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Observations of breaking waves on sloping bottoms by use of laser Doppler velocimetry

Citation

Skjelbreia, James Eric (1986) Observations of breaking waves on sloping bottoms by use of laser Doppler velocimetry. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-06142006-112209

Abstract

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.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Civil Engineering
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Raichlen, Fredric
Thesis Committee:
  • Raichlen, Fredric (chair)
  • Brooks, Norman H.
  • Wu, Theodore Yao-tsu
  • Caughey, Thomas Kirk
Defense Date:1 May 1986
Record Number:CaltechETD:etd-06142006-112209
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-06142006-112209
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2589
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:29 Jun 2006
Last Modified:26 Dec 2012 02:52

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