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Subharmonic edge wave excitation by narrow-band, random incident waves

Published online by Cambridge University Press:  12 April 2019

Giovanna Vittori*
Affiliation:
Department of Civil, Chemical and Environmental Engineering, University of Genoa, Via Montallegro 1, 16145 Genova, Italy
Paolo Blondeaux
Affiliation:
Department of Civil, Chemical and Environmental Engineering, University of Genoa, Via Montallegro 1, 16145 Genova, Italy
Giovanni Coco
Affiliation:
School of Environment, University of Auckland, 1010 Auckland, New Zealand
R. T. Guza
Affiliation:
Integrative Oceanography Division – Scripps Institution of Oceanography, University of California, La Jolla, CA 92093-0209, USA
*
Email address for correspondence: vittori@dicat.unige.it

Abstract

A monochromatic, small amplitude, normally incident standing wave on a sloping beach is unstable to perturbation by subharmonic (half the frequency) edge waves. At equilibrium, edge wave shoreline amplitudes can exceed incident wave amplitudes. Here, the effect of incident wave randomness on subharmonic edge wave excitation is explored following a weakly nonlinear stability analysis under the assumption of narrow-band incident random waves. Edge waves respond to variations in both incident wave phase and amplitude, and the edge wave amplitudes and incident wave groups vary on similar time scales. When bottom friction is included, intermittent subharmonic edge wave excitation is predicted due to the combination of bottom friction and wave phase. Edge wave amplitude can be near zero for long times, but for short periods reaches relatively large values, similar to amplitudes with monochromatic incident waves and no friction.

Type
JFM Rapids
Copyright
© 2019 Cambridge University Press 

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