竖直较大管径内气液两相流截面含气率实验研究

截面含气率是气液两相流动过程中的关键参数之一.在大管径流道内的气液两相流,弹状流难以形成,与常规通道相比,其流型特征明显不同.适用于常规通道截面含气率的一般计算方法,对于大管径流道而言,其适用性也较差.本文通过研究较大直径圆管内的气液两相流动过程,寻找适合于过渡尺寸流道内两相流动截面含气率的计算方法,从而建立起完整的、针对各个尺度范围内截面含气率的计算方法.实验选圆管直径为50 mm,介于常规通道和大通道之间;以空气和水作为工质,气相、液相折算速度的范围分别为0.05-2.0 m/s及0.01-2.0 m/s.首先利用获得的截面含气率实验数据,对适用于常规通道和大通道的截面含气率计算模型进行了评价;然后通过分析几类漂移流模型计算方法的分布系数和漂移速度的变化规律,解释了Hibiki-Ishii、Kataoka-Ishii、Kawanishi等几个模型计算误差较大的原因.     

垂直上升通道内气液两相绕圆柱流动旋涡脱落频率和脉动升力的数值模拟

采用有限容积法，综合考虑了由剪切引起的紊流和由气泡引起的紊流关系式，基于RNGk-ε紊流模型对气液两相绕圆柱流动进行了数值模拟。通过计算发现：对于气一液两相绕圆柱流动而言，旋涡脱落频率随含气率的增大而增大；脉动升力系数先随含气率的增大而缓慢增加，在含气率增大到0．1后增大得较快。并通过实验对模拟结果进行了验证，实验结果与模拟结果较吻合，验证了模拟结果的正确性。     

钢筋钢纤维混凝土牛腿正截面开裂弯矩的计算方法

根据钢筋钢纤维混凝土牛腿的试验结果，研究了钢纤维体积率对牛腿正截面开裂弯矩的影响，将梁的正截面开裂弯矩计算方法运用于牛腿的正截面开裂计算中，给出了钢筋钢纤维混凝土牛腿正截面开裂弯矩的计算公式．该计算方法与试验结果符合较好，且计算简便，实用性强，并与钢筋混凝土牛腿的计算公式相衔接，可供实际工程设计时参考应用，     

气-液两相流横掠圆柱表面脉动压力特性的研究

对垂直上升矩形截面管内气一液两相流绕水平布置的圆柱流动时圆柱表面的脉动压力特性进行了试验研究，试验中来流雷诺数的范围为4．4×10^3～1．04×10^4，截面含气率的范围为0～0．06。在功率谱图上得出了圆柱表面脉动压力随含气率、雷诺数及测量角度的变化规律。试验结果表明，在该试验范围内，随着含气率增大，圆柱表面的脉动压力功率谱图峰值逐渐降低，而所对应的漩涡脱落频率增大；圆柱不同角度对功率谱特性有一定影响；雷诺数对功率谱特性的影响相对较小。     

浅谈农村电网改造导线截面选择方法

本文介绍了农村电网改造导线截面选择两种方法：一是按经济电流密度选择导线截面；二是按允许的电压损耗选择导线截面。并列举一个在农村电网改造中导线截面选择的实例。     

小型水电站送电线路截面选择分析

以保证功率输出为技术条件，得出小型水电站送电线路最小截面计算模型，并分析了影响截面选择的因素，提出合理的选择方案。     

基于考虑含气量变化浆体水击模型的复合管道水击数值计算

作者在提出了考虑含气量变化的同液两相流浆体水击基本方程的基础上，建立了考虑含气量变化的浆体水击模型。运用该模型对某电厂除灰系统管道进行了水击数值计算，根据计算结果提出了合理的建议，该建议已被采纳和应用。同时将计算结果与原有清水水击模型和浆体水击模型的计算结果进行比较，结果表明：该水击计算模型在进行同液两相流水击计算时精度高，可用于工程计算。     

渠网非恒定流图论原理

本文研究了气液均相流的模型相似律，推导得出竖井式水平旋流洞的模型相似律是：原、模型几何相似；原、模型佛罗德数 相同；原、模型含气率相同。推导得出竖井式水平旋流洞原、模型通气管截面积的换算关系和原、模型含气率分布的换算关系。最后，应用所得理论公式分析公伯峡水电站竖井式水平旋流式泄洪洞模型试验结果，为改进和完善模型设计提供了科学依据。     

喷嘴与水平圆管的气—液两相流动阻力特性

本文应用一维变密度气－液两相流动量于喷嘴和水平圆管的气水两相流动，建立了喷嘴进口压力及流速之间的关系，将动量方程在有限管道长度内积分，从而可由试验得的压力差计算通过水平圆管的气－液两相流阻力系数，并在大量试验的基础上建立了考虑截面含气率的喷嘴动量修正系数的相关关系式和水平圆管中大气两相流阻力系数与雷诺数之间的关系式。     

喷嘴与水平圆管的气－液两相流动阻力特性

本文应用一维变密度气－液两相流动量方程于喷嘴和水平圆管的气水两相流动，建立了喷嘴进出口压力及流速之间的关系，将动量方程在有限管道长度内积分，从而可由试验测得的压力差计算通过水平回管的气－液两相流阻力系数，并在大量试验的基础上建立了考虑截面含气率的喷嘴动量修正系数的相关关系式和水平因管中气水两相流阻力系数与雷诺数之间的关系式。     

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。