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On the critical free-surface flow over localised topography

Published online by Cambridge University Press:  26 October 2017

J. S. Keeler ,
B. J. Binder Open the ORCID record for B. J. Binder [Opens in a new window]  and
M. G. Blyth Open the ORCID record for M. G. Blyth [Opens in a new window]
J. S. Keeler*
Affiliation:
Department of Mathematics, University of East Anglia, Norwich NR4 7TJ, UK Department of Mathematical Sciences, University of Adelaide, Adelaide 5005, Australia
B. J. Binder
Affiliation:
Department of Mathematical Sciences, University of Adelaide, Adelaide 5005, Australia
M. G. Blyth
Affiliation:
Department of Mathematics, University of East Anglia, Norwich NR4 7TJ, UK
*
†Email address for correspondence: j.keeler@uea.ac.uk
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Abstract

Flow over bottom topography at critical Froude number is examined with a focus on steady, forced solitary wave solutions with algebraic decay in the far field, and their stability. Using the forced Korteweg–de Vries (fKdV) equation the weakly nonlinear steady solution space is examined in detail for the particular case of a Gaussian dip using a combination of asymptotic analysis and numerical computations. Non-uniqueness is established and a seemingly infinite set of steady solutions is uncovered. Non-uniqueness is also demonstrated for the fully nonlinear problem via boundary-integral calculations. It is shown analytically that critical flow solutions have algebraic decay in the far field both for the fKdV equation and for the fully nonlinear problem and, moreover, that the leading-order form of the decay is the same in both cases. The linear stability of the steady fKdV solutions is examined via eigenvalue computations and by a numerical study of the initial value fKdV problem. It is shown that there exists a linearly stable steady solution in which the deflection from the otherwise uniform surface level is everywhere negative.

JFM classification

Waves/Free-surface Flows: Channel flow Waves/Free-surface Flows: Solitary waves Waves/Free-surface Flows: Waves/Free-surface Flows

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Papers
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Journal of Fluid Mechanics , Volume 832 , 10 December 2017 , pp. 73 - 96
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© 2017 Cambridge University Press 

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