Constructing simplified models for dynamic analysis of monopile-supported offshore wind turbines

Accurately modeling the complicated dynamic mechanisms of offshore wind turbines (OWTs) requires high numerical fidelity. However, since these models are computationally expensive for both forward and inverse problems, simplified OWT models are needed. The present study develops two approaches to constructing simplified numerical models based on full-order finite element models, which aim to accurately and efficiently simulate dynamic behaviours of monopile-supported OWTs. The first approach decomposes the structure into substructures and establishes a reduced-order model based on the similarity principle of modal parameters and time-domain responses, in accordance with full-order models. The second approach uses proper orthogonal decomposition and modal truncation techniques to construct a state-space model, which produces consistent time-domain responses with full-order models. For both approaches, model updating is used to improve the accuracy of the simplified models. The effectiveness of the approaches is demonstrated through the monopile-supported, 10 MW DTU reference wind turbine. The results show that the computational time required for both simplified models is less than 10% that of the full-order model, without the compromise of accuracy, i.e., less than 5% difference in modal frequency and an excellent agreement in time-domain responses. The proposed approach provides an efficient and accurate dynamic analysis solution for offshore structures.