Abordagem transiente sobre os efeitos do amortecimento viscoelástico na estabilidade aeroelástica de estruturas aeronáuticas

Abstract

Flutter is a kind of aeroelastic instability caused by the simultaneous interaction of aerodynamic, elastic and inertial forces upon a structure. In the design of1 an aircraft, Ćutter is always a major concern due to its high risk of structural collapse. The constant search for solutions intended to increase aircraft performance and consequently reduce environmental impacts has motivated the use of new concepts, such as high aspect ratio wings and the employment of new materials. However, those solutions become an important structural challenge, since they induce an increase of Ćexibility making the structure prone to Ćutter. Thus, the use of passive vibration control techniques, such as viscoelastic materials may be a feasible solution to increase the system aeroelastic performance as a result of its high structural damping rate. Automotive and aeronautical industries largely employ viscoelastic materials to mitigate noise and small vibrations. Little is known about the real effect of viscoelastic damping to reduce aeroelastic instabilities. In this scenario, aeroelastic models always involve high computational costs and introducing viscoelasticity within it may cause them to be unfeasible. Therefore, the creation and employment of computational low costs models capable of representing the dynamic behavior of aeroviscoelastic systems is a real challenge. The focus here is to create feasible aeroviscoelastic models by applying reduction model techniques and mathematically improving the existent ones. Three kinds of aeroviscoelastic systems has been studied: aeronautical panels, a non linear typical section and a representative high aspect ratio wing. For those, three aerodynamic theories are used: the Piston Theory for panels, the Unsteady WagnerŠs Theory and the Unsteady Strip Theory. Except for the panel models, experimental validation were carried through in wind tunnel.

Combining viscoelastic damping and nonlinearities to widen the operational speed range of flutter energy harvesting

“…For the baseline airfoil without the energy harvesting circuit and with linear springs (a h 0 = 1, a h 1 = 0, a θ 0 = 1, a θ 1 = 0) this happens at V * = 14.01 m/s (Fig. 4), agreeing with the experimental measures of [38], who found the flutter speed to be around 14 m/s. To facilitate the distinction between the subcritical and supercritical regions, the next results will display the flow speed V speed normalized by the critical speed of the linear airfoil, V * .…”

“…So far, there is no viscoelastic damping. The airfoil considered is a NACA 0012 profile, which was studied by [38] without the harvesting circuit. Its parameters are listed in Table 2.…”

Contribuição aos métodos de redução de modelos aplicados a sistemas aeroviscoelásticos

“…Os esforços aerodinâmicos associados são introduzidos nos modelos MEF viscoelásticos desenvolvidos nos capítulos anteriores. Finalmente o princípio da análise de flutter para o sistema aeroviscoelástico na frequência baseado no trabalho original de Cunha [44]é descrito. Para o sistema no tempoé proposto um novo método de predição do flutter, baseado na avaliação das respostas temporais obtidas por integração de Newmark.…”

“…Estes sistemas serão ulteriormente submetidos a um carregamento aerodinâmico com o intuito de se determinar a instabilidade de flutter. Para controlar passivamente este fenômenoé proposto um tratamento viscoelástico superficial por camada restrita passiva [28], para o qual a influência já foi tratada em detalhes em [44]. Será apresentada as etapas de construção de um modelo de elementos finitos baseado em deslocamento no domínio da frequência que aproximará as soluções exatas de uma placa retangular simples quadriapoiada completamente tratada, e um sistema de interesse industrial representado por um painel curvo enrijecido parcialmente tratado com camada restrita passiva.…”

“…Por outro lado, para problemas de autovalor, a resolução se torna muito mais complexa, uma vez que os autovalores dependem da frequência. Desta maneira, e preciso recorrer a processos iterativos, como descrito em[44]. Isto será visto com mais detalhes no capítulo IV.…”