Search

Addressing the demand for low-frequency noise control in ships and aiming to overcome the limitations imposed by the mass law of traditional materials, a sandwich thin-plate acoustic metamaterial (SPAM) was developed in this study. This structure is characterized by its simplicity and superior sound insulation performance. A sound insulation test was conducted to validate the exceptional low-frequency acoustic suppression capability of SPAM, and the effectiveness of the analytical model was also demonstrated. Subsequently, based on this model, a sensitivity analysis of the sound insulation characteristics of the SPAM relative to structural parameters was carried out. For the optimization process, the Logistic-Sine fusion chaotic mapping was employed to refine the dung beetle optimizer (DBO), enhancing the initial population distribution. The improved dung beetle optimizer (IDBO) was then used to further optimize and elevate the sound insulation performance of the SPAM. The outcomes indicate that the IDBO boasts superior optimization proficiency and accelerated convergence, while the optimized SPAM exhibits more remarkable sound insulation capabilities. Within the frequency range of 100–315 Hz, the average sound transmission loss (STL) has increased by 11.94 dB when compared to the pre-optimization values. [ABSTRACT FROM AUTHOR]

Compared with insulating glass, tempered vacuum glass (TVG) is not only safer, but also more effective in sound insulation and heat insulation. In this paper, for the sound insulation performance of tempered vacuum glass, the acoustic wave transfer model of TVG is established, and the equation for sound insulation is deduced by using wave transfer method (WTM). Then the actual sound insulation loss of tempered vacuum glass was tested based on the method of reverberation room and anechoic room. finally, the sound insulation loss of tempered vacuum glass under different factors is analyzed. The results show that the theoretical calculation results are consistent with the experimental results about the general change trend of the sound insulation. The thicker the glass, the better the sound insulation. The more the supports in vacuum layer of tempered vacuum glass, the smaller the sound insulation loss. The thickness of the vacuum layer has different sound insulation loss at different frequencies. When the thickness of the vacuum layer is about 0.25 mm, tempered vacuum glass has the best sound insulation performance. This research will have important guiding significance for the selection of building sound insulation glass and the design of sound insulation glass. [ABSTRACT FROM AUTHOR]

Abstract Eco-friendly natural fiber composites, such as basalt fiber composites, are gaining traction in material science but remain vulnerable to environmental degradation. This study investigates the mechanical and vibrational properties of quasi-isotropic basalt fiber composites subjected to aging in two different environments: ambient (30 ºC) and subzero (-10 ºC), both in distilled water until moisture saturation. Aged specimens absorbed 8.66% and 5.44% moisture in ambient and subzero conditions, respectively. Mechanical testing revealed significant strength reductions in tensile, flexural, impact, and short beam shear tests, with ambient-aged specimens showing the largest decline (up to 31.7% in flexural strength). Vibrational analysis showed reduced natural frequencies, particularly under ambient conditions (27.27%). Sound absorption tests showed that pristine specimens had the highest transmission loss, while moisture-rich ambient-aged specimens had the lowest. SEM analysis confirmed surface degradation, with fiber pull-out and matrix debonding contributing to property loss. This research provides valuable insights into the environmental limitations of basalt fiber composites, emphasizing the need for enhanced durability in eco-friendly materials.

Cylindrical sandwich structure with excellent mechanical properties has attracted extensive attention from researchers and been applied in various fields. The cylindrical sandwich structure meets the mechanical requirements of the application and new requirements emerge at this time. The structure should have multifunctionality which can withstand multiple different loads simultaneously. To improve its sound insulation ability while maintaining its mechanical properties, membrane-type metamaterials are introduced into cylindrical sandwich structure in this article. A theoretical model according to the harmonic expansion method is established. Then, the sound transmission loss (STL) of the structure is predicted. Besides, the influence of boundary conditions on its STL is analyzed and the sound insulation mechanism of the structure is investigated by discussing various parameters effect on the STL curve. [ABSTRACT FROM AUTHOR]

The low frequency sound transmission loss (STL) behavior of cellular truss-like auxetic structures is investigated. For this purpose, cellular truss-like auxetic structures are used as the core of sandwich panels and the two-dimensional in-plane STL of the sandwich structures are calculated using validated FE simulations. Significant superiority of the STL behavior in terms of high bandwidth at low frequency domain (1–1000 Hz) is observed compared with other cellular materials. The results of parametric studies demonstrate strong effects of geometric parameters on the STL of the structure and could allow for fine-tuning of the acoustic properties. [ABSTRACT FROM AUTHOR]

