抄録
This work presents a detailed morphodynamic modelling of bed forms under unsteady discharge, using large eddy simulation (LES). This model reproduces the temporal development of river dunes and accurately replicates the physical properties associated with bed form evolution. Several numerical experiments with different grain sizes and different discharges are performed to analyse the hysteresis of drag under variable discharges. It is shown that the hysteresis is more significant for gradually varying discharges, because the bed can adapt itself to the discharge. In a rapid change of discharge, the bed has not enough time to adapt. Furthermore, we observed that the size of sediment has a significant effect on the hysteresis. Sediment with large diameter affects the hysteresis significantly. If difference between the relaxation time of a particle and Kolmogorov time scale increases, it leads to a large time lag between discharge variability and morphodynamics, which leads to a significant hysteresis effect.
