- 學位論文
斜坡底床因波浪淺化及碎波引致之土壤反應
Soil Response induced by Wave Shoaling and Breaking On a Sloping Seabed
摘要
台灣特殊的地理位置且四面環海，因此在進行工程規劃時，波浪對其產生的影響是需要考慮的重點，當波浪從外海傳遞至近岸時，波浪會因而產生變化，其變化包含淺化、折射、碎波，而碎波效應帶來之能量對近岸底床影響巨大。早期研究對於波浪淺化及產生碎波後之動壓作用於斜坡底床影響的研究有限；為了探討此現象本研究建立一數值模式，以分析規則週期波通過海岸斜坡底床時因波浪淺化與碎波底層土壤造成的超額孔隙水壓與應力的變化。 本研究應用開源流體力學計算軟體OpenFOAM建立數值模式，分成波浪模式以及土壤模式，各別使用不同的求解器waves2Foam及upFoam。研究中使用stress-ω紊流模式探討不同碎波型態對於土壤底床之影響、不同土壤飽和含水率及滲透係數對於多孔彈性土壤底床之影響，並分析探討在何種情況下對於土壤會有較大影響。 從結果可以發現spiiling waves 與 plunging waves 兩種碎波型態，波浪在淺化階段中隨著波高升高，對於土壤之孔隙水壓力也逐漸加大。在碎波後波高會大幅降低；土壤之孔隙水壓力也隨之降低，但因水下逆流現象，孔隙水壓會朝正方向偏移。若比較兩種碎波型態之影響範圍，plunging waves會比spiiling waves將孔隙水壓傳遞至更深處土壤底部。此外從孔隙水壓的分佈來看，滲透係數值越大則孔隙水壓傳遞越深，且發現隨著滲透係數的減少會有較明顯的相位延遲現象發生，而土壤飽和率Sr值越大則有越大的孔隙水壓分佈。綜合來說，滲透係數值越大及土壤飽和率Sr值越大之土壤，孔隙水壓力越大。
並列摘要
Taiwan's unique geographical location, surrounded by the sea on all sides, makes it crucial to consider the impact of waves when undertaking engineering planning. As waves propagate from the open ocean to the nearshore areas, they undergo changes including shoaling, refraction, and breaking, with wave breaking generating significant effects on nearshore sediment beds. Previous research has provided limited insight into the effects of wave shoaling and the resulting pressure from wave breaking on sloping seabeds. To investigate this phenomenon, this study establishes a numerical model to analyze the variations in excess pore pressure and stress in seabed caused by wave shoaling and breaking as regular, periodic waves pass over coastal sloping seabeds. The study employs the open-source computational fluid dynamics software OpenFOAM to create the numerical model, dividing it into a wave model and a soil model, utilizing different modules- waves2Foam and upFoam, respectively. The study employs the stress-ω model to investigate the turbulence effects on different wave breaking patterns and seabeds and to analyze the impacts of varying soil saturation and permeability on porous, elastic seabeds. Furthermore, the study examines the conditions under which the soil is most affected. Results show that two types of wave breaking patterns, spilling waves and plunging waves, both exhibit increasing excess pore pressure in the seabed as wave height increases during the shoaling process. After wave breaking, there is a significant reduction in wave height and subsequent decrease in excess pore pressure. However, due to undertow phenomena, the quasi perdiodic pore pressure shifts in the positive direction. Comparing the effects of the two wave breaking patterns, plunging waves transmit excess pore pressure to greater depths in the seabed compared to spilling waves. Additionally, from the distribution of pore pressure, larger permeability values lead to deeper pore pressure transmission, and a notable phase lag is observed with decreasing permeability. Moreover, higher soil saturation (Sr) values correspond to a wider distribution of pore pressure. In summary, soils with higher permeability and greater soil saturation experience higher excess pore pressures.