bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of RANS modelling and LES to the prediction of noise from a simple cold propane jet
Authors: Stanko Tanya , Fairweather Michael , Pourkashanian Mohamed , Ingham Derek
Published: May 2008

Numerical simulation, combining computational fluid dynamic and acoustic models, is useful as an aeroacoustic tool that is effective in identifying components or surfaces that generate significant amounts of noise, and can thereby provide opportunities for early design changes. In this work, numerical solutions of a cold turbulent jet of propane issuing from a circular nozzle are used to provide velocity information at a Reynolds number of 68,000. Predictions provided by large eddy simulation are compared with Reynolds-averaged Navier-Stokes solutions derived using a second-moment turbulence closure, as well as with experimental data available in the literature. Reasonable agreement with data is found, and these solutions are used subsequently as the basis for noise predictions. The first acoustic model employed is based on Lighthill's theory using the Goldstein broadband noise source formalisation that postulates axisymmetric turbulence superposed on the mean flow. The second approach is based on Ffowcs-Williams and Hawkings theory which implies that the far field sound is computed from an integral formulation with all quantities evaluated on a control surface, with the control surface itself assumed to enclose all nonlinear flow effects and noise sources. The simulation results reported in this paper confirm previous experimental works presented in the literature demonstrating that jet noise is modified by inlet conditions.
Uncertainties of Measured and Calculated Aircraft Noise and Consequences in Relation to Noise Limits
Authors: Thomann Georg
Published: May 2008

The uncertainties of measuring and calculating aircraft noise have been analysed in a thesis at the ETH Zurich. The thesis provides information and methods for estimating uncertainties. It shows possibilities for handling these uncertainties and provides guidance to legal and administrative bodies on how to deal with such uncertainties when applying the legal noise limits. To estimate the uncertainties of calculations and measurements the Swiss aircraft noise calculation program FLULA2 and a great deal of measured data have been analysed. Using radar data it is possible to achieve a standard uncertainty of the calculated Leq between 0.5 dB for day-time and 1.0 dB for night-time. The analyses also show that the uncertainty of measurements at automated stations is in the same order of magnitude as the calculations. Therefore the annual calculations and measurements of aircraft noise show no significant deviations. Furthermore with FLULA2 it is possible to present the uncertainty at a confidence level of 90%. It is now up to administrative and legal bodies to set up rules on how to account for uncertainties of calculations in evaluating noise situations close to the legal noise limits.
Nonlinear Propagation of Screech Noise
Authors: Punekar Jothi , Avital Eldad
Published: May 2008

This study investigates the non-linear propagation of screech noise emitted by supersonic jets. Supersonic jet noise consists of three components: mixing, broadband and screech noise. In order to generate broadband and screech noise the jet has to expand imperfectly, meaning shock waves are formed inside the potential core and interact with the surrounding shear layer. The feedback between the generated noise and the nozzle cause the screech noise pattern. It is associated with high frequency (annoying to the human ear). Near field screech noise obtained from Large Eddy Simulation (LES) of circular supersonics jets is investigated using the Burgers equation, taking into account thermo-viscous effects. The Burgers equation is commonly used to investigate non-linear propagation effects. The initial screech signal is found to consist of two main frequency modes. Significant non-linear effects appear during propagation although the pressure amplitude is no more than a few percentages of the ambient pressure. Saw tooth waves are generated and the amplitude is found to decrease as 1/sqrt(t) for low viscous medium according to Lighthill' 'bunching' theory. Further high frequencies are also generated. Finally, geometrical attenuation is discussed by transforming the plane wave propagation to cylindrical form.
Decomposition of the Lighthill source term and analysis of acoustic radiation from mixing layers
Authors: Margnat Florent , Fortuné Véronique , Jordan Peter , Gervais Yves
Published: May 2008

