土坡稳定Hasofer-Lind可靠度指标的计算方法

工程中较为常用的是Hasofer和Lind提出的不变二阶矩可靠度指标,可采用正交变换法、MonteCarlo法、优化等方法求解β值。使用优化方法求解Hasofer-Lind可靠度指标,避免了相关变量的独立变换以及求极限状态函数对基本变量的偏导数这两个问题。本文明确了Hasofer-Lind可靠度指标的物理意义,提出了Hasofer-Lind可靠度指标在Fortran语言中的优化求解方法,通过与Excel规划求解器计算结果对比,表明本方法计算结果可靠,多变量情况下可靠度指标能够迅速收敛。该方法直接在基本变量空间求解,与已有的利用Fortran语言编制的边坡稳定程序无缝连接,除了可以用于求解边坡稳定分析中c和φ相关问题之外,还可以计算考虑土工参数空间变异情况下的土坡可靠度指标。     

土坡稳定Hasofer-Lind可靠度指标的计算方法

工程中较为常用的是Hasofer和Lind提出的不变二阶矩可靠度指标,可采用正交变换法、MonteCarlo法、优化等方法求解β值.使用优化方法求解Hasofer-Lind可靠度指标,避免了相关变量的独立变换以及求极限状态函数对基本变量的偏导数这两个问题.本文明确了Hasofer-Lind可靠度指标的物理意义,提出了H...     

基于稳定分析法的碎石桩复合地基承载力的可靠度

采用圆弧滑动稳定分析方法 ,按实用的优化方法计算碎石桩复合地基承载力的可靠度指标 ,并讨论了建立在可靠度基础上的复合地基置换率的设计问题 .所用的可靠度计算公式直接在基本变量空间中求解 ,避免了繁琐的求偏导数和正交变换工作 .并且在分析中考虑了模型不确定性的影响 .由于在稳定分析时 ,最危险滑弧事先并不知道 ,所以用优化方法求可靠度指标有巨大的优越性 .本文利用 Microsoft Excel97中的“规划求解器”来求解安全系数和可靠度指标 .最后用一个算例说明了求解过程     

基于稳定分析法的碎石桩复合地基承载力的可靠度

采用圆绵滑动稳定分析方法，按实用的优化方法计算碎石桩复合地基承载力的可靠度指标，并讨论了建立在可靠度基础上的复合地基置换率的设计问题。所用的可靠度计算公式直接在基本变量空间中求解，避免了繁琐的求偏导数和正交变换工作，并且在分析中考虑了模型不确定性的影响，由于在稳定分析时，最危险滑绵事先并不知道，所以用优化方法求可靠度指标有巨大的优越性。本文利用Ｍｉｃｒｏｓｏｆｔ Ｅｘｃｅｌ９７中的”规划求解器”来     

基于非线性随机有限元的堤坝边坡可靠度分析

针对边坡稳定性分析中土体力学参数存在空间变异性的问题,提出了计算堤坝边坡安全系数分布的随机有限元方法,以及求解边坡可靠度的蒙特卡罗(MC)强度折减联合法与MC直接法。以各向同性二维边坡为例,首先抽样得到相应的材料特性随机场,随后求得边坡位移、应力及塑性区;然后在对随机场进行N_MC次抽样的基础上采用以下方法得到边坡的失效概率并对可靠度指标进行求解分析：(1)联合法(M1),通过强度折减法得到各样本条件下的折减系数及其分布;(2)MC直接法(M2),利用黏塑性方法直接求解并判断边坡的失稳情况,对所有样本条件下的失稳情况进行统计。结果表明：考虑材料特性随机场的边坡稳定分析,通过边坡安全系数的均值、方差、分布及可靠度指标对边坡安全进行综合评价,能够得到可靠的边坡稳定分析结果。     

基于中心复合设计的RSM边坡可靠度研究

为提高边坡可靠度的计算精度与效率,基于响应面法(RSM)的思想,考虑影响边坡稳定的主要强度参数粘聚力c、内摩擦角的不确定性,同时计入边坡稳定计算模型不确定性,分别采用中心复合设计(CCD)和拉丁超立方抽样(LHS)获取2种不同试验设计的样本数据,借助岩土工程极限平衡Slide程序获取Bishop、Spencer、Morgenstern-Price等3种稳定模型的样本响应值,编写Matlab程序求解边坡可靠度指标和验算点。以Monte Carlo(MC)法计算结果作为可靠性分析的基准解,并与基本二层土模型和托巴110 k V施工变电站边坡计算结果进行对比分析。结果表明,CCD求解的可靠度指标更接近MC基准解,满足精度的同时,提高了求解效率。     

