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Sheep wool is a precious, renewable raw material that is nowadays disregarded and wasted. To better use local sources of wool, it was used to manufacture tufted carpets. The coarse wool of mountain sheep was used to form a carpet pile layer, while the waste wool from the tannery industry was applied to form carpet underlayment. During investigations, the acoustic performance of the carpets was assessed. The carpets' sound absorption coefficients and transmission loss were determined using the impedance tube. It was revealed that the adding of underlayment improves the carpet's sound absorption only at medium sound wave frequencies. The underlayment significantly increases transmission loss in the whole frequency range. The acoustic performance of the carpets with the wool underlayment is similar to the acoustic characteristics of the carpets with an underlayment made from polyester. It was concluded that wool nonwovens can be used as an effective, eco-friendly, sound-absorbing carpet underlayment, which can improve wool utilisation and contribute to the reduction in environmental pollution caused by plastic residues. [ABSTRACT FROM AUTHOR]

Newly emerged acoustic barriers provide effective solutions for noise reductions of varied kinds in which acoustic barriers made of Fano resonance-based space-coiling metamaterial are reported to have promising application prospects for their broadband noise reduction ability and good ventilation performance. However, current Fano resonance-based acoustic ventilation barriers are hard to practically apply since most of them are difficult to manufacture or install. To this end, this research proposes a novel acoustic ventilation barrier based on block-shaped space-coiling metamaterial, which is not only as functional as other acoustic ventilation barriers but also easy to manufacture and install. To obtain a more in-depth understanding of the noise reduction effect, the influence of the design parameters on transmission loss is numerically studied. Additionally, we conduct both numerical and experimental studies on the transmission loss and the ventilation performance of a full-scale meta-unit. Furthermore, through the corresponding optimization process, the proposed acoustic ventilation barrier can have transmission loss consistently above 10 dB across the frequency range of 495~1063 Hz. Lastly, a composite ventilation acoustic barrier obtained by stacking two layers of different proposed metamaterials is presented, which achieves multiband noise reduction performance across the ultra-broad frequency range of 479~1758 Hz. [ABSTRACT FROM AUTHOR]

The paper explores the increasing concern over environmental vibrations resulting from machine operation and rail transit. Notably, low-frequency vibrations generate surface waves with characteristics like significant energy carrying capacity, long-distance propagation, and slow attenuation. The primary challenge in ground vibration attenuation lies in addressing low-frequency vibrations. The study employs the finite element method to investigate the vibration attenuation of a three-component local resonance pile in three-dimensional space. The analysis delves into the impact of the unit cell structure's geometry size on bandgaps, and the influences of the period number on the Attenuation Zones (AZs) are also discussed. Furthermore, a comparison is made regarding the vibration attenuation performance of a two-component local resonance pile. The findings reveal that the appropriate design of a three-component local resonance pile can generate low-frequency complete bandgap. The concrete radius, rubber layer thickness, and buried depth of the pile significantly affect Rayleigh wave bandgap. Frequency domain analysis indicates that an increase in period number expands AZs into the bandgap range. Time domain analysis demonstrates a noticeable decrease in ground acceleration amplitude within the bandgap range. The research results presented in this paper offer a novel approach to address the low-frequency vibration attenuation. [ABSTRACT FROM AUTHOR]

Noise reduction in various industrial and building systems such as ventilation ducts, vehicles, wind tunnels, and test facilities for jet engines, automobiles, and factories has always interested engineers, especially the problematic noise reduction at low frequencies. This problem is even more important with passive silencers, which require absorbent materials and more space. Passive silencers include reactive and dissipative silencers. Among reactive silencers, Helmholtz resonators, expansion chambers, flute-like, drum-like, and plate silencers have proven effective at low frequencies. Combining some of these silencers with a dissipative silencer, called a hybrid silencer, can achieve excellent performance at a wide range of low to high frequencies. In these silencers, the reactive part reduces noise at low frequencies, and the dissipative part reduces noise at medium and high frequencies. The aim of this work, which focuses more on experimental studies, is to introduce the mentioned silencers, investigate the presented methods to improve the performance of these silencers at low frequencies, and offer the practical advantages and disadvantages of these methods. [ABSTRACT FROM AUTHOR]

Numerical simulation was carried out on the transmission loss of the split-stream rushing exhaust muffler, and the accuracy of the simulation method was verified through experiments. Taking the transmission loss as the response value, the experiment was designed by using Box-Behnken module of Design Expert software. A mathematical regression model of transmission loss with experiment factors was established by using the Box-Behnken experimental design scheme, the experiment factors include the diameter of the interior pipe, the shape of the rushing hole, the center distance of the rushing hole, the cone angle of the interior pipe as well as the number of rushing holes, and the mathematical regression model's significance was tested. The response curvatures of second order interaction to the transmission loss by different variables were obtained and the interaction relationships among variables were analyzed. The results showed that the diameter of the interior pipe and the center distance of the rushing hole are the main factors that affect the transmission loss. The transmission loss increases with the increase of the diameter of the interior pipe. When the diameter of the interior pipe is between 70 mm and 80 mm, the transmission loss firstly increases and then decreases with the center distance of the rushing hole changes from Smin to Smax. When the diameter of the interior pipe is between 80 mm and 90 mm, the transmission loss decreases with the center distance of the rushing hole changes from Smin to Smax. The effect of the rushing hole shape on transmission loss is not significant. The transmission loss increases with the increase of the number of rushing holes, but the increase of transmission loss is not significant with the number of rushing holes changes from 4 to 6 groups. Taking the transmission loss as the optimization index, the better experimental condition was obtained. Compared to the not optimized muffler of the sample engine, the average transmission loss of the optimized muffler is increased by 48.70 % when the frequency is 0-1000 Hz, the average insertion loss of the optimized muffler is increased by 7.4 %. At inlet air velocity of 40 m/s, the pressure loss is reduced by 56.8 %. [ABSTRACT FROM AUTHOR]

