Optimal design of nonlinear energy sinks for random excitations

Passive control devices are often used to protect slender and flexible structures from a variety of events, including earthquakes, winds, waves and traffic. Among them, Nonlinear Energy Sinks (NESs) have recently received increasing attention from researchers because of their capability to passively and irreversibly absorb a significant amount of energy over a wide range of frequencies. In most studies, the dynamic response of a main structure coupled with one or more NESs is analysed for impulsive loading. In this thesis, the performance of the NES attached to a Single Degree of Freedom (SDOF) system, under random base excitations, is investigated through several numerical simulations. In order to determine the optimal configuration for the device, different objective functions are considered. Sensitivity analyses with respect to the intensity of the random loads, the mass ratio and the main parameters of the primary structure are presented. Accurate empirical formulae are proposed for the evaluation of the optimal NES parameters, linking these latter to the characteristics of the main structure and the random base excitation. In particular, random loadings have been derived for the cases of white noise excitations and seismic excitations generated by Power Spectral Density consistent with response spectra provided by Eurocode 8. Numerical results are validated by Monte Carlo simulations. Moreover, numerical applications for two-DOF systems equipped with a NES are presented in order to validate the applicability of the proposed empirical formulae for Multi Degrees of Freedom structures.