DYNAMIC INSTABILITY OF WIND TOWERS

Resumo

In this work the dynamic instability of a coupled tower-blade wind turbine system is
investigated numerically. For this, the linear Euler-Bernoulli theory is used to describe the coupled
tower-blade system and considering the lateral acceleration of the nacelle at the top of the tower,
which is the base of the flexible blade. The Galerkin method is applied to obtain a set of linear
ordinary differential equations of dynamic equilibrium which are, in turn, solved using the runge-kutta
method. First, the coupled eigenvalues are obtained considering several blade rotational speeds and
both the veering and instability phenomena are studied. Second, an external harmonic load is applied
to the system and the linear dynamic behavior is analyzed. A parametric analysis is performed to

observe their influence on the linear oscillations of the system. Obtained results show that the tower-
blade system can show instability or veering regions mainly due to blade rotation and, it is possible to

observe jumps or large amplitude oscillations due to external loads