Copyright of International Journal of Advances in Engineering & Pure Sciences is the property of Marmara University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study proposes sonic crystal green walls based on combined cylinder scatterers and vegetation. It has been known that the vegetation or greenery system is effective in dealing with environmental pollutants, while the cylinder scatterer arranged periodically, also known as a sonic crystal, is preferable owing to the capability of noise attenuation, light transmission, and air circulation simultaneously. Combining both components into a single noise abatement system is expected to provide acoustical and non-acoustical features for urban design, where such an approach maximizes the merit of each component. Moreover, the system is useful for advocating sustainability amid global warming issues. In this work, a numerical model is developed using finite element method (FEM), while experimental results are provided to validate the absorption and attenuation results. It is found that the sonic crystal can attain an attenuation of 13.5 dB around 1.6 kHz. Such a promising result is extended further to lower frequency under a specific configuration of scatterers corresponding to lattice distance and filling faction ratio parameters. Meanwhile, the vegetation can enhance overall attenuation at higher frequencies. [ABSTRACT FROM AUTHOR]

The even more restrictive regulations imposed on chemical and acoustic emissions of ships necessitate the installation of after-treatment systems onboard. The spaces onboard are limited, and the Exhaust Gas Cleaning Systems (EGCSs) have big dimensions, so an appropriate integration and optimization of EGCSs allows to save space and comply with international regulations. Moreover, in the available literature, there is a lack of guidelines about the design of integrated EGCSs. This study aims to develop an ad hoc optimization methodology that uses combined Computational Fluid Dynamics (CFD)–Finite Element Method (FEM) simulations, surrogate models, and Genetic Algorithms to optimize the acoustic properties of EGCSs while considering the limits imposed by the efficiency of chemical reactions for the abatement of NOx and SOx. The developed methodology is applied to a Diesel Oxidation Catalyst (DOC), and the obtained results lead to a system that integrates the silencing effect into the DOC. [ABSTRACT FROM AUTHOR]

The horizontal-transverse coherence of low-frequency (300 Hz) and long-range (10–40 km) acoustic fields near the bottom in deep water is investigated based on experimental data obtained from the South China Sea. The results indicate that the horizontal-transverse coherence length exhibits a strong dependence on the source-receiver distance, with fluctuations consistent with sound intensity trends. In high-intensity regions, the horizontal-transverse coherence is relatively high, with a coherence length exceeding 600 λ, where λ is the acoustic wavelength, whereas in low-intensity regions, the horizontal-transverse coherence decreases significantly, with the coherence length shortening to 10–30 λ. The physical mechanisms underlying the horizontal-transverse coherence are analyzed using the ray theory. In high-intensity regions, the energy of the dominant ray (the ray with the highest energy) accounts for over 70% of the total energy of the rays, exerting a decisive influence on the coherence coefficient and leading to stable horizontal-transverse coherence in the received acoustic field. In contrast, in low-intensity regions, the energy distribution is dispersed, and when amplitude and phase disturbances due to spatial inhomogeneity are introduced, the horizontal coherence deteriorates significantly. The numerical simulations are also performed, and the results are consistent with the experimental observations. [ABSTRACT FROM AUTHOR]

This study investigates acoustic propagation and transmission loss in shallow water at an unexplored site in the northern Arabian Sea near the Pakistan coastline using a normal mode theoretical framework. Sound propagation in shallow water with range-independent bathymetry was analyzed using a customized Kraken C program to compute eigenvalues and eigenfunctions. The sound speed profile and clay silt sediment samples of the northern Arabian Sea, which characterize the water column and ocean bottom, respectively, were determined. Coherent and incoherent transmission losses for frequencies ranging from 50 to 500 Hz were calculated across different ranges and depths. Results indicate significant intensity fluctuations with increasing range, leading to higher transmission loss. Low frequencies (50–225 Hz) exhibit more significant transmission loss, while higher frequencies (230–500 Hz) show reduced loss. Transmission loss is higher for receivers at 19 m depth compared to those at shallower depths (8 m and 12 m) because the receivers are positioned near the layer of bottom sediments. Factors such as source and receiver depth, sediment properties, bottom roughness, and sound frequency significantly influence transmission loss. The novel dataset for the region supports the assessment of sonar performance, underwater communication, navigation, and marine life exploration. [ABSTRACT FROM AUTHOR]

Most conventional power systems adopt radial distribution network wherein multiple loads are connected across the distribution transformer. As the number of loads increases, it results in poor voltage profile at the distant receiving end reducing power delivery. This issue worsens with the largescale influx of electric vehicles and power converter-fed loads, which draw constant power irrespective of supply voltage. Such loads exhibit negative incremental resistance behavior and also have a dynamic response which affects the network in a manner different from constant impedance loads. This paper compares the effects of constant power and constant impedance loads by modeling adjustable converter dynamics for constant power loads. It analyzes line currents, load voltages and power transmitted in a four-load radial test system with optional distributed sources. Results show poorer voltage profile and the effect of power converter dynamics in constant power loads compared to conventional loads. Adding distributed sources improves voltage profile considerably, and transmission losses are reduced. Steady state analysis is then extended to an IEEE 31-bus 23 kV distribution test system with similar results. Transmission losses are computed along different branches, and the influence of loads and sources are analyzed. The outcomes of the analysis can be used in arrival of loss allocation in a system where peer to peer energy sharing is envisaged. [ABSTRACT FROM AUTHOR]

