  The flow within an oscillatory boundary layer, which approximates the flow
generated by propagating sea waves of small amplitude close to the bottom, is
simulated numerically by integrating Navier-Stokes and continuity equations.
The bottom is made up of spherical particles, free to move, which mimic
sediment grains. The approach allows to fully-resolve the flow around the
particles and to evaluate the forces and torques that the fluid exerts on their
surface. Then, the dynamics of sediments is explicitly computed by means of
Newton-Euler equations. For the smallest value of the flow Reynolds number
presently simulated, the flow regime turns out to fall in the intermittently
turbulent regime such that turbulence appears when the free stream velocity is
close to its largest values but the flow recovers a laminar like behaviour
during the remaining phases of the cycle. For the largest value of the Reynolds
number turbulence is significant almost during the whole flow cycle. The
evaluation of the sediment transport rate allows to estimate the reliability of
the empirical predictors commonly used to estimate the amount of sediments
transported by the sea waves. For large values of the Shields parameter, the
sediment flow rate during the accelerating phases does not differ from that
observed during the decelerating phases. However, for relatively small values
of the Shields parameter, the amount of moving particles depends not only on
the bottom shear stress but also on flow acceleration. Moreover, the numerical
results provide information on the role that turbulent eddies have on sediment
dynamics.
