Laboratory experiments for wave motions and turbulence flows in front of abreakwater

In this paper, laboratory data for free surface displacements and velocity fields in front of a caisson breakwater covered with wave-dissipating block s, together with wave pressures acting on the caisson, are presented and di scussed. The core of the breakwater is made of a concrete caisson with a ve rtical front wall. The caisson is protected by a thick layer of tetrapods a nd is supported by a rubble mound. The breakwater is placed on the 1/25 imp ermeable slope. Two types of incident waves are used in the experiments: no nbreaking waves and spilling-type breaking waves. In the breaking wave case , the incident wave breaks offshore before it reaches the breakwater. The v elocity data are obtained by using both the Laser Doppler Velocimeter (LDV) and the Electromagnetic Current Meter (EMCM). The raw data are analyzed us ing a numerical-filtering scheme so that turbulent fluctuations are separat ed from the phase-dependent wave motions. The vertical profiles of the time -averaged (over a wave period) turbulent velocity components at several ver tical cross-sections in front of the breakwater are then analyzed. The spat ial variations of the time-averaged turbulence velocity suggest that turbul ence is generated inside the protective armor layer and transported into th e flow region in front of the breakwater. The wave pressures on the vertica l face and on the bottom of the caisson are also reported. (C) 2001 Elsevie r Science B.V. All rights reserved.