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Supersonic jet noise, a significant concern in military and civilian aerospace due to its impact on aircraft operability, environmental compliance, and community noise standards, drives the need for studies on jet mixing to optimize processes and reduce noise emissions effectively. This study presents the design and development of a Mach 1.6 nozzle, designed to evaluate the jet decay, directional spread and noise attenuation character. Incorporated at the nozzle exit are two rectangular tabs, with perforation angles of zero and 30 degrees. These tabs, with a blockage ratio of 0.09, are strategically positioned to modify the exhaust flow pattern. Experimental analyses, inclusive of jet decay and acoustic assessments, were conducted at a nozzle pressure ratio of 4.25, corresponding to optimal expansion conditions. Observations were made on the centerline pressure decay along the jet axis and the lateral jet spreading for baseline and controlled jets. Utilizing the Schlieren optical method, the shockwave structures were visualized to understand the flow physics. The results indicated a substantial reduction in the length of the potential core, amounting to 65.13% and 80.76% for zero- and thirty-degrees perforation angles, respectively, compared to an unmodified baseline jet. Moreover, as compared to the baseline jet the 30 degrees perforation configuration demonstrated a significant 9 dB reduction in jet noise. [ABSTRACT FROM AUTHOR]

Aircraft engine noise has become a significant concern for air operators to address. Engineering strategies have resulted in the development of easily applicable solutions, known as "passive solutions", that do not necessitate real-time control. These solutions include the incorporation of corrugations or cutouts at critical locations on the engine's aerodynamic surfaces. Realistic solutions, whether approached numerically or tested at small scales, as well as computational models, have been found to closely match experimentally observed behaviors, both in 2D and 3D scenarios. The identified geometries serve as promising starting points for devising combined concepts that may offer even better performance under specific flow conditions. [ABSTRACT FROM AUTHOR]

Due to the increasing noise pollution, noise control has drawn more and more public attention. Different from traditional methods to reduce noise energy such as active and passive noise control, suppressing noise annoyance through adding sounds is another choice. In previous studies, water sounds are usually used to adjust the annoyance of traffic noise, but the suppression effect of the water sounds varies from person to person. Low-frequency tonal noise is one kind of typical and common mechanical noise, i.e., substation noise, whose annoyance is caused by tonal perception and higher energy in low frequency is difficult to suppress even though adding sounds. In this study, different controllable sounds (water sounds and narrow-band color noises) with different masker-to-noise ratios (MNRs) were added to low-frequency tonal noise to investigate the annoyance suppression effect through listening tests. Furthermore, in order to evaluate the quantitative suppression effect, the standard sample method (SSM) was applied in the listening tests to convert the annoyance difference into the difference of equivalent sound pressure level of 1 kHz and 70 dB pure tone ( Δ S P L 1 k H z , 70 d B ). Results show that different kinds of water sounds and narrow-band color noises effectively reduce noise annoyance. The optimal result comes from adding one kind of water sound, which reduces the annoyance of substation noise by 27.24%, equivalent to reducing Δ S P L 1 k H z , 70 d B by 6.5 dB. Finally, the annoyance prediction model of combined noises is established to choose controllable sounds and predict the suppression effect of annoyance. [ABSTRACT FROM AUTHOR]

Acoustic events exceeding a certain threshold of intensity cannot benefit from a linearization of the governing wave equation, posing an additional burden on the numerical modelling. Weak shock theory associates nonlinearity with the generation of high frequency harmonics that compensate for atmospheric attenuation. Overlooking the persistence of this phenomenon at large distances can lead to mispredictions in gun detection procedures, noise abatement protocols, and auditory risk assessment. The state-of-the-art mostly addresses aircraft jet noise, a stationary and largely random type of signal. The extension of such conclusions to muzzle blasts requires caution in considering their peculiar impulsive and broadband nature. A methodology based on the time and frequency analysis of an experimental dataset of eight calibres intends to find quantitative metrics linked to acoustic nonlinearity in outdoor muzzle blast propagation. Propagating three waveforms (SCAR-L 7.62 mm, Browning 9 mm, and Howitzer 105 mm) up to 300 [m] with the in-house numerical solver based on the nonlinear progressive wave equation, demonstrates that the propagation does not downgrade to truly linear. [ABSTRACT FROM AUTHOR]

This article discusses the possibilities of reducing noise pollution in the vicinity of a selected airport, with an emphasis on practical measures. The proposed procedures, which are routinely employed at commercial airports, would be ineffective or financially unsustainable under the circumstances of the military airports. The objective at military airports is not to maximise capacity, as at civil airports, where the desire to increase capacity is primarily related to profit. The primary objective for military airports is to perform defined tasks, which may include pilot training, search and rescue exercises and combat training. The main measures proposed to reduce noise pollution in the vicinity of the villages are changes in departure and arrival routes, the splitting of night operations into two parts and the introduction of a new article in the AIP and Airport Regulations prohibiting air operations over and in close proximity to the villages nearby. Finally, it is stressed that a significant reduction in noise will only be possible with the support of changes in legislation or above-standard financial investment by the airport operator. [ABSTRACT FROM AUTHOR]

Noise pollution is a consequence of socioeconomic development processes and urbanization. Noise action plans, urban planning, and traffic management are costly, and their undertaking raises the issue of the value of noise reduction to households. We use hedonic pricing to estimate the value of traffic noise for urban residents in Quito, Ecuador. Results were obtained using instrumental variables in order to control the possible omitted variables due to any spatial effect. Considering a large dataset of property attributes and noise exposure, properties inside the mixed land use were compared to those right behind them in a 20-meter buffer, which was characterized by similar structural attributes but different noise exposure levels. [ABSTRACT FROM AUTHOR]

