CN107727744B - Acoustic emission source positioning method and system for rock mechanics triaxial test - Google Patents

Acoustic emission source positioning method and system for rock mechanics triaxial test Download PDF

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CN107727744B
CN107727744B CN201710978572.0A CN201710978572A CN107727744B CN 107727744 B CN107727744 B CN 107727744B CN 201710978572 A CN201710978572 A CN 201710978572A CN 107727744 B CN107727744 B CN 107727744B
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acoustic emission
arrival time
source
time difference
acoustic
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CN107727744A (en
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周子龙
芮艺超
周静
陈卫军
董陇军
蔡鑫
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Central South University
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Central South University
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/14Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object using acoustic emission techniques
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44Processing the detected response signal, e.g. electronic circuits specially adapted therefor

Abstract

The invention discloses an acoustic emission source positioning method and system for a rock mechanics triaxial test, wherein a refraction effect of acoustic emission on an interface of a triaxial loading oil cylinder and an internal sample is considered, a path equation of acoustic wave propagation is established according to Snell's law, the time used for transmitting an acoustic emission source to a sensor is calculated, and the position coordinate of an acoustic source is obtained by calculating the difference between a time difference matrix and an actually measured time difference matrix. The invention provides a new method for accurately calibrating acoustic emission of a rock mechanics triaxial test, and considers the condition that the path of a test piece is changed at the contact surface of different media due to the generation of acoustic waves caused by internal cracks of the test piece under pressure in the triaxial test. Meanwhile, the acoustic emission sensor and the acoustic source can be used in other situations where the acoustic emission sensor and the acoustic source are located in different media and the media are curved media.

