共查询到20条相似文献,搜索用时 171 毫秒
1.
2.
采用通用的有限元计算软件分析了水电站对称Y形钢筋混凝土岔管结构,计算出了钢筋混凝土岔管结构环向应力及变形的分布情况,并分析了内水压力对岔管围岩的影响.计算结果表明,采用钢筋混凝土岔管结构是安全可靠的,能够满足工程要求. 相似文献
3.
4.
5.
大型地下钢筋混凝土岔管结构优化分析 总被引:2,自引:0,他引:2
本文根据岩体和混凝土衬砌联合受力特点,系统地提出了大型地下钢筋混凝土岔管结构优化分析方法。针对岔管空间几何特征,结合三维有限元的原理,提出了采用程序分析判断,自动生成各种不同类型的三维有限元地下钢筋混凝土岔管结构网格的计算方法。该方法只须输入几个关键的控制参数,便能自动剖分所须岔管网格,为大型地下钢筋混凝土岔管结构优化分析提供一种快速网格生成方法。根据岩体损伤开裂和弹塑性破坏特征,从岩体开挖应力扰动的塑性耗散能扩散理论和混凝土衬砌结构开裂损伤原理,提出了大型地下钢筋混凝土岔管结构型式优化的评估方法。通过对工程实例分析,证明该方法能综合反应地下钢筋混凝土岔管结构型式和参数选择以及岔管所处的地质环境和条件的影响,为优化地下钢筋混凝土岔管结构合理型式提供了一种有效的分析方法。 相似文献
6.
7.
钢衬钢筋混凝土无梁企管结构研究 总被引:2,自引:0,他引:2
钢材钢筋混凝土无梁岔管与无梁钢岔管与其它梁式岔管相比,具有受力条件好、钢管较薄、施工方便等优点,是一种新的岔管结构型式,特别适合于中高水头的中小型水电站,通过一个大比尺物理模型试验,对钢衬钢筋混凝土气梁岔管的承载机理和结构特性进行了深入的研究,取得了令人满意的结果。 相似文献
8.
高压钢筋混凝土平底岔管的边界元分析 总被引:1,自引:1,他引:0
广州抽水蓄能电站(下称广蓄电站)二期工程高压钢筋混凝土岔管采用平底岔管的型式,以利放空排水。平底岔管的内体型比已建成的广蓄电站一期工程的非平底、对称于洞轴线的卜型岔管更加复杂。根据广蓄电站一期工程高压钢筋混凝土岔管设计的成功经验,用边界元法对广蓄电站二期工程高压平底岔管进行了详细的结构分析,其成果是广蓄电站二期工程高压钢筋混凝土平底岔管结构设计的依据。 相似文献
9.
10.
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.
15.
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
16.
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
17.
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
18.
19.
20.
We tested the recolonization of the phytobenthic community in the tailwaters of Glen Canyon Dam following long- and short-term experimentally induced desiccation. The response of Cladophora glomerata, Oscillatoria spp., miscellaneous phytobenthos species and periphyton was studied over 18 weeks using three treatments: (1) undisturbed control cobbles from the submerged zone; (2) cobbles desiccated and replaced into the submerged zone; and (3) cobbles desiccated and replaced into the varial zone. Periphyton density and compositional response resulting from these treatments were also examined. Desiccation treatments were significantly different in biomass from controls throughout the study. The biomass of desiccated and replaced river cobbles averaged <30% of the controls for C. glomerata and periphyton during the 18-week recolonization period. In contrast, the biomass of the control Oscillatoria and miscellaneous phytobenthos species averaged only 3 and 50% of that in the desiccation treatments, respectively. Cladophora, the dominant alga, comprised 77% of the phytobenthic biomass. A significant positive relationship between discharge, Cladophora and periphyton biomass was present in all treatments, while there was a negative relationship with discharge for Oscillatoria and miscellaneous phytobenthos species. There was a significant inverse correlation, as well as a pattern of separate biomass dominance, between C. glomerata and Oscillatoria. Cladophora was the dominant phytobenthos species on cobbles below the baseflow and Oscillatoria was dominant on cobbles in the varial zone. In general, the Cladophora biomass decreased under intermittent drying conditions, while Oscillatoria declined under permanently wet conditions. Diatom composition was not significantly different between treatments; however, their density was lower on desiccated cobbles. Diatom density on desiccated cobbles in the submerged and varial zones averaged 69 and 42% of that of the controls, respectively. Recovery and maintenance of benthic resources are hindered by fluctuating flow regimes driven by electricity and irrigation requirements. Repeated desiccation of the phytobenthos has major effects on the bottom-up interactions in the Colorado River ecosystem. © 1998 John Wiley & Sons, Ltd. 相似文献