Featured Application: Potential use by aerodrome operators for strategic noise mapping as a cheaper alternative to contemporary methods. Subject of further research. The main goal of this article is to examine the impact of various factors, including the aircraft take-off weight and configuration, on the noise and gaseous emissions. The analysis was based on trajectory data obtained from the X-Plane 11 simulator and a MATLAB noise engine created in accordance with ECAC.CEAC (European Civil Aviation Conference) Doc 29 recommendations. It allowed us to present various noise metrics in the form of noise maps and conduct a general analysis of how certain factors, e.g., flap settings, impact the noise and gaseous emissions. The study indicates that, from the "global" perspective (i.e., the entire airport vicinity), the NADP1 procedure shows better noise reduction, while the NADP2 procedure exhibits lower C O 2 emissions. Conversely, from the perspective of individual observers (i.e., the local perspective), it may (but not necessarily) be the case that the NADP2 procedure allows for achieving both minimal noise and C O 2 emissions compared to the NADP1 procedure. For example, reducing take-off thrust may reduce the SEL > 85 [dB] area in NADP2 by twice as much as in NADP1, but at the cost of almost four times less C O 2 emission reductions. The study may be further developed to find an algorithm for designating individual noise-abatement procedure parameters that will account for various factors in order to minimize the aforementioned emissions. [ABSTRACT FROM AUTHOR]

Today the aviation industry is strongly exposed to criticism based on its impact on climate change. While this is a very important challenge, the industry and especially airports also have a second important challenge: noise impact, which needs to be managed more strategically and proactively. This paper discusses the key factors that influence noise impact, looking at the influence of the evolution of passenger numbers and movements, the influence of the time slots used for these movements and the movements of the lowest noise class aircraft. It will also examine why the permissible noise curve currently under discussion is much larger than that of the 2009 noise register, the first definition by the Swiss aviation regulator of the foreseen noise impact of Geneva Airport. The paper will investigate to what extent Geneva Airport can influence the noise curves through opening hours and slot availability, as well as ways in which the airport might achieve the 20 per cent noise reduction announced in the aeronautical infrastructure sector plan of 2018. Finally, it will suggest a methodology to produce a forecast of noise impact based on key variables such as movements during specific hours of the day and the percentage of movements of aircraft of the lowest noise class. [ABSTRACT FROM AUTHOR]

This article, published in the Journal of the Acoustical Society of America in 2024, discusses the history and impact of noise pollution research. The author, Schultz, reviews social surveys conducted between the 1950s and 1975 to assess the annoyance caused by various sources of noise, such as aircraft, street traffic, expressway traffic, and railroads. Schultz finds that the results of 11 surveys show consistent levels of annoyance and proposes that the average of these curves is the best predictor of community annoyance due to transportation noise. Schultz's work has had a significant impact on noise assessment, with the day-night average sound level (DNL) becoming the accepted noise metric and the percentage of highly annoyed individuals becoming the accepted noise descriptor. Despite some criticism and skepticism, Schultz's simplification of noise assessment has become the basis for current standards on environmental noise assessment. [Extracted from the article]

An approach to creating compact and miniature infra- and low-frequency vibration isolation systems based on layered composite elastic elements with adjustable negative and quasi-zero stiffness is presented. New problems of modeling the given parameters of the stiffness and bearing capacity of elements of certain geometry under combined loading have been solved by varying the structure, elastic properties, and arrangement of layers and controlling the local mobility of the binder. The correctness of the approach is based on the results of experimental design and research of system models. This approach can qualitatively change the solution of a number of critical problems in vibroacoustics of aviation and other advanced engineering. [ABSTRACT FROM AUTHOR]

Introduction: Aircraft noise is one of the most significant sources of environmental pollution in large cities. During the COVID-19 pandemic, strict lockdown in community might increase residents' discomfort with the noise, which could disrupt public activities and reduce subjective well-being. Most of the existing studies considered aircraft noise as a single sound source, which have ignored the influence of other sounds in the community. This paper applied field survey to identify the soundscape and non-acoustic factors related to aircraft noise evaluation. Methods: Paper questionnaires were delivered to select residents of three sample residential areas near Shenzhen Bao'an International Airport to investigate residents' general health, evaluation of aircraft noise, community activities, and attitudinal factors. The relationship between respondent's noise evaluations and subjective factors were investigated through statistical analyses controlling for measured aircraft noise levels and the existence of soundscape facilities. Results: The results indicated that the negative effects of aircraft noise were enhanced during the lock down, especially for frequent space users and those residents in poor health status. Under conditions of similar levels of aircraft noise exposure, communities with more birdsong and fountain sounds had lower proportion of highly annoyed respondents and higher level of soundscape ratings. This paper further indicated that personal factors including fear of air travel, noise sensitivity, and the frequency of outdoor activity had increased the level of annoyance to aircraft noise, while higher degree of annoyance to aircraft noise was associated with poor health status. Discussion: The findings implied the moderating effects of subjective factors and the restorative effects of natural sounds, which could inform aircraft noise control and community consultation strategies by protecting vulnerable populations and creating community soundscape facilities. Future research might conduct a preand post-experiment to estimate the potential causal impact of the soundscape intervention. [ABSTRACT FROM AUTHOR]

