Gianluca Pepe

Fractional dissipation generated by hidden wave-fields

This paper considers the damping induced on a single degree-of-freedom system when it is coupled at one end of a waveguide in which waves are radiated producing an energy loss in the oscillator motion that appears as a damping effect. In general, the whole system is described by the equation of the motion of the harmonic oscillator coupled with the wave equation of the propagation field. Hiding the variable that describes the wave motion and expressing it in terms of the oscillator vibration, a new equation for the oscillator is determined. In general, a nonconventional damping effect is born from the coupling terms. This paper examines cases in which the induced damping effect is of fractional-derivative type. This point of view produces physical examples of the way that simple mechanical structural systems, familiar to engineers, can exhibit fractional damping, a concept that does not always have a clear physical interpretation.

A multisensing setup for the intelligent tire monitoring

The present paper offers the chance to experimentally measure, for the first time, the internal tire strain by optical fiber sensors during the tire rolling in real operating conditions. The phenomena that take place during the tire rolling are in fact far from being completely understood. Despite several models available in the technical literature, there is not a correspondently large set of experimental observations. The paper includes the detailed description of the new multi-sensing technology for an ongoing vehicle measurement, which the research group has developed in the context of the project OPTYRE. The experimental apparatus is mainly based on the use of optical fibers with embedded Fiber Bragg Gratings sensors for the acquisition of the circumferential tire strain. Other sensors are also installed on the tire, such as a phonic wheel, a uniaxial accelerometer, and a dynamic temperature sensor. The acquired information is used as input variables in dedicated algorithms that allow the identification of key parameters, such as the dynamic contact patch, instantaneous dissipation and instantaneous grip. The OPTYRE project brings a contribution into the field of experimental grip monitoring of wheeled vehicles, with implications both on passive and active safety characteristics of cars and motorbikes.

Nonlinear unsteady energy analysis of structural systems

The problem of vibration of large systems undergoing shocks and unsteady loads is one of the field of great interest in vibro-acoustic engineering. Statistical Energy Analysis-SEA is one of the most acknowledged methods in this field. However, SEA has many limitations, and is based on several questionable hypotheses. In the present paper, on the basis of a new theory of vibration thermodynamics, the authors consider a set of systems characterized by (i) unsteady loads, such as shocks, (ii) nonlinear coupling between the different subcomponents. The analysis is carried on considering different prototype systems, starting from a very simple pair of nonlinear resonators, a 2-dof system, up to consider a system of plates coupled through nonlinear joints. It is shown how the energy flow relationship between subsystems pair, comes out to be a power series of the energy storage difference. These results are systematically considered in the light of the thermodynamic theory of vibrating systems, showing how a gen...