In order to improve efficiency of coal seam gas drainage, many fracturing techniques, such as waterjet fracturing, hydraulic fracturing and explosive fracturing, etc, have been developed and widely used in China coal ...In order to improve efficiency of coal seam gas drainage, many fracturing techniques, such as waterjet fracturing, hydraulic fracturing and explosive fracturing, etc, have been developed and widely used in China coal mining industry. How- ever, during the engineering applications, it is observed that the efficiency of gas drainage initially improves, but reduces there- after. Thus, it is speculated that the contrasts in coalbed methane drainage efficiency may reflect variation of the closure be- havior of the artificial fracture created. Based on comprehensive gas drainage monitoring data in underground coal mines, the work presented herein uses numerical simulation to show the behavior of the time-dependent closure of coal seam fractures as- sociated with various levels of waterjet fracturing parameters and geomechanical conditions.展开更多
Dam structures are prime targets during wars,and a tragedy is likely to happen in a populated area downstream of a dam exposed to explosions.However,experimental investigations of the failure of a concrete gravity dam...Dam structures are prime targets during wars,and a tragedy is likely to happen in a populated area downstream of a dam exposed to explosions.However,experimental investigations of the failure of a concrete gravity dam subjected to underwater explosion(UNDEX)are extremely scarce.In this study,centrifuge tests and numerical simulations were performed to investigate the failure of a concrete gravity dam subjected to a near-field UNDEX.The results revealed the existence of two tensile fractures inside the dam,one in the upper part and the other in the lower part.Due to the narrowness of the upper part,there were coupled effects of bending tensile loads in the upstream face and a reflected tensile stress wave in the downstream face,resulting in severe tensile damage to the upper part in both the upstream and downstream faces.The fracture in the lower part was measured at around one third of the height of the dam.This fracture was produced mainly by the bending tensile loads in the upstream face.Driven by those loads,this fracture started from the upstream face and developed towards the downstream face,with a horizontal angle of about 15?.The underlying mechanisms behind the two tensile fractures were confirmed by recorded strain histories.The dam failures presented in this study are similar to those produced in historical wars,in which dams were under similar attack scenarios.展开更多
We calculate numerically the hydrodynamic evolution of a γ-ray burst fireball. The results show that refluence will emerge during fireball expansion due to negative-pressure effect. The refluence will collide with ou...We calculate numerically the hydrodynamic evolution of a γ-ray burst fireball. The results show that refluence will emerge during fireball expansion due to negative-pressure effect. The refluence will collide with outward fluid, then shock wave will form. Electrons moving between the inward and outward fluid shells can be accelerated to 104–105 MeV by one order Femi-type acceleration with high efficiency after several collisions. Radiation of electrons with such high energy may be the observed γray bursts.展开更多
文摘In order to improve efficiency of coal seam gas drainage, many fracturing techniques, such as waterjet fracturing, hydraulic fracturing and explosive fracturing, etc, have been developed and widely used in China coal mining industry. How- ever, during the engineering applications, it is observed that the efficiency of gas drainage initially improves, but reduces there- after. Thus, it is speculated that the contrasts in coalbed methane drainage efficiency may reflect variation of the closure be- havior of the artificial fracture created. Based on comprehensive gas drainage monitoring data in underground coal mines, the work presented herein uses numerical simulation to show the behavior of the time-dependent closure of coal seam fractures as- sociated with various levels of waterjet fracturing parameters and geomechanical conditions.
基金Project supported by the National Natural Science Foundation of China(Nos.51879283 , 51339006)。
文摘Dam structures are prime targets during wars,and a tragedy is likely to happen in a populated area downstream of a dam exposed to explosions.However,experimental investigations of the failure of a concrete gravity dam subjected to underwater explosion(UNDEX)are extremely scarce.In this study,centrifuge tests and numerical simulations were performed to investigate the failure of a concrete gravity dam subjected to a near-field UNDEX.The results revealed the existence of two tensile fractures inside the dam,one in the upper part and the other in the lower part.Due to the narrowness of the upper part,there were coupled effects of bending tensile loads in the upstream face and a reflected tensile stress wave in the downstream face,resulting in severe tensile damage to the upper part in both the upstream and downstream faces.The fracture in the lower part was measured at around one third of the height of the dam.This fracture was produced mainly by the bending tensile loads in the upstream face.Driven by those loads,this fracture started from the upstream face and developed towards the downstream face,with a horizontal angle of about 15?.The underlying mechanisms behind the two tensile fractures were confirmed by recorded strain histories.The dam failures presented in this study are similar to those produced in historical wars,in which dams were under similar attack scenarios.
文摘We calculate numerically the hydrodynamic evolution of a γ-ray burst fireball. The results show that refluence will emerge during fireball expansion due to negative-pressure effect. The refluence will collide with outward fluid, then shock wave will form. Electrons moving between the inward and outward fluid shells can be accelerated to 104–105 MeV by one order Femi-type acceleration with high efficiency after several collisions. Radiation of electrons with such high energy may be the observed γray bursts.
