Multi-component fiber grating detection device and method for ice crack positioning

Abstract

The invention discloses a multi-component fiber grating detection device and method for ice crack positioning, and belongs to the technical field of optical fiber sensing. The multi-component fiber bragg grating detection device comprises a fiber bragg grating multi-component detector, a mounting base station and a counter weight, wherein the fiber bragg grating multi-component detector comprises a rigid supporting rod, a cylindrical fixed base, an arc-shaped mass block, a cantilever beam structure, an FBG and an annular base. The multi-component fiber bragg grating detection device obtains a vibration signal through an FBG, determines the source of the maximum polarization direction of the vibration signal, and determines the position of an ice crack in the direction by using a distance positioning algorithm; a Bayesian method is utilized to optimize a measurement result through multi-path signal feedback information; and determining the determined position of the ice crack in the direction by using a distance positioning algorithm. The method can adapt to a multi-component fiber grating detection device to solve the spatial positioning problem of ice cracks, applies the positioning idea of single-point positioning to ice crack positioning, reduces the layout difficulty, and provides a new safety guarantee means for ice surface operation in an extreme environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber optic sensing, and relates to a multi-component fiber grating detection device and method for ice crack positioning. By real-time monitoring of the stress accumulation effect (vibration) inside the ice body, the direction and magnitude of the mutation are determined, effectively ensuring the safety of manual operations on the ice surface. Background Art

[0002] Ice cracks refer to the structural fractures or disintegration phenomena of ice sheets caused by natural (such as temperature, expansion and extrusion) or human factors. Currently, for the research on ice crack monitoring, the method of image recognition is mostly used. For example: China University of Geosciences (Chinese invention patent CN118832604A) and Polar Research Institute of China (Chinese invention patent CN118408536A) respectively proposed a detection robot for ice crack detection, which can timely construct the ice condition and evaluate the risk level by real-time collecting ice crack image data. Although the above methods do not require on-site manual monitoring and can identify ice cracks on the ice surface within a large monitoring range (several hundred meters), since the expansion of internal defects in the ice body is likely to induce ice cracks extending in unknown spatial directions, it is difficult to accurately judge and identify through surface cracks.

[0003] Usually, the rupture inside a solid will release energy in the form of elastic waves. Therefore, the position of ice cracks can be indirectly judged by means of picking up vibration signals (detection). Detection technology is currently mostly applied to the microseismic monitoring of coal mine rock masses, and multiple detectors (or microseismic sensors) can be arranged for rupture positioning. For example: Southwest Jiaotong University (Chinese invention patent CN119393185A) proposed a method for locating the source of rock mass internal fissure expansion based on multiple microseismic sensors. By recording the microseismic signals of multiple microseismic sensors arranged in advance boreholes, the time and space distribution laws of microseismic signals are mastered to determine the range of rock mass fissure expansion; Shandong University of Science and Technology (Chinese invention patent CN118911775A) proposed a "microseismic + ground sound" joint monitoring system for tunnel rock bursts and its application method. By collecting and analyzing the microseismic signals and ground sound signals picked up by multiple detectors, real-time monitoring, positioning and evaluation of rock burst events are realized. The existing technology still relies on a combination array of multiple detectors for rupture source positioning, and there is no case of using a single detector to achieve rupture source positioning.

[0004] In summary, for the location of ruptured seismic sources, although multi-component and multi-detector arrays can provide more comprehensive seismic source information, they are difficult to deploy in the ice crack identification scenario of extreme environments. There is no example in existing research of using a single detector for seismic source location. Based on the actual needs of ice crack monitoring in extreme environments, there is an urgent need to develop an ice crack detection device and positioning method relying on a single detector. By optimizing the sensor structure and positioning algorithm, while ensuring the monitoring accuracy, the device deployment density is reduced to meet the engineering requirements of long-term unmanned monitoring in harsh environments such as polar regions / glaciers. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present invention proposes a multi-component fiber Bragg grating detection device and method for ice crack location, which is an ice crack azimuth detection device mainly composed of a multi-component fiber Bragg grating detection device and its adapted spatial positioning method. It can use a single detector to solve the problem of spatial positioning of ice cracks. At the same time, the fiber Bragg grating device can overcome the inherent problems of electrical detectors, such as easy corrosion and susceptibility to electromagnetic interference.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] A multi-component fiber Bragg grating detection device for detecting the azimuth of ice body cracks, the multi-component fiber Bragg grating detection device includes a fiber Bragg grating multi-component detector I, an installation base II, and a counterweight III. The installation base II includes a housing 1, a disk-shaped installation table 2, an annular limiting structure 3, a cylindrical tubular main body 4, a wire outlet hole 5, and a transmission optical cable 6; the counterweight III is a hemispherical solid counterweight block 7; the fiber Bragg grating multi-component detector I includes a rigid support rod 8, a cylindrical fixed base 9, an arc-shaped mass block 10, a cantilever beam structure 11, an FBG 12, and an annular base 13. The multi-component fiber Bragg grating detection device is put into water during the freeze-thaw period, and the multi-component fiber Bragg grating detection device is kept in a critical buoyancy state through the bottom counterweight III, and is stably embedded in the ice layer during the freezing phase change. Specifically:

[0008] The fiber Bragg grating multi-component detector I includes three main component unit structures with the same structure and orthogonal distribution. Each main component unit structure includes an annular base 13, six multi-cantilever beam structures 11 evenly distributed along the circumference of the annular base 13 and located on the same horizontal plane, FBGs 12 respectively installed on the six cantilever beam structures 11, and an arc-shaped mass block 10. Specifically: the bottoms of the annular bases 13 on the three main component unit structures are fixedly connected to the tops of the rigid support rods 8; the ends of the rigid support rods 8 are embedded in the side surface of the cylindrical fixed base 9 at a certain angle; the bottom of the cylindrical fixed base 9 is fixedly connected to the disc-shaped mounting table 2 by bolts; the disc-shaped mounting table 2 can be provided with a transmission hole for optical fiber access. Two positive and negative FBGs 12 are fixed between the annular base 13 and the arc-shaped mass block 10 as vibration sensing units. Among them, the FBG 12 is a fiber Bragg grating. The reverse FBG 12 can eliminate the interference of the external environmental temperature and at the same time enhance the ability of the fiber Bragg grating multi-component detector to pick up vibration signals.

