Characteristics Of Noise Sources Research Articles

CORE SIM+: A flexible diffusion-based solver for neutron noise simulations

The paper presents CORE SIM+, a tool developed for diffusion-based neutron noise simulations. The simulator is based on the 3-dimensional, two-energy group neutron diffusion equation in the frequency domain. The tool includes the necessary solvers to calculate the criticality problems associated with the system and then the response to a variety of perturbations such as absorbers of variable strength, perturbations travelling with the coolant flow and vibrations of core components. Numerical methods suitable for different types of problems have been implemented. A capability that allows to apply non-uniform computational meshes is available so that the discretization of the domain can be optimized with respect to the characteristics of the neutron noise sources. The simulator can generate neutron noise databases for nuclear power reactors via the Green’s function method in a fully automated manner. These databases can be useful when studying the neutron noise response in a reactor and when training machine learning algorithms for core monitoring and diagnostics. As part of the verification process, the CORE SIM+ response of a realistic reactor model to a given perturbation at various frequencies is used to estimate the corresponding point-kinetic component, compared to an exact analytical expression. In addition, the Green’s function generator is used to calculate the response of a system to a fuel cell vibration. The solution is then compared to the one of the direct solver of CORE SIM+. As part of the validation work, a neutron noise experiment with vibrations of fuel rods is simulated, showing a reasonable agreement with the measurements. A representative neutron noise database generated for a generic pressurized water reactor is described. From the database the simulations of fuel assembly and core barrel vibrations are chosen as illustrative examples for demonstrating the capabilities of the tool.

Characteristics analysis of near-field and far-field aerodynamic noise around high-speed railway bridge.

The aerodynamic noise around the high-speed railway bridge is studied by the train-bridge-flow field numerical model and theory analysis. With the background of the Beijing-Shanghai high-speed railway line in China, based on the broadband noise sources method and acoustic analogy theory, both the intensity characteristics of near-field aerodynamic noise sources of the train and the spatial distribution characteristics of far-field aerodynamic noise around the bridge are analyzed. The results show that there is the largest sound source energy on the nose tip of the high-speed train; the fluctuating pressure between air and train surface contributes the most to aerodynamic noise; along the longitudinal direction of the bridge, the aerodynamic noise energy near the junction of train tail and body is the strongest; along the transverse direction of the bridge, the aerodynamic noise energy decreases gradually with the distance from the centerline of the railway; along the vertical direction, the aerodynamic noise energy is the strongest at a location of 1.2 m above the top surface of the rail; the train speed, train type, and the height variation of the bridge pier can affect the distribution of far-field aerodynamic noise.

Classification of Noise Sources for Port Area Noise Mapping

Maritime transportation is recognized to have advantages in terms of environmental impact compared to other forms of transportation. However, an increment in traffic volumes will also produce an increase in noise emissions in the surroundings for a greener source, as ports are frequently surrounded by urban areas. When more sources or higher noise emissions are introduced, the noise exposure of citizens increases, and the likelihood of official complaints rises. As a consequence, among the most demanding aspects of port management is effective noise management aimed at a reduction in the exposure of citizens while ensuring the growth of maritime traffic. At the same time, the topic has not been thoroughly studied by the scientific community, mostly because port areas are challenging from a noise management point of view; they are often characterized by a high degree of complexity, both in terms of the number of different noise sources and their interaction with the other main transportation infrastructure. Therefore, an effective methodology of noise modeling of the port area is currently missing. With regard to the INTERREG Maritime Program, the present paper reports a first attempt to define noise mapping guidelines. On the basis of the current state-of-the-art and the authors’ experiences, noise sources inside port areas can be divided into several different categories: road sources, railway sources, ship sources, port sources, and industrial sources. A further subdivision can be achieved according to the working operation mode and position of the sources. This classification simplifies actions of identification of the responsible source from control bodies, in the case that noise limits are exceeded or citizen complaints arise. It also represents a necessary tool to identify the best placing of medium/long-term noise monitoring stations. The results also act as a base for a future definition of specific and targeted procedures for the acoustic characterization of port noise sources.

