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论文类型：期刊论文
发表时间：2010-10-25
发表刊物：JOURNAL OF FLUID MECHANICS
收录刊物：SCIE、EI、Scopus
卷号：661
页面范围：108-129
ISSN号：0022-1120
关键字：surface gravity waves; wave breaking
摘要：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.