再生能源的運用為全球發展趨勢，而就台灣的地理條件而言，海上風力發電為再生能源發展中最具潛力的項目之一。目前在歐美地區的風力發電技術雖已十分成熟，但因台灣地震發生頻繁，故位於外海之離岸風機耐震問題變成重要的課題。為強化風機支承結構的耐震能力，吾人或可考慮採用結構控制技術。由於風機支承結構為高達百餘公尺屬細長型結構，原應適合採用調諧質量阻尼器 (tune mass damper，TMD)，但若採用傳統外加式TMD阻尼器作為制震系統，需佔用額外之空間，且會增加機艙之重量，造成海上運輸的不便，因此TMD在離岸風機的應用有其先天上之限制。為改善此問題，本文乃改以風機機艙本身之質量作為反力質塊，形成所謂的質量阻尼器(mass damper，MD)。MD系統與TMD不同處在於，前者質塊之自振頻率並不一定與下部結構之振頻調諧，而是於機艙及下部支承結構間安置具高度消能能力之減震元件，如此可藉由機艙及支承結構間之互制相對運動以提高整體系統之阻尼效應。由於一般機艙之重量約佔風機總重(含支承構造)40%左右，故可有效降低機艙及支承結構之地震反應。本文研究結果顯示，經由適當的選取MD的參數(如：阻尼比及頻率比)，可同時大幅降低風機支承結構在地震力作用下之基底總剪力及機艙之最大加速度反應。相比TMD僅在外力靠近自振頻率時有效，MD在各震波作用下其減震效能皆相當優秀，亦即使用MD系統可同時提升風機支承結構及機艙內發電設備之耐震性能，為十分有效之風機抗震方法。

Taiwan has one of the best wind-farms in the world; therefore, it is beneficial for Taiwan to develop renewable energy by using off-shore wind turbines. Nevertheless, since Taiwan is also prone to earthquakes, the problem of seismic protection for the offshore wind turbines becomes an important issue. To this end, a mass damper (MD) system is developed to mitigate the seismic response of offshore wind turbines in this study. Different from a traditional TMD, which usually needs an added reactive mass with an oscillating frequency tuned to that of the primary structure, the MD uses the mass of the nacelle of the wind turbine itself as the reactive mass and its frequency does not have to be tuned to the frequency of the supporting structure. Moreover, since the nacelle mass of a wind turbine can reach 40% of the total weight, it is expected that the seismic responses of the wind turbine can be effectively reduced by the MD. The simulation result of the study demonstrates that by properly selecting the MD parameters, i.e., the frequency and damping ratios, the absolute acceleration of the nacelle and the base shear of the supporting structure can be greatly reduced. Compared with an optimally designed TMD, the MD system is effective over a wider range of ground motions, while TMD is only effective when the excitation frequency is close to that of the TMD.

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