2020 Vol. 46, No. 10

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Research on cyclic liquid nitrogen fracturing technology for enhancing coalbed methane drainage and its application prospect
ZHAI Cheng, XU Jizhao
2020, 46(10): 1-8.. doi: 10.13272/j.issn.1671-251x.17669
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Hydraulic fracturing technology is widely used in fracturing coal seam and improving efficiency of coalbed methane drainage, but due to large water consumption, environment pollution by fracturing fluid and other problems, it is difficult to be used in water-deficient areas where are rich in coalbed methane. Based on conventional liquid nitrogen fracturing technology, a cyclic liquid nitrogen fracturing technology is proposed through altering the single injection mode of liquid nitrogen, and application of the technology in enhancing coalbed methane drainage is prospected. The technology uses cyclic injection mode of liquid nitrogen, which can make liquid nitrogen to fulfill micro-crack space continuously, so as to form complex crack networks. The principle of fracturing coal-rock of the technology is coupling mechanism of cyclic cumulative damage, low temperature fracturing and gas fracturing: ① During cyclic injection process of liquid nitrogen, different deformation responses appear among grains with different collocation, and accumulated damages among grains could weaken coal body strength of pressure resistance in local area to some degree, so as to generate new cracks and extend the primary cracks. ② Cold shock of liquid nitrogen to coal-rock leads to break of inner structure of coal-rock, so a large number of micro-cracks are generated and continuously extended with cyclic injection of liquid nitrogen. Meanwhile, water-ice phase transition caused by low temperature property of liquid nitrogen could further damage inner structure of coal-rock. ③ The generated high-pressure gas by vaporization of liquid nitrogen could make coal-rock volume to repeatedly extend and shrink, which further enhances growth and connection. Cyclic liquid nitrogen fracturing technology, which takes liquid nitrogen as fracturing fluid, greatly relieves dependence on water resources, and has no pollution to environment. The technology can be applied in coalbed methane drainage.
Analysis of development framework of intelligent coal mine underground drilling technology
LI Quanxin, LIU Fei, FANG Ju
2020, 46(10): 9-13. doi: 10.13272/j.issn.1671-251x.17662
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Development and application of intelligent drilling tool and acquisition and analysis of drilling data are outstanding characteristics of intelligent underground drilling. However,research foundation of intelligent underground drilling in China's coal mine is weaker at the present stage, and scientific and elaborate technical means of intelligent underground drilling is lacked as well as systematic development framework. For the above problems, the research status of intelligent underground drilling technology in China's coal mine is expounded, and development achievements and shortcomings of intelligent coal mine underground drilling are summarized from the aspects of automatic drilling rig, guided drilling technology, multi-parameter acquisition in hole, intelligent analysis and decision-making, etc. On this basis, the development framework of intelligent coal mine underground drilling technology is proposed, and it is pointed out that the development framework should be focused on accurate guidance system, data measurement system, data transmission system, intelligent decision-making system and automatic control system, so as to create an integrated and intelligent underground drilling platform from hole bottom to hole ostiole and from underground to ground. Meanwhile, a closed-loop control system of parameter measurement, intelligent decision-making and controlling execution for underground drilling process should be constructed, which real-timely transmits measurement parameters while drilling in hole bottom to remote ground data support center through data transmission system, cooperatively analyzes geological parameters, geometrical parameters and engineering parameters by use of artificial intelligence algorithms, and updates 3D visual geological model real-timely, so as to draw up intelligent adjustment and control strategies of drilling technology parameters and borehole trajectory for controlling intelligent underground drilling rig to run.
