipeline transport are a serious safety concern; leaks of liquids like gasoline can cause significant economic and energy losses, environmental pollution, and potential injuries or fatalities. Real-time pipeline monitoring, timely leak location and repair, can greatly reduce economic losses and prevent large-scale safety accidents.

[0004] In pipeline flow testing, leak monitoring, and third-party disturbance detection, fiber optic sensing technology is becoming a standard technology and playing an increasingly important role. Chinese patent CN201910195421.7 discloses a pipeline liquid flow velocity monitoring system and method based on distributed fiber optic temperature sensing technology, capable of monitoring the flow velocity of multiple pipelines; however, it requires the simultaneous laying of heating cables, making implementation complex. Chinese patent CN202211247692.0 proposes a leak monitoring device based on distributed fiber optic strain sensing technology, utilizing the principle of expansion bands upon contact with liquid to monitor liquid leaks at all temperatures. Chinese patent CN202122144034.6 proposes a pipeline multi-parameter monitoring system, using different types of fiber optic gratings to monitor temperature, flow velocity, and pressure within the pipeline; however, it is difficult to achieve comprehensive monitoring of leak events at all locations along the pipeline.

[0005] Furthermore, DAS technology, due to its significant advantages such as long monitoring distance and high testing frequency, is increasingly being reported for real-time monitoring of oil and gas pipeline leaks and third-party disturbances. Chinese patent CN201910599778.1 proposes a system that utilizes multiple sensing optical fibers and multiple DAS data processing systems working together to measure parameters such as flow velocity and leakage. However, the data processing method is complex and requires the laying of multiple sensing optical fibers; an excessive number of beam splitters can also affect the monitoring distance.

[0006] Based on current technology, there is a lack of a device and method for simultaneously monitoring the flow and leakage of liquid pipelines that is simple in structure and data processing and has the ability to monitor over long distances. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a device and method for monitoring flow and leakage in liquid pipelines based on fiber optic sensing; it can accurately measure pipeline flow while simultaneously monitoring pipeline leakage in real time.

[0008] This invention is achieved through the following technical solution: A flow and leakage monitoring device for liquid pipelines based on fiber optic sensing, the device comprising: a scattering enhancement detection system, a scanning laser, a second fiber optic coupler, a fiber optic circulator, a fiber wavelength division multiplexer, a fiber optic grating strain sensor, a fourth photodetector, a data acquisition unit, a data processing unit, and a scattering enhancement fiber. The second fiber coupler, the fiber wavelength division multiplexer, and the data acquisition unit are all connected to the scattering enhancement detection system; the scattering enhancement detection system is used to detect and demodulate vibration signals. The scanning laser, the second fiber coupler, and the fiber circulator are connected in sequence; the scattering enhancement fiber and the fiber grating strain sensor are disposed in the pipeline containing the liquid to be detected. The fiber optic circulator, the fiber optic wavelength division multiplexer, the fourth photodetector, the data acquisition unit, and the data processing unit are connected in sequence.

[0009] Furthermore, one input end of the scanning laser and the second fiber coupler are connected; the other input end of the second fiber coupler is connected to the scattering enhancement detection system; therefore, the output end of the second fiber coupler is connected to the first port of the fiber circulator. The third port of the fiber optic circulator is connected to the fiber optic wavelength division multiplexer; the output port of the fiber optic wavelength division multiplexer corresponding to the scattering enhancement band is connected to the scattering enhancement detection system; and the output end of the fiber optic wavelength division multiplexer corresponding to the fiber optic grating strain sensor is connected to the fourth photodetector; the output end of the fourth photodetector is connected to the channel of the data acquisition unit; the analog output interface of the data acquisition unit is connected to the scattering enhancement detection system; and the data output interface of the data acquisition unit is connected to the data processing unit.

[0010] Furthermore, the second port of the fiber optic circulator is connected to the scattering enhancement fiber, and the scattering enhancement fiber is connected to the fiber optic grating strain sensor; or, the second port of the fiber optic circulator is connected to the fiber optic grating strain sensor, and the fiber optic grating strain sensor is connected to the scattering enhancement fiber.

