PCCP (prestressed concrete cylinder pipe) three-dimensional space positioning online monitoring system based on distributed optical fiber sound field

Abstract

The invention discloses a PCCP pipeline three-dimensional space positioning online monitoring system based on a distributed optical fiber sound field. The PCCP pipeline three-dimensional space positioning online monitoring system comprises a signal processing module, a DAS system, and a first optical cable, a second optical cable and a third optical cable which are distributed and installed on the inner wall of a PCCP pipeline. The average refractive indexes of the first optical cable, the second optical cable and the third optical cable are consistent, and the phase difference between every two optical cables is 120 degrees; the DAS demodulates to obtain a sound wave signal transmitted by a pipe wall, water or air; the signal processing module obtains a vibration source type according to vibration signal feature analysis, and calculates a longitudinal position of a vibration source based on arrival time of sound wave signals propagated in various paths; and calculating the section position of the vibration source according to the arrival time of the vibration signal transmitted by the pipe wall and received by the optical cable and the section position of the optical cable. According to the method, external invasion and wire breakage of the PCCP can be monitored in real time, and the positions of the external invasion and the wire breakage can be accurately positioned.

Description

Technical Field

[0001] The present invention belongs to the technical field of signal processing of distributed optical fiber sensing, and in particular relates to a PCCP pipeline three-dimensional spatial positioning online monitoring system based on a distributed optical fiber acoustic field. Background Art

[0002] Prestressed Concrete Cylinder Pipe (PCCP) refers to a pipe made by winding annular prestressed steel wire on the outside of a concrete pipe core with a steel cylinder and making a cement mortar protective layer. The innermost layer is a concrete pipe core, a layer of steel cylinder is wrapped outside the pipe core, prestressed steel wire is wound outside the steel cylinder, and finally a cement mortar protective layer is poured. Therefore, the PCCP pipe has the characteristics of strong rigidity, corrosion resistance, and good sealing. The length of a section of PCCP pipeline is generally 4 to 5 meters, and the inner diameter is generally about 3 to 5 meters. Pipes can be connected by hot melting, electric melting, gluing, etc. PCCP pipes are widely used in water conservancy projects, and are usually used as water pipelines in large-scale water diversion and regulation projects.

[0003] External intrusion of PCCP pipelines refers to the impact or damage to the pipeline caused by external factors, including mechanical damage, human damage, natural disasters and other physical damage. Severe intrusion will not only cause irreparable damage to the pipeline itself, but also cause pollution sources in the external environment to affect the water quality transported inside the pipeline, leading to further safety problems.

[0004] In actual work, due to material defects, non-standard production, construction, environmental corrosion and other reasons, PCCP pipelines will be damaged to varying degrees. These damages may cause prestressed steel wire breakage, mortar protective layer peeling and pipe core concrete cracking. The increase in the number of local broken wires will cause the PCCP pipe wall to yield, and eventually lead to pipeline rupture, causing leakage, pipe burst and other accidents. The strength of PCCP depends on the high-strength prestressed steel wire wrapped around the pipe core. The uniform compressive prestress generated by the steel wire on the pipe core can compensate for the stress generated by internal pressure and external load. Therefore, the failure of the PCCP pipeline can be judged by detecting whether the prestressed steel wire has broken wires. The current monitoring methods are mainly divided into electromagnetic monitoring methods and fiber optic sensor methods. The electromagnetic monitoring methods are mainly divided into far-field eddy current monitoring methods and orthogonal electromagnetic monitoring methods. The main difference is that according to the relative position of the excitation coil and the monitoring coil, the monitoring method of the fiber optic sensor has a series of advantages such as long transmission distance and anti-electromagnetic interference compared with the electromagnetic monitoring method.

[0005] During the water delivery process, the pipeline needs to monitor flow rate at intervals. On the one hand, the amount of water delivered can be controlled according to different water demands; on the other hand, the flow rates at different monitoring locations can be compared to determine whether there may be leakage, ensuring the safe operation of the pipeline within this monitoring range, thereby improving pipeline operation efficiency and refining pipeline management. Therefore, when delivering water over long distances, valves are usually installed at key locations of the PCCP pipeline to control whether water will continue to be delivered and the size of the water flow in the next distance. The use of valves covers a variety of functions from simple on / off control to complex flow regulation and pressure management, and valves may also leak due to aging, damage and other factors. Valve leakage will lead to inaccurate flow monitoring, and continuous leakage will also aggravate valve damage, waste of water resources, and further economic losses.

