Affiliations: School of Engineering, Swansea University, Swansea,
UK | Department of Civil Engineering, University of
Bristol, Bristol, UK
Note: [] Corresponding author: Chair of Aerospace Engineering, School of
Engineering, Swansea University, Singleton Park, Swansea SA2 8PP, UK.
E-mail: [email protected]
Abstract: Offshore wind turbines are considered as an essential part to
develop sustainable, alternative energy sources. The structures themselves are
both slender and highly flexible, with a subsea foundation typically consisting
of a single large diameter monopile. They are subject to intense wind and wave
loadings, with the result that significant movement of both the exposed
structure and the upper part of the monopile can occur. Although the structures
are intended for design life of 25 to 30 years, very little is known about the
long term behaviour of these structures. This paper characterizes the dynamic
behaviour of these structures. A simplified approach has been proposed for the
free vibration analysis of wind turbines taking the effect of foundation into
account. The method is based on an Euler-Bernoulli beam-column with elastic end
supports. The elastic end-supports are considered to model the flexible nature
of the interaction of these systems with the foundation. A closed-form
expression of the characteristic equation governing all the natural frequencies
of the system has been derived. Theoretical developments are explained by
practical numerical examples. Analytical as well as a new experimental approach
has been proposed to determine the parameters for the foundation. Some design
issues of wind turbine towers are discussed from the point of view of the
foundation parameters.
Keywords: Wind turbine, natural frequencies, foundation stiffness, structural dynamics, offshore