[0011] Furthermore, the scattering enhancement detection system is a scattering enhancement system based on a 3x3 coupler; The scattering enhancement system based on the 3x3 coupler includes a narrow linewidth laser, a first fiber coupler, an acousto-optic modulator driver, an acousto-optic modulator, a fiber amplifier, a fiber bandpass filter, a 3x3 fiber coupler, a first photodetector, a second photodetector, a third photodetector, and a polarization controller. The output of the narrow linewidth laser is connected to the input of the fiber coupler, one output of the fiber coupler is connected to the acousto-optic modulator, and the other output of the fiber coupler is connected to the input of the polarization controller. The output of the polarization controller is connected to one input port of the 3x3 fiber coupler; the output port of the scattering enhancement band of the fiber wavelength division multiplexer is connected to the other input port of the 3x3 fiber coupler; the output port of the scanning laser band of the fiber wavelength division multiplexer is connected to the fourth photodetector. The output of the acousto-optic modulator is connected to the input of the fiber optic amplifier, the output of the fiber optic amplifier is connected to the input of the fiber optic bandpass filter, and the output of the fiber optic bandpass filter is connected to one input of the second fiber optic coupler. The three output ports of the three-by-three fiber coupler are respectively connected to the first photodetector, the second photodetector, and the third photodetector; the three outputs of the first photodetector, the second photodetector, and the third photodetector are respectively connected to the three inputs of the data acquisition unit. The analog output terminal of the data acquisition unit is connected to the input terminal of the acousto-optic modulator driver; and the output terminal of the acousto-optic modulator driver is connected to the acousto-optic modulator.

[0012] Furthermore, the scattering enhancement detection system is a heterodyne scattering enhancement detection system; the heterodyne scattering enhancement detection system includes a narrow linewidth laser, a first fiber coupler, an acousto-optic modulator driver, an acousto-optic modulator, an electro-optic modulator, a fiber amplifier, a fiber bandpass filter, a polarization controller, a third fiber coupler, and a first photodetector; The output of the narrow linewidth laser is connected to one input port of the first fiber coupler; the two outputs of the first fiber coupler are respectively connected to the acousto-optic modulator and the polarization controller. The output of the acousto-optic modulator is connected to the input of the electro-optic modulator; the electro-optic modulator is used to frequency shift the optical signal; the electro-optic modulator, the erbium-doped fiber amplifier, and the fiber bandpass filter are connected in sequence; the fiber bandpass filter is connected to one input of the second fiber coupler. The output of the polarization controller is connected to one input of the third fiber coupler, and the other input of the third fiber coupler is connected to the output port corresponding to the scattering enhancement band of the fiber wavelength division multiplexer; the output of the third fiber coupler is connected to the first photodetector, and the output of the first photodetector is connected to the data acquisition unit; the analog output of the data acquisition unit is connected to the acousto-optic modulator driver to provide a modulation signal, and the acousto-optic modulator driver is connected to the acousto-optic modulator.

[0013] Furthermore, the narrow linewidth laser operates at a wavelength of 1550nm and is used to output optical signals with different pulse widths.

[0014] Furthermore, the operating wavelength of the scanning laser is 1310nm, used for wavelength scanning within a range of ±20nm; the fiber wavelength division multiplexer is used to distinguish between the 1550nm optical band and the 1310nm optical band.

[0015] A method for monitoring flow and leakage in liquid pipelines based on fiber optic sensing, the method comprising: Step 1: Turn on the scanning laser and measure the wavelength of light returned by the fiber optic strain sensor when there is no liquid flow in the pipe and under different liquid flow rates, so as to obtain the strain change and establish the relationship curve between strain and flow rate. Step 2: Turn on the narrow linewidth laser to enable the scattering enhancement detection system, record the demodulated phase data along the pipeline under no-leak and different leakage conditions, and establish a dataset; use the dataset to train the convolutional neural network to obtain the turbulence feature convolution kernel; Step 3: The system officially starts working. The data acquisition unit performs phase demodulation on the data acquired from the 3x3 coupler-based scattering enhancement system using a 3x3 fiber coupler to obtain demodulated phase data; or the data acquisition unit performs phase demodulation on the data acquired from the heterodyne scattering enhancement detection system using a heterodyne-based method to obtain demodulated phase data. After filtering and noise reduction of the data from the fiber Bragg grating strain sensor, the data is sent to the data processing unit. Using the strain-flow velocity relationship curves and turbulence feature convolution kernels obtained in steps one and two, the data processing unit performs convolutional neural network operations on the demodulated phase data to identify turbulence caused by leakage, converts the strain data into flow velocity to obtain the flow velocity result, and finally displays the result.

