Third-order resonant wave interactions under the influence of background current fields
Third-order resonant wave interactions under the influence of background current fields
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DOI：
10.1017/jfm.2015.578
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发表时间：
2015-10
影响因子：
3.7
通讯作者：
T. Waseda;T. Kinoshita;L. Cavaleri;A. Toffoli
中科院分区：
文献类型：
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作者：
T. Waseda;T. Kinoshita;L. Cavaleri;A. Toffoli
在一个长50m、宽10m、深5m的水池中进行了一系列实验，由定向造波机产生成一定角度传播的两个波。当这两个波从一个共振的三联体中挑选出来时，一个最初不存在的波随着波沿着水箱传播而增长。共振波的线性增长率与基于Zakharov约化引力方程的三阶共振理论符合得很好。此外，还进行了具有较大时间和空间变化的对流和同流平均流实验。随着流量的增加，线性增长受到抑制。正如用Zakharov方程数值再现的那样，在时间尺度上饱和的共振相互作用与强迫随机共振失谐的大小成反比。推测由于波长相关的多普勒频移和波射线的折射，共振的失谐是由变化而不是电流场的平均值引起的。对频谱演化的进一步分析表明，虽然由于动力学级联，在高频处出现了离散的峰，但随着电流速度的增加，背景中会出现连续饱和的频谱。另外，还进行了实验，研究了在水流影响下，随机方向波在动态时间尺度上的演变。由于电流的随机共振失谐，光谱尾部往往受到抑制。
A series of experiments were conducted in a wave basin (50 m long, 10 m wide and 5 m deep) generating two waves propagating at an angle by a directional wavemaker. When the two waves were selected from a resonant triplet, an initially non-existing wave grew as the waves propagated down the tank. The linear growth rate of the resonating wave agreed well with third-order resonance theory based on Zakharov’s reduced gravity equation. Additional experiments with opposing and coflowing mean current with large temporal and spatial variations were conducted. As the flow rate increased, the linear growth was suppressed. As reproduced numerically with Zakharov’s equation, the resonant interaction saturated at time scales inversely proportional to the magnitude of the forced random resonance detuning. It is conjectured that the resonance is detuned by the variation and not by the mean of the current field due to wavelength-dependent Doppler shift and to the refraction of wave rays. Further analysis of the spectral evolution revealed that while discrete peaks appear at high frequencies as a result of dynamical cascading, a continuously saturated spectrum develops in the background as the current speed increases. Additional experiments were conducted studying the evolution of the random directional wave on a dynamical time scale under the influence of current. Due to random resonance detuning by the current, the spectral tail tended to be suppressed.