共查询到19条相似文献，搜索用时 203 毫秒
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应用作者提出的动床阻力、非均匀沙挟沙力、床沙交换调正及滩槽水沙交换等关系与新的不平衡输沙等初步经验关系,建立了黄河下游及水库河床变形计算一维数学模型。经1960年～1988年共28年实测水沙资料的验证计算,结果与实际基本符合。该模型的特点是可预报各种水流及河床边界条件下的动床阻力;可同时计算确定混合沙中各粒径组的推移质、悬移质挟沙力、含沙浓度垂线分布及上滩水流含沙量;能较好地反映浑水上滩淤积减沙使主槽减淤增冲的实际情况;能够基本反映泥沙多来多排及高含沙水流的冲淤特性;能综合反映出来水流量、含沙量及级配的调节变化产生的输沙冲淤差别。应用该模型计算黄河小浪底水库库区及下游河道的冲淤,成果比较合理。 相似文献
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采用浑水控制方程,建立了基于耦合解法的一维非恒定非均匀沙数学模型,用于模拟高含沙洪水演进时的河床冲淤过程.然后采用黄河下游游荡段1977年7—8月实测高含沙洪水资料对该模型进行率定,基于水沙耦合解法的各水文断面流量、总含沙量及分组含沙量的计算过程与实测过程符合更好,计算的沿程最高水位及累计河段冲淤量与实测值也较为符合.最后还采用2004年8月高含沙洪水资料对该模型进行了验证.模型率定及验证计算结果表明,采用一维水沙耦合模型计算高含沙洪水过程,能取得较高的精度. 相似文献
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植物的存在改变了河流水动力特性,造成独特的床面冲淤态势。利用实验室水槽模拟含淹没植物的河道,对床面形态和紊流统计特性参数进行测量,研究不同类型紊流作用下的床面冲淤特征以及床面起伏对流动的影响。结果表明:床面剪切紊流条件下,床面形态为马蹄坑-沙沟/沙脊与沙波复合分布,床面变形加剧了流速沿水深不均匀分布并促进水流动量交换;在自由剪切混合层紊流条件下,床面形态为植物根部马蹄形冲坑及其后方沙沟、沙脊交错分布,床面变形对流动的影响并不显著;“类二重紊流”条件下,床面形态同样表现为马蹄坑-沙沟/沙脊-沙波复合,床面变形促进植物层内部的水流动量交换、抑制紊动清扫,抑制植物层外部的动量交换、促进紊动喷射。 相似文献
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滚波(roll wores)是明渠均匀水流自由面失稳后发育的一系列波动现象.它的发生会带来诸多不利后果,如溢流、掺气、对河(渠)道水工建筑物的超负荷压力或应力等.滚波具有浅水长波的特征,因而利用一维浅水方程开展滚波问题的研究,取得了丰富的成果:如判定自由面稳定性的临界弗劳德数、演化方程的理论解及试验、数值研究等.构建能够更好地刻画滚波波动特征的理论模型,研究浑水、动床(包括床面变形)条件下滚波的形成及其演化规律,是今后滚波研究的一个重要方向. 相似文献
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为解析波流边界层内泥沙运动,建立了基于水动力-泥沙-床面互馈过程的波流边界层1DV泥沙数学模型,可用于模拟不同床面形态下粉沙-沙的含沙量过程。床面形态模块提供床面形态类型和相应参数;给出了平底和沙波床面粗糙高度和泥沙扩散系数的确定方法;采用了适宜粉沙及沙的制约沉速、底部参考浓度和起动剪切应力等公式;引入含沙量层化效应和制约沉降反映水动力与泥沙之间的相互影响。水槽试验资料验证表明,建立的模型较好地模拟了不同床面不同波流组合条件下的含沙量剖面。在此基础上,讨论了不同床面含沙量剖面模拟方法的差异,指出床面形态是决定含沙量变化的重要因素之一,仅通过改变床面粗糙高度不足以反映漩涡沙波床面的含沙量剖面特征。该模型可为研究波流边界层内泥沙运动和物质输运提供工具。 相似文献
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为了解析底部高含沙层特征,研究了物理影响机制和时均含沙量剖面。采用波流边界层1DV泥沙数学模型,结合试验资料,通过设置不同的计算工况进行了影响因素敏感性分析;在此基础上,提出波浪相关的时均泥沙扩散系数分布,考虑主要影响机制,推导了基于边界层物理过程的波浪作用下时均含沙量剖面表达式。结果表明,底部高含沙层与波浪边界层密切相关,是受水动力和床面形态综合影响的结果。仅建立高含沙层与水动力或床面形态的单一关系是有局限性的。含沙量层化效应和制约沉速对底部高含沙层具有重要影响。提出的平底床面含沙量剖面表达式为幂函数-Rouse-指数分布,漩涡沙波床面为指数-幂函数-Rouse分布。预期可应用于二维和三维泥沙数值模拟。 相似文献
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基于波作用量守恒方程建立了波流共存场中多向随机波浪传播变形数学模型,模型中考虑了波浪绕射的影响和水流引起的波浪弥散多普勒效应,应用包含水流和地形影响的激破波模式计算波浪破碎的能量耗散,采用一阶上迎风有限差分格式离散控制方程。分别计算了有无近岸流情况下单向和多向随机波浪的波高分布,考虑水流影响的数值计算结果与物理模型实验数据吻合良好,比较分析表明,所建立的数学模型能够复演由于离岸流引起的波高增大,可用于波流共存场多向随机波浪传播变形的模拟和预报。 相似文献
