Luc Jaouen

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests)

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.

How reproducible is the acoustical characterization of porous media

There is a considerable number of research publications on the characterization of porous media that is carried out in accordance with ISO 10534-2 (International Standards Organization, Geneva, Switzerland, 2001) and/or ISO 9053 (International Standards Organization, Geneva, Switzerland, 1991). According to the Web of ScienceTM (last accessed 22 September 2016) there were 339 publications in the Journal of the Acoustical Society of America alone which deal with the acoustics of porous media. However, the reproducibility of these characterization procedures is not well understood. This paper deals with the reproducibility of some standard characterization procedures for acoustic porous materials. The paper is an extension of the work published by Horoshenkov, Khan, Bécot, Jaouen, Sgard, Renault, Amirouche, Pompoli, Prodi, Bonfiglio, Pispola, Asdrubali, Hübelt, Atalla, Amédin, Lauriks, and Boeckx [J. Acoust. Soc. Am. 122(1), 345-353 (2007)]. In this paper, independent laboratory measurements were performed on the same material specimens so that the naturally occurring inhomogeneity in materials was controlled. It also presented the reproducibility data for the characteristic impedance, complex wavenumber, and for some related pore structure properties. This work can be helpful to better understand the tolerances of these material characterization procedures so improvements can be developed to reduce experimental errors and improve the reproducibility between laboratories.

Applications of the Dual Porosity Theory to Irregularly Shaped Porous Materials

Summary Non planar acoustic materials may be used in building and environmental acoustics to achieve as ignificant absorption at lo wf requencies. Examples of these materials are anechoic wedges or advanced design noise barriers. The shape of these materials is mainly based on empirical knowledge because afi ne numerical modeling (e.g. FEM, BEM )r equires large computational costs. Therefore, the optimisation of the general form and of the material used to realise these absorbing systems is limited. The purpose of this paper is to propose an original alternative to these limitations. The work basis relies on the theory for the acoustics of multi-scale porous materials, and in particular on double porosity materials, which has been initiated by Oln ya nd Boutin (J. Acoust. Soc. Am. 2003, 114(1)). It is shown in this paper that this theory could be successfully applied to the modeling of non planar sound absorbing materials. Examples are give nf or multi-layer systems involving perforated panels, material samples having an irregular surface and anechoic wedges. The discussion is based on comparisons between analytical simulations and measurements.

Noise control strategies using composite porous materials - Simulations and experimental validations on plate/cavity systems

This paper examines the potential of using composite porous materials to design robust noise control packages. Composite porous are meso-perforated porous materials in which perforations are filled with another porous material. The work presented here shows that the association of two carefully selected materials could lead to interesting combined properties of sound absorption and sound insulation. A canonical plate/cavity system excited with an internal acoustic source is chosen to illustrate the potential of these materials for noise enclosures. The coupled problem is solved using Finite Element Method. The sound propagation in composite porous materials is described by Biot-Allard�s poroelasticity equations. Noise reductions obtained using composite porous are compared to those obtained using homogeneous materials. The sound powers dissipated into the system are also examined to give further insights into the physics of the involved phenomena. The results show that the achieved performances take full benefit of the efficiencies of either materials which form the composite porous for different frequency ranges

Development of an analytical solution of modified Biot’s equations for the optimization of lightweight acoustic protection

During lift-off, space launchers are submitted to high-level of acoustic loads, which may damage sensitive equipments. A special acoustic absorber has been previously integrated inside the fairing of space launchers to protect the payload. A new research project has been launched to develop a low cost fairing acoustic protection system using optimized layers of porous materials covered by a thin layer of fabric. An analytical model is used for the analysis of acoustic wave propagation within the multilayer porous media. Results have been validated by impedance tube measurements. A parametric study has been conducted to determine optimal mechanical and acoustical properties of the acoustic protection under dimensional thickness constraints. The effect of the mounting conditions has been studied. Results reveal the importance of the lateral constraints on the absorption coefficient particularly in the low frequency range. A transmission study has been carried out, where the fairing structure has been simulated by a limp mass layer. The transmission loss and noise reduction factors have been computed using Biots theory and the local acoustic impedance approximation to represent the porous layer effect. Comparisons between the two models show the frequency domains for which the local impedance model is valid.

