Dynamics of offshore wind turbine-seabed foundation under hydrodynamic and aerodynamic loads: A coupled numerical way

The offshore wind power industry has significantly contributed to the production of green energy in China and Europe etc. and made significant contributions to the reduction of carbon emissions. However, the extreme wave and wind loads in typhoon weather bring a great threat to the stability of offshore wind turbines (OWT). It is crucial to understand the dynamic characteristics of OWT and develop reliable methods of stability evaluation to guarantee the stability of OWT. In this study, taking the software FssiCAS as the computational platform, and taking the open-source solver OlaFlow to determine the wave impact on OWT and its seabed foundation, as well as the fluctuating wind theory is applied to estimate the wind load on the turbine blades and tower cylinder, the dynamic characteristics and stability of a monopile OWT with a capacity of 1500 kW in typhoon weather are investigated adopting a coupled way for the first time worldwide. The influence of the complex geometric shape and mass distribution of OWT is considered, and the generalized elastoplastic constitutive model, Pastor-Zienkiewicz-Mark III, is used to describe the complex dynamic behavior of the seabed foundation. The computational results show that the seabed soil within 4-5 m below the seafloor surface becomes liquefied under extreme wind and wave loads, resulting in the horizontal bearing capacity of the seabed foundation being weakened. As a result, the tower cylinder of OWT tilts aside by 0.5 degrees, which exceeds the limit specified in some design codes. Through comparative analysis, it is found that the wind load contributes up to 50% to the lateral displacement of the OWT, and the maximum bending moment in the tower cylinder. It is indicated that wind loads can significantly affect the stability of OWTs. Additionally, this study proves that the software FssiCAS is applicable to evaluate the dynamics and the stability of OWTs under a complex marine dynamic environment. FssiCAS could hopefully become a computational platform for the design of OWTs.