Pipeline flange connection integral and local bolt loosening positioning method and system

Abstract

The invention discloses a pipeline flange connection whole and local bolt loosening positioning method and system, and the method comprises the steps: inputting probe light into an optical fiber, enabling the probe light to generate modulation based on the vibration of a pipeline structure, carrying out the polarization diversity of the modulated reflected light, and carrying out the polarization diversity of the modulated reflected light; demodulating, calculating and analyzing the two paths of light in the cross-polarization state obtained by the polarization diversity to obtain the position information and the optical fiber phase damping ratio of the flange connecting part with the loosened bolts, and searching to obtain the number of the loosened bolts at the flange connecting part according to the corresponding relation between the optical fiber phase damping ratio and the number of the loosened bolts; activating the corresponding multichannel front-end measurement nodes, measuring the impedance of all bolts at the flange joint, and calculating the root-mean-square deviation; and identifying the specific position of the loosened bolt. According to the invention, the flange joint of the pipeline structure with the loose bolts can be accurately positioned, and the number and specific positions of the loose bolts can be accurately obtained.

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 of a pipeline flange connection. Background Art

[0002] Flange connection, as a connection method for pipeline transportation, has the advantages of high efficiency, low cost, and strong continuity, and has important applications in the fields of energy supply, petrochemicals, etc. Therefore, health monitoring of pipeline flange connection structures can prevent and detect damage in advance when there is a trend of damage or the structure is in the early stage of damage, which is of great engineering significance.

[0003] Distributed optical fiber acoustic sensing (DAS) technology can globally identify structural vibrations by monitoring the phase changes of light along the optical fiber, and can measure parameters such as amplitude and frequency, which is suitable for pipeline leakage 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. Therefore, such systems can only passively identify the damaged location of the pipeline after the gas or liquid inside the pipeline has leaked, and it is difficult to identify damage at the stage when the pipeline components have minor damage (such as loose bolts, local rust, deformation, etc.) but no substantial rupture.

[0004] Electromechanical impedance (EMI) technology monitors the safety and damage status of structures by detecting changes in the impedance signal of the object being measured. It has high sensitivity for monitoring early minor damage to the structure and has the advantages of simple implementation, applicability to complex structures, good long-term stability, and good damage quantification performance. However, traditional impedance-based damage detection technology can only identify damage changes in local areas. When applied to large-scale projects, it is impossible to identify the location of damage from a global perspective. In order to ensure the safety of the structure, all monitoring nodes need to be monitored and operated continuously for a long time, which leads to overload of the monitoring device and accelerates the consumption of the service life of the monitoring device.

[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 bolt looseness of a pipeline flange connection, which combines a global positioning method based on optical fiber with 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 the overall and local bolt loosening of a pipeline flange connection, wherein an optical fiber is 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 method comprises:

[0008] A detection light is input into the optical fiber, the detection light is modulated based on the vibration of the pipeline structure, polarization diversity is performed on the modulated reflected light, and 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, and the number of loose bolts at the flange connection is found according to the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts; 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 bolts 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, divide the range of the optical phase damping ratio into sections according to the fitted relationship, and 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, and obtain the corresponding relationship between the optical phase damping ratio and the number of loose bolts at flange connections of different specifications.

[0009] According to the position information of the flange connection where the bolts are loose, the corresponding multi-channel front-end measurement node is activated, the impedance of all the bolts at the flange connection is measured, and the root mean square deviation is calculated according to the impedance measurement result and the impedance reference signal of the bolts at different positions of the flange connection; the impedance reference signal of the bolts at different positions of the flange connection is measured when the bolts are fixed. Furthermore, the measurement method includes: pasting a piezoelectric sensor on 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 the bolts at the flange connection; performing impedance measurement on different measurement channels to obtain the reference impedance signal of each bolt; repeating the above steps for each specification of flange connection to obtain the reference impedance signal of all bolt parts on different flange connections.

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

[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, and the two initial phase signals are unwrapped along the spatial axis;

[0013] The standard deviation matrices of the S channel and the P channel are calculated respectively according to the two initial phase signals unwrapped along the spatial axis, and the standard deviation matrices are denoised. A positioning feature map matrix is ​​calculated based on the standard deviation matrices of the S channel and the P channel after the denoising process. The time information of the pipeline structure vibration and the position interval of the pipeline structure where the vibration occurs 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 paths of initial phase signals unwrapped along the time axis are integrated to obtain an integrated phase time history signal; according to the time information of the pipeline structure vibration and the position interval of the pipeline structure where the vibration occurs, 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 adopts the Hilbert-Huang transform of limited bandwidth empirical mode demodulation to obtain each order of intrinsic mode function of each spatial sampling point in the position interval of the pipeline structure where the vibration occurs, and the spatial sampling point corresponds to the sampling point where the electrical signal is continuously sampled at a preset rate.

