Vibrações não lineares e controle de torres eólicas com seção variável e fundação elástica

Abstract

This dissertation is devoted to an in-depth study of vibration control in wind turbine towers subjected to wind action or base displacement. The emphasis is placed on the analysis of the tower-blade system, considering the rotation of the blade and interactions with external forces. A rigorous modeling approach is implemented, based on the non-linear geometrical theory of Euler-Bernoulli beams, in both its linear and non-linear forms. The Rayleigh-Ritz method and the Hamilton principle are applied to derive the ordinary differential equations that describe the motion of the structure. The study takes into account a variety of determining factors, such as variation in the tower’s cross-sectional area, an elastic foundation, base displacement, and a real seismic load (Norridge earthquake), in order to evaluate the structural response. The differential equations are transformed into algebraic equations and solved numerically with the aid of specialized software such as Maple and C++. The study of dynamic instability highlights a "veering"phenomenon resulting from variations in the rotational speed of the blades, which can lead to abrupt changes in the direction of the natural frequencies. This work investigated the vibration control of a coupled tower-blade wind turbine system, considering towers with constant and variable cross sections under lateral loads, base displacements, and blade rotation. The inclusion of an elastic foundation significantly reduced the amplitudes of free vibration. Vibration control is achieved by means of a tuned liquid column damper (TLCD). The use of a TLCD demonstrated an effective efficiency of up to 60% in the reduction of vibrations, even in non-linear regimes. The variable-section tower was observed to exhibit lower stiffness. In seismic analyzes, the TLCD maintained its effectiveness, with reductions of up to 24% in vibration amplitudes, also highlighting the influence of blade rotation on attenuating vibrations during seismic events.