Unsteady ripple generation on steep gravity–capillary waves
Unsteady ripple generation on steep gravity–capillary waves
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陡峭重力毛细波上不稳定波纹的产生
DOI：
10.1017/s0022112099004450
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发表时间：
1999
影响因子：
3.7
通讯作者：
M. Perlin
中科院分区：
文献类型：
--
作者：
Lei Jiang;Huanjay Lin;W. Schultz;M. Perlin
寄生纹波产生的短重力波（4厘米至10厘米波长）进行了研究，使用完全非线性计算和实验室实验。时间推进仿真显示了波纹陡度对初始条件的敏感性，特别是对波峰不对称性的敏感性。显著的波峰前后不对称及其非定常性增强了中等波陡下的纹波产生，例如ka在0.15和0.20之间，这一机制在以前的研究中没有讨论过。在我们的模拟中发现最大纹波陡峭度（随时间）随底层（低频带通）波陡峭度单调增加。这与Longuet-Higgins（1995）预测的亚临界或超临界波纹产生不同。下面重力-毛细波的不稳定性导致纹波调制和一个有趣的“波峰移动”现象——重力-毛细波波峰和前坡上的第一个纹波合并形成一个新的波峰。在自由表面条件下加入边界层效应扩展了在大波幅下的一些模拟。然而，寄生纹波产生的基本过程是无粘流中的非线性相互作用。机械产生的重力-毛细波具有类似的波纹产生特征，并且波纹陡度与波峰不对称性之间具有很强的相关性。
Parasitic ripple generation on short gravity waves (4 cm to 10 cm wavelengths) is examined using fully nonlinear computations and laboratory experiments. Time-marching simulations show sensitivity of the ripple steepness to initial conditions, in particular to the crest asymmetry. Significant crest fore–aft asymmetry and its unsteadiness enhance ripple generation at moderate wave steepness, e.g. ka between 0.15 and 0.20, a mechanism not discussed in previous studies. The maximum ripple steepness (in time) is found to increase monotonically with the underlying (low-frequency bandpass) wave steepness in our simulations. This is different from the sub- or super-critical ripple generation predicted by Longuet-Higgins (1995). Unsteadiness in the underlying gravity–capillary waves is shown to cause ripple modulation and an interesting ‘crest-shifting’ phenomenon – the gravity–capillary wave crest and the first ripple on the forward slope merge to form a new crest. Including boundary layer efects in the free-surface conditions extends some of the simulations at large wave amplitudes. However, the essential process of parasitic ripple generation is nonlinear interaction in an inviscid flow. Mechanically generated gravity–capillary waves demonstrate similar characteristic features of ripple generation and a strong correlation between ripple steepness and crest asymmetry.