Layered medium acoustic emission source wave-velocity-free positioning method based on refraction correction

Abstract

The invention discloses a stratified medium acoustic emission source wave-velocity-free positioning method based on refraction correction, which comprises the following steps: arranging a plurality of probes on an upper-layer medium to detect elastic waves emitted by an acoustic emission source in a lower-layer medium, and recording the time when the elastic waves reach the probes; any two probes are selected to construct a time difference equation, a virtual wave velocity equation is obtained based on the time difference equation, and a target function is constructed; and iteratively solving the coordinates of the refraction points corresponding to the probes, then substituting the coordinates of the refraction points into the time difference equation, and carrying out global search and adjustment on the variables to be optimized based on an optimization algorithm to minimize the target function so as to obtain the optimal coordinates of the acoustic emission source. According to the method, the wave velocity ratio is introduced to replace independent wave velocity measurement, positioning precision reduction caused by wave velocity measurement errors or real-time changes is avoided, an elastic wave propagation path is accurately corrected by solving refraction point coordinates, and the problem of insufficient positioning precision caused by wave velocity errors and refraction neglect in a non-uniform medium is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of acoustic emission nondestructive testing, in particular to an acoustic emission source positioning method suitable for two-layer media. BACKGROUND

[0002] Acoustic emission source positioning technology is a key means in the field of nondestructive testing, and has important applications in rock mechanics, material damage monitoring and other fields. In the prior art, the positioning method is mainly based on the following assumptions: elastic waves propagate along a straight line in a single homogeneous medium, and the wave velocity is a constant value. This method eliminates the wave velocity by simultaneously solving the time difference equation of multiple probes, simplifying the positioning process. However, when the acoustic emission source and the probe are in different media (such as two-layer media), elastic waves are refracted at the interface, and the traditional method causes a significant increase in positioning error due to the neglect of refraction effects.

[0003] The current improved method has the following limitations:

[0004] Wave velocity dependence defect: the traditional method requires prior determination of wave velocity, but the actual wave velocity is affected by factors such as medium non-uniformity and temperature, resulting in a deviation between the measured value and the true value, which leads to a decrease in positioning accuracy.

[0005] Insufficient refraction correction: the existing positioning method for complex media has limited applicability, is sensitive to the distance between the probe and the acoustic emission source, and has low computational efficiency.

[0006] Model simplification error: the existing method assumes a single medium, which cannot accurately describe the refraction path of elastic waves at the interface, resulting in a deviation of the acoustic emission source coordinate inversion result from the actual position. SUMMARY

[0007] Therefore, the present application provides a wave-velocity-free positioning method for acoustic emission sources in layered media based on refraction correction, to solve the problems of large acoustic emission source positioning error and limited applicability caused by neglecting refraction effects and relying on prior determination of wave velocity in non-uniform media.

[0008] The wave-velocity-free positioning method for acoustic emission sources in layered media based on refraction correction includes the following measures:

[0009] 1) A plurality of probes are arranged in the upper medium to detect acoustic emission signals in the lower medium; a three-dimensional coordinate system is established, the plane determined by the intersection of the x-axis and the y-axis in the three-dimensional coordinate system is parallel to the interface between the upper medium and the lower medium, and the position parameters of the interface between the upper medium and the lower medium in the monitoring area and the probe in the three-dimensional coordinate system are determined.

[0010] 2) Record the time of arrival of elastic waves emitted by the acoustic emission source at each probe.

[0011] 3) Divide the propagation path of the elastic wave from the acoustic emission source to the probe into two segments: the first segment is from the acoustic emission source to the refraction point, and the second segment is from the refraction point to the probe.

[0012] Based on the arrival times of the elastic wave at any two probes, a time difference equation is constructed:

[0013]

[0014] in, Let i be the time when the elastic wave initially arrives at the i-th probe. The time it takes for the elastic wave to initially reach the j-th probe; Wave speed ratio; For virtual wave speed; , , m is the total number of probes;

[0015] Let the coordinates of the acoustic emission source be ( , , Let the distance from the acoustic emission source to the i-th probe be ( , , The coordinates of the elastic wave refraction point in the elastic wave propagation path are ( ). , , ); Let the distance from the acoustic emission source to the j-th probe be ( , , The coordinates of the elastic wave refraction point in the elastic wave propagation path are ( ). , , );

[0016] From the acoustic emission source s to the refraction point ( , , The distance to () is expressed as follows:

[0017]

[0018] To the point of refraction ( , , The distance to the i-th probe is expressed as follows:

[0019]

[0020] From the acoustic emission source s to the refraction point ( , , The distance to () is expressed as follows:

[0021]

[0022] To the point of refraction ( , , The distance to the j-th probe is expressed as follows:

[0023]

[0024] The virtual wave velocity equation is derived based on the time difference equation:

[0025]

[0026] And construct the objective function:

[0027]

[0028] in This represents the average virtual wave velocity corresponding to all probe groups;

[0029] 4) Determine the coordinates of the refraction points corresponding to each probe, including:

[0030] Iteratively solve for the x-coordinate of the refraction point:

[0031] Set the initial search interval for the x-coordinate of the refraction point corresponding to the probe. , ,in It is the set x-coordinate of the acoustic emission source. This corresponds to the x-coordinate of the probe;

[0032] Calculate the x-coordinate of the midpoint of the search interval: The search interval is divided into the left half based on the x-coordinate of the midpoint. and the right half of the interval ;

[0033] Calculate the refraction ratio of the elastic wave at the left and right endpoints of the left half-interval, respectively. The formula for calculating the refraction ratio is as follows:

[0034] ,

[0035] in The angle of incidence of an elastic wave is the angle between the line connecting the acoustic emission source point and the refraction point and the interface. The emission angle of the elastic wave is the angle between the line connecting the refraction point and the probe coordinate point and the interface.

[0036] The refractive index at the left end point The refractive ratio error is obtained by comparing it with a given wave velocity ratio n. The refractive index that will be refracted at the right end point The refractive ratio error is obtained by comparing it with a given wave velocity ratio n. ;

[0037] like If the left half of the interval is retained as the new search interval, then the right half of the interval is retained as the new search interval.

[0038] Repeat steps - Continue until the length of the search interval is less than the set value, thus obtaining the abscissa of the corresponding refraction point of the probe;

[0039] Based on the geometric property that points along the refraction path lie in the same plane, the y-coordinate of the refraction point is:

[0040]

[0041] Since the z-axis coordinate of the refraction point is equal to the position of the interface on the z-axis of the coordinate system, the y-axis coordinate of the refraction point is obtained as follows: , The height of the interface in the three-dimensional coordinate system;

[0042] 5) Globally optimize the location of acoustic emission sources:

[0043] Substitute the coordinates of the refraction point obtained from measure 4) into measure 3) and use the time difference equation obtained from the corresponding probe to determine the coordinates of the acoustic emission source. In the coordinates of the refraction point The wave velocity ratio n is used as the variable to be optimized. An optimization algorithm is used to perform a global search in the monitoring area. By continuously adjusting the variable to be optimized, the objective function is made to be less than the set value, and finally the optimal coordinates of the acoustic emission source are obtained.

[0044] Furthermore, the optimization algorithm is the simplex method.

[0045] The beneficial effects of this invention are:

[0046] 1. When locating an acoustic emission source, the method of the present invention introduces a wave velocity ratio instead of independent wave velocity measurement, thereby avoiding a decrease in positioning accuracy caused by wave velocity measurement errors or real-time changes.

[0047] 2. The method of the present invention takes into account the refraction problem of elastic waves when passing through the interface of the medium when locating the acoustic emission source. By solving the coordinates of the refraction point, the propagation path of the elastic wave is accurately corrected, which solves the problem of insufficient positioning accuracy caused by wave velocity error and neglect of refraction in non-uniform media.

[0048] 3. This invention significantly improves the accuracy, computational efficiency, and stability of acoustic emission source localization in two-layer media without requiring prior wave velocity measurement. It solves the problem of the significant impact of abnormal wave velocity values ​​on localization performance in complex engineering environments, and enhances the fault tolerance and real-time performance of acoustic emission source localization. This method is applicable to scenarios such as rock mechanics and composite material damage monitoring, breaking through the technical bottleneck of traditional acoustic emission source localization methods in non-homogeneous media. Attached Figure Description

[0049] Figure 1 This is a flowchart of a wave-velocity-free method for locating acoustic emission sources in layered media based on refraction correction.

[0050] Figure 2 This is a simulation model for locating acoustic emission sources in layered media without wave velocity. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0052] As shown in the figure, the wave velocity-free positioning method for layered medium acoustic emission sources based on refraction correction in this embodiment includes the following measures:

[0053] 1) Install several probes in the upper medium to detect acoustic emission signals in the lower medium; establish a three-dimensional coordinate system, where the plane defined by the intersection of the x-axis and y-axis is parallel to the interface between the upper and lower media, and determine the position parameters of the interface between the upper and lower media and the probes in the three-dimensional coordinate system within the monitoring area. In practice, the position parameters of the interface between the upper and lower media can be obtained through geophysical survey methods (such as seismic exploration). Then, based on the actual data, set the position of the interface on the z-axis in the three-dimensional coordinate system, and set the position coordinates of the probes in the three-dimensional coordinate system based on the actual positions of the probes.

