VELOCITY MEASUREMENTS UNDER BROKEN WAVES AND BORES

Abstract

1. ABSTRACT The dynamics of waves after breaking is widely investigated because it controls several phenomena in the surf zone and swash zone. Several numerical models based essentially on non-linear shallow water equations (NLSWE) have been developed, but all of them fail to model turbulence in the bore. Many authors have measured fluid velocity in bores using Laser Doppler Velocimetry (LDV), Hot Wire and Hot Film anemometry, and Particle Image Velocimetry (PIV) with good results, though such studies possess several limitations imposed mainly by the presence of air bubbles. In order to overcome such limitations, a set of experiments was carried out in a flume using the Doppler Ultrasonic Technique for fluid velocity measurements. The instrument, a DOP1000, works essentially as a radar and utilizes ultrasound in the range 1 MHz-8 MHz as a carrier. This instrument is able to measure fluid velocity in several points along the US beam with negligible time delay. The maximum data rate obtained is ≈30 profiles per second for each probe, with three probes being employed and a maximum of 255 points per profile. The generated waves have a period of T=2.0, 2.5 and 3.0 s, and break as spilling on a 1:20 bottom. UDVP velocity profiles have been collected in three sections: one at the breaking point and two in the bore region after breaking.