Search

Copyright of Railway Construction Technology is the property of Railway Construction 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.)

This study presents a novel method for wideband acoustic analysis using the Boundary Element Method (BEM), addressing significant computational challenges. Traditional BEM requires repetitive computations across different frequencies due to the frequency-dependent system matrix, resulting in high computational costs. To overcome this, the Hankel function is expanded into a Taylor series, enabling the separation of frequency-dependent and frequency-independent components in the boundary integral equations. This results in a frequency-independent system matrix, improving computational efficiency. Additionally, the method addresses the issue of full-rank, asymmetric coefficient matrices in BEM, which complicate the solution of system equations over wide frequency ranges, particularly for large-scale problems. A Reduced-Order Model (ROM) is developed using the Second-Order Arnoldi (SOAR) method, which retains the key characteristics of the original Full-Order Model (FOM). The singularity elimination technique is employed to directly compute the strong singular and super-singular integrals in the acoustic equations. Numerical examples demonstrate the accuracy and efficiency of the proposed approach, showing its potential for large-scale applications in noise control and acoustic design, where fast and precise analysis is crucial. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering 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.)

This study was conducted to assess noise annoyance following the installation of various types of sound barriers on elevated roads and to forecast the noise reduction effect. The level of annoyance was evaluated using a five-level linguistic rating scale, and noise values were anticipated for each floor of the building using Cadna/A software based on different road service levels. The results showed that for each service level road, the sound barrier’s noise reduction impact was most pronounced at heights of 3.5–5m, and the ratio of the acoustic barrier’s length extension to its distance from the building should not be greater than 4:1. After comparison, it was found that the fully enclosed sound barrier has the best noise reduction effect. Additionally, the noise annoyance level varied significantly at different service levels, with 60.5dB chosen as the noise threshold value. This study could offer an optional path for noise reduction facility design. [ABSTRACT FROM AUTHOR]

Copyright of Micronanoelectronic Technology is the property of Micronanoelectronic 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.)

This study presents a novel method for wideband acoustic analysis using the Boundary Element Method (BEM), addressing significant computational challenges. Traditional BEM requires repetitive computations across different frequencies due to the frequency-dependent system matrix, resulting in high computational costs. To overcome this, the Hankel function is expanded into a Taylor series, enabling the separation of frequency-dependent and frequency-independent components in the boundary integral equations. This results in a frequency-independent system matrix, improving computational efficiency. Additionally, the method addresses the issue of full-rank, asymmetric coefficient matrices in BEM, which complicate the solution of system equations over wide frequency ranges, particularly for large-scale problems. A Reduced-Order Model (ROM) is developed using the Second-Order Arnoldi (SOAR) method, which retains the key characteristics of the original Full-Order Model (FOM). The singularity elimination technique is employed to directly compute the strong singular and super-singular integrals in the acoustic equations. Numerical examples demonstrate the accuracy and efficiency of the proposed approach, showing its potential for large-scale applications in noise control and acoustic design, where fast and precise analysis is crucial.

Investigations into the aerodynamic properties of vertical sound barriers exposed to high-speed operations employ computational fluid dynamics. The primary focus of this research is to evaluate the influence of train speed and the distance (D) from the track centerline under various operating conditions. The findings elucidate a marked elevation in the aerodynamic effect amplitude on sound barriers as train speeds increase. In single-train passages, the aerodynamic effect amplitude manifests a direct relationship with the square of the train speed. When two trains pass each other, the aerodynamic amplitude intensifies due to an additional aerodynamic increment on the sound barrier. This increment exhibits an approximate quadratic correlation with the retrograde train speed. Notably, the impact of high-speed trains on sound barrier aerodynamics surpasses that of low-speed trains, and this discrepancy amplifies with larger speed differentials between trains. Moreover, the train-induced aerodynamic effect diminishes significantly with greater distance (D), with occurrences of pressure coefficient (CP) exceeding the standard thresholds during dual-train passages. This study culminates in the formulation of universal equations for quantifying the influence of train speed and distance (D) on sound barrier aerodynamic characteristics across various operational scenarios. [ABSTRACT FROM AUTHOR]