Acoustic radiation from jet flow has been studied extensively by means of theoretical, experimental and numerical approaches over the past decades. Unfortunately, the mechanisms responsible for the production of sound by unbounded turbulence in subsonic flows remain unclear. For advancing our fundamental understanding of these mechanisms, the development of specific analysis tools is needed. Our study is based on a decomposition of the Lighthill source term, which is known to contain all the existing links between the fluid flow and the acoustic field. Ten subterms are written with the help of physically meaningful quantities such as velocity, density, dilatation and vorticity. The methodology is tested through the two-dimensional compressible mixing layer flow in spatial development, at a Reynolds number of 400 and a Mach number of 0.25. A direct numerical simulation of the flow and its acoustic radiation is performed and used as a reference solution. Acoustic field generated by each source terms is predicted computing the integral solution of Lighthill's equation. Effect of the compressibility on the balance between the contribution of major subterms is of key importance. Directivity and convective effects are identified as well.
Increase of sound proofing of air duct
Authors: Shubin Igor , Gusev Vladimir , Pestereva Marina
Published: May 2008

One of ways of noise protection from transit air duct is increase of sound insulation of air duct by different acoustical materials. The main interest of this work is in comparative analysis of acoustic efficiency different thermal insulation materials for use as sound insulation coverings. The report contains analysis of the distribution of noise through round and rectangular air ducts. There was discovered different tipes of thermal insulation materials such as easy made foam materials and fibrous materials. Tests are executed in the reverberation chamber. The received results have shown advantage of a fibrous material.
On the correlation of the acoustic signal of microphones mounted on a flat plate to the turbulence of an impinging jet
Authors: Reichl Christoph , Boeck Michelle , Tilser Wolfgang , Lang Hermann , Haindl Klaus , Reining Friedrich , Opitz Martin
Published: May 2008

An axial symmetric fan driven by a brushless actuator with variable frequency is used to generate a turbulent circular jet leading to typical core-velocities of around 10 m/s (Re = 99000). The jet impinges on a flat plate. Turbulence is generated using different sets of turbulence generators in the pipe consisting of meshes, rods, cubes and spikes. The turbulent flow field downstream of the pipe outlet is measured using two-axis hot wire anemometry with a temporal resolution of a minimum of 48 kHz. The CTA probe is positioned using an automated three-axis traversing system. 12 Microphones are mounted on a flat plate and are used to capture the wall pressure fluctuations. CFD calculations are performed for the different turbulence generators and are compared to the acoustic and CTA signals. An important aspect of the work is the simultaneous recording of both the CTA- and the acoustic signals in the experimental and numerical approach. This allows for the calculation of correlation patterns between turbulence and the acoustic signals of the plate mounted microphones.
Acoustic feedback of control elements in cars
Authors: Treiber Alexander S. , Gruhler Gerhard
Published: May 2008

Due to the complexity of modern car's on-board systems, car manufacturers tend to use menu based user interfaces. These interfaces offer a relatively low number of control elements for a large number of functions. Optimization of both haptical and acoustical feedback of the remaining control elements can improve both acceptance and security of operation. Since cars nowadays are no longer sold simply as technical but as lifestyle products it is crucial for the success that the potential customer perceives every single aspect of the car to be valuable. Obvious examples are exterior design and material quality. Since the user interface of the car can be judged even before a test drive the feeling of buttons and switches is a key aspect. This work presents the results of a jury test which is part of an ongoing research project focused on acoustical feedback. Subjects were asked to judge both recordings of real control elements as well as synthesized signals which were presented on purpose-built hardware. Based on the subjective results the recorded signals were analyzed in order to identify spectral features which correlate with the subject's responses.
Influence of time-varying booming noise on automotive comfort
Authors: Richard Florent , Costes Francois , Roussarie Vincent
Published: May 2008

Noise level reduction is the main preoccupation for acoustic engineers in the automotive industry. Huge progresses were made during the past decades thanks to the use of acoustic materials and specific intake or exhaust silencers. In the future, vehicles will have to be lighter and engines optimized to ensure very low energy consumption. This sets new compromises between mass, performances and acoustics, in particular for booming noise that can be very affected by mass reduction or exhaust modifications. Acoustic specifications must therefore be optimized to guarantee customer's comfort in spite of these new constraints. In this paper, we study the impact of time-varying booming noise on customer's comfort on acceleration sound samples. We performed several customer tests to evaluate the impact of different time-varying booming profiles on comfort and to find out an acceptability threshold for booming.
Time-domain modeling of porous media acoustics
Authors: Wilson David K. , Collier Sandra L. , Ostashev Vladimir E. , Marlin David H. , Aldridge David F. , Symons Neill P.
Published: May 2008

