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Títol:
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A subcritical instability of wave-driven alongshore currents
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Autor/a:
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Dodd, Nick; Iranzo, Vicente; Caballeria, Miquel
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Altres autors:
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Universitat de Vic. Escola Politècnica Superior; Universitat de Vic. Grup de Recerca en Medi Ambient i Alimentació |
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Notes:
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The development of shear instabilities of a wave-driven alongshore current is
investigated. In particular, we use weakly nonlinear theory to investigate the possibility
that such instabilities, which have been observed at various sites on the U.S. coast and in
the laboratory, can grow in linearly stable flows as a subcritical bifurcation by resonant
triad interaction, as first suggested by Shrira eta/. [1997]. We examine a realistic
longshore current profile and include the effects of eddy viscosity and bottom friction. We
show that according to the weakly nonlinear theory, resonance is possible and that these
linearly stable flows may exhibit explosive instabilities. We show that this phenomenon
may occur also when there is only approximate resonance, which is more likely in
nature. Furthermore, the size of the perturbation that is required to trigger the instability is
shown in some circumstances to be consistent with the size of naturally occurring
perturbations. Finally, we consider the differences between the present case examined and
the more idealized case of Shrira et a/. [ 1997]. It is shown that there is a possibility of
coupling between triads, due to the richer modal structure in more realistic flows,
which may act to stabilize the flow and act against the development of subcritical
bifurcations. Extensive numerical tests are called for. |
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Matèries:
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-Oceanografia
-Geofísica |
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Drets:
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(c) American Geophysical Union, 2004
Tots els drets reservats
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Tipus de document:
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Article
Article - Versió publicada |
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Publicat per:
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American Geophyisical Union
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Compartir:
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