立方体模型周边风致积雪飘移的数值模拟

基于两相流理论模拟立方体周围的积雪飘移.采用各向异性的雷诺应力模型(RSM),通过改进动量方程和湍流方程的源项来考虑雪的浮力和惯性力对风(空气相)的影响.以立方体模型为研究对象,首先将改进模型计算的表面风压分布与实测结果进行了对比,接着把改进模型的雪飘移计算结果与未改进模型的计算结果、实测结果进行了对比.结果显示,改进后模型的模拟结果与实测结果更加吻合,立方体模型周边雪颗粒的沉积侵蚀趋势表现一致.在立方体迎风侧的前方区域及两侧气流分离区出现了明显的侵蚀,紧靠背风侧后方区域出现了沉积.     

非规则颗粒与滚筒球磨机相互作用的离散元–有限元耦合分析

非规则颗粒形态显著影响球磨机中颗粒材料的运动行为，同时对球磨机结构产生不同的力学响应。采用超二次曲面方程描述非规则颗粒材料，并发展了离散元（discrete element method,DEM）–有限元（finite element method, FEM）耦合算法以分析非规则颗粒材料与滚筒球磨机间的相互作用。在该算法中，滚筒球磨机被划分为一系列四边形单元，并且超二次曲面颗粒与球磨机间的接触判断可转化为超二次曲面颗粒与四边形单元间的接触判断。将计算得到的碰撞力向节点插值，该节点力作为载荷条件在有限元中进行隐式动力学求解，并通过求解颗粒运动方程和有限元动力方程实现颗粒运动更新和结构力学响应分析。进一步分析了滚筒球磨机中球体、圆柱体和立方体颗粒材料的运动行为以及滚筒球磨机的变形及应力分布规律。研究结果表明：颗粒形状显著影响球磨机研磨效果和球磨机结构位移；立方体颗粒具有最好的研磨效果，而圆柱体颗粒比球体颗粒具有更好的研磨效果；在结构位移上，立方体颗粒有最大的峰值位移，其次是圆柱体和球体颗粒；相比于规则的球体颗粒，超二次曲面颗粒有不规则的表面形状，这会导致更好的研磨效果和更大的结构位移。     

两个单位胞体模型数值模拟结果比较

利用三维有限元方法，通过建立立方体、六棱柱单位胞体数值分析模型，对颗粒增强复合材料做模拟计算，在单向外载荷作用下，讨论两模型中正应力、von Mises应力的分布规律。结果显示两模型的应力场分布相近或相似，将在相同的区域里发生材料剪切屈服和界面脱胶破坏。计算了复合材料弹性系数，经过同整体体积平均分析方法和实验测量结果的比较，结果显示六棱柱模型较立方体模型更加符合真实情况。     

基于PFC~(3D)的无黏性土渗流临界水力梯度模拟分析

为了实现渗流作用下无黏性土临界水力梯度的计算,应用PFC3D中的渗流模型,对渗流实验算例进行了数值计算模拟,计算结果与实验结果基本吻合,说明该模型用来模拟渗流问题是正确和有效的.对不同颗粒摩擦系数下的无黏性颗粒模型进行了渗流破坏的数值模拟.结果表明:无黏性土的渗流临界水力梯度随着颗粒摩擦系数增加而增大;计算结果与使用经验公式计算所得到的结果基本一致,表明了对渗流临界水力梯度模拟计算的正确有效性.而相较经验公式,应用PFC3D进行渗流数值计算适用于更为复杂的工程和地质条件,因而具有更强的适用性,可为复杂条件下的渗透稳定计算提供可靠的参考和依据.     

基于离散元的碎片尺寸随机的颗粒破碎模拟方法

依据天然堆石颗粒的破碎特性，构建了子颗粒粒径随机的碎片替换模式，即立方体替换模式.采用立方体替换模式可得到符合天然堆石颗粒破碎特性的子颗粒粒径分布.单轴压缩模拟试验表明，与子颗粒粒径固定的4球和18球替换模式相比，立方体替换模式能提高试样级配曲线的连续性，并改善中间粒径缺失的问题.对比不同子颗粒数量替换模式的模拟结果可知，立方体替换模式对应试样的接触数目和平均接触力分布符合替换模式子颗粒数量对分布的影响规律；剔除无接触和单接触颗粒后，3种替换模式的细观力学特性的变化规律一致，表明立方体替换模式可以用于模拟粗粒土的颗粒破碎.     