Featured Application: Acoustic liners for aircraft turbofan engines. The design technology was used to build a 4-foot inner diameter, 9-inch axial length, and 2-inch thick acoustic liner to test on NASA-GRC's ANCF low-speed test bed at the Turbomachinery Lab at the University of Notre Dame. The Technology Readiness Level (TRL) 3–4 test was successful. Noise is a concern in industries like aviation. Existing acoustic materials have limitations in terms of effective broadband sound attenuation and operating conditions. This work addresses these limitations by designing and developing a noise mitigation system using lightweight graded micro-porous material made from Cenospheres and high-char binder. However, Cenospheres are nearly spherical with rough surfaces, so determining the flow properties of sound propagation is challenging, and direct measurements are expensive. We developed a multivariable-fit inverse method to estimate these properties using an experimental absorption coefficient, validated first with smooth-surface glass beads and then applied to micro-porous material. The determined flow properties were used in a predictive acoustic analysis and validated experimentally. It was demonstrated that a microstructurally graded material is needed to optimize both sound absorption and transmission loss. A graded material system designed for turbofan engine acoustic liners (50 mm thick) met the target broadband sound absorption coefficient of ≥0.50 and transmission loss of ≥20 dB above 500 Hz. The study also highlights that larger particles in thicker layers enhance sound absorption, while a graded micro-structure improves overall acoustic performance. This research offers a novel approach for designing a lightweight acoustic material for aviation, marking a breakthrough in passive noise mitigation technology. [ABSTRACT FROM AUTHOR]

Abstract To enhance the low-frequency sound absorption capabilities of expansion chamber mufflers, a novel Helmholtz-ring phononic crystal cell was developed. This innovative design integrates ring Helmholtz resonators as the phononic crystal scatterer, which is periodically arranged within the expansion chamber of a muffler to achieve enhanced sound attenuation at deep sub-wavelength scales. The transmission loss characteristics of the phononic crystal muffler were thoroughly examined and found to reveal a pronounced enhancement in sound absorption within the low-frequency bandgap. A critical aspect of this study was the analysis of the influence of defect states on transmission loss of the muffler. The introduction of defect states significantly expanded the sound attenuation bandwidth, effectively compensating for reduced sound absorption performance of the muffler outside the bandgap. The proposed phononic crystal muffler demonstrated a marked improvement in both transmission loss and aerodynamic performance compared to the traditional expansion chamber muffler. Notably, the sound attenuation was further augmented when in defective states. Corresponding experimental investigations were conducted and confirmed the effectiveness of the phononic crystal muffler within its designated bandgap range. This research presents a new way for the development of more efficient noise control solutions.

Abstract This paper presented a study on the security constrained optimal power flow (SCOPF) of a practical transmission utility grid network (TUGN). The objectives of reduction in the transmission losses of TUGN (TLGN) and to minimize the bus voltage deviations (BVD) are achieved by addition of thermal power plant (TPP) and network restructuring (NR). Identification of best fit node for generation injection is achieved using the method based on hybrid combination of analytic approach and genetic algorithm (GA). Efficacy of the proposed study is evaluated using the computation of energy equivalent to network loss saving, percentage derating of the load (PDOL), voltage profile, bus voltage deviations, and financial analysis (FA). Study is performed without and with contingency (N-1) for the base case network, TUGN with addition of TPP and TUGN with addition of TPP and NR. This is established that addition of TPP, addition of TPP with NR are effective to reduce the TLGN, improve the voltage profile and minimize the bus voltage deviations. This study is more efficient compared to various studies reported in literature.

To enhance the low-frequency sound absorption capabilities of expansion chamber mufflers, a novel Helmholtz-ring phononic crystal cell was developed. This innovative design integrates ring Helmholtz resonators as the phononic crystal scatterer, which is periodically arranged within the expansion chamber of a muffler to achieve enhanced sound attenuation at deep sub-wavelength scales. The transmission loss characteristics of the phononic crystal muffler were thoroughly examined and found to reveal a pronounced enhancement in sound absorption within the low-frequency bandgap. A critical aspect of this study was the analysis of the influence of defect states on transmission loss of the muffler. The introduction of defect states significantly expanded the sound attenuation bandwidth, effectively compensating for reduced sound absorption performance of the muffler outside the bandgap. The proposed phononic crystal muffler demonstrated a marked improvement in both transmission loss and aerodynamic performance compared to the traditional expansion chamber muffler. Notably, the sound attenuation was further augmented when in defective states. Corresponding experimental investigations were conducted and confirmed the effectiveness of the phononic crystal muffler within its designated bandgap range. This research presents a new way for the development of more efficient noise control solutions. [ABSTRACT FROM AUTHOR]

