A method and monitoring system for three-dimensional precise localization of broken wires in prestressed steel cylinder concrete pipe using fiber optic grating sensor arrays

Abstract

A method and monitoring system for three-dimensional precise localization of broken wires in prestressed concrete cylinder pipes (PCCP) using fiber optic grating (FBG) sensor arrays, belonging to the field of engineering structure inspection technology, is proposed. Based on the acoustic emission mechanism of broken wires, near-wall acoustic waves are used as characteristic information of the broken wires. An FBG sensor array is installed in each PCCP pipe section to establish a broken wire monitoring system based on FBG sensor monitoring of near-wall acoustic waves. Based on the first arrival time (TAT) of the near-wall acoustic waves monitored by the broken wire monitoring system, a broken wire localization model based on the time difference of arrival (TDOA) is established using six sensors, and a genetic algorithm is used to identify the broken wire location. This method can achieve three-dimensional localization of broken wires, overcoming the limitations of existing acoustic fiber optic (AFO) monitoring techniques in circumferential localization. Real-time online monitoring of PCCP pipes is of great significance for understanding the broken wire situation, conducting pipeline safety assessments, and deciding whether to take measures such as reinforcement, pipe section replacement, or reducing the operating water pressure.

Description

Technical Field

[0001] This invention belongs to the field of structural safety monitoring technology. Specifically, it is a method for accurately locating broken wires in three dimensions by using an FBG sensor array to monitor near-wall acoustic waves excited by broken wires into water, establishing a time difference positioning model for broken wires by monitoring the initial arrival time of the near-wall acoustic waves. Background Technology

[0002] Prestressed concrete cylinder pipe (PCCP) consists of a concrete core, a steel cylinder, prestressed steel wires, and a mortar protective layer. Figure 7 As shown, it has advantages such as high working pressure, high impermeability, large diameter, and long-distance transportation. Since its first use in the United States in 1942, PCCP has been widely used in basic projects such as long-distance pressurized water transmission and municipal drainage in countries such as the United States, Mexico, and Canada. China introduced PCCP production technology in the late 1980s, and the technology has gradually matured, and it has been widely used in water transmission projects such as the South-to-North Water Diversion Project and the Liaoning Northwest Water Supply Project.

[0003] Most PCCP pipelines are buried underground, and their failure after a period of service will cause significant losses to society. In actual engineering, most PCCP failures are caused by a combination of factors. If the PCCP undergoes some form of deterioration, it usually manifests as broken wires in the prestressed steel wires. The failure of prestressed steel wires, especially the failure of a large number of prestressed steel wires, is a fair warning sign of a reduced safety factor and impending finite life assessment of the PCCP. Therefore, regular inspection and real-time online monitoring of PCCP pipelines to understand the status of broken steel wires is of great significance for conducting pipeline safety assessments and deciding whether to take measures such as reinforcement, replacement of pipe sections, or reduction of internal water pressure.

[0004] Currently, the commonly used methods for locating broken wires in PCCP (Polycarbonate Collision Pipeline) systems are electromagnetic detection (EM) and acoustic fiber optic monitoring (AFO). EM generally requires pipeline shutdown for maintenance, and due to interference from the steel socket, it cannot detect broken wires within a few centimeters of the socket. Current research progress in acoustic fiber optic monitoring can only roughly determine the number of broken wires and the occurrence of the event, but not the specific location. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a three-dimensional precision positioning and monitoring system for broken wires in prestressed concrete cylinder pipes using a fiber optic grating sensor array. The system includes a fiber optic grating pressure sensor, a fiber optic grating high-frequency dynamic demodulator, a computer, a transmission optical cable, a sensor fixing device, a PCCP pipe, a socket, and a broken wire point. The computer is connected to the fiber optic grating high-frequency dynamic demodulator, which is connected to the fiber optic grating pressure sensor via the transmission optical cable. The fiber optic grating pressure sensor is fixed to the PCCP pipe using the sensor fixing device. A socket is provided at the connection point between two connected PCCP pipe sections. A monitoring section is set at a distance of 0.1m from the socket on each PCCP pipe section. One fiber optic sensor is deployed at each of the four locations on the top, sides, and bottom of each monitoring section of the PCCP pipe section. Eight fiber optic grating pressure sensors of different wavelengths are connected in series in one PCCP pipe section to form a sensor array. The shortest distance from the fiber optic grating pressure sensor to the inner wall of the pipe is controlled within 0.1m.

