Acoustic Noise Emission Research Articles

Acoustic emission noise reduction: A case of a uniaxial compression test of gypsum-like rock

In acoustic emission tests, the effective signal generated by crack initiation and propagation inside a sample is easily affected by the testing machine, earth vibration and other external noise, which increases the difficulty of data processing and analysis. To solve this problem, a gypsum sample under uniaxial compression is taken as an example to analyze and process the acoustic emission signal during the experiment. The test results show that these noises generally have the characteristics of acoustic sources far from the probe and signal types different from the effective signal. Therefore, a series of methods concerning the noise reduction of acoustic emission signals, including acoustic emission signal preprocessing, acoustic source distance denoising, and acoustic source type denoising, is proposed. Through three analyses and treatments of acoustic emission parameters, noise reduction was achieved with good results. According to the principles of these methods, some suggestions have been put forward for the position of probes in acoustic emission tests; that is, the connection of two probes should not be perpendicular to a weak plane (bedding, joints, etc.). These results could provide a theoretical reference for the postprocessing of acoustic emission signals in mechanical tests.

Environmental Impact Assessment of Onshore Wind Power Plants: A Case Study of a 50 MW Wind Power Plant in Northeastern Thailand

This research aims to assess the environmental feasibility of a wind power plant by investigating its noise disturbances, shadow flicker, and zones of visual influence. The model is applied as a case study for a 50 MW wind power plant, located in the Nakhon Ratchasima province of northeastern Thailand. The acoustic noise emissions were analyzed using the sound propagation and absorption models under the wind conditions on the site studied. The shadow flicker around each wind turbine generator, in terms of the number of hours per year, was also simulated along with the analysis of the zones of visual influence according to the number of wind turbines that can be seen by an observer from a certain distance. The results show a maximum sound level of 47 dBA, within the allowed limits of the 50 dBA legislation of the Department of Pollution Control of the Royal Thai Government. Similarly, the shadow flicker within 1 km of the wind turbines is 10 hours/year, well below the international standard of 30 hours/year. Results of the zones of visual influence indicate that between 15 and 20 turbines are visible from observation points surrounding the potential wind power plant. The results applied to this case study suggest that the potential wind power plant is well-suited regarding its environmental impacts and should typically not incur negative impacts for the local communities. Studies like these are vital to gaining the trust of the communities living near wind power plants to address their concerns and minimize opposition.

Use of Metamaterials to Reduce Acoustic Noise Emissions from Lower Limb Prostheses: An Experimental Validation.

Recent human-centred design studies suggest that acoustic noise could affect the physical use and psychological acceptance of a biomedical device. These aspects are especially relevant in the prosthetic field, in which device loudness is often related to rejection. The aim of the study is to inquire on the possibility to reduce the acoustic noise emitted by a robotic leg prosthesis by improving its casing. First, acoustic noise emissions are characterized experimentally using an anechoic chamber, both for the whole prosthesis, and for its actuator (i.e., noise source) in isolation. The characterizations show that the whole prosthesis including its casing amplify the actuator noise, and that noise emissions are concentrated within a certain frequency range. Based on these findings, the prosthesis casing has been redesigned to include a panel of Helmholtz resonator-based acoustic metamaterials as proof of concept, which attenuate respective noise emissions. Experimental validations show that the use of such metamaterials in the prosthesis casing can significantly reduce noise emissions without compromising on prosthesis size and weight.

Acoustic noise emission of air turbines for wave energy conversion: Assessment and analysis

The oscillating-water-column (OWC) system is one of the most developed wave energy conversion technologies, and several prototypes have been deployed and tested on the sea. Noise emission is essential to this technology’s long-term environmental impact assessment. The power take-off system of an OWC comprises a self-rectifying air turbine that directly drives an electrical generator. The paper compares the noise emission of a biradial turbine with that of a Wells turbine. The noise emission of the biradial turbine was measured at the Instituto Superior Técnico variable-flow test rig, while the Wells turbine data were collected in the literature. Acoustic measurement procedures followed the guidelines of the ISO 3746 Standard. A definition of specific noise level is used to compare the noise emission from geometrically similar air turbines or other air turbines performing the same duty. The results show that the noise levels of the biradial turbine are significantly lower than those of the Wells turbine at off-design conditions for the same pneumatic power.