This paper proposes a sublaminate layer-wise finite element modeling method to accurately evaluate the damping and sound insulation characteristics of composite constrained layer damping plates. It incorporates the frequency-dependent property of viscoelastic interlayer into fully coupled structure-acoustic interaction equations, and employs the generalized high-order displacement hypothesis with tailored polynomial series expansion. The method is applicable to various boundary conditions and material layer combinations. Validation is conducted using numerical and experimental data. Parametric study identifies optimal thickness and stiffness for maximizing modal loss factor. Additionally, sound insulation performance is examined in narrow frequency bands, highlighting the damping enhancement of viscoelastic interlayer. [ABSTRACT FROM AUTHOR]

The main scope of this work is to study the effect of embedding a periodic pattern inside a porous material, in order to passively improving its acoustic performance in terms of sound transmission loss. A contemplated application is the improvement of classical aeronautical soundproofing packages. In order to reach this goal, numerical models of an acoustic package including periodic patterns are implemented using the finite element method and the Transfer Matrix Method. Firstly, some of the proposed configurations are experimentally tested, providing a comparison and validation of the obtained numerical results. Afterwards, several configurations of inclusions are numerically studied, and incorporate hollow cylindrical inclusions, half-cut hollow cylindrical inclusions and cylindrical Helmholtz resonators. The improvements in terms of transmission loss, essentially brought by a periodicity peak, are evaluated under plane wave excitation with various incidence angles. The main novelties of the present work are represented by an experimental validation of the proposed acoustic meta-materials that were only numerically studied in previous works. The effect of the inclusion of a periodic pattern of Helmholtz resonators inside the foam core is also considered. The presented numerical results are also evaluated for different incidence angles of an exciting acoustic plane wave. [ABSTRACT FROM AUTHOR]

The unique core structure makes the corrugated sandwich plate with enhanced strength and stiffness while maintaining a relatively lighter mass, with simple structure and low manufacturing cost, which has a significant potential for widespread applications. To better evaluate its acoustic performance, a theoretical model for vibration analysis under simply supported boundary conditions is established using the first-order shear deformation theory (FSDT) and Hamilton's principle, as well as formulates the sound insulation equation for the sandwich panel subjected to simple harmonic pressure excitation. The solution is further solved analytically based on the fluid-structure coupling condition and the Navier method, and the sound transmission loss (STL) is described analytically. The validity of the proposed model is verified by comparing with the results of impedance tube acoustic insulation experiment and commercial software COMSOL finite element simulation. Based on the approach presented in this article, the effects of sandwich layer thickness, corrugation angle, sandwich plate size and corrugation wall thickness on the acoustic and vibration characteristics of the structure are discussed. The findings demonstrate that, the natural frequency of the sandwich panel undergoes a decrease as the corrugated inclination increases. Specifically, when the corrugated inclination angle rises from 30° to 70°, the overall sound insulation effect improves by 8.73 %. An increase in the core thickness results in a decrease in the resonance frequency of the sandwich plate, and the sandwich plate exhibits good sound insulation across a wide frequency band when the core thickness reaches 12 mm. As the thickness of the corrugated wall increases, a trend towards lower frequencies of the sound insulation trough is observed, and when the corrugated wall thickness increases from 1 mm to 3 mm, the average STL of sandwich panel enhanced by 12.57 % in the whole frequency analysis. [ABSTRACT FROM AUTHOR]

With increasing urbanization and industrialization, noise pollution has become a significant environmental issue. This study compares the sound insulation performance of two different sound barrier designs: water drop and trapezoidal. COMSOL Multiphysics software for computational simulations is used to calculate sound transmission loss (STL). The results indicated that the water drop design provides more effective sound insulation compared to the trapezoidal model. Additionally, economic analyses suggest that the water drop design may offer long-term advantages despite higher initial costs. [ABSTRACT FROM AUTHOR]

This paper proposes a universal vibroacoustic coupling theoretical analysis model for investigating the sound insulation characteristic of corrugated core sandwich panel (CCSP) under different boundary conditions. The vibroacoustic coupling model consists of CCSP (structural field) and two three-dimensional acoustic cavities which simulate the incident sound field and accept the sound field, respectively. Based on first-order shear deformation plate and shell theories and acoustic theory, the dynamic model of CCSP and three-dimensional acoustic cavities are established by employing the differential quadrature finite element method in conjunction with the energy principle. The coupling of CCSP and three-dimensional acoustic cavities is realized by the velocity continuity condition at the acoustic–structure interfaces. The validation of the vibroacoustic coupling model is verified by comparing the results calculated by the established model with the corresponding results calculated by ABAQUS. The influence of model parameters on the vibroacoustic characteristic of vibroacoustic coupling model is investigated systematically for determining the critical structure parameters which have influence on the vibroacoustic behaviors. The effect of critical structure parameters on the sound insulation characteristic of CCSP is analyzed systematically for the optimization of the sound insulation performance of CCSP and provides theoretical basis and technique guidance. [ABSTRACT FROM AUTHOR]