This article analyzes aircraft noise measurements from the Airbus A321neo at 7.5 and 5 nautical miles from the runway threshold. Using correlation, analysis of variance, and hierarchical regression analysis, we assessed the influence of flight data recorder variables and meteorological parameters on the measured sound level variations. A combination of aircraft speed and configuration of the high lift devices can predict approximately 60% of the sound level variations. Sound level dependence on speed ranges between 0.5 and 1.5 dB/10 kn for different configurations and landing gear deployment had a +3 dB impact on sound levels. At the same time, weather and wind conditions accounted for a relatively small proportion of the variation. Overall, this study sheds light on the factors contributing to aircraft noise during the final approach and provides insights into potential noise reduction strategies. [ABSTRACT FROM AUTHOR]

The high-frequency content of high-resolution aeromagnetic data is of particular interest to geophysic ists to identify mineral deposits, shallow faults, and dikes. However, high-resolution aeromagnetic data is contaminated by cultural noise generated from aircraft and man-made features. The culture noise must be removed before starting the interpretation process. Manual techniques are more selective of the noise; however slower and more expensive because they require considerable hands-on interaction. The present study develops a novel method for detecting and removing the culture noise from aeromagnetic data based on an artificial neural network (ANN) in an automatic way and comparing the results with a conventional algorithm using the nonlinear filter. The proposed method is tested using a theoretical example that combine a magnetic anomaly due to a dyke with three sources of cultural noise, besides using a practical example to increase the number of training pattern. The network is trained based on the backpropagation training function, where the algorithm updates the weight and bias states as per the Levenberg--Marquardt optimization. The optimization is reached during the training and validation process after 3,000 iterations. The correlation coefficient (R) is utilized along with the mean squared error (MSE) as performance indices of the ANN. The ANN demonstrates the capability to detect the spiky data based on the optimal weights, thus allowing for removing and replacing them with clean data using the piecewise cubic Hermite interpolating polynomial (PCHIP) function. The practical utility of the two-method is discussed using highresolution aeromagnetic data from the Tushka area located in the southwestern desert of Egypt. Comparing the denoising results using the two methods shows that the current approach is more effective in processing and more closely recovering the original magnetic data. [ABSTRACT FROM AUTHOR]

Housewives are individuals who take on the caregiving role in the family in virtually every society and while discharging their duties experience serious psychological difficulties due to external environmental pollutants like air, noise, etc., which influences their efficiency of performing household activities. This study hypothesizes a causal association between perception of traffic noise and the reduction in performance of housewives in their daily household activities. A simple mediation model was utilized for the study with traffic noise perception as the exposure variable. The sensitivity to traffic noise, annoyance caused due to traffic noise, and the effect of traffic noise on housewives were evaluated using questionnaire survey. Of the respondents, 57.33% reported high level of traffic noise perception, while 65.81% reported high annoyance due to traffic noise perception. Of the respondents, 88.69% reported higher levels of agreement with regard to negative effect of traffic noise on their household activities. The results supported the hypothesis with respondents belonging to high and moderate noise perception groups reporting a higher reduction in performance as compared to those belonging to the low noise perception group at higher values of sensitivity. There was no significant direct effect among those who perceived traffic noise as high and moderate. However, the indirect path revealed that there was a significantly higher reduction in performance among those belonging to the high and moderate noise perception group as compared to those belonging to the low noise perception group while those who perceived traffic noise as high and moderate did not differ significantly only at higher levels of sensitivity. Using OGRS computational tool, a sensitivity value of 5.586 was identified as the Johnson-Neyman boundary of significance for the direct effect. The results from the study highlight the need for including environmental noise related regulations with regard to residential structures by the concerned authorities and also the need for undertaking more rigorous studies by health authorities and organizations so that the effects are minimized if not eliminated completely. [ABSTRACT FROM AUTHOR]

In this paper, a multidisciplinary optimization design method and its verification of low-noise aircraft propellers considering aerodynamics, noise, and structural strength were carried out to further reduce the aerodynamic noise of the aircraft propellers. The Vortex Lattice Method-based Lift Surface Method and the Frequency-Domain-based Hanson Method were deployed to evaluate the aerodynamic performance and far-field noise of the propeller with validation by benchmark test result comparison, respectively. Integrating both of the aforementioned methods, the constraints, and a genetic algorithm with coding, a joint program was successfully proposed so that the aircraft propeller performance could be optimized comprehensively. In this program, the design variables contain blade structural strength-constrained distribution patterns of the chord length, twist angle, and dihedral angle along the blade radius. A maximum amount of noise reduction was settled as an optimization target. Meanwhile, it ensured no penalty for aerodynamic thrust and efficiency. The optimized propeller was successfully delivered by performing the developed program. Its structure examined strength tests such as static load and dynamic response, and its aerodynamic and aeroacoustic performances were tested at an aeroacoustic wind tunnel. As a result, the optimized propeller reduced its far-field noise emission peak by 2.7 dB at the first BPF under typical conditions and performed a maximum noise reduction of 4 dB for lower-thrust operations compared with the baseline propeller. For the latter operation, noise reduction at the second BPF was also obviously observed. [ABSTRACT FROM AUTHOR]

