氣候變遷所帶來的沿海威脅日益嚴重，特別是在海平面上升與熱帶氣旋頻繁發生的背景下，如何有效降低波浪對沿岸區域的影響已成為全球共同關注的課題。根據政府間氣候變遷專門委員會（IPCC）報告，全球平均海平面在1901年至2018年間上升15至25公分，且近期的上升速率明顯加快。此外，極端氣候事件的強度增加，進一步加劇了沿海地區的風險，導致海岸侵蝕與生態系統退化，影響生物多樣性及漁業資源。潛堤作為海岸保護措施之一，廣泛應用於消散波浪能量，減輕波浪對岸線的侵蝕與破壞。當波浪傳遞至潛堤前方時，部分能量會被反射，其餘則越過堤頂向後傳遞，在通過堤頂的淺水區時，波浪會因淺化效應而變形，然而，目前對於潛堤後方因坡度突然下降而導致波浪碎波的詳細動態特性仍缺乏深入研究。

本研究透過實驗方式，於國立成功大學水利與海洋工程學系之二維玻璃波浪水槽進行了詳細的流場分析實驗。水槽全長20米，寬0.5米，深0.8米，為便於觀測採用玻璃牆與玻璃底設計。實驗中使用可程式化數位伺服馬達驅動的活塞式造波器，其衝程達2米，能產生規則波、孤立波等不同類型波形，模擬實際海岸波浪條件。造波控制以LabVIEW介面設計的自動化程式進行驅動。

水槽內配置九組超音波波高計，其中WG1-WG9依序設置於造波板前方、堤前、堤趾、堤頂與堤後等重要位置，並針對堤的不同區段進行水位監測。此外，設置三個量測視窗（FOV1~FOV3）對應堤趾、堤頂與堤後，透過雷射光頁與高速攝影機進行粒子追蹤，量測區域覆蓋自水面至底床之垂直流場。為提高測速精度，實驗採用二氧化鈦(TiO₂)作為示踪粒子，其具備高折射率與良好穩定性，適合於水中PIV實驗使用。高速攝影機設定為每秒1000幀的拍攝速率，並與波高計同步觸發，確保資料時序一致。所得影像以Davis進行分析，設定interrogation window並透過中值濾波器去除異常向量。為強化分析的可靠度，每組實驗重複進行至少30次以計算整體平均與波動速度。另外，在堤後位置架設聲學都卜勒測速儀（Acoustic Doppler Velocimetry, ADV）進行流速的量測，旨在與粒子影像測速法（Particle Image Velocimetry, PIV）的結果進行交叉比對與驗證。透過比較ADV所測得的單點流速時序，與PIV在同一位置的流場數據，可評估兩種不同量測技術的一致性，並確保整體流場分析的準確度與可靠性。

研究結果顯示，潛堤後方坡度的突然下降會有效促使波浪碎波現象發生，並顯示波浪高度越大，其碎波效果越明顯，波浪能量的消散效果也更佳。與理論波形對照後可見，本實驗生成之波形具良好穩定性與重現性，且PIV所測得速度場與自由液面變化高度吻合。

The coastal threats driven by climate change are becoming increasingly severe, particularly due to sea-level rise and the heightened frequency of tropical cyclones. This underscores the urgent need for effective strategies to mitigate wave impacts on coastal areas. The intensification of extreme weather events has further exacerbated coastal risks, leading to shoreline erosion and ecosystem degradation, affecting biodiversity and fishery resources. Submerged bars are widely used in coastal protection engineering to dissipate wave energy and reduce erosion. When waves propagate over a submerged bar, part of the energy is reflected, while the remainder is transmitted over the crest. In the shallow region above the crest, waves deform due to shoaling effects, which may trigger wave breaking.
This study conducts detailed experimental flow field analysis in a two-dimensional glass-walled wave flume at the Department of Hydraulic and Ocean Engineering, National Cheng Kung University, measuring 20 m in length, 0.5 m in width, and 0.8 m in depth. A piston-type wavemaker generated various wave types, including regular and solitary waves. Nine ultrasonic wave gauges were deployed to monitor time histories of water surface variations. In addition, three measurement windows (FOV1–FOV3) corresponding to the toe, crest, and rear of the bar were equipped with a Particle Image Velocimetry (PIV) system, utilizing laser light sheets and a high-speed camera to measure vertical flow fields from the free surface to the seabed. An Acoustic Doppler Velocimetry (ADV) system was also installed behind the bar to conduct measurements for cross-validation with the PIV results.
The experimental results indicate that wave breaking primarily occurs due to shoaling over the shallow crest of the submerged bar, with larger wave heights producing more pronounced breaking and energy dissipation. Comparisons with theoretical waveforms confirm the stability and reproducibility of the generated waves, while the PIV-measured velocity fields exhibit high consistency with free surface variations. By comparing different wave types and heights, this study quantitatively evaluates the influence of wave breaking on wave energy dissipation, providing valuable references for designing coastal protection structures and validating related numerical models.

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