TRANSIENT THERMOELASTIC SOLUTION OF A MULTILAYERED ORTHOTROPIC HOLLOW CYLINDER FOR AXISYMMETRIC PROBLEMS

The thermoelastic dynamic solution of a multilayered orthotropic hollow cylinder in the state of axisymmetric plane strain is obtained. By the method of superposition, the displacement is divided into two parts: one is quasi static and the other is dynamic. The quasi-static solution is derived by the state-space method, and the dynamic solution is obtained by the separation-of-variables method coupled with the initial parameter method as well as the orthogonal expansion technique. The present method is suitable for a multilayered orthotropic hollow cylinder consisting of arbitrary layers and subjected to arbitrary axisymmetric thermal loads. Numerical results are finally presented and discussed.     

CYCLIC LOADING OF THERMAL STRESSES

The isotropic and kinematic hardening theories of plasticity are used to evaluate the cyclic loading behavior of structures under thermal stresses. The material of the structures used in this article is assumed to follow nonlinear strain hardening property. The material's strain hardening curve in tension and compression is assumed to be both identical for isotropic material and different for anisotropic material. The method of successive approximation is used to calculate the stresses and plastic strains in the structure due to cyclic loadings. The results of the analysis are checked with the known experimental test. The thermal stresses are categorized into load- and deformation-controlled stresses. It is concluded that the isotropic hardening theory, excluding creep, will always result in structural shakedown. The kinematic hardening theory under deformation-controlled conditions, excluding creep, will result in reversed plasticity. The load-controlled cyclic loading under kinematic hardening theory with isotropy assumption results in reversed plasticity. Under the anisotropy assumption of tension/compression curve, the load-controlled stress based on kinematic hardening theory predicts ratcheting behavior. When creep deformation is considered, the load-controlled thermal stresses results in ratcheting, and the deformation-controlled thermal stresses result in shakedown behavior, regardless of the material's isotropic and anisotropic properties or the hardening theories.     

THERMOELASTIC INTERACTIONS WITHOUT ENERGY DISSIPATION IN AN UNBOUNDED MEDIUM WITH A SPHERICAL CAVITY DUE TO A THERMAL SHOCK AT THE BOUNDARY

Thermoelastic interactions without energy dissipation in an unbounded elastic medium with a spherical cavity have been investigated. The cavity surface is assumed to be stress free and is subjected to a thermal shock. The solutions for displacement, temperature, and stresses are obtained using the Laplace transform procedure. The discontinuities of the distributions of the physical quantities are determined and compared with earlier findings. The inversions are also carried out with a numerical method based on Fourier series expansions of functions. The results are compared with the corresponding results obtained in cases of conventional thermoelasticity theory and the generalized theories of thermoelasticity with thermal relaxation time parameters.     

基于GIS的云南泸水市生态安全评价

云南省泸水市位于"三江并流"的世界自然遗产地,是中国香格里拉生态旅游区的重要组成部分,近年来由于各种原因导致其生态环境恶化,需要对泸水市开展生态安全评价,以为泸水市生态保护工作提供参考。从研究区主要的生态问题、人类干扰、自然要素角度,构建了该区生态安全评价指标体系,综合运用层次分析法、熵值法和GIS空间分析技术对泸水市进行了区域生态安全评价。结果表明:泸水市平均生态安全指数为41.95,总体处于较安全水平;空间上,以怒江为轴线,沿怒江呈现出南北向带状分布特征,东西向以怒江为界,越接近怒江,生态安全水平越低,呈现一定的对称分布规律;不安全区与居民点的空间分布呈现一致性。以上结果说明:人类活动对生态安全的影响较大;组成生态不安全的区域中,耕地面积最大,超过了50%,其次为未利用地、建设用地;泸水市总体生态安全状况最好的乡镇为片马镇。     

Spatial ecology of reintroduced walleye (Sander vitreus) in Hamilton Harbour of Lake Ontario

