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A new type of porous sound-absorbing sound barrier was developed with quartz sand and self-developed polysiloxane resin. The forming process of the material was studied. The test specimens of the porous sound-absorbing sound barrier were prepared with different mesh numbers of quartz sand and different proportions of resin, and the void properties, compressive strength, durability, and acoustic performance were investigated. Based on the mix design results, it is suggested that 20-mesh quartz sand and a 10:1 mass ratio of quartz sand are used to prepare the porous sound-absorbing sound barrier. The durability study showed that the porous sound-absorbing sound-barrier material had good salt and alkali resistance, poor acid resistance, good water stability, and freeze–thaw stability. The laboratory acoustic test and practical engineering application results showed that the porous sound-absorbing sound barrier had excellent acoustic performance and good noise-reduction effects. [ABSTRACT FROM AUTHOR]

Laboratory and field measurements of the impact sound acoustic performance of a CLT wood-based floors have been performed. French national regulation requires the use of the standardized tapping machine for impact sound performance measurements. Since the early 2000s, rubber ball impact source has been standardized in some Asian countries to measure and evaluate the low frequency impact sound performance of floors; this excitation source is now part of international standards concerning building acoustic measurement in laboratories and in-situ. Indeed, the impact sound level associated to this soft impact source is supposed to provide a better correlation with annoyance from jumping and/or running children in buildings. The paper reviews the measurements performed using the standard tapping machine and the rubber ball as impact source, on CLT based floors in a laboratory, as well as those on the CLT based experimental building. Impact sound improvements are presented and discussed. The necessity of measuring with both impact sources, rather than only with the tapping machine is examined. [ABSTRACT FROM AUTHOR]

Fused Filament Fabrication (FFF) is one of the most emerging techniques nowadays. Affordable, easy to use, economical, for a broad audience − from specialists to home users. These are only several of its advantages. A disadvantage is the limited number of available filament types, especially those with high performance. Therefore, the aim of the work was to investigate the properties of custom–made filament printouts based on polylactic (PLA), graphite (G) and molybdenum disulfide (MoS2).This work looked at structural and thermal analysis, acoustic performance, EMI shielding, and electrical and thermal properties, including thermal conductivity and heat diffusivity. The following were considered during the study: type of printing architecture, infill density, and filament formulations. Among the best values, which were obtained for the highest loaded sample based on 15 wt% graphite and 2 wt% MoS2 (G15/M2), where EMI shielding effectiveness surpassed SETOT ∼ 17 dB (per 1 mm sample thickness), electrical conductivity remained at a low level. It exceeded σ ∼ 0.2 S/m; thermal conductivity was slightly over κ ∼ 0.4 W/mK, and heat diffusivity was almost α ∼ 0.4 mm2/s.This work is the first step in designing high-performance materials dedicated to advanced applications based on the FFF technique.

This paper attempts to ascertain the thermal and acoustic impacts of introducing a vegetative roof layer on insulated and uninsulated metal roofs for tropical climates, through field measurements in Skudai, Johor, Malaysia, that were conducted for both dry and wet days. Four small-scale roof modules were tested, namely an uninsulated metal roof (uiMDR), an insulated metal roof (iMDR), and two identical corresponding modules with an additional vegetative component (uiGR and iGR, respectively). Outdoor ambient temperature (Tamb) was the most influential correlated variable affecting the roof outer surface temperature (RTOS) in 50% of the assessed scenarios. On the selected dry day, the inter-quartile ranges (IQR) of iGR, iMDR, uiGR, and uiMDR were 6.21 °C, 8.32 °C, 6.69 °C, and 1.66 °C, respectively; the IQRs were 1.6 °C, 4.11 °C, 2.59 °C, and 1.78 °C, respectively, on the selected wet day. Based on design U-value calculations, iGR was better than iMDR and uiMDR for both dry and wet days. The U-value of uiGR was also better than iMDR under dry-day conditions. The Wilcoxon signed-rank test also indicated a statistically significant difference in the roof inner surface temperature (RTIS) measurements (p-value = 0.00) during Malaysian daylight hours, between 8.00 a.m. and 6.00 p.m., regardless of the weather. In terms of sound level reduction under dry-day conditions, the Kruskal–Wallis and Wilcoxon signed-rank tests showed statistically significant differences in sound level reductions, with iGR and uiGR performing better than iMDR and uiMDR (p-values = 0.00). The sound level reductions for iGR, iMDR, and uiGR were 51%, 32%, and 31%, respectively, while uiMDR experienced sound level amplifications by 6%, possibly due to the acoustic resonance effect. This proof of concept may encourage a broader application of extensive GRs in Malaysia using metal roofs, beyond the conventional RC base construction method. [ABSTRACT FROM AUTHOR]

Polymeric layers or multilayers with air cavities or solid particles have considerable attenuation properties and can be tailored to have acoustic impedance close to water. So, many underwater sound absorbers are made from such multilayer structures. In this work, first, we present a transfer matrix method (TMM) based on force equilibrium to be used for variable cross-section viscoelastic multilayers with cavities. The method can be used for layers with various cavity designs; also, the outer boundary can be conical or any other axisymmetric shape. The formulation is derived for different outer impedance-matched boundary conditions. The study of anechoic coatings with periodic holes is then studied as a special case of the developed TMM. In this regard, the difference between the present formulation and related literature is explained and the TMM results are compared with numerical simulations which are performed using COMSOL. Moreover, the effect of cavity shape and bulk loss factor on the echo reduction properties of the coatings are investigated. It is concluded that for small cavity sizes and with an abrupt change of multilayer cross sections, the echo reduction values are more dependent on bulk loss factor, especially near the resonance frequency. [ABSTRACT FROM AUTHOR]