Application of pneumatic directional drilling technology for soft-fragmentized coal seam in Qinglong Coal Mine
KONG Qingjun, CHU Zhiwei
2020, 46(10): 14-18.. doi: 10.13272/j.issn.1671-251x.2020070056
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In view of problems of rotary drilling technology for soft-fragmentized coal seam, such as shallow borehole completed depth, uncontrollable borehole trajectory, low drilling efficiency and poor gas drainage effect, pneumatic directional drilling technology was put forward to carry out gas drainage borehole construction in soft-fragmentized coal seam. Compressed air output by underground explosion-proof air compressor is used as drilling power and slag discharge medium. Wired measurement while drilling device is used to obtain borehole trajectory parameters. Compressed air monitoring device is applied to monitor parameters such as air supply pressure, temperature and flow rate in real time, which provide basis for judgment of working condition in borehole. In order to realize efficient coal dust treatment, compressed air dust removal device is used to purify coal dust in orifice. The field test was carried out in drilling field of southern region of 21608 roadway in Qinglong Coal Mine of Yankuang Guizhou Nenghua Co., Ltd. The pneumatic directional drilling technology was adopted to construct directional boreholes in soft-fragmentized coal seam with firmness coefficient of 0.37. The maximum borehole depth is 345 m, and the average effective footage of single shift is more than 30% higher than that of ordinary rotary borehole.The average gas drainage volume fraction of single borehole remains at about 70%, which is about 60% higher than that of ordinary rotary borehole. The average gas drainage volume fraction of main pipeline in drilling field is 71.2%, the average gas drainage purity is up to 4.0 m3/min, and accumulated gas drainage volume reaches 115 000 m3, which effectively covers gas drainage area of 300 m roadway to be excavated. The pneumatic directional drilling technology has advantages of controllable borehole trajectory, long borehole completed depth, high drilling efficiency and good gas drainage effect. It can be applied to gas regional drainage and pre-drainage in soft-fragmentized coal seam, which provides a new technical approach for gas control in soft-fragmentized coal seam.
Research on influence characteristics of water jet impact on borehole gas drainage
GAO Yabin, HAN Peizhuang, GUO Xiaoya, XIANG Xin, WANG Fei
2020, 46(10): 19-25. doi: 10.13272/j.issn.1671-251x.17651
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Water jet based borehole permeability enhancement technology is an effective way to increase coal-seam permeability and gas drainage rate. However, influence characteristics of water jet impact on borehole gas drainage are indeterminate at present. For the above problem, flow field characteristics and pressure characteristics of water jet on borehole wall are researched by use of numerical simulation method. Influence of water jet impact on coal body stress around borehole is analyzed, and gas drainage characteristics of ordinary borehole and water jet impact borehole are compared. The research results show that water jet in borehole diffusely flows with a small diffusion angle. Axial speed of water jet is the peak value. When water jet impacts the borehole wall, a circular truncated cone forms where water speed is low. There are three pressure concentration areas in process of water jet impacting borehole named exit pressure concentration area, contact surface pressure concentration area and wall pressure concentration area. Pressure on borehole wall increases with increase of water jet impact pressure. There are two stages in influence of water jet impact borehole on stress distribution of surrounding coal body named sudden stress reduction stage and stress enhancement and recovery stage separately, and stress variation degree of coal body has positive correlation with impact pressure. Whether water jet impact borehole or ordinary borehole is used for gas drainage, gas pressure of coal body around borehole decreases gradually from borehole to coal body interior with time passing. But water jet impact borehole can significantly improve drainage range and drainage rate of borehole, and the larger the water jet impact pressure is, the more obvious the influence on borehole drainage is.
