Institute of Fundamental Technological Research

The surging quest for safety is a clearly visible trend in modern societies. One of the related areas of research is the design of systems protecting against heavy dynamic loads such as low and medium velocity traffic-related impacts and environmental loadings. Commonly applied passive systems are typically designed to withstand a specified, well-defined heavy load scenario, which limits their performance over any wider range of loads, including the less heavy loads that are encountered in the lifetime of a typical structure much more often than the maximum limiting loads.

Active sandwich panels are an example of smart noise attenuators and a realization of hybrid active-passive approach for the problem of broadband noise reduction. The panels are composed of thin elastic faceplates linked by the core of a lightweight absorbent material of high porosity. Moreover, they are active, so piezoelectric actuators in the form of thin patches are fixed to their faceplates. Therefore, the passive absorbent properties of porous core, effective at high and medium frequencies, can be combined with the active vibroacoustic reduction necessary in a low frequency range. Important convergence issues for fully coupled finite-element modeling of such panels are investigated on a model of a disk-shaped panel under a uniform acoustic load by plane harmonic waves, with respect to the important parameter of the total reduction of acoustic transmission. Various physical phenomena are considered, namely, the wave propagation in a porous medium, the vibrations of elastic plate and the piezoelectric behavior of actuators, the acoustics-structure interaction and the wave propagation in a fluid. The modeling of porous core requires the usage of the advanced biphasic model of poroelasticity, because the vibrations of the skeleton of porous core cannot be neglected; they are in fact induced by the vibrations of the faceplates. Finally, optimal voltage amplitudes for the electric signals used in active reduction, with respect to the relative size of the piezoelectric actuator, are computed in some lower-to-medium frequency range.

Active sandwich panels, Multiphysics, Vibroacoustics, Poroelasticity, Piezoelectricity

The problem of estimation of a structural loss factor for a beam covered with a viscoelastic layer is addressed in the paper. Two estimation methods based on analytical models for wave propagation in viscoelastic homogenous beams are tested. The methods use different theoretical solutions for spatial distribution of a wave field in the beam. The solutions depend on a complex wave number and frequency. At each frequency within an investigated range the wave number, for which model predictions best approximate experimental response, is found. Structural loss factor is calculated based on the identified value of wave number. Experimental data are measured in a cantilever beam test. For verification purposes the obtained values of loss factor are compared with the results of Oberst test. The presented methods enable determination of loss factor for arbitrary discrete frequencies. They provide an alternative to modal techniques which estimate only values of the parameter corresponding to resonant frequencies.

This paper presents a complete finite-element description of a hybrid passive/active sound package concept for acoustic insulation. The sandwich created includes a poroelastic core and piezoelectric patches to ensure high panel performance over the medium/high and low frequencies, respectively. All layers are modelled thanks to a Comsol environment*. The piezoelectric/elastic and poroelastic/elastic coupling are fully considered. The study highlights the reliability of the model by comparing results with those obtained from the Ansys finite-element software and with analytical developments. The chosen shape functions and mesh convergence rate for each layer are discussed in terms of dynamic behaviour. Several layer configurations are then tested, with the aim of designing the panel and its hybrid functionality in an optimal manner. The differences in frequency responses are discussed from a physical perspective. Lastly, an initial experimental test shows the concept to be promising.

Poroelasticity, Piezoelectricity, Finite-element modelling, Acoustic insulation, Active-passive approach

The paper presents further development in modeling of active elasto-poroelastic sandwich panels. In fact, a new design of a demi-sandwich panel is proposed and analysed. A numerical model of panel is implemented in COMSOL Multiphysics environment using the most fundamental but very flexible Weak Form PDE Mode. Various physical problems are modeled using Finite Element Method: the wave propagation in acoustic and poroelastic medium, the vibrations of elastic plate, the piezoelectric behavior of actuator. All these problems interact. in the examined application of active panel. The presented results of FE analysis and some analytical solutions prove the necessity of modeling the panel's interaction with an acoustic medium. Again, confirmed is the fact that an active control is necessary for lower resonances while for the higher frequencies the passive reduction of vibroacoustic transmission performed by a well-designed poroelastic layer is sufficient.

Active sandiwch panels, Poroelasticity, Piezoelectricity, Vibroacoustics

The paper addresses the issue of an active sandwich panel made of elastic faceplates and a poroelastic core. The panel is supposed to be active thanks to piezoelectric patches glued to the one of elastic layers. This piezoelectric actuator is used to excite the panel vibrations in the low frequency range with the aim to reduce the transmitted wave. A complete description of the sandwich behaviour is obtained using a finite element model implemented in FEMLAB environment. The poroelastic material is modeled using a recent formulation (by Atalla et al.) valid for harmonic oscillations, but the classical Biot formulation is also implemented. Coupling occurring between poroelastic material and plates, and between elastic plate and piezoelectric patches is fully considered. The achieved numerical model allows prediction of transmission coefficient for plane waves under normal incidence. Hence, some numerical experiments can be offered for multiple assembly configurations whose ultimate goal is to determine the best assembly and the best control strategy for reducing the transmission over a wide frequency range.

Poroelacticity, Piezoelectricity, Active vibroacoustic panles