A uniaxial load experiment on coal rocks at different stress rates was carried out,based on the characteristics of acoustic emission(AE)signals in cracking coal rocks,decomposition,de-noising and reconstruction for th...A uniaxial load experiment on coal rocks at different stress rates was carried out,based on the characteristics of acoustic emission(AE)signals in cracking coal rocks,decomposition,de-noising and reconstruction for the AE signals through wavelet packet transform for solving the current problems created by the presence of noise in AE signals and the existing problems in AE signal processing.The results show that the various characteristics of AE signals in coal rocks cracking under different situations can be clearly reflected,after the AE signals are de-noised by the wavelet packet.Compared to dry coal rocks,the number of AE occurrences in damp coal rocks was significantly reduced,as well as the average amplitude.The number of AE occurrences in damp and dry coal rocks clearly increased with increases in the loading rate,but the largest amplitude of the AE signals in damp coal rocks has been reduced.There is no clear evidence of change in dry coal rocks.展开更多
This article presents the evolution law of temperature fields in a large-scale laboratory Underground Coal Gasification reactions using Ulanqab lignite under actual conditions.The results show that in the cultivation ...This article presents the evolution law of temperature fields in a large-scale laboratory Underground Coal Gasification reactions using Ulanqab lignite under actual conditions.The results show that in the cultivation stage of oxidation zone,the main direction of the temperature field expansion is consistent with the crack direction of the coal seam.In the gasification stabilization stage,the main direction of the temperature field expansion is along the channel.The temperature of the coal seam and the overlying rock mass at its interface with the furnace directly above the gasification channel is equivalent to that of the coal seam temperature,and this temperature is much greater than the temperatures observed near both side walls of the gasification channel at the interface.However,temperatures perpendicular to the axis of the gasification channel are similar at a vertical distance of 40 cm away from the interface.The temperature distributions indicate that the transmission of heat through the overlying rock mass is more rapid in the vertical direction than in the horizontal direction.Moreover,some degree of thermal dispersion is observed in the vertical direction near the outlet.The thermal dispersion coefficient is 0.72 and dispersion angle γ is 78.7°.展开更多
In this paper, simulated experiment device of coal and gas outburst was employed to perform the experiment on gas-containing coal extrusion. In the experiment, coal surface cracks were observed with a high-speed camer...In this paper, simulated experiment device of coal and gas outburst was employed to perform the experiment on gas-containing coal extrusion. In the experiment, coal surface cracks were observed with a high-speed camera and then the images were processed by sketch. Based on the above description, the paper studied the fractal dimension values from different positions of coal surface as well as their changing laws with time. The results show that there is a growing parabola trend of crack dimension value in the process of coal extrusion. Accordingly, we drew the conclusion that extruded coal crack evolution is a process of fractal dimension value increase. On the basis of fractal dimension values taken from different parts of coal masses, a fractal dimension of the contour map was drawn. Thus, it is clear that the contour map involves different crack fractal dimension values from different positions. To be specific, where there are complicated force and violent movement in coal mass, there are higher fractal dimension values, i.e., the further the middle of observation surface is from the exit of coal mass, and the lower the fractal dimension value is. In line with fractal geometry and energy theory of coal and gas outburst, this study presents the relation between fractal dimension and energy in the process of extruding. In conclusion, the evolution of crack fractal dimension value can signify that of energy, which has laid a solid foundation for the quantification research on the mechanism of gas-containing coal extrusion.展开更多
The split-Hopkinson pressure bar(SHPB)and digital image correlation(DIC)techniques are combined to analyze the dynamic compressive failure process of coal samples,and the box fractal dimension is used to quantitativel...The split-Hopkinson pressure bar(SHPB)and digital image correlation(DIC)techniques are combined to analyze the dynamic compressive failure process of coal samples,and the box fractal dimension is used to quantitatively analyze the dynamic changes in the coal sample cracks under impact load conditions with different loading rates.The experimental results show that the fractal dimension can quantitatively describe the evolution process of coal fractures under dynamic load.During the dynamic compression process,the evolution of the coal sample cracks presents distinct stages.In the crack propagation stage,the fractal dimension increases rapidly with the progress of loading,and in the crack widening stage,the fractal dimension increases slowly with the progress of loading.The initiation of the crack propagation phase of the coal samples gradually occurs more quickly with increasing loading rate;the initial cracks appear earlier.At the same loading time point,when the loading rate is greater,the fractal dimension of the cracks observed in the coal sample is greater.展开更多
基金Financial support for this study,provided by the Key Basic Research Program of China(973)(No.2007CB209407),is gratefully acknowledged
文摘A uniaxial load experiment on coal rocks at different stress rates was carried out,based on the characteristics of acoustic emission(AE)signals in cracking coal rocks,decomposition,de-noising and reconstruction for the AE signals through wavelet packet transform for solving the current problems created by the presence of noise in AE signals and the existing problems in AE signal processing.The results show that the various characteristics of AE signals in coal rocks cracking under different situations can be clearly reflected,after the AE signals are de-noised by the wavelet packet.Compared to dry coal rocks,the number of AE occurrences in damp coal rocks was significantly reduced,as well as the average amplitude.The number of AE occurrences in damp and dry coal rocks clearly increased with increases in the loading rate,but the largest amplitude of the AE signals in damp coal rocks has been reduced.There is no clear evidence of change in dry coal rocks.
