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Laboratory observations of wave evolution, modulation and blocking due to spatially varying opposing currents

Published online by Cambridge University Press:  19 August 2010

Y. MA ,
G. DONG ,
M. PERLIN ,
X. MA ,
G. WANG  and
J. XU
Y. MA*
Affiliation:
State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116023, China
G. DONG
Affiliation:
State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116023, China
M. PERLIN
Affiliation:
Department of Naval Architecture and Marine Engineering, University of Michigan, Ann Arbor, MI 48109, USA
X. MA
Affiliation:
State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116023, China
G. WANG
Affiliation:
State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116023, China
J. XU
Affiliation:
CCCC-Fourth Harbor Design Institute Engineering Company Ltd., Guangzhou 510230, China
*
†Email address for correspondence: yuxma@126.com
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Abstract

The nonlinear evolution of waves propagating on a spatially varying opposing current has been observed in a wave–current flume. Regular waves with different initial periods and different initial steepness, s (0.05 < s < 0.19), were generated and observed. Frequency downshift, even with very small initial steepness, was identified. As expected, it was found that opposing currents can have significant interactions with wavetrains. The ultimate frequency downshift increases with the increase in initial steepness. The evolution of frequency modulation was observed via the instantaneous frequency extracted by the Morlet-wavelet transform. The instantaneous frequency showed that often the process of frequency downshift can be local in time and gradual, but abrupt changes of local frequency were also detected. The presence of an opposing current can gradually block the primary wave energy and destroy the conservation of the wave action at downwave locations, thus increasing the asymmetric modulation and accelerating the effective frequency downshift.

JFM classification

Waves/Free-surface Flows: Surface gravity waves Waves/Free-surface Flows: Wave breaking
Type
Papers
Information
Journal of Fluid Mechanics , Volume 661 , 25 October 2010 , pp. 108 - 129
Copyright
Copyright © Cambridge University Press 2010

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