Generating Faraday rogue waves through particle focusing by the surrounding waves

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题名:	Generating Faraday rogue waves through particle focusing by the surrounding waves
作者:	劉俊佑;Liu, Chun-Yu
贡献者:	物理學系
关键词:	法拉第波;極高振幅偶發突波;預測指標;Faraday wave;rogue wave;pattern formation;precursor
日期:	2019-06-18
上传时间:	2019-09-03 14:58:04 (UTC+8)
出版者:	國立中央大學
摘要:	突波為時空間突發的非確定局域超高振幅波 (extreme amplitude wave event)，廣存於各類非線性失穩波系統，例如：法拉第波、水面波、非線性介質中的光波和微粒電漿聲波，生活中常見於海洋上的瘋狗浪 (rogue wave)。過去的研究指出極高振幅偶發突波源於調制非穩性 (modulation instability) 而產生如孤立子般的超高振幅調制波包，而突波研究為近年來非線性波動研究的重要議題，突波形成是否具有與如何尋得預警指標，為爭議性的重要問題。此篇論文將探討非線性法拉第波因外界上下振動之驅動振幅增加而失穩後，所形成時空上突發之不穩定突波，找出預警指標 (precursor)，並從波動與粒子間交互作用 (wave-particle interaction) 的觀點重新了解水流如何造成時空突波。此研究發現極高振幅偶發突波的產生取決於時空周遭波型變化，在極高振幅偶發突波發生的前數週，環繞突波的波峰環場稜線 (preceding surrounding water ridge) 積分高度和波峰環場稜線高度的離散程度為重要的突波生成預警條件。此外更發現在類晶格排列的法拉第波系統中，極高振幅偶發突波的產生和前數週波峰環場稜線的高階鍵角取向有序度 (high-order bond orientational order) 並無直接的關聯。透過時空上波形的演化資訊，波峰環場稜線的積分高度為極高振幅偶發突波生成的重要預警指標。;The uncertainly occurred and highly localized extreme amplitude rare event, called rogue wave event, occurs in various nonlinear systems such as Faraday waves, water surface waves, optical waves, and dust acoustic waves in plasma. Modulation instability, causing wave-amplitude modulation and the formation of amplitude soliton-like structure, has been widely accepted as the underlying mechanism for rogue wave generation. However, how the generation mechanism for extreme wave events can be understood from the Lagrangian view and whether the precursors can be identified are still open issues. In this work, the generation and the precursors of rogue wave events are experimentally investigated through a Faraday water wave system exhibiting disordered oscillon pattern. The above issues are addressed from wave-particle interaction view by using the surrounding waveform information preceding the rogue wave events. It is found that the oscillon peak height is correlated with high angular average and the low standard deviation of its prior surrounding waveform, but uncorrelated with preceding waveform with high-order orientational symmetries. The preceding water ridge with high angular average and the low standard deviation of ridge height is the key to determining the strong inward water focusing, which further leads to the subsequent rogue wave generation. The angular average normalized by the standard deviation of the surround waveform serves as a good precursor for rogue wave generation before several periods.
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