【作者】 许栋；

【导师】 白玉川；

【作者基本信息】 天津大学 ， 港口、海岸及近海工程， 2008， 博士

【摘要】 作为构成蜿蜒河流的基本要素,形状规则而又极其相似的河弯形态蕴涵着深层次的动力机制。蜿蜒河流的河弯随时间变化而不断地蠕动、迂回和迁移,这种运动称为河弯动力过程或蜿蜒河流演变动力过程。河弯动力过程的研究对河流开发与治理工程、跨河桥梁及沿河交通设施的选址、油气资源勘探以及河流生态修复等均有着重要意义。河弯问题的研究涉及到多种时间和空间尺度、以及多个学科内容,本文从水动力学、河流动力学以及地貌动力学的角度对冲积性蜿蜒河流河弯问题进行多角度、交叉学科研究,主要内容和创新之处有:对自然界中大型蜿蜒河流的平面形态进行多尺度分析和几何分形分析,建立了对河弯形态识别、概化以及特征量统计分析的方法。分析结果表明,与弯曲度参数相比,分形维数能够更好地描述大型河流平面形态的蜿蜒性和不规则性,河流平面形态小尺度的分形维数主要反映河弯的发育情况,而大尺度的分形特征则反映流域地形的不规则性。建立了模拟明渠水流运动的三维数学模型,研究了弯曲度、水深、河宽、床面形态等因素对弯道水流运动特性的影响;对弯道水流运动各特征量进行量级分析,为基本方程向二维和一维简化提供了理论依据。数值试验结果表明,自然河流河弯中的主流、二次环流和流速重分布特征是与自然河弯的特殊几何形态特征、水深条件紧密相连的,水深越小则流速沿横向的重分布越为显著;河宽越小则水流动力轴线在凹岸的顶冲点越为提前。自然河流流量的非恒定性是对河弯演变过程的一种强烈扰动,本文建立了弯曲河道中非恒定水流运动的平面二维数学模型,对该扰动展开了初步研究。基于河弯水流运动的线性理论以及地形沉积的概念模型建立了河弯运动和地形沉积发展的耦合数学模型,模型中对传统的线性河岸侵蚀模式进行改进,建立了非线性的河岸侵蚀模型。根据大量的模拟结果,揭示了在一定条件下河流具有消除外界施加的随机扰动的河道滤波功能。利用室内模型试验研究了弯道水流泥沙运动特性以及模型河流造床特性、河弯演变特性;作为另外一项创新性工作,本文根据模型试验测量的需要,研制了基于粒子跟踪技术(PTV)的表面流场测速系统和高效的断面地形测量系统。更多还原

【Abstract】 As the basic element of sinuous rivers, the regular and similar river meander planforms imply profound dynamics. River meanders on alluvial sinuous river migrate crossstream and downstream continuously, which is called the dynamic process of river meanders. Research on the dynamic process of river meanders plays an important role on river development and regulation, locating of river crossing bridges and highways along rivers, oil and gas exploration and ecological restoration of rivers etc.Research on river meandering involves different spatial and temporal scales, as well as multiple subjects. In this thesis, river meanders on alluvial sinuous river are interdisciplinarily studied from the aspect of hydrodynamics, river dynamics and morphodynamics. Main contents and innovations are:The planforms of large scale rivers were studied by multi-scale analysis and fractal analysis. A set of methods for meander recognization, generalization and statistic analysis was also developed. Analysis shows that fractal dimension can describe the meandering and irregularity of the planforms of large scale rivers better than curvature. Small scale fractal dimensions reflect the development of river meanders, while large scale ones reflect the irregularity of landform of watershed.A three-dimensional mathematical model was established to simulate the flow in open channel. Numerical experiments were carried out with this model to study the influence of curvature, water depth, channel width and bed topography on flow in channel bends. Scale analysis was also carried out for characteristic flow parameters as a foundation of simplification of control equations to two-dimensional and one-dimensional ones. Numerical simulation results show that the typical features of primary flow, secondary flow and velocity redistribution in natural river bends are closely related to the special planform and flow depth conditions of natural river meanders. The lateral redistribution of flow is significant when water depth is small. The main stream approaches the concave bank upstream the bend vertex when river width is small.The unsteady flow of natural rivers causes strong perturbation on meander developing process. A two-dimensional model was established for sinuous channels to simulate unsteady flow movement as a pilot study on this perturbation effect. Mathematical model coupling river meander migration and landform development was established based on linear river meandering theory and conceptual deposition model. The traditional linear theory of bank erosion was improved to a nonlinear one. Simulation results reveal that rivers have the function of channel filtering to smooth out the given initial random disturbance under certain conditions.Laboratory experiments were carried out to study the characteristics of flow and sediment transport in channel bends, as well as river meander migration laws. According to the requirement of measurement in experiment, particle tracking velocimetry and high efficiency sectional topographic surveying system were developed, which was another innovational work of this thesis.更多还原