A new type of porous sound-absorbing sound barrier was developed with quartz sand and self-developed polysiloxane resin. The forming process of the material was studied. The test specimens of the porous sound-absorbing sound barrier were prepared with different mesh numbers of quartz sand and different proportions of resin, and the void properties, compressive strength, durability, and acoustic performance were investigated. Based on the mix design results, it is suggested that 20-mesh quartz sand and a 10:1 mass ratio of quartz sand are used to prepare the porous sound-absorbing sound barrier. The durability study showed that the porous sound-absorbing sound-barrier material had good salt and alkali resistance, poor acid resistance, good water stability, and freeze–thaw stability. The laboratory acoustic test and practical engineering application results showed that the porous sound-absorbing sound barrier had excellent acoustic performance and good noise-reduction effects.

Engine noise, as a source of sound pollution for humans and the environment, can be reduced by designing a high-performance muffler. This study presents a novel, organized design process of that muffler for the KTM390 engine as a case study. The acoustic simulation analysis is performed in COMSOL software and aerodynamic analysis is performed in ANSYS Fluent. The features of the muffler considered in this designing process are the overall length of the muffler, the presence of baffles and related parameters (baffle distance, baffle hole diameter, and baffle hole offset), and the effects of extended tubes. In order to evaluate the acoustic performance of the muffler, an objective function has been defined and measured on two frequency ranges, 75–300 Hz and 300–1500 Hz. For evaluating the aerodynamic performance of that, the amount of backpressure is analyzed to achieve a maximum of 3.3 kilopascals for this muffler. The selection of the appropriate parameters includes comparing the resulting transmission loss curves and quantitative evaluation of objective functions (for transmission loss) and backpressure. This organized design process (i.e., tree diagram) leads to an increase in the efficiency of designing mufflers (for example, 41.2% improvement on backpressure).

The inadequate disposal of waste tires has caused environmental and public health problems. One of the direct harmful effects is the noise due to traffic. Waste rubber has been used in concrete to improve its acoustic performance and energy absorption. Studies carried out by the U. S. Federal Highway Administration show that barriers, regardless the material used, do not block completely but can reduce the volume of traffic noise by half. This study proposes concrete mixes containing waste tires and vermiculite to verify their acoustic properties for road barriers. The experiments include concrete with waste tires and vermiculite to replace the sand mass from 10% to 40%. An improvement in the acoustic properties was observed, reducing the total sound intensity level of the concrete acoustic barrier to 20 dB and 29 dB, for the frequencies of 500 Hz and 1000 Hz, respectively.

Due to the high impact of the building sector on the environment, a growing interest focuses on insulating materials able to ensure good thermo-acoustic performance for the building envelope from a sustainable and circular economy perspective. In this context, Moroccan natural gypsum was mixed with local natural waste materials. The thermal and acoustic properties of the samples were measured; they were compared to those of synthetic- and mineral-based gypsum plasters manufactured with the same technique. A Small Hot Box apparatus was used for thermal characterization, whereas acoustic performance was investigated by means of a Kundt's Tube. Natural and synthetic additives result in a reduction in density and an improvement in thermal performance. Conductivity values in the 0.181–0.238 W/mK range were obtained, depending on the type of natural additive, with respect to 0.275–0.323 W/mK of mineral-based gypsum plasters. The acoustic measurements showed that all the composites have similar performance in terms of acoustic absorption, whereas high transmission loss values were obtained for the natural additives (TL = 35–59 dB). Petiol of Palm and Stipa Tenacissima were found to be materials able to improve both thermal and acoustic properties. [ABSTRACT FROM AUTHOR]

In this paper, a blade with unconventional structure, corrugations and BERP tip, used in UAV helicopters, was designed, analyzed and additively manufactured. Aerodynamically, the unconventional blade shows better performance compared to the conventional blade at positive angles of attack. Acoustically, the unconventional blade showed a reduced noise level compared to the conventional blade. Acoustic testing of additively manufactured samples with five honeycomb core configurations showed higher performance for the 1.5 mm honeycomb cell samples 3D printed from T-PLA. [ABSTRACT FROM AUTHOR]

Engine noise, as a source of sound pollution for humans and the environment, can be reduced by designing a high-performance muffler. This study presents a novel, organized design process of that muffler for the KTM390 engine as a case study. The acoustic simulation analysis is performed in COMSOL software and aerodynamic analysis is performed in ANSYS Fluent. The features of the muffler considered in this designing process are the overall length of the muffler, the presence of baffles and related parameters (baffle distance, baffle hole diameter, and baffle hole offset), and the effects of extended tubes. In order to evaluate the acoustic performance of the muffler, an objective function has been defined and measured on two frequency ranges, 75–300 Hz and 300–1500 Hz. For evaluating the aerodynamic performance of that, the amount of backpressure is analyzed to achieve a maximum of 3.3 kilopascals for this muffler. The selection of the appropriate parameters includes comparing the resulting transmission loss curves and quantitative evaluation of objective functions (for transmission loss) and backpressure. This organized design process (i.e., tree diagram) leads to an increase in the efficiency of designing mufflers (for example, 41.2% improvement on backpressure). [ABSTRACT FROM AUTHOR]

This paper attempts to ascertain the thermal and acoustic impacts of introducing a vegetative roof layer on insulated and uninsulated metal roofs for tropical climates, through field measurements in Skudai, Johor, Malaysia, that were conducted for both dry and wet days. Four small-scale roof modules were tested, namely an uninsulated metal roof (uiMDR), an insulated metal roof (iMDR), and two identical corresponding modules with an additional vegetative component (uiGR and iGR, respectively). Outdoor ambient temperature (Tamb) was the most influential correlated variable affecting the roof outer surface temperature (RTOS) in 50% of the assessed scenarios. On the selected dry day, the inter-quartile ranges (IQR) of iGR, iMDR, uiGR, and uiMDR were 6.21 °C, 8.32 °C, 6.69 °C, and 1.66 °C, respectively; the IQRs were 1.6 °C, 4.11 °C, 2.59 °C, and 1.78 °C, respectively, on the selected wet day. Based on design U-value calculations, iGR was better than iMDR and uiMDR for both dry and wet days. The U-value of uiGR was also better than iMDR under dry-day conditions. The Wilcoxon signed-rank test also indicated a statistically significant difference in the roof inner surface temperature (RTIS) measurements (p-value = 0.00) during Malaysian daylight hours, between 8.00 a.m. and 6.00 p.m., regardless of the weather. In terms of sound level reduction under dry-day conditions, the Kruskal–Wallis and Wilcoxon signed-rank tests showed statistically significant differences in sound level reductions, with iGR and uiGR performing better than iMDR and uiMDR (p-values = 0.00). The sound level reductions for iGR, iMDR, and uiGR were 51%, 32%, and 31%, respectively, while uiMDR experienced sound level amplifications by 6%, possibly due to the acoustic resonance effect. This proof of concept may encourage a broader application of extensive GRs in Malaysia using metal roofs, beyond the conventional RC base construction method.

In this paper, a blade with unconventional structure, corrugations and BERP tip, used in UAV helicopters, was designed, analyzed and additively manufactured. Aerodynamically, the unconventional blade shows better performance compared to the conventional blade at positive angles of attack. Acoustically, the unconventional blade showed a reduced noise level compared to the conventional blade. Acoustic testing of additively manufactured samples with five honeycomb core configurations showed higher performance for the 1.5 mm honeycomb cell samples 3D printed from T-PLA.

Aiming at the problem of high noise generated by the rotation of centrifugal fan blades during operation, the windward surface structure of the blades was taken as the object of study, and the acoustic performance of the blades was simulated. The influence of blade perforation on the acoustic performance of centrifugal fan was analyzed. Firstly, the windward surface of the blade was perforated, and the effect of different perforation shapes, different perforation diameters, and different porosity on the fan noise was investigated using FLUENT simulation software. Then, the effect on the acoustic performance of the fan was discussed after the blade was filled with porous media material. Finally, orthogonal experiments of original blade, blade perforation, blade perforation and filling material were carried out, and the reliability of simulation results of different blade perforation structures was verified by experiments. The simulation results show that when the perforation shape is round, the perforation diameter is 1.5 mm, and the porosity is 5%, the fan noise is reduced by 5.6%. After the blade is filled with porous media material inside, it can further reduce the fan noise. Comparing with the original blade, the noise reduction effect is improved by 9.1%, and the negative pressure performance of the fan is improved by 11%. Experimental results show that blade perforation and material filling can increase the noise reduction effect by 5.3% and air volume by 7.5%. The research results show that the perforation of the blade surface structure and the inside filling of porous material can effectively reduce fan noise, and the conclusions obtained provide reference for the noise reduction treatment technology of centrifugal fans. [ABSTRACT FROM AUTHOR]

A modified strain-hardening cementitious composite (SHCC) material, fabricated using corundum aggregates (SHCC-Cor), has been proposed for roadway applications as it offers high structural performance and high skid resistance. However, the acoustic performance of SHCC is unclear and has not been well studied in the past. Theoretically, SHCC may not provide the optimum solution in acoustic performance as it provides a low texture profile, high density, and low porosity. In this study, the acoustic performance of pavement slabs made of SHCC and modified SHCC-Cor are investigated using a nondestructive method to determine the surface roughness (macro texture) of slab surfaces. The pavement–tire noise level was then simulated using SPERoN software. As result, the noise level coming from the pavement made of SHCC could be up to 65 dB(A), while the noise level for SHCC-Cor increased up to 69.2 dB(A) because of the lower shape factor (G) due to a rougher surface as a result of the existence of corundum aggregate on the SHCC surface. The aeroacoustics were also increased compared to the SHCC slab. The modification of SHCC-Cor by introducing grooves (SHCC-Cor-Gro) successfully reduced the sound level coming from the vibration.

In the calculation of the acoustic performance of mufflers, the walls of mufflers are usually treated rigidly without considering the acoustic-structural coupling, but the results so calculated differ significantly from the actual situation. Based on the basic equations, the article derives the finite element equations of the muffler system while considering the acoustic-structural coupling effect and theoretically analyses the connection between the acoustic-structural coupling system and the structural and acoustic modes. The structural and acoustic modes of the muffler are calculated and the reasons for the mutation of the transmission loss curve of the muffler when the acoustic-structural coupling is considered are analysed. The results show that the acoustic-structural coupling is the result of the interaction between the structure and the air inside the expansion chamber under acoustic excitation, which manifests mutations in the sound pressure inside the muffler in some frequency bands. Then, using a single-chamber muffler as an example, the transmission loss is used to characterise the performance of the muffler. The effects of different factors such as shell thickness, structure, porous media material lining, and restraint method on the acoustic-structural coupling effect of the muffler are analysed, and the structure of a double-chamber muffler is successfully optimised according to the conclusions.

