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针对连续Bernoulli-Euler和Timoshenko梁单元的动态刚度矩阵，分析了在使用连续梁单元 进行结构动态特性分析中的数值问题. 基于连续梁单元的运动方程，导出了连续 Bernoulli-Euler和Timoshenko梁单元的动态刚度矩阵. 分析了影响动态刚度矩阵中双曲函 数自变量的各个独立变量及其产生的影响，并给出了初估连续梁单元合理长度的方法. 使用 单一连续Bernoulli-Euler和Timoshenko梁单元的动态刚度矩阵分别进行了悬臂梁频响曲线 的数值求解. 研究表明，在合理选择连续梁单元的长度时，大多数工程结构的动态特性分析 中都不会产生数值问题.     

岩体力学中流变与断裂的耦合作用

本文首先分析含Ｉ型裂纹岩石的流变断裂特性，提出了Ⅰ型裂纹流变断裂初度的三个阈值；然后应用断裂力学和粘塑性理论。得出了具有屈服、蠕变和Ⅱ型裂纹扩展等物理力学特性的岩体隧洞的衬砌与围岩应力的解析表达式。     

强震作用下考虑岩石塑性应变梯度的地下隧道失稳分析

本文首先引入岩石塑性应变梯度理论，地下隧道受开挖的影响，岩石的原岩应力重新分布，靠近隧道岩石变形局部化，往往出现塑性变形区，作者进一步论证了，靠近隧道岩石在建立地下震动作用下的数学力学模型时须考虑塑性应变梯度，进而从地下隧道弹塑性区内抽象出一个单元体，这个单元体在地震横波作用下受力状态必须是纯剪应力状态，并假设岩石的力学本构关系为双线性，建立了单元体在地震横波作用下受力状态必然是纯剪应力状态，并假设岩石的力学本构关系为双线性，建立了单元体数学力学模型，推导出软化区的宽度为α（α＝2πl)，基于上述，最后解决了地下隧道失稳破坏的力学机理。     

数值流形方法及其在岩石力学中的应用

数值流形方法是目前岩石力学分析的主要方法之一.该方法起源于不连续变形分析,主要用于统一求解连续和非连续问题,其核心技术是在分析时采用了双重网格:数学网格提供的节点形成求解域的有限覆盖和权函数;而物理网格为求解的积分域.数学网格被用来建立数学覆盖,数学覆盖与物理网格的交集定义为物理覆盖,由物理覆盖的交集形成流形单元.流形方法的优点在于它使用了独立的数学和物理网格,具有和有限元明显不同的定义形式,且数学网格对于同一问题不同的求解精度的需求可以很方便地细化.由于该方法考虑了块体运动学,可以模拟节理岩体裂隙的开裂和闭合过程,因而在岩石力学中得到了广泛应用,近年来许多学者对该方法进行了研究.本文简要叙述了节理岩体的数值方法从连续到非连续的发展过程,详细地介绍了数值流形方法的组成和数值流形方法在岩石力学及其相关领域的研究和发展概况,最后就作者所关心的一些问题,如三维问题的数值流形方法、数值流形方法在物理非线性问题和裂纹扩展问题中的应用、相关的耦合方法等进行了探讨.     

连续梁在周期荷载下的动力稳定性简化分析方法

对于一般任意支撑的连续梁结构动力稳定性问题，已有的计算方法求解过程都很复杂，给工程设计带来极大的不便．本文提出了一个简化的分析方法，利用现有的商业软件，只需求得连续梁的自然频率及静力屈曲（失稳）荷载，就可容易得到结构的动力失稳区域，当考虑结构阻尼对不稳定区域的影响时，可将阻尼矩阵表达为Rayleigh阻尼的形式．研究结果表明：采用本文计算方法与已有的理论计算方法得到的连续梁主参数共振的不稳定边界非常吻合，而本文计算方法更为简单，计算结果可靠，计算精度高，可满足工程设计的需要．     

