Video DCIV measurements of mass and momentum fluxes and kinetic energies in laboratory waves breaking over a bar

Abstract

The experimental investigation of water waves breaking over a barred beach in a glass walled flume is presented. The time series of the water levels along the flume were measured using wave gauges and video imaging of the water surface, providing estimates of the mean wave-heights and water levels at various positions along the flume. The instantaneous velocity fields were measured using digital correlation image velocimetry for positions beyond the initial breaking point. The mass (/velocity) and momentum fluxes, and kinetic energies were computed from the velocity flow fields by means of phase ensemble averaging and then time averaging of relevant quantities derived from the instantaneous velocity fields. These parameters reached a maximum value some distance shorewards of the break point on the bar. The relative density of the fluid in the crest of the wave, estimated using the forward and reverse velocity fluxes, was found to be in the range from 0.4 to 0.8. Preliminary analysis of the momentum fluxes and mean water levels indicates a decreasing dynamic pressure shorewards of a peak that occurs shortly after wave breaking.