The efficacy of silencers in reducing piping noise is contingent upon the specific installation and operating environment. Among the various forms of silencers, the acoustic characteristics of dissipative silencers with sound-absorbing materials attached internally exist in an area that is difficult to explain by existing theories. This is dependent upon the specific type and placement of the attached sound-absorbing materials. This paper presents a methodology for calculating the acoustic transmission loss (TL) of a cylindrical silencer filled with a multilayer poroelastic material, employing the mode-matching method. To describe the numerical process of treating waves propagating within a poroelastic material and determine the modes in accordance with the boundary conditions necessary for analyzing the acoustic performance of the silencer, the Biot model and the Johnson–Champoux–Allard–Lafarge model were employed. The obtained modes were utilized to calculate the acoustic TL of silencers filled with single, double, and triple layers of poroelastic materials. In particular, the results obtained for the single layer were validated by comparing them with the results of a finite element analysis, and the results obtained for multiple layers with the same material were validated by comparing them with the equivalent single-layer results. Moreover, the results of the numerical calculations of the acoustic TLs of the silencer for three distinct types of poroelastic materials, including those with varying degrees of frame rigidity or softness, were compared, and the acoustic characteristics were analyzed in relation to the intrinsic properties of the materials and their arrangement. It is anticipated that the methodology presented in this paper will facilitate the design of silencers using poroelastic materials in accordance with the specific requirements of users or designers by allowing for a comprehensive consideration of the thickness of layers and the arrangement of materials. [ABSTRACT FROM AUTHOR]

As a type of locally resonant phononic crystal, alloy steel phononic crystals have achieved notable advancements in vibration and noise reduction, particularly in the realm of low-frequency noise. Their exceptional band gap characteristics enable the efficient reduction of vibration and noise at low frequencies. However, the conventional transmission loss (TL) simulation of finite structures remains the benchmark for plate structure TL experiments. In this context, the TL in the XY-direction of phononic crystal plate structures has been thoroughly investigated and analyzed. Given the complexity of sound wave incident directions in practical applications, the conventional TL simulation of finite structures often diverges from reality. Taking tungsten steel phononic crystals as an example, this paper introduces a novel finite element method (FEM) simulation approach for analyzing the TL of alloy steel phononic crystal plates. By setting the Z-direction as the excitation source, the tungsten steel phononic crystal plate exhibits distinct responses compared to excitation in the XY-direction. By combining energy band diagrams and modes, the impact of various excitation source directions on the TL simulations is analyzed. It is observed that the tungsten steel phononic crystal plate exhibits a more pronounced energy response under longitudinal excitation. The TL map excited in the Z-direction lacks the flat region present in the XY-direction TL map. Notably, the maximum TL in the Z-direction is 131.5 dB, which is significantly lower than the maximum TL of 298 dB in the XY-direction, with a more regular peak distribution. This indicates that the TL of alloy steel phononic crystals in the XY-direction is closely related to the acoustic wave propagation characteristics within the plate, whereas the TL in the Z-direction aligns more closely with practical sound insulation and noise reduction engineering applications. Therefore, future research on alloy steel phononic crystal plates should not be confined to the TL in the XY-direction. Further investigation and analysis of the TL in the Z-direction are necessary. This will provide a novel theoretical foundation and methodological guidance for future research on alloy steel phononic crystals, enhancing the completeness and systematicness of studies on alloy steel phononic crystal plates. Simultaneously, it will advance the engineering application of alloy steel phononic crystal plates. [ABSTRACT FROM AUTHOR]

This paper presented a study on the security constrained optimal power flow (SCOPF) of a practical transmission utility grid network (TUGN). The objectives of reduction in the transmission losses of TUGN (TLGN) and to minimize the bus voltage deviations (BVD) are achieved by addition of thermal power plant (TPP) and network restructuring (NR). Identification of best fit node for generation injection is achieved using the method based on hybrid combination of analytic approach and genetic algorithm (GA). Efficacy of the proposed study is evaluated using the computation of energy equivalent to network loss saving, percentage derating of the load (PDOL), voltage profile, bus voltage deviations, and financial analysis (FA). Study is performed without and with contingency (N-1) for the base case network, TUGN with addition of TPP and TUGN with addition of TPP and NR. This is established that addition of TPP, addition of TPP with NR are effective to reduce the TLGN, improve the voltage profile and minimize the bus voltage deviations. This study is more efficient compared to various studies reported in literature.Article Highlights: A study on security constrained optimal power flow of a practical transmission grid network is presented to meet the objectives of reduction in transmission losses and to minimize bus voltage deviations. A best fit node for generation injection is identified by hybrid combination of analytic approach and genetic algorithm to add thermal power plant and generation injection by network restructuring to achieve research objectives. Energy equivalent to network loss saving, percentage derating of load, voltage profile, bus voltage deviations, and financial analysis are used to establish efficacy of method. Study is performed without and with contingency (N-1). This study is more efficient compared to various studies of literature and can be implemented for practical transmission grid to achieve huge energy savings. [ABSTRACT FROM AUTHOR]

We report the first work on the development of biodegradable acoustic foams from self‐grown bacterial cellulose (BC) from kombucha solution and green processing techniques. Kombucha BC‐agar and kombucha BC‐polyvinyl alcohol foams were fabricated by using slurries of BC pellicles mixed with the additives, froze for 24 h, and recast into foams using the freeze‐drying method. The foams were aerogel‐like with a density 20 kg/m3, thermally stable upto 220 °C, and crystallinity ~74%. Morphological analysis revealed macropores with coarse walls in agar‐based foams, whereas the PVA‐based foams comprised a polydisperse pore network with coarse walls. A broadband absorption was observed with a maximum of 0.4 for the 2.5‐mm‐thick single‐layer foams and 0.9 for the 12‐mm‐thick multilayer foams. The sound absorption was found to be on par with the biodegradable foams of agar and other cellulose‐rich materials such as agricultural residue, yet with a lightweight. Being largely porous, the foams had little transmission loss. As the densities and the crystallinities of these foams are tunable by the addition of other polymers, the results from this study provide scope to explore BC‐based lightweight materials for large‐scale fabrication suitable for sound absorption over specific regimes. [ABSTRACT FROM AUTHOR]

