Laboratory Study on the Characteristics of Deep-water Breaking Waves☆

Abstract In this paper, deep-water breaking waves are generated by the method of energy focusing in a wave flume and the intensity of wave breaking is toned by changing input wave steepness. In the experiment, the time series of surface elevation fluctuation along the flume are obtained utilizing 22 wave probes which are mounted along the mid-stream of the flume. The characteristics of wave surface are analyzed. The spectrum are computed for surface elevations by a fast Fourier transform (FFT). It is concluded that the energy keeps stable in low frequencies part and spreads toward the higher frequencies of the first harmonic band as the wave approaching the breaking zone. After the breaking, the spectrum restores almost its initial shape, but the spectrum energy is lost in the high-frequency end of the first harmonic band, which is more appreciable when the wave breaking happens and is stronger. As the energy is spread to higher frequencies for non-breaking wave, the “spectrally weighted wave frequency” f s becomes bigger and the “spectrally weighted group velocity” C gs become smaller after the wave focusing. When the wave breaking occurs, the loss in energy is obvious leading to f s decreasing and C gs increasing after wave breaking, which is more appreciable for plunging wave.