bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of brass performer gestures
Authors: Causse René E. , Freour Vincent
Published: May 2008

Brass instrument playing requires the musican to control his respiratory gesture and the elastic properties of his lips. This raises the question of musician gesture optimisation and strategy in order to complete a musical exercise. It also makes gesture characterization very hard to conduct in a non-invasive way. On the other hand, it is possible to measure some control parameters (linked to the respiratory and lip-adjustment gesture) like lip force applied on the mouthpiece and mouth air pressure. Theses parameters measurements and also the specific mouthpiece receiver developed to measure lip force with a minimum interference to the player are presented. Respiratory flows during live playing are also evaluated thanks to the calibration of respiratory belts used on the thoracial and abdominal regions of musicians. Details of the method for carrying out this type of measurement and preliminary results are reported. During this measurement sound recording and analysis are also conducted thanks to a set of audio descriptors. Links between control parameters measurements and sound characterisation are examined. Parallel development of a automated artificial mouth, used for experimental validations, is also outlined. [Work, within the CONSONNES project, is lead with the support of the French Research National Agency ANR].
On the generation of axial modes in the nonlinear vibration of strings
Authors: Watzky Alexandre
Published: May 2008

Vibrating strings are known to be nonlinear. Transverse vibrations induce axial motion as well as a modulation of the string's tension. An overview of the nonlinear models of the vibrating string has been presented at the 150th Meeting of the ASA. It has been shown that if temporal considerations are prevalent from an acoustical point of view, the involved coupling mechanisms are mainly ruled by the spatial shape of the modes. The purpose of this communication is to investigate the specific case of transverse-axial interactions and to examine the possible generation of axial modes through transverse vibrations. It also gives the opportunity to discuss the common hypotheses. Despite the complex modal couplings that can occur, this results enable to avoid or favor axial modes in the design of the string itself or of the boundary conditions i.e. the bridge.
A complex model for piano action
Authors: Lozada José , Boutillon Xavier , Hafez Moustapha
Published: May 2008

Available mechanical models of piano action are extremely simplified in view of the complexity of an actual mechanism. Several arguments will be presented which indicate that more dynamical complexities than those offered by the current models are considered as intrinsic properties of good piano actions. A more complete model of a grand piano action during the attack of a note will be presented which includes the six degrees of freedom of the action, all considered as rigid bodies: the key, the damper, the whippen, the repetition lever, the jack, and the hammer. In this model, coupling features are represented by lumped elements: Coulomb friction, linear and nonlinear springs. Methods for characterizing each element of the model will be presented. The final result will be given in terms of dynamical equations, coupling equations, and geometrical constrains.
Feature exaggeration in scale performance on the piano
Authors: Morita Shinya , Emura Norio , Miura Masanobu , Akinaga Seiko , Yanagida Masuzo
Published: May 2008

This paper proposes a set of parameters for describing features of scale-playing on the piano. The parameter set consists of 15 parameters, among which 12 are three sets of four parameters pi1 through pi4 where i ={1, 2, 3} distinguishes three basic features; onset time, velocity, and duration. Each of these basic features is modeled as the sum of a global curve and the deviation from it, where the spline interpolation is employed using locally averaged points, or representative points, as the points to be passed. The local average is calculated for each sequence of notes played without finger crossing. The suffix j in pij distinguishes the standard deviations (j=0), the rms deviation from the spline curve (j=1), the range of the curve (j=2), the rms difference between successive notes (j=3), and the rms of the spline curve from the metronomic line (j=4). All parameters are made controllable with slider bars from 0% to 200% for synthesizing suppressed performance or exaggerated performance, where 100% represents the original performance. Proposed parameter set is expected to be useful in self-training of piano, as it can indicate the features and undesirable habits of the player by setting values above 100% in exaggerated form.
Modal analysis and transient string response of solid body electric bass guitars with effects of the instrumentalist
Authors: Woolworth Dave , Scarton Henry A.
Published: May 2008

This paper documents modal analysis of seven solid body electric basses. The basses are modeled in one dimension of motion normal to the face of the instrument in both free-free state and with boundary conditions imposed by a musician. The results are compared and analyzed in terms of bending and torsion. Analysis is done regarding open string harmonic content of the electromagnetic output over time versus the resonant frequencies of the instruments. Results of finite element analysis modeling of a simplified bass guitar structure will be presented, and significance of damping effects on harmonic output will be considered in terms of the listener.
Controllable pitch-bending effects in the accordion playing
Authors: Llanos-Vazquez R. , Elejalde-García M. J. , Macho-Stadler E.
Published: May 2008

