低雷诺数非线性k—ε湍流模型及其应用

本文发展了一人低雷诺数非线性ｋ－ε湍流模型，其特点是考虑了湍动能及湍动能耗散速度的非线性扩散过程，采用了一个非线性雷诺应力表达式，引入了壁面修正函数以考虑湍流的近壁低雷诺数效应。应用该模型计算了湍流槽流和湍流库埃特流。与实验结果的比较表明，所建模型对包括近壁区在内的整个计算域的各湍流量都能给出非常满意的预测结果。     

湍流平板边界层近壁区对称与非对称单个相干结构演化机理的比较

本文利用流动稳定性理论中的共振三波概念,构造湍流平板边界层近壁区对称与非对称单个相干结构的理论模式,采用紧致有限差分及Fourier谱展开相结合的方法,数值计算湍流平板边界层近壁区对称与非对称单个相干结构的演化规律,详细分析了对称与非对称单个相干结构的演化结果,得到了一些有意义的结果。     

船舶粘性流动计算中湍流模式应用的比较

针对六种不同的湍流模型，本文数值模拟了油轮SR196A的粘性绕流场，计算得到的阻力系数和桨盘面处流场和试验结果进行了比较。结果表明，SSTκ-ω模型和试验结果符合较好，是目前硬件条件下比较适合船舶粘性流场数值计算的一种湍流模式，本文结果可以为复杂船型粘性流场计算中湍流模式的选取提供参考意见。     

湍流理论的发展及其在水轮机中的应用

针对湍流计算在水轮机优化设计中日益突出的作用，本将沿着统计理论、模式理论、直接数值模式、大涡模拟等方向发展起来的湍流基础理论进行了简要的历史回顾，并着重论述了为解决工程应用问题而发起来的湍流模式理论及湍流模型。同时回顾了水轮机流场计算的发展历程，指出目前在工程上对水轮机过流部件初步设计时仍然采用不考虑粘性的准3D和3D欧拉法，而进一步精确计算则依赖于模式理论基础上的湍流模型计算。目前出现的各种湍流模型都需要确定常数，因此均缺乏普遍性。可以说，目前工程上水轮南过流部件的计算是准3D、3D欧拉法计算以及各种湍流模型计算并存的局面。     

潮流和波浪作用下悬移质挟沙能力的研究

本文将湍流猝发理论用于潮流与波浪共同作用下挟沙能力的研究。基于湍流猝发的时空尺度得到波浪和潮流作用下床面泥沙上扬通量 ,然后根据连续律 ,建立了平衡近底含沙量的理论表达式。进而根据波浪掀沙和潮流输沙的模式 ,推导得出了物理概念清晰和充分考虑床面附近泥沙交换力学机理的潮流和波浪共同作用下的挟沙能力公式 ,经过黄河口实测资料的验证 ,计算与实测符合良好。     

绕流流场无穷远处流函数边值条件的数值研究

利用流函数－涡量方程求解二维不可压缩低雷诺数绕圆柱流动，在与其它学者计算结果一致的情况下，本文数值研究了无穷远处流函数边值对圆柱定常绕流、圆柱起动流动以及非定常周期性卡门涡街形成的影响。本文计算了各种条件下绕圆柱的阻力系数、流函数涡量分布以及扰动流函数等。计算结果显示，对于定常绕流及圆柱起动流动，几种无穷无流函数边值条件求得的结果基本一致。对于非定常周期性圆柱绕流，不同的无穷远流函数边值条件对计算     

泥沙数学模型近底边界条件Ⅰ：平衡输沙

床面泥沙的上扬是湍流猝发直接作用的结果．本文首先改进作者基于这一基本力学机理所构造的可自由冲刷床面泥沙上扬通量函数，然后利用输沙平衡时泥沙上扬与有效沉降通量相等之条件建立近底含沙量的理论模式．该理论与现有实验数据吻合甚好，较已有经验和半理论方     

光滑及粗糙明槽湍流流动大涡模拟

采用大涡模拟（Ｌａｒｇｅ Ｅｄｄｙ Ｓｉｍｕｌａｔｉｏｎ）方法和Ｓｍａｇｏｒｉｎｓｋｙ亚格子模型数值计算了光滑及粗糙明槽湍流运动。以槽高为参考长度的雷诺数分别为３０００，２２８００和１０＾５，数值离散方法为有限体积法，自由面的处理使用了简单了刚盖假定，固壁面采用了壁函数，与低雷诺数直接模拟（Ｄｉｒｅｃｔ Ｓｉｍｕｌａｔｔｉｏｎ）和物理实验结果相比，本文数模呈现了良好的预测效果，估计的湍流宏尺度（Ｍ     

基于拟序结构的离心泵内空泡运动规律研究

从近壁区湍流拟序结构出发,研究离心泵内的空泡运动规律。首先利用空泡的Morrison方程得出了近壁区法向运动速度upx,然后基于拟序结构推导出了空泡在"扫掠"情况下的流向速度upy,最后用两个速度得到了基于近壁拟序结构的离心泵内的空泡对叶轮壁面的冲击角。研究表明离心泵内正是由于近壁区拟序时的"扫掠"作用造成了沙粒对叶轮壁面以小角度的冲击破坏,这与前人的试验观测结果基本吻合。     

用三维不定常RANS方程求解船尾绕流

本文详细介绍了用雷诺平均的不定常全三维Ｎ－Ｓ方程求解船尾绕流的数值计算方法。在本方法中，不引入任何简化、近似，使用了Ｋ－Ｅ二方程湍流模式进行了控制方程组的封闭。利用壁函数，指数格式、ＳＩＭＰＬＥＣ计算了ＳＳＰＡ－７２０的船尾绕流，详细给出了计算结果，并与其它算法及试验结果作了比较。     

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.