A computer code for simulating hyper-concentrated sediment motions in steady and unsteady flows

A numerical model based on the two-phase flow equations is developed for pr edicting the intense sediment motions in steady and unsteady flows. As the governing equations are coupled and highly nonlinear, the failure of some e arlier attempts in applying two-phase flow models to reproduce the laborato ry measurements of flow properties has been found to be largely due to the deficiencies in the numerical schemes rather than the parameterisations of physical processes. In this paper, a numerical scheme for the complete set of two-phase flow equations is presented. It is a two-step implicit-explici t finite difference scheme and particularly designed to resolve flow detail s in the highly concentrated region at a mobile sand bed where vertical gra dients of concentration and flow velocities are very large. Two typical coa stal/river flow cases were used to verify the model by comparing the comput ed sediment motions with experimental data. A detailed evaluation of the co nvergence characteristics, stability and robustness of the scheme is also p rovided for these test cases. The initial results indicate that the propose d scheme is stable and sufficiently accurate for predicting the fluid and s ediment motions under both steady and unsteady conditions. (C) 2000 Elsevie r Science Inc. All rights reserved.