Research on drag reduction technology for long boreholes drilling in coal mine
WANG Siyi, ZHAO Jiangpeng, YANG Dongdong
2020, 46(10): 26-31. doi: 10.13272/j.issn.1671-251x.2020020025
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In view of problem in long boreholes drilling in coal mine that frictional resistance between the drill string and the borehole wall seriously affects the transmission of weight-on-bit and hinders the further increase of the borehole depth, drag reduction technology for long borehole drilling were studied. Technical bottlenecks of the current composite directional drilling technology are analyzed, that is, it ca't be oriented in the composite drilling, and the efficiency is low in the deep hole sliding direction, as a result, it is impossible to develop branches and correct deviations when the drilling is deep. The solutions of hydraulic oscillator drag reduction technology，roller centralizer drag reduction technology，impact vibration drag reduction technology and rotary steering technology were proposed, and the principles, technical advantages and limitations of each scheme were introduced, and the stratum adaptability of related technologies and the requirements for drilling equipment were pointed out. The actual application results of the related technology were put forward:after application of hydraulic oscillator in Huainan Mining Group Zhangji Mine,average feed gauge pressure was about 4 MPa, which was 33% lower than before, and the average drilling efficiency was increased by 126%, the pressure drop consumption was about 2 MPa, although the mud pump pressure increases to 1.7-2.5 MPa, it could still meet the needs of mud pumps in current coal mine underground drilling system and deep hole drilling with directional drilling tools;Two directional test boreholes were completed on the site of Tangjiahui Coal Mine with single-bend screw motor and hydraulic impactor compound drilling tool,and the drilling depths were 546 m and 564 m,the construction footage using the drilling tool combination were 411 m and 429 m,the time were 8 230 min and 8 570 min respectively, and the ROP was about 3 m/h,while the ROP of conventional directional drilling in the same formation was 0.83 m/h,the ROP of composite drilling tools increased by about 260%;Impact screw motor was used in Sihe Mine of Jinmei Group for drilling footage of 1 743 m, the cumulative time was 200 h, and the average mechanical speed could reach 8.34 m/h, which was 20%-30% higher than the conventional screw motor.It was proposed that the development of small-diameter rotary steering technology is a new break through direction for underground drilling tools in coal mines.
Research on underground drill pipe counting method based on improved ResNet network
GAO Rui, HAO Le, LIU Bao, WEN Jingyi, CHEN Yuhang
2020, 46(10): 32-37.. doi: 10.13272/j.issn.1671-251x.2020040054
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In view of problems that the existing underground drill pipe quantity statistics method has low accuracy and is easily affected by environmental changes,an underground drill pipe counting method based on improved ResNet network was proposed combining with convolutional neural network, signal filtering and other technologies. According to the difference between unloading action and non-unloading action in video image, the sample set is classified and trained based on the ResNet-50 network model to determine whether each frame of the video contains the unloading action; linear learning rate preheating and Logistic-based learning rate attenuation strategy are combined to update learning rate and improve the accuracy of model classification; the video classification confidence is filtered through the integration method, and the number of falling edges of the confidence curve is counted to realize drill pipe counting. Experimental results show that the preheating + attenuation learning rate update strategy can effectively improve classification accuracy of the image classification model to 89%. The actual application results show that underground drill pipe counting method based on improved ResNet network can efficiently identify unloaded rod images in the video with an average accuracy of 97%, which meets the actual application requirements.
Research on a novel combined sealing airbag for high gas working face corner
QIAO Lei, FAN Fuhuai, HUANG Xiaosheng
2020, 46(10): 38-42. doi: 10.13272/j.issn.1671-251x.17660
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Corner sealing is an effective solution to air leakage and gas overrun in working face corner. Existing double anti-bagging sealing, air duct cloth sealing and airbags filling are difficult to seal the whole section, and light flexible airbag has little bearing pressure and cannot be recycled and reused. For the above problems, a novel combined sealing airbag for high gas working face corner is designed, which is made into combined structure of big airbag and miniature airbag to meet needs of different sealing sections of roadway. Physical tests of pressure resistance and impact resistance of the combined sealing airbag are carried out, and following conclusion are gotten: Deformation speed of the airbag is large in the initial phase of physical test of pressure resistance, and then decreases gradually with the increase of pumping pressure. When working pressure of the airbag achieves rated value (0.05 MPa), the airbag shape tends to be stable. With the quality increase of gangue impacting on the airbag, deformation value of the airbag increases, rebound height of gangue decreases, and kinetic energy absorption effect of gangue is better. The combined sealing airbag is tested in N1101 working face of Yuwu Coal Mine. The test results show that: When the combined sealing airbag is used to seal upper corner, average gas volume fraction in goaf increases by 13.85% compared to that when traditional air duct cloth sealing is used, the ones in upper corner and return airway decrease by 16.04% and 8.69% separately, and gas volume fraction changes smoothly with small fluctuation, which verify the combined sealing airbag can effectively solve local air leakage in goaf and gas overrun in upper corner; The combined sealing airbag can be recycled and reused, so as to decrease corner sealing cost.