Many coastal embayments in the Laurentian Great Lakes have been subjected to extensive human physical modification and pollution that has led to the loss of freshwater biodiversity. For example, Hamilton Harbour is a large coastal embayment situated at the western end of Lake Ontario, with a long history of industrial and urban development that has resulted in the loss and degradation of aquatic habitat and the extirpation of several fish species. To restore the fish community in Hamilton Harbour, several attempts have been made to increase apex predator biodiversity by reintroducing native walleye (Sander vitreus). To assess how reintroduced (i.e., stocked) walleye use Hamilton Harbour, we used acoustic telemetry to characterize the residency of individuals within the boundaries of the harbour as well as their seasonal space use, with a focused interest on the spring spawning period. During the 1?yr tracking period tagged walleye spent an average of 357?days (range 135–365?days) within the harbour. Most individuals (12/15) remained within the harbour during the entire spring spawning period, and over half of the tagged fish departed (n?=?7) at the end of summer and beginning of fall. Core use areas appeared to gradually shift more easterly as the seasons progressed from winter to summer. Results from this study indicate that stocked fish are resident within Hamilton Harbour for most of the year, including the reproductive period, which suggests that stocking efforts to re-establish walleye populations may be an effective restoration strategy if recruitment is successful.     

土壤剖面硝态氮浓度分布的随机-对流传递函模模拟

依据地中渗透计出流口处观测的硝态氮通量平均浓度动态, 建立土壤硝态氮迁移时间的概率密度函数, 由随机-对流假设, 得出某一时刻土壤剖面不同埋深处硝态氮迁移距离的驻留概率密度函数, 以其作为响应函数构造对流对数正态传递函数模型, 仿真拟稳定流条件下田间土壤剖面硝态氮的驻留浓度分布. 经与实测资料对比, 表明模拟值与实测值有着较好的一致性.     

数值计算中一类病态不适定问题的求解方法

利用奇异值分解研究了工程计算中常见的最小二乘法及大条件数下病态问题的不适定，并给出了具体的求解方法，结果表明，该算法是有效的。     

基于抽水试验的渗流问题摄动随机反演方法

针对地下水渗流随机参数反演问题,在正演随机模拟方法的基础上,结合非平稳随机过程变量的一阶Taylor展开式和随机参数的摄动方程,讨论了多随机参数反演问题,提出了基于抽水试验的渗流问题摄动随机反演方法,给出一阶均值反演准则,得到多随机变量的均值和方差的近似表示方法。该方法在计算均值时采用改进的遗传算法,在计算方差时采用分组统计的方法。最后给出了一个基于Thies模型反演导水系数和贮水系数的例子,计算结果表明,该方法可以较好的求取参数的均值,近似地求取参数方差。     

物理性流域水文模型研究新进展

在计算机、空间观测等相关学科发展的推动下,物理性流域水文模型目前己成为流域水文模拟研究的重要发展方向。国内外很多学者通过一些新理论、新方法的应用,促进了物理性水文模型的研究,同时也使它成为了一个充满机遇和挑战的活跃领域。传统的物理性流域水文模型以数值求解控制水流运动的偏微分方程组为基本手段,存在模型应用尺度和方程适用尺度不匹配的尺度问题。为了解决这一问题,学者们开展了大量的思考和研究,同时也构成了当代水文学理论研究的中心内容,目前在物理性流域水文模型方面的研究可以归结为3个代表性的发展方向：在物理性和计算效率之间取得平衡的准物理性水文模型、基于不规则网格的物理性水文模型以及直接在宏观尺度建立数学物理方程的尺度协调的物理性水文模型。     

三峡船闸高边坡设计实践中几个问题的再认识

根据前期设计论证,三峡船闸上部边坡开挖达到基本自稳,辅以排水及锚固,下部为直立坡与薄混凝土衬砌闸墙相结合.在施工过程中,遇到如何控制边坡开挖形态与闸室结构型式,中隔墩岩体保留与利用,坡面块体,排水隧洞的完整性,锚索的结构型式及钢绞线的强度利用系数等一系列问题.这些问题在施工过程中进行了分析.并通过动态设计方法,得到了较好的解决.