For high-speed railway sound barriers, determining the aerodynamic pressure generated by high-speed trains is crucial for their structural design. This paper investigates the distribution of aerodynamic pressure on the sound barrier caused by high-speed trains with different nose lengths, utilizing the computational fluid dynamics (CFD) simulation method. The accuracy of the numerical simulation method employed is verified through comparison with field test results from the literature. Research findings reveal that when a high-speed train passes through a sound barrier, significant "head wave" and "wake wave" effects occur, with the pressure peak of the "head wave" being notably greater than that of the "wake wave". As the distance between the sound barrier and the center of the train gradually increases, the aerodynamic pressure on the sound barrier gradually decreases. The nose length of the train has a considerable impact on the aerodynamic pressure exerted on the sound barrier. The streamlined shape of longer-nose trains can significantly reduce the aerodynamic effects on the sound barrier, resulting in a notably smaller pressure peak compared to shorter-nose trains. Finally, by establishing the relationship between the train nose length and the aerodynamic pressure peak, a calculation formula for the train-induced aerodynamic pressure acting on the sound barrier is proposed, taking into account the nose length of the high-speed train. [ABSTRACT FROM AUTHOR]

Abstract Investigations into the aerodynamic properties of vertical sound barriers exposed to high-speed operations employ computational fluid dynamics. The primary focus of this research is to evaluate the influence of train speed and the distance (D) from the track centerline under various operating conditions. The findings elucidate a marked elevation in the aerodynamic effect amplitude on sound barriers as train speeds increase. In single-train passages, the aerodynamic effect amplitude manifests a direct relationship with the square of the train speed. When two trains pass each other, the aerodynamic amplitude intensifies due to an additional aerodynamic increment on the sound barrier. This increment exhibits an approximate quadratic correlation with the retrograde train speed. Notably, the impact of high-speed trains on sound barrier aerodynamics surpasses that of low-speed trains, and this discrepancy amplifies with larger speed differentials between trains. Moreover, the train-induced aerodynamic effect diminishes significantly with greater distance (D), with occurrences of pressure coefficient (C P) exceeding the standard thresholds during dual-train passages. This study culminates in the formulation of universal equations for quantifying the influence of train speed and distance (D) on sound barrier aerodynamic characteristics across various operational scenarios.

Purpose: To mitigate the urban traffic noise within the frequency range of 100–400 Hz, this paper proposes a novel ventilated metamaterial barrier (VMB). Methods: With the help of the finite-element method, the sound mitigation property of the proposed VMB is simulated. Using the Monte Carlo method, the proposed VMB is designed. The ventilation efficiency of the proposed VMB is evaluated in terms of flow resistivity. Furthermore, a parametric analysis is conducted to investigate the influences of the geometric size of the unit cell, acoustic incident angle, layer spacing, and layer number on the noise mitigation performance. Results and Conclusions: Numerical results confirm that the VMB has a significant noise reduction effect in the low-frequency sound range. After passing through the VMB, the peak normal incidence sound absorption coefficient displays a reduction of 92.5%. Overall, the VMB solves the conflict between acoustic performance and ventilation efficiency of traditional road sound barriers, which has lots of potential applications in traffic engineering. [ABSTRACT FROM AUTHOR]

The screw air-source heat pump can cause incessant high noise levels during operation, which might hinder adoption of this energy-efficient heat pump. First, acoustic measurements and comparison testing were performed in this research. The measurements revealed that the compressor is the main noise source of the heat pump, and it shows a multipeak frequency distribution and a wide frequency spectrum under different work conditions, with multiple peaks at 63, 250, and 1000 Hz. Then, a compressor sound insulation cover with broadband absorption was proposed, and it was experimentally proven that the insulation cover can reduce the maximum sound pressure level of one unit from 89.8 dBA to 79.1 dBA. Third, we proposed several noise reduction strategies and compared their noise reduction effects using computer simulation. The results showed that the noise problem can be effectively improved through the rational design of the sound barrier and the layout and opening options of heat pump. The distance between the sound barrier and heat pump and the sound attenuation due to diffraction ΔLd exhibit a U-shaped relation. For buildings of different heights, the optimal heights of noise barrier are proposed. The 5.5-meter is the optimal height of the sound barrier for single-story buildings. The conclusions can be applied to other building projects for heat pump noise reduction. [ABSTRACT FROM AUTHOR]