Low-frequency sound wave reduction is hardly feasible for traditional sound absorbers such as porous media. In contrast, locally resonant acoustic metamaterials act as spatial frequency filters, effectively reducing low-frequency noise. However, these materials can have narrow bandgaps, add extra mass to the main system, and function only within a specifically adjusted frequency range. Therefore, this paper proposes a methodology for designing three-dimensional (3D) chiral honeycomb membrane-type acoustic metamaterials (MAM) based on acoustic circular dichroism (ACD), negative effective mass, and local resonance mechanisms (LRM). The paper also uses the genetic algorithm (GA) to maximize sound transmission attenuation and widen bandgaps. The accuracy of the simulations is validated with available experimental data. The key idea of the present study is to automatically design a MAM structure using modern optimization tools. A developed GA aims to maximize the average sound transmission loss (STL) across the desired low-frequency range of 0–850 Hz by optimizing the value of structural parameters associated with the configurations of masses, including rotation and linear offset, as well as their geometrical dimensions, including length and width. COMSOL Livelink with MATLAB is employed as a practical co-simulation tool to find an optimum value for structural parameters. Results indicate a 35% improvement in average STL along with an ultra-wide bandgap with a 507% bandgap coverage factor (BGCF) in the frequency range of interest, verifying the reliability of the developed algorithm. In addition, sound mitigation incidence is justified by exploring the negative effective parameters of the unit cell and displacement vector fields. The proposed designs demonstrate superior performance as both initial and optimized models broke the mass law within the investigated frequency range. Finally, the effect of the selected geometrical parameters on the objective function is observed through sensitivity analysis. This study presents the practical use of optimization algorithms to develop MAMs. [ABSTRACT FROM AUTHOR]

Sound transmission mechanisms and sound transmission losses are of great importance in providing acoustic comfort. Research has focused on developing materials and structures that will reduce sound transmission loss. The increasing amount of waste disrupts the ecological balance; this situation brings about global warming, air and soil pollution. These environmental effects negatively affect the lives of all living things, especially humans, and also harm the economy. Combating global pollution has become one of the primary goals of scientists. Recycling provides significant economic benefits as well as protecting both human health and natural resources. In this study, polyurethane foams used in the automotive industry and many other areas were produced by adding waste soda glass powder at various rates while keeping the isocyanate/polyol ratio constant. The durability of the produced foams was tested by apparent density measurement, wettability by contact angle analysis, organic bond structures by FT-IR spectroscopy and acoustic properties by sound transmission loss analysis. It was determined that soda glass powder did not react with the foams and that the produced foams exhibited hydrophobic properties. The acoustic properties of the filler foams were higher than the neat foam in almost the entire frequency range (65-6300 Hz). The sample coded PU-SG4 is the sample that exhibits the best acoustic properties by reaching 9.28 dB, 9.10 dB and 13.48 dB values in the low, medium and high frequency regions, respectively. In the high frequency range region, all of the soda glass added foam composites reached a sound transmission loss of over 13 dB. [ABSTRACT FROM AUTHOR]

Sandwich structures with functionally graded (FG) cores have gained interest in vibroacoustic applications. This article considers the vibroacoustic properties of double-walled sandwich magneto-electro-elastic (MEE) plates with a functionally graded carbon nanotube-reinforced composite (FG-CNTRC) core layer in a thermal environment. A coupled multiphysics model is developed based on third-order shear deformation theory (TSDT) and acoustic-structure interaction. Special attention is paid to the transmission loss of this arrangement for simply supported and clamped boundaries for four different kinds of CNT distributions, namely, UD, FG-V, FG-O, and FG-X. Sound velocity potential, normal velocity continuity conditions, and Hamilton's principle are used to generate the coupled vibroacoustic equations, which are then solved using the Galerkin method. The effects of boundary conditions, CNT distributions, cavity depth, multiphysics coupling fields, and temperature on the STL are comprehensively studied. The results provide guidelines for tailoring the dynamic response of these materials to achieve enhanced acoustic insulation performance. It enhances fundamental understanding and enables the engineering design of multilayered composite panels with optimized vibration and noise control capabilities. [ABSTRACT FROM AUTHOR]

