垂直式風機之複合材料風力葉片疲勞壽命分析

Abstract

本文提出一套快速的疲勞損傷分析方法來估算葉片損傷情況，並實際推估一座實體的複合型垂直式複合材料葉片的疲勞損傷值。在理論上，使用單一管流理論與葉片元素法來計算不同風速下風所作用在風機葉片上的風力，然後建立有限元素法模型，在實驗中，使用靜態負載實驗與動態Zigbee無線應變傳輸實驗來驗證有限元素模型。造成疲勞損傷的因素有兩種，一、首先是風機旋轉時在不同方位角下因風力的不同所造成的複材應力改變；二、在運轉時因風速的落差所產生的風力改變而造成的複材應力改變，風機旋轉所造成的損傷由有限元素法得到風速與應力的關係，而風速的落差所造成的損傷則先由雨流法簡化實測風速，再利用有限元素法尋找風速與應力關係。以古德曼圖轉換成等效振幅應力並代入由實驗得到的疲勞曲線作Miner’s rule 線性累積疲勞損傷值分析，最後使用風速和中央氣象局一年的風速資料作此複合型垂直式風機的一年損傷值評估。

The prediction of fatigue damage of a vertical-axis wind turbine is considered in this thesis using the load history of the wind blades. The single stream tube model and the blade element theory are used to calculate the load at different wind speeds. The stresses in the blades are determined in the finite element (FE) analysis of the turbine using the FE code ANSYS. The wireless device Zigbee together with strain gages is also used to measure the stresses in the blades. The experimental results are used to validate the FE model. There are two types of stresses that can cause fatigue damages in the blades. One is the stresses induced in the blades at the specific azimuthal position; the other is the stresses induces by the variation of wind speed. Using the finite element model, the fatigue fraction caused by the stresses at the specific azimuthal position is related to the wind speed. The rainflow cycle counting method is used to estimate the load cycles at different wind speeds in a period of time. Because the S-N curve is not available for the stress histories with different mean stresses, the Goodman diagram is thus established to get equivalent completely reversed stresses. Finally, the Miner’s rule is used to calculate the accumulative damages of the blades caused by the wind in one year based on the historical wind speed data from the Central Weather Bureau.