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A numerical model is used to simulate channelized lahars, flowing with a near-constant sediment concentration and volume. Water and debris are usually mobilized in short times and the peak discharge of lahars may reach many thousands of cubic meters per second in a few minutes. A relation for the energy dissipation term must be provided in the model, which in turn depends on debris flow rheology and shape and status of channel bed. A discussion of the form of this term is performed through the simulation of some historical (among the well-documented) lahars and lahar-runout flows with concentrations ranging in a wide spectrum up to 70 percent by volume and irregularly shaped sand and coarser particles dispersed in a fluid matrix of water and fine material. As concentration increases and turbulence decreases, the dissipative term, which, in the first case, is proportional to the square average flow velocity (Manning or Chezy formulation) is well described by a linear dependence on flow velocity, as expected in the laminar case. The numerical reproduction of the examined historical cases suggests that the model can be used for hazard assessment, if some hypotheses are made about lahar hydrograph at the source, its volume, and the shape of the dissipative term. 相似文献
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通过室内模拟试验,在坡度为3°和9°、流量为20和60L/min条件下研究了不同浓度(0～350kg/m3)含沙水流流经草地的泥沙沉积过程及其水力学特性。结果表明,坡面泥沙沉积量随含沙量的增加而增大,3°时泥沙沉积率与含沙量呈正相关,而9°时沉积率与含沙量呈反势。坡度对泥沙沉积影响显著,而在相同坡度条件下,两种流量试验的泥沙沉积量无明显差异。相同坡面坡上部位流速小于坡下部位,且含沙量对坡面流速影响较小。在相同坡度和流量条件下,水流雷诺数随含沙量的增大而减小。3°时水流阻力系数和曼宁糙率均随含沙量的增加而增大,而9°时含沙量对阻力影响不明显,因此在土壤侵蚀较严重地区进行坡面水文过程演算时需考虑含沙量对缓坡糙率的影响。 相似文献
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建立了土质陡坡降雨侵蚀的数学模型,模型包括陡坡细沟间坡面流控制方程、变沟宽陡坡细沟流控制方程、陡坡细沟间坡面侵蚀泥沙连续方程及陡坡变沟宽细沟侵蚀泥沙连续方程。通过紊流冲击分布概率确定土壤剥蚀方程,确定了泥沙源/汇项的表达形式及细沟高程与宽度的表达式。通过有限元和有限差分相结合的方法求解该数学模型,利用有限单元法对数学模型的水动力方程、运动方程及泥沙连续方程进行空间上的离散,利用有限差分法解决时间域的问题,得出了顺序求解的数值计算公式及模型数值求解的具体方法和步骤。 相似文献
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Sediment dynamics in the lowermost Mississippi River 总被引：1，自引：0，他引：1
Joann Mossa 《Engineering Geology》1996,45(1-4):457-479
There is much to be gained from investigating sediment dynamics in the lower Mississippi system, the largest river in terms of discharge and sediment load in North America. Such work can improve conceptual knowledge concerning downstream changes at the lower end of large river systems and can be applied to manage sediment diversions for wetland restoration in south Louisiana. Suspended sediment dynamics in the lowermost Mississippi River system in Louisiana are characterized using three approaches: (1) temporal changes in discharge-suspended sediment relationships showing interannual variations and the effects of floods over short timescales; (2) empirical relationships between discharge and suspended sediment variables at various locations; and (3) downstream changes in discharge-suspended sediment relationships. Interpretation of this data set is enhanced with other secondary data regarding processes, morphology, and bed materials.
