Effects of sand ripples on the wave-induced seabed instability of the surface seabed

Wave-induced seabed instability significantly impacts the hydrodynamics of flow-particle interaction near the seabed surface. Previous studies on seabed instability mostly assume a flat seabed, neglecting the influence of sand ripple morphology on wave-induced soil dynamics. In the present study, the effects of sand ripples on the wave-induced seabed instability of the surface seabed are investigated. The numerical model is first validated by comparing the present simulations with results from prior experimental studies and empirical equations. Through model application, the present study investigated how sand ripples affect seabed instability, explicitly focusing on pore pressure, incipient motion of particles, and liquefaction depth. The present findings indicate the following: (1) variables related to seabed instability (pore pressure, Shields parameter, liquefaction depth) undergo spatial fluctuations in a sinusoidal pattern beneath the rippled surface, (2) the minor sand ripples may have significant effects on the incipient motions of sand particles, for instance, the very low coefficient of variation $C_v=1.2\text{\%}$ in sand ripple profile can induce as much as $C_v=23\text{\%}$ in the modified Shields parameter, and (3) these effects are most pronounced at the troughs of sand waves, especially for a relatively low Shields parameter and small seabed depth.