Coal deformation measuring system and method based on acoustic emission

Abstract

The invention discloses a coal deformation measuring system and method based on acoustic emission, and the method comprises the steps: an upper computer generates sound waves, the sound waves are amplified by a power amplifier, and the amplified sound waves are transmitted to a sound wave emitter in a push box for emission; a sound wave receiving sensor I and a sound wave receiving sensor II which are located on the two sides of a coal sample sequentially receive sound wave signals, the two signals are converted and then sent to a data collector, and then an upper computer calculates the time difference of the two signals. The expansion distance and the contraction distance of the coal sample under the gas adsorption condition and the gas desorption condition are obtained after calculation, and an expansion curve and a contraction curve within a certain time are output. During measurement, the external interference is small, and the experiment precision is high.

Description

Technical Field

[0001] The invention relates to the technical field of the mechanism of coal-rock gas dynamic disasters, and in particular to a coal body deformation measurement system and a measurement method based on acoustic emission. Background Art

[0002] Coal will expand and deform when it absorbs gas, and shrink and deform when it desorbs gas. This deformation will cause changes in the strength, stress state and porosity of the coal, which will in turn affect the coal and gas outburst characteristics and coal seam permeability. Therefore, studying the dynamic evolution characteristics and mechanism of coal adsorption and desorption of gas deformation is of great significance for in-depth understanding of the evolution mechanism of coal rock gas dynamic disasters, obtaining the true migration law of coal seam gas, and guiding the high-yield and efficient mining of coal seam methane. In recent years, with the continuous deepening of research on the adsorption characteristics of coal rocks, instruments and devices for testing the adsorption deformation of coal rocks have been developed. Most of these devices collect information by pasting resistance strain gauges on coal samples and obtain relevant data through data analysis systems. These devices have the following shortcomings during the experiment: the device uses strain gauges as strain sensors to measure the deformation of the coal body, but the strain gauges themselves are easily affected by the environment, such as electromagnetic fields, humidity, chemical corrosion, etc., and the adhesion during the connection to the test coal sample also greatly affects the experimental results. Summary of the invention

[0003] In order to overcome the defects in the prior art, the present invention proposes a coal deformation measurement system and method based on acoustic emission. The acoustic emission technology is adopted, and the acoustic wave delay estimation algorithm based on the cross-correlation function is used to realize the conversion of the acoustic wave flight time. The coal deformation is measured in a non-contact manner, which can effectively avoid the measurement errors caused by the environment and the pasted strain gauges, and improve the accuracy of the coal deformation measurement.

[0004] The technical solution adopted by the present invention is: in the first aspect, the present invention proposes a coal deformation measurement system based on an acoustic emission device, comprising a host computer, a power amplifier, at least one measuring tube, a data collector, an acoustic wave transmitter and an acoustic wave receiver, wherein the acoustic wave receiver comprises an acoustic wave receiving sensor I and an acoustic wave receiving sensor II;

[0005] The measuring cylinder comprises a cylinder body, a left end cover and a right end cover, wherein a coal sample placement bin (310) is arranged in the cylinder body for placing coal samples; a push box is arranged on one side of the coal sample placement bin, and a sensor placement rack II is arranged on the other side, wherein the sensor placement rack II contacts the bin wall of the coal sample placement bin; the acoustic wave receiving sensor II is installed in the middle of the sensor placement rack II; the push box can slide in the cylinder body and is detachably connected to the bin wall of the coal sample placement bin; a sensor placement rack I and an acoustic wave transmitter are arranged in the push box body, wherein the sensor placement rack I is installed near the port of the push box, the acoustic wave receiving sensor I is installed in the middle of the sensor placement rack I, and the acoustic wave transmitter is installed on the side panel of the push box;

[0006] The left end cover and the right end cover are respectively threadedly connected to the left and right ends of the cylinder;

[0007] The host computer is electrically connected to the power amplifier, and the power amplifier is electrically connected to the sound wave transmitter; the sound wave receiving sensor I and the sound wave receiving sensor II are electrically connected to the data collector respectively, and the data collector is electrically connected to the host computer.

