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溢流反弧段的紊流边界层及摩阻特性 总被引:1,自引:0,他引:1
本文介绍不同曲率半径和不同粗糙度时反弧段紊流边界层的研究成果,导出反弧段的摩阻计算公式,并计算了反弧段摩阻流速及壁面切应力等,发现在反弧末端,壁面切应力明显增大,对粗糙度变化反应敏感。 相似文献
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通过水槽试验,采用6种方法:对数流速分布回归法、外延雷诺应力分布法、三维紊动能法、垂向紊动能法、韩其为经验公式法和拖曳力系数法,计算了卵砾石河床的摩阻流速。以韩其为计算摩阻流速的经验公式为标准,分析了各种方法中参数取值对计算结果的影响及其在不同水力和床面条件下各种方法的适用性。提出了2种可行的计算途径:光滑床面条件下各方法计算摩阻流速所得结果最大均方差为2.15,其中对数流速分布回归法较准确,三维紊动能法计算值普遍偏小;相对粗糙床面条件下各方法计算摩阻流速的结果均方差最大达到8.84,其中对数流速分布回归法和三维紊动能法较准确。 相似文献
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《水动力学研究与进展(A辑)》2015,(4)
该文采用三维数值模型研究风应力对水流运动和摩阻特性的影响。首先通过试验数据验证了数值模型对风生流结果的合理性;然后通过平底水槽的数值试验,研究了风应力的变化,尤其是在风向顺流和风向逆流条件下,对于定常水流涡黏系数分布、流速分布、雷诺切应力分布以及底部摩阻的影响。发现传统使用广泛的涡黏系数抛物线分布在风向顺流条件下基本与紊流模型结果吻合,而在风向逆流条件下,尤其是风应力较小情况下,抛物线分布与紊流模型结果有相当的偏差。流速分布则和传统双对数分布基本吻合,但须考虑风生流和定常流之间的相互作用,而不能简单看成两者间的线性叠加。雷诺切应力基本符合线性分布。底部摩阻受风生底流的影响,在平底条件下,风向顺流会减小底部摩阻,而风向逆流则会增加底部摩阻;但在非平底条件下,只有在较深处规律和平底类似,而在较浅处,风向顺流也会增加底部摩阻。 相似文献
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试验采用承插式PVCΦ200mm双壁波纹管和对接式PVCΦ250mm肋式卷绕管两种管道,并对在有压流和明流均匀流,不同充满度的条件下进行了分析,试验分析表明,PVC双壁波纹管属光滑管,PVC肋式卷绕管介于光滑管与粗糙管之间;材料相同而加工工艺和接口形式不同,其阻力系数的选择计算有所不同,充满度与糙率系数关系随管道底坡的变化而改变。 相似文献
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风洞边壁对挟沙气流流速分布的影响 总被引:3,自引:0,他引:3
鉴于现有挟沙气流流速分布研究中对风洞边壁影响的认识不足,本文通过改变风洞宽度的方法对风洞边壁的影响进行了探索性实验研究。在五种宽高比条件下,对风洞断面挟沙气流流速分布进行了测量。发现风洞边壁对挟沙气流流速分布有较为明显的影响。在风洞宽度比相同的条件下,断面内中垂线上的有效粗糙度系数大于其它垂线上对应的系数。从靠近边壁的垂线到断面中垂线,各垂线对应的跃移层内区及外区流速分布的上界高度、气流摩阻速度均逐渐增大。随着风洞宽高比的减小,断面内中垂直线上的气流摩阻速度与自由流速的比值以及受风洞边壁影响的气流厚度均增大。 相似文献
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由于运行中管道实际摩阻因数与设计采用值的不一致会影响供水系统的运行质量和安全,为得到准确的摩阻因数以反馈设计,以及对运行中的供水系统进行系统诊断和优化调度,提出一种基于混合粒子群优化算法(hybrid particle swarm optimization,HPSO)和管网水力计算模型的管段摩阻因数智能反分析方法,该方法以监测点处的水压监测值与水力计算模拟水压值的二乘误差最小为目标,通过HPSO的强大全局寻优能力计算不同管段的摩阻因数。对室内试验管网模型的反演结果表明:采用正常工况下反演得到的摩阻因数模拟水压监测点处水压与实际测量值之间误差最大为2.87%;在爆管工况下,水压模拟值与实际测量值最大相对误差为2.63%,说明通过该方法进行摩阻因数的反演具有较强的稳定性。 相似文献
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水力瞬变现象是长距离输水系统安全运行时需要考虑的主要问题。由于传统"拟稳态"模型不能准确预测压力波的峰值以及水锤波的衰减过程,因此引入更准确的非恒定摩阻模型模拟瞬变流成为工程安全运行研究的重要内容。本文利用模型试验,通过采用恒定摩阻模型及MIAB摩阻模型进行数值模拟计算,定量分析了两种模型的模拟计算结果与实测压力值的吻合程度,对比分析模型的优劣,提出了通过改进Brunone摩阻系数k的经验公式、现场校正波速和摩阻系数f及研究长距离复杂供水系统的瞬变流动特性,以期进一步提高MIAB摩阻模型模拟计算精度。 相似文献
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管道的水头损失直接影响水管和水泵尺寸的确定,也就是管网的水力平衡。所有沿程水头损失计算公式,在估算水管内壁糙率时都有误差。对于一定材料一定管径和流量的管道的阻力系数,不同的方程式可以估算出不同的沿程水头损失。在复杂管道网络系统中,方程式或系数的小误差的累积,使各个管子水头损失或流量的计算值产生较大的误差。本文提出了三个广泛应用于管道摩阻方程摩阻系数有关的解决水头损失计算误差的数学关系式和诺模图。对象聚氯乙烯和铸铁管道来说,用Hazen—Willians(H—W)和Manning(Mn)公式得的水头损失与Darcy—Weisbach(D—W)得的水头损失相同。还介绍了摩阻系数随直径和水流条件而变化的情况,并讨论了运用计算机计算变化的沿程损失系数问题。 相似文献