基金supported by the National High Technology Research and Development Program of China(No.2011AA050106)Hubei Technological Innovation Special Fund(CN)(No.343-0402-YQN-TWEP).
文摘This article presents the evolution law of temperature fields in a large-scale laboratory Underground Coal Gasification reactions using Ulanqab lignite under actual conditions.The results show that in the cultivation stage of oxidation zone,the main direction of the temperature field expansion is consistent with the crack direction of the coal seam.In the gasification stabilization stage,the main direction of the temperature field expansion is along the channel.The temperature of the coal seam and the overlying rock mass at its interface with the furnace directly above the gasification channel is equivalent to that of the coal seam temperature,and this temperature is much greater than the temperatures observed near both side walls of the gasification channel at the interface.However,temperatures perpendicular to the axis of the gasification channel are similar at a vertical distance of 40 cm away from the interface.The temperature distributions indicate that the transmission of heat through the overlying rock mass is more rapid in the vertical direction than in the horizontal direction.Moreover,some degree of thermal dispersion is observed in the vertical direction near the outlet.The thermal dispersion coefficient is 0.72 and dispersion angle γ is 78.7°.
基金the National Natural Science Foundation of China (Nos. 50904067 and 51104156)the New Century Excellent Talents in University (No. NCET-10-0768) for their support of this project
文摘In this paper, simulated experiment device of coal and gas outburst was employed to perform the experiment on gas-containing coal extrusion. In the experiment, coal surface cracks were observed with a high-speed camera and then the images were processed by sketch. Based on the above description, the paper studied the fractal dimension values from different positions of coal surface as well as their changing laws with time. The results show that there is a growing parabola trend of crack dimension value in the process of coal extrusion. Accordingly, we drew the conclusion that extruded coal crack evolution is a process of fractal dimension value increase. On the basis of fractal dimension values taken from different parts of coal masses, a fractal dimension of the contour map was drawn. Thus, it is clear that the contour map involves different crack fractal dimension values from different positions. To be specific, where there are complicated force and violent movement in coal mass, there are higher fractal dimension values, i.e., the further the middle of observation surface is from the exit of coal mass, and the lower the fractal dimension value is. In line with fractal geometry and energy theory of coal and gas outburst, this study presents the relation between fractal dimension and energy in the process of extruding. In conclusion, the evolution of crack fractal dimension value can signify that of energy, which has laid a solid foundation for the quantification research on the mechanism of gas-containing coal extrusion.
基金Projects(51822403,51827901)supported by the National Natural Science Foundation of ChinaProject(2019ZT08G315)supported by the Department of Science and Technology of Guangdong Province,China。
文摘The split-Hopkinson pressure bar(SHPB)and digital image correlation(DIC)techniques are combined to analyze the dynamic compressive failure process of coal samples,and the box fractal dimension is used to quantitatively analyze the dynamic changes in the coal sample cracks under impact load conditions with different loading rates.The experimental results show that the fractal dimension can quantitatively describe the evolution process of coal fractures under dynamic load.During the dynamic compression process,the evolution of the coal sample cracks presents distinct stages.In the crack propagation stage,the fractal dimension increases rapidly with the progress of loading,and in the crack widening stage,the fractal dimension increases slowly with the progress of loading.The initiation of the crack propagation phase of the coal samples gradually occurs more quickly with increasing loading rate;the initial cracks appear earlier.At the same loading time point,when the loading rate is greater,the fractal dimension of the cracks observed in the coal sample is greater.