[0008] As a further improvement of the present invention, a horizontally placed cylindrical cavity is provided in the coal sample storage bin.

[0009] As a further improvement of the present invention, an annular groove is opened on one side of the coal sample placement bin wall, the push box end is embeddedly connected to the annular groove, and the acoustic wave receiving sensor I is placed close to the left side of the coal sample.

[0010] As a further improvement of the present invention, a sound insulation layer is provided on the inner wall of the push box and the sensor placement rack I.

[0011] As a further improvement of the present invention, an air inlet is provided on the left end cover, and an air outlet is provided on the right end cover.

[0012] As a further improvement of the present invention, a handle is provided on the outer side of the side panel, and the interior of the handle is a hollow cavity; at least one air inlet is provided on the side panel, and the air inlet is connected to the air inlet pipeline.

[0013] As a further improvement of the present invention, a rubber sleeve is put on the surface of the coal sample before being placed in the coal sample placement bin.

[0014] As a further improvement of the present invention, it also includes an air extraction unit and an air charging unit, the air extraction unit is a vacuum pump, the vacuum pump is connected to the air inlet pipeline, and the air charging unit is connected to the air inlet pipeline.

[0015] As a further improvement of the present invention, the inflation unit includes a methane gas cylinder, a helium gas cylinder and a carbon dioxide gas cylinder connected in parallel through pipelines.

[0016] In a second aspect, the present invention further proposes a method for measuring coal deformation based on an acoustic emission device, using the above-mentioned coal deformation measuring system based on an acoustic emission device, comprising the following steps:

[0017] Step S1, putting a rubber sleeve on the outside of the cylindrical coal sample, and sending it horizontally into the coal sample storage bin, so that the right side of the coal sample is close to the acoustic wave receiving sensor II;

[0018] Step S2, push the push box into the inner cavity from the left entrance of the cylinder through the handle, so that the end of the push box is embedded and connected with the annular groove on the wall of the coal sample storage bin, and the acoustic wave receiving sensor I is close to the left side of the coal sample;

[0019] Step S3, threading the left end cap to the left port of the cylinder, and threading the right end cap to the right port of the cylinder;

[0020] Step S4, close the gas outlet, and the gas extraction unit slowly extracts the gas in the measuring cylinder; the host computer generates a sound wave signal, which is amplified by the power amplifier and sent to the sound wave transmitter. The sound wave transmitter transmits the sound wave, and the sound wave receiving sensor I and the sound wave receiving sensor II receive the sound wave respectively, and the sound wave is converted into an electrical signal and sent to the data acquisition device, and the data acquisition device then sends it to the host computer to calculate the time difference between the sound wave receiving sensor I and the sound wave receiving sensor II receiving the sound wave, and calculate the contraction distance of the coal sample;

[0021] Step S5, open the air outlet, and inflate the measuring cylinder through the inflation unit; generate an acoustic wave signal through the host computer, amplify the acoustic wave through the power amplifier, and send it into the measuring cylinder, the acoustic wave receiving sensor I and the acoustic wave receiving sensor II receive the acoustic wave respectively, and convert the acoustic wave into an electrical signal and send it to the data collector, and the data collector then sends it to the host computer to calculate the time difference of the acoustic wave and the expansion distance of the coal sample;

[0022] Step S6: The host computer generates sound waves at a certain frequency, and produces an expansion curve and a contraction curve of the coal sample within a certain period of time.

[0023] In this method, the calculation of time difference and deformation distance adopts the acoustic wave delay estimation method based on the cross-correlation function, that is, the cross-correlation algorithm. Its main principle is: when the host computer processes the signal, it uses the cross-correlation function to calculate the two homologous signals with time delay, and finds the horizontal coordinate corresponding to the maximum point of the cross-correlation function composed of the two homologous signals, which is the flight time of the two acoustic wave signals. By multiplying the flight time at different times by the propagation speed of the acoustic wave in the coal sample (about 2000m / s, which varies according to the coal density, and the specific value can be obtained through experiments), the deformation of the coal sample between the two acoustic wave emission times can be obtained.

[0024] Compared with the prior art, the present invention has the following technical effects:

[0025] (1) The present invention sets two sound wave receiving sensors to receive the left side sound wave and the right side sound wave of the coal sample respectively, and uses the time difference between the two sound waves to calculate the expansion distance and contraction distance of the coal sample through a cross-correlation algorithm, thereby avoiding the problem of inaccurate measurement caused by sticking strain gauges on the coal sample;

[0026] (2) The measuring cylinder of the present invention is arranged in three sections and is threadedly connected to each other. On the one hand, it is convenient to place the coal sample from both sides of the cylinder body and place two sensor placement racks and a push box. On the other hand, it is convenient to maintain its sealing when performing the vacuum test and the inflation test. The present invention arranges a push box in the cylinder body. The push box is a cylindrical cavity. When the coal sample is inflated, the left side of the coal sample can be inflated in a directional manner, rather than the entire measuring cylinder. This method can improve the adsorption efficiency of the coal sample. At the same time, the sound wave transmitter is installed on the side plate of the push box, and its emission space is limited in the push box, which also avoids interference from the space in the cylinder body during emission, making its emission directional. And because a coal sample placement bin is arranged in the cylinder body, the placement bin has a certain thickness, so that the walls on both sides can be used as the positioning basis of the left and right sensor placement racks, so that the distance between the two sound wave receiving sensors and the two sides of the coal sample can be more easily positioned. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Figure 1 It is a schematic diagram of a coal deformation measurement system based on acoustic emission according to the present invention;

[0029] Figure 2 It is a schematic diagram of the external structure of the measuring tube;

[0030] Figure 3 yes Figure 2 Yes, the cutaway view;

[0031] Figure 4 It is a cross-sectional view of the cylinder;

[0032] Figure 5 It is the structural diagram I of the push box;

[0033] Figure 6 This is the structure diagram of the push box II

[0034] Figure 7 It is a schematic diagram of the structure of the sensor placement rack II;

[0035] Figure 8 It is the structural diagram of the left end cover;

[0036] Fig. 9 It is the structural diagram of the right end cover;

[0037] In the figure, 1-host computer, 2-power amplifier, 3-measuring cylinder, 31-cylinder body, 32-left end cover, 320-air inlet, 33-right end cover, 330-air outlet, 310-coal sample storage bin, 3100-annular groove, 311-push box, 3110-side panel, 3111-handle, 3112-air inlet, 312-sensor placement rack II, 313-sensor placement rack I, 4-data collector, 5-sound wave transmitter, 6-sound wave receiving sensor I, 7-sound wave receiving sensor II, 8-air extraction unit, 9-inflation unit, 10-coal sample. DETAILED DESCRIPTION

[0038] like Figure 1 As shown, a coal deformation measurement system based on an acoustic emission device includes a host computer 1, a power amplifier 2, two measuring tubes 3, a data collector 4, an acoustic wave transmitter 5, an acoustic wave connector, an air extraction unit 8 and an air filling unit 9, wherein a coal sample 10 is placed in the measuring tube 3.

[0039] like Figure 2-Figure 9 As shown, Figure 2 As shown, the measuring cylinder 3 includes a cylinder body 31, a left end cover 32 and a right end cover 33. Specifically, as Figure 3As shown, a coal sample placement bin 310 is provided in the cylinder 31 for placing coal samples 10. A push box 311 is provided on one side of the coal sample placement bin 310, and a sensor placement rack II312 is provided on the other side, and an acoustic wave receiving sensor II7 is placed in the middle of the sensor placement rack II312. The push box 311 is a cylindrical cavity made of rubber. Its diameter is similar to the inner diameter of the cylinder 31. When the push box is pushed into the cylinder 31, there is a certain friction resistance between them. A sensor placement rack I313 and an acoustic wave transmitter 5 are provided in the push box 311. An acoustic wave receiving sensor I6 is placed in the middle of the sensor placement rack I313, and the acoustic wave transmitter 5 is fixed in the middle of the side plate of the push box 311. The specific models of the acoustic wave receiving sensor I6 and the acoustic wave receiving sensor II7 are GD150 differential waterproof narrow-band acoustic emission sensors with a frequency range of 60KHz to 400KHz and a resonant frequency of 150KHz.

