旋轉葉片受溫度影響下之疲勞分析

Abstract

本研究使用實際風速和風力葉片來評估水平式風機的疲勞壽命。 從苗栗縣的後龍風場量測到一段時間的風速資料，以及從中央氣象局蒐集2014年的風速資料來評估葉片的疲勞壽命。在分析風速資料時，透過快速傅立葉轉換與傅立葉級數將風速資料分解，得到在高頻譜密度下的低頻頻率之振幅風速，以分析風力葉片的應力。

在風力葉片應力分析中，首先利用葉片元素動量理論，計算風速作用在葉片上的等效力量，再考慮不同季節及颱風天期間的溫度變化、離心力對於應力分析的影響。使用有限元素分析軟體，找出葉片的最大應力的值和位置。為了評估疲勞損傷，將此應力代入古德曼圖與線性累積損傷公式，使用老化後不同年份的S-N curve，計算葉片的累積損傷以估算葉片壽命。本文將以一個例子說明風力葉片的疲勞壽命評估程序。

The prediction of fatigue life of a horizontal-axis wind turbine is considered in this research using real wind speed and wind blades. The wind speed data measured at Houlong wind field, Miao Li county, and 2014 year wind data of the Central Weather Bureau are used in the fatigue life assessment of the blade. Through the decomposition of the wind speed data using the Fast Fourier Transformation (FFT) and Fourier series in analyzing the wind speed data, the amplitudes of the components of the wind speed series at the frequencies of high power spectral densities in the low frequency range are determined for the wind blade stress analysis. In the wind blade stress analysis, the equivalent forces on the blade under the wind speed are calculated using the Blade Element Momentum Theory (BEM).

The effects of temperature and centrifugal force at different operating conditions and seasons including typhoon periods are also considered in the stress analysis. The finite element code ANSYS is used to find the location where the maximum stress in the blade occurs. The stress information is then used to assess the fatigue damage in the blade based on the Goodman diagram and Miner’s rule. In the fatigue life estimation, the aged S-N curves at different years are used to calculate the cumulative damage in the blade. An example is given to illustrate the proposed procedure for fatigue life assessment of wind blades.