[0006] A method for precise three-dimensional localization of broken wires in prestressed steel cylinder concrete pipes using a fiber optic grating sensor array comprises the following steps:

[0007] S1. Two monitoring sections are set along the length of each PCCP pipe section at a distance of 0.1m from the socket. One fiber optic pressure sensor is installed at each of the four positions at the top, sides, and bottom of the pipe in these two monitoring sections. A total of eight fiber optic pressure sensors are installed in each pipe section, and the shortest distance between each fiber optic pressure sensor and the pipe wall is controlled within 0.1m.

[0008] S2. When the PCCP wire breakage monitoring system detects a wire breakage event in a pipe section, the first negative pressure peak point of the near-wall acoustic wave is taken as the signal arrival time. Three sensors from group A and three sensors from group B are selected. For each group, the sensor farthest from the wire breakage location in the monitoring section is selected and combined with the second and third farthest sensors from the wire breakage location in another monitoring section, for a total of 6 fiber optic pressure sensors.

[0009] S3. Determine the geometric position coordinates of the selected 6 fiber Bragg grating pressure sensors. For each group of fiber Bragg grating pressure sensors, take one sensor as the reference sensor and the other two sensors as ordinary sensors. Calculate the time difference between the ordinary sensors and the reference sensor to obtain 4 time differences. Substitute these 4 time differences and the two-dimensional plane coordinates of the 6 fiber Bragg grating pressure sensors into the fiber breakage location objective function.

[0010] The beneficial effects of this invention are as follows: The near-wall acoustic wave monitoring scheme based on FBG sensor array proposed in this invention can monitor the occurrence of wire breakage events in real time and determine the initial arrival time of the near-wall acoustic waves excited by the wire breakage to each FBG sensor; the three-dimensional positioning method for PCCP wire breakage based on TDOA positioning proposed in this invention overcomes the limitation of existing acoustic fiber optic monitoring technology that cannot achieve circumferential positioning; this invention can realize three-dimensional positioning of PCCP in operation, identify the location and number of wire breakages in real time, provide a reference for the redistribution of pipeline stress after wire breakage, and provide a safety assessment of the possibility and degree of danger of engineering accidents of PCCP under the current damage condition.

[0011] By studying the stress wave transmission mechanism after PCCP wire breakage, it was found that the acoustic energy first transmitted to the water after wire breakage is the energy of the small displacement caused by the P-wave in the pipe. Subsequently, the energy transmitted to the water near the pipe wall is the energy of the large displacement caused by the S-wave in the pipe, while the energy of the direct wave transmitted to the water far from the pipe wall is the energy of the PCCP wire breakage. Using the acoustic energy of the small displacement caused by the P-wave in the pipe as the characteristic information of PCCP wire breakage, this acoustic energy is called near-wall acoustic wave. Therefore, based on the acoustic emission mechanism of PCCP wire breakage, this invention proposes a real-time near-wall acoustic wave acquisition and monitoring scheme based on an FBG sensor array, using the near-wall acoustic wave in the water as the characteristic signal of the wire breakage. The scheme establishes a time difference positioning model by picking up the initial arrival time of the near-wall acoustic wave, and identifies the three-dimensional position of the wire breakage using a genetic algorithm, overcoming the limitations of existing acoustic fiber optic monitoring technology in circumferential positioning. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the PCCP wire breakage acoustic monitoring system for the entire pipeline according to the present invention;

[0013] Figure 2 This is a schematic diagram of the sensor fixing device of the present invention;

[0014] Figure 3 This is a detailed schematic diagram of the sensor fixing device of the present invention;

[0015] Figure 4 This is a schematic diagram of the optical fiber structure of the present invention;

[0016] Figure 5 This is a schematic diagram of a two-dimensional coordinate system for the inner wall of the pipe in this invention being a plane;

[0017] Figure 6 This is a schematic diagram of the combination of the two sets of FBG sensors of the present invention;

[0018] Figure 7 This is a schematic diagram of the multi-layer material composition of the prestressed steel cylinder concrete pipe of the present invention.