Tanjung Pinang II Village is located 10 km from the administrative center of Ogan Ilir Regency, Indralaya. Tanjung Pinang II Village can be developed as a tourist area due to the easy access. The problems of to be tourist village is unproductive of potential land, the emergence of noise pollution from blacksmith activities in residential areas, do not have a tourism management master plan; and The absence of basic infrastructure supporting ecotourism-based Edutourism. The solution of this problem is Counseling on Strengthening Human Resources in Edutourism Villages and Revitalizing Non-Productive Multi Sector Integrated Land as well as Cultivation Technique Training, Relocation of Blacksmiths to Integrated Areas and Planting Sound Barrier Plants, Making a Master Plan for Mapping the Development of Integrated Edutourism Areas in Science Techno Park (STP), Building Edutourism Supporting Facilities Based on Low Cost Ecotourism. The solutions offered are in accordance with the background of the expertise. The purpose of PIPK in Tanjung Pinang-II Village is to provide the solutions in the fields of production, management, marketing, infrastructure and the environment. The method of implementing this PIPK is analyzing the situation and conditions of partners, providing solutions to problems, Making Appropriate Technology (TTG) that will be transferred to partners, Training and Mentoring and Evaluation of Implementation of Activities. The results of the service can be concluded that this activity is a solution for Tanjung Pinang II Village to prepare itself as a tourist village.

Today, the majority of the commercial electrified vehicles use Interior Permanent Magnet Motors (IPMSMs) for propulsion. An IPMSM can deliver high starting torque and high efficiency in the low- and medium-speed operation, which makes it attractive for propulsion applications. However, IPMSMs generally utilize rare-earth permanent magnets and there are growing concerns about the price volatility and supply chain of these materials. Switched Reluctance Motors (SRMs) can potentially replace IPMSMs in various applications including propulsion. An SRM has a simple and low-cost construction, and it can provide reliable operation at high-speed and high-temperature conditions. Compared to IPMSMs, SRMs radiate considerably higher acoustic noise, which have historically hindered their widespread acceptance. Various approaches to mitigate acoustic noise and vibration at the source level have already been explored in the literarture by improving the electromagnetic design and current control. This paper explores multiple noise and vibration mitigation methods that can be applied at the transmission stage. First, the noise comparison between the Internal Combustion Engine (ICE) and SRMs is discussed, and then the methods used for ICEs are presented for their applicability to SRMs.

Copyright of Railway Standard Design is the property of Railway Standard Design 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.)

For high-speed railway sound barriers, determining the aerodynamic pressure generated by high-speed trains is crucial for their structural design. This paper investigates the distribution of aerodynamic pressure on the sound barrier caused by high-speed trains with different nose lengths, utilizing the computational fluid dynamics (CFD) simulation method. The accuracy of the numerical simulation method employed is verified through comparison with field test results from the literature. Research findings reveal that when a high-speed train passes through a sound barrier, significant “head wave” and “wake wave” effects occur, with the pressure peak of the “head wave” being notably greater than that of the “wake wave”. As the distance between the sound barrier and the center of the train gradually increases, the aerodynamic pressure on the sound barrier gradually decreases. The nose length of the train has a considerable impact on the aerodynamic pressure exerted on the sound barrier. The streamlined shape of longer-nose trains can significantly reduce the aerodynamic effects on the sound barrier, resulting in a notably smaller pressure peak compared to shorter-nose trains. Finally, by establishing the relationship between the train nose length and the aerodynamic pressure peak, a calculation formula for the train-induced aerodynamic pressure acting on the sound barrier is proposed, taking into account the nose length of the high-speed train.

A sound barrier is a structure or device that reduces the level of airborne sound. The basic tasks of such a construction are to provide acoustic insulation and sound absorption. There are many materials available on the market ready to use as such structures used for soundproofing passenger vehicles, construction machinery, power units, etc. In this case, however, the practical use of ready-made materials for minimizing noise requires the use of barriers more complicated in construction than those made of a single material. Thus, each time it is necessary to adjust acoustic parameters of barrier to the individual characteristics of equipment whose acoustic emission we want to reduce. Tests according to standards of such structures require work- and time-consuming and expensive research, e.g. special rooms are required for do this (reverberation and anechoic chambers), which are not always available. In this paper, the author proposes a comparative measurement using a simplified method, which can be used in industrial conditions or small measurement laboratories.

