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Natural frequency assessment of some installed OWTs using an efficient FE nonlinear model including soil/monopile interaction

Bouzida, DA, Bhattacharya, Subhamoy and Otsmane, L (2018) Natural frequency assessment of some installed OWTs using an efficient FE nonlinear model including soil/monopile interaction Journal of Rock Mechanics and Geotechnical Engineering.

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An efficient finite element nonlinear model has been applied to examine the lateral behavior of real-world monopiles supporting Offshore Wind Turbines (OWTs) chosen from five different offshore wind farms currently under operating service in Europe, in the aim to accurately estimate the natural frequency of these slender structures which is function of the interaction of their foundations with the subsoil. After a brief introduction giving the advantages of wind power energy as a reliable alternative to fossil fuel based one, the paper focuses on the importance of the concept of natural frequency as a primary indicator in designing the foundations of OWTs and gives the target range of frequencies where the natural frequency should lie for a safe design. Then, an analytical expression of an OWT natural frequency is presented in function of soil monopile interaction through monopile head springs characterized by lateral stiffness K_L, rotational stiffness K_R and cross-coupling stiffness, where their different constituting terms are discussed. The nonlinear pseudo 3D Finite Element vertical slices model has been used to analyze the lateral behavior of monopiles supporting OWTs of the different wind farm sites considered. Through the monopiles head movements (displacements and rotations) K_L, K_R and K_LR were obtained and soon substituted in the analytical expression of natural frequency for comparison. The results of comparison between computed and measured natural frequencies showed an excellent agreement for ones and slight deviations for the others. This confirms the convenience of the finite element model used for the accurate estimation of the monopile head stiffness.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Civil and Environmental Engineering
Authors :
Date : 22 February 2018
Copyright Disclaimer : This is an Open Access article funded by the Chinese Academy of Sciences Under a Creative Commons license
Uncontrolled Keywords : Finite element analysis, Vertical slices model, Nonlinear analysis, Monopiles under horizontal loading, Natural frequency, Monopile head stiffness, Offshore Wind Turbines (OWTs).
Depositing User : Melanie Hughes
Date Deposited : 22 Nov 2017 12:13
Last Modified : 22 Nov 2017 12:13

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