Machinery Noise Research Articles

Review of Lattice Boltzmann Method Applied to Computational Aeroacoustics

This paper presents the research studies carried out on the application of lattice Boltzmann method (LBM) to computational aeroacoustics (CAA). The Navier-Stokes equation-based solver faces the difficulty of computational efficiency when it has to satisfy the high-order of accuracy and spectral resolution. LBM shows its capabilities in direct and indirect noise computations with superior space-time resolution. The combination of LBM with turbulence models also work very well for practical engineering machinery noise. The hybrid LBM decouples the discretization of physical space from the discretization of moment space, resulting in flexible mesh and adjustable time-marching. Moreover, new solving strategies and acoustic models are developed to further promote the application of LBM to CAA.

Simulation study on the flow-induced vibration and noise in marine centrifugal pumps

Due to the three-dimensional non-axisymmetric shape of the volute, its interaction with the impeller increases the internal flow field complexity and instability of the marine centrifugal pump, representing the main reason for pump body vibration and hydraulic noise. First, the basic principle of fluid machinery noise calculation was explained based on the Lighthill acoustic analogy method and Curle’s theory. Then, the fluid pressure pulsation and flow characteristics of centrifugal pumps were analyzed using the Fluent software, after which the Actran software was used to examine the flow-induced vibration noise properties. The results showed that the clearance size significantly impacted the pump head, while the peak value of the flow-induced vibration response was mainly twice the blade frequency. Although a larger ring clearance increased the structural vibration, it had little impact on the sound pressure level changes in the external sound field. The results provided a new method for the structural optimization and low-noise design of marine centrifugal pumps.

Deep learning-based active noise control on construction sites

Although construction noise pollution has always been a severe issue for governments in metropolitan cities, there is no effective and practical solution to control it. Due to the high nonlinear and transient nature of machinery noises on construction sites, traditional active noise control (ANC) algorithms show a marginal ability to mitigate them. In this paper, a novel high-performance deep-learning-based feedforward ANC controller is proposed to attenuate construction-related noise by considering the delay and nonlinear behavior of acoustic devices. The developed network, with around 128,500 parameters, can be expanded to a multi-channel ANC method without increasing computational costs, and it is suitable for ANC in open space environments like construction sites. Broadband noise attenuation of around 8.3 dB was achieved of a wide variety of construction noises with minor degradation at very high-frequency ranges (7.5–8 kHz). The presented network outperformed traditional and state-of-the-art ANC algorithms.

Experiences with source characterization methods within and beyond the scope of EN 15657

Prediction of machinery noise in buildings requires knowledge about the airborne sound radiation and the structure-borne sound excitation from the source of interest. Laboratory methods to determine the airborne sound power of sources are well established since many years. However, standard methods for the characterization of structure-borne sound from building service equipment were first described in EN 15657-1:2009 which was then superseded by EN 15657:2017. In recent years the test methods described in this standard were applied in several research and development projects in the laboratory for sound measurement (LaSM) at Rosenheim Technical University of Applied Sciences. For this purpose the experimental equipment and the facilities of the laboratory were expanded which involves a variable reception plate test rig that was built in 2017. This paper describes the experience with test methods within and beyond the scope of the EN 15657:2017 using the available laboratory resources.

Analysis of the Underwater Radiated Noise Generated by Hull Vibrations of the Ships.

Shipping traffic is recognised as the main man-noise source of the anthropogenic noise generated in the marine environment. The underwater acoustic pollution is increased due to the increment of the human activity at seas supposing a threat for marine habitats. The ship as acoustic source must be understood and controlled to manage the maritime areas both in time and space to reduce the impact of noise in marine fauna. Shipping noise is mainly composed of flow noise, propeller noise and machinery noise. This research is focused on the analysis and estimation of the underwater radiated noise generated by the vibrations of the onboard machinery or structure-borne noise based on the calculation of the transfer function. This function relates the acceleration levels of the vibrations of the hull's panels and the radiated noise by them using the radiation efficiency. Different analytical methods to estimate the radiation efficiency are presented and compared with data collected at sea. The measurements are performed acquiring simultaneously acceleration and acoustic levels by means on accelerometers installed on the hull's panels at different positions and hydrophones deployed close to the bow, middle and stern of the ship. The analysis of the transmission of the vibrations along the ships is performed using the data from different locations of the hydrophones. The quality of the measurements is analysed using the coherence function through the spectral correlation between the measurement of vibrations and acoustic levels. On the other hand, signal-to-noise ratio is computed to verify the strength of the noise sources. The computed transfer function is used to predict the underwater radiated noise from vibrations showing differences less than 2 dB re to 1 μPa2.

