There exists diversity when it comes to porous materials either artificial or natural. Sintered, steel wool, perforated materials and fiber metal are among the porous materials that have been increasingly used in automotive noise control. Following the diversity and variety of porous material characteristics, the study of porous media has proved to be wide and interesting. The review begins with outlining and comparing the models that are intended to be used in predicting the fundamental acoustical characteristics that are applicable in automotive. The paper introduces both the theoretical, empirical and numerical modeling and demonstrates how the models are used to determine the acoustic characteristics of porous materials. The analytical models indicate that the solid constituents of porous material are rigid and the fluid constituents are similar to that of a homogenous isotropic fluid that has been modified. The review also considers the acoustical characterization of porous materials and goes further to look at the porous materials modeling while having particular interests on porous materials that are elastic. The fundamental characteristics of porous materials are then illustrated using computational and experimental examples . Introduction In automotive, absorptive materials have various applications in different locations. Absorber pads can serve effectively in several locations such as in the door panel, pillar trim, headliner and bellow the carpet. Porous materials like fibers and foams are normally used in such applications. There acoustic characteristics enable them to serve as absorbers. It is the viscous losses that results in the conversion of energy to heat while sound waves navigate through the fibers or pores that are interconnected in the material. A porous material that is bonded with a barrier that is non-porous conducts the sound energy in waves that are in form of structure-borne. The characteristics which have the desirable influence on this wave form are the structural loss and bulk stiffness (Allard, 1993,p. 56). With reference to automotive applications, absorption is preferred at frequencies that are lower while the weight and thickness are to be limited. Porous materials with air flows resistance that are specific yet different have been identified as to achieve the results that are desired. However, the action of decreasing or increasing the given air flow resistance in order to achieve low frequency results affect high frequency performances. The review thus gives a presentation of a number of different material’s studies which illustrate such behavior. Several models such as the penalization approach demonstrate this behavior by simulating fluids inside and porous regions surrounding the obstacle. Such models are easy to implement and do not need a body fitting or a specific interface treatment. The models are successfully used in the introduction of new passive control methods that entail the implementation of a porous layer in between the fluid and the blue-body so as to change the characteristics of the boundary layer. Such a passive control model results in regularization that is drastic especially when it comes to high Reynolds numbers (Allard, 1992, p. 3349). Porous materials come in two phases, namely; the fibrous solid component termed as the frame and the interstitial fluid located in the pores resulting from the frame. Following their low density, porous materials cannot be generally used to make barriers but are commonly applied in the making of materials that absorb
This review mainly concerns itself with the acoustic characteristics of porous materials in various automotive applications. The porous materials in question include; artificial and natural fiber, porous material and polymer foams…
Several models have thus been proposed to easily predict the acoustical behaviour of poroelastic materials. These models often use various physical parameters that are based on definitions from theory or measurements from experiments (Seppi 2009). However, the accurate prediction or characterization of poroelastics is still a difficult issue, especially in the case of numerical simulations of materials having complex geometries, due to limitations of convergence and time taken for computation (Seppi).
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8 pages (2000 words)Research Paper
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