Design for resonance area avoidance by changing the geometry of offshore wind turbine substructures

Abstract

The larger the topside tower size, the more the fatigue loads can generate, especially at the connection joints; additionally, problems due to resonance occur in the high-frequency area due to the movement of the tower blades and substructure. Therefore, the resonant area generated the motion of the tower blades and substructure must be considered when designing the structure. Therefore, the purpose of this study is to change the tower shape based on the substructure of a 12 MW offshore wind generator designed using the expansion method to identify the inherent vibration area of the structure's six-degrees-of-freedom (6DoF) motion. Moreover, the movement trends of the resonant areas per case are analyzed based on the tower rotor speed to present the designs to follow and avoid for the resonant areas. Seven models were designed for the transformed model, and a 6DoF motion response analysis was performed according to the wave incidence angle. In addition, the tower rotor speed frequency and substructure frequency were compared and analyzed, and an avoidance design method was presented to show the effect of 6DoF on the structure.