Research on key technologies of mine-used intelligent inspection robot
PAN Xiangsheng, CHEN Xiaojing
2020, 46(10): 43-48. doi: 10.13272/j.issn.1671-251x.2020080042
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The research status of mine-used intelligent inspection robot was introduced. In view of characteristics of mine-used intelligent inspection robot, the key technologies of mine-used intelligent inspection robot were analyzed in detail from mobile platforms, positioning and navigation, image recognition, autonomous charging, background management and diagnosis. Mobile platform is an important component of mine-used intelligent inspection robot, different mobile platforms work in different ways, wheel, crawler or track type mobile platform should be selected according to environmental characteristics of inspection site, and explosion-proof, moisture-proof, anti-vibration, dust and other issues should be considered in platform design. Positioning and navigation technology is key technology of mine-used intelligent inspection robot to realize intelligent and completely autonomous movement, from current underground application, laser radar+SLAM technology can be used for positioning and navigation of wheel type and crawler type mine-used intelligent inspection robot, due to fixed inspection line, RFID technology is suitable for positioning and navigation of track type mine-used intelligent inspection robot. Image recognition technology is an important technology widely used in mine-used intelligent inspection robot, which can determine running state of equipment by taking device images, moreover, according to difference of structure and networking mode of mine-used intelligent inspection robot, the image processing methods can be divided into background processing and local processing. Autonomous charging technology is an important means for mine-used intelligent inspection robot to supply electric energy for long-term autonomous work, the design of the battery should consider not only increasing battery capacity, but also having autonomous charging ability, so as to achieve unattended intelligent inspection; Intrinsically safe battery with small size, light weight and large reserves is the research difficulty. Mine-used intelligent inspection robot will collect a large amount of data in the process of inspection, so it must have background management and data analysis diagnosis function, but the current mine-used inspection robot ca't process or upload collected real-time data due to the influence of power supply and network transmission technology, therefore, a more efficient background management and on-line fault diagnosis system needs to be developed. At last, it is pointed out that intelligent data analysis, light weight mobile platform, modularized function and accurate inspection positioning are the development trends of mine-used intelligent inspection robot, which provides reference for further research on the key technologies of mine-used intelligent inspection robot.
Research on data-driven detection technology of smart coal mine
PAN Hongguang, PEI Jiabao, HOU Yuanbi
2020, 46(10): 49-54. doi: 10.13272/j.issn.1671-251x.17606
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Data-driven detection technology is an effective part of development of smart coal mine. It can predict behavior of future object system without knowing accurate analytical model of smart coal mine big data system. For the difficult problems of intelligent production operation, inherent safety production,scientific operation mode of smart coal mine, application status of data-driven detection technology in fault diagnosis of coal mine equipment, detection of foreign object in belt transportation and detection and identification of coal-gangue was analyzed.The development trend of data-driven detection technology in these three aspects was prospected: ① Fuzzy mathematics and artificial neural network should be integrated into fault diagnosis of coal mine equipment more effectively; ② Video anti-shake, image segmentation and target detection technologies should be more effectively integrated into detection of foreign object in belt transportation; ③ Sorting robot, computer vision and image recognition technologies should be more effectively integrated into detection and identification of coal-gangue, and improving universality of the algorithm would be one of the development directions of coal-gangue image recognition.
An information interaction method for smart mine
HU Wentao, ZHUO Minmin, ZHAO Lichang, ZHANG Xiaoguang
2020, 46(10): 55-60. doi: 10.13272/j.issn.1671-251x.17585
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In view of "information island" problem which is common in coal mines, a smart mine information interaction method based on resource model and constrained application protocol (CoAP) was proposed from practical point of view. Two key issues to be solved in realizing information interaction are analyzed: data modeling and presentation issue, that is, how information sources display the information and services they can provide; interaction protocol issue, that is, how to communicate between information consumers and producers. For the data modeling and representation issue, a resource model is defined, and the information provided by sensors,corresponding operation authorities and data types can be obtained through resource model definition file. For the interactive protocol issue, the characteristics of declarative protocol and imperative protocol are analyzed and compared, and CoAP is selected as the information interaction protocol which is more in line with the openness and expansibility requirements of coal mine Internet of things. Experimental results show that the method can increase flexibility through options and resources on the basis of maintaining the stability of the interfaces, and can easily and quickly implement information interaction operations such as creation, query, modification, deletion and notification; unified information interaction can be easily achieved by modifing existing equipments software, which lays a foundation for realization of smart mine.
Discussion on construction and key technologies of intelligent mine from production perspective
LUO Mingkun, LI Sheng, FAN Chaojun
2020, 46(10): 61-68.. doi: 10.13272/j.issn.1671-251x.2020030033
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In view of existing problems in construction of intelligent working face of coal mine in China, such as thin thickness of mining coal seam, large Platts coefficient of mining coal seam, main cutting track is memory cutting, and poor adaptability to complex geological conditions, a hierarchical design concept of intelligent mine was put forward combining with a wealth of experience and application requirements of site production of coal enterprises. Intelligent mine system was divided into four levels, namely perception control layer, communication layer, data layer and application layer. At the same time, the functions and construction contents of each level were defined, each level is independent and relies on each other. The key technologies of intelligent mine construction was discussed, it is pointed out that many key technologies, such as multi-source sensor system construction, underground complex condition information transmission, intelligent mine cloud platform development, safety production system construction, intelligent linkage control of mine equipment, intelligent mine emergency response and so on, are the foundation of intelligent mine construction. In particular, cloud platform development and safety production system construction are the core of intelligent mine construction. In view of the traditional concept, fund raising, talent team and technical problems, the corresponding countermeasures were put forward. It is suggested that the construction of intelligent mine should follow the construction idea of "overall consideration, clear priorities, module construction, step-by-step implementation, base demonstration", which provides a reference for the construction of intelligent mine.
Optimal energy saving control of mine coal transportation system based on machine visio
GUO Weidong, LI Ming, KANG Junming, LEI Meng, ZHU Meiqiang
2020, 46(10): 69-75. doi: 10.13272/j.issn.1671-251x.17625
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In order to optimize control of energy saving, the key to coal transportation system is real-time detection of coal flow of belt conveyor and frequency conversion speed regulation control according to coal flow. At present, most of mine belt conveyor adopts frequency conversion drive mode, but frequency converter does not adjust speed in stable operation stage, and keeps running under power frequency, so optimal energy saving of coal transportation system cannot be realized. Aiming at the above problem, an optimal energy saving control method of mine coal transportation system based on machine vision was proposed. Real-time coal flow image of belt conveyor is obtained by using laser emitter to assist digital camera, and noise interference of abnormal highlight spot in the image is removed through preprocessing. Direction template method is adopted to extract center line of laser stripe in the image and linear interpolation method is used to repair broken center line. Center line of belt laser baseline under no-load state and center line of coal flow laser profile under load state are superimposed to form a closed envelope curve, and instantaneous coal flow in the section enclosed by the curve is calculated. PLC fuzzy controller controls inverter output frequency according to expected belt speed calculated depending on coal flow and current belt speed collected by speed sensor, and then adjusts motor speed, so as to realize automatic adjustment of operating speed of belt conveyor according to coal flow. Information processing platform of ground control center is responsible for data collection, processing and display, and realizes visual monitoring and intelligent management of the mine coal transportation system. The method can quickly and effectively detect coal flow and adjust operating speed of belt conveyor in real time according to the coal flow, so as to achieve goal of energy saving, consumption reduction and economic operation of the mine coal transportation system.
Mine flood perception method based on spatiotemporal generalization modeling in Gabor domai
CAO Yuchao
2020, 46(10): 76-79. doi: 10.13272/j.issn.1671-251x.17666
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Compared with coal and rock images, water inrush texture in mine water inrush images has strong variability characteristics in spatiotemporal domain. Existing mine flood identification methods based on image texture features have limited extraction ability and low recognition rate for complex water inrush texture features. For the above problems, a mine flood perception method based on spatiotemporal generalization modeling in Gabor domain is proposed. In the method, Gabor decompositions of training sample images and tested sample images under different receptive fields and directions are carried out separately, and expectation and standard deviation of each sub-band are combined to form learning feature vector and the tested one in a direction. Spatiotemporal generalization modeling of the feature vectors is carried out according to the minimum entropy principle, so as to remove spatiotemporal sensitivity. Angles between each component of the feature vector are taken as the similarity measure of similarity comparison between the learning feature vector and the tested one, so as to realize water inrush recognition. The experimental results show that recognition rate of the method is 89.4% and recognition time is 136 ms, which basically meets real-time perception demand of mine flood.
Deformation and failure characteristics and support technology of deep roadway with composite roof
QIN Haizhong, FU Yukai, WANG Tao
2020, 46(10): 80-86. doi: 10.13272/j.issn.1671-251x.2020020009
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In view of problems of deep roadway with composite roof, such as easily roof falling, large deformation and difficult support, taking 53182 roadway of Chengzhuang Coal Mine of Jincheng Blue Flame Coal Industry Co., Ltd. as research object, deformation and failure characteristics of deep roadway with composite roof were analyzed. It is found that roof deformation is dominated by shallow separation layer, which mainly occurs at interface of different rock strata. Shear deformation of bolts in top corner and two sides of roof occurs mainly at coal-rock interface, and shear deformation of bolts in the middle of roof is relatively large at weakly cemented strata and interface between anchor section and free section. Roof strata experiences processes of original rock state during initial excavation of roadway, and stable state, critical instability state and instability state after roadway excavation. The numerical simulation results show that with the increase of bolt preload, plastic zone range and vertical displacement of roof decrease obviously, which indicate bolt has better inhibiting effect on roof separation and subsidence. High prestressed bolt plays an active support role and greatly improves self-bearing capacity of surrounding rock. Support countermeasures of deep roadway with composite roof with high prestressed long and short anchor cables combined with steel mesh and W steel strip were put forward, which could greatly improve support stiffness of composite roof, form constraints on roof subsidence and separation, and enhance overall stability of composite roof strata. The engineering practice shows that high prestressed support effectively controls separation and subsidence of composite roof. Shallow separation value is controlled within 30 mm, deep separation value is controlled within 10 mm, two sides displacement is controlled within 80 mm, and roof subsidence is controlled within 43 mm. The above values indicate stability and integrity of surrounding rock.
Calculation and simulation research on leakage magnetic field of broken wire damage of wire rope
DOU Liancheng, ZHAN Weixia
2020, 46(10): 87-91. doi: 10.13272/j.issn.1671-251x.2019120048
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In view of problems that states and characteristics of wire rope defects are random, and it is too difficult to physically calculate the damage of different forms of wire rope, two-dimensional magnetic load model is used to analyze leakage magnetic field of broken wire damage of wire rope, and calculation formula and magnetic field distribution of axial leakage magnetic field are obtained. The finite element simulation analysis of the axial leakage magnetic field of broken wire of wire rope is carried out by Ansoft Maxwell software to verify the correctness of the theoretical analysis result based on the magnetic charge model. The analysis results show that the magnetic flux leakage intensity changes obtained by the two methods are roughly the same, which can reflect the change law of axial flux leakage component of a single wire rope; within a certain range, as the fracture width increases, the axial flux leakage intensity of defects presents a nonlinear decreasing trend, and a single peak gradually differentiates into two peaks.
