Noise Sources Research Articles

Noise reduction and visual disturbance performances of horizontal facade profiles for a multi-story high-rise apartment building

This paper simulates the noise reduction performance of horizontal profiles installed on the façade to reduce the external noise in high-rise residential buildings. The simulation used commercial software based on the ray tracing method and evaluated the performance by modeling a representative rectangular-shaped 30-story apartment building in South Korea. The simulation assumed a four-lane road traffic noise source parallel to the front of the apartment. The key simulation values were cited from configurations derived in previous studies. The sound absorption points were set at the center of each living room on every floor, and windows facing the road were considered for ventilation, being set to be partially open. Horizontal profiles for noise reduction were placed on the exterior of the building, starting from the 20th floor, with protrusion height and vertical spacing as variables. These profiles were combined with noise barriers to assess their impact. As a result, it was confirmed that the noise barrier only reduced the noise in the lower floors, while the horizontal profiles on the upper part of the building could also reduce noise in the upper floors. Additionally, the paper discusses the visual disturbance of the horizontal facade profiles visible from the living rooms.

Refinement method of equivalent source power level determination for traffic noise in urban noise mapping

For traffic noise prediction, the predictive models of source power level determination commonly in use are the Technical Guidelines for Noise Impact Assessment in China or the Calculation of Road Traffic Noise model in the United Kingdom, which incorporate traffic flow and car speeds. However, the accuracy of these models is often compromised due to urban traffic's complexity, vehicle diversity, and unforeseen events. This study investigates a refinement method based on noise on-site measurement and aforementioned approaches for equivalent source power level determination for traffic noise in urban noise mapping. In the study, onsite measurements are conducted to collect noise and traffic data, and source power level calculated by refinement method is validated using measurement data. Different prediction methods are employed for measurement sites calculations. By comparisons between predictions with noise on-site measurement data, the refinement method proposed in the study demonstrates a significant accuracy enhancement in traffic noise prediction over previous models for determining equivalent source power level. This enhancement highlights the efficacy of adopting noise measurement-based methods for setting traffic noise source power levels, leading to more precise traffic noise predictions in complex urban settings, particularly in areas surrounding urban arterial roads.

Ultrabroadband sound control of 3D spaces using plasmacoustic metalayers

Controlling sound in three-dimensional spaces is a complex task, challenged by the intricacies of acoustic modal structures, the variety of noise sources, and the propagation of waves. This research analyzes the influence of local impedance control on the global sound field within a parallelepipedal volume characterized by high reverberation. The employed electroacoustic transducer is based on a corona discharge mechanism and utilizes the Plasmacoustic Metalayer concept. The sound field is regulated directly by the interaction between the air particles and the ionized air produced in the discharge area. The inertia-free plasmacoustic Metalayer contributes to an increased control bandwidth. Experimental tests conducted with several actively controlled transducers distributed throughout the volume demonstrate the dampening of multiple modes. This leads to a more consistent frequency response and a broadband reduction in sound pressure levels across the entire space, demonstrated here up to 700 Hz. Numerical simulations suggest that such a systemcan also be potentially efficient in a more realistic space such as a vehicle cabin.

Aeroacoustic modeling of a low Reynolds number rotor in the wake of a cylindrical beam

In micro air vehicles, low Reynolds number rotors operating in close proximity to the fuselage raises the question of interaction noise as a prominent acoustic source. This paper proposes to comprehensively explore the interaction noise generation mechanisms, employing numerical simulations, experimental approaches, and analytical modelling. The focus is on scenarios where a low Reynolds number rotor is located in the wake of a cylindrical beam, and oppositely when the beam is in the wake of the rotor. In both scenarios, it is observed experimentally that the amplitudes of the BPF harmonics are increased with respect to that obtained without beam. This increase is higher when the rotor is in the wake of the beam compared to when the beam is in the wake of the rotor. The numerical simulation is shown to reproduce quite well the envelope of the amplitudes of the BPF harmonics obtained experimentally in both scenarios. Interestingly, by applying Ffowcs-Williams and Hawkings analogy on elementary surfaces, and not on the whole rotor-beam surface, the main sound generation mechanism was found to be the unsteady loading on the beam in both scenarios. Finally, an analytical modeling of the noise source mechanism is compared with experimental and numerical results.

