摘要 海嘯湧潮之行為與潰壩湧潮非常相似，利用潰壩湧潮研究海嘯湧潮衝擊結構物之交互作用，為海嘯減災研究另闢蹊徑。充分了解潰壩湧潮與碎波傳遞之物理過程，對於減少海嘯破壞、制定有效之防災及減災措施至關重要。 本文以數值方法研究潰壩湧潮通過近岸植生與結構物之能量消散，並將植生與結構物在數值模式中以方柱陣列表示。本研究採用Splash 3D模式進行數值計算，求解三維N-S方程式，其中大渦模擬（LES）作為紊流模式，並以流體體積法（VOF）追蹤複雜之自由液面。 數值實驗中，研究潰壩波通過兩組不同高度之方柱陣列，分別為高度0.1m 及 0.2m，並分析上游至下游之流速與渦度場。研究結果表示，紊流導致次網格尺度之數值擴散為潰壩波能量下降之主因。湧潮向下游傳遞時，流速逐漸增大，而方柱高度會影響通過方柱陣列後之渦度場及流速表現。雖然通過較高之方柱會導致更慢之下游流速，但流速會持續較長時間才開始減速。此外，也會在底床產生較大之流場及渦度。 ;Abstract The behavior of dam-break bore is very similar to the tsunami bore. Using dam-break wave as a tsunami bore to study its interaction with rigid structures opens a new approach for study tsunami. Fully understanding the physical process of dam-break is crucial for reducing damage and formulating effective disaster prevention and mitigation measures. In this thesis, we study how the energy of a dam-break bore is dissipated by the square cylinders numerically, which present for the coastal vegetation and coastal structures. The computational model, Splash3D, is adopted in this study. Splash3D solves the three-dimensional Navier-Stokes equations directly with Large-Eddy Simulation (LES) as a turbulent closure model. The Volume-of-fluid (VOF) method is used to track the complex free surface. The dam-break flows with two different cylinder array: 0.1 m and 0.2 m in height are numerically investigated. Both velocity magnitude and vorticity are analyzed in upstream as well as downstream region. The results show that the sub-grid scale diffusion is the main reason for energy decline in the dam-break cases due to the domination of turbulent flow. The velocity of the dam-break flows becomes higher when the waves travel downstream. The cylinders’ height affects the wave-breaking and the velocity magnitude as well as vorticity field after the cylinder arrays. The cylinders are taller which causes velocity magnitude downstream smaller. However, the resident time of a high velocity is longer. In addition, the tall-cylinder case has a larger value of velocity magnitude and vorticity near the bottom. Key words: Tsunami, Dam-break wave, Navier-stokes equations, cylinder array.
