| The Internal solitary waves play an important role in determining the biology and optical properties of the water column in costal areas. Direct numerical simulations of the wave-induced boundary layer under internal waves in shallow water are performed for the purpose of exploring the appearance of a local dynamics favorable for sediment resuspension. In particular, the flow in the footprint of an internal solitary wave of elevation propagating in a sheared current with a two-layer stratification is examined for the spontaneous onset of global instability. A critical boundary in wave amplitude-wave Reynolds number space is found as a function of the parameters defining the environmental state, and the character of the dynamics of the unstable state is explored as a function of the super-criticality. A well-defined bifurcation sequence exists along which the globally unstable motion in the footprint of the solitary wave transitions from a state of synchronous motion to a chaotic state. Characteristics of the flow structure for different regimes in state space are described, along with some conjectures as to the relation of these flow structures to possible sediment resuspension by long internal waves. By tracing those passive particles precisely in the simulations, it was found that thin-layer formation of the particles could be caused by the long internal waves frequently. The global instability can be triggered easily and frequently by an internal wave with proper shear and wave amplitude at certain Reynolds number to resuspend the benthic sedimentary particles and to from thin layers. |
