波流悬沙输移对多尺度紊动结构的响应机制

Estuaries and coasts in China are always characterized by complex boundary conditions, lots of islands and bed materials of silt. Under co-action of combined waves and currents, silt is easily in incipient and suspension. Moreover, sand ripples formed on the bed, vortex structures developed in the bottom currents, and further enhance sediment suspending, exhibiting a fluid-boundary-sediment interactive system. This system comprises of wave induced fluctuation, ripple induced vortex motion and the real high frequency turbulence, which can be defined as generalized turbulence with multi-scales. Its influence on suspended load transport is still not well known..By theoretical analysis, and flume experiment, this project mainly investigates the characteristics of multi-scale turbulence structure, time averaged velocity profile and time averaged suspended concentration profile under co-action of combined waves and currents, and try to reveal the formation and evolution mechanism of the multi-scale turbulences and distinguish the driving mechanism of multi-scale turbulences to time averaged velocity profile and concentration profile. In addition, formulas for distribution of fluctuation, vortex motion and real turbulence, time averaged velocity, and concentration will be derived. It would provide a theoretical basis for improving the precision of sediment transport prediction with coastal engineering.

我国河口海岸边界地形复杂、岛屿众多，且底床多为细粉沙所覆盖，在波流作用下泥沙易于起动、悬浮和输移，且床面常伴有一定尺度的沙纹，底部水流的涡动力结构又进一步增强了泥沙的悬浮，形成动力、边界及泥沙三个过程相互反馈系统。该系统存在波浪所致全水深范围的低频波动、沙纹所致底部低频涡动及水体运动所致全水深范围高频脉动等多时空尺度的紊动结构（广义），其对悬沙输移的作用机制仍不明晰。.拟采用理论分析与水槽试验结合，开展波流多尺度紊动结构特征、边界层内外时均流速分布特征及悬沙分布特征的研究，揭示多尺度紊动结构的形成和演化机理，辨析不同时空尺度的紊动结构对时均流剖面及含沙量剖面的驱动机制，建立波流共同作用下波动、涡动及脉动分布表达式，边界层内外时均流分布统一表达式，时均含沙量分布及临底含沙量表达式。为提高河口海岸工程泥沙预报精度提供理论基础。

波流共同作用下泥沙输移体现为动力、边界及泥沙三个过程相互反馈系统，多尺度紊动结构作用下泥沙运动机制复杂。构建了多尺度紊动及泥沙输移观测系统，发展了多尺度紊动结构数据处理技术，获得波流多尺度紊动结构及泥沙输移精细数据。阐明了多尺度紊动结构演化及相互作用机制，建立了波动应力、涡量分布、紊动分布的表达式。 揭示了波流时均流速分布对多尺度紊动结构的响应机制，导出了波流边界层内外时均流速分布统一表达式。刻画了多尺度紊动结构挟沙的物理图式，建立波动、涡动、紊动的挟沙能力定量表达式，基于波流悬沙对流扩散方程，导出波流边界层内外统一的悬沙分布表达式。从而对波流泥沙输移多尺度过程进行精细解析，并形成理论模式，丰富和发展了河口海岸动力学，为河口海岸工程泥沙预报提供科学依据。