In the open ocean, the formation of large waves is non-linear. This non-linearity modifies the shape and structure of steep waves relative to that expected in a linear model. Work by Adcock et al. ["Nonlinear dynamics of wave-groups in random seas: Unexpected walls of water in the open ocean," Proc. R. Soc. A 471(2184), 20150660 (2015)] used a numerical model to show that, for a wave spectrum representative of that of a storm in the North Sea, non-linear dynamics resulted in the following changes to the shape of extreme wave groups relative to a linear model: expansion of the wave-crest laterally, contraction of the wave-group in the mean wave direction, and a movement of the largest wave to the front of the wave-group. They found only moderate elevation above that expected by the linear model. This paper extends this work to explore the influence of spectral bandwidth and directional spreading on these results. We find that sea-states with low directional spreads are more likely to see significant non-linear changes to extreme wave-groups. However, rather surprisingly, extreme waves formed in seas with broader spectra generally, although not always, see greater non-linear changes for the range of spectra studied here. We also observe that the lateral expansion to the wave-group occurs even for relatively modest sea-states and is a predictable feature. By contrast, the contraction of the wave-group in the mean wave direction only occurs occasionally in the steepest seastates- although when this is triggered the change can be very dramatic. Published by AIP Publishing.
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机译：在公海中，大浪的形成是非线性的。相对于线性模型中的预期，这种非线性改变了陡波的形状和结构。 Adcock等人的工作。 [“随机海域中波群的非线性动力学：公海中意外的水壁，” Proc.Natl.Acad.Sci.USA，87：3877-2877。 R. Soc。 A 471（2184），20150660（2015）]使用数值模型显示，对于代表北海暴风雨的波谱，非线性动力学导致极端波群的形状发生以下变化相对于线性模型：波峰横向扩展，波组在平均波方向上收缩，最大波向波组的前面移动。他们发现仅比线性模型期望的高一些。本文扩展了这项工作，以探索频谱带宽和方向扩展对这些结果的影响。我们发现，具有低方向性扩散的海州更有可能看到极端波群的明显非线性变化。然而，出乎意料的是，虽然并非总是如此，但通常在较宽光谱的海洋中形成的极端波在这里研究的光谱范围内会看到更大的非线性变化。我们还观察到，即使在相对温和的海况下，向波群的横向扩展也会发生，并且这是可预测的特征。相比之下，波浪组在平均波浪方向上的收缩仅偶尔出现在最陡峭的海域中，尽管触发此变化可能会非常剧烈。由AIP Publishing发布。
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