Acoustic Noise in Moscow during the Covid-19 Quarantine Period in 2020

This paper addresses the results of instrumental observation of acoustic oscillations in the atmosphere above the city of Moscow during the COVID-19 quarantine period. Instrumental observations made by the Geophysical Monitoring Center (GMC) at the Institute of Geosphere Dynamics (IGD), Russian Academy of Sciences, show that the quarantine-related decrease in production activity caused significant changes in the amplitude and spectral characteristics of acoustic noise above the city, as compared to the long-term averages. During the quarantine period, the amplitude of the main spectral components and the average amplitude of acoustic noise decreased by more than two times. The diurnal variation of the amplitude of noise caused by production activities in the daytime was much less evident. Our findings can be useful in determining the characteristics of technogenic noise sources and assessing its contribution to the total acoustic noise level of the city.

EMI Noise Source Characterization for SiC and GaN Power Transistors in Synchronous Rectification DC-DC Converter

EMI Noise Source Characterization for SiC and GaN Power Transistors in Synchronous Rectification DC-DC Converter

Wind noise source characterization and transmission study through a side glass of DrivAer model based on a hybrid DES/APE method

Based on a DrivAer model with notchback, the characteristics of convective and acoustic pressure fluctuations on the side window, as well as their contributions to interior noise were studied. Firstly, a full-size DrivAer clay model was produced with a real glass set on the front left window, and the rest parts with thick clay. In this way, the side glass becomes the exclusive transmission path for the exterior convective and acoustic pressures into acoustic cabin inside. In this study, the acoustic pressure fluctuation on the side window surface was calculated by solving the acoustic perturbation equation (APE) based on the calculation results of convective pressure fluctuation with the incompressible Detached Eddy Simulation (DES). Furthermore, with the convective and acoustic pressure fluctuations as power inputs, the interior noise was calculated with Statistical Energy Analysis (SEA). The calculated interior noise level shows good agreement with the tested results in the wind tunnel, which indirectly validates the reliability of the calculated acoustic pressures with APE method. The contributions of the convective and acoustic pressure fluctuations to the interior noise show that the acoustic pressure fluctuation takes much higher transmission efficiency than the convective one, especially at the high frequency range above the coincidence frequency of the glass, the contribution of acoustic pressure fluctuation is absolutely dominant.

Analysis and control of ventilation noise reduction for box-type transformer in urban area

Noise generated by outdoor box transformer in the working process has a certain impact on the production and life of the surrounding residents. Combining with the current situation of box transformer in 10kV urban area of a residential district, the paper analyses the problems and causes of noise transmission and control. According to the characteristics of noise sources and transmission ways of substation, the paper puts forward and implements ventilation, heat dissipation and sound insulation cover to reduce noise, improve room temperature and ventilation effect, and compares and compares them. The effect of noise control before and after modification is analyzed. The result shows that the effect of modification is obvious and the noise at boundary of box transformer meets the national standard.

소음지도를 이용한 금속재료품 제조공정의 소음저감

The purpose of this study was to establish the noise characteristics of noise sources and the corresponding noise reduction measures during each manufacturing process closest to the workers in the metalworking factory. To this end, the noise generated in the manufacturing process of metal products was measured and analyzed, and the frequency characteristics of noise sources and the causes of noise were identified. The noise map was used to predict the noise reduction effect. Moreover, it is expected that this will ultimately contribute to the reduction of human risks caused by the noise of the civil environment around metalworking factories.

Anisotropic source modelling for turbulent jet noise prediction.

An anisotropic component of the jet noise source model for the Reynolds-averaged Navier–Stokes equation-based jet noise prediction method is proposed. The modelling is based on Goldstein's generalized acoustic analogy, and both the fine-scale and large-scale turbulent noise sources are considered. To model the anisotropic characteristics of jet noise source, the Reynolds stress tensor is used in place of the turbulent kinetic energy. The Launder–Reece–Rodi model (LRR), combined with Menter's ω-equation for the length scale, with modified coefficients developed by the present authors, is used to calculate the mean flow velocities and Reynolds stresses accurately. Comparison between predicted results and acoustic data has been carried out to verify the accuracy of the new anisotropic source model.This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

