Abstract
In the nearshore environment, viscous effects of wave- induced boundary layer flows above sea beds are important in evaluating sediment fluxes and wave damping. These effects need to be included in phase- resolved nearshore models for accurate determination of quantities such as the bed shear stress and the decrease in wave height due to frictional dissipation. In this work, we analyze the boundary layers induced by a solitary wave on permeable sea beds (extending previous work of wave-induced boundary layers on an impermeable bed). We find that the velocity profiles and bed shear stress are sensitive to the hydraulic conductivity of the bed, but not extremely sensitive to the precise boundary condition at the bed-fluid interface.
Highlights
The boundary layer in the fluid domain is calculated using perturbation approach as before
The effects of the permeable bed are taken into account via altering the bottom boundary condition using two different methods: (1) assuming that Darcy’s law applies right up to the upper edge of the permeable bed; (2) using a slip velocity at the permeable wall based on the Beavers and Joseph (1967) boundary condition
For the case of a solitary wave travelling over a permeable bed, they found that there is potential for the wave-induced flow to momentarily and locally fluidize the bed and that the seepage flow in the bed can induce significant wave damping
Summary
The boundary layer in the fluid domain is calculated using perturbation approach as before (separation of fluid velocities into an irrotational and rotational component). The effects of the permeable bed are taken into account via altering the bottom boundary condition using two different methods: (1) assuming that Darcy’s law applies right up to the upper edge of the permeable bed; (2) using a slip velocity at the permeable wall based on the Beavers and Joseph (1967) boundary condition. As the hydraulic conductivity increases, the boundary layer dynamics change qualitatively because the pressure-gradient-induced flow in the seabed becomes significant.
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