Tonality Analysis of Wind Turbine Noise Based on IEC Standard

Abstract: The tonality is a notable factor during the development of wind farms. Tonality is a component of acoustic noise emission from the wind turbine which annoys the surrounding area of the wind farm. This paper focuses to evaluate the tonality of the wind turbine acoustic measurement data based on the standard IEC 61400-11 AMD 2018: ed. 3.1. The narrowband analysis of the wind turbine tonal noise component is fully evaluated as given in the standard. The identification of tone and classification of spectral lines is performed for all spectra of the specified wind speed bin. The results are obtained based on the IEC approach: masking level, tonality, and tonal audibility for the sample data of a specific wind speed bin. The audible tones are found for all spectra and reported in the results. The IEC method gives a good prospect of tonality assessment for wind turbine noise measurement from this result.

Investigating the influence of microphone mismatch for acoustic traffic monitoring

The development of robust acoustic traffic monitoring (ATM) algorithms based on machine learning faces several challenges. The biggest challenge is to collect and annotate large high-quality datasets for algorithm training and evaluation. Such a dataset must reflect a broad variety of vehicle sounds since their emitted acoustic noise patterns depend on a variety of factors such as engine noises at different speeds and road conditions. Additionally, the characteristics of the employed microphones have a strong influence on the data. If microphones with different directionality and frequency responses are used during the model development and the final deployment phase, a data mismatch is caused, which can have a deteriorating effect on the performance of machine learning algorithms. In this paper, the influence of mismatched recording locations and microphone characteristics on the proposed ATM system is investigated. To evaluate these effects, we implement state-of-the-art convolutional neural networks to detect passing vehicles, classify their type, and estimate their speed and direction of movement. The evaluated models perform well on low- and high-quality recordings at different locations when using the same recording device for training and testing. However, the results indicate that microphone mismatch causes several issues, which need to be carefully addressed.

The effects of post-processing on longitudinal magnetostriction and core losses of high saturation flux density FeSiBC amorphous alloy ribbons and cores

Fe-based amorphous soft magnetic materials play an attractive role in energy saving and emission reduction due to low core losses. One of the problems is the acoustic noise resulting from magnetostriction during AC magnetization process. In this work, amorphous ribbons with a nominal composition of Fe81.5Si4B14C0.5 (at. %) were produced by planar flow casting and subjected to various postprocessing treatments. The influences of annealing conditions on the longitudinal magnetostriction, acoustic noise and core losses of the ribbons measured at low-field were studied. The effects of bending stress and epoxy impregnation and curing on medium frequency core losses of the alloy cores with different shapes were also investigated. It is shown that larger longitudinal magnetostriction of amorphous ribbons leads to higher acoustic noise emission from amorphous cores. Although the longitudinal magnetostriction was found to be reduced by applying a longitudinal magnetic field during annealing, the core loss was increased. The minimum longitudinal magnetostriction value at 1000 A/m is 7 ppm for ribbon annealed at 350 °C for 90 min. under an applied longitudinal magnetic field, while the lowest core losses at 1.4 T and 50 Hz is 0.213 W/kg for toroidal core annealed at 350 °C for 90 min. under an applied transverse magnetic field. The coupling between longitudinal magnetostriction and bending stress of amorphous ribbon results in an increase in core losses. Furthermore, extra stress was introduced after epoxy impregnation and curing, which also results in an increase in core losses. Thus, low longitudinal magnetostriction is important for stress insensitivity and soft magnetic properties.