In this work, the sound transmission loss (STL) of a simply supported doubly curved shallow aluminum shell covered by two layers of piezoelectric material, PZT-5H is presented. The study takes into account the presence of uncertain ambient temperature which is shown to significantly affect piezoelectric control of sound transmission. To derive the equations of motion, the assumed mode method combined with the first-order shear deformation theory and Hamilton's principles are employed. The modeling process incorporates the ambient temperature and thoroughly investigates its effects on STL, vibrational displacement, and piezoelectric voltage in terms of thermal strain, piezoelectric constants, and the pyroelectric coefficient uncertainties. Results show that uncertainty in environmental temperature significantly affects STL uncertainty up to 10% and vibrational displacement of the shell to the 15 times of its lowest value. The piezoelectric voltage also fluctuates with the variation in the temperature in a maximum range of 0.12–5.2 Volt. Further, the piezoelectric sensing voltage which accounts for the piezoelectric sensor thickness is observed to be highly sensitive to the temperature uncertainty with a maximum range of 0.65–7.6 Volt, causing depolarization and hysteresis nonlinearity. Thus, environmental temperature variation is considered as one of the main uncertain aspects for robust sound transmission controller. The proposed study provides an insightful investigation for robust piezoelectric control of STL in the presence of thermal uncertainty. [ABSTRACT FROM AUTHOR]

Featured Application: The Flexible Soundproofing Metapanel (FSM) developed in this study has potential applications where lightweight, flexible, and effective noise control solutions are crucial. This study addresses the critical challenge of developing lightweight, flexible soundproofing materials for contemporary applications by introducing an innovative Flexible Soundproofing Metapanel (FSM). The FSM represents a significant advancement in acoustic metamaterial design, engineered to attenuate noise within the 2000–5000 Hz range—a frequency band associated with significant human auditory discomfort. The FSM's novel structure, comprising a box-shaped frame and vibrating membrane, was optimized through rigorous finite element analysis and subsequently validated via comprehensive open field tests for enclosure-type soundproofing. Our results demonstrate that the FSM, featuring an optimized configuration of urethane rubber (Young's modulus 6.5 MPa) and precisely tuned unit cell dimensions, significantly outperforms conventional mass-law-based materials in sound insulation efficacy across target frequencies. The FSM exhibited superior soundproofing performance across a broad spectrum of frequency bands, with particularly remarkable results in the crucial 2000–5000 Hz range. Its inherent flexibility enables applications to diverse surface geometries, substantially enhancing its practical utility. This research contributes substantially to the rapidly evolving field of acoustic metamaterials, offering a promising solution for noise control in applications where weight and spatial constraints are critical factors. [ABSTRACT FROM AUTHOR]

The acoustic performance of metal hollow sphere (MHS) A356 aluminum matrix composites has a significant impact on their application, making it worthy of in-depth investigation. To investigate the acoustic performance and mechanism of MHS A356 aluminum matrix composites, in this study MHS A356 aluminum matrix composites with different structural parameters were fabricated using a casting method. The density of the MHS A356 aluminum matrix composites was measured using the direct measurement method, and the acoustic performance of the composites was measured using the impedance tube. The research results indicated that the average sound absorption coefficient of MHS A356 aluminum matrix composites increased with the decrease in sintering temperature and diameter of MHSs, and the increase in volume fraction of MHSs. When the sintering temperature of the MHS was at 1,100°C, with the volume fraction being 48.50% and the diameter being 1.88 mm, the average sound absorption coefficient of the MHS A356 aluminum matrix composites reached the optimal level, which was 0.23. Conversely, the sound transmission loss of MHS A356 aluminum matrix composites decreased with the increase in sintering temperature, volume fraction, and diameter of MHSs. When the sintering temperature of the MHS stood at 1,100°C, with the volume fraction being 40% and the diameter being 2.88 mm, the average sound transmission loss of the MHS A356 aluminum matrix composites attained the maximum value, which was 24.6 dB.

The escalating demand for polyurethane rigid foams (PURF) has resulted in a substantial increase in waste polyurethane products. In view of the difficulty in recycling waste PURF, this study introduces a novel mechanical recycling process that is cost-effective and features a straightforward fabrication process for producing PUW (waste PURF combined with wood veneers), which solves the problem of low strength products obtained from mechanical recycling of PU waste. Through investigation of the PURF (ground into particles before using) particle size, core layer density, the amount of resin and thickness, the optimal fabrication process was confirmed as follows: particles with the size of 1 to 3 mm as its core layer components, 0.9 g/cm3 as its core layer density, the addition of MDI to be 20 wt%, and 8 mm thickness of whole composite. The resulting PURF-based composite exhibited superior thermal insulation properties, mechanical strength, and sound insulation performance. The optimized PUW composite had a notably low thermal conductivity of 0.04126 W/(m·K), slightly higher than that of rock wool board (0.04 W/(m·K)). In terms of mechanical performance, the wet shear strength of the optimal PUW composite reached 0.61 MPa. Furthermore, the PUW composite exhibited relatively high sound insulation, particularly at high frequencies.