The influence of acoustic radiation is considered in the prediction of noise attenuation effect of sound barrier, which provides a theoretical reference for further improving the insertion loss of sound barrier. Based on the theory of thin plate vibration, the vibration mode and natural frequencies of sound barrier under arbitrary boundary conditions are established by using two-dimensional beam function method, and the forced vibration response of the sound barrier is calculated based on the modal superposition method. MATLAB software (MathWorks Company, Natick, Massachusetts, USA) is used to calculate the natural frequencies and the radiated sound power level of the sound barrier, which indicated that the sound radiation caused by external excitation would significantly increase the sound pressure level at the received point, which should be considered as one of the influencing factors in the prediction of noise attenuation effect. The influence of diverse structural parameters on the radiated acoustic power is compared, providing an excellent reference for the design of sound barrier with low noise.

We analyze the impact of sound barriers on residential satisfaction and well-being manifested in housing prices in Singapore. Using the difference-in-difference approach, we demonstrate a significant price effect of sound barriers in high-rise residential environments. There was a 0.6% price increase for public housing units located within 300 m from a railway track after public announcement of sound barriers and a 1.2% further increase after barrier installation. Price effects of sound barriers are heterogeneous by the noise level prior to installation as well as the degree of noise mitigation by barriers. In contrast to the result for public housing, no significant price change was observed for private housing units that have better building design to be shielded from noise even before sound barrier installation. Among public housing, higher-floor units experienced more substantial price increases compared with lower-floor units exposed to less noise prior to barrier installation. Finally, the units that are very close to the railway did not enjoy price premiums brought by sound barriers potentially because noise did not fall below the threshold level of annoyance even after barrier installation. [ABSTRACT FROM AUTHOR]

Since the invention of the train, the problem of train noise has been a constraint on the development of trains. With increases in train speed, the main noise from high-speed trains has changed from rolling noise to aerodynamic noise, and the noise level and noise frequency range have also changed significantly. This paper provides a comprehensive overview of recent advances in the development of high-speed train noise. Firstly, the train noise composition is summarized; next, the main research methods for train noise, which include real high-speed train noise tests, wind tunnel tests, and numerical simulations, are reviewed and discussed. We also discuss the current methods of noise reduction for trains and summarize the progress in current research and the limitations of train body panels and railroad sound barrier technology. Finally, the article introduces the development and potential future applications of acoustic metamaterials and proposes application scenarios of acoustic metamaterials for the specific needs of railroad sound barriers and train car bodies. This synopsis provides a useful platform for researchers and engineers to cope with problems of future high-speed rail noise in the future. [ABSTRACT FROM AUTHOR]

Traffic noise and solid waste pollution are two major problems that restrict urban development and affect urban environments. In this study, a new kind of cement-based material for sound barriers was prepared using industrial waste fly ash cenosphere to explore the material ratio of the sound absorption, sound insulation, and composite layers and to optimize the material's properties. The research findings showed that the compressive strength had significant effects on the material properties of the sound absorption layer, with the optimal compressive strength range being 0.2–0.4 MPa. At 0.4 MPa, the material with an aggregate-to-binder ratio of 1.0 had the best comprehensive properties. The sound insulation layer had the best compressive strength of 29.00 MPa at a 45% fiber admixture. The composite had the best sound insulation when the thickness ratio of the sound absorption and insulation layers was 60:40, and the sound transmission loss was 38 dB. The embodied carbon (EC) and embodied energy (EE) of the new fly ash cenosphere across the whole life cycle were 57.57 kgCO2e and 477.08 MJ, respectively, which were 4.8−52.9% and 53.2−82.3% lower than other traditional sound barriers, respectively. Thus, they were environmentally friendly and had satisfactory energy-saving and environmental protection values. [ABSTRACT FROM AUTHOR]

