Main Noise Sources Research Articles

Theoretical modeling and analysis of an equipment–shell multiple-transmission-path system with attached liquid-filled pipe

Vibrations generated by mechanical equipment are the main source of radiation noise for ships. In actual systems, there are multiple transmission paths for mechanical vibrations from the equipment to shell. Common paths include vertical support structures, such as vibration isolators, and lateral attachment structures, such as pipes. However, most existing models only consider a single-path scenario. Multi-path systems have more complex modal and vibration transmission characteristics and introduce more complex coupling problems. There is a lack of theoretical modeling and physical analyses of common multiple transmission systems in ships. In this study, a theoretical model of an equipment–shell multiple-transmission-path system with an attached liquid-filled pipe is established as a typical multiple-transmission-path system for ships. In this model, the liquid-filled pipe is solved using a newly proposed traveling-wave method based on Kennard shell theory. Based on the theoretical model, the effects of each type of traveling wave on the pipe on the system modal characteristics, the mechanism behind each path on the system coupling characteristics, the influence of structural parameters on system modal and vibration transmission characteristics, and the proportion of vibration transmitted by the two transmission paths are analyzed. This study provides theoretical insights and guidance for practical vibration and noise reduction engineering.

Using passive acoustics to identify a quiet winter foraging refuge for an endangered beluga whale population in Alaska

Cook Inlet beluga (CIB), Delphinapterus leucas, have not recovered from subsistence overharvest despite conservation efforts initiated in 2000. Reasons for this lack of recovery are still unclear with anthropogenic noise identified as a high threat in this population’s recovery plan. Baseline information on CIB habitat use and soundscape characterization is crucial in evaluating impacts from anthropogenic activities. Using passive acoustic monitoring, we documented the seasonality and foraging occurrence of CIB, together with killer whale (Orcinus orca), harbor porpoise (Phocoena phocoena) and humpback whale (Megaptera novaeangliae), for one year in Chinitna and Tuxedni bays and rivers, two historically important but recently overlooked areas of their critical habitat in western lower Cook Inlet, Alaska. This area’s ecological interest converges with planned mining, marine renewable energy, offshore oil and gas production, and commercial shipping. Results revealed higher presence of harbor porpoise, killer whale, and humpback whale in Chinitna compared to Tuxedni but much lower CIB presence. CIB were not detected in Chinitna Bay but were in the river on 21 days September-February and one day in June. However, CIB were never detected feeding in Chinitna River. CIB acoustic crypsis and preferential use of very shallow habitat in Chinitna revealed a perceived predation risk from killer whales. In contrast, CIB were recorded foraging in both Tuxedni Bay and River and were detected September-April on 127 days making it an important winter foraging ground. Low levels of anthropogenic noise disturbance were quantified in both bays making them some of the most undisturbed sections of their critical habitat, but at the same time highly sensitive to further noise disturbance. Commercial shipping was the main noise source likely causing acoustic disturbance to CIB due to communication masking despite current low levels of temporal overlap with beluga presence. We recommend that applicable regulators consider restricting high sound producing anthropogenic activities in and adjacent to Tuxedni Bay from September 1st to May 15th when CIB are actively using this area. Managing future anthropogenic activities to minimize habitat degradation and acoustic disturbance in this winter foraging refuge will be a key component to support the recovery of this endangered population.

Comparison Of Full-Scale PIV Measurements With CFD Simulations Of A Ship Propeller Inflow

Flow around the ship's hull and specifically the inflow conditions of the propeller(s) critically influence the propeller efficiency and cavitation behaviour. In a typical single-propeller vessel, the hull of the ship creates a velocity deficit in the top part of the propeller disk. This creates suitable conditions for cavitation, which is the main source of noise and vibration both inside the vessel as well as in the marine environment. Recently, two measurement campaigns were performed using a novel full-scale stereo-PIV device built to measure flows around vessels sailing at sea. During the first campaign, performed in one of MARIN's basins, the device was commissioned. The second campaign was performed during a sea trial; it resulted in propeller inflow data that can be used for validating CFD codes. The uncertainty of the PIV measurements was assessed using both campaigns. In the basin, uncertainty bias could be determined by comparing the PIV results with the carriage speed. At sea, the random part of uncertainty was determined by quantifying the standard deviation of the mean velocity for all three velocity components in the wake peak area of the propeller inflow. Overall, the uncertainty was found to be acceptably small, given the scale of the measurement and the necessity to work with naturally occurring seeding particles in the sea. CFD calculations of the same full-scale flow were performed using an in-house flow solver. The CFD results predicted the propeller RPM and the delivered power measured during the full-scale trial well, which gives confidence in the ability of CFD to predict ship trial performance. The comparison of the flow fields was good, with the PIV results demonstrating that full-scale PIV can be done reliably, and that the CFD is able to capture the major features of the flow in the considered area. For a large part of the flow field, the CFD was within the measurement uncertainty band. The wake peak was slightly underpredicted, which may be related to roughness effects on the boundary layer thickness.

