Oliviero Giannini | Università degli studi Niccolò Cusano, telematica Roma (original) (raw)

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Papers by Oliviero Giannini

International Journal of Vehicle Structures and Systems, 2011

Spie Proceedings Series, 2002

This paper presents a model that can predict development of squeal sounds in a simple laboratory ... more This paper presents a model that can predict development of squeal sounds in a simple laboratory disk brake. The disk brake, designed and manufactured to evaluate the behavior of a real automotive brake, consists of a rotating disk and a caliper that can be appropriately adjusted to simulate different operating conditions. The model describes the modal interaction of the disk and the caliper coupled together through friction. The results of this reduced-order model show very good agreement with the corresponding experiments and suggest a physical description of the squeal generation mechanism.

ABSTRACT The complex envelope vectorization (CEV) is a recent method that has been successfully a... more ABSTRACT The complex envelope vectorization (CEV) is a recent method that has been successfully applied to structural and internal acoustic problems. Unlike other methods proposed in the last two decades to solve high frequency problems, CEV is not an energy method, although it shares with all the other techniques a variable transformation of the field variable. By such transformation involving a Hilbert transform, CEV allows the representation of a fast oscillating signal through a set of low oscillating signals. Thanks to such transformation it is possible to solve a high frequency dynamic problem at a computational cost that is lower than that required by finite elements. In fact, by using finite elements, a high frequency problem usually implies large matrices. On the contrary the CEV formulation is obtained by solving a set of linear problems of highly reduced dimensions. Although it was proved that CEV is in general a successful procedure, it was shown that it is particularly appropriate when the modes of the system have a negligible role on the solution. Moreover, the numerical advantage of the CEV formulation is much more pronounced when full matrices are used. Thus, for the first time it is applied to a boundary element formulation (BEM). Both external and internal acoustic fields of increasing complexity are considered: the internal and external field generated by a pulsating sphere; the external field of a forced box, where the velocity field is determined by finite elements; a set of 4 plates that form an open cavity. The results are compared with those obtained by a BEM procedure (SYSNOISE), highlighting the good quality of the proposed approach. An estimate of the computational advantage is also provided. Finally it is worthwhile to point out that the reduction of the BE matrices allows for an in-core solution even for large problems.

Brake noise is an example of noise caused by vibration induced by friction forces. During brake o... more Brake noise is an example of noise caused by vibration induced by friction forces. During brake operation, the friction between the pad and the disc can induce a dynamic instability in the system. The onset of squeal is supposed to occur in linear conditions, during braking phase. A complex eigenvalues analysis of the finite element model of a simplified brake apparatus is here adopted to investigate the squeal occurrence. Several experimental tests are performed to reproduce different squeal frequencies and to study the dynamics of the system in function of driving parameters. The paper shows a good agreement between the dynamic behaviour predicted by the parametrical complex eigenvalues analysis on the model and the dynamic and squeal behaviour measured on the experimental set-up. The simple dynamics of the system allows distinguishing three main substructures: disc, caliper and pad. A clear distinction between squeal events involving the modes of the caliper or of the pad is high...

In this paper, an experimental analysis performed on a simplified brake apparatus is presented. B... more In this paper, an experimental analysis performed on a simplified brake apparatus is presented. Brake squeal is a major concern in braking design. During past years a common approach for squeal prediction was the complex eigenvalues analysis. Squeal phenomenon is treated like a dynamic instability. When two modes of the brake system couple at the same frequency, one of them becomes unstable leading to increasing vibration. The presented experimental analysis is focused on correlating squeal characteristics with the dynamic behavior of the system. The experimental modal identification of the set-up is performed and different squeal conditions and frequencies are reproduced and analyzed. Particular attention is addressed to the system dynamics in function of the driving parameters on squeal occurrence. Squeal events are correlated with the modal behavior of the system in function of the main parameters, like contact pressure, friction material properties and system geometry. The robus...

The phenomenon of mode veering is analyzed in this paper. Veering occurs when there is a varying ... more The phenomenon of mode veering is analyzed in this paper. Veering occurs when there is a varying parameter in the system: it produces a change in the systems and it often happens that, when the frequencies approach each other, instead of crossing they veer, and the mode shapes swap from one branch to the other. The problem is presented for a general weakly-coupled two-degrees of freedom systems, showing also the lock-in phenomenon that is of importance to explain the instability behavior of several mechanical systems (e.g. squeal noise in brakes). How things change when the coupling is not weak or a continuous system is address is also discussed to highlight phenomena of particular interest

Volume 2: Automotive Systems; Bioengineering and Biomedical Technology; Computational Mechanics; Controls; Dynamical Systems, 2008

Volume 2: Dynamics, Vibration and Control; Energy; Fluids Engineering; Micro and Nano Manufacturing, 2014

Conference Proceedings of the Society for Experimental Mechanics Series, 2014

ABSTRACT The phenomena of mode veering, crossing and lock-in are experimentally analyzed in this ... more ABSTRACT The phenomena of mode veering, crossing and lock-in are experimentally analyzed in this paper. Their occurrence is generally found, under different conditions, when there is a parameter varying in the system, producing a change in its behavior. It often happens that, when the natural frequencies of two modes approach each other, they can cross, veer and eventually present a lock-in state. The problem is analytically investigated for a general weakly-coupled two-degrees of freedom systems and experiments, appropriately designed to highlight these phenomena, are presented. In particular, experimental evidences of the damping-dependent transition from veering to crossing is investigated in a two beam system, and experimental lock-in in brake squeal are recalled to show how in gyroscopic systems, when two coupled mechanical parts have the same eigenvalues (lock-in state), the whole system may becomes unstable.

Volume 1: Applied Mechanics; Automotive Systems; Biomedical Biotechnology Engineering; Computational Mechanics; Design; Digital Manufacturing; Education; Marine and Aerospace Applications, 2014