A method and system for locating overall and local bolt loosening in pipe flange connections

Abstract

The application discloses a pipeline flange connection integral and partial bolt loosening positioning method and system, wherein the method comprises the following steps: inputting a detection light into an optical fiber, the detection light is modulated based on the vibration of a pipeline structure, the modulated reflected light is subjected to polarization diversity, the light in two orthogonal polarization states obtained through the polarization diversity is subjected to demodulation, calculation and analysis, position information of a flange connection position where a bolt is loosened and an optical fiber phase damping ratio are obtained, the number of the loosened bolts at the flange connection position is found out according to the corresponding relationship between the optical fiber phase damping ratio and the number of the loosened bolts; a corresponding multi-channel front end measurement node is activated, the impedance of all the bolts at the flange connection position is measured, and a root mean square deviation is calculated; and the specific position of the loosened bolt is identified. The application can accurately position the flange connection position of the pipeline structure where the bolt is loosened, and accurately obtain the number and the specific position of the loosened bolt.

Description

Technical Field

[0001] The present invention relates to the technical field of structural health monitoring, and in particular to a method and system for locating overall and local bolt loosening in a pipeline flange connection. Background Art

[0002] Flange connections, as a connection method for pipeline transportation, offer advantages such as high efficiency, low cost, and strong continuity, and are crucial for applications in energy supply, petrochemicals, and other fields. Therefore, health monitoring of pipeline flange connection structures is crucial for preventing and detecting damage trends or early stages of structural damage, which is of great engineering significance.

[0003] Distributed optical fiber acoustic sensing (DAS) technology can globally identify structural vibrations by monitoring optical phase changes along an optical fiber. It can measure parameters such as amplitude and frequency, making it suitable for pipeline leak monitoring. However, traditional DAS systems mostly focus on the fluctuations of the vibration signal itself, ignoring the changes in the structural dynamic parameters reflected by the signal. As a result, such systems can only passively identify pipeline damage locations after gas or liquid leaks have already occurred. They are unable to identify damage at a stage where minor damage to pipeline components (such as loose bolts, localized corrosion, and deformation) has not yet occurred.

[0004] Electromechanical impedance (EMI) technology monitors structural safety and damage status by detecting changes in the impedance signal of the object being measured. It is highly sensitive to detecting early, subtle structural damage and offers advantages such as ease of implementation, applicability to complex structures, good long-term stability, and superior damage quantification. However, traditional impedance-based damage detection technology can only identify damage changes in localized areas and, when applied to large-scale projects, is unable to globally identify the location of damage. To ensure structural safety, all monitoring nodes must operate continuously, leading to overloaded monitoring devices and accelerating their lifespan.

[0005] In view of the defects of the existing technology, there is an urgent need for a method and system for locating the overall and local bolt loosening of pipeline flange connections to solve the problem of difficulty in identifying early minor damage to pipelines and global damage to engineering structures. Summary of the Invention

[0006] The main purpose of the present invention is to provide a method and system for locating the overall and local loose bolts of a pipeline flange connection, which combines a global positioning method based on optical fiber and a local positioning method based on piezoelectric impedance to accurately locate the position of the loose flange and obtain the number and specific position of the loose bolts.

[0007] The technical solution adopted by the present invention is: a method for locating overall and local bolt loosening in pipeline flange connections, wherein optical fibers are arranged in the pipeline structure, and multi-channel front-end measurement nodes are arranged at each flange connection in the pipeline structure; the multi-channel front-end measurement nodes are used to measure the impedance of all bolts at the flange connection; the method includes:

[0008] A probe light is input into the optical fiber, the probe light is modulated based on the vibration of the pipeline structure, the modulated reflected light is polarized, and the two orthogonal polarization states of light obtained by the polarization diversity are demodulated, calculated and analyzed to obtain the position information of the flange connection where the bolts are loose and the optical fiber phase damping ratio. According to the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts, the number of loose bolts at the flange connection is found; the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts is obtained by calibration; further, the calibration method includes, for each flange connection, loosening the screws on the flange connection one by one Bolt, when each bolt is completely loosened, knock on the pipes at both ends of the flange connection in turn, and collect optical phase time history signals after each knock; process and analyze the collected optical phase time history signals, and output the optical phase damping ratio corresponding to the number of different loose bolts; fit the relationship between the optical phase damping ratio and the number of loose bolts, and divide the range of the optical phase damping ratio into segments according to the fitted relationship to obtain the corresponding relationship between the range of the optical phase damping ratio and the number of loose bolts; repeat the above steps for flange connections of different specifications to obtain the corresponding relationship between the optical phase damping ratio and the number of loose bolts at flange connections of different specifications.

[0009] Based on the location information of the flange connection where the bolts are loose, the corresponding multi-channel front-end measurement node is activated to measure the impedance of all bolts in the flange connection. The root mean square deviation is calculated based on the impedance measurement results and the impedance reference signals of the bolts at different locations in the flange connection. The impedance reference signals of the bolts at different locations in the flange connection are measured with the bolts in a fixed state. Furthermore, the measurement method includes: attaching a piezoelectric sensor to each bolt cap in the flange connection and electrically connecting each piezoelectric sensor to a different measurement channel of the front-end measurement node; fully tightening all bolts in the flange connection; performing impedance measurements on the different measurement channels to obtain a reference impedance signal for each bolt; and repeating the above steps for each flange connection specification to obtain a reference impedance signal for all bolt locations in the different flange connections.

[0010] The specific positions of the loose bolts are identified according to the number of the loose bolts and the root mean square deviation of the bolts at different positions of the flange connection.

[0011] According to the above technical solution, the method for demodulating, calculating, and analyzing the two orthogonal polarization states of the S channel and the P channel obtained by the polarization diversity to obtain the position information of the flange connection where the bolts are loose includes:

[0012] The optical signals of the two orthogonal polarization states of the S channel and the P channel are converted into electrical signals and then into digital signals, and then processed into initial phase signals respectively. The two initial phase signals are deconvolved along the spatial axis;

[0013] The standard deviation matrices of the S channel and the P channel are respectively calculated based on the two initial phase signals deconvolved along the spatial axis, and the standard deviation matrices are subjected to noise reduction processing. A positioning feature map matrix is ​​calculated based on the standard deviation matrices of the S channel and the P channel after the noise reduction processing. The time information of the pipeline structure vibration and the position interval of the vibrating pipeline structure are obtained according to the positioning feature map matrix. The time information of the pipeline structure vibration includes the start time and duration of the pipeline structure vibration.

[0014] According to the position interval of the vibrating pipeline structure, the two initial phase signals are unwrapped along the time axis.

[0015] The two initial phase signals deconvolved along the time axis are integrated to obtain an integrated phase time history signal; a trial function search is performed on the integrated phase time history signal based on the time information of the pipeline structure vibration and the position interval of the pipeline structure where the vibration occurs, to obtain its optimal phase time history segment and analyze it; the trial function search uses a Hilbert-Huang transform with limited bandwidth empirical mode demodulation to obtain each order intrinsic mode function of each spatial sampling point within the position interval of the vibrating pipeline structure, where the spatial sampling points correspond to sampling points where the electrical signal is continuously sampled at a preset rate.

[0016] The phase vibration mode of the optimal segment of each order intrinsic mode function of each spatial sampling point in the position interval of the vibrating pipeline structure is calculated, and the position information of the flange connection where the bolts are loose is obtained according to the peak value of the phase vibration mode.

[0017] According to the above technical solution, the method for processing the two digital signals of the S channel and the P channel into initial phase signals includes: processing the two digital signals respectively according to a first formula; the first formula includes: in, is the initial optical phase of each spatial sampling point along the optical fiber at time τ, t is the time delay of the reflected light at each spatial sampling point, H is the Hilbert operator, and I(t,τ) is the S-channel or P-channel digital signal at time τ.

[0018] The method for unwrapping the two initial phase signals along the spatial axis comprises processing the two initial phase signals according to a second algorithm, a third algorithm and a fourth algorithm; the second algorithm comprises: The third algorithm comprises The fourth algorithm comprises Wherein, represents all spatial sampling points from position t m to t N on the optical fiber, N is the total number of spatial sampling points on the optical fiber, m represents that the current spatial sampling point to be unwrapped is at position t m , and τ0 is the current time.