[0019] The attached figures are labeled as follows: 1. Fiber Bragg grating pressure sensor; 2. Fiber Bragg grating high-frequency dynamic demodulator; 3. Computer; 4. Transmission optical cable; 5. Sensor fixing device; 51. Shock-absorbing foam; 52. Armored jacket; 53. Fiber optic core; 6. PCCP pipe; 7. Pipe socket; 8. Broken wire point; 9. Three sensors in group A; 10. Three sensors in group B. Detailed Implementation

[0020] A three-dimensional precision positioning and monitoring system for broken wires in prestressed steel cylinder concrete pipes using a fiber optic grating sensor array is proposed, such as... Figure 1 As shown, the PCCP (Prestressed Conduit) breakage monitoring system includes a fiber Bragg grating pressure sensor 1, a fiber Bragg grating high-frequency dynamic demodulator 2, a computer processing system 3, a transmission optical cable 4, and a sensor fixing device 5. The fiber Bragg grating high-frequency dynamic demodulator 2, with multi-channel measurement capabilities, is selected to monitor PCCP breakage events online throughout the entire pipeline 6. Each channel connects eight sensors 1 of different wavelengths in series to form a sensor array. Each sensor array corresponds to the monitoring and location of a specific PCCP breakage section within the entire pipeline. Figures 2-4 As shown, the armored jackets protecting the optical fibers at both ends of sensor 1 are fixed to the inner layer of the narrow-band steel ring 5, and the pressure elastic sensing element of sensor 1 is made parallel to the inner surface of the steel ring. A layer of shock-absorbing foam is wrapped around the outer layer of the steel ring, and the steel ring is expanded and tightly adhered to the inner wall of the PCCP pipe 6 by turning the screws. The shortest distance from sensor 1 to the inner wall of pipe 6 is controlled within 0.1m. A monitoring section is set at a position 70.1m away from the socket of each section of PCCP pipe 6, as detailed in [link to documentation]. Figure 1 One fiber optic sensor is installed at each of the four locations—the top, both sides, and the bottom—of each PCCP pipe section 6, across two monitoring sections. See details... Figure 2 Each sensor array has 8 sensors. When the PCCP wire breakage monitoring system detects a wire breakage event at a certain section of the pipeline, it establishes a two-dimensional coordinate system for wire breakage location with the inner wall of the pipeline where the event occurred as the plane. See details. Figure 5 In a two-dimensional coordinate system with the inner wall of the pipe as the plane, the point on the inner wall of the pipe socket closest to the broken wire point, which is the closest to the broken wire point, is taken as the origin. The positive direction of the Y-axis is the direction from the origin along the inner wall of the pipe to the point on the pipe socket section where the second closest sensor to the broken wire point is projected. The positive direction of the Z-axis is the direction from the origin to the sensor closest to the broken wire in the monitoring section. Then, the coordinates of the broken wire position in the two-dimensional coordinate system with the inner wall of the pipe as the plane are P'(πRθ / 180,z).

[0021] For the same wire breakage location (x, z), the time difference τ between the near-wall acoustic wave arriving at the i-th and j-th sensors is... ij for:

[0022]

[0023] In the formula, R is the inner radius of the PCCP pipe, θ i Let z be the circumferential angle of the i-th fiber optic sensor. i Let θ be the longitudinal position of the i-th fiber optic sensor. j Let z be the circumferential angle of the j-th fiber optic sensor. j Let θ be the longitudinal distance of the j-th fiber optic sensor, θ be the circumferential angle of the broken wire, z be the longitudinal position of the broken wire, and v be the near-wall acoustic velocity. Select the sensor furthest from the broken wire location in one monitoring section and combine it with the second and third furthest sensors from the broken wire location in another monitoring section. Figure 3 The sensors are divided into group A (9 sensors) and group B (10 sensors), totaling 6 sensors. Based on the geometric positions and time differences of these 6 sensors, the objective function for wire breakage localization is established in the least squares sense as follows:

