Stability analysis of the tunnel face in the cohesive-frictional soils considering the arch effect and rotational mechanism

ABSTRACT

This article proposes a new 3D failure mechanism to analyze the stability of the tunnel face driven by a closed shield in cohesive-frictional soils. The failure mechanism consists of a single block in the lower part defined by logarithmic-spiral and a distributed force caused by the weight of a half-ellipsoid in the upper part. The logarithmic-spiral surface represents the shear band and the distributed force is applied to simulate the arch effect. The arch effect and rotational mechanism are considered simultaneously. Comparisons among the proposed mechanism, numerical simulation and existing mechanism are conducted. The results show that the proposed mechanism provides improved limit support pressure values, and the failure patterns of the proposed mechanism agree well with those of the numerical simulation and experimental tests. This verifies that the proposed mechanism is effective and reasonable.     

Investigation of oscillating flow friction factor for cryocooler regenerator considering cryogenic temperature effect

In this paper, experimental results and correlations on the friction factor of screen regenerators are presented, being focused on the effect of cryogenic temperature. Cryogenic environment of helium gas is simulated by performing a simple room-temperature experiment using a higher density gas. Based on the experimental results, the proper correlations are proposed with several non-dimensional parameters. Numerical simulation results from the model with the proposed friction factor are compared to the experimental data under actual operating condition of cryocoolers. The experimental data confirm the accuracy and the availability of the proposed friction factor.     

基于事故树的深孔爆破边坡稳定性分析

为了能够对爆破后形成的露天边坡稳定性进行合理的分析评价,结合大小鱼山岛露天爆破边坡失稳的情况,采用事故树分析方法,建立了工程爆破现场露天边坡失稳事故树模型。计算出事故树的最小割集96个,最小径集3个以及基本事件的结构重要度系数,并得到基本事件结构重要度排序,找出了导致边坡失稳的主要原因是边坡监测和边坡支护。然后根据基本事件结构重要度的排序,制定合理有序的预防措施。事故树分析方法可以全面阐述露天矿边坡失稳的各种因素和逻辑关系,并通过对结构重要性分析,提出合理预防措施,为爆破露天边坡的安全管理提供参考依据。     

基于事故树的深孔爆破边坡稳定性分析

为了能够对爆破后形成的露天边坡稳定性进行合理的分析评价,结合大小鱼山岛露天爆破边坡失稳的情况,采用事故树分析方法,建立了工程爆破现场露天边坡失稳事故树模型。计算出事故树的最小割集96个,最小径集3个以及基本事件的结构重要度系数,并得到基本事件结构重要度排序,找出了导致边坡失稳的主要原因是边坡监测和边坡支护。然后根据基本事件结构重要度的排序,制定合理有序的预防措施。事故树分析方法可以全面阐述露天矿边坡失稳的各种因素和逻辑关系,并通过对结构重要性分析,提出合理预防措施,为爆破露天边坡的安全管理提供参考依据。     

Checking the slope angle of helical gear teeth

Conclusions The above method of checking has provided the plant, which has no special instruments for this purpose, with the means of discovering and elminating large errors which arise during the setting or resetting of machines, and also provided it with a better control of the cutting tools by their geometrical parameters thus greatly improving the machining quality of helical gears.     

Finite element analysis of punch height effect on V-bending angle

Considering the advantages of the V-bending die, the economical set-up time and the fabrication of a wide range of part size and complex shape, the V-bending die is generally used, especially in the Press Brake machine. However, the punch heights in the partial V-bending die affected the bending angle. In this study, the finite element method (FEM) was used to investigate the effects of punch height. The FEM simulation results revealed that the effects of punch height on the bending angle were clearly theoretically clarified based on the material flow analysis and stress distribution. The punch height affected the gap between the workpiece and the die, as well as the reversed bending zone, which resulted in a non-required bending angle. Therefore, applying a suitable punch height created a balance of compensating the gap between the workpiece and the die, and the stress distribution on the bending allowance and the reversed bending zone. This resulted in achieving the required bending angle.     

