11 research outputs found
General method to retrieve all effective acoustic properties of fully-anisotropic fluid materials in three dimensional space
Anisotropic fluid materials are of growing interest with the development of
metamaterials and transformation acoustics. In the general three-dimensional
case, such materials are characterized by a bulk modulus and a full symmetric
matrix of density. Here, a method is presented to retrieve the bulk modulus and
all six components of the density matrix from a selected set of six incident
plane waves impinging on a layer of the material. From the six components of
the density tensor, the three principal directions and the three principal
densities of the material are recovered. The approach relies on the analytical
expression of the reflection and transmission coefficients derived from a state
vector analysis. It results in simple, closed-form, and easily-implementable
inverse relations for the material parameters. As an illustration, the case of
sound propagation through an orthorhombic lattice of overlapping air-filled
ellipsoids is considered, the effective complex and frequency-dependent bulk
modulus and density matrix of which are derived from homogenization cell
problems and account for viscothermal losses. The retrieval method is then
applied to the homogenized layer and results bear testament to its robustness
to extract accurately all seven material parameters. This makes possible the
characterization and design of anisotropic fluid materials in three dimensions
Acoustic wave propagation in effective graded fully anisotropic fluid layers
International audienc
Optimally graded porous material for broadband perfect absorption of sound
International audienceThis article presents a numerical optimization procedure of continuous gradient porous layer properties to achieve perfect absorption under normal incidence. This design tool is applied on a graded porous medium composed of a periodic arrangement of ordered unit cells allowing to link the effective acoustic properties to its geometry. The best micro-geometry continuous gradient providing the optimal acoustic reflection and/or transmission is designed via a nonlinear conjugate gradient algorithm. The acoustic performances of the so-designed continuous graded material are discussed with respect to the optimized homogeneous, i.e. non-graded, and monotonically graded material. The numerical results show a shifting of the perfect absorption peak to lower frequencies or a widening of the perfect absorption frequency range for graded materials when compared to uniform ones. The results are validated experimentally on 3D-printed samples therefore confirming the relevance of such gradient along with the efficiency of the control of the entire design process. a) [email protected]
Broadband acoustic attenuation with multiresonant lossy three- dimensional sonic crystal for the train noise reduction.
International audienc
Graded and Anisotropic Porous Materials for Broadband and Angular Maximal Acoustic Absorption
The design of graded and anisotropic materials has been of significant interest, especially for sound absorption purposes. Together with the rise of additive manufacturing techniques, new possibilities are emerging from engineered porous micro-structures. In this work, we present a theoretical and numerical study of graded and anisotropic porous materials, for optimal broadband and angular absorption. Through a parametric study, the effective acoustic and geometric parameters of homogenized anisotropic unit cells constitute a database in which the optimal anisotropic and graded material will be searched for. We develop an optimization technique based on the simplex method that is relying on this database. The concepts of average absorption and diffuse field absorption coefficients are introduced and used to maximize angular acoustic absorption. Numerical results present the optimized absorption of the designed anisotropic and graded porous materials for different acoustic targets. The designed materials have anisotropic and graded effective properties, which enhance its sound absorption capabilities. While the anisotropy largely enhances the diffuse field absorbing when optimized at a single frequency, graded properties appear to be crucial for optimal broadband diffuse field absorption
Acoustic wave propagation in graded effective anisotropic fluid layers under oblique incidence
International audienc
Acoustic wave propagation in effective graded fully-anisotropic fluid layers
International audienc
Non-locality of the Willis coupling in fluid laminates
The closed form expressions of the effective properties in periodic fluid laminates are
derived thanks to the Padé approximation of the transfer matrix. A second-order Taylor
expansion of the transfer matrix elements exhibits Willis coupling. This coupling is the
sum of a local term and a nonlocal term. The nonlocal term arises from the apparent
bulk modulus in quasi one-dimensional problems. The nonlocality directly impacts the
governing equations modeling the acoustic wave propagation in these Willis materials,
which then involve convolution products in space. As an example, a two-orthotropic
porous material laminate is considered. The theoretically derived effective properties
and scattering coefficients are found in excellent agreement with those numerically
calculated. The Willis coupling widens the frequency range of validity and accuracy of
the effective properties and thus of the calculated scattering coefficients when compared
to classical homogenization results for which the Willis coupling is absent. This widening
mostly relies on the effect of Willis coupling on the impedance of the fluid laminate. The
effective properties are finally derived for a general laminate
Numerical optimization method of continuously graded porous material
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