  Understanding the sediment transport in oscillatory flows is essential to the
investigation of the overall sediment budget for coastal regions. This overall
budget is crucial for the prediction of the morphological change of coastline
in engineering applications. Since the sediment transport in oscillatory flows
is dense particle-laden flow, appropriate modeling of the particle interaction
is critical. Although traditional two-fluid approaches have been applied to the
study of sediment transport in oscillatory flows, the approaches do not resolve
the interaction of the particles. Particle-resolved modeling of sediment
transport in oscillatory flows and the study of micromechanics of sediment
particles are still lacking. In this work, a parallel CFD-DEM solver that can
resolve the inter-particle collision is applied to study the granular
micromechanics of sediment particles in oscillatory flows. The results obtained
from the CFD-DEM solver are validated by using the experimental data of coarse
and medium sands. The comparison with experimental results suggests that the
flow velocity, the sediment flux and the net sediment transport rate predicted
by are satisfactory. Moreover, the micromechanic quantities of the sediment bed
are presented in detail, including Voronoi concentration, coordination number,
and particle interaction force. It is demonstrated that variation of these
micromechanic quantities at different phases in the oscillatory cycle is
significant, which is due to different responses of the sediment bed. To
investigate the structural properties of the sediment bed, the correlation of
the Voronoi volume fraction and coordination number are compared to the results
from the fluidized bed simulations. The consistency in the comparison indicates
the structural micromechanics of sediment transport and fluidized bed are
similar despite the differences in flow patterns.