Over the last couple of decades, there is an increasing demand to control interior noise occurring in aircraft, automobiles, railways, and construction works. Interior noise could impair people’s health, affecting passenger comfort and active safety performance. One of the contemporary noise control technologies is the use of sound-absorbing materials. Traditionally, mineral fibers, foams, and composites are used as sound-absorbing materials. However, they are expensive and energy consumptive as they add to the structure’s weight and affect structural integrity. Natural fibers could contribute to the replacement of conventional mineral fibers with decreased environmental impact, carbon neutrality, and improved sound-absorbing qualities. Also, previous research proved that sound-absorbing materials having natural fiber possess better acoustic properties comparable to those of synthetic fibers. However, high water absorption, termite attack, low fire resistance, and low strength are some of the issues restricting natural fibers usage. Here, an attempt is made to present the potential of natural fibers for acoustic absorbers by understanding the benefits of their inherent porous and tortuous structure. This paper involves a review study of experimental methods and parameters used to regulate the acoustic performance of natural fibers. Natural fibers seem a proven alternative as an acoustic absorber, thereby reducing sustainability concerns related to synthetic materials in acoustics applications.

ObjectiveThis paper aims to establish a dynamic model of a floating raft vibration isolation system with a liquid tank in order to study the mass effect of the liquid medium, tank form, structural stiffness and loading rate on acoustic performance. MethodsA floating raft system with a cuboidal or cylindrical liquid tank is taken as the research object, and a fluid-structure coupling finite element dynamic model is established. The dynamic force transmission rate and power flow are then used to evaluate the acoustic performance of the system. The influence of the mass effect of the liquid medium, tank form, structural stiffness and loading rate of tank volume on the acoustic performance of the floating raft system are analyzed.ResultsThe results show similar laws obtained through the calculation and analysis of the floating raft system with two types of tanks. The structural stiffness of the tank affects the mass effect of the liquid medium in the tank to a certain extent. ConclusionsIf full advantage is to be taken of the liquid mass effect in the tank with a large loading rate to improve the acoustic performance of the floating raft system, the design of the liquid tank and raft structure must have sufficient stiffness. In addition, under the condition that the floating raft structure has sufficient stiffness, its acoustic performance will improve significantly as the tank loading rate increases in the relevant low frequency range.

Copyright of Plastics Science & Technology / Suliao Ke-Ji is the property of Plastics Science & Technology Editorial Office 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.)

A modified strain-hardening cementitious composite (SHCC) material, fabricated using corundum aggregates (SHCC-Cor), has been proposed for roadway applications as it offers high structural performance and high skid resistance. However, the acoustic performance of SHCC is unclear and has not been well studied in the past. Theoretically, SHCC may not provide the optimum solution in acoustic performance as it provides a low texture profile, high density, and low porosity. In this study, the acoustic performance of pavement slabs made of SHCC and modified SHCC-Cor are investigated using a nondestructive method to determine the surface roughness (macro texture) of slab surfaces. The pavement–tire noise level was then simulated using SPERoN software. As result, the noise level coming from the pavement made of SHCC could be up to 65 dB(A), while the noise level for SHCC-Cor increased up to 69.2 dB(A) because of the lower shape factor (G) due to a rougher surface as a result of the existence of corundum aggregate on the SHCC surface. The aeroacoustics were also increased compared to the SHCC slab. The modification of SHCC-Cor by introducing grooves (SHCC-Cor-Gro) successfully reduced the sound level coming from the vibration. [ABSTRACT FROM AUTHOR]

Due to its excellent properties, monolithic silica aerogel is a promising material for innovative glazing systems. Since glazing systems are exposed to deteriorating agents during building service life, it is essential to investigate the long-term performance of aerogel. In the present paper, several 12.7 mm-thick silica aerogel monoliths produced by a rapid supercritical extraction method were tested, including both hydrophilic and hydrophobic samples. After fabrication and characterization of hydrophobicity, porosity, optical and acoustic properties, and color rendering, the samples were artificially aged by combining temperature and solar radiation effects in an experimental device specifically developed at the University of Perugia. The length of the experimental campaign was determined using acceleration factors (AFs). Temperature AF was evaluated according to the Arrhenius law using thermogravimetric analysis to estimate the aerogel activation energy. A natural service life of 12 years was achieved in about 4 months, and the samples' properties were retested. Contact angle tests supported by FT-IR analysis showed loss of hydrophobicity after aging. Visible transmittance values in the 0.67–0.37 range were obtained for hydrophilic and hydrophobic samples, respectively. The aging process involved optical parameter reduction of only 0.02–0.05. There was also a slight loss in acoustic performance (noise reduction coefficient (NRC) = 0.21–0.25 before aging and NRC = 0.18–0.22 after aging). For hydrophobic panes, color shift values in the 10.2–59.1 and 8.4–60.7 ranges were obtained before and after aging, respectively. The presence of aerogel, regardless of hydrophobicity, results in a deterioration in light-green and azure tones. Hydrophobic samples had lower color rendering performance than hydrophilic aerogel, but this did not worsen after the aging process. This paper makes a significant contribution to the progressive deterioration assessment of aerogel monoliths for applications in sustainable buildings. [ABSTRACT FROM AUTHOR]

With the increasing prominence and complexity of environmental noise problems, there is an urgent need for novel acoustic materials to meet noise reduction requirements. In this paper, two auxetic microstructures and three typical lattice microstructures are established, and a microscopic-macroscopic acoustic performance study scheme is established through the Johnson-Champoux-Allard-Pride-Lafarge (JCAPL) model. Auxetic-BCC porous materials have lower acoustic resistance and reactance amplitudes than many typical porous materials through experimental verification and comparative analysis of numerical calculations. The porous material's thickness and the backing cavity's thickness have similar effects on sound absorption performance when controlling a single change in structural parameters, and there is an optimum thickness. As acoustic resistance and reactance are dominant at low and high frequencies, respectively, noise reduction is better at low (high) frequencies than at minor (large) porosity, and the porosity of 76.4%–82.0% has the best sound absorption effect. Changes in prism length of materials with high porosity are more sensitive than those with low porosity, so the prism length with porosity of 76.4%, 79.0%, and 82.6% shall be designed to be less than 1.1 mm, 0.9 mm, 0.8 mm, respectively. This study provides theoretical guidance for designing multifunctional porous materials in extreme environments.

