On the coupling between surface waves and the motion in a flexible porous surface layer

Abstract

The coupling between surface waves and the motion in a flexible porous surface layer is investigated theoretically. We apply a Lagrangian formulation for the viscous fluid and the fluid-saturated porous medium. In the floating porous layer, which we assume to be much thinner than the wavelength, we apply a macroscopic version of Darcy’s law. The interface between the porous layer and the underlying fluid is permeable, and the wave-induced vertical motion at the interface leads to wave damping. In addition, the viscous shear stress at the interface also dampens the waves. We here investigate the relative strength of the two mechanisms. Furthermore, we calculate the Lagrangian mean drift in the porous surface layer. The present study may provide a physical model for wave damping in the presence of unconsolidated rubble ice and the slow particle drift in rubble-ice layers.