近岸地區受風作用下之捲浪破碎機制研究;An investigation of plunging breakers in the nearshore area under the influence of wind

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Title:	近岸地區受風作用下之捲浪破碎機制研究;An investigation of plunging breakers in the nearshore area under the influence of wind
Authors:	張明南;Truong, Nhat-Minh
Contributors:	水文與海洋科學研究所
Keywords:	卷浪;碎波;風效應;LES;VOF;plunging waves;breaking waves;wind effects;LES;VOF
Date:	2022-08-25
Issue Date:	2022-10-04 11:02:59 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究旨在了解風效應對近岸地區卷浪發展之作用，尤其是衝浪波。這項研究有三種不同風的類型：陸風、海風和無風。本文利用結合大渦模擬 (LES) 之 Navier-Stokes 方程進行流場模擬與分析。流體體積函數 (VOF) 被用於追蹤水與空氣之界面。數值模擬採用內源造波器以生成目標波浪，在邊界上則採用海綿層法吸收反射波。驗證案例為存在和不存在陸風之情況下波浪淺化過程。比對結果可以看出數值模式與實驗波高計時序紀錄有良好之一致性。完成驗證後，進行實驗室尺度和野外尺度之波浪淺化過程模擬，並討論陸風和海風對卷浪發展過程之影響。為了解風力對於波浪上溯中碎波對於底床之影響，本研究添加數值染料以追蹤碎波帶水體運動過程。數值結果顯示，在海風情況下，卷浪破碎點發生較晚，其對海床之衝擊較海風或無風條件下之卷浪碎波機制更強。對於現場尺度模擬部分，本文探討吹程(Fetch)、風速大小和斜坡坡度效應對卷浪破碎過程之影響。數值結果顯示，隨著風速的增加，較長之吹程會影響卷浪破碎點位置以及卷浪波傳播速度。此外，較強之陸風會導致波碎點較早出現，而較強之海風會導致破碎點較晚出現。底床坡度對卷浪點位置有很大影響。陡峭的斜坡使卷浪破碎點位置更靠近海岸線。在上下文中提供詳細之分析和討論。;This study aims to understand the role of wind effects on the development of plunging waves in the nearshore region especially surfing waves. There are three different types of wind for this study: onshore, offshore, and no wind. In this study, the Navier-Stokes Equation associated with Large Eddy Simulation (LES) is used to simulate and analyze the flow field. The Volume-of-Fluid function (VOF) has been adopted to track the air and water interface. The numerical experiments are deployed and validated with laboratory experiments. The numerical simulations used the internal-source wavemaker and sponge-layer methods to generate the incident waves and absorb the reflected waves on the boundary. The validation cases are the shoaling processes in the absence and presence of onshore wind. The comparison results show that numerical model is good agreement with experimental altimeter time series records. After the verification is completed, the simulation of the wave shallowing process at the laboratory scale and the field scale is carried out, and the influence of the offshore and onshore wind on the wave development is discussed. In order to understand the effect of wind on the near-bed of breaking waves in the up-going wave, numerical dyes were added in this study to track the water movement process in the breaking wave zone. The numerical results show that the breaking points occurred later in the case of offshore wind, and its impact on the seabed is stronger than the breaking wave mechanism of the breaking waves under the sea breeze or no wind conditions. As for the field-scale simulations, this paper discusses the influence of blowing distance (Fetch), wind speed and slope effect on the wave-breaking process. The numerical results show that with the increase of wind speed, the longer blowing distance will affect the position of the breaking point and the propagation speed of the wave. In addition, the stronger onshore wind will cause earlier breaking points, while stronger offshore wind will cause later breaking points. The slope of the bed has a great influence on the position of the breaking point. The steep slope brings the breaking point of the wave closer to the shoreline. A steeper slope made the location of the breaking point closer to the shoreline. Detailed analysis and discussions are presented in the context.
Appears in Collections:	[Graduate Institute of Hydrological and Oceanic Sciences] Electronic Thesis & Dissertation

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