Antonio Carcaterra

The aim of the work is the analysis of fluid-structure systems, when excited by a flow consisting of an incompressible potential fluid with embedded vortexes. In fact, in many problems of relevant application interests, the monitoring and the potentially detection of structural damages in structures undergoing loads in operative conditions is important. The present method tries to identify simultaneously the load characteristics together with the structural damage. The flow is characterized by the average velocity of the fluid conveying the vortexes and by the position and intensity of the conveyed vortexes. A method for the identification of these flow parameters, based on vibration signals measured at the elastic fluid-structure interface, is proposed. Vibration signals are numerically generated and then processed with time-frequency techniques, such as the ensemble empirical mode decomposition and the normalized Hilbert transform. The sensitivity of the algorithm to the measurement position and to single versus multi-points acquisitions are also investigated. A particular instantaneous frequency is firstly employed to estimate the load characteristics. The influence of the load is then removed from the instantaneous frequency, so that the damage position can be identified. The validity of the proposed method is analyzed varying the flow parameters, the damage locations and depths; effect of ambient noise is also taken into account.

We investigate the interaction of a particle with a finite-size bath represented by a set of independent linear oscillators with frequencies that fall within a finite bandwidth. We discover that when the oscillators have particular frequency distributions, the finite-size bath behaves much as an infinite-size bath exhibiting dissipation properties and thus allowing irreversible energy absorption from a particle immersed in it. We also present a reinterpretation of the Langevin equation using a perturbation approach in which the small parameter represents the inverse of the number of oscillators in the bath, elucidating the relationship between finite-size and infinite-size bath responses.

Statistical vibroacoustics, also called statistical energy analysis (SEA) in the field of engineering, is born from the application of statistical physics concepts to the study of random vibration in mechanical and acoustical systems. This article is a discussion on the thermodynamic foundation for that approach with particular emphasis devoted to the meaning of entropy, a concept missing in SEA. The theory focuses on vibration confined to the audio frequency range. In this frequency band, heat is defined as random vibration that is disordered vibration and temperature is the vibration energy per mode. Always in this frequency band, the concept of entropy is introduced and its meaning and role in vibroacoustics are enlightened, together with the related evolutionary equation. It is shown that statistical vibroacoustics is non-equilibrium thermodynamics applied to the audio range.

This paper discusses a class of unexpected irreversible phenomena that can develop in linear conservative systems and provides a theoretical foundation that explains the underlying principles. Recent studies have shown that energy can be introduced to a linear system with near irreversibility, or energy within a system can migrate to a subsystem nearly irreversibly, even in the absence of dissipation, provided that the system has a particular natural frequency distribution. The present work introduces a general theory that provides a mathematical foundation and a physical explanation for the near irreversibility phenomena observed and reported in previous publications. Inspired by the properties of probability distribution functions, the general formulation developed here is based on particular properties of harmonic series, which form the common basis of linear dynamic system models. The results demonstrate the existence of a special class of linear nondissipative dynamic systems that exhibit nearly irreversible energy exchange and possess a decaying impulse response. In addition to uncovering a new class of dynamic system properties, the results have far-reaching implications in engineering applications where classical vibration damping or absorption techniques may not be effective. Furthermore, the results also support the notion of nearly irreversible energy transfer in conservative linear systems, which until now has been a concept associated exclusively with nonlinear systems.