Observations of breaking waves on sloping bottoms by use of laser Doppler velocimetry
Creators: name: Skjelbreia, James Eric
Publisher: name: California Institute of Technology
Year: 1987

description: Wave breaking is investigated experimentally by use of laser doppler velocimetry for two cases: a plunging breaker and a spilling breaker. Specifically, emphasis is given to the kinematics at breaking, the early breaking phase, and the turbulent wake generated from wave breaking. A significant contribution is provided on the amplitude behavior for a solitary wave on a beach, as it is the solitary wave that is used to conduct this study. Associated with the use of the solitary wave, a technique of flow field construction by repeated measurement with an LDV is presented. 

Four well defined regions of the shoaling-through-breaking solitary wave on a beach are identified and termed according to the wave amplitude behavior within each region. They are: the zone of gradual shoaling, the zone of rapid shoaling, the zone of rapid decay and the zone of gradual decay. The plunging wave case studied exhibited a definite transitional zone, between the previously known -1/4 and -1 power laws, following a power law of -3/5. 

Velocity fields for a plunger and a spiller at the point of breaking are measured and the corresponding acceleration fields are computed for each. The results show good qualitative comparison to those obtained by theoretical approaches, however, no clear mechanism is demonstrated to initiate breaking for the spilling breaker studied. 

The existence of counter-rotating vortices, generated from breaking, is established from velocity measurements of the flow taken during the early breaking phase and within the turbulent wake of the plunging breaker studied. The measurements indicate that the size of the vortices are roughly the same as the undisturbed depth at the point of breaking. Turbulent intensities determined within the wake of the plunging breaker illustrate its character and show that level of turbulent intensity does not progressively decrease behind the turbulent source.
description: My adviser, Fredric Raichlen, had constant involvement throughout this study and was a guiding influence for the work presented. He was responsible for arranging my support and for suggesting the topic of this thesis; for this, he is gratefully acknowledged. 

Members of my thesis committee, Norman Brooks, Tom Caughey, John List, and Ted Wu, each of whom I came to know quite well through their excellent teachings, insightful discussions and joyful friendships, were a tremendous influence on me and helped shape the professional character that I have today. Gentlemen, it was my pleasure to have gotten to know each of you and to have had you all on my thesis committee; thanks for everything, you will not be forgotten. 

Persons which might be categorized as support personnel for this study, but were really much more than that, at least to me, include: Elton Daly, Rich Eastvedt, Joe Fontana, Rayma Harrison, Gunilla Hastrup and Joan Mathews. How lucky it was to have had you around, and yes, it's true, this thesis would not have been possible without you. Thank you, thank you all. 

Friends, each that know who they are, were so very important to me. All contributing to this thesis in one form or another and to a greater or lesser extent. Sharing good times and bad, we survived; thanks for the help in pulling me through. 

Caltech, I'd like to thank you, if such a thing is possible. You're a very special place and such a wonderful place to do one's graduate studies. Thank you very much Caltech for all the experiences you have given me. 

This study was funded by the National Science Foundation under Grant Numbers MSM83-ll374, CEE83-ll374 and CEE79-l2434. 

This report is essentially the thesis of the same title submitted by the writer May 20, 1987 to the California Institute of Technology, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering.