Coal body deformation measuring system and measuring method based on acoustic emission

Abstract

This invention discloses a system and method for measuring coal deformation based on acoustic emission. In the method, a host computer generates sound waves, which are amplified by a power amplifier and transmitted to a sound wave transmitter inside a pushbox. Sound wave receiving sensors I and II, located on either side of the coal sample, sequentially receive the sound wave signals. The two signals are converted and sent to a data acquisition unit. The host computer then calculates the time difference between the two signals and calculates the expansion and contraction distances of the coal sample under adsorbed and desorbed gas conditions, outputting the expansion and contraction curves over a certain time period. This invention is less susceptible to external interference during measurement and has high experimental accuracy.

Description

Technical Field

[0001] This invention relates to the field of coal and rock gas dynamic disaster occurrence mechanism technology, specifically to a coal body deformation measurement system and method based on acoustic emission. Background Technology

[0002] Coal adsorbing gas undergoes expansion and deformation, while desorbing gas causes contraction and deformation. This deformation alters the coal's strength, stress state, and porosity, thus affecting coal and gas outburst characteristics and coal seam permeability. Therefore, studying the dynamic evolution characteristics and mechanisms of coal adsorption and desorption gas deformation is crucial for understanding the evolution mechanism of coal-rock gas dynamic disasters, obtaining the true migration patterns of coal seam gas, and guiding high-yield and efficient coalbed methane extraction. In recent years, with the deepening research on coal adsorption characteristics, instruments for testing coal adsorption deformation have been developed. Most of these devices collect information by attaching resistance strain gauges to coal samples and obtaining relevant data through data analysis systems. However, these devices have the following shortcomings in the experimental process: While strain gauges are used as strain sensors to measure coal deformation, the strain gauges themselves are easily affected by the environment, such as electromagnetic fields, humidity, and chemical corrosion. Furthermore, adhesion during the connection to the test coal sample significantly impacts the experimental results. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention proposes a coal deformation measurement system and method based on acoustic emission. It employs acoustic emission technology and uses an acoustic wave time delay estimation algorithm based on cross-correlation function to convert the acoustic wave transit time, thereby measuring coal deformation in a non-contact manner. This effectively avoids measurement errors caused by the environment and bonded strain gauges, and improves the accuracy of coal deformation measurement.

[0004] The technical solution adopted by the present invention is as follows: In the first aspect, the present invention proposes a coal deformation measurement system based on an acoustic emission device, including a host computer, a power amplifier, at least one measuring cylinder, a data acquisition unit, an acoustic wave transmitter and an acoustic wave receiver, wherein the acoustic wave receiver includes an acoustic wave receiving sensor I and an acoustic wave receiving sensor II.

[0005] The measuring cylinder includes a cylinder body, a left end cap, and a right end cap. A coal sample placement chamber (310) is provided inside the cylinder for placing coal samples. A push box is provided on one side of the coal sample placement chamber, and a sensor placement frame II is provided on the other side. The sensor placement frame II is in contact with the wall of the coal sample placement chamber. The acoustic wave receiving sensor II is installed in the middle of the sensor placement frame II. The push box can slide inside the cylinder and is detachably connected to the wall of the coal sample placement chamber. A sensor placement frame I and an acoustic wave transmitter are provided inside the push box. The sensor placement frame 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 frame I, and the acoustic wave transmitter is installed on the side plate of the push box.

[0006] The left end cap and the right end cap are respectively threaded 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 acoustic wave transmitter; the acoustic wave receiving sensor I and the acoustic wave receiving sensor II are respectively electrically connected to the data acquisition unit, and the data acquisition unit is electrically connected to the host computer.

[0008] As a further improvement of the present invention, the coal sample placement chamber is provided with a horizontally placed cylindrical cavity.

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

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

[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 plate, and the handle is a hollow cavity; at least one air inlet is provided on the side plate, and the air inlet is connected to the air inlet pipe.

[0013] As a further improvement of the present invention, the coal sample is covered with a rubber sleeve before being placed into the coal sample storage bin.

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

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

[0016] Secondly, the present invention also proposes a method for measuring coal deformation based on an acoustic emission device, using the aforementioned coal deformation measurement system based on an acoustic emission device, comprising the following steps:

[0017] Step S1: Cover the cylindrical coal sample with a rubber sleeve and horizontally place it into the coal sample placement chamber, so that the right side of the coal sample is close to the acoustic wave receiving sensor II.

[0018] Step S2: Use the handle to push the push box into the inner cavity from the left inlet of the cylinder, so that the end of the push box is embedded in 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: Thread the left end cap to the left port of the cylinder, and thread the right end cap to the right port of the cylinder.

