Wave Crest Kinematics of Deep Water Breaking Waves

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Measurements of the kinematics of three cases of breaking waves have been conducted using the Particle Image Velocimetry (PIV) method. A set of four parameters are used do describe the kinematics, and the development of the waves as they approach breaking is studied using these parameters. The parameters reveal significant features in the temporal development of the internal kinematics of steep, asymmetric transient waves. Introduction Knowledge of the mechanisms leading to the generation of breaking waves in deep water is still not fully understood, and breaking of waves can not be defined uniquely by any parameter at present. A breaking criterion is of fundamental importance, and also enters in practical applications, e.g. in estimating the probability of occurrence of breaking waves at sea. Several criteria have been suggested, but none have proven to give a unique definition of the inception of breaking (Tulin and Li, 1992). In this paper we present measurements of the crest kinematics in three different cases of breaking waves: A plunging breaker, a spilling breaker, and an intermediate breaker (see Figure 1). The intermediate breaker is a breaker that is initiated by a microscale plunging event, and evolves further as a spilling breaker. The classification of breakers follows Kjeldsen and Myrhaug (1978). The plunging and intermediate breakers were generated by using the method of phase focusing (see e.g. LonguetHiggins, 1974 and Kjeldsen and Myrhaug, 1979). The spilling breaker was generated 1. Research Scientist, SINTEF Fisheries and Aquaculture, N-7465 Trondheim, Norway, Phone: +47 73 59 76 92, fax: +47 73 59 56 60, e-mail: Pal.Lader@fish.sintef.no 2. Professor, Department of Marine Hydrodynamics, Norwegian University of Science and Technology. 3. Professor, Department of Marine Hydrodynamics, Norwegian University of Science and Technology.