In this paper, a 2.5-dimensional boundary element method was used to establish the sound field propagation prediction model in bridge sections of urban railway. Influences of the near-field acoustic boundary such as car body, track slab, anti-collision wall and sound barrier on the sound source were discussed, and the noise distribution in space was studied. The research results show that the environmental noise satisfies the attenuation law with-alg(d), in which the attenuation coefficient a increases with the increase of the vehicle speed, and the attenuation coefficient of 1h equivalent A-weighted sound pressure level is lower than that of the equivalent sound A in the period of the train passing by. When the environmental field point is far from the track centerline, the influence of the height of the evaluation point on the wheel-rail deduced sound pressure level will be weakened. The higher the height of the environmental field point from the track surface, the easier it is for the noise to exceed the standard limit. Therefore, when planning buildings beside railways, the distance between the building and the track centerline should increase with the increase of the building height. The insertion loss of the sound barrier will increase with the increase of the train speed. When the sound barrier is low, the insertion loss will decrease rapidly with the increase of the field point height, and when the height of the sound barrier reaches a certain number, the gain effect of the sound barrier height on the insertion loss will decrease rapidly. Therefore, noise reduction effect and economic benefit should be considered simultaneously in the selection of sound barrier. [ABSTRACT FROM AUTHOR]

• Field tests were implemented to obtain noise source characteristics. • The noise propagation model for wet cooling towers was established. • Two noise reduction schemes of vertical and curved sound barriers were proposed. • A-SPL is predicted to be 42.08 dB(A) with the optimal scheme. To weaken the noise pollution of wet cooling towers, a large-scale wet cooling tower with a 660 MW unit is used as an example, and the water-splashing noise is measured in a field test. The sound source characteristics are determined based on the field test results, and the sound source surface is specified as the initial parameters of the simulation. Then, the noise propagation model for the wet cooling tower is established based on the ray-tracing method, with a maximum relative error of only 2.22%. Two noise reduction schemes, vertical and curved sound barriers, are proposed based on this model. Furthermore, the noise reduction effects of two different types of sound barriers are investigated. Under identical conditions, the simulation reveals that the vertical sound barrier performs better than the curved sound barrier in terms of noise reduction. In addition, The results also show that a vertical sound barrier with a length of 90 m, a height of 10 m, and a distance of 15 m from the tower is an optimal scenario, with an A-weighted sound pressure level (A-SPL) of just 42.08 dB(A). In summary, the noise problem associated with wet cooling towers may be effectively addressed in this instance. [ABSTRACT FROM AUTHOR]

Copyright of Diagnostyka is the property of Polish Society of Technical Diagnostics 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.)

• Meta-barriers achieve broadband sound reduction and efficient ventilation. • Transformation acoustics allow for multiple working mechanisms. • Robust sound reduction resists placement distances and incident angles. • Experiments validate the effectiveness of the proposed meta-barrier. Resolving the trade-off problem between wave obstructing and flow transport is an intriguing but challenging task that may find potential applications in many noise control scenarios. Herein, we present a meta-barrier for achieving broadband sound reduction yet keeping efficient ventilation based on transformation acoustics. The proposed meta-barrier consists of an internal core and a coating made of double-negative acoustic metamaterial with high damping dissipation. Unlike conventional barriers, the meta-barrier has a magnified scattering cross-section far beyond its actual size, allowing it to provide the coherent interference effect in addition to the enhanced blocking effect. The coherent interference effect can directly reduce the sound radiation efficiency of sound waves radiating from an aperture. Moreover, the inherent material loss in the coating has a positive effect on the sound reduction performance of the meta-barrier over a wide frequency range. The robust sound reduction performance of the meta-barrier is demonstrated numerically for the cases of large placed distances and wide-range incident angles. Experiments were conducted to confirm the effectiveness of a meta-barrier sample constructed of a plate-type double-negative acoustic metamaterial with multiple constituent layers for sound reduction and ventilation. The fabricated meta-barrier sample, with the wind-speed ratio of 75 %, can achieve superior sound attenuation in the frequency range of 500–1000 Hz. This work may inspire the design and development of passive acoustic devices to suppress low-frequency airborne noise while supporting large-area ventilation. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, based on statistical energy analysis (SEA), the noise attenuation effect of highway sound absorbing barrier is predicted. The theoretical formula value is compared with the calculated value of statistical energy analysis (SEA) to verify its effectiveness in the prediction of sound barrier. And the insertion loss of sound barrier of mineral wool with diverse material thicknesses and coverage are calculated. The results showed that the noise attenuation of the sound barrier increased by 1.5 dB when the sound absorbing materials are attached to the sound barrier near the acoustic source. The noise attenuation effect of mineral wool is improved in the frequency band below 600 Hz when the thickness is increased. The coverage of mineral cotton increased by 25%, and the noise attenuation increased by 0.4 dB. Meanwhile, it also reflects the advantages of fast and convenient statistical energy analysis (SEA) – only one time modelling and changing its parameters can obtain the corresponding statistical results, which has some excellent reference function. [ABSTRACT FROM AUTHOR]