Source kernels for noise cross-correlation

A wave-theoretic tool, the source kernel, is introduced to describe the sensitivity of the finite-frequency underwater noise cross-correlation function to the location of the noise sources taking into account the refractive features of the ocean environment. The cross correlation of the noise field at two receivers conveys information about the corresponding time-domain Green’s function (TDGF), provided that sufficient energy is channeled into the acoustic paths connecting the two locations. The efficiency of the TDGF recovery is determined by the receiver and noise source locations and characteristics, as well as by the refraction properties of the ocean sound channel. The source kernel takes these characteristics into account and highlights the locations where noise sources can have maximum impact on the cross-correlation output. The distribution and coherence of the noise sources can be specified in a variety of ways to investigate a wide range of scenarios, from random noise-source distributions to coherent radiators. [Work supported by the Office of Naval Research.]

Connecting high-power jet noise characteristics with human annoyance

DoD has funded the development of advanced modeling tools for community noise exposures and for exploring noise reduction techniques. However, inadequate understanding of high-power jet noise sources and the effects of radiated noise on people are both limiting factors in mitigating community noise exposure. In the meantime, both ground personnel and community noise exposure lead to annoyance and disturbance, costly noise mitigation, and burdensome restrictions on operations. Therefore, DoD is exploring acoustical metrics that may better correlate jet noise exposure to human response. More broadly, DoD and the jet noise research community desire an increased understanding of jet noise source characterization to best focus on promising strategies for reducing jet noise impacts. This research project seeks to address these two needs by increasing the understanding of tactical jet noise sources and by correlating their physical noise features, such as noise source distribution, directivity, and shock content, with human response related to annoyance, disturbance, and the perception of crackle. This presentation will provide an overview of the project’s objectives. [Work Supported by AF SBIR Program.]DoD has funded the development of advanced modeling tools for community noise exposures and for exploring noise reduction techniques. However, inadequate understanding of high-power jet noise sources and the effects of radiated noise on people are both limiting factors in mitigating community noise exposure. In the meantime, both ground personnel and community noise exposure lead to annoyance and disturbance, costly noise mitigation, and burdensome restrictions on operations. Therefore, DoD is exploring acoustical metrics that may better correlate jet noise exposure to human response. More broadly, DoD and the jet noise research community desire an increased understanding of jet noise source characterization to best focus on promising strategies for reducing jet noise impacts. This research project seeks to address these two needs by increasing the understanding of tactical jet noise sources and by correlating their physical noise features, such as noise source distribution, directivity, and shock content...

Characterization of noise sources in a microfabricated single-beam zero-field optically-pumped magnetometer.

We present an experimental noise characterization of a miniature single-beam absorption-based optically-pumped magnetometer with a noise floor of 7 fT/Hz1/2 operating in the spin-exchange relaxation-free regime. We experimentally evaluate noise arising from the laser intensity, laser frequency, laser polarization, cell temperature, and magnetic field coils used for the phase-sensitive detection of the magnetometer signal. We find that noise in the range between DC and 30 Hz is a result of noise sources coupling to the atoms in a manner similar to a magnetic field, while the noise at frequencies above 30 Hz is mainly due to laser intensity noise. Our results place an upper limit on the noise sources for our system that matches well with the noise spectrum of the magnetometer at frequencies above 5 Hz.

The Effect of Airfoil Shape on Trailing Edge Noise

This paper investigates the effect of airfoil shape on trailing edge noise. The boundary layer profiles are obtained by XFOIL and the trailing edge noise is predicted by a TNO semi-empirical model. In order to investigate the noise source characteristics, the wall pressure spectrum is decomposed into three components. This decomposition helps in finding the dominant source region and the peak noise frequency for each airfoil. The method is validated for a NACA0012 airfoil, and then five additional wind turbine airfoils are examined: NACA0018, DU96-w-180, S809, S822 and S831. It is found that the dominant source region is around 40% of the boundary layer thickness for both the suction and pressure sides for a NACA0012 airfoil. As airfoil thickness and camber increase, the maximum source region moves slightly upward on the suction side. However, the effect of the airfoil shape on the maximum source region on the pressure side is negligible, except for the S831 airfoil, which exhibits an extension of the noise source region near the wall at high frequencies. As airfoil thickness and camber increase, low frequency noise is increased. However, a higher camber reduces low frequency noise on the pressure side. The maximum camber position is also found to be important and its rear position increases noise levels on the suction side.

