Laboratory observations of continuous and intermittent subharmonic edge waves

IF 4.5 2区 工程技术 Q1 ENGINEERING, CIVIL
Xuelin Ding , Roland Garnier , Colin Whittaker , Pablo Blondeaux , Giovanna Vittori , Robert A. Dalrymple , Pedro Lomonaco , R.T. Guza , Giovanni Coco
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引用次数: 0

Abstract

The theoretical suggestion that subharmonic edge wave growth is inhibited by incident wave randomness is confirmed with observations in a large laboratory basin. Edge waves, gravity waves trapped near the shore by shoreline reflection and refraction, can be excited by an instability of waves normally incident from offshore. In the much-studied case of monochromatic, unidirectional incident waves, phase locking with incident waves allows continuous edge wave growth, culminating in edge waves with larger amplitudes than the incident waves. We present the first laboratory observations of edge wave excitation with random incident waves. Randomness associated with frequency and directional spread in incident waves disrupts phase locking between edge and incident waves, and subharmonic edge wave amplitudes never reach an equilibrium. Edge wave generation can be suppressed completely by relatively rapid variation of incident wave amplitude and (especially) phase. With moderate randomness, edge waves can be intermittent, with near zero amplitudes for many wave periods, followed by intervals with relatively energetic edge waves. Observed time-varying edge wave amplitudes and phases are broadly consistent with existing nonlinear perturbation theory but with significant disagreement. With both monochromatic and random incident waves, observed edge wave amplitudes are underpredicted by about a factor of ∼2, possibly owing to violation of the theoretical assumptions of weakly nonlinear and narrow-banded waves, simplified damping, and complete shoreline reflection. Intermittency will complicate detecting natural subharmonic edge waves.

Plain language summary

Edge waves travel parallel to the shoreline and are confined to shallow water. Subharmonic edge waves, with period twice that of waves incident on a beach, are studied in a large-scale wave basin with regular and (for the first time) random incident waves more representative of realistic ocean conditions. We confirm the recent theoretical finding that random incident waves can suppress edge wave excitation.
连续和间歇次谐波边缘波的实验室观测
理论认为,入射波的随机性抑制了次谐波边缘波的增长,这一观点得到了大型实验室盆地观测的证实。边缘波,即被海岸线反射和折射困在海岸附近的重力波,可以被通常从近海入射的波浪的不稳定性激发。在被广泛研究的单色、单向入射波的情况下,与入射波相锁允许连续的边缘波增长,最终形成比入射波振幅更大的边缘波。我们提出了随机入射波的边缘波激发的第一个实验室观测。与入射波的频率和方向传播相关的随机性破坏了边缘波和入射波之间的相位锁定,并且次谐波边缘波振幅永远不会达到平衡。通过相对快速的入射波振幅和(特别是)相位变化,可以完全抑制边缘波的产生。在中等随机性下,边缘波可以是间歇性的,在许多波周期中振幅接近于零,然后是相对有能量的边缘波的间隔。观测到的时变边波幅值和相位与现有的非线性摄动理论基本一致,但存在很大的分歧。对于单色波和随机入射波,观测到的边缘波振幅都被低估了约2倍,这可能是由于违反了弱非线性和窄带波、简化阻尼和完全海岸线反射的理论假设。间断性将使探测自然次谐波边缘波复杂化。浅浅的语言概括边波与海岸线平行,只限于浅水。在大尺度波盆中研究了周期为海滩入射波两倍的次谐波边缘波,其中规则波和(首次)随机入射波更能代表现实海洋条件。我们证实了最近的理论发现,即随机入射波可以抑制边缘波的激发。
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来源期刊
Coastal Engineering
Coastal Engineering 工程技术-工程:大洋
CiteScore
9.20
自引率
13.60%
发文量
0
审稿时长
3.5 months
期刊介绍: Coastal Engineering is an international medium for coastal engineers and scientists. Combining practical applications with modern technological and scientific approaches, such as mathematical and numerical modelling, laboratory and field observations and experiments, it publishes fundamental studies as well as case studies on the following aspects of coastal, harbour and offshore engineering: waves, currents and sediment transport; coastal, estuarine and offshore morphology; technical and functional design of coastal and harbour structures; morphological and environmental impact of coastal, harbour and offshore structures.
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