VIDEO-BASED IMAGE PROCESSING OF LABORATORY-SCALE RIP CURRENTS

摘要

Particle image velocimetry (PIV) is applied to investigate the variability of rip currents over variable topography using iterative FFT-based correlation algorithms. Images are preprocessed to remove background noise before PIV analysis and post-processing is employed to smooth spurious vectors afterwards. Rip channels of varying incision depth are constructed and the corresponding rip current dynamics are investigated. On all three geometries, the rip current strength increases with increased incoming wave height (from 0.03 m to 0.05 m) as the wave field is the predominant driving force of rips. Bathymetry plays a secondary role in the complex hydrodynamic response. Thus, the rip current flow with varying rip channel topography does not change significantly. As the rip channel is incised from 1/3 to 2/3 and further down to full channel, the rip current feedback system changes from positive to negative, which suggests an increase and then a decrease in rip current strength. This variable trend is shown in the spatial distribution of maximum and mean offshore velocity. Forcing mechanics, wave-current interaction effect and continuity standpoint are combined in an attempt to explain the observations.