[0020] Step S4: Close the air outlet and slowly evacuate the gas in the measuring cylinder using the extraction unit; 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 emits a sound wave, and sound wave receiving sensor I and sound wave receiving sensor II receive the sound wave respectively. The sound wave is converted into an electrical signal and sent to the data acquisition unit. The data acquisition unit then sends the signal to the host computer to calculate the time difference between the sound wave received by sound wave receiving sensor I and sound wave receiving sensor II, and calculates the shrinkage distance of the coal sample.

[0021] Step S5: Open the air outlet and fill the measuring cylinder with air through the air filling unit; generate a sound wave signal through the host computer, amplify the sound wave through the power amplifier, and send it into the measuring cylinder. Sound wave receiving sensor I and sound wave receiving sensor II receive the sound wave respectively, convert the sound wave into an electrical signal and send it to the data acquisition unit. The data acquisition unit then sends it to the host computer to calculate the time difference of the sound wave and calculate the expansion distance of the coal sample.

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

[0023] In this method, the calculation of time difference and deformation distance adopts the acoustic time delay estimation method based on cross-correlation function, namely the cross-correlation algorithm. Its main principle is as follows: During signal processing, the host computer uses the cross-correlation function to calculate the cross-correlation function of two co-source signals with time delay, obtaining the x-coordinate corresponding to the maximum point of the cross-correlation function formed by the two co-source signals. This x-coordinate represents the transit time of the two acoustic signals. By multiplying the transit time at different times by the propagation speed of sound in the coal sample (approximately 2000 m / s, varying depending on coal density; the specific value can be obtained experimentally), the deformation of the coal sample between the two acoustic emission times can be obtained.

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

[0025] (1) This invention sets up two acoustic wave receiving sensors to receive acoustic waves from the left side and the right side of the coal sample respectively. By using the time difference between these two acoustic waves and the cross-correlation algorithm, the expansion distance and contraction distance of the coal sample are calculated, thus avoiding the problem of inaccurate measurement caused by the strain gauge being pasted on the coal sample.

[0026] (2) The measuring cylinder of this invention is designed as a three-section structure with interconnected threads. This facilitates the placement of coal samples from both sides of the cylinder, as well as the placement of two sensor holders and the push box. It also helps maintain its airtightness during vacuuming and filling tests. The push box, a cylindrical cavity, is installed inside the cylinder. When filling the coal sample, it allows for directional filling of the left side of the sample, rather than filling the entire measuring cylinder. This improves the adsorption efficiency of the coal sample. Simultaneously, the acoustic transmitter is mounted on the side plate of the push box, confining its emission space within the box and preventing interference from the internal space of the cylinder, thus ensuring directional emission. Furthermore, the coal sample placement chamber within the cylinder, with its thickness, allows its side walls to serve as the positioning base for the two sensor holders, making it easier to determine the distance between the two acoustic receiving sensors and the sides of the coal sample. Attached Figure Description

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

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

[0029] Figure 2 This is a schematic diagram of the external structure of the measuring cylinder;

[0030] Figure 3 yes Figure 2 Yes, it is a sectional view;

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

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

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

[0034] Figure 7 This is a schematic diagram of the sensor mounting bracket II;

[0035] Figure 8 This is a structural diagram of the left end cap;

[0036] Figure 9 This is a structural diagram of the right end cap;

[0037] In the diagram, 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 placement chamber, 3100-Annular groove, 311-Push box, 3110-Side plate, 3111-Handle, 3112-Air inlet, 312-Sensor placement rack II, 313-Sensor placement rack I, 4-Data acquisition unit, 5-Sound wave transmitter, 6-Sound wave receiving sensor I, 7-Sound wave receiving sensor II, 8-Air extraction unit, 9-Air filling unit, 10-Coal sample. Detailed Implementation

[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 cylinders 3, a data acquisition unit 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 inside the measuring cylinder 3.

[0039] like Figures 2-9 As shown, Figure 2 As shown, the measuring cylinder 3 includes a cylinder body 31, a left end cap 32, and a right end cap 33. Specifically, as... Figure 3As shown, a coal sample placement chamber 310 is provided inside the cylinder 31 for placing coal sample 10. A push box 311 is provided on one side of the coal sample placement chamber 310, and a sensor placement frame II 312 is provided on the other side. An acoustic wave receiving sensor II 7 is placed in the middle of the sensor placement frame II 312. The push box 311 is a cylindrical cavity made of rubber. Its diameter is similar to the inner diameter of the cylinder 31, and there is a certain frictional resistance when the push box is pushed into the cylinder 31. The push box 311 contains a sensor placement frame I 313 and an acoustic wave transmitter 5. An acoustic wave receiving sensor I 6 is placed in the middle of the sensor placement frame I 313, 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 I 6 and the acoustic wave receiving sensor II 7 are GD150 differential waterproof narrow-band acoustic emission sensors with a frequency range of 60KHz~400KHz and a resonant frequency of 150KHz.

