Study of solitary-wave-induced fluid motions and vortices in a cavity using a two-dimensional viscous flow model

This study presents a combined numerical and experimental investigation of the free-surface variation and induced fluid motion for a solitary wave propagating past a submerged cavity (or trench). The formation of vortices and the trajectories of fluid particles showing the transport of fluid content within the cavity zone are examined. A two-dimensional viscous flow is simulated by solving the stream function and vorticity equations using the finite-analytic method. Equations of free-surface boundary conditions are discretized by a two-step finite-difference scheme. To obtain more detailed motions in a cavity, a transient boundary-fitted grid system with locally refined grids is adopted. Experimental measurements of the free-surface elevations and the visual observations of the vortex motion were carried out to compare to the numerical solutions. The simulated free-surface elevations and fluid particle motion at various times are found to agree reasonably well with measurements and recorded observations. The formation and subsequent growth of a pair of recirculating vortices around the front corner of the cavity are clearly simulated by the present model. The effects of cavity size and incident-wave height on the flow patterns and the transport displacement of the fluid particles along the vertical and horizontal directions are analyzed. The results indicate that the greater the incident-wave height, the larger the values of the horizontal and vertical transporting distances. With an increase of cavity length, the strength of induced up-rolling vortices and the amount of downstream transporting fluid particles increases. However, the depth of the cavity has an insignificant influence on the height of the up-rolling vortices.