[0016] The phase vibration modes of the optimal segments of the eigenmode functions of each order at each spatial sampling point within the position interval of the vibrating pipeline structure are 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 of processing the two digital signals of the S channel and the P channel into initial phase signals respectively includes: processing the two digital signals respectively according to a first formula; the first formula includes: in, is the initial light 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 of unwrapping the two initial phase signals along the spatial axis respectively 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 N All spatial sampling points, N is the total number of spatial sampling points on the optical fiber, m means the current spatial sampling point to be unwound is at position t m , τ0 is the current time.

[0019] 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 invention discloses a method for performing noise reduction processing on the standard deviation matrix of the S channel and the P channel by unwrapping the two initial phase signals along the spatial axis direction. The method 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. The processing method is based on the output principle of the block matrix operator.

[0020] The positioning indicators 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 where the bolts are loose 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 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 ik 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 -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 Custom constants determined based on the peak width of each order of characteristic frequencies in the structure spectrum.

[0022] According to the above technical solution, the method of unwrapping the two initial phase signals along the time axis includes: according to the sixth formula, the seventh formula, the eighth formula and the ninth formula, two spatial sampling points are randomly selected in the optical fiber interval corresponding to the position interval of the vibrating pipeline structure, and the phase difference of the two spatial sampling points is taken and unwrapped along the time axis; according to the tenth formula, the eleventh formula, and the twelfth formula, the phase difference of the two spaces after unwrapping along the time axis is baseline calibrated; 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, Indicates 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 indicates that the current spatial sampling point to be deconvoluted is 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 phase average value of is the time τ m-T At time τ m The phase average value, T is the preset signal segment duration, 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.

[0023] The method for integrating the initial phase signal unwrapped along the time axis includes: integrating the two initial phase signals unwrapped 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 course signal, m is taken according to the fourteenth and fifteenth formulas, the fourteenth formula includes m=0, if 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 based on The scaling factor selected for the number of abnormal peaks.

[0024] According to the above technical solution, the method of performing a trial function search on the integrated phase time-course signal x(τ) specifically includes:

[0025] 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).

[0026] The pseudo-analysis signal x(τ) is superimposed with the preset limited bandwidth signal s(τ) to obtain the 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, the first-order intrinsic mode function of the spatial sampling point is h1(τ), otherwise, let x(τ) = h1(τ), repeat the above steps until the modal aliasing of h1(τ) is eliminated, or the number of iterations exceeds the preset number; the intrinsic mode functions of each order of each spatial sampling point in the position interval of the vibrating pipeline structure are obtained by the above method.

[0027] According to the time information of the vibration of the pipeline structure, 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, and a preset time channel is used to include 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 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 is gradually calculated at each time step, and 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.

[0028] According to the above technical solution, the method for obtaining the phase vibration modes of all spatial sampling points includes: for each spatial sampling point within the optical fiber interval corresponding to the position interval of the vibrating pipeline structure, the instantaneous amplitude average value of the optimal phase time-history segment of each order of the intrinsic mode function is calculated, that is, the vibration mode value of each modal order of the spatial sampling point, and the phase vibration mode of the optimal segment of each order of the intrinsic mode function of each spatial sampling point is calculated based on the vibration 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 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.

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

[0031] 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, and 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] A 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 pipeline flange connection overall and local bolt loosening positioning system, the system implements the above-mentioned pipeline flange connection overall and local bolt loosening positioning method, including 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 polarized diverse, and two orthogonal polarization state lights obtained by demodulating the polarization diversity are 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 demodulated two orthogonal polarization state lights 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 out the number of loose bolts at the flange connection according to the correspondence between the optical fiber phase damping ratio and the number of loose bolts obtained by pre-calibration;

[0035] The local positioning subsystem includes a remote measurement and control server and a multi-channel front-end measurement node network; wherein the remote measurement and control server is used to activate the front-end measurement node corresponding to the flange connection according to the position information of the flange connection where the bolts are loose determined by the global positioning subsystem; the multi-channel front-end measurement node is used to complete the impedance measurement of all the bolts at the flange connection, calculate the root mean square deviation according to the impedance reference signal of the bolts at different positions of the flange connection stored in advance, and identify the specific position of the loose bolts in combination with the number of loose bolts at the flange connection. Further, 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 is connected to the remote control server in a wireless communication manner. 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 implements the control calibration resistor network switching, feedback resistor network switching and multiple measurement channel switching based on multiple low-voltage multiplexers.

