複合材料風力葉片考慮溫溼度之可靠度評估

Abstract

本文提出一套葉片可靠度分析法，對型號NACA4418的2.5米葉片進行評估。利用動量理論以及葉片元素法計算出葉片應力負載，經由有限元素法計算葉片風與溫度或者風與溼度下的應力。分析得知隨著溫度或者溼度上升，產生挫屈的臨界風速(挫屈風速)會下降。葉片可靠度分析中將破壞模式中的挫屈視為極限狀態。蒐集中央氣象局的歷史颱風資料並統計颱風最大瞬間風速、溫度與溼度的機率分佈，計算出各資料的平均與標準差推導出機率分佈方程式。經過一系列的挫屈分析以及分段線性近似法以構築出不同負載條件下之極限狀態方程式。根據不同的極限狀態經數值積分法計算出葉片可靠度値。在不同負載條件下的可靠度值利用蒙地卡羅法進行驗證，經驗證比較後誤差不大以證明本套可靠度分析可信度高。最後提出改善方法，透過增加龍骨以提高挫屈風速，挫屈風速提高相對的可靠度就會提升。

This thesis proposes a reliability method to assess the reliability of a 2.5 meter composite wind blade with NACA4418 airfoil cross section. The blade momentum theory and blade element method are used to calculate the wind load on the wind blade. The finite element method is used to analyze the stresses in the blade with the consideration of the effects induced by wind, temperature, and/or moisture. It has been shown that the critical wind speed to produce buckling (buckling wind speed) decreases when the temperature or moisture rises. The failure mode of buckling is treated as the limit state of the blade in the reliability analysis. The data of maximum instantaneous wind speed, temperature, and moisture provided by the Central Weather Bureau are used to derive the probability distributions of the load parameters. The results of a series of buckling analyses and a piecewise linear approximation technique are used to construct the limit state equations of the blade under different loading conditions. For each limit state, a numerical integration technique is adopted to determine the blade reliability. The Monte Carlo method is also used to calculate the reliabilities of the cases under consideration. The small differences between the reliabilities obtained using the proposed method and Monte Carlo method have demonstrate the feasibility of the proposed method.