Optimization and Practice for Partition Pressure Relief of Deep Mining Roadway Using Empty-Hole and Deep-Hole Blasting to Weaken Coal

Rockbursts are among the most harmful dynamic disasters, threatening the personnel safety and mine operation. In order to alleviate stress concentration of roadsides and prevent rockbursts, the large-diameter boreholes and deep-hole blasting are employed for partition pressure relief in the deep mining roadway. Combined with failure behavior and stress distribution of the coal, the multilevel division of risk degree for roadsides stress is determined. Based on the orthogonal test of borehole pressure relief in the general danger partition, the response degree of quantitative indexes to main factors influencing the pressure relief effect is considered. The optimal drilling parameters of 120.0 mm diameter, 20.0 m depth, 1.0 m hole spacing, and 5° elevation angle are obtained, determining the stress boundary of safe pressure relief with boreholes. At higher dangerous stress divisions, the optimized blasting parameters through numerical simulation could be obtained as follows: 15.0 m depth, 1.3 decoupling coefficient, and 2.0 m hole spacing, and meanwhile, a stress relief partition of crisscross cracks with 0.61 m height is formed. The roadsides stress could be well controlled within the safe level. Then, an optimal combination of pressure relief is applied to different stress partition of roadsides, and the effectiveness is validated by field test, which proves remarkably applicable for engineering.

Scattering of anti-plane waves by scalene trapezoidal boundary with embedded cavity in anisotropic material based on mapping space

Both surface motion and hole stress concentration have always been concerned in anisotropic medium. In this paper, a theoretical approach is used to study the scattering problem of circular holes under a scalene trapezoid on the surface. The mapping function that anisotropic medium to homogeneous medium is established, and the relationship between the free boundary of anisotropic medium and the mapping of homogeneous medium boundary is proved. In the space of homogeneous medium mapping, the wave displacement function is obtained by solving the equation of motion that meets the zero-stress boundary conditions by separating the variable method and the symmetric method. Based on the complex function, multi-polar coordinate method and region-matching technique, algebraic equations are established at auxiliary boundary and free boundary conditions in complex domain. Then according to sample statistics, least square method is used instead of the Fourier expansion method to solve the undetermined coefficient of the algebraic equations by discrete boundary. Numerical results shows that the continuity of the auxiliary boundary and the accuracy of the zero-stress boundary are nice, and the displacement of the free surface and the stress of the circular hole are related to the parameters of material medium, the position of the circular hole, the direction of the incident wave and the frequency content of the excitation. Finally the process of the wave propagation and scattering around trapezoid and shallow circle are shown in time domain through the inverse fourier transform.

A SPH-GFDM Coupled Method for Elasticity Analysis

SPH (smoothed particle hydrodynamics) is one of the oldest meshless methods used to simulate mechanics of continuum media. Despite its great advantage over the traditional grid-based method, implementing boundary conditions in SPH is not easy and the accuracy near the boundary is low. When SPH is applied to problems for elasticity, the displacement or stress boundary conditions should be suitably handled in order to achieve fast convergence and acceptable numerical accuracy. The GFDM (generalized finite difference method) can derive explicit formulae for required partial derivatives of field variables. Hence, a SPH–GFDM coupled method is developed to overcome the disadvantage in SPH. This coupled method is applied to 2-D elastic analysis in both symmetric and asymmetric computational domains. The accuracy of this method is demonstrated by the excellent agreement with the results obtained from FEM (finite element method) regardless of the symmetry of the computational domain. When the computational domain is multiply connected, this method needs to be further improved.

Molecular Dynamics Study of Bulk Properties of Polycrystalline NiTi

Molecular dynamics (MD) simulations were carried out to study the bulk polycrystalline properties of NiTi. Thermally driven phase transitions of NiTi between martensite and austenitewere simulated using single crystalline simulation domains. With external stress boundary conditions, MD simulation successfully predicted experimentally observed phase transformation temperatures of bulk polycrystalline. Elastic characteristics of NiTi martensite were simulated using polycrystalline simulation domains that consist of realistic disorientations and grain boundary structures. The existence of grain disorientation and grain boundary lowered the potential energy of the simulation domain, which led to more realistic elastic modulus prediction. Analysis of simulation domains that predicted realistic bulk polycrystalline properties showed that the major difference between single crystalline and polycrystalline structures is atomic stress distribution.

The numerical calculation of statically admissible slip-line field for plane strain compression of a three-layer symmetric strip between rigid plates

This paper present a method to build up statically admissible slip-line field (the field of characteristics) and, as a result, the field of statically admissible stresses of the compression of a three-layer symmetric strip consisting of two different rigid perfectly plastic materials between rough, parallel, rigid plates (for the case: the shear yield stress of the inner layer is greater than that of the outer layer). Under the conditions of sticking regime at bi-material interfaces and sliding occurs at rigid surfaces with maximum friction, the appropriate singularities on the boundary between the two materials have been assumed, then a standard numerical slip-line technique is supplemented with iterative procedure to calculate characteristic and stress fields that satisfy simultaneously the stress boundary conditions as well as the regime of sticking on the bi-material interfaces

Issues of Utilizing Social Networking as an Informal Organizational Communication Channel: Evidence from China

Social networking has been increasingly used by both individual and organization in the workplace. This paper addresses gaps in the current literature and tries to demonstrate the negative impacts and consequences of social networking. Qualitative study is applied in this study, including the conduction of user survey, interviews and case studies, which are conducted in the context of China. The article reports on work in progress on the research. The early findings highlight that despite the benefits generated by social networking, issues are also obvious, including such as data security, privacy protection, work-life imbalance, increased work pressure and stress, boundary and role ambiguity. Such findings contribute to organizational policy making and generating modern management practice in the context of information society.

Material Flow Behavior Modelling and Strain Distribution Prediction During Self-Reacting Friction Stir Welding Process Based on Computational Fluid Dynamics Method

Self-reacting friction stir welding (SRFSW) is an advanced variant of friction stir welding (FSW) and shows several superiorities with the double-sided tool configuration. Despite the considerable amount of experimental studies in this field, most of the tool development efforts are still empirical and resort to trial-and-error solutions. To reveal effects of tool features on process physics and guide tool designs, in this study, a multi-physics SRFSW process model is developed within the framework of computational fluid dynamics (CFD). A shear stress boundary condition is applied at the tool-workpiece contact interface. First, the velocity distribution at weld cross section are calculated and the results show that the threads on the pin contribute to the enhancement of stirring effect. Second, the temperature evolutions at advancing side (AS) and retreating side (RS) are compared, and position in RS has higher temperature than position in AS accordingly. Finally, the plastic strain distribution behind pin tool is calculated by integrating effective stain rate along pathlines. The result shows that AS has a more definable strain boundary than RS, which corresponds to the general macroscopic observations in SRFSW. The results may provide a reference on SRFSW tool design.