[0006] Conventional flow detection methods usually include electromagnetic method and differential pressure method. However, these detection methods require the placement of sensors inside the pipeline, which will damage the integrity of the pipeline and may also introduce additional crosstalk such as electromagnetic interference. Therefore, a non-invasive real-time pipeline monitoring technology is particularly important. According to the flow-induced vibration theory (FIV), when liquid flows through the pipeline, due to the existence of the pipeline wall, the flow direction of the liquid can only be along the axial direction. Combined with the first law of thermodynamics, when liquid molecules collide with the pipe wall, a small part of the kinetic energy will be converted into heat energy, and most of the remaining kinetic energy will be converted into potential energy in the form of pressure. Therefore, the liquid will exert pressure on the contact surface of the pipeline, causing the pipeline surface to vibrate. On this basis, according to the Euler-Bernoulli-beam theory, a flow perception model based on FIV can be established. According to the experiment designed by Evans et al. in 2004 to measure the acceleration values ​​corresponding to different flow rates by placing an accelerometer close to the outer wall of the pipe, it was concluded that the flow rate is quadratically proportional to the standard deviation of the pressure fluctuation of FIV. Lannes et al. used an accelerometer based on piezoelectric ceramics to test the FIV signal and found that the flow rate and the signal standard deviation are in a quadratic function relationship.

[0007] Pipeline leakage monitoring is to monitor the water pipeline around the clock. Once a perforation leak occurs, it must be able to respond to the alarm in time and determine the specific location. There are two main types of leak detection methods: direct leak detection method and indirect method. The direct method is to use the detection element (such as water sensitive element) preset outside the pipeline to directly measure the leaking medium. This method can detect tiny leaks and locate them, but it requires installation at the same time as the pipeline construction. The indirect method is to infer the occurrence of leakage by detecting changes in pipeline operating parameters, such as detecting pressure, flow, etc. The sensitivity of this method is not as high as the direct method, and it is suitable for detecting larger leaks (generally about 1%). The advantage is that it can be installed after the pipeline construction without affecting production, and can be continuously upgraded.

[0008] The invention with publication number CN118032716A discloses a PCCP pipeline broken wire monitoring system and method based on high-frequency parameter fusion, including a mutually compatible φ-OTDR system and a Michelson interferometer system, and combined with a data acquisition and analysis system. The PCCP pipeline broken wire monitoring system and method based on high-frequency parameter fusion provided by the invention adds a Michelson interferometer detection system on the basis of the traditional φ-OTDR, and deeply integrates the high-frequency signal provided by the Michelson interferometer system with the precise positioning signal of the φ-OTDR, effectively solving the shortcomings of the traditional single φ-OTDR monitoring of PCCP, solving the problem of limited detection bandwidth of the φ-OTDR, and greatly improving the efficiency of PCCP pipeline broken wire monitoring. However, the invention cannot accurately locate the location of broken wires or other external events, nor can it simultaneously monitor information such as flow or water level.

[0009] The invention with publication number CN105221936B discloses a device for monitoring and locating leakage points of directly buried thermal pipelines and its control method. Through three optical fibers distributed in the pipeline at an angle of 120° to each other, the approximate position of the leakage point in the pipeline cross section can be determined. When a pipeline leaks, the device can accurately locate the leakage point and issue an alarm and leakage point location report in a timely manner. The leakage point location is fast and accurate. After a pipeline leak occurs, the fault point can be located within a few minutes, shortening the repair time of the thermal pipeline. The device can locate multiple leakage points at the same time, realizing distributed monitoring and positioning of directly buried thermal pipelines. However, the device determines whether a leak occurs by comparing the temperature, and is not suitable for locating broken wires or external events in the PCCP pipeline. It is also impossible to simultaneously monitor information such as the flow rate or water level in the PCCP pipeline. Summary of the invention

[0010] The invention discloses a PCCP pipeline three-dimensional spatial positioning online monitoring system based on a distributed optical fiber acoustic field, which can monitor external intrusion and broken wires of the PCCP pipeline in real time and accurately locate the positions of the external intrusion and broken wires.

[0011] Technical solution:

[0012] A PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field, the PCCP pipeline three-dimensional spatial positioning online monitoring system comprising a signal processing module, a DAS system, and a first optical cable, a second optical cable and a third optical cable distributed and installed on the inner wall of the PCCP pipeline;

[0013] The first optical cable, the second optical cable and the third optical cable have the same average refractive index, and the phase difference between them is 120°; wherein the first optical cable is close to the bottom of the pipeline, and the second optical cable and the third optical cable are both located in the upper half of the pipeline and there is a height difference between them;

[0014] The first optical cable, the second optical cable and the third optical cable are all connected to the DAS system, and the DAS system collects the beat frequency signal of the back Rayleigh scattered light and the intrinsic light of the detection light pulse, and demodulates it to obtain the sound wave signal transmitted by the pipe wall, water or air;

[0015] The signal processing module obtains the type of vibration source based on the characteristic analysis of the vibration signal; at the same time, the signal processing module calculates the longitudinal position of the vibration source based on the arrival time of the sound wave signal propagated through various paths including the pipe wall, water or air, combined with the sound speed in different media; and locates the cross-sectional position interval of the vibration source based on the time difference of the vibration signal propagating along the pipe wall to the three optical cables.