The accordion employs reeds in which the tongue is mounted outside the reed frame in such a way that sounding is normally possible only on one direction of airflow. Under normal operating conditions the reeds behave as blown-closed. Pitch bending technique allows players to make a controllable glide, non tempered glissando, from one pitch to another. Pitch-bending frequency shift, defined as the percentage of the ratio of the frequency change and the original frequency has been measured in a series of experiments. Some of the results involving the dependence of the function on pitch, direction of the bellows movement, cassoto possibilities and harmonic number are reported here. If the player qualifies, he/she can make controllable pitch-bending effects where the glissando may fall an exact semitone.
Automated fingering services for woodwinds: development of a "virtual clarinet"
Authors: Kulik Yakov , Botros Andrew , Smith John
Published: May 2008

The Virtual Flute is a popular web service that recommends alternative fingerings for difficult passages, timbre variations, intonations or multiphonics. Its database was generated by a machine-learned expert system analysing waveguide models for all 39,744 fingerings. The relatively simple geometry of the flute and its tone holes allowed a simple yet accurate model. The development of similar systems for other woodwinds faces greater modelling and computational challenges. For example, the clarinet has a more complex geometry, with tone holes whose radius and length vary by factors of 4.2 and 2.8. Further, it has several million different fingerings. To achieve the required accuracy, individual measurements of each hole separately and of mouthpiece and bell, as well as several dozen fingering examples, were used to determine parameters of a still simple waveguide model. The model uses conical and cylindrical segments with parallel and shunt impedances at junctions, representing tone holes. This approach of incrementally enhancing our waveguide model allows computational advantages: an efficient, woodwind-generic software framework is built that can adapt to the instrument of interest. We report interim results with such a system, with further potential applications in the design of woodwind instruments and other acoustic duct systems.
Measuring and Modeling Violin Sound Radiation for Sound Equalization
Authors: Perez Carrillo Alfonso , Bonada Jordi , Maestre Esteban , Guaus Enric , Blaauw Merlijn
Published: May 2008

During a performance a violin is put into vibration and this vibration is radiated to the air. Depending on the distance and direction of the listener, he perceives a slightly different sound. Sound radiation at each point in the space is determined by the impulse response or transfer function between vibration of the violin and sound pressure at that point. There is variety of methodologies to obtain acoustic impulse responses of violins. They differ mainly in the way of exciting the violin, the point of excitation, the position where the acoustic response is measured and how excitation and response signals are deconvolved. In this work we measure violin vibration with a bridge pickup and we 1) propose a method to calculate the transfer function between signals from the bridge pickup and a microphone, 2) use a 3D motion tracker to get the position of the microphone respect to the violin so that we can calculate the response for different directions and distances and 3) we model sound radiation as a "reference" impulse response and a parametric filter whose response depends on distance and orientation with respect to the "reference" position.
Virtual electric guitars and associated audio effects in Faust and C++
Authors: Smith Julius O.
Published: May 2008

Advances in computing technology, both in hardware and software, are enabling new levels of performance in real-time for virtual musical instruments based on acoustic principles. This paper is concerned with software implementation technology for such instruments, written in high-level languages that compile down to efficient low-level implementations on a wide variety of platforms. Specific results will be presented for the case of virtual electric guitars and associated digital audio effects expressed in the Faust and C++ languages, and compiled to become plugins for VST, Pure Data, and other real-time performance environments. This work builds upon a previous paper at the Linux Audio Conference (LAC-2008), and laboratory module written for the RealSimple project at CCRMA (http://ccrma.stanford.edu/realsimple/).
Interfacing Digital Waveguide with CORDIS ANIMA networks
Authors: Kontogeorgakopoulos Alexandros , Cadoz Claude
Published: May 2008

The aim of this article is mainly to offer a link between the Digital Waveguide and the CORDIS-ANIMA physical modeling formalism. The first one is highly a modular lumped physical modeling and simulation system based on the mass-interaction paradigm while the second one offers accurate and efficient discrete time distributed models synthesized typically by delay lines and scattering junctions, in combination with digital filters. Both of them are widely developed and used in the domain of computer music field by scientists and artists. Although Digital Waveguide models have already been combined with Wave Digital Filters, they have never been exploited and integrated with CORDIS ANIMA networks. Wave Digital Filters are lumped models which are based on a scattering theoretic formulation which simplifies interfacing to Digital Waveguide models in contrast with the CORDIS ANIMA models. This research investigates the similarities of those formalisms, as well as focuses on the advantages of each modeling technique and proposes a real time computable interface between them. Moreover it results as well in a common convenient structural representation of their computational algorithms using signal processing block diagrams. These hybrid models were designed directly by their block diagrams, simulated and run in differ time using the Simulink software package of the matlab technical computing language.
Thresholds for the perception of fore-and-aft, lateral and vertical vibration by seated persons
Authors: Morioka Miyuki , Griffin Michael J.
Published: May 2008

Vibration experienced in transport and in buildings can yield discomfort or annoyance if the vibration exceeds the threshold for vibration perception. Knowledge of thresholds makes it possible to determine which frequencies and directions of low magnitude vibration give rise to perception. The effect vibration frequency (2 to 315 Hz) on absolute thresholds for the perception of whole-body vibration has been determined experimentally with 12 seated persons for each of the three axes of excitation (fore-and-aft, lateral and vertical). The frequency-dependence of the thresholds differed between the three axes. At frequencies, greater than 10 Hz, sensitivity was greatest for vertical vibration. At frequencies less than 3.15 Hz, sensitivity was greatest to fore-and-aft vibration. In all three axes, the acceleration threshold contours at frequencies greater than 80 Hz were U-shaped, suggesting the same psychophysical channel mediated high frequency thresholds for fore-and-aft, lateral and vertical vibration. It is shown that the frequency-dependence of absolute thresholds for the perception of whole-body vibration are not consistent with the frequency weightings used in current standards.
Toward a comprehensive hospital noise reduction research program
Authors: Busch-Vishniac Ilene , West James
Published: May 2008

Over the last few years there has been a growing interest in the control of hospital noise. This is prompted by a number of drivers: the recognition that hospital noise is a top complaint of patients, staff, and visitors; the move to a digital hospital and the impediment of speech recognition in very noisy environments; the implications of HIPAA and speech privacy on hospitals; and concerns about safety when communication is compromised by noise. Although there are now a number of studies of various issues associated with hospital noise, each views only a small piece of the very complicated problem. This presentation outlines a comprehensive noise research program designed to link acoustical measures with noise interventions and with staff and patient outcomes. Only through such an approach will it be possible to answer important questions such as which noise interventions are most effective and what hospital design strategies are most effective in terms of noise mitigation.
Vibration Effects on Laboratory Mice during Building Construction
Authors: Carman Richard A. , Jue Deborah A. , Glickman Gary M.
Published: May 2008

Laboratory animals, in particular mice, are an integral part of medical and scientific research. Genetic research involving mice can be substantially affected by disruptions to the animals' environment. A new research facility is being built in close proximity to an existing one and the work will involve both demolition and new construction. Prior to construction, a study was conducted at the research facility to establish acceptable vibration levels in the vivaria areas. The study involved an experiment using an electrodynamic shaker to determine the effect of whole-body vibration on pregnant mice. The results of that study have been published. During construction, continuous vibration monitoring was conducted and the program and instrumentation used for monitoring are described. Results are presented, which include the researchers' data on the observed effects on the mice as well as the measured vibration levels during the construction.
The influence of tyre design on tyre/road noise - some fundamental thoughts
Authors: Kropp Wolfgang , Sabiniarz Patrick
Published: May 2008

Tyre/road noise generation mechanisms are divided into two categories, tyre vibrations (due to time varying contact forces) and airflow related processes (e.g. air-pumping) in the contact between tyre and road. The paper only focuses on tyre vibrations. An existing model for the simulation of tyre/road interaction is used to investigate the influence of tyre design on the vibrational energy stored in the tyre structure during rolling. It can be shown that ,although design is changed substantially, very little changes can be observed with respect to input power through the contact into the tyre structure. Changes in driving point mobilities of tyres are not directly related to changes in noise generation. Geometry changes leading to different contact geometry and in this way to different modal composition of the vibrational field as well as design changes leading to changes in wave speed are of higher importance. These changes have a strong influence on the radiation efficiency of tyres.
Analysis of truck tire rolling noise and structural vibrations
Authors: Blanc Samuel , Leyssens Jan
Published: May 2008

Legislators are increasingly demanding towards the vehicle and tire industry for further reduction of tire/road noise emissions. With the need to develop quieter tires, noise has become one of the driving performance criteria in the design process, together with safety, wear and rolling resistance. Next generation truck tires will have to meet more severe legal requirements. In this context, noise has to be improved both at constant speed for the tire regulation and under acceleration for the vehicle legislation. Field test results of different tire tread designs under accelerated and constant speed conditions are given in this presentation. Noise mechanisms and effects of rolling conditions are discussed based on pass-by and near-field microphones. In addition, the dynamic vibration of a truck tire casing is analysed using both detailed FEA modelling and experimental results.
Noise(s) and sound(s): comparing various conceptualizations of acoustic phenomena across languages
Authors: Dubois Danièle S. , Guastavino Catherine
Published: May 2008

