| Because all natural river flows around the world are turbulent and the channel beds are often composed of rough elements such as sand and gravel particles,the study of turbulent open channel flows over rough beds is of significant engineering interest.In recent years,mesh-free particle modelling approaches,such as SPH,have been investigated for their potential in simulating open channel flows,but their potential has not been fully explored for the turbulent channel flows over rough wall boundaries.Hence,the numerical modeling of turbulent open channel flows over rough beds is studied.The main achievements of the present paper are summarized as follows:(1)Theoretical achievements of the WCSPH method and turbulent open channel flows over rough beds are studied in detail.The difficulties of the WCSPH numerical model are identified.There are two difficulties for this,firstly the lack of adequate turbulence models which can be used to close with the Lagrangian SPH equations,and secondly the difficulty in modelling the flow structure near wall boundaries,especially when the wall is composed of rough elements.(2)The SPS turbulence model based on the Smagorinsky assumption and the mixing length theory is selected to carry out numerical model experiments,and it is found that the latter is more suitable for the simulation of open channel turbulence.(3)A wall function model for rough bed surface treatment was developed and applied to simulate hydraulically smooth flow,hydraulically rough flow and hydraulically transitional flow.Good results were obtained.In order to ensure the simulation accuracy,it is only applied to the simulation of small-scale rough bed,while the improved drag force model is used to simulate the large-scale rough bed.(4)In order to facilitate the application of the wall function model,the BP neural network based on genetic algorithm is used to fit the formula,and the wall function formula which can be applied to different turbulent flow states is obtained. |
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