Control mechanism and technique of floor heave with reinforcing solid coal side and floor corner in gob-side coal entry retaining

Floor heave is the most common convergence in gob-side entry retaining.The paper analyzes the form,process and characteristics of gob-side entry retaining with the comprehensive methods of theoretical analysis,numerical simulation and the field trial.Research results present that bending and folding floor heave is the main factor in the stage of the first panel mining;squeezing and fluidity floor heave plays a great role in the stable stage of gob-side entry retaining;the combination of the former two factors affects mainly the stage of the second mining ahead;abutment pressure is a fundamental contribution to the serious floor heave of gob-side entry retaining,and sides corners of solid coal body are key part in the case of floor heave controlling of gob-side entry retaining.Floor heave of gob-side entry retaining can be significantly controlled by reinforcing sides and corners of solid coal body,and influence rules on the floor heave of gob side entry retaining of sides supporting strength and the bottom bolt orientation in solid coal side are obtained.Research results have been successfully applied in gob-side entry retaining of G20-F23070 face haulage roadway in #2 coal mine of Pingmei Group,and the field observation shows that the proposed technique is an effective way in controlling the floor heave of gob-side entry retaining.

Synchronization of two coupled exciters in a vibrating system of spatial motion

The paper proposes an analytical approach to investigate the synchronization of the two coupled exciters in a vibrating system of spatial motion. Introducing the distur- bance parameters for average angular velocity of two excit- ers, we deduce the non-dimensional coupling equations of angular velocities of two exciters, in which the inertia cou- pling matrix is symmetric and the stiffness coupling matrix is antisymmetric in a non-resonant vibrating system. The analysis of the coupling dynamic characteristic shows that the coupled cosine effect of the phase angles will cause the torque acting on two motors to limit the increase of phase difference between two exciters as well as sustain its sym- metry of two exciters during the running process. It physi- cally explains the peculiarity of self-synchronization of two exciters. The cosine effect of phase angles of the vibrations excited by each exciter will decrease its moment of inertia. The residual moment of inertia of each exciter represents its relative moment of inertia. The stability condition of synchro- nization of two exciters is that the relative non-dimensional moments of inertia of two exciters are all greater than zero and four times their product is greater than the square of their coefficient of coupled cosine effect of phase angles, which is equivalent to that the inertia coupling matrix is positive definite and all its elements are positive. The numeric results show that the structure of the vibrating system can ensure the stability condition of synchronous operation.

A study of rock bolting failure modes

Rock bolting has advanced rapidly during the past 4 decades due to a better understanding of load transfer mechanisms and advances made in the bolt system technology. Bolts are used as permanent and temporary support systems in tunnelling and mining operations. A review of has indicated that three systems of reinforcement devices have evolved as part of rock bolt and ground anchor while the rock is not generally thought of as being a component of the reinforcement system. A classification of rock bolting reinforcement systems is presented, followed by the fundamental theory of the load transfer mechanism. The failure mode of two phases of rock bolting system is formularised. The failure modes of cable bolting are discussed using a bond strength model as well as an iterative method. Finally, the interfacial shear stress model for ribbed bar is introduced and a closed form solution is obtained using a tri-line stress strain relationship.

A study of laboratory testing and calculation methods for coal sorption isotherms

Measurement of the volume of gas adsorbed per unit mass of coal with increasing pressure at a constant temperature produces an isotherm that describes the gas storage capacity of this type of coal. The accurate testing and interpretation of coal sorption isotherm plays an important role in the areas of coal mine methane drainage, coalbed methane （CBM） reservoir resource assessment, enhanced coalbed methane （ECBM） recovery, as well as the carbon dioxide （CO2） sequestration in deep coal seams or similar geological formations. Different coal sorption isotherm testing apparatus and associated calculation methods are critically reviewed and presented in this paper. These include both volumetric and gravimetric based methods, as well as experimental sorption tests with confining stress and direction sorption methods. The volumetric techniques utilise experimental apparatus with sample cell and injection pump and that with both sample cell and reference cell. Whilst the gravimetric approachesinclude methods with sample cell and suspension magnetic balance and that with both sample cell and reference cell. Different testing methods are compared and discussed in this study. A unique in-house-built coal sorption isotherm testing apparatus at the University of Wollongong was presented together with the calculation method, procedures and experimental results. The isotherm results can be calculated by both Soave-Redlich-Kwong （SRK） equation and calibration cure methods which can be used directly to convert the volume of adsorbed gas in different test conditions to standard condition （NTP）.

塑料排水板结合真空预压法的径向固结解析解

塑料排水板结合真空预压的软土地基加固方法是一种经济高效并被逐渐广泛应用的地基加固方法,该方法不仅可以减少堆载预压坝体的高度,还能减少土体的侧向位移.推导的塑料排水板与真空预压结合的非线性径向固结解析解可以较好地用于该种地基加固的预测和分析.求解过程认为软土在一维固结条件下孔隙比与平均有效应力、水平渗透系数成对数线性关系,而非以前认为的一维线性关系,因排水板周围土体被扰动,所以涂抹区中水平渗透系数采用抛物线分布形式,同时还考虑真空预压对固结的作用.退化提出的解析解与前人解析解进行对比验证、完成解析解与试验结果验证,证明了该解析解的正确性.最后,分析了参数κ和C_k/C_c对固结的影响,结果表明C_k/C_c值越大,固结时间越短,κ值增大,固结时间增长.

Tungsten/steel diffusion bonding using Cu/W-Ni/Ni multi-interlayer

Diffusion bonding between tungsten and 0Cr13Al stainless steel using a Cu/90W-10Ni powder mixtures/Ni multi-interlayer was carried out in vacuum at 1150 °C with a pressure of 5 MPa for 60 min. The microstructures, composition distribution and fracture characteristics of the joint were studied by SEM and EDS. Joint properties were evaluated by shear experiments and thermal shock tests. The results showed that the joints comprised tungsten/Cu-Ni sub-layer/W-Ni composites sub-layer/Ni sub-layer/0Cr13Al stainless steel. The W-Ni composites sub-layer with a homogeneous and dense microstructure was formed by solid phase sintering of 90W-10Ni powder mixtures. Sound bonding between tungsten base material and W-Ni composites sub-layer was realized based on transient liquid phase (TLP) diffusion bonding mechanism. Joints fractured at bonding zone of W-Ni composites sub-layer and Ni sub-layer during shear testing, and the average strength was 256 MPa. Thermal shock tests showed that joints could withstood 60 thermal cycles quenching from 700 °C to room temperature.

基于R-N非线性疲劳损伤累积模型的砂土震陷计算方法

构造不同加载次序的阶跃荷载进行应变控制循环单剪试验,并基于R-N模型与传统P-M模型进行土体材料损伤计算,对比分析计算值与试验值,验证R-N模型的有效性;基于R-N模型既能考虑荷载幅值和加载次序的特征,根据R-N非线性疲劳累积损伤理论推导并建立砂土震陷计算方法;利用GCTS测试系统对美国Filter净砂展开研究,进行404组剪应变控制动循环单剪试验,考虑荷载幅值、上覆荷载、砂土特性及地震动特性等影响,测定模型参数,并建立模型参数回归模型;同时,进行202组不同特性的真实地震荷载输入剪应变控制动循环单剪试验,测定不同工况下的砂土试样在地震荷载作用下引起的竖向变形;最后,将基于本文方法预测的砂土震陷时程曲线和累积值与试验值对比分析,验证了该方法的正确性。

地震荷载特征及其对砂土震陷影响试验研究

介绍美国最新一代动循环单剪系统的组成及其特点,分析原始真实地震荷载的输入方法,并对真实地震荷载的输入有效性进行验证。以美国Filter净砂为对象,选择冲击型与振动型地震波作为试验输入荷载,考虑砂土相对密度、上覆荷载,设计不同试验工况研究地震荷载特征及其对砂土震陷的影响,共计试验组数202组。试验结果表明:在同一砂土相对密度和上覆荷载条件下,振幅相同的振动型地震波引起的砂土震陷比冲击型地震波引起的砂土震陷大;砂土震陷主要由最大地震荷载峰值之前的各个较大峰值的地震波引起,其中最大峰值对应的地震波引起的砂土竖向应变最大;对于最大峰值之后的地震波,其峰值应达到该地震波最大峰值的80%左右才对砂土变形具有较明显的贡献作用;冲击型地震波最大峰值之后的各地震波对砂土变形影响不明显;对于振动型地震波,其最大峰值之前及最大峰值之后一定范围内的地震波作用共同决定着砂土变形的大小。

Synthesis of Al_2O_3-SiC Composite and Its Effect on the Properties of Low-carbon MgO-C Refractories

Al2O3-SiC composite was synthesized with pyrophyllite and natural graphite as raw materials by carbothermal reduction reaction under argon atmosphere. The effect of synthesis temperature on phase composition and microstructure was investigated. Low-carbon MgO-C refractories were prepared by using the synthesized Al2O3-SiC composite as additive. The effect of its addition on the slag penetration and corrosion resistance as well as oxidation resistance of the refractories was investigated, and the slag resistance and oxidation resistance mechanisms of the Al2O3-SiC composite were also discussed. The results show that the synthesis temperature has a great influence on preparation of Al2O3-SiC composite. The Al2O3-SiC composite can be synthesized at 1873-1973 K under argon atmosphere, with pyrophyllite and natural graphite as raw materials, and particle sizes of the composite synthesized at 1973 K are mainly distributed as 1-2 μm. The slag penetration and corrosion resistance of low-carbon M80-C refractories can be remarkably improved by adding the synthesized Al2O3-SiC composite, and the oxidation resistance has an improvement to some extent. The increase of slag viscosity and the formation of MgAl2O4 can effectively inhibit the slag penetration and corrosion for the refractories.

Analysis of Fishscaling Resistance of Low Carbon Heavy Plate Steels

The precipitates and hydrogen permeation behavior in three kinds of hot rolled low carbon heavy plate steels for enameling were analyzed; then, both sides of the steels were enameled. The experimental results show that a large amount of coarse Ti4 Cz $2 and fine Ti（C, N） particles exist in the optimized Ti-bearing steel, quite a lot of fine Ti（C,N） particles exist in the optimized carbon steel, but only a little bit fine Ti（C,N） particles exist in the carbon steel. The fishscaling resistance of the steels can be correlated to the effective hydrogen diffusion coefficient, and a model of correlation between the effective hydrogen diffusion coefficient and the volume fraction of the precipitates was established and verified. The effective hydrogen diffusion coefficient should be lower than 3.96×10-6 cm2/s to avoid fishscaling in heavy plate steels.

Characteristic analysis of hydraulic hybrid vehicle based on limit cycle

The theory of limit cycles was applied to hydraulic hybrid vehicle (HHV) to analyze the dynamic characteristics of the system. The exact mathematical models based on configuration diagram of HHV were built to study on equilibrium points, nonexistence of limit cycle and stability of equilibrium points. The analysis showed that if the Young's modulus of fluid is neglected, the equilibrium points of the system will be distributed on both sides of the initial function. In addition, there is a unique equilibrium point according to the practical signification of the system parameters. The nonexistence analysis showed that there is no limit cycle for the system, no matter how the viscosity coefficient B changes. The stability analysis of equilibrium points showed that the system is asymptotically stable about the equilibrium point at B≥0 and the equilibrium point is the center point of the system at B=0. Finally, the phase diagrams of global topological structure of HHV system were entirely described according to qualitative analysis of the singular points at infinity.

How to Purify a Polluted Lake Quickly—A Case Study from Shanghai, China

Water pollution has become a serious worldwide problem, especially for lakes with a large stagnant water body. Is it possible to develop high quality water from a heavily polluted river system quickly? This paper introduces an innovative technology termed SPP (separation, prevention and protection) for this purpose. Its feasibility is preliminarily examined using Dianshan Lake in Shang- hai as an example. Due to its very high population density and intensive industrial activities, almost all waterways in Shanghai are heavily polluted, including the lake. However, the data analysis shows that clean water always appears after heavy rains, especially in its suburban areas. Once the 1st flush water is discharged to downstream, high-quality water can be developed from its Dianshan Lake by using the SPP strategy. The Vollenweider model is used to analyze SPP’s feasibility. The results show that the water quality of the Dianshan Lake can be remediated as a drinking water source within 120 days if the SPP strategy is applied. It is suggested that Jinze reservoir’s water should come from the Dianshan lake, not Taipu River to improve the quality of water supply. It is highly recommended for other cities in the world to consider the SPP technology if needed.