Purpose: The aim of the current study is to employ a formal optimization approach and to find the optimal sawtooth shape of trailing-edge serrations that maximize the turbulent boundary layer-trailing edge (TBL-TE) interaction noise reduction. Methods: Lyu's semi-empirical model is used for the optimization approach to investigate a semi-infinite flat plate at zero angle of attack (AoA) and low Mach Number. The ability of sawtooth trailing-edge serrations to reduce TBL-TE noise is analyzed through a single-objective numerical optimization study and trailing-edges tested in a wind tunnel. Four different cases of sawtooth serration geometries are tested for NACA-0012 airfoil and flat-plate trailing edges. Results: Results from the optimization study are used to examine and validate the influence of serration design parameters. For all the cases, the optimum size shows that the maximum noise reduction is located in regions of the design space where the amplitude is maximal, and the wavelength is minimal. Moreover, based on the optimization analyses, the Saw-1 serration provides the greatest noise reduction up to 12.89 dB over a wider range of frequencies. Experimental and optimization results are then compared. Conclusion: It is concluded that numerical and experimental results agree that optimized sawtooth trailing-edge configurations can yield less TBL-TE noise compared to the traditional straight-trailing-edge configuration. The optimization studies underestimated the measurements by about 2 to 12 dB, but the tendency between the different serration geometries was predicted correctly. [ABSTRACT FROM AUTHOR]

Aircraft noise is generally regarded as the most annoying source of environmental noise and is the most common source of complaints raised by residents living in the vicinity of airports. Many different types of abatement measures can be utilized by airports to reduce the noise impact, but the manner of their implementation can vary between airports. To assess how noise control strategies are implemented across the United States (US), a national survey of noise abatement strategies was conducted. The paper provides a summary of this survey and reports the noise control approaches at 42 different airports across the US. The survey considered general aspects of noise control, as well as specific questions related to noise abatement procedures, noise limits and curfews. Participants were also asked their opinion on the impact of the International Civil Aviation Organization (ICAO) Balanced Approach, which is the ICAO recommended framework to address aircraft noise. Although just a snapshot of activities across the US is presented, results indicate that a wide array of noise abatement procedures is being implemented. Results also suggest that the ICAOBalanced Approach has yet to be fully embraced in the US, with a large proportion of respondents reporting that they are not familiar with this approach. [ABSTRACT FROM AUTHOR]

An aircraft nacelle acoustic liner is a key mean of aircraft noise reduction. The success of its design depends strongly on the development of experimental technology, which is generally divided into two stages: impedance eduction and the modal verification of acoustic performance. The comparative study summarizes the impedance eduction technology based on the in-situ method and the straight forward method, and the acoustic modal measurement and control technology, as well as their applications in the design of the acoustic liner of an engine intake and exhaust ducts. The results show that the in-situ method has higher accuracy at low frequencies, and the accuracies of both methods are decreased in the high frequency range. Both methods show an acceptable accuracy and good applicability in the mid-frequency range. A modal generator was designed and used to emit separate and pure acoustic modes in sequence, and a comparative test was carried out on the two types of acoustic liner. Compared with the seamed acoustic liner, the seamless acoustic liner significantly improved its noise reduction effect at the multi-acoustic modes and target frequencies, which further increases the overall reduction up to 5.2 dB. Through research, reliable and validated technologies of acoustic performance tests for a nacelle acoustic liner were established. [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]

For tilt-rotor aircraft with coaxial rotors (coaxial rotor aircraft), reduction of radar cross section as well as acoustic noise can be essential for stealth design, and the rotation of the coaxial rotors can have an influence on noise and dynamic radar cross section (RCS) characteristics. In this paper, an approach to the prediction of both the sound pressure level (SPL) of noise and the dynamic RCS of coaxial-tilt aircraft is carried out, based on the theories of the FW-H equation, the physics optics method (PO) and the physical theory of diffraction (PTD) method. In order to deal with the rotating parts (mainly including coaxial rotors), a generated rotation matrix (GRM) is raised, aiming at giving a universal formula for the time-domain grid coordinate transformation of all kinds of rotation parts with arbitrary rotation centers and rotation axis directions. Moreover, a compass-scissors model (CSM) reflecting the phase characteristics of coaxial rotors is established, and a method of noise reduction and RCS reduction based on the phase modulation method is put forward in this paper. The simulation results show that with proper CSM parameter combinations, the reduction of noise SPL can reach approximately 3~15 dB and the reduction of dynamic RCS can reach 1.6 dBsm at most. The dynamic RCS and noise prediction and reduction method can be meaningful for the radar-acoustic stealth design of coaxial tilt-rotor aircrafts. [ABSTRACT FROM AUTHOR]

Computational models of sufficient quality are indispensable to quantitatively assess aircraft noise reduction measures. Within this study, a multi-level simulation framework is established in order to predict the environmental noise of holding approach procedures by coupling simulation models from three different domains: flight performance calculation employing the base of aircraft data (BADA), jet engine performance using the software Gasturb and aircraft noise simulations based on the software sonAIR. Two different concepts of holding approach procedures are investigated, namely, the vertical holding stack and the linear hold point merge. The study is conducted considering generic air traffic scenarios at a single-runway airport. Thereby, the investigated air traffic is based on a statistical analysis of traffic data at existing airports and thus assumed to be representative. As the aircraft's noise emission depends on both the aircraft and the engine performance, reliable results can be expected only if all individual challenges and interdependencies are accounted for simultaneously. Addressing this challenge is the main contribution of the presented work. The presented results show the plausibility of the proposed multi-level simulation framework, thus supporting its use to investigate the environmental noise impact of air traffic scenarios. [ABSTRACT FROM AUTHOR]

This paper presents the development of a dynamic Active Noise Control (ANC) algorithm aimed towards reducing the broadband noise inside the helmet earcups of a fighter aircraft pilot helmet. The dynamic ANC involves a Variable Step-Size Griffiths (VSSG) FxLMS algorithm to attenuate noise entering directly through helmet, a LMS based adaptive noise canceller to attenuate noise entering through the pilot microphone, and energy detectors for failure protection and optimized battery power usage. The algorithms are implemented on Texas Instruments’ TMS320C6748 processor and are tested in a helmet ANC experimental setup. [ABSTRACT FROM AUTHOR]

