由於負壓沉箱基礎於安裝時造成之水下施工噪音較低，且於離岸風機使用年限後易於移除，為達離岸風場永續經營目標及考量施工成本經濟效益，負壓沉箱基礎為近年來歐洲國家積極發展之離岸風機基礎型式之一。離岸風機長期受到風、波、流之反覆側向載重，評估離岸風機基礎於運轉年限內受環境反覆側向載重下造成之累積變形反應為確保風機運轉功能性之重要檢核項目。
目前針對負壓沉箱基礎受反覆側向載重引致之變形反應，多利用室內縮尺模型試驗進行研究，並以其成果建立半經驗公式進行估算[陳克維，2015]。然而，受限於模型試驗條件，依模型試驗建立之半經驗公式仍有其使用限制。為了分析負壓沉箱基礎置於不同緊密程度之無凝聚性海床土壤時，受反覆側向載重作用下之行為反應，本研究利用Achmus et al.(2013)提出之建議手法，結合勁度衰減模型，建立Abaqus6.14三維有限元素數值分析模型，計算埋置於不同緊密程度砂土之負壓沉箱基礎受反覆側向載重下的長期變形反應。
藉由模型驗證及Zhu et al.(2013)與Foglia and Ibsen (2016)提出之分析方法，本研究將數值模型模擬成果進行參數分析評估不同載重條件下（作用力大小與側向載重作用次數）之沉箱基礎變形反應。分析成果顯示，於靜態條件下基礎受力-變形反應可透過指數函數或乘冪函數模擬無因次彎矩M/Mu與負壓沉箱基礎傾角θ關係。對於負壓沉箱基礎受到反覆側向載重之受力-變形反應，本研究提出與Foglia and Ibsen (2016)相似之負壓沉箱基礎永久變形傾角估算式，並對該估算式之參數進行修正並加入土壤相對密度之影響。依本研究提出之分析方法，離岸風機基礎設計人員僅需取得離岸風場場址之海床土壤進行物性分析及土壤動態三軸試驗，並計算負壓沉箱基礎之側向極限承載力或極限彎矩，再透過本研究提出之負壓沉箱礎傾角估算式，計算埋置於不同緊密程度砂土中之負壓沉箱基礎於靜態側向力與反覆側向力作用下之變形反應，即可初步評估基礎之穩定性。

In order to achieve objectives of sustainable development of offshore wind farm and cost-effective foundation, the suction bucket becomes one of the foundation types actively developed in European countries in recent years. The offshore wind turbine subjects to long-term cyclic lateral loads from waves, wind, and currents, and therefore it is important to check the stability of the foundation during its lifetime to ensure the functionality of the wind turbine. In this study, the numerical model of suction bucket foundation was built using ABAQUS, combined with the stiffness degradation model, to calculate the long-term deformation of the foundation embedded in the dense, medium dense and loose sand under cyclic lateral loads. The numerical results are compared to the experimental results of 1-g testing done by Zhu et al. (2013) and Foglia and Ibsen (2016). It is demonstrated that the rotational displacement of the foundation accumulates with the increase of load cycles, and the rotational displacement increases at a smaller rate when the foundation is embedded in the sand with higher relative density. Parameter studies of suction bucket foundation under static and cyclic lateral load are presented. An exponential formula is suggested to determine the dimensionless moment-rotation relation of suction bucket foundation under monotonic lateral load. And we propose a method for estimating the long-term deformation of suction bucket foundation and the influence of soil relative density and the rotational displacement accumulate rate were also assessed. The numerical model proposed in this study can be a useful method to evaluate the stability of suction foundation under long-term cyclic lateral load.

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