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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。 相似文献
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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. 相似文献
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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. 相似文献
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简述天湖水电站投运以来各种故障的表现形式,分析其原因,提出了相应的处理方法及措施,并对合理利用国内外设备提出建议。 相似文献
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Various designs of low‐head dams are used to rehabilitate streams or forestall upstream channel incision after channelization. We report on the efficacy of using notched sills and grade control structures (GCS) to restore the fish assemblage in Luxapallila Creek, Mississippi. We tested the null hypotheses that habitat variables and species richness, evenness, and assemblage structure would not differ among: (1) a channelized segment with no modifications; (2) a channelized segment mitigated by the installation of sills and GCS; (3) a segment upstream of the installations and undergoing channel incision; and (4) an unaltered segment. Although habitat variables changed, neither species richness, evenness, nor fish assemblage structure differed between mitigated and channelized segments with both exhibiting less richness and different assemblage structures than the unaltered segment. Lack of differences in species richness between the incised and unaltered segments suggest that the GCS may have halted the negative effects of upstream channel incision before species were extirpated. Conspicuous habitat differences between the altered (channelized and mitigated) and unaltered segments were lack of backwaters and canopy coverage and finer substrates in the altered segments. Our results suggest a more comprehensive rehabilitation strategy is required in Luxapallila Creek. Published in 2003 by John Wiley & Sons, Ltd. 相似文献
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NUMERICAL STUDY OF WAVE EFFECTS ON SURFACE WIND STRESS AND SURFACE MIXING LENGTH BY THREE-DIMENSIONAL CIRCULATION MODELING 总被引:1,自引:0,他引:1
LIANG Bing-chen LI Hua-jun LEE Dong-yong 《水动力学研究与进展(B辑)》2006,18(4):397-404
1. INTRODUCTION Coastal and continental shelf regions are characterized by intensive interaction between wave and current. These regions are of great economic significance to mankind. Therefore, the modeling of wave and current as well as their mutual int… 相似文献