A noise reduction strategy was proposed for Panyu District of Guangzhou City based on its traffic noise map, which considered both road and railway traffic noise. Commercial software was applied to compute the noise maps with and without noise barriers based on the field traffic flow measurements. Noise compliance maps were further developed to assess the effects of noise barriers on the quality of the sound environment. The change in populations exposed to unhealthy traffic noise with noise barriers was calculated, and the group noise indicators Gdn and Gnight, which indicate the populations of highly annoyed and sleep-disturbed people, were evaluated. The results showed that the traffic noise level was significantly decreased after the implementation of noise barriers. It was predicted that with the strategy of applying suitable noise barriers, the overall areas under heavy noise pollution could be reduced by 24.5 and 24.3 km2 during daytime and nighttime, respectively. Meanwhile, the total areas that could meet the regulated standard for noise levels were increased by 97.4, and 66.9 km2, corresponding to compliance rate increments of 18.38% and 12.62%, respectively, in daytime and nighttime. The results further revealed that the installation of noise barriers could significantly reduce the population of highly annoyed people, while the reduction of the population experiencing sleep disturbances was insignificant. [ABSTRACT FROM AUTHOR]

In 2018, the World Health Organization (WHO) stated that transport noise is the second biggest environmental problem affecting people's health, after air pollution. The Australian Environmental Health Standing Committee (enHealth) also provides suggested health-based limits for transport noise exposure. To better understand the impact of transport noise in Australia, a strategic national transport noise model was developed, representative of the year 2018. The transport noise model presented included parameters for terrain, buildings, and noise barriers, with results verified against measured data. The model calculated the road, rail, and aircraft noise levels for the day, evening, and night-time periods, across all façades of all storeys for over 15 million buildings across Australia. The State of Victoria was chosen as a case study to document noise exposure levels to the community. Australian Census of Population and Housing data and planning zones allowed a population within each dwelling to be calculated and paired to the modelled noise levels. Based on noise levels at the most exposed façade, it is estimated that 48% of the Victorian population are exposed to road traffic noise levels that exceed the 2018 WHO recommendations. Additionally, 10% are estimated to be exposed to aircraft noise levels, and 11% are estimated to be exposed to rail noise levels, that exceed the 2018 WHO recommendations. These percentages are commensurate with higher affected European Member states based on 2017 noise mapping completed as part of the European Noise Directive. When compared against environmental noise exposure recommendations from enHealth (2018), it is estimated that 11% of the Victorian population are exposed to combined road, rail, and aircraft noise levels above the recommended day/evening 60 dB LAeq 16 h health-based limit, and 10% above the health-based night-time limit of 55 dB LAeq 8 h. This national transport noise model provides a base for further research into the impacts of transport noise on the community, particularly regarding health and property values. The model can also support government planning, complaints handling, and asset management in the planning of future noise abatement in Australia. [ABSTRACT FROM AUTHOR]

Urban air mobility (UAM), a transformative concept for the transport of passengers and cargo, faces several integration challenges in complex urban environments. Community acceptance of aircraft noise is among the most noticeable of these challenges when launching or scaling up a UAM system. Properly managing community noise is fundamental to establishing a UAM system that is environmentally and socially sustainable. In this work, we develop a holistic and equitable approach to manage UAM air traffic and its community noise impact in urban environments. The proposed approach is a hybrid approach that considers a mix of different noise mitigation strategies, including limiting the number of operations, cruising at higher altitudes, and ambient noise masking. We tackle the problem through the lens of network system control and formulate a multi-objective optimization model for managing traffic flow in a multi-layer UAM network while concurrently pursuing demand fulfillment, noise control, and energy saving. Further, we use a social welfare function in the optimization model as the basis for the efficiency-fairness trade-off in both demand fulfillment and noise control. We apply the proposed approach to a comprehensive case study in the city of Austin and perform design trade-offs through both visual and quantitative analyses. • Considers a hybrid approach with a mix of different noise mitigation strategies for UAM noise mitigation. • Explores the use of ambient noise data and ambient noise masking to manage UAM's community noise impact. • Formulates a multi-objective optimization model for managing urban air traffic flow and proposes a numerical method to solve the problem. • Conducts efficiency-fairness trade-offs for aspects that involve multiple parties. [ABSTRACT FROM AUTHOR]

As urbanization and population growth escalate, the challenge of noise pollution intensifies, particularly within the aviation industry. This review examines current insights into noise-induced hearing loss (NIHL) in aviation, highlighting the risks to pilots, cabin crew, aircraft maintenance engineers, and ground staff from continuous exposure to high-level noise. It evaluates existing noise management and hearing conservation strategies, identifying key obstacles and exploring new technological solutions. While progress in developing protective devices and noise control technologies is evident, gaps in their widespread implementation persist. The study underscores the need for an integrated strategy combining regulatory compliance, technological advances, and targeted educational efforts. It advocates for global collaboration and policy development to safeguard the auditory health of aviation workers and proposes a strategic framework to enhance hearing conservation practices within the unique challenges of the aviation sector. • (NIHL) is a major occupational hazard in aviation. • Aviation workers are exposed to noise levels that often exceed safe thresholds, • Recent technological advancements have reduced noise in aircraft and ground operations. • Effective strategies combine regulatory compliance, tech innovations, and educational • Global collaboration and policy development are essential for worker auditory health workers. [ABSTRACT FROM AUTHOR]

