A influência do amortecimento viscoelástico na estabilidade aeroelástica de painéis aeronáuticos

Since the creation of supersonic vehicles, during the Second World War, the engineers have given special attention to the interaction between the aerodynamic efforts and the structures of the aircrafts due to a highly destructive phenomenon called flutter in aeronautical panel. Flutter in aeronautical panels is a self-excited aeroelastic phenomenon, which can occurs during supersonic flights due to dynamic instability of inertia, elastic and aerodynamic forces of the system. In the flutter condition, when the critical aerodynamic pressure is reached, the vibration amplitudes of the panel become dynamically unstable and increase exponentially with time, affecting significantly the fatigue life of the existing aeronautical components. Thus, in this paper, the interest is to investigate the possibility of reducing the effects of the supersonic aeroelastic instability of rectangular plates by applying passive constrained viscoelastic layers. The rationale for such study is the fact that as the addition of viscoelastic materials provides decreased vibration amplitudes it becomes important to quantify the suppression of plate flutter coalescence modes that can be obtained. Moreover, despite the fact that much research on the suppression of panel flutter has been carried out by using passive, semi-active and active control techniques, very few of them are adapted to deal with the problem of estimating the flutter speeds of viscoelastic systems, since they must conveniently account for the frequency- and temperature-dependent behavior of the viscoelastic material. In this context, two different model of viscoelastic material are developed and applied to the model of sandwich plate by using finite elements. After the presentation of the theoretical foundations of the methodology, the description of a numerical study on the flutter analysis of a three-layer sandwich plate is addressed.

Esgotamento do padrão de acumulação de capital e política econômica brasileira: do II PND aos anos 2000

This work aim to show that the reach to the limits of capital accumulation, which is showing its first signs since the 60 s, has and still is exercising great importance in Brazilian economic policies. In the first chapter, we establish a reference to what is understood as the limit of capital accumulation after World War II and how the accumulation process drives itself to its own limits. In the following chapters, we detach the importance of the reached limit to the most relevant moments of Brazilian economic policy. Since the IIPND, when the first signs of influence raise in Brazilian economy, passing through the stabilizing attempts during the 80 s and 90 s and the emergence of the pro-market State in Brazil, until the 00 s, when macroeconomic prudence took shape and delimited the conduction of the country s economic policy, we will show how the limit of capital accumulation has played an important role.