The primary issue in evaluating airborne sound insulation lies in quantifying the sound energy emitted by the barrier. This is typically accomplished by measuring sound pressure levels in sending and receiving rooms and acoustic absorption within the receiving room. When significant fluctuations in sound pressure levels occur within a reverberation room, it indicates the presence of standing waves, necessitating the incorporation of diffusing elements. The paper presents the results of computational modelling calculations for various configurations of diffusing elements in a reverberation room. These diffusers aim to improve the uniformity of the acoustic field in terms of acoustic pressure. Therefore, the focus of the model was on these parameters. The simulation results were verified by conducting acoustic measurements in an actual room. The ultimate goal was to assess the impact of changes in the arrangement of diffusers on the results of sound insulation measurements. As an additional criterion for evaluating the obtained results, the measurement uncertainty of sound insulation with partial uncertainties was adopted. [ABSTRACT FROM AUTHOR]

Numerous studies have been conducted to examine the vibroacoustic characteristics of lightweight double-walled structures due to the anticipated applications of these structures in noise reduction engineering. In this study, third-order shear deformation theory (TSDT) is used to develop a theoretical model that predicts sound transmission loss (STL) across double-walled electro-rheological fluid (ERF) sandwich plates with functionally graded carbon nanotube reinforced composite (FG-CNTRC) facesheets. The extended rule of mixture is utilized to evaluate the properties of the FG-CNTRC material in the thickness. Depending on the four FG models, the CNT volume fraction varies. A sufficient displacement continuity condition is taken into account between layers. Furthermore, it should be noted that changing the electric field affects the pre-yield zone's ERF features. The vibroacoustic equations are derived using Hamilton's principle and solved utilizing weighted residual (Galerkin) technique considering simply supported and clamped boundary conditions. Several studies are done to compare the results of the suggested model with other results found in the literature. An extensive numerical study is conducted to examine the dependence of STL on several parameters, including electric field strength, volume percentage of the CNTs, CNTs distribution, depth of acoustic cavity. [ABSTRACT FROM AUTHOR]

This paper introduces glass/polyester fiber composite felts (GPCFs) to expand the application of glass fiber felt in composite fields, for satisfying the lightweight, high strength and excellent acoustic requirements. The effects of different weight ratios of polyester fiber on the physical properties, mechanical properties, and acoustic performance of GPCFs are mainly investigated. The results show that air permeability, tensile strength and flexural strength of GPCFs increase with polyester fiber weight ratios. The burst strength of GPCFs grows with polyester fiber weight ratios until it reaches a maximum value at 30 wt% and then the value tends to stabilize. GPCFs with fiber weight ratios of 20% and 30% have the best sound transmission loss (STL) and excellent sound absorption coefficients (SACs), respectively. Overall, polyester fibers can significantly improve the mechanical and acoustic performance as an adhesive and are quite convenient for lightweight design. [ABSTRACT FROM AUTHOR]

Electric propulsion motors are more efficient than internal combustion engines, but they generate high-frequency tonal noise, which can be perceived as annoying. Acoustical materials are typically suitable for high-frequency noise, making them ideal for acoustic noise mitigation. This paper investigates the effectiveness of three acoustical materials, namely, 2″ Polyurethane foam, 2″ Vinyl-faced quilted glass fiber, and 2″ Studiofoam, in mitigating the acoustic noise from an induction motor and a variable frequency inverter. Acoustic noise rates at multiple motor speeds, with and without the application of acoustical materials, are compared to determine the effectiveness of acoustical materials in mitigating acoustic noise at the transmission stage. Acoustical materials reduce acoustic noise from the induction motor by 5–14 dB(A) at around 500 Hz and by 22–31 dB(A) at around 10,000 Hz. Among the tested materials, Studiofoam demonstrates superior noise absorption capacity across the entire frequency range. Polyurethane foam is a cost-effective and lightweight alternative, and it is equally as effective as Studifoam in mitigating high-frequency acoustic noise above 5000 Hz. [ABSTRACT FROM AUTHOR]

