bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustics of Low Mach Number Nozzles with Area Expansions
Authors: Lau Fernando J. , Oliveira João M.
Published: May 2008

The acoustic wave equation for quasi-one-dimensional propagation is obtained, along a cylindrical duct with a significant area expansion and containing a low Mach number mean flow. The motivation is the study of the reflection in cross-sectional expanding area. The ray approximation, which holds only for wavelengths which are short compared with the length scales of the variation of the cross-section and mean flow velocity, is used as a factor to reduce the wave equation to a Schrodinger form, in a nozzle with a hyperbolic tangent expansion. The exact solutions are obtained, without restriction, as power series solutions around the middle of the duct; since this solution fails to converge at the two ends of the duct it is matched to the other solutions there, by application of the causality principle. In this way it is possible to calculate everywhere the pressure and velocity perturbation profiles, for both the transmitted and reflected waves, as well as the reflection and transmission coefficients. These are plotted as a function of the longitudinal coordinates along the duct for several values of the three dimensionless parameters in the problem, viz. (i) the area expansion ratio , ii) the Mach number of the mean flow at the central section and iii) the wavenumber.
Measurements of curve squeal from Oslo's subway
Authors: Olafsen Sigmund , Killengreen Tore
Published: May 2008

Curve squeal from the subway line at Brattlikollen, Oslo, has led to severe noise complaints through the years. Two important steps have been taken to reduce the problem. An automatic rail lubrication system has been installed on the critical spot, and Oslo's old subway trains (1300 series) are being replaced. One of the new trains (MX) has also been fitted with wheel dampers. Continuous measurements during 16 days and nights with 2238 train passages have been analyzed to verify the effectiveness of these steps to reduce noise. The main results are as follows: 1300 series trains without rail lubrication give severe curve squeal during 18% of the train passages. 1300 series trains with rail lubrication give severe curve squeal during less than 1% of the train passages MX trains give substantially less curve squeal than 1300 series trains, with or without lubrication The MX trains with wheel dampers gives no curve squeal, even without lubrication
Reduction of Noise from Composite Steel/Concrete Aerial Structures by Damping Steel Plates
Authors: Wilson George P. , Kirschner Francis
Published: May 2008

Noise radiated from steel girders at bridges and aerial structures has been a long standing problem for steel wheel and rail systems. During the initial design period for the San Francisco Bay Area Rapid Transit System, a full scale model girder and deck was constructed in 1964 and tested with and without constrained layer damping on the steel girder plates. The radiated noise from 20 Hz to 150 Hz was reduced by 9 dB with full plate area damping. A test track installation in 1965 also showed about 9 dB reduction in wayside noise with the overall result within about 1 dB of the noise radiated by an all-concrete structure. Because full plate area constrained damping is expensive, a scheme with small area damping pads was developed in the 1970's and applied to composite steel/concrete aerial structures at the Atlanta rail transit system. The result was 9 to 10 dB reduction of low frequency radiated noise, allowing sound barrier walls at the outer edges of the decks to be fully effective in reducing overall wayside noise levels from trains. Drawings of the aerial structures and graphical results from vibration and noise tests are presented.
Noise reduction applied to an engine cooling system for a diesel railway vehicle
Authors: Frid Anders , Fehse Karl-Richard
Published: May 2008

In recent years there there has been growing attention to reduce the noise from rail traffic in urban areas. In or around stations and depots, noise from cooling systems and traction and auxiliary equipment normally dominates. New legislation setting noise limits for stationary and accelerating trains puts further emphasis on increased noise reduction of such sources. An experimental investigation has been carried out in which several design changes on a roof-mounted diesel engine cooler from the AGC (Autorail Grande Capacité) train have been assessed in laboratory and on a train. Even though this train is considered as a state-of-the-art product having very low noise emission, the engine cooler is identified as the dominating noise source when operating at its maximum capacity. The wide range of minor and major modifications tested includes different ways to guide the air flow into the fans, reduced tip clearance, absorption material in various positions inside and outside the cooler. Also different fan types have been tried (an axial fan with swept blades and a radial fan). The work has been carried out within the 6th framework EU-project "Silence" (ref TIP4-CT-2005-516288)
Noise reduction strategies for a light metro rail traction system
Authors: Rusciano Nicola , Viscardi Massimo , Ferraiuolo Stefano
Published: May 2008