Copyright of China Rubber Industry is the property of Editorial Office of China Rubber Industry 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 aims to investigate the thermo-acoustic and hygrothermal properties of innovative panels made of leather waste produced by a bag factory from a circular economy perspective. Their performance was compared with other residual-based insulation panels. The leather scraps were chipped and three boards were fabricated by means of a mold with different compositions, adding adhesive glue. In order to improve the sustainability aspects, a sample was assembled by using a water-based polyurethane glue, in addition to the two panels with vinyl glue. Panels were tested for thermal, acoustic, and hygrothermal performance. Thermal conductivity values in the range of 0.064–0.078 W/mK at 10 °C were measured depending on the composition and the adhesive. A slight thermal performance deterioration occurs when using the natural water-based glue. The samples were characterized by good performance both in terms of sound absorption coefficient (Noise Reduction Coefficient NRC = 0.21–0.28) and Transmission Loss, up to 59 dB values. Water vapor resistance factor values in the 35–48 range were obtained, close to the values of standard materials, such as expanded polystyrene and polyurethane. [ABSTRACT FROM AUTHOR]

In order to improve the acoustic performance of an internal combustion forklift exhaust muffler, this paper considered the influence of air flow and temperature, based on the flow field analysis theory, the exhaust muffler's fluid domain model at the highest engine speed was established, that is, the complex flow and temperature fields were numerically simulated with a computational fluid dynamics (CFD) model, and the acoustic calculation was carried out by the finite element mothod (FEM), obtaining the velocity and temperature cloud maps and transmission loss curve. In addition, according to the simulation results, the improvement strategy towards intake pipe structural parameters was proposed. Numerical simulations indicate that for the improved exhaust muffler, flow eddy regions are obviously decreased, temperature gradient distribution is uniform, the transmission loss in most frequency bands and the overall sound attenuation effect are improved, which will lay a technical foundation for future physical application and multi-field coupling research. [ABSTRACT FROM AUTHOR]

Over the last couple of decades, there is an increasing demand to control interior noise occurring in aircraft, automobiles, railways, and construction works. Interior noise could impair people's health, affecting passenger comfort and active safety performance. One of the contemporary noise control technologies is the use of sound-absorbing materials. Traditionally, mineral fibers, foams, and composites are used as sound-absorbing materials. However, they are expensive and energy consumptive as they add to the structure's weight and affect structural integrity. Natural fibers could contribute to the replacement of conventional mineral fibers with decreased environmental impact, carbon neutrality, and improved sound-absorbing qualities. Also, previous research proved that sound-absorbing materials having natural fiber possess better acoustic properties comparable to those of synthetic fibers. However, high water absorption, termite attack, low fire resistance, and low strength are some of the issues restricting natural fibers usage. Here, an attempt is made to present the potential of natural fibers for acoustic absorbers by understanding the benefits of their inherent porous and tortuous structure. This paper involves a review study of experimental methods and parameters used to regulate the acoustic performance of natural fibers. Natural fibers seem a proven alternative as an acoustic absorber, thereby reducing sustainability concerns related to synthetic materials in acoustics applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Custom-made filaments of PLA, carbon black, graphite and molybdenum disulfide were fabricated and printed in various architectures and infill densities. • The thermal analysis, acoustic performance, EMI shielding, electrical and thermal conductivity, and heat diffusivity were measured. • The sound absorption shows selective behaviour favouring the best and the lowest infill density and gyroid type of structure. • The EMI shielding is influenced the most by as well the lowest infill density and is less sensitive to the architecture type or formulation of the sample. • The thermal conductivity and heat diffusivity are affected by sample formulation, remaining the best for the highest graphite and MoS 2 concentrations. Fused Filament Fabrication (FFF) is one of the most emerging techniques nowadays. Affordable, easy to use, economical, for a broad audience − from specialists to home users. These are only several of its advantages. A disadvantage is the limited number of available filament types, especially those with high performance. Therefore, the aim of the work was to investigate the properties of custom–made filament printouts based on polylactic (PLA), graphite (G) and molybdenum disulfide (MoS 2). This work looked at structural and thermal analysis, acoustic performance, EMI shielding, and electrical and thermal properties, including thermal conductivity and heat diffusivity. The following were considered during the study: type of printing architecture, infill density, and filament formulations. Among the best values, which were obtained for the highest loaded sample based on 15 wt% graphite and 2 wt% MoS 2 (G15/M2), where EMI shielding effectiveness surpassed SE TOT ∼ 17 dB (per 1 mm sample thickness), electrical conductivity remained at a low level. It exceeded σ ∼ 0.2 S/m; thermal conductivity was slightly over κ ∼ 0.4 W/mK, and heat diffusivity was almost α ∼ 0.4 mm2/s. This work is the first step in designing high-performance materials dedicated to advanced applications based on the FFF technique. [ABSTRACT FROM AUTHOR]