[0036] The beneficial effects of the present invention are as follows: the present invention provides a method and system for locating the overall and local bolt loosening of a pipeline flange connection, which combines a global positioning method based on optical fiber with a local positioning method based on piezoelectric impedance, and 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. Compared with the prior art, the present invention has the advantages of low consumption of monitoring equipment, low energy consumption, high monitoring efficiency, wide bolt loosening positioning range, high bolt loosening positioning accuracy, and good automatic 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, which can dig deeper into the structural dynamic characteristic information implied in the optical phase time history signal, and locate the loose flange connection when the pipeline bolts have loosened but have not caused leakage, greatly reducing the risk of medium leakage inside the pipeline structure and preventing the occurrence of secondary disasters;

[0038] Furthermore, the present invention designs an unwinding process that unwinds along the optical fiber spatial axis and unwinds the phase difference between the two spatial points along the time axis based on the phase jump between the two time points, thereby overcoming the problem that conventional DAS only unwinds along the optical fiber spatial axis and cannot be applied to unwinding structural components with large vibration strains due to the restriction of the unwinding algorithm.

[0039] Furthermore, the present invention designs a baseline calibration algorithm, which removes the abnormal increment of the time-course signal after extracting the phase difference time-course between two spatial sampling points, and can obtain a phase time-course 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, and 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 briefly introduces 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 creative work.

[0043] Figure 1is a flow chart 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 It is a flow chart of demodulating, calculating and analyzing reflected light in the method for locating overall and local bolt looseness of a pipe flange connection according to an embodiment of the present invention;

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

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

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

[0048] Figure 6 2 is a schematic diagram of the structure 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 It is a structural schematic diagram of a pipeline structure, an optical fiber, a flange connection, and a front-end measurement node in a specific application of the overall and local bolt loosening positioning method of a pipeline flange connection according to an embodiment of the present invention;

[0051] Fig. 9 It is a schematic diagram of flange connection dimensions and bolt settings in a specific application of the overall and local bolt loosening positioning method for a pipe flange connection according to an embodiment of the present invention;

[0052] Fig.10 It is a schematic diagram of the sequence of loosening bolts in a specific application of the method for loosening and locating the overall and local bolts of a pipe flange connection according to an embodiment of the present invention;

[0053] Fig.11 It is a reference impedance signal data diagram in a specific application of the overall and local bolt loosening positioning method for a pipeline flange connection according to an embodiment of the present invention;

[0054] Fig.12 It is a positioning feature diagram in a specific application of the overall and local bolt loosening positioning method for 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] Fig.14 An integrated phase time history signal diagram of the S channel and the P channel in a specific application of the overall and local bolt loosening positioning method for a pipe flange connection according to an embodiment of the present invention;

[0057] Fig.15 It is an optimal phase time history signal segment obtained by searching a pilot function for a specific application of the overall and local bolt loosening positioning method for a pipeline flange connection according to an embodiment of the present invention;

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

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

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

[0061] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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 used to limit the present invention.

[0062] It should be noted that the illustrations provided in the embodiments of the present invention are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout type may also be more complicated.

[0063] In the present invention, it is also necessary to explain that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, if the terms "first" and "second" appear, they are only used for description and distinction purposes, and cannot be understood 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, wherein an optical fiber is 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 As shown, including:

[0066] S1. Input a detection light into the optical fiber, the detection light is modulated based on the vibration of the pipeline structure, polarization diversity is performed on the modulated reflected light, and 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, and the number of loose bolts at the flange connection is found according to the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts; the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts is obtained by calibration.

[0067] Specifically, the calibration method includes, for each flange connection, loosening the bolts on the 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-course signals after each tapping; processing and analyzing the collected optical phase time-course 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 the loose bolts at the flange connection. The method flow adopted is as follows: Figure 2 As shown, including:

[0069] T1. Convert the two orthogonal polarization states of the optical signals of the S channel and the P channel into electrical signals and then into digital signals, and then process them into initial phase signals respectively, and unwrap 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: The digital signals of the S channel and the P channel are processed respectively; wherein, is the initial light 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 unwrapping the two initial phase signals along the spatial axis respectively 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 N All spatial sampling points, N is the total number of spatial sampling points on the optical fiber, m means the current spatial sampling point to be unwound is at position t m , τ0 is the current time.

[0074] T2. Calculate the standard deviation matrices of the S channel and the P channel respectively according to the two initial phase signals unwrapped along the spatial axis, perform noise reduction on the standard deviation matrices, calculate the positioning feature map matrix based on the standard deviation matrices of the S channel and the P channel after the noise reduction, and obtain the time information of the pipeline structure vibration and the position interval of the pipeline structure where the vibration occurs according to the positioning feature map matrix, wherein 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, and the matrix element of the standard deviation matrix is ​​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 according to the parameters obtained by the processing, and the processing method is based on the output principle of the block matrix operator. Furthermore, the output principle of the block matrix operator includes that for each matrix sub-block contained in the standard deviation matrix and corresponding to the block matrix operator, if the d of the matrix sub-blockik 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 matrix elements 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 Custom constants determined based on the peak width of each order of characteristic frequencies 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 usually only unwinds the phase along the spatial axis of the optical fiber. Due to the constraints of 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 pulse light emission frequency of DAS is generally much higher than the natural frequency of the structure, and the phase jump between two time points can meet the requirements of the unwinding algorithm. Based on the above principles, the overall and local bolt loosening positioning method of the pipeline flange connection of this embodiment, in addition to unwinding along the spatial axis, also unwinds the phase difference between two spatial points along the time axis to obtain the phase time history.

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

[0080] Specifically, the method of unwinding the two initial phase signals along the time axis includes: according to the following formula, two spatial sampling points are selected in the optical fiber interval corresponding to the position interval of the vibrating pipeline structure, the phase difference between the two spatial sampling points is taken and unwinding is performed along the time axis, and the formula includes:

[0081]

[0082] Among them, the subscripts i and j represent the spatial sampling points at positions i and 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, Indicates 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 deconvoluted at time τ m , is the extracted initial phase time history.

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

[0084]

[0085] Where d0 is the preset step threshold, is the time τ m At time τ m+T The phase average value of is the time τ m-T At time τ m The phase average value, T is the preset signal segment duration, 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.

[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 increment of the time history signal, thereby obtaining a phase time history with higher linearity with the structural response.

[0087] T4, integrating the two initial phase signals unwrapped along the time axis to obtain an integrated phase time-history signal; performing a trial function search on the integrated phase time-history signal according to the time information of the pipeline structure vibration and the position interval of the pipeline structure where the vibration occurs, obtaining its optimal phase time-history segment and analyzing it; the trial function search uses the Hilbert-Huang transform of limited bandwidth empirical mode demodulation to obtain each order of intrinsic mode function of each spatial sampling point within the position interval of the pipeline structure where the vibration occurs, and the spatial sampling point corresponds to the sampling point where 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: according to the first The two initial phase signals after unwinding 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 the 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 based on The scaling factor selected 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), and the superimposed signal y(τ) is subjected to standard empirical mode demodulation to obtain an initial first-order intrinsic mode function IMF of a 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, the first-order intrinsic mode function of the spatial sampling point is h1(τ), otherwise, let x(τ) = h1(τ), repeat the above steps until the modal aliasing of h1(τ) is eliminated, or the number of iterations exceeds the preset number; the intrinsic mode 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 taken as the starting moment, and the duration is taken 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 trial function. In this embodiment, the exponential function selects x1exp(x2τ)(x2<0), fits the normalized instantaneous amplitude curve of each spatial sampling point, and calculates the fitting root mean square error of all spatial sampling points; moves the time channel, and gradually calculates the root mean square error in the time channel at each time step, takes the phase time history fragment in the time channel with the smallest root mean square error as the optimal phase time history fragment, and obtains the amplitude parameter and attenuation coefficient obtained by fitting the optimal phase time history fragment.

[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 interval of the vibrating pipeline structure, and obtain the position information of the flange connection where the bolts are loose according to the peak value of the phase vibration mode.