An innovative approach for enclosure design of power generators to meet noise regulation targets

The use of diesel-powered engine generators as a power source is very common for various industrial and residential applications. There are strict regulatory requirements and legislations to limit the noise levels from these generators below statutory limits. The purpose of the paper is to present an approach using statistical energy analysis (SEA) augmented by experimental inputs for the prediction of noise levels for the generators and propose strategies for optimized enclosure design that effectively mitigate noise to achieve regulatory requirements. The study begins by developing an SEA model that represents the acoustic behavior of the generator and enclosure. The airborne sources such as engine, alternator, radiator fan and exhaust are modelled explicitly using experimental noise source characterization. Based on the established SEA model and excitation sources, noise levels are predicted through the calculation of energy flow between subsystems. The predicted sound levels for an existing Diesel Generator with enclosure were validated with its test data to ensure correctness of SEA model. Parametric studies were carried out using simulations on key variables, including critical noise paths, panel thickness, and noise control treatments. These investigations helped identify optimal process parameters that reduce noise levels emitted by genset in adherence to noise regulations.

A survey of integrating wireless technology into active noise control

Active Noise Control (ANC) is a widely adopted technology for reducing environmental noise across various scenarios. This paper focuses on enhancing noise reduction performance, particularly through the refinement of signal quality fed into ANC systems. We discuss the main wireless technique integrated into the ANC system equipped with some innovative algorithms in diverse environments. Instead of using microphone arrays, which increase the computation complexity of the ANC system, to isolate multiple noise sources to improve noise reduction performance, the application of the wireless technique avoids extra computation demand. Wireless transmissions of reference, error, and control signals are also applied to improve the convergence performance of the ANC system. Furthermore, this paper lists some wireless ANC applications, such as earbuds, headphones, windows, and headrests, underscoring their adaptability and efficiency in various settings.

Acoustic evaluation: microphone array measurements on a multi-megawatt individual pitch control wind turbine

As rotor diameters of wind turbines approach 200 m, aerodynamic noise becomes a significant issue, especially for onshore turbines. The rapid expansion of wind energy has led to increased concerns regarding the noise generated by wind turbines particularly in proximity to residential areas. This study investigates the noise emissions from a full-scale multi-megawatt individual pitch control (IPC) onshore wind turbine, with rotor diameter of 158 m and a hub height of 120 m, across 12 scenarios-six upstream and six downstream. The wind turbine under investigation operates under both IPC and non-IPC modes. Utilizing a microphone array and beamforming algorithm techniques, we conducted comprehensive acoustic measurements to analyses the noise sources and their characteristics. Our findings indicate that turbine operating in IPC mode produces higher sound pressure levels dB (A-weighted) as compared to the turbine under non-IPC modes. This observation emphasizes the need for a balanced approach in wind turbine operations, considering both load reduction and noise mitigation.

Exploring the effects of phase delay on propeller noise: an experimental study in tandem configuration

Noise cancellation is a revolutionary control strategy, so effective that it has been integrated into high-end headphones. Implementing this approach on drones may seem challenging, but at the same time, it is highly appealing. The idea is to use some rotors, which constitute the main noise source, as a secondary pressure wave to eliminate the noise emitted by the entire propulsion system by inducing destructive interference among the individual sources. Implementing this kind of technology requires a significant understanding of the interaction mechanism of pressure waves emitted by the blades. The associated signature is not sinusoidal and exhibits strong directivity. This article will clearly demonstrate the potential of this approach by focusing attention not only on the effects but also on the nature of the interference mechanism. This finding is pivotal for the design of an active noise control system.

Prediction and evaluation of the low-frequency noise impact from industrial noise sources

German legislation requires an assessment of low-frequency noise in addition to the regular noise assessment for industrial plants. The detailed prediction and assessment of low-frequency noise immissions is carried out according to the administrative regulation for noise TA Lärm and the German standard DIN 45680. However, a standardised procedure for predictions of low-frequency noise does not exist. For this reason, different approaches for the prediction of low-frequency noise immissions have been developed over the last two decades. Typically, the method according to DIN ISO 9613-2 for sound propagation outside is extended heuristically to the lower frequency range. The predicted low-frequency noise level outside the room is taken as a basis for determining the noise immission level inside the room. The level of knowledge about the quality of sound propagation modeling of low-frequency noise is still debatable. A forecast method of low-frequency noise components should be on the "safe side" in terms of noise control; however, the scope of the required measures to meet the noise requirements must be comprehensible and proportionate. We present an overview of the building blocks of a forecasting process and the challenges that arise. The topic is illustrated by a practical example.

Mechanical noise for architectural students

Noise control of mechanical equipment is one of the requirements established in energy certificates (LEED, BREEAM, WELL, etc.) as well as in different design standards or national codes. At the Higher Technical School of Architecture of Madrid, Technical University of Madrid (UPM), several courses are offered to students on the design of mechanical systems, from the selection of the equipment, its location, distribution, and its integration with the architecture. Its acoustic implications are not explained in any course. During the last year of the degree, in the course "Proyecto de instalaciones", (Technical Equipment Design) students are asked to fully integrate the building services (heating, cooling, ventilation, fire safety, emergency signals...) in one building designed by their own, and for the first time a 2-hour masterclass on mechanical noise for architects has been organized. In it, the main noise sources, design recommendations and the most common ways to attenuate and control it are addressed. The aim of this work is to share the learned experiences and discuss the next steps to be taken.

