Numerical simulation of failure of coal and rock blocks under different dynamic loads

The numerical simulation of HJC constitutive model is carried out to analyze the dynamic changes of the stress field, strain field and energy field of coal and rock mass under dynamic loading process. The results show that the change of load change rate has the greatest influence on the failure mode of coal and rock mass, followed by the maximum pressure value of the load, and finally the action time. Under the five kinds of load pressures, the kinetic energy, internal energy and total energy of coal and rock mass are consistent with time. When coal and rock mass is not destroyed, these three kinds of energy increase with time. When coal and rock mass is destroyed, the kinetic energy is finally reduced to zero, and the internal energy is reduced. The more severe coal and rock mass damage, the greater the reduction of the three types of energy. When coal and rock mass reaches the critical stress, only minor damage occurs, and then the maximum damage is reached when the maximum total energy is reached. When the pressure and the action time reach a certain value, coal and rock mass will be destroyed, and the change of the load change rate will increase the damage capacity of coal and rock mass

The pressure relief protection effect of different strip widths, dip angles and pillar widths of an underside protective seam.

To design underside protective seam strip layout. Similarity model experiments, numerical simulations and theoretical calculations are used to quantitatively study the pressure relief protection effect of different strip widths, dip angles and coal pillar widths of a thin underside protective seam under deeply buried conditions. The optimal strip width range is obtained according to the change law of strain during the mining process of the underside protective seam in a similar model experiment. The change law of the expansion of the protected coal seam is obtained and the fitting surfaces among the dip angle and strip width of the coal seam with the protection distance and pressure relief angle along the strike and dip of the protected coal seam are established according to the numerical simulation results of underside protective seam mining. It is concluded that the best pressure relief effect can be achieved when the dip angle is 16.7° and the strip width is 70 m. According to the stability threshold of coal pillars considered in strip mining theory, the coal pillar width is calculated to be 50 m. Similarity model experiments and numerical simulations of protected coal seam mining verify the pressure relief effect of the designed protective seam strip width and pillar width. A calculation method of the protective seam strip width, position and pillar width required by the specific width of the protected seam is proposed

Progress on the use of satellite technology for gravity exploration

In this paper, the technological progress on Chinese gravity exploration satellites is presented. Novel features such as ultra-stable structure, high accurate thermal control, drag-free and attitude control, micro-thrusters, aerodynamic configuration, the ability to perform micro-vibration analyses, microwave ranging system and mass center trimmer are described. Keywords: Ultra-stable structure, Precision thermal control, Drag-free, Micro-thruster, K-band ranging, Aerodynamics, Micro-vibration, Gravity satellit