Coherent structures in an oscillatory separated flow: numerical experiments

The process which leads to the formation of three-dimensional sand waves is investigated by means of a stability analysis which considers the time development of a small amplitude bottom perturbation of a shallow tidal sea. The weakly nonlinear interaction of a triad of resonant harmonic components of the bottom perturbation is considered. The results show that the investigated resonance mechanism can trigger the formation of a three-dimensional bottom pattern similar to that observed in the field.