浮体在浅水中运动产生的孤立波

本文对在浅水中以跨临界速度运动的浮体产生的兴波问题作了数值计算，用作者提出的求解浮体波动问题的新方法，将浮体与流体接触的物面作为自由表面处理，使Ｂｏｕｓｓｉｎｅｓｑ方程用于此问题的全域直接数值求解，数值结果使我们得到了新颖的浮体运动产生的孤立波解。     

高速方尾船斜航状态的水动力试验研究和数值计算

本文通过流场观测和斜拖试验,分析了高速方尾船在斜航状态下的绕流流态,船体运动姿态和水动力特点,认为航速引起船体航行姿态的变化是导致这类船水动力变化的首要因素。采用Hess-Smith方法计算了船体运动姿态随漂角和航速的变化规律;用在重叠模表面分布复合型奇点的边界元法,并在船体背流面分布剥离涡片,直接求得船体表面压力分布和绕流场。计算中考虑到方尾船尾流特点,将船尾流线延长形成“假尾”。文中计算了船体横向力、首摇力矩和压力分布,与试验数据吻合良好。     

计及自由面影响的船舶三维湍流边界层计算

本文用有波势流和薄边界层理论,在计及自由表面影响之下,对船体的三维湍流边界层作了数值计算,其目的是考察自由面对船体边界层发展的影响。 通过数值试验表明:船体兴波对边界层的发展,在自由面附近的影响很大,沿流线方向动量厚度和摩擦阻力系数均有波动,θ_(11)的峰谷位置与波形一致,C_1则相反。傅氏数越大,波动越大。相对地说,兴波对形状因子的影响要小得多了。     

基于时域面元法的非对称双体船兴波阻力计算

该文基于格林定理,应用时域面元法求解非对称双体船的兴波问题,计算了非对称双体船于不同纵向、横向布局下的兴波阻力,研究了兴波阻力随航速的变化规律,分析了主船体与侧船体之间的相互影响规律.计算过程中,在边界面上布置Rankine源及偶极子,在自由面上满足非线性自由面边界条件,并采用时间步进法计算模拟非对称双体船运动时的自由面波形.数值计算过程中则采用一种精确积分的方法计算影响系数以避免数值发散.     

深浅水中KVLCC船体横荡运动水动力数值计算

通过求解非定常RANS方程,选取SST k-ω湍流模型,采用全六面体网格进行离散,在忽略自由面兴波影响的情况下,对KVLCC1裸船体在深水和浅水中的PMM试验纯横荡运动粘性流场进行了数值模拟,计算了作用在船体上的水动力和力矩;通过将计算结果与现有的试验数据对比,验证了该文方法的有效性.在此基础上,根据水动力和力矩计算结果,计算得到了船舶横荡运动线性水动力导数.     

二维浅水狭航道船舶变速航行的有限元计算

本文从二维浅水波方程出发,采用有限元计算船舶变速驶进、驶出大坝升船机承船厢时的水动力学过程.二维浅水波方程理论把行驶船舶对水面的作用力直接加在二维浅水波方程里,以此来计算水表面波动和水平流速.水动力波产生的水动压力又影响到船舶的运动.本文研究船舶和水体的相互作用.它描述了水面波动、水平流速、船舶的纵倾角、船和厢底的最小间隙、以及承船厢受的水体总重量、水动力矩等重要物理量在船舶行驶过程中的变化规律.本文算例的结果和文献[5]给出的实验数据大体一致.计算结果还发现,船舶驶出承船厢时下沉和纵倾的幅度比船只驶进承船厢时要稍大一点.工程上应当予以重视.     

