Sound Propagation In Porous Materials Research Articles

Predictive model of sound propagation in porous materials: Quantification of fiber nonwoven fabric by material density and fiber diameter

Predictive model of sound propagation in porous materials: Quantification of fiber nonwoven fabric by material density and fiber diameter

Sound propagation in porous materials containing rough tubes

A theoretical model is developed to quantify the influence of surface roughness on sound propagation in porous materials containing rough tubes by extending the Johnson–Champoux–Allard–Lafarge (JCAL) model. The five transport parameters of the JCAL model, including the viscous permeability, thermal permeability, tortuosity, viscous characteristic length, and thermal characteristic length, are calculated by modeling the rough tubes in the porous material as parallel rough tubes having idealized sinusoidal morphologies. The transport parameters obtained using the proposed model are validated by full finite element simulations. Based on these transport parameters, the sound absorption coefficient of the porous material containing idealized rough tubes is calculated, which agrees well with the FE result. The roughness effect is investigated by comparing sound absorption performance between parallel smooth tubes and parallel rough tubes. The existence of tube roughness weakens the thermal effect but dramatically strengthens the viscous effect in sound energy dissipation, resulting in enhanced sound absorption. This work provides fundamental insights on how surface roughness affects the acoustic performance of sound-absorbing porous materials.

Sound propagation in porous materials with annular pores.

Long-wavelength sound propagation in porous materials with annular pores is investigated in this paper. Closed-form analytical expressions for the effective acoustical properties of this type of material were obtained. These are compared with both direct numerical calculations of the effective properties and their calculations obtained by using semi-phenomenological models. Analytical expressions for the input parameters of the latter, i.e., static viscous and thermal permeabilities, viscous and thermal characteristic lengths, and tortuosity, are also provided. The introduced model is successfully validated by comparing its predictions with measured data taken from literature. A parametric analysis that allows highlighting the influence of the different geometrical parameters of porous materials with annular pores on their sound absorptive properties is also presented.

Wave theoretical study on viscous damping and thermal conduction damping of sound propagation in porous materials

Wave theoretical study on viscous damping and thermal conduction damping of sound propagation in porous materials

A design of an impedance tube for teaching acoustic material properties and laboratory techniques

The design and implementation of an adaptable acoustic impedance tube for instructional use will be presented. This system, which was designed for use in a graduate-level laboratory environment, is in accordance with ASTM standard E1050-98. The system is configurable for both horizontal and vertical measurements. Vertical use enables acoustic property measurement of granular materials, allowing characterization of a wide variety of media. The academic content is delivered by engaging students in measurements using the impedance tube. Specific acoustics content objectives include modeling of sound propagation in porous materials and the role of acoustic parameters such as porosity, tortuosity, and flow resistivity in quantifying acoustic behavior of materials. Instructional goals also include mastery of computer based data acquisition and processing. This aspect of modern laboratory practice is a critical part of our graduate acoustics curriculum. Students participated actively in the development of the software used to collect data and calibrate the impedance tube. The system design required the students to solve practical problems such as cutting and positioning of the sample as well as more demanding tasks such as design of a multilayer porous medium with desired acoustic properties.

Acoustic transmission performance of double-wall active sound packages in a tube: Numerical/experimental validations

A method based on the combination of the ( u, p) formulation and the finite element approach is proposed for calculating the transmission loss of double-wall active sound packages with porous-material cores in a rectangular tube. The ( u, p) formulation based on the displacement in the solid phase and the pressure in the fluid phase is rewritten to investigate sound propagation in porous materials, and the coupled boundary conditions and related parameters involved are given. The transmission loss of the double-wall active sound packages excited by a plane wave is calculated via the COMSOL environment with passive and active control. Moreover, a two source-location method is developed to measure the transmission loss of these double-wall active sound packages in a rectangular tube. Some results from numerical examples are shown to be in good agreement with the measured data. It is concluded that with active control, the transmission loss of double-wall active sound packages can be improved by more than 10 dB around resonance frequencies.

Predictive model of sound propagation in porous materials : Application of Biot theory in Kato model

Predictive model of sound propagation in porous materials : Application of Biot theory in Kato model

Predictive model of sound propagation in porous materials : Extension of applicability in Kato model

Predictive model of sound propagation in porous materials : Extension of applicability in Kato model

Predictive model of sound propagation in porous materials : Quantification of fiber nonwoven fabric by material density and fiber diameter

Predictive model of sound propagation in porous materials : Quantification of fiber nonwoven fabric by material density and fiber diameter

Method of designing layered sound absorbing materials

A widely used model for describing sound propagation in porous materials is the Johnson–Champoux–Allard model. This rigid frame model is based on five geometrical properties of the porous medium: resistivity, porosity, tortuosity, and viscous and thermal characteristic lengths. Using this model and with the knowledge of such properties for different absorbing materials, the design of a multiple layered system can be optimized efficiently and rapidly. The overall impedance of the layered systems can be calculated by the repeated application of single layer impedance equation. The knowledge of the properties of the materials involved in the layered system and their physical meaning, allows to perform by computer a systematic evaluation of potential layer combinations rather than do it experimentally which is time consuming and always not efficient. The final design of layered materials can then be confirmed by suitable measurements. A method of designing the overall acoustic absorption of multiple layered porous materials is presented. Some aspects based on the material properties, for designing a flat layered absorbing system are considered. Good agreement between measured and computed sound absorption coefficients has been obtained for the studied configurations. [Work supported by N.S.E.R.C. Canada, F.C.A.R. Quebec, and Bombardier Aerospace.]

Propagation of an ultrasonic impulse in porous media having a rigid frame

The sound propagation in porous materials having a rigid frame filled by air, is well described by the equivalent fluid model where the interactions between fluid and structure are taken into account in the dynamic tortuosity α(ω) and in the dynamic compressibility β(ω) defined by the basic equations ρα(ω)(∂〈v〉/∂t)=−∇〈p〉, (β(ω)/Ka)(∂〈p〉/∂t)=−∇〈v〉. In the domain of the low-frequency approximation, the behavior of these response factors leads to a wave equation with a dissipative term due to the viscous effects. For high frequencies, a porous material becomes a dispersive medium in which the phase and group velocities are functions of frequency; in such a material a transient pulse changes its shape by spreading. A theoretical model of the sound propagation in a dispersive porous material is presented. This problem is posed in the time domain for an ultrasonic pulse in a slab of porous material. A method is proposed for computing the sound field in the medium. This allows one to deduce the transmission and reflection coefficients which are dependent only on the physical parameters of the medium (but not of the incident wave), which is important for inverse problems. The spreading of the transient pulse is calculated for various porous media and compared to experimental data.

Inverse scattering for porous media with rigid frame

The sound propagation in porous materials having a rigid frame filled by air is well described by the equivalent fluid model. In this framework, the interactions between fluid and structure are taken into account in two response factors, the dynamic tortuosity α(ω) and the dynamic compressibility β(ω) defined by the equations

Propagation of Sound in Porous Media: Modeling Sound Absorbing Materials

<i>Propagation of Sound in Porous Media: Modeling Sound Absorbing</i> <i>Materials</i>

The effect of viscous relaxation on sound propagation in porous materials

The Biot theory treats a porous, fluid‐filled material as a composite of two, interpenetrating elastic continua. In the theoretical description this composite nature is reflected by a set of two equations of motion which are coupled via a flow term. It can be shown that this formulation includes viscous relaxation due to a local flow of the pore fluid relative to the frame. This local flow is strongly frequency‐dependent because the geometry of the pores supports flow only for a certain wavelength range in which the fluid flow can follow the excitation by the elastic wave. Accordingly we derive a relaxation time τ which is partly determined by geometrical factors. τ is expressed in terms of permeability, porosity, viscosity, and effective modulus. The viscous relaxation in a porous material can result in a local minimum in the frequency dependence of the reflectivity and a corresponding step in the sound velocity. These and other unusual features predicted by the Biot theory are explained in terms of a viscous relaxation process.

Energy relations in sound propagation in porous materials with rigid skeleton

The paper deals with the determination of the frequency dependence of the acoustic resistance, of the structure factor, the porosity factor and the constant giving whether the process in the propagation of sound in porous materials with a rigid skeleton is isothermal, adiabatic or polytropic. The latter dependence enables a conclusion to be reached on the energy relations during sound propagation in porous materials.