Impact of Acoustic Noise Reduction on Patient Experience in Routine Clinical Magnetic Resonance Imaging

Acoustic noise emission from MRI scanners is considered a major factor of patient discomfort during routine MRI examinations. We prospectively evaluated the impact of acoustic noise reduction using software implementations in routine clinical MRI on subjective patient experience and image quality. Two-hundred consecutive patients undergoing one of four MRI examinations (brain, lumbar spine, shoulder, and knee) at a single center were prospectively randomized into two groups at a 1 to 1 ratio: standard MRI examination and MRI examination with acoustic noise reduction. After the examination, patients were asked to complete a questionnaire aimed at defining their subjective experience (primary endpoint). Two readers assessed subjective image quality of all patient studies in consensus (secondary endpoint). Nonparametric tests and logistic regression models were used for statistical analysis. Hundred-seventy-four patients were included in the final study. Patients in the intervention group felt less discomforted by the acoustic noise (p = 0.01) and reported increased audibility of music through the headphones (p = 0.03). No significant difference in subjective image quality was found. Our study indicates that the effects of acoustic noise reduction in routine clinical MRI can be translated into reduced patient discomfort from acoustic noise and improved audibility of music. Acoustic noise reduction thus significantly contributes to increased patient comfort during MRI examinations.

Acoustic Noise of Axial Flux Permanent Magnet Generators in Locally Manufactured Small Wind Turbines

During the last decade, the local manufacturing of small wind turbines has become a common approach in rural electrification applications, especially among international networks of renewable energy practitioners. Locally manufactured small wind turbines (LMSWTs) used in off-grid battery based renewable energy systems, typically utilize coreless axial flux permanent magnet generators (AFPMGs) due to their simple manufacturing. Typically, low cost three phase uncontrolled diode bridge rectifiers are used for the direct coupling of the AFPMG to the battery bank, which increases significantly the total harmonic distortion (THD) content in the stator current. LMSWT users have occasionally reported AFPMG noise as contributing to the overall acoustic noise emissions of the small wind turbine, especially during low wind speeds. In this paper the relation between current harmonics and acoustic noise emissions in AFPMGs is investigated and verified experimentally, while appropriate passive filtering techniques are utilized in order to reduce their effect. Furthermore, the overall acoustic noise emissions of a LMSWT are measured experimentally in the field and are compared to noise standards for residential areas. Finally, electromagnetic and aerodynamic sources of acoustic noise are investigated experimentally in the field, while design recommendations are developed for LMSWTs towards the reduction of acoustic noise emissions.

Dependence of acoustic noise emission on the dissipated energy of plunging waves

Summary The results of experiments performed in a wave flume designed to explore associations between the dissipation of surface wave energy during breaking and acoustic noise emission are presented. The experiments were carried out using tap water in the wave laboratory of the Institute of Hydro-Engineering of the Polish Academy of Sciences, Gdansk, Poland. In particular, being shown are the parameters of empirical dependency between the dissipated wave energy during plunging and the energy of pre-breaking wave trains. Relationships between wave energy losses in the case of breakers with an amplitude of about 10 cm and the noise acoustic energy in the frequency band from 80 to 12,500 Hz were estimated. Taking into consideration the phenomena of reverberations and propagation in an acoustical waveguide, a numerical model was used for the correction of the observed noise's acoustic spectra. A detailed analysis of the factors affecting the noise level in the semi-enclosed volume allowed us to specify the rate of conversion of the wave energy dissipated during breaking into acoustic energy, which was found to be in the order of 10−8.

Analysis of the Acoustic Noise Spectrum of Domestic Induction Heating Systems Controlled by Phase-Accumulator Modulators

In domestic induction heating applications, the modulation technique applied to the inverter has a high influence on the acoustic noise emissions. These noise emissions must be avoided, since they may be audible and annoying to the final user. This paper analyzes the acoustic noise emissions that appear when a series half-bridge resonant inverter is operated with a phase-accumulator-based modulator. This modulation technique has the advantage of operating in the frequency domain, and it is compared with the classical pulsewidth modulator regarding the audible noise generated. The frequencies of the tones in the acoustic noise spectrum are theoretically calculated from the parameters of the phase-accumulator-based modulator. The spectral flatness measure is used to quantify the number of cases in which tones are generated by the modulation. Two techniques are applied to the phase-accumulator-based modulator, and their effect is tested. Theoretical results are experimentally verified.