[0016] Furthermore, the first optical cable, the second optical cable and the third optical cable are all desensitized optical cables.

[0017] Furthermore, the vibration sources include broken wires and external intrusion events acting on the pipeline.

[0018] Furthermore, the first optical cable, the second optical cable and the third optical cable are arranged in three directions of 40°, 160° and 280°.

[0019] Furthermore, the signal processing module determines the positioning accuracy of the pipeline profile according to the maximum measurement distance, and then calculates the pulse repetition frequency.

[0020] Furthermore, the signal processing module obtains the transmission time of the vibration signal through the optical cable after it is converted into an optical signal by combining the following formula:

[0021]

[0022] In the formula, t is the propagation time of the optical signal in the optical fiber, z is the distance from the vibration source, and c is the speed of light in a vacuum. is the average refractive index of the optical cable.

[0023] Furthermore, the signal processing module collects the optical fiber vibration signal to fit the standard deviation of the water flow pressure fluctuation in the pipeline, and uses the formula X sd =Au 2 -Bu calculates the internal flow rate of the pipeline at that time, where:

[0024]

[0025] Where K1 and K2 are correction factors introduced by the actual adhesion between the optical fiber and the pipe wall, T, r, I, and α are the wall thickness, radius, bending stiffness, and internal dissipation coefficient caused by the elastic material of the circular pipe, ρ is the fluid density, ξ is the friction coefficient between the pipe and the fluid, and L is the pipe length; the friction coefficient g is the acceleration due to gravity, Q is the fluid flow rate, d is the pipe diameter, and ΔP is the pressure difference between the two ends of the pipe.

[0026] Furthermore, the signal processing module divides the water level into three intervals according to the installation positions of the first optical cable, the second optical cable and the third optical cable;

[0027] The signal processing module analyzes different modes of the collected vibration signal to determine the water level range in the pipeline; and then combines the arrival time of the vibration signal and the propagation speed of the vibration signal in water and in air to analyze and obtain the real water level in the pipeline.

[0028] Furthermore, the PCCP pipeline three-dimensional spatial positioning online monitoring system includes transient pressure detection modules distributed at pipeline branch points and valve areas to measure the pipeline pressure at the location;

[0029] The signal processing module compares the pipeline pressures measured by two adjacent transient pressure detection modules to determine whether there is a pipeline leak between the two.

[0030] Furthermore, the transient pressure test module includes a cylindrical structure cast inside the pipeline, and an optical cable wound around the outside of the structure; the optical cable is connected to the DAS system.

[0031] Beneficial effects:

[0032] First, the PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field of the present invention proposes a unique optical fiber deployment method, which can identify different types of events according to the vibration signal frequency and amplitude generated when different events occur and the time difference caused by different propagation media of the same event, and non-destructively monitor the PCCP pipeline transportation process, while being able to accurately locate the position of external intrusion and broken wires.

[0033] Second, the PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field of the present invention can simultaneously measure information such as flow or water level in the PCCP pipeline to achieve multi-parameter monitoring.

[0034] Thirdly, the PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field of the present invention can monitor leakage problems at key positions in real time by setting a transient pressure test module. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a working flow chart of the PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field of the present invention;

[0036] Figure 2It is a cross-sectional diagram of the optical cable layout inside the PCCP pipeline and a schematic diagram of the degree of contact between the optical cable inside the PCCP pipeline and water at different water levels;

[0037] Figure 3 This is a simulation diagram of the optical cable layout inside the PCCP pipeline;

[0038] Figure 4 This is a schematic diagram of the layout of the PCCP pipeline transient pressure test module. DETAILED DESCRIPTION

[0039] The following examples will enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0040] The present invention discloses a PCCP pipeline three-dimensional spatial positioning online monitoring system based on a distributed optical fiber acoustic field, wherein the PCCP pipeline three-dimensional spatial positioning online monitoring system comprises a signal processing module, a DAS system, and a first optical cable, a second optical cable and a third optical cable distributedly installed on the inner wall of the PCCP pipeline;

[0041] The first optical cable, the second optical cable and the third optical cable have the same average refractive index, and the phase difference between them is 120°; wherein the first optical cable is close to the bottom of the pipeline, and the second optical cable and the third optical cable are both located in the upper half of the pipeline and there is a height difference between them;

[0042] The first optical cable, the second optical cable and the third optical cable are all connected to the DAS system, and the DAS system collects the beat frequency signal of the back Rayleigh scattered light and the intrinsic light of the detection light pulse, and demodulates it to obtain the sound wave signal transmitted by the pipe wall, water or air;

[0043] The signal processing module obtains the type of vibration source based on the characteristic analysis of the vibration signal; at the same time, the signal processing module calculates the longitudinal position of the vibration source based on the arrival time of the sound wave signal propagated through various paths including the pipe wall, water or air, combined with the sound speed in different media; and locates the cross-sectional position interval of the vibration source based on the time difference of the vibration signal propagating along the pipe wall to the three optical cables.