Musical listening focuses on perceptual attributes of the sound itself (e.g. pitch, loudness), whereas everyday listening focuses on events to gather relevant information about what happens in our environment (e.g. car approaching), that is, not about the sound itself but rather about noise as produced by sources and actions, and the effect of sound/noise on listeners. Previous linguistic analyses of discourses identified different conceptualizations of everyday/environmental noises and of musical sounds, as well as different conceptualizations for acousticians and non-acousticians. A more extensive psycholinguistic investigation was conducted to evaluate how different languages (not only consensual vocabularies) differently structure the semantic space of acoustic phenomenon. An open questionnaire was administered to expert listeners (acousticians) and naïve listeners from 5 different languages (French, Italian, Spanish, German and English) to collect linguistic resources available in each language and used in discourse to describe acoustic phenomena in their native languages. Presented in this paper are the first results of the comparative psycholinguistic analysis, in terms of linguistic devices and correlated conceptualizations, focusing on - the distinction between noise(s) and sound(s) across languages - the difference between scientific discourses and common sense discourses within and across languages.
Experimental approach for reducing uncertainties associated with road vehicle noise according to ISO 362
Authors: Pardo Louis-Ferdinand , Ageron Thierry , Ficheux Serge , Berthou Celine
Published: May 2008

This paper proposes an approach for reduction uncertainties related to sound pressure levels measured in accordance with procedures given in ISO 362 for noise emitted by road vehicles under acceleration This approach is based on an experimental assessing of several disturbing factors that lead to variation in the resulting level observed day to day and site to site for the same vehicle. The assessment of corrections to build the model is based on an independent analysis on each influent factor (test track, noise measuring device and temperature) taking into account of vehicle noise behaviour depending on power unit and tyres.
Noise control of laboratories: case studies
Authors: Asselineau Marc
Published: May 2008

Laboratories for research and production usually feature work areas complete with exhaust equipment as well as specific equipment (e.g. heaters, shakers, etc.). More to the point, such research and production areas are often linked to open plan offices where workers process their results, as well as partitioned offices where supervising engineers or researchers work. Suchfitting out is supposed to help circulate information around the team and save valuable space. Unfortunately, it easily can be noisy and rather uncomfortable, especially when coming from older fully partitioned laboratories and offices. This paper aims to illustrate a few acoustical highlights of laboratories through a few cases studies, looking at such parameters as spatial sound level decay, background noise level and reverberation time, but also at such additional factors as general background and psychological aspects, and looking at tentative standards. It turns out that both the acoustical quality of the room and the space planning must be developed according to the users' needs.
Case Study of MRI Installation in Existing Hospitals
Authors: Perry James
Published: May 2008

Medical facilities frequently seek to add function and capacity to their imaging facilities. The addition of new MRI units into existing hospital spaces is quite common, however many manufacturers impose and stringent low-frequency vibration limits which must be met before a unit can be delivered and installed. Vibration sources such as mechanical systems and external transit can degrade the achievable imaging resolution at levels undetectable by unaided humans. A case study is presented for one such project which required significant vibration controls to existing ventilation, water, and electrical systems to ensure acceptable vibration levels at an unlikely equipment installation.
Dispersal of measured sound power levels for wind turbines
Authors: Gamba René , Garrigues Sébastien
Published: May 2008

The standard IEC 61400-11 provides guidance in the measurement, analysis and reporting of acoustic emissions (sound power levels) from wind turbine generator systems. The application of this standard aims to provide accurate results that can be replicated by others. We did several measurement operations according to this standard on various wind farms fitted with many turbine manufacturers on different ground types. Important differences have been noticed with equal working conditions between the most and the less noisy wind turbine on a single farm. We will present these results compared to the manufacturers' guaranteed values and initiate explanations (like the difficulties to link the wind speed at 10m above ground with the wind speed received at hub height; or the influence of wind incidence on blades).
Prediction of blade trailing-edge noise of an axial flow fan
Authors: Guedel Alain , Finez Arthur , Perrin Gérald , Roger Michel
Published: May 2008

Broadband noise is a major part of the noise radiated by low-speed fans such as industrial and domestic fans. One of the main mechanisms of broadband noise is blade trailing-edge noise, which is due to the convection of the turbulent flow of the boundary layer past the blade trailing edge. The objective of this work is to predict trailing-edge noise of an axial flow-fan with an analytical model adapted from Amiet's formulation. The input data of the model are the spectra and correlation length scales of the wall pressure fluctuations on the blade suction side close to the trailing edge. These data are measured with small pressure transducers flush mounted on the blade suction side. A first study was performed on a 800-mm axial fan without shroud. The comparison between the predicted and measured far-field sound pressure spectra proved quite good, which validated the model in this impeller configuration. The next stage in progress is to insert a shroud on the same impeller and validate the noise prediction in this case for different fan operating points. The importance of additional broadband noise sources, such as blade tip noise, could also be assessed on this fan configuration.
Fan Blade Trailing-Edge Noise Prediction Using RANS Simulations
Authors: Rozenberg Yannick , Roger Michel , Moreau Stéphane
Published: May 2008