This tutorial demonstrates the use of information geometry tools in analyzing environmental parameter sensitivities in underwater acoustics. Sensitivity analyses quantify how well data can constrain model parameters, with application to inverse problems like geoacoustic inversion. A review of examples of parameter sensitivity methods and their application to problems in underwater acoustics is given, roughly grouped into "local" and "non-local" methods. Local methods such as Fisher information and Cramér-Rao bounds have important connections to information geometry. Information Geometry combines the fields of information theory and differential geometry by interpreting a model as a Riemannian manifold, known as the model manifold, that encodes both local and global parameter sensitivities. As an example, 2-dimensional model manifold slices are constructed for the Pekeris waveguide with sediment attenuation, for a vertical array of hydrophones. This example demonstrates how effective, reduced-order models emerge in certain parameter limits, which correspond to boundaries of the model manifold. This example also demonstrates how the global structure of the model manifold influences the local sensitivities quantified by the Fisher information matrix. This paper motivates future work to utilize information geometry methods for experimental design and model reduction applied to more complex modeling scenarios in underwater acoustics. [ABSTRACT FROM AUTHOR]

This paper investigates the nonlinear vibro-acoustic performance of simply supported cylindrical shell under oblique incident plane sound wave including companion modes participation. The cylindrical shell equation of motion is obtained employing Donnell's nonlinear shallow shell theory. The Galerkin method is applied to the equations of motion in order to obtain the system of nonlinear nonhomogeneous second order ordinary differential equations. The considered mode shapes are two asymmetric driven and companion modes and one axisymmetric mode. Multiple Scales Method is used to determine the response of resultant nonlinear differential equations. Next, the effects of incident sound characteristics on the transmission loss factor are studied. According to the results, effect of companion mode on the transmission loss (TL) through the shell can be seen only in high frequency of the incident sound wave. In addition, at high incident angle of acoustic wave, the companion mode effect on the TL of the system is very small. [ABSTRACT FROM AUTHOR]

In this study, the acoustic damping performances of the dual Helmholtz resonators were numerically evaluated using a 3D model. The grazing flow passes tangentially through the resonator neck, with a Mach number range of 0 ≤ Ma ≤ 0.1. The numerical model operates by solving the linearized Navier–Stokes equations. The current model is validated through a comparison with experimental data. The model is then utilized to explore the effects of the dual Helmholtz resonators on acoustic transmission loss performance in the presence of a grazing flow. Three key parameters are examined: 1) different implementation configurations of the dual Helmholtz resonators (including Models (b), (c), and (d)), 2) the mean temperature of the grazing flow, and 3) the axial distance between the dual Helmholtz resonators. For comparison, the acoustic damping performance of these dual Helmholtz resonators is compared to the single Helmholtz resonator case (Model (a)). The maximum transmission loss of Model (c) is significantly higher, recording values of 91%, 89.4%, and 92.5% than those observed for Model (a) at Ma = 0, Ma = 0.05, and Ma = 0.1, respectively. It is observed that the dual Helmholtz resonators dramatically increase the transmission loss. Model (c) is demonstrated to be associated with the most significant damping on the acoustic plane waves in comparison with that of Model (a). Additionally, the maximum transmission loss of Model (c) is 23.23 dB, 30.32 dB, and 34.58 dB at mean temperatures of 300 K, 600 K, and 900 K, respectively. Therefore, increasing the mean temperature is shown to be beneficial to enhance transmission losses in the presence of the grazing flow. Furthermore, under Ma = 0.1, the resonant frequency of Model (c) is 127 Hz, 152 Hz, and 172 Hz, corresponding to mean temperatures of 300 K, 600 K, and 900 K. It can be concluded that increasing the temperature has the effect of broadening the resonant frequency, especially at a high grazing flow Mach number. However, increasing the mean temperature results in a reduction of transmission loss in the absence of the grazing flow. In the case of Model (c), a 32 cm axial distance results in a 5.6% larger transmission loss at Ma = 0 and a 26.4% larger loss at Ma = 0.1 compared to a 16 cm axial distance. This indicates that increasing the axial distance between the dual Helmholtz resonators improves transmission loss. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive overview of the various types of mufflers that researchers have studied based on their acoustic performance. Mufflers are a crucial component in noise control to minimize the noise generated by various machines such as internal combustion engines, fans, and other sources that include gas flow. They leverage a combination of resonance, absorption, reflection, and expansion principles to mitigate sound waves. The effectiveness of mufflers in reducing noise pollution is evaluated based on certain parameters, notably transmission loss (TL), insertion loss (IL), and noise reduction (NR). TL serves as an essential parameter to evaluate the acoustic efficiency of mufflers and is widely used by scholars. It is calculated as the difference in sound power at both ends of the muffler in the absence of energy reflecting back to the pipe. Although this measure is easy to compute, it is difficult to obtain accurate measurements. Generally speaking, mufflers play a pivotal role in lowering noise emanating from a vehicle's exhaust system, and they conform to the prevailing noise pollution standards. Consequently, muffler designers aim not only to minimize noise emissions but also to satisfy customer demands. This article examines the design criteria used for mufflers so that researchers can utilize this information to achieve the optimal muffler design. This study reviews various muffler types, including expansion mufflers with circular, elliptical, and polygonal/rectangular cross-sections, mufflers with inlet/outlet pipes with non- perforated extensions, mufflers with inlet/outlet pipes with perforated extensions, multi-chambered mufflers, mufflers with three-pass perforated pipes, mufflers with microperforated plates, plug mufflers, and mufflers with U-shaped pipes (corrugated). [ABSTRACT FROM AUTHOR]