Due to the high impact of the building sector on the environment, a growing interest focuses on insulating materials able to ensure good thermo-acoustic performance for the building envelope from a sustainable and circular economy perspective. In this context, Moroccan natural gypsum was mixed with local natural waste materials. The thermal and acoustic properties of the samples were measured; they were compared to those of synthetic- and mineral-based gypsum plasters manufactured with the same technique. A Small Hot Box apparatus was used for thermal characterization, whereas acoustic performance was investigated by means of a Kundt’s Tube. Natural and synthetic additives result in a reduction in density and an improvement in thermal performance. Conductivity values in the 0.181–0.238 W/mK range were obtained, depending on the type of natural additive, with respect to 0.275–0.323 W/mK of mineral-based gypsum plasters. The acoustic measurements showed that all the composites have similar performance in terms of acoustic absorption, whereas high transmission loss values were obtained for the natural additives (TL = 35–59 dB). Petiol of Palm and Stipa Tenacissima were found to be materials able to improve both thermal and acoustic properties.

There is little knowledge from occupied buildings of the impact of radiant heating and cooling systems on indoor environmental quality aspects such as thermal comfort, indoor air quality, and acoustics. We present indoor environmental quality survey results from 3,892 respondents in 60 office buildings located in North America; 34 of which used all-air systems and 26 of which used radiant systems as the primary conditioning system. In the current study, we present the survey results of 1,645 occupants in buildings with radiant systems. To our knowledge, this is the largest dataset used in a comparison of occupant satisfaction in radiant buildings. We used an existing database to extract a subset of occupant responses from all-air buildings whose key characteristics match those radiant buildings. The results indicate that radiant and all-air spaces have equal indoor environmental quality, including acoustic satisfaction, with a tendency towards improved temperature satisfaction in radiant buildings.

In the calculation of the acoustic performance of mufflers, the walls of mufflers are usually treated rigidly without considering the acoustic-structural coupling, but the results so calculated differ significantly from the actual situation. Based on the basic equations, the article derives the finite element equations of the muffler system while considering the acoustic-structural coupling effect and theoretically analyses the connection between the acoustic-structural coupling system and the structural and acoustic modes. The structural and acoustic modes of the muffler are calculated and the reasons for the mutation of the transmission loss curve of the muffler when the acoustic-structural coupling is considered are analysed. The results show that the acoustic-structural coupling is the result of the interaction between the structure and the air inside the expansion chamber under acoustic excitation, which manifests mutations in the sound pressure inside the muffler in some frequency bands. Then, using a single-chamber muffler as an example, the transmission loss is used to characterise the performance of the muffler. The effects of different factors such as shell thickness, structure, porous media material lining, and restraint method on the acoustic-structural coupling effect of the muffler are analysed, and the structure of a double-chamber muffler is successfully optimised according to the conclusions. [ABSTRACT FROM AUTHOR]

With the large-scale construction of suburban railway viaducts, the noise problem along the viaducts is becoming more and more prominent. Conventional vertical noise barriers have been widely used to alleviate the noise problem along the suburban railway viaducts. However, conventional vertical noise barriers often have an adverse effect on the urban landscape and also block the view of train drivers and passengers. A type of near-rail low-height noise barrier was planned to install on the viaducts of Wenzhou Rail Transit Line S1 to reduce the impact of noise on residents along the railway lines. To assess the acoustic performance of the near-rail low-height noise barrier, a numerical procedure for railway viaduct comprehensive noise considering wheel-rail noise and structure-borne noise of the bridge and noise barriers was proposed and then verified by a field test. On this basis, numerical models were established to compare the acoustic performances of the near-rail low-height noise barrier and conventional vertical noise barrier. The influences of the height and top shape of the near-rail low-height noise barrier on the acoustic performance were discussed. Based on the numerical analysis results, it is found that both the near-rail low-height noise barrier and conventional vertical noise barrier have good acoustic performances. The noise reduction effect of the near-rail low-height noise barrier is slightly better than that of the conventional vertical noise barrier. The acoustic performance of the near-rail low-height noise barrier gradually improves, but the improvement rate gradually slows down as the height of the noise barrier increases. The noise reduction effects of both the inverted L-shaped and Y-shaped near-rail low-height noise barrier are obviously better than that of the vertical one, while the noise reduction effects of the inverted L-shaped near-rail low-height noise barrier are slightly better than the Y-shaped one. [ABSTRACT FROM AUTHOR]

Introduction: The acoustic performance of natural fiber adsorbents has been investigated in numerous studies. A part of these materials show a poor adsorption within the frequency range of less than 1000 Hz. In the present study, attempts were made to investigate the effect of layout sequence of double-layered composites consisting of natural and synthetic fibers on improving the acoustic adsorption coefficient of natural fiber in the low-frequency range (63 to 1000 Hz) using the numerical finite element method. Material and Methods: In this study, the finite element method and the Johnson-Champoux-Allard model in COMSOL software version 5.3a were used to investigate the acoustic performance of the double-layered composites consisting of natural and synthetic adsorbents. The acoustic absorbers under study included date palm fiber, polyurethane foam and cellular rubber. Each double-layered composite included a date palm fiber with 10mm in thickness and a synthetic adsorbent (polyurethane foam or cellular rubber) with 10mm in thickness. In sum, four double-layered composite structures with different layouts of adsorbents in each structure were studied. Results: The location of natural fiber can play a critical role in the acoustic performance of the double-layered composite structures such that comparing the studied double-layered composites revealed that when the natural fiber was the first layer exposed to the normal sound in the double-layered composites with 20mm in thickness, the trend of acoustic performance was approximately the same as the single-layered composite of natural fiber with 20mm in thickness; but in the composite structures, when the synthetic adsorbent was the first layer exposed to the sound, the trend of acoustic absorption was improved. Conclusion: On the basis of the results, the double-layered composite structure with a higher-density and lower-porosity upper layer showed a better acoustic absorption trend than the single-layered composite including the natural adsorbent.