[0044] 1. Fiber optic deployment method

[0045] The present invention proposes a special optical fiber layout method, in which three optical cables are laid out at equal angles in a triangular shape inside the PCCP pipeline to be monitored, with a phase difference of 120°, evenly fixed on the inner wall of the pipeline, and one of them is close to the bottom of the pipeline. During signal transmission, the sensing optical fiber adopts space division multiplexing technology to simultaneously transmit the data collected by the three optical cables, thereby improving the transmission efficiency and ensuring the realization of long-distance signal transmission and high anti-interference ability.

[0046] Assume that the overall fiber optic cable is laid out over a distance of 10 km and is fixed inside a PCCP pipe with a diameter of 5 m. At the same time, ensure that the three optical cables are located in the first, second, and fourth quadrants of the pipe cross section. Since when one optical fiber is located directly below, the optical fibers on the left and right sides above must be symmetrical, and the ability to determine the specific quadrant is lost. Figure 2 For example, the polar coordinates of the three optical fibers in the first, second, and fourth quadrants are assumed to be (2.5, 40°), (2.5, 160°), and (2.5, 280°), respectively, which are converted into rectangular coordinates of (1.92, 1.61), (-2.35, 0.86), and (0.43, -2.46). According to the equation group:

[0047] (x-1.92) 2 +(y-1.61) 2 =d1 2

[0048] (x+2.35) 2 +(y-0.86) 2 =d2 2

[0049] (x-0.43) 2 +(y+2.46) 2 =d3 2

[0050] The specific value of d can be obtained by the time it takes for the three optical cables to collect vibration signals. The "pin"-shaped layout can achieve higher resolution through multi-point distribution and combined signal processing. Figure 3 This is a simulation diagram of the optical cable layout inside the PCCP pipeline. It should be understood that 40°, 160° and 280° are just one of the optional angle parameter combinations. In fact, as long as the setting of "the first optical cable is close to the bottom of the pipeline, the second optical cable and the third optical cable are both located in the upper half of the pipeline and there is a height difference between the two" is met, the monitoring needs of vibration, flow and water level can be met at the same time.

[0051] (II) Fiber Type Selection

[0052] Considering that during data acquisition, according to the Nyquist sampling theorem: to restore the original signal from the sampled signal without distortion, the sampling frequency should be greater than 2 times the highest signal frequency. In the case of broken wire monitoring, the signal frequency is usually between 10 and 30kHz. Using an optical fiber with normal sensitivity to collect signals requires the sampling frequency of the subsequent system to be at least 100kHz, and the pressure of subsequent data processing is relatively large. Therefore, the first optical cable, the second optical cable, and the third optical cable of the present invention can use desensitized optical fiber, and the outer part of the optical cable is wrapped with an acoustic bandpass sheath, so that the signal in the broken wire frequency range is enhanced, the influence of the environment and other types of noise is reduced, and the data processing burden caused by the three optical cables is avoided. The desensitized optical fiber amplifies or enhances the specific frequency signal by reducing the sensitivity of the optical fiber itself, relies on specific doping to reduce the sensitivity to environmental changes, and enhances the signal in the broken wire signal frequency band, so that the transmitted signal noise is lower and the bit error rate is lower. The overall pressure of subsequent signal processing algorithms such as signal enhancement and noise filtering will be reduced during operation.

[0053] Three optical cables adopt the mode of space division multiplexing, which is realized by separating the three optical cable signals in space, using a single optical cable containing multiple optical fiber cores, and each optical fiber core transmits an independent signal. In theory, three optical cables need three devices for real-time demodulation. Considering the space division multiplexing mode, the DAS system can be used to receive the signals of the three optical cables, and the space division multiplexing signals are separated into independent signal channels by demultiplexing, and each channel is analyzed to extract the information of external invasion, broken wire, internal flow of pipeline and leakage in valve, so as to reduce the cost of hardware part. The space division multiplexing technology adopted by the system of the present invention mainly adopts multi-core multiplexing. On the one hand, three optical cables can transmit independent signals at the same time, so that more data can be transmitted in the same time, which is equivalent to increasing the overall bandwidth and channel capacity of the system. On the other hand, by arranging three optical cables in different spatial positions, multi-point acquisition and monitoring of signals can be realized, and spatial resolution is improved.

[0054] (III) DAS system measurement principle

[0055] During signal collection, a coherent detection DAS system is used to collect physical disturbance signals along the optical fiber in real time. The system collects the beat frequency signal of the backscattered Rayleigh light and the intrinsic light of the detection light pulse; after filtering, amplifying and analog-to-digital conversion of the beat frequency signal, the Rayleigh backscattered (RBS) signal curve is obtained; the RBS signal is demodulated to obtain vibration information.