ОЦЕНКА ЭФФЕКТИВНОСТИ ШУМОЗАЩИТНЫХ ЭКРАНОВ ПРИ ЗАЩИТЕ ВЫСОТНЫХ ЗДАНИЙ ОТ ТРАНСПОРТНОГО ШУМА

The article assesses the impact of traffic noise on the facades of high-rise buildings in order to identify the floors most affected by traffic noise using the example of two objects in Moscow. The sources of noise are considered streams of road and rail transport. Noise characteristics of noise sources were determined using field measurements and calculations based on data on the intensity of ytaffic flows. The forecast of sound levels at 2 m from the facades of buildings was made using approved software that implements the provisions of GOST 31295.2-2005. It is shown that without the use of noise protection screens on the objects in question, significant exceedances of permissible sound levels occur, especially on facades that go directly to noise sources. A computer simulation of noise protection screens has been carried out in order to assess the possibility of their effective use to reduce noise levels on different floors of the buildings under consideration. It is illustrated that the use of noise protection screens has a limited effect of protection against noise for high-rise buildings, depending on the proximity of the location of the screen to the source of noise. To protect the upper floors of the buildings in question, the use of noise screens is inefficient.

Characteristics and Mechanism Analysis of Aerodynamic Noise Sources for High-Speed Train in Tunnel

We aim to study the characteristics and mechanism of the aerodynamic noise sources for a high-speed train in a tunnel at the speeds of 50 m/s, 70 m/s, 83 m/s, and 97 m/s by means of the numerical wind tunnel model and the nonreflective boundary condition. First, the large eddy simulation model was used to simulate the fluctuating flow field around a 1/8 scale model of a high-speed train that consists of three connected vehicles with bogies in the tunnel. Next, the spectral characteristics of the aerodynamic noise source for the high-speed train were obtained by performing a Fourier transform on the fluctuating pressure. Finally, the mechanism of the aerodynamic noise was studied using the sound theory of cavity flow and the flow field structure. The results show that the spectrum pattern of the sound source energy presented broadband and multipeak characteristics for the high-speed train. The dominant distribution frequency range is from 100 Hz to 4 kHz for the high-speed train, accounting for approximately 95.1% of the total sound source energy. The peak frequencies are 400 Hz and 800 Hz. The sound source energy at 400 Hz and 800 Hz is primarily from the bogie cavities. The spectrum pattern of the sound source energy has frequency similarity for the bottom structure of the streamlined part of the head vehicle. The induced mode of the sound source energy is probably the dynamic oscillation mode of the cavity and the resonant oscillation mode of the cavity for the under-car structure at 400 Hz and 800 Hz, respectively. The numerical computation model was checked by the wind tunnel test results.

Large-eddy simulation of supersonic jet noise emanating from an F404 nozzle at model scale

Large-eddy simulations of supersonic jet noise emanating from an F404 nozzle at the model scale have been carried out using the JENRE flow solver. A wall-model method that was previously validated for a high subsonic flow over a flat plate is used to model the boundary layer effect inside the nozzle. The nozzle geometry is a faceted bi-conic convergent-divergent nozzle with a design Mach number equal to 1.65 and the nozzle-exit diameter equal to 5.07 inches. Both mildly and highly overexpanded conditions are tested for heated jets. The time averaged flow field, turbulence intensities, and the far-field noise are compared with available experimental data. The effects of both the boundary-layer thickness and turbulence intensity at the nozzle exit are investigated to assess their impact on jet noise generation and the noise source characteristics.

