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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/39834

Title: 非線性波場中之異常波浪發生機率預測研究
Study of Occurrence Probability of Freak Wave in Nonlinear Wave Field
Authors: 曾薐璇
Cheng-Han Tsai
Leng-Hsuan Tseng
Dong-Jiing Doong
Chia-Chuen Kao
Contributors: 國立臺灣海洋大學:海洋環境資訊學系
Keywords: Freak wave
Occurrence probability
Date: 2014-03
Issue Date: 2017-01-04T05:43:31Z
Publisher: 第 34 屆海洋工程研討會論文集
Abstract: 異常波浪發生在大洋中,對於航行船隻造成潛在威脅,截至目前為止尚難以用定率方式預測,本文研究以序率方法,根據非線性波理論從事異常波浪發生機率預測研究。理論推導結果顯示,異常波浪的發生機率與水位變化的峰度(μ_4)以及波浪數目(N)有關。數值模擬的結果顯示,根據非線性波理論估算之異常波浪發生機率高於線性雷禮分布估算所得,在高度非線性波場以及觀測時間不長的條件下(如μ_4 = 3.6, N = 100),非線性理論估算之異常波浪發生機率高於雷禮分布5.4倍。本文採用基隆碧砂漁港連續波浪觀測資料進行驗證,結果顯示在臺灣海域水位峰度分佈範圍(3.1 < μ_4 < 3.3)內所驗證之均方根誤差平均為12%,全部資料驗證之均方根誤差平均為22.4%,本文認為推導過程中,假設H_(1/3)/η_(rms)為常數可能是造成誤差的來源之一,事實上H_(1/3)/η_(rms)應為水位峰度係數的函數。基於本文對異常波浪發生機率的推導,或者未來推導過程的改進,結合波浪模式所提供的波譜,有助於未來從事異常波浪發生機率預測。

Abstract: Freak waves that occur in the sea cause risks to ships. Prediction of freak wave occurrence by deterministic approach was still not possible. This study uses stochastic method and applies the nonlinear wave theory to study the occurrence probability of freak wave. According to the derivation, the occurrence probability of freak wave is correlated with number of waves (N) and the kurtosis of surface elevation (μ_4). Numerical results show the occurrence probability of freak wave derived by nonlinear wave theory is higher than derivation from linear Rayleigh distribution. Under the conditions of short observation period and highly nonlinear wave field (for example, μ_4 = 3.6 and N = 100), the nonlinear derivation shows 5.4 times probability than linear results. Continuous field data measured at Bisa Harbor are used for validation. It shows the RMSE is 22.4% for all data but 12% for the data locate between μ_4 = 3.1 to 3.3 which is the main kurtosis distribution in Taiwan waters. It is found the constant of H_(1/3)/η_(rms) ratio used in the derivation may lead the error. The ratio is actually correlated with kurtosis. Imported with wave spectra provided by numerical wave models, prediction of oceanic freak wave occurrence probability is possible in the near future.
Relation: 14(1)
URI: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/39834
Appears in Collections:[海洋環境資訊系] 期刊論文

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