Inside the paper the vibro-acoustic characterization of a light rail vehicle is presented, with special reference to the traction noise emission identification. As a first step , on board measurements and pass by measurements, were performed in order to separate traction noise from rolling noise; these test revealed the electrical engine, as the most relevant sources at low speed. The electrical engine has then been characterized during specific laboratory test and innovative noise control solution were proposed to be tested. The first one could be a modification of inverter algorithm; this trying to reduce the influence of most relevant acoustic tones. This approach is essentially based on a software modification of the PWM algorithm through which modify the engine's spectral response. The second possible tested approach involved the enclosure of the engine in a sort of semi-active skin panels co-located at short distance from the engine; it has been demonstrated that this approach, by the merging of passive and active peculiarities, potentially lead to a wide frequency range application area. Following laboratory tests, the PWM solution was also decided to be implemented during "on board" test; a wide set of experimental results will be presented and discussed.
Tram noise emission: Spectral analysis of the noise source contributions
Authors: Pallas Marie-Agnès , Lelong Joel , Chatagnon Roger
Published: May 2008

In France we can assist to a wide development of tram networks for public transportation in main cities. At the same time arises questioning on the noise emission of trams and possible consequences for resident exposure. A French research project has been conducted for studying noise and vibration emission of trams : this paper concerns the description of the noise emission of passing-by trams. A measurement campaign was achieved on the city of Nantes network, involving two kinds of trams with distinct technologies and equipment, and tested on two types of tracks having different platform surfaces. Acoustic measurement included both a 2D-array for noise source identification and a microphone set for vertical directivity analysis. The dominant noise sources are mainly the bogie areas (powered bogies, unpowered bogies) and an extended noise source along the track and the lower part of the tram, all of them involving rolling noise. This paper focuses on the spectral description of the main sources. A parametric study is presented, pointing out the effect of speed, tram type and track type on the frequency distribution of the emitted noise.
A comparison of SONAH and IBEM for near-field acoustic holography
Authors: Juhl Peter , Gomes Jesper
Published: May 2008

Among the popular techniques for acoustic source identification in complex environments are the Statistically Optimal Near Acoustic Holography (SONAH) and the Inverse Boundary Element Method (IBEM). These two methods are quite different regarding the underlying assumptions and the practical implementations: Whereas SONAH performs the back-propagation of the sound field to a plane surface; the IBEM has no restrictions on the radiating geometry. On the other hand, IBEM requires the generation of a surface mesh and a time consuming solution process. The present paper compares the performance of the two methods for a number of simulated test cases and studies the influence on the performance of the models when changing selected parameters. Finally, the performance of the methods is compared in a simple measurement setup.
Tire radiation in vehicle environment: A review of some source identification methods
Authors: Picard Christophe , Fiack Matthieu , Tanneau Olivier , Sauvage Olivier , Gagliardini Laurent
Published: May 2008

The REBECA research project aims at defining new architectural concepts and reduction strategies of vehicle external noise emission regarding the international pass-by noise certification standard (ISO 362). The first task of the project is to qualify and quantify the major contributor of the external emission, the tires/road surface source. To this end, a 3D array composed of 164 microphones has been set up in the near and far field around vehicle. Measurements have been performed for several operational conditions with the use of a chassis dyno in a semi-anechoic chamber. A review and a comparison of some source identification methods has been led including experimental FRFs based on inverse techniques (Nelson), conventional and optimized beamforming approaches (Elias, Dougherty, Brooks and Humphreys, Ravetta) and inverse BEM method (Hamdi, Omrani). This study permits to identify the more appropriate microphone array technique with respect to source identification robustness, power level and directivity radiation reconstruction in the far field.
Optimized thin layers for urban roads
Authors: Thomsen Sigurd N. , Bendtsen Hans , Andersen Bent
Published: May 2008

In the EU project SILENCE work has been carried out to optimize the noise reduction of different types of pavements for urban roads. The Danish Road Institute (DRI) participated in this work together with the Swedish National Road and Transport Research Institute (VTI) and BAST in Germany. Joint international development work has been carried out including laboratory experiments. The objective was to find pavements with promising noise reduction. It was decided to carry out a full scale field testing in some countries. DRI has in cooperation with the municipality of Copenhagen and the Colas road construction company tested series of SMA pavements and open graded pavements, optimized for noise reduction by using small aggregate size of 4 to 6 mm and by constructing a relatively high builtin air void. Eight different pavements were constructed in June 2007 on Kastrupvej in Copenhagen. DRI has conducted SPB and CPX noise measurements. An initial noise reduction for passenger cars of 4.3 dB in relation to a DAC 11 reference pavement has been achieved. It is planned to continue the measurements in the coming years in order to be able to analyse the long time acoustical and structural performance of these test pavements.
Traffic noise levels after replacing the top of two-layer porous asphalt at Øster So/gade
Authors: Kragh Jo/rgen , Bendtsen Hans
Published: May 2008