An analytical model based on Paterson & Amiet's work dealing with the trailing-edge noise of a blade has been previously validated thanks to a dedicated experiment on a low speed axial fan. Wall-pressure spectra near the trailing-edge of the blade and at different radii are needed for an accurate prediction. Only experiments and LES simulations are able to provide them. In an industrial context, both methods can not be applied since they are too expensive and time-consuming. To overcome this difficulty, RANS simulations are combined with semi-empirical wall-pressure spectra to obtain the needed input data. The effect of the mean-pressure gradient is taken into account. The model is applied first to the noise radiated by an airfoil placed in the open-jet of an anechoic wind tunnel, then to an automotive cooling fan and finally to an aircraft engine fan. RANS simulations are post-processed to run the analytical model with appropriate input data. The noise predictions are then compared with experimental results.
Measurement of wall pressure fluctuations for noise prediction in axial flow fans
Authors: Hurault Jérémy , Kouidri Smaine , Bakir Farid , Rey Robert
Published: May 2008

The unsteady pressure field on fan blades is an important investigation topic. Both numerical simulation and experimental techniques are used in order to achieve this purpose. However neither has given yet entire satisfaction. The CFD tools using the resolution of the averaged Navier Stokes equations do not really give the unsteady aerodynamic characteristics of the flow needed for an accurate noise prediction. In addition, tools using large eddy simulation are still expensive for industrial users in the case of a complex geometry such as turbomachinery. When a lifting surfaces goes through turbulence, pressure fluctuations occur on their surfaces that can radiate noise. To calculate these fluctuations and thus the noise requires a theoretical model of the unsteady aerodynamics. The validation and development of these models require data and understanding from experiments. Unsteady surface pressure measurements were carried out on one fan blade with an array of pressure transducers with high sensitivity. The fan studied is a low pressure and low Mach number axial flow fan. Investigations of unsteady surface pressure are carried out in different configuration, spanwise, chordwise, pressure side and suction side. Data are gathered through a slip ring by an analyser. The unsteady wall pressure spectra is used as an input for trailing edge noise analytical prediction model.
Acoustical Variety of Soundscapes - Comparison of Soundscapes
Authors: Genuit Klaus , Fiebig André
Published: May 2008

Noise of urban places varies not only with regard to its physical parameters, but also it is perceived and assessed differently because of cultural, sociological, historical and economic influences. The physical description of a soundscape does not cover the complexity of human perception in a specific environmental setting. Therefore, the task of soundscape researchers has to consider more aspects than the measurement and interpretation of the acoustical differences caused by location-specific noise sources. Moreover, semantic and cognitive aspects relating to culture, tradition and economy must be extensively analyzed. Cultural and sociological conditions influence the people's evaluations of their surroundings. A deeper understanding is necessary to adequately analyze soundscapes, especially where specific noise phenomena - e.g. temporal and spectral effects - are of more importance to the listeners' well-being than an averaged SPL value. The presented paper compares and analyses environmental sounds of different cities scattered all over the world by means of conventional and advanced acoustical analyses. The results could provide reliable data for further investigations covering sociological and cultural issues.
Cultural variations and constants in emotional reactions to sounds
Authors: Vastfjall Daniel
Published: May 2008

In this talk I will argue that emotional reactions to sounds can be both constant and vary between different cultures. A model of sound perception that was developed by Chalmers room acoustics group, the Emotional Reaction Model (ERM) will be reviewed. The ERM predicts that emotional reactions to auditory events can be both elicited by 1) certain form features (eg. a steep rise time, a loud sound, a rough sound) and 2) content features (eg. the qualitative experience of the sound source; the loud, rough sound is a tiger roaring). The influence of form features are expected to be rather constant across people and cultures, while content features are expected to vary more between people. Empirical evidence supporting these predicitions will be reviewed and the implications for our understanding sound perception will be discussed.
Elastic characterization of ceramic balls using resonant ultrasound spectroscopy of spheroidal modes
Authors: Deneuville François , Duquennoy Marc , Ouaftouh Mohammadi , Jenot Frédéric , Ourak Mohamed , Desvaux Sébastien
Published: May 2008