Sound source localization of harmonic sources in entire 3D space using just 5 acoustic signals

Sound Source Localization (SSL) has numerous applications namely machinery noise control, machinery fault localization, localization of explosives and weaponry in defense, development of hearing aids and robot’s auditory system. Beamforming and holographic SSL methods require numerous microphones and measurements for predicting source location; hence are highly expensive and time consuming. The simpler alternatives require less microphones; but are inaccurate, require high SNR, and have space of non-convergence where source cannot be uniquely localized. There is also a lack of method to localize pure harmonic sources. This paper proposes a method that addresses these limitations by accurately and quickly identifying the exact location of a harmonic sound source in the complete 3D space in acoustic free-field using just five acoustic signals. The novelties of this method are: new array design, spatially averaged Time Delay Estimation (TDE), TDE-ER (Energy Ratio) based localization, ER to remove mirror points, spectral de-noising, and solution of non-convergence. The method is rigorously tested through numerous simulations and real-life free-field experiments. A performance comparison shows that proposed method is more accurate (6.7% error) compared with the existing 3D SSL technique (11.7% error). Overall, it accurately identifies the coordinates of dominant sound source with 9.17% mean error, in presence of inherent sensor noise (14 dB SNR onwards) and background noise (8 dB SNR onwards) in complete 3D space. Interestingly, the sound source location, and sound source frequency is found to effect the consistency of TDE-based SSL methods. The presented work paves way for further advancement in 3D SSL.

Active Control of Highly Autocorrelated Machinery Noise in Multivariate Nonminimum Phase Systems

In this paper, a novel multivariate active noise control scheme, designed to attenuate disturbances with high autocorrelation characteristics and preserve background signals, is proposed. The algorithm belongs to the class of feedback controllers and, unlike the popular feedforward FX-LMS approach, does not require availability of a reference signal. The proposed approach draws its inspiration from the iterative learning control and repetitive mode control methods, and employs a modified inverse model learning law. The classical inverse model learning law is well known to offer fast convergence and high steady-state performance, provided that the secondary path is minimum phase and well known. The proposed modified inverse model learning law employs a spectral factorization trick, which allows one to use the method with nonminimum phase plants of arbitrary order. Moreover, our scheme includes a controller bandwidth limiting mechanism that can be used to tune the disturbance rejection bandwidth and to improve the closed-loop robustness to errors in the model of the secondary path. The algorithm’s behavior and performance are verified with computer simulations that demonstrate suppression of electrical transformer noise and include realistic models of the secondary path. The results show high-level selective attenuation and fast convergence.

Visualization of Rotating Machinery Noise Based on Near Field Acoustic Holography

<p>In order to solve the problem of fast identification of the noise source of rotating machinery, the time-space complex envelope model of monopole sound source is studied, and a modulation method of the complex envelope is proposed. A method combining near-field acoustic holography technology and complex envelope information is proposed to reconstruct the sound field and realize the identification of rotating machinery noise sources. Using the overall fluctuation of the signal to identify the noise source of the rotating machinery greatly reduces the amount of calculation, and speeds up the positioning speed while ensuring the positioning accuracy. According to the sound field radiation characteristics of rotating machinery noise, different measurement distances, different sampling points numbers and different reconstruction distances are selected to reconstruct the sound field. The simulation data analysis results show that the near-field acoustic holography technology can still obtain high sound field reconstruction accuracy under the condition of large reconstruction distance, and does not require high sampling points numbers. Using the envelope information extracted by envelope modulation technology to reconstruct the sound field can accurately identify the number and geometric distribution of sound sources. This technology not only speeds up data processing, but also ensures the accuracy of sound field reconstruction.</p> <p> </p>

A multidimensional assessment of construction machinery noises based on perceptual attributes and psychoacoustic parameters

Traditional decibel-based measures in predicting annoyance from construction activities are limited to reflect high acoustic variability of construction machinery noises. Hence, a multidimensional approach based on perceptual attributes and psychoacoustic parameters is proposed. In-situ audio-visual recordings of 16 construction machinery in operation were evaluated subjectively on both perceived annoyance and a 12-item semantic differential perceptual attribute scale. The 16 machinery noises formed three clusters based on four perceptual components (Incisiveness, Strength, Intermittency, and Periodicity) derived via principal component analysis of the perceptual attributes. Notably, individual perceptual components strongly correlate with mean values of psychoacoustic parameters (loudness, sharpness, roughness, and fluctuation strength) over time, which we use to develop an annoyance model for construction noise. Both loudness and fluctuation strength were critical parameters to discriminate between clusters. The model can be used to automatically categorize construction noises by cluster and manage it based on known cluster characteristics.

Noise source localization in permanent magnet synchronous motors under time-varying speed working conditions

Noise source localization of rotating machinery plays an important role in machinery noise diagnosis and control. Various beamforming methods have been developed for stationary sound source localization. However, for rotating machinery working under time-varying speed conditions, the radiated acoustic signals are typically nonstationary. Under these conditions, characterizing and localizing nonstationary sound sources remains a challenge. Permanent magnet synchronous motors are one of the most widely used rotating machinery in modern industries and often work under variable speed conditions. Herein, the noise source localization problem of motors under time-varying speed conditions was studied. A nonstationary noise source localization method based on the Vold-Kalman filter and time-domain beamforming is proposed to restore the spatial acoustic maps of permanent magnet synchronous motors(PMSMs) at a characteristic order. First, the Vold-Kalman filter is adopted to extract acoustic signals at a characteristic order from the nonstationary measurements using a microphone array. Then, the filtered multichannel acoustic signals are fed into the time-domain beamforming algorithm to obtain the noise source localization result in a characteristic order. Combining Vold-Kalman filter with time-domain beamforming enables the characterization of non-stationary sound sources in the time, spatial, and order domains. The experimental results verify the effectiveness of the proposed method in noise source localization for motors under time-varying speed conditions. In addition, the experimental case with two motors further proves that the proposed method can simultaneously realize noise source separation at different characteristic orders.

ASSESSMENT OF THE ACOUSTIC MICROCLIMATE AND RATING OF NOISE HAZARDS IN THE INNER TRANSPORT SYSTEM OF A BUCKET WHEEL EXCAVATOR: A CASE STUDY

Noise and acoustic microclimate have an important influence on working conditions in industry. However, there are many sources of noise in machinery that create occupational hazards. In particular, these problems occur in belt conveyors, which are components of integrated continuous material handling systems. In large heavy-duty machines used for surface mining (bucket wheel, bucket chain excavators, and stackers), the most acoustically active areas are located in the zones of conveyor lines. For this reason, the present article presents the results of comprehensive research of noise in a transport system in a bucket wheel excavator operated in a surface mine. The most significant sources of noise were tested. Two analysis approaches (deterministic and probabilistic) were applied. Lower values of permissible exposure time were obtained using the latter method. This approach should be selected, as it takes into account the real conditions of operation of the tested object. The research and analysis showed that in real operating conditions of large working machines (multi-bucket wheeled excavators), the noise level cannot be treated in deterministic categories. This is due (among other factors) to the fact that the working loads are randomly variable in various operating conditions, which also causes the nature of noise in the area of these machines and their surroundings to change randomly. For this reason, the acoustic climate and the assessment of the level of noise hazards in such machines should be analyzed by taking into account the random nature of noise.

A Computer simulation of noise of construction machinery operating in parallel

Prolonged, repeated or very intense noise exposure can damage human health. To reduce any dangerous effects of noise on human health, policies and restrictions are enshrined in national law and legislative regulations. In the Czech Republic, this issue is subject to the Ministry of Health. In other states it can be the Ministry of Health or more often the Ministry of the Environment. The protection of human health against noise and vibration is enshrined in Act No. 258/2000 Coll., on Protection of Public Health, specifically in şş 30-34 of this Act. Other restrictions are described in Act No. 309/2006 Coll., which regulates other requirements for safety and health protection at work in labour relations and on ensuring safety and health protection in activities or the provision of services outside of labour relations. Furthermore, hygienic limits for workplaces, protected indoor areas of buildings and protected outdoor areas are set in the new Regulation of the Government of the Czech Republic, No. 272/2011 Coll. as amended. This Regulation also sets limits for construction noise. They set limitations in so-called outdoor protected areas and the so-called outdoor protected areas of buildings. The hygienic limit of the equivalent sound pressure level A for noise from construction activities is set here by adding a correction of 5dB or 15dB according to the type of protected space to the basic value of the equivalent sound pressure level A 50dB. This limit must be adhered to. For buildings nearby, the term „protected facades“ is used, i.e. „protected façades“ include the nearest buildings that are inhabited and their occupants could be exposed to noise for a long period of time. We can measure the intensity of noise in these places if we have a "sound level meter". Predicting the intensity of noise and its longevity for future construction is more challenging. The computational evaluation of the noise load of the outdoor area of the monitored territory is based on the recommended theoretical acoustic relations for the transmission of sound from stationary noise sources according to ČSN ISO 9613/1-2. One of the possibilities of calculating the intensity of noise is the application of software programmes used for determining traffic noise, which, in contrast to construction noise, is handled very carefully and predicted in detail during the construction of transport infrastructure. Because here are the values and methodologies for the calculation of noise indicators set correctly and in detail, it is possible to use them also, provided that we work well with the background and input data. The calculation indicators are the values of the equivalent sound pressure level falling in front of the façade, on which we determine various measuring points. If the noise sources and acoustically significant elements are entered correctly, we obtain both correct values and also the possibility of displaying a map of the area with colour isophone bands, which expresses the level of noise in the construction site and its surroundings.

Knowledge, Attitude and Practice (Kap) on Occupational Noise Exposure among Ambulance Drivers at Hospitals in Klang Valley, Malaysia

There has been a great concern of occupational noise-included hearing loss (NIHL) among health care workers. Prior research revealed that ambulance drivers are at high risk of noise on hearing. The aim of this study is to assess the level of noise emitted from the ambulance siren and knowledge, attitude and practice (KAP) on occupational noise exposure. A cross-sectional study in Klang Valley, Malaysia was conducted from February 2019 to March 2019 among 82 ambulance drivers. Data was collect using a self-administered questionnaire consisting sociodemographic, 13 questions for knowledge, 13 questions on attitude and 13 on the practice toward occupational noise exposure. In addition, a Solo 01dB Sound Level Meter was used to measure the level of noise emitted from the siren of the ambulance. Data was analysis by using SPSS version 22. Average noise level (Laeq) was 88.9 db (A) which can be considered as high than permissible exposure limit specified in Factories and Machinery (Noise Exposure) Regulations 1989. The KAP on occupational noise exposure among respondents were moderate. In addition, there was a significant difference between knowledge and attitude on occupational noise (p=0.002, r=-0.339). Improved of KAP is recommended through conducting training and seminars on occupational noise frequently to ensure high level of KAP among ambulance drivers. Besides, engineering controls such as installing noise barrier were advised to be implemented and enforcement of law should be taken seriously to minimize and void hearing related problems in the near future.

Annoyance modeling using personal and situational variables for construction site noise in urban areas

Construction site noise is the most significant cause of noise disputes in South Korea. We conducted an annoyance evaluation to produce annoyance prediction models for four kinds of construction noise that cause the most complaints, namely construction machinery noise from pile drivers, excavators, and concrete pumping vehicles and noise from concrete mold removal working. We adjusted these four noises recorded at construction sites to noise stimuli with 35–80 dB(A), and subjects evaluated annoyance with a score for these stimuli. Participants in the experiment listened to one or two noises at the same time and evaluated their annoyance. We created multiple linear regression models and logistic regression models for annoyance scores of the subjects using acoustic features of noise stimuli and personal and situational variables. Acoustic features included traditional indicators such as Leq, Lmax, and sound quality indices. We calculated mean, maximum, and percentile values of sound quality indices such as loudness, sharpness, roughness, and fluctuation strength. The personal variables were results from a demographic survey and attitudes toward noise, while the situational variables were results from a survey on the living environment and past experiences about noise. Also, we considered the health condition and residence environment of the subjects. Using multiple linear regression, we confirmed that the acoustic features and personal and situational variables influence annoyance from construction noise. Also, we calculated the importance of each variable to the annoyance. Finally, to confirm that the percentage of highly annoyed persons (%HA) varies with personal and situational variables, we classified subjects in accordance with the variables and created a %HA curve for each group. From the result, we confirmed that there is a large difference in %HA in accordance with the health condition of the subjects.

Effects of trailing-edge modification of guide vanes on the wake vortices under different inflow conditions

Karman vortices forming behind blades or guide vanes may induce severe vibration and noise in hydraulic machinery. To solve these problems, the trailing edge of vanes or blades is usually trimmed as a remedy. However, this type of modification is not always effective. Based on an engineering project, two sides of the tail of an asymmetric guide vane were modified respectively. The influence of the modification on the wake flow under different inflow conditions was studied using numerical simulation. The results show that, for the studied case, a 45°-bevel cut on the side of a vane with larger velocity gradient near the trailing edge can effectively suppress the Karman vortex. However, the effect of trimming on the side with smaller velocity gradient is poor. These two ways of trimming can reduce the amplitude of the vortex-excitation force by 73.6% and 35.4%, respectively. When guide vanes opening or head increases, the trimming effect is weakened. In addition, the inflow angle and velocity magnitude have a significant impact on the wake flow behind a hydrofoil. When the attacking angle decreases from 0° to –5°, the amplitude of the vortex-excitation force doubles. When the attacking angle increases to 5°, the Karman vortex street almost disappears. The strength of the Karman vortex is related to the difference between the velocity gradient on the two sides of a vane. The greater the difference, the more stable the wake flow.

Design and Simulation of Vibration Isolator by Hexahedron Finite Element

Composite material and Vibration are the main research areas in which today’s industries are growing. Vibration Isolator is a material which is used in mechanical industries to reduce vibration of machine by placing them at the bottom of small and heavy machineries under dynamic conditions. In designers and engineering life, composite materials help to increase material efficiency resulting in the reduction of cost and for utilization of resources as best as possible. Generally, composite materials are wide in Automobile sectors, manufacturing industries. In this experiment, study on isolator involves different types of composite materials. The design model was designed using CATIA and analyses have been performed using ANSYS Workbench. Anti-vibration mounts, also known as AV mounts, are key components in reducing noise and vibration in heavy machinery and equipment. AV mounts are a low cost, effective component, with a range of different uses. Machinery used in a variety of industries ranging from agriculture to the defence sector can be subject to excessive noise and vibrations which affects the longevity, efficiency and safety of the equipment used. Anti-vibration mounts possess effective shock absorption properties and act as a vibration dampener to reduce noise and improve the lifespan of machine applications.