Description

Acoustic emission source positioning method and system for rock mechanics triaxial test
Technical Field
The invention relates to an acoustic emission source positioning method and system for a rock mechanics triaxial test under the condition that acoustic waves are refracted on a test piece and an oil cylinder interface.
Background
Rock mechanics triaxial test is an important experimental method for obtaining rock mechanics characteristics and parameters under high pressure. Because the rock sample is sealed in the three-axis pressurizing oil cylinder, the cracking process and the cracking information of the sample can not be accurately obtained and determined. The acoustic emission testing technology can monitor the position condition of cracks generated in the loading process of materials such as rocks and the like, and provides an effective means for researching rock cracking and the like, but the existing acoustic emission source positioning method is mainly used for positioning a single medium acoustic source, the medium where the acoustic source is located is assumed to be a single homogeneous medium, the mixed wave speed of the medium is adopted, and the refraction and reflection of the acoustic wave in the transmission process are not considered. In a triaxial test of rock mechanics, a rock test piece and a triaxial loading oil cylinder belong to different material media, and the traditional method adopts the uniform assumption of mixed wave velocity, does not consider that sound waves are refracted at the contact surface of two different media, and obviously generates larger errors. A new acoustic emission source positioning method and algorithm considering the refraction of acoustic waves at the interface of a curved medium are needed.
In the prior art, CN105842343A discloses an acoustic emission testing apparatus with an acoustic emission sensor built in a true triaxial chamber, which provides an effective method for acquiring acoustic emission signals in a true triaxial test, but has great limitation, and is only suitable for fixed rock size and cannot be used in a conventional triaxial test. Moreover, the acoustic emission sensor is arranged in the true triaxial chamber, so that the operation is complex, and the triaxial loading effect is also adversely affected. CN106442743A discloses an acoustic emission source positioning algorithm considering the refraction of acoustic waves at the interface between two media, which considers the refraction of acoustic waves when encountering different media during propagation, but does not consider the case that the media layer is curved, and does not have a positioning algorithm for the refraction of curved media.
Disclosure of Invention
The invention aims to solve the technical problem that aiming at the defects of the prior art, the invention provides the acoustic emission source positioning method and system for the rock mechanics triaxial test, and the error caused by the use of mixed wave velocity and the propagation according to a straight line path is avoided.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: an acoustic emission source positioning method for a rock mechanics triaxial test comprises the following steps:
1) obtaining a simplified two-layer curved surface medium by a rock mechanics triaxial test;
2) the rock fracture sends out an acoustic emission signal at an acoustic source point S, the acoustic emission signal is transmitted to the interface of two layers of media, the acoustic emission signal is transmitted to an acoustic emission sensor arranged outside the triaxial loading oil cylinder after being refracted, the acoustic emission signal is received, and arrival times received by the acoustic emission sensors are recorded;
3) calculating theoretical arrival times from the sound source to each acoustic emission sensor;
4) and 3) forming a arrival time difference matrix equation by the theoretical arrival time obtained in the step 3) and the arrival time received by the acoustic emission sensor, and solving the minimum value of the arrival time difference matrix equation by using a complex shape method to obtain the coordinates of the acoustic emission source.
In step 3), assume a cylindrical coordinate system in which the sound source S (θ)0,r0,h0) An acoustic emission signal is emitted and transmitted to the contact surface of the two layers of media at R (theta)ri,rri,hri) Refracts and continues to propagate to the probe position I (theta)i,ri,hi) The theoretical arrival time calculation formula from a sound source to a certain acoustic emission sensor I is as follows:
wherein the content of the first and second substances,is the distance between the sound source S and the corresponding refraction point R;is the distance between the acoustic emission sensor I to the refraction point R.
In step 4), the specific solving process of the coordinates of the acoustic emission source comprises the following steps:
1) determining the equation of the arrival time difference between the same sound source and any two acoustic emission sensors:
2) and obtaining a corresponding arrival time difference matrix by the arrival time difference equation:
the arrival time difference matrix measured by the acoustic emission acquisition system is:
3) calculating the difference between the arrival time difference and the actually measured arrival time difference: error ═ T _ M-T;
4) and when the difference value between the arrival time difference and the actually measured arrival time difference is zero, obtaining the coordinates of the sound emission source.
Correspondingly, the invention also provides an acoustic emission source positioning system for a rock mechanics triaxial test, which comprises:
the simplified module is used for obtaining a simplified two-layer curved surface medium through a rock mechanics triaxial test;
the recording module is used for recording the arrival time received by each acoustic emission sensor;
the calculation module is used for calculating the theoretical arrival time from the sound source to each acoustic emission sensor;
and the acoustic emission source coordinate determination module is used for forming a arrival time difference matrix equation by the theoretical arrival time and the arrival time received by the acoustic emission sensor, and solving the minimum value of the arrival time difference matrix equation by using a complex shape method to obtain the coordinates of the acoustic emission source.