[0096] Specifically, for each spatial sampling point in 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 of the intrinsic mode function is calculated, that is, the vibration mode value of each modal order of the spatial sampling point, and the phase vibration mode of the optimal segment of each order of the intrinsic mode function of each spatial sampling point is calculated based on the vibration mode value.

[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, the formula 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. According to the position 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 the bolts at the flange connection, and the root mean square deviation is calculated according to the impedance measurement result and the impedance reference signal of the bolts at different positions of the flange connection. The impedance reference signal of the bolts at different positions of the flange connection is measured when the bolts are fixed.

[0102] Specifically, the measurement method includes: sticking a piezoelectric sensor on 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 reference impedance signals for all bolt parts on different flange connections.

[0103] Specifically, the method for calculating the root mean square deviation includes: according to Calculate the root mean square deviation, where RMSD is the root mean square deviation, N is the number of frequency points that 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 positions of the loose bolts according to the number of the loose bolts and the root mean square deviation of the bolts at different positions 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 a 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 pipeline flange connection overall and local bolt loosening positioning method, this embodiment also provides a pipeline flange connection overall and local bolt loosening positioning system, which executes the above-mentioned pipeline flange connection overall and local bolt loosening positioning method, and the structure is as follows Figure 3 As shown, it includes a global positioning subsystem and a local positioning subsystem. Among them,

[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 the 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, and the modulated reflected light is polarized diverse. The two orthogonal polarization states of light obtained by demodulating the polarization diversity are 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 orthogonal polarization states of light to obtain the position 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 time 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 to 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 nodes corresponding to the flange connection where the bolts are loose according to the activation instructions 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 a WH-LTE-7S4 module may be selected.

[0115] The structure of the impedance measurement module is as follows Figure 6As shown, it 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 realizes the impedance measurement function based on the AD5933 chip; based on the #1 low-voltage multiplexer, the calibration resistor network switching can be controlled; based on the #2 low-voltage multiplexer, the feedback resistor network switching can be controlled; based on the #3 low-voltage multiplexer, the measurement channel switching can be controlled. The #1 and #2 low-voltage multiplexers can use the ADG706 chip to realize the switching of 16 calibration resistors and 16 feedback resistors respectively, and the #3 low-voltage multiplexer can use the ADG708 chip to realize the switching of 8 measurement channels.

[0116] The microprocessor module controls the communication module and the impedance measurement module based on the STM32 chip, realizes the reception and analysis of the measurement instructions and the sending of the 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, the feedback resistor and the measurement channel used for the measurement are respectively selected, and finally the control of the data measurement and collection can be realized.

[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 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 optical 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 the form of spiral winding 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 the acousto-optic modulator, and the intrinsic light is input into the 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 back the backscattered light of the detection light; the polarization diversity detector and the two-channel acquisition card are used in combination to realize the simultaneous acquisition of optical signals of two orthogonal polarization states of the S channel and the P channel, and convert them into electrical signals and input them into the processor and the memory; the processor and the memory can be connected through 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 program includes 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 looseness of the pipeline flange connection by running the non-volatile software program and instructions stored in the memory.

[0121] The principle of the function of the above device is that the incident light emitted by the narrow linewidth laser is divided into two paths by the 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 the erbium-doped fiber amplifier in sequence as detection light, and modulation is generated based on the vibration of the monitoring pipeline structure. The modulated reflected light also enters the polarization beam splitter through the 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 the 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 looseness of a pipe flange connection, this embodiment also provides a non-volatile computer storage medium, which stores computer executable instructions, which are executed by one or more processors and are used for the above-mentioned method for locating overall and local bolt looseness 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 pipeline flange connection described in Embodiment 1. In this embodiment, Figure 8As shown in FIG. 1 , the pipeline structure is a 3.2-meter-long steel pipe model formed by assembling 4 sections of pipelines and 3 flange connections. Single-mode optical fiber is laid along the entire length of the pipeline structure, and the optical fiber with a length of about 20 meters between 157 meters and 177 meters marked is wound on the pipeline structure; the size of the flange connection and the bolt setting are as follows: Fig. 9 As shown, a front-end measurement node is arranged on each flange connection, and a piezoelectric sensor is pasted on the bolt cap of each bolt. The piezoelectric sensor is electrically connected to the measurement channel of the front-end measurement node through a connecting cable.

