Three-Dimensional Stochastic Distribution Characteristics of Void Fraction in Longwall Mining-Disturbed Overburden of Inclined Coal Seam

AbstractFractures in the overburden induced by mining disturbances provide a channel for fluid flow between the surface and the underground. Mining-induced strata movement and fracture distribution are influenced by the gravity and dip angles of rock seams. In this paper, a new three-dimensional theoretical distribution model for void fraction in each partition of overlying rock strata disturbed by inclined coal seam mining was constructed. Based on the theoretical determination model, the three-dimensional random distribution characteristics for void fraction were obtained by combining the random distribution law of void fraction obtained by similar physical simulation experiments and image processing techniques. Theoretical deterministic models, stochastic theoretical models, and similar physical simulations all show that void fraction distribution in the tendency direction of the coal seam shows a bimodal asymmetric distribution with high and low peaks and a symmetric distribution in the strike direction. The void fraction of the overburden in the central part of the mining area is smaller than that of the surrounding area. The results of the theoretically determined model and stochastic model of the void fraction for the strata with different mining lengths and different coal seam inclinations were compared with the results of similar simulation experiments, respectively. The results are in agreement, further verifying the practicality of the model

Responses of Pre-Holed Granite under Coupled Biaxial Loading and Unloading Stress Condition

Underground excavation is a necessary process for constructing mines, tunnels and depots in granite rock mass. In this study, the numerical granite specimens were established by the discrete element method and confirmed by laboratory experiments in order to investigate the peak stress, cracking development and failure properties of pre-holed granite under coupled biaxial loading and unloading conditions. The results show that, for the specimens containing D-type and square holes, the peak biaxial unloading strengths first decrease, then increase and finally decrease as the inclination angles of the holes increase. For the specimens with elliptical holes, the peak biaxial unloading strengths first decrease and then increase with the increases in the inclination angles of the holes. The biaxial unloading strengths of specimens containing elliptical, circular, D-type and square holes decrease in that order. The cracks initially appear near the crossover points between the X-type shear fracturing plane and the pre-hole in the center and gradually expand along the X-type shear direction, which indicates that the failure of pre-holed granite is primarily shear failure. When the overall length of cracks expanding along the X-type shear direction extends to the size of the pre-hole in the center, the failure of the pre-holed specimen occurs. When the existing pre-hole in the center of the granite specimen extends to connect with the shear slip in the vicinity of the hole, this triggers overall failure

Digital Image Processing Method for Characterization of Fractures, Fragments, and Particles of Soil/Rock-Like Materials

Natural soil and rock materials and the associated artificial materials have cracks, fractures, or contacts and possibly produce rock fragments or particles during geological, environmental, and stress conditions. Based on color gradient distribution, a digital image processing method was proposed to automatically recognize the outlines of fractures, fragments, and particles. Then, the fracture network, block size distribution, and particle size distribution were quantitatively characterized by calculating the fractal dimension and equivalent diameter distribution curve. The proposed approach includes the following steps: production of an image matrix; calculation of the gradient magnitude matrix; recognition of the outlines of fractures, fragments, or particles; and characterization of the distribution of fractures, fragments, or particles. Case studies show that the fractal dimensions of cracks in the dry mud layer, ceramic panel, and natural rock mass are 1.4332, 1.3642, and 1.5991, respectively. The equivalent diameters of fragments of red sandstone, granite, and marble produced in quasi-static compression failures are mainly distributed in the ranges of 20–40 mm, 25–65 mm, and 10–35 mm, respectively. The fractal dimension of contacts between mineral particles and the distribution of the equivalent diameters of particles in rock are 1.6381 and 0.8–3.6 mm, respectively. The proposed approach provides a computerized method to characterize quantitatively and automatically the structure characteristics of soil/rock or soil/rock-like materials. By this approach, the remote sensing for characterization can be achieved

Bending and Buckling of Circular Sandwich Plates with a Hardened Core

Hard-core sandwich plates are widely used in the field of aviation, aerospace, transportation, and construction thanks to their superior mechanical properties such as sound absorption, heat insulation, shock absorption, and so on. As an important form, the circular sandwich is very common in the field of engineering. Thus, theoretical analysis and numerical simulation of bending and buckling for isotropic circular sandwich plates with a hard core (SP-HC) are conducted in this study. Firstly, the revised Reissner’s theory was used to derive the bending equations of isotropic circular SP-HC for the first time. Then, the analytic solutions to bending deformation for circular and annular sandwich SP-HCs under some loads and boundary conditions were obtained through the decoupled simplification. Secondly, an analytic solution to bending deformation for a simply supported annular SP-HC under uniformly distributed bending moment and shear force along the inner edge was given. Finally, the differential equations of buckling for circular SP-HCs in polar coordinates were derived to obtain the critical loads of overall instability of SP-HC under simply supported and fixed-end supported boundary conditions. Meanwhile, the numerical simulations using Nastran software were conducted to compare with the theoretical analyses using Reissner’s theory and the derived models in this study. The theoretical and numerical results showed that the present formula proposed in this study can be suitable to both SP-HC and SP-SC. The efforts can provide valuable information for safe and stable application of multi-functional composite material of SP-HC

TURBINE DISK PROFILE OPTIMIZATION APPLYING DESIGN OF EXPERIMENT AND RESPONSE SURFACE METHOD

Profile of a turbine disk was optimized in ANSYS Workbench platform and results suggested that disk stresses were decreased significantly while the disk mass was lightened as well. Present research demonstrates that ANSYS Workbench platform integrating geometry modeling,stress analysis and optimization module can minimize the difficulties of optimization work,the accuracy of surrogate model using Design of Experiments（ DOE） and Response Surface Method（ RSM） can satisfy engineering requirements and the application of combination optimization strategy involving DOE,RSM and Multi-Objective Genetic Algorithm（ MOGA） can obviously enhance the optimization efficiency

Mitochondrial Permeability Transition in the CNS - Composition, Regulation, and Pathophysiological Relevance

Mitochondrial permeability transition (MPT) is induced in isolated brain mitochondria by calcium and oxidants and is inhibited by adenine nucleotides. When induced, MPT is associated with equilibration of solutes of <1500 Da across the inner mitochondrial membrane. A persistent induction of MPT depolarizes the inner membrane and causes cessation of ATP synthesis, swelling of the matrix, and bursting of the mitochondrial membranes. The rupture of the membranes releases calcium stored in the mitochondrial matrix and apoptogenic factors from the intermembrane space, leading to cell death. MPT has been implicated in acute brain injury and neurodegenerative disease since inhibitors of MPT such as cyclosporin A (CsA) are brain protective. Whether MPT has a physiological role is unclear, but MPT may be important in calcium homeostasis under conditions of excessive neuronal activity