The present study aims to utilize the carbonaceous filler (pyrolytic carbon black (PCB)) obtained from tire waste to fabricate composites for thermal, vibrational, and acoustical applications. Four composites were fabricated by increasing the PCB content (0, 10, 20, and 30 parts per hundred rubber (phr)) in the natural rubber (NR) matrix following ASTM D3182-21a standard. The optimum curing time was determined using a Moving Die Rheometer based on the ASTM D2084-19 standard. The physical, functional, microstructural, wettability, thermal, and mechanical properties of fabricated NR/PCB composites were comprehensively examined. Further, from an application standpoint, the study influence of increasing PCB content in a polymer matrix on thermal conductivity (TC), vibration damping, and sound transmission loss (STL) of the fabricated NR/PCB composites was investigated following ASTM E1530-19, ASTM E756-05, and ASTM E2611-17 standards, respectively. The study results indicate significant enhancement in the properties of the composites with increased PCB content. Specifically, the reinforcement of 30 phr of PCB in the polymer matrix led to a notable increase in TC (at 40 °C) by approximately 21.16% compared to NR/PCB0 composite. Also, the configuration mild steel (MS) + NR/PCB30 achieved the highest damping ratio, measuring 6.56 at the third vibration mode. Moreover, the average STL value of the NR/PCB30 composite showed a notable improvement of approximately 17.19% when compared to the NR/PCB0 composite, underscoring the effectiveness of PCB in enhancing the desired properties of the NR-based composites. [ABSTRACT FROM AUTHOR]

Machine learning (ML) and Deep learning (DL) are increasingly pivotal in the design of advanced metamaterials, seamlessly integrated with material or topology optimization. Their intrinsic capability to predict and interconnect material properties across vast design spaces, often computationally prohibitive for conventional methods, has led to groundbreaking possibilities. This paper introduces an innovative machine learning approach for the optimization of acoustic metamaterials, focusing on Multiresonant Layered Acoustic Metamaterial (MLAM), designed for targeted noise attenuation at low frequencies (below 1000 Hz). This method leverages ML to create a continuous model of the Representative Volume Element (RVE) effective properties essential for evaluating sound transmission loss (STL), and subsequently used to optimize the overall topology configuration for maximum sound attenuation using a Genetic Algorithm (GA). The significance of this methodology lies in its ability to deliver rapid results without compromising accuracy, significantly reducing the computational overhead of complete topology optimization by several orders of magnitude. To demonstrate the versatility and scalability of this approach, it is extended to a more intricate RVE model, characterized by a higher number of parameters, and is optimized using the same strategy. In addition, to underscore the potential of ML techniques in synergy with traditional topology optimization, a comparative analysis is conducted, comparing the outcomes of the proposed method with those obtained through direct numerical simulation (DNS) of the corresponding full 3D MLAM model. This comparative analysis highlights the transformative potential of this combination, particularly when addressing complex topological challenges with significant computational demands, ushering in a new era of metamaterial and component design. [ABSTRACT FROM AUTHOR]

Sandwich structures are widely used in various fields. Curved sandwich structures have attracted the attention of researchers owing to their superior stiffness and strength. With the application of the structures in engineering, it is required that the structures can not only meet the needs of mechanical loads but also can cope with thermal, acoustic, optical, and electrical loads. Sound insulation is one of the most common problems in the fields of aerospace, transportation, and architecture, so it is imperative to research new structures with good mechanical and acoustic properties. In this paper, a composite structure which is coupled with curve shell sandwich structure and acoustic metamaterials is proposed to obtain good mechanical and acoustic properties. Based on the harmonic expansion method and principle of virtual work, the theoretical model is established and the sound transmission loss (STL) performance is studied. Then, the effects of the geometry of the structure and material parameters on the STL of the structure are discussed. [ABSTRACT FROM AUTHOR]

In this study, mathematical modeling design based on Sound Transmission Loss measurement results of new acoustic material samples with natural content was carried out. Using the test samples in question, transfer function of acoustic materials based on electronic filter circuit design and a transition design method for the production of new acoustic materials by utilizing the transfer function is presented. Based on the experimental results of the test samples, it is the most suitable low-pass filter structure for the proposed design. In this study, active Sallen-Key lowpass filter structure is preferred and used. Sound Transmission Losses in dB (decibels) of acoustic samples were obtained experimentally for 500, 1000, 2000 and 4000 Hz. fundamental frequencies in the literature. Based on these data, transfer function simulation suppression gain results were obtained in TINA-TI program, active filter circuit designed, and MATLAB program. When the other results were compared in the experimental results, it was seen that very close values were obtained. It has been demonstrated that the proposed method can be used effectively in the design and examination of new acoustic materials. [ABSTRACT FROM AUTHOR]