[0024] min F(θ,z,v)=||T ia -T ia m || 2 +||T jb -T jb m || 2

[0025] In the formula, T ia =(τ 1a τ 2a ), i represents the common sensor in group A, a represents the reference sensor in group A, and T represents the... jb =(τ 3b τ 4b ), j is a common sensor in group B, T ia T ia m T represents the time difference between the theoretical and measured values ​​of the two ordinary sensors and the reference sensor in group A. jb T jb m The time difference between the theoretical and measured values ​​of the two ordinary sensors in group B and the reference sensor are shown. The three-dimensional location of the broken wire is identified by solving the objective function using a genetic algorithm.

[0026] A method for precise three-dimensional localization of broken wires in prestressed concrete cylinder pipes based on fiber optic grating sensor arrays includes the following steps:

[0027] Step 1: Install two monitoring sections along the length of each PCCP pipe section, 0.1m away from the socket. See details. Figure 1 FBG sensors were installed at four locations: the top of the pipe, both sides of the pipe, and the bottom of the pipe at these two monitoring sections. See details below. Figure 2 Eight sensors are installed in each section of the pipe, and the shortest distance between each sensor and the pipe wall is controlled within 0.1m.

[0028] Step 2: When the PCCP wire breakage monitoring system detects a wire breakage event (8) in a pipe section, the first negative pressure peak of the near-wall acoustic wave is taken as the signal arrival time. Sensors from group A (9) and group B (10) are selected. For each group, the sensor furthest from the wire breakage location in one monitoring section is combined with the second and third furthest sensors from the wire breakage location in another monitoring section. See details below. Figure 6 There are a total of 6 sensors.

[0029] The third step is to determine the geometric position coordinates of the selected 6 sensors 1. For each group of sensors 1, one sensor is used as the reference sensor and the other two sensors are ordinary sensors. The time difference between the ordinary sensors and the reference sensor is calculated to obtain 4 time differences. These 4 time differences and the two-dimensional plane coordinates of the 6 sensors 1 are substituted into the wire breakage positioning objective function.

[0030] Step 4: Set the range of values ​​for the broken wire location and the near-wall acoustic wave velocity, determine the genetic algorithm parameters, generation number T and population size N, and encode the longitudinal position z of the broken wire, the circumferential angle θ and the longitudinal wave velocity v of the pipe into binary codes to establish an initial population of individuals with N genotypes and L lengths.

[0031] Step 5: Decode the genotype of each individual into the phenotypes of the longitudinal position z of the broken filament, the circumferential angle θ, and the near-wall acoustic wave velocity v. Substitute these into the broken filament localization time difference model, calculate the minimum value of the objective function, and calculate the fitness of the corresponding individual.

[0032] Step 6: Select individuals based on their fitness values ​​according to a fitness ratio. Send the selected individuals to the pairing pool to reproduce the next generation. The selection principle is to ensure that individuals with high fitness have a higher probability of reproducing one or more next generations.

[0033] Step 7: Use arithmetic crossover according to the crossover probability P c Two individuals with different genotypes are randomly selected from the pairing library for crossover. After the crossover operation, uniform mutation is performed according to the mutation probability P. m By performing mutation operations on each genotype individual, a certain number of new individuals are generated.

[0034] Step 8: Decode the genotype of each individual in the new generation population, calculate the minimum objective function for each individual, calculate their fitness, and execute the optimal individual preservation strategy. If the number of generations is less than T, proceed to step 5; otherwise, output the optimal longitudinal position z of the broken wire, the circumferential angle θ, and the near-wall acoustic wave velocity v.

[0035] Step 9: Apply the genetic algorithm to the objective function 2000 times independently for the same broken wire sound source to obtain the longitudinal position z and circumferential angle θ of the broken wire from the 2000 solutions. Calculate the average value of these 2000 solutions as the final position for locating the broken wire.

[0036] The genetic algorithm parameters are set as follows: population size 200, crossover probability 0.8, mutation probability 0.05, and termination generation number 500.

