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This paper investigates a metamaterial solution for efficient vibration attenuation and acoustic radiation reduction of an aluminum pipe. To this end, using unit cell predictions, locally resonant structures are designed to have a pronounced flexural resonance frequency at the vicinity of a dominant vibration mode of the pipe. A direct approach of the Bloch-Floquet theorem is adopted to provide the dispersion relation representing wave motion in an infinite metamaterial pipe. Using these wave dispersion relations, the frequency range of the stopband zone created by the metamaterial solution is predicted. The dynamic behavior of the finite counterpart is predicted using the Finite Element Method (FEM). The resonant structures are produced from polymethyl methacrylate (PMMA) panels and are added to the host structure. In order to properly characterize both the vibrational behavior of the metamaterial pipe and the acoustic radiation from its wall, impact tests using roving hammer technique is performed on the pipe and both accelerations and acoustic pressures are measured at different locations. The experimental results show a pronounced stopband zone created by the addition of a few rows of resonant structures. Moreover, comparisons between the measurements and numerical predictions show a good agreement. ispartof: Journal of Sound and Vibration vol:455 pages:96-117 status: published

This paper investigates the mechanisms that can be used to enhance the absorption performance of poro-elastic materials in the viscous regime. It is shown that by adding small inclusions in a poro-elastic foam layer, a mass–spring effect can be introduced. If the poro-elastic material has relatively high viscous losses in the frequency range of interest, the mass–spring effect can enhance the sound absorption of the foam by introducing an additional mode in the frame and increasing its out-of-phase movement with respect to the fluid part. Moreover, different effects such as the trapped mode effect, the modified-mode effect, and the mass–spring effect are differentiated by decomposing the absorption coefficient in terms of the three energy dissipation mechanisms (viscous, thermal, and structural losses) in poro-elastic materials. The physical and geometrical parameters that can amplify or decrease the mass–spring effect are discussed. Additionally, the influence of the incidence angle on the mass–spring effect is evaluated and a discussion on tuning the inclusion to different target frequencies is given.

Recently, locally resonant metamaterials have come to the fore in noise and vibration control engineering, showing great potential due to their superior noise and vibration attenuation performance in targeted and tunable frequency ranges, referred to as stop bands. Damping has an important influence on the performance of these materials, broadening the frequency range of attenuation at the expense of peak attenuation. As a result, understanding and including the effects of damping is necessary to more accurately predict the attenuation performance of these locally resonant metamaterials. Classically, these often periodic structures are analysed using a unit cell modelling approach to predict wave propagation and thus stop band behaviour, discarding damping. In this work, a unit cell method including damping is used to analyse the complex dispersion curves of a locally resonant metamaterial design. The wave solutions in and around the stop band frequency range are compared to those of the unit cell method discarding damping. The influence on the dispersion curves of damping in resonator and host structure is discussed and the obtained dispersion curves are validated through an experimental dispersion curve measurement based on an Extended Inhomogeneous Wave Correlation method using Scanning Laser Doppler Vibrometry for a metamaterial plate manufactured at a representative scale. Excellent agreement is obtained between the numerically predicted and experimentally retrieved dispersion curves. ispartof: Journal of Sound and Vibration vol:409 pages:1-23 status: published

Porous materials are often used in the context of passive noise control applications due to their low cost and good sound absorption properties. As the most commonly used predictive tool, the finite element (FE) method is often applied in the design phase to obtain detailed information on the performance of complex vibro-acoustic systems with porous damping treatments. In this case, however, its use inevitably leads to very large, complex-valued and frequency-dependent numerical models, which makes original full-order model evaluation intractable due to time and memory limitations. In this paper, an adaptive model order reduction strategy is presented to reduce the number of degrees of freedom involved in the associated problems such that the required computational cost can be largely alleviated while a desired high accuracy can be achieved in a controllable way. This technique consists of making use of Taylor expansion to the multiple frequency-dependent scalar functions coming from the complex material behavior, and then performing the structure-preserving second-order Arnoldi algorithm based on a robust error indicator to solve the underlying FE model in the frequency domain. A further improvement in terms of the approximation accuracy of the constructed compact reduced-order model is also proposed to incorporate all available moment-matching information. Two widely used model types for porous materials are investigated, i.e. the equivalent fluid description and the Biot theory. Mono-physical poroelastic-poroelastic coupling and multiphysical acoustic-porous coupling are considered in order to demonstrate the simplicity, versatility and efficiency of the approach. ispartof: Journal Of Sound And Vibration vol:485 pages:1-19 status: published

This paper deals with an efficient strategy to improve the vibro-acoustic behavior of a structure over frequency bands. Genetic Algorithms are used to identify the optimal resonance frequency and location of Dynamic Vibration Absorbers (DVAs) which minimize the band-averaged input power into a plate, leading to an indirect reduction of the radiated acoustic power and global vibration. Instead of classic numerical quadrature schemes, the residue theorem is used to evaluate the band-averaged input power. This results into a considerable reduction of computational effort, as it requires only few function evaluations at complex frequencies, regardless of the analyzed bandwidth. The structural response is simulated by using the Wave Based Method (WBM). Besides an increased convergence rate as compared to classical element-based techniques, the WBM is also free in determining the optimal position of the DVAs, not restricting it to nodal grid locations. Moreover, when point connections are taken into account, only a small part of the WB matrices needs to be recomputed at each iteration, resulting in a strong reduction of the computation time. Numerical examples illustrate the benefits and the efficiency of the proposed optimization strategy. publisher: Elsevier articletitle: Optimal dynamic vibration absorber design for minimizing the band-averaged input power using the residue theorem journaltitle: Journal of Sound and Vibration articlelink: http://dx.doi.org/10.1016/j.jsv.2014.10.030 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved. ispartof: Journal of Sound and Vibration vol:338 pages:60-75 status: published

Metamaterials have been proven to hold potential to enhance the Noise, Vibration and Harshness (NVH) performance in several applications, as they can create stop bands, which lead to frequency zones of pronounced noise and/or vibration attenuation. This paper investigates the influence of the footprint between resonant inclusions and host structure on the stop band behavior of metamaterials. The impact of this design feature is assessed both numerically and experimentally. Numerically, it is shown that by increasing the footprint, the stop bands (SB) become narrower and shift to higher frequencies. Applied to finite structures, it is shown that the zones of pronounced vibration attenuation tend to follow the changes in the stop band limits. The experimental validation is performed on metamaterial beams and the results comply with the numerical model. This investigation demonstrates that the footprint of resonators is a design parameter which can have a beneficial effect when taken into account during the design stage of matematerials.