arXiv subjects

Philippe Leclaire

Publications and source records attributed to Philippe Leclaire.

5 recordsLinked to original sources

arXiv2019

Acoustic Probing of the Jamming Transition in an Unconsolidated Granular Medium

Experiments with acoustic waves guided along the mechanically free surface of an unconsolidated granular packed structure provide information on the elasticity of granular media at very low pressures that are naturally controlled by the gravitational acceleration and the depth beneath the surface. Comparison of the determined dispersion relations for guided surface acoustic modes with a theoretical model reveals the dependencies of the elastic moduli of the granular medium on pressure. The experiments confirm recent theoretical predictions that relaxation of the disordered granular packing through non-affine motion leads to a peculiar scaling of shear rigidity with pressure near the jamming transition corresponding to zero pressure. Unexpectedly, and in disagreement with the most of the available theories, the bulk modulus depends on pressure in a very similar way to the shear modulus.

physics.class-ph↗

arXiv2009

On the variations of acoustic absorption peak with flow velocity in Micro-Perforated Panels at high level of excitation

The acoustic behavior of micro-perforated panels (MPP) is studied theoretically and experimentally at high level of pressure excitation. A model based on Forcheimer's regime of flow velocity in the perforations is proposed. This model is valid at relatively high Reynolds numbers and low Mach numbers. The experimental method consists in measuring the acoustical pressure at three different positions in an impedance tube, the two measurement positions usually considered in an impedance tube and one measurement in the vicinity of the rear surface of the MPP. The impedance tube is equipped with a pressure driver instead of the usual loudspeaker and capable of delivering a high sound pressure level up to 160 dB. Several MPP specimens made out of steel and polypropylene were tested. Measurements using random noise or sinusoidal excitation in a frequency range between 200 and 1600 Hz were carried out on MPPs backed by air cavities. It was observed that the maximum of absorption can be a positive or a negative function of the flow velocity in the perforations. This suggests the existence of a maximum of absorption as a function of flow velocity. This behavior was predicted by the model and confirmed experimentally.

physics.flu-dyn↗

arXiv2009

Experimental investigation of perforations interactions effects under high sound pressure levels

Most models for predicting the acoustic response of perforated panels are based on the assumption that there is no interactions between the holes. The common way of taking into account the perforates effects is the use of Fok's functions. The few papers that deal with these effects study the case of low sound pressure levels. This paper investigates the Holes Interaction Effects (HIE) of perforated and micro-perforated panels when submitted to high sound pressure levels. Analysis of the data yields to the fact that even with HIE, the nonlinear reactance dependency with velocity is very slight. The HIE can provide good absorption of the perforated panel backed by an air cavity at low and high sound pressure levels if the holes positions are well configured. Perforated panels of holes diameters less than 2 millimeters were built out of steel with different interstices (distance between two adjacent holes) and tested. Experimental results (performed with an impedance tube) in the cases of interaction are done and compared with the exact cases of no interactions. The results can be used for designing optimal perforated panels for ducts silencers for instance.

physics.flu-dyn↗

arXiv2006

Use of specific Green's functions for solving direct problems involving a heterogeneous rigid frame porous medium slab solicited by acoustic waves

A domain integral method employing a specific Green's function (i.e., incorporating some features of the global problem of wave propagation in an inhomogeneous medium) is developed for solving direct and inverse scattering problems relative to slab-like macroscopically inhomogeneous porous obstacles. It is shown how to numerically solve such problems, involving both spatially-varying density and compressibility, by means of an iterative scheme initialized with a Born approximation. A numerical solution is obtained for a canonical problem involving a two-layer slab.

physics.comp-ph↗

arXiv2006

Acoustic wave propagation in a macroscopically inhomogeneous porous medium saturated by a fluid

The equations of motion in a macroscopically inhomogeneous porous medium saturated by a fluid are derived. As a first verification of the validity of these equations, a two-layer rigid frame porous system considered as one single porous layer with a sudden change in physical properties is studied. A simple wave equation is derived and solved for this system. The reflection and transmission coefficients are calculated numerically using a wave splitting-Green's function approach (WS-GF). The reflected and transmitted wave time histories are also simulated. Experimental results obtained for materials saturated by air are compared to the results given by this approach and to those of the classical transfer matrix method (TMM).

physics.flu-dyn↗