[0037] The near-wall acoustic wave monitoring scheme based on FBG sensor array proposed in this invention can monitor the occurrence of wire breakage events in real time. By monitoring the first arrival time of the near-wall acoustic wave excited by the wire breakage through each FBG sensor, a three-dimensional precise positioning method for PCCP wire breakage based on TDOA positioning is established. This method can realize three-dimensional positioning of PCCP in operation, identify the location and number of wire breakages in real time, provide a reference for the redistribution of pipeline stress after wire breakage, and provide a safety assessment of the possibility and degree of danger of engineering accidents of PCCP under the current damage condition.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for precise three-dimensional positioning of broken wires in prestressed steel cylinder concrete pipe using a fiber optic grating sensor array, characterized in that, The monitoring system includes a fiber Bragg grating pressure sensor (1), a fiber Bragg grating high-frequency dynamic demodulator (2), a computer (3), a transmission optical cable (4), a sensor fixing device (5), a PCCP pipe (6), a socket (7), and a broken wire point (8). The computer (3) is connected to the fiber Bragg grating high-frequency dynamic demodulator (2), which is connected to the fiber Bragg grating pressure sensor (1) via the transmission optical cable (4). The fiber Bragg grating pressure sensor (1) is fixed to the PCCP pipe (6) via the sensor fixing device (5). A socket (7) is set at the connection point between two connected PCCP pipe sections (6). A monitoring section is set at a distance of 0.1m from the socket (7) of each PCCP pipe section (6). One fiber optic sensor is set at each of the four positions of the top, sides and bottom of the two monitoring sections of each PCCP pipe section (6). Eight fiber optic pressure sensors (1) of different wavelengths are connected in series in one PCCP pipe section (6) to form a sensor array. The shortest distance from the fiber optic pressure sensor (1) to the inner wall of the pipe is controlled within 0.1m. The monitoring system performs the following steps to locate the target: S1. Two monitoring sections are set at a distance of 0.1m from the socket (7) along the length of each PCCP pipe (6). One fiber optic pressure sensor (1) is installed at each of the four positions at the top, sides and bottom of the pipe of the two monitoring sections. A total of 8 fiber optic pressure sensors (1) are installed in each pipe section. The shortest distance between each fiber optic pressure sensor (1) and the pipe wall is controlled within 0.1m. S2. When the PCCP wire breakage monitoring system detects a wire breakage point (8) event in a certain pipe section, the first negative pressure peak point of the near-wall acoustic wave is taken as the signal arrival time. Three sensors (9) from group A and three sensors (10) from group B are selected. Each group selects the sensor that is farthest from the wire breakage point in the monitoring section and combines it with the second and third farthest sensors in the monitoring section from the wire breakage point. A total of 6 fiber optic pressure sensors (1) are used. S3. Determine the geometric position coordinates of the selected 6 fiber optic pressure sensors (1). For each group of fiber optic pressure sensors (1), take one sensor as the reference sensor and the other two sensors as ordinary sensors. Calculate the time difference between the ordinary sensors and the reference sensors to obtain 4 time differences. Substitute these 4 time differences and the two-dimensional plane coordinates of the 6 fiber optic pressure sensors (1) into the wire breakage positioning objective function.

2. The method for three-dimensional precise positioning of broken wires in prestressed steel cylinder concrete pipe using a fiber optic grating sensor array according to claim 1, characterized in that: The sensor fixing device (5) is a narrow band steel ring. The armor jacket (52) of the fiber core (53) at both ends of the fiber optic grating pressure sensor (1) is fixed to the inner layer of the narrow band steel ring, and the pressure elastic sensitive element of the fiber optic grating pressure sensor (1) is parallel to the inner surface of the narrow band steel ring. A layer of shock-absorbing foam (51) is wrapped around the outer layer of the narrow band steel ring. The narrow band steel ring is expanded and tightly attached to the inner wall of the PCCP pipe (6) by twisting the screw.

