Sound Absorption Model Research Articles

Improving and Optimizing Sound Absorption Performance of Polyurethane Foam by Prepositive Microperforated Polymethyl Methacrylate Panel

Sound absorption performance of polyurethane foam could be improved by adding a prepositive microperforated polymethyl methacrylate panel to form a composite sound-absorbing structure. A theoretical sound absorption model of polyurethane foam and that of the composite structure were constructed by the transfer matrix method based on the Johnson–Champoux–Allard model and Maa’s theory. Acoustic parameter identification of the polyurethane foam and structural parameter optimization of the composite structures were obtained by the cuckoo search algorithm. The identified porosity and static flow resistivity were 0.958 and 13078 Pa·s/m2 respectively, and their accuracies were proved by the experimental validation. Sound absorption characteristics of the composite structures were verified by finite element simulation in virtual acoustic laboratory and validated through standing wave tube measurement in AWA6128A detector. Consistencies among the theoretical data, simulation data, and experimental data of sound absorption coefficients of the composite structures proved the effectiveness of the theoretical sound absorption model, cuckoo search algorithm, and finite element simulation method. Comparisons of actual average sound absorption coefficients of the optimal composite structure with those of the original polyurethane foam proved the practicability of this identification and optimization method, which was propitious to promote its practical application in noise reduction.

Identification of Acoustic Characteristic Parameters and Improvement of Sound Absorption Performance for Porous Metal

Porous metal is widely used in the fields of sound absorption and noise reduction, and it is a critical procedure to identify acoustic characteristic parameters and to improve sound absorption performances. Based on the constructed theoretical sound absorption model and experimental data, acoustic characteristic parameters of the porous metal were identified through the cuckoo search identification algorithm, and their reliabilities were certified through comparing with these labeled parameters and further experimental validation. By adding the microperforated metal panel in front of the porous metal, a composite sound-absorbing structure was formed, which aimed to improve the sound absorption performance of the original porous metal by optimizing the parameters. Finite element simulation and a standing wave tube measurement were conducted to validate the effectiveness and practicability of the optimal composite sound-absorbing structure. Consistencies among theoretical predictions, simulation results, and experimental data proved the effectiveness of the identification and optimization method. When the target frequency ranges were 100–1000 Hz, 100–2000 Hz, 100–3000 Hz, and 100–4000 Hz. Actual average sound absorption coefficients of the optimal composite structures were 0.5154, 0.6369, 0.6770, and 0.7378, respectively, which exhibited the obvious improvements with a tiny increase in the occupied space and a small addition in weight.

Mathematical model of sound absorption by lungs with acoustic stimulation of the respiratory system

According to the results of theoretical and experimental analysis of the characteristics of the propagation of acoustic oscillations in the respiratory system, it is necessary to determine the resonant frequency of the respiratory tract to increase the vital capacity of the lungs by opening back-up alveoli by acoustic stimulation of the respiratory system, and then to affect the respiratory system maximum sound absorption range (at a level of ±3 dB from the maximum value of the absorption coefficient).

Mathematical Model of Sound Absorption by Lungs with Acoustic Stimulation of the Respiratory System.

According to the results of theoretical and experimental analysis of the characteristics of the propagation of acoustic vibrations in the respiratory system, it is necessary to determine the resonant frequency of the respiratory tract to increase the vital capacity of the lungs by opening reserve alveoli by acoustic stimulation of the respiratory system and then to affect the respiratory system with scanning tonal sounds in the maximum sound absorption range (at a level of ±3 dB of the maximum absorption coefficient value).

Optimization and Validation of Sound Absorption Performance of 10-Layer Gradient Compressed Porous Metal

Sound absorption performance of a porous metal can be improved by compression and optimal permutation, which is favorable to promote its application in noise reduction. The 10-layer gradient compressed porous metal was proposed to obtain optimal sound absorption performance. A theoretical model of the sound absorption coefficient of the multilayer gradient compressed porous metal was constructed according to the Johnson-Champoux-Allard model. Optimal parameters for the best sound absorption performance of the 10-layer gradient compressed porous metal were achieved by a cuckoo search algorithm with the varied constraint conditions. Preliminary verification of the optimal sound absorber was conducted by the finite element simulation, and further experimental validation was obtained through the standing wave tube measurement. Consistencies among the theoretical data, the simulation data, and the experimental data proved accuracies of the theoretical sound absorption model, the cuckoo search optimization algorithm, and the finite element simulation method. For the investigated frequency ranges of 100–1000 Hz, 100–2000 Hz, 100–4000 Hz, and 100–6000 Hz, actual average sound absorption coefficients of optimal 10-layer gradient compressed porous metal were 0.3325, 0.5412, 0.7461, and 0.7617, respectively, which exhibited the larger sound absorption coefficients relative to those of the original porous metals and uniform 10-layer compressed porous metal with the same thickness of 20 mm.