Since the invention of the train, the problem of train noise has been a constraint on the development of trains. With increases in train speed, the main noise from high-speed trains has changed from rolling noise to aerodynamic noise, and the noise level and noise frequency range have also changed significantly. This paper provides a comprehensive overview of recent advances in the development of high-speed train noise. Firstly, the train noise composition is summarized; next, the main research methods for train noise, which include real high-speed train noise tests, wind tunnel tests, and numerical simulations, are reviewed and discussed. We also discuss the current methods of noise reduction for trains and summarize the progress in current research and the limitations of train body panels and railroad sound barrier technology. Finally, the article introduces the development and potential future applications of acoustic metamaterials and proposes application scenarios of acoustic metamaterials for the specific needs of railroad sound barriers and train car bodies. This synopsis provides a useful platform for researchers and engineers to cope with problems of future high-speed rail noise in the future.

Traffic noise and solid waste pollution are two major problems that restrict urban development and affect urban environments. In this study, a new kind of cement-based material for sound barriers was prepared using industrial waste fly ash cenosphere to explore the material ratio of the sound absorption, sound insulation, and composite layers and to optimize the material’s properties. The research findings showed that the compressive strength had significant effects on the material properties of the sound absorption layer, with the optimal compressive strength range being 0.2–0.4 MPa. At 0.4 MPa, the material with an aggregate-to-binder ratio of 1.0 had the best comprehensive properties. The sound insulation layer had the best compressive strength of 29.00 MPa at a 45% fiber admixture. The composite had the best sound insulation when the thickness ratio of the sound absorption and insulation layers was 60:40, and the sound transmission loss was 38 dB. The embodied carbon (EC) and embodied energy (EE) of the new fly ash cenosphere across the whole life cycle were 57.57 kgCO2e and 477.08 MJ, respectively, which were 4.8−52.9% and 53.2−82.3% lower than other traditional sound barriers, respectively. Thus, they were environmentally friendly and had satisfactory energy-saving and environmental protection values.

To study the influence of classical phononic crystal (PC) structures on the acoustical characteristics of a sound source, a combined acoustics/perceptual analysis is conducted on a PC specially designed to exhibit several spectral and wave vector properties in different audible frequency ranges. The properties, confirmed by both numerical calculations and experiments, consist in both partial and absolute band gaps, as well as a negative refraction band. A psychoacoustic feature, namely the loudness in third-octave bands, is estimated from numerical simulations of the acoustic field behind the crystal. Additional perceptual tests are conducted to evaluate the efficiency of the PC slab. In the frequency range of the band gaps, sound stimuli filtered by the PC’s impulse response are perceived as softer than stimuli resulting from a free-field propagation (FF), they also are perceived as equally (or close to equally) loud than sounds attenuated by a free-standing rigid wall (FS). In the frequency range of the focalization (negative refraction), PC sound stimuli sound louder than both FS and FF sound stimuli. The possibility of designing an efficient sound barrier based on the considered PC is finally discussed.

