Geometry and Kinematics of Breaking Waves

• Main Author: Lader, Pål Furset
• Format: Doctoral Thesis
• Language: English
• Published: Norges teknisk-naturvitenskapelige universitet, Fakultet for ingeniørvitenskap og teknologi 2002
• Subjects: Marin hydrodynamikk; Havbølger - Bryting
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-69; http://nbn-resolving.de/urn:isbn:82-471-5426-9

The objective of this thesis is to experimentally study different breaking waves cases. This is done by measuring in detail the free surface geometry and the internal kinematics of the waves as they approach breaking. Three principal wave cases were chosen for the study: A plunging breaker, a spilling breaker, and an intermediate breaker. A major part of this work is the design, construction and building of a wave laboratory. The laboratory contains a glass wall waveflume which is 13.5m long, 1m deep and 0.6m wide, as well as equipment for measuring both the wave kinematics and geometry optically. The wave kinematics is measured using the Particle Image Velocimetry (PIV) method, while the wave profile geometry is measured using image analysis (space domain geometry), as well as standard wave gauges (time domain geometry). The analysis of both the wave kinematics and geometry is done using parameters describing quantitatively important features in the wave evolution. The surface geometry is described using the commonly known zero-downcross parameters, and in addition, new parameters are suggested and used in the study, The kinematics are described by a set of four parameters suggested for the first time in this work. These parameters are: Velocity at the surface, velocity at the still water line (z = 0), mean velocity direction, and local wave number. The purpose of these parameters is to give a better understanding of the space and time domain development of the kinematics, and they appear to be a reasonable compromise between simplicity and accuracy. The results presented here represents a thorough and detailed mapping of the breaking process. Much data is gathered and analysed, and throughout this thesis it is sought to present the data in the most intuitive way, so that other investigations may benefit from it.