The problem of obtaining vehicles speed input for road traffic noise microscopic models: a comparison between field measurements and a stochastic approach

Mitigating environmental noise harmful effects is a relevant goal in the EU "Zero Pollution Action Plan", which targets a 30% reduction in chronic annoyance from transportation noise by 2030. Since road traffic is a major noise source in urban and non-urban settings, much effort has been invested in analyzing and modeling it. To assess noise levels, numerous Road Traffic Noise Models (RTNMs) exist, each requiring multiple inputs like vehicle flows, percentage of heavy vehicles, and average speed. Specifically, when dealing with microscopic models, the single vehicle speeds are needed. To obtain them, on-site measurements offer accurate data but are time consuming and expensive. This paper explores two approaches: an alternative measurement approach, based on video processing and object detection tools, and a stochastic approach, which randomly assigns a speed to each vehicle from a distribution curve, depending on traffic conditions and vehicle category. These methodologies are used to provide input data to a road traffic noise microscopic model, whose results are compared with field measured data. This comparison will allow to get useful insights on the performances of the proposed techniques in providing reliable inputs and their potential applications in different scenarios where single vehicle measured speeds are not available.

Target setting and practical Improvement for sound quality of electric vehicles

For electric vehicles, because there is no masking effect of combustion engine noise, the middle frequency and high frequency noise of electric components become distinct and annoying. Electric driven unit, electric compressor, electric pump, and motors of seat adjusting device are always major noise sources for electric vehicles. Some of those noise signals are steady, some are transient and some are time-variable. So only SPL is hard to reflect human's true perception. Psychoacoustic metrics, such as loudness, roughness, sharpness, and tonality, is hard to evaluate all complicated NVH phenomenon of electric vehicles using one metrics. In this paper, the author tested different operation noises of above-mentioned electric components of several popular EVs, and finalized proper psychoacoustic metrics for different operations based on loudness, modulation, tonality and objective evaluation. Furthermore, the author studied target setting for dedicated metrics, and effective improving methods for sound quality of EVs from the point of source and path. For example, effective designing for acoustic encapsulation of EDU and electric compressor, and good insulation performance designing for dash inner and trunk floor trim. Keywords: Sound quality, Psychoacoustic metrics, electric vehicle, objective evaluation, target setting

Drone fleet noise impact calculation - a methodology

The introduction of drones into an already dense urban infrastructure is expected to have an important impact on the population. The goal of the SESAR MUSE project, " Measuring U-Space Social and Environmental Impact ", is to develop a set of key performance indicators, methods and tools for the comprehensive and rigorous assessment of the impact of UAM operations on the liveability and quality of life in European cities. One focus domain is drone-generated noise. In the frame of this project, a number of ONERA tools is chained in order to create noise maps, from scratch, for realistic drone fleet scenarios. Hence, in this paper a methodology is presented where a flight mechanics tool, noise source models, an en-route tool and an open-source urban noise propagation tool are chained, allowing complete freedom with regard to choice and number of drones, concept of operations and type of urban environment.

Influencing parameters and indicators assessment for aircraft external noise tonality perception

Reducing the annoyance related to the noise generated by aircraft flyovers near airports is a major concern of the aeronautical industry. Noise source reduction is one of the pillars of the balanced approach, but further research is still needed to understand and reduce unpleasantness and annoyance due to aircraft noise. From a psychoacoustics point of view, it is particularly important to understand and assess the effects related to perceived phenomena such as tonality which increases unpleasantness at similar noise levels. This article presents the results of a parametric study looking at the influence on tonality of frequency, emergence level and number of harmonics and the assessment of tonality indicators. The particularity of this study is the non stationarity of the tonal noise due to the Doppler effect and the low frequency investigation.

Psychoacoustic assessment of automotive fan-systems

In the automotive industry, electrification trends worldwide are inducing an increase of noise sources emergences. This reinforces the acoustic assessment metrics and thresholds set by stakeholders to ensure acoustic comfort of car passengers and passersby. The main acoustic indicator, the overall Sound Pressure Level, is not relevant enough to depict pedestrian annoyance during exposure to fan-system noises. Currently, psychoacoustic assessment of these products is not systematic as the psychoacoustic metrics taken separately are not sufficient for sound quality ranking. In order to address this weakness, studies were performed by Valeo based on fan-system noise jury evaluations. It aims at providing a preference model consisting of an equation which combines several psychoacoustic metrics to assess fan-system noise annoyance; keeping in mind that Loudness -or overall SPL- high levels could mask underlying annoyances biasing its assessment. In a first step, the correlation between Overall SPL, Loudness and aeraulic power is highlighted based on standard benchmark test database. In a second step, since tonal noises affect the perceived annoyance, additional tonal metrics are analyzed versus Loudness, or acoustic classes. Tonality especially is then compared to other tonal criteria, before potential assessment of a preference model equation.