大模量比短纤维增强复合材料应力分布预测

提出了适用于纤维模量远大于基体模量时短纤维增强复合材料(SFRC)轴向应力分布的预测公式。建立了SFRC的轴对称单胞模型,对不同模量比下SFRC的纤维轴向应力分布进行了数值计算。通过与现有理论模型得到的应力分布对比表明,当纤维和基体弹性模量比小于37时,现有理论模型得到的纤维轴向应力和界面剪切应力均与有限元分析结果相吻合;当模量比大于37时,现有理论模型得到的界面剪应力与有限元分析结果基本保持一致,但是纤维轴向应力与有限元分析结果相差较大。与Hsueh模型相比,提出的预测公式与实验结果更为接近。     

基于CFD-DEM耦合模型的大粒径非常规岩屑颗粒运移规律研究

采用CFD-DEM耦合计算模型,利用DEM软件建立大粒径(2 cm)、非球体岩屑颗粒的离散元模型,与FLUENT实现无缝耦合并行计算,颗粒间相互作用采用Hertz-Mindlin弹性接触模型,对大粒径的、非常规岩屑颗粒在水平井段的运移规律进行了数值模拟计算。基于钻井实测数据,建立水平井段环空内含不同形状(片状,立方体状及球状)相同等效球体粒径颗粒的计算模型,展示了井眼环空内颗粒运移、沉积状态,对环空钻井液流速、不同形状的岩屑颗粒运移速度进行了计算分析,本文还计算得到片状大粒径岩屑含量对钻井液携岩效果的影响规律。结果显示:2 cm等效体积球体粒径的颗粒在井眼环空内的运移状态较差,出现局部堆积;立方体状颗粒的运移效果最差,片状颗粒次之;在所选用计算条件下,片状颗粒含量大于10%时会加剧削弱携岩效果。计算结果可对钻井携岩问题的研究提供一定的参考价值。     

颗粒形状对铝基复合材料力学行为影响的模拟

采用有限元分析的方法,用平面应变和轴对称两种单胞模型,分析了形状不同的SiC增强颗粒对经T6处理的铝基复合材料力学行为的影响.两种单胞模型的模拟结果均显示,对于颗粒是多边形状的铝基复合材料,随着颗粒边数的逐渐增大,颗粒的平均受力逐渐减小,复合材料的屈服强度也逐渐降低.平面应变单胞模型模拟的结果显示,三角形颗粒对于提高复合材料的屈服强度贡献最大;而用轴对称单胞模型模拟时,矩形颗粒对提高材料的屈服强度贡献最大.     

TiC颗粒增强钛基复合材料宏细观力学性能分析

结合均匀化理论与不动点迭代法,提出了均匀化方法用于解决周期性多尺度问题的有限元框架,建立了具有典型微观结构的TiC颗粒增强钛基复合材料的单胞有限元模型.从宏观尺度出发采用不动点迭代方法给出了微观尺度下单胞有限元的位移边界条件,对其拉伸力学性能进行了数值模拟研究.给出了TiC颗粒增强钛基复合材料在拉伸载荷作用下的宏观等效力学性能,并与实验结果进行对比,验证了该方法的有效性和可靠性.     

风沙跃移中颗粒冲击起动的数值模拟

采用考虑颗粒碰撞的Euler-Lagrange数值模拟方法,对风沙跃移中颗粒冲击起动过程进行了数值计算.在模型中,把气相视为连续介质,在Euler坐标中建立控制方程,对离散颗粒采用Lagrange方法模拟,颗粒间的相互碰撞作用采用软球模型描述.计算结果表明该模型可以模拟出风沙运动中颗粒冲击床面的动态起跳过程,并且与均匀平整床面相比,在非均匀床面上的颗粒更易碰撞起跳,也更具有随机性.这进一步揭示了风沙运动中颗粒碰撞起跳机理.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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