[0019] The method for calculating the standard deviation matrix comprises: differentiating the two initial phase signals unwrapped along the spatial axis according to a fifth algorithm to obtain two differential signals of the S channel and the P channel; introducing a sliding time window, calculating the standard deviation of the two differential signals of each spatial sampling point within the sliding time window to obtain a matrix of the standard deviation distribution along time and space of the S channel and the P channel, and the matrix element of the standard deviation matrix is denoted as d ik ; the fifth algorithm comprises: Wherein, is a differential signal, i and j represent that the current spatial sampling point to be unwrapped is at position i or position j, is a signal obtained by unwrapping the two initial phase signals along the spatial axis; the method for denoising the standard deviation matrix of the S channel and the P channel comprises: introducing a block matrix operator with a preset row and column size, processing the standard deviation matrix in a preset order using the block matrix operator, calculating a positioning index of the S channel and the P channel according to the parameters obtained by processing, and the processing method is based on the output principle of the block matrix operator.

[0020] The positioning indexes of the S channel and the P channel are superimposed to obtain a positioning feature map matrix, and the time information of the pipeline structure vibration and the position information of the flange connection with bolt loosening are obtained according to the time axis position of the peak value of the positioning feature map matrix.

[0021] According to the above technical solution, the output principle of the block matrix operator comprises: for each matrix sub-block corresponding to the block matrix operator contained in the standard deviation matrix, if the d ik value of the matrix sub-block is less than the average value a0 of the standard deviation matrix d ik , output 0, otherwise, output 1, to obtain a 0-1 matrix with the row and column size of the block matrix operator, and the average value of the matrix elements of the 0-1 matrix is denoted as a1; when |f ik -fn |>f d When a2=0, otherwise, a2=1, where f ik The matrix sub-block corresponds to The main frequency in the spectrum, n is the modal order to be investigated, f n is the nth order natural frequency of the pipeline, f d A custom constant determined based on the peak width of each order characteristic frequency in the structure spectrum.

[0022] According to the above technical solution, the method for deconvolving the two initial phase signals along the time axis includes: selecting two spatial sampling points within the optical fiber interval corresponding to the position interval of the vibrating pipeline structure according to the sixth, seventh, eighth, and ninth formulas, taking the phase difference between the two spatial sampling points, and deconvolving along the time axis; performing baseline calibration processing on the two spatial phase differences after deconvolving along the time axis according to the tenth, eleventh, and twelfth formulas; the sixth formula includes: The seventh formula includes: The eighth formula includes: The ninth formula includes: Among them, the spatial sampling point t i Traverse all the spatial sampling points in the optical fiber interval, the spatial sampling point t j Take the spatial sampling point t i Subsequent spatial sampling points separated by a preset interval, Represents the time τ m to τ N All time sampling points, N is the total number of time sampling points on the time axis, the sampling time of the time sampling point corresponds to the incident time of the detection light pulse in the optical fiber interval, m represents the current time m of the spatial sampling point to be deconvolved, is the extracted initial phase time course; the tenth formula includes: The eleventh formula includes The twelfth formula includes Where d0 is the preset step threshold, is the time τ m At time τ m+T The average phase value of is the time τ m-T At time τ m The phase average value, T is the preset signal segment length, is the time τ m to τ m+T The central trend line of the phase time history is obtained by a nonlinear least squares method.

[0023] The method for integrating the initial phase signals unwrapped along the time axis comprises: integrating the two initial phase signals unwrapped along the time axis according to a thirteenth algorithm to obtain an integrated phase time history signal, the thirteenth algorithm comprising: wherein i represents the i-th spatial sampling point on the optical fiber, S or P respectively corresponds to the S channel or the P channel, is the phase time history signal, m is valued according to a fourteenth algorithm and a fifteenth algorithm, the fourteenth algorithm comprising m = 0, if The fifteenth algorithm comprises m = 1, else; wherein, I E S or I E P is the I S or I P upper envelope line of I , N is the total number of all spatial sampling points on the optical fiber, and k is a scaling factor selected according to the number of abnormal peaks of I

[0024] According to the above technical solution, the method for performing a trial function search on the integrated phase time history signal x(τ) specifically comprises:

[0025] determining whether the integrated phase time history signal x(τ) is a pulse response signal, if yes, taking the phase time history signal x(τ) as an analysis signal x(τ), otherwise, taking the cross-correlation function of the initial phase signal as the analysis signal x(τ).

[0026] superimposing the analysis signal x(τ) and a preset limited bandwidth signal s(τ) to obtain a superimposed signal y(τ), performing standard empirical mode decomposition on the superimposed signal y(τ) to obtain an initial first intrinsic mode function IMF 01 of the spatial sampling point to which the superimposed signal y(τ) belongs; 01 determining whether h1(τ) has modal aliasing; when there is no modal aliasing, the first intrinsic mode function of the spatial sampling point is h1(τ), otherwise, x(τ) = h1(τ), and the above steps are repeated until the modal aliasing of h1(τ) is eliminated, or the number of iterations exceeds a preset number; and each order intrinsic mode function of each spatial sampling point in the position interval of the pipeline structure subjected to vibration is obtained through the above method.

[0027] According to the time information of the pipeline structure vibration, the vibration start time is taken as the starting time, the duration is taken as the fitting interval, the eigenmode order to be investigated is specified in the fitting interval, the preset time channel is used to cover all the spatial sampling points included in the pipeline structure which vibrates at the same time, and the eigenmode function fragments exceeding the preset time length are obtained; a preset exponential function is taken as a trial function to fit the normalized instantaneous amplitude curve of each spatial sampling point, the fitting root mean square error of all spatial sampling points is calculated, the root mean square error in the time channel is calculated step by step at each time step, the phase time history fragment in the time channel with the minimum root mean square error is taken as the optimal phase time history fragment, and the amplitude parameter and the attenuation coefficient fitted by the optimal phase time history fragment are obtained.

[0028] According to the above technical solution, the method for obtaining the phase mode of each spatial sampling point comprises: calculating the instantaneous amplitude average value of the optimal phase time history fragment of each order eigenmode function of each spatial sampling point in the optical fiber interval corresponding to the position interval of the pipeline structure which vibrates, that is, the mode value of each mode order of the spatial sampling point, and calculating the phase mode of the optimal fragment of each order eigenmode function of each spatial sampling point according to the mode value.

[0029] According to the above technical solution, the method for demodulating, calculating and analyzing the reflected light to obtain the optical fiber phase damping ratio comprises: calculating the optical fiber phase damping ratio according to the sixteenth formula, the seventeenth formula and the eighteenth formula; the sixteenth formula comprises w dn (τ)=dθ n (τ) / dτ, the seventeenth formula comprises The eighteenth formula comprises wherein the subscript n represents the n-th mode, w dn is the damped circular frequency, θ n is the instantaneous phase, x2 is the attenuation coefficient, ξ n is the optical fiber phase damping ratio, w n is the circular frequency.

[0030] According to the above technical solution, the method for identifying the specific position of the loose bolt according to the number of loose bolts and the root mean square deviation comprises:

[0031] The identification threshold of the root mean square deviation is determined based on the number of loose bolts at the flange connection, and the calculation method of the root mean square deviation comprises: calculating the root mean square deviation according to the nineteenth formula, and the nineteenth formula comprises wherein RMSD is the root mean square deviation, N is the number of frequency points scanned by the signal on the frequency axis, S i,ref is the impedance reference signal of the bolt with position number i, S i,x is the current impedance signal of the bolt with position number i.

[0032] The measurement channel whose root mean square deviation of the measured impedance is greater than the identification threshold is selected, and the corresponding bolt is the loose bolt. The specific position of the loose bolt is obtained according to the pre-stored correspondence between the measurement channel and the bolt position.

[0033] Another aspect of the present invention provides a system for locating the overall and local bolt loosening of a pipe flange connection. The system implements the above-mentioned method for locating the overall and local bolt loosening of a pipe flange connection, and includes a global positioning subsystem and a local positioning subsystem; wherein,

[0034] The global positioning subsystem includes a polarization diversity unwinding module, a pipeline interval positioning module, a loose node positioning module and a loose bolt quantity identification module; wherein the polarization diversity module is used to generate detection light in the optical fiber laid along the entire length of the pipeline structure, the detection light is modulated based on the vibration of the pipeline structure, the modulated reflected light is polarization-diversified, and the two orthogonal polarization states of light obtained by polarization diversity are demodulated and input into the pipeline interval positioning module and the loose node positioning module; the pipeline interval positioning module and the loose node positioning module are used to calculate and analyze the two orthogonal polarization states of light after demodulation to obtain the position information of the flange connection where the bolts are loose; the loose bolt quantity identification module is used to calculate the corresponding optical fiber phase damping ratio of the flange connection where the bolts are loose, and find the number of loose bolts at the flange connection based on the correspondence between the optical fiber phase damping ratio and the number of loose bolts obtained in advance;

[0035] The local positioning subsystem includes a remote measurement and control server and a multi-channel front-end measurement node network. The remote measurement and control server is configured to activate the front-end measurement node corresponding to a flange connection with loose bolts, based on the location information of the flange connection determined by the global positioning subsystem. The multi-channel front-end measurement node is configured to perform impedance measurement on all bolts in the flange connection, calculate the root mean square deviation based on pre-stored impedance reference signals for bolts at different locations in the flange connection, and identify the specific location of the loose bolts based on the number of loose bolts in the flange connection. Furthermore, the multi-channel front-end measurement node network includes a communication module, an impedance measurement module, a microcontroller module, and a power supply module. The communication module connects to the remote control server via wireless communication. The impedance measurement module includes an impedance measurement chip, multiple low-voltage multiplexers, a calibration resistor network, a feedback resistor network, and a measurement channel network. The impedance measurement module implements the impedance measurement function based on the chip and controls the switching of the calibration resistor network, the feedback resistor network, and multiple measurement channels using multiple low-voltage multiplexers.

[0036] The present invention provides a method and system for locating loose bolts in both the overall and local areas of a pipeline flange connection. This system combines a global positioning method based on optical fiber with a local positioning method based on piezoelectric impedance. This system not only accurately locates flange connections in pipeline structures with loose bolts, but also precisely determines the number of loose bolts in the flange connection and the specific locations of the loose bolts. Compared to existing technologies, the present invention offers advantages such as low wear and tear on monitoring equipment, low energy consumption, high monitoring efficiency, a wide range of bolt loosening location, high bolt loosening location accuracy, and excellent automated monitoring performance.

[0037] Furthermore, the present invention designs a modal analysis method that can extract the optical phase time history modal vibration mode and the optical fiber phase damping ratio. This method can further explore the structural dynamic characteristics information implicit in the optical phase time history signal. It can locate loose flange connections when pipeline bolts have loosened but have not caused leakage, greatly reducing the risk of medium leakage within the pipeline structure and preventing the occurrence of secondary disasters.

[0038] Furthermore, the present invention designs an unwinding process that not only unwinds along the spatial axis of the optical fiber, but also unwinds the phase difference between the two spatial points along the time axis based on the phase jump between the two time points. This overcomes the problem that conventional DAS only unwinds along the spatial axis of the optical fiber and is restricted by the unwinding algorithm and cannot be applied to unwinding structural components with large vibration strains.

[0039] Furthermore, the present invention designs a baseline calibration algorithm, which, after extracting the phase difference time history between two spatial sampling points, removes the abnormal increments of the time history signal, and can obtain a phase time history with higher linearity with the structural response;

[0040] Furthermore, the present invention designs a local positioning method based on piezoelectric impedance technology, which realizes coverage monitoring of flange connections by deploying a multi-channel front-end measurement node network. During the monitoring process, the multi-channel front-end measurement nodes have low usage consumption and high monitoring efficiency.

[0041] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1Flowchart of a method for locating overall and local bolt loosening of a pipe flange connection according to an embodiment of the present invention;

[0044] Figure 2 This is a flow chart of demodulating, calculating, and analyzing reflected light in a method for locating overall and local bolt loosening in a pipe flange connection according to an embodiment of the present invention;

[0045] Figure 3 2. It is a structural diagram of the overall and local bolt loosening positioning system for a pipe flange connection according to an embodiment of the present invention;

[0046] Figure 4 2. It is a structural diagram of a global positioning subsystem in the overall and local bolt loosening positioning system for a pipe flange connection according to an embodiment of the present invention;

[0047] Figure 5 2. It is a structural diagram of a multi-channel front-end measurement node network in a system for locating overall and local bolt loosening of a pipe flange connection according to an embodiment of the present invention;

[0048] Figure 6 2 is a schematic structural diagram of an impedance measurement module in a system for locating overall and local bolt loosening of a pipe flange connection according to an embodiment of the present invention;

[0049] Figure 7 is a schematic structural diagram of a distributed optical fiber pipeline health monitoring device according to an embodiment of the present invention;

[0050] Figure 8 Schematic diagram of the structure of the pipeline structure, optical fiber, flange connection, and front-end measurement node in a specific application of the method for locating overall and local bolt loosening of a pipeline flange connection according to an embodiment of the present invention;

[0051] Figure 9 Schematic diagram of flange connection dimensions and bolt arrangement thereof in a specific application of the method for locating overall and local bolt loosening of a pipe flange connection according to an embodiment of the present invention;

[0052] Figure 10 Schematic diagram of the sequence of loosening bolts in a specific application of the method for loosening and positioning the overall and local bolts of a pipe flange connection according to an embodiment of the present invention;

[0053] Figure 11 This is a diagram of reference impedance signal data in a specific application of the method for locating overall and local bolt loosening in a pipe flange connection according to an embodiment of the present invention;

[0054] Figure 12 This is a positioning feature diagram in a specific application of the method for positioning overall and local bolt loosening of a pipe flange connection according to an embodiment of the present invention;

[0055] 13 is a diagram of initial phase signals of the S channel and the P channel in a specific application of the method for locating overall and local bolt loosening of a pipe flange connection according to an embodiment of the present invention;

[0056] Figure 14 An integrated phase time history signal diagram of the S channel and the P channel in a specific application of the method for locating overall and local bolt loosening of a pipe flange connection according to an embodiment of the present invention;

[0057] Figure 15 The optimal phase time history signal segment obtained by searching a pilot function in a specific application of the method for locating overall and local bolt loosening of a pipe flange connection according to an embodiment of the present invention;

[0058] Figure 16 These are five sets of intrinsic mode functions and instantaneous amplitude curve results in a specific application of the method for locating overall and local bolt loosening of a pipe flange connection according to an embodiment of the present invention;

[0059] Figure 17 This is a phase vibration mode diagram in a specific application of the method for locating overall and local bolt loosening in a pipe flange connection according to an embodiment of the present invention;

[0060] Figure 18 This is a diagram showing the analysis results of the root mean square deviation of bolts in a specific application of the method for locating overall and local bolt loosening in a pipe flange connection according to an embodiment of the present invention. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present 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 only used to explain the present invention and are not intended to limit the present invention.

[0062] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic illustrations of the basic concept of the present invention. Therefore, the drawings only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0063] In the present invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like are used to indicate positions or locations based on those shown in the accompanying drawings. These terms are intended solely to facilitate the description of the present application and to simplify the description. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present application. Furthermore, the terms "first" and "second" are used solely for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0064] Example 1

[0065] This embodiment provides a method for locating the overall and local bolt looseness of a pipeline flange connection. Optical fibers are arranged in the pipeline structure, and a multi-channel front-end measurement node is arranged at each flange connection in the pipeline structure; the multi-channel front-end measurement node is used to measure the impedance of all bolts at the flange connection. The process of this method is as follows: Figure 1 Shown, including:

[0066] S1. Input probe light into the optical fiber, where the probe light is modulated based on the vibration of the pipeline structure. Polarization diversity is performed on the modulated reflected light. The two orthogonal polarization states of light obtained by the polarization diversity are demodulated, calculated, and analyzed to obtain position information and the fiber phase damping ratio of the flange connection where loose bolts exist. Based on the corresponding relationship between the fiber phase damping ratio and the number of loose bolts, the number of loose bolts at the flange connection is found. The corresponding relationship between the fiber phase damping ratio and the number of loose bolts is obtained through calibration.