Compared with the prior art, the invention has the beneficial effects that: the method breaks through the condition of a single medium in the past, namely a method for transmitting the sound wave along a straight line, considers that the sound wave can be refracted when meeting different media in the transmission process, considers the condition that the contact surface of the medium is a curved surface, provides a reasonable and accurate method for positioning the sound emission source in the rock mechanics triaxial test, can be used for positioning the sound emission source of other multilayer curved surface media, and avoids errors caused by using mixed wave velocity and transmitting the sound emission source according to a straight line path.
Drawings
FIG. 1 is a schematic diagram of a propagation and positioning method of an acoustic emission source in a simplified two-layer curved surface medium model in a rock mechanics triaxial test;
FIG. 2 is a diagram of a two-layer curved surface medium acoustic emission source positioning algorithm;
FIG. 3 is a diagram of the positioning results of the method of the present invention and a conventional algorithm; wherein (a) a front view; (b) a right view; (c) a top view;
→: the method path of the invention;a traditional approach path;an acoustic emission source;a conventional method;the method of the invention.
Detailed Description
As shown in FIG. 2, the rock mechanics triaxial test simplified two-layer curved surface medium model, S is a sound source point generated by the fracture of the internal rock medium, and the wave velocity of the medium is C1S is an acoustic emission sensor positioned on the surface of the outer layer oil cylinder medium, and the wave velocity of the medium is C2An acoustic emission signal is generated at the sound source point S, and is transmitted to the interface of the two media along a straight line, after being refracted, the acoustic emission signal is continuously transmitted to the acoustic emission sensor I along the straight line, and the signal is received.
Suppose that under a cylindrical coordinate system, the coordinates are S (theta)0,r0,h0),R(θri,rri,hri),I(θi,ri,hi) Then can obtain
The distance between the sound source S and the corresponding refraction point R is
The distance between the sensor I and the refraction point R is
The time taken for the acoustic emission signal to propagate in the external medium is
The acoustic emission signal takes a time to propagate in the internal measurement medium of
The time taken for the acoustic emission signal to propagate in the two layers of curved media can be expressed as
The same method can obtain the time for the same sound source to propagate to another sensor
The equation of the arrival time difference between the same sound source and any two sensors can then be obtained as
The corresponding arrival time difference matrix can be obtained from the arrival time difference equation
The arrival time difference matrix measured by the acoustic emission collection system is
The difference between the calculated arrival time difference and the actually measured arrival time difference is recorded as the error between the calculated arrival time difference and the actually measured arrival time difference
Error=T_M-T (12)
The sum of squares of errors is shown below
error=∑Error(i)2(13)
For each set of observations (θ)i,ri,hi;θj,rj,hj) Assuming initial source coordinates (θ) in the space where one acoustic source is located0,r0,h0) Formula (9) determines a calculated arrival time difference TijAnd any two sensors in a series of sensors are combined to obtain a group of calculated arrival time difference matrixes T. The acoustic emission monitoring equipment can simultaneously obtain the arrival time of the same acoustic emission source signal transmitted to each sensor, and a group of measured arrival time difference matrixes T-M can be obtained by combining any two signals. When the difference (Error) between the calculated arrival time difference and the actually measured arrival time difference is zero, the coordinates (theta, r, h) of the sound emission source can be obtained.
Presetting the position of the sound emission source under a cylindrical coordinate system as coordinates (0, 0,200), (30,10,200), (270, 20, 160), (330,30,150) of five sensors (0, 100, 30), (60, 100, 45), (90, 100, 60), (180,100,75) (240, 100, 93); the diameter of the inner cylinder is 100mm, and the height is 200 m; the inner diameter of the outer cylinder is 100 mm; the outer diameter is 200mm, and the height is 200 mm; lead was broken at these determined acoustic source points and the time at which the sensors were triggered when each acoustic source was transmitted to five sensors was recorded. The positioning problem of the two-layer curved medium is explained in detail by using the example, in the actual positioning, the known quantity is the coordinates of five sensors and the moment when the sensors trigger to record, the position of the sound emission source is unknown, and the method provided by the invention is used for verification. The specific implementation steps are as follows:
1. arranging five sensors near the object to be measured, ensuring that the sensors are not in a plane, and the coordinates are (0, 100, 30), (60, 100, 45), (90, 100, 60), (180,100,75) respectively (240, 100, 93); the wave velocities in the two media are respectively c1=5128.21m/s,c2=5882.35m/s。
2. The method is characterized in that known data are substituted into a formula by utilizing an acoustic emission source positioning algorithm suitable for a triaxial mechanical test, an initial value of an acoustic emission source is assumed, then the coordinate of a refraction point and the arrival time difference can be obtained, and the assumed coordinate of the acoustic emission source is the actual sound source coordinate when the error sum of squares is minimum.
3. The positioning results are (177.52, 0.45, 197.86), (29.66,10.13,200.63), (269.94,20,161.04), (330.21,29.97,150.67) whose distance errors from the true preset sound source position are respectively 2.19mm,0.65mm,1.04mm,0.68mm, and in the same case, the conventional calculation without considering refraction algorithm, and the obtained positioning results are (210.21,0.88,186.74), (26.77,12.14,194.45), (267.16,22.21,148.54), (330.48,35.55,150.72) whose distance errors from the true preset sound source position are respectively 13.29mm,5.98mm, 11.72mm, 5.60 mm. The real coordinates, the positioning result obtained by the method provided by the invention and the traditional algorithm are drawn as shown in figure 3, and the positioning result obtained by the algorithm of the invention is better matched with the preset coordinates and has high positioning precision by comparison.

