Long‐period waves on a natural beach
Long‐period waves on a natural beach
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天然海滩上的长周期波浪
DOI：
10.1029/jc081i036p06441
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发表时间：
1976
影响因子：
--
通讯作者：
D. Huntley
中科院分区：
文献类型：
--
作者：
D. Huntley
描述了现场实验，其中使用三个二分量电磁流量计同时测量沿着垂直于海岸线的线和离岸 100 m 的沿岸 (υ) 和陆上-离岸 (u) 速度分量。对本实验数据的频谱分析表明，存在一组离散的低频频谱峰值（0.014-0.05 Hz），这些峰值在靠近海岸线的风波峰值上占主导地位，并且其幅度随着距海岸的距离而衰减。四个最低频率（也是最清晰）峰值中每一个的速度分量的幅度都已根据距海岸线的距离绘制出来，并且与计算出的海滩边缘波幅度变化进行了令人满意的比较。从交叉光谱中还发现了一台流量计处的 u、υ 之间以及离岸不同距离处的 u、u 之间的相位，并确认这些峰值是由边缘波引起的。建议每个低频峰值对应于海滩截止频率处的渐进边缘波模式。 Ball (1967) 以及 Guza 和 Inman (1975) 计算出 n 模式边缘波的截止频率 υ 应与 [n(n + 1 )]1/2 成比例，其中比例常数取决于水下海滩剖面。四个最低频率峰值的频率与截止边缘波最低模式的预测频率非常吻合（n = 1，····，4），并且观察到的每个频率的离岸振幅衰减表明将峰值分配给这些模式是正确的。结果还表明，这些截止模式之间通过非线性相互作用进行能量交换。简要讨论了在该海滩上观测渐进边缘波的意义。
A field experiment is described in which three two-component electromagnetic flowmeters were used to measure simultaneously the longshore (υ) and onshore-offshore (u) velocity components along a line normal to the shoreline and up to 100 m offshore. Spectral analysis of the data from this experiment reveals the presence of a set of discrete spectral peaks of low frequency (0.014–0.05 Hz) which dominate over the wind wave peak close to the shoreline and which decay in amplitude with distance from the shore. The amplitudes of the velocity components for each of the four lowest-frequency (and clearest) peaks have been plotted against distance from the shoreline and are found to compare satisfactorily with the calculated edge wave amplitude variation for the beach. Phases between u, υ at one flowmeter and between u, u at different distances offshore have also been found from cross spectra and confirm that the peaks are due to edge waves. It is suggested that each of these low-frequency peaks corresponds to a progressive edge wave mode at the cutoff frequency for the beach. Ball (1967) and Guza and Inman (1975) calculate that the cutoff frequency υ for an edge wave of mode n should be proportional to [n(n + 1 )]1/2, where the constant of proportionality is dependent on the subaqueous beach profile. The frequencies of the four lowest-frequency peaks agree well with the predicted frequencies for the lowest modes of cutoff edge waves (n = 1, · · ·, 4), and the observed offshore decay of amplitude at each frequency indicates that assigning the peaks to these modes is correct. Energy exchange between these cutoff modes, through nonlinear interaction, is also suggested by the results. The significance of observing progressive edge waves on this beach is briefly discussed.