Low Frequency Sound Absorption by Optimal Combination Structure of Porous Metal and Microperforated Panel

The combination structure of a porous metal and microperforated panel was optimized to develop a low frequency sound absorber. Theoretical models were constructed by the transfer matrix method based on the Johnson—Champoux—Allard model and Maa’s theory. Parameter optimizations of the sound absorbers were conducted by Cuckoo search algorithm. The sound absorption coefficients of the combination structures were verified by finite element simulation and validated by standing wave tube measurement. The experimental data was consistent with the theoretical and simulation data, which proved the efficiency, reliability, and accuracy of the constructed theoretical sound absorption model and finite element model. The actual average sound absorption coefficient of the microperforated panel + cavity + porous metal + cavity sound absorber in the 100–1800 Hz range reached 62.9615% and 73.5923%, respectively, when the limited total thickness was 30 mm and 50 mm. The excellent low frequency sound absorbers obtained can be used in the fields of acoustic environmental protection and industrial noise reduction.

Impulse Response Analysis Method considering Sound Absorption Model and Auralization using VR Technology

Impulse Response Analysis Method considering Sound Absorption Model and Auralization using VR Technology

On the accuracy and optimization application of an axisymmetric simplified model for underwater sound absorption of anechoic coatings

The finite element method (FEM) is commonly used to analyze the underwater acoustic performances of rubbery coatings due to its flexibility to model scatterers of complex geometric dimensions. However, its calculation efficiency is always denounced as a drawback for its application on optimization design where a large number of repeated calculations should be fulfilled. In this paper, the accuracy of an axisymmetric simplified model, to model the unit cell as circular cross section, is systematically discussed by respectively comparing the absorption coefficients with those calculated by the square and hexagonal models under different punching rates of the cavities. Results show that the axisymmetric model can better describe the sound absorption of the coating with a hexagonal arrangement; however, it may cause comparative large deviations to describe the results of the coating with a square arrangement under not only large punching rates but also small punching rates. This phenomenon can be related to the different boundary differences between two arrangements of cavities and can be relieved when the rubber material possesses a large loss factor. Then, a shape optimization of the embedded cavity using the axisymmetric simplified model and a genetic algorithm has been done to achieve optimal sound absorption in 1–20 kHz. Compared with the coating with isochoric cylindrical cavities, the optimized coating can achieve better sound absorption in low frequencies due to the larger pore-aperture radius of the optimized cavity than that of the isochoric cylindrical cavity. The frequency-dependent parameters of the rubber material play an important role for the broadband high absorption of the optimized coating.

Sustainable sound absorbers obtained from olive pruning wastes and chitosan binder

A significant interest in sustainable sound absorbing materials is fostering many researches on the use of recycled and vegetable products, that normally would have been sent to wastes, as compounds to obtain new building materials. One key issue when preparing new composite materials is the choice of the binder, which, in many cases, may significantly reduce the sustainability of the product by introducing synthetic and plastic elements. In the present paper olive tree pruning wastes bounded with chitosan are investigated to obtain sound absorbing materials. Experimental results showed that absorption coefficients as high as 0.9 can be obtained above 1 kHz using a 50 mm sample, and that a very good agreement with the phenomenological model for sound absorption through a rigid frame is obtained, suggesting that the model can be conveniently used to further improve the sound absorption characteristics of the samples.

A model for the sound absorption coefficient of multi-layered elastic micro-perforated plates

In this paper, a model for the sound absorption coefficient of multi-layered elastic micro-perforated plates (MPPs) in an impedance tube is developed using an analytical approach. Under the plane wave condition, a low-frequency solution is derived by including the symmetric modes of the plate vibration and the sound pressure field. The sound absorption model derived in this study can handle multi-layered structures composed of any combination of thin elastic plates with or without micro-perforations and rigid MPPs. The effects of the parameters of the plate thickness, hole diameter, perforation ratio, cavity depth, and damping on the sound absorption capabilities are described. For a single MPP, when the perforation ratio is very small, it is observed that the combined effect of the elastic behavior and micro-perforation results in a significant increase of the sound absorption coefficient compared to that of a rigid MPP. However, when the perforation ratio is order of a few percent, the effect of the elastic behavior is negligible compared to that of micro-perforations. Some guidelines for selecting optimum parameters to achieve the maximum average sound absorption coefficient for a given frequency band are discussed for double- and triple-elastic MPPs. It is important to ensure that the perforation ratio of the last MPP is small such that the elastic behavior is dominant, while for the first MPP (and for the second MPP in the triple configuration), the elastic behavior should not be dominant. In addition, maintaining equal cavity depths is beneficial for a high average sound absorption coefficient.