[0067] Specifically, the calibration method includes: loosening the bolts on each flange connection one by one, and then, when each bolt is completely loosened, tapping the pipes at both ends of the flange connection in turn, and collecting optical phase time history signals after each tapping; processing and analyzing the collected optical phase time history signals, and outputting optical phase damping ratios corresponding to different numbers of loosened bolts; fitting the relationship between the optical phase damping ratio and the number of loosened bolts, and dividing the range of the optical phase damping ratio into segments according to the fitted relationship to obtain the corresponding relationship between the range of the optical phase damping ratio and the number of loosened bolts; repeating the above steps for flange connections of different specifications to obtain the corresponding relationship between the optical phase damping ratio and the number of loosened bolts at flange connections of different specifications.

[0068] The reflected light is demodulated, calculated and analyzed to obtain the position information of the flange connection where the bolts are loose and the number of loose bolts at the flange connection. The method flow used is as follows: Figure 2 Shown, including:

[0069] T1. Convert the two orthogonal polarization states of the S channel and P channel optical signals into electrical signals and then into digital signals. Then, process them into initial phase signals respectively and deconvolve the two initial phase signals along the spatial axis.

[0070] Specifically, the method of processing the digital signals of the S channel and the P channel into initial phase signals respectively includes: Process the digital signals of the S channel and the P channel respectively; wherein, is the initial optical phase of each spatial sampling point along the optical fiber at time τ, t is the time delay of the reflected light at each spatial sampling point, H is the Hilbert operator, and I(t,τ) is the S-channel or P-channel digital signal at time τ.

[0071] The method of deconvolving the two initial phase signals along the spatial axis includes processing the two initial phase signals according to the following formula:

[0072]

[0073] in, Indicates the position t on the optical fiber m to t N All spatial sampling points, N is the total number of spatial sampling points on the optical fiber, m represents the current spatial sampling point to be deconvoluted at position t m , τ0 is the current moment.

[0074] T2. Calculate the standard deviation matrices of the S channel and the P channel respectively based on the two initial phase signals deconvolved along the spatial axis, perform noise reduction processing on the standard deviation matrices, calculate a positioning feature map matrix based on the standard deviation matrices of the S channel and the P channel after noise reduction processing, and obtain time information of the pipeline structure vibration and the position interval of the vibrating pipeline structure based on the positioning feature map matrix. The time information of the pipeline structure vibration includes the start time and duration of the pipeline structure vibration.

[0075] Specifically, the method for calculating the standard deviation matrix includes: The two initial phase signals deconvolved along the spatial axis are differentiated to obtain two differential signals of the S channel and the P channel; a sliding time window is introduced to calculate the standard deviation of the two differential signals of each spatial sampling point within the sliding time window to obtain a matrix of the standard deviation distribution of the S channel and the P channel along time and space. The matrix elements of the standard deviation matrix are recorded as d ik ;in, is a differential signal, i and j indicate that the current spatial sampling point to be deconvolved is at position i or position j. It is the signal obtained by unwrapping the two initial phase signals along the spatial axis.

[0076] The method for performing noise reduction processing on the standard deviation matrix of the S channel and the P channel includes introducing a block matrix operator with a size of M rows and N columns, using the block matrix operator to process the standard deviation matrix in a left-to-right and top-to-bottom order, and calculating the positioning index of the S channel and the P channel based on the parameters obtained by the processing. The processing method is based on the output principle of the block matrix operator. Furthermore, the output principle of the block matrix operator includes, for each matrix sub-block corresponding to the block matrix operator contained in the standard deviation matrix, if the d of the matrix sub-block isik If the value is less than a0, output 0, otherwise, output 1. a0 is the standard deviation matrix d ik The average value of the block matrix operator is obtained, and the average value of the matrix elements of the 0-1 matrix is ​​recorded as a1; when |f ik -f n |>f d When a2=0, otherwise, a2=1, where f ik The matrix sub-block corresponds to The main frequency in the spectrum, n is the modal order to be investigated, f n is the nth order natural frequency of the pipeline, f d A custom constant determined based on the peak width of each order characteristic frequency in the structure spectrum.

[0077] The positioning indicators obtained from the S channel and the P channel are superimposed to obtain a positioning feature map matrix. According to the time axis position of the peak value of the positioning feature map matrix, the time information of the pipeline structure vibration and the position information of the flange connection where the bolts are loose are obtained.

[0078] Conventional DAS typically unwinds the phase only along the spatial axis of the optical fiber. Constrained by the unwinding algorithm, the phase difference between two adjacent spatial points must be less than π. However, the vibration strain of structural components can often reach tens or even hundreds of microstrains, and the phase jump between two spatial points is usually much larger than π, making it impossible to unwind the original phase. The pulsed light emission frequency of the DAS is generally much higher than the natural vibration frequency of the structure, and the phase jump between two time points can meet the requirements of the unwinding algorithm. Based on the above principle, the overall and local bolt loosening positioning method for pipeline flange connections in this embodiment not only unwinds along the spatial axis, but also unwinds the phase difference between two spatial points along the time axis to obtain the phase time history.

[0079] T3. Deconvolving the two initial phase signals along the time axis according to the position interval of the vibrating pipeline structure.

[0080] Specifically, the method of unwrapping the two initial phase signals along the time axis includes: selecting two spatial sampling points in the optical fiber interval corresponding to the position interval of the vibrating pipeline structure according to the following formula, taking the phase difference between the two spatial sampling points, and unwrapping them along the time axis. The formula includes:

[0081]

[0082] Among them, the subscripts i and j represent the spatial sampling points at position i and position j, and the spatial sampling point t i Traverse all the spatial sampling points in the optical fiber interval, the spatial sampling point t j Take the spatial sampling point t i Subsequent spatial sampling points separated by a preset interval, Represents the time τ m to τ N All time sampling points, N is the total number of time sampling points on the time axis, the sampling time of the time sampling point corresponds to the incident time of the detection light pulse in the optical fiber interval, m represents the current spatial sampling point to be deconvolved at time τ m , is the extracted initial phase time history.

[0083] The phase difference between the two spaces after deconvolution along the time axis is baseline-calibrated according to the following formula:

[0084]

[0085] Where d0 is the preset step threshold, is the time τ m At time τ m+T The average phase value of is the time τ m-T At time τ m The phase average value, T is the preset signal segment length, is the time τ m to τ m+T The central trend line of the phase time history is obtained by a nonlinear least squares method.

[0086] Generally, the phase signal on the time axis is more sensitive to light source fluctuations, fading effects, and noise, and is prone to step and baseline drift. Therefore, after extracting the phase difference time history between two spatial sampling points, this embodiment designs the above-mentioned baseline calibration algorithm to remove the abnormal increments of the time history signal, thereby obtaining a phase time history that is more linear with the structural response.

[0087] T4. Integrate the two initial phase signals deconvolved along the time axis to obtain an integrated phase time history signal; perform a trial function search on the integrated phase time history signal based on the time information of the pipeline structure vibration and the position interval of the pipeline structure where the vibration occurs, obtain its optimal phase time history segment, and analyze it; the trial function search uses a Hilbert-Huang transform with limited bandwidth empirical mode demodulation to obtain each order intrinsic mode function of each spatial sampling point within the position interval of the vibrating pipeline structure, where the spatial sampling points correspond to sampling points at which the electrical signal is continuously sampled at a preset rate.

[0088] Specifically, the method for integrating the initial phase signal deconvolved along the time axis includes: The two initial phase signals after deconvolution along the time axis are integrated to obtain an integrated phase time course signal. Where i represents the i-th spatial sampling point on the optical fiber, S or P corresponds to the S channel or P channel respectively, is the phase time-course signal, and m is determined according to the following formula:

[0089]

[0090] Among them, I E S or I E P For I S or I P The upper envelope of N is the total number of all spatial sampling points on the optical fiber, and k is the The scaling factor for the number of abnormal peaks.

[0091] The method of performing a trial function search on the integrated phase time history signal x(τ) specifically includes:

[0092] Determine whether the integrated phase time-course signal x(τ) is an impulse response signal. If so, use the phase time-course signal x(τ) as the quasi-analysis signal x(τ); otherwise, use the cross-correlation function of the initial phase signal as the quasi-analysis signal x(τ).