The use of ceramic balls, in particular silicon nitride balls, allows a substantial improvement of bearing performances. For critical aerospace and space applications, there is a need for developing new nondestructive techniques for the characterization of these balls. We propose in this work to study the possibilities offered by a specific technique of resonant ultrasound spectroscopy of spheroidal modes. As shown by the theoretical study on elastic sphere vibrations, these modes allow to characterize the whole volume of balls or only the close-to-surface layers, according to the considered frequency range. To acquire the resonance spectra of these modes, a specific measurement system composed of a piezoelectric ultrasonic probe and an optical interferometer was developed. A self-implemented numerical processing of measured spectra allows to detect the resonance frequencies and to deduce from them the propagation velocity of the spheroidal waves in each inspected subsurface layers. Then, we propose a method based on these results that permit to estimate the elastic coefficients of the balls according to various inspection depths. This method has the advantage of providing very high precision evaluations of the elastic coefficients over a wide frequency range.
Thermoacoustic waves near the liquid-vapor critical point
Authors: Carles Pierre
Published: May 2008

The thermal relaxation in a fixed-volume cell filled with a near-critical fluid is governed by the rapid expansion of thermal boundary layers, which drive a series of thermo-acoustic waves in the bulk fluid. The long-term cumulative effect of these waves is to increase the pressure in the cell, which in turn leads to a global temperature increase (a process named the Piston Effect). Recently and for the first time, the thermo- acoustic waves produced by the Piston Effect have been measured experimentally using interferometric methods [Y. Miura et al., to appear in Phys. Rev. E (2006)]. In the present work, we use asymptotic methods in order to derive a complete theoretical model of the Piston-Effect-driven acoustic waves, applicable to real fluid equations of state and to arbitrary reduced temperatures. The predictions of this model are compared to the above-mentioned experimental data, and an excellent agreement is observed without any fitting parameter. This result confirms the high precision of the data in question, and shows that asymptotic models such as ours can be a powerful tool for analyzing the results of such experiments.
Prediction of noise emissions from industrial flares
Authors: Hantschk Carl-Christian , Schorer Edwin
Published: May 2008

In many industries where combustible waste gases are obtained, flares are used to burn these gases in a controlled manner. Among other environmental aspects, the noise emissions associated with flaring are becoming increasingly important in many countries as population density goes up and residential and industrial areas move closer together. Installing noise control equipment on flares is almost impossible while they are in service, since flares are typically a safety related plant component that can only be turned off after the connected plant has been shut down. Accordingly, in order to plan appropriate noise control measures in time and to avoid unnecessary costs, predicting the noise emissions of flares as early in the design process as possible is crucial. This requires knowledge of the relevant individual noise sources associated to the flare system and the ability to calculate their respective contribution - in the operating condition in question - to the overall noise emission, based on the data available in the planning stage. The present paper summarizes these sources and outlines some of the individual effects and parameters having an influence on the acoustical characteristics of flares.
Modelling of acoustic losses with the wave equation for the analysis of combustion instabilities
Authors: Wanke Elke , Weyermann Fabian , Hirsch Christoph , Sattelmayer Thomas
Published: May 2008

A numerical design tool for the assessment of the stability of combustion chambers has been developed, which is able to compute geometrically complex systems with thermoacoustic feedback in the time domain. It is shown that internal acoustic losses can be considered although the method is based on the solution of the wave equation. The presented method overcomes a serious limitation of the original approach and allows to make quantitative predictions. The model is based on the Bernoulli equation and derives the required information from the spatial distribution of the loss of total pressure. For the purpose of a comprehensive validation of the model, simulations were carried out in the frequency domain before the model was implemented. As the internal acoustic losses in combustors stem almost completely from the flow separation at the exit of the burners the losses are independent from temperature. For this reason the influence of the flame was neglected in the study to only focus on the modelling of acoustic losses. The numerical results are validated with single burner test rig experiments.
Evolution of ultrasound transmission during the sol-gel transition
Authors: Gadomska Bożena , Gadomski Wojciech
Published: May 2008

The velocity of the ultrasound wave has been detected during the gelation process of the aqueous gelatin solution. We observe monotonic decrease of the ultrasound transmission in train of the gel network formation. In order to find the dependance of the ultrasound velocity on the number of the intermolecular bonds, responsible for gel formation, we have performed the simultaneous measurements of the optical activity evolution. The experiments have been performed in the gelatin gel and in the silica gel. We have described the process in terms of the percolation theory by power law, according to Landau theory of the second order phase transitions, and by fitting the theoretical results to the experimental curves we have found the appropriate critical exponents. We have also shown how the ultrasound velocity depends on the concentration of the gelling substance and on the temperature, in which the process of the sol-gel transition has been performed.
Ultrasonic annealing of radiation defects in silicon
Authors: Podolian Artem , Korotchenkov Oleg
Published: May 2008

