Free-stream velocity descriptions under waves with skewness and asymmetry
Free-stream velocity descriptions under waves with skewness and asymmetry
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具有偏斜和不对称的波浪下的自由流速度描述
DOI：
10.1016/j.coastaleng.2012.04.009
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发表时间：
2012
影响因子：
4.4
通讯作者：
A. Davies
中科院分区：
文献类型：
--
作者：
J. Malarkey;A. Davies
在浅水中，当波浪浅滩时，其轨道速度随自由水面的相应变化而呈现偏态（速度偏态）和不对称（加速度偏态）。在河床附近，随时间变化的速度的偏度和不对称性的变化对底部摩擦“旋转”的剩余速度和沉积物的输运有重要影响。在经常发生最大泥沙输运的波边界层中，需要以系统的方式表示自由流速度（波边界层边缘的轨道速度），以便在通常不表示自由表面的波洞实验和波边界层模型中可以模拟它。由于没有容易获得的包括偏态和不对称的浅滩波的动力学理论，有必要在一个足够普遍的自由流速度描述中综合浅滩效应，以拟合观测到的速度时间序列。本文回顾了以前的自由流速度描述，包括Abreu等人（2010）的描述，并介绍了一种基于锯齿波形状的新描述。本文量化了每个描述的所有相关的偏度和不对称度量。然后证明Abreu等人（2010）的描述代表了最一般的描述，并改进了他们对观察到的自由流速度的拟合技术，以进一步简化它。当这种描述与不规则波的速度特征（如Elfrink等人（2006）的描述）结合使用时，可以将速度偏斜和不对称直接与无因次波和海滩参数（波高、表面波长和冲浪相似参数作为海滩坡度的代表）联系起来。MATLAB脚本提供了Abreu等人（2010）和Elfrink等人（2006）特征的改进描述。
In shallow water, when waves shoal their orbital velocities exhibit skewness (velocity skewness) and asymmetry (acceleration skewness) in response to corresponding changes in the free surface. Near the bed, changes in the skewness and asymmetry of the time-varying velocities have important consequences for the residual velocities ‘spun up’ by the bottom friction and for sediment transport. In the wave boundary layer, where the largest sediment transport often occurs, there is a need to represent the free-stream velocity (the orbital velocity at the edge of the wave boundary layer) in a systematic way such that it can be mimicked in wave tunnel experiments and wave boundary layer models which usually do not represent the free surface. Since there is no readily accessible dynamical theory for shoaling waves that includes both skewness and asymmetry, it is necessary to synthesize the shoaling effect in a free-stream velocity description that is general enough to fit observed velocity time series. This paper reviews previous free-stream velocity descriptions, including the description of Abreu et al. (2010), and introduces a new description based on generalising a sawtooth wave shape. The paper quantifies all the relevant measures of skewness and asymmetry for each description. It then demonstrates that Abreu et al.'s (2010) description represents the most general one and improves upon their fitting techniques to observed free-stream velocities to further simplify it. When this description is used in conjunction with a characterisation of the velocity for irregular waves, such as that of Elfrink et al. (2006), it is possible to relate velocity skewness and asymmetry directly to the non-dimensional wave and beach parameters (wave height, surface wavelength and surf similarity parameter as a proxy for beach slope). MATLAB scripts are provided for the improved description of Abreu et al. (2010) and Elfrink et al.'s (2006) characterisation.