Prediction of tire-pavement noise of porous asphalt mixture based on mixture surface texture level and distributions

An accurate tire-pavement noise prediction model is highly needed by transportation agencies and pavement designers during the porous asphalt mixture design to reduce the tire-pavement noise which has been recognized as a dominant contributor to the overall traffic noise. In this paper, the surface texture level and distributions of porous asphalt mixture are acquired by a recently developed program named as 2-Dimensional Image Texture Analysis Method (2D-ITAM). The acoustic absorption coefficient of porous asphalt mixture is calculated using a proposed sound absorption model based on the micro-structure of porous asphalt mixture. Also, a prediction model correlating the tire-pavement noise level with macro-texture and short wavelength of mega-texture of pavement is established using a multivariate non-linear regression analysis. This prediction model is validated through laboratory experiment demonstrating its effectiveness of predicting the tire-pavement noise level. The model is anticipated to serve as an improved tool which could be considered by practitioners in an optimized porous asphalt mixture design incorporating the evaluation of noise produced by asphalt pavement.

Micro-perforated acoustic metamaterial with honeycomb-corrugation hybrid core for broadband low frequency sound absorption

A novel acoustic metamaterial is proposed by making micro-perforations on both the top facesheet and the corrugate plates of sandwich plate with honeycomb-corrugation hybrid core. The hybrid-cored metamaterial is ultra-lightweight, occupies a small volume, and exhibits excellent mechanical properties and good low-frequency sound absorption property. Based on the classical Maa theory of thin plates with micro-perforations, a theoretical model of sound absorption is established for the proposed metamaterial. The method of finite elements is subsequently used to validate the model, showing that their good agreement is achieved. Physical mechanism behind the energy dissipation in each sub-structure of the metamaterial is explored. It is found that the main route of energy dissipation is via viscous effect at the micro-perforation, and thermal dissipation is negligible. The influence of key geometrical parameters, such as upper facesheet thickness, perforation diameter and corrugated plate thickness, on sound absorption is systematically investigated. The present results are helpful for designing multifunctional lightweight materials/structures for simultaneous load-bearing, energy absorption and noise control.

An acoustic approach to assess natural gas quality in real time

The natural gas industry needs fast and robust techniques to monitor the quality of the natural gas, if possible during the flow measurement process. A potential technique relies on extrapolating the dynamic specific heat of the gaseous mixture via measurements at a few frequencies (Petculescu and Lueptow, Phys. Rev. Lett. 94, 238301 (2005); Sensors and Actuators B: Chemical 169, 121–127 (2012)). At the core of this approach lies a first-principles model for sound absorption and dispersion in polyatomic gases. We will show and discuss the applicability and limitations of this potential technique to predicting the content of nitrogen, oxygen, carbon dioxide, and water in natural gas.

Acoustic Models for Cooled Helmholtz Resonators

Helmholtz resonators are commonly used to damp thermoacoustic oscillations in aeroengine and gas turbine combustors. In practice, the Helmholtz resonator is often maintained at a cooler temperature than the combustor, but this tends to be neglected when modeling. In this work, we derive an analytical model for both the acoustic damping and the effect on the combustor thermoacoustics of Helmholtz resonators for which the volume is at a different temperature to the combustor. The energy conservation equation based on stagnation enthalpy, together with the mass and momentum conservation equations, is incorporated into a linear Helmholtz resonator sound-absorption model. These are coupled with linear wave-based models for the plane acoustic waves in the system to which the Helmholtz resonator is attached: here, a combustor. The temperature difference is found to generate an entropy wave that advects downstream of the resonator (and may generate further acoustic waves if accelerated) and to change the acoustic damping near the resonant frequency. This model for the Helmholtz resonator acoustics is then incorporated into a low-order network model for combustor thermoacoustics. The importance of capturing the effect of the Helmholtz resonator temperature difference on the overall thermoacoustic modes is clearly demonstrated.

