Date of Award

Winter 2003

Document Type


Degree Name

Doctor of Philosophy (PhD)


Civil & Environmental Engineering

Committee Director

David R. Basco

Committee Member

Jaewan Yoon

Committee Member

John M. Klinck


The relative trough Froude number (RTFN) theory is a new phase-resolving type, wave breaking trigger model introduced by Utku (1999) and Utku and Basco (2002). Based on the moving hydraulic jump concept, this model provides a better implementation of wave breaking in terms of hydrodynamics. Development of computer resources permits the use of the phase-resolving type, Boussinesq wave models in nearshore areas. The Boussinesq equation, however, does not include the physics of wave breaking, so that an additional mechanism is required to initiate wave breaking in the model. The main objective of this study is to develop a new wave breaking trigger model for the Boussinesq equation model by using the RTFN theory.

A theoretical analysis is performed to determine the analytical expression of the RTFN theory and the critical condition for wave breaking (CTFN). The RTFN theory is redefined for this purpose. Coupling with wave theories (both linear and nonlinear), the analytical form of the RTFN is obtained. The Miche (1944) formula provides a wave breaking condition. All results agree with RTFN = 1.45 as the theoretical CTFN.

A wave tank experiment is performed to obtain data for model confirmation. Wave breaking locations are measured with the assistance of a digital video recording. Wave gauge records are used to adjust input wave heights in the numerical model.

Wave celerity calculation methods for the RTFN calculation are investigated intensively because 90% of the RTFN calculation is the contribution due to the celerity (Utku and Basco, 2002). To satisfy both applicability and robustness, a hybrid method is introduced.

Extensive numerical experiments are executed for the confirmation, calibration, and verification of the model. Qualitative studies confirm that the RTFN evolution along with the nonlinear wave transformation correctly behave for a wave breaking trigger. The model calibration performed with data obtained from the wave tank experiment determines the CTFN = 1.47 for the numerical model, which is very close to the theoretical value. Verification tests with calibrated CTFN reveal that the momentum sink term locating mechanism associated with the RTFN theory is also needed for completing the RTFN wave breaking model. This aspect of the work is left for the future.


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