BRRC is seeking an experienced acoustical engineer for our Asheville, NC office. This position involves conducting research in a wide range of environmental acoustic areas including sound and noise source measurements, general and specialized modeling, soundscape and transportation noise visualizations, and outdoor warning system design. Current research areas include noise source characterization of military aircraft and rockets, long-range sound propagation modeling, and operational noise reduction studies. Responsibilities include applied acoustic research as well as interacting with clients, noise analysis modeling, and technical reporting. Read more...
Aviation Noise Analyst
BRRC is seeking an experienced environmental noise analyst for our Asheville, NC office. This position involves work on a diverse set of projects including preparation of airport/airfield noise analyses for civilian and military customers in support of FAA Part 150, Environmental Impact Analysis, and/or DoD AICUZ studies. Responsibilities include modeling aviation and other transportation noise sources, interaction with commercial and DoD clients, and technical reporting. In addition, contributing to our applied research projects will provide the successful applicant with interesting and rewarding work. Read more...
Jaouher Ben Ali | Nader Fnaiech | Lotfi Saidi | Brigitte Chebel-Morello | Farhat Fnaiech
© 2014 Elsevier Inc. All rights reserved. Condition monitoring and fault diagnosis of rolling element bearings (REBs) are at present very important to ensure the steadiness of industrial and domestic machinery. According to the non-stationary and non-linear characteristics of REB vibration signals, feature extraction method is based on empirical mode decomposition (EMD) energy entropy in this paper. A mathematical analysis to select the most significant intrinsic mode functions (IMFs) is presented. Therefore, the chosen features are used to train an artificial neural network (ANN) to classify bearings defects. Experimental results indicated that the proposed method based on run-to-failure vibration signals can reliably categorize bearing defects. Using a proposed health index (HI), REB degradations are perfectly detected with different defect types and severities. Experimental results consist in continuously evaluating the condition of the monitored bearing and thereby detect online the severity of the defect successfully. This paper shows potential application of ANN as effective tool for automatic bearing performance degradation assessment without human intervention.
William J. Davies | Mags D. Adams | Neil S. Bruce | Rebecca Cain | Angus Carlyle | Peter Cusack | Deborah A. Hall | Ken I. Hume | Amy Irwin | Paul Jennings | Melissa Marselle | Christopher J. Plack | John Poxon
This paper takes an overall view of findings from the Positive Soundscape Project, a large inter-disciplinary soundscapes study. Qualitative fieldwork (soundwalks and focus groups) have found that soundscape perception is influenced by cognitive effects such as the meaning of a soundscape and its components, and how information is conveyed by a soundscape, for example on the behaviour of people within the soundscape. Three significant clusters were found in the language people use to describe soundscapes: sound sources, sound descriptors and soundscape descriptors. Results from listening tests and soundwalks have been integrated to show that the two principal dimensions of soundscape emotional response seem to be calmness and vibrancy. Further, vibrancy seems to have two aspects: organisation of sounds and changes over time. The possible application of the results to soundscape assessment and design are briefly discussed. © 2011 Elsevier Ltd. All rights reserved.
Jacek Dybała | Radosław Zimroz
Rolling bearing faults are one of the major reasons for breakdown of industrial machinery and bearing diagnosing is one of the most important topics in machine condition monitoring. The main problem in industrial application of bearing vibration diagnostics is the masking of informative bearing signal by machine noise. The vibration signal of the rolling bearing is often covered or concealed by other structural vibrations sources, such as gears. Although a number of vibration diagnostic techniques have been developed over the last several years, in many cases these methods are quite complicated in use or only effective at later stages of damage development. This paper presents an EMD-based rolling bearing diagnosing method that shows potential for bearing damage detection at a much earlier stage of damage development. By using EMD a raw vibration signal is decomposed into a number of Intrinsic Mode Functions (IMFs). Then, a new method of IMFs aggregation into three Combined Mode Functions (CMFs) is applied and finally the vibration signal is divided into three parts of signal: noise-only part, signal-only part and trend-only part. To further bearing fault-related feature extraction from resultant signals, the spectral analysis of the empirically determined local amplitude is used. To validate the proposed method, raw vibration signals generated by complex mechanical systems employed in the industry (driving units of belt conveyors), including normal and fault bearing vibration data, are used in two case studies. The results show that the proposed rolling bearing diagnosing method can identify bearing faults at early stages of their development. © 2013 Elsevier Ltd. All rights reserved.
Rebecca Cain | Paul Jennings | John Poxon
People have emotional reactions to the built environment, and the sonic environment is one of the major contributing factors of people's experiences of places. It is useful for decision makers such as planners, architects, engineers and designers to understand the link between the soundscapes of built environments, and their resultant emotional reactions within users of those environments. This understanding can allow these decision makers to make better informed decisions about built environment design, and achieve the desired positive emotional responses from users. The issue under question, and the subject of this paper, was to understand and define the emotional dimensions of a soundscape, and then to explore how the resultant dimensional space could have a practical application in decision making. Through data generated through the Positive Soundscapes Project, a Principal Component Analysis was conducted to decompose descriptors of the urban soundscape into two independent emotional dimensions. It was found that the two independent emotional dimensions of a soundscape relate to its "Calmness" and "Vibrancy", and these could be positioned to describe a 2-Dimensional (2-D) perceptual space. Listening evaluations were then conducted to explore how perceptions of different types of urban soundscape could be plotted with the 2D emotional perceptual space, and to illustrate how (i) introducing design interventions can change the position of soundscapes within this space and (ii) how metrics such as dB(A) do not necessarily correlate with calmness and vibrancy scores. Through illustrative examples, we suggest how such a 2-D perceptual space might have a practical use in the planning process, primarily as a means for presenting users' perceptions of soundscapes in a simple, visual, and easy to compare manner, and for setting targets for current and future soundscape design. We conclude with recommendations for further work required to fully develop these emotional dimensions and the 2-D perceptual space into a useful tool. © 2011 Elsevier Ltd. All rights reserved.
Monika Rychtáriková | Gerrit Vermeir
A soundscape assessment method that is suitable for the automatic categorization of binaurally recorded sound in urban public places is presented. Soundscape categories are established as a result of an automatic clustering algorithm based on multi-parameter analysis by 13 acoustical parameters used as similarity measures, on a large set of sound recordings. One of the main advantages of the followed approach allows to take into account an optimized set of parameters that are judged relevant and necessary for an appropriate description of the sampled acoustical scenarios. The Euclidian distance based clustering of the 370 recordings of typical situations based on these parameters, allows to categorize each binaurally recorded sound sample into one of 20 proposed clusters (soundscape categories). The common features among members within each cluster allow to identify "how the acoustical scenario of the members sounds like". The hybrid use of an optimized set of standard acoustical quantities, such as sound pressure level, together with well known psychoacoustical parameters that directly relate to human perception of sound, makes the propose method very robust. © 2011 Elsevier Ltd. All rights reserved.
Fredrik Ljunggren | Christian Simmons | Klas Hagberg
Traditionally, multi-family houses have been constructed using heavy, homogenous materials like concrete and masonry. But as a consequence of the progress of lightweight building systems during the last decades, it has been questioned whether standardized sound insulation evaluation methods still are appropriate. An extensive measurement template has been applied in a field survey where several vibrational and acoustical parameters were determined in ten Swedish buildings of various constructions. In the same buildings, the occupants were asked to rate the perceived annoyance from a variety of natural sound sources. The highest annoyance score concerned impact sounds, mainly in the buildings with lightweight floors. Statistical analyses between the measured parameters and the subjective ratings revealed a useful correlation between the rated airborne sound insulation and Rw′+C50 -3150 while the correlation between the rated impact sound insulation and Ln,w′+CI, 50-2500 was weak. The latter correlation was considerably improved when the spectrum adaptation term with an extended frequency range starting from 20 Hz was applied. This suggests that frequencies below 50 Hz should be considered when evaluating impact sound in lightweight buildings. © 2014 Elsevier Ltd. All rights reserved.
M. Hajihassani | D. Jahed Armaghani | H. Sohaei | E. Tonnizam Mohamad | A. Marto
Blasting is an inseparable part of the rock fragmentation process in hard rock mining. As an adverse and undesirable effect of blasting on surrounding areas, airblast-overpressure (AOp) is constantly considered by blast designers. AOp may impact the human and structures in adjacent to blasting area. Consequently, many attempts have been made to establish empirical correlations to predict and subsequently control the AOp. However, current correlations only investigate a few influential parameters, whereas there are many parameters in producing AOp. As a powerful function approximations, artificial neural networks (ANNs) can be utilized to simulate AOp. This paper presents a new approach based on hybrid ANN and particle swarm optimization (PSO) algorithm to predict AOp in quarry blasting. For this purpose, AOp and influential parameters were recorded from 62 blast operations in four granite quarry sites in Malaysia. Several models were trained and tested using collected data to determine the optimum model in which each model involved nine inputs, including the most influential parameters on AOp. In addition, two series of site factors were obtained using the power regression analyses. Findings show that presented PSO-based ANN model performs well in predicting the AOp. Hence, to compare the prediction performance of the PSO-based ANN model, the AOp was predicted using the current and proposed formulas. The training correlation coefficient equals to 0.94 suggests that the PSO-based ANN model outperforms the other predictive models. © 2014 Elsevier Ltd. All rights reserved.
A. Mostafapour | S. Davoudi
Leak detection is one of the most important issues in the oil and gas pipelines, as it can lead to financial losses, as well as severe human and environmental impacts. Acoustic emission test is a new technique for leak detection. Leakage in high pressure pipes creates stress waves caused by localized loss of energy. Stress waves are transmitted through the pipe wall which can be recorded by using acoustic sensor or accelerometer installed on the pipe wall. Knowledge of how the pipe wall is vibrated by acoustic emission resulting from leakage is a key parameter for leak detection and localization. This paper aims to model acoustic emission generated by pipe vibration due to leakage. Donnell's non-linear theory for cylindrical shell was used to derive motion equation under simply supported boundary condition. Then, the motion equation was solved by using Galerkin method that resulted in a system of non-linear equations with 6 degrees of freedom. To solve these non-linear equations, ODE tool of MATLAB software and Runge-Kutta numerical method was employed to obtain pipe wall radial displacement. For verifying this method, acoustic emission by a continuous leak source was measured. Experiments were carried out with a linear array of sensors on steel pipe (ASTM A 106/99) of nominal length 6 m, 7.35 mm wall thickness and external diameter of 169 mm. The pressurized air was flown inside the pipe through the compressor. Two simulated continues leak sources with 0.6-mm and 1-mm diameter holes were used under 5 bar air pressure. This source propagated waves in a large of frequencies about 0-400 kHz. In this study the vibration behavior of the pipe is investigated per resonance frequencies of the used AE sensors which are near 150 and 300 kHz. Signals generated by the pipe wall vibration were recorded by using acoustic emission sensors. In the next step, Fast Fourier Transform (FFT) was used in the signal analysis. Comparison of the obtained results, indicate the good agreement between the experimental and modeled frequencies ranges. The mean error between analytical modeling and experimental results is less than 6%. © 2012 Elsevier Ltd. All rights reserved.
Guoyong Jin | Xianglong Ma | Shuangxia Shi | Tiangui Ye | Zhigang Liu
Free vibration analysis of truncated conical shells with general elastic boundary conditions is presented in this paper. An accurate modified Fourier series solution is developed, in which, regardless of the boundary conditions, each displacement of the conical shell is invariantly expressed as a new form of improved series expansions composed of a standard Fourier series and closed-form auxiliary functions introduced to ensure and accelerate the convergence of the series expansion. All the expansion coefficients are treated as the generalized coordinates and determined using the Rayleigh-Ritz method. By using the present method, conical shells with arbitrary boundary conditions including all classical and elastic end restraints can be solved in a unified form. The accuracy and convergence of the current approach are validated by numerical examples and comparison with FEM results and those from the literature, and excellent accuracy is demonstrated. Comprehensive studies on the effects of elastic restraint parameters, semi-vertex angle and the ratio of length to radius are also reported. Some new results are presented for cases with elastic boundary restraints which may serve as benchmark solution for future researches.© 2014 Elsevier Ltd. All rights reserved.
Bin Li | Andrew J. Laviage | Jeong Ho You | Yong Joe Kim
An acoustic energy harvester is introduced that uses a quarter-wavelength straight-tube acoustic resonator with polyvinylidene fluoride (PVDF) piezoelectric cantilever beams placed inside the resonator. When the tube is excited by an incident wave at its first acoustic eigenfrequency, an amplified acoustic resonant standing wave is developed inside the tube. The acoustic pressure gradient of the amplified standing wave then drives the vibration motion of the PVDF piezoelectric beams, generating electricity due to the direct piezoelectric effect. In order to maximize the amount of the harvested energy, each PVDF piezoelectric beam has been designed to have the same structural eigenfrequency as the acoustic eigenfrequency of the tube. With a single PVDF beam placed inside the tube, the harvested voltage and power become the maximum near the tube open inlet where the largest acoustic pressure gradient vibrates the PVDF beam. As the beam is moved to the tube closed end, the voltage and power gradually decrease due to the decreased acoustic pressure gradient. Multiple piezoelectric beams have been placed inside the tube with two different configurations: the aligned and zigzag configurations. With the zigzag configuration which has the more open path for acoustic air particle motions, the significant increases in the harvested voltage and power have been observed. Due to the interruption of acoustic air particle motion caused by the beams, it is found that placing PVDF beams near the closed tube end is not beneficial. The total output voltage of the piezoelectric beams increases linearly as the incident sound pressure increases. © 2013 Elsevier Ltd. All rights reserved.
Ilyas Potamitis | Stavros Ntalampiras | Olaf Jahn | Klaus Riede
The primary purpose for pursuing this research is to present a modular approach that enables reliable automatic bird species identification on the basis of their sound emissions in the field. A practical and complete computer-based framework is proposed to detect and time-stamp particular bird species in continuous real field recordings. Acoustic detection of avian sounds can be used for the automatized monitoring of multiple bird taxa and querying in long-term recordings for species of interest for researchers, conservation practitioners, and decision makers, such as environmental indicator taxa and threatened species. This work describes two novel procedures and offers an open modular framework that detects and time-stamps online calls and songs of target bird species and is fast enough to report results in reasonable time for non-processed field recordings of many thousands files and is generic enough to accommodate any species. The framework is evaluated on two large corpora of real field data, targeting the calls and songs of American Robin Turdus migratorius, a Northamerican oscine passerine (true songbird) and the Common Kingfisher Alcedo atthis, a non-passerine species with a wide distribution throughout Eurasia and North Africa. With the aim of promoting the widespread use of digital autonomous recording units (ARUs) and species recognition technologies the processing code and a large corpus of audio recordings is provided in order to enable other researchers to perform and assess comparative experiments. © 2014 Elsevier Ltd. All rights reserved.
A. Fernández | M. Iglesias | A. De-Juan | P. García | R. Sancibrián | F. Viadero
In this work a non-linear dynamic model of spur gear transmissions previously developed by the authors is extended to include both desired (relief) and undesired (manufacture errors) deviations in the tooth profile. The model uses a hybrid method for the calculation of meshing forces, which combines FE analysis and analytical formulation, so that it enables a very straightforward implementation of the tooth profile deviations. The model approach handles well non-linearity due to the variable meshing stiffness and the clearances involved in gear dynamics, also including the same phenomena linked to bearings. In order to assess the ability of the model to simulate the impact of the deviations on the transmission dynamics, an example is presented including profile deviations under different values of transmitted torque. Several results of this example implementation are presented, showing the model's effectiveness. © 2013 Elsevier Ltd. All rights reserved.
X. F. Li | Y. A. Kang | J. X. Wu
Free vibration of axially inhomogeneous beams is analyzed. For exponentially graded beams with various end conditions, characteristic equations are derived in closed form. These characteristic or frequency equations can analytically reduce to the classical forms of Euler-Bernoulli beams if the gradient index disappears. The gradient has a strong influence on the frequency spectrum, and the natural frequencies noticeably depend on the variation of the gradient parameter and end support conditions. For certain beams with exponential gradients, there exists a critical frequency depending on the gradient parameter. Vibration can be only excited by propagating waves with frequencies in excess of the critical frequency, and otherwise vibration is prohibited for pseudo-frequencies lower than the critical frequency. For some gradient index with small change, the natural frequencies have an abrupt jump when across its critical frequencies. Obtained results can serve as a benchmark for other numerical procedures for analyzing transverse vibration of axially functionally graded beams. The minimal natural frequency can be sought for certain gradient index, and this helps engineers to optimally design vibrating nonhomogeneous beam structures. Obtained results also apply to free vibration of nonuniform beams with constant thickness and exponentially decaying width. © 2012 Elsevier Ltd. All rights reserved.
E. P. Bowyer | D. J. O'Boy | V. V. Krylov | F. Gautier
In the present paper, experimental results are reported on damping flexural vibrations in rectangular plates containing tapered indentations (pits) of power-law profile, with the centres of the indentations covered by a small amount of absorbing material. In the case of quadratic or higher-order profiles, such indentations materialise two-dimensional acoustic 'black holes' for flexural waves that can absorb almost 100% of the incident elastic energy. In the present investigation, pits have been made in different locations of rectangular plates, and the corresponding frequency response functions have been measured. It has been found that basic power-law indentations, with no or very small central hole, result in rather low reduction in resonant peak amplitudes, which may be due to the relatively small effective absorption area in this case. To increase the damping efficiency of power-law profiled indentations, this absorption area has been enlarged by increasing the size of the central hole in the pit, while keeping the edges sharp. As expected, such pits, being in fact curved power-law wedges, result in substantially increased damping. When multiple indentations are used, the resultant damping increases substantially, as expected, and may become comparable if not greater than that achieved by one-dimensional wedges of power-law profile. © 2012 Elsevier Ltd. All rights reserved.
Lu Dai | Tiejun Yang | Jingtao Du | W. L. Li | M. J. Brennan
In this paper, an exact series solution for the vibration analysis of circular cylindrical shells with arbitrary boundary conditions is obtained, using the elastic equations based on Flügge's theory. Each of the three displacements is represented by a Fourier series and auxiliary functions and sought in a strong form by letting the solution exactly satisfy both the governing differential equations and the boundary conditions on a point-wise basis. Since the series solution has to be truncated for numerical implementation, the term "exactly satisfying" should be understood as a satisfaction with arbitrary precision. One of the important advantages of this approach is that it can be universally applied to shells with a variety of different boundary conditions, without the need of making any corresponding modifications to the solution algorithms and implementation procedures as typically required in other techniques. Furthermore, the current method can be easily used to deal with more complicated boundary conditions such as point supports, partial supports, and non-uniform elastic restraints. Numerical examples are presented regarding the modal parameters of shells with various boundary conditions. The capacity and reliability of this solution method are demonstrated through these examples. © 2012 Elsevier Ltd. All rights reserved.
Deborah A. Hall | Amy Irwin | Mark Edmondson-Jones | Scott Phillips | John E.W. Poxon
The present study reports an exploration of the multi-dimensional space involved in listening to soundscape recordings made in different city-based settings. A range of perceptual, psychoacoustic and acoustical properties were examined using a range of statistical methods including principal components analysis and multiple regression. Just as the affective responses to individual sound sources have often been described in terms of pleasantness and arousal (or vibrancy), so could the acoustic scenarios of urban life. However, different from previous research, the acoustic and psychoacoustic variables contributed very little to judgements about pleasantness and vibrancy. We surmise that the perceived quality of the soundscape is very much an individual subjective experience that is likely to be embedded within contextual domain and that it probably relates to personal preference, past history and other social and cultural factors. © 2011 Elsevier Ltd. All rights reserved.
Y. S. Wang | Q. H. Ma | Q. Zhu | X. T. Liu | L. H. Zhao
Based on the techniques of Hilbert-Huang transform (HHT) and support vector machine (SVM), a noise-based intelligent method for engine fault diagnosis (EFD), so-called HHT-SVM model, is developed in this paper. The noises of a sample engine under normal and several fault states are first measured and denoised by using the wavelet packet threshold method to initially lower the noise level with negligible signal distortion. To extract fault features of the engine, then, the HHT is selected and applied to the measured noise signals. A nine-dimensional vector, which consists of seven intrinsic mode functions (IMFs) from the empirical mode decomposition (EMD), maximum value of HHT marginal spectrum and its corresponding frequency component, is specified to represent each engine fault feature. Finally, an optimal SVM model is established and trained for engine failure classification by using the fault feature vectors of the noise signals. Cross-validation results show that the proposed noise-based HHT-SVM method is accurate and effective for engine fault diagnosis. Due to outstanding time-frequency characteristics and pattern recognition capacity of the HHT and SVM, the newly proposed HHT-SVM can be used to deal with both the stationary and nonstationary signals, and even the transient ones. In the view of applications, the HHT-SVM technique may be suggested not only to detect the abnormal states of vehicle engines, but also to be extended to other fields for failure diagnosis in engineering. © 2013 Elsevier Ltd. All rights reserved.
Seif E. Hamdi | Alain Le Duff | Laurent Simon | Guy Plantier | Anthony Sourice | Mathieu Feuilloy
One of the most important difficulties faced by in situ structural health monitoring approaches when establishing a relationship between a specific damage mechanism and its acoustic signature is the lack of an appropriate signal processing method able to deal with the non-stationary acoustic signals. The purpose of this paper is to use the Hilbert-Huang transform for the extraction of new relevant damage descriptor to be adopted for Acoustic Emission (AE) pattern recognition in order to help understanding the damage process. AE signals collected from unidirectional glass-fiber reinforced polymer composites samples were studied. First, the frequency content of the recorded signals in each test is analyzed. Secondly, the performance of the Hilbert-Huang transform damage classification approach is evaluated. © 2012 Elsevier Ltd. All rights reserved.