[0016] In this invention, a weakly reflective Bragg fiber grating is etched in the middle of the scattering-enhancing fiber. The center wavelength of the weakly reflective Bragg fiber grating is consistent with the wavelength of the narrow-linewidth laser in the scattering-enhancing detection system, so as to effectively reflect the light emitted by the narrow-linewidth laser. Furthermore, a strain-sensitive fiber grating is connected to the front or rear end of the scattering-enhancing fiber. The center wavelength of the strain-sensitive fiber grating is consistent with the scanning center wavelength of the scanning laser, so as to properly demodulate the strain change on the fiber grating. The strain fiber grating is reflective and needs to be encapsulated to enhance robustness while isolating it from temperature effects.

[0017] Beneficial technical effects of the present invention: In the method provided by this invention, leakage and flow velocity monitoring are located in the 1550nm and 1310nm bands, respectively, so they can be monitored simultaneously without interference. This method has the advantages of long monitoring distance and simple structure and data processing.

[0018] The present invention provides a flow and leakage monitoring device and method for liquid pipelines based on scattering-enhanced distributed optical fiber acoustic sensing (DAS) technology. It has a simple structure and data processing method, long-distance monitoring capability, and can accurately measure pipeline flow while monitoring pipeline leakage in real time. Attached Figure Description

[0019] Figure 1 This is a system diagram of the pipeline flow and leakage monitoring implementation based on the 3x3 coupler scattering enhancement system in Embodiment 1 of the present invention; Figure 2 This is a system diagram of the pipeline flow and leakage monitoring implementation based on the heterodyne demodulation scattering enhancement system in Embodiment 2 of the present invention; The attached figures are labeled as follows: 1. Narrow linewidth laser; 2. First fiber coupler; 2'. Second fiber coupler; 3. Acousto-optic modulator driver; 4. Acousto-optic modulator; 5. Fiber amplifier; 6. Fiber bandpass filter; 7. Scanning laser; 8. Electro-optic modulator; 9. Fiber circulator; 10. Fiber wavelength division multiplexer; 11. Three-by-three fiber coupler; 12. First photodetector; 12'. Second photodetector; 12''. Third photodetector; 12'''. Fourth photodetector; 13. Data acquisition unit; 14. Polarization controller; 15. Fiber Bragg grating strain sensor; 16. Data processing unit; 17. Scattering enhancement fiber. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0022] Example 1: A flow and leakage monitoring device for liquid pipelines based on fiber optic sensing, see attached document. Figure 1 The device includes: a scattering enhancement detection system, a scanning laser 7, a second fiber coupler 2', a fiber circulator 9, a fiber wavelength division multiplexer 10, a fiber grating strain sensor 15, a fourth photodetector 12''', a data acquisition unit 13, a data processing unit 16, and a scattering enhancement fiber 17. The second fiber coupler 2', the fiber wavelength division multiplexer 10, and the data acquisition unit 13 are all connected to the scattering enhancement detection system; the scattering enhancement detection system uses optical principles to detect and demodulate vibration signals with high sensitivity. The scanning laser 7, the second fiber coupler 2', and the fiber circulator 9 are connected in sequence; the scattering enhancement fiber 17 and the fiber grating strain sensor 15 are disposed in the pipeline of the liquid to be detected. The fiber optic circulator 9, the fiber optic wavelength division multiplexer 10, the fourth photodetector 12''', the data acquisition unit 13, and the data processing unit 16 are connected in sequence.

[0023] In this embodiment, one input end of the scanning laser 7 and the second fiber coupler 2' are connected; the other input end of the second fiber coupler 2' is connected to the scattering enhancement detection system; therefore, the output end of the second fiber coupler 2' is connected to the first port of the fiber optic circulator 9. The third port of the fiber optic circulator 9 is connected to the fiber optic wavelength division multiplexer 10, and the output port of the fiber optic wavelength division multiplexer 10 corresponding to the scattering enhancement band is connected to the scattering enhancement detection system; the output end of the fiber optic wavelength division multiplexer 10 corresponding to the fiber optic grating strain sensor 15 is connected to the fourth photodetector 12'''; the output end of the fourth photodetector 12''' is connected to the channel of the data acquisition unit 13; the analog output interface of the data acquisition unit 13 is connected to the scattering enhancement detection system; and the data output interface of the data acquisition unit 13 is connected to the data processing unit 16.

[0024] In this embodiment, the second port of the fiber optic circulator 9 is connected to the scattering enhancement fiber 17, and the scattering enhancement fiber 17 is connected to the fiber optic strain sensor 15; or, the second port of the fiber optic circulator 9 is connected to the fiber optic strain sensor 15, and the fiber optic strain sensor 15 is connected to the scattering enhancement fiber 17.