[0054] 2) Record the time it takes for the elastic waves emitted by the acoustic emission source to reach each probe.

[0055] 3) Divide the propagation path of the elastic wave from the acoustic emission source to the probe into two segments: the first segment is from the acoustic emission source to the refraction point, and the second segment is from the refraction point to the probe.

[0056] Based on the arrival times of the elastic wave at any two probes, a time difference equation is constructed:

[0057]

[0058] in, Let i be the time when the elastic wave initially arrives at the i-th probe. Let be the time when the elastic wave initially arrives at the j-th probe. Wave speed ratio, This represents the propagation speed of elastic waves in the underlying medium. This represents the propagation speed of the elastic wave in the upper medium. For virtual wave speed; , , , where m is the total number of probes.

[0059] Let the coordinates of the acoustic emission source be ( , , Let the distance from the acoustic emission source to the i-th probe be ( , , The coordinates of the elastic wave refraction point in the elastic wave propagation path are ( ). , , Let the distance from the acoustic emission source to the j-th probe be ( , , The coordinates of the elastic wave refraction point in the elastic wave propagation path are ( ). , , ).

[0060] From the sound emission source to the refraction point ( , , The distance to () is expressed as follows:

[0061]

[0062] To the point of refraction ( , , The distance to the i-th probe is expressed as follows:

[0063]

[0064] From the sound emission source to the refraction point ( , , The distance to () is expressed as follows:

[0065]

[0066] To the point of refraction ( , , The distance to the j-th probe is expressed as follows:

[0067]

[0068] The virtual wave velocity equation is derived based on the time difference equation:

[0069]

[0070] And construct the objective function:

[0071]

[0072] in The average value is taken for the virtual wave velocity corresponding to all probe groups.

[0073] 4) Determine the coordinates of the refraction points corresponding to each probe, including:

[0074] Set the initial search interval for the x-coordinate of the refraction point corresponding to the probe. , ,in It is the set x-coordinate of the acoustic emission source. It corresponds to the x-coordinate of the probe.

[0075] Calculate the x-coordinate of the midpoint of the search interval: The search interval is divided into the left half based on the x-coordinate of the midpoint. and the right half of the interval .

[0076] Calculate the refraction ratio of the elastic wave at the left and right endpoints of the left half-interval, respectively. The formula for calculating the refraction ratio is as follows:

[0077] ,

[0078] in The angle of incidence of an elastic wave is the angle between the line connecting the acoustic emission source point and the refraction point and the interface. The emission angle of the elastic wave is the angle between the line connecting the refraction point and the probe coordinate point and the interface.

[0079] The refractive index at the left end point The refractive ratio error is obtained by comparing it with a given wave velocity ratio n. The refractive index that will be refracted at the right end point The refractive ratio error is obtained by comparing it with a given wave velocity ratio n. .

[0080] like If the left half of the interval is retained as the new search interval, then the right half of the interval is retained as the new search interval.

[0081] Repeat steps -③, until the length of the search interval is less than the set value, that is, the x-coordinate of the corresponding refraction point of the probe is obtained.

[0082] Based on the geometric property that points along the refraction path lie in the same plane, the y-coordinate of the refraction point is:

[0083]

[0084] Since the z-axis coordinate of the refraction point is equal to the position of the interface on the z-axis of the coordinate system, the y-axis coordinate of the refraction point is obtained as follows: , The height of the interface in the three-dimensional coordinate system.

[0085] 5) Globally optimize the location of acoustic emission sources:

[0086] Substitute the coordinates of the refraction point obtained from measure 4) into measure 3) and use the time difference equation obtained from the corresponding probe to determine the coordinates of the acoustic emission source. In the coordinates of the refraction point The wave velocity ratio *n* is used as the variable to be optimized. An optimization algorithm is used to perform a global search within the monitoring area. By continuously adjusting the variable to be optimized, the objective function is made to be less than a set value, ultimately obtaining the optimal coordinates of the acoustic emission source. In this embodiment, the optimization algorithm uses the simplex method; however, the Geiger method can also be used in different embodiments.

[0087] like Figure 2 The diagram shows a hypothetical acoustic emission localization system composed of two 100mm thick layers of different materials. The propagation velocity of elastic waves in the lower medium, v1, is 4000 m / s, and the wave velocity in the upper medium, v2, is 5000 m / s. The probe is positioned on the surface of the upper medium, while the acoustic emission source points are located on the surface and inside the lower medium. Four different acoustic emission source point locations were selected for this test, with coordinates S1 (40, 0, 50), S2 (100, 25, 30), S3 (25, 35, 20), and S4 (70, 80, 80). The acoustic emission probe position coordinates are: E (10, 0, 120), F (90, 10, 200), G (100, 90, 185), H (75, 100, 125), I (25, 75, 200), and J (0, 20, 155).