基于LHS抽样RSM数据表的边坡可靠度研究

为有效求解边坡可靠度,采用拉丁超立方(LHS)抽样提出了基于响应面法(RSM)数据表的边坡可靠度计算模型。考虑影响边坡稳定性的主要强度参数c,φ的不确定性,采用LHS抽样构建RSM随机样本点,借助岩土工程极限平衡的Slide程序获取样本响应值;通过将数据表法与RSM结合求解边坡可靠指标及失效概率。以Monte Carlo法计算结果作为可靠性分析的基准解,并与基本2层土坡模型和托巴110 kV施工变电站边坡计算结果进行对比分析,结果表明此方法不仅精度满足要求,且计算量较小、效率高,对实际工程边坡可靠度分析具有一定指导意义。     

边坡稳定计算中的可靠度分析

提出了一种应用可靠度理论进行边坡稳定性计算的实用方法。该方法利用“三σ准则”估计基本变量的标准差和变异系数，采用传递系数法建立功能函数，计算边坡的可靠指标和失效概率。     

基于改进均值滤波的多响应面法 高陡边坡可靠度分析

采用改进均值滤波法对多响应面法进行改进,构建了基于空间滤波的多响应面法消除多响应面子区域交接处的突兀点,提高可靠度计算精度和计算效率。用matlab语言编程实现改进后的空间滤波多响应面法应用于永吉县西阳河高陡边坡可靠度计算。结果表明,采用改进均值滤波法对多响应面法计算精度明显提高,适用于大型复杂边坡工程的可靠度计算。     

基于Fortran与VB混编的水库群联合优化调度系统研究

介绍了Visual Basic与Fortran两种语言混合编程的基本方法,研究并解决了两种语言之间结构体数组传递的技术关键。建立基于Fortran语言的水库群联合优化调度模型,并采用粒子群优化算法进行求解。最后结合了VB人机交互界面的优点和Fortran在数值运算方面的长处,实现水库群联合优化调度计算数据输入输出的可视化。     

地下厂房施工过程的三维非线性数值模拟分析

根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。     

Evaluation of freshwater mussel relocation as a conservation and management strategy

The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects.     

基于模型试验的河床砂砾石层基本特性研究

为了经济可靠地确定深厚覆盖层的基本特性参数,以大渡河双江口水电站坝基河床砂砾石层基本特性研究为工程背景,进行大尺寸模型试验,研究河床砂砾石层的旁压模量和动探击数随密度、级配以及上覆压力的变化规律。根据室内模型试验结果,结合现场旁压试验及钻孔试验成果,推断出坝址区河床砂砾石相关层位的密度,并依此进行砂砾石室内力学试验,获得设计所需力学参数。研究成果可为深厚覆盖层基本特性测试提供新的方法。     

Serial discontinuities in a Rocky mountain river. I. Distribution and abundance of plecoptera

Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m^?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m^?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m^?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m^?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m^?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river.     

基于BP神经网络-马尔科夫链模型的隧道围岩位移预测

在隧道工程施工中,围岩位移预测起着很重要的作用。将BP神经网络-马尔科夫链模型引入到隧道围岩位移预测中来,通过对训练样本的学习,利用BP神经网络实现了对位移时间序列的滚动预测,同时得到了实测值与预测值的相对误差;在此基础上利用马尔科夫链对相对误差进行修正,有效地提高了预测结果的精度。并将该模型应用于某公路隧道拱顶下沉位移时序预测中,结果表明该模型具有精度高、科学可靠的特点,为隧道围岩变形的预测提供了新的途径。     

Short communication. Pipelines as a refuge for freshwater snails

In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment.     

浙江省水域调查录入系统的设计和应用

浙江省水域调查录入系统将调查数据与电子地图相整合,对分类水域数据进行统计计算,并对输入数据进行合理性和完整性检查,得到调查范围内现有水域的详细数据,实现了水域调查数据输入、计算、统计和查询的数字化管理,提高了工作效率和工作质量,为各地下阶段水域保护规划编制和水域管理工作提供了数据支持。对该系统的设计原则、功能和技术设计等作了介绍。     

基于CT-连续加荷水泥乳化沥青混凝土细观损伤规律研究

利用CT技术对水泥乳化沥青混凝土的细观损伤过程进行实时扫描观测,获得了混凝土试件在连续加荷下的CT图像。通过采用直观分析法、CT数分析法、CT数与损伤变量关系3种方法分析表明,水泥乳化沥青混凝土的破坏过程可分为压密、扩容、裂纹扩展、破坏4个阶段,同时混凝土在受压过程中具有韧性,在极限荷载之前各断面处于压密和微扩容的强化阶段,极限荷载之后混凝土从损伤到破坏发展比较平稳。     

Automated system for removal and pneumatic transport of fly ash from electric precipitator hoppers

A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system, configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants of dry ash utilization and the advantages of producing of size-separated particles are considered. __________ Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008).     

The flood pulse advantage and the restoration of river-floodplain systems

The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed.