Continual skipping on water
Continual skipping on water
复制标题
持续在水上跳跃
DOI：
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发表时间：
2011
影响因子：
3.7
通讯作者：
J. McElwaine
中科院分区：
文献类型：
--
作者：
I. Hewitt;N. Balmforth;J. McElwaine
对矩形桨在浅水水面上的滑行和跳跃运动进行了实验研究。桨被允许自由移动上下连接到一个枢转的手臂。一个稳定的滑行状态，其中从水的升力平衡桨上的重量，被发现是稳定的小流速度，但变得不稳定，超过一定的阈值速度，这取决于重量和攻角。超过这个阈值，桨在水中振荡，并可以起飞到一个连续的弹跳，或跳跃，运动，具有明确的幅度和频率。这种转变有时是不稳定的，因此对于相同的实验参数，稳定的滑行状态和规则的跳跃状态都是可能的。浅水理论被用来构建简单的模型，解释定性特征的规划和跳跃状态的实验。它被发现，一个简单的参数化的桨上的升力成比例的深度的条目是不足以解释的意见，它的结论是，水的上升，特别是在桨的前面，这随着时间的推移而变化的方式，是负责导致滑行状态变得不稳定，并使一个持续的跳跃状态。
Experiments are conducted to study the planing and skipping of a rectangular paddle on the surface of a shallow stream. The paddle is allowed to move freely up and down by attaching it to a pivoted arm. A steady planing state, in which the lift force from the water balances the weight on the paddle, is found to be stable for small stream velocities but to become unstable above a certain threshold velocity which depends upon the weight and the angle of attack. Above this threshold, the paddle oscillates in the water and can take off into a continual bouncing, or skipping, motion, with a well-defined amplitude and frequency. The transition is sometimes bistable so that both a steady planing state and a regular skipping state are possible for the same experimental parameters. Shallow-water theory is used to construct simple models that explain the qualitative features of the planing and skipping states in the experiments. It is found that a simple parameterisation of the lift force on the paddle proportional to the depth of entry is not sufficient to explain the observations, and it is concluded that the rise of water ahead of the paddle, in particular the way this varies over time, is responsible for causing the planing state to become unstable and for enabling a continual skipping state.