[0088] By controlling the acoustic emission source to emit elastic waves and obtaining the arrival time of the elastic waves at each probe and the known sensor coordinates, the method of this invention was used to locate four acoustic emission sources. The resulting location results are (40, 0, 50), (100, 25, 30), (25, 35, 20), and (70, 80, 80) (unit: mm). The location errors are all within four decimal places and can be ignored, proving the feasibility of the location method.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A refractive correction based layered medium acoustic emission source non- wave velocity positioning method, characterized in that: The method comprises the following steps: 1) A plurality of probes are arranged in the upper medium to detect acoustic emission signals in the lower medium; a three-dimensional coordinate system is established, the plane determined by the intersection of the x-axis and the y-axis in the three-dimensional coordinate system is parallel to the interface between the upper medium and the lower medium, the interface between the upper medium and the lower medium in the monitoring area and the position parameters of the probes in the three-dimensional coordinate system are determined; 2) The time for the elastic wave emitted by the acoustic emission source to reach each probe is recorded; 3) The propagation path of the elastic wave from the acoustic emission source to the probe is divided into two sections, the first section is the path from the acoustic emission source to the refraction point, and the second section is the path from the refraction point to the probe; According to the time for the elastic wave to reach any two probes, a time difference equation is constructed: wherein, is the time of initial arrival of the elastic wave at the i-th probe, is the time of initial arrival of the elastic wave at the j-th probe; is the wave velocity ratio; is the virtual wave velocity; , , , m is the total number of probes; Let the coordinates of the acoustic emission source be (x0, y0, z0) , , ), let the coordinates of the elastic wave refraction point in the elastic wave propagation path from the acoustic emission source to the i-th probe (xi, yi, zi) , , ); let the coordinates of the elastic wave refraction point in the elastic wave propagation path from the acoustic emission source to the j-th probe (xj, yj, zj) , , ) , , ) , , ) The distance from the acoustic emission source s to the refraction point (r) is expressed as follows: , , ​ The distance from the refraction point (Ri) to the i-th probe is expressed as follows: , , ) to the i-th probe, the expression is as follows: The distance from the acoustic emission source s to the refraction point (r) is expressed as follows: , , ​ The distance from the refraction point (R) to the jth probe is expressed as follows: , , jth probe. Based on the time difference equation, a virtual wave velocity equation is obtained: And a target function is constructed: wherein is the average of the virtual wave velocities for all probe sets; 4) The coordinates of the refraction points corresponding to each probe are solved, including: The transverse coordinate of the refraction point is iteratively solved: Setting an initial search interval for the abscissa of the refraction point corresponding to the probe , wherein is the set abscissa of the acoustic emission source, is the abscissa of the corresponding probe; calculating a midpoint abscissa of the search interval: dividing the search interval into a left half interval and a right half interval according to the midpoint abscissa; The refraction ratios of the elastic wave at the left end point and the right end point of the left half interval are respectively calculated, and the refraction ratio calculation formula is as follows: ， wherein the angle of incidence of the elastic wave, i.e. the angle between the line connecting the acoustic emission source point and the refraction point and the interface; the angle of emergence of the elastic wave, i.e. the angle between the line connecting the refraction point and the probe coordinate point and the interface; refractive ratio of the refraction at the left end point compared with the given wave velocity ratio n, the error of the refractive ratio is obtained refractive ratio of the refraction at the right end point compared with the given wave velocity ratio n, the error of the refractive ratio is obtained ; If , the left half interval is reserved as the new search interval; otherwise the right half interval is reserved as the new search interval; repeating step - until the length of the search interval is less than a set value, i.e. the abscissa of the corresponding refractive point is obtained. According to the geometric characteristics that the points on the refraction path are located in the same plane, the y-axis coordinate of the refraction point is: According to the z-axis coordinate of the refraction point being equal to the position of the interface on the z-axis of the coordinate system, the y-axis coordinate of the refraction point is obtained as: , is the height of the interface in the three-dimensional coordinate system; 5) Global optimization of the acoustic emission source position: The refracted point coordinates obtained by solving measure 4) are brought into the time difference equation obtained according to the corresponding probe in measure 3) to obtain the coordinates of the acoustic emission source , the wave velocity ratio n in the refracted point coordinates and the wave velocity ratio n are taken as the optimization variables, a global search is performed in the monitoring area by using an optimization algorithm, the target function is made less than a set value by continuously adjusting the optimization variables, and finally the optimal coordinates of the acoustic emission source are obtained.

2. The refractive correction based layered medium acoustic source location method without wave speed of claim 1, wherein: The optimization algorithm is the simplex method or the Geiger method.

Images