Environmental Engineering Reference
In-Depth Information
CHAPTER 4
Spyros G. Voutsinas
National Technical University of Athens, Greece.
Structural dynamics of wind turbines aims at assessing the integrity and reliability
of the complete construction against varying external loading over the targeted
life time. Since wind induced excitation is the most important, structural dynam-
ics is closely connected to aeroelasticity. Most of structural analysis is based on
modelling while tests are reserved for prototype assessment. To this end elastic
modelling at component level and dynamic modelling of the complete system are
required. The aim of the present chapter is to provide an overview on the theory
and approximation tools of structural dynamic analysis of modern wind turbines
on these two aspects. At component level beam models of varying complexity are
discussed while at system level the multi-body approach is defi ned and its use in
formulating the dynamic model of the complete wind turbine is explained. Next,
after a short introduction to aeroelastic coupling, the issue of stability is outlined.
Finally some indicative results show the kind of information structural analysis
can provide. The focus of the presentation is on the procedures rather than the
details of derivations for which appropriate pointers to the literature are given.
1 Wind turbines from a structural stand point
A typical wind turbine confi guration includes as main components the rotor blades,
the drive train and the tower, all considered as fl exible structures. When considering
the wind turbine as a system, all components are modelled as slender beams sub-
jected to combined bending, torsion and tension with distributed material prop-
erties like stiffness, damping and density. At this level, the elastic behaviour of
the different components is described by continuous displacement and rotation
fi elds along the span of each component. In the discrete context the displacements
and rotations will correspond to the
elastic degrees of freedom
(
DOF
) . The beam
like modelling associated to structural fl exibility is discussed in Sections 3 and 7.
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