| The main disasters of underground coal mine are coal and gas outburst and gas explosion. As is known, gas migration in underground coal mine often results in the gas excessive and even coal-mining pit explosion. To explore the regularity of such gas migration and risk, it is necessary to simulate gas migration and evaluate the risk of gas aggregation in underground coal mine, and then provide decision basis for mine management. The behaviors of gas migration in underground coal mine are special fluid flow with characteristics of multicomponents, multiphase, seepage, buoyancy and turbulence. Lattice Boltzmann method (LBM)is a new method to solve the partial differential equation of fluid systems and a means of modeling for physical phenomenon. It can simulate a rich variety of behaviors, including multiphase flow, multicomponent flow, seepage, et al. So, this paper wishes to propose an approach to the coal-mining gas migration simulation based on the lattice Boltzmann method, major achievements of this thesis are as follows:1.Simulation of concentrative emission gas spreading in tunnel systems based on LBM. A simulation model of concentrative emission gas spreading in tunnel systems has been developed, in which a double distributed velocity-concentration LBM was adopted. In the model, in order to simulate the complicated situations, tunnels were separated into some relative regular blocks through the block coupling algorithms. Each block was calculated in parallel, with the data exchanged only on boundaries. As a result, the redundant grids are removed and the grid computation has been simplified with the system resource efficiency ameliorated. A method which can process rough surface of tunnel or working face by adding flow resistance in LBM model was provided. The simulation results showed that the so-called LBM model is in a position to obtain essential data and information on the velocity, pressure and visual information about the gas in the tunnels. The simulation results also help to disclose the regularities on the distribution of gas bulk fraction in the tunnels, and those on the speed, pressure and bulk fraction of the gas in different points and places in the tunnels, which are of great benefit for mine safety control and management.2. Simulation of gas migration in mining stope based on LBM. Studying the Brinkman-Forchheimer-Darcy amended law, this paper wishes to propose a control system which can reflect the characters of gas migration regularity in heterogeneous goaf of coal mines. To make the complicated control system simple, a Lattice Boltzmann(LB) model constructed to simulate the gas seepage velocity field with another LB model constructed to simulate the gas concentration change have been established. Simulation contrasts in control gas migration methods were also done. This paper also constructed a unified simulation model of gas migration in mining stope based on LBM. The mixed air movement in mining stope is very complex with turbulent flow in the working face and seepage movement in the goaf with heterogeneous porous media. The mining stope unified simulation model reflects the characters of these two fields by different relaxation times and distribution functions. A case study showed:This method can simulate and analyze the situation of gas migration in mining stope and get mass data about gas migration such as speed and gas bulk fraction in every time and every space of the mining stope, and many laws are gained such as laws of streamtrace, speed and gas distribution.3.Simulation of gas migration in coal seam based on LBM. Two 3D double grid LB models which can simulate diffusion of gas adsorbed in pore space and seepage of free gas in fracture have been constructed for Isothermal and non-isothermal coal seam respectively. Double grid technique has been adopted to simulate gas diffusion and seepage in double-porosity of same coal seam, that is, a fine grid was used to simulate adsorbed gas desorbing form pore space, becoming free gas and diffusing to fracture; another coarse grid was used to simulated free gas seeping process in fracture. Two grids exchanged data by interpolation. By this way, simulation of gas migration in coal seam is realized. A case study showed, this method can simulate gas migration in coal seam effectively and get gas mass data such as speed and gas concentration in every time and every space of coal seam, and also obtain law of gas flow streamtrace, speed, press and gas migration. This method can provide a new method for revealing law of gas migration, emission, outburst and volume of emission, and also provide basis for risk evaluation and analysis. 4. Gas migration in stope when reversing air-current. A multi-field coupled model with fields of speed, concentration and temperature has been constructed after analyzing the flow field characteristics when reversing air-current. The paper presented algorithm and simulation case of gas migration in reversing air-current status. The simulation results present basis for decision making when fire accident occurs whether we can control the fire smoke flow by using reversing air-current method. A case study showed, the simulation can get mass data such as gas flow speed, pressure, and temperature and gas bulk fraction in tunnel and goaf when reversing air-current. It can provide a new method to reveal gas migration when reversing air-current, and provide basis for risk evaluation and analysis of reversing air-current.5.Risk evaluation method of gas aggregation based on both-branch decision-making and fuzzy Petri net. After comprehensively considered with factors such as promoting and counteracting influencing factors, an evaluation risk method of gas aggregation in tunnels which based on both-branch decision-making and fuzzy Petri net is presented. A case study showed:The Evaluation risk method can effectively describe the propagation relationship of gas aggregation factors. The model is expressed by figure and is easy to understand, which fully reflects the ability of both-branch fuzzy Petri net to depict the dynamic behaviors of system. The reasoning process adopts simple matrix calculation which improves the efficiency of the risk evaluation.This paper researches on numeric simulation of gas migration in underground coal mine. It discloses the regularities on the gas emission, diffusion, migration, buoyancy and aggregation, and then provides the regularities of gas migration, aggregation position and the control methods. The risk evaluation method of gas aggregation based on both-branch decision-making and fuzzy Petri net can provide decision basis for preventing gas aggregation and coal-mining pit explosion.
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