河道采沙对大桥基础安全影响研究

近年来河道大量无序采沙对大桥安全带来丫隐患。由于采沙破坏了天然河床的平衡状态,可引起长距离河床整体下切,对已有跨河桥梁工程不利。采沙坑距大桥较近时,在水流剪应力作用下沙坑演变可很快造成大桥基础变浅,影响大桥的正常安全运用。本文分析了采沙位置和采沙坑深度对桥墩基础安全的影响,根据采沙坑演变的平衡比降,认为采沙坑距大桥的安全距离主要与河床粒径及水流流速有关。     

不同条件下矩形沙坑影响的数值模拟对比研究

应用有限体积法建立了河道平面二维水流泥沙数学模型并将模型应用于典型河段的计算,验证了模型的计算精度.设置了不同来水来沙条件和沙坑几何边界条件,将本模型应用于几种工况的理想矩形河道中矩形沙坑影响模拟研究,计算表明采砂对河道的正常演变产生影响,影响结果与离沙坑的距离、沙坑的深度和面积大小以及来水来沙情况等因素有关.初步分析了在采沙规划中可控制采沙影响后果的措施.     

顺直河道采砂效应平面二维数值模拟

不规范的河道采砂对堤岸防护、通航及水工建筑物安全等均会产生较大影响.运用平面二维数学模型,概化河道采砂有关影响因素后,模拟并探讨了矩形采沙坑对河床产生的不同程度的影响.结果表明,沙坑改变了局部河道的水流结构和含沙浓度分布,在不同河段、不同方向上,沙坑对河床床面变形影响是不一样的.对沙坑变形影响的细致分析有助于进行科学采砂规划.     

平面二维河床变形的数值模拟

为了研究河道平面二维的河床变形问题，及由此而引起的对防洪、航运等造成的影响，本文给出出非均匀沙的平面二维全沙动床数学模型方程组，并考虑了移质不和饱和输移、非均匀沙推移质输移及床沙级配的调整。在求解水流泥沙运动方程时，采用控制体和只法及动边界技术，对水流速度场、悬移质浓度场及河床变形进行了数值模拟。该模型采用正交曲线网格来克服天然河道边界形状复杂、长度尺度相差悬殊以及由于水位波动引起计算边变化等等困     

珠江三角洲河道无序采沙影响及管理措施

河道无序不均衡采沙使珠江三角洲网河分流比剧变，腹部洪水位异常壅高，对河势稳定、防洪安全、通航安全等带来严重的影响。阐述了河道采沙的基本情况，重点分析珠江三角洲河道无序采沙产生的不利影响，并提出加强管理的措施。     

黄河洛阳段河势演变特征及采沙疏浚研究

黄河洛阳段河床的沙卵石特性使得河道工程无法充分发挥调整河势的作用,只有河道疏浚才能有效改善河势,而按照一定的规划要求进行采沙是目前可以达到疏浚效果的可行手段。由历史河势分析可知,该河段河势演变有着独特复杂的特性,而沙卵石心滩、边滩对河势有着明显影响。将影响河势的边滩、心滩规划为采沙优先开采区域,并提出了疏挖部分汊河、在一些常规禁采区内实施有限的采挖来改善河势等方法。同时,就保证采沙效果提出了细化许可、严格监管等措施。     

渭河临渭区段河道采沙堆沙对行洪蓄洪的影响

对渭河下游临渭区沙石资源情况进行了介绍,分析了河道管理要求、堆沙点位置与转运成本以及河道采沙堆沙方式对河道行、蓄洪的影响。结果表明:临渭区河道采沙堆沙对河道管理影响较大;当前有关河道采沙堆沙规定需要在实际工作中进行适度调整;当临渭区河段滩地沉沙场沙堆宽度在200 m以下、汛期滩地堆沙在100万m3以下时,对临渭区河段行、蓄洪的影响甚微。同时,提出了适当调整采沙规划部分沙场分布、进一步深入论证滩地堆沙对河道的影响等建议。     

动床k—ε紊流模型研究

紊流ｋ－ε模型是近２０年发展起来的，并较适于模拟紊流运动的数学模型之一，它的特点是，用紊动动能ｋ和紊动能量耗散率ε来表征紊流的局部状态并封闭雷诺方程式。本文在紊流ｋ－ε模型和窦国仁悬沙冲淤模式的基础上，提出二维动床紊流ｋ－ε模型。并据此计算在明渠水流中设置方墩以后的河床冲淤变化。计算结果表明，该模型所预报的水流流态和河床冲淤部位与实际情况基本一致，且特别适用于有回流分离区的局部河段的河床变形的计算     

黄河潼关河段清淤效果分析

１９９６－１９９９年黄河潼关河段清淤采流冲少，以冲为主，冲扰结合的作业方式，因势利导，理顺河势，集中水流，调整局部河段比降。浅滩段河床冲刷及河道态改善了河道泄洪沙条件，增大了洪水对潼关河床的冲作用。４年来，在汛期水量偏枯５０％以上，水沙组合不利的情况下，各年汛末潼关高程基本稳定在３２８．１０ｍ左右，比１９９５年同期约下降０．２０ｍ。     

荆江重点浅滩整治的二维动床数学模型研究

本文针对荆江河道边界形状复杂、长宽相差悬殊及水沙具有明显的二维特征．建立了贴体正交曲线坐标系下河道二维动床数学模型。给出了正交曲线坐标系下二维动床数学模型的控制方程、控制方程的离散及数值解法、边界条件及动边界技术。细致地模拟了荆江卵石夹沙河床及沙质河床浅滩河段的水面线、流速场、含抄量浓度场及河床变形。计算的水位、流速分布及河床变形与实测资料吻合良好。在分析河床演变规律及浅滩成因的基础上．进行了不同组次来水来沙水文年的多个整浩方案的数值试验，探讨了重点浅滩段整治原则及整治工程的初步布置。     

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。     

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.     

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。