Numerical modelling of void inclusions in porous media

Numerical modelling of porous flow in a low‐permeability matrix with high‐permeability inclusions is a challenging task because the large ratio of permeabilities ill‐conditions the finite element system of equations. We propose a coupled model where Darcy flow is used for the porous matrix and potential flow is used for the inclusions. We discuss appropriate interface conditions in detail and show that the head drop in the inclusions can be prescribed in a very simple way. Algorithmic aspects are treated in full detail. Numerical examples show that this coupled approach precludes ill‐conditioning and is more efficient than heterogeneous Darcy flow. Copyright © 2003 John Wiley & Sons, Ltd.     

Three‐dimensional finite element computations for frictional contact problems with non‐associated sliding rule

This paper presents an algorithm for solving anisotropic frictional contact problems where the sliding rule is non‐associated.The algorithm is based on a variational formulation of the complex interface model that combine the classical unilateral contact law and an anisotropic friction model with a non‐associated slip rule. Both the friction condition and the sliding potential are elliptical and have the same principal axes but with different semi‐axes ratio. The frictional contact law and its inverse are derived from a single non‐differentiable scalar‐valued function, called a bi‐potential. The convexity properties of the bi‐potential permit to associate stationary principles with initial/boundary value problems. With the present formulation, the time‐integration of the frictional contact law takes the form of a projection onto a convex set and only one predictor–corrector step addresses all cases (sticking, sliding, no‐contact). A solution algorithm is presented and tested on a simple example that shows the strong influence of the slip rule on the frictional behaviour. Copyright 2004 John Wiley & Sons, Ltd.     

Molecular dynamics studies of atomic-scale tribological characteristics for different sliding systems

A slider-slab sliding model for hard-to-soft and soft-to-soft sliding systems with abrasive and non-abrasive wear conditions is used to investigate atomic-scale friction. The molecular dynamics simulation uses the Morse potential to calculate interatomic forces between atoms. Separation distance between the slider and the slab is changed to simulate repulsive and attractive interactive force fields exerted on interface between two sliding components. Effects of the interaction potential parameters on the sliding friction are investigated. The relationship of frictional force, normal force and temperature rise of the slider and the slab during sliding are established. Comparison of the hard-to-soft and the soft-to-soft sliding system are carried out and shows different tribological phenomena.     

增强蚁群算法的机器人最优路径规划

为解决复杂环境中机器人最优路径规划问题,本文结合增强学习和人工势场法的原理,提出一种基于增强势场优化的机器人路径规划方法,引入增强学习思想对人工势场法进行自适应路径规划.再把该规划结果作为先验知识,对蚁群算法进行初始化,提高了蚁群算法的优化效率,同时克服了传统人工势场法的局部极小问题.仿真实验结果表明,该方法在复杂环境中,对机器人的路径规划效果令人满意.     

碘量电位滴定法测定锌锰废旧电池中二氧化锰

在测定锌锰干电池锰粉中活性二氧化锰含量时,由于制备电池时正极锰粉中添加了乙炔黑、石墨等导电材料,使制得的样品溶液显色且混浊,影响用淀粉作为指示剂进行碘量法滴定终点的判断。本文提出结合电位滴定技术用碘量法测定废旧锌锰干电池锰粉中剩余活性二氧化锰含量的新方法,对方法中反应时间、温度、碘化钾用量等影响因素进行试验,确定了最优实验条件。结果表明:选择在室温下加入1～1.5g碘化钾、5mL1mol/L硫酸,静置30min,结果准确,精密度高。样品加标回收率为96.9%～99.2%,RSD为0.2%,0.8%。     

电脱氧法电解效率主要影响因素的研究进展

熔盐电脱氧工艺是直接电解还原金属氧化物制备金属或合金的方法,以其工艺简单、环境友好、易于调控等优点广泛应用于金属及合金的制备,但该工艺目前存在电解效率低等问题。影响该方法电解效率的主要因素有:氧化物阴极导电性、O2-扩散、阴极电势、阳极材料。阴极导电性主要受氧空穴的形成,阴极晶型结构的影响,增加阴极氧空穴及有效控制晶型转变有利于增加阴极导电性,从而提高电解效率;O2-扩散影响电解反应速率,增加阴极表面积及合理选择熔盐组分可促进O2-扩散,促进电解脱氧;阴极电势和阳极材料影响阴极有效脱氧,合理控制阴极电势、选择过电位小,性质稳定的阳极材料均有利于提高电解效率。并展望了今后的研究中重点关注通过改进阴极,改进电解装置等提高电脱氧效率。     

辽宁排山楼金矿T4矿体Au元素富集规律及其对找矿的指示意义

排山楼金矿位于华北地台北缘,为受控于韧性剪切带的大型金矿床。该矿床成因与韧性剪切带密切相关,矿区成矿地质条件优越,具有很好的找矿潜力。通过总结排山楼金矿地质特征及其主要控矿因素,认为区内韧性剪切带为控岩（控矿）构造,控制着赋矿糜棱岩和金矿体的空间展布,向矿区深部赋矿岩石变薄,找矿空间变小。通过分析T4矿体的品位和厚度分布规律发现,矿体厚度及品位分布规律在空间上表现出高度一致性,根据金品位等值线图判断矿体向南西侧伏。研究认为T4矿体在南西深部其厚度及品位降低趋势明显,向深部工业价值不大,应重点加强对其他韧性剪切带找矿潜力的研究。     

低压供电系统中零线电位升高的原因及安全措施

论述了三相四线制供电系统中零线电位升高的原因及带来的危害。介绍了防止零线电位过份升高应采取的措施及注意事项。     

Ab initio Calculations of Electron-Impact Excitation Cross Sections for N_2 Molecule

One of the great difficulties in understanding nitrogen plasma elementary processes is the lack of an available database of the cross-sections of electron-impact excitations and radiations. Ab initio calculations of vibrational excitation cross sections for electron collisions with nitrogen molecules in low-lying states using similarity function approach, such as a-a＇, a-w, B-B＇ and B-W transition systems, are reported here for the first time. In the meantime, the average excitation energies of neighboring levels of these systems have been calculated. In order to obtain the cross sections, accurate spectroscopic constants and transition dipole moments have been investigated. Potential energy curves and other electronic transition dipole moments for the low-lying states of N2 have been re-evaluated using complete active space self-consistent field （CASSCF） approach with aug-cc-pVqZ basis set. The calculated cross-sections could provide a database for studying the elementary processes and the properties in N2 plasma.     

不同介质环境条件下黏性土的分散性及其微观结构

采用碎块试验、双比重计试验、电动电位、扫描电镜等测试方法,对典型的分散性土和非分散性土在不同介质环境条件下的分散性及其微观结构特征进行了研究.研究表明,介质环境中的钠离子含量和pH值高低是决定土体是否产生分散的本质因素,两种因素缺一不可.如果土体中含有大量的钠离子,并且酸碱度呈强碱性,则土体具有分散性.通过掺加高价阳离子和酸性物质,降低土体中钠离子的相对含量和酸碱度,可对分散性土进行改良.在自然沉积条件下,分散性土的微观结构中含有较多的孔隙;而非分散性土比较密实,孔隙较少.