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The objective of this paper is to present an efficient beam formulation based on the boundary element method (BEM), for the nonlinear dynamic analysis of wind turbine towers of variable cross section founded either on surface or on monopile foundation system. The whole structure may undergo moderately large displacements, taking into account the effect of soil–structure kinematic and inertia interaction. The tower is subjected to the combined action of arbitrarily distributed or concentrated transverse wind loading as well as to seismic excitation together with axial loading arising from the self-weight of the tower and the mechanical parts. The Blade element momentum theory is taken into consideration in order to produce the wind load time histories, while the site seismic response is obtained through one dimensional shear wave propagation analysis. The soil–surface foundation system is formulated as equivalent lateral and rotational springs, while the case of monopile system is treated as a prismatic beam on elastic foundation assigning the corresponding springs and dashpots along its length. An extensive case study is carried out on a wind turbine tower–foundation system employing the generated wind velocity time histories and recorded earthquake accelerograms, providing insight to several structural phenomena. The results of the proposed model are compared wherever possible with those obtained from a commercial finite elements software package, illustrating the validity and the efficiency of the developed method. From the obtained results, the strong influence of the nonlinear effects on the dynamic response of the wind turbine tower is verified.

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In this paper, a boundary element method is developed for the nonlinear flexuraltorsional dynamic analysis of beams of arbitrary, simply or multiply connected,

SummaryIn this paper, an advanced 20 × 20 stiffness matrix and the corresponding nodal load vector of a member of arbitrary composite cross section is developed taking into account shear lag effects due to both flexure and torsion (the case of the three‐dimensional beam element of arbitrary homogeneous cross section is treated as a special one). The composite member consists of materials in contact each of which can surround a finite number of inclusions. Nonuniform warping distributions are taken into account by employing four independent warping parameters multiplying a shear warping function in each direction and two torsional warping functions. Ten boundary value problems with respect to the kinematical components are formulated and solved employing the analog equation method, a BEM‐based technique. The aforementioned boundary value problems are formulated employing either an improved stress field arising from the correction of shear stress components or the stress field arising directly from displacement considerations. The warping functions and the geometric constants including the additional ones due to warping are evaluated employing a pure BEM approach, that is, only boundary discretization of the cross section is used. Numerical results are presented to illustrate the method and demonstrate its efficiency and accuracy. The deviations arising from the use of the advanced 20 × 20 stiffness matrix and the classical 12 × 12 or 14 × 14 ones employed in commercial software packages are illustrated through examples of great practical interest. Moreover, the influence of nonuniform warping effects necessitating the use of the aforementioned ‘advanced’ stiffness matrix is also demonstrated. Copyright © 2015 John Wiley & Sons, Ltd.

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