基于颗粒流模拟的黏性土宏细观参数相关性分析

利用颗粒流方法(Particle Flow Code,PFC)建立数值模型,对红黏土进行大量三轴不固结不排水数值模拟试验.通过改变摩擦系数、黏结强度、刚度比、孔隙率的取值,分析了细观参数的变化对应力-应变关系曲线的影响.通过记录不同围压下样本的应力峰值,依据摩尔-库伦强度准则对数值试样的剪切强度参数进行标定,探讨并定量...     

损伤断裂的宏细观过程

损伤断裂的宏细观过程（１９９４—１９９６年工作总结）国家自然科学基金重大项目“材料损伤、断裂机理和宏微观力学理论”子课题国家自然科学基金委员会设立的重大项目“材料损伤断裂机理和宏微观力学理论”第２课题“损伤断裂的宏细观过程”自１９９４年１月至１９９６...      

砂土类材料离散元细观参数的自动识别

准确的细观参数是采用离散元进行合理模拟的前提,基于最优化理论,本文提出了一种砂土类材料离散元细观参数的自动标定方法:采用PFC离散元软件模拟砂土的双轴压缩试验,以使PFC数值模拟的应力–应变曲线与某标准砂土室内双轴压缩实验结果的误差最小为优化目标,采用模式搜索法实现砂土类材料离散元细观参数的自动标定。本文提出的离散元细观参数自动标定方法具有识别效率快,精度高的优点。     

核级石墨PFC2D模型的宏细观参数分析

颗粒流软件PFC能够很好地处理非连续介质力学的问题,模拟核级石墨的损伤和断裂过程具有独特的优势。在采用PFC^2D模拟核级石墨时,为了增加模拟的便捷性,实现了PFC^2D细观参数的快速标定。本文首先设计了四因素四水平的正交试验,分析了核级石墨的宏观参数与PFC^2D的细观参数关系;然后基于建立的核级石墨宏细观参数的关系,采用PFC^2D模拟石墨IG11的三点弯曲试验,并从位移场变形、荷载-位移曲线和断裂参数三个方面验证其宏细观参数关系的正确性。结果表明,弹性模量E随平节理模量E_c的增加线性增加;抗拉强度σ_t随平节理抗拉强度σ_b的增加线性增加;泊松比ν随平节理刚度比k_n/k_s的增加先增大后减小;数值模拟的位移场变化和荷载-裂缝口张开位移P-CMOD曲线与试验结果较吻合,此外,断裂参数的最大误差不超过3.57%。     

材料强韧化的宏细观断裂力学理论

材料强韧化理论是本世纪末断裂力学理论及应用发展的一个主要方向.本文结合金属、精细结构陶瓷、结构高分子和复合材料中的强韧化力学原理来展示宏细观断裂力学理论的主要框架.     

颗粒离散元岩石模型的宏细观抗拉强度关联

颗粒离散元数值模型由于具有反映材料宏细观力学特征的天然优势, 而被大量学者采用开展岩石力学课题相关研究, 但DEM数值模型涉及的跨尺度关联和参数标定问题给研究者带了挑战, 且尚未形成获得统一认可的定量分析方法. 基于规则排列的圆形颗粒DEM岩石试件拉伸模型, 开展细观接触破裂模式与宏观拉伸破坏强度相关性的力学分析, 指出岩石试样宏观抗拉强度取决于内部细观接触破裂模式, 而细观破裂模式则受到接触抗拉强度、接触抗剪强度、接触法向刚度、接触切向刚度, 甚至颗粒大小及排列方式的共同影响. 根据理论分析及数值模拟结果提出了4种细观破裂模式及相应宏观抗拉强度理论计算公式, 并将公式修正应用于随机颗粒排列的类岩石材料DEM模型, 从细观角度揭示了宏观DEM岩石材料拉伸破坏机理, 构建了宏细观抗拉强度参数关联. 所建立关联公式的合理性得到了大量随机数值模拟结果的有效验证, 可为研究者利用颗粒DEM数值模型进行岩石和混凝土等类脆性材料模拟的参数选取及标定工作提供重要的参考依据.     

