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Underground coal gasification (UCG) as an alternative coal mining technology is attracting much attention. However, due to the high experimental cost of UCG, the evolution mechanism of coal seam should be deeply explored prior to the implement of experiments. By virtue of the great computational power of computers, the computational fluid dynamics (CFD) is able to simulate the production process of UCG at a relatively lower cost. The in-situ ignition and combustion of deep coal seam heated by 1 000 K flue gas is simulated and the changes of temperature, molar O2 fraction and porosity are analyzed by the CFD software, Fluent, developed by Ansys cor-poration. It is elucidated that pumping 1 000 K flue gas for 500 s is inadequate for coal seam ignition, while 1 000 s heating has been enough for coal seam ignition. On the internal surface of coal seam, the high temperature is accumulated in the 0−0.6 m coal seam near inlet. The maximum temperature before ignition is below inlet temperature of heating flue gas, 1 000 K, while the maximum temperature after ignition exceeds 1 000 K and reaches up to 1 250 K. Almost all O2 is consumed in the high-temperature zone, while less than 2% molar O2 fraction arrives at the internal surface of coal seam in other lower-temperature zones. The porosity rapidly increases in high-temperature zone and at 1000 s the porosity in the part of coal seam reaches up to 0.9. In the interior of coal seam, the thicker the coal seam is, the lower the temperature rises. The maximum temperature on 7 cm line is only 500 K at 1 000 s and 2 000 s, much lower than that on the internal surface of coal seam when it is heated for the same time. During 2 000 s ignition, little O2 penetrates 7 cm and 14 cm coal seam and the porosities of interior coal seam are all below 0.4. The low porosities are attributed to the low temperature and low molar O2 fraction. The simulation on temperature, molar O2 fraction and porosity may provide a reference for how to promote the reaction in the interior of coal seam.

In order to accurately evaluate the strength and fatigue characteristics of the double arc planetary gear transmission system in actual work，the three-dimensional geometric model of the double-arc planetary gear transmission system is established，by using HyperMesh a high-quality hexahedral mesh is obtained，combining with Ansys a finite element model is established and the transient dynamic analysis is carried out，the change curve of equivalent stress and contact pressure during the movement of the transmission system are obtained. At the same time，the fatigue life analysis is carried out based on the finite element model using Fatigue Tool. The results show that the stress of the transmission system is concentrated on the meshing end surface of the planetary gear and the sun gear during the meshing process. The contact stress changes smoothly，and the entire structure has a small impact. Fatigue damage is concentrated on the meshing position of the planetary gear and the sun gear.