Emmanuel Gourdon

The effect of particle shape and size distribution on the acoustical properties of mixtures of hemp particles

Hemp concrete is an attractive alternative to traditional materials used in building construction. It has a very low environmental impact, and it is characterized by high thermal insulation. Hemp aggregate particles are parallelepiped in shape and can be organized in a plurality of ways to create a considerable proportion of open pores with a complex connectivity pattern, the acoustical properties of which have never been examined systematically. Therefore this paper is focused on the fundamental understanding of the relations between the particle shape and size distribution, pore size distribution, and the acoustical properties of the resultant porous material mixture. The sound absorption and the transmission loss of various hemp aggregates is characterized using laboratory experiments and three theoretical models. These models are used to relate the particle size distribution to the pore size distribution. It is shown that the shape of particles and particle size control the pore size distribution and tortuosity in shiv. These properties in turn relate directly to the observed acoustical behavior.

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.

Seven-Parameter Linear Viscoelastic Model Applied to Acoustical Damping Materials

In this paper, linear viscoelastic rheological properties of acoustical damping materials are predicted. A rheological model, based on a mechanical element approach, is presented. It consists of a combination of two springs, two parabolic elements, and one dashpot (2S2P1D). This model is applied to different acoustical damping materials. Its specificity comes from the fact that elements might be linked to structural and physical features. Parameters might be experimentally determined by tests. Application of the 2S2P1D linear viscoelastic model can adequately predict the behavior of acoustical damping materials with good accuracy. If the material verifies the time–temperature superposition principle (TTSP), the proposed model can predict the behavior on a wide frequency range, even with a small number of available data.

Use of image analysis to predict the sound absorption coefficient of bituminous mixtures

Sound absorption coefficients of bituminous mixtures are predicted owing to image analysis. A three-parameter semi-phenomenological model, well adapted to porous road materials, is used. Three geometrical parameters: porosity, resistivity and tortuosity, are estimated. Image analysis on high-quality digital photographs allows one to obtain porosity and pore-size distribution. A specific relation is assumed to express tortuosity in function of porosity. This relation has been already used in previous papers for granular media and porous asphalts. It is shown that the obtained pore-size distribution is close to a log-normal distribution so by using log-normal distribution properties, resistivity is then determined. The predicted parameters are compared to direct measurements. The proposed methodology is tested on three bituminous mixtures commonly used for quiet roads.

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.

A global modelling approach of natural ventilation with acoustic and daylighting constraints

ABSTRACT Natural ventilation helps to cool buildings in summer without energy consumption, but its application may be restricted by acoustic and glare constraints. Here, a modelling approach integrating different physical aspects was developed and connected to TRNSYS. Different control strategies of glazed openings were defined and simulations were performed with an office room and a detached family house. We find the natural ventilation potential is largely reduced due to acoustic and visual comfort constraints. An acoustic shutter, which facilitates more frequent window opening during occupancy by decreasing outdoor noise transmission, was equally studied in detail with the help of this modelling approach. The acoustic shutter improves the acoustic and thermal comforts for intelligent control strategy and is an attractive solution to enhance the natural ventilation potential under a moderate noisy environment.

Characterizing a porous road pavement using surface impedance measurement: A guided numerical inversion procedure

This paper deals with a numerical procedure to identify the acoustical parameters of road pavement from surface impedance measurements. This procedure comprises three steps. First, a suitable equivalent fluid model for the acoustical properties porous media is chosen, the variation ranges for the model parameters are set, and a sensitivity analysis for this model is performed. Second, this model is used in the parameter inversion process, which is performed with simulated annealing in a selected frequency range. Third, the sensitivity analysis and inversion process are repeated to estimate each parameter in turn. This approach is tested on data obtained for porous bituminous concrete and using the Zwikker and Kosten equivalent fluid model. This work provides a good foundation for the development of non-destructive in situ methods for the acoustical characterization of road pavements.