3. The method for three-dimensional precise positioning of broken wires in prestressed steel cylinder concrete pipe using a fiber optic grating sensor array according to claim 1, characterized in that: When the PCCP broken wire monitoring system detects a broken wire point (8) event in a section of the entire pipeline, a two-dimensional coordinate system for locating the broken wire is established with the inner wall of the pipeline where the broken wire event occurred as the plane. For the same broken wire location... Near-wall sound waves reach the first and the Time difference between sensors for: In the formula, , , , The inner radius of the PCCP pipe. For the first The circumferential angle of each fiber optic sensor For the first The longitudinal position of each fiber optic sensor For the first The circumferential angle of each fiber optic sensor For the first The longitudinal distance of each fiber optic sensor The circumferential angle of the broken wire. This indicates the longitudinal position of the wire breakage point. The near-wall acoustic wave velocity; This indicates the lateral position of the wire breakage point. For the first The lateral position of each fiber optic sensor For the first The lateral distance of each fiber optic sensor is considered. The sensor furthest from the broken wire location in one monitoring section is combined with the second and third furthest sensors in another monitoring section, resulting in three sensors in group A (9) and three sensors in group B (10), for a total of six fiber optic pressure sensors (1). Based on the geometric positions and time differences of these six fiber optic pressure sensors (1), an objective function based on the time difference of arrival (TDOA) is established in the least squares sense: In the formula, , , This is a standard sensor for group A. As the reference sensor for group A, , , This is a standard sensor for group B. , These represent the time differences between the theoretical and measured values ​​of the two ordinary sensors and the reference sensor in Group A. , The time difference between the theoretical and measured values ​​of the two ordinary sensors in group B and the reference sensor are respectively; the three-dimensional location of the broken wire is identified by solving the objective function through a genetic algorithm.

4. The method for three-dimensional precise positioning of broken wires in prestressed steel cylinder concrete pipe using a fiber optic grating sensor array according to claim 3, characterized in that: Also includes S4. Set the range of values ​​for the broken wire location and the near-wall acoustic velocity, determine the genetic algorithm parameters (generation number T and population size N), and set the longitudinal position of the broken wire accordingly. Circumferential angle and the longitudinal wave velocity of the pipeline Binary encoding is performed to establish an initial population of individuals with N genotypes and L lengths.

5. The method for three-dimensional precise positioning of broken wires in prestressed steel cylinder concrete pipe using a fiber optic grating sensor array according to claim 4, characterized in that: Also includes S5. Decode the genotype of each individual into the longitudinal position of the broken fibers. Circumferential angle and near-wall sound wave velocity The phenotype is substituted into the time difference model for wire breakage localization to calculate the minimum value of the objective function and the fitness of the corresponding individual.

6. The method for three-dimensional precise positioning of broken wires in prestressed steel cylinder concrete pipe using a fiber optic grating sensor array according to claim 5, characterized in that: Also includes S6. Select individuals based on their fitness values ​​according to a ratio, and send the selected individuals to the pairing pool for breeding the next generation. The selection principle is to ensure that individuals with high fitness have a higher probability of breeding one or more next generations.

7. The method for three-dimensional precise positioning of broken wires in prestressed steel cylinder concrete pipe using a fiber optic grating sensor array according to claim 6, characterized in that: Also includes S7. Use arithmetic crossover according to the crossover probability. Two individuals with different genotypes are randomly selected from the pairing library for crossover. After the crossover operation, uniform mutation is performed according to the mutation probability. By performing mutation operations on each genotype individual, a certain number of new individuals are generated.

8. The method for three-dimensional precise positioning of broken wires in prestressed steel cylinder concrete pipe using a fiber optic grating sensor array according to claim 7, characterized in that: Also includes S8. Decode the genotype of each individual in the new generation population, calculate the minimum objective function for each individual, calculate their fitness, and execute the optimal individual preservation strategy. If the number of generations is less than T, proceed to S5. If the condition is met, output the optimal longitudinal position of the broken filament. Circumferential angle and the wave speed of near-wall sound waves .

9. The method for three-dimensional precise positioning of broken wires in prestressed steel cylinder concrete pipe using a fiber optic grating sensor array according to claim 8, characterized in that: Also includes S9. Apply a genetic algorithm to the objective function 2000 times independently for the same broken wire sound source, and obtain the longitudinal position of the broken wire from the 2000 solutions. Circumferential angle The average value of these 2000 solutions is used as the final location for wire breakage.

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