In 1999 three different types of two-layer porous asphalt pavement with 5 mm or 8 mm maximum aggregate in the top layer were built in a city street in Copenhagen. A section with dense asphalt concrete was built as a reference. The pavements have been monitored since then. The initial noise reduction of 6 - 7 dB compared with the noise level at the reference section has vanished over the years due to gradual clogging of the porosities in the pavement. After 8 years in service the drainage asphalt in the spring of 2007 was worn and ravelling had begun. The municipality of Copenhagen decided to have the top layer milled away and replaced by new porous asphalt with 8 mm maximum aggregate. This type had proven most durable, acoustically and structurally. Noise measurements were carried out in 2007 as part of the SILENCE project, both before and after replacing the top layer. The measurements showed that at two of the test sections most of the initial noise reduction was regained while this was not the case at the one test section that was thinnest (a total of 55 mm while the other were 70 mm and 90 mm, respectively).
Evaluation of the ASTM Standard Reference Test Tire for purposes of standardized measurement of on-bound tire/pavement noise
Authors: Donavan Paul
Published: May 2008

Currently in the US, efforts are underway to develop standard methods for on-board sound intensity (OBSI) measurement of tire/pavement noise. Up until recently, the default standard tire was the Goodyear Aquatred 3 tire originally selected due to its apparent similarity to Tire A specified in the ISO CPX procedure. Because of longer-term availability, the ASTM Standard Reference Test Tire (SRTT) is the primary candidate for replacement of the Aquatred 3. Issues of concern for the SRTT include tire-to-tire variation, the relation of the SRTT to previously used reference tire, and the "break-in" period required for stable test tires. To address tire-to-tire variability, six SRTT's were tested on variety of asphalt (AC) and Portland cement concrete (PCC) surfaces. These included four new tires and two that had been in use for some time. Two of the new tires were retested with increasing use to examine any break-in period effect. For comparison, the older Aquatred 3 was also tested on these same surfaces using both OBSI and controlled pass-by measurements. The results of these measurements are presented along with their implication to for reference tire selection.
Evaluation of effects of pavement characteristics on the OBSI levels using Principal Components Regression
Authors: Ongel Aybike , Kohler Erwin , Harvey John
Published: May 2008

Tire/pavement noise is a major contributor to traffic noise at highway speeds. Tire/pavement noise is affected by different pavement properties. A study conducted in California measured the noise levels of different mix types and the mix characteristics affecting noise levels. In this study, tire/pavement noise was measured using the on-board sound intensity (OBSI) method. Data was collected on four different types of pavement mixes: conventional open graded asphalt concrete (OGAC), rubberized asphalt concrete that are open graded (RAC-O), rubberized asphalt concrete that are gap graded (RAC-G), and dense graded asphalt concrete mixes (DGAC). A total of 72 field pavement sections were included in the study, all of which were less than 8 years old at the time of the measurements. This paper evaluates the pavement characteristics affecting noise levels using principal components regression. This technique was used due to the multicollinearity found among the variables. Two principal components were extracted from the measured parameters such as air void content, gradation properties, pavement roughness, age, and pavement surface condition.
Acoustical characterisation and life-cycle of porous road surfaces
Authors: Altreuther Beate , Bartolomaeus Wolfram
Published: May 2008

The German Federal Highway Research Institute (Bundesanstalt für Straßenwesen, BASt) is planning to develop an assessment procedure to characterize the acoustical properties of porous road surfaces. Final objective is to specify the life-cycle of these pavements with respect to their acoustical performance based on civil engineering properties. In 2007 comprehensive measurements of the acoustically relevant parameters absorption coefficient, air flow resistance and surface texture have been performed on a multitude of bavarian motorways with porous asphalt pavements of different types of construction and different ages. Additional measurements of the near-field rolling noise (CPX) as well as measurements of the statistical pass-by-noise (SPB) have been performed. From precedent projects for the sections under investigation there is an extensive database covering details on asphalt mixtures as well as the results of drill core investigations concerning void content, binder content etc. The results of the present investigation allow to draw new conclusions with respect to acoustical performance and durability of porous asphalt pavements. We gratefully acknowledge the project funding by the German Federal Ministry of Transport, Building and Urban Affairs (project No. FE 02.276/2006/LRB).
DEUFRABASE: A German-French acoustic database on road pavements
Authors: Berengier Michel C. , Droste Bettina , Gauvreau Benoit , Duhamel Denis , Auerbach Markus
Published: May 2008

In the framework of a DEUFRAKO (German/French cooperation) project on the Prediction and Propagation of Rolling Noise (P2RN), it has been proposed to rank the different German and French road pavements with respect to noise for different long distance configurations representative of real road topographies, ground characteristics and meteorological situations. After identification of those typical 28 configurations, the attenuations between a reference point in the near field and several receiving points in the far field have been computed according to the most relevant and adapted modelling methods currently available. The main goal being the accuracy of the prediction and not the computation time, analytical (ray tracing) and numerical (BEM, Parabolic Equation) approaches have been implemented. In the following, a technique permitting to estimate day and night LAeq and Lden has been used to classify the various pavements for the whole configurations. All those results have been gathered in a common database (DEUFRABASE) which will be directly available on the website of the authors' Institutes. The paper deals with the description of the ranking procedures, how the database is implemented on the web and how to use it for road traffic noise prediction.
Road noise characterization by Harmonoise procedures reviewed for the Italian case
Authors: Alfinito Luca , Licitra Gaetano , Cerchiai Mauro , Magni Lorenzo , Losa Massimo
Published: May 2008