三峡工程中的若干力学问题

简要介绍了三峡水利枢纽工程概况，工程建设中主要技术难点，以及几个主要工程力学问题，包括流体力学、固体力学、二相流及爆破力学等问题．结合三峡工程侧重叙述岩石（体）力学应考虑的新问题．大型岩土工程是庞大的复杂系统，岩石力学涉及众多学科．建议应用系统工程的理论和方法研究岩石（体）力学，使其在国民经济中发挥更大作用，在岩石（体）力学研究中还需针对不同的目标、任务考虑各种非线性问题．因此，岩石（体）力学应与工程问题更紧密地结合．     

岩石强度准则的主应力显式表达式几何推导及应用

主应力是岩石强度准则的基本量，然而，给定应力张量求解主应力的三次特征方程通常难以求解。本文通过几何关系将主应力的三次代数方程转化为三元一次方程组的求解，最终建立了三个主应力关于应力张量不变量的显式表达式，并着重推演了其在静水压力效应的刻画、三维强度准则的推导和空间屈服面的绘制中的应用。可为岩石真三轴试验数据可视化提供参考，同时丰富了弹塑性力学教学内容。     

轴向力作用任意不连续梁自由振动分析的广义函数解

摘要：首先运用分布理论建立了轴向力作用下含多个不连续点的欧拉梁的自由振动的统一微分方程。不连续点的影响由广义函数（Dirac delta函数）引入梁的振动方程。微分方程运用Laplace变换方法求解;与传统方法不同的是,本文方法适用于含任意类型的不连续点和多种不连续点组合情况的梁,求得的模态函数为整个不连续梁的一般解。由于模态函数的统一化以及连续条件的退化,特征值的求解得到了极大的简化。最后,以轴向力作用下多跨梁—弹簧质量块系统模型为例验证了本文方法的正确性与有效性。     

梁-桩-土竖向耦合振动特性分析

针对桩与连续梁组合这一基础形式,研究了梁-桩-土竖向耦合振动特性. 首先,将桩假设为一维黏弹性杆件,采用平面应变模型模拟桩侧成层土对桩的动力作用. 同时,桩顶对梁的支撑简化为竖向点支撑. 然后,分别根据一维杆件纵向振动理论和Timoshenko梁理论给出桩和梁的竖向振动控制方程并求解,进而借助离散傅里叶逆变换获得在梁上瞬时激振下梁和土层以上桩段的时域响应半解析解. 通过与有限元模拟结果对比,验证了解的合理性. 在此基础上,讨论了梁几何参数和桩身缺陷对梁-桩-土竖向耦合振动特性的影响.     

A p-TYPE SUPERCONVERGENT RECOVERY METHOD FOR FE ELASTIC STABILITY ANALYSIS OF EULER BEAMS1)

本文将有限元p型超收敛算法应用于欧拉梁弹性稳定分析。该法基于有限元解答中失稳载荷和失稳模态结点位移的超收敛特性，建立了单元上失稳模态近似满足的线性常微分方程边值问题，在每个单元上，对该边值问题采用一个高次元进行求解，获得失稳模态的超收敛解，再将失稳模态的超收敛解代入瑞利商的解析表达式，最终获得失稳载荷的超收敛解。该法思路简明，通过少量计算即可显著提高失稳载荷和失稳模态的精度与收敛阶。数值算例表明，该法高效、可靠，值得进一步研究和推广到各类杆系结构。     

Preface: Current research progress on mechanics of high speed rail

The construction and operation of high-speed rail（HSR）grid within the past two decades in China,in terms of the scale,may be possibly comparable to any national-wide construction in the history of China,even the Great Wall.By counting railways with commercial train service at the speed of200 km/h,China has the world’s longest HSR network with over 19 369.8 km of track in service today and this number     

ACTA MECHANICA SINICA 2014 ANNUAL SUBJECT INDEX

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人造地震动合成中的位移误差分析

三角函数级数法是合成人工地震动常用算法之一,但是通过对加速度积分求取位移时,却存在与零线漂移相类似的位移漂移现象。     

Rainwater rivulets on a cable subject to windFilets d'eau de pluie sur un câble soumis au vent

Rainwater rivulets appear on inclined cables of cable-stayed bridges when wind and rain occur simultaneously. In a restricted range of parameters this is known to cause vibrations of high amplitudes on the cable. The mechanism underlying this effect is still under debate but the role of rainwater rivulets is certain. We use a standard lubrication model to analyse the dynamics of a water film on a cylinder under the effect of gravity and wind load. A simple criterion is then proposed for the appearance and position of rivulets, where the Froude number is the control parameter. Experiments with several geometries of cylinder covered with water in a wind tunnel show the evolution of the rivulets with the Froude number. Comparison of the prediction by the model with these experimental data shows that the main mechanism of rivulet formation and positioning is captured. To cite this article: C. Lemaitre et al., C. R. Mecanique 334 (2006).     

