ABSTRACT:

Three velocity components of water particles in the spilling and plunging breakers, respectively, have been measured simultaneously by means of an elaborate flowmeter in a two-dimensional wave tank. This new flowmeter measures the flow drag on three " tension threads" with each recording a separate flow component. Then," the steady flow and unsteady flow, turbulent fluctuat10n, and power spectral density are discussed for understanding and modelling the surf zone in a laboratory.

INTRODUCTION

Much of what is visible of a breaking wave is the combination of air and surface tension in drops and bubbles, containing salt(Scott, 1975). Breaking waves are one of the permanent subjects that has attracted numeral researchers and artists as well. Excellent reviews on this subject can be found in Peregrine(1983) and Battjes(1988). Offshore breaker types are either spilling or plunging: For spilling breaker, the wave shape remains more or less symmetric, while plunging breaker is characterized by a steepening and overturning of the front face, and the formation of a jet that plunges into the water ahead of the wave. The breaking process of spilling breaker is, however, essentially same as that of plunging breaker in the initial phases, except that for the former breaker it is confined to a relatively small region near the top of the wave. The progress of study on breaking waves has been greatly hampered by difficulties encountered in modelling the surf zone in a laboratory, and in measuring the water particle velocity. In the laboratory, water particle velocity 1n breaking waves has been measured by Morison and Crooke(1953), using neutral buoyant particles. This study has shown that the greatest horizontal water particle velocity occurs when a wave breaks and that there is a difference between the onshore and offshore velocities.

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