Design and Structural Analysis of Mono Pile Foundation for Offshore Wind Turbines

Offshore wind energy offers a huge potential for expansion of renewable energy in the world. However, placement of wind turbines in harsh offshore environments is an engineering challenge, which requires development of suitable foundation designs. This paper shows different foundation types which are decided by different cases of the seabed. The mono pile foundation for 1.5MW offshore wind turbine is designed for Bohai Bay in China considering the soil and seabed condition. A three dimensional (3D) finite element model of mono pile is established to analyze horizontal ultimate bearing capacity, stress and deformation under lateral loads. Through the modal analysis, the natural frequencies of the mono-pile are given. Results show that the designed mono pile can effectively preclude resonance with the wind turbine. Dynamic responses under wave and seismic loads are analyzed by transient analysis method. And at same time, dynamic amplification factors of stress and deformation are studied. The paper reaches the conclusion that the dynamic effect must be attached importance in the design. Moreover, based on the theory of stability, the simplified method to assess the ultimate buckling moment of the mono pile is put forward. Comparisons are also made with results calculated by codified rules of DNV and ABS and Finite Element Method. Besides, fatigue analysis is carried out according the codified rules of API. The numerical results demonstrate that the design of mono pile is reasonable and reliable. The research results can provide the reference for practical engineering in China.