Optimal Filter Design of a Virtual Mechanical Impedance Control System for Multifrequency Active Sound Power Reduction of Enclosure Panels

An optimal filter design method for a virtual mechanical impedance (VMI) control system is presented in this report. Existing passive methods for reducing machinery noise have limited applications because of weight reduction, cooling, and appearance problems. The VMI control method, which does not require a sensor and can be implemented using a small number of actuators, is an active approach that can be used to replace passive methods when mechanical tuning is difficult. However, VMI control methods can only reduce single-tone noise. In this regard, we improved the VMI control system to reduce the radiated sound power of the enclosure panel at multiple frequencies. To achieve this, we propose an optimal filter design method for a multichannel feedback controller. Unlike conventional VMI control, the presented technique is capable of multifrequency control and considers the radiation efficiency, damping, and estimates the errors of the structural-acoustic system. The controller designed using the proposed method satisfies the required robustness and minimum steady-state error in the target frequency band. Thus, this filter design method facilitates the quantitative determination of several criteria that are needed to evaluate system parameter changes such as radiation efficiency, damping, and estimation error, which are overlooked in a standard active structural acoustic controller. The results obtained using a finite element-based model and experimental investigations show that the radiated sound power of the enclosure panel is reduced at multiple target frequencies after the implementation of control.

Acoustical absorptive properties of meltblown nonwovens for textile machinery

Noise pollution is one of the harmful physical sources in the textile industry, which is among those industries that are faced with noise exposure problems. The results of environmental sound measurements at modern textile mills have shown that the sound pressure level varied from 95 to 130 dB, where the highest sound pressure level was at weaving machines. Textile insulation materials can be fitted in order to decrease sound pollution at a low cost. The objective of this work is to design a sound absorber that can be fixed to the body of the machines, at the point of the noise generation, to reduce noise pollution. Poly(lactic acid) (PLA), which is an environmentally friendly material, was used to produce different samples of meltblown nonwoven absorbers to be used for damping the noise of textile machinery. PLA meltblown nonwoven fabric with the areal density of 16.7 g/m2, average fiber diameter of 1.1 µm, mean pore diameter of 9.8 µm and thickness of 0.27 mm exhibited significant sound absorption. The sample with the smallest average fiber diameter among those investigated had the highest damping effect: 23.95, 41.29 and 29.32 dBA at frequencies of 400, 1000 and 1500 Hz, respectively. Our goal is to have a practical tool that accurately evaluates the absorber sound damping under the actual running conditions of the textile machinery. The design of the absorber from one layer of the PLA meltblown nonwoven over a rigid polyurethane foam sheet had an excellent sound absorption property.

Forty-six years of learning, experiencing, and enjoying work with Larry Royster

It was late August 1973, on my first day as an undergraduate student, when I meet my academic advisor—Dr. Larry H. Royster. As I crammed 4 years of education into the next 5 years Larry was always there to provide counsel and guidance. Then I started grad school and it turned out he also had a research assistantship available to study occupational hearing loss. Two years later I completed my graduate program under Larry's direction. My professional career started in 1980 at Standard Oil Corporation of Indiana. Eight years later I decided to become a consultant in occupational noise, which I remain to this day. Throughout my career Larry continued to mentor me. We worked together on many different ventures from teaching professional development courses, working on machinery noise control, hearing loss litigation support, to co-authoring publications. My talk will describe many of these professional experiences. However, it is the personal relationship and fun I shared with Larry that I cherish the most, and I am pleased to share with you, too. To say Larry shaped my professional life is an understatement – overuse of hyperbole not withstanding meeting Larry was the turning point in my life.

Richard H. Lyon: Sound propagation, acoustic modeling, and the MIT A&V Lab

In the mid 1970s, the Acoustics and Vibration Laboratory at the Massachusetts Institute of Technology was an exciting place for any student interested in acoustics and noise control. As one of the directors of the lab, Professor Lyon had a profound influence on the activities, students, and researchers working and studying there. Among the other things that Dick is known for such as Statistical Energy Analysis, Machinery Noise Diagnosis, and Product Sound Quality, he was also overseeing research on urban sound propagation and applications of acoustical scale modeling. This presentation will discuss some of this research, the culture of the A&V Lab, and personnel interactions with Professor Lyon from one of his student's and researcher's point of view.