Effects of Leading Edge Erosion on the Power Performance and Acoustic Noise Emissions of Locally Manufactured Small Wind Turbine Blades

The local manufacturing of small wind turbines has become increasingly popular over the last decade, among international networks of renewable energy practitioners, for the implementation of rural electrification applications. Locally manufactured small wind turbines (LMSWTs), used most frequently in off-grid battery based renewable energy systems, typically utilize wooden blades and coreless axial flux permanent magnet generators due to their simple manufacturing process and local availability of materials. In this paper the effects of leading edge erosion on locally manufactured small wind turbine blades are researched experimentally, both in terms of power performance and acoustic noise emissions. From the research it is concluded that a yearly maintenance of the wooden blades of a LMSWT can lead to less acoustic noise emissions and better power performance, with the latter becoming more significant as the mean wind speed of the installation site increases. For practitioners, installers and manufacturers of LMSWTs, these findings can significantly guide manufacturing processes and techniques in terms of preventing leading edge erosion, while also advising preventative maintenance procedures on the field, in order to keep small wind electric systems quiet and productive.

Investigation of Vibration and Acoustic Noise Emission of Powder Core Inductors

In power electronics applications, where the switching frequency is below the audible frequency, the design of magnetic components considering acoustic noise and vibration is as important as designing for efficiency. For the case of the powder core, which is widely used in grid-connected inverters, much research has been conducted in terms of efficiency and core loss. However, there has been limited research dealing with the topic of acoustic noise and vibration. In this paper, Sendust (Fe–Si–Al), MegaFlux (Fe–Si), and HighFlux (Fe–Ni) powder core materials, which have low magnetostriction and low core loss, are analyzed in terms of acoustic noise induced by Maxwell force and magnetostriction. Three types of powder core materials having a rectangular shape are designed for a 4-kW grid-connected inverter. Various building structures, such as rectangular, toroidal, and oval-shaped, for a Sendust core are compared with sound pressure level and efficiency. The effects of the magnetic flux density, Maxwell force, and magnetostriction are analyzed using the finite element method and are verified experimentally. In addition, the experimental results of sound pressure and inductor efficiency are presented according to core materials and building structures.

Optimum Design of Nozzle Geometry of Dry Ice Blasting Using CFD for the Reduction of Noise Emission

Dry ice blasting has been used in the modern cleaning industry. However, the primary disadvantage of dry ice blasting is high noise exposure. At a high blasting pressure, the process reaches a harmful noise level of up to 130 dBA. The situation significantly impairs to a human being when the noise emission occurs in an inaudible frequency area. Present safety measures are only based on administrative control by encapsulating the entire system with sound insulation. The main objective of this project is to study the optimum nozzle configuration on the effect of dry ice blasting particle velocity and acoustic noise emission. Different nozzle geometry were simulated several times until optimization is achievable. Three-dimension models are designed using CATIA V5. Then the models are simulated with Ansys Fluent V18.2. The numerical studies have been carried out using density based, standard k- e turbulence and Acoustic Broadband Noise Sources model. Six (6) different nozzle configuration namely divergent length, the angle of particle inlet, convergent diameter, expansion ratio, gas inlet diameter and length ratio are analyzed in term of particle velocity magnitude and acoustic power level. The result shows that the optimum nozzle configuration for divergent length, the angle of particle inlet, convergent diameter, expansion ratio, gas inlet diameter and length ratio are 230 mm, 30 mm, 35 mm, 1.00, 6 mm and 0.80 respectively. This configuration provides minimum lowest acoustic noise emission and maximum particle velocity magnitude.

Effect of Clocking on Compressor Noise Generation

The effect of stator clocking on the acoustic noise-generation characteristics in an axial high-pressure compressor is analyzed. A realistic geometry with 1.5 stages is assessed using high-fidelity and low-order numerical methods for different clocking positions at approach operating conditions. The compressor efficiency and the acoustic noise emission are found to vary insignificantly between the simulated clocking configurations. Nonetheless, the pressure distribution is altered significantly, right upstream of the inlet guide vanes. Although the cut-on modes exhibit at least 10-dB-higher amplitudes, the cutoff modes contribute decisively to the wave pattern in the near field. An optimal acoustic liner design can expand on the differently evolving interference pattern of acoustic waves at discrete frequencies. The low-order model is found to predict the directionality of the acoustic waves, and the cut-on criteria for the individual modes is in excellent agreement with the high-fidelity simulations. However, the phase cannot be estimated due to the simplicity of the low-order formulation.

