非对称矩阵特征值问题密集模态重分析方法

本文提出了一种非对称矩阵特征值问题的密集模态重分析方法。它将原密集特征值问题表达为与其临近的某一重特征值问题的小摄动,从而密集模态的重分析问题就转化为重频模态的重分析问题。     

非对称矩阵特征值问题密集模态重分析方法

本文提出了一种非对称矩阵特征值问题的密集模态重分析方法，它将原密集特征问题表达为与其临近的某一重特征值的小摄动。从而密集模态的重分析问题就转重频模态的重分析问题。     

密集模态摄动的新方法

本文提出了一种密集模态结构系统(M_0,K_0)振动分析的矩阵摄动新方法.它将密集模态结构系统特征解的摄动问题转化为重特征值的摄动问题.文中给出了一个数值例子.     

对胡海昌的小参数法的补充

专著提出了计算特征向量摄动的一种非模态展开法，本文对这一方法中参数μ或者矩阵μ如何选取的问题进行了研究，分析了μ的数学本质，并指出对于重特征值问题，μ只要是一个适当选定的标量常数既可，无需是个矩阵。     

矩阵摄动法在汽车车架模态分析中的应用

本文采用以模态迭加原理为基础的实模态分析技术及初参数优选法对汽车车架的模态参数进行了识别,讨论了振动特征值问题中关于非重特征值和重特征值的矩阵摄动法,提出了利用有弹性元件悬挂的结构振动测试数据来得到自由——自由结构的模态参数的摄动修正方法.文中还给出了一些数值例子来说明此方法的应用,同时得到了一些重要结论.     

任意非亏损系统特征灵敏度分析的直接摄动法

本文发展了一种任意非亏损系统特征灵敏度分析的二阶段摄动法，将未摄动的问题的解作为零阶近似，把摄动影响作为摄动后问题的高阶修正，经过严格的数学推导，得到了支配高阶修正量的完全方程组。本方法无损知道摄问题的全部特征向量，仅需知被摄模态的特征对。本方法可处理被摄问题具有重特征值，甚至具有等导重特征值这一高度退化极难处理的情况。算例显示了本方法的正确性。     

矩阵摄动理论在六轴机车横向运动稳定性分析中的应用

本文提出了一种分析机车横向运动稳定性的方法,即利用复膜态的矩阵摄动法来计算临界速度,该方法避免了反复计算矩阵的特征值从而可节约大量的计算时间,对矩阵摄动法计算精度的研究结果表明,该方法的的精度是足够的。     

基于有限元分析的特征值反问题求解的逆摄动方法

本文研究特征值反问题的求解方法,根据广义特征值反问题理论和有限元法的特点,以转子系统平面梁单元有限元模型结构分析的特征值反问题求解为例,给出一种新的逆摄动方法,给出了本逆摄动法较完整的理论基础,给出了其逆摄动参数的显式计算公式及相应的取值方法,本逆摄动法也可推广到其他单元类型的有限元模型特征值反问题的求解。     

不确定参数闭环控制系统特征值的区间分析

运用区间理论,讨论了区间参数的结构振动控制问题,给出了求解闭环系统区间特征值的一种方法．基于区间参数导出了区间刚度矩阵和质量矩阵,然后利用矩阵摄动理论和区间扩张理论,推导了复区间特征值上下界估计的算法．这些结果是从二阶系统的左右特征向量出发得到的．将该文方法应用到悬臂梁的控制问题,数值结果表明它是有效的．     

结构固有频率区域的两种摄动算法

当结构参数具有误差或有界不确定性时，区间数学可以在不知道不确定变量的概率分布的情况下定量地考察不确定参数对响应的影响。为计算出不克腚结构参数对结构振动固有频率影响范围的上下界，本文通过对所的两种区间摄动方法分析和数值运算可以看出，相对区间矩阵摄动法，参数摄动方法不仅可提高结构特征值的求解效率，而且所计算结构特征值上下界的宽度比区间矩阵摄动方法所计算出的要小，数值结果说明所提出方法的有效性。     

一种基于直接计算高阶奇异积分的断裂力学双边界积分方程分析法

相对于有限元法,边界单元法在求解断裂问题上有着独特的优势,现有的边界单元法中主要有子区域法和双边界积分方程法.采用一种改进的双边界积分方程法求解二维、三维断裂问题的应力强度因子,对非裂纹边界采用传统的位移边界积分方程,只需对裂纹面中的一面采用面力边界积分方程,并以裂纹间断位移为未知量直接用于计算应力强度因子.采用一种高阶奇异积分的直接法计算面力边界积分方程中的超强奇异积分;对于裂纹尖端单元,提供了三种不同形式的间断位移插值函数,采用两点公式计算应力强度因子.给出了多个具体的算例,与现存的精确解或参考解对比,可得到高精度的计算结果.      