Coal mine dual prevention information system based on Apriori algorithm
HUANG Yuxin, YAN Zhenguo, FAN Jingdao, LI Chuan
2020, 46(10): 92-98. doi: 10.13272/j.issn.1671 -251x.2020040095
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The current information systems have relatively single function, and most of them are still in the stage of simple mathematical statistics and information reporting. Moreover, most systems split risk control and accident hidden into two different systems for management, and fail to integrate them, so it is difficult to achieve closed management, thus resulting many vulnerabilities in management process;At the same time, a large amount of data collected by the system in the daily safety production process of coal mine has not been effectively utilized, so it is difficult to find deep laws hidden in the data and the association rules between the data, resulting in a large amount of data waste. For the above problems,a coal mine dual prevention information system based on Apriori algorithm was designed, and the system architecture and function realization were introduced in detail. Based on the Apriori algorithm and basic theory of the dual prevention mechanism of coal mine, hidden dangers of accidents and risk control were integrated,while realizing the closed management of the two, the Apriori algorithm is used to conduct in -depth analysis of the hidden danger data of accidents, excavate its potential association rules, and formulate relevant daily preventive measures through analysis of the potential association rules to realize risk of accidents source identification, control and troubleshooting and control of hidden danger. The application results show that the system realizes full life cycle management of hidden accidents and risk management. Through in -depth analysis, the law of occurrence of hidden accidents is obtained, and the prevention, early warning and pre -control of coal mine accidents are realized, and the level of coal mine safety production management is improved.
Measurement and analysis of underground ultra wide band signal path loss
DOU Xueli, NIU Yonggang, YIN Peng, LI Jingsheng, LUAN Liangliang, LAN Xiang
2020, 46(10): 99-103. doi: 10.13272/j.issn.1671 -251x.17667
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In view of problem that theoretical modeling and simulation experiment are mostly used in research of underground path loss characteristics of high -precision ultra wide band (UWB) signal, actual measurement research of UWB signal is less. The path loss measurement and analysis of UWB signal are carried out in two typical scenarios of running roadway of overhead passenger device (monkey car) with relatively common environmental conditions such as roadway size, roadway wall material and pipe facilities，and heading face with bad environment, high coal dust concentration and serious water accumulation. The results show that: ① The path loss index of UWB signal in two kinds of roadway environments is less than 2, and wave guide effect of roadway leads to better propagation characteristics of UWB signal than that of free space. The base station deployment interval of the UWB positioning system in roadway is larger than that of the ground free space propagation scene.② In the same mine, the roadway environment is different, and the path loss characteristics are also different. The path loss index and shadow fading variance of heading face are significantly different from those of monkey car running roadway. ③ From comparison of single test point in roadway of heading face, the path loss in NLOS environment is larger than that in LOS environment. More intensive positioning base stations need to be deployed in roadway in NLOS environment.The results can be used to guide deployment scheme design of mine UWB precise positioning system.