Sound waves propagating in porous media are subject to strong dissipation and dispersion. This paper elaborates upon several recent publications by the authors regarding the time-domain description of these effects. The foundation is a relaxational description of the viscous and thermal dissipation in a rigid porous medium, which is shown to possess an exact, analytical conversion from the frequency to the time domain. The complex density and bulk modulus operators transform to temporal convolutions between a causal response function and the acoustic field variables. When the convolutions are neglected, the equations reduce to the well known Zwikker-Kosten phenomenological model. The relaxation function can be inverted to provide an equivalent time-domain formulation from the complex volume and compressibility operators. Although a direct time-domain transformation of the specific impedance from the relaxation model has not been found, an accurate broadband approximation thereof can be transformed. The resulting time-domain boundary condition (TDBC) describes the absorptive and reactive response of the material. The response of the boundary decays slowly, as the inverse square root of time, but efficient numerical procedures are formulated that allow the TDBC to be approximated with a small number of recursive filters.
Effect of curvature on the scattering coefficients of Herschel-Quincke tubes
Authors: Poirier Benjamin , Ville Jean-Michel , Maury Cédric , Foucart Félix
Published: May 2008

The concept of Herschel-Quincke (HQ) tubes has been known since the beginning of the 20th century and was shown to be of interest to reduce tonal and broadband noise from turbofan engine. To help to understand the physical phenomena underlying the HQ concept, Hallez & Burdisso have developed a 3D theoretical model. The 3D modelling technique considers the tubes-inlet interfaces as finite piston sources that couple the acoustic field inside a hard-walled duct with the acoustic field within the HQ tubes. This model makes a geometrical approximation by considering the tube as a straight duct whereas in reality it corresponds to a curved duct. In this paper, a model is presented which takes into account the curvature of the bend by integrating two differential equations for the pressure and velocity in the bend, projected on the local transverse modes. Results of some typical coefficients of the scattering matrix [S] deduced from the curved HQ model are compared with the 3D straight tube model, the experimental results and the numerical results. The curvature is shown to modify the HQ resonances and then have to be taken into account in the analytical formulation.
On effectiveness of vibration isolation using super-elastic rail support combined with booted sleeper or floating slab
Authors: Wu Tianxing X.
Published: May 2008

Ground vibration or structure vibration of viaduct due to railway traffic can be reduced by use of super-elastic rail support, booted sleeper and floating slab to isolate vibration transmission from the track to the infrastructure. In this study modeling in the frequency domain of track structure dynamics and wheel/rail interaction is carried out. Wheel/rail interaction and transmission to the infrastructure of the interaction force due to a relative displacement excitation are simulated. The effectiveness of vibration isolation is analyzed for booted sleeper or floating slab combined with super-elastic rail fastener. It is found that the combination of super-elastic rail fastener with booted sleeper or floating slab can effectively reduce the wheel/rail interaction force in the medium frequencies, compared with the booted sleeper or floating slab track using usual rail pad. The combination also shows better ability to block vibration transmission from the track to the infrastructure in the medium and high frequencies.
Noise and vibrations at tram track intersection
Authors: Lakusic Stjepan , Bogut Marijan , Tkalcevic Lakusic Visnja
Published: May 2008

In urban areas noise and vibration due to public traffic diminish the quality of life. In Zagreb, tram traffic is the most important form of public transport. Tram network has 120 km of the tracks and 190 trams are used for passengers transport every day. In the movement of the vehicle over track, the interaction between the wheel and track plays the most important role in the field of noise and vibrations. The increasing of noise and vibrations are particularly emphasized at track intersection where a given number of track switches and crossings are installed. This paper presents an experimental study of noise and ground vibrations through the passage of three types of tram vehicles. The measurements were done on the tram intersection with the highest traffic volume in Zagreb's tram network. Two types of track construction were analyzed, discrete and continuous rail fastening system. During the track reconstruction at this intersection, the existing discrete rail fastening system was replaced with a continuous. Because of that, the measurements were carried before and after reconstruction at the same test points. Test results have showed significant reductions of noise and vibrations at track intersection in the case of continuous rail installation.
A parametric study on the isolation of ground-borne noise and vibrations in a building using a coupled numerical model
Authors: Fiala Péter , Gupta Shashank , Degrande Geert , Augusztinovicz Fülöp
Published: May 2008

