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无浮托引张线系统及其应用 总被引:4,自引:2,他引:2
引张线法是观测混凝土大坝水平位移的一种重要方法,其金属线体通常使用小船浮托,以克服线体重力产生挠度。因此,引张线系统需经常检查浮船和水箱水位,给引张线实现自动化观测带来不利,影响了引张线观测精度。无浮托引张线系统采用了DPRP材料制作的线体和自动化监测引张线仪,实现了引张线系统在无浮托装置、完全自由状态下的自动化观测。 相似文献
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目前国内一般采用不测量时卸载50%砝码的方法以减小引张线式水平位移计铟钢丝的徐变量,而国外认为铟钢丝的徐变量很小,所以不必进行卸栽.文中通过理论计算和试验分析总结了对铟钢丝进行卸载的必要性,同时归纳了一些引张线式水平位移计的使用经验. 相似文献
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双向引张线设计有关问题浅析 总被引:1,自引:0,他引:1
本文简略地介绍了引张线的主要设计方法.它首先介绍引张线在自重作用下的悬链线的方程并对其各参数的性质进行讨论.在对现有公式进行分析的基础上提出了温度变化对引张线垂度影响的新的、正确的公式和结论.最后,通过实例,推荐引张线悬挂结构的设计方法.故只要适当地设计悬挂结构,且廊道内不产生冷凝水和结冰现象,引张线是可以用作混凝土坝的竖直向位移测量的参考(基准)的. 相似文献
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大坝变形监测自动化中的几个问题 总被引:1,自引:1,他引:0
指出了大坝变形监测系统中自动化监测与人工观测方法的差异,对引张线自动监测系统的构建方法进行了论述;通过分析说明了试图采用双向引张线监测垂直位移尚不可取;分析表明,引张线端点外延将明显降低引张线准直系统的精度,长的引张线应避免采用端点外延布置;采用相对测量方法、配合双金属管标的液体静力水准系统是一种灵活、简便的高精度垂直位移自动化监测系统;分析比较测斜仪和垂线的精度表明,试图利用测斜仪来取代垂线的想法是不可行的. 相似文献
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龚建军 《水电自动化与大坝监测》2000,24(3):57-58
实现引张线自动化监测与传统的人工监测相比有许多问题需要解决,如坝顶系统的防雷、抗干扰问题,引张线系统浮船浮液的防结冰,防蒸发问题、引张线线体的热胀冷缩问题等。介绍了潘家口大坝坝顶引张线系统在实施过程中解决上述几个问题的措施。 相似文献
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介绍了一种新型大坝水平位移监测系统———无浮托引张线自动监测系统。该系统改进了有浮托引张线存在的问题,实现了引张线监测的全自动化。 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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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
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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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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.
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Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008). 相似文献
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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