Search

Achieving crack propagation and rapid deterioration of high-temperature rock masses by using cooling shocks is important for improving the efficiency of low-permeability oil and gas production, geothermal well pumping, and other engineering facilities. In this study, the temperatures of four groups of granite samples with holes were set as 150, 350, 550, and 750 °C. To study the crack propagation in high-temperature granite suffering from different cooling shocks, the cooling shock temperatures were set as −20, 0, 20, and 25 °C in experiments and an RFPA2D-Thermal numerical simulation. The results indicated that in the range of 350–550 °C, there is a critical temperature for the sudden change of the crack macroscopic shape. Numerous open cracks appeared on the rock surface, and the thermal damage caused by the cooling shocks was significantly enhanced within the temperature range. Additionally, under the action of the cooling shocks, cracks were initiated in the high-temperature granite at the boundary of the cooling shock hole and the sample and extended radially to the interior of the sample. Moreover, in the process of crack propagation, there was always an annular heat-balance zone inside the rock. Thus, the cracks generated at the boundary of the cube are not connected to the cracks formed at the center hole. A larger temperature gradient in the rock led to a higher crack propagation rate, larger penetration depth, and higher density of cooling-induced cracks. The results of this study can not only improve the permeability of reservoir rocks but also have important reference value for rock engineering in high-temperature environments. [ABSTRACT FROM AUTHOR]

Dynamic mitigation for the tearing mode instability in the current sheet in collisionless plasmas is demonstrated by applying a wobbling electron current beam. The initial small amplitude modulations imposed on the current sheet induce the electric current filamentation and the reconnection of the magnetic field lines. When the wobbling or oscillatory motion is added from the electron beam having a form of a thin layer moving along the current sheet, the perturbation phase is mixed and consequently the instability growth is saturated remarkably, like in the case of the feed-forward control. [ABSTRACT FROM AUTHOR]

How the outer substance could penetrate through the skin lies in the stratum corneum, because it is the main barrier in the multi-layers of the skin. Supposing the keratin cell with a special geometry as tetrakaidecahedron, the penetration property of stratum corneum was the key problem which was numerically simulated with finite element method. At first the discretization of the stratum corneum region was given in two steps: first, the discretization of the keratin cell; second, the discretization of fattiness that surrounds the keratin. Then there was the work of numerical simulation. In this procedure, the finite element method and the multi-grid method were used. The former was to obtain the discretization of basic elements; the latter was to decrease the high frequency error. At last the visualization of the numerical simulation was shown. [ABSTRACT FROM AUTHOR]