Underground traffic induced vibrations and noise in buildings are a major environmental concern in urban areas. To quantify these vibrations a numerical prediction model has been developed and validated. A coupled FE-BE model is used to compute the incident ground vibrations due to the passage of a train in the tunnel. A dynamic soil-structure interaction model is used to determine the vibration levels of the building. The soil-structure interaction problem is solved by means of a 3D boundary element method for the soil coupled to a 3D finite element method for the structural part. An acoustic 3D spectral finite element method is used to predict the acoustic response. The coupled numerical model is used to quantify the efficiency of vibration and noise mitigation measures at different stages of the vibration propagation chain. Vibration isolation with a floating slab track is modeled on the source side, base isolation is incorporated in the structure model, and a box-within-box arrangement is considered for the isolation of re-radiated noise in the building's rooms. The insertion gain of the three methods is compared using the model of a multi-story portal frame office building subjected to ground-borne vibrations from an underground railway line.
Noise mapping of major roads in Milan District
Authors: Bisceglie Alessandro , Zambon Giovanni , Artom Fabrizio , Viganò Mattia , Bertellino Franco , Longoni Marco
Published: May 2008

The paper deals with noise map calculation, according to the first deadline of the END (Environmental Noise Directive, 2002/49/EC), for Milan district major roads. The roads with more than six million vehicle passages per year have been estimated to cover 405 km out of 1090 km total. Noise emission has been calculated from peak hour flow data for each segment of the whole road network and from some local traffic direct measurements. A statistical method to assign mean flow values to each road segment has been used, according to Italian reference periods. These data enable to use an acoustic model on a wide area with several line sources in order to obtain noise propagation maps of Lden and Lnight indicators. A procedure to estimate people exposed to different noise levels, as required by the END, has been also studied. Through a geographic information system it has been possible to intersect population input data (demographic density for different areas, buildings use type and buildings volumetric data) and noise mapping data. Every step of the procedure has been carried out complying with WG-AEN Good Practice Guide recommendations, on the basis of the best available data in Milan district.
Strategic noise mapping in slovak republic
Authors: Kamenicky Milan , Petrak Peter
Published: May 2008

In the EU there is an ongoing process of strategic noise mapping and action planning. The goal is to determine the noise produced by the main noise sources - road, rail and air transport and industrial facilities and the exposure caused by them in densely populated agglomerations. Subsequently it is necessary to consider possibilities, how to reduce additional increase of noise levels in the environment. Authors participated in the strategic noise map development process and this paper comprises the information about the measurement and calculation results of traffic and industrial noise in Bratislava and in the slovak republic. Presentation of strategic noise maps and actions plans in Slovakia.
Dynamic wheel/rail forces induced by trams at low frequencies
Authors: Chiello Olivier , Maldonado Marc
Published: May 2008

This work is part of various experimental and theoretical investigations into the noise and the vibrations caused by trams in Nantes, France. It focuses on the problem of the low frequency vibrations induced in the track and the ground and particularly on the excitation mechanism at the wheel/rail interface. In order to estimate the corresponding dynamic wheel/rail forces, axle-box vibrations have been measured on a carrying bogie in various vehicle and track configurations. Additionally, a specific instrument has been used to measure the rail unevenness at large wavelengths likely to excite the vehicle/track system in the low frequency range. Finally, the vertical receptance of the different tracks has been measured by using an impact hammer. In the paper, all these experimental results are presented and the validity of a simple vehicle/track interaction model is discussed.
Variance in predicted structure borne sound power due to simplified characterisation of the source
Authors: Evans Tomos A. , Moorhouse Andy T.
Published: May 2008

Theoretically the structure borne sound power transmission from a vibration source to a receiving structure can be predicted using the mobility method. In order for all the power transmission mechanisms to be accounted for the source and receiver mobility matrices must contain the mobilities for all