本研究分為兩個部分，第一部分針對NREL 5MW OWT風力機基座進行裂縫應力分析，選擇IEC 61400-3中屬於需分析極限負載的工況，並配合台灣西部沿岸之海洋參數進行模擬，模擬軟體為GH-Bladed，GH-Bladed用於計算作用在基座上的實際載荷，包括力和力矩，最後將轉換後的負載輸入ANSYS Workbench，接著挑選局部應力最大的地方建立裂縫，接著將裂縫尖端的應力強度因子結合失效評估圖即可判斷裂縫是否會造成結構失效，結果顯示在裂縫深度4mm左右時，結構可能會因為裂縫附近有過大的塑性變型而導致結構失效。第二部分則是選擇IEC 61400-3中屬於需分析疲勞負載的工況，進行NREL 5MW OWT風力機基座裂縫疲勞分析，首先選擇合適的風況浪況之後進行模擬並提取10分鐘之環境負載，再將轉換後的應力輸入至ANSYS Workbench，進行應力分析，之後同樣在擁有最大拉伸應力處建立裂縫，提取裂縫尖端的應力強度因子歷時以後，將該歷時等效為等振幅的應力強度因子歷時，再通過另一幾何形狀較為單純的有限元素模型，在該模型上建立一個相同的裂縫，並在該模型上施以一等幅應力負載使其的應力強度因子振幅與之前計算出的等振幅的應力強度因子歷時的振幅相同，便可使用ANSYS Workbench中的 Smart Crack Growth功能來預測疲勞工況的循環次數與裂縫尺寸的關係，當裂縫尺寸成長至無法承受極限負載工況時，便判斷為該情況有危險。;This research studied the offshore wind turbine NREL 5MW OWT and focused on the mechanics of the crack in the foundation. First, to analyze the ultimate load, we select specific design conditions in IEC 61400-3 with marine parameters corresponding to the western coast of Taiwan. The wind turbine software BLADED is used for finding the actual loadings, including forces and moments, acting on the foundation. Then, these loadings were used in FEM software ANSYS to perform detailed stress strength and fatigue analysis. The position of the crack was selected, where the local stress was maximum. The stress intensity factor at the crack tip was combined with the failure evaluation diagram to determine whether the crack would cause structural failure. The second part of the research is to select the working condition corresponding to fatigue load in IEC 61400-3. With appropriate wind and wave parameters, BLADED can provide 10-minute loadings to the foundation. Then, its stresses were found using ANSYS. A crack is established at the bottom of the base with the largest tensile stress. For fatigue analysis, the transient stress intensity factor duration was transformed to an equivalent stress intensity factor duration with constant amplitude. Then, the same crack was established on a simplified model. The “Smart Crack Growth” function of ANSYS was used to predict the relationship between the number of cycles of fatigue conditions and the growth of the crack size. The situation is dangerous when the crack size grows to the extreme. This research can provide a systematic method of analyzing the failure of the wind turbine foundation.
