A laboratory experiment of rip currents between the ends of breaking wave crests

Abstract

abstract In order to investigate the rip current formed between the ends of breaking wave crests, a laboratory experiment was conducted over a bathymetry with an equilibrium profile. For the experiment, pseudo intersecting wave trains were produced in a wave basin, where regular waves were generated by running two parts of wave maker out of phase. The pseudo intersecting wave trains were compared with the intersecting wave trains, which are formed by the interference of two wave trains with slightly different directions and are the cause of the rip current, by conducting numerical simulations using FUNWAVE. The rip current developments between the ends of breaking wave crests through their node regions were confirmed similarly in both numerical simulations. In the hydraulic experiment using the pseudo intersecting wave trains, the rip current flow was observed by utilizing Large Scale Particle Image Velocimetry and Acoustic Doppler Velocimetry, and the wave height and the mean surface were measured. From the observations, it was confirmed that the rip current was developed through the node region with relatively low wave height, and it was found that its strength was varied by the refraction and dissipation of the ends of wave crests due to the wave-current interaction. The horizontal and vertical velocity profiles of the rip current were presented in the present experiment. The comparison between the measured results and the numerical results showed a reasonable agreement, however, also confirmed the limitation of the numerical model on breaking and mixing process. Using particle trajectories, it was observed that vortices were developed at the ends of breaking wave crests, which played a role of generating and accelerating the rip current.