The research described in the article addresses the problem of measurement, prediction and practical use of the acoustic properties of materials determined in an impedance tube. The aim of the research was to develop a simple calculation model for the insertion loss of small machinery enclosures, based on the normal incidence sound transmission loss and the normal incidence sound absorption coefficient of porous and fibrous materials. Both experimental and model tests were carried out on materials such as mineral wool, melamine foam and rebonded polyurethane foam. Assessing the absorption properties of the tested porous and fibrous materials was performed using selected theoretical models, relating the calculations of the normal incidence sound absorption coefficient to measurements of this parameter conducted using an impedance tube. The application of the modified Allard and Champoux model brought the best results with the smallest discrepancies of the obtained results in relation to the experimental tests. Assessing the sound-insulating properties of the tested mineral wool was carried out using the proposed calculation model for the normal incidence sound transmission loss, relating the obtained results to measurements conducted using an impedance tube. The assessment of the sound-insulating properties of porous and fibrous materials was performed using the proposed calculation model for insertion loss, which was validated using two prototype test stands for determining the insertion loss of cubic enclosures, in this case with walls made of porous and fibrous materials. Satisfactory results were obtained for engineering applications in the calculation results using the proposed models with respect to measurements. The results may have practical applications in assessing the effectiveness of acoustic enclosures, in which the basic construction material is an appropriate porous or fibrous plate, selected to have both sound-absorbing and sound-insulating properties. [ABSTRACT FROM AUTHOR]

A theoretical model of the normal sound insulation of a rectangular locally resonant (LR) plate with simply supported boundary conditions is established. The accuracy of the model is verified through comparison with finite element simulation results. Considering a 1-m2 aluminum plate as the research object, a non-dominated genetic algorithm is introduced. The algorithm optimizes the lightweight sound insulation of an LR finite plate with a center frequency band of 20–800 Hz as the optimization objective of maximum average sound insulation and minimum mass. The optimization parameters are substrate thickness and local resonance parameters (including resonator target frequency (f obj), number of resonators, additional mass ratio, and resonator damping). Optimization results indicate that the average sound insulation fluctuates at approximately 2 dB due to changes in f obj. The results also provide an optimal solution to the algorithm. The optimal sound insulation value curve of LR plates corresponding to different surface densities of intermediate improved cases is fitted and compared with the sound insulation value of an equal-mass bare plate. Under lightweight optimization, the resonators are deemed capable of improving the local frequency band sound insulation. In contrast, the wideband average sound insulation can approximate but not surpass the insulation provided by the equal-mass bare plate. In practical applications, an LR plate that can improve the local frequency band sound insulation and ensure the overall lightweight sound insulation performance of the wide frequency band can be obtained. This can be achieved by analyzing the frequency spectrum of optimal points in the lightweight sound insulation optimization process. Relevant research can provide a basis for the evaluation and design of the low-frequency sound insulation of plates for transportation equipment, such as airplanes, high-speed trains, and cars. [ABSTRACT FROM AUTHOR]

Low frequency noise control is difficult due to the large wavelength. Acoustic metamaterials (AMs) bring a new sight for low frequency noise control because they can control low frequency wave with subwavelength structures. Since plate type structures are widely used in engineering, the plate type AM structures with different types of resonators are studied by both experiments and numeric simulations. The measured sound transmission loss (STL) curves of the samples show that there are several peak points appearing in the low frequency range. It is found from the numerical simulations that sound wave cannot transmit the plate at these points. The certain locally resonant modes of the resonators lead to good sound insulation properties of the plate type structures. By combing different types of resonators together, enhancement of STL in wide frequency ranges can be achieved. The results in this paper provide good guidance for noise control in engineering applications. [ABSTRACT FROM AUTHOR]

In the present study, the sound transmission loss (STL) through the air-filled rectangular double-walled cross-ply fiber metal laminated (FML) nanoplates under simply supported and clamped boundary conditions is studied using the nonlocal strain gradient theory (NSGT) and third-order shear deformation theory (TSDT). NSGT is complemented with hardening and softening material effects, which can significantly enhance the accuracy of small-scale results. The sound velocity potential and Hamilton's principle are employed to derive the coupled size-dependent vibroacoustic equations. The Galerkin method is exploited to solve vibroacoustic equations and obtain the STL. The developed solution is examined in terms of its accuracy and precision via a comparison with other available data in existing research. The effects of different parameters such as boundary conditions, nonlocal and strain gradient parameters, lay-ups, incident angles, and acoustic cavity depth on the STL through the double-walled FML nanoplates are investigated. [ABSTRACT FROM AUTHOR]

