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Title: Longshore currents generated by sea waves
Author: Austin, D. I.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1981
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Computer programs are developed to model the process of longshore current generation by sea waves in the region of a harbour using the finite element method. Wave behaviour is modelled using a solution of the medium-depth wave equation due to Berkhoff. Reflection, refraction and diffraction effects are encompassed. A non-reflecting boundary condition is developed for use on the artificial boundaries. The radiation stress theory of Longuet Higgins is applied in conjunction with a limiting ratio wave breaking criterion to obtain forcing terms for use in the shallow water equations. A generalisation of the radiation stress theory is attempted. The influence of the eddy viscosity and bottom friction terms used in the shallow water equations on the longshore currents is investigated. The computer programs are verified by comparison of the longshore current patterns generated in the region of a harbour when an oblique angle of wave incidence is used with the patterns from a physical model. Very good qualitative agreement is found. The influence of modifications to the eddy viscosity term on the current pattern is analysed. Wave oscillations found in the wave program solution are shown to be caused by partial wave reflection due to changes in the water depth. It is found necessary to refine the finite element mesh when the wave program is used in large models with a short wavelength. The partial reflected waves are found to have major effects on the expected eddy circulation when wavelengths long relative to the model are used. Circulation cells are generated when an angle of wave incidence normal to the shoreline is used. Longshore variations in water depth cause the radiation stress imbalances which result in the circulation patterns.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available