弹塑性耦合张量的宏细观对偶形式

依据弹塑性耦合问题的不同类型，应用广义正交原理，在应变空间上推导出已知宏、细观形变规律情况下两种不同形式的弹塑性耦合张量理论表达式及其显形式。该两类弹塑性耦合张量作为宏、细观的对耦形式可应用于体胞模型的损伤力学理论分析与数值计算。     

弹塑性耦合张量的宏细观对耦形式

依据弹塑性耦合问题的不同类型，应用广义正交原理，在应变空间上推导出已知宏、细观形变规律情况下两种不同形式的弹塑性耦合张量理论表达式及其显形式。该两类弹塑性耦合张量作为宏、细观的对耦形式可应用于体胞模型的损伤力学理论分析与数值计算。     

一种新的宏、细观变形全场测量方法

基于光学干涉和衍射理论,提出了一种新的用于宏、细观面内变形测量的光学方法。利用三束准直相干光之间的干涉,分别得到面内位移U V和U-V的两幅耦合条纹图。借助于FFT相移技术,直接计算出全场的U和V分布。本实验系统中包含有长距离显微镜,三光束系统,数字图像采集和处理系统等。它具有光路简单,避开条纹级次的确定,直接计算得到U、V场等优点。将它用于热塑性复合材料 56层板AS4/PEEK[0/±45/90]7S三点弯曲梁位移场的宏、细观测量。得到了层间的变形规律。本文还利用三维各向异性弹性有限元法对AS4/PEEK[0/±45/90]7S三点弯曲梁进行了数值计算,得到了自由表面的位移场和应变场的数值解。定量分析了层间的变形传递规律,有助于进一步分析AS4/PEEK[0/±45/90]7S层合板宏、细观变形。     

基于三维离散元堆积碎石土细-宏观力学参数相关性研究

以室内三轴压缩试验为基础,运用PFC3D离散元软件生成含有不同形状碎石块的1∶1堆积碎石土数值模型,标定得到相应的细观参数(相对误差控制在10%以内)。改变细观参数,定量探讨其与宏观力学参数(粘聚力和内摩擦角)关系,得到细观参数与粘聚力、内摩擦角的细-宏观参数关系式,并对其可靠性进行了验证。研究发现,(1)粘聚力与接触粘结力、颗粒摩擦系数呈线性正相关;同时受粘结力比值M=σc/τc的影响,当M1时,粘聚力随着M的增加而线性增加;M≥4时,粘聚力趋于稳定。(2)内摩擦角与颗粒摩擦系数呈对数关系,与接触粘结力呈抛物线关系。(3)细-宏观参数关系式是在含水率为7%室内试验结果基础上研究得出,将关系式运用到含水率为9%和11%的室内试验结果进行标定验证:依据含水率为9%和11%室内试验得到的c和φ值,运用细-宏观参数关系式计算得到细观参数,经验证其数值-室内试验结果相对误差在10%以内,说明通过细-宏观力学关系式得到的细观参数符合精度要求,关系式可靠。为后续土石混合体数值试验研究者进行细观参数标定工作提供了参考依据。     

Comparison Study of Constitutive Models for Overconsolidated Clays

Widely distributed in natural deposits,the overconsolidated(OC)clays have attracted extensive experimental investigations on their mechanical behaviors,especially in the 1960s and 1970s.Based on these results,numerous constitutive models have also been established.These models generally fall into two categories:one based on the classical plasticity theory and the other the bounding surface(BS)plasticity theory,with the latter being more popular and successful.The BS concept and the subloading surface(SS)concept are the two major BS plasticity theories.The features of these two concepts and the representative models based on them are introduced,respectively.The unified hardening(UH)model for OC clays is also based on the BS plasticity theory but distinguishes itself from other models by the integration of the reference yield surface,unified hardening parameter,potential failure stress ratio,arid transformed stress tensor.Modification is made to the Hvorslev envelop employed in the UH model to improve its capability of describing the behaviors of clays with extremely high overconsolidation ratio in this paper.The comparison among the BS model,SS model,and UH model is performed.Evidence shows that all these three models can characterize the fundamental behaviors of OC clays,such as the stress dilatancy,strain softening and attainment of the critical state.The UH model with the revised Hvorslev envelop has the fewest parameters which are identical to those of the modified Cam-Clay model.     

高速磁浮双向主动控制系统模型参数分析

磁浮控制系统是磁浮列车的重要组成部分,是保证磁浮运行的安全性和平稳性的关键部分.本文以PID控制器为研究对象,为了研究磁浮列车中悬浮控制的动态性能与控制参数的变化规律,建立了基于状态反馈的PID磁浮控制系统的数学模型,并通过多体动力学软件SIMPACK联合可视化仿真工具MATLAB/SIMULINK建立了耦合分析模型,进行了多参数的比较分析.系统讨论了单磁铁控制器在不同PID控制参数下,磁浮间隙和磁浮电磁铁加速度等监测控制量的变化曲线,并针对双向受力状态的不同,分别研究了具体工况下高速磁浮的竖向和横向控制性能.研究表明:本文所使用的高速磁浮控制系统模型,具有较强的抗干扰性和鲁棒性,控制性能优秀,其参数分析方法可为未来实际工程的建设提供技术支撑.     