汶川地震诱发文家沟巨型滑坡 碎屑流基本特征及成因机制初步分析


2008年5月12日,汶川M80地震在四川省绵竹市清平乡文家沟内诱发一巨型滑坡。通过现场调查得知,滑坡前后缘高差455m,厚度20～30m,滑面为基岩层面,初始方量2750×107m3。滑体在运动中转化为碎屑流。滑坡-碎屑流总的水平运动距离为4022m,垂直运动距离为1443m,遗留的堆积物体积达5×107m3。滑坡距映秀—北川断裂仅36km,位于其下盘,地震烈度达XI度。滑坡导致文家沟中48人遇害,并形成一条完整的地震次生地质灾害链。初步分析表明滑坡启动速度快,滑坡向碎屑流转化过程明显、地点明确。碎屑流运动过程复杂,伴有强烈的“气垫效应”和“前缘气浪冲击效应”。作者认为,文家沟滑坡的高启动速度是长持时强烈地震动作用的结果,与山体的猛烈碰撞是导致滑体解体并转化为碎屑流的原因。     

Preface: Orbits around asteroid

One of the core issues in modern celestial mechanics is the orbital dynamics in the near-regime gravitational field of as- teroids, which provides deep insights into the mathematical nature of a class of nonlinear systems, and plays as a critical basis for in situ explorations of different science goals. Lots of efforts have been made to reveal the characteristics of orbital motion in the vicinity of asteroids, and to improve the skills of asteroid research in methodology.     

Effet de l'anisotropie élastique cristalline sur la distribution des facteurs de Schmid à la surface des polycristauxInfluence of crystalline elasticity anisotropy on Schmid factor distribution at the free surface of polycrystals

Experimental studies of the plasticity mechanisms of polycrystals are usually based on the Schmid factor distribution supposing crystalline elasticity isotropy. A numerical evaluation of the effect of crystalline elasticity anisotropy on the apparent Schmid factor distribution at the free surface of polycrystals is presented. Cubic elasticity is considered. Order II stresses (averaged on all grains with the same crystallographic orientation) as well as variations between averages computed on grains with the same crystallographic orientation but with different neighbour grains are computed. The Finite Element Method is used. Commonly studied metals presenting an increasing anisotropy degree are considered (aluminium, nickel, austenite, copper). Concerning order II stresses in strongly anisotropic metals, the apparent Schmid factor distribution is drifted towards small Schmid factor values (the maximum Schmid factor is equal to 0.43 instead of 0.5) and the slip activation order between characteristic orientations of the crystallographic standard triangle is modified. The computed square deviations of the stresses averaged on grains with the same crystallographic orientation but with different neighbour grains are a bit higher than the second order ones (inter-orientation scatter). Our numerical evaluations agree quantitatively with several observations and measures of the literature concerning stress and strain distribution in copper and austenite polycrystals submitted to low amplitude loadings. Hopefully, the given apparent Schmid factor distributions could help to better understand the observations of the plasticity mechanisms taking place at the free surface of polycrystals. To cite this article: M. Sauzay, C. R. Mecanique 334 (2006).     

Nonlinear behavior of matrix-inclusion composites under high confining pressure: application to concrete and mortar

This paper is devoted to a micromechanics-based simulation of the response of concrete to hydrostatic and oedometric compressions. Concrete is described as a composite made up of a cement matrix in which rigid inclusions are embedded. The focus is put on the role of the interface between matrix and inclusion which represent the interfacial transition zone (ITZ). A plastic behavior is considered for both the matrix and the interfaces. The effective response of the composite is derived from the modified secant method adapted to the situation of imperfect interfaces. To cite this article: T.H. Le et al., C. R. Mecanique 336 (2008).     

Dynamics and Breakup of Viscoelastic Liquids (A Review)

The phenomena of hydrodynamic breakup of liquid jets, drops, films, bridges, and filaments are reviewed for liquids with viscoelastic properties. The reasons for breakup are capillary instabilities, collisions with rigid obstacles, and other forms of dynamic action. The relationship between the properties of the liquids and the features of the breakup process is discussed.     

Flow stability analysis and excitation using pulsating jets

Classical flow stability applied to transition from laminar to turbulent flow may also describe the behavior of vorticity fluctuations created by a pulsating jet placed along a solid boundary. A numerical laminar flow experiment involving a pulsating jet placed along the surface of a duct with flow separation downstream, resulted in eliminating most part of the separated flow region. Applying the same approach to a turbulent flow, it was possible to develop a turbulent stability flow formulation and apply successfully turbulent pulsating jet flow separation control. To cite this article: D. Skamnakis, K. Papailiou, C. R. Mecanique 333 (2005).