Hermitian space-time finite elements for estuarine mass transport

Space-time finite element solutions of the convection–dispersion equation using higher-order nodal continuity and Hermitian polynomial shape functions are described. Five separate elements ranging from a complete linear element with C^0,0 nodal continuity to a complete first-order Hermitian element with C^1,1 nodal continuity are subjected to detailed analysis. Wave deformation analyses identify the source of leading or trailing edge oscillations, trailing edge oscillations being the major source of difficulty. These observations are confirmed by numerical experiments which further demonstrate the potential of higher-order nodal continuity. The performance of the complete first-order Hermitian element is quite satisfactory and measurably superior to the linear element.     

Cristallisation par onde acoustique : le cas de l'héliumCrystallization by acoustic waves: the case of helium

We establish a theoretical model to explain the nucleation of a crystal of helium by an acoustic over-pressure. We explain the interfacial laws for this ultra-fast cristallization, close to the sound speed. Assuming spherical symmetry and taking into account the experimental data, we recover the dynamics of the growth and melting during an over-pressure impulse. To cite this article: M. Ben Amar et al., C. R. Mecanique 331 (2003).     

Structure initiale et propriétés de liquéfaction statique d'un sableInitial structure and static liquefaction properties of sand.

Based on the use of two different preparation procedures for reconstituting triaxial samples of sand, i.e. wet tamping and dry pluviation, significant differences in associated mechanical behaviour are observed on a reference sand with respect to the phenomenon of ‘static’ liquefaction. Wet tamping favours the initiation of liquefaction instability, whereas dry pluviation favours a more stable behaviour, less susceptible to liquefaction. Microscopic observation of corresponding sand specimens allows us to identify two well differentiated structures, i.e., for wet tamping, an irregular structure with predominance of aggregates (aggregated grains) and macropores, very contractant and unstable and, for dry pluviation, a more regular structure, without macropores, more dilatant and more stable. These observations show the importance of further characterization, based on the introduction of appropriate parameters, of the initial structure of sandy materials, strongly dependant upon their mode of formation (natural or artificial). To cite this article: N. Benahmed et al., C. R. Mecanique 332 (2004).     

Sources of Complexity in Human Systems

Complex is a special attribute we can give to many kinds of systems. Although it is used often as a synonym of difficult, it has a specific epistemological meaning, which is going to be shared by the incoming science of complexity. Difficult is an object which, by means of an adequate computational power, can be deterministically or stochastically predictable. On the contrary complex is an object which can not be predictable because of logical impossibility or because its predictability would require a computational power far beyond any physical feasibility, now and forever. For complexity refers to some observing system, it is always subjective, and thus it is defined as observed irreducible complexity. Human systems are affected by several sources of complexity, belonging to three classes, in order of descending restrictivity. Systems belonging to the first class are not predictable at all, those belonging to the second class are predictable only through an infinite computational capacity, and those belonging to the third class are predictable only through a trans-computational capacity. The first class has two sources of complexity: logical complexity, directly deriving from self-reference and Gödel's incompleteness theorems, and relational complexity, resulting in a sort of indeterminacy principle occurring in social systems. The second class has three sources of complexity: gnosiological complexity, which consists of the variety of possible perceptions; semiotic complexity, which represents the infinite possible interpretations of signs and facts; and chaotic complexity, which characterizes phenomena of nonlinear dynamic systems. The third class coincides with computational complexity, which basically coincides with the mathematical concept of intractability. Artificial, natural, biological and human systems are characterized by the influence of different sources of complexity, and the latter appear to be the most complex.