板结构功率流的参数研究

板以及肋板结构在工程中有着广泛的应用，其振动嗓声问题一直受到理论和工程领域的关注。本文在板结构功率流理论的基础上￣［１］，对板的损耗因子和不同加肋形式对其功率流的影响进行了分析和测量。     

Chemo-Mechanical Consolidation of Clays: Analytical Solutions for a Linearized One-Dimensional Problem

Consolidation (and swelling) of clayey soils caused by change in chemistry of pore fluid is addressed. Such phenomena are caused by changes in the concentration of various species in the solution and result primarily from a stress-independent deformation of individual clusters, and from a mechanical weakening or strengthening of the clay solid matrix in the presence of stress. Second, transport of chemicals that involves concentration gradients induces additional driving forces of osmotic consolidation due to semipermeable membrane nature of clay. In this paper an extension of Terzaghi's model of the mechanical consolidation to incorporate chemical loading of soil is proposed. A linearized model is used to solve analytically two one-dimensional problems of consolidation of a homogeneous layer simulating a landfill liner with drained or undrained boundaries. The numerical results show a strong dependence of distribution of pore pressure on the chemical load and chemically induced settlements of soil to be comparable to the mechanical ones.     

Study of the Dynamical Parameters of Vibration Machine for Compaction of Construction Mixes

International Applied Mechanics - The interaction between the construction mix and the work tool of an electromagnetic shock-vibrating machine during vibrocompaction is studied. The physical model...     

柱状电极屈曲或裂纹扩展的临界力学参数研究

柱形结构电极是近年来使用最为广泛的锂电池电极结构之一.本文以硅材料细长柱形电极为例,研究了充电电流大小、电极长径比、初始裂纹长度以及断裂韧性对于电极的屈曲现象和裂纹扩展现象发生时间的影响.计算结果表明,屈曲与裂纹扩展现象出现的先后顺序与充电电流大小无关;具有小的长径比,大的初始裂纹长度以及较小断裂韧性的电极,裂纹扩展比屈曲现象更早发生.对于硅材料,不同长径比的电极具有不同临界断裂韧性值,当材料的断裂韧性小于该临界值,在锂化过程中裂纹扩展会先于屈曲现象发生;该临界断裂韧性值随初始裂纹长度的增加而增加.本文的结论对于电极的结构设计以及材料选取具有一定指导意义.     

Macroscopic and Micromechanical Approaches to the Modelling of the Osmotic Swelling in Clays

The osmotic swelling in clays has been extensively studied at the physico-chemical scale. The present paper addresses the question of the modelling of this phenomenon from the mechanical point of view. First, the classical macroscopic thermodynamic framework for saturated porous continua is extended in order to take into account the solid-salt interaction through the concept of macroscopic activity coefficient of the salt. The micromechanical approach then incorporates this interaction through the concept of swelling pressure which is used for describing the internal forces in the fluid phase at the microscopic scale. The results of a physico-chemical theory for the solid-salt interaction, such as the e.d.l. theory, can be introduced in both approaches. Each of them leads to the identification of a deviation, of chemical origin, to Terzaghi's effective stress principle. Besides, the micromechanical approach allows us to clearly differentiate the mechanical and the chemical parts of clay materials elasticity.     

相近参数拉索的同/异步振动特性研究

辅助索被认为是一种具有潜力的减振手段,但仅在拉索间发生异步振动时才能取得良好的效果．然而,目前对拉索同/异步振动机理尚缺乏系统研究,为此对双水平索进行了模型试验研究．试验主要关注两根不同垂跨比水平拉索跨中面内响应的相位关系．首先对模型进行不同激励频率和保持激励幅值不变下的振动测试,发现垂跨比相同时,两根索相位差基本保持一致;垂跨比不同时,两根索由同步振动转为异步振动．同时采用有限元软件模拟测试实验,其结果与实验吻合良好．为更进一步探究其机理,对试验模型进行了相同激励幅值下的扫频试验．通过对双索幅频特性和相频特性的分析,发现拉索相近参数导致共振区错位是双索存在异步振动现象的根本原因．     

The Relevance of a Back-Scatter Model for Depth-Averaged Flow Simulation

This study demonstrates the importance of a sophisticated sub-grid model when performing a depth-averaged unsteady RANS simulation of a shallow flow. The reduction of resolution and the spatial dimensions exclude important physical processes as present in three-dimensional turbulence. Especially the effect of the bottom turbulence on the formation of horizontal eddies appears of key importance. A method is proposed to incorporate these effects by means of a kinematic simulation that mimics the residual turbulent fluctuations in a straight channel flow after depth-averaging. This method is developed in the context of the evolution of large eddies in a shallow mixing layer. A comparison with experiments shows that the proposed method works satisfactory. Naturally, it does not fully account for the omission of all 3D-effects.     

The Relevance of Water Vapour Transport for Water Vapour Sorption Experiments on Small Wooden Samples

Transport in Porous Media - To characterise the sorption behaviour of wood or other hygroscopic materials with the use of water vapour sorption experiments, an accurate understanding of water...