水面船非线性兴波数值方法研究

本文在线性兴波数值方法的基础上,利用Rankine源法开展了非线性兴波数值方法的研究.采用迭代的方式来满足非线性自由面条件,并在迭代中考虑真实的船体湿表面;此外将自由面面元升高来提高数值稳定性、而配置点前移则用来满足辐射条件.通过对Series60船型,以及一条集装船的计算来验证本文所开发的非线性兴波数值计算方法,经比较发现非线性方法的计算结果比线性方法明显改善;证实本文方法已经成功建立了非线性兴波问题的迭代框架,实现了非线性兴波数值计算方法.     

船体砰击问题的非线性边界元分析

本文运用边界元法分析外飘和Ｕ型船体载面的砰击问题，在分析过程中自由液面采用完全非线性边界条件以及计算自由液面的大变形，而边界单元则采用线性单元假设。数值计算表明，针对二维楔形体常速入水的结果与已有的结果吻合得很好，具有外飘和Ｕ型特性的船体截面在入水砰击过程中其压力分布及其演变具有完全不同的特性。     

基于改进控制方程的土石坝溃坝洪水演进数值模拟

基于常规二维浅水方程的改进,建立适应于不规则边界的浅水流动有限体积法,在水平项和垂直项的自由水面相对高度进行分裂后的守恒性改进控制方程。对土石坝进行二维溃坝洪水演进数值模拟,并通过对典型算例验证改进控制方程可行性。     

Kelvin源求解船行波及其在总阻力估算上的应用

针对船行波与船体总阻力预报,采用Kelvin源格林函数的远场波动项及其偏导数在水平线段上的解析积分公式计算Wigley船型、S60船型的兴波问题和船体表面速度分布。基于兴波问题所得的速度分布计算船体面元的局部雷诺数和摩擦阻力系数,又根据巴普米尔经验公式估算黏压阻力系数从而进一步求解船舶总阻力系数,对比该文方法所得的船舶总阻力系数和实验测量数据,证明该文的方法可以准确高效地计算船舶总阻力。     

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。     

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.     

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.     

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。     

Desiccation and recolonization of phytobenthos in a regulated desert river: Colorado River at Lees Ferry,Arizona, USA

We tested the recolonization of the phytobenthic community in the tailwaters of Glen Canyon Dam following long- and short-term experimentally induced desiccation. The response of Cladophora glomerata, Oscillatoria spp., miscellaneous phytobenthos species and periphyton was studied over 18 weeks using three treatments: (1) undisturbed control cobbles from the submerged zone; (2) cobbles desiccated and replaced into the submerged zone; and (3) cobbles desiccated and replaced into the varial zone. Periphyton density and compositional response resulting from these treatments were also examined. Desiccation treatments were significantly different in biomass from controls throughout the study. The biomass of desiccated and replaced river cobbles averaged <30% of the controls for C. glomerata and periphyton during the 18-week recolonization period. In contrast, the biomass of the control Oscillatoria and miscellaneous phytobenthos species averaged only 3 and 50% of that in the desiccation treatments, respectively. Cladophora, the dominant alga, comprised 77% of the phytobenthic biomass. A significant positive relationship between discharge, Cladophora and periphyton biomass was present in all treatments, while there was a negative relationship with discharge for Oscillatoria and miscellaneous phytobenthos species. There was a significant inverse correlation, as well as a pattern of separate biomass dominance, between C. glomerata and Oscillatoria. Cladophora was the dominant phytobenthos species on cobbles below the baseflow and Oscillatoria was dominant on cobbles in the varial zone. In general, the Cladophora biomass decreased under intermittent drying conditions, while Oscillatoria declined under permanently wet conditions. Diatom composition was not significantly different between treatments; however, their density was lower on desiccated cobbles. Diatom density on desiccated cobbles in the submerged and varial zones averaged 69 and 42% of that of the controls, respectively. Recovery and maintenance of benthic resources are hindered by fluctuating flow regimes driven by electricity and irrigation requirements. Repeated desiccation of the phytobenthos has major effects on the bottom-up interactions in the Colorado River ecosystem. © 1998 John Wiley & Sons, Ltd.