Road traffic noise is one of the most prominent sources of urban noise pollution. Recently, as a result of the electrification of vehicles, lower noise levels are expected in urban areas at speeds below 50 km/h. The commonly used physical descriptor, the A-weighted sound pressure level, does not sufficiently characterize the perceived annoyance of either combustion engine or electric passenger car pass-by noises. Psychoacoustical descriptors are advantageous for characterization purposes. The objective of this study was to evaluate the perceived annoyance caused by the noise from internal combustion engine, electric, and hybrid passenger cars using psychoacoustical properties. To achieve this objective, the following steps were conducted. First, the binaurally recorded sounds of 40 cars from different brands with different motorization were presented to the subjects who indicated the intensity of their perceived annoyance on a quasi-continuous scale. Second, the signal and psychoacoustical properties of the recorded sounds were analyzed. Third, a new annoyance index was developed, based on annoyance judgments and signal and psychoacoustical properties, to characterize the annoyance caused by pass-by noises. One of the novel aspects of this study is the consideration of not only the pass-by sounds of the internal combustion engine passenger cars, but also the pass-by sounds of hybrid and electric passenger cars. An acceleration from idle to a target speed of 50 km/h was selected as a traffic pass-by situation, which differs from those considered in previous studies. The results of the study show that psychoacoustical properties, such as loudness, tonality, roughness, and fluctuation strength, are very useful to characterize the annoyance perception, which is caused by single passenger car pass-by sounds in the above mentioned traffic situation. The developed index, which is a weighted combination of chosen psychoacoustical properties, can be very useful for traffic planning and traffic noise prevention measures. [ABSTRACT FROM AUTHOR]

The comfort in helicopter cabin is significantly affected by the mid- and high-frequency noise caused by the main gearbox. Based on its noise transfer path, the development of cabin noise control technology is summarized in three aspects, including the supporting structure, the bulkhead and the internal cavity with passive, active and semi-active control methods. The results show that helicopter cabin noise in abroad is mainly controlled through the passive technologies such as damping vibration attenuation of panel, sound barrier with sealing, and sound absorption in cabin. However, some problems are appeared with respect to weight, economy, and limited control effect. The vibration reduction technology on the supporting structure has provided a new way for the efficient noise reduction of main gearbox, which has been combined with the comprehensive optimization to make some helicopters reach the cabin noise level of commercial aircraft. Nevertheless, the research and application of helicopter cabin noise control technology are inadequate in domestic. To obtain the new methods and ideas suitable for the helicopter development in China, the researches like the noise transmission mechanism, noise reduction design, verification and optimization should be further developed according to the realistic engineering application background of helicopters. [ABSTRACT FROM AUTHOR]

This paper investigates the acoustics of a side-by-side urban air mobility (UAM) aircraft with 0%, 5%, 15%, and 25% rotor overlaps in forward flight based on high-fidelity computational fluid dynamics (CFD) simulations. The CFD and acoustics simulations are carried out using the HPCMP CREATE™-AV rotorcraft simulation and analysis tool Helios and the acoustic prediction tool PSU-WOPWOP. First, the influence of the finest wake-grid spacing (Δfinest) on the side-by-side rotor acoustics is studied. No significant difference in overall sound pressure level (OASPL) is found between the two wakegrid spacing cases: Δfinest = 5% Ctip and 10% Ctip. Physical noise sources, such as impulsive self blade--vortex interactions, rotor-to-rotor blade--vortex interactions, and separated flow and blade interactions, are investigated in details based on high-fidelity CFD simulation results and noise-integrand analyses. The effect of rotor overlap on rotor acoustics is also assessed. It is found that the maximum OASPL difference among the overlap cases is about 1 dB, but the radiation patterns are different for each overlap case. Furthermore, the noise of the side-by-side rotor with 0% and 25% overlaps is compared against the noise of a conventional helicopter and various background noises. The side-by-side rotor noise is comparable with the helicopter noise around 1000 Hz. The results also show that the side-by-side rotor noise could not be fully masked by the freeway background noise even at an altitude of 1500 ft and exceed Uber's noise guideline of 62 dBA at 500 ft. Thus, noise reduction technology should be pursued to lower UAM aircraft noise, which is one of major technical barriers for UAM public acceptance. [ABSTRACT FROM AUTHOR]

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Noise pollution is an emerging environmental threat, prolonged exposure of which can cause annoyance, sleep disturbance, hypertension, psychiatric disorders, and also hormonal dysfunction. Among all the sources of noise pollution, the noise generated by road vehicle traffic significantly affects the quality of urban environments. Concerning the recent imposition of COVID-19 societal lockdown, this study attempts to investigate the impacts of COVID-19 lockdown on the changes in noise pollution levels before, during, and after lockdown phase in different residential, commercial, industrial, and silence zones of the city of Kanpur, India. Utilizing data collected from portable environmental sensors, the average noise levels before lockdown and during lockdown were found to be in the range of 44.85 dB to 79.57 dB and 38.55 dB to 57.79 dB, respectively, for different zones. Although a significant reduction in the noise levels was observed during lockdown, except for commercial zone, all other monitoring stations had reported sound levels quite higher than the recommended noise limits set by the Central Pollution Control Board (CPCB) of India. Results further indicated that the impact of road traffic noise on risk of high annoyance and sleep disturbance was found to be lower during lockdown as compared to that of pre-lockdown and unlock phase. While the annoyance level in residential (86.23%), industrial (87.44%), and silence (84.47%) was higher in pre-lockdown period, it reduced to 41.25, 50.28, and 43.07% in the lockdown phase. Even the risk of sleep disturbance in the residential zone was found to reduce from 37.96% during pre-lockdown to 14.72% during lockdown phase. Several noise mitigation strategies are also proposed, which may indeed pave the way for devising noise control measures in the local and regional level. [ABSTRACT FROM AUTHOR]