Research on stress distribution characteristics of coal pillar in fully mechanized caving face
LIU Ming, CAO Minyuan, LI Bo
2020, 46(10): 104-108. doi: 10.13272/j.issn.1671 -251x.17533
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For fully mechanized caving face with high gas and fault occurrence, coal pillar with reasonable reserved width can not only support overlying strata pressure, but also isolate gas in goaf and reduce gas diffusion. However, there is a lack of research on distribution characteristics of surrounding rock stress under the condition of reasonable reserved width of different coal pillars at present, and it is difficult to accurately determine the basis for calculating reserved width of coal pillars because factors affecting coal pillar width in different mines are different. For the above problems, taking M9 -10 coal seam on fully mechanized caving face of Tunbao Coal Mine as engineering background, the minimum width of coal pillar is obtained by theoretical calculation, and stress distribution characteristics around coal pillars with different width are studied by numerical simulation. The results show that: reasonable coal pillar width is 30 -40 m; horizontal stress in coal pillar tends to goaf side with the increase of coal pillar width, which verifies that the increase of coal pillar width can transfer influence of horizontal stress on roadway, so as to improve roadway stability; vertical stress of coal pillar has characteristics of double wave peaks,and the vertical stress peak and stress concentration coefficient at roadway side and goaf side decrease with the increase of coal pillar width; location of stress peak at roadway side is 2.5 m away from the roadway, then as the distance from the roadway increases, the vertical stress first decreases rapidly and then increases slowly, and then slowly decreases after the stress peak appears on the goaf side. In order to verify rationality of 40 m coal pillar width, field monitoring of drilling stress and gas concentration is carried out on the fully mechanized caving face. The result shows that the coal pillar width of 40 m can meet actual requirements of roadway support strength and gas diffusion.
Networking architecture of large -scale electromechanical equipment in coal mine based on Redis
CHEN Qing
2020, 46(10): 109-113. doi: 10.13272/j.issn.1671-251x.2020050019
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Networking architecture of large -scale electromechanical equipment in coal mine based on FTP has problems such as complex data exchange protocol, high pressure of database reading and writing, easy damage of server disk and failure of reading text file after network blocking. According to data characteristics of large -scale electromechanical equipment in coal mine, a networking architecture of large -scale electromechanical equipment in coal mine based on Redis was proposed. The collected data of large -scale electromechanical equipment in coal mine is transmitted from Redis client to Redis server in Redis publish/subscribe mode, which reduces data flow link and improves efficiency of data transmission. The Redis server pushes the received data to data parsing program, which completes data reverse parsing, and the parsed real -time data is cached into Redis memory database, so as to improve real -time data access speed and reduce reading and writing pressure of relational database. Data transmission interrupt caching mechanism is used to realize data continuous transmission after interruption and avoid data loss. Distributed deployment of the Redis server and data parsing program is realized by using Redis cluster function, which improves efficiency of data parsing. The practical application results show that the proposed architecture has characteristics of low real -time data delay and fast real -time data query speed, which can meet needs of superior supervision department of coal mine for online, rapid and effective control of large -scale electromechanical equipment in coal mine.
Video monitoring system of mine working face based on wireless multi -hop network
LIANG Hong
2020, 46(10): 114-118. doi: 10.13272/j.issn.1671 -251x.17413
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Abstract:
In view of problems that underground wired transmission mode has difficulty in cable deployment and cables are extremely vulnerable, traditional wireless local area network has short communication distance and cannot adapt to the long and narrow environment of coal mine underground working face, a video monitoring system of mine working face based on wireless multi -hop network was designed.The system consists of video acquisition node,wireless multi -hop network (including gateway nodes, transmission nodes and network switches) and clients. The video acquisition node completes video information collection, encoding and packaging, and sends the collected video as data stream through the push streaming software MJPG -streamer; the wireless multi -hop network adopts optimal link state routing (OLSR) protocol for ad -hoc networking, so as to realize the connection between collection node and gateway node; the clients receive the video streams from various monitoring channels, and realize the functions of multi -channel video real -time display, remote monitoring, storage and playback. The actual test results show that after 3 -hop transmission, the system throughput is 10.1 Mbit/s, the packet loss rate is 2.2%, and the average delay jitter and system end -to -end transmission delay are better than traditional wireless LAN -based video transmission systems. Practical application results show that when the distance between nodes in the working face is within 70 m, the system operates well; the video monitoring system based on wireless multi -hop network and the video monitoring system based on wired transmission basically have the same image quality.

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