Several methods have been introduced to describe acoustical properties of road pavements in situ, such as the extended surface technique (Adrienne), the Statistical Pass-By and the Close Proximity methods. In general the aim of these techniques, normed in ISO standards, is to evaluate some indexes that may be representative of noise generation and propagation with respect to tyre-road interaction and surface absorption. In this paper we use results obtained in the LEOPOLDO project, that involves measurements carried out on many sites all over Tuscany Region characterized by typical conditions of Italian roads, to review the state-of-the-art of acoustical parameters in the modelling of road vehicles showed in the HARMONOISE documents. This task has been accomplished by comparing the theoretical results obtained from the HARMONOISE prediction method with the energy levels measured at the microphone locations close to the road borders, in order to apply corrections to the parameters influencing sound generation and propagation. As a consequence, we introduce a new parameter, related to transfer function between source and receiver sound energy levels, which involves directivity and ground reflection effects, obtaining a more suitable characterization of road surface acoustical behaviour.
Airframe noise prediction
Authors: Guo Yueping
Published: May 2008

This presentation discusses the prediction of aircraft airframe noise, namely, the noise that is generated by non-propulsion components of aircraft, including the leaning edge slats, the side edges of flaps and the landing gears. An overview will be given on various methodologies, ranging from empirical prediction to more physics-based modeling to full-blown numerical simulation. The advantages of each method will be discussed and compared with each other to reveal the most suitable application domain of each method. Detailed discussions will be given to the physics-based modeling, such as the acoustic analogy, which is ranked in between empirical and numerical methods in various aspects, including accuracy, turn-around time, limitations on geometry and flow conditions, and applicability/ feasibility in practical design applications. Examples will be given to demonstrate the applications of acoustic analogy in both noise prediction and noise reduction treatment design. Critical elements of the method that can and need to be improved to further mature the method will also be identified and discussed, providing potential directions for future research and development.
Landing gear noise assessment on Airbus aircraft
Authors: Molin Nicolas
Published: May 2008

During the last two decades, airframe noise sources (high lift devices and landing gears) have become noticeable in new aircraft technology, especially during approach. Aircraft manufacturers need prediction tools, in order to include noise modelling at the early stages of aircraft design. Such tools can be developed on the basis of simple formulations. As long as the dominant features are preserved in the simplified problems, the solution is believed to behave correctly in terms of EPNdB. Such a model of landing gear noise prediction was developed in the late 1990s. It is based on the decomposition of a landing gear into different noise sources: the primary structure (massive elements) and the secondary structure (wire, pipes, œ), whose noise is estimated with existing classical source noise model fed with empirical constants based on wind tunnel test results. Airbus implemented this model into its total aircraft noise program and validated it with dedicated flight tests. As the model takes into account all main components with their geometry, it is well adapted to predict the impact of add-on treatment such as fairings on the gear or the impact of an advanced low noise gear with simplified geometry.
Modeling auditory attention focusing in multisource environments
Authors: De Coensel Bert , Botteldooren Dick
Published: May 2008

In this paper, a mathematical submodel for auditory attention focusing is discussed in the framework of our ongoing research towards a unified model for soundscape perception. The submodel implements a balance between top-down focusing, in which higher level cognition guides attention towards expected sources, and bottom-up focusing, in which attention is triggered by the noticing of sound events. Attention elasticity - the ability to switch attention between different environmental sounds - depends on the current context (natural, urban...) as well as on the current activity of the modeled individual. The soundscape perception model is applied to case studies of simulated sound exposure in open area and in environments with a mixture of natural and man-made sounds. A comparison of the simulation results with survey results shows that introducing a submodel for auditory attention focusing into our model for soundscape perception enhances its ability to predict the emergence of annoyance.
Soundscape and California planning guidelines
Authors: Rodkin Richard B. , Thill Michael S.
Published: May 2008

Community noise has been recognized as a significant environmental concern in California for more than 30 years. All cities and counties are mandated by state law to include a Noise Element as a part of the community's General Plan to provide "a basis for comprehensive local programs to control and abate environmental noise and to protect citizens from excessive exposure." What is, and has been missing from this process, is how the soundscape in a particular setting may affect the compatibility of land uses there. Generalized noise and land use planning guidelines are no longer sufficient. Specific attention must be given to the development of guidelines and policies that address "smart growth" in and around urban and suburban transportation corridors, residential and agricultural interactions, mixed-use developments, industrial-to-residential conversions (e.g., the gentrification of traditionally industrial areas like ports). A new soundscape vocabulary must be introduced to describe the acoustical environments in these settings to facilitate other goals in land use planning. Examples are presented of specific communities where planning goals and traditional noise and land use compatibility guidelines were in conflict and how these were resolved.
Three wave mixing test of hyperelasticity in sedimentary rocks
Authors: Johnson David L. , Winkler Kenneth , D'Angelo Ralph
Published: May 2008

