In this paper, the smoothed particle hydrodynamics method is used to simulate experimental shallow free surface turbulent flows over a rough bed made of regularly packed uniform spheres. The numerical program is based on the open source code SPHysics and significant improvement is made in the turbulence modelling and rough bed treatment within the code. A modified sub-particle-scale eddy viscosity model is proposed to simulate the effect of turbulence transfer mechanisms in the highly-sheared free surface flow, and a drag force term is introduced into the momentum equation as a source term to account for the existence of the bed roughness. To validate the numerical model, a laboratory experiment is carried out to study shallow, turbulent flow behaviour under different flow conditions. The SPH simulations are then compared with the flow velocity, shear stress and turbulent intensity profiles measured via acoustic doppler velocimeters. Several issues with regard to the rough bed hydraulics are investigated, including the study of water surface behaviour and its interaction with the bulk flow.

The Dujiangyan Irrigation System (DIS), located in the western portion of the Chengdu Plain at the transitional junction between the Qinghai-Tibet Plateau and Sichuan Basin, has been in operation for about 2300 years. The system automatically uses natural topographical and hydrological features and provides automatic water diversion, sediment drainage and intake flow discharge control, thus preventing disastrous events in the region in a ‘natural’ way. Using a numerical modeling approach, this study aims to investigate the reasons behind this natural behavior of the system and provide a better understanding of the complex mechanisms which have caused the sustainability of the DIS for over two millennia. For this purpose, a two-phase flow model based on the Shallow Water Equations (SWEs) is developed to simulate the fluid and sediment motions in the DIS. A coupled explicit-implicit technique based on the Finite Element Method is applied for the fluid flow and a Sediment Mass (SM) model in the framework of the Lagrangian particle method is proposed to simulate the sediment motion under different flow discharge conditions. The results show how different components of the DIS make full use of the hydrodynamic and topographical characteristics of the river to effectively discharge sediment and excess flood to the downstream and create an environmentally sustainable irrigation system.

In this study, a three-dimensional (3D) numerical model based on the smoothed particle hydrodynamics (SPH) approach was developed to simulate the near-shore current flows over a rough topographic surface in the coastal area, where the flows are shallow and demonstrate strong turbulent characteristics. The numerical program is based on the open-source code SPHysics (http://www.sphysics.org), and two major improvements are made to treat the turbulence and rough boundary effects: A modified sub-particle-scale (SPS) eddy viscosity model is developed to address the turbulence transfer of flows, and a drag force equation is included in the momentum equations to account for the influence of roughness element on the bed and lateral boundaries. The computed results of flow velocity, shear stress, and free surface characteristics are compared with the laboratory measurements for a variety of test conditions. It has shown that the present SPH model can accurately simulate 3D-free surface near-shore current flows over a realistic topography with roughness.

In this study, a fully 3D numerical model based on the Smoothed Particle Hydrodynamics (SPH) approach has been developed to simulate turbulent open channel flows over a fixed rough bed. The model focuses on the study of dynamic free surface behavior as well as its interaction with underlying flow structures near the rough bed. The model is improved from the open source code SPHysics ( http://www.sphysics.org ) by adding more advanced turbulence and rough bed treatment schemes. A modified sub-particle-scale (SPS) eddy viscosity model is proposed to reflect the turbulence transfer mechanisms and a modified drag force equation is included into the momentum equations to account for the existence of roughness elements on the bed as well as on the sidewalls. The computed results of various free surface patterns have been compared with the laboratory measurements of the fluctuating water surface elevations in the streamwise and spanwise directions of a rectangular open-channel flow under a range of flow conditions. The comparison has demonstrated that the proposed 3D SPH model can simulate well the complex free surface flows over a fixed rough bed.