[0093] The pseudo-analysis signal x(τ) is superimposed with a preset bandwidth-limited signal s(τ) to obtain a superimposed signal y(τ). In this embodiment, the preset bandwidth-limited signal s(τ) is A0exp(-ξ0τ)sin(2πfτ). Standard empirical mode demodulation is performed on the superimposed signal y(τ) to obtain the initial first-order intrinsic mode function IMF of the spatial sampling point to which the superimposed signal y(τ) belongs. 01 ; Let h1(τ)=IMF 01 -s(τ), determine whether h1(τ) has modal aliasing; when no modal aliasing exists, the first-order intrinsic mode function of the spatial sampling point is h1(τ); otherwise, let x(τ) = h1(τ), and repeat the above steps until the modal aliasing of h1(τ) is eliminated or the number of iterations exceeds a preset number; the eigenmode functions of each order of each spatial sampling point in the position interval of the vibrating pipeline structure are obtained by the above method.

[0094] According to the time information of the vibration of the pipeline structure, the vibration start time is used as the starting moment, and the duration is used as the fitting interval. The eigenmode order to be investigated is specified in the fitting interval, and a preset time channel is used to cover the eigenmode function fragments exceeding the preset duration at all spatial sampling points contained in the pipeline structure that vibrates at the same time; a preset exponential function is used as a test function. In this embodiment, the exponential function selects x1exp(x2τ) (x2<0) to fit the normalized instantaneous amplitude curve of each spatial sampling point, and calculate the fitting root mean square error of all spatial sampling points; the time channel is moved, and the root mean square error in the time channel at each time step is gradually calculated. The phase time history fragment in the time channel with the smallest root mean square error is taken as the optimal phase time history fragment, and the amplitude parameter and attenuation coefficient obtained by fitting the optimal phase time history fragment are obtained.

[0095] T5. Calculate the phase vibration mode of the optimal segment of each order intrinsic mode function of each spatial sampling point within the position range of the vibrating pipeline structure, and obtain the position information of the flange connection where the bolts are loose based on the peak value of the phase vibration mode.

[0096] Specifically, for each spatial sampling point within the optical fiber interval corresponding to the position interval of the vibrating pipeline structure, the instantaneous amplitude average of the optimal phase time-history segment of each order intrinsic mode function is calculated, that is, the vibration mode value of each modal order of the spatial sampling point. Based on the vibration mode value, the phase vibration mode of the optimal segment of each order intrinsic mode function of each spatial sampling point is calculated.

[0097] The method of demodulating, calculating and analyzing the reflected light to obtain the optical fiber phase damping ratio includes: calculating the optical fiber phase damping ratio according to the following formula, which includes:

[0098] w dn (τ) = dθ n (τ) / dτ

[0099]

[0100] Where, the subscript n represents the nth mode, w dn is the damped circular frequency, θ n is the instantaneous phase, x2 is the attenuation coefficient, ξ n is the fiber phase damping ratio, w n is the circular frequency.

[0101] S2. Based on the location information of the flange connection where the bolts are loose, activate the corresponding multi-channel front-end measurement node, measure the impedance of all bolts in the flange connection, and calculate the root mean square deviation based on the impedance measurement results and the impedance reference signals of the bolts at different locations in the flange connection. The impedance reference signals of the bolts at different locations in the flange connection are measured when the bolts are in a fixed state.

[0102] Specifically, the measurement method includes: attaching a piezoelectric sensor to each bolt cap at the flange connection, and electrically connecting each piezoelectric sensor to different measurement channels of the front-end measurement node; fully tightening all bolts at the flange connection; performing impedance measurement on different measurement channels to obtain a reference impedance signal for each bolt; repeating the above steps for each specification of flange connection to obtain a reference impedance signal for all bolt parts on different flange connections.

[0103] Specifically, the method for calculating the root mean square deviation includes: Calculate the root mean square deviation, where RMSD is the root mean square deviation, N is the number of frequency points the signal sweeps on the frequency axis, and S i,reg is the impedance reference signal of the bolt with position number i, S i,x is the current impedance signal of the bolt with position number i.

[0104] S3. Identify specific locations of the loose bolts based on the number of the loose bolts and the root mean square deviation of the bolts at different locations of the flange connection.

[0105] Specifically, the identification threshold of the root mean square deviation is determined based on the number of loose bolts at the flange connection, and the measurement channel whose root mean square deviation of the measured impedance is greater than the identification threshold is selected. The corresponding bolt is the loose bolt, and the specific position of the loose bolt is obtained according to the pre-stored correspondence between the measurement channel and the bolt position.

[0106] Based on the above-mentioned method for locating the overall and local bolt loosening of the pipe flange connection, this embodiment also provides a system for locating the overall and local bolt loosening of the pipe flange connection. The system executes the above-mentioned method for locating the overall and local bolt loosening of the pipe flange connection, and the structure is as follows: Figure 3 As shown, it includes a global positioning subsystem and a local positioning subsystem.

[0107] The global positioning subsystem includes a polarization diversity deconvolution module, a pipeline interval positioning module, a loose node positioning module and a bolt loose quantity identification module, and its structure is as follows: Figure 4 shown.

[0108] The polarization diversity module is used to generate detection light in the optical fiber laid along the entire length of the pipeline structure. The detection light is modulated based on the vibration of the pipeline structure. The modulated reflected light is polarization-diversified. The two orthogonal polarization states of light obtained by polarization diversity are demodulated and input into the pipeline section positioning module and the loose node positioning module.

[0109] The pipeline interval positioning module and the loose node positioning module are used to calculate and analyze the demodulated two paths of orthogonal polarization states of light to obtain location information of the flange connection where the bolts are loose. Specifically, the pipeline interval positioning module is used to complete the demodulation of the initial phase time course signal of the light along the spatial axis, and the loose node positioning module is used to complete the demodulation of the initial phase time course signal of the light along the temporal axis.

[0110] The loose bolt quantity identification module is used to calculate the corresponding optical fiber phase damping ratio of the flange connection where the bolts are loose, and find the number of loose bolts at the flange connection based on the correspondence between the optical fiber phase damping ratio and the number of loose bolts obtained in advance.

[0111] The local positioning subsystem includes a remote measurement and control server, a communication module and a multi-channel front-end measurement node network.

[0112] Among them, the multi-channel front-end measurement node network is used to activate the multi-channel front-end measurement node corresponding to the flange connection where the bolts are loose according to the activation instruction of the remote measurement and control server, complete the impedance measurement of all bolts at the flange connection, and transmit it to the remote measurement and control server.

[0113] Furthermore, the multi-channel front-end measurement node network includes a communication module, an impedance measurement module, a microcontroller module and a power supply module, and the structure is as follows: Figure 5 shown.

[0114] The communication module is connected to the remote control server by wireless communication, and the WH-LTE-7S4 module can be selected.

[0115] The structure of the impedance measurement module is as follows Figure 6As shown, the module includes an AD5933 impedance measurement chip, a #1 low-voltage multiplexer, a #2 low-voltage multiplexer, a #3 low-voltage multiplexer, a calibration resistor network, a feedback resistor network, and a measurement channel network. The impedance measurement module implements impedance measurement using the AD5933 chip; the #1 low-voltage multiplexer controls the switching of the calibration resistor network; the #2 low-voltage multiplexer controls the switching of the feedback resistor network; and the #3 low-voltage multiplexer controls the switching of the measurement channels. The #1 and #2 low-voltage multiplexers can use the ADG706 chip to switch 16 calibration resistors and 16 feedback resistors, respectively. The #3 low-voltage multiplexer can use the ADG708 chip to switch eight measurement channels.

[0116] The microprocessor module controls the communication module and the impedance measurement module based on the STM32 chip, realizes the reception and parsing of measurement instructions and the transmission of measurement data between the multi-channel front-end measurement node network and the remote control server, and is also used to control the impedance measurement module. Based on the control of the #1 low-voltage multiplexer, the #2 low-voltage multiplexer, and the #3 low-voltage multiplexer, the calibration resistor, feedback resistor, and measurement channel used for measurement are respectively selected, thereby ultimately realizing control over data measurement and acquisition.

[0117] The power supply module converts the external voltage into a specific voltage to supply electrical energy to each module.