[0056] Distributed Acoustic Sensing (DAS) is a distributed fiber optic sensor based on Rayleigh scattering, which has the advantages of long detection distance, simultaneous detection of multiple events, and anti-electromagnetic interference. When an external vibration signal acts on the optical fiber, the refractive index and fiber diameter of the optical fiber part affected by the force will change slightly. When light waves propagate in an inhomogeneous medium, the light will interact with the particles in the medium, so that part of the light that should have propagated in a straight line cannot follow the original path and propagates in all directions. When a pulsed laser is injected into the optical fiber, it is equivalent to the interaction between the laser and the scattering particles in it, thus generating Rayleigh scattering, Brillouin scattering and Raman scattering. Different scattering can be monitored using the corresponding optical time domain reflectometry technology. In DAS, the φ-OTDR system based on Rayleigh scattering is used. Since the optical phase signal contains vibration information, the original vibration signal can be restored by collecting the back Rayleigh scattered light for demodulation. After demodulating and extracting the phase information of the scattered signal along the sensing optical fiber, the DAS system can reconstruct the acoustic information of the external disturbance along the optical fiber, and then reconstruct and identify the external disturbance information (strain, temperature, micro-vibration, etc.).

[0057] Multi-frequency DAS is an advanced fiber optic sensing technology that uses optical fiber as a continuous sensing element and detects acoustic events along the fiber path by analyzing tiny changes in light reflected from the optical fiber. It can simultaneously monitor at different frequencies and is used to capture acoustic events along the fiber path. Compared with traditional DAS systems, multi-frequency DAS can collect and analyze data at multiple frequencies, thereby being able to capture a wider range of physical phenomena. Therefore, the DAS system of the present invention adopts a multi-frequency DAS system, which collects data at multiple frequencies and effectively distinguishes and identifies different types of events. Considering that frequency is inversely proportional to measurement distance, the multi-frequency DAS system can ensure high sensitivity and resolution on the basis of a larger monitoring range.

[0058] The relationship between the system performance parameter selection and the three-dimensional positioning accuracy of the present invention. The propagation speed of vibration signals in the pipe wall, water, and air is quite different. The speed in the pipe wall can reach 3000m / s, which is much higher than the speed in the other two media. For a circular PCCP pipe, the minimum resolution distance for locating the specific quadrant position of a section should be related to the time difference of the vibration transmission to different positions, which is determined by Calculation, the limit pulse repetition frequency is According to the formula: The maximum unambiguous distance L is inversely proportional to the pulse repetition frequency (PRF), which limits the relationship between the detection distance and the minimum resolution distance. The spatial resolution is given by the formula It is calculated that τ is the pulse width. The smaller the pulse width, the higher the spatial resolution. The three optical cables are marked as 1, 2, and 3 respectively. The time when the corresponding optical cables detect vibration is measured. The specific position of the broken wire in a certain section can be accurately monitored. The higher the resolution of the instrument, the more accurate the positioning.

[0059] The actual hardware will result in limited resolution of a certain section, and some parameters need to be optimized. Calculated based on the PCCP pipe diameter of 5m, the circumference is approximately 15.7m and the semi-circumference is 7.85m. Since the propagation speed on the pipe wall is about 3000m / s, the longest time for the vibration signal to reach the optical fiber is 2.6ms, which means that the vibration signal usually propagates on the pipe wall in milliseconds. The layout of the three optical cables ensures that when vibration occurs at any position, the difference in angle between the optical cables at two positions and the vibration source is 120°, so the propagation time difference is The pulse repetition frequency is related to the resolution of the profile. If the resolution accuracy on the profile is required to be 10 cm, the minimum propagation time difference is The theoretical limit of the pulse repetition frequency is 33kHz. Considering the actual situation, the pulse repetition frequency should be at least 50kHz and the pulse repetition period should be 20μs, which limits the detection distance to 4.5km. If you want to improve the resolution, you must increase the pulse repetition frequency, according to the formula: The maximum unambiguous distance is inversely proportional to the pulse repetition frequency (PRF), which results in a shorter maximum distance for measurement. Therefore, the positioning accuracy of the profile and the maximum distance for measurement are mutually restricted, and appropriate parameters need to be selected based on actual conditions. For general 10km water pipeline monitoring, the resolution accuracy of the profile should not be less than 20cm. For the spatial resolution of the optical cable, assuming the pulse width is 100ns, the spatial resolution is calculated according to the formula τ is the pulse width, n is the refractive index of the optical fiber, then along the direction of the optical cable, the spatial resolution is about 10m. This parameter is mainly related to the pulse width of the pulse light and can be considered independently.