[0125] The process performed in this embodiment includes:

[0126] S1. Input a detection light into the optical fiber, the detection light is modulated based on the vibration of the pipeline structure, polarization diversity is performed on the modulated reflected light, and 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, and the number of loose bolts at the flange connection is found according to the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts; 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: loosening the bolts on the flange connection one by one, and the order of loosening the bolts is as follows: Fig.10 As shown, when each bolt is completely loosened, the pipes at both ends of the flange connection are tapped in turn, and the optical phase time history signal is collected after each tapping.

[0128] The collected optical phase time history signal is processed and analyzed, and the optical phase damping ratio corresponding to different numbers of loose bolts is output.

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

[0130]

[0131] Table 1 Correspondence between the range of optical fiber phase damping ratio and the number of loose bolts

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

[0133] In this embodiment, considering the use of spirally wound fiber layout, according to the fiber spatial resolution and the fiber winding length at the monitoring flange connection, a 5-meter fiber range near the loose flange connection is comprehensively selected for calculation. The calculation result of the damping ratio of the optical phase time-course signal within this range is 0.89. The calculation result is compared with Table 1, and the predicted number of loose bolts is 3.

[0134] T1. Convert the optical signals of the two orthogonal polarization states of the S channel and the P channel 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 Figures 13(a) and 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 denoising, and the positioning feature map matrix is ​​calculated based on the standard deviation matrices of the S channel and the P channel after denoising, such as Fig.12 As shown, according to the positioning feature map matrix, the vibration range of the pipeline is 148 meters to 188 meters, including the optical fiber attached to the pipeline between 157 meters and 177 meters. When the surface is knocked, the pipeline model in this experiment vibrates as a whole and affects the adjacent optical fiber. Fig.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-course 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-course signals of the S channel and the P channel, as shown in Fig.11 shown.

[0136] T3. Unwrapping 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: Fig.14 As shown; according to the time information of the vibration of the pipeline structure 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 adopts the Hilbert-Huang transform of limited bandwidth empirical mode demodulation to obtain the intrinsic mode functions of each order of each spatial sampling point in the position interval of the vibrating pipeline structure, and the spatial sampling points correspond to the sampling points for continuously sampling the electrical signal at a preset rate.

[0138] T5, calculating 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: Fig.17 As shown. Search and extract the signal period with the smallest 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 Fig.15 The identification results of each mode and its instantaneous amplitude curve are shown in Fig.16 As shown, according to the peak value of the phase vibration mode, the flange connection where the bolts are loose is obtained as 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 of the flange connection. The calculation results are as follows: Fig.18 As shown, the impedance reference signals of bolts at different positions of the flange connection are measured when the bolts are fixed.

[0140] The measurement process includes:

[0141] The piezoelectric sensor is adhered to 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 of 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: Fig.11 shown.