[0118] The remote measurement and control server is used to send an activation instruction to the multi-channel front-end measurement node network based on the position information of the flange connection where the bolts are loose, as determined by the global positioning subsystem, and calculate the root mean square deviation based on the received impedance measurement data and the impedance reference signal of the bolts at different positions of the flange connection measured in advance, and combine the root mean square deviation with the number of loose bolts at the flange connection to identify the specific location of the loose bolts.

[0119] Based on the structural composition of the global positioning subsystem of the above-mentioned pipeline flange connection overall and local bolt loosening positioning system, this embodiment also provides a distributed optical fiber pipeline health monitoring device, the structure of which is as follows: Figure 7 As shown, it includes a single-mode sensing fiber, a narrow linewidth laser, an acousto-optic modulator, an optical circulator, an optical coupler, a polarization diversity detector, a two-channel acquisition card, an erbium-doped fiber amplifier, a processor, and a memory.

[0120] The single-mode sensing optical fiber is arranged in a spirally wound form in the pipeline structure interval to be monitored; the optical coupler can separate the incident light generated by the narrow-linewidth laser into intrinsic light and detection light, the detection light is input into an acousto-optic modulator, and the intrinsic light is input into a polarization diversity detector; the acousto-optic modulator modulates the detection light into an optical pulse signal; the erbium-doped fiber amplifier can amplify the power of the optical pulse signal; the optical circulator can transmit backscattered light of the detection light; the polarization diversity detector is used in combination with a two-channel acquisition card to simultaneously acquire optical signals in two orthogonal polarization states of the S channel and the P channel, and convert them into electrical signals to be input into a processor and the memory; the processor and the memory can be connected via a bus or other means, and the memory, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs and non-volatile computer executable programs, and the programs include a series of demodulation, calculation and analysis of optical signals in the above-mentioned overall and local bolt loosening positioning method of the pipeline flange connection. The processor executes a series of demodulation, calculation and analysis of the optical signal in the above-mentioned method for locating the overall and local bolt loosening of the pipeline flange connection by running the non-volatile software program and instructions stored in the memory.

[0121] The principle of the above-mentioned device to achieve its function is that the incident light emitted by the narrow-linewidth laser is divided into two paths by an optical coupler. One path enters the polarization beam splitter as local light, and the other path enters the monitoring pipeline structure after passing through the acousto-optic modulator and erbium-doped fiber amplifier in sequence as detection light. Modulation is generated based on the vibration of the monitoring pipeline structure. The modulated reflected light also enters the polarization beam splitter through an optical circulator. The two beams of S-channel and P-channel optical signals after polarization diversity by the polarization beam splitter are converted into electrical signals through a photoelectric balanced detector. The electrical signals are input into the acquisition card for continuous sampling and finally enter the acquisition and storage device for a series of demodulation, analysis and calculation.

[0122] Based on the above-mentioned method for locating overall and local bolt loosening of a pipe flange connection, this embodiment also provides a non-volatile computer storage medium, which stores computer-executable instructions. The computer-executable instructions are executed by one or more processors for the above-mentioned method for locating overall and local bolt loosening of a pipe flange connection.

[0123] Example 2

[0124] This embodiment provides a specific application of the method for locating the overall and local bolt loosening of the pipe flange connection described in Example 1. In this embodiment, as Figure 8As shown, the pipeline structure is a 3.2-meter-long steel pipe model assembled by 4 sections of pipes and 3 flange connections. A single-mode optical fiber is arranged along the entire length of the pipeline structure, and about 20 meters of the optical fiber between the marked 157 meters and 177 meters is wound on the pipeline structure; the size of the flange connection and the bolt arrangement are as shown in Figure 9 As shown, one front-end measurement node is arranged on each flange connection, and a piezoelectric sensor is attached to the bolt cap of each bolt, and the piezoelectric sensor is electrically connected to the measurement channel of the front-end measurement node through a connecting cable.

[0125] The flow executed by the embodiment includes:

[0126] S1, input a probe light into the optical fiber, the probe light is modulated based on the vibration of the pipeline structure, polarize the modulated reflected light, demodulate, calculate and analyze the light in two orthogonal polarization states obtained by polarization diversity, to obtain the position information of the flange connection with loose bolts and the optical fiber phase damping ratio, and according to the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts, the number of loose bolts of the flange connection is found; the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts is obtained by calibration.

[0127] Specifically, the calibration process includes: for the flange connection, loosen the bolts on the flange connection one by one, and the loosening bolt sequence is as shown in Figure 10 As shown, then knock the two ends of the pipeline of the flange connection in turn when each bolt is completely loosened, and collect the optical phase time history signal after each knock.

[0128] Process and analyze the collected optical phase time history signal, and output the optical phase damping ratio corresponding to different number of loose bolts.

[0129] Fit the relationship between the damping ratio and the number of loose bolts, and according to the fitted relationship, divide the damping ratio range into sections to obtain the corresponding table of the optical phase damping ratio range interval and the number of loose bolts, as shown in Table 1, which is used for query during actual monitoring.

[0130]

[0131] Table 1 Corresponding table of optical fiber phase damping ratio range interval and number of loose bolts

[0132] Repeat the above steps for flange connections of different specifications to obtain the corresponding table of the optical fiber phase damping ratio range interval and the number of loose bolts for each type of flange connection.

[0133] In this example, considering the spirally wound fiber layout, the calculation was performed using a 5-meter fiber range near the loose flange connection, taking into account the fiber's spatial resolution and the fiber winding length at the monitoring flange connection. The damping ratio of the optical phase time history signal within this range was calculated to be 0.89. Comparing this result with Table 1, the predicted number of loose bolts is three.

[0134] T1. Convert the two orthogonal polarization states of the S channel and the P channel optical signals into electrical signals and then into digital signals, and then process them into initial phase signals respectively. The initial phase signals of the S channel and the P channel are shown in Figure 13(a) and Figure 13(b). The two initial phase signals are unwrapped along the spatial axis.

[0135] T2, according to the two initial phase signals deconvolved along the spatial axis, the standard deviation matrices of the S channel and the P channel are calculated respectively, and the standard deviation matrices are subjected to noise reduction processing, and the positioning feature map matrix is ​​calculated based on the standard deviation matrices of the S channel and the P channel after noise reduction processing, such as Figure 12 As shown, according to the positioning feature map matrix, the vibration range of the pipeline is 148 meters to 188 meters, which includes the optical fiber attached to the pipeline between 157 meters and 177 meters. When the surface is knocked, the entire pipeline model in this experiment vibrates and affects the adjacent optical fibers. Figure 10 The analysis shows that the vibration time is about 4-7 seconds, and the main vibration duration is about 1.5 seconds. The optical phase time history signal in the time range of 4.0 seconds to 7.0 seconds in the original signal is extracted, and 4.0 seconds is adjusted as the initial point of the signal to obtain the optical phase time history signals of the S channel and P channel, as shown in the figure. Figure 11 shown.

[0136] T3. Deconvolving the two initial phase signals along the time axis according to the position interval of the vibrating pipeline structure.

[0137] T4, integrating the two initial phase signals deconvolved along the time axis to obtain an integrated phase time-course signal. The integrated phase time-course signals of the S channel and the P channel are as follows: Figure 14 As shown; based on the time information of the pipeline structure vibration and the position interval of the vibrating pipeline structure, a trial function search is performed on the integrated phase time history signal to obtain its optimal phase time history segment and analyze it; the trial function search uses the Hilbert-Huang transform of limited bandwidth empirical mode demodulation to obtain each order intrinsic mode function of each spatial sampling point within the position interval of the vibrating pipeline structure, and the spatial sampling points correspond to the sampling points at which the electrical signal is continuously sampled at a preset rate.

[0138] T5. Calculate the phase vibration mode of the optimal segment of each order intrinsic mode function of each spatial sampling point within the position interval of the vibrating pipeline structure. The phase vibration mode is as follows: Figure 17 As shown. Search and extract the signal period with the minimum sum of fitting errors at all spatial sampling points in the 1.5 second time channel. The phase time history segment corresponding to the search result is shown as follows Figure 15 The identification results of each mode and its instantaneous amplitude curve are shown in Figure 16 As shown, according to the peak value of the phase vibration mode, the flange connection where the bolts are loose is located at position M.