[0060] The multi-frequency DAS solution uses a light source to emit pulsed light of different frequencies, and can collect signals at multiple frequencies. Since pulsed light of different frequencies has different characteristics in propagation, reflection, absorption, etc., multi-frequency detection can obtain richer and more accurate results. In terms of the maximum detection distance and spatial resolution, the limit distance of a single frequency of 10kHz is 15km, while in the case of multi-frequency detection, if there is a signal with a frequency of 5kHz, the measurement distance can reach 30km; similarly, under the same duty cycle, the pulse width corresponding to the high-frequency signal will become lower, which can improve the spatial resolution of the system.

[0061] When external vibration signals such as natural geological activities and artificial excavation work act on the pipeline, the generated sound waves will propagate through the pipe wall or air. Due to the difference in the propagation paths in the two media, the optical cable will receive the sound wave signals at different times. The specific position of the vibration source can be calculated by using the arrival time of the signals collected by the three optical cables and combining them with the speed of sound in the medium. In addition, in this embodiment, the first optical cable, the second optical cable, and the third optical cable are distributed in three quadrants of the cross section. Considering that the time for the vibration signal to propagate along the pipe wall to the three optical cables is different, the time difference of the optical cable can be relied on to locate the specific quadrant of the cross section of the vibration source and obtain the cross-sectional position interval of the vibration source. In practical applications, other cross-sectional interval division methods can be selected to lay out optical fibers according to actual needs, and the number and position of optical fibers are both optional.

[0062] (IV) External intrusion monitoring

[0063] Monitor whether external intrusion signals are generated along the pipeline. The position of the intrusion signal along the optical fiber can be determined based on the propagation time of the back-scattered Rayleigh light in the optical fiber. The specific position is calculated according to L=ct, where c is the speed of light and t is time. External intrusion signals are simulated through experimental behaviors such as excavation, heavy object dropping, and vehicle operation. Compared with broken wire signals, external intrusion signals usually have a lower frequency, generally in the range of tens to hundreds of hertz. On this basis, the vibration signal can be analyzed and judged based on whether it is continuous and whether the range is extended forward or backward.

[0064] When the PCCP pipeline is invaded from outside, the specific location of the invasion along the line can be determined by the transmission time of the optical signal in the optical fiber, and the specific quadrant of the determined location can be located by the different sound speeds of the vibration signal in the PCCP pipeline wall, water in the pipeline, and air. is the propagation time of the optical signal in the optical fiber, z is the distance at which the intrusion event occurs, c is the speed of light in a vacuum, It is the average refractive index in the optical fiber. It can be used to obtain the transmission time of the vibration signal converted into a light signal through the optical fiber, thereby determining the specific position.

[0065] On this basis, each optical cable will obtain three signals of inconsistent intensities during collection, representing the vibration signals transmitted from the pipe wall, water, and air respectively. By judging whether the three vibration signals are generated, it is also possible to roughly determine whether the collection is correct and effective.

[0066] (V) Wire break monitoring

[0067] When wire breaks occur in a PCCP pipeline, considering that the frequency of wire breaks reaches 10 kHz or even higher and the short-time energy is very strong, it is very easy to judge whether there is an event of suspected wire break. The sound speed in the PCCP pipeline wall is about 3000 m / s, the sound speed in water at 25° is about 1500 m / s, and in air it is about 340 m / s. Each optical fiber will collect vibration signals transmitted through different media. Coupled with the extremely fast propagation speed of the vibration signal through the pipeline wall, the acquisition time difference of the three optical cables is at the millisecond level, and the delay caused by propagation through air is about dozens of milliseconds. Due to the time difference, the quadrant and specific location where the intrusion signal occurs can be judged through relevant calculations.

[0068] Specifically, when a wire break signal is generated along the monitored pipeline, the position of the wire break signal along the optical fiber can be determined according to the propagation time of the backward Rayleigh scattered light in the optical fiber. On this basis, the three optical cables are respectively marked as 1, 2, and 3, and the time when the corresponding optical cable monitors vibration is measured, and the specific position of the intrusion signal or wire break at a certain cross-section can be accurately monitored. Taking a pipeline with a diameter of 5 m as an example, the propagation speed of the vibration signal in the pipeline wall is 3000 m / s. Assuming that the position of the vibration source forms an angle of 30° with optical cable 1, 90° with optical cable 2, and 150° with optical cable 3, this means that in the case of propagation along the arc, the distances between the vibration source and the three optical cables are Specifically, they are 1.3 m, 3.9 m, and 6.5 m respectively. The specific times when the three optical cables receive the vibration signal can be calculated as 0.4 ms, 1.3 ms, and 2.2 ms respectively. In fact, the angles with the three optical cables can be inversely calculated from these three times. Assuming that it is now monitored that the signal acquisition time differences between optical cables 2, 3 and optical cable 1 are 0.9 ms and 1.8 ms respectively, it can be calculated that the vibration source is 2.7 m and 5.4 m farther from optical cables 2 and 3 than from 1. This means that the vibration source must be between optical cables 1 and 2, and the sum of the distances from the vibration source to optical cables 1 and 2 is 1 / 3 of the pipeline wall, about 5.2 m. Simple calculation shows that the distance between the vibration source and optical cable 1 is Corresponding to the angle is 28.6°. Ignoring the errors in calculation and measurement, 28.6° and 30° can be regarded as the same, so that positioning can be achieved. The wire break signal will generate a high-frequency signal lasting for more than 10 ms, with a frequency of about 10 - 30 kHz. A vibration signal that meets these two conditions is very likely to be a wire break signal. Compared with the monitoring method of a single optical cable, the 120° "pin" layout can accurately judge the specific quadrant where the wire break signal is generated, and has a better monitoring effect on the wire break position.