[0009] Further, the annular base 13 is a hemispherical arch structure, equipped with six mounting grooves for fixing the cantilever beam structure.

[0010] Further, the axis of the rigid support rod 8 coincides with the central normal of the annular base 13, that is, the bottoms of the annular bases 13 on the three main component unit structures are vertically connected to the rigid support rods 8 and fixed by bolts. The three rigid support rods 8 are orthogonal to each other, and the angle of embedding into the cylindrical fixed base 9 is 45°.

[0011] Further, the cantilever beam structure 11 is an arc-shaped flat structure. Its fixed end is horizontally and non-angularly embedded in the corresponding mounting groove of the annular base 13, and the free end extends radially from the annular base 13. The outermost side is installed with an arc-shaped mass block 10. Grooves are provided on both the front and back sides of the cantilever beam structure 11 for embedding the FBG 12 and are fixed by gluing.

[0012] Further, the six cantilever beam structures 11 are annularly arrayed at equal intervals with a 60° angle in the same detection plane, presenting a petal-shaped radiation topological structure as a whole, and can simultaneously obtain omnidirectional vibration signals in the corresponding plane. Each main component unit structure can simultaneously output 6 channels of low-frequency dynamic response data.

[0013] Further, for each main component unit structure, the total 12 FBGs 12 fixed on the six cantilever beam structures 11 are connected end to end by optical fibers, cascaded, and encapsulated into the grooves of the annular base 13 by epoxy resin.

[0014] The installation base II includes a housing 1, a disc-shaped mounting table 2, an annular limiting structure 3, a cylindrical tubular body 4, an outlet hole 5, and a transmission optical cable 6. Specifically: The housing 1 is a hard hemispherical transparent outer shell, and the inner wall of the bottom is provided with an annular inner protrusion, serving as the annular limiting structure 3 for fixing the housing 1 on the disc-shaped mounting table 2, and at the same time reserving an epoxy resin filling layer for the encapsulation of the fiber Bragg grating multi-component detector I; The fiber Bragg grating multi-component detector I is placed inside the housing 1 and is connected to the disc-shaped mounting table 2 through a cylindrical fixing base 9; The cylindrical tubular body 4 has a hollow interior and is filled at both ends. Its upper end in the axial direction is fixedly connected to the disc-shaped mounting table 2, and its lower end in the axial direction is connected to a hemispherical solid counterweight 7. At the same time, an outlet hole 5 is provided for leading out the transmission optical cable 6; The optical fiber tails of the FBG12 cascaded at the upper level of each main component unit structure are fused with the transmission optical cable 6 passing through the inside of the cylindrical tubular body 4 through the center of the disc-shaped mounting table 2. The transmission optical cable 6 is led out through the outlet hole 5 and is connected to the optical fiber demodulation system at the far end to collect sensing signals.

[0015] Furthermore, the center of the sphere of the hemispherical solid counterweight 7 and the geometric center of the cylindrical fixing base 9 are arranged collinearly along the gravity direction. The hemispherical solid counterweight 7 is fixed to the bottom of the cylindrical tubular body 4 by bolts and is detachable. By replacing hemispherical solid counterweights 7 of different models, the depth of the multi-component fiber Bragg grating detection device in water can be changed.

[0016] A multi-component fiber Bragg grating detection method for ice crack positioning is realized based on the above multi-component fiber Bragg grating detection device and is used to determine the azimuth and distance of ice cracks. The multi-component fiber Bragg grating detection device transmits the vibration signal obtained through the FBG12 to the acquisition system, reads the vibration signal in real time and records it; Select the data within the n time windows of different main component unit structures for coordinate transformation and covariance matrix analysis to determine the source of the maximum polarization direction of the vibration signal; Use the distance positioning algorithm to determine the specific position of the ice crack in this direction; Use the Bayesian method to optimize the measurement results through multi-channel signal feedback information; Use the distance positioning algorithm to determine the determined position of the ice crack in this direction. Specifically, it includes the following steps:

[0017] S1: Pick up multi-component vibration signals. First, obtain the vibration signal through the fiber Bragg grating multi-component detector. According to the structure of the fiber Bragg grating multi-component detector, each main component unit structure of the fiber Bragg grating multi-component detector can obtain 12 vibration signals, and a total of 36 vibration signals mainly based on 3 main components can be obtained. After removing the channels corresponding to the reference FBG12 on the reverse side of the cantilever beam structure 11, finally 18 vibration signals of different components are obtained.

[0018] S2: Determine the source propagation direction based on the polarization analysis method. When the rupture causes the vibration of the surrounding medium particles, the trajectory of the generated vibration signal often needs to be represented by a complex space curve, which can be approximately fitted into an ellipsoid (the wave with an ellipsoidal trajectory is called an ellipsoidal polarized wave). The azimuth of the source is determined by solving the maximum polarization direction of the ellipsoidal polarized wave through the polarization analysis method. Perform polarization analysis on the vibration signals collected by the fiber Bragg grating multi-component detector to determine the direction of the source. The polarization analysis and the method for determining the source propagation direction can be divided into the following sub-steps:

[0019] s200: Detector data correction. In the present invention, the vibration signals of 18 components collected by the three main component unit structures are divided into three categories according to their respective units where they are located. The 18 signals can be respectively set as , , according to the positions of different cantilever beam structures 11. Since it is difficult to ensure that the vertical directions of the main component units of the fiber Bragg grating multi-component detector are consistent with the directions of the geographical rectangular coordinate system during the structural design and on-site installation of the fiber Bragg grating multi-component detector, in order to facilitate the subsequent data processing, it is necessary to correct the 18 collected data. The corrected three-component data is consistent with the data in the geographical rectangular coordinate system in the picking direction. For the data collected by different FBG12s, the specific rotation correction algorithm according to their respective main component unit structures can be expressed as follows:

[0020]

[0021] In the formula, the azimuth angle , the pitch angle , and the roll angle correspond to the angles of rotation of different main component units , , in the fiber Bragg grating multi-component detector towards the X-axis, Y-axis, and Z-axis of the geographical rectangular coordinate system respectively. The azimuth angle , the pitch angle , and the roll angle are all obtained through on-site measurement. In the present invention, during the assembly of the main component unit structure, it is installed at 45°. Therefore, the azimuth angle , the pitch angle , and the roll angle can be set to 45° here.

[0022] s201: Construct a multi-component data matrix R. Take the data points within n time windows at the same time interval of the respective cantilever beam structures 11 in different main component unit structures. The 18 signals collected within n time windows can be composed into a 6n×3 multi-component data matrix R according to the cantilever beam structure:

[0023]

[0024] Among them, ( , , ) represents the vibration signal picked up by any one of the cantilever beam structures 11 in each main component unit structure within the first time window; ( , , ) represents the vibration signal picked up by any one of the other cantilever beam structures 11 except the just-collected cantilever beam structure 11 in each main component unit structure within the first time window; and so on, ( , , ) represents the vibration signal picked up by the only uncollected cantilever beam structure 11 in each main component unit structure within the nth time window.

[0025] S202: Construct the covariance matrix P using the R matrix. Calculate the covariance matrix of matrix R to obtain the 3×3 three-component data matrix P:

[0026]

[0027] In the formula, , , respectively represent the data in the t-th row and the j-th column of the R matrix, where t, j = 1, 2, 3.

[0028] S203: Solve the matrix eigenvector to determine the source direction. Use the data points within n time windows to perform eigenanalysis on the multi-component data matrix R to obtain the eigenvectors and eigenvalues of the three-component data matrix P, where the largest eigenvalue corresponds to the eigenvector . When the vibration signal is linearly polarized, the multi-component data matrix R has only one non-zero eigenvalue, so the corresponding eigenvector can represent the direction source of the wave. In practical applications, the vibration signal is polarized in the entire three-dimensional space. At this time, it is considered that the main energy source of the ice crack is concentrated on the largest eigenvalue, and thus the azimuth angle and the incident angle in the space are determined:

[0029]

[0030] Among them, represents the first item of the eigenvector; represents the second item of the eigenvector; represents the third item of the eigenvector.

[0031] S3: Determine the source distance. Use the time difference of the vibration signal arriving at different cantilever beam structures 11 for distance positioning, specifically as follows:

[0032] Suppose a certain point source is S. When the vibration signal caused by the source S passes through any main component unit structure, it will successively cause the vibration of the cantilever beam structure 11. Therefore, there will be a wave path difference between the cantilever beam structures 11 of any main component unit structure , in the case of known wave velocity, the wave path difference and the wave velocity v satisfy the following:

[0033]

[0034] Among them, the time difference is obtained by recording the vibration signal through the fiber Bragg grating multi-component detector.

[0035] Since the distance from the source S to the FBG12 arranged on any two cantilever beam structures 11 in any main component unit structure is much greater than the distance between the FBG12 arranged on any two cantilever beam structures 11, the angle formed by the connection lines of the source S to these two FBG12 is very small. Take the FBG12 closer to the source (set the position as point A) and set its distance as , the distance of the FBG12 farther from the source (set the position as point B) is , where represents the wave path difference. Set a point O on the path of the source S and the FBG12 farther from the source so that the length of the point O from the source is also , then for the triangular region enclosed by the source S, point B, and point O, it can be approximately regarded as an isosceles triangle with a very small vertex angle and a base angle of 90° (see attachment Figure 5 ), that is, the following equation is satisfied:

[0036]

[0037] Therefore, the wave path difference and the distance l between the two FBG12 satisfy the following equation (7):

[0038]

[0039] Among them, represents the angle of the region enclosed by the source S and the two FBG12 (A, B).

[0040] According to the cosine theorem formula, the following equation (8) is satisfied in the triangle enclosed by the source S and the two FBG12:

[0041]

[0042] Furthermore, through the wave path difference The sum of the wave travel differences and the distance difference l can determine the source distance. For any main component unit structure, among the six FBGs 12 embedded in the six cantilever beam structures 11 thereon, one of the FBGs 12 always picks up the vibration signal first. Let it be the reference grating. According to the above principle, five distance results can be obtained through the five distance differences and five wave travel differences between the other FBGs 12 on the six cantilever beam structures 11 and the reference grating. The five distance differences can be expressed as (see Appendix Figure 6 ), the five wave travel differences can be expressed as , and the distance results can be respectively expressed as .

[0043] S4: Optimize the distance results using probability methods. Since multiple FBGs 12 can output multiple results, in order to further determine the reliability of the results, the Bayesian method is used to optimize the results and improve the positioning accuracy. The specific method is as follows:

[0044] First, limit the monitoring area of ice sheet fracture. The prior probability function is obtained by counting the number of ice sheet fractures in the monitoring area , and then, according to the distance results measured by each main component unit of the fiber optic grating multi-component detector and the observed actual ice crack results, and according to the statistical law, a likelihood function is constructed. Then, the likelihood functions obtained from the distance results measured by the 18 cantilever beam structures 11 in the main component unit structure are multiplied to obtain the joint likelihood function as shown in formula (9):

[0045]

[0046] Combining the prior probability function and the observed distance results, the latest probability distribution of the source location can be obtained as shown in formula (10):

[0047]

[0048] In the case of filtering out clutter, the posterior distribution function can be used to generate a probability cloud map related to the distance, providing more accurate information for ice cracks, and optimizing the geometric positioning and auxiliary decision-making through probability means.

