DISTRIBUTION OF RANDOM ELEMENTS SUBJECTED TO A FLEXIBLE BOUNDARY CONDITION

The probability distribution function of n random elements subjected to the flexible boundary condition is derived. The probability density is a descending curve and converges to a delta function as n tends to infinity. The distribution of the minimum value is discussed in context of ordered statistics.     

各向异性非线性固体力学的规范空间理论

本文在弹性规范空间概念基础上，利用非平衡态热力学理论，证明了各向异性固体力学非线性问题规范空间场以及不可逆过程本征解的存在。损伤对结构刚度的弱化效应和损伤诱发各向异性效应分别反映在本征弹性和相应的模态向量中。在简正坐标中考察各向异性体变形时，材料的行为以六个普通的粘弹性Ｍａｘｗｅｌｌ方程描述，总的响应由模态叠加得到。以此为基础给出的非线性本构方程具有坐标转换不变性，最后给出了二个具体的算例。     

多失效模式重要抽样法的方差分析及应用

在计算结构体系失效概率时,基于Monte-Carlo数值模拟的重要抽样技术已被实践证明是一种非常有效的方法。重要抽样法中估计量的方差是影响收敛速度和计算精度的重要指标,因此重要抽样法的方差分析是非常必要的。对于单模式而言,其方差分析比较容易。对于多模式情况,其方差分析有一定的困难。这有可能影响重要抽样法在多模式结构体系失效概率计算中的应用。本文详细推导了几种常见重要抽样法的方差计算公式。然后用方差分析的概念,阐明了多模式重要抽样法应用中的一些问题。     

工程力学矢量的规范表示与弹性力学的不变性

通过引入规范变换，消除了工程力学矢量数学表示上的物理缺陷，使规范化力学矢量与力学张量具有物理上的等价表示，从而奠定了不变性弹性力学的基础，为它在不同坐标下的具体应用提供了理论保障。     

基于反应谱值分析的爆破震动破坏评估研究

采用反应谱方法研究了爆破震动信号的振动速度和频率特征,提出了采用反应谱曲线积分值来评估爆破震动破坏效应。通过对289组爆破地震波数据的统计表明,在反应谱曲线的积分值小于5时,爆破地震动不会对所研究的普通民房结构物产生震动破坏效应。     

Disk-shaped compact tension test for asphalt concrete fracture

A disk-shaped compact tension (DC(T)) test has been developed as a practical method for obtaining the fracture energy of asphalt concrete. The main purpose of the development of this specimen geometry is the ability to test cylindrical cores obtained from in-place asphalt concrete pavements or gyratory-compacted specimens fabricated during the mixture design process. A suitable specimen geometry was developed using the ASTM E399 standard for compact tension testing of metals as a starting point. After finalizing the specimen geometry, a typical asphalt concrete surface mixture was tested at various temperatures and loading rates to evaluate the proposed DC(T) configuration. The variability of the fracture energy obtained from the DC(T) geometry was found to be comparable with the variability associated with other fracture tests for asphalt concrete. The ability of the test to detect changes in the fracture energy with the various testing conditions (temperature and loading rate) was the benchmark for determining the potential of using the DC(T) geometry. The test has the capability to capture the transition of asphalt concrete from a brittle material at low temperatures to a more ductile material at higher temperatures. Because testing was conducted on ungrooved specimens, special care was taken to quantify deviations of the crack path from the pure mode I crack path. An analysis of variance of test data revealed that the prototype DC(T) can detect statistical differences in fracture energy resulting for tests conducted across a useful range of test temperatures and loading rates. This specific analysis also indicated that fracture energy is not correlated to crack deviation angle. This paper also provides an overview of ongoing work integrating experimental results and observations with numerical analysis by means of a cohesive zone model tailored for asphalt concrete fracture behavior.     

毫瓦计──功率变化量测量仪

本文介绍的毫瓦计是测量陀螺马达轴承摩擦力矩稳定性的一种新型仪器，为该仪器专门设计了功率测量和变化量测量方案，其优点是测量精度高、简单、可靠、实用性强。     

流对波边界层湍流运动的影响

采用大涡模拟方法和Smagorinsky亚格子模型，求解三维Navier-Stokes方程，研究了波流边界层中的湍流特性．将大涡模拟结果与相应的直接数值模拟结果和实验数据进行比较，吻合较好．获得了不同波雷诺数，不同波流比情况下的大涡模拟数据库，并由此分析了波流边界层中各种湍流统计量，如速度廓线、剪应力、湍流强度等的变化规律．     

Elastic properties of model random three-dimensional open-cell solids

Most cellular solids are random materials, while practically all theoretical structure-property relations are for periodic models. To generate theoretical results for random models the finite element method (FEM) was used to study the elastic properties of open-cell solids. We have computed the density (ρ) and microstructure dependence of the Young's modulus (E) and Poisson's ratio (ν) for four different isotropic random models. The models were based on Voronoi tessellations, level-cut Gaussian random fields, and nearest neighbour node-bond rules. These models were chosen to broadly represent the structure of foamed solids and other (non-foamed) cellular materials. At low densities, the Young's modulus can be described by the relation E∝ρⁿ. The exponent n and constant of proportionality depend on microstructure. We find 1.3<n<3, indicating a more complex dependence than indicated by periodic cell theories, which predict n=1 or 2. The observed variance in the exponent was found to be consistent with experimental data. At low densities we found that ν≈0.25 for three of the four models studied. In contrast, the Voronoi tessellation, which is a common model of foams, became approximately incompressible (ν≈0.5). This behaviour is not commonly observed experimentally. Our studies showed the result was robust to polydispersity and that a relatively large number (15%) of the bonds must be broken to significantly reduce the low-density Poission's ratio to ν≈0.33.     

基于激光雷达的垂直能见度反演算法及其误差评估

针对大气垂直方向上消光系数分布不均匀难以用传统方法直接测量垂直能见度的问题,提出了一种基于激光雷达探测垂直能见度的计算方法。根据大气辐射传输基本原理,借助于辐射传输方程,推导出了垂直能见度的计算公式;然后利用激光雷达原理方程和Klett算法反演出大气垂直方向上的消光系数分布,基于此提出了垂直能见度的迭代算法。最后,利用灰色模型GM(1,1)和批统计算法,对激光雷达反演得到的后向散射系数进行了评估,给出了误差置信区间为(0.760±0.339)×10^-4(srad·km)^-1。结果表明,该方法是一种特别有效的计算垂直能见度的方法,符合探测的基本需求,且误差小精度高。