We report measurements of 3-wave mixing amplitudes on solids whose 3rd order elastic constants have also been measured by means of the elasto-acoustic effect. Because attenuation and diffraction are important aspects of our measurement technique we analyze our results using a frequency domain version of the KZK equation, modified to accommodate an arbitrary frequency dependence to the attenuation. We find that the value of β so deduced for polymethylmethacrylate (PMMA) agrees quite well with that predicted from the stress-dependent sound speed measurements, establishing that PMMA may be considered a hyperelastic solid, in this context. The β values of sedimentary rocks, though they are typically two orders of magnitude larger than e.g. PMMA's, are still a factor 3-10 less than those predicted from the elasto-acoustic effect. Moreover, these samples exhibit significant heterogeneity on a centimeter scale, which heterogeneity is not apparent from a measurement of the position dependent sound speed.
Fatigue Damage Monitoring and Remaning Life Assessment using Nonlinear Vibro-Modulation Technique
Authors: Donskoy Dimitri , Chudnovsky Alexander , Zagrai Andrei , Golovin Edvard , Agarwala Vinod
Published: May 2008

Assessment of structural deterioration due to in-service and environmental loads is an essential element in ensuring safety, operability and long life of various structures and structural components. We applied vibro-acoustic modulation technique to monitor material degradation at the micro/meso scale before the onset of the macro-scale fracture. The technique explores nonlinear acoustic interaction of high frequency ultrasound and low frequency structural vibration at the site of the incipient damage. It is shown that micro/meso scale degradation increases the material nonlinearity leading to modulation of the high frequency ultrasonic signal by low frequency vibration, quantified by the nonlinear acoustic Damage Index (DI). Numerous tests with hundreds of test coupons proved high sensitivity of the developed technique to micro/meso scale fatigue damage accumulation. The study further demonstrated that the remaining life of the fatigued material can be predicted using phenomenological damage accumulation rule expressed through measured Damage Index. Work supported by NAVAIR.
Use of synchronous nonlinear interaction of flexural Lamb waves in NDT-application
Authors: Izosimova Maria Y. , Korobov Alexandr I. , Mekhedov Dmitrii
Published: May 2008

Workability of synchronous nonlinear interaction of flexural Lamb waves in NDT-application is demonstrated. During experiments traveling and standing A0 waves were used. Lamb waves are dispersive, so to provide synchronous nonlinear mode for traveling waves, non-collinear interaction of two waves with frequency f were realized in aluminum alloy plate with defects. In the area of waves' nonlinear interaction, traveling wave of 2f frequency appeared. Standing Lamb waves were excited with amplitude-modulated signal in a cylindrical resonator of aluminum plate. Carrier frequency f and modulating frequency F≪f are equal to natural modes of the resonator. Spectrum of amplitude-modulated waves contained oscillations with frequencies f, f+F, and f-F. As a result of interaction, oscillation on heterodyne frequency F appeared in the plate and excited a natural mode. Amplitudes of traveling and standing waves on heterodyne frequencies depend on presence of defects in investigated area (non-classic nonlinearity). Spatial distribution of amplitudes of initial waves and ones on heterodyne frequency in samples were measured with laser vibrometer PolytecPSV300. In area containing heterogeneities, amplitude increase of waves on heterodyne frequencies was observed. The possibility to define the spatial distribution of defects using measurements of heterodyne wave amplitude distribution was shown experimentally. Work supported by RFBR.
Prediction of Self Excitation Frequencies and Amplitudes for a Model Gas Turbine Burner
Authors: Gardner Catherine , Hosseini S. M. Reza , Lawn Chris J.
Published: May 2008

Forced excitation of a swirl stabilised methane/air flame by acoustic waves at atmospheric pressure has been characterised in order to show that the frequencies and amplitudes where self-excitation occurs, but the natural limit cycle takes effect, can be predicted from these data. Chemiluminescent emission was therefore recorded to measure the Flame Transfer Function (FTF), as the flame was acoustically excited by two loud speakers. The experiments covered a wide range of frequencies and amplitudes with particular emphasis on the FTF at high amplitudes of excitation, where a non-linear response is often reported. The system was modelled by the 1D thermo-acoustic element method, in which each acoustic element, such as a duct or a contraction, is described by a four-pole matrix. The flame is incorporated as another four-pole matrix that describes the measured flame transfer function. The solution of this set of equations without forcing predicts self-excitation frequencies and amplitudes that can be compared with the experimental data. The minimum magnitudes of the FTF for excitation may also be calculated. When proven at this small scale, the procedure will be applied to predict the limit cycling of actual installations from rig tests.
The acoustic wave propagation equation in a turbulent combusting flow
Authors: Kok Jim B.
Published: May 2008