[0049] The beneficial effects of the present invention are as follows:

[0050] (1) The multi-component fiber optic grating detection device independently designed by the present invention can simultaneously read the vibration signals of the X, Y, and Z components, and can reflect the polarization characteristics of the vibration signals through multiple FBGs 12 in different directions on the main component unit, providing more azimuth information for the analysis of vibration signals. At the same time, compared with traditional electrical detectors, it has the advantages of being passive, anti-interference, corrosion-resistant, cascade multiplexing, and high transmission rate, and is suitable for vibration signal acquisition in extreme environments.

[0051] (2) The positioning method designed in the present invention can adapt to multi-component fiber Bragg grating detection devices to solve the spatial positioning problem of ice cracks. At the same time, applying the positioning idea of single-point positioning to ice crack positioning greatly reduces the layout difficulty and provides a new means of safety guarantee for ice surface operations in extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Design drawing of a multi-component fiber Bragg grating detection device designed for the present invention;

[0053] Figure 2 Design drawing of a fiber Bragg grating multi-component detector designed for the present invention;

[0054] Figure 3 Flow chart describing the positioning of the ice crack source for the present invention;

[0055] Figure 4 Specific steps for positioning the source direction by the polarization analysis method for the present invention;

[0056] Figure 5 Schematic diagram describing the principle of source distance positioning for the present invention;

[0057] Figure 6 Simplified diagram of multi-cantilever beam distance positioning.

[0058] In the figure: Ⅰ Fiber Bragg grating multi-component detector, Ⅱ Installation base, Ⅲ Counterweight; 1 Housing, 2 Disk-shaped installation platform, 3 Ring-shaped limiting structure, 4 Cylindrical tubular main body, 5 Wire outlet hole, 6 Transmission optical cable, 7 Hemispherical solid counterweight, 8 Rigid support rod, 9 Column-shaped fixed base, 10 Arc-shaped mass block, 11 Cantilever beam structure, 12 Fiber Bragg grating FBG, 13 Ring-shaped base. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will combine the attached drawings in the embodiments of the present invention Figure 1 to Figure 6 , and clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0060] A multi-component fiber Bragg grating detector for detecting the orientation of ice body cracks, the multi-component fiber Bragg grating detector comprising a fiber Bragg grating multi-component detector I, an installation base II, and a counterweight III; the installation base II includes a housing 1, a disc-shaped installation table 2, an annular limiting structure 3, a cylindrical tubular main body 4, a wire outlet hole 5, and a transmission optical cable 6; the counterweight III is a hemispherical solid counterweight block 7; the fiber Bragg grating multi-component detector I includes a rigid support rod 8, a cylindrical fixed base 9, an arc-shaped mass block 10, a cantilever beam structure 11, an FBG 12, and an annular base 13. The multi-component fiber Bragg grating detector is put into water during the freeze-thaw period, and the multi-component fiber Bragg grating detector is kept in a critical buoyancy state through the bottom counterweight III, and stably embedded in the ice layer during the freezing phase change. Specifically:

[0061] The fiber Bragg grating multi-component detector I includes three main component unit structures with the same structure and orthogonal distribution. Each main component unit structure includes an annular base 13, six multi-cantilever beam structures 11 evenly distributed along the circumference of the annular base 13 and located on the same horizontal plane, FBGs 12 respectively installed on the six cantilever beam structures 11, and an arc-shaped mass block 10. Specifically: the bottoms of the annular bases 13 on the three main component unit structures are fixedly connected to the top of the rigid support rod 8; the end of the rigid support rod 8 is embedded in the side surface of the cylindrical fixed base 9 at a certain angle; the bottom of the cylindrical fixed base 9 is fixedly connected to the disc-shaped installation table 2 by bolts; the disc-shaped installation table 2 can be provided with a transmission hole for optical fiber access. Two positive and negative FBGs 12 are fixedly arranged between the annular base 13 and the arc-shaped mass block 10 as vibration sensing units, where the FBG 12 is a fiber Bragg grating, and the reverse FBG 12 can be used as a reference grating to eliminate the interference of the external environmental temperature, and at the same time enhance the ability of the fiber Bragg grating multi-component detector to pick up vibration signals;

[0062] Further, the annular base 13 is a hemispherical arched structure, and is provided with six installation grooves for fixing the cantilever beam structure.

[0063] Further, the axis of the rigid support rod 8 coincides with the central normal of the annular base 13, that is, the bottoms of the annular bases 13 on the three main component unit structures are perpendicularly connected to the rigid support rod 8 and fixed by bolts. The three rigid support rods 8 are orthogonal to each other, and the angle of embedding into the cylindrical fixed base 9 is 45°.

[0064] Further, the cantilever beam structure 11 is an arc-shaped flat structure, its fixed end is horizontally and angularly embedded into the corresponding installation groove of the annular base 13, the free end extends radially from the annular base 13, and the outermost side is provided with an arc-shaped mass block 10. Grooves are provided on both the front and back sides of the cantilever beam structure 11 for embedding the FBG 12, and are fixed by gluing.

[0065] Furthermore, six cantilever beam structures 11 are evenly distributed in a circular array at a 60° angle in the same detection plane, presenting a petal-shaped radiation topology as a whole, capable of simultaneously acquiring omnidirectional vibration signals in the corresponding plane. Each main component unit structure can output 6 channels of low-frequency dynamic response data simultaneously.

[0066] Furthermore, for each main component unit structure, a total of 12 FBGs 12 fixed on the six cantilever beam structures 11 are connected end to end through optical fibers, cascaded for use, and encapsulated into the grooves of the annular base 13 through epoxy resin.

[0067] The mounting base II includes a housing 1, a disc-shaped mounting table 2, an annular limiting structure 3, a cylindrical tubular main body 4, a wire outlet hole 5, and a transmission optical cable 6. Specifically: The housing 1 is a hard hemispherical transparent outer shell, and an annular inner protrusion is provided on the inner wall of the bottom as the annular limiting structure 3 for fixing the housing 1 on the disc-shaped mounting table 2, while reserving an epoxy resin filling layer for the encapsulation of the fiber Bragg grating multi-component detector I; The fiber Bragg grating multi-component detector I is placed inside the housing 1 and is connected to the disc-shaped mounting table 2 through a cylindrical fixing base 9; The cylindrical tubular main body 4 is a structure with a hollow interior and filled at both ends. Its upper end in the axial direction is fixedly connected to the disc-shaped mounting table 2, and its lower end in the axial direction is connected to a hemispherical solid counterweight 7. At the same time, a wire outlet hole 5 is provided for leading out the transmission optical cable 6; The optical fiber tails of the FBGs 12 cascaded on each main component unit structure are fused with the transmission optical cable 6 passing through the inside of the cylindrical tubular main body 4 through the center of the disc-shaped mounting table 2. The transmission optical cable 6 is led out from the wire outlet hole 5, and the distal end is connected to an optical fiber demodulation system to collect sensing signals.

[0068] Furthermore, the center of the hemispherical solid counterweight 7 and the geometric center of the cylindrical fixing base 9 are arranged collinearly along the direction of gravity. The hemispherical solid counterweight 7 is fixed to the bottom of the cylindrical tubular main body 4 through bolts and is detachable. By replacing hemispherical solid counterweights 7 of different models, the depth of the multi-component fiber Bragg grating detection device in water can be changed.

[0069] The acceleration value can be regarded as an important parameter when the detector measures vibration signals. Generally, there is a linear relationship between the central wavelength shift of a standard single-component fiber Bragg grating detector and the acceleration value of the measured vibration signal. Since there is a phenomenon of inter-dimensional coupling during the process of the multi-component fiber Bragg grating detection device picking up vibration signals, this phenomenon will make the relationship between the FBG central wavelength shift signal of the detector and the measured acceleration value present a complex non-linear relationship. Therefore, an effective non-linear decoupling method needs to be adopted to ensure the normal use of the multi-component fiber Bragg grating detection device.

[0070] Any main component unit structure of the geophone can be fixed to the vibration table separately according to the original installation position of the geophone. By applying acceleration values with the same step size within a certain range to a single cantilever beam (for example, the acceleration value range is , and the step size is , and the range is restricted according to the actual situation of elastic waves generated by ice cracks), the corresponding relationship is obtained. Then, continuously increase the number of cantilever beams and repeat the above experiment to obtain the measured acceleration values, and the corresponding relationships are obtained:

[0071]

[0072] Then, substitute the obtained measured values into the BP neural network to train it to obtain a decoupling model. Among them, the central wavelength shift value serves as the input layer of the neural network, and the six-component central wavelength shift values in the cantilever beam structure group correspond to the six nodes of the input layer. The measured acceleration values in the experimental data are used as the output layer of the BP neural network, and the six-dimensional measured value a corresponds to the six nodes of the output layer. Finally, the three main component units are sequentially increased to two and three according to the installation position, and the above experimental operations are repeated to complete the inter-dimensional decoupling.

[0073] A multi-component fiber Bragg grating geodetic method for ice crack positioning, which is realized based on the above multi-component fiber Bragg grating geodetic device and is used to determine the azimuth and distance of ice cracks. The multi-component fiber Bragg grating geodetic device transmits the vibration signal obtained through FBG12 to the acquisition system, reads the vibration signal in real time and records it; selects the data within the n time windows of different main component unit structures for coordinate transformation and covariance matrix analysis to determine the source of the maximum polarization direction of the vibration signal; uses the distance positioning algorithm to determine the specific position of the ice crack in this direction; uses the Bayesian method to optimize the measurement result through multi-channel signal feedback information; uses the distance positioning algorithm to determine the determined position of the ice crack in this direction. Specifically, it includes the following steps:

[0074] S1: Pickup of multi-component vibration signals. First, obtain the vibration signal through the fiber Bragg grating multi-component geophone. According to the structure of the fiber Bragg grating multi-component geophone, each main component unit structure of the fiber Bragg grating multi-component geophone can obtain 12 vibration signals, and a total of 36 vibration signals mainly based on 3 main components can be obtained. Excluding the channels corresponding to the reference FBG12 on the reverse side of the cantilever beam structure 11, finally 18 vibration signals with different components are obtained.

[0075] S2: Determine the source propagation direction based on the polarization analysis method. When the rupture causes the vibration of the surrounding medium particles, the trajectory of the generated vibration signal often needs to be represented by a complex space curve, which can be approximately fitted into an ellipsoid (the wave with an ellipsoidal trajectory is called an ellipsoidal polarization wave). The azimuth of the source is determined by solving the maximum polarization direction of the ellipsoidal polarization wave through the polarization analysis method. Perform polarization analysis on the vibration signals collected by the fiber Bragg grating multi-component detector to determine the direction of the source. The polarization analysis and the method for determining the source propagation direction can be divided into the following sub-steps:

[0076] s200: Detector data correction. In the present invention, the vibration signals of the 18 channels collected by the three main component unit structures are divided into three categories according to their respective units, and the 18 channels of signals can be respectively set as , , according to the positions of different FBG12. Since it is difficult to ensure that the directions of the main component units are consistent with the directions of the geographical rectangular coordinate system during the structural design and on-site installation of the fiber Bragg grating multi-component detector, in order to facilitate the subsequent data processing, it is necessary to correct the 18 channels of data collected. The corrected three-component data is consistent with the data in the geographical rectangular coordinate system in the pickup direction. For the data collected by different FBG12, the specific rotation correction algorithm according to the respective main component unit structures can be expressed as follows:

[0077]

[0078] In the formula, the azimuth angle , the pitch angle , and the roll angle correspond to the angles by which different main component units , , in the fiber Bragg grating multi-component detector rotate towards the X-axis, Y-axis, and Z-axis of the geographical rectangular coordinate system respectively. The azimuth angle , the pitch angle , and the roll angle are all obtained through field measurement. In the present invention, during the assembly of the main component unit structure, it is installed at 45°, so the azimuth angle , the pitch angle , and the roll angle can be set to 45° here.

[0079] s201: Construct a multi-component data matrix R. Take the data points within n time windows with the same time interval of the respective cantilever beam structures 11 in different main component unit structures. According to the cantilever beam structure, the 18 channels of signals collected within n time windows can form a 6n×3 multi-component data matrix R:

[0080]

[0081] Among them, ( , , ) represents the vibration signal picked up by any one of the cantilever beam structures 11 in each main component unit structure within the first time window; ( , , ) represents the vibration signal picked up by any one of the other cantilever beam structures 11 except the just-collected cantilever beam structure 11 in each main component unit structure within the first time window; and so on, ( , , ) represents the vibration signal picked up by the only uncollected cantilever beam structure 11 in each main component unit structure within the nth time window.

[0082] S202: Construct the covariance matrix P using the R matrix. Calculate the covariance matrix of matrix R to obtain the 3×3 three-component data matrix P:

[0083]

[0084] In the formula, , , respectively represent the data in the t-th row and the j-th column of the R matrix, where t, j = 1, 2, 3.

[0085] S203: Solve the matrix eigenvector to determine the source direction. Use the data points within n time windows to perform eigenanalysis on the multi-component data matrix R to obtain the eigenvectors and eigenvalues of the three-component data matrix P, where the largest eigenvalue corresponding eigenvector is . When the vibration signal is linearly polarized, the multi-component data matrix R has only one non-zero eigenvalue, so the corresponding eigenvector can represent the direction source of the wave. In practical applications, the vibration signal is polarized in the entire three-dimensional space. At this time, it is considered that the main energy source of the ice crack is concentrated on the largest eigenvalue, and thus the azimuth angle and the incident angle in the space are determined:

[0086]

[0087] Among them, represents the first item of the eigenvector; represents the second item of the eigenvector; represents the third item of the eigenvector.

[0088] S3: Determine the source distance. Use the time difference of the vibration signal arriving at different cantilever beam structures 11 for distance positioning, specifically as follows:

[0089] Let a point source be S. When the vibration signal caused by the source S passes through any main component unit structure, it will successively cause the vibration of the cantilever beam structure 11. Therefore, there will be a wave path difference between the cantilever beam structures 11 of any main component unit structure. , Given the wave speed, the wave path difference and the wave speed v satisfy the following:

[0090]

[0091] where the time difference is obtained by recording the vibration signal with a fiber Bragg grating multi-component detector.

[0092] From the geometric relationship, the source distance and the wave path difference and the distance l between the two FBGs 12 satisfy the following relationship:

[0093]

[0094] The source distance can be preliminarily determined through the wave path difference .

[0095] To further determine the reliability of the results, the Bayesian method is used to optimize the results and improve the positioning accuracy.

[0096] For ice cracks with randomness and non-informative rupture events with little prior knowledge, the prior information is represented by a uniform distribution to model the parameter distribution (Equation (13)):

[0097]

[0098] Here, since the model parameter is the distance, the upper and lower limits correspond to the maximum and minimum values of the measurable distance of the detector, and this parameter is determined through experiments.

[0099] For the same main component unit, since there is a cantilever beam that receives the signal first, according to the distance positioning principle, five distances can be received within a specific time window. The likelihood function can be constructed respectively according to the measurement results of the detector. The energy release or ice mass loss of ice crack events shows a right-skewed positive distribution (i.e., most rupture scales are small and a few extreme events have extremely large scales), and the gamma distribution is more in line with the actual observations. The likelihood function can be set in the following form (Equation (14)):

[0100]

[0101] where It represents one of the five received distances, where i = 1, 2, 3, 4, 5. k is the shape parameter, which is obtained through specific experiments and simulation experiments. Then, the likelihood functions obtained from the distance measurement results of multiple FBG12s in the principal component unit are multiplied to obtain the joint likelihood function as shown in Equation (15):

[0102]

[0103] Combining the prior information and the observed data, the updated probability distribution of the earthquake source location is obtained as shown in Equation (16).

[0104]

[0105] In the case of clutter filtering, the posterior distribution function can be used to generate a probability cloud map related to the distance, providing more accurate information for ice cracks, and optimizing the geometric positioning-assisted decision-making through probability means.

[0106] The present invention aims to solve the problem that it is often impossible to accurately locate with a small number of geophones in the face of icequake activities in extreme environments. A multi-component detection structure designed independently is used to solve the ice crack positioning problem by using a single geophone.

[0107] The above-described embodiments only represent the implementation manners of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A multi-component fiber Bragg grating detector for ice crack positioning, characterized in that The multi-component fiber Bragg grating detection device includes a fiber Bragg grating multi-component detector I, a mounting base II, and a counterweight III; the mounting base II includes a housing (1), a disc-shaped mounting table (2), an annular limiting structure (3), a cylindrical tubular main body (4), a wire outlet hole (5), and a transmission optical cable (6); the counterweight III is a hemispherical solid counterweight block (7); when in use, the multi-component fiber Bragg grating detection device is kept in a critical buoyancy state by the bottom counterweight III and stably embedded in the ice layer during the freezing phase change; The fiber Bragg grating multi-component detector I includes three main component unit structures with the same structure and orthogonal distribution. Each main component unit structure includes an annular base (13), six multi-cantilever beam structures (11) evenly distributed along the circumference of the annular base (13) and located on the same horizontal plane, FBGs (12) respectively installed on the six cantilever beam structures (11), and an arc-shaped mass block (10); The center of the hemispherical solid counterweight block (7) is arranged collinearly with the geometric center of the cylindrical fixed base (9) along the gravity direction.