Claims (4)

1. An acoustic emission source positioning method for a rock mechanics triaxial test is characterized by comprising the following steps:
1) obtaining a simplified two-layer curved surface medium by a rock mechanics triaxial test;
2) the rock fracture sends out an acoustic emission signal at an acoustic source point S, the acoustic emission signal is transmitted to the interface of two layers of media, the acoustic emission signal is transmitted to an acoustic emission sensor arranged outside the triaxial loading oil cylinder after being refracted, the acoustic emission signal is received, and arrival times received by the acoustic emission sensors are recorded;
3) calculating theoretical arrival times from the sound source to each acoustic emission sensor;
4) and 3) forming a arrival time difference matrix equation by the theoretical arrival time obtained in the step 3) and the arrival time received by the acoustic emission sensor, and solving the minimum value of the arrival time difference matrix equation by using a complex shape method to obtain the coordinates of the acoustic emission source.
2. The method of claim 1, wherein step 3) is performed in a cylindrical coordinate system, wherein the sound source S (θ) is assumed to be located in the cylindrical coordinate system0,r0,h0) An acoustic emission signal is emitted and transmitted to the contact surface of the two layers of media at R (theta)ri,rri,hri) Refracts and continues to propagate to the probe position I (theta)i,ri,hi) Sound source to a certain sound emissionThe theoretical arrival time calculation formula of the sensor I is as follows:
wherein the content of the first and second substances,is the distance between the sound source S and the corresponding refraction point R;is the distance between the acoustic emission sensor I to the refraction point R.
3. The method for positioning the acoustic emission source for the triaxial rock mechanics test according to claim 2, wherein in step 4), the specific solving process of the coordinates of the acoustic emission source comprises the following steps:
1) determining the equation of the arrival time difference between the same sound source and any two acoustic emission sensors:
2) and obtaining a corresponding arrival time difference matrix by the arrival time difference equation:
the arrival time difference matrix measured by the acoustic emission acquisition system is:
3) calculating the difference between the arrival time difference and the actually measured arrival time difference: error ═ T _ M-T;
4) and when the difference value between the arrival time difference and the actually measured arrival time difference is zero, obtaining the coordinates of the sound emission source.
4. An acoustic emission source positioning system for a rock mechanics triaxial test, comprising:
the simplified module is used for obtaining a simplified two-layer curved surface medium through a rock mechanics triaxial test;
the recording module is used for recording the arrival time received by each acoustic emission sensor;
the calculation module is used for calculating the theoretical arrival time from the sound source to each acoustic emission sensor;
and the acoustic emission source coordinate determination module is used for forming a arrival time difference matrix equation by the theoretical arrival time and the arrival time received by the acoustic emission sensor, and solving the minimum value of the arrival time difference matrix equation by using a complex shape method to obtain the coordinates of the acoustic emission source.
CN201710978572.0A 2017-10-19 2017-10-19 Acoustic emission source positioning method and system for rock mechanics triaxial test Active CN107727744B (en)

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JPS59225374A (en) * 1983-06-06 1984-12-18 Hitachi Ltd Method and apparatus for locating sound source position
CN102262220B (en) * 2011-04-28 2013-07-17 中南大学 Positioning method of micro-seismic source or acoustic emission source based on non-linear fitting
RU2498293C2 (en) * 2011-12-30 2013-11-10 Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования "Тольяттинский государственный университет" Method of determining coordinates of acoustic emission source
CN203785967U (en) * 2014-04-08 2014-08-20 中国矿业大学 Multifunctional high-temperature high-pressure triaxial coal rock testing device
CN104515807A (en) * 2014-10-27 2015-04-15 浙江省特种设备检验研究院 Pressure pipeline ultrasonic internal detection automation device
CN105866253B (en) * 2016-06-07 2018-09-21 北京航空航天大学 A kind of alliteration emitting source positioning method based on K mean cluster
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