Thin, lightweight, and durable broadband acoustic absorbers capable of absorbing sounds over a wide frequency range, especially below 1000 Hz, while also surviving harsh operational conditions such as exposure to sprays of liquid and solid debris and high temperatures are desired for many noise control applications. While today's commercially available broadband acoustic liners are impressive, such as melamine foam and perforate-over-honeycomb structures, each style has its limitations. Motivated by the need to reduce aircraft engine noise pollution NASA has recently patented a broadband acoustic absorber that claims some benefit over existing acoustic liners. Inspired by nature, these structures resemble the geometry and acoustic absorption of bundles of natural reeds, slender grasses that grow in wetlands across the world. Proof-of-concept experiments have begun at NASA. This report summarizes the design, fabrication, and normal incidence impedance tube tests performed for assemblies of natural reeds and additively-manufactured plastic prototypes that resemble the irregular geometry of bundles of natural reeds. Some synthetic prototypes were tested with and without perforated face sheets. Results indicate that there are a number of synthetic designs that exhibit substantial acoustic absorption in the frequency range of 500 Hz to 3000 Hz, and especially below 1000 Hz, as compared to baseline acoustic absorbers of similar thicknesses and weights. Many of these prototypes have an average acoustic absorption coefficient greater than 0.6. Additionally, an annular prototype was designed and printed but not yet subjected to tests. This annular prototype of a multifunctional structure designed to transfer heat and absorb sound was developed to fit inside the NASA Glenn Research Center's DGEN Aeropropulsion Research Turbofan engine testbed. This invention can be considered and developed for a variety of aerospace, automotive, industrial, and architectural noise control applications. [ABSTRACT FROM AUTHOR]

Review and discussion of substantive to revolutionary concepts to enable a commercially viable, societally acceptable supersonic transport. Issues addressed include economic viability, take off noise, sonic boom, emissions and frontier aircraft configurations. Solution spaces include an enabler for most of the issues, which is doubling the lift-to-drag ratio. Approaches in most cases require serious further research for application to and optimization of frontier aircraft configurations. [ABSTRACT FROM AUTHOR]

This paper reviews several decades' worth of research on the topic of slat noise arising from high-lift systems of commercial aircraft. A high-lift system is commonly used for providing additional lift by deploying the leading-edge slat(s) and trailing-edge flap(s) during the takeoff and landing phases of flight. Slat noise can be one of the main sources of airframe noise, along with the deployed landing gear, and airframe noise can be dominant during the approach phase when aircraft engine noise is reduced. This review synthesizes historical investigations related to the generation/radiation of slat noise, including both experimental and numerical approaches. Characteristics of noise and corresponding generation mechanisms have been well investigated, and numerical tools have been developed to predict noise levels. Scaling laws to map the results from models to real aircraft are proposed based on the combined analytical and experimental investigations. Noise-reduction technologies are also discussed. [ABSTRACT FROM AUTHOR]

Aims Nighttime aircraft noise exposure has been associated with increased risk of hypertension and myocardial infarction, mechanistically linked to sleep disturbance, stress, and endothelial dysfunction. It is unclear, whether the most widely used metric to determine noise exposure, equivalent continuous sound level (L eq), is an adequate indicator of the cardiovascular impact induced by different noise patterns. Methods and results In a randomized crossover study, we exposed 70 individuals with established cardiovascular disease or increased cardiovascular risk to two aircraft noise scenarios and one control scenario. Polygraphic recordings, echocardiography, and flow-mediated dilation (FMD) were determined for three study nights. The noise patterns consisted of 60 (Noise60) and 120 (Noise120) noise events, respectively, but with comparable L eq, corresponding to a mean value of 45 dB. Mean value of noise during control nights was 37 dB. During the control night, FMD was 10.02 ± 3.75%, compared to 7.27 ± 3.21% for Noise60 nights and 7.21 ± 3.58% for Noise120 nights (P  <   0.001). Sleep quality was impaired after noise exposure in both noise scenario nights (P  <   0.001). Serial echocardiographic assessment demonstrated an increase in the E / E ′ ratio, a measure of diastolic function, within the three exposure nights, with a ratio of 6.83 ± 2.26 for the control night, 7.21 ± 2.33 for Noise60 and 7.83 ± 3.07 for Noise120 (P  =   0.043). Conclusions Nighttime exposure to aircraft noise with similar L eq, but different number of noise events, results in a comparable worsening of vascular function. Adverse effects of nighttime aircraft noise exposure on cardiac function (diastolic dysfunction) seemed stronger the higher number of noise events. [ABSTRACT FROM AUTHOR]

Aircraft noise pollution has adverse physical and mental health effects that are capitalized in the affected home values. We contribute to the literature estimating these noise discounts by our novel identification strategy that analyzes the "treatment effect" of two local government subsidized soundproofing initiatives near the Minneapolis-Saint Paul International Airport. Combining a repeat-sales sample with data on aircraft noise pollution (1990–2014), we find a causal noise discount of around $25,000 per sale of noise-affected, but abatement-ineligible, properties, whereas abatement-eligible homes experience a negligible effect post soundproofing indicating a return on abatement investments as a high as 40% in Minneapolis. [ABSTRACT FROM AUTHOR]