2. The multi-component fiber Bragg grating detection device for ice crack positioning according to claim 1, characterized in that, In the fiber Bragg grating multi-component detector I: The bottoms of the annular bases (13) on the three main component unit structures are fixedly connected to the top of the rigid support rod (8); the end of the rigid support rod (8) is embedded in the side surface of the cylindrical fixed base (9) at a certain angle; The bottom of the cylindrical fixed base (9) is fixedly connected to the disc-shaped mounting table (2); the disc-shaped mounting table (2) is provided with a transmission hole for optical fiber access; Two positive and negative FBGs (12) are fixedly arranged between the annular base (13) and the arc-shaped mass block (10) as vibration sensing units. The FBG (12) is a fiber Bragg grating. The reverse FBG (12) is used as a reference grating to eliminate the interference of the external environmental temperature and at the same time enhance the ability of the fiber Bragg grating multi-component detector to pick up vibration signals.

3. The multi-component fiber Bragg grating detection device for ice crack positioning according to claim 2, characterized in that, The annular base (13) is a hemispherical arched structure, equipped with six mounting grooves for fixing the cantilever beam structure (11); the cantilever beam structure (11) is an arc-shaped flat structure, and its fixed end is horizontally and angularly embedded in the corresponding mounting groove of the annular base (13), and the free end extends radially from the annular base (13), and the outermost side is provided with an arc-shaped mass block (10); both the front and back sides of the cantilever beam structure (11) are provided with grooves for embedding the FBG (12).

4. The multi-component fiber Bragg grating detection device for ice crack positioning according to claim 2, wherein The six cantilever beam structures (11) are annularly arrayed at equal intervals with a 60° angle in the same detection plane, presenting a petal-shaped radiation topology as a whole, capable of simultaneously obtaining omnidirectional vibration signals in the corresponding plane, and each main component unit structure can output 6 channels of low-frequency dynamic response data at the same time.

5. The multi-component fiber Bragg grating detection device for ice crack positioning according to claim 2, wherein The axis of the rigid support rod (8) coincides with the central normal of the annular base (13), and the bottoms of the annular bases (13) on the three main component unit structures are all perpendicularly and fixedly connected to the rigid support rod (8); the three rigid support rods (8) are orthogonal to each other, and the angle of embedding into the cylindrical fixed base (9) is 45°.

6. The multi-component fiber Bragg grating detection device for ice crack positioning according to claim 1, wherein On each main component unit structure, the total 12 FBGs (12) fixed on the six cantilever beam structures (11) are connected end to end through optical fibers, cascaded for use, and encapsulated into the groove of the annular base (13) through epoxy resin.

7. A multi-component fiber Bragg grating detection device for ice crack positioning according to claim 1, characterized in that, The mounting base II includes a housing (1), a disc-shaped mounting table (2), an annular limiting structure (3), a cylindrical tubular main body (4), a wire outlet hole (5), and a transmission optical cable (6); specifically: an annular inner protrusion is provided on the inner wall of the bottom of the housing (1) as the annular limiting structure (3) for fixing the housing (1) on the disc-shaped mounting table (2), and at the same time, an epoxy resin filling layer is reserved for the encapsulation of the fiber Bragg grating multi-component detector I; the fiber Bragg grating multi-component detector I is placed in the housing (1) and connected to the disc-shaped mounting table (2) through a cylindrical fixed base (9); the cylindrical tubular main body (4) is a structure with a hollow interior and filled at both ends, its upper end in the axial direction is fixedly connected to the disc-shaped mounting table (2), the lower end in the axial direction is connected to a hemispherical solid counterweight (7), and at the same time, a wire outlet hole (5) is provided for leading out the transmission optical cable (6); the optical fiber tails of the cascaded FBGs (12) on each main component unit structure are fused with the transmission optical cable (6) passing through the inside of the cylindrical tubular main body (4) through the center of the disc-shaped mounting table (2), and the transmission optical cable (6) is led out from the wire outlet hole (5), and the distal end is connected to an optical fiber demodulation system to collect sensing signals.

8. A multi-component fiber Bragg grating detection device for ice crack positioning according to claim 7, characterized in that, The housing (1) is a hard hemispherical transparent shell; the hemispherical solid counterweight (7) is fixedly and detachably connected to the bottom of the cylindrical tubular main body (4), and by replacing hemispherical solid counterweights (7) of different models, the depth of the multi-component fiber Bragg grating detection device in water can be changed.

9. A multi-component fiber Bragg grating detection method implemented based on the multi-component fiber Bragg grating detection device according to any one of claims 1-8, for determining the azimuth and distance of ice cracks, characterized in that, After the multi-component fiber Bragg grating detection device obtains vibration signals through the FBGs (12), it transmits them to the acquisition system, reads the vibration signals in real time and records them; selects data within the n time windows of different main component unit structures for coordinate transformation and covariance matrix analysis to determine the source of the maximum polarization direction of the vibration signal; uses a distance positioning algorithm to determine the position of the ice crack in this direction; uses the Bayesian method to optimize the measurement results through multi-channel signal feedback information; uses the distance positioning algorithm to determine the definite position of the ice crack in this direction; including the following steps: S1: Obtain vibration signals through the fiber Bragg grating multi-component detector I; S2: Determine the propagation direction of the seismic source based on the polarization analysis method; s200: Detector data correction; s201: Construct a multi-component data matrix R; s202: Use the R matrix to construct a covariance matrix P; s203: Solve the matrix eigenvector to determine the seismic source direction; S3: Determine the distance of the seismic source; use the time difference of the vibration signals reaching different cantilever beam structures (11) for distance positioning; S4: Optimize the distance result using probability methods; adopt Bayesian methods to optimize the result and improve the positioning accuracy.

