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This letter develops a simple approach of duct mode identification and reconstruction based on genetic algorithms, which can extend the azimuthal mode order range compared to the conventional method based on the (spatial) discrete Fourier transform. The underlying principle is reconstructing the dominant mode from the modal identification forward model through optimization by exploiting the sparsity of the mode amplitude vector. The performance is experimentally demonstrated for detections of one and two azimuthal modes under noisy conditions with nondominant modes. Overall, the proposed genetic-algorithm-based framework for solving acoustic inverse problems is beneficial to duct acoustic testing, particularly design evaluations of fan blades and acoustic liners for aeroengines. [ABSTRACT FROM AUTHOR]

Determining reliable noise emission values for machinery is key to successfully implement the Sell and Buy Quiet concept. ISO 11202 is a basic noise emission standard to determine the emission sound pressure level of machines outside of special acoustic test rooms (in situ measurements) and enables machinery manufacturers to determine the noise emission data of their products within their own premises. However, a recent amendment to this standard was made on the basis of an unsatisfactory amount of experimental data. Therefore, this paper systematically examines the validity and accuracy of the amended part of the method. It answers the question, whether the amendment represents an improvement of the existing method. Measurements on a model machine with two configurations allow for an extensive investigation of the effects of the amendment. To that end, the emission sound pressure levels at eight positions near the machine are determined in three different acoustic environments. One finds that the amendment leads to an overestimation of the local environmental correction for the L p A , which, in turn, could lead to an underestimation of the determined emission sound pressure level. [ABSTRACT FROM AUTHOR]

Determining reliable noise emission values for machinery is key to successfully implement the Sell and Buy Quiet concept. ISO 11202 is a basic noise emission standard to determine the emission sound pressure level of machines outside of special acoustic test rooms (in situ measurements) and enables machinery manufacturers to determine the noise emission data of their products within their own premises. However, a recent amendment to this standard was made on the basis of an unsatisfactory amount of experimental data. Therefore, this paper systematically examines the validity and accuracy of the amended part of the method. It answers the question, whether the amendment represents an improvement of the existing method. Measurements on a model machine with two configurations allow for an extensive investigation of the effects of the amendment. To that end, the emission sound pressure levels at eight positions near the machine are determined in three different acoustic environments. One finds that the amendment leads to an overestimation of the local environmental correction for the LpA, which, in turn, could lead to an underestimation of the determined emission sound pressure level.

Background This article explores the Canadian artist Greg Curnoe's experiments with computer- based composition with an emphasis on the Computer Journals project (1969-1971). The Computer Journals project is situated in relation to the art scene in London, Ontario, the development of computer art during the late 1960s, and contemporary theories of technology and culture. Analysis It is argued that the project elaborates an innovative analysis of the relationship between technology and creativity that offers a critical understanding of power, agency, and expression. Conclusion and implications It is suggested that a return to Curnoe's computer-based work offers an alternative to dominant schools of media theory and the philosophy of technology in Canada during the second half of the twentieth century, as well as anticipating contemporary discussions of digital media and creativity. [ABSTRACT FROM AUTHOR]

In this work, a rib design process is proposed to improve the local stiffness of gearbox housing for agricultural electric vehicles. Unlike conventional engines, electric powertrain noise includes high frequency factors and pure tones. Considering these characteristics, local stiffness was evaluated in the frequency range of interest for the prediction of dynamic behavior. The local stiffness of the gearbox housing was evaluated using the finite element (FE) model. Experimental modal analysis and FE model update were conducted to ensure the reliability of the results. Using the results of local stiffness evaluations, the stiffness weak point was identified, and the rib design location was selected through a strain analysis. The shape of the ribs was parameterized by width, length, and height, and parameter studies were used to compare the local stiffness increase rate according to the rib design pattern. According to the results, the stiffness increase rate against the same mass was distributed differently according to the rib shape, and the most efficient rib shape was selected from a manufacturing perspective. [ABSTRACT FROM AUTHOR]

Copyright of Praktiker is the property of DVS Media GmbH and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Vibration diagnosis has developed rapidly, the practice of applying it proving to be highly effective, along with the development of measurement and signal processing techniques. Vibration diagnosis is preferred, with rare exceptions, to noise diagnosis, which is too much affected by ambient noise sources, requiring either special methods or devices or special measurement conditions. Vibrodiagnose, is one of the applications of fault diagnosis methods through vibration analysis to centrifugal pumps [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, a technique is proposed to reduce the carrier noise of pulse width modulation (PWM) inverters for a permanent magnet motor drive. The carrier noise is generated by the motor and the reactor driven by the inverter and affected by the switching frequency. When a motor rotates and drives a machine, the carrier noise is hidden by the machine noise. However, when the motor speed is approximately zero, the carrier noise becomes dominant and raucous. The typical method to reduce the noise employs a switching frequency higher than the audible frequency of human hearing. However, the increase in switching frequency results in the inverter suffering a higher switching loss and lower efficiency. In particular, when the permanent magnet motor operates at approximately zero-speed and full-load, for example, in the hill-start conditions of electric vehicles and the start and stop conditions of elevators, the current flows in specific power devices and the switching loss further increases. The proposed technique uses a zero-sequence voltage, which is generated randomly with the M-sequence signal, and diffuses the frequency components of the ripple contained in the current. The technique is able to reduce the noise without increasing the switching frequency of the inverter when the motor speed is almost zero. Simulation and experimental results show that the proposed technique can diffuse the carrier noise and the cycle of the M-sequence signal changes the diffusion effect of the carrier noise. [ABSTRACT FROM AUTHOR]

This paper analyses the major noise producing machines, the effects of the noise, its control methods and the extent of the utilisation of these methods by the Nigerian manufacturing companies. Nine companies were chosen as models to represent the overall manufacturing sectors in Nigeria. The noise produced by the various machines and equipment used in the production processes in the companies was analysed. Results obtained showed that electricity generating sets produced the highest noise, followed by air compressor, boiler, pressing machine and other machines put together, in that order. The results also revealed that more than half of the total effects of noise are on workers. The effects of noise on workers are more of physiological than psychological. It is recommended that engineering controls combined with administrative controls should be considered as the methods that will provide thorough and permanent solution to the noise problem in the manufacturing companies. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of noise emitted by selected machine tools in a production hall (under industrial conditions). Noise monitoring is a fundamental task for maintaining workplaces which are safe and healthy. This paper presents the noise measurements obtained for several machine tools, performed in accordance with the PN ISO 230-5:2002 standard. The identification of noise sources and levels was conducted by means of the UNIT 352 measurement system for DMU 50, BGO-CNC/RV/R, FU 251, FW 801, FWC 25/H. Detection of noise sources in the tested machine tools allows to maintain safety of workers and effective means of noise reduction, which are highly significant from the perspective of minimising noise at various workstations. The method of performing noise measurements at workstations using specific machines is normalised, so that the results of such measurements for different machines could be compared. The test results were presented in the form of diagrams and tables. The results of the tests are concluded by a detailed recommendation for the CNC machine tool operators to use hearing protection when at work. The results showed that the level of noise at the operator's workstation significantly exceeds the standard at certain machining parameters. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, we present an analysis of low complexity signal processing algorithms capable of identifying special noises, such as the sounds of forest machinery (used for forestry, logging). Our objective is to find methods that are able to detect internal combustion engines in rural environment, and are also easy to implement on low power devices of WSNs (wireless sensor networks). In this context, we review different methods for detecting illegal logging, with an emphasis on autocorrelation and TESPAR audio techniques. The processing of extracted audio features is to be solved with limited memory and processor resources typical for low cost sensors modes. The representation of noise models is also considered with different archetypes. Implementations of the proposed methods were tested not by simulations but on sensor nodes equipped with an omnidirectional microphone and a low power microcontroller. Our results show that high recognition rate can be achieved using time domain algorithms and highly energy efficient and inexpensive architectures. [ABSTRACT FROM PUBLISHER]

Magnetic forces in electrical machines cause vibrations on the structure and its connected components. This leads to undesired noise and vibration in the total system. This paper deals with explanation and reduction of alternating force generation at the connection point of a motor due to radial forces acting on the stator teeth with an electric wheel hub drive being used as example. These alternating forces have a disturbing effect on the driver in the form of noise or vibrations. In our research, we developed a multi-physical simulation of the system which is compared with an operational vibration analysis from an experiment. The simulation shows that the main cause is the axially asymmetric structure of the housing. We reduced the alternating forces at the connection point by using an axially symmetric structure. An axially symmetric design also of other electric machines is to be expected to significantly improve the vibro-acoustic behaviour. [ABSTRACT FROM AUTHOR]

The article presents results of a noise dosimetry study indicating the noise reduction of the lawn tractor. Topics discussed include the development of noise exposure during sub-urban lawn tractor operations, the implementation of feasible engineering controls for noise level reduction, and the enhancement of the lawn tractor-associated noise hazards communication.

Firstly, the paper established a finite element model for a steel motor shell and computed related modals, vibration velocities, stress and strain respectively. Computational results show that the flange and end shield of the motor shell had the maximum vibration velocities and strain because these locations lacked the reinforcing ribs, while the maximum stress was mainly at joints between different structures. Secondly, the steel material was replaced by the aluminum alloy. Mechanical parameters of the motor shell were recomputed and compared with those of the steel structure. Results show that modal frequency on each order increased, which is good for avoiding the structural resonance. In addition, the maximum stress of the structure decreased by 4.4 MPa, and the maximum strain decreased by 0.27 mm, which could effectively improve the fatigue characteristics of the motor shell under long-term excitation. Then, the boundary element method was used to compute radiation noises of the motor shell in far field, where the radiation noise presented an obvious directivity. Finally, the paper proposed a GA-BP neural network model to predict the radiation noise of the motor and compared the prediction results with the boundary element. In the whole analyzed frequency band, the maximum difference between the neural network prediction and the real values did not exceed 5 dB, indicating that it is feasible to predict radiation noises of the motor by the neural network. Additionally, experiments were also conducted and compared with two kinds of numerical methods. Methods proposed in this paper provide some references for realizing the rapid noise reduction and light weight of motors. [ABSTRACT FROM AUTHOR]

In bearings research, noise is an important evaluation index for mechanical property, in particular in muting machinery technology. Environmental pollution caused by bearing noise has always been the focus in bearing industry. In this paper we consider: i) sliding incentive of the rolling element bearing, and ii) its own variable stiffness incentive, to: i) accomplish the vibration coupling between the bearing and bearing seat, and ii) the coupling between bearing vibration and noise. This is achieved by means of combination of: i) kinetic model, ii) FEM method and iii) BEM method. The aim is to: i) build a perfect coupled vibro-acoustic model of the bearing, and ii) compare the test results and numerical simulation results of the bearing vibration velocity in order to verify the feasibility of the simulation model. Then the noise is calculated by the simulation model. Based on this, the improved design was carried out for low-noise rolling bearings, and the feasibility of the improvement program was verified by means of simulation. [ABSTRACT FROM AUTHOR]

The objective of the research has been to provide an answer to the question of what the possibilities of determining the direction of approach of the auditory danger signal emitted by an overhead crane appropriately are. Cases of use and no use of earmuffs (in the passive mode and level-dependent ones) were all taken into consideration. Material and Methods: The auditory danger signal and ambient noise were recorded in an industrial hall. Signals were reproduced at an experimental set-up, using a large number of speakers. Eight speakers for reproduction of the auditory danger signal were placed above a subject's head. The study participants would indicate the direction from which, according to them, the auditory danger signal was being emitted. Results: The average percentage rate of the correct localization amounted to 75.8% when the overhead crane’s signal wasn't masked. The presence of ambient noise caused a reduction of the number of correctly identified localization to 66.6%. The use of earmuffs in the passive mode resulted in the worst results (44.5%). There is some improvement when level-dependent earmuffs are used (57.3%). Conclusions: In situations where it is important to identify the direction from which the auditory danger signal generated by the crane’s signaling device is approaching, it is beneficial to use level-dependent earmuffs rather than earmuffs in the passive mode. Correct identification of whether the auditory danger signal generated by the crane’s signaling device is approaching from the left or right side is almost perfect, however correct identification of whether the signal is approaching from the front or back of a person is not always possible. [ABSTRACT FROM AUTHOR]

Different standards to measure the sound power of a machine can be chosen. Historically, in a place with extremely loud background noise, the intensity standard (UNE-EN ISO 9614-X) has been used because there is not enough signal-to-noise relation for the pressure method (UNE-EN ISO 374x). Nevertheless, in some cases, the interfering intensity will make the measurement impossible. To solve this problem for both techniques, a new methodology based on the use of blind source separation algorithms is proposed in order to allow an estimation of the signals of the primary sources from some mixed signals and, therefore, to calculate the sound power of the machine of interest. To make the estimated signals as similar as possible to the real signals of the machine under test, different preprocessing techniques (FFT, DCT, cepstrum or wavelets) have been used before the blind source separation algorithms. Once the tests have been conducted for every machine, it is possible to establish at least one process, or combination to obtain results similar to those obtained using the international standards. Finally, since the signals can be scaled at the output of the blind source separation algorithms, one possible signal correction scheme is analyzed. [ABSTRACT FROM AUTHOR]

It is well-known that the reduction of noise levels is not strictly linked to the reduction of noise annoyance. Even earthmoving machine manufacturers are facing the problem of customer complaints concerning the noise quality of their machines with increasing frequency. Unfortunately, all the studies geared to the understanding of the relationship between multidimensional characteristics of noise signals and the auditory perception of annoyance require repeated sessions of jury listening tests, which are time-consuming. In this respect, an annoyance prediction model was developed for compact loaders to assess the annoyance sensation perceived by operators at their workplaces without repeating the full sound quality assessment but using objective parameters only. This paper aims at verifying the feasibility of the developed annoyance prediction model when applied to other kinds of earthmoving machines. For this purpose, an experimental investigation was performed on five earthmoving machines, different in type, dimension, and engine mechanical power, and the annoyance predicted by the numerical model was compared to the annoyance given by subjective listening tests. The results were evaluated by means of the squared value of the correlation coefficient, R2, and they confirm the possible applicability of the model to other kinds of machines. [ABSTRACT FROM AUTHOR]

The paper gives an overview of previous trends in development of silent-running gearboxes and presents solutions enabling vibration and noise reduction. Advantages and disadvantages of these solutions are discussed. In addition, the paper describes a new original gear design which enables reducing gear vibration and noise without changing gear contact conditions. [ABSTRACT FROM AUTHOR]

The noise level was assessed by measuring and processing the sound pressure during the mechanical treatment of large size aluminum extrusions utilized in high-speed trains. The noise control tests were proposed by various machining technologies including the adjustments of cutter tool, machining feed rate, cutting way and sealing the openings with sound-absorbing material or not. The results indicated that obvious noise suppression can be obtained by using monolithic cutters, and sealing the openings and ports with sound-absorbing materials, which has little effect on the whole machining efficiency. It is helpful for noise reduction using the machining technologies of cutting along milling and slowing the feed rate down, which requires a balance between noise level and machining efficiency. [ABSTRACT FROM AUTHOR]

Noise prediction is very important for new wind farms located near to noise sensitive receivers. To minimize uncertainties of noise level calculation, the effect of cylindrical spreading must be taken into account far away from a turbine. Cylindrical spreading of sound from point source (wine turbine) results from downwind refraction, induced by low level jet. An LLJ is characterized by a wind speed maximum of at least 10–20 m/s with peak speeds up to 30 m/s, at a height a few hundred meters above the ground. Two categories of LLJ are discussed: concaved upward and concaved downward. Cylindrical spreading begins at the critical distance, R , where the superposition of the direct and once reflected rays occurs. The method for calculation of R , for two LLJ categories, is discussed. [ABSTRACT FROM AUTHOR]

The work deals with tonal noise of an axial turbo machinery stage due to rotor-stator interaction. The objective of this study is the reduction of this noise by ejection of a secondary mass flow at the rotor blades' trailing edge (trailing edge blowing, TEB). A widely investigated strategy is a perfect filling of the wake downstream of the blade trailing edge. Recent studies, however, indicated that this state of the art trailing edge blowing strategy is problematic since it may stimulate undesired secondary flows which overcompensate for the benefits of trailing edge wake filling. Hence, in this paper a novel strategy of trailing edge blowing is described. The key idea is the application of an evolutionary optimization algorithm to trailing edge blowing experiments with the measured far field sound pressure level as target function. As a result spanwise trailing edge blowing distributions that reduce the fundamental tone at blade passing frequency (BPF) by 2.4 dB, and at its first harmonic by 21.4 dB (the former representing a small benefit, but the latter corresponding to a complete elimination of the tone), have been found. The required blowing mass flow rate is 2% of the mass flow rate through the stage and hence relatively moderate. 3D hot wire measurements proved that the acoustically relevant upwash velocity fluctuations as seen by the stator are not only caused by the wakes from the rotor blades but also by vortex structures at the rotor's hub and tip. TEB, which is obtained by optimization as proposed in this contribution, either does not enhance these secondary flow structures or puts them out of action. [ABSTRACT FROM AUTHOR]

This paper presents the verification of two partial indices proposed for the evaluation of continuous and impulse noise pollution in quarries. These indices, together with the sound power of machines index and the noise hazard index at the workstation, are components of the global index of assessment of noise hazard in the working environment of a quarry. This paper shows the results of acoustic tests carried out in an andesite quarry. Noise generated by machines and from performed blasting works was investigated. On the basis of acoustic measurements carried out in real conditions, the sound power levels of machines and the phenomenon of explosion were determined and, based on the results, three-dimensional models of acoustic noise propagation in the quarry were developed. To assess the degree of noise pollution in the area of the quarry, the continuous and impulse noise indices were used. [ABSTRACT FROM AUTHOR]

A necessity for the suitable recognition of different machinery and equipment based on the sound they generate is constantly present and will increase in the future. The main motivation for the discrimination between different types of machinery sounds is to develop algorithms that can be used not only for final quality inspection but for the monitoring of the whole production line. The objective of our study is to recognize the operation of the individual machine in a production hall, where background noise level is high and constantly changing. An experimental plan was designed and performed in order to confirm the hypothesis proposing that automatic speech recognition algorithms can be applied to automatic machine recognition. The design of the automatic machine recognition procedure used in our study was divided into three stages: feature extraction, training, and recognition (classification). Additionally, a traditional mel-frequency cepstral coefficient (MFCC) procedure was adjusted for machinery noise by using different filter compositions. Finally, two classifiers were compared, the k-NN classifier and the multivariate Gaussian distribution. The results of the experiment show that machinery noise features frequency cepstral coefficients (FCC) should be extracted by using linear filter compositions and processed with recognition algorithm based on the multivariate Gaussian distribution. [ABSTRACT FROM AUTHOR]

Wind power is a rapidly growing technology, with an estimated 35% of national end-use electricity demand to be met from wind by 2050 in the US. With such a projected rapid growth, it is necessary to improve and innovate relevant technological areas with due considerations of possible impacts of wind energy harnessing through wind turbines. This paper presents a systematic review of current literature on the issues of noise and vibration of wind turbines and their impact on human health and wild life. The paper reviews the literature on the issues of noise and vibration in wind turbines, the generation mechanisms, the propagation, the impact on human health and wild life. The current status of technology and future developments to mitigate the health and environmental impacts of wind turbine noise and vibration are also reviewed. The paper includes a review of current standards on measurement of acoustic noise of wind turbines and data analysis. [ABSTRACT FROM AUTHOR]

The effectiveness of adjusting the excitation input as a method for modifying impact sound was investigated. The radiation from the impact can be described using a convolution of an impulse response function for a vibro-acoustic system and the corresponding impact excitation function. Therefore, the radiated sound can be changed by modifying both the impact excitation function and the structural response. Excitation with complicate shapes of input which is required to make an arbitrary shape of wave form, such as selective excitation or rejection of a specific frequency component, is not easy for manually operated traditional system. However, the modification of excitation input is useful for the automated system with an electrically controlled impactor, such as a servo-motor. As a practical application, a punching process of a punch press machine was designed to not only reduce the overall sound pressure level but also improve the perceived sound quality. Sound from a punch press can be improved by dividing the punching process into several steps with different stroke speeds without substantially reducing the cutting surface quality. [ABSTRACT FROM AUTHOR]

Noise is one of the most pervasive occupational health problems. Noise contours provide useful information by clearly identifying areas where noise hazards exist. This study finds an efficient algorithm for computing sound level in industrial buildings that accounts for reverberation effects. This study proposes an analytical image method to calculate workplace noise distribution by using machinery noise labeling. Contours are then obtained by joining locations with equal noise levels using commercially available software. To demonstrate the application of the proposed method, a manufacturing plant building is considered. The computation algorithm accounts for distance and sound reflection to construct noise contours. The proposed approach could be used in industry for noise management when designing new plant buildings and installing machines.Practical applications: Machine noise emission information will be widely used in practice to evaluate the potential and performance of noise levels in industrial buildings. Plant buildings should be designed to prevent or minimize any risks to health or safety resulting from the emission of noise. The construction of noise contours will have direct implications for the hearing conservation program. [ABSTRACT FROM AUTHOR]

Marine propeller hydrodynamics and noise study is an important issue in considering the suitable performance of the ships and submarines. At the first step of this study, the hydrodynamics of two propellers was studied under different operating conditions. Then the sheet cavitation inception and development conditions were obtained in order to determine the impact of varying rotational speeds of the propeller and pressure drop on the propeller noise. At the second step, the overall Sound Pressure Levels (SPLs) for each one of these models were extracted under non-cavitating and sheet cavitating conditions. The overall SPLs were calculated through the Ffowcs Williams-Hawkings (FWH) equation and its integral solutions. In this work, the flow field was analysed through the FVM, and then the flow data, including pressure fluctuations, sheet cavitation volume, and velocity magnitude results of the flow solution were used as the inputs for the FW-H formulation to predict the overall SPLs. The results of the flow analysis are significant since they are used as the noise sources in the FW-H equations to obtain the overall SPLs. Therefore, these results must be thoroughly analysed. The numerical hydrodynamic results were compared with the experimental results from the two propellers and a good coordination was found. [ABSTRACT FROM AUTHOR]

This paper presents the design, development, and initial testing results of a small-bore railgun and test bench for the study of muzzle voltage traces. An analysis of the noise observed on voltage traces taken from the muzzle during motional and locked-armature operations is presented and discussed. The average velocities for a 3.38-g projectile were 50 m/s over a series of 21 tests. The railgun is powered by a sequentially fired pulse-forming network consisting of six electrolytic capacitor banks. Typical current and voltage characteristics are approximately 20-kA peak current at 275 V for a 6-ms pulse train length. Noise root-mean-square voltage and noise margins are extracted from the muzzle voltage waveforms and discussed. This investigation also develops a quantitative method to analyze muzzle voltage noise, which can be applied to any electromagnetic launcher. The technique reveals a new and interesting result that shows noise levels were greatest during early pulses of the firing sequence and generally decreased with subsequent pulses. This demonstrates that the technique has the potential to provide insight into the nature of the armature–rail sliding contact. [ABSTRACT FROM PUBLISHER]

Aiming at the problems of noise, hard conveying of conveying chain in the three dimensional space, a new style of poly-directional conveying chain, which consisted of inner link, outer linker, sleeve, roller, pin, was designed. The chain elements were secured each other by inner link and outer link, so the links could not be moved between each other and the work noise was reduced. The transmiision dynamics performance of the chain was researched and the force of each component and parts was analyzed on the mechanical system dynamics software ADAMS. The results could provide design reference for the chain. The results indicate that the new poly-directional conveying chain can realize any conveying route in the three dimensional space under complex operating conditions and the test results show that it has an excellent performance in the mechanical property. [ABSTRACT FROM AUTHOR]