We develop a pure characteristics equilibrium sorting model to recover estimates of willingness to pay (WTP) for both marginal and non-marginal changes in urban noise exposure. Using data from Vienna, Austria, we provide several new insights in the urban noise literature. First, we demonstrate the importance of considering general equilibrium feedback effects following large changes in noise levels. We document impacts to residents in policy targeted and non-targeted locations due to changes in both noise and equilibrium prices. Second, we confirm evidence of the importance of noise thresholds with significant and increasing negative impacts associated with increases in area covered by high levels of noise at 50 dB and 60 dB thresholds, respectively. Finally, we use an equilibrium sorting model to predict new price patterns and welfare implications following hypothetical policy changes that alter the distribution and intensity of nighttime noise in Vienna and are relevant to other urban settings seeking to reduce noise levels. Our work additionally provides a roadmap for conducting similar equilibrium sorting work in data limited settings outside the U.S. [ABSTRACT FROM AUTHOR]

Air traffic has developed rapidly in the last decades. The noise generated from aircraft can impair the health of passengers and airport residents, so it is necessary to reduce aircraft noise and relieve the annoyance due to aircraft noise. As one important component of aircraft wings, the high-lift device is a barrier to the noise reduction of the large commercial civil aircraft in the next stage, especially during the approach and landing phases. When the slat and flap of the high-lift device are both stowed, some gaps and cavities will emerge and radiate strong noise. However, little attention has been paid to these geometric structures on real aircraft. This paper presents an experimental investigation on the far-field aeroacoustic characteristics of the stowed 30P30N high-lift configuration in the cruise condition, namely with slat and flap both stowed absolutely. The experiment of acoustic field measurements with a far-field microphone and acoustic microphone array shows that the gap between the main element and stowed flap on the pressure surface is the main noise source and can radiate tonal noise in the low-frequency range. The flow field measurement aided by a hot-wire anemometer reveals that the frequencies of the intense fluctuations near this gap are close to the tonal frequencies in the far-field noise spectra. Finally, with the applications of a gap cover and tripping device, the tonal noise of the stowed 30P30N high-lift configuration can be obviously suppressed because the feedback loop between the boundary layer instability upstream and the pressure wave from the flap–main element gap has been disturbed. [ABSTRACT FROM AUTHOR]

The European Region of the World Health Organization (WHO) recently published revised recommendations for transportation noise exposure intended to limit adverse health effects. WHO's newly recommended "safe" limit for aircraft noise exposure is about an order of magnitude lower than the limits currently adopted by most European countries. WHO defines "safe exposure" as the level corresponding to an annoyance prevalence rate of 10% highly annoyed. The revised recommendations are based on a limited selection of post-2000 publications. About half of the cited studies rely on nonstandard questionnaires, respondent selection, and definitions of annoyance prevalence rates which over-estimate annoyance. A re-analysis of a larger and more representative selection of studies that relies on standard procedures shows that no meaningful changes in prevalence rates of high annoyance with aircraft noise have occurred and that existing evidence does not support WHO's revised recommendations. [ABSTRACT FROM AUTHOR]

Background: Large epidemiological studies point towards a link between the incidence of arterial hypertension, ischaemic heart disease, metabolic disease and exposure to traffic noise, supporting the role of noise exposure as an independent cardiovascular risk factor. We characterised the underlying molecular mechanisms leading to noise-dependent adverse effects on the vasculature and myocardium in an animal model of aircraft noise exposure and identified oxidative stress and inflammation as central players in mediating vascular and cardiac dysfunction. Here, we studied the impact of noise-induced oxidative DNA damage on vascular function in DNA-repair deficient 8-oxoguanine glycosylase knockout (Ogg1–/–) mice. Methods and results: Noise exposure (peak sound levels of 85 and mean sound level of 72 dB(A) applied for 4d) caused oxidative DNA damage (8-oxoguanine) and enhanced NOX-2 expression in C57BL/6 mice with synergistic increases in Ogg1–/– mice (shown by immunohistochemistry). A similar pattern was found for oxidative burst of blood leukocytes and other markers of oxidative stress (4-hydroxynonenal, 3-nitrotyrosine) and inflammation (cyclooxygenase-2). We observed additive impairment of noise exposure and genetic Ogg1 deficiency on endothelium-independent relaxation (nitroglycerine), which may be due to exacerbated oxidative DNA damage leading to leukocyte activation and oxidative aldehyde dehydrogenase inhibition. Conclusions: The finding that chronic noise exposure causes oxidative DNA damage in mice is worrisome since these potential mutagenic lesions could contribute to cancer progression. Human field studies have to demonstrate whether oxidative DNA damage is also found in urban populations with high levels of noise exposure as recently shown for workers with high occupational noise exposure. [ABSTRACT FROM AUTHOR]

Landing aircraft create noise that disturbs residents living close to airports. One method to reduce such noise is to fly the final approach at a steeper glide slope than the normal 3.0 glide slope, thus increasing the distance between the source of the noise and the ground. If this is performed, there is a risk that the operational behavior of the pilot counteracts the noise reduction possible to achieve, due to the fact that the pilot must manage the aircraft's speed on a steeper glide slope. For practical reasons, there are few live trials and studies on pilot behavior during steeper approaches. In this project, a method to approximate pilot operational behavior during slightly steeper approaches, using flight data recorder data from standard approaches, was developed. The method exploits the fact that flying an approach in tailwind conditions creates the same operational challenges for a pilot as flying a steeper than normal approach does. The method was applied to 1159 flights. The results indicate that the pilots' operational behavior will change when glide slope angle increases. Extension of final flap and landing gear in steeper approaches will take place at a greater height but closer to the airport than for standard 3.0 ILS approaches. The result can be a reduction of the noise from arriving aircraft by up to 2 dB in some areas beneath the approach path if a 3.5 glide slope angle is used. [ABSTRACT FROM AUTHOR]