Sound generation by turbulent flames originates from the fluctuating heat release in the flame. The description of this fluctuating heat release and its effect on acoustics in turbulent flames is complicated due to the interaction of chemical reactions with turbulence, mixing and pressure fluctuations. In a turbulent flame the instantaneous density, velocity, pressure, temperature and species concentrations are determined by the transport equations for mass, momentum, enthalpy and species and by the equation of state. In the proposed paper an equation is formulated that describes the propagation of acoustic pressure fluctuations, and that determines the source terms. These source terms are compared with various terms derived in the literature. Significant differences are found between several approaches. An effort is made to come to a reliable and generally acceptable formulation. Subsequently events are ordered on basis of their typical time scale. That way source terms can be evaluated for the situation where the combustion is described with the use of time averaged chemical reaction progress variables and a mixture fraction variable. Subsequently the consequences of Reynolds and Favre averaging on these source terms and conservation of acoustical variables in a domain with turbulent flow are discussed.
Acoustical imaging with bending waves based on sparse inversion
Authors: Hörchens Lars , De Vries Diemer
Published: May 2008

Bending waves can be employed in the context of acoustical imaging for the detection of material defects or localization of vibration sources. The obtainable spatial resolution is limited by the minimal wavelength contained in the excitation signal. The evanescent part of the wave field can usually not be used for the imaging of sources at distances exceeding a wavelength. Therefore only the propagating part of the field can be employed, which means that the minimum size of the region where energy can be focused is in the order of half a wavelength due to the diffraction limit. If the recovery of vibration sources and reflections is posed as an inverse problem, regularization techniques can be applied in order to force a sparse solution. Preliminary results indicate that the assumption of a sparse source distribution can be used to resolve features significantly smaller than half a wavelength. The approach is therefore applied as a high-resolution imaging technique for bending wave fields.
Interaction of elastic waves with dislocations
Authors: Maurel Agnes , Pagneux Vincent , Barra Felipe , Lund Fernando
Published: May 2008

This work concerns the effective propagation of elastic waves in a medium filled with randomly placed dislocations. Multiple scattering theory is applied to derive the effective velocity and attenuation of the waves (both transverse and longitudinal) because of the effect of the dislocations. Our work is a generalization of Granato & Lucke theory since it takes into account the polarization of the elastic waves. Two principal results have been obtained, in connexion with experiments: 1) we have explained the different attenuations experimentally measured between longitudinal and transverse waves. The difference between the two values is obtained in quantitative agreement with no adjustable parameter. 2) we have offered a scenario for the frequency law in the attenuation measured in polycrystals (a combination of quadratic and quartic law). This has been done by taking into account the dislocations at the grain boundaries that can contribute to the attenuation process.
Simple and versatile non-contact technique for measuring the interfacial tension of a liquid-liquid interface using pulsed acoustic radiation pressure
Authors: Issenmann Bruno , Wunenburger Regis , Delville Jean-Pierre
Published: May 2008

We present a versatile non-contact technique for measuring the interfacial tension of a liquid-liquid interface using the acoustic radiation pressure. This technique is based on the analysis of the shape of the time-dependent deformation of the liquid interface induced by the radiation pressure of a focused, pulsed ultrasonic beam. It combines a simple optical detection step and a novel analytical model of interface deformation dynamics that accurately takes into account interfacial, gravitational, as well as viscous effects in both weakly and highly viscous limits. The accuracy of this technique is experimentally demonstrated on liquid-air and liquid-liquid interfaces.
Experimentation in physics-based sound modeling
Authors: Rocchesso Davide
Published: May 2008

Since 2001, as part of the Sounding Object and CLOSED projects, we have been developing physics-based sound models for everyday events and processes. The procedure of describing a sound-producing phenomenon in physical terms, building a model, and accessing its parameters, easily gives the illusion of controlling sound production in the most effective and convenient way. For example, it is trivial to connect a force sensor to the rubbing pressure variable of a friction model. However, one soon realizes that it is often difficult to predict changes in perceived sound in response to physical changes, and that robust models are difficult to achieve. These issues can partially be addressed with experimental research in perception, psychophysics, and phenomenology. Although this approach is inherently time consuming, it will eventually lead to sound models whose parametric layout is more suitable to human manipulation and control. Conversely, in the practice of designers we find that problems are tackled by rapidly producing a multiplicity of attempts, or sketches, and by critically comparing them. In our practice of sound modelers, there are several examples where both approaches, the one based on experimental psychology and the one based on design, proved to be compelling and useful.
Evaluation and modification of listener decision strategy in human gait perception
Authors: Pastore Richard E. , Flint Jesse D. , Gaston Jeremy R.
Published: May 2008