In this study, a kind of structural gradient metal hollow spheres composites (SG-MHSCs) were fabricated using two kinds of 316L stainless steel hollow spheres with different diameters and A356 aluminum through the casting method. Then the density of the SG-MHSCs was measured by the direct measurement; the microstructure of the SG-MHSCs was characterized by the Scanning Electron Microscope. Meanwhile, the acoustic performance of MHSCs was tested by the impedance tube, and the sound absorption and insulation mechanism SG-MHSCs were discussed and analyzed.

There are subjective and objective acoustic parameters in the creation of acoustic performance for speech action in room acoustics. Control of reverberation time affecting subjective and objective acoustic parameters is a main parameter in room acoustics. In this study, the acoustic performance assessment of the TOBB Twins Headquarters Reception Hall, which is current enclosed space with square plan and flat floor, has been performed as a case study. The evaluation focused on the relationship between reverberation time and interior surface absorption. Primarily, the reverberation time was determined according to the international standard with in-situ measurements in the current enclosed space. The reverberation time of the space was found over the reference value range. Models have been developed with the use of materials to reduce the reverberation time. In the assessment of room acoustics parameters, reverberation times of the models developed using Ecotect v.5.20 and Odeon 14.00 simulation programs have been determined. The model in which the optimum reverberation time for the speech action was obtained was constructed. After the construction, reverberation time measurements have been made again. As a result of the study, the effect of surface absorptions on the improvement of reverberation time in the enclosed spaces with square plan and flat floor for speech action has been evaluated. Suggestions have been developed to control the reflective and absorption properties of all surfaces in accordance with the evaluation and improvement of reverberation time. [ABSTRACT FROM AUTHOR]

In the US, people spend about 90% of their time indoors. This long exposure to indoor conditions affects our well-being, performance and health. Design and operation of these spaces also impacts energy use in building which, in the US, accounts for 40% of primary energy use. With these dual challenges, researchers and building professionals seek design strategies to simultaneously address the challenge of indoor environmental quality (IEQ) and energy use. Radiant heating and cooling systems have the potential to achieve significant energy savings primarily due to the use of lower temperature differences between the space and the heating or cooling source. Compared to buildings with all-air systems, buildings with radiant systems have been commonly associated with increased thermal comfort but decreased acoustic quality. The concern of reduced acoustics is particularly the case with regard to massive radiant systems and the need to preserve heat transfer, thereby keeping radiant surfaces uncovered. Achieving improved IEQ is fundamental for the successful adoption of radiant technologies in buildings. This dissertation proposed to address thermal comfort and acoustic quality in spaces using radiant systems through two major questions: -           How do spaces with radiant systems compare to spaces with all-air systems in terms of thermal comfort and acoustic quality? -           Can the combination of free-hanging acoustical clouds and fans below a massive radiant ceiling address simultaneously thermal comfort, cooling capacity and acoustical performance issues? As part of a larger research team I utilized literature review, occupant surveys, statistical analysis, and laboratory experiments of a market-ready solution to address these questions. We performed a literature review to assess if there was existing evidence that radiant systems provide better, equal or lower thermal comfort than all-air systems. This review identified five studies that could not establish a preference between the two systems and three studies showing a preference for radiant systems. These studies used multiple methods to demonstrate their findings and, in addition, several types of all-air and radiant systems were tested. This limited number of available studies did not allow us to draw a conclusion about the effectiveness of radiant systems for thermal comfort. Following this review, we conducted occupant surveys in buildings using radiant systems. We gathered responses from 1284 occupants (20 buildings) that we complemented with responses form 361 occupants (6 buildings) previously surveyed. We used an existing database to extract a subset of occupant responses from all-air buildings whose key characteristics match those radiant buildings. This comparison involved 3892 responses from 60 buildings total. All-air and radiant buildings have equal indoor environmental quality, including acoustical satisfaction (assessed for noise and sound privacy), with a tendency towards improved thermal comfort in radiant buildings. There is a 16% probability of temperature satisfaction superiority for occupants exposed to radiant systems. In a third phase, we experimentally assessed the combined effect of free-hanging acoustic clouds and fans for an office room. Free-hanging acoustic clouds are intended to reduce acoustical issues of a radiant massive ceiling, yet, they will also reduce its cooling capacity. Fan-induced air movement can be used to compensate for the cooling capacity reduction and enhance thermal comfort. In the test configuration, we installed a ceiling fan between the clouds (blowing in the upward or downward direction) and small fans above the clouds (blowing horizontally) both at the ceiling level. The two types of fans were tested independently. The acoustical results showed that if the clouds covered 40-50% of the ceiling area, acceptable reverberation time (one of the metrics for acoustical quality) was achieved. The cooling capacity experiments conducted without fans showed that for 47% cloud coverage, the cooling capacity only decreased by 11%. The ceiling fan increased cooling capacity by up to 22% when blowing upward and up to 12% when blowing downward, compared to the reference case and over the different cloud coverage ratios. For variants with small fans, the cooling increases with coverage proving that the combination of a cloud and a small fan has a positive effect on cooling capacity. Elevated air motion in the occupied space can provide further advantages from a thermal comfort perspective for the ceiling fan variants. Combining fans with acoustical absorbents close to the radiant surface has the potential to increase cooling capacity while simultaneously providing improved acoustic quality. In summary, the dissertation work has: (1) summarized the state of current research on thermal comfort for radiant systems compared to all-air systems; (2) developed and analyzed the largest database of occupant responses in buildings using radiant systems; (3) used occupant feedback to show that radiant and all-air buildings have overall equal indoor environmental quality, including acoustical satisfaction, but with a tendency towards improved thermal comfort in radiant spaces; and (4) experimentally tested two practical solutions of combined acoustic clouds and fans below a radiant chilled ceiling, herein showing that it is possible to overcome the limitation of ceiling sound absorption often associated with radiant slab systems.