[0025] In this embodiment, the scattering enhancement detection system is a scattering enhancement system 101 based on a 3x3 coupler; The scattering enhancement system 101 based on the 3x3 coupler includes a narrow linewidth laser 1, a first fiber coupler 2, an acousto-optic modulator driver 3, an acousto-optic modulator 4, a fiber amplifier 5, a fiber bandpass filter 6, a three-by-three fiber coupler 11, a first photodetector 12, a second photodetector 12', a third photodetector 12'', and a polarization controller 14. The output end of the narrow linewidth laser 1 is connected to the input end of the fiber coupler 2, one output end of the fiber coupler 2 is connected to the acousto-optic modulator 4, and the other output end of the fiber coupler 2 is connected to the input end of the polarization controller 14. The output of the polarization controller 14 is connected to one input port of the 3x3 fiber coupler 11; the output port of the scattering enhancement band of the fiber wavelength division multiplexer 10 is connected to another input port of the 3x3 fiber coupler 11; and the output port of the scanning laser band of the fiber wavelength division multiplexer 10 is connected to the fourth photodetector 12'''. The output of the acousto-optic modulator 4 is connected to the input of the fiber optic amplifier 5, the output of the fiber optic amplifier 5 is connected to the input of the fiber optic bandpass filter 6, and the output of the fiber optic bandpass filter 6 is connected to one input of the second fiber optic coupler 2'. The three output ports of the three-by-three fiber coupler 11 are respectively connected to the first photodetector 12, the second photodetector 12', and the third photodetector 12''; the three outputs of the first photodetector 12, the second photodetector 12', and the third photodetector 12'' are respectively connected to the three inputs of the data acquisition unit 13; The analog output terminal of the data acquisition unit 13 is connected to the input terminal of the acousto-optic modulator driver 3; and the output terminal of the acousto-optic modulator driver 3 is connected to the acousto-optic modulator 4.

[0026] In this embodiment, the narrow linewidth laser 1 operates at a wavelength of 1550nm and is used to output optical signals with different pulse widths.

[0027] In this embodiment, the operating wavelength of the scanning laser 7 is 1310nm, which is used to perform wavelength scanning within a range of ±20nm; the fiber wavelength division multiplexer 10 can at least distinguish between the 1550nm optical band and the 1310nm optical band.

[0028] In this embodiment, the scanning laser 7, the second fiber coupler 2', the fiber optic circulator 9, the scattering enhancement fiber 17, and the fiber optic strain sensor 15 are connected sequentially in the device; or The scanning laser 7, the second fiber coupler 2', the fiber optic circulator 9, the fiber optic strain sensor 15, and the scattering enhancement fiber 17 are connected in sequence.

[0029] Example 2: A flow and leakage monitoring device for liquid pipelines based on fiber optic sensing. This example is basically the same as Example 1, except for the scattering enhancement detection system. See Appendix. Figure 2 In this embodiment, the scattering enhancement detection system is a heterodyne scattering enhancement detection system 201; the heterodyne scattering enhancement detection system 201 includes a narrow linewidth laser 1, a first fiber coupler 2, an acousto-optic modulator driver 3, an acousto-optic modulator 4, an electro-optic modulator 8, a fiber amplifier 5, a fiber bandpass filter 6, a polarization controller 14, a third fiber coupler 2'', and a first photodetector 12; The output end of the narrow linewidth laser 1 is connected to one input port of the first fiber coupler 2; the two output ends of the first fiber coupler 2 are respectively connected to the acousto-optic modulator 4 and the polarization controller 14. The output of the acousto-optic modulator 4 is connected to the input of the electro-optic modulator 8; the electro-optic modulator 8 is used to frequency shift the optical signal; the electro-optic modulator 8, the erbium-doped fiber amplifier 5, and the fiber bandpass filter 6 are connected in sequence; the fiber bandpass filter 6 is connected to one input of the second fiber coupler 2'. The output of the polarization controller 14 is connected to one input of the third fiber coupler 2'', and the other input of the third fiber coupler 2'' is connected to the output port corresponding to the scattering enhancement band of the fiber wavelength division multiplexer 10; the output of the third fiber coupler 2'' is connected to the first photodetector 12, and the output of the first photodetector 12 is connected to the data acquisition unit 13; the analog output of the data acquisition unit 13 is connected to the acousto-optic modulator driver 3 to provide a modulation signal, and the acousto-optic modulator driver 3 is connected to the acousto-optic modulator 4.

