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題名 | 我國海岸海洋環境潛在災害:瘋狗浪生成數值研究之初步發展與建置=Preliminary Development for Numerical Modeling of the Potential Threat in Our Coastal and Ocean Environment: Generation of Freak Waves |
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作 者 | 楊智傑; | 書刊名 | 海洋工程學刊 |
卷期 | 15:2 2015.06[民104.06] |
頁次 | 頁101-115 |
分類號 | 351.941 |
關鍵詞 | σ座標; 非靜水壓; 自由液面波; 瘋狗浪; σ-coordinate; Non-hydrostatic pressure; Free-surface waves; Freak waves; |
語文 | 中文(Chinese) |
中文摘要 | 瘋狗浪係指波形極不對稱且波高大於2至2.2倍示性波高之異常波浪現象。依據目擊者描述瘋狗浪之特徵,其波谷相當深,像是在海中的洞,或是異常大的波高像是一道水牆等。神出鬼沒的瘋狗浪往往發生於深海的波群中,其驚人的破壞力對於海上航行之船隻及海洋結構物有相當嚴重的危害,過往已造成許多不幸的災難。過去二十年來,學者們致力於瘋狗浪生成機制之研究。本研究的目的為利用數值水槽重現我國海岸環境中的潛在災害─瘋狗浪。研究使用σ座標高階精度非靜水壓模式,其利用隱式有限差分法搭配交錯網格求解非穩態那維爾史托克方程式,並包含自由液面邊界條件。此外,透過表層非靜水壓力項的高階處理,可準確地模擬不同相對水深下之波傳現象。本模式利用線性/非線性行進波及非線性雙頻深水波群進行驗證。最後,模式被用以檢視二維與三維之瘋狗浪現象。從瘋狗浪在時間和空間域上的模擬結果可發現聚焦平移及波形不對稱等特性。藉由前述模式的架構及充分的現地量測資料,預期在不久的將來能夠建立一套有效的瘋狗浪預警系統。 |
英文摘要 | The so-called freak waves are exceptionally large, steep, and asymmetric waves whose heights usually exceed by 2 ~ 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 this study, the purpose is to reproduce the potential threat in our coastal environment - generation of freak waves in a numerical wave tank. A higher-order non-hydrostatic model in a σ-coordinate system was developed. The model used an implicit finite difference scheme on a staggered grid to solve the unsteady Navier-Stokes equations with the free-surface boundary conditions simultaneously. Besides, an integral method was employed to resolve the top-layer non-hydrostatic pressure, allowing for accurately resolving free-surface wave propagation. Model accuracy was validated by linear/nonlinear progressive waves and nonlinear bi-chromatic deep-water wave groups. The model was then used to examine the two-dimensional and three-dimensional freak waves. Features of downshifting focusing location and wave asymmetry characteristics are predicted on the temporal and spatial domains of a freak wave. In the near future, an effective freak wave warming system could be developed by the present modeling framework together with sufficient observation data. |
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