[0040] The left end cap 32 is threadedly connected to the left port of the cylinder 31, and the right end cap 33 is threadedly connected to the right port of the cylinder 31. The host computer 1 is electrically connected to the power amplifier 2, and the power amplifier 2 is electrically connected to the sound wave transmitter 5. The sound wave receiving sensor I6 and the sound wave receiving sensor II7 are electrically connected to the data collector 4, respectively, and the data collector 4 is electrically connected to the host computer 1. Specifically, a horizontally placed cylindrical cavity is provided in the coal sample storage bin 310. In other embodiments, the coal sample 10 can be a cube, and the corresponding coal sample storage bin 310 is also set as a cubic cavity.

[0041] An annular groove 3100 is provided on one side of the wall of the coal sample storage bin 310, and the end of the push box 311 is embedded in the annular groove 3100, so as to fix the push box 311 and the coal sample storage bin 310, and the depth of the annular groove 3100 needs to be set according to the requirements. Specifically, a sound insulation layer is provided on the inner wall of the push box 311 and the sensor placement frame 1313. An air inlet 320 is provided on the left end cover 32, and an air outlet 330 is provided on the right end cover 33. A handle 3111 is provided on the outside of the side plate 3110 of the push box 311, and the handle 3111 is a hollow cavity. Four air inlet holes 3112 are provided on the side plate 3110, and the air inlet holes 3112 are connected to the air inlet 320 pipeline. Before the coal sample 10 is placed in the coal sample storage bin 310, a rubber sleeve is put on its surface to facilitate fixing in the bin. The above arrangement makes the sealing of the measuring tube 3 better, and it is more convenient to take and place the components placed inside the coal sample, such as the sensor placement rack, and position these components. At the same time, the push box 311 has a cylindrical cavity, and the cavity outlet is aligned with the wall of the coal sample, which can have better guidance and anti-interference when inflating the coal sample and emitting sound waves.

[0042] Specifically, the air extraction unit 8 is a vacuum pump, which is connected to the air inlet 320 through a pipeline, and the gas charging unit 9 is connected to the air inlet 320 through a pipeline. The gas charging unit 9 includes a methane gas cylinder, a helium gas cylinder and a carbon dioxide gas cylinder connected in parallel through pipelines.

[0043] The system is provided with two measuring cylinders 3, which can simultaneously conduct tests according to different pressures, different temperatures, and different types of coal, effectively improving the efficiency of coal sample testing and obtaining more extensive test data. Of course, the number of the measuring cylinders 3 can also be set to be larger.

[0044] The present invention also proposes a method for measuring coal deformation based on an acoustic emission device, comprising the following steps:

[0045] Step S1, put a rubber sleeve on the outside of the cylindrical coal sample 10, and put it horizontally into the coal sample storage bin 310; make the right side of the coal sample 10 close to the acoustic wave receiving sensor II7 but not touch it; the left side of the cylindrical coal sample should be flush with the left wall of the coal sample storage bin 310. When the sensor placement rack II312 is pushed in from the right port of the cylinder 31 and fixed, the left end face of the placement rack needs to be tightly fixed to the right end face of the coal sample storage bin.

[0046] Step S2, use the handle 3111 to push the push box 311 into the inner cavity from the left entrance of the cylinder 31, so that the end of the push box 311 is embedded in the annular groove on the wall of the coal sample placement bin 310, and the acoustic wave receiving sensor I6 is close to the left side of the coal sample 10 without touching it.

[0047] Step S3, threading the left end cover 32 to the left port of the cylinder 31, and threading the right end cover 33 to the right port of the cylinder 31.