The insert-pipe double expansion chamber muffler has less passbands and higher sound attenuation in the plane wave range, which is widely used to reduce noise of industrial equipment. But there are many parameters that affect the transmission loss of the insert-pipe double expansion chamber muffler, and the sensitivity of each factor is not clear. Identifying the most influential factor among numerous parameters is an important challenge. It is necessary to investigate the sensitivity of all parameters and study parameter optimization algorithms. Based on the method of transfer matrix analysis, this paper studies the insert-pipe double expansion chamber muffler and its sound elimination mechanism. The global sensitivity analysis of the transmission loss of insert-pipe double expansion chamber muffler was conducted using Sobol's method, and the influence of each parameter sensitivity was examined. According to the noise characteristics of an air conditioner compressor, the external penalty function method (EPFM) algorithm is used to optimize the insert-pipe double expansion chamber muffler, and the maximum transmission loss is obtained in a specific frequency band. According to the optimized parameters, the muffler is designed, manufactured, and installed in a pipeline system to carry out a noise experiment to verify the effectiveness of the optimization scheme. [ABSTRACT FROM AUTHOR]

Clear-air echo studies are usually based on isotropic turbulence theory. But the theory has been considered incomplete by modern turbulence theory. The intermittence of turbulence can reveal obvious shortcomings in the existing studies of clear-air echoes. The mechanism of clear-air echo scattering needs to be supplemented. This paper introduces the troposcatter theory, normally used in over-the-horizon communication, to fill the gap left by Bragg scattering. By treating radar as a self-transmitted and self-received device, the equivalent transmission loss of weather radar is established and compared with the recommendations of the Radiocommunication Sector of the International Telecommunication Union (ITU-R). The results show that the S-band radar transmission loss aligns with ITU-R recommendations. There is also a linear regression relationship between the radar transmission loss and height, which conforms to the troposcatter theory. This means that the theory of troposcatter scattering is a supplement to the theory of Bragg scattering. Tropospheric scattering can be thought of as general Bragg scattering. Meanwhile, based on ITU-R recommendations, this study also provides a new way for the recognition of biological echoes. [ABSTRACT FROM AUTHOR]

A demising wall assembly that is frequently being specified for mid-rise and high-rise building constructions is a double steel stud wall assembly with one or more sheets of fire rated gypsum board installed inside the wall cavity between the rows of studs, creating a triple leaf wall. Locating the gypsum board inside the wall cavity can sharply decrease the transmission loss below the 200 Hz one-third octave band due to the creation of two mass-air-mass resonances centered around the 80 Hz onethird octave band. For the walls tested as part of this study, this decrease in the transmission loss was 14 to 17 dB. One theory for why gypsum board is being specified inside the wall cavity is the belief that the gypsum board in the wall cavity maintains the transmission loss of the wall even if residents create small holes in the outer gypsum board layers by hanging decorations on the wall or securing furniture to the wall. To disprove this theory, an increasingly larger number of holes were drilled into the gypsum board on both sides of a wall to determine the effect on the transmission loss. It was found that a significant number of holes, well in excess of normal use of a wall needed to be drilled into the gypsum board before the transmission loss was affected. [ABSTRACT FROM AUTHOR]

A compression ignition (CI) engine can produce significant pressures and temperatures in its combustion chamber. The exhaust system's outlet is the atmosphere so that a conventional silencer can investigate pressure wave attenuation. As a result of an adverse pressure gradient, the exhaust system may not function properly. For computational fluid dynamics simulations, hot exhaust gas can be selected from muffler pipes exiting engine exhaust systems. This study examines a Mahindra Maximo C.I. engine's rectangular chambered muffler model. In the design of one of the two mufflers considered, the inlet, outlet, and center pipes are perforated, which may result in better, more efficient noise reduction. CFD analysis results are used to establish the pressure distribution used in both muffler models to compute transmission loss. Ansys Fluent 2022 R2 is used in this study to compare two reactive-type muffler designs, one without perforations and one with perforations, and Fusion 360 (V.2.0.13168) software is used to design reactive-type mufflers. It was found that the perforated muffler model exhibits a higher transmission loss than the non-perforated muffler model, thereby establishing its superiority over the non-perforated muffler model. Static pressure and transmission loss are proportional in the rectangular chamber muffler model, with a 1.56% increase in static pressure corresponding to a 25% increase in transmission loss. [ABSTRACT FROM AUTHOR]

To solve the problem of array detection performance in environments with mesoscale eddies, this study utilizes the Gaussian eddy model to describe the sound speed structure disturbed by eddies. Through numerical simulations, the corresponding sound field is obtained, and the transmission loss influenced by the eddy is analyzed. Furthermore, to investigate the relation between the array gain and spatial correlation in the eddy environments, the differences in vertical correlation at different positions and their effects on the vertical array gain of conventional beamforming (CBF) are studied. When the source is around the eddy center, the conclusions drawn are as follows: (1) The presence of an eddy changes the turning-point depth and the sound field distribution, significantly affecting the direct sound region and the first convergence zone, while having a minor impact on the first shadow zone. (2) In different eddy-induced environments, the first convergence zone maintains a high vertical correlation, but the vertical correlation of the direct sound region is greatly influenced by the eddy. (3) The array gain of CBF is consistent with the vertical correlation. When the correlation between each element of the sound field is great, the array gain increases with the number of array elements. [ABSTRACT FROM AUTHOR]