最终边坡预裂爆破技术参数及应用效果分析

为了保证边坡稳定性及减小爆破振动效应,对大宝山矿区889～877 m平台最终边坡采用了深孔台阶爆破、缓冲爆破与预裂爆破相结合的技术方案。根据边坡预裂爆破中预裂缝的形成是爆炸应力波和髙压气体联合作用的分析结果,和889～877 m平台最终边坡的主爆孔、缓冲孔、预裂孔相关的爆破参数,进行了现场实验。结果表明:爆破实施后,889～877 m平台最终边坡的半孔率高达85%,不平整度较低,较好地保证了最终边坡的稳定性,并将爆破振动的影响控制在安全范围之内。     

Numerical analysis of panels’ dent resistance considering the Bauschinger effect

The Bauschinger effect should be considered in the analysis of panels’ dent resistance, because sheet metal experiences a complex loading history from stamping to denting. This paper studies the modeling and simulation of panels’ static dent resistance, taking the Bauschinger effect into consideration. Our work covers two parts: simulation and experiment. Procedures of drawing, springback I, indenting and springback II are simulated in a multiple step analysis. Different hardening models, including the isotropic hardening model, the linear kinematic hardening model and the nonlinear combined hardening model are used, respectively, in simulation. Comparing the simulation results with the experiment results, we find that the Bauschinger effect has a great influence on panels’ dent resistance. When panels are made of high strength steel or stamped with a high Blank Holder Force (BHF), the Bauschinger effect on panels’ dent resistance is more severe. Considering the effect in numerical analysis would improve the simulation accuracy effectively. The work of this paper is beneficial to material selection and processing optimization for automobile exterior panels.     

基于模态耦合的摩擦自激振荡系统稳定性研究

模态耦合是摩擦引起系统自激振荡的主要不稳定性机理之一.针对此类问题,构建了两自由度非线性质量一传动带系统.首先,通过劳斯判据分析系统的稳定性,给出了计算Hopf分岔点的数学表达式以及系统参数改变时分岔点和特征值分岔图的变化状态.其次,将扩展谐波平衡法加以利用和延伸,得到了自激振荡系统极限环幅值的解析解,进而研究了系统外界参数和结构参数变化对极限环幅值的影响.外界参数(带速和摩擦系数)变化可造成极限环幅值的规律性变化,而结构参数(阻尼比和固有频率)的改变会引起极限环幅值复杂的动力学行为.研究方法及结果可为机械系统结构设计和减振等方面提供理论分析参考.     

Stability of some mechanical systems with dry friction

Mechanical systems subjected to dry friction forces can be studied by differential equations with discontinuous vector fields. The stability of equilibria of some such systems is considered     

Distinct simulation of earth pressure against a rigid retaining wall considering inter-particle rolling resistance in sandy backfill

The focus of this paper is to analyze earth pressure against a rigid retaining wall under various wall movement modes with a contact model considering inter-particle rolling resistance implemented into the distinct element method (DEM). Firstly, a contact model considering rolling resistance in particles was generally explained and implemented into the DEM. The parameters of the contact model are determined from DEM simulation of biaxial tests on a sandy specimen. Then, the influence of inter-particle rolling resistance in the backfill is discussed by comparing the active and passive earth pressure against a rigid wall subjected to a translational displacement with and without inter-particle rolling resistance in the material. Third, the DEM model considering the rolling resistance is used to investigate active and passive earth pressures while the rigid wall moves in a more general manner such as rotation or translation. The influence of rolling resistance on the earth pressures is examined from the microscopic particle scale (e.g., shear strain field) as well as the macroscopic scale (e.g., the magnitude and action point of resultant earth pressures). Finally, the effect of the initial density and the particle size of the backfill are discussed. The results show that when rolling resistance in the particles is taken into account in the DEM simulation, the simulation results are more appropriate and are in line with practical situation. Hence, particles rolling resistance should be taken into account to get more realistic results in DEM analyses.     