[0030] Example 3: A method for monitoring flow and leakage in liquid pipelines based on fiber optic sensing, using the device described in Example 1 or Example 2, the method comprising: Step 1: Turn on the scanning laser and measure the wavelength of light returned by the fiber optic strain sensor when there is no liquid flow in the pipe and under different liquid flow rates, so as to obtain the strain change and establish the relationship curve between strain and flow rate. Step 2: Turn on the narrow linewidth laser to enable the scattering enhancement detection system. Record the demodulated phase data along the pipeline under both leak-free and leak-prone conditions, and establish a dataset. The turbulence caused by the leak is reflected in the demodulated phase data. Use the dataset to train the convolutional neural network to obtain the turbulence feature convolution kernel. The conventional techniques for processing fiber optic data using convolutional neural networks in existing technologies can be employed (such as the method for obtaining convolution kernels based on neural networks disclosed in patent CN202111521196.5).

[0031] Step 3: The system officially starts working. The data acquisition unit performs phase demodulation on the data acquired from the 3x3 coupler-based scattering enhancement system using a 3x3 fiber coupler to obtain demodulated phase data; or the data acquisition unit performs phase demodulation on the data acquired from the heterodyne scattering enhancement detection system using a heterodyne-based method to obtain demodulated phase data. After filtering and noise reduction of the data from the fiber Bragg grating strain sensor, the data is sent to the data processing unit. Using the strain-flow velocity relationship curves and turbulence feature convolution kernels obtained in steps one and two, the data processing unit performs convolutional neural network operations on the demodulated phase data to identify turbulence caused by leakage, converts the strain data into flow velocity to obtain the flow velocity result, and finally displays the result.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flow and leakage monitoring device for liquid pipelines based on fiber optic sensing, characterized in that, The device includes: a scattering enhancement detection system, a scanning laser, a second fiber coupler, a fiber circulator, a fiber wavelength division multiplexer, a fiber grating strain sensor, a fourth photodetector, a data acquisition unit, a data processing unit, and a scattering enhancement fiber. The second fiber coupler, the fiber wavelength division multiplexer, and the data acquisition unit are all connected to the scattering enhancement detection system; the scattering enhancement detection system is used to detect and demodulate vibration signals. The scanning laser, the second fiber coupler, and the fiber circulator are connected in sequence; the scattering enhancement fiber and the fiber grating strain sensor are disposed in the pipeline containing the liquid to be detected. The fiber optic circulator, the fiber optic wavelength division multiplexer, the fourth photodetector, the data acquisition unit, and the data processing unit are connected in sequence. The scattering enhancement detection system is a scattering enhancement system based on a 3x3 coupler; The scattering enhancement system based on the 3x3 coupler includes a narrow linewidth laser, a first fiber coupler, an acousto-optic modulator driver, an acousto-optic modulator, a fiber amplifier, a fiber bandpass filter, a 3x3 fiber coupler, a first photodetector, a second photodetector, a third photodetector, and a polarization controller. The output end of the narrow linewidth laser is connected to the input end of the first fiber coupler, one output end of the first fiber coupler is connected to the acousto-optic modulator, and the other output end of the first fiber coupler is connected to the input end of the polarization controller. The output of the polarization controller is connected to one input port of the 3x3 fiber coupler; the output port of the scattering enhancement band of the fiber wavelength division multiplexer is connected to the other input port of the 3x3 fiber coupler; the output port of the scanning laser band of the fiber wavelength division multiplexer is connected to the fourth photodetector. The output of the acousto-optic modulator is connected to the input of the fiber optic amplifier, the output of the fiber optic amplifier is connected to the input of the fiber optic bandpass filter, and the output of the fiber optic bandpass filter is connected to one input of the second fiber optic coupler. The three output ports of the three-by-three fiber coupler are respectively connected to the first photodetector, the second photodetector, and the third photodetector; the three outputs of the first photodetector, the second photodetector, and the third photodetector are respectively connected to the three inputs of the data acquisition unit. The analog output terminal of the data acquisition unit is connected to the input terminal of the acousto-optic modulator driver; and the output terminal of the acousto-optic modulator driver is connected to the acousto-optic modulator. The scanning laser operates at a wavelength of 1310nm and is used for wavelength scanning within a range of ±20nm; the fiber wavelength division multiplexer is used to distinguish between the 1550nm optical band and the 1310nm optical band. The steps for using the fiber optic sensing-based liquid pipeline flow and leakage monitoring device to monitor flow and leakage in liquid pipelines are as follows: Step 1: Turn on the scanning laser and measure the wavelength of light returned by the fiber optic strain sensor when there is no liquid flow in the pipe and under different liquid flow rates, so as to obtain the strain change and establish the relationship curve between strain and flow rate. Step 2: Turn on the narrow linewidth laser to enable the scattering enhancement detection system, record the demodulated phase data along the pipeline under no-leak and different leakage conditions, and establish a dataset; use the dataset to train the convolutional neural network to obtain the turbulence feature convolution kernel; Step 3: The system officially starts working. The data acquisition unit performs phase demodulation on the data acquired from the 3x3 coupler-based scattering enhancement system using a 3x3 fiber coupler to obtain demodulated phase data; or the data acquisition unit performs phase demodulation on the data acquired from the heterodyne scattering enhancement detection system using a heterodyne-based method to obtain demodulated phase data. After filtering and noise reduction of the data from the fiber Bragg grating strain sensor, the data is sent to the data processing unit. Using the strain-flow velocity relationship curves and turbulence feature convolution kernels obtained in steps one and two, the data processing unit performs convolutional neural network operations on the demodulated phase data to identify turbulence caused by leakage, converts the strain data into flow velocity to obtain the flow velocity result, and finally displays the result.