Comparing two inverse array methods for source reconstructions of noise radiated from a high-performance jet aircraft

Because direct flow measurements of tactical aircraft jet engines are not currently possible, acoustic source characteristics are instead inferred from array processing. This paper compares two array processing methods using the same array data from a high-performance military aircraft. Hybrid beamforming (HBF) and multisource statistically optimized near-field acoustical holography (M-SONAH) have both been used previously for frequency-dependent jet noise source characterization, but are compared here for the same input data. A 71-element linear array of equally spaced microphones was placed approximately parallel to the shear layer covering a distance of 32 m. Complex pressures obtained from this array served as the input to both methods. Favorable agreement in terms of maximum source location, source shape, and source extent was seen between the two methods' respective results. While the methods continue to have their relative strengths and reasons for use, this favorable agreement indicates that an improved understanding of military jet noise sources has been achieved. [Work supported by an AFRL SBIR.]

Investigating CM Voltage and Its Measurement for AC/DC Power Adapters to Meet Touchscreen Immunity Requirement

The common-mode (CM) noise at the output of ac/dc power adapters can interfere with touchscreen's normal operation in consumer electronic products. Existing power adapter's output CM voltage measurement used in power electronics industry does not align with the touchscreen's sensitivity test used by touchscreen manufacturers. This paper first reviews existing measurement setups and identifies the technical issues in the tests. The CM noise source impedance of ac/dc power adapters and the characteristics of touchscreens are investigated. A new measurement setup is proposed based on both the characteristics of CM noise source of power adapters and touchscreens. A CM voltage limit is also proposed with industry companies. A measurement device is developed for the proposed measurement setup and procedure. The experimental results validate the proposed techniques.

Complexity Study on the Unsteady Flow Field and Aerodynamic Noise of High-Speed Railways on Bridges

To study complexity distributions of unsteady flow field and aerodynamic noise of a high-speed railway on bridges, an aerodynamic noise model of a railway was obtained. Meanwhile, detailed structures such as 6 bogies, 3 air conditioning units, 1 pantograph fairing, and 1 pantograph were considered. Numerical simulation was conducted to flow fields around the high-speed railway running on the bridge under a crosswind-free environment, with running speed of 350 km/h. Hence, unsteady flow behavior characteristics of the complete high-speed railway were obtained. Numerical simulation was conducted to noises of the railway on the bridge in combination with detached eddy simulation and acoustic analogy theory. Meanwhile, the broadband noise model was used for the quantitative analysis on distribution characteristics of the dipole noise source and quadrupole noise source of the high-speed railway on the bridge. Studied results proved that aerodynamic noise of the railway was caused by eddy shedding and fluid separation. Main noise sources of the high-speed railway include areas such as pantographs, train head streamline, bogies, windshield, and an air conditioning unit. Maximum sound pressure level and average sound pressure level of the high-speed railway on the bridge were 2.7 dBA and 2.3 dBA, respectively, more than those of the high-speed railway on a flat ground. On the bridge, the maximum sound pressure level of the pantograph on the bridge was 3.1 dBA larger than that on the flat ground. In addition, incoming flows of the high-speed railway on the bridge had greater impacts on aerodynamic noises around the railway compared with those of wake flows. Meanwhile, in directions of incoming flows and wake flows, linear relationship was between the sound pressure levels of noise monitoring points which had different distances from the train head nose and the logarithm of the distances.

Acoustic energy harvesting using piezoelectric generator for railway environmental noise

High-speed trains have a sustained high-noise level for long periods during operation. Although such high-noise levels are effective for acoustic energy harvesting, a practical design for an acoustic energy harvesting system from a high-speed train is lacking. In this study, the design of an energy harvesting system was implemented utilizing noise from a high-speed train during practical operation. We investigated the noise generated from a high-speed train and derived the characteristics of the main noise sources. The results confirmed that low-frequency noise of 50–200 Hz was generated in the passenger, cab, and between car sections. Results from this investigation were used to design a Helmholtz resonator for a target noise of 174 Hz based on a theoretical model. Moreover, numerical simulation was conducted using sound source speakers to investigate vibrations in the walls of the resonator. Finally, energy harvesting experiments were conducted using various types of piezoelectric elements such as rectangular and circular plates. Experimental results indicate that approximately 0.7 V was generated for an incident sound pressure level of 100 dB using a large rectangular plate. Such power level is sufficient to power a variety of low-power electric devices.