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关于水文时间序列的混沌特性识别,目前已有多种方法和指标,但单独一种方法一般不能作为混沌特性识别的充分条件。根据相空间重构和混沌理论,对宜昌站1900~2007年的月径流序列进行了较全面的混沌特性分析。首先采用C-C法计算重构参数对月径流序列进行相空间重构,然后分别计算其关联维数、Lyapunov指数和Kolmogorov熵,用这3个不同的混沌判别指标并行分析宜昌站月径流序列是否具有混沌特征。经计算,宜昌站月径流序列各个混沌判别指标均表明其具备混沌特征。 相似文献
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受诸多因素的影响,径流时间序列具有非线性和混沌特征.单一的BPNN模型可以进行径流的中长期预测,但存在对径流影响因素量化不够的缺点;单一的混沌模型可以量化径流的影响因素,但只能实现短期预测.为此建立了混沌理论与BPNN耦合的径流中长期预测模型.针对黑河上游莺落峡水文站1944-2017年的径流序列,利用混沌理论计算了径... 相似文献
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目前已有多种方法和指标来识别水文序列的混沌特性,但单独一种方法一般不能作为混沌特性识别的充分条件。根据相空间重构和混沌理论,对红河流域上游大东勇站1958-2010年、中游元江站1953-2010年和下游蛮耗站1957—2010年的月径流序列进行了较全面的混沌特性分析。首先采用去偏复自相关函数法和CAO法计算重构参数来对各站月径流序列进行相空间重构,然后分别计算其最大Lyapunov指数、Kolmogorov熵和关联维数,用这3个不同的混沌判别指标共同分析各站月径流序列是否具有混沌特征。经计算,红河流域各站月径流序列各个混沌判别指标均表明其具备混沌特征,为利用混沌理论建立预测模型提供了科学的依据。 相似文献
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以混沌理论和相空间重构原理为基础,分析计算大峪水文站1955-2006年月径流序列的最佳延迟时间和嵌入维数;运用最大Lyapunov指数λ10证实大峪月径流序列具有混沌特性,从而建立了基于混沌特性的BP神经网络预测模型。仿真及预测结果表明:该模型预测精度较高,可用于大峪月径流预测。 相似文献
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不同时间尺度的径流时间序列混沌特性分析 总被引:1,自引:0,他引:1
径流序列的动力行为是在复杂非线性和多尺度现象综合作用下的外在表现.基于混沌理论和相空间重构理论,以金沙江和美国Umpqua河统计的日径流序列为研究对象,对不同时间尺度(日、旬和月)的径流序列,首先利用0-1混沌测试算法计算其渐进增长率,探讨径流序列混沌特性随时间尺度的变化规律,然后重构以上径流序列的相空间,分别计算关联维数、最大Lyapunov指数和Kolmogorov熵.用这3个混沌判别指标分析不同时间尺度下径流序列的混沌特性及其随时间尺度的变化规律.研究结果表明,时间尺度和径流序列非线性特征之间的关系并不明显,渐进增长率随时间尺度的增加并无明显的变化规律,嵌入维数则随时间尺度的增大呈减小趋势,最大lyapunov指数和Kolmogorov熵随着时间尺度的增加逐渐增大. 相似文献
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越来越多的研究表明水文系统是一个高度非线性、复杂性的巨型系统。混沌理论为研究变化环境下水文要素特性提供了新方法。以汀江流域上杭水文站月尺度降雨径流时间序列为对象,采用饱和关联维数和最大Lya-punov指数指标识别混沌特性。分析结果表明,汀江流域月尺度降雨、径流的饱和关联维数均为分数维数,最大Lyapunov指数均大于零,可推断其存在明显的混沌特性,为进一步研究降雨径流预报提供依据。 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