The present study deals with the development of a mathematical equation that effectively predicts the sound insulation performance of a single-leaf structure constructed using jute composites with varying resin uptake ratios. The investigation employs a reference device to measure the transmission loss (TL) of sound energy as it propagates through a single-leaf structure. The objective is to investigate the impact of structural parameters, namely thickness, theoretical density, and compaction factor, on the attenuation of sound waves within the frequency range of 50–3150 Hz. It has been revealed that an increase in resin uptake, i.e. lower fibre content, is associated with a higher occurrence of voids inside the structure. The presence of voids inside the jute composites is inversely related to TL, while at a given fibre content, transmission loss is linearly related to the areal density of a single-leaf structure, regardless of the thickness of the jute composite. The derived equation for predicting the transmission loss of sound propagating through a single-leaf is expressed as the modified mass law of sound. This equation demonstrates that the mass of an individual leaf structure has a substantial effect on transmission loss, surpassing the influence of frequency. The study provides evidence that the jute composite can be engineered to achieve a degree of transmission loss that is comparable to the materials commonly used for sound insulation applications. [ABSTRACT FROM AUTHOR]

The Strait of Hormuz, as a crucial link between the Persian Gulf and the Gulf of Oman, exhibits complex and distinct currents that are influenced by the connection of saline waters from the Persian Gulf and the Gulf of Oman. These currents contribute to the formation of seasonal eddies, influencing the deviation and dissipation of sound energy and causing notable changes in sound speed profiles in the region. This study utilized the ROMS 3D software to simulate variable circulation patterns and the development of mesoscale eddies in the Persian Gulf based on data from 2009. The simulations, conducted with a resolution of approximately 3 km and 16 layers at the sigma level, revealed a correlation between fluctuations in wind stress and variations in flows within the Strait of Hormuz. The exchange circulation induced by wind stress led to local instability and the formation of cyclonic eddies, particularly prominent in August. Following the simulations, acoustic modeling was performed using parabolic equations and the RAMGEO model. The study focused on frequencies of 100 and 500 Hz, covering a transmission range of 10 km at six stations within the Strait of Hormuz. Sound sources were strategically placed in the surface layer, thermocline layer, and homogeneous layer near the seabed. Analysis of the two-dimensional outputs of transmission loss indicated that the position of the sound source near the seabed had the most significant impact, followed by the thermocline layer and the surface layer. [ABSTRACT FROM AUTHOR]

The non-convexity of the Optimal Power Flow (OPF) feasible region complicates the solution process and affects the applicability of various optimization techniques, which is crucial for understanding the OPF problem. This paper systematically investigates the non-convexity properties of the AC OPF feasible (power) injection region (FIR) and identifies key factors influencing its non-convexity from both analytical and numerical perspectives. Specifically, a necessary condition for FIR convexity and a sufficient condition for FIR non-convexity are derived. Based on these findings, it is concluded that the feasible region of ACOPF is inherently non-convex, with network losses playing a significant role. To avoid misjudgment of non-convexity, a non-convexity degree index for the FIR is introduced, and a numerical method to compute it is proposed. Numerical results on 9-bus and 57-bus systems indicate that the non-convexity degree of a lossless FIR is 0, whereas for a lossy FIR, it ranges from 70% to 100%. Furthermore, factors contributing to non-convexity and their impact on the location of the optimal solution and the effectiveness of convex relaxation methods (CRMs) are discussed. The numerical results demonstrate that for the same system, the optimality gap of CRMs can be as low as 0.02% in lossless networks but increases to 0.28% or more in lossy networks. These findings elucidate the relationship between network losses and the optimality gap of CRMs, providing deeper insights into the characteristics of the ACOPF problem.

Transportation tracks of railways and highways are the highest noise pollution contribution to the inhabitant urban due to the sources near residential areas. Many researchers proved that the composite material could help reduce the noise by 30%. This study focuses on designing local nature fiber composite for developing a good sound absorption material by providing experimental methods. Three natural fibers of coconut, palm oil, and sugarcane are used to make a composite by varying filler content for sound absorption and transmission loss observation. The results found that sugar cane bagasse is suitable for average performance in varied filler content for both sound absorption and transmission loss. The overall results showed a successful improvement in both sound absorption coefficient and transmission loss with the addition of fiber content

Considering the green transformation, more and more attention must be paid to reducing noise pollution, which is one of the most important environmental problems today. Internal combustion engine (ICE) powered hand tools and small appliances, such as leaf blowers, brush cutters, chainsaws, and lawn mowers, are examples of the most undesirable sources of noise in todayâs human environment. This paper discusses the acoustic properties of a novel and compact silencer for a small two­stroke ICE and proposes a novel concept with corresponding acoustic properties. The proposed solution has been measured on a test bench, and its properties, including transmission loss (TL) and reflection and absorption properties, have been experimentally determined. Using 3D printing technology and technological advantages, an innovative silencer with up to two microperforated (MP) panels, integrated into the expansion chamber of the original silencer, has been applied for rapid prototyping. As a result, noise reduction has been increased by at least 20 dB in the frequency range 800â4000 Hz.

Newly emerged acoustic barriers provide effective solutions for noise reductions of varied kinds in which acoustic barriers made of Fano resonance-based space-coiling metamaterial are reported to have promising application prospects for their broadband noise reduction ability and good ventilation performance. However, current Fano resonance-based acoustic ventilation barriers are hard to practically apply since most of them are difficult to manufacture or install. To this end, this research proposes a novel acoustic ventilation barrier based on block-shaped space-coiling metamaterial, which is not only as functional as other acoustic ventilation barriers but also easy to manufacture and install. To obtain a more in-depth understanding of the noise reduction effect, the influence of the design parameters on transmission loss is numerically studied. Additionally, we conduct both numerical and experimental studies on the transmission loss and the ventilation performance of a full-scale meta-unit. Furthermore, through the corresponding optimization process, the proposed acoustic ventilation barrier can have transmission loss consistently above 10 dB across the frequency range of 495~1063 Hz. Lastly, a composite ventilation acoustic barrier obtained by stacking two layers of different proposed metamaterials is presented, which achieves multiband noise reduction performance across the ultra-broad frequency range of 479~1758 Hz.