10. A multi-component fiber Bragg grating detection method according to claim 9, characterized in that, The specific steps are as follows: S1: Obtain vibration signals through the fiber Bragg grating multi-component detector Ⅰ; Each main component unit structure of the fiber Bragg grating multi-component detector Ⅰ can obtain 12 vibration signals. A total of 36 vibration signals mainly composed of 3 main components are obtained. After removing the channels corresponding to the reference FBG (12) on the reverse side of the cantilever beam structure (11), 18 vibration signals of different components are finally obtained; S2: Determine the propagation direction of the seismic source based on the polarization analysis method; s200: Geophone data correction; the vibration signals of 18 components collected by the three main component unit structures are divided into three categories, and the 18 signals are respectively set as , , according to the positions of different cantilever beam structures (11); and the 18 collected data are corrected. The corrected three-component data is consistent with the data in the geographical rectangular coordinate system in the picking direction. The specific rotation correction algorithms for the data collected for different FBGs (12) according to their respective main component unit structures are as follows: , where the azimuth angle , the pitch angle , and the roll angle respectively correspond to the angles rotated by different main component units in the fiber Bragg grating multi-component detector , , to the X-axis, Y-axis, and Z-axis of the geodetic rectangular coordinate system; the azimuth angle , the pitch angle , and the roll angle are all obtained through on-site measurement. In the assembly of the main component unit structure of the present invention, it is installed at 45°. Therefore, the azimuth angle , the pitch angle , and the roll angle can be set to 45°; s201: Construct a multi-component data matrix R; take the data points within n time windows of the respective cantilever beam structures (11) in different main component unit structures at the same time interval, and form an 18-channel signal collected within n time windows into a 6n×3 multi-component data matrix R: , where, ( , , ) represents the vibration signal picked up by any one of the cantilever beam structures (11) in each main component unit structure within the first time window; ( , , ) represents the vibration signal picked up by any other cantilever beam structure (11) in each main component unit structure within the first time window except for the just-acquired cantilever beam structure (11); and so on, ( , , ) represents the vibration signal picked up by the only remaining unacquired cantilever beam structure (11) in each main component unit structure within the nth time window; s202: Use the R matrix to construct a covariance matrix P; calculate the covariance matrix of matrix R to obtain a 3×3 three-component data matrix P: , where , , respectively represent the data of the t-th row and the j-th column in the R matrix, where t, j = 1, 2, 3; s203: Solve the eigenvector of the matrix to determine the source direction; use the data points within n time windows to perform eigenanalysis on the multi-component data matrix R to obtain the eigenvectors and eigenvalues of the three-component data matrix P, where the maximum eigenvalue The corresponding eigenvector is ; when the vibration signal is linearly polarized, the multi-component data matrix R has only one non-zero eigenvalue, so the corresponding eigenvector can represent the direction source of the wave; in practical applications, the main energy source of the ice crack is concentrated on the maximum eigenvalue, and thus the azimuth angle of the source in space is determined and the incident angle : , where represents the first item of the feature vector; represents the second item of the feature vector; represents the third item of the feature vector; S3: Determine the distance to the seismic source; use the time difference of the vibration signals reaching different cantilever beam structures (11) for distance positioning, specifically as follows: Let a certain point source be S. When the vibration signal caused by the source S passes through any principal component unit structure, it will successively cause the vibration of the cantilever beam structure (11). Therefore, there will be a path difference between the cantilever beam structures (11) of any principal component unit structure. , in the case where the wave speed is known, the path difference and the wave speed v satisfy the following: , wherein the time difference is obtained by recording vibration signals through a fiber Bragg grating multi-component detector; Since the distance from the seismic source S to the FBGs (12) arranged on any two cantilever beam structures (11) in any main component unit structure is much greater than the spacing between the FBGs (12) arranged on any two cantilever beam structures (11), the included angle between the connecting lines from the seismic source S to these two FBGs (12) is small; take the position where the FBG (12) closer to the seismic source is located as point A, and set its distance as , and the position where the FBG (12) farther from the seismic source is located as point B, then its distance is , where represents the wave path difference; set a point O on the path between the seismic source S and the FBG (12) farther from the seismic source, so that the length from point O to the seismic source is also , then for the triangular region formed by the seismic source S, point B, and point O, it can be approximately regarded as an isosceles triangle with a very small apex angle and a base angle of 90°, and the following equation is satisfied: , so the optical path difference and the distance l to the two FBGs (12) satisfy the following equation (7): , where represents the angle of the area enclosed by the seismic source S and two FBGs (12) (A, B); According to the cosine theorem formula, the following equation (8) is satisfied in the triangle formed by the seismic source S and two FBGs (12): , and then determine the source distance through the wave path difference and the distance difference l ; For any main component unit structure, among the six FBGs (12) embedded in the six cantilever beam structures (11) thereon, there is always one FBG (12) that picks up the vibration signal first. Let it be the reference grating. Then, five distance results are obtained through the five distance differences and five optical path differences between the other FBGs (12) on the six cantilever beam structures (11) and the reference grating. The five distance differences are expressed as , and the five optical path differences are expressed as . The distance results are respectively expressed as ; S4: Optimize the distance result using probability methods; First, define the monitoring area of ice sheet rupture, and obtain the prior probability function by counting the number of ice sheet ruptures in the monitoring area. Secondly, compare the distance results measured by each main component unit of the fiber Bragg grating multi-component detector with the observed actual ice crack results, and construct the likelihood function according to the statistical law. Finally, multiply the likelihood functions obtained from the distance results measured by the 18 cantilever beam structures (11) in the main component unit structure to obtain the joint likelihood function, as shown in Equation (9): , the latest probability distribution of the earthquake source location is obtained by combining the prior probability function and the observed distance results, as shown in Equation (10): , in the case of filtering out clutter, generate a probability cloud map related to distance through the posterior distribution function to provide accurate information for ice cracks.

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