Scattering of swell by currents
Scattering of swell by currents
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涌浪被水流散射
DOI：
10.1017/jfm.2023.686
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发表时间：
2023
影响因子：
3.7
通讯作者：
Vanneste, Jacques
中科院分区：
文献类型：
--
作者：
Wang, Han;Villas Bôas, Ana B.;Young, William R.;Vanneste, Jacques
海流对重力波的折射导致波场的空间调制，特别是有效波高。我们研究这种现象的情况下，波散射的局部电流功能，假设（i）电流速度和波群速度之间的比率很小，和（ii）一个膨胀状，高方向性的波谱。我们将匹配渐近性应用于四维位置-波数空间中的波作用守恒方程。由此得到的显式公式表明，调制波的作用和有效波高过去的本地化电流控制的涡度集成沿着的主要方向的膨胀。我们评估的渐近预测对数值模拟使用WAVEWATCH III的高斯涡。我们还考虑了涡偶极子，以证明“涡隐身”的可能性，即某些电流（渐近）没有显着波高的影响。我们讨论的两个小参数的比例的作用，表征假设（i）和（ii）以上，并表明焦散线是显着的，只有不切实际的大值的这个比例，对应于不切实际的窄方向谱。
The refraction of surface gravity waves by currents leads to spatial modulations in the wave field and, in particular, in the significant wave height. We examine this phenomenon in the case of waves scattered by a localised current feature, assuming (i) the smallness of the ratio between current velocity and wave group speed, and (ii) a swell-like, highly directional wave spectrum. We apply matched asymptotics to the equation governing the conservation of wave action in the four-dimensional position–wavenumber space. The resulting explicit formulas show that the modulations in wave action and significant wave height past the localised current are controlled by the vorticity of the current integrated along the primary direction of the swell. We assess the asymptotic predictions against numerical simulations using WAVEWATCH III for a Gaussian vortex. We also consider vortex dipoles to demonstrate the possibility of ‘vortex cloaking’ whereby certain currents have (asymptotically) no impact on the significant wave height. We discuss the role of the ratio of the two small parameters characterising assumptions (i) and (ii) above, and show that caustics are significant only for unrealistically large values of this ratio, corresponding to unrealistically narrow directional spectra.