An alternative Biot's formulation for dissipative porous media with skeleton deformation

This paper presents an alternative formulation of Biots theory to account for the elastic frame effects in a porous medium in which the acoustical properties of the fluid phase are predicted with an equivalent fluid model. This approach was originally developed for a double porosity medium. In this paper, the alternative formulation is applied to predict the transmission loss and absorption coefficient in the case of a single layer fibrous material, a multi-layer system, vibrating perforated plates, and porous composite materials. In the proposed formulation the coupling coefficients in Biots poroelasticity equations are expressed in terms of the dynamic volumic mass and dynamic bulk modulus. By doing so, the elastic properties of the material frame are considered independently from the properties of the fluid. This formulation is implemented in the form of a transfer matrix algorithm which is validated against experimental data on sound absorption and sound transmission which are obtained for a range of various sound excitations and material arrangements. It is shown that this approach is able to predict accurately the acoustical properties of vibrating perforated plates and porous composites. The proposed approach is sufficiently general to be implemented in a finite element method.

Analytical microstructural model for acoustical porous materials with single or double porosity

An analytical model of sound propagation for porous materials with single or double scale of porosity is described. For each scale, pores and interconnections between them are modeled by a serie of two cylinders; a cylindrical periodical cell is thus considered. Scales are supposed to be separated, the porous medium is supposed to be periodic and to have a motionless skeleton. The geometrical parameters needed to quantify visco‐thermal effects are directly related to the microstructure of the material. These parameters: lengths and radii of pores and interconnections can be extracted from image analysis for example. From additional conditions on cell morphology, independent parameters per porosity scale can be reduced to a number of three. Good comparisons between theoretical calculations of the sound absorption coefficient at normal incidence and impedance tube measurements are obtained for single and double porosity (meso‐perforated) materials.

How reproducible are methods to measure the dynamic viscoelastic properties of poroelastic media

There is a considerable number of research publications on the acoustical properties of porous media with an elastic frame. A simple search through the Web of Science™ (last accessed 21 March 2018) suggests that there are at least 819 publications which deal with the acoustics of poroelastic media. A majority of these researches require accurate knowledge of the elastic properties over a broad frequency range. However, the accuracy of the measurement of the dynamic elastic properties of poroelastic media has been a contentious issue. The novelty of this paper is that it studies the reproducibility of some popular experimental methods which are used routinely to measure the key elastic properties such as the dynamic Youngs modulus, loss factor and Poisson ratio of poroelastic media. In this paper, fourteen independent sets of laboratory measurements were performed on specimens of the same porous materials. The results from these measurements suggest that the reproducibility of this type of experimental method is poor. This work can be helpful to suggest improvements which can be developed to harmonize the way the elastic properties of poroelastic media are measured worldwide.

Rolling noise modeling in buildings

New buildings in urban areas are divided in commercial and living surfaces. This usage has revealed critical disturbances due to the noise of the trolleys delivering at time where the buildings are mostly occupied, e.g., early times in the morning. Rolling trolleys indeed generate low frequency vibrations (below 100 Hz) which propagate easily in the entire building structure and in upper storeys. This work presents an original model for rolling noise in buildings. The developed model is able to account for the ground surface roughness as well as the rolling wheel asperity profile. It also enables to consider the mechanical impedance of the ground including some possible flooring noise treatment. It is shown that the model is able to correctly reproduce the measured level of vibrations and measured noise levels. It is also proved to accurately predict the sensitivity to different types of rolling noise and floorings having various properties, based on a single layer or a multi-layer construction.

On the modeling of visco-thermal dissipations in heterogeneous porous media

Based on a modified equivalent fluid model, the present work proposes a composite model which analytically includes the shape of the inclusions, whether they are porous or not. This model enables to describe the acoustic behavior of a large range of media from perforated plates to arbitrarily shaped porous composites including configurations of porous inclusions in solid matrix or double porosity media. In addition, possible permeability interactions between the substrate material and the inclusions are accounted for.