Windows are commonly the primary way for noise to enter the building environment. Most windows achieve higher sound insulation targets by simply increasing glass thickness or laminate. However, the glass thickness cannot be increased freely due to the window frame's limitation. This research selects eleven kinds of asymmetric insulating laminated glass (glass + polyvinyl butyral + glass + air + glass) within 27 mm, which are the typical thicknesses of window frames. The three pieces of glass have equal thicknesses. The half-space acoustics method investigated the acoustic properties and modal behavior of the glass with finite thickness. The results show that when PVB or three glass increases simultaneously, and the sound insulation of each glass can be improved by 0.9∼3.4 dB or 3.7∼21.8 dB at first resonant frequencies, respectively. The glass with the best sound insulation is 7 mm glass + 0.76 mm polyvinyl butyral + 7 mm glass + 5 mm air + 7 mm glass (7 + 0.76 + 7 + 5A + 7 for short). Its sound transmission loss (TL) is 38.5 dB from 125 to 4000 Hz and 16.8 dB in the first resonant frequency (200 Hz). In addition, its first resonant frequency is the highest among eleven kinds of glass, and the number of natural frequencies in the low frequency range is only 9. These findings can provide a basis for designing asymmetric insulating laminated glass to improve the low frequency noise reduction effect effectively. [ABSTRACT FROM AUTHOR]

Based on the hyperbolic tangent parabola mixed shear deformation theory, the paper studied the sound radiation and the sound insulation of the functionally graded (FG) sandwich microplates under thermal-electric effects. The sandwich plate is composed of piezoelectric skin layers and FGM core layer. By using Hamilton's principle, a size-dependent model considering the thermal-piezoelectric effects are established. The acoustic response and sound insulation are calculated with Rayleigh integral and solid-fluid coupling conditions. The accuracy of the presented method is verified by the numerical simulations. Then the effects of various parameters on the vibro-acoustic characteristics are analyzed and discussed. Numerical results show that the temperature variations, the length scale parameter to thickness ratio and the gradient index have great impacts on the FG sandwich microplates. [ABSTRACT FROM AUTHOR]

The subject of the research described in the article are the sound insulating properties of a cube-shaped enclosures, the walls of which are made of plates of homogeneous materials and two-layer baffles. As an enclosure for an omnidirectional sound source imitating a noisy machine or device, a prototype test stand for testing the acoustic properties of materials and enclosures was used. The three tested variants were enclosures with walls made of plastic plates, such as polyethylene, solid polycarbonate, and plates in the form of rigid polyethylene foam. The fourth variant was an enclosure with walls made of sandwich baffles in the form of a steel plate with a rubber layer glued on. Calculations of the effectiveness of the enclosure were carried out using the previously developed theoretical calculation model for insertion loss (IL). The obtained results were related to the IL obtained in the course of experimental tests. The research showed slight discrepancies between the calculations and the measurement results for almost all tested materials in the entire frequency range (100-5000 Hz), with the exception of rigid polyethylene foam, for which the discrepancies were relatively the largest in the lower frequency range, i.e. below 400 Hz. Research has shown that the best sound insulation performance was achieved for an enclosure with two-layer walls. [ABSTRACT FROM AUTHOR]

Cylindrical structures are used in various fields owing to their good mechanical properties. At the same time, the requirements for their acoustic performances continue to increase in the application of cylindrical shell structures. Thus, the acoustic performance and application in sound insulation attract increasing attention. Sandwich cores have been inserted into cylindrical structures to improve the sound insulation performance of the structure. To improve both mechanical and acoustic properties of the cylindrical sandwich structure, a frame structure that strengthens the internal nodes of the pyramidal truss core was added. A theoretical model corresponding to the structure was established to study the sound insulation performance of the structure. The influences of the overall thickness of the structure, number of lattice unit cells, material density, and angle of incident sound waves on the sound insulation performance were analyzed. [ABSTRACT FROM AUTHOR]

This paper deals with sound propagation through a two-layer sandwich plate in which the carbon nanotubes with functionally graded (FG) distribution are coated by a thin layer of magneto-electro-elastic (MEE) materials. Firstly, the derivation of governing equations for each layer of the sandwich plate is followed according to the three-dimensional elasticity theory. In this regard, the relationship between the equations of motion for the layer, made of MEE materials, and the electric and magnetic potentials is established. Additionally, the effective properties of the nanocomposite layer are extracted by employing the rule of mixture. Afterward, the solution is finalized by employing the approximate layer and transfer matrix technique, in accordance with the definition of state space and sound transmission loss. In the next stage, to confirm the reliability of the derived relationships, three configurations of the panel are examined. Firstly, according to the obtained results, it is evident that adding a thin coating layer of triple-phase MEE materials effectively improves the sound insulation in the sandwich plate. Secondly, considering the electromagnetic boundary conditions can lead to a noticeable enhancement in the STL in the stiffness region. Moreover, the magnetic potential, compared to the electric one, is seen to be more effective on the acoustic radiation of the sandwich panel. [ABSTRACT FROM AUTHOR]