Due to its excellent properties, monolithic silica aerogel is a promising material for innovative glazing systems. Since glazing systems are exposed to deteriorating agents during building service life, it is essential to investigate the long-term performance of aerogel. In the present paper, several 12.7 mm-thick silica aerogel monoliths produced by a rapid supercritical extraction method were tested, including both hydrophilic and hydrophobic samples. After fabrication and characterization of hydrophobicity, porosity, optical and acoustic properties, and color rendering, the samples were artificially aged by combining temperature and solar radiation effects in an experimental device specifically developed at the University of Perugia. The length of the experimental campaign was determined using acceleration factors (AFs). Temperature AF was evaluated according to the Arrhenius law using thermogravimetric analysis to estimate the aerogel activation energy. A natural service life of 12 years was achieved in about 4 months, and the samples’ properties were retested. Contact angle tests supported by FT-IR analysis showed loss of hydrophobicity after aging. Visible transmittance values in the 0.67–0.37 range were obtained for hydrophilic and hydrophobic samples, respectively. The aging process involved optical parameter reduction of only 0.02–0.05. There was also a slight loss in acoustic performance (noise reduction coefficient (NRC) = 0.21–0.25 before aging and NRC = 0.18–0.22 after aging). For hydrophobic panes, color shift values in the 10.2–59.1 and 8.4–60.7 ranges were obtained before and after aging, respectively. The presence of aerogel, regardless of hydrophobicity, results in a deterioration in light-green and azure tones. Hydrophobic samples had lower color rendering performance than hydrophilic aerogel, but this did not worsen after the aging process. This paper makes a significant contribution to the progressive deterioration assessment of aerogel monoliths for applications in sustainable buildings.

Both the building design and the construction process determine the indoor acoustic quality of enclosures. A suitable indoor acoustic environment is crucial for the productivity and well-being of users. For this purpose, Reverberation Time (RT) is often calculated or measured in situ. Recently, Building Information Modelling (BIM) has provided a new paradigm to face building projects. Nevertheless, little research has been conducted on the optimisation of indoor acoustics using BIM methodology. In this context, the objective of this work is to propose and develop a BIM-based framework for the analysis, evaluation and optimization of the RT. The proposed procedure allows designers to explore alternatives in order to achieve an adequate acoustic performance without any further needs of specific software. This proposal is devised to consider some important characteristics of the project, such as its location, applicable regulations, room uses, materials and costs. This framework calculates the solution set that meets the requirements, showing the set of optimal solutions according to the minimization of both the cost and the optimum absorbent surface area. BFRT contributes by offering a tool to support the decision making process of designers during the initial design phase in the field of acoustic conditioning of buildings. [ABSTRACT FROM AUTHOR]

The velocity sections and acoustic parameters of the sedimentary cover in the Central (Japan), Yamato (Honshu), and Tsushima basins, and the Kita–Yamato Trough of the Sea of Japan, as well as the rocks of the basement and the Cenozoic cover of the submarine Yamato Rise were studied. A comparative analysis of similar parameters of the Cenozoic basins in the South China and East China marginal seas was performed. The relationship between the acoustic properties (P-wave velocity, Vp) of the basal horizons and the age of the Cenozoic cover in the above basins was analyzed. The values of Vp = 3.0–3.6 km/s have been validated as the acoustic parameter of Paleocene–Eocene sedimentary strata. According to the studies we performed, the basal layers in the supposed depocenters of the Japan basins (Central, Yamato, and Tsushima) have Vp = 3.0–3.3 km/s, which indicates the Paleocene–Eocene age of the onset of their formation. [ABSTRACT FROM AUTHOR]

An investigation is conducted on the Francis turbine's cavitation characteristics and its influence on system hydraulic stability using two experimental methods, namely the flow visualization and acoustic emission methods. The investigated turbine is of Francis type with a 15-blade runner and has a specific speed of 202 rpm and a rated head of 30 m. Having tested the machine under a wide range of cavitation conditions, the gap cavitation is the earliest to develop as the cavitation coefficient gradually decreases and has no obvious effect on the machine's external performance characteristics. The airfoil cavitation follows and causes the increase and decrease in machine flow rate and head, respectively, showing its drag reduction effect, where, at the same time, the pressure pulsation amplitude gets to its peak value. There is also the formation of constant cavitation zones and the involvement of an unsteady surge close to the wall of the draft tube's cone. Pushing the cavitation coefficient to even lower values, there is the formation of an annular cavitation zone, accompanied by a sharp drop in cone pressure pulsation amplitudes while the former drag reduction effect disappears. The trend of noise is basically the same as that of pressure fluctuation, which confirms its trustworthiness when it comes to cavitation occurrence detection within Francis turbines. [ABSTRACT FROM AUTHOR]