共查询到20条相似文献,搜索用时 62 毫秒
1.
水跃消能是水利工程中经常用到的消能形式,国内外许多学者对水跃进行了大量的研究。在工程实践中发现,c型折坡水跃的水力特征值与规范方法计算得到的值有较大差异。文章针对c型折坡水跃特性进行了试验研究,并结合量纲分析和数值分析方法,得出以斜坡段坡角θ为参数的c型折坡水跃跃后水深、水跃长度的计算公式,并利用水槽试验数据和实际工程水工模型试验对公式进行了验证。结果表明:所得公式的计算误差不超过±12%,可供工程设计计算参考。 相似文献
2.
顺坡渐扩矩形明渠水跃计算公式 总被引:1,自引:0,他引:1
顺坡渐扩矩形明渠常被用在排水工程中作为排水口与河道的连接段。由于河道水位变化,水跃将发生在连接段。本文从动量守恒原理出发推导了顺坡渐扩矩形明渠水跃方程,在假定水跃水质点作二维运动和水跃段内质点垂向加速度近似为常量的基础上推导了水跃长度近似计算公式。并与扩散角为9°、水平坡度角为6°特定条件的模型试验结果进行了对比,结果吻合良好,可供类似工程参考。 相似文献
3.
折坡水跃的水力计算是设计折坡水跃消力池时经常遇到的问题。为了得到计算B型和D型水跃第二共轭水深的简便有效的计算关系式,应用Microsoft Excel97和VisualC^++5.0等软件,对坡度从0.05到0.3:1的B型和D型水跃试验数据进行了分析和研究。 相似文献
4.
试验研究了3个相对粗糙度(0.51、0.86、1.34)和6个坡度(?0.02、?0.03、?0.04、?0.05、?0.07、?0.10)对反坡正弦波形底板上F型水跃水力特性的影响。在弗劳德数从5到11的范围内,总共进行了57次试验。试验结果表明:与经典水跃和光滑底板上的F型水跃相比,反坡正弦波形底板能有效减小漩滚长度和共轭水深比,粗糙底板有利于稳定F型水跃。剖面速度分布对相对粗糙度比反坡坡度更敏感,坡度和相对粗糙度影响速度剖面的相似性和边界层厚度的发展。在距离F型水跃起始点40%漩滚长度附近,剖面速度分布最不均匀;在1.2倍的漩滚长度后,剖面动量修正系数基本上都接近1.0。反坡正弦波形底板的综合剪切应力系数是水平光滑床的10~16倍,这表明反坡正弦波形底板在短距离消能方面非常有效。 相似文献
5.
扩散水跃共轭水深的计算和分析 总被引:1,自引:0,他引:1
扩散水跃由于水流的扩散使得跃后水深小于普通二元水跃的其轭水深.其水力计算的要点在于确定侧墙反力的计算模式,而侧墙反力的计算又取决于水跃表面轮廓的形态.早期的一些计算方法多假定水跃轮廓为简单的几何图形(如矩形、梯形以及折线形等),或者完全忽略侧墙反力,以简化计算,其结果为计算的跃后水深不是过分偏小就是过分偏大,有的甚至大于二元水跃的跃后水深,从而导致错误的结果.本文根据试验研究,以1/2次抛物线为水跃轮廓,求出了侧墙反力的表达式,并应用动量原理导出了矩形扩散水跃的理论公式.最后,以试验数据为准对各家公式作了对比分析,得出了相应的结论. 相似文献
6.
7.
波浪形底板上水跃的数值模拟 总被引:6,自引:2,他引:4
利用标准κ-ε模型封闭Reynolds方程作为紊流控制方程,引入水气二相流体积率模型跟踪自由水面,对5种不同工况下的波浪形底板上水跃的演变进行数值模拟,充分显现了水跃的发展过程、自由水面的变化、流速的分布和水跃漩滚长度等。实测结果验证了模型和数值方法的可靠、合理性。对比平滑与波浪形底板上形成的水跃长度可以看出,波浪形底板上的水跃长度小于光滑形底板上水跃长度,可以有效地缩短消力池的长度,从而减少工程造价。 相似文献
8.
水平矩形扩散水跃跃长的研究 总被引:1,自引:0,他引:1
水平矩形扩散水跃跃长是设计扩散消力池的一个重要参数,但由于扩散水跃比较复杂,所以矩形扩散水跃跃长的计算迄今无理论公式可循,工程界仍采用实验公式,目前水平矩形扩散水跃跃长的实验公式较多,各家对水跃长度的定义不同,跃后断面的不稳定性,以及由模型和原型间比尺效应引起水跃跃长的差别,这 相似文献
9.
矩形扩散水跃水力计算新公式 总被引:3,自引:0,他引:3
通过对矩形扩散水跃研究,给出了不同的宽深比,不同的佛劳德数及不同的扩散角下的水跃表面轮廓曲线,水跃长度及侧墙压力系数的计算公式,并应用动量原理导出矩形扩散水跃的理论公式,以便设计和实际应用。 相似文献
10.
该文在总结抽水试验水跃值产生原因的基础上,建议采用阿勃拉莫夫经验公式计算水跃值,提出了在工程实践中可行的3种消减水跃值的方法,并通过工程实例的应用验证,表明未考虑水跃值计算的渗透系数误差较大,偏于不安全。 相似文献
11.
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
12.
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
13.
14.
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. 相似文献
15.
16.
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
17.
18.
19.
V. K. Konovalov O. V. Yashkin V. V. Ermakov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2008,42(2):105-109
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). 相似文献
20.
Peter B. Bayley 《河流研究与利用》1991,6(2):75-86
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. 相似文献