Cold annealing of radiation defects in silicon is reported and the likely origin of the effect is suggested. The data on photocurrent transients and photoluminescence spectra are contrasted in γ-irradiated float zone and Czochralski silicon. The ultrasonic load is shown to slow down the current decay, indicative of the decreased defect densities. The microscopic model includes the likely pathways for E-center annealing in zone and C-O-V2 complex redistribution in Czochralski materials. The carbon involvement into the annealing effect is further evidenced by taking the photoluminescence spectral evolution with applied ultrasonic loads. The usage of the presented technique in improving the performance of radiatively damaged silicon detectors is furthermore discussed.
Acoustic properties of TaCl - TaBr mixed crystals
Authors: Akhmedzhanov Farkhad
Published: May 2008

Attenuation coefficient and phase velocity of transversal and longitudinal acoustic waves in TaCl - TaBr mixed crystals have been investigated by Bragg light diffraction on the acoustic waves. The measurements were carried out at the frequencies from 200 to 1200 MHz at home temperature. Moreover, the phase velocity was determined by using Raman-Nath diffraction and optical heterodyning at 10 MHz. The investigations shown, that the change of acoustic properties in the investigated mixed crystals is nonadditive. Nonlinear interaction constants have been calculated taking into consideration various factors, which can influence on the propagation of acoustic waves in mixed crystals. The results were compared with similar investigations in NaCl - NaBr mixed crystals.
Manipulation of the behavior of SiC particles and oil bubbles using ultrasonic standing wave field
Authors: Cho Seung Hyun , Seo Dae-Cheol , Ahn Bong Young
Published: May 2008

Using ultrasound, particles submerged or flowing in fluid can be manipulated since ultrasound has an effect on the behavior of particles. Specifically, in standing wave field, particles generally move to pressure nodes or pressure antinodes due to acoustic radiation force. In this work, the behavior of SiC particles and oil bubbles in flowing water by standing wave field was investigated. Standing wave field in frequencies between 2 and 2.5 MHz was formed in a few mm narrow flow channel using a water coupled ultrasonic transducer and a steel reflector. We observed the effect of the standing wave parameters such as frequency, flow channel width, or sound intensity on the behavior of the particles. Various interesting results were obtained through some experiments. We separated SiC particles and oil bubbles. It was shown that the operating frequency of standing wave can control the particle moving location. Sound intensity increase also leads to the entrapment of moving particles. The resulted observations reveal the possibility of various applications of the ultrasonic standing wave to the manipulation of particles.
Ultrasonic pulse propagation in a bonded three-layered structure
Authors: San Emeterio Jose Luis , Ramos Antonio , Pardo Emilia , Leite Julio C. , Miguel Alvarez Jose , Perez Trigo Carlos
Published: May 2008

Bonded layers are used in the assembly of many critical functional parts of industrial equipment. In this work, ultrasonic pulse propagation in a steel-rubber-rubber bonded composite structure is investigated by means of computer simulation and pulse echo experimental evaluation. Ultrasonic pulse propagation is modelled using a 2D time domain finite-difference software. For the experimental measurements, two test samples were fabricated by bonding a thin layer of steel and two thin layers of rubber, including debonded areas at marked regions of each interface. Several ultrasonic traces were acquired by contact pulse-echo testing, using a 5 MHz wideband transducer, from the external steel surface. The large acoustic impedance mismatch existing between steel and rubber layers makes that only a very small part of the ultrasonic energy is transmitted through the first (steel-rubber)interface. The high attenuation in rubber materials and the possible overlapping of multiple echoes are additional characteristics of the complex ultrasonic pulse propagation in this flat structure. Some differences in time and frequency domains, between the received signals from normal bonded areas and completely debonded areas are discussed, looking for defect detection at the first (steel-rubber) and second (rubber-rubber) interfaces.
Prediction of ultrasonic noise and attenuation for the simulation of non destructive testing
Authors: Jenson Frédéric , Dorval Vincent , Corneloup Gilles
Published: May 2008

Ultrasonic non destructive testing of some polycrystalline materials can be significantly affected by their microstructure. In such materials a fraction of the acoustic energy is redirected in all directions, which leads to both attenuation and structural noise and causes significant loss in detection performances. Consequently, being able to predict these phenomena would help in designing better testing procedures. During previous works at CEA-LIST, noise and attenuation models have been developped and implemented into the simulation software for non destructive testing CIVA. The noise model describes the microstructure of the material as a set of point-like scatterers and the attenuation model uses a filtering approach. They both require reference ultrasonic measurements to reproduce the behaviour of a given material. The connection of this approach to a scattering model relating noise and attenuation to microstructural characteristics is studied in this work. The selected model is based on the Born approximation and allows one to relate physical quantities such as the scattering cross section and the attenuation coefficient to second order statistical properties of the microstructure and to elastic properties of a single crystallite. This model accounts for important effects such as anisotropic scattering and mode conversions, but neglects multiple scattering events. Simulation results obtained with this approach are compared to experimental results.
Simultaneous Sum-Frequency and Vibro-Acoustography Imaging for Nondestructive Evaluation (NDE) and Testing (NDT) Applications
Authors: Mitri Farid , Silva Glauber T. , Greenleaf James , Fatemi Mostafa
Published: May 2008

