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Indexed by:期刊论文

Date of Publication:2010-10-25

Journal:JOURNAL OF FLUID MECHANICS

Included Journals:SCIE、EI、Scopus

Volume:661

Page Number:108-129

ISSN No.:0022-1120

Key Words:surface gravity waves; wave breaking

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.