Aerospace as a whole, primarily aviation and planes, for a short time after 1903, greatly advance the frontiers of human activity. Initially, unsafe "flying device" the plane, has become a factor in loose resolving wars and one of the reliable means of transport and communication between people around the world. Quick technical and technological development required a special approach. Mass production and use of aircraft, brought in light the need for standardization in the production, testing and lead into operational use of combat aircraft, as well as in commercial use for the purposes of air traffic. Testing the aircraft, is now more disciplinary research activity of a large number of experts from various fields, including test pilot who is an irreplaceable member. At that goal the test-measuring equipment (IMO), are specifically designed, and test pilots are trained in specialized schools for the experiment pilots. / Авиация в целом, а в частности развитие конструкций самолетов, в течение короткого времени, начиная с 1903 года, в значительной степени расширили границы человеческой деятельности. Первые «воздухоплавательные снаряды» трудно было назвать безопасными, но вскоре самолеты стали решающим фактором в войнах и одним из самых надежных средств передвижения и связи между людьми по всему миру. Быстрое техническое и технологическое развитие нуждалось в специальной методологии. Массовое производство и применение летательных аппаратов выявили необходимость в стандартизации в области производства, испытаний и их внедрения в военно-боевую эксплуатацию, а также в коммерческую эксплуатацию в целях воздушных перевозок. Таким образом, на сегодняшний день испытания самолетов включают мультидисциплинарные методы, в применении которых задействована большая команда специалистов и экспертов, представляющих различные области науки и техники, а главным участником данной команды неминуемо является летчик- испытатель. Для нужд испытательных мероприятий специально разрабатывается контрольно-измерительное оборудование, а сами летчики проходят специальное обучение в центре по подготовке летчиков-испытателей. / Vazduhoplovstvo u celini, a pre svega avijacija i avioni za kratko vreme, nakon 1903. godine, uveliko su pomerili granice ljudske delatnosti. Od 'klimavih' i nebezbednih letećih sprava, avion je postao rešavajući faktor u ratovima i jedno od pouzdanih sredstava prevoza i komunikacije među ljudima širom sveta. Brzi tehničko-tehnološki razvoj zahtevao je i poseban pristup. Masovna proizvodnja i korišćenje aviona iznedrili su potrebu za standardizacijom u proizvodnji, ispitivanju i uvođenje u operativnu upotrebu borbenih aviona, kao i uvođenje aviona za potrebe vazdušnog saobraćaja. Ispitivanje aviona danas je više diciplinarna istraživačka aktivnost velikog broja stručnjaka iz različitih oblasti, među kojima je opitni pilot nezaobilazni član. Radi toga se ispitno-merna oprema (IMO) posebno dizajnira, a opitni piloti obučavaju u specijalizovanim školama za opitne pilote.

Abstract Conventional sound barriers are constrained by fixed geometry which results in many limitations. In this research, origami , the paper folding technique, is exploited as a platform to design deployable and reconfigurable sound barriers, as well as to actively tailor the attenuation performance. As a proof of concept, a three-dimensional barrier structure is constructed based upon Miura-ori unit cells, whose shape can be significantly altered via folding with a single degree of freedom. Folding also generates periodic corrugations on the origami sheets, which can be exploited as backing cavities to form resonant sound absorbers with a micro-perforated membrane. The absorption performance of the constructed absorber and the insertion loss of the origami barrier are investigated using both numerical and experimental tools. The proposed origami barrier involves two fundamental mechanisms: sound reflection and absorption, and the origami offers unique tunability to enrich both mechanisms owing to the folding-induced geometric evolutions. Specifically, the sound reflection effect can be effectively tuned via changing the acoustic shadow zone and the diffracted sound paths by folding, and the sound absorption effect can also be regulated by altering the depth/shape of the backing cavities during folding. Overall, the results of this research offer fundamental insights into how folding would affect the acoustic performance and open up new opportunities for designing innovative origami-inspired acoustic devices. [ABSTRACT FROM AUTHOR]

Great efforts have been dedicated during the last decades to the research and development of hypersonic aircrafts that can fly at several times the speed of sound. These aerospace vehicles have revolutionary applications in national security as advanced hypersonic weapons, in space exploration as reusable stages for access to low Earth orbit, and in commercial aviation as fast long-range methods for air transportation of passengers around the globe. This review addresses the topic of supersonic combustion, which represents the central physical process that enables scramjet hypersonic propulsion systems to accelerate aircrafts to ultra-high speeds. The description focuses on recent experimental flights and ground-based research programs and highlights associated fundamental flow physics, subgrid-scale model development, and full-system numerical simulations. [ABSTRACT FROM AUTHOR]

Copyright of Military Technical Courier / Vojnotehnicki Glasnik is the property of Military Technical Courier / Vojnotehnicki Glasnik 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.)