Infrasound is observed in all environments at varying levels and is generated by a range of natural and anthropogenic sources. Some studies have suggested that modern wind turbines can generate a relatively low level of measurable noise at frequencies corresponding to the blade pass frequency of turbines. People walk at a variety of speeds, with typical walking frequencies similar to the blade passing frequency of modern commercial wind turbines. Measurements have been conducted of the levels of infrasound generated at the human ear when walking and compared to measured levels near wind farms. The measured level of infrasound generated at the ear at blade pass frequency when people walk can be considerably higher than the level near wind farms. In both cases, measured levels were significantly below the audibility threshold for very low frequency noise. [ABSTRACT FROM AUTHOR]

Noise from wind farms is contentious: people who live nearby complain of annoyance, and yet broadband measurements of infrasound seem to indicate the noise is generally not above audibility criteria. The paradox can be resolved by supposing that wind farms generate a strong tonal signal at the blade passing frequency, 0.8 Hz, and that this infrasound, with a wavelength of 400 m, can constructively interfere if two or more wind turbines operate in synchrony and the path lengths differ by a multiple of 400 m. Coherent infrasound at 0.8 Hz could propagate many kilometres, would tend to carry many harmonics due to the rapid changes within its waveform, and the high harmonics in the 20--30 Hz band have the potential to be heard by human ears. The existence of coherent infrasound from wind turbines has not been specifi cally recognised, but evidence of the phenomenon can be discerned in two anomalies contained in data from recent infrasound monitoring of wind farms in South Australia. This paper interprets the anomalies in terms of a model which suggests that wind farms produce enhanced sound pressure levels when the blades of multiple machines become mutually entrained and the sound from them becomes coherent. The inference is that acoustic measures, which assume wind turbine signals are stationary, may not be accurate indicators of peak noise levels. [ABSTRACT FROM AUTHOR]

The dynamic and lubrication characteristics are all very complex problem in piston-liner analysis, and they have great effect on the power output, vibration, noise emission. In this paper, the numerical model which concludes lubrication part and dynamic motion is established, the lubrication is solved by the finite element method, and dynamic equation is solved by Runge-Kutta. The effect of piston skirt parameters on dynamic characteristics are compared based on a typical inline six-cylinder engine, such as: clearance, offset of piston pin, length of piston skirt, position of bump, curvature parameter and ellipticity of the piston, all the result mainly focus on the slap noise of the engine. All the analyses are very useful to design of piston-liner at the development of the engine, and it can provide the guidance for the design of the low noise engine. [ABSTRACT FROM AUTHOR]

The electric motor is present in life very often used device, which is needed to study its terms of noise. In this article we analyze the reasons of electromotor vibration and species of electromotor noises. The electromotor noise is a admixture of different frequency and different intensity of noise. Control and detecting of main noise sources is important in term of product quality, safety and impact on human health. Designers make choices regarding structure, materials and components in a product. The tools they use should allow them to anticipate the effect of these choices on sound quality. This discussion recounts the role of psychoacoustics in product design and product acceptability and notes the results of that work in metrics for sound quality and consumer/ user perceptions about the product. [ABSTRACT FROM AUTHOR]

Despite the advantages associated to mechanization, the noise generated by machines and equipment may cause discomfort to workers, possibly even jeopardizing their health. Thus, this paper is aimed at assessing the noise level of two agricultural machines (hedge trimmer and backpack blower) and to characterize them spatially by means of geostatistics. Data collection was performed at the average height of the worker's ear and within an equidistant circumference of 1 m up to the limit of a sample area with a radius of 22 m. The data fitted models of gaussian and spherical semivariograms for the evaluated equipment, a hedge trimmer and backpack blower, respectively. The spatial noise analysis allows for the definition of a work regime and the need for the use of personal protection equipment. [ABSTRACT FROM AUTHOR]

Abstract: Weak machinery fault detection is a difficult task because of two main reasons (1) At the early stage of fault development, signature of fault related component performs incompletely and is quite different from that at the apparent failure stage. In most instances, it seems almost identical with the normal operating state. (2) The fault feature is always submerged and distorted by relatively strong background noise and macro-structural vibrations even if the fault component already performs completely, especially when the structure of fault components and interference are close. To solve these problems, we should penetrate into the underlying structure of the signal. Sparse representation provides a class of algorithms for finding succinct representations of signal that capture higher-level features in the data. With the purpose of extracting incomplete or seriously overwhelmed fault components, a sparse representation based latent components decomposition method is proposed in this paper. As a special case of sparse representation, shift-invariant sparse coding algorithm provides an effective basis functions learning scheme for capturing the underlying structure of machinery fault signal by iteratively solving two convex optimization problems: an L1-regularized least squares problem and an L2-constrained least squares problem. Among these basis functions, fault feature can be probably contained and extracted if optimal latent component is filtered. The proposed scheme is applied to analyze vibration signals of both rolling bearings and gears. Experiment of accelerated lifetime test of bearings validates the proposed method׳s ability of detecting early fault. Besides, experiments of fault bearings and gears with heavy noise and interference show the approach can effectively distinguish subtle differences between defect and interference. All the experimental data are analyzed by wavelet shrinkage and basis pursuit de-noising (BPDN) method for comparison. [Copyright &y& Elsevier]

Abstract: The High Speed Machining (HSM) spindle is one of the most critical bearing applications, because it requires both high speed and high power in order to obtain high quality and productivity. Therefore, bearing condition monitoring is important. Firstly, this paper presents a real and typical spindle life example. The vibration signals and their evolution are discussed in relation to the bearing failures that have been observed after the spindle disassembly. Cleavage notably occurred on the ceramic balls of the hybrid ball bearing. Damaged balls and their chippings then damaged uniformly the rings raceways on the whole circumference. As a consequence, a noise component increases in vibration signal due to the worsening of the ball-race contact during the rolling process. In a second section, the noise component produced by bearing condition is studied and characterized. The frequency spectrum distribution is briefly discussed in relation to a signal model. It is demonstrated by Pearson’s test that the distribution follows a Gaussian law all along the spindle life. Besides, it evolves with bearing condition. Thus, a new criterion, called SBN (Spindle Bearing Noise), is proposed for the monitoring of the uniformly distributed defect. A specific monitoring device was also developed in order to collect real industrial data during the spindle lifetime. Vibration signals are used in order to evaluate the criterion relevancy by comparison with the current best practices. The analyses through three required conditions for bearing condition monitoring and based on three spindles signals, have shown some good results. [Copyright &y& Elsevier]

Synchronous lateral vibration is a frequent cause of machine failure and is probably the most common source of machine noise and vibration. Among the broad ranges of faults that cause synchronous vibration, mass unbalance and bow are the most common faults present in the rotor and hence their detailed understanding is required. In the present study, a rotor model having both mass unbalance and bow is analyzed to find the influence of these faults on the synchronous response. The synchronous response of a rotor is a function of influence coefficients due to mass unbalance and bow. The influence coefficients are analytically derived using transfer matrix method for rotor bearing system having both mass unbalance and bow. The correction unbalance vector required to balance the rotor at its first bending critical speed is computed using these analytically derived influence coefficients and the rotor responses measured at a speed much lower than the first bending critical speed. The balancing method needs a good mathematical model for the rotor system in finding the influence coefficients for mass unbalance and bow. This procedure helps in estimating the correction mass in a single trial run and using a single balancing plane, thus reducing the cycle time for balancing flexible rotors. Experiments are carried out on a test rig to verify the procedure. [ABSTRACT FROM PUBLISHER]

The article presents abstracts on the effects of noise on machinery including health monitoring of machines, comparison of artificial neural network (ANN) and K-nearest neighbor (KNN) and fault diagnosis in Francis turbine.

A physical recovery line had been constructed in plant for the increasing waste toner cartridges in previous work. However, with the production, severe lacks of the line emerged: (1) there was little proper technology of treating the collected toner; (2) strong noise was produced from the line and influenced the health of worker. For disposing toner properly, a new collected system of toner was developed. An air current separator (ACS) was designed to separate organic materials from inorganic materials of toner. Then, the separated organic materials can be incinerated and the inorganic materials can be dumped. Movement behaviors of toner particles in the ACS were analyzed, and the optimized operation parameter (13.5 m/s) of air current speed was obtained by theory analysis and experiments. For controlling the noise, noise levels emitted from the different process of the line were measured. The results indicated noise levels emitted from crusher (95.2 dB(A)) and agitator/magnetic separator (AMS, 91.9 dB(A)) were greater than the permissible noise exposure level of the Occupational Safety and Health Standards (90 dB(A)). The noise levels of other processes of the line were relatively safe. An acoustic hood was developed to reduce the noise levels of the crusher and the AMS. Then, the noise levels were both decreased to 67.6 dB(A). This paper provided important data for the environment on the industrialization of waste toner cartridges recovery. [ABSTRACT FROM AUTHOR]

The potential burden of noise-induced permanent threshold shift (NIPTS) in U.S. urban settings is not well-characterized. We used ANSI S3.44-1996 to estimate NIPTS for a sample of 4585 individuals from New York City (NYC) and performed a forward stepwise logistic regression analysis to identify predictors of NIPTS >10 dB. The average individual is projected to develop a small NIPTS when averaged across 1000-4000 Hz for 1- to 20-year durations. For some individuals, NIPTS is expected to be substantial (>25 dB). At 4000 Hz, a greater number of individuals are at risk of NIPTS from MP3 players and stereos, but risk for the greatest NIPTS is for those with high occupational and episodic nonoccupational (e.g., power tool use) exposures. Employment sector and time spent listening to MP3 players and stereos and participating in episodic nonoccupational activities associated with excessive noise levels increased the odds of NIPTS >10 dB at 4000 Hz for 20-year durations. Our results indicate that the risk of NIPTS may be substantial for NYC and perhaps other urban settings. Noise exposures from "noisy" occupational and episodic nonoccupational activities and MP3 players and stereos are important risk factors and should be a priority for public health interventions. [ABSTRACT FROM AUTHOR]

Crackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal. These strong positive pressure impulses are associated with N-shaped waveforms involving a shock like compression and, thus, is very annoying to observers when it occurs. Unlike broadband shock-associated noise which dominates at upstream angles, crackle reaches a maximum at downstream angles associated with the peak jet noise directivity. Recent experiments (Martens et al., 2011, "The Effect of Chevrons on Crackle--Engine and Scale Model Results," Proceedings of the ASME Turbo Expo, Paper No. GT2011-46417) have shown that the addition of chevrons to the nozzle lip can significantly reduce crackle, especially in full-scale high-power tests. Because of these observations, it was conjectured that crackle is associated with coherent large scale flow structures produced by the baseline nozzle and that the formation of these structures are interrupted by the presence of the chevrons, which leads to noise reduction. In particular, shocklets attached to large eddies are postulated as a possible aerodynamic mechanism for the formation of crackle. In this paper, we test this hypothesis through a high-fidelity large-eddy simulation (LES) of a hot supersonic jet of Mach number 1.56 and a total temperature ratio of 3.65. We use the LES solver CHARLES developed by Cascade Technologies, Inc., to capture the turbulent jet plume on fully unstructured meshes. [ABSTRACT FROM AUTHOR]

Voltage source inverters (VSIs) supply nonsinusoidal voltages to induction motor drives, leading to line current distortion and torque pulsation. Conventional space vector pulsewidth modulation (PWM) techniques are widely used in VSIs on the account of good waveform quality and high dc bus utilization. In a conventional space vector PWM technique, the switching sequence begins with one zero state and ends with the other zero state in a subcycle. Some novel switching sequences have been proposed, which employ only one zero state but apply one of the two active states twice in a subcycle. One pair of such special switching sequences has recently been shown to reduce the pulsating torque considerably. In this paper, the conventional and special switching sequences are compared experimentally in terms of acoustic noise. In the low- and medium-speed ranges, the special switching sequence is seen to reduce the amplitude of the tonal component of noise at the switching frequency considerably and is also found to result in spread spectrum. [ABSTRACT FROM PUBLISHER]

Bearing faults of rotating machinery are observed as impulses in the vibration signal, but it is mostly immersed in noise. In order to effectively remove this noise and detect the impulses, a novel technique with morphological operators and fuzzy inference is proposed in this paper. The effectiveness of the morphological operators lies with the correct selection of structuring elements (SEs). This paper also proposes a new algorithm for this SE selection based on kurtosis, thereby making the analysis free of empirical methods. When analyzed with three different sets of faults, the results show that this method is effective and robust in bringing out the impulses. With fuzzy inference being coupled to this new technique, it makes the algorithm to be able to detect early faults also. [ABSTRACT FROM PUBLISHER]

The article presents abstracts on topics related to machine diagnostics which include the monitoring of squirrel-cage induction machine for rotor failure detection, a wavelet-based technique for detecting gear tooth defects, and the use of wavelet bicoherence (WB) for detecting local tooth damage.

Abstract: In this paper, we describe a study on compliant-parallel (C-P) mechanism with high precision and wide range of working area using bio-inspired compliant joints. C-P mechanism is a parallel mechanism in which all of joints are composed by wide deformable compliant joints. In the integration of the compliant joint and the parallel mechanism, a deformation of the compliant joint can be guided by mechanical constraints from the parallel mechanism; thus C-P mechanism can be precisely driven. C-P mechanism has no back-lash, requires no lubrication, and is free from machine noise and abrasion power. And, unlike conventional mechanisms, C-P mechanism can be integrated into compact, lightweight, and simple structure. From these backgrounds, we developed a widely deformable circular compliant joint inspired by Drakaea, which is an orchidaceous species. The circular compliant joint was implemented on a 3-DOF (rotational 2 and translational 1 DOF) parallel mechanism as a first prototype. Then, our second prototype was developed to realize further wide range of working area. A serially layered-flat spring compliant joint was developed based on the bio-inspired circular compliant joint, and was implemented on a traditional 3-DOF DELTA mechanism, as the second prototype. From the evaluation tests of these prototypes, the feasibility of C-P mechanism was shown positive to be applied to a high precision assembly robot within a wide range of working area. [Copyright &y& Elsevier]