本研究針對NREL 5MW OWT離岸風力機塔架進行開機負載及失效評估分析。選擇IEC 61400-3規範中DLC 3.2與3.3之開機工況，根據DNVGL-ST-0437規範設定風況與操作條件之耦合情況，並配合台灣西部沿岸之海洋參數進行模擬。 先利用GH-Bladed軟體進行風力機塔架負載分析，然後將負載轉換輸入至ANSYS Workbench進行應力分析，最後在塔架環銲與縱銲處設置半橢圓裂縫，並採用BS 7910規範進行塔架失效評估分析。 研究結果顯示在開機與極端運轉陣風耦合期間，塔頂在風力機轉軸方向會產生極大的軸向力。在開機與極端風向變化耦合時，塔頂之軸向力會降低，但側向力會因風向改變而提高。在額定風速(11.4 m/s)時，塔架在沒有裂縫下承受開機與陣風耦合情況，安全係數為1.62，符合IEC 61400-3規範建議值。在塔架環銲裂縫深度為20 mm、裂縫長度為50 mm時，將有塔架發生崩潰之危險，應立即執行維修程序。塔架縱銲裂縫的最大應力強度因子皆非常小，並不會發生嚴重損害與倒塌。對於塔架環銲裂縫而言，裂縫深度每增加1 mm，應力強度因子之最大提升量為1.20 MPa√m，而裂縫長度每增加1 mm，其最大提升量為0.34 MPa√m，可知裂縫深度的增加較裂縫長度的增加更容易使塔架發生斷裂情況。 ;In this study, start-up load and failure assessment of NREL 5MW OWT offshore wind turbine tower were analyzed. Start-up conditions of DLC 3.2 and 3.3 in IEC 61400-3 standard were selected. Coupling conditions of wind and operating conditions set in DNVGL-ST-0437 standard and the ocean parameters of Taiwan west coast were adopted for simulation. Firstly, the load analysis of wind turbine tower is carried out by using GH-Bladed software, and then the load conversion is input to ANSYS Workbench for stress analysis. Finally, semi-elliptical cracks were set at the circumferential and longitudinal welds of the tower, and the failure assessment analysis of the tower was carried out by BS 7910. The results show that the top of the tower produces a great axial force in the direction of the rotating axis of the wind turbine during the start-up and the extreme operating gust coupling period. When start-up coupled with the extreme wind direction change, the axial force at the top of the tower will decrease, but the lateral force will increase due to the wind direction change. At the rated wind speed (11.4 m/s), the tower withstands the start-up and gust coupling condition without cracks, and the safety factor is 1.62, which is in line with the recommended value of IEC 61400-3 standard. When the circumferential welding crack depth of the tower is 20 mm and the crack length is 50 mm, the tower will be in danger of collapse, and maintenance procedures should be carried out immediately. The maximum stress intensity factor of the longitudinal welding cracks of the tower is very small and will not cause serious damage and collapse. For the circumferential welding cracks of the tower, the maximum increase of stress intensity factor is 1.20 MPa√m with the increase of crack depth 1 mm, and 0.34 MPa√m with the increase of crack length 1 mm. It can be concluded that the increase of crack depth is more likely to cause the tower to fracture than the increase of crack length.