2. The flow and leakage monitoring device for liquid pipelines based on fiber optic sensing according to claim 1, characterized in that, The scanning laser is connected to one input of the second fiber coupler; the other input of the second fiber coupler is connected to the scattering enhancement detection system; and the output of the second fiber coupler is connected to the first port of the fiber circulator. The third port of the fiber optic circulator is connected to the fiber optic wavelength division multiplexer; the output port of the fiber optic wavelength division multiplexer corresponding to the scattering enhancement band is connected to the scattering enhancement detection system; and the output end of the fiber optic wavelength division multiplexer corresponding to the fiber optic grating strain sensor is connected to the fourth photodetector; the output end of the fourth photodetector is connected to the channel of the data acquisition unit; the analog output interface of the data acquisition unit is connected to the scattering enhancement detection system; and the data output interface of the data acquisition unit is connected to the data processing unit.

3. The flow and leakage monitoring device for liquid pipelines based on fiber optic sensing according to claim 1, characterized in that, The second port of the fiber optic circulator is connected to the scattering enhancement fiber, and the scattering enhancement fiber is connected to the fiber optic grating strain sensor; or, the second port of the fiber optic circulator is connected to the fiber optic grating strain sensor, and the fiber optic grating strain sensor is connected to the scattering enhancement fiber.

4. The flow and leakage monitoring device for liquid pipelines based on fiber optic sensing according to claim 1, characterized in that, The scattering enhancement detection system is a heterodyne scattering enhancement detection system; the heterodyne scattering enhancement detection system includes a narrow linewidth laser, a first fiber coupler, an acousto-optic modulator driver, an acousto-optic modulator, an electro-optic modulator, a fiber amplifier, a fiber bandpass filter, a polarization controller, a third fiber coupler, and a first photodetector. The output of the narrow linewidth laser is connected to one input port of the first fiber coupler; the two outputs of the first fiber coupler are respectively connected to the acousto-optic modulator and the polarization controller. The output terminal of the acousto-optic modulator is connected to the input terminal of the electro-optic modulator; The electro-optic modulator is used for frequency shifting of optical signals; The electro-optic modulator, the fiber amplifier, and the fiber bandpass filter are connected in sequence; the fiber bandpass filter is connected to one input end of the second fiber coupler. The output of the polarization controller is connected to one input of the third fiber coupler, and the other input of the third fiber coupler is connected to the output port corresponding to the scattering enhancement band of the fiber wavelength division multiplexer; the output of the third fiber coupler is connected to the first photodetector, and the output of the first photodetector is connected to the data acquisition unit; the analog output of the data acquisition unit is connected to the acousto-optic modulator driver to provide a modulation signal, and the acousto-optic modulator driver is connected to the acousto-optic modulator.

5. The flow and leakage monitoring device for liquid pipelines based on fiber optic sensing according to claim 1 or 4, characterized in that, The narrow linewidth laser operates at a wavelength of 1550nm and is used to output optical signals with different pulse widths.

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