複合材料三明治風力葉片之損傷識別與完整性研究

Abstract

在减碳及能源短缺的壓力下, 各國正積極開發再生能源。目前再生能源中，風力發電為較成熟的產業之一。風力發電系统中, 葉片是吸取風能的一個關鍵元件, 它需有足夠高的可靠性, 並能長期經得起惡劣環境對葉片材料性質的影的及承受所施予的負荷。複合材料質輕強度大, 已廣泛用來製作風力葉片, 但葉片在製造過程中或使用一段時間後其材料性質會改變或內部產生損傷, 若因此而發生突然的斷裂將會使風機完全失效或甚致引發意外, 故如何確保其完整性及掌握其壽命便成為一重要研究課題。 本計畫研究建立一套藉識別複合材料三明治風力葉片的材料常數來評估其損傷的非破壞檢測方法，此法利用量測葉片的自然頻率或受力激震振幅來識別葉片的材料常數，從而判斷葉片的老化或受損情形。本研究將利用有限單元法建立一分析葉片不同區域振動行為的模型，其中葉片各區段的銜接處將以線性彈簧模擬，並分別探討利用葉片各區段的自然振動頻率或葉片各區段受激震產生之振動量來識別葉片之材料常數。若原始測得的振動資訊與老化後得到的振動行為有異，則葉片的材料常數顯然有所改變，亦即材料特性已不如原本預期, 根據材料常數的衰減速度來找出葉片的損傷程度及位置。本研究利用最佳化方法來找尋葉片材料的真實材料常數，藉使理論與實驗自然振頻間的誤差最小化或振幅資訊誤差最小化進而找到正確的材料常數。本研究將探討如何選取最佳化方法中合適的係數，使尋找的過程更快速及有效。葉片的自然振頻可藉敲擊法的振動試驗來取得，而其振幅資訊可用簡諧激震掃頻振動方法來求得，這些方法都非常方便使用及有效。本研究將探討本方法在風力葉片的損傷識別能力，進而建立一套葉片損傷的非破壞評估檢測方法，結果可供產業界及學術界參考。

The issues of carbon dioxide reduction and petroleum shortage have pushed the governments of many countries to put more efforts to develop renewable energies. Among the available renewable energies, wind energy is one of the most efficient and economical energy sources. The wind blades of a wind power system are used to absorb wing energy. In general, the wind blades have to survive severe environments for a long period of time. Unreliable wind blades may fail due to the degradation of the material properties or damages induced in the blades. The failure of the blades will interrupt the power supply and may also be possible to cause accidents. Therefore, the assurance of high quality and reliability of wind blades are essential in the design of wind power systems. Composite materials have high stiffness-to-weight ratio and are suitable to be used in making wind blades. Nowadays, wind blades are made of fiberglass material to be cost effective, but they can be damaged by loads from different sources. After a period of operation, the properties of the composite blade may degrade due to environmental effects or damages may be induced in the blade due to fatigue. It is important to detect the damage before the blade fails catastrophically which could destroy the entire wind turbine or even cause a fatal accident. The identification of the materials constants or the damage of the composite wind blade has thus become an important issue for reliability assurance of the blade. In this project, a nondestructive evaluation method is proposed for material constant and damage identification of composite sandwich wind blades. The finite element method and an optimization method are used to construct the proposed method. Measured natural frequencies or vibration response of different regions of the composite sandwich wind blade are used in the proposed method to identify the material constants. The identified material constants obtained at different regions of the blade are then used to predict the integrity of the wind blade.