An adapted two-step approach to simulate nonlinear vibrations of patterned tires rolling on a smooth surface

The tire/road noise is one of the major problems facing the tire industry due to the nuisance felt by the vehicle's driver and passengers. Moreover, it is expected in the coming years that this sound nuisance will be one of the main sources of vehicle noise due to the transition from combustion engine driven vehicles to electric vehicles. Tire manufacturers have therefore refined the design of their tire structures to find technological solutions to reduce traffic noise. Tire/road noise is also generated by various mechanisms which depend on different parameters such as the properties of the tire, road texture and driving conditions. This noise is partly caused by the acoustic radiation induced by the tire vibrations due to contacts with the road. The simulation and analysis of the tire's vibrations remains a challenge for the tire industry. Indeed, the simulation of the full dynamic response of a rolling patterned tire requires not only taking onto account various nonlinearities but also the multi-scale nature of the generated dynamic response. Contrary to a straightforward strategy that consists in using a time integrator to predict the multi-scale dynamic response, the strategy proposed in this study is based on a two-step approach to separate the dynamics occurring at different scales. The mathematical formulation of the proposed method is detailed as are the different modeling choices to simulate tire rolling under imposed load. The sensitivity of the tire's vibrations response is analyzed under different rolling conditions and with respect to certain key tire tread pattern parameters.

RESEARCH OF THE NOISE LOAD OF VEHICLES

Noise can be viewed as an undesirable component of a signal that can affect the quality of perception or transmission of information in a system. In different contexts, the term «noise» may have different meanings, but a common feature is the random impulsive nature of this phenomenon. Automotive noise is sound energy generated by the movement of a vehicle and its components. The study of road traffic noise is an important area, especially in environments where noise can have a significant impact. This includes analyzing noise levels, identifying noise sources, assessing its impact on the environment, and developing strategies to reduce noise. This study analyzes the causes of automobile noise and their noise sources, and provides classification features. The research methodology included measuring the noise level at different points of the bus interior using a specialized acoustic sound level meter Testo 816. The Sound Meter program was additionally used to obtain current time values of noise level changes with graphical data interpretation. When the bus is idling, a monotonous noise load level in the range of 58-63 dB is observed in the cabin, which is typical for a running diesel engine, which is the main source of noise. The movement of the bus in urban conditions is accompanied by a change in traffic conditions, which in turn increases the maximum noise load to 73 dB. The movement of the bus in the city is accompanied by an increase in the noise load up to 74 dB and the equivalent up to 67 dB. This is due to an increase in speed, contact of tires with the asphalt road, interaction of the air environment with bus elements, the appearance of vibrations and other noises.Although the noise load in the bus interior is within the upper permissible limits, it requires the introduction of noise reduction measures, especially for long-distance buses for a comfortable ride for passengers. Therefore, it is important to take noise levels into account when designing and operating vehicles, as well as when planning urban infrastructure projects.

Noise Pollution Exposure Among Nurses in a Public Hospital in Palestine

Noise pollution affects our health adversely. At hospital, noise can harm health care professionals and patients too. It also affects the performance of the whole staff and therefore, the quality of the delivered services. This study aimed to assess noise levels nurses exposed to and to determine the sources of noise and nurses' complaints about it. A quantitative, descriptive cross sectional study was used. Noise levels at different departments in Palestine Medical Complex (PMC) were measured using an integrating sound level meter. A total of 180 nurses participated in the interviewing questionnaire. The results of the study showed that main sources of noise were: the loud arguments occurred between the health care staff and the relatives/visitors of the patients, loud conversations, the construction work and the renovation in the hospital, patients' crying/shouting, the medical equipment and the staff shouting. The main complaints were discomfort, bad communication, headache, fatigue, stress, irritability, low concentration, inattention, memory problems and noise effect on work efficiency. In most departments, morning shift was the noisiest shift and nurses (61.1%) considered work environment stressful and uncomfortable. Noise levels in all departments exceeded what is recommended by WHO with an average of 64.48 dBA. The minimum value of LAeq was 54.8 dBA in one CCU and the maximum one was 73.5 dBA in NICU. Conclusion: Different noise sources at PMC and many noise complaints were reported by nurses. Noise levels in different departments were above that recommended by WHO. The educational intervention should target nurses and the whole health care staff in order to increase their awareness about noise and to modify their behaviors to reduce it, as well as the effective management of medical devices and machines, repairing devices and physical space arrangement.

Study of hydraulic turbine flow-induced noise distribution law based on defective runner blade

Abstract In order to analyse flow-induced noise distribution law under the defective runner blade, this paper performs defective treatment on the runner blade according to the HLA855a-LJ-250 hydraulic turbine model. Two kinds of blade models, intact blade and outlet side abrasive blade, are established respectively, and the Realizable k-ε turbulence model and broadband noise source model are used to simulate the hydraulic turbine under rated operating conditions. The simulation results show: 1)Double-row leaf grilles and runner blade are the main dipole flow-induced noise sources; 2)Significant differences in the distribution of the acoustic power levels of the double-row leaf grilles’ characteristic blades and the runners’ characteristic blades under different Schemes; 3)Runner defective blades have less effect on the acoustic power level of spiral case, the rest of the overflow components acoustic power level has a tendency to increase, especially the runner has the greatest impact. The maximum increase in acoustic power level of the runner is almost 17 dB, followed by double-row leaf grilles with an increase of around 8 dB. Therefore, critical attention needs to be paid to the abnormal noise signals of runner and double-row leaf grilles.

SEISMONOISY: A Quasi-Real-Time Seismic Noise Network Monitoring System.

This paper introduces SEISMONOISY, an application designed for monitoring the spatiotemporal characteristic and variability of the seismic noise of an entire seismic network with a quasi-real-time monitoring approach. Actually, we have applied the developed system to monitor 12 seismic networks distributed throughout the Italian territory. These networks include the Rete Sismica Nazionale (RSN) as well as other regional networks with smaller coverage areas. Our noise monitoring system uses the methods of Spectral Power Density (PSD) and Probability Density Function (PDF) applied to 12 h long seismic traces in a 24 h cycle for each station, enabling the extrapolation of noise characteristics at seismic stations after a Seismic Noise Level Index (SNLI), which takes into account the global seismic noise model, is derived. The SNLI value can be used for different applications, including network performance evaluation, the identification of operational problems, site selection for new installations, and for scientific research applications (e.g., volcano monitoring, identification of active seismic sequences, etc.). Additionally, it aids in studying the main noise sources across different frequency bands and changes in the characteristics of background seismic noise over time.

Optical properties of germania and titania at 1064 nm and at 1550 nm

One of the main noise sources in current gravitational-wave detectors is the thermal noise of the high-reflectivity coatings on the main interferometer optics. Coating thermal noise is dominated by the mechanical loss of the high-refractive index material within the coating stacks, Ta2O5 mixed with TiO2 . For upgrades to room-temperature detectors, a mixture of GeO2 and TiO2 is an interesting alternative candidate coating material. While the rather low refractive index of GeO2 increases with increasing TiO2 content, a higher TiO2 content results in a lower threshold temperature before heat treatment leads to crystallisation, and potentially to a degradation of optical properties. For future cryogenic detectors, on the other hand, a higher TiO2 content is beneficial as the TiO2 suppresses the low-temperature mechanical loss peak of GeO2. In this paper, we present the optical properties of coatings—produced by plasma-assisted ion-beam evaporation—with high TiO2 content at 1550 nm, a laser wavelength considered for cryogenic gravitational-wave detectors, as a function of heat-treatment temperature. For comparison, the absorption of pure GeO2 was also measured. Furthermore, results at the currently-used wavelength of 1064 nm are presented.

The Effect of Soundscape on Sense of Place for Residential Historical and Cultural Areas: A Case Study of Taiyuan, China

A soundscape carries the culture and memories of historical and cultural areas, capable of evoking people’s emotions towards a place. This paper aims to explore the influence of the soundscape on the sense of place in historical and cultural areas using a mixed-method approach. Conducting on-site measurements, questionnaires, and semi-structured interviews in four areas in Taiyuan, China, this research utilized structural equation modeling and grounded theory for analysis. Research findings: Firstly, the soundwalk method identified 11 categories of soundscapes and the main sources of noise in residential areas were traffic sounds and commercial sounds. Secondly, residents showed the highest preference for natural sounds and traditional activity sounds. Preferences for activities’ sounds and traditional sounds, along with the perceived frequency of daily life sounds, entertainment activities’ sounds, and natural sounds were positively associated with the sense of place, while the perceived frequency of commercial sounds, traffic sounds, and pet sounds was negatively associated. Lastly, from the grounded theory, this research showed that traditional sounds effectively enhanced residents’ sense of place by triggering memories, embodying culture, and connecting emotions. Daily life sounds linked residents’ lives and prompted visions, while local dialects evoked emotion and culture. Activities’ sounds served as lubricants for the place, primarily triggering residents’ sense of place from a lifestyle and emotional connection.

Sound-absorbing structures to reduce cabin and community noise of aircraft (Review)

The analysis of sound-absorbing structures is carried out taking into account their modern classification. The considered sound-absorbing structures can be used to reduce aircraft cabin and community noise levels. Depending on the spectrum of the main noise sources, the required type of sound-absorbing structure is selected, which is then adjusted to the problematic frequency range. Semiempirical and experimental methods are used to adjust sound-absorbing structures, and numerical methods are currently being actively developed.

Analysis of the cause of noise when the drawbridge goes up and down through non‐destructive diagnosis

AbstractIn the case of the Yeongdodaegyo bridge, abnormal noise occurred only in summer when it was opened, and the expected cause of noise was expected to be due to bearing damage or deformation friction. Therefore, a non‐destructive test was performed around the spherical bearing, which is a major part of the drawbridge components connected to the rotating shaft girder. For the measurement to analyze the cause of noise, the real‐time noise source was tracked during hoisting using an acoustic sensor according to the angular displacement of the rotating shaft. Through this, we tried to identify the noise source by identifying the left and right real‐time deformation (torsion, deflection, inclination) and the friction part of the damaged bearing. As a result of the analysis, irregular noise was generated from the left and right sides, and noise was generated when the twist, deflection, or tilt of the rotation shaft occurred. The bottom of the left and right bearings was found to be the main source of noise, and the bearing contact during deformation is considered to be the cause of the noise.

Numerical investigation of the flow noise of an underwater vehicle

Flow noise is an important issue of underwater vehicles. In this paper, the ability of different numerical methods to predict the flow noise of the DARPA SUBOFF underwater vehicle model is investigated and compared. It is found that the front of the command deck and the tail fins are the main noise sources. Numerical results show that delayed detached eddy simulation is a suitable computational model for flow noise simulations.

Noise Analysis and Optimization Design of an Electric–Mechanical–Hydraulic Power Coupler for the Vehicle

This article proposes a new electric–mechanical–hydraulic power coupler (EMHPC). The EMHPC is integrated by a swash plate axial piston pump and permanent magnet synchronous motor, which can realize the conversion of electric, mechanical, and hydraulic energy. To analyze the noise characteristics of the EMHPC, the mathematical models of fluid noise and electromagnetic noise are established, respectively. An optimization model is built based on Isight, and the multi‐island genetic algorithm is used to optimize the triangular groove structure. The optimization results show that the sound pressure level of sound field monitoring points decreases at different frequencies, and the vibration displacement of the cylinder block decreases. The maximum sound pressure level of the directivity curve of the radiated sound field decreases by 9 dB. For the electrodynamic structure optimization of the EMHPC, this article establishes a combination approximation model with higher accuracy. The structure of the stator and rotor is optimized based on the combined approximate model. The optimization results show that the sinusoidal property of the radial air‐gap magnetic density curve is better after optimization, and the harmonic amplitude of the radial electromagnetic force decreases. The maximum sound pressure level in the air domain of the external sound field is reduced from 69 to 60 dB. Moreover, the superposition analysis of fluid noise and electromagnetic noise is carried out, and the main noise sources of the EMHPC in different working modes are determined.

Evaluating an Additive Manufactured Acoustic Metamaterial Using the Advanced Noise Control Fan

This paper examines the performance of a 3D printed acoustic metamaterial as an acoustic treatment for aircraft engine nacelles in the Advanced Noise Control Fan. As the level of air travel continues to increase, so too does the demand for better noise-reduction technologies for aircraft. Engines are one of the two main sources of noise generated by aircraft, with fan noise, in particular, being of concern due to its broadband and tonal contributions. Small and lightweight methods of addressing both broadband and tonal noise are necessary due to the limitations presented by the current engine design. Presented in this paper is a novel acoustic metamaterial that has undergone design optimization for broadband noise reduction. The final design was produced using 3D printing and tested using the Advanced Noise Control Fan at the University of Notre Dame. It was found that the material is capable of reducing the first harmonic of the blade passing frequency by up to 18.5 dB, with an overall noise reduction of 3.7 dB.

VACUUM MUFFLER AS A MEANS OF REDUCING THE EXTERNAL NOISE LEVEL OF THE KOZAK-7 ARMORED CAR

An important characteristic of military equipment is the level of camouflage properties. Among the methods of masking, an important role is played by reducing the external noise of military equipment. In this work, masking itself by reducing external noise will be considered. The Kozak-7 armored combat wheeled vehicle (hereinafter referred to as an armored car) was chosen as the object of the study. On the basis of the Kozak-7 armored car, a line of special vehicles can be developed: command and headquarters, control points, anti-tank complexes, medical, etc. This armored car, like most cars, has several main sources of noise, which together create its external noise. Exhaust gas noise is the most powerful component of external noise. Appropriate mufflers are used to reduce this type of noise. A highly efficient noise muffler, the so-called vacuum, has been developed, the principle of operation of which is to artificially create a vacuum with the help of a pumping unit directly in the muffler and in the inlet and outlet nozzles at the moment when the exhaust gases leave the engine, which makes it impossible for the latter to create acoustic noise. The dependence of the working time of the working cylinder of the muffler on the frequency of rotation of the engine crankshaft, the working volume of the engine, the volume of the working cylinder, the pressure and temperature in the engine intake manifold, the temperature of the exhaust gases, etc. This dependence will make it possible to determine the optimal parameters and limits of possibilities for the application of the described vacuum muffler system. Calculations made for an engine with a working volume of 5 liters show that at a rotation frequency of 2000-2500 min-1, the working time does not exceed ~ 0.05 s. This means, in turn, that the speed of the valves should be of the order of 0.01 s. Calculations of the efficiency of the pumping unit were made, which showed that for the efficient pumping of exhaust gases, and even more so to create sufficient vacuum in the exhaust system, the volume performance of the pumping unit must exceed the volume performance of the engine (for the case of theoretical one-hundred percent noise suppression of exhaust gases, which is not necessary in practice – at least several times). A forecast of the dependence of the external noise level of the Kozak-7 armored car on the speed of movement with the existing silencer and with the developed one was made.

Noise analysis of dry scroll vacuum pump based on experiment and CFD

The scroll vacuum pump is a dry vacuum pump with a wide range of applications. The radiated noise of a multi-stage scroll vacuum pump under different suction pressures is tested. The discharge velocity field is measured by the PIV technique. When the suction pressure changes from 101 kPa to 5 Pa, the average sound pressure level of the scroll pump decreases from 80.37 dB to 58.13 dB, which is reduced by 22.24 dB. The maximum and minimum sound power levels are 97 dB and 74.76 dB, respectively. The spectrum characteristics and the distribution law of radiated noise are analyzed. The measured noises at the rear of all operating conditions are the smallest, followed by the positions above the front part, and the next is the directly above position. Aeroacoustics is the main noise source in the scroll pump. Based on the CFD method, the simulation calculation is carried out at different suction pressures and the maximum simulation error is −5.7%. The location and formation mechanism of the aeroacoustics source are analyzed. In different working processes, the main excitation sources of aeroacoustics are different. The results are helpful to the noise source identification and aeroacoustics improvement of the scroll vacuum pump.

Algorithm for Surface Wave Suppression on 2D Seismic Data Using the Slant Karhunen–Loeve Transform in a Time-Frequency Domain

Abstract —Surface waves are the main source of coherent noise in land seismic survey, and their suppression is one of the main stages of common depth point data processing designed to improve the quality of tracking primary reflections on time sections. In practice, noise reduction is carried out using procedures from modern software based on numerical modeling of waveforms. However, they are too resource-intensive and have a large number of subjectively customizable parameters. The known algorithms have a common drawback: either the energy of reflected waves is distorted in an interference zone with a noise wave or the noise suppression quality is unsatisfactory. The current research is aimed at improving the filtering algorithm in a time-frequency domain using the slant Karhunen–Loeve transform in order to overcome these limitations, to increase the accuracy and rate of its software implementation, and also to test it when processing profile field data from land-based 2D seismic surveys. The algorithm is modified by developing a new method for determining static corrections for surface wave hodograph rectification in a time-frequency domain and by the application of preprocessing in which the reflected wave signal is removed preliminarily. These and other modifications ensure faster calculations and improve the quality of surface wave interference suppression. In addition, the slant Karhunen–Loeve transform is accelerated by parallelizing calculations across logical processor cores. In this paper, the algorithm is described in detail, its significant advantage over the standard methods of bandpass filtering and F–K filtering is shown, and the results of processing the field data obtained by the SWANA procedure (Geovation 2.0) and by the slant Karhunen–Loeve transform. The result obtained by the slant Karhunen–Loeve transform is superior to the SWANA procedure in terms of the surface wave filtering quality and has only four adjustable parameters (SWANA has 20 parameters)

Acoustic Impact of Rail Transport on Residential Areas of the City of Voronezh

Introduction: Adverse human health effects of railway noise are examined in many foreign and domestic studies. The purpose of our work was to assess the noise impact of rail transport and its contribution to creating an acoustic discomfort zone in residential areas of the city of Voronezh. Materials and methods: We took 36 noise measurements at nine monitoring points in the residential area of single-family housing construction at the distances of 25, 50, and 75 meters from the main local source of noise, i.e. railway traffic, including long-distance and suburban passenger trains. The “Assistant” sound level meter (accuracy class 1) was used for measurements taken in November 2023 – January 2024 on weekends (Sat–Sun) in the daytime and at night. Contribution of railway transport to the overall noise level was then estimated. Results: Field measurements showed that in the daytime, the equivalent noise level along the railway track exceeded hygienic standards by 1.4 to 1.7 dBA in the absence of railway traffic due to the proximity to a highway (70 m) and by 14 to 18.6 dBA in its presence; at night – by 2.2 to 3.2 dBA and by 25 to 29.9 dBA, respectively. This means that during 24 hours, 30 % of the territory of the study object is exposed to higher noise levels in the absence of railway traffic. During the passage of long-distance passenger trains and suburban electric trains, the discomfort zone increases to 60 % in the daytime and to 100 % at night. Conclusions: In our case, rail transport noise pollution can be reduced by installing additional translucent noise shields, landscaping the adjacent territory to separate residential buildings from railway tracks, and planting trees and shrubs. In general, when designing railway lines and their infrastructure facilities, it is important to envisage sanitary gaps with modern means of protection against noise.

Development of an acoustic design support tool for HVAC ventilation units

HVAC equipment is one of the main sources of noise inside or outside a building. Furthermore, many people are exposed daily to HVAC noise, which can lead to health-related troubles. Therefore, an HVAC mechanical unit must be selected to provide an acceptable sound level transmitted to the occupied spaces of a building and not disturb the community. This paper presents a prediction tool named Sound Prediction Tool (SPT) developed by MJM Acoustical Consultants Inc. in 2021 that allows the engineer (i) to design an HVAC unit with specific mechanical components (filter, coil, etc.) according to his input parameters and (ii) to predict and optimize the sound levels produced by the selected design through its casing and openings (inlet and outlet air). This tool has been validated firstly with acoustical tests ‘’in situ’’ on several separate Air Handling Units (AHU) manufactured by our customer and secondly with Finite Elements Method (FEM) models using Comsol-Multiphysics. Several examples are presented to demonstrate the usefulness of the proposed tool.