On Lagrangian drift in shallow-water waves on moderate shear
On Lagrangian drift in shallow-water waves on moderate shear
复制标题
中等剪切作用下浅水波的拉格朗日漂移
作者：
W. Phillips;A. Dai;K. Tjan
考虑剪切流上特征速度小于波相速度的O（λ）的单色波场中的拉格朗日漂移。据发现，虽然剪切只有一个很小的影响漂移在深水波，其影响变得越来越重要，随着深度的减小，它在浅水波中起着重要的作用。剪切流的细节同样影响漂移。正因为如此，在沿海沃茨常见的两个时间的情况下进行了研究，即应力引起的剪切，会出现的边界层风驱动，和电流驱动的剪切，会出现从沿海流。在前者中，浅水波中的漂移幅度（最大值减去最小值）明显高于其对应物，即在其他静止环境中的类似波中的斯托克斯漂移。另一方面，在后者中，幅度减小。然而，虽然在自由表面的漂移总是在应力驱动剪切波传播的方向取向，这并不总是在电流驱动剪切的情况下，特别是在长波的边界层增长，以填补层。后一个发现维斯朗缪尔环流维斯特别有趣，朗缪尔环流是通过需要相同符号的微分漂移和切变的不稳定性产生的。这意味着，朗缪尔环流在海面附近形成，并向下（自上而下）增长，也许是为了填充层，在应力驱动的剪切中，它们在海流驱动的流动中的对应物从海底向上（自下而上）增长，但永远不能填充层。
The Lagrangian drift in an O(ϵ) monochromatic wave field on a shear flow, whose characteristic velocity is O(ϵ) smaller than the phase velocity of the waves, is considered. It is found that although shear has only a minor influence on drift in deep-water waves, its influence becomes increasingly important as the depth decreases, to the point that it plays a significant role in shallow-water waves. Details of the shear flow likewise affect the drift. Because of this, two temporal cases common in coastal waters are studied, viz. stress-induced shear, as would arise were the boundary layer wind-driven, and a current-driven shear, as would arise from coastal currents. In the former, the magnitude of the drift (maximum minus minimum) in shallow-water waves is increased significantly above its counterpart, viz. the Stokes drift, in like waves in otherwise quiescent surroundings. In the latter, on the other hand, the magnitude decreases. However, while the drift at the free surface is always oriented in the direction of wave propagation in stress-driven shear, this is not always the case in current-driven shear, especially in long waves as the boundary layer grows to fill the layer. This latter finding is of particular interest vis-à-vis Langmuir circulations, which arise through an instability that requires differential drift and shear of the same sign. This means that while Langmuir circulations form near the surface and grow downwards (top down), perhaps to fill the layer, in stress-driven shear, their counterparts in current-driven flows grow from the sea floor upwards (bottom up) but can never fill the layer.