[0040] The left end cap 32 is threaded to the left port of the cylinder 31, and the right end cap 33 is threaded 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 acoustic transmitter 5. Acoustic receiving sensors I6 and II7 are electrically connected to the data acquisition unit 4, which is in turn electrically connected to the host computer 1. Specifically, the coal sample placement chamber 310 has a horizontally placed cylindrical cavity. In some other embodiments, the coal sample 10 can be a cube, and the corresponding coal sample placement chamber 310 is also a cubic cavity.

[0041] An annular groove 3100 is formed on one side of the coal sample placement chamber 310. The end of the push box 311 is embedded in the annular groove 3100 to fix the push box 311 to the coal sample placement chamber 310. The depth of the annular groove 3100 needs to be set according to requirements. The inner wall of the push box 311 and the sensor placement rack I313 are provided with sound insulation layers. 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 outer side of the side plate 3110 of the push box 311, and the handle 3111 has a hollow cavity inside. Four air inlets 3112 are provided on the side plate 3110, and the air inlets 3112 are connected to the air inlets 320 by pipes. Before the coal sample 10 is placed into the coal sample placement chamber 310, a rubber sleeve is put on its surface for easy fixation inside the chamber. The above-mentioned design improves the sealing of the measuring cylinder 3, and makes it easier to place and remove coal samples, such as the sensor holder, and to position these components. Meanwhile, the push box 311 has a cylindrical cavity with its outlet aligned with the coal sample wall, providing good guidance and anti-interference capabilities when filling the coal sample with gas and emitting sound waves.

[0042] Specifically, the pumping unit 8 is a vacuum pump, which is connected to the inlet pipe 320. The filling unit 9 is also connected to the inlet pipe 320. The filling unit 9 includes methane cylinders, helium cylinders, and carbon dioxide cylinders connected in parallel.

[0043] This system is equipped with two measuring cylinders 3, which can conduct tests simultaneously under different pressures, temperatures, and coal types, effectively improving the efficiency of coal sample testing and obtaining a wider range of test data. Of course, the number of cylinders can also be set to more.

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

[0045] Step S1: Cover the cylindrical coal sample 10 with a rubber sleeve and horizontally insert it into the coal sample placement chamber 310; ensure that the right side of the coal sample 10 is close to but not in contact with the acoustic wave receiving sensor II7, and that the left side of the cylindrical coal sample is flush with the left wall of the coal sample placement chamber 310. When pushing and fixing the sensor placement frame II312 from the right port of the cylinder 31, the left end face of the placement frame must be firmly attached to the right end face of the coal sample placement chamber.

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

[0047] Step S3: Thread the left end cap 32 to the left port of the cylinder 31, and thread the right end cap 33 to the right port of the cylinder 31.

[0048] Step S4: Close the air outlet 330, and the extraction unit 8 slowly extracts the gas from the measuring cylinder 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, which then emits the sound wave. Sound wave receiving sensors I6 and II7 receive the sound wave and convert it into an electrical signal, which is then sent to the data acquisition unit 4. The data acquisition unit 4 then sends the signal to the host computer 1 to calculate the time difference between the sound wave received by sensor I6 and sensor II7, and to calculate the contraction distance of the coal sample 10.

[0049] Step S5: Open the air outlet 330 and inflate the measuring cylinder 3 through the air filling 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 cylinder 3. The acoustic wave receiving sensor I6 and the acoustic wave receiving sensor II7 receive the sound wave respectively, convert the sound wave into an electrical signal, and send it to the data acquisition unit 4. The data acquisition unit 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.

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

[0051] In existing technologies, strain gauges are typically used to measure the expansion and contraction distances of coal samples. These strain gauges need to be attached to the surface of the coal sample, and their accuracy is unstable due to susceptibility to environmental factors and human operation. This invention, however, uses an acoustic transmitter in conjunction with two acoustic wave receiving sensors to directly measure the time difference between the two sensors. The results are then calculated by a host computer to obtain more accurate expansion and contraction distances.

