Nonlinear Analysis And Coupling Catastrophe Mechanism Of Coal And Gas Outbursts

Based on theoretical analysis, numerical simulation and filed-testing, the coupling catastrophe mechanism and nonlinear characteristics of coal and gas outbursts are studied in this dissertation.Using the implicit-explicit analytical function of ANSYS/LS-DYNA, the response of laneway surrounding rock under the stress wave is simulated and the induced effect of stress wave is studied. It is found that, under stress wave, tensile stress and compressive stress will occur in laneway surrounding rock and the stress value would increase along with the increase of stress wave intensity.The formation and instable failure of layer-crack structure is the crucial step of coal and gas outburst. Based on fracture mechanics, FEM and self-organization theory, the expansion of single crack, the breakthrough of adjacent parallel cracks and forming mechanics of layer-crack structure under the gas pressure and stress wave are studied. The study indicates that adjacent parallel cracks are broken easily by shearing breakthrough and tensile breakthrough. The factors which affect breakthrough are crack inclination, permutation style and crack distance. The tensile stress generated by unloading and gas stress field can be considered as generalized driving force, by which the non-linear feature in the crack evolvement is analyzed, and the statistic indicates that the length and generating frequency obey the power rule.The procedure of coal and gas outburst can be simplified as the destabilization procedure of the layer-crack structure under the coupling function of crustal stress and gas pressure. The quasistatic process of destabilization of the layer-crack structure is analyzed by the fold catastrophe theory. Then released energy and strength when coal and gas outburst happened are calculated. Moreover, the unified dynamic equation of hyperbolic shallow layer-crack structure is established, and it is found that, along with the increase of dynamic perturbation and gas pressure, layer-crack structure goes through the evolution of from period 1, period 2, and period 3 to chaos state.Phenomenological study is carried out. The chaos attractor of coal and gas outburst in gestation process is identified by analyzing local data. Time delay and embed dimension are calculated using C-C method, subsequently correlation dimension and the largest Lyapunov exponent are calculated. It is discovered that the possibility of coal and gas outburst is closely correlated with correlation dimension and the largest Lyapunov exponent.Based on chaos theory, the prediction method for time series of monitoring data in the process of coal and gas outburst gestation is studied, and results indicate that the prediction accuracy of global region method and zero-order local region method is low, but to adding-weight one-rank local-region method, the reverse is true.