Upstream, near Old River, LA, empirical relationships show nonlinearity, particularly in fine sediments, with decreased concentrations at highest discharges. During high discharge years, suspended sediment concentration peaks precede discharge crests by 40–85 days. The lead generally decreases with decreasing discharge maxima so that in low discharge years sediment peaks and discharge crests closely coincide in time. Downstream, near Belle Chasse, LA, fine bottom materials are resuspended and the timing of sediment peaks and discharge crests is coincident, regardless of flow magnitude. Conceptually, results suggest caution when generalizing about the relative timing of the sediment wave and flood wave and their downstream progression. These phenomena are influenced by local bed material and hydraulic conditions, and depend on the causative factors of sediment peaks. From an applied perspective, diversions should be managed differently depending upon where they are constructed along the river and upon the magnitude of the annual maximum flow. During high discharge years, when concerns for navigation and water supply are minimal, flow should be diverted on the rising limb upstream, near Old River, and during the discharge crest downstream near New Orleans. 相似文献
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Distribution of suspended sediment concentration in wide sediment‐laden streams: A novel power‐law theory 
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下载免费PDF全文 Francisco Nicolás Cantero‐Chinchilla Oscar Castro‐Orgaz Subhasish Dey 《Sedimentology》2016,63(6):1620-1633
The diffusion equation of suspended sediment concentration in a wide sediment‐laden stream flow is dependent on the vertical gradient of streamwise velocity and the sediment diffusivity. This study aims at investigating the influence of the streamwise velocity laws on the suspended sediment concentration distributions, resulting from the solution of the diffusion equation. Firstly, the sediment concentration distributions are obtained numerically from the solution of the diffusion equation using different velocity laws and compared with the experimental data. It is found that the power‐law approximation produces good computational results for the concentration distributions. The accuracy of using a power‐law velocity model is comparable with the results obtained from other classical velocity laws, namely log‐law, log wake‐law and stratified log‐law. Secondly, a novel analytical solution is proposed for the determination of sediment concentration distribution, where a power‐law, wall‐concentration profile is coupled with a concentration wake function. The power‐law model (for velocity and concentration) is calibrated using the experimental data, and then a generalized wake function is obtained by choosing a suitable law. The developed power‐law model involving the wake function adjusted by an exponent predicts the sediment concentration distributions quite satisfactorily. Finally, a new explicit formula for the suspended‐load transport rate is derived from the proposed theory, where numerical computation of integrals, as needed in the Einstein theory, is avoided. 相似文献
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Numerical modeling of salinity changes in marine environment of Persian Gulf is investigated in this paper. Computer simulation of the problem is performed by the solution of a convection-diffusion equation for salinity concentration coupled with the hydrodynamics equations. The hydrodynamic equations consist of shallow water equations of continuity and motion in horizontal plane. The effects of rain and evaporations are considered in the continuity equation and the effects of bed slope and friction, as well as the Coriolis effects are considered in two equations of motion. The cell vertex finite volume method is applied for solving the governing equations on triangular unstructured meshes. Using unstructured meshes provides great flexibility for modeling the flow problems in arbitrary and complex geometries, such as Persian Gulf domain. The results of evaporation and Coriolis effects, as well as imposing river and tidal boundary conditions to the hydrodynamic model of Persian Gulf (considering variable topology rough bed) are compared with predictions of Admiralty Tide Table, which are obtained from the harmonic analysis. The performance of the developed computer model is demonstrated by simulation of salinity changes due to inflow effects and diffusion effects as well as computed currents. 相似文献