[0048] Step S4, close the gas outlet 330, and the gas extraction unit 8 slowly extracts the gas in the measuring tube 3. The host computer 1 generates a sound wave signal, which is amplified by the power amplifier 2 and sent to the sound wave transmitter 5, and the sound wave transmitter 5 emits sound waves. The sound wave receiving sensor I6 and the sound wave receiving sensor II7 receive the sound waves respectively, and convert the sound waves into electrical signals and send them to the data collector 4, which then sends them to the host computer 1 to calculate the time difference between the sound wave receiving sensor I6 and the sound wave receiving sensor II7 receiving the sound waves, and calculate the contraction distance of the coal sample 10.

[0049] Step S5, open the air outlet 330, and inflate the measuring tube 3 through the inflation unit 9; generate an acoustic emission signal through the host computer 1, amplify the sound wave through the power amplifier 2, and send it into the measuring tube 3, the sound wave receiving sensor I6 and the sound wave receiving sensor II7 respectively receive the sound waves, and convert the sound waves into electrical signals and send them to the data collector 4, and the data collector 4 sends them to the host computer 1 to calculate the time difference of the sound waves and calculate the expansion distance of the coal sample 10.

[0050] Step S6: The host computer 1 emits sound waves at a certain frequency, and produces an expansion curve and a contraction curve of the coal sample 10 within a certain period of time.

[0051] In the prior art, the expansion distance and contraction distance of coal samples are usually measured by strain gauges, which need to be attached to the surface of the coal sample. Since the strain gauge is easily affected by the environment and human operation, its measurement accuracy is unstable. The present invention uses an acoustic transmitter in conjunction with two acoustic wave receiving sensors to directly measure the time difference between the two acoustic wave receiving sensors, and then calculates through the host computer, thereby obtaining a more accurate expansion distance and contraction distance.

[0052] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited thereto. Various changes that can be made within the knowledge scope of technicians in the relevant technical field without departing from the spirit of the present invention are all within the protection scope of the claims of the present invention.

Claims

1. A coal deformation measurement system based on an acoustic emission device, characterized in that: It comprises a host computer (1), a power amplifier (2), at least one measuring tube (3), a data acquisition device (4), a sound wave transmitter (5) and a sound wave receiver, wherein the sound wave receiver comprises a sound wave receiving sensor I (6) and a sound wave receiving sensor II (7); The measuring cylinder (3) comprises a cylinder body (31), a left end cover (32) and a right end cover (33); a coal sample placement bin (310) is provided in the cylinder body (31) for placing the coal sample (10); a push box (311) is provided on one side of the coal sample placement bin (310), and a sensor placement rack II (312) is provided on the other side; the sensor placement rack II (312) is in contact with the bin wall of the coal sample placement bin (310); the acoustic wave receiving sensor II (7) is installed in the middle of the sensor placement rack II (312); The push box (311) can slide in the cylinder (31) and is detachably connected to the wall of the coal sample storage bin (310); a sensor storage rack I (313) and a sound wave transmitter (5) are provided in the push box (311); the sensor storage rack I (313) is installed near the port of the push box (311); the sound wave receiving sensor I (6) is installed in the middle of the sensor storage rack I (313); and the sound wave transmitter (5) is installed on the side plate (3110) of the push box (311); The left end cover (32) and the right end cover (33) are respectively threadedly connected to the left and right ends of the cylinder (31); the host computer (1) is electrically connected to the power amplifier (2), and the power amplifier (2) is electrically connected to the sound wave transmitter (5); the sound wave receiving sensor I (6) and the sound wave receiving sensor II (7) are respectively electrically connected to the data acquisition device (4), and the data acquisition device (4) is electrically connected to the host computer (1).

2. The coal deformation measurement system based on the acoustic emission device according to claim 1 is characterized in that: A horizontally placed cylindrical cavity is provided in the coal sample (10) storage bin (310).

