Nonlinear dynamic response analysis of 15 MW monopile offshore wind turbine under annular typhoon

Annular typhoons have been extensively studied in meteorology, and as a subset of mature-stage intense typhoons, exhibiting distinctive features such as annular eyewall structure, greater destructiveness, and longer duration compared to non-annular typhoons. However, there is currently a lack of research in the field of wind engineering and structural wind resistance specifically addressing the structural response to annular typhoons. This study focuses on the National Renewable Energy Laboratory of America (NREL) 15 MW monopile offshore wind turbine dynamic responses under non-annular typhoons and two categories of annular typhoons. A comparative analysis of the wind turbine under three typhoon scenarios revealed that the along-wind direction load was most significant. Under annular typhoons, the average bending moment exceeded that of non-annular typhoons, while the maximum bending moment exhibits different characteristics for different blades. The trends in lift, drag, and resultant force coefficient for each blade remained consistent across the three typhoon conditions, with the resultant force coefficient predominantly influenced by the drag coefficient. Furthermore, there are differences in the distribution of shear forces and moments along the tower. The non-annular typhoon induces a stronger displacement response under maximum wind speeds. The characteristic of a broad eyewall in annular typhoons results in both the median and mean displacement responses being higher. This study reveals the nonlinear load and vibration characteristics of wind turbines under annular typhoons, highlighting the distinctions from non-annular typhoons, which aims to enhance the understanding of typhoon-prone regions and the wind fields experienced by offshore wind turbines in these areas.