Main Noise Sources Research Articles

Sound absorption analysis of carbon steel varied in density and microstructures

In many factories, noise is an important issue considering workers' health and safety; and metal blocks of the machinery is the main source of noise generated while running. Hence, the acoustical characteristics of the metal parts of machineries need to be considered in design. This study aims to determine the effect of metal density to sound absorption (α) in order to reduce noise impact, including its correlation to the metal microstructures. The αvalues of specimen were measured on 5mm thick carbon steel -varies in carbon densities and well-known in metal industries as ST 30, ST 42, and ST 60 standards. Through 5000x magnification of Scanning Electron Microscopic (SEM), the microstructures of carbon steel are identified. The results showed that in the high-frequency range (1200-1400 Hz) the highest α values occurred on ST 60 steel, while in the low-frequency range (200-400 Hz), the α values were relatively similar for all specimen with a small discrepancy on ST 42. Homogenous metal grains with less gaps are clearly shown on ST 30 microstructures, while for ST 60 the grains seem varied in size and types, dominate with carbon particles, making the steel more rigid and better for sound absorptive function.

Research on particle noise based on second-order effect

The development of integrated circuits has gone through several stages, from the invention of transistors to the emergence of very large scale integrated circuits and system level integrated circuits. Now, the size of integrated circuits enters the nanometer level, and short-channel shot noise becomes an important issue. Short-channel shot noise increases due to factors such as device size reduction and scattering during channel formation. It has a serious impact on the performance, power consumption and reliability of integrated circuits. The formation mechanism of short channel shot noise can be explained from two aspects: one is due to the existence of thermal noise inside the channel, and the other is due to the noise caused by the shot. As the device size decreases, the channel thermal noise gradually changes into shot noise and becomes one of the main noise sources. Aiming at the noise generation mechanism, this paper proposes several methods to solve the short-channel shot noise. Through the research of short-channel shot noise and the exploration of solutions, the impact of shot noise on IC performance can be better understood and dealt with, and the development and innovation of IC technology can be promoted.

Toward Airframe Noise Reduction for Passenger Aircraft

Airframe noise is one of the main noise sources of the latest passenger aircraft during the approach phase. To demonstrate noise reduction technology based on unsteady Computational Fluid Dynamics (CFD) and wind tunnel tests, JAXA conducted flight tests using the JAXA Experimental Aircraft "Hisho" in 2016 and 2017 in cooperation with industries in Japan. The noise data obtained from flyover noise source measurements successfully showed consistent characteristics with the noise reduction designs for the flaps and the main landing gear. The noise measurement data from the flight test 2017 were used to validate the wind tunnel tests and CFD used in the design phase. Subsequently, the research activities proceeded towards the research and development targeting regional jet aircraft, aiming for practical application in passenger aircraft. This paper overviews these research activities toward developing airframe noise reduction technology for passenger aircraft.

Psychological and physiological evaluations of time-varying noises produced by air conditioners

Air conditioners are widely used in buildings to maintain thermal comfort for long time. Air conditioners produce sounds during operation, and air conditioners are regarded as one of the main noise sources in buildings. Most sounds produced by the air conditioner do not fluctuate over time and sound quality of the steady sounds produced by the air conditioner have been evaluated. However, air conditioners sometimes produce time-varying noises. Customers criticizes such noises are annoying when they sleep and they spend time quietly in the living room. The aim of this study was to determine the factors that significantly influence the psycho-physiological response to the time-varying noises produced by air conditioners. We assessed the A-weighted equivalent continuous sound pressure level (LAeq) and factors extracted from the autocorrelation function (ACF). Subjective loudness, sharpness, annoyance, and electroencephalography (EEG) were evaluated. Relationships between psychological and physiological responses and physical parameters, LAeq, the ACF factors, and their standard deviation, were determined. The LAeq and peak of the first maximum peak of the ACF were identified as significant factors for the time-varying noises.

The impact of telescope aberrations on the magnitude of tilt to length coupling noise in space based gravitational wave detectors

Tilt-to-length (TTL) coupling noise is one of the main noise sources that affect space gravitational wave detection, and the Tianqin project requires that the internal TTL coupling noise of the telescope used be less than 0.4 pm/Hz1/2 within the frequency band from 0.1 mHz to 1 Hz. In order to design a telescope that meets the requirements of TTL coupling noise and carry out preliminary error allocation research, it is necessary to analyze and calculate the TTL coupling noise, and then guide the design and optimization of the telescope system. This paper establishes a computational analysis model for the non-geometric TTL coupling noise inside the telescope using the first 36-order edge Zernike polynomials. A method was proposed to reduce the internal TTL coupling noise of the telescope by reducing the proportion of sensitive aberrations caused by non-geometric TTL coupling noise. Simulation results show that, with the RMS value of wavefront aberration at the telescope exit pupil unchanged, reducing the proportion of sensitive aberrations at the telescope exit pupil can effectively reduce the internal TTL coupling noise of the telescope. By optimizing the telescope optical system to reduce the proportion of noise-sensitive aberrations, the non-geometric TTL coupling noise inside the telescope has been reduced from 0.34 pm/Hz1/2 @ 0.1 mHz ∼ 1 Hz to 0.25 pm/Hz1/2. This result can provide some guidance for the design of telescope optics based on the suppression of internal TTL coupling noise in the telescope.

Noise reduction for high-lift devices on a swept wing model by droop nose

The noise of slat in the high-lift device of large aircraft is one of the main noise sources of large aircraft during take-off and landing. This paper investigates a noise reduction measure which consists in droop nose for high-lift device of three-dimensional sweep wing instead of leading-edge slat. The unsteady flow field and the far-field noise are predicted by a hybrid SA-IDDES method coupled with the integration of the Ffowcs Williams–Hawkings equation (FW-H). Based on the optimal droop nose configuration from 2D airfoil, the results of the 3D swept wing model with the droop nose on the leading edge of the inner wing are given. Numerical results show that the droop nose configuration can reduce the overall sound pressure level (OASPL) of the intermediate frequency noise, and the peak noise can be reduced by 15 dB, and the sound pressure level of the broadband noise at low and high frequencies is also partially suppressed. The maximum lift-to-drag ratio of the droop nose configuration increased by 2.7 %. In addition, the noise reduction mechanism of leading-edge droop is analyzed by combining the vortex sound theory and the generation and evolution process of the vortex structure. The leading-edge droop nose configuration fundamentally not only eliminates the vortex structure of the slat cove of the leading-edge slat configuration, but also avoids the interaction between the slat slot flow and the upper surface of the main wing. These directly lead to a thinner boundary layer vortex near the top of the main wing, and the wall pressure pulsation is smaller than that of the leading-edge slat high-lift device, thereby reducing noise. The reduction of the BEF distribution on the upper surface boundary shows again that the droop nose inhibits the vortex on the upper surface of the main wing. The change of the Lamb vector divergence reveals the noise reduction mechanism of the drooping leading edge configuration directly from the sound source.

Background noise model of spaceborne photon-counting lidars over oceans and aerosol optical depth retrieval from ICESat-2 noise data

The ICESat-2 (Ice, Cloud, and land Elevation Satellite-2) photon-counting lidar is a revolutionary active remote sensing device and is extremely sensitive to both laser signal and solar background induced noise photons. The weak laser signals, such as aerosol and water subsurface backscattered laser photons, may be buried in noise in the daytime. A noise model for spaceborne photon-counting lidars is of vital importance in understanding and evaluating the performance of a lidar system, as well as in data processing and applications. From the reciprocity perspective, the main noise source for photon-counting lidars is solar background radiation, which in turn is the signal source of ocean color sensors. In the absence of clouds, it is possible to estimate the aerosol information using background noise data of ICESat-2 if the background noise is accurately modeled. In this study, a background noise model of photon-counting lidars over oceans is proposed that carefully considers the contributions of gas molecules, aerosol, water surface, subsurface, and detector dark noise. As the background rate from clouds are much larger than the sum of other factors, in this study, we only consider the cloudless atmosphere by using a cloud screening process. By inputting the system and environmental parameters, the theoretical predictions of noise level in six study areas have an average MAPE of ∼5% compared with ICESat-2 measured noise data. The results also indicate that without clouds, the variation of aerosols dominates the variation of ICESat-2 total background noise in open ocean areas. Then, based on this noise model, a method to estimate aerosol optical depths (AODs) over oceans is proposed solely on the ICESat-2 product including background noise rate and environmental data. Validation against MODIS (Moderate Resolution Imaging Spectroradiometer) daily AODs indicates that the average MAPE is <20% and the average correlation coefficient is 0.95 in six study areas. This method may provide a new AOD retrieval way over oceans in the daytime, when it is difficult to directly calculate AODs using lidar backscattered signal under strong background noise. In addition, the background noise of the ICESat-2 photon-counting lidar in its six channels (or pixels) has the potential to be regarded as the signal of an “ocean color camera” with only a single narrow green band. Based on this consideration, future works may be conducted to combine ocean color remote sensing with ICESat-2 photon-counting lidar.

Studi Kualitatif Gangguan Pendengaran Akibat Bising di Bengkel Bubut X Sidoarjo

Noise is one of the most dangerous factors in the workplace. Noise can lead to hearing impairment and the risk of temporary or permanent damage to the sense of hearing after exposure for a certain period of time without the use of adequate protective equipment. The aim of the study is to find out the picture of hearing impairment due to noise experienced by workers X Sidoarjo. This study uses a qualitative descriptive approach with observational methods. The result of this study was that 2 out of 10 informants suffered from hearing impairment. The main source of noise in the powder workshop X Sidoarjo is the powdering machines and tooling and scrubbing. Prevention can be done through the use of ear protectors against workers and the implementation of socialization of safety and health at work in order to create a safe and secure workplace environment.

Underwater Noise Characteristics of the Tidal Inlet of Zhanjiang Bay

The coupling mechanism between natural and anthropogenic noise in shallow marine areas is of great significance for maintaining the ecological safety of these regions. In this study, a section of Zhanjiang Bay’s entrance was selected as a typical research area, and environmental noise data at different depths were collected during the spring and autumn seasons. The spectral characteristics, sound pressure levels, and underwater noise frequency correlation matrices of environmental noise were analyzed to reveal the underwater noise characteristics of tidal channels in Zhanjiang Bay and their main influencing factors. The results show that underwater noise in this study area had a stable frequency band distribution. In the low-frequency range of 20–50 Hz, the main source of noise was the flow noise influenced by tides and topography, with a peak sound pressure level of approximately 97 dB. In the frequency range of 50 Hz to 500 Hz, the main noise sources were ships at sea, followed by wind-generated noise. At frequencies above 500 Hz, the noise intensity decreased. In addition, it was found that the sound pressure level in the low-frequency range had a significant correlation with the tidal level, increasing with the rise of the tide and decreasing during low tides. This study provides a research case on the impact that human noise activity has on environmental noise in shallow marine bays. These research findings can support the selection of sites and reduce construction noise from offshore wind farms, as well as ensure the acoustic ecological environment in the vicinity of marine ranches.

Research on Characteristics of Flow Noise and Flow-Induced Noise

The noise control of flank array sonar is a primary approach to enhance the sonar detection range. During submarine navigation, hydrodynamic noise is the main noise source in the platform region of the flank array sonar, which includes flow noise and flow-induced noise. Therefore, an in-depth investigation of hydrodynamic noise is necessary. In this paper, we firstly take the teardrop submarine as a computational model to validate the computational method. Afterwards, we numerically simulate the flow and flow-induced noise characteristics for the cylindrical shell model, and investigate differences in noise at different detection points along the X, Y, and Z axes. Finally, experiments are conducted to confirm the accuracy of the simulation results. The research findings reveal that, at the same frequency, flow-induced noise exceeds flow noise, and the noise decreases as the distance between the walls of the cylindrical shell increases. The experimental and simulation results are consistent, suggesting that the selected computational method can precisely simulate the submarine’s noise.

Experimental demonstration of weak-light inter-spacecraft clock jitter readout for TianQin.

The space-based gravitational wave detection mission, TianQin, requires high-level synchronization between independent clocks of all spacecrafts to extract the gravitational wave signals. It is necessary to measure the inter-spacecraft relative clock jitter based on laser phase-sideband clock transfer. The main challenge is the tracking and locking of clock sideband beatnote signals with low signal-to-noise ratio and frequency variation. In this paper, a systematic scheme of inter-spacecraft clock jitter readout is reported. The requirement of the clock transfer link for TianQin based on the time-delay interferometry algorithm is derived. A bi-directional laser interferometer system with a transmission optical power below 1 nW and a time delay of ∼50 µs is built up to demonstrate the weak-light clock transfer. In this scheme, frequency modulation is performed on the laser to simulate the inter-spacecraft Doppler frequency shift and its variation. Based on electrical and optical clock transfer comparison experiments, it is demonstrated that the GHz frequency synthesizer is the main noise source below the 50 mHz frequency range. The residual clock jitter noise introduced by the optical transfer link is below 40 fs/Hz1/2 above the 6 mHz frequency range, and the fractional frequency instability is less than 6.7 × 10-17 at 1000 s, which meets the requirement of the TianQin mission. Ultimately, The carrier phase measurement accuracy reaches 1 × 10-4 cycles/Hz1/2 above 6 mHz after differential clock noise correction using measured clock jitter.

Analysis of Water Hammer and Pipeline Vibration Characteristics of Submarine Local Hydraulic System

The hydraulic pipeline vibration noise is one of the main noise sources in submarine stealth conditions. Taking the local hydraulic system of a certain type of submarine as the research object, a model is first developed to simulate water hammer pressures and to study the influence of component parameters on the generation and transmission of water hammers. Then, using the maximum water hammer as the excitation, fluid–structure interaction (FSI) vibration characteristics analysis of the pipeline is carried out. Additionally, the simulation method of clamp bolt pre-tightening is discussed. Finally, the modal test of various specifications of the pipeline is carried out. The results show that the error between the simulation and the test results is within 10%, which verifies the correctness of the model settings. On this basis, with the position of the clamp as the independent variable and the maximum stress of pipelines as the dependent variable, the optimization of pipeline passive vibration control is carried out by genetic algorithm, and the finite element verification shows that the pipeline vibration stress is effectively reduced.

A Study of the Relationship between Dipole Noise Sources and the Flow Field Parameters around the Rearview Mirror of Passenger Cars

When air flows through the mirrors, A-pillars, and other surfaces of a passenger car, airflow separation occurs to generate vorticity and generates aerodynamic noise. The dipole noise source is the main source of aerodynamic noise when the passenger car is travelling at high speed. In order to reveal the relationship between the physical quantities in the flow field and the intensity of the dipole noise source, this paper equates each dipole noise source to a sphere radiating noise to the outside. The acoustic wave fluctuation equations expressed as spherical coordinates are combined with the acoustic boundary conditions and the equations of motion of an ideal fluid medium to obtain the relationship between the intensity of the dipole noise source and the flow velocity and vorticity in the flow field. Then, through flow field simulation, we establish a method of identifying the dipole noise source and its distribution area, and analyze the generation mechanism of the dipole noise source. Through the analysis, it is concluded that the dipole noise sources are mainly concentrated in the airflow separation areas, which easily generate vortices. The size of the vorticity is the key factor affecting the intensity of the dipole noise source. When the intensity of the dipole noise source reaches its peak, the direction of the flow vorticity is perpendicular to the direction of the flow velocity and the peak of the flow velocity occurs before the peak of the dipole noise source, which indicates that the angle between the flow vorticity and the flow velocity, as well as the flow velocity, also has a certain effect on the generation of the dipole noise source.

Active electric machine control to reduce compressor noise in heat pumps

As heat pumps help to reduce CO2 emission in residential heating, rapidly growing heat pump sales are predicted. In order to install heat pumps in densely populated residential areas, they must comply with strict noise requirements. Due to advances in control technology in recent years, it seemed promising to investigate the noise reduction potential of a heat pump by means of optimized control. An active control strategy called Current Shaping (CS) has been applied to reduce compressor induced heat pump noise by applying suitable currents to the compressors electric machine. For this purpose, by CS we superimposed suitable current harmonics on the almost constant Iq driving current. In this article we focus on how these modified driving currents affect the noise emitted from the compressor and how this reduces heat pump noise. A compressor test bench was built to perform the CS optimization procedure and to determine noise optimal currents by minimizing compressor vibration. An important finding of this investigation is that the compressor vibrations can be efficiently reduced by CS, and hence also the noise emissions. The vibration reduction potential depends on the compressor harmonic and the operating condition. Additionally, pressure pulsations were measured within the refrigerant pipes and found not to be affected by CS. After the test bench optimization, we applied the optimized currents to a heat pump in a sound chamber to proof that these optimized currents efficiently reduce heat pump noise. For the investigated frequency range of up to 400 Hz our investigations show the three following: First, active electric machine control CS is a suitable method to reduce heat pump noise. Second, the test bench, presented in this paper is suitable to determine the CS current harmonics to reduce heat pump noise. Third, it can be confirmed that the main heat pump noise source is compressor vibration. In general, the two main noise sources of a heat pump are the fan and the compressor. For the compressor there are three noise paths, namely structure-borne and air-borne noise, both excited by compressor vibration, and fluid-borne noise, excited by pressure pulsations in the refrigerant in the piping system. Therefore, from the investigations presented here, it can be derived that the compressor noise is dominating heat pump noise. Moreover, compressor vibrations are dominating heat pump noise and not pressure pulsations in the piping system.

Flow field analysis and noise characteristics of an automotive cooling fan at different speeds

As the core component of the automotive air conditioning cooling system, the automotive cooling fan directly affects the cooling performance of the entire system. Therefore, it is necessary to study the flow field and noise of the automotive cooling fan. This study focuses on the analysis off low field characteristics and noise generation in an automotive air conditioning systems, specifically related to an automobile cooling fan at different speeds. The flow field properties of the fan are examined through the distribution off low line trajectory, pressure distribution on the blade surface, and velocity distribution characteristics at various speeds. The analysis reveals that the maximum air velocity occurs at the point where the fan blade meets the wind guard, while the maximum pressure is observed at this point and at the edge where the fan blade cuts through the cavity. Furthermore, a monitoring point located 1 m in front of the fan is selected to study the average value of fan pneumatic noise pulsation and generate a noise cloud map, aiming to identify the main noise source of the fan. To better understand the noise distribution and variation at different speeds, various noise metrics are utilized, including noise Sound Pressure Level (SPL) spectrum, 1/3-octave SPL spectrum, and 1/3-octave A-weighted SPL spectrum. The noise characterization results indicate that the primary areas of fan noise generation are located at the tip of the leaf margin of the forward swept wing. This research provides valuable insights for the improvement and optimization of the cooling fan design, as well as subsequent noise reduction efforts.

Analysis of flow field and aerodynamic noise of marine gas turbine air intake system.

The aerodynamic noise of air intake system is one of the main noise sources of a gas turbine power plant. In this study, large eddy simulation in conjunction with acoustic finite element method were used to simulate the flow field and acoustic field of the air intake system of marine gas turbine. Based on the acoustic analogy methods, the internal sound source distributions and inlet radiated noise characteristics of the air intake system under different working conditions and wind speeds were analyzed. The simulated flow fields show that the highest vorticity magnitude occurs around the output shaft as the flow largely separates when passing through. The total pressure loss across the intake system increases with the increasing of the air mass flow rate and the ambient wind speed. The acoustical results show that the low frequency noise of the intake system is more prominent than the high frequency noise. The far field sound pressure level increases quadratically with the intake mass flow rates. The introduction of the ambient wind speed at the inlet boundaries reduces the high frequency aerodynamic noise of the intake system, but the overall sound pressure level of the aerodynamic noise increases with the wind speeds.

Use of Acoustic Camera for Noise Sources Localization and Noise Reduction in the Industrial Plant

The paper presents results of the localization of main noise sources in the industrial plant. Identification of main noise sources was made with an acoustic camera using Beamforming Method. Parallel to the measurements by means of the acoustic camera, sound level measurements on the main noise sources have been performed. Based on the calculations, prediction regarding the noise emission at residential buildings located near to the plant has been determined. Acoustic noise maps have been performed with LEQ Professional software, which includes the 3D geometry of the buildings inside the plant. It has been established that, after introduction of noise reduction measures in the plant, the noise levels at the observation points in the residential area meets the limit values.

Acoustical behavior of periodic flank modifications under dynamic operating conditions

Noise emissions belong to the crucial design characteristics in modern transmissions. The most efficient way to achieve beneficial noise behavior is to reduce the excitation in the tooth contact, since the tooth contact represents the main source of noise in gearboxes. Special flank modifications may optimize the noise behavior, but the common design approach uses static assumptions, whereas operating conditions include dynamic operation.The application of periodic flank modifications as a special type of flank form provides a possibility to avoid the typical compromise between the flank design objectives load carrying capacity and low excitation behavior which results from the exclusive usage of standard modifications such as crownings or tip- and root relieves. The principle of periodic modifications is based on the direct compensation of the inconstant part of the elastic deformations in the tooth mesh. For this reason, the static loaded transmission error (LTE) is typically used as specific value to evaluate the effect of these flank forms on the excitation. In theoretical and experimental studies, the effectiveness of periodic modifications to optimize the excitation behavior could be verified. However, the analysis of these modifications under dynamic operating conditions is still scarcely documented. In this paper, the mesh excitation of periodic and standard modifications under various dynamic operating conditions in the subcritical, resonance and supercritical operating range is simulated and compared to each other. In addition, experimental investigations at the dynamic test rig of the Gear Research Center (FZG) were performed. Due to the measurement of the torsional acceleration level during continuous speed runups, the simulated results can be validated by experimental data.

Results of study of environmental noise before, during and after COVID-19 period in conditions of Samara region of Russia and approaches to noise reduction

The acoustical pollution in conditions of urban territories is rapidly increasing and causing a negative impact to the population and to the staff of industrial enterprises. The sources of environmental noise generations are analyzed. Transport and industrial plants may be considered as the main noise sources in the city environment. New results of research of environmental noise in urban conditions before, during and after COVID-19 period on the Samara region of Russia are presented. Experimental results of noise measurements caused by traffic movement and industrial enterprises operation are discussed. Comparison of results of environmental noise measurements in urban conditions before and during COVID-19 period shows that transport noise level was reduced, but the industrial noise level was almost the same, especially in low frequency range. Approaches to reduction of increased environmental noise levels in urban conditions are suggested.

Assessment of Motor Vehicle Noise Levels on the Territory of New Residential Complexes in Voronezh City

Introduction: Adverse human health effects of motor vehicle noise, which levels are the highest in urban areas, are considered in many foreign and domestic studies. Objective: To establish the zone of acoustic discomfort related to motor vehicle noise on the territory of new residential complexes in the city of Voronezh. Materials and methods: Using the “Assistant” sound level meter (accuracy class 1), we conducted 72 noise measurements at 36 monitoring points within the 20.5 hectare area of two residential complexes at distances of 7.5, 50, 100, 200, 300, 350, and 430 meters from the four-lane highway, the main local source of traffic noise. The measurements were taken in May 2023 on working days (Monday to Friday) in the daytime and at night. Results: We have established that modern urban planning technologies and solutions used in the construction of new residential complexes are unable to eliminate the zone of acoustic discomfort. According to the results of field measurements, the equivalent noise level along the highway in the daytime exceeds permissible levels by 17.8–19.7 dBA and at night – by 22.6–25.7 dBA. The noise limit is also exceeded in the inner yard (on the playground, in the recreation area). The significant area of the study object is almost completely affected by traffic noise at the distances of up to 100 m and 200 m in the daytime and at night, respectively, which creates an unfavorable acoustic environment that has a negative impact on the local residents. Conclusions: To reduce the area of the acoustic discomfort zone, it is recommended to take measures to reduce traffic intensity in the study area by developing the road network and public transport system, prohibiting motorcycle and freight traffic on this street, especially at nighttime, improving landscaping of the adjoining territory, and installing transparent noise barriers that will prevent noise transfer between houses to the inner territory of the residential complex and the lower floors of the buildings.