Sensitivity series and friction surface analysis of non-metallic friction materials

Nine non-metallic friction material formulations contained fibers, fillers and binder without strong abrasives were designed using Golden Section sequence combined with least-square method. Seven ingredients used without strong abrasives were selected based on the combinatorial approach. Wear (w) and coefficient of friction (μ) are expressed as a function of volume fraction of the ingredients selected as and . The formulations were optimized using the sensitivity series obtained from least-square method. An optimized formulation (S-10) was obtained with a total wear loss of 6.69 wt% and an average μ of 0.375. Friction surface of both brake pad and disc was observed using SEM, EDX and XRD. The non-metallic friction materials without abrasives exhibit unique friction performance and phenomena compared with the non-metallic friction materials with abrasives and semi-metallic brake linings. The temperature measured during friction is lower and the oxidation of the cast iron disc is not rigorous.     

入射角对微波在面内各向异性磁性薄膜中传播特征的影响

基于Maxwell方程组，探讨了面内各向异性磁性薄膜内磁导率的旋磁特性对微波在膜内传播性质的影响，揭示出不同角度入射的微波在膜内的传播性质具有显著差异。     

Stability assessment of earth slope using modified particle swarm optimization

This paper has proposed an effective method to determine the minimum factor of safety (FS) and associated critical failure surface in slope stability analysis. The search for the minimum FS based on limit equilibrium methods is a complex optimization problem as the objective function is non-smooth and non-convex. Recently, particle swarm optimization (PSO) as a meta-heuristic optimization algorithm has been developed with success in treating various types of problems. In the current study, a new approach of PSO is proposed to calculate the safety factor of earth slopes. The safety factors of the general slip surfaces are calculated using Spencer method of slices, and each new slip surface is randomly generated by straight line technique. The reliability and efficiency of the proposed algorithm are examined by considering a number of published cases. The results indicate that the new method can predict a more critical failure mechanism with a lower FS and can outperform the other methods in the literature as well as standard PSO. Finally, the proposed method will be validated by considering an existing slope failure in Ulu Klang, Malaysia.     

Bullwhip effect and complexity analysis in a multi-channel supply chain considering price game with discount sensitivity

This paper constructs a multi-channel supply chain that includes a manufacturer, a dual-channel retailer and an online retailer. The dual-channel retailer has a traditional channel and an online channel, while the manufacturer cooperates with the retailers and opens a direct channel simultaneously. The horizontal and historical price discount sensitivities are taken into account to establish the price-sensitive demand functions. A price game model with the heterogeneous expectations is proposed and analysed with the methods of the stability domain, the bifurcation diagram and the maximum Lyapunov exponent. The complexity and bullwhip effect of each channel are investigated with respect to the price adjustment speed and historical price discount sensitivity. The results show that a moderate or low price discount sensitivity keeps the system stable and a high price discount sensitivity brings the system into the twofold cycle state or chaotic state. It is interesting that if both online channels increase the adjustment speeds with similar strategy the system will enter chaos through the Neimark–Sacker bifurcation. The bullwhip effect is affected by the price adjustment speed and the price discount sensitivity, especially in the double-period or chaotic state, where the bullwhip of the overall supply chain is increased significantly. The results show that controlling price discount sensitivity is useful for supply chain node companies.     

Finite element analysis of the effect of the inner corner angle in equal channel angular pressing

The inner corner angle (ICA) is one of the major factors affecting deformation homogeneity in workpieces during equal channel angular pressing (ECAP). In this study, the effect of the ICA on the plastic deformation behavior in ECAP was investigated using the finite element method. A round ICA induces highly inhomogeneous deformation in the head, tail, top and bottom regions of the workpiece due to increasing compressive and decreasing shear deformation components. It was found that a round inner corner with an angle up to 9° is acceptable in finite element simulations for reproducing a sharp inner corner. These results can serve as a design guide for processing and dies of ECAP.     

Perturbation analysis of optical anisotropy in organic molecular films

Dipping-induced in-plane anisotropy in organic molecular films is characterized by use of second-harmonic generation (SHG) measurement and analyzed by use of a new perturbation method. We derived theoretical formulas for the dependence of SHG intensity on the polarizations of an incident fundamental beam, an output second-harmonic beam, and an azimuthal angle of samples, which agreed well with our experimental measurements.