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21.
Long‐term variations and temporal scaling of hydroclimatic time series with focus on the German part of the Elbe River Basin 下载免费PDF全文
Long‐term variations and temporal scaling of mean monthly time series of river flow, precipitation, temperature, relative humidity, air pressure, duration of bright sunshine, degree of cloud cover, short wave radiation, wind speed and potential evaporation within or in vicinity of the German part of the Elbe River Basin are analyzed. Statistically significant correlations between the 2–15 year scale‐averaged wavelet spectra of the hydroclimatic variables and the North Atlantic Oscillation‐ and Arctic Oscillation index are found which suggests that such long‐term patterns in hydroclimatic time series are externally forced. The Hurst parameter estimates (H) based on the Detrended Fluctuation Analysis (DFA) indicate persistence for discharge, precipitation, wind speed, air pressure and the degree of cloud cover, all having an annual cycle and a broad low‐frequency distribution. Also, DFA H parameter estimates are higher for discharge than for precipitation. The major long‐term quasi‐periodic variability modes of precipitation detected using Singular Spectrum Analysis coincide with those detected in the discharge time series. Upon subtraction of these low‐frequency quasi‐periodic modes, the DFA H parameter estimates suggest absence of the persistence for both precipitation and discharge. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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This paper aims to present the critical top tension for static equilibrium configurations of a steel catenary riser(SCR) by using the finite element method. The critical top tension is the minimum top tension that can maintain the equilibrium of the SCR. If the top tension is smaller than the critical value, the equilibrium of the SCR does not exist. If the top tension is larger than the critical value, there are two possible equilibrium configurations. These two configurations exhibit the nonlinear large displacement. The configuration with the smaller displacement is stable, while the one with larger displacement is unstable. The numerical results show that the increases in the riser's vertical distances, horizontal offsets, riser's weights, internal flow velocities, and current velocities increase the critical top tensions of the SCR. In addition, the parametric studies are also performed in order to investigate the limit states for the analysis and design of the SCR. 相似文献
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Long‐term monitoring of a mercury contaminated estuary (Ria de Aveiro,Portugal): the effect of weather events and management in mercury transport 下载免费PDF全文
J. P. Coelho P. Pato B. Henriques A. Picado A. I. Lillebø J. M. Dias A. C. Duarte M. E. Pereira M. A. Pardal 《水文研究》2014,28(2):352-360
The main aim of this research was to assess the mercury transport from an estuarine basin with a background of anthropogenic contamination during a spring tidal cycle (year 2009) and compare it with two previous tidal cycles (years 1994 and 1999), as part of a long‐term monitoring program. Results showed that effective mercury transport occurs both in the dissolved and particulate fractions (0.18 and 0.20 kg per tidal cycle, respectively), and despite an overall decrease in environmental contamination, results more than double previous findings on particulate transport in the system. These findings result essentially from changes in the tidal prism (net export of 2 million m3 of water), given that both dissolved and particulate concentrations did not increase over time. Hydrodynamic simulations were performed to evaluate the effect of physical disturbance (dredging) and weather events (increased freshwater flow) in these processes, and results suggest the increased freshwater flow into the system as the main forcing function for the mercury transport increment. These results highlight the importance of long‐term monitoring programs, since despite an overall improvement in local contamination levels, the enhancement of transport processes through hydrological changes increases environmental pressure away from the contamination source. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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整体式桥台无伸缩缝桥梁(以下简称整体桥)桩基应设计为柔性桩,以保证较好的抗水平变形能力。但是,我国相关规范中判别柔性桩的算法主要应用于单向水平受荷桩,可否沿用至整体桥桩基还有待验证。为此,根据一种特殊设计的桩身变形测量方法,对3根埋深不同的混凝土模型桩进行了低周水平往复位移下的拟静力试验,研究单桩-土体系的抗震性能和相互作用机制。研究表明,水平往复位移下混凝土桩在埋深为3D~6D(D为桩径)范围内开裂;桩的埋深越大,桩身挠曲程度越大、变形特征点位置也越深、桩-土体系的抗弯刚度也越大、水平极限承载力也越高、抗震性能也越强。研究还表明,桩-土体系进入弹塑性阶段后,柔性桩的水平工作性状将逐渐向刚性桩退化。另外,在判别整体桥桩基的水平工作性状时,我国相关规范中的规定偏不安全。实际工程中,建议以Broms方法进行参考计算。 相似文献
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研发了一种适合于大范围1∶500的无人机测图方案,围绕平面和高程点位中误差在5 cm以内这一核心目标,从无人机的平台稳定性、空中精准定位飞控、空三与三维建模及模型与影像结合的多视角测图等方面进行了设计。在广州马沥村的应用表明,本文研究的无人机倾斜摄影方案可以满足1∶500高精度的三维测图,并具有较高的效率。 相似文献
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高温高压下海底管道的整体屈曲稳定性分析是管道设计的重要组成部分,而选取多长的管道进行分析对其整体屈曲稳定性结果影响显著。依据临界管长将管道分为"长管"与"短管",基于动力显式分析方法,揭示了长管与短管在发生整体屈曲过程中,屈曲幅值与波长、管壁轴向压力、轴向应变及轴向位移的变化规律;研究了土体约束力影响管道临界长度的规律性,分析了土体约束力系数对长管与短管整体屈曲变形的影响。研究发现,土体约束力对短管的整体屈曲行为影响显著,短管的整体屈曲幅值随土体约束力系数的增大呈现先增大后减小的趋势。该项研究对区分不同长度管道的整体屈曲类型进而采取有效防控措施具有重要参考价值。 相似文献