[0069] (VI) Flow monitoring

[0070] The internal flow is monitored long-term by the bottom optical fiber. Since the bottom optical fiber is close to the bottom, it basically meets the requirements for measuring the internal flow. Considering the use of space division multiplexing, the vibration signals of the three positions of the "pin" shape can be collected and processed at the same time. According to the Euler-Bernoulli-beam equation The standard deviation of the pressure fluctuation of the pipeline vibration is quadratically proportional to the flow rate. The standard deviation of the pressure fluctuation is fitted by collecting the optical fiber vibration signal, and the internal flow rate of the pipeline at that time is calculated using the following formula:

[0071] X sd =Au 2 -Bu

[0072]

[0073] K1 and K2 are correction factors introduced by the actual adhesion between the optical fiber and the pipe wall, where T, r, I, and α are the wall thickness, radius, bending stiffness, and internal dissipation coefficient caused by the elastic material of the circular pipe, ρ is the fluid density, ξ is the friction coefficient between the pipe and the fluid, and L is the pipe length. Parameters such as wall thickness, radius, fluid density, and correction factors can be obtained directly, while friction coefficient, bending stiffness, etc. need to be considered through formulas or actual tests. The friction coefficient is f is the friction coefficient, g is the acceleration of gravity, L is the length of the pipeline, Q is the fluid flow rate, d is the pipeline diameter, ΔP is the pressure difference between the two ends of the pipeline, and the bending stiffness can be known from the test results of the batch of pipelines. Based on this, the specific flow rate at a certain moment can be determined by calculating the pressure signals received by the three optical cables.

[0074] (VII) Water level monitoring

[0075] Three optical cables are used for water level monitoring. The flow rate in the pipeline can be measured according to the flow sensing model, but the flow rate cannot directly reflect the water level. Considering the water flow velocity, the degree of contact with the pipeline wall, and the difference between air and water as propagation media under different water level conditions, there are differences in the vibration signal modes received by the optical fibers at the three positions. The vibration mode shape in the air is more complex and easily affected by boundary conditions and obstacles; in contrast, the water body has greater damping and density, which makes the vibration mode shape maintain good consistency during the propagation process. The collected vibration data is processed using experimental modal analysis (EMA) or numerical modal analysis (such as finite element analysis, FEA) methods to extract modal parameters, including modal frequency, modal shape, and modal damping. Combined with the propagation time of the vibration signal in different media, the real water level information can be obtained. When the water level is very low, only higher than the optical fiber at the bottom, the data collected by the three optical cables only have one set of signals transmitted through the water. When it exceeds all optical fibers, the three optical cables all transmit through the water. By judging different modes, the water level can be preliminarily judged. On this basis, the real water level in the pipeline can be analyzed by combining the propagation speed in water and the propagation speed in air.

[0076] (VIII) Pipeline leakage monitoring

[0077] The judgment of pipeline leakage requires the analysis of two transient pressure test modules. The optical cable wrapped around the transient pressure test module is also close to the pipeline wall. The pressure at this position can be monitored by using the principle of flow-induced vibration. In the system, there are multiple transient pressure test modules. The pressure can be compared between any two modules. The pressure module measurement results before and after the water pipeline during normal operation can be used to determine whether there is a leakage problem in the middle part. Furthermore, in areas that need to be monitored, such as near valves, the connection between two PCCP pipelines, and near the pipeline branch point, a transient pressure test module can be deployed to monitor leakage problems at key locations. The transient pressure test module is used to measure the pressure at a certain position of the pipeline. It is arranged at a certain distance at the bottom of the PCCP pipeline. The optical cable near the bottom is wrapped around the module to detect the pressure. By comparing the pressure values ​​of two adjacent modules, it is determined whether there is a leakage within this range.

[0078] For a normally functioning water pipeline, the pressures before and after the pipe joints and before and after the valves should be consistent. For these locations, the monitoring values ​​of the two pressure modules can be compared to make a judgment. Transient pressure detection modules are arranged at both ends of the fault-prone area. When a pipeline or valve leak occurs, an instantaneous negative pressure will be generated in the monitoring area, which will cause a difference in the pressures of the two modules to determine that a leak has occurred. The location of the leak is calculated based on the time when the two modules collect the pressure change signal. At the branch of the pipeline, pressure loss will occur due to changes in flow rate and direction, which means that the value of the transient pressure test module at the branch is relatively smaller. However, when designing the pipeline, pressure compensation is generally performed by increasing the pressure or selecting a suitable pipe shape. Therefore, leakage monitoring at the branch requires a measurement when the pipeline is just laid as a standard for subsequent comparison.

[0079] Exemplarily, the transient pressure detection module itself is cylindrical, the optical cable is wound on the outside, the transient pressure detection module is cast on the inner side of the pipe, and the optical cable is led out and connected to the DAS module.

[0080] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field, characterized in that: The PCCP pipeline three-dimensional spatial positioning online monitoring system includes a signal processing module, a DAS system, and a first optical cable, a second optical cable and a third optical cable distributed and installed on the inner wall of the PCCP pipeline; The average refractive index of the first optical cable, the second optical cable and the third optical cable is consistent, and the phase difference between the two is 120°; the first optical cable, the second optical cable and the third optical cable are all connected to the DAS system, and the DAS system collects the beat frequency signal of the back Rayleigh scattered light and the intrinsic light of the detection light pulse, and demodulates it to obtain the sound wave signal transmitted by the pipe wall, water or air; The signal processing module obtains the type of vibration source based on the characteristic analysis of the vibration signal; at the same time, the signal processing module calculates the longitudinal position of the vibration source based on the arrival time of the sound wave signal propagated through various paths including the pipe wall, water or air, combined with the sound speed in different media; and locates the cross-sectional position interval of the vibration source based on the time difference of the vibration signal propagating along the pipe wall to the three optical cables.

2. The PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field according to claim 1 is characterized in that: The first optical cable, the second optical cable and the third optical cable are all desensitized optical cables.

3. The PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field according to claim 1 is characterized in that: The vibration sources include broken wires and external intrusion events acting on the pipeline.

4. The PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field according to claim 1 is characterized in that: The first optical cable is adjacent to the bottom of the pipeline, and the second optical cable and the third optical cable are both located in the upper half of the pipeline and there is a height difference between the two.

5. The PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field according to claim 1 is characterized in that: The signal processing module determines the positioning accuracy of the pipeline profile according to the maximum measurement distance, and then calculates the pulse repetition frequency.

6. The PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field according to claim 1 is characterized in that: The signal processing module obtains the transmission time of the vibration signal through the optical cable after it is converted into an optical signal by combining the following formula: In the formula, t is the propagation time of the optical signal in the optical fiber, z is the distance from the vibration source, and c is the speed of light in a vacuum. is the average refractive index of the optical cable.

7. The PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field according to claim 1 is characterized in that: The signal processing module collects the optical fiber vibration signal to fit the standard deviation of the water flow pressure fluctuation in the pipeline, and uses the formula X sd =Au 2 -Bu calculates the internal flow rate of the pipeline at that time, where: Where K1 and K2 are correction factors introduced by the actual adhesion between the optical fiber and the pipe wall, T, r, I, and α are the wall thickness, radius, bending stiffness, and internal dissipation coefficient caused by the elastic material of the circular pipe, ρ is the fluid density, ξ is the friction coefficient between the pipe and the fluid, and L is the pipe length; the friction coefficient g is the acceleration due to gravity, Q is the fluid flow rate, d is the pipe diameter, and ΔP is the pressure difference between the two ends of the pipe.

8. The PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field according to claim 1 is characterized in that: The signal processing module divides the water level height intervals into three intervals according to the installation positions of the first optical cable, the second optical cable and the third optical cable; The signal processing module analyzes different modes of the collected vibration signal to determine the water level range in the pipeline; and then combines the arrival time of the vibration signal and the propagation speed of the vibration signal in water and in air to analyze and obtain the real water level in the pipeline.

9. The PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field according to claim 1 is characterized in that: The PCCP pipeline three-dimensional spatial positioning online monitoring system includes transient pressure detection modules distributed at pipeline branch points and valve areas to measure the pipeline pressure at the location; The signal processing module compares the pipeline pressures measured by two adjacent transient pressure detection modules to determine whether there is a pipeline leak between the two.

10. The PCCP pipeline three-dimensional spatial positioning online monitoring system based on distributed optical fiber acoustic field according to claim 9 is characterized in that: The transient pressure test module includes a cylindrical structure cast inside the pipeline and an optical cable wound around the outside of the structure; the optical cable is connected to the DAS system.

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