[0052] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes that can be made within the scope of knowledge possessed by those skilled in the art 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 includes a host computer (1), a power amplifier (2), at least one measuring cylinder (3), a data acquisition unit (4), a sound wave transmitter (5) and a sound wave receiver, wherein the sound wave receiver includes a sound wave receiving sensor I (6) and a sound wave receiving sensor II (7). The measuring cylinder (3) includes a cylinder body (31), a left end cap (32), and a right end cap (33). The cylinder body (31) is provided with a coal sample placement chamber (310) for placing coal samples (10). A push box (311) is provided on one side of the coal sample placement chamber (310), and a sensor placement frame II (312) is provided on the other side. The sensor placement frame II (312) is in contact with the wall of the coal sample placement chamber (310). The acoustic wave receiving sensor II (7) is installed in the middle of the sensor placement frame II (312). The push box (311) can slide inside the cylinder (31) and is detachably connected to the wall of the coal sample placement bin (310); the push box (311) is provided with a sensor placement rack I (313) and a sound wave transmitter (5). The sensor placement 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 placement rack I (313), and the sound wave transmitter (5) is installed on the side plate (3110) of the push box (311). The left end cap (32) and the right end cap (33) are respectively threaded 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 acoustic transmitter (5); the acoustic receiving sensor I (6) and the acoustic receiving sensor II (7) are electrically connected to the data acquisition unit (4), and the data acquisition unit (4) is electrically connected to the host computer (1).

2. The coal deformation measurement system based on an acoustic emission device according to claim 1, characterized in that, The coal sample (10) placement chamber (310) is equipped with a horizontally placed cylindrical cavity.

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

4. The coal deformation measurement system based on an acoustic emission device according to claim 3, characterized in that, The inner wall of the push box (311) and the sensor placement rack I (313) are provided with sound insulation layers.

5. The coal deformation measurement system based on an acoustic emission device according to claim 4, 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 an acoustic emission device according to claim 5, characterized in that, The side plate (3110) is provided with a handle (3111) on the outside, and the handle (3111) has a hollow cavity inside; at least one air inlet (3112) is provided on the side plate, and the air inlet (3112) is connected to the air inlet (320) pipe.

7. The coal deformation measurement system based on an acoustic emission device according to claim 6, characterized in that, The coal sample (10) is covered with a rubber sleeve before being placed into the coal sample storage bin (310).

8. The coal deformation measurement system based on an acoustic emission device according to claim 7, characterized in that, It also includes a vacuum pump unit (8) and an air filling unit (9). The vacuum pump unit (8) is a vacuum pump connected to the air inlet (320) pipeline, and the air filling unit (9) is connected to the air inlet (320) pipeline.

9. The coal deformation measurement system based on an acoustic emission device according to claim 8, characterized in that, The inflation unit (9) includes a methane cylinder, a helium cylinder, and a carbon dioxide cylinder connected in parallel via pipelines.

10. A method for measuring coal deformation based on an acoustic emission device, using the coal deformation measurement system based on an acoustic emission device as described in claim 9, characterized in that... Includes the following steps: Step S1: Cover the cylindrical coal sample (10) with a rubber sleeve and send it horizontally into the coal sample placement chamber (310); so that the right side of the coal sample (10) is close to the acoustic wave receiving sensor II (7); Step S2: Using the handle (3111), push the push box (311) into the inner cavity from the left inlet of the cylinder (31), so that the end of the push box (311) is embedded in the annular groove (3100) on the wall of the coal sample placement bin (310), and the acoustic wave receiving sensor I (6) is close to the left side of the coal sample (10). Step S3: Thread the left end cap (32) to the left port of the cylinder (31) and thread the right end cap (33) to the right port of the cylinder (31); Step S4: Close the air outlet (330), and the air extraction unit (8) slowly extracts the gas in the measuring cylinder (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) emits a sound wave, and the sound wave receiving sensor I (6) and the sound wave receiving sensor II (7) receive the sound wave respectively. After converting the sound wave into an electrical signal, it is sent to the data acquisition unit (4). The data acquisition unit (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 calculates the shrinkage distance of the coal sample (10). Step S5: Open the air outlet (330) and fill the measuring cylinder (3) with air through the air filling unit (9); generate a sound wave signal through the host computer (1), amplify the sound wave through the power amplifier (2), and send it into the measuring cylinder (3). The sound wave receiving sensor I (6) and the sound wave receiving sensor II (7) receive the sound wave respectively, convert the sound wave into an electrical signal and send it to the data acquisition unit (4). The data acquisition unit (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 the expansion curve and contraction curve of the coal sample (10) within a certain time.

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