離岸風力發電為目前最具代表性之再生能源之一，其低汙染、低成本、對環境之低衝擊性成為各國積極發展的重要能源。但因離岸風場存在許多環境負載且需考量與歐洲不同之地質條件與受震反應。除對離岸風機結構做基本結構設計以及耐震技術考量，於結構受震時之最大反應亦需有較精確之模擬，避免結構受外在刺激時達共振反應，因此研究中將分析離岸風機結構之自然振動頻率。
本研究採以ABAQUS有限元素軟體進行樁土互制高度非線性行為分析，模擬離岸風機結構之自然振動頻率。藉由美國石油協會(API)所建議之土壤反力及位移關係轉換為土壤彈簧進行簡易模擬，藉此求得離岸風機結構之自然振動頻率。而為驗證土壤彈簧之可行性，研究中將採以有樁土互制之有限元素模型與土壤彈簧模型對土壤反力以及位移進行分析，最後以風機結構於樁土互制行為下之無限元素混合模型與土壤彈簧模型之自然振動頻率比較，以作為結構設計之用。

In recent years, nations over the world are actively looking for new alternative energy due to environmental problems caused by traditional energy, renewable energy such as hydraulic power, wind power, and solar thermal power, become one of the most prospected energy, because of its low pollution and low cost. Before adopt the design of the turbine structure in Europe as the prototype, the geological condition and the frequency of the occurrence of the earthquake in Taiwan should be taken into account. The nature frequency of the turbine structure obtained from this study would help build the foundation of the follow-up research considering the environmental load.
In this study, the Abaqus finite element program is used to calculate the fundamental frequency of offshore wind turbine supporting structure considering the nonlinear behavior of soil. The jacket-type offshore wind turbine was taken as the prototype for the analysis. The comparison was made between the model adopt the soil spring which built upon the empirical equation proposed by API, and the finite element model in which the soil is modeled by infinite element.
According to the result, comparing the reaction of the pile-soil under the static force, the numerical result showed that the stiffness obtained from the soil spring model proposed by API was higher than the results of the finite element model. On the other hand, the natural frequency obtained from the soil spring model was also higher than that of the finite element model. The difference was attributed to that the initial stiffness which adopted by the soil spring model was a constant, was higher than that of the finite element model.

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