This study investigates acoustic propagation and transmission loss in shallow water at an unexplored site in the northern Arabian Sea near the Pakistan coastline using a normal mode theoretical framework. Sound propagation in shallow water with range-independent bathymetry was analyzed using a customized Kraken C program to compute eigenvalues and eigenfunctions. The sound speed profile and clay silt sediment samples of the northern Arabian Sea, which characterize the water column and ocean bottom, respectively, were determined. Coherent and incoherent transmission losses for frequencies ranging from 50 to 500 Hz were calculated across different ranges and depths. Results indicate significant intensity fluctuations with increasing range, leading to higher transmission loss. Low frequencies (50–225 Hz) exhibit more significant transmission loss, while higher frequencies (230–500 Hz) show reduced loss. Transmission loss is higher for receivers at 19 m depth compared to those at shallower depths (8 m and 12 m) because the receivers are positioned near the layer of bottom sediments. Factors such as source and receiver depth, sediment properties, bottom roughness, and sound frequency significantly influence transmission loss. The novel dataset for the region supports the assessment of sonar performance, underwater communication, navigation, and marine life exploration.

The horizontal-transverse coherence of low-frequency (300 Hz) and long-range (10–40 km) acoustic fields near the bottom in deep water is investigated based on experimental data obtained from the South China Sea. The results indicate that the horizontal-transverse coherence length exhibits a strong dependence on the source-receiver distance, with fluctuations consistent with sound intensity trends. In high-intensity regions, the horizontal-transverse coherence is relatively high, with a coherence length exceeding 600 λ, where λ is the acoustic wavelength, whereas in low-intensity regions, the horizontal-transverse coherence decreases significantly, with the coherence length shortening to 10–30 λ. The physical mechanisms underlying the horizontal-transverse coherence are analyzed using the ray theory. In high-intensity regions, the energy of the dominant ray (the ray with the highest energy) accounts for over 70% of the total energy of the rays, exerting a decisive influence on the coherence coefficient and leading to stable horizontal-transverse coherence in the received acoustic field. In contrast, in low-intensity regions, the energy distribution is dispersed, and when amplitude and phase disturbances due to spatial inhomogeneity are introduced, the horizontal coherence deteriorates significantly. The numerical simulations are also performed, and the results are consistent with the experimental observations.

The even more restrictive regulations imposed on chemical and acoustic emissions of ships necessitate the installation of after-treatment systems onboard. The spaces onboard are limited, and the Exhaust Gas Cleaning Systems (EGCSs) have big dimensions, so an appropriate integration and optimization of EGCSs allows to save space and comply with international regulations. Moreover, in the available literature, there is a lack of guidelines about the design of integrated EGCSs. This study aims to develop an ad hoc optimization methodology that uses combined Computational Fluid Dynamics (CFD)–Finite Element Method (FEM) simulations, surrogate models, and Genetic Algorithms to optimize the acoustic properties of EGCSs while considering the limits imposed by the efficiency of chemical reactions for the abatement of NOx and SOx. The developed methodology is applied to a Diesel Oxidation Catalyst (DOC), and the obtained results lead to a system that integrates the silencing effect into the DOC.

This study addresses the noise challenges associated with roots blowers, pivotal devices in water treatment technology, by developing an innovative duct silencer. To construct an efficient internal structure for noise reduction, a novel rectangular design altering sound propagation direction was implemented. Additionally, an array of Helmholtz resonators giving substantial transmission loss within specific frequency ranges, was used. Experimental validation and acoustic analysis were employed to evaluate the silencer's performance, ultimately confirming its noise reduction capabilities. The optimized silencer through a parametric study of the Helmholtz resonator structure exhibited an impressive transmission loss of 14.75 dB, signifying a remarkable 74 % enhancement over the existing circular silencer design. This remarkable performance substantiated its effectiveness in mitigating noise. To validate the optimized design, a physical prototype was manufactured and subjected to noise measurement experiments, revealing a significant noise reduction of 17.3 dB. [ABSTRACT FROM AUTHOR]

In order to suppress the low-frequency ultrasound vibration in the broadband range of 20 kHze100 kHz, this paper proposes and discusses an acoustic metamaterial with low-frequency ultrasound vibration attenuation properties, which is configured by hybrid arc and sharp-angle convergent star-shaped lattices. The effect of the dispersion relation and the bandgap characteristic for the scatterers in star-shaped are simulated and analyzed. The target bandgap width is extended by optimizing the geometry parameters of arc and sharp-angle convergent lattices. The proposed metamaterial configured by optimized hybrid lattices exhibits remarkable broad bandgap characteristics by bandgap complementarity, and the simulation results verify a 99% vibration attenuation amplitude can be obtained in the frequency of 20 kHze100 kHz. After the fabrication of the proposed hybrid configurational star-shaped metamaterial by 3D printing technique, the transmission loss experiments are performed, and the experimental results indicate that the fabricated metamaterial has the characteristics of broadband vibration attenuation and an amplitude greater than 85% attenuation for the target frequency. These results demonstrate that the hybrid configurational star-shaped metamaterials can effectively widen the bandgap and realize high efficiency attenuation, which has capability for the vibration attenuation in the application of highprecise equipment. [ABSTRACT FROM AUTHOR]

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