The good damping performance and inherent stability of viscoelastic materials in relatively broad frequency bands, besides cost effectiveness, offers many possibilities for practical engineering applications. However, for viscoelastic dampers subjected to dynamic loadings superimposed on static preloads, especially when good isolation characteristics are required at high frequencies, traditional design guidelines can lead to poor designs due to the rapidly increasing rate of temperature change inside the material. This paper is devoted to the numerical and experimental investigation in the degradation of the stiffness and capacity of a viscoelastic material induced by the thermal runaway phase, when it is subjected to dynamic and static loads simultaneously. After the theoretical background, the obtained results in terms of the temperature evolutions at different points within the volume of the material and the hysteresis loops for various static preloads are compared and the main features of the proposed study are highlighted.

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The vortex-induced vibrations may have disastrous effects in engineering practice, affecting significantly the durability, reliability and safety of engineering structures. This is a reason for which a great deal of effort has been dedicated to the proposition of control strategies to deal with the vortex-induced vibration problem. However, few works have proposed the use of viscoelastic materials to suppress the vibrations induced by vortex shedding, which motivates the present study. Here, the immersed boundary method combined with the virtual physical model is used to investigate the dynamics of a viscoelastically-mounted rigid cylinder in a fluid flow under transverse oscillations induced by vortex shedding. A straightforward time-domain modeling procedure of immersed viscoelastic system by using a four-parameter fractional derivative model is proposed. After the theoretical aspects, numerical tests are performed to investigate the vortex-induced oscillations and flow characteristics of the immersed viscoelastic system at Reynolds number 10,000 for a range of reduced velocity and temperature for two values of mass ratios. The results demonstrate the interest in using viscoelastic materials to mitigate the vortex-induced vibrations.

À Deus, pela presença constante no delinear de meus passos. À minha família por toda à ajuda e apoio incondicional. Sem vocês não seria possível. Ao meu orientador Prof. Dr. Antonio Marcos Gonçalves de Lima pelo sério trabalho de orientação na realização da pesquisa, por toda à dedicação, incentivo, amizade e pela confiança concedida ao me propiciar esta e outras oportunidades de trabalho durante o mestrado e o doutorado. Muito obrigado! Ao meu orientador Prof. Dr. Romes Antonio Borges pela parceria iniciada durante à graduação, estendendo-se ao mestrado e doutorado, mais de 8 anos me acompanhando, sempre incentivando e preocupado com a minha formação profissional, e pela valiosíssima amizade a mim concedida. Muito obrigado por ter acreditado em mim lá no início, me concedendo à oportunidade da iniciação científica, à qual fez toda a diferença! À Prof. Dr. Núbia dos Santos Saad e ao Prof. Dr. Hélder Barbieri Lacerda pela disponibilidade e auxílio para com à realização dos ensaios experimentais. Ao Laboratório de Mecânicas de Estruturas Prof. José Eduardo Tannús Reis-LMEst, por todo o suporte físico e operacional.

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This chapter addresses the finite element modeling methodologies intended for performance evaluation, analysis, and design of viscoelastic systems. The mathematical models widely used to represent the frequency and temperature dependent behavior of viscoelastic materials are also considered, namely the complex modulus approach, the fractional derivative model, the Golla-Hughes-McTavish (GHM) model, and the anelastic displacement fields (ADFs) model. The straightforward strategies to integrate the viscoelastic effects into finite element matrices of structural systems such as threelayer sandwich plates, intended for the modeling of medium and large-scale engineering structures, are presented. In the same context, emphasis is placed on the condensation methods for the reduction of the order of the finite element matrices to perform frequency-response functions, complex eigenvalue problem, and time domain analyses. Based on the fact that for viscoelastic materials subjected to dynamic loadings superimposed on static preloads, the classical modeling assuming isothermal conditions can lead to poor designs, since the energy dissipated within the volume of the material leads to temperature rises, an experimental investigation of the self-heating phenomenon is also addressed.