小型風力機用複合材料葉片的可靠度模式之建立及應用研究

Abstract

小型風力發電機的三個重要研發課題是效率、可靠性和成本，其中風力葉片與這些課題 均是息息相關的。葉片是風機的吸能元件，其效率及可靠性可直接影响風機的發電效率 及效益，目前的葉片在這方面仍有很多尚待改進之處。複合材料具有多項優點，且因玻 璃纖維布的價格較低，故目前的葉片多用玻璃纖維複合材料來製作。但這種葉片在日曬 雨淋的環境下長期運轉會有疲勞及老化的問題，其材料的強度及常數會隨時間的增加而 下降，若在葉片的設計過程中沒有加以考慮，將嚴重影响葉片的可靠度。另一方面，葉 片在其設計年限內所受到的極端風力為一隨機變數，其值會受到隨機的風速和風向所影 响，所以在葉片的設計過程中須考慮這些不確定因素，以確保葉片可達到一定可靠度的 水平。本計畫擬建立一葉片可靠度分析方法，供設計複合材料葉片承受極端風力之用， 其中玻璃纖維複合材料的性質遞減模式由老化及疲勞試驗的結果來建立，風速和風向設 為隨機變數，並藉葉片元素理論來求得風力。在葉片的破壞分析中，考慮首層破壞、挫 屈和折斷等破壞模態，並在風速和風向的聯合機率分布座標平面中建立葉片的極限方程 式，然後利用數值積分方法求取葉片在不同負載狀况下的可靠度，結果可供改善葉片設 計之用。本計畫將以一5kW 玻璃纖維複合材料葉片為例來進行研究，探討提升該葉片 可靠度的設計方式。

The three major issues of R&D in wind power are efficiency, reliability and cost which are closely cross-related. The wind blades of a wind power generator are the important element for energy absorption. The efficiency and reliability of the blades, which is still a major problem to be tackled, can directly affect the efficiency and effectiveness of the power generator. Composite materials have many advantages to be used in the industry. In particular, due to its relatively low cost, glass fabric composites have been widely used to make wind blades. Regardless of its many good points, glass fabric composites still have a number of weaknesses, especially, when the wind blades are operated in a hostile environment for a long period of time. The material properties of the glass fabric composites, when exposed to heat and ultraviolet for a long time, will progressively degrade and such material degradation may significantly affect the reliability of the wind blade. On the other hand, the wind load applied to the wind blade changes stochastically and depends on the wind speed and direction which can be treated as random variables. Therefore, the design of a reliable wind blade should take these uncertain factors into consideration. In this project, a reliability assessment method is proposed for the design of glass fabric composite wind blades is proposed. The material degradation model of the glass fabric composites is constructed using the experimental data obtained in this study. The blade element method is used to determine the wind load on the wind blade for any given wind speed and wind direction. The finite element method and an appropriate failure criterion are used to determine the wind speed and direction for inducing the failure modes of the first-ply failure, buckling, and total fracture. The limit state curves of different failure modes are constructed in the wind speed and wind direction coordinate system. A numerical technique is used to evaluate the reliability of the wind blade for any failure mode. As an example, the proposed method will be used to improve the reliability design of a glass fabric composite wind blade for a 5kW wind turbine.