In this paper, we present a new computationally-efficient and high-resolution depth-averaged two-phase flow model for hydro-sediment-morphydynamic processes, featuring an advance over existing models in terms of accuracy and efficiency of numerical solution. Under the framework of finite volume method (FVM) on unstructured grids, the Harten-Lax-van Leer-Contact (HLLC) approximate Riemann solver is proposed to compute inter-cell fluxes by applying the classical upwind HLLC approach to the water-sediment mixture and the sediment phases separately, in contrast to previous two-phase flow models using centered schemes. Moreover, to improve computational efficiency, the local-time-stepping (LTS) approach is implemented, the first attempt in the field of two-phase flow modelling. After a convergence rate study, the model is tested against a series of flow-sediment-bed evolutions induced by (1) two refilling processes of dredged trenches, (2) two instantaneous dam-break flooding flows, and (3) one levee breaching process by overtopping flows. It features encouraging performance when compared to a two-phase flow model based on a centered scheme and global time bound, characterized by more accurate results and much less computational cost. The present modelling framework shows promise in practical shallow water hydro-sediment-morphodynamic modelling applications.

在本文中，我们提出了一种新的计算效率高、分辨率高的水文-沉积物-形态动力学过程的深度平均两相流模型，在数值求解的准确性和效率方面优于现有模型。在非结构化网格有限体积法（FVM）的框架下，提出了Harten-Lax-van Leer-Contact（HLLC）近似黎曼求解器，通过将经典迎风HLLC方法应用于水-泥沙混合物来计算单元间通量和沉积物相分开，与以前使用中心方案的两相流模型形成对比。此外，为了提高计算效率，实现了本地时间步长 (LTS) 方法，这是两相流建模领域的首次尝试。经过收敛速度研究，该模型针对由 (1) 两次疏浚沟渠的回填过程、(2) 两次瞬时溃坝洪水流和 (3) 一次溢流冲破堤坝过程引起的一系列流沉积床演化进行了测试。与基于中心方案和全局时间界限的两相流模型相比，它具有令人鼓舞的性能，其特点是结果更准确，计算成本更低。目前的建模框架在实际的浅水水文沉积物形态动力学建模应用中显示出前景。与基于中心方案和全局时间界限的两相流模型相比，它具有令人鼓舞的性能，其特点是结果更准确，计算成本更低。目前的建模框架在实际的浅水水文沉积物形态动力学建模应用中显示出前景。与基于中心方案和全局时间界限的两相流模型相比，它具有令人鼓舞的性能，其特点是结果更准确，计算成本更低。目前的建模框架在实际的浅水水文沉积物形态动力学建模应用中显示出前景。