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Even with the flow of water over a soil surface in which roughness elements are well inundated, and in less erosive situations where erosional bed forms are not pronounced, the magnitude of resistance coefficients in equations such as those of Darcy–Weisbach, Chezy or Manning vary with flow velocity (at least). Using both original laboratory and field data, and data from the literature, the paper examines this question of the apparent variation of resistance coefficients in relation to flow velocity, even in the absence of interaction between hydraulics and resulting erosional bed forms. Resistance equations are first assessed as to their ability to describe overland flow velocity when tested against these data sources. The result is that Manning's equation received stronger support than the Darcy–Weisbach or Chezy equations, though all equations were useful. The second question addressed is how best to estimate velocity of overland flow from measurements of slope and unit discharge, recognizing that the apparent flow velocity variation in resistance coefficients is probably a result of shortcomings in all of the listed resistance equations. A new methodology is illustrated which gives good agreement between estimated and measured flow velocity for both well-inundated sheet and rill flow. Comments are given on the predictive use of this methodology. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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扰动重力梯度的非奇异表示 总被引:5,自引:0,他引:5
在局部指北坐标系中用地心球坐标来表示扰动重力梯度张量,当计算点趋近于两极时,由于Legendre函数的一阶和二阶导数以及分母上所含余纬的正弦函数,将导致扰动重力梯度张量的计算出现无穷大。因此,本文引入了Legendre函数的一阶和二阶导数以及 无奇异性的计算公式,并且进一步推导了 无奇异性的计算公式。在将Legendre函数的一阶和二阶导数以及 、 无奇异性的计算公式代入到扰动重力梯度张量各分量的求解中时,又充分考虑了m等于0,1,2以及其它量时的复杂情况,建立了扰动重力梯度张量各分量无奇异性的详细计算模型。通过模拟实验表明,本文所建立的详细计算模型不仅能够完全满足当前卫星重力梯度张量计算的精度要求,而且模型稳定、可靠、易于编程实现。 相似文献
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Rivers with discontinuous watercourses are part of the spectrum of river diversity. Chain-of-ponds types contain irregularly spaced, steep-sided ponds that are separated by preferential flow paths on swampy valley fill. They often contain endangered ecological communities and are receiving greater attention for conservation and restoration. Very little is known about how these river types form, how they have evolved and how they function. Here we present the Late-Quaternary evolution of one of the last remaining large-scale chain-of-ponds systems in Australia, the Mulwaree Ponds. The chain-of-ponds was fully formed by 4.5 ka, with the position and alignment of the ponds being related to the position of pools of a palaeo-river that is up to 100 ka old. Contemporary hydrogeomorphic processes are insufficient to create the ponds, but sufficient to maintain and keep them open. The phases of evolution for this chain-of-ponds system are synchronous with Late-Quaternary changes in fluvial activity documented for other rivers in southeastern Australia. The ponds at Mulwaree have significant preservation potential over thousands of years. In the current landscape they are rare forms, providing significant grounds for conservation and protection of their distinctive geodiversity. © 2020 John Wiley & Sons, Ltd. 相似文献
187.
活动断裂对深埋隧洞影响的研究概述 总被引:2,自引:0,他引:2
简要叙述了南水北调西线工程面临的活动断裂的问题;介绍了活动断裂的运动方式、几何特征、运动的力学机制及其与地震的关系;详细讨论了活动断裂对隧洞工程的影响机理,并且总结了活动断裂的研究手段,系统地阐述了关于活动断裂的数值模拟方法并提出了有待进一步解决的问题。 相似文献
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Introduction In order to understand the formation of the geological structure and its evolution of the Asian continent, it is needed to investigate the driving forces from the around continents and oceans and from its underlying mantle as well. The super parallel computer has been used to simulate the geodynamical processes in the lithosphere and mantle for a long time in many international works (Bird, 1995; Tackley, 1995). We also calculated the patterns of the global mantle convection on o… 相似文献
189.
Jie Cui Xin Chen Xiaokang Deng Chunyan Ji Qian Li 《Marine Georesources & Geotechnology》2020,38(3):266-276
AbstractIn this paper, series of experimental studies under regular wave actions to investigate the hydrodynamic performance of the rectangular floating breakwater (FB) affected by reefs with different slopes were carried out in a wave flume. The wave transmission coefficients, motion responses and mooring forces can be calculated on the basis of the data obtained from the experiments. A comparative experiment of the only rectangular FB is also conducted. The experimental results reveal that the rectangular FB with different reefs can make more positive effects on wave energy dissipation than that of the only rectangular FB, especially for short-period waves. The characteristics of three degrees of freedom of the rectangular FB affected by reefs are also observed, which can be used to further explain the variation tendency appeared in transmission coefficients. The roll motion of the FB influenced by reefs is intenser than that of the only FB and the changes of slopes have limited effects on the sway motion of the FB. Furthermore, the heave motion of the only rectangular FB is intenser than that of the FB affected by reefs for short-period waves and vice versa for long-period waves. 相似文献
190.
将基于二维简化浅水波模型的间断Galerkin有限元与连续Galerkin有限元耦合方法推广至形式更为复杂的浅水波方程,并给出了误差分析以及模型问题的数值算例。 相似文献