Dynamic response of OWTs under wind-wave loads considering 3D water-pile-soil interactions

• Published in: Ocean engineering 2023-09, Vol.283, p.115057, Article 115057
• Main Authors: Cao, Guangwei, Chian, Siau Chen, Ding, Xuanming, Zheng, Changjie, Luan, Lubao, Zhou, Qiujie
• Format: Article
• Language: English
• Subjects: Accumulative deformation; Numerical analysis; Water-pile-soil interactions; Wind turbine; Wind-wave loads
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2023.115057

A new three-dimensional (3D) integrated model of offshore wind turbine (OWT) is proposed, which considers the soil-monopile-water interactions and the accumulative deformation of foundations under cyclic loads. The effects of three different modelling methods on the dynamic response of wind turbine are discussed, where three modelling methods are the new WOT model, OWT model with a 3D soil-pile medium without a seawater domain and OWT model with API's spring-type foundation. The numerical results show that the use of API's soil spring may overestimate the fundamental frequency of OWT by up to 32.2%. This leads to inaccurate structural resonance. Meanwhile, a significant displacement drift of the tower top of the new model is observed due to the ratcheting effect, and the OWT with API's spring cannot correct this phenomenon. Consequently, the API method should be used with care in assessing dynamic performance under wind-wave loads. The added mass method considers only the water-structure interaction and excludes the soil-water interaction, and it may underestimate the responses of the tower, blades and monopile, which can render the design of wind turbines unsafe. Additionally, assumption of the parked condition underestimates the structural response, and the frequency of the blades may change during operation. •A new 3D integrated model of offshore wind turbines (OWT) was proposed, which considers the soil-monopile, water-soil and water-structure interactions and the soil accumulative deformation.•Neglecting the soil-water interaction can underestimate the responses of the tower, blades and monopile.•Frequencies of the blades may change during the operation due to the centrifugal stiffness of the rotating blades.•The use of API's soil spring may overestimate the fundamental frequency of an OWT by up to 32.2% compared to the new integrated model. This leads to an inaccurate structural resonance.•A significant drift of the displacement time history of the tower is observed under wind-wave loads due to soil accumulative deformation, but the API's p-y method cannot reflect this phenomenon.