High-resolution ultrasound imaging systems for inspection of defects and flaws in materials are of great demand in many industries. Among these systems, Vibro-acoustography (VA) has shown excellent capabilities as a non-contact method for non-destructive high-resolution imaging applications. This method consists of mixing two confocal ultrasound beams, slightly shifted in frequency, to produce an acoustic emission field at the difference frequency of the primary incident ultrasound beams. In addition to the difference frequency signal, there exists another signal at the sum frequency, formed in the intersection region of the two primary beams. The goal of this study is to investigate the formation of high-resolution images using the sum frequency of ultrasound waves in VA while concurrently forming the conventional difference-frequency VA image, thereby increasing the amount of information acquired during a single scan. A theoretical model describing the sum frequency wave propagation, including beam forming and image formation in the confocal configuration is developed and verified experimentally. Moreover, sample experiments are performed on a flawed fiber-reinforced ceramic composite plate. Images at both the difference and sum frequencies are compared and discussed. Results show that the sum frequency image produces a high-resolution C-scan of the plate by which the flaws and structural details of the plate can be detected.
Ultrasonic polar c-scan system for range of material sizes and its capabilities for non-destructive testing
Authors: Barbour Kyle , Vander Weide John M. , Herbison Sarah W. , Declercq Nico F.
Published: May 2008

The principle of multi-directional incident ultrasound has already shown to be a promising technique for the nondestructive evaluation of composites and other materials. The advantage is the correspondence between stiffness, damage and the registered double through transmission patterns. C-scans are widely used as a tool for the detection of defects in materials. A new ultrasonic scanner has been developed, called the Polar C-Scan, which enables efficient polar scan measurements in combination with C-scan capabilities. The scanner opens many possibilities for nondestructive testing by means of polar scans, C-scans, single transmission, double through transmission and even reflection. Furthermore the system produces almost no noise, which enables highly sensitive measurements in the time domain and the frequency domain. The presented work shows a thorough investigation of all the capabilities of the system and presents results for fiber reinforced composites after different fatigue cycles.
Theoretical investigations into the use of linear and nonlinear inhomogeneous waves for non-destructive testing
Authors: Vander Weide John M. , Declercq Nico F.
Published: May 2008

Following the shift to incorporate more materials by design into modern engineering is the theoretical need to model an increasingly more complicated material structure and predict a design life for complex engineered materials. The presence of defects, interface cracks and delaminations adds to the inherent nonlinearity of a structure by degrading material stiffness and other physical properties contributing to fracture. The presence of local defects either at interfaces between two different materials or grain boundaries within the bulk material provide a natural location for the formation and subsequent propagation of cracks. This work provides initial theoretical investigations into the use of ultrasonic inhomogeneous waves to nondestructively probe such interface defects. Characterized theoretically by a complex valued wave number, the inhomogeneous wave is the more general plane wave solution of the wave equation. The complex valued wave number allows for the material effects of damping along the propagation direction and wave inhomogeneity or amplitude decay along the wavefront. To study the interaction with cracks, a singular integral equation formulation like that of Krenk and Schmidt is extended to farfield simulations with ultrasonic inhomogeneous waves.
Acoustic emission of structures basis on the A3B5 compounds
Authors: Veleschuk Vitaly V. , Lyashenko Oleg V. , Vlasenko Olexander I.
Published: May 2008

Failure of internal mechanical pressure at origin and movement of dislocations in processes of fast degradation and defect formation in LED and semiconductor lasers lead to occurrence of acoustic emission (AE) - to the phenomenon of radiation of pulse spontaneous acoustic wave's noise character. This failure of internal mechanical pressure in local volumes with occurrence AE is possible only at action of external fields (influences) of the certain physical nature, in our case - non-uniform fields of the thermomechanical pressure created by a constant direct current. In work were investigated n+-n-p- structures basis on the GaP:N, GaP0,85As0,15:N, Zn-O, InGaN/GaN and p+-p-n- structures basis on the Ga0,7Al0,3As and Ga0,65Al0,35As. During step-by-step increase of a current 10-25 multiple change of AE occurrence threshold and a destruction threshold of structures was revealed at natural ageing structures after 6̇108 s. For some samples of structures at low temperatures (77) AE occurrence threshold came nearer or even corresponded to a destruction threshold. The given effect explains gradual saturation of dislocations by atoms of impurity with formation of Cottrell cloud, that considerably lowers their mobility and increases activation energy and accordingly a AE occurrence threshold