异重流挟带泥沙长距离传播机制的数值与理论研究

While it has been long recognized that sediment-laden turbidity currents can propagate long distances, the phenomena of long-range propagation of turbidity currents is an aimed but difficult regulation target for reservoir managers. The reason behind this is the poorly understood mechanism for the long-range propagation of turbidity currents and the resultant sediment transport, which drives the development of this project idea. The asymptotic analytical solutions will be firstly derived for two potential categories of turbidity currents that are likely to propagate long distances. Stability analysis of the asymptotic analytical solutions will be conducted by introducing small disturbances. The resultant stability conditions serve as threshold energy conditions for initiation of those specific categories of turbidity currents. A layer-averaged fully coupled numerical model will be developed for turbidity currents, which allows for simulations of natural turbidity currents. Systematic numerical case studies can then be conducted, which allows for assessment of the interactions among the current-sediment erosion/deposition-topography-ambient water. It is expected that along with the threshold energy conditions, the numerical case studies can help reveal under what conditions and when turbidity currents can propagate long distances.

浊积砂岩在海底大规模分布的发现，使异重流挟带泥沙长距离传播特性得到了海洋沉积学家的广泛认同。然而，水库异重流长距离传播却是调控部门力求却不能常得的现象。本项目结合数值模拟和理论分析，旨在从力学角度增加对异重流长距离传播的机制的认识。本项目将推导异重流均匀平衡态、自加速态等具备长距离传播特性的异重流渐进解析解，应用摄动法分析其稳定性，得到上述异重流演化状态的临界能量条件。基于非结构三角形网格，采用现代高性能数值计算技术求解异重流层平均控制方程，建立具备健全物理基础的异重流层平均耦合动力学数学模型。通过较缓和较陡地形、渠堤地形和台阶状地形等复杂地形上异重流传播的数值算例研究，分析异重流-泥沙冲淤-地形之间、异重流-水交换(水卷吸、旁侧溢流)-水环境之间的相互作用与反馈机制，结合前述临界能量条件，阐明自加速态和均匀平衡态异重流发生和持续条件，从而增加对异重流长距离传播机理的理解。

浊积砂岩在海底大规模分布的发现，使异重流挟带泥沙长距离传播特性得到了海洋沉积学家的广泛认同。然而，水库异重流长距离传播却是调控部门力求却不能常得的现象。本项目结合数值模拟和理论分析，旨在从力学角度增加对异重流长距离传播的机制的认识，取得如下成果。首先，本项目从欧拉-拉格朗日耦合的角度建立了异重流LES-DEM数学模型，精确追踪每个颗粒的运动轨迹和运动特征，通过求解流体-颗粒相互作用和颗粒碰撞过程提出了促使异重流长距离输运的自悬浮机制的力学解释。其次，基于非结构三角形网格，采用现代高性能数值计算技术求解异重流层平均控制方程，建立具备健全物理基础的异重流层平均耦合动力学数学模型。再次，基于现有冲淤理论定义了高低流速区。通过对深海台阶状地貌上异重流水力状态复演和分析表明，在相同的流态下位于高流速区异重流更易造成全面的侵蚀并进行长距离传播，而位于低流速区时异重流减速会导致侵蚀能力的快速下降从而导致侵蚀和淤积的转换。