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

[0145] S3. According to the number of loose bolts and the root mean square deviation of bolts at different positions of the flange connection, the specific positions of the loose bolts are identified. According to the number of loose bolts identified as 3, the 3 bolt positions with the largest root mean square deviation values ​​are selected, and the loose bolt positions accurately identified are P1, P2 and P8 respectively. Fig.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. The 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 obtained monitoring results are consistent with the preset damage conditions, which effectively verifies 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 looseness in pipeline flange connections, which combines a global positioning method based on optical fiber with a local positioning method based on piezoelectric impedance. It can not only accurately locate flange connections of pipeline structures where loose bolts exist, but also accurately obtain the number of loose bolts at the flange connection and accurately locate the specific positions 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, and 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 order of execution of each step in the above embodiment does not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment 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 these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A method for locating the looseness of the overall and local bolts of a pipeline 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; The method includes: A detection light is input into the optical fiber, the detection light is modulated based on the vibration of the pipeline structure, polarization diversity is performed on the modulated reflected light, and the light of two orthogonal polarization states of the S channel and the P channel obtained by polarization diversity is 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, and the number of loose bolts at the flange connection is found according to the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts; the corresponding relationship between the optical fiber phase damping ratio and the number of loose bolts is obtained by calibration; According to the position 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 the bolts at the flange connection, and the root mean square deviation is calculated according to the impedance measurement result and the impedance reference signal of the bolts at different positions of the flange connection; the impedance reference signal of the bolts at different positions of the flange connection is measured when the bolts are fixed; 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 overall and local bolt loosening of pipeline flange connection according to claim 1 is characterized in that: The method of demodulating, calculating and analyzing the two orthogonal polarization states of the S channel and the P channel obtained by polarization diversity to obtain the position information of the flange connection where the bolts are loose includes: The optical signals of the two orthogonal polarization states of the S channel and the P channel are converted into electrical signals, and then converted into digital signals, and then processed into initial phase signals respectively, and the two initial phase signals are unwrapped along the spatial axis; The standard deviation matrices of the S channel and the P channel are calculated respectively according to the two initial phase signals unwrapped along the spatial axis, and the standard deviation matrices are subjected to noise reduction processing, and 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, and the time information of the vibration of the pipeline structure and the position interval of the vibrating pipeline structure are obtained according to the positioning feature map matrix, wherein the time information of the vibration of the pipeline structure includes the start time and duration of the vibration of the pipeline structure; According to the position interval of the vibrating pipeline structure, the two initial phase signals are unwrapped along the time axis; The two initial phase signals unwrapped along the time axis are integrated to obtain an integrated phase time history signal; according to the time information of the pipeline structure vibration and the position interval of the pipeline structure where the vibration occurs, 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 of the intrinsic mode function of each spatial sampling point in the position interval of the pipeline structure where the vibration occurs, and the spatial sampling point corresponds to the sampling point where the electrical signal is continuously sampled at a preset rate; The phase vibration modes of the optimal segments of the eigenmode functions of each order at each spatial sampling point within the position interval of the vibrating pipeline structure are 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 overall and local bolt loosening of pipeline flange connection according to claim 2 is characterized in that: The method for processing the two digital signals of the S channel and the P channel into initial phase signals respectively 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 unwrapping the two initial phase signals along the spatial axis respectively 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 N All spatial sampling points, N is the total number of spatial sampling points on the optical fiber, m means the current spatial sampling point to be unwound is at position t m , τ0 is the current time; 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 a preset row and column size, using the block matrix operator to process the standard deviation matrix in a preset order, and calculating the positioning index of the S channel and the P channel according to the parameters obtained by the processing, and 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, and the time information of the pipeline structure vibration and the position information of the flange connection where the bolts are loose are obtained according to the time axis position of the peak value of the positioning feature map matrix.

4. The method for positioning overall and local bolt loosening of pipeline flange connection according to claim 3 is 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 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 connection according to claim 2, characterized in that: The method of unwrapping the two initial phase signals along the time axis respectively includes: according to the sixth formula, the seventh formula, the eighth formula and the ninth formula, two spatial sampling points are randomly selected in the optical fiber interval corresponding to the position interval of the vibrating pipeline structure, and the phase difference of the two spatial sampling points is taken and unwrapped along the time axis; according to the tenth formula, the eleventh formula, and the twelfth formula, the phase difference of the two spaces after unwrapping along the time axis is baseline calibrated; 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, Indicates 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 deconvoluted is 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 duration, is the time τ m to τ m+T The central trend line of the phase time course, wherein the central trend line 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 unwrapped along the time axis includes: integrating the two initial phase signals unwrapped 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-course signal, and m is taken 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 based on The scaling factor selected for the number of abnormal peaks.

6. The method for positioning overall and local bolt loosening of pipeline flange connection 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-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). The pseudo-analysis signal x(τ) is superimposed with the preset limited bandwidth signal s(τ) to obtain the 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, the first-order intrinsic mode function of the spatial sampling point is h1(τ), otherwise, let x(τ) = h1(τ), repeat the above steps until the modal aliasing of h1(τ) is eliminated or the number of iterations exceeds the preset number; obtain the intrinsic mode functions of each order of each spatial sampling point in 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 time, 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 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 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 is gradually calculated at each time step, and 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.

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

8. The method for locating overall and local bolt loosening of pipeline flange connection 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 comprises: 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 connection according to claim 1, characterized in that: According to the number and root mean square deviation of the loose bolts, the method for identifying the specific positions 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, and 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 pipeline flange connection overall and local bolt loosening positioning system, characterized in that: The system implements the method for positioning overall and local bolt loosening of pipeline flange connection as described in any one of claims 1 to 9, including 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 polarized diverse, and two orthogonal polarization state lights obtained by demodulating the polarization diversity are 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 demodulated two orthogonal polarization state lights 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 out the number of loose bolts at the flange connection according to the correspondence between the optical fiber phase damping ratio and the number of loose bolts obtained by pre-calibration; 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 nodes corresponding to the flange connection where 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 according to the position information of the flange connection where 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 identify the specific position of the loose bolts by combining the root mean square deviation with the number of loose bolts at the flange connection.

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