船舶尾流的结构和持续性以及朗缪尔型环流的作用
Structure and Persistence of Ship Wakes and the Role of Langmuir-Type Circulations
摘要：
在海浪中工作的水面船舶会产生横向表面电流，这种电流在最初的船舶感应电流衰减后会持续很长时间。这些表面流是由于形成了大规模的朗缪尔型环流，并被认为是表面活性物质集中成条纹或条带的机制，这在海洋表面的合成孔径雷达图像中经常看到。这些环流是由Craik-Leibovich涡力产生的，该涡力是由船舶感应电流与环境表面波相互作用产生的。一旦产生，环流会持续存在，因为它们的大尺度几乎是无粘性的。本文对水面舰船在静水、头浪和尾浪中的尾流进行了数值模拟，结果与海上试验的雷达图像吻合较好。它表明，表面电流不存在的表面波，但可以持续几十公里，通过形成朗缪尔型环流。由于环流是由斯托克斯漂移和尾流涡度的叉积驱动的，因此持续尾流的结构是船舶相对于表面波传播方向的相对航向的函数。
英文摘要：
Surface ships operating in ocean waves are shown to generate transverse surface currents which persist long after the initial ship-induced currents have decayed. These surface currents are due to the formation of large-scale Langmuir-type circulations and are suggested to be the mechanism for the concentration of surface-active substance into streaks or bands, which are regularly seen in synthetic aperture radar imagery of the ocean surface. These circulations are generated by the Craik-Leibovich vortex force, which results from interaction of ship-induced current with ambient surface waves. Once generated, the circulations persist due to their large-scale nearly-inviscid nature. Numerical simulations of the wake behind a surface ship in calm, head, and following seas are presented and show good agreement with radar imagery from at-sea experiments. It is demonstrated that surface currents do not persist in the absence of surface waves, but can persist for tens of kilometers through the formation of Langmuir-type circulations. Since the circulations are driven by the cross product of the Stokes drift and the wake vorticity, the structure of the persistent wake is a function of relative heading of the ship with respect to the direction of surface-wave propagation.
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