A Study on the Characteristics and Formation Mechanism of Freak Waves Using Non-Linear Wave-Wave Interaction Theory and Non-Hydrostatic Numerical Modeling

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Project title

Code/計畫編號

MOST105-2221-E019-078

Translated Name/計畫中文名

發展非線性波浪交互作用理論與非靜水壓sigma數值模式研究瘋狗浪生成機制及特性

Project Coordinator/計畫主持人

Chih-Chieh Young

Funding Organization/主管機關

National Science and Technology Council

Co-Investigator(s)/共同執行人

柳文成

Department/Unit

Department of Marine Environmental Informatics

Website

https://www.grb.gov.tw/search/planDetail?id=11880964

Year

2016

Start date/計畫起

01-08-2016

Expected Completion/計畫迄

01-07-2017

Bugetid/研究經費

688千元

ResearchField/研究領域

土木水利工程

瘋狗浪為波形極不對稱且波高大於2.2倍示性波高之異常波浪，其所挾帶驚人的破壞力對海上航行之船隻及海洋結構物造成相當大的危害。根據過去海事災害生還者或目擊者的描述，瘋狗浪大致有以下幾種特徵：(1)在波峯出現前，常有一深邃的波谷，似海中的洞；(2)波峯甚陡，似一堵水牆，且未有碎波發生；(3)可能是單一波或是一列波群(三姊妹波)。近二十年來，瘋狗浪生成機制、特性，甚至預警系統之研究逐漸受到專家學者與政府當局的重視。相較過去瘋狗浪觀測統計分析與資料探勘等研究，本計劃將以非線性波浪力學探討瘋狗浪之生成機制與特性。首先，將推導適用於深水至淺水條件之非線性波浪交互作用理論，並提升非靜水壓模式之數值精度、計算效率與平行化運算能力。透過本研究發展之理論與模式，可分析驗證各種可能生成瘋狗浪之海氣象條件(如：當地的波浪、海流、地形水深及遠方的天氣系統)。此外，亦利用二維傅立葉轉換與一維毛利小波轉換法進行波譜分析，以瞭解瘋狗浪生成時波群中各成份波產生非線性耦合、波能轉移分配及聚焦。最後，可嘗試將模式應用於易發生異常波浪之附近海域進行模擬，以現地浮標或雷達觀測資料作為模式輸入及驗證之用。未來，可進一步與大尺度之海洋環流、頻譜波浪及大氣模式結合，分析瘋狗浪災害潛勢，並可望建立一套具物理機制且有效的瘋狗浪預警系統。 The so-called freak waves are exceptionally large, steep, and asymmetric waves whose heights usually exceed by 2.2 times the significant wave height. These waves, described as ‘holes in the sea’ or ‘wall of waters’, have been long known to be notorious hazards to navigation vessels and marine structures. With little warning, these transient giant and steep waves can mysteriously occur from deep-water wave groups in random open seas. Many freak waves’ devastating impacts and sinister marine episodes have raised great interests in predicting their occurrence. Over the past two decades a great deal of efforts has been paid to examine the mechanisms that cause formation of freak waves. In comparison with those earlier studies that analyzed freak waves statistically from the marine observation data, the purpose of this study is to examine the characteristics and formation mechanism of freak waves based upon non-linear water wave dynamics. A theoretical work will be derived to describe nonlinear wave-wave interaction in the deep and shallow water. The accuracy and efficiency of the non-hydrostatic model in the -coordinate system will be improved through implementing the high-order numerical scheme and parallel computation technique. In addition, 2D-FFT and 1D-Morlet wavelet transform will be utilized to analyze the wave signals for better understanding the nonlinear coupling of waves and energy re-distribution/focusing. The proposed approaches will be validated against the available solutions of linear/nonlinear progressive waves and experimental data of nonlinear bi-chromatic deep-water wave groups and then will be applied to investigate the two-dimensional and three-dimensional freak waves. The features of oceanic (deep-water) and coastal (shallow-water) freak waves with the presence of depth-varying current and irregular bottom or with the influence of weather system will be carefully discussed. Furthermore, the numerical simulation for a specific coastal area will be carried out under the support of sufficient field observation data. In the near future, an effective freak wave warming system could be developed by integrating the present modeling framework with the large-scale oceanic circulation model, spectral wave model, and atmospheric model.

Keyword(s)

瘋狗浪
非線性波浪交互作用理論
非靜水壓數值模式
二維傅立葉轉換
一維毛利小波轉換
Freak waves
Non-linear wave-wave interaction
Non-hydrostatic model
2D-FFT
1D-Morlet wavelet transform

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A Study on the Characteristics and Formation Mechanism of Freak Waves Using Non-Linear Wave-Wave Interaction Theory and Non-Hydrostatic Numerical Modeling

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