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Holes Effects in Plane Periodic Multilayered Viscoelastic Media

Open Journal of Acoustics 2013年第3期3卷 80-87页

作者： emmanuel siryabe Guy-Edgar Ntamack Pierre Maréchal Département de Physique Groupe de Mécanique et des Matériaux (GMM) Université de Ngaoundéré Ngaoundéré Cameroun Laboratoire Ondes et Milieux Complexes (LOMC) UMR 6294 CNRS Université du Havre Le Havre France

This work deals with the study of the reflection and transmission properties of plane periodic structures composed of N periods (1 ≤ N ≤ 3) in the MHz frequency range. The period consists of two bounded plates presenting a high acoustic impedance contrast one of which is in aluminum, the other is in polyethylene. The longitudinal and transversal attenuations are considered in polyethylene and neglected in aluminum. We take into account the case of emerging holes in the polyethylene layer. Simulations are based on the stiffness matrix method (SMM) developed by Rokhlin. When attenuation is considered in polyethylene, the reflection coefficients are different depending on the insonification side. The comparison of results without or with holes configurations are performed and showed that throughout holes allow the rapid observation of forbidden bands. The attenuation of the whole multilayer is also determined.

关键词： Periodic Structures Holes Porosity Phononic Crystal Forbidden Bands Transmission Reflection Attenuation

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On the Simulation of the Influence of Defects on Immersed Plane Periodic Multilayer Viscoelastic Media

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Open Journal of Acoustics 2021年第2期11卷 17-30页

作者： Massaï Hatoumva emmanuel siryabe Pierre Marechal Guy Edgar Ntamack Gambo Betchewe Faculté des Sciences Département de Physique Université de Maroua Maroua Cameroon Safran Helicopter Engines Groupe Evaluation Non Destructive Bordes France Laboratoire Ondes et Milieux Complexes (LOMC) UMR 6294 CNRS Université du Havre Le Havre France Groupe de Mécanique Matériaux et Acoustique P.B: 454 Département de Physique Faculté des Sciences Université de Ngaoundéré Ngaoundéré Cameroon

This work deals with the study of a plane periodic multilayer structure in which the elementary stack consists of two plates in contact: one in aluminum (AL) and the other one in polyethylene (PE). These isotropic materials, present a high acoustic impedance contrast. The attenuation of the longitudinal and transverse waves is taken into account in the polyethylene but neglected in the aluminum plate. The effect of different defects is analyzed. Firstly, we focus on the effect of the presence of grease inclusion in the polyethylene plate (considering the two plates of the elementary stack in perfect contact). Secondly, the effect of disbond simulated by the insertion of a thin Teflon layer between the interfaces of the two layers constituting the elementary stack of the multilayer structure is investigated. Finally, the effect of the stacking sequences of the multilayer is analyzed. In order to obtain the effective acoustic parameters of polyethylene layer, allowing to evaluate the reflection and transmission coefficients using the stiffness matrix method developed by Rokhlin et al., four homogenization models are analyzed, then the best one to our configuration is chosen. The comparison of the simulation results is carried out.

关键词： Reflection Coefficients Transmission Coefficients Defects Multilayer Peri-odic Structure

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High Temperature Effect on Absorption Coefficient of M-MPPs and Sandwich Structures Coupled with MPPs

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Open Journal of Acoustics 2020年第1期10卷 1-18页

作者： Daliwa Joseph Bainamndi emmanuel siryabe Serge Yamigno Doka Guy Edgar Ntamack Groupe de Mé canique des Mat&#233 riaux et Acoustique (GMMA) Universit&#233 de Ngaoundé ré Ngaound&#233 ré Cameroun Safran Helicopter Engines Groupe Evaluation Non Destructive Bordes France

This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a frequency range from 10 to 3000 Hz. The structure is backed with a rigid wall which can either be Aluminium or Al-Alloy used in aeronautic or automobile. The wave propagation in porous media is addressed using Johnson Champoux Allard model (JCA). The FEM model developed using COMSOL Multiphysics software makes it possible to predict the acoustic absorption coefficient in multilayer microperforated panels (M-MPPs) and sandwich structure. It is shown that, when structures made by MPPs or sandwich materials are submitted to high temperature, the absorption performance of the structure is strongly modified in terms of amplitude and width of the bandgap. For application in sever environment (noise reduction in engines aircrafts), Temperature is one of the parameters that will most influence the absorption performance of the structure. However, for application in the temperature domain smaller than 50?C (automotive applications for example), the effect of temperature is not significant on absorption performance of the structure.

关键词： Absorption Coefficient Finite Element Model Microperforated Plates Poroelastic Core Sandwich Structures

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