Validity of the One-Dimensional Limp Model for Porous Media

A straightforward criterion for determining the validity ofthe limp model validity for porous materials is addressed here. The limp model is an “equivalent fluid” model which gives a better description of porous behavior than the well known “rigid frame” model. It is derived from the poroelastic Biot model, assuming that the frame has no bulk stiffness. A criterion is proposed for identifying the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI, based on porous material properties. The critical values of FSI under which the limp model can be used are determined using 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.

Coupling FEM, Bloch Waves and TMM in Meta Poroelastic Laminates

The propagation of airborne plane waves in the pres- ence of a meta poroelastic laminate, that is a poroelas- tic matrix coated with thin elastic layers at its facings 5 and periodically-embedded with inclusions, is studied. Using the Finite Element Method (FEM) only would result in a drastic increase of the degrees of freedom due to the fine mesh required to account for the very thin coatings. Here, the approach relies on: the Bloch 10 wave expansion of the fields in air; the modal Trans- fer Matrix Method to account for the coatings; and the coupling with the FEM model of the poroelas- tic matrix and the resonant inclusions. The model is developed for reflection and transmission problems 15 and it can account for coatings with multiple layers. The procedure induces the addition of the Bloch co- efficients in the FEM’s linear system at a negligible additional computational cost. It is applied to the meta poroelastic laminates with poroelastic inclusions 20 and rubber shell inclusions. The results are compared with those from the Multiple Scattering Theory and an excellent agreement between the methods is found. The approach offers a numerically-efficient way to ac- count for coatings applied to meta poroelastic layers, 25 and finds applications in industrial prototypes where coatings are widely used

Biot Effects for Sound Absorbing Double Porosity Materials

International audienc

A normal modes technique to reduce the order of poroelastic models: application to 2D and coupled 3D models

International audienc

Validity of the One-Dimensional Limp Model for Porous Media

A straightforward criterion for determining the validity ofthe limp model validity for porous materials is addressed here. The limp model is an “equivalent fluid” model which gives a better description of porous behavior than the well known “rigid frame” model. It is derived from the poroelastic Biot model, assuming that the frame has no bulk stiffness. A criterion is proposed for identifying the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI, based on porous material properties. The critical values of FSI under which the limp model can be used are determined using 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.

Absorption of sound by porous layers with embedded periodic arrays of resonant inclusions

The aim of this work is to design a layer of porous material with a high value of the absorption coefficient in a wide range of frequencies. It is shown that low frequency performance can be significantly improved by embedding periodically arranged resonant inclusions (slotted cylinders) into the porous matrix. The dissipation of the acoustic energy in a porous material due to viscous and thermal losses inside the pores is enhanced by the low frequency resonances of the inclusions and energy trapping between the inclusion and the rigid backing. A parametric study is performed in order to determine the influence of the geometry and the arrangement of the inclusions embedded in a porous layer on the absorption coefficient. The experiments confirm that low frequency absorption coefficient of a composite material is significantly higher than that of the porous layer without the inclusions

Geometric Simplification of a Wooden Building Connector in Dynamic Finite Element Model

International audienceThe characteristics of boundary conditions of a wood joist floor are critical in the dynamic behavior at low frequency. Furthermore, the properties of junctions between floor and wall are determinant in the vibrationalenergy transfer (flanking transmission). For this floor system, the junction between the wall and the joist frameis usually done by wood connectors which present a relatively complex form : folded sheet plate with nails orscrews fixing). The aim of this study is to replace the complete model of the connector by an equivalent elementin term of transfer functions. The identification of the equivalent parameters is build jointly by numeric analysisand experimental study. In the vibro-acoustic domain, this simplified model reduces the number of vertices, andthe resolution time of CAD model building. This simplified structural model can thus be coupled to the acousticsof the adjacent rooms

Enhancing the absorption coefficient of a backed rigid frame porous layer by embedding circular periodic inclusions

International audienc

Linear and nonlinear Biot waves in a noncohesive granular medium slab: Transfer function, self-action, second harmonic generation

International audienc

Prediction of sound reflection by corrugated porous surfaces

International audienc