smart technologies for safety engineering

8
Modeling and Analysis of Smart
Technologies in Vibroacoustics
Tomasz G. Zieliński
8.1 Introduction
8.1.1 Smart Hybrid Approach in Vibroacoustics
Effective noise reduction is nowadays a very important topic, relevant for many applications.
Certainly, noise has become a crucial factor in the design of automotive vehicles and aircraft.
Noise reduction techniques can be traditionally divided into two groups, namely:
(1) passive techniques: porous liners, screens with air-gaps, multilayered panels, etc.;
(2) active techniques: the active noise control (ANC) and active structural acoustic control
(ASAC).
The first approach is suitable for attenuation of the high-frequency contributions of noise and
vibrations, while the active control technologies appear to be the only way to reduce the lowfrequency
components. As a matter of fact, the active noise control and active structural acoustic
control have become classic approaches to cope with low-frequency noise. In the ANC, the
noise is cancelled in some areas by the addition of a secondary noise field, which is an inverse
replica of the first noise field [1] (and, in practice, causes a noise augmentation in some other
areas), while in the ASAC the vibrations of noise radiating surfaces (plates, beams, shells) are
actively controlled to reduce the generation of low-frequency noise [2]. These classic solutions
have drawbacks and practical limitations and a commonly drawn conclusion is that combined
solutions should be the most suited to cover the entire frequency range. Thus, a smart hybrid
approach was proposed [3–8] that is relevant especially for barriers limiting the transmission
of acoustic waves and, in general, for attenuators and dissipative materials for noise insulation
and absorption. In such applications porous liners and multilayered panels (usually with a core
of porous material and thin elastic faceplates) are widely used, but since they are passive, their
efficiency is limited only to high and medium frequencies. The hybrid approach is also termed
Smart Technologies for Safety Engineering Edited by J. Holnicki-Szulc
© 2008 John Wiley & Sons, Ltd. ISBN: 978-0-470-05846-6