大型複合材料風力葉片設計與疲勞壽命分析

Abstract

本研究之目的為探討長度為四十米之大型風力葉片的疲勞壽命行為，而疲勞壽命之評估結果將與真實風機維修時程做比較。 疲勞壽命評估流程中，將風力分為兩種風速狀態分別作用於葉片上，即為風速穩定與風速變化兩種情況。風速穩定時利用韋伯分布得到四季的風速與機率分布關係，透過各風速的機率分布，可計算得到各風速所持續的時間，並透過翼尖速度比算得葉片旋轉之圈數，再將葉片考慮重力、風力與離心力後進行有限元素的分析，得到葉片旋轉一圈所受到的應力值，找出各風速下最大的應力，並將此應力代入古德曼圖與線性累積損傷公式，計算葉片的累積損傷以估算疲勞壽命。風速持續變化的狀態，則透過快速傅立葉轉換，得到不同頻率的正弦波所合成的平均風速與振幅風速，透過分析得葉片之應力，再用如風速穩定之計算方法，計算其疲勞損傷值。 疲勞分析之結果可用於規畫真實風機葉片之運作及維修時程，透過定期維護與檢修，可延續風機葉片之壽命。

The purpose of the thesis is to establish a method for assessing the fatigue life of 40-meter large wind turbine blade. The correlation between the estimated fatigue life results and the real operation condition of wind blades is discussed. In the process of fatigue life assessment, wind speed is decomposed into two parts, namely, steady and variable wind speeds. Under steady wind speed, Weibull distribution is used to model the distributions of the wind data at different seasons. The number of blade rotation at each season is calculated. The blade finite element analysis is undertaken with the consideration of gravitational loading, wind loading and centrifugal force. The stress information is then used to assess the fatigue damage in the blade based on the Goodman diagram and Miner’s rule. Under variable wind speed, the averages and amplitudes of wind speeds at different frequencies are determined through Fast Fourier Transform. Through the analysis of stresses in the blade, using the similar method adopted for the case of steady wind speed, the cumulative damage is calculated. The results of fatigue life assessment can be applied to the real condition for planning blade operation and maintenance program. Through periodical maintenance, the fatigue life of a wind turbine blade can be extended.