Numerical tank for suspended sediment transport under strong nonlinear waves in shallow water zones

Abstract

Wave nonlinearity and free surface effects are recognized as important factors for sediment transport under nonlinear waves. Existing studies primarily focus on oscillatory water tunnel (OWT) instead of real waves for sediment transport due to the challenges in constructing real-scale wave tank. In contrast to OWT, the wave tank performs both wave nonlinearity and free surface effect on sediment transport. A numerical wave-sediment tank is developed for strong nonlinear wave propagation over sediment bed with low computational cost. The nonlinear wave is generated by defining the inlet boundary condition and absorbed by using a damping function, and the classical volume of fluid method is used to handle the free surface. The numerical tank further considers particle wake vortex effect and modifications in relative velocity of high sediment concentration, and incorporates phase lag, mass conservation, acceleration effect, and asymmetric wave boundary layer into near-bed sediment conditions. Therefore, the numerical tank avoids complex calculations for near-bed hyper-concentrated sediment in comparison with a two-phase model, i.e., the calculation of particle collision, friction, and detection of mobile bed surface. The numerical tank reasonably agrees with large-scale wave flume experiments and a two-phase model including free surface wave, and successfully performs sediment transport induced by strong nonlinear (second-order Cnoidal) wave. Compared to the OWT, the extra onshore streaming caused by free surface wave significantly enhances onshore sediment transport.