Beyond obvious differences, there are many similarities in the challenges faced in studies of speech and natural (nonspeech) sounds. The source events are dynamic, complex and highly variable. Source properties map only statistically in the sounds produced, resulting in many acoustic properties that are only sometimes accurate indicators of specific source properties. Finally, beyond the nonlinear mapping of acoustic to perceptual properties, listeners vary in decision weights assigned to the perceived attributes of the sounds. Beginning with this complex conceptualization of source-sound-perception relationships, our research on the perception of human gait from walking sounds investigated the perception of walker posture. The current research extends this project on human gait perception, evaluating both the decision strategy of listener individual listeners and alternative approaches to improving that decision strategy. Implications for studying of both natural nonspeech and speech will be briefly discussed.
Cognitive influences on spatial hearing
Authors: Keen Rachel
Published: May 2008

In reverberant rooms a listener perceives a sound coming from its source but simultaneously suppresses reflected sound or echoes. This phenomenon is known as the precedence effect because the preceding (original) sound is given heavier weight than its subsequent reflections. Our research has explored this perceptual process and found that listeners are sensitive to the acoustic information contained in the reflected sound even though it is "suppressed". Specifically, below echo-threshold information relevant to room acoustics (e.g., delay between lead and lag sounds, filtering of the echo's spectrum, presence or absence of an echo at a particular location) is processed by the listener and influences perception. Listeners' expectations about ongoing input can raise or lower echo threshold. Recent ERP data on listeners' responses to click pairs near echo threshold found that when listeners perceived lead and lag sounds as separate sources, a negativity between 100 and 250 ms was elicited, termed object-related negativity (ORN). When the same stimulus was heard as a single fused sound, no ORN was elicited. These findings suggest that higher-level cognitive processes exert top-down influences over early neurosensory processing.
From binaural hearing to auralization: A triumph of Blauert's 40 years in room acoustics
Authors: Xiang Ning , Hess Wolfgang
Published: May 2008

In the late 60's when Jens Blauert's work on sound localization in the median plane was recognized by the psychoacoustics community, he had already started on a long journey from binaural-hearing research to many aspects of what nowadays is called Communication Acoustics. In addition to initiating many new research activities such as binaural auditory modelling, binaural technology, sound-quality, and speech synthesis, his unremitting endeavour in room acoustics has led to innovative developments in the fields of analysis and synthesis of auditory scenes. For example, binaural room-acoustics modelling, real-time dynamic room-impulse response processing, and auditory virtual environments (nowadays known as "auralization") were particularly driven by his work and his supervision of over 50 doctoral students. In this regard the first head-tracking and fast-convolution patent application was filed in the early 70's. Recently auditory models have been applied in auditory spatial evaluations of rooms and cars. Not only his excellent analytical skills and theoretical knowledge, but also his vision for transfer to practical applications in room acoustics and human-auditory spatial perception led to an outstanding life-work. This paper will highlight just a few of Jens Blauert's major contributions to room-acoustics.
How can we model a quality event? Some considerations on describing quality judgment and prediction processes
Authors: Möller Sebastian
Published: May 2008

Jens Blauert has introduced a systemic view on a listener in an auditory experiment. This view helps to separate sound events from auditory events and from their descriptions, and to identify and describe the processes involved in such experiments. The notion has later been extended to listeners in a quality judgment situation by Jekosch and Raake, leading to the notion of a "quality event". On the one hand, knowledge of the involved processes is necessary to design appropriate measurement processes for, e.g., sound quality, transmission quality, auditory-scene quality, or product-sound quality. On the other hand, such knowledge enables us to define algorithms which estimate quality - or sub-aspects of it - in the system design process. The talk will mainly follow the second line and will identify components which are necessary for an algorithmic description of the processes involved in the formation of a quality event. Taking the example of telecommunication services, it will be shown which components of quality prediction models are already available, and which others are still out-of-reach and require further study.
Practical modeling of acoustic losses in air due to heat conduction and viscosity
Authors: Christensen René , Juhl Peter , Cutanda Henriquez Vicente
Published: May 2008

Accurate acoustics models of small devices with cavities and narrow slits and ducts should include the so-called boundary layer attenuation caused by thermal conduction and viscosity. The purpose of this paper is to present and compare different methods for including these loss mechanisms in analytical and numerical models. A simple circular geometry with a narrow tube has been used as a reference and is investigated both through measurements and the different models. The simulation methods compared are: i) traditional analytical approaches such as lumped parameter modelling and transmission line modelling, ii) numerical methods implemented into commercial packages, such as the low reduced frequency models as proposed by W. M. Beltman and implemented in ACTRAN and the linearized Navier-Stokes equations used in COMSOL Multiphysics, and iii) an implementation specifically made for this purpose using BEM and the full linearized model by M. Bruneau.
Vibroacoustic interface conditions between prestressed structures and moving fluids
Authors: Treyssède Fabien
Published: May 2008