[0139] S2, activate the multi-channel front-end measurement node 2 corresponding to the M position, measure the impedance of all bolts at the flange connection, and calculate the root mean square deviation based on the impedance measurement results and the impedance reference signals of the bolts at different positions at the flange connection. The calculation results are as follows: Figure 18 As shown in Figure 1, the impedance reference signals of bolts at different positions on the flange connection are measured when the bolts are in a fixed state.

[0140] The measurement process includes:

[0141] The piezoelectric sensor is pasted on each bolt cap of the flange connection through epoxy resin, and each piezoelectric sensor is electrically connected to different measurement channels of the front-end measurement node through a cable.

[0142] Fully tighten all bolts on the flange connections.

[0143] Impedance measurement is performed on different measurement channels to obtain a reference impedance signal for each bolt. The impedance reference signal obtained in this embodiment is as follows: Figure 11 shown.

[0144] Repeat the above steps for each specification of flange connection to obtain the benchmark impedance signals of all bolt positions on different flange connections.

[0145] S3. Identify the specific locations of the loose bolts based on the number of loose bolts and the root mean square deviation of the bolts at different locations on the flange connection. As the number of loose bolts identified is 3, select the 3 bolt locations with the largest root mean square deviation values. The loose bolt locations thus accurately identified are P1, P2, and P8, respectively. Figure 15 As shown by the middle dotted line, this identification result is consistent with the simulated damage position applied in this embodiment.

[0146] The present embodiment provides a specific application of the method for locating overall and local bolt looseness of a pipe flange connection described in Example 1. A damage position is pre-imposed on the monitoring pipe structure. By implementing the method for locating overall and local bolt looseness of a pipe flange connection, the flange connection with loose bolts is located, and the number of loose bolts at the flange connection and the specific positions of the loose bolts are obtained. The monitoring results obtained are consistent with the preset damage conditions, effectively verifying the accuracy and reliability of the method and system for locating overall and local bolt looseness of a pipe flange connection of the present invention.

[0147] In summary, the present invention provides a method and system for locating overall and local bolt loosening in pipeline flange connections, which combines a global positioning method based on optical fiber and a local positioning method based on piezoelectric impedance. It can not only accurately locate the flange connection of the pipeline structure where loose bolts exist, but also accurately obtain the number of loose bolts at the flange connection and accurately locate the specific position of the loose bolts.

[0148] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0149] The size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0150] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A method for locating loose bolts in the overall and local areas of a pipe flange connection, characterized in that: Optical fibers are arranged in the pipeline structure, and multi-channel front-end measurement nodes are arranged at each flange connection in the pipeline structure; The multi-channel front-end measurement node is used to measure the impedance of all bolts at the flange connection; This method includes: Probe light is input into the optical fiber, where the probe light is modulated based on the vibration of the pipeline structure. Polarization diversity is performed on the modulated reflected light, and light in two orthogonal polarization states, an S-channel and a P-channel, obtained by the polarization diversity are demodulated, calculated, and analyzed to obtain position information and a fiber phase damping ratio of a flange connection where loose bolts are present. Based on a corresponding relationship between the fiber phase damping ratio and the number of loose bolts, the number of loose bolts at the flange connection is determined. The corresponding relationship between the fiber phase damping ratio and the number of loose bolts is obtained through calibration. Based on the position information of the flange connection where the bolts are loose, activating the corresponding multi-channel front-end measurement node, measuring the impedance of all bolts at the flange connection, and calculating the root mean square deviation based on the impedance measurement results and the impedance reference signals of the bolts at different positions of the flange connection; the impedance reference signals of the bolts at different positions of the flange connection are measured when the bolts are in a fixed state; The specific positions of the loose bolts are identified according to the number of the loose bolts and the root mean square deviation of the bolts at the flange connection.

2. The method for positioning the overall and local bolt loosening of pipeline flange connections according to claim 1, characterized in that: A method for demodulating, calculating, and analyzing two orthogonal polarization states of light in the S channel and the P channel obtained by polarization diversity to obtain position information of a flange connection where a bolt is loose includes: The two orthogonal polarization state optical signals of the S channel and the P channel are converted into electrical signals, and then converted into digital signals. Then, they are processed into initial phase signals respectively, and the two initial phase signals are deconvolved along the spatial axis; Calculating standard deviation matrices of the S channel and the P channel respectively based on the two initial phase signals deconvolved along the spatial axis, performing noise reduction processing on the standard deviation matrices, calculating a positioning feature map matrix based on the standard deviation matrices of the S channel and the P channel after the noise reduction processing, and obtaining time information of pipeline structure vibration and a position interval of the pipeline structure where the vibration occurs based on the positioning feature map matrix, wherein the time information of the pipeline structure vibration includes a start time and a duration of the pipeline structure vibration; Deconvolving the two initial phase signals along the time axis according to the position interval of the vibrating pipeline structure; The two initial phase signals deconvolved along the time axis are integrated to obtain an integrated phase time history signal; a trial function search is performed on the integrated phase time history signal based on the time information of the pipeline structure vibration and the position interval of the pipeline structure where the vibration occurs, to obtain and analyze the optimal phase time history segment; the trial function search uses a Hilbert-Huang transform with limited bandwidth empirical mode demodulation to obtain each order intrinsic mode function of each spatial sampling point within the position interval of the vibrating pipeline structure, where the spatial sampling points correspond to sampling points where the electrical signal is continuously sampled at a preset rate; The phase vibration mode of the optimal segment of each order intrinsic mode function of each spatial sampling point in the position interval of the vibrating pipeline structure is calculated, and the position information of the flange connection where the bolts are loose is obtained according to the peak value of the phase vibration mode.

3. The method for positioning the overall and local bolt loosening of a pipe flange connection according to claim 2, characterized in that: The method for processing the two digital signals of the S channel and the P channel into initial phase signals includes: processing the two digital signals respectively according to a first formula; the first formula includes: in, is the initial optical phase of each spatial sampling point along the optical fiber at time τ, t is the time delay of the reflected light at each spatial sampling point, H is the Hilbert operator, and I(t,τ) is the S-channel or P-channel digital signal at time τ; The method of deconvolving the two initial phase signals along the spatial axis includes processing the two initial phase signals according to a second formula, a third formula, and a fourth formula; the second formula includes: The third formula includes The fourth formula includes in, Indicates the position t on the optical fiber m to t N All spatial sampling points, N is the total number of spatial sampling points on the optical fiber, m represents the current spatial sampling point to be deconvoluted at position t m , τ0 is the current moment; The method for calculating the standard deviation matrix includes, according to the fifth formula, performing differentiation on the two initial phase signals deconvolved along the spatial axis to obtain two differential signals of the S channel and the P channel; introducing a sliding time window, calculating the standard deviation of the two differential signals of each spatial sampling point within the sliding time window, and obtaining a matrix of the standard deviation distribution of the S channel and the P channel along time and space, wherein the matrix elements of the standard deviation matrix are recorded as d ik ; The fifth formula includes: in, is a differential signal, i and j indicate that the current spatial sampling point to be deconvolved is at position i or position j. The method for performing noise reduction processing on the standard deviation matrix of the S channel and the P channel comprises introducing a block matrix operator with preset row and column sizes, processing the standard deviation matrix in a preset order using the block matrix operator, and calculating the positioning index of the S channel and the P channel according to the parameters obtained by the processing, wherein the processing method is based on the output principle of the block matrix operator; The positioning indicators of the S channel and the P channel are superimposed to obtain a positioning feature map matrix. According to the time axis position of the peak value of the positioning feature map matrix, the time information of the pipeline structure vibration and the position information of the flange connection where the bolts are loose are obtained.

4. The method for positioning overall and local bolt loosening of pipeline flange connections according to claim 3, characterized in that: The output principle of the block matrix operator includes: for each matrix sub-block corresponding to the block matrix operator contained in the standard deviation matrix, if the d ik The value is less than the standard deviation matrix d ik The average value a0 of the block matrix operator is output as 0, otherwise, it is output as 1, and a 0-1 matrix with the same row and column size as the block matrix operator is obtained. The average value of the matrix elements of the 0-1 matrix is ​​recorded as a1; when |f ik -f n |>f d When a2=0, otherwise, a2=1, where f ik The matrix sub-block corresponds to The main frequency in the spectrum, n is the modal order to be investigated, f n is the nth order natural frequency of the pipeline, f d It is a custom constant determined according to the peak width of each order characteristic frequency in the structure spectrum.

