Numerical investigation of ripple in oscillating water tank by DEM-MPS coupled solid–liquid two-phase flow model

Abstract

The height of ripples, representing roughness in the shallow-water area, is an important factor in the prediction of coastal processes. However, the characterization of ripples under violent flow conditions has proven challenging. For instance, in shallow water in the swash zone, significant water fluctuation occurs owing to interactions between the up-rush and down-rush of waves. Because such phenomena shows strong nonlinearity, sufficient knowledge of swash-ripple formation remains lacking. In this study, experiments generating ripples in an oscillating water tank are conducted. Furthermore, numerical simulation using the three-dimensional DEM-MPS coupled method is performed. By comparing numerical and experimental results, validation of the present numerical simulation is demonstrated, followed by an investigation of the mechanics of ripple formation. Numerical results show that not only the drag force but pressure gradient force resulting from the water surface gradient considerably affect sand-particle motion, revealing the need for accurate evaluation of the free surface flow. Moreover, pressure gradient force plays an important role in the ripple formation process, so it should be reflected in the numerical model for ripple simulations.