3. The coal deformation measurement system based on the acoustic emission device according to claim 2 is characterized in that: An annular groove (3100) is provided on one side of the wall of the coal sample placement bin (310), and the end of the push box (311) is embeddedly connected to the annular groove (3100), so that the sound wave receiving sensor I (6) is close to the left side of the coal sample (10).

4. The coal deformation measurement system based on the acoustic emission device according to claim 1 is characterized in that: A sound insulation layer is provided on the inner wall of the push box (311) and the sensor placement rack I (313).

5. The coal deformation measurement system based on the acoustic emission device according to claim 1 is characterized in that: An air inlet (320) is provided on the left end cover (32), and an air outlet (330) is provided on the right end cover (33).

6. The coal deformation measurement system based on the acoustic emission device according to claim 5 is characterized in that: A handle (3111) is provided on the outside of the side panel (3110), and the inside of the handle (3111) is a hollow cavity; at least one air inlet hole (3112) is provided on the side panel, and the air inlet hole (3112) is connected to the air inlet (320) pipeline.

7. The coal deformation measurement system based on the acoustic emission device according to claim 1 is characterized in that: The coal sample (10) is covered with a rubber sleeve on its surface before being placed in the coal sample placement bin (310).

8. The coal deformation measurement system based on the acoustic emission device according to claim 1 is characterized in that: It also includes an air extraction unit (8) and an air charging unit (9), wherein the air extraction unit (8) is a vacuum pump, the vacuum pump is connected to the air inlet (320) pipeline, and the air charging unit (9) is connected to the air inlet (320) pipeline.

9. The coal deformation measurement system based on the acoustic emission device according to claim 1 is characterized in that: The gas charging unit (9) comprises a methane gas cylinder, a helium gas cylinder and a carbon dioxide gas cylinder connected in parallel via pipelines.

10. A method for measuring coal deformation based on an acoustic emission device, using the coal deformation measuring system based on an acoustic emission device according to claims 1 to 9, characterized in that: The following steps are involved: Step S1, putting a rubber sleeve on the outside of the cylindrical coal sample (10), and horizontally placing it into the coal sample storage bin (310); making the right side of the coal sample (10) close to the acoustic wave receiving sensor II (7); Step S2, using the handle (3111), the push box (311) is pushed into the inner cavity from the left entrance of the cylinder (31), so that the end of the push box (311) is embedded and connected with the annular groove (3100) on the wall of the coal sample storage bin (310), and the sound wave receiving sensor I (6) is close to the left side of the coal sample (10); Step S3, threading the left end cover (32) to the left port of the cylinder (31), and threading the right end cover (33) to the right port of the cylinder (31); Step S4, closing the gas outlet (330), and the gas extraction unit (8) slowly extracts the gas in the measuring tube (3); the host computer (1) generates a sound wave signal, which is amplified by the power amplifier (2) and sent to the sound wave transmitter (5); the sound wave transmitter (5) transmits the sound wave, and the sound wave receiving sensor I (6) and the sound wave receiving sensor II (7) respectively receive the sound wave, and convert the sound wave into an electrical signal and send it to the data acquisition device (4); the data acquisition device (4) then sends it to the host computer (1) to calculate the time difference between the sound wave receiving sensor I (6) and the sound wave receiving sensor II (7) receiving the sound wave, and calculate the contraction distance of the coal sample (10); Step S5, opening the air outlet (330), and inflating the measuring tube (3) through the inflation unit (9); generating a sound wave signal through the host computer (1), amplifying the sound wave through the power amplifier (2), and sending it into the measuring tube (3); the sound wave receiving sensor I (6) and the sound wave receiving sensor II (7) respectively receive the sound wave, and convert the sound wave into an electrical signal and send it to the data acquisition device (4); the data acquisition device (4) then sends it to the host computer (1) to calculate the time difference of the sound wave, and calculate the expansion distance of the coal sample (10); Step S6: The host computer (1) generates sound waves at a certain frequency, and produces an expansion curve and a contraction curve of the coal sample (10) within a certain period of time.

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