5. The method for positioning overall and local bolt loosening of pipeline flange connections according to claim 2, characterized in that: The method of deconvolving the two initial phase signals along the time axis includes: selecting two spatial sampling points in the optical fiber interval corresponding to the position interval of the vibrating pipeline structure according to the sixth, seventh, eighth, and ninth formulas, taking the phase difference between the two spatial sampling points, and deconvolving along the time axis; performing baseline calibration processing on the two spatial phase differences after deconvolving along the time axis according to the tenth, eleventh, and twelfth formulas; the sixth formula includes: The seventh formula includes: The eighth formula includes: The ninth formula includes: Among them, the spatial sampling point t i Traverse all the spatial sampling points in the optical fiber interval, the spatial sampling point t j Take the spatial sampling point t i Subsequent spatial sampling points separated by a preset interval, Represents the time τ m to τ N All time sampling points, N is the total number of time sampling points on the time axis, the sampling time of the time sampling point corresponds to the incident time of the detection light pulse in the optical fiber interval, m represents the current spatial sampling point to be deconvolved at time m, is the extracted initial phase time course; the tenth formula includes: The eleventh formula includes The twelfth formula includes Where d0 is the preset step threshold, is the time τ m At time τ m+T The average phase value of is the time τ m-T At time τ m The phase average value, T is the preset signal segment length, is the time τ m to τ m+T The central trend line of the phase time course is obtained by a nonlinear least squares method. is the phase time course obtained after baseline calibration; The method for integrating the initial phase signal deconvolved along the time axis includes: integrating the two initial phase signals deconvolved along the time axis according to a thirteenth formula to obtain an integrated phase time course signal, wherein the thirteenth formula includes: Where i represents the i-th spatial sampling point on the optical fiber, S or P corresponds to the S channel or P channel respectively, is the phase time signal, m is calculated according to the fourteenth and fifteenth formulas; the fourteenth formula includes The fifteenth formula includes m=1, else; wherein, I E S or I E P For I S or I P The upper envelope of N is the total number of all spatial sampling points on the optical fiber, and k is the The scaling factor for the number of abnormal peaks.

6. The method for positioning overall and local bolt loosening of pipeline flange connections according to claim 5, characterized in that: The method of performing a trial function search on the integrated phase time history signal x(τ) specifically includes: Determine whether the integrated phase time-history signal x(τ) is an impulse response signal; if so, use the phase time-history signal x(τ) as the quasi-analysis signal x(τ); otherwise, use the cross-correlation function of the initial phase signal as the quasi-analysis signal x(τ); The pseudo-analysis signal x(τ) is superimposed with the preset bandwidth-limited signal s(τ) to obtain a superimposed signal y(τ), and the superimposed signal y(τ) is subjected to standard empirical mode demodulation to obtain the initial first-order intrinsic mode function IMF of the spatial sampling point to which the superimposed signal y(τ) belongs 01 ; Let h1(τ)=IMF 01 -s(τ), determine whether h1(τ) has modal aliasing; when there is no modal aliasing, take the first-order eigenmode function of the spatial sampling point as h1(τ); otherwise, let x(τ) = h1(τ), and repeat the above steps until the modal aliasing of h1(τ) is eliminated or the number of iterations exceeds a preset number; obtain the eigenmode functions of each order of each spatial sampling point within the position interval of the vibrating pipeline structure through the above method; According to the time information of the vibration of the pipeline structure, the vibration start time is used as the starting moment and the duration is used as the fitting interval. The order of the intrinsic mode function to be investigated is specified in the fitting interval, and a preset time channel is used to cover the intrinsic mode function segments exceeding the preset duration at all spatial sampling points contained in the pipeline structure vibrating at the same time. A preset exponential function is used as a trial function to fit the normalized instantaneous amplitude curve of each spatial sampling point, and the fitting root mean square error of all spatial sampling points is calculated. The time channel is moved, and the root mean square error in the time channel at each time step is gradually calculated. The phase time history segment in the time channel with the smallest root mean square error is taken as the optimal phase time history segment, and the amplitude parameters and attenuation coefficient obtained by fitting the optimal phase time history segment are obtained.

7. The method for positioning overall and local bolt loosening of pipeline flange connections according to claim 6, characterized in that: The method for obtaining the phase vibration modes of all spatial sampling points includes: calculating the instantaneous amplitude average of the optimal phase time history segment of each order intrinsic mode function of each spatial sampling point within the optical fiber interval corresponding to the position interval of the vibrating pipeline structure, that is, the vibration mode value of each modal order of the spatial sampling point; and calculating the phase vibration mode of the optimal segment of each order intrinsic mode function of each spatial sampling point based on the vibration mode value.

8. The method for positioning overall and local bolt loosening of pipeline flange connections according to claim 6, characterized in that: The method for demodulating, calculating and analyzing the reflected light to obtain the optical fiber phase damping ratio includes: calculating the optical fiber phase damping ratio according to the sixteenth formula, the seventeenth formula and the eighteenth formula; the sixteenth formula includes w dn (τ) = dθ n (τ) / dτ, the seventeenth formula includes The eighteenth formula includes Where, the subscript n represents the nth mode, w dn is the damped circular frequency, θ n is the instantaneous phase, x2 is the attenuation coefficient, ξ n is the fiber phase damping ratio, w n is the circular frequency.

9. The method for positioning overall and local bolt loosening of pipeline flange connections according to claim 1, characterized in that: The method for identifying the specific locations of the loose bolts according to the number and root mean square deviation of the loose bolts includes: The identification threshold of the root mean square deviation is determined based on the number of loose bolts at the flange connection. The method for calculating the root mean square deviation includes: calculating the root mean square deviation according to the nineteenth formula, and the nineteenth formula includes Among them, RMSD is the root mean square deviation, N is the number of frequency points that the signal sweeps on the frequency axis, S i,ref is the impedance reference signal of the bolt with position number i, S i,x is the current impedance signal of the bolt with position number i; A measurement channel whose root mean square deviation of the measured impedance is greater than the identification threshold is selected. The bolt corresponding to the measurement channel is the loose bolt. The specific position of the loose bolt is obtained according to the pre-stored correspondence between the measurement channel and the bolt position.

10. A system for locating the loosening of the overall and local bolts of a pipe flange connection, characterized in that: The system implements the method for locating overall and local bolt loosening of a pipe flange connection as described in any one of claims 1 to 9, comprising a global positioning subsystem and a local positioning subsystem; wherein: The global positioning subsystem includes a polarization diversity unwinding module, a pipeline interval positioning module, a loose node positioning module and a loose bolt quantity identification module; wherein the polarization diversity module is used to generate detection light in the optical fiber laid along the entire length of the pipeline structure, the detection light is modulated based on the vibration of the pipeline structure, the modulated reflected light is polarization-diversified, and the two orthogonal polarization states of light obtained by polarization diversity are demodulated and input into the pipeline interval positioning module and the loose node positioning module; the pipeline interval positioning module and the loose node positioning module are used to calculate and analyze the two orthogonal polarization states of light after demodulation to obtain the position information of the flange connection where the bolts are loose; the loose bolt quantity identification module is used to calculate the corresponding optical fiber phase damping ratio of the flange connection where the bolts are loose, and find the number of loose bolts at the flange connection based on the correspondence between the optical fiber phase damping ratio and the number of loose bolts obtained in advance; The local positioning subsystem includes a remote measurement and control server and a multi-channel front-end measurement node network; wherein, the multi-channel front-end measurement node network is used to activate the multi-channel front-end measurement node corresponding to the flange connection where the bolts are loose according to the activation instruction of the remote measurement and control server, complete the impedance measurement of all bolts at the flange connection, and transmit it to the remote measurement and control server; the remote measurement and control server is used to issue an activation instruction to the multi-channel front-end measurement node network based on the position information of the flange connection where the bolts are loose determined by the global positioning subsystem, and calculate the root mean square deviation based on the received impedance measurement data and the impedance reference signal of the bolts at different positions of the flange connection measured in advance, and combine the root mean square deviation with the number of loose bolts at the flange connection to identify the specific position of the loose bolts.

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