Many applications involve coupling between prestressed solids and fluids (possibly flowing). Typical problems might be given by vibroacoustics of fluid-filled pressurized cavities, wave propagation, dynamics and stability of pipes conveying fluids. The goal of this work is to investigate jump conditions that hold for small linear perturbations at any impermeable interfaces, slip or bonded, plane or not, between fluids and structures in the presence of initial flow and prestress. First, the mixed Eulerian-Lagrangian description is briefly recalled. It yields an interesting unification between existing formulations for inviscid fluids (Galbrun's equation) and solids (updated Lagrangian formulation). Based on conservative equations obtained from this description, interface conditions are derived in an elegant manner thanks to the concept of generalized functions in distribution theory. These conditions are written in terms of a curvilinear coordinate system attached to the interface. They are shown to coincide with a direct linearization of standard Eulerian jump conditions. General interface conditions for displacement, stress, heat flux and temperature are given. As an example, these conditions are applied to the analysis of elastoacoustic wave propagation inside an inviscid fluid-filled pressurized duct. The combined effects of slip, prestress and initial flow are briefly discussed.
Segmental variability related to speech prosody - An articulatory-functional perspective
Authors: Xu Yi
Published: May 2008

Just like in the tonal aspect, variability abounds in the segmental aspect of speech. Here I argue that segmental variability, similar to supra-segmental variability, can be understood from an articulatory- functional perspective. That is, two independent sources of segmental variability co-exist: a) multiple layers of communicative functions, and b) articulatory mechanisms of their encoding. From an articulatory perspective, much of the segmental variability arises from the nature of the syllable as a product of generating time markers, namely, synchronized onsets of consonant, vowel, tone and phonation register at the start of each syllable as recurrent events that serve like clock ticks to enable time tracking by both speakers and listeners. Such time marking results in complete overlap of initial consonant and the following vowel, which is responsible for most of the variability known as coarticulation, and sequential offset of coda components in a syllable, making them susceptible to deletion and merger. From a functional perspective, segments as supralaryngeal articulatory movements encode not only lexical contrast, but also other functional contrasts such as focus, grouping, attitude, etc. Like the tonal aspect of speech, these extra-lexical information are probably encoded as modification of segmental targets that have been lexically assigned.
Prosodic Variation: Understanding Scope, Categoricity, and Recursion in Speech Production and Perception
Authors: Byrd Dani , Krivokapic Jelena
Published: May 2008

Prosodic structure refers to the level of linguistic structure above the segmental level, namely prominence and phrasal organization. We will examine both articulatory and perceptual characteristics of phrasal organization, and their interrelation. An experiment using articulatory movement tracking examines how far in time remotely from a boundary the effect of the boundary extends. In a second experiment (Krivokapic 2007), we examine how structural properties of a range of prosodic boundaries are reflected in perception--specifically, whether boundary perception is categorical or gradient. A third study considers whether prosodic junctures of the same category type (e.g, an intonational phrase boundary) can, when embedded, give rise in articulation to boundary signatures of measurably different strengths. That is, we evaluate the possibility of recursive prosodic structures of the kind that Ladd (1996) postulates. Taken together, these experiments inform us about structurally induced variability. They provide the opportunity to evaluate standard assumptions about prosodic structure such as the question of boundaries as symbolic or temporal events, categoricity, and strict layering. Throughout, we will consider how the pi-gesture framework (Byrd & Saltzman 2003) offers theoretical insight regarding issues of prosodic representation and realization. [Supported by NIH]
Stress, focus, and the roots of segmental variation
Authors: De Jong Kenneth
Published: May 2008

de Jong (JASA, 1995) proposed a definition of linguistic stress as variation in the articulation of segmental material; stress is variation on the hypo- to hyper-articulation dimension (Lindblom, 1990) localized to the syllable. This definition has suggested that the interaction of stress and segmental articulation will involve 1) linguistic conventionalization, since stress is a property of particular linguistic systems, 2) the structure of segmental contrasts, since hyper-articulation is driven by contrast enhancement, and 3) propensities in articulation, since hypo-articulation is driven by motor considerations. This paper reviews evidence for effects of linguistic conventionalization of stress. It further examines and compares the results of a number of experiments in segmental variation related to focus. Some dimensions of acoustic contrast, vowel quality, transition dynamics, and glottal timing, exhibit readily detectable and gradient variation as expected by a hyperarticulation model, and such variation is specific to the language's contrastive structure. Not all contrastive dimensions, however, are so affected, for example, noise associated with obstruent consonants. These patterns of results together suggest a functional interaction between the various speech gestures which may define a unit of speech at about the level of the syllable; the level which is the domain of expression of stress.