Study of the acoustic features and exposures of some typical construction noise sources in India

Occupational noise research and occupational noise standards to date are limited to continuous, non-fluctuating broadband noise and uniform exposure. However, in many occupational environments, such as the construction sites, the workers may be exposed to continuous or intermittent noise of varied spectral and temporal patterns, and their exposure may not be continuous or uniform. These differences in sound signals and sound exposures may have different effect on humans. This paper studies the sound signals of various sources in construction sites of the institute campus through in-situ measurements. The key acoustic features and the spectral content of the sound signals are analyzed. The findings show that construction workers in India are exposed to construction noise with widely varying spectral content. A modified permissible upper limit of construction noise is developed for the presented case study and it is found that five out of eight studied construction sources violate the permissible limit and pose a noise hazard to the construction workers. The study suggests the need for updating occupational noise guidelines based on the noise types and exposure types; and imposing stricter measures for protecting the workers against the construction noise.

Acoustic Black Holes ceiling for noise control on board cruise ships

Entertainment is one of the principal noise sources on board cruise ships. To ensure high comfort standards in cabins located above public areas, ceilings made by rockwool and honeycomb panels are used as acoustic insulation. Engineers are searching for new solutions to substitute the traditional system, as the rockwool presents health concerns. Acoustic metamaterials are among the candidates for new products in this field. This paper aims to verify the feasibility of an innovative ceiling design with enhanced Acoustic Black Holes (ABH). The proposed solution is compared with the traditional ones, using the Sound Reduction (R) as Key Performance Index (KPI). Traditional solutions are experimentally tested, and the data are used to assess an acoustic Finite Element Method (FEM) model, which is then used to simulate the acoustic properties of the proposed ceiling.

A new noise source modelling tool for shooting sheds using novel edge diffraction methodology

Shooting ranges may have a shooting shed to protect the shooter against weather and to reduce noise to neighbours. The noise reduction depends on both shielding and reflection effects and can be difficult to measure due to complex surroundings. In this paper, a new tool will be presented to predict the influence of the shed on the emitted noise. The tool produces a substitute source which models the combined effect of the weapon and the shed, meant for efficient use in regular noise mapping software. It combines advanced edge diffraction methodology for the body of the shed, with a boundary element solution for minor areas representing openings or absorbers in the shed. With this approach we cover the full spectral range (up to 10 kHz) at low calculation time, with an intended precision comparable to traditional models based on boundary element methods. The tool is also intended for opposite use, by reciprocity, for instance to model quietness on the backside of a house by a road.

Comparing acoustic models with measured noise levels in a Polypropylene production industrial complex

This paper presents a detailed comparison between the final noise source data, as documented in the Project Report, produced noise map during design phase, and the field-measured noise values, along with the empirically generated noise map during the plant's operational phase. The study investigates into the accuracy and reliability of the assessed noise map, evaluating its alignment with actual noise levels recorded on-site, identifies discrepancies between both the noise maps, pinpointing areas for improvement in predictive modelling. The goal is to see how well the predicted noise levels match up with the real-world situation, helping improve noise control strategies, specifically focus on noisy equipment, checking if the expected or calculated noise levels are the same with field measured values. By shedding light on these disparities, this study contributes to refining noise prediction models and improving the effectiveness of noise control measures in industrial settings.

The mitigation of airframe noise using a Krueger flap as a leading-edge device in a high-lift configuration

High-lift device is a potent airframe noise contributor. The conventional slat, commonly used in a high-lift device, is known as one of the dominant noise sources. Here, we combine an experimental and a numerical approach to investigate the noise generation of a conventional slat and two Krueger flaps as leading-edge devices in a high-lift configuration. To reduce the computational cost, a short span of the entire high-lift device is selected as the focusing region for scale-resolving and acoustic computations using Improved Delayed Detached Eddy Simulation (IDDES) coupled with the Ffowcs-Williams and Hawkings (FWH) analogy. Simulation results show that turbulent cross flows induce slightly lower-level noise spectra at frequencies less than 300 Hz when the two spanwise sides of the FWH permeable integral surface are closed. Wind-tunnel test results show that the reference and optimal Krueger configurations effectively attenuate the dominant tone of the conventional slat by 4 and 6 dB, respectively. Besides, the optimal configuration is very effective in noise reduction in a wide frequency range. However, the reference Krueger configuration increases the noise level by 0 − 4 dB at frequencies exceeding 5, 500 Hz. Overall, the optimal Krueger configuration is a good choice for high-lift device noise mitigation.