Experimental Investigation of Cycle Properties, Noise, and Air Pollutant Emissions of an APS3200 Auxiliary Power Unit

Auxiliary power unit (APU) operators face increasingly stricter airport requirements concerning exhaust gas and noise emission levels. To simultaneously reduce exhaust gas and noise emissions and to satisfy the increasing demand of electric power on board, optimization of the current technology is necessary. Prior to any possible demonstration of optimization potential, detailed data of thermodynamic properties and emissions have to be determined. Therefore, the investigations presented in this paper were conducted at a full-scale APU of an operational aircraft. A Pratt & Whitney (East Hartford, CT) APS3200, commonly installed in the Airbus A320 aircraft family, was used for measurements of the reference data. In order to describe the APS3200, the full spectrum of feasible power load and bleed air mass flow combinations were adjusted during the study. Their effect on different thermodynamic and performance properties, such as exhaust gas temperature, pressure as well as electric and overall efficiency is described. Furthermore, the mass flows of the inlet air, exhaust gas, and fuel input were determined. Additionally, the work reports the exhaust gas emissions regarding the species CO2, CO, and NOx as a function of load point. Moreover, the acoustic noise emissions are presented and discussed. With the provided data, the paper serves as a database for validating numerical simulations and provides a baseline for current APU technology.

Vibration and acoustic noise emitted by dry-type air-core reactors under PWM voltage excitation

According to coupling way between the magnetic field and the structural order, structure mode is discussed by engaging finite element (FE) method and both natural frequency and modal shape for a dry-type air-core reactor (DAR) are obtained in this paper. On the basis of harmonic response analysis, electromagnetic force under PWM (Pulse Width Modulation) voltage excitation is mapped with the structure mesh, the vibration spectrum is gained and the consequences represents that the whole structure vibration predominates in the radial direction, with less axial vibration. Referring to the test standard of reactor noise, the rules of emitted noise of the DAR are measured and analyzed at chosen switching frequency matches the sample resonant frequency and the methods of active vibration and noise reduction are put forward. Finally, the low acoustic noise emission of a prototype DAR is verified by measurement. At the request of the authors, this article is being retracted effective 30 October 2018.

Reduction of acoustic cavitation noise emission with textile materials

Reduction of acoustic cavitation noise emission with textile materials

AIRCRAFT ENVIRONMENTAL NOISE LEVEL ESTIMATION AT LANDING APPROACH

Three approximate methods are proposed for the estimated noise level of an aircraft performing approach. The noise level from the power plant is determined using existing software packages. In the first two methods, the estimation of the airframe noise level is based on modern concepts of the ratio of the acoustic noise emission from the power plant and that of the aircraft airframe, or on the known data on the relationship between the noise emissions from the chassis and the high lift devices, and the chassis noise level is calculated using known semi-empirical methods. In the third method, to estimate aircraft noise it is proposed to use experimental data on the statistically minimum environmental noise level at landing approach of an airplane with a conventional airframe layout.

Influence of Material Properties and Geometric Shape of Magnetic Cores on Acoustic Noise Emission of Medium-Frequency Transformers

Medium-voltage, medium-frequency transformers (MFTs) are much smaller in size and weight compared to conventional line frequency transformers. MFTs are very attractive for applications where full control of the power flow and high power density are required, such as power electronic interfaces in smart grids and traction converter systems. Because of the switching loss of high-voltage semiconductor switches and the limitation of volume reduction at high frequency due to isolation requirement, MFTs are usually operated in the kHz range, which results in acoustic noise emission. In this paper, the origins of acoustic noise associated with MFTs are investigated based on vibration and acoustic measurements. The work focuses on the influence of material properties and geometric shape of the magnetic core. Based on the measurement results, nanocrystalline uncut cores with oval shape is the best solution for MFT design regarding high efficiency, high power density, and low acoustic noise emission. Finally, the low acoustic noise emission of a prototype transformer built with nanocrystalline uncut cores is verified by measurement. The winding is found to have major contribution to transformer acoustic noise if the low-magnetostrictive uncut core is used.