Sensitivity analysis of a sound absorption model with correlated inputs

Sound absorption in porous media is a complex phenomenon, which is usually addressed with homogenized models, depending on macroscopic parameters. Since these parameters emerge from the structure at microscopic scale, they may be correlated. This paper deals with sensitivity analysis methods of a sound absorption model with correlated inputs. Specifically, the Johnson-Champoux-Allard model (JCA) is chosen as the objective model with correlation effects generated by a secondary micro-macro semi-empirical model. To deal with this case, a relatively new sensitivity analysis method Fourier Amplitude Sensitivity Test with Correlation design (FASTC), based on Iman's transform, is taken into application. This method requires a priori information such as variables' marginal distribution functions and their correlation matrix. The results are compared to the Correlation Ratio Method (CRM) for reference and validation. The distribution of the macroscopic variables arising from the microstructure, as well as their correlation matrix are studied. Finally the results of tests shows that the correlation has a very important impact on the results of sensitivity analysis. Assessment of correlation strength among input variables on the sensitivity analysis is also achieved.

Modeling of sound absorption based on the fractal microstructures of porous fibrous metals

A fractal micro-structural acoustic model for sound absorption of sintered fibrous metals was established by adopting the fractal geometric theory. Based on the pore area fractal dimension and the tortuosity fractal dimension, the dynamic airflow resistivity and the sound absorption coefficient were calculated. The pore area fractal dimension is related to the number of the micro-pores of sintered fibrous metals, and the tortuosity fractal dimension describes the sinuosity of sound propagation pathway. The two fractal dimensions were determined by the theoretical calculations as well as the box-counting method. The fractal acoustic model was verified by comparing the specific surface acoustic impedance and the sound absorption coefficient with experimental measurements, with good agreements achieved. The results were also compared with those of Biot-Allard model, which demonstrates that the calculated values of the fractal acoustic model fit the tested data better than Biot-Allard model in high frequency range. In addition, the influences of the fractal dimensions on the specific surface acoustic impedance and the effect of thickness and fractal dimension on the sound absorption coefficient were presented and discussed. Results indicate that the acoustic performance of sintered fibrous metals are significantly affected by the fractal dimensions.

Application and Analysis of the New Functional Materials of Foam Aluminum

As a typical metal foams materials, aluminum foam which is a new type of functional materials has excellent properties of sound absorption and damping. In view of its complex internal micro-structure, on the basis of microcosmic cell theory, the paper set a BCC model of sound absorption of aluminum foam that can control its structure and size parameters such as porosity and aperture in micro-structural. The paper gets parameter factors of aluminum foam structure and size and studies its effect to sound absorption of aluminum foam though micro-modeling and proceeds experiment verification. Its turn out that this BCC model can apply to the research of aluminum foam sound absorption, and it can control the sound absorption of aluminum foam through controlling the microcosmic size of aluminum foam cell.

A simplistic unit cell model for sound absorption of cellular foams with fully/semi-open cells

Abstract We present a simplistic yet accurate unit cell model of sound absorption for highly porous foams having either fully-open or semi-open cells. Employing an idealized periodic cubic unit cell to mimic the foam topology, we establish an analytical model for predicting the sound absorption coefficient of the foam. Analytical links between key non-acoustic parameters (viscous permeability and flow tortuosity) and cellular topological characteristics are also established. For fully-open foams, the model requires only two morphological parameters, porosity and pore window size, significantly reducing the complexity of sound transport modeling. For semi-open foams, an additional parameter, open-pore rate representing the influence of thin membrane covering on pore window, is introduced. The analytical model predictions are compared with existing experimental data and numerical simulation results for polyurethane foams, with good agreement achieved.

Sound Absorption Analysis of Micro Perforated Panel with Ladder Change Type Cross Section

A kind of variable cross section micro perforated panel (MPP) with ladder micro porous is introduced in this paper. Based on the double layers MPP theory and neglected the effect of cavity between two layers of MPP, sound absorption model of MPP with ladder micro porous is established. Numerical simulations are carried out to predict the sound absorption of MPP with ladder micro porous. The predicted results show good agreement with measurements. Through analyzing the weight to the sound-absorbing of orifice size, this study also points out that the smaller orifices play the major role in the sound absorption.

IJARCCE - Computer and Communication Engineering

This paper reports the comparative study of acoustic wave absorption carried out by means of modeling in MATLAB. The results of simulation have been compared with the practically measured values in the Arabian Sea near Goa and Atlantic Ocean. The model has been used to determine sound absorption for given values of depth (D), salinity (S), temperature (T), pH, and acoustic wave transmitter frequency (f). The sim model of sound absorption can predict the coefficient of absorption at any place on the earth.