A Methodology for Bridge Condition Evaluation

Due to the substantial role of bridges in transportation networks and in accordance with the limited funding for bridge management, remediation strategies have to be prioritised. A conservative bridge assessment will result in unnecessary actions, such as costly bridge strengthening or repairs. On the other hand, any bridge maintenance negligence and delayed actions may lead to heavy future costs or degraded assets. The accuracy of decisions developed by any manager or bridge engineer relies on the accuracy of the bridge condition assessment which emanates from visual inspection. Many bridge rating systems are based on a very subjective procedure and are associated with uncertainty and personal bias. The developing condition rating method described herein is an important step in adding more holism and objectivity to the current approaches. Structural importance and material vulnerability are the two main factors that should be considered in the evaluation of element structural index and the causal factor as the representative of age, environment, road class and inspection is implemented as a coefficient to the OSCI （overall structural condition index）. The AHP （analytical hierarchy process） has been applied to evaluate the priority vector of the causal parameters.

Reinforced concrete-like Na_(3.5)V_(1.5)Mn_(0.5)(PO_(4))_(3)@graphene hybrids with hierarchical porosity as durable and high-rate sodium-ion battery cathode

Realizing high-rate capability and high-efficiency utilization of polyanionic cathode materials is of great importance for practical sodium-ion batteries(SIBs) since they usually suffer from extremely low electronic conductivity and limited ionic diffusion kinetics. Herein, taking Na_(3.5)V_(1.5)Mn_(0.5)(PO_(4))_(3)(NVMP) as an example, a reinforced concrete-like hierarchical and porous hybrid(NVMP@C@3DPG) built from 3D graphene(“rebar”) frameworks and in situ generated carbon coated NVMP(“concrete”) has been developed by a facile polymer assisted self-assembly and subsequent solid-state method. Such hybrids deliver superior rate capability(73.9 m Ah/g up to 20 C) and excellent cycling stability in a wide temperature range with a high specific capacity of 88.4 m Ah/g after 5000 cycles at 15 C at room temperature, and a high capacity retention of 97.1% after 500 cycles at 1 C(-20 ℃), and maintaining a high reversible capacity of 110.3 m Ah/g in full cell. This work offers a facile and efficient strategy to develop advanced polyanionic cathodes with high-efficiency utilization and 3D electron/ion transport systems.

商业纯钛等温热变形的再结晶行为

利用Gleeble3500热力模拟试验机研究了商业纯钛(Grade 2)高温下的等温热变形行为。纯钛的高温变形中发生的动态再结晶由高温淬火后金相组织的观察及应力-应变曲线所表征。结果表明,变形温度及应变速率对纯钛的变形组织及流变曲线影响较大,同时,也观察到动态软化现象的发生。软化率则主要受变形温度、应变速率影响。与未变形的纯钛组织相比,变形对纯钛的组织有明显的细化作用。

Validated scale-up procedure to predict blockage condition for fluidized dense-phase pneumatic conveying systems

This paper presents results of an ongoing investigation into modelling fluidized dense-phase pneumatic conveying of powders. For the reliable design of dense-phase pneumatic conveying systems, an accurate estimation of the blockage boundary condition or the minimum transport velocity requirement is of sig- nificant importance. The existing empirical models for fine powder conveying in fluidized dense-phase mode are either based on only a particular pipeline and product or have not been tested for their accuracy under a wide range of scale-up conditions. In this paper, a validated test design procedure has been devel- oped to accurately scale-up the blockage boundary with the help of a modelling format that employs solids loading ratio and Froude number at pipe inlet conditions using conveying data of two different samples of fly ash, electro-static precipitation （ESP） dust and cement （particle densities： 2197-3637 kgJm3; loose poured bulk densities： 634-1070kg/m3; median size： 7-30 l^m）. The developed models （in power func- tion format） have been used to predict the blockage boundary for larger diameter and longer pipelines （e.g. models based on 69 mm I.D. ~ 168 m long pipe have been scaled up to 105 mm I.D. and 554 m length）. The predicted blockage boundaries for the scale-up conditions were found to provide better accuracy compared to the existing models.