The dynamics of sliding, rolling and saltating sediments in oscillatory flows

The dynamics of sediment grains picked-up from the seabed and dragged by the oscillatory flow induced by wind waves close to the bottom is investigated for moderate values of the Shields parameter. The results of particle-resolved direct numerical simulations are analysed, which consist of the flow field and the trajectories of spherical particles mimicking the dynamics of the sediment grains. The Reynolds number of the flow is large enough to observe the turbulent regime. Moreover, the interaction between the turbulent eddies and the small vortex structures shed by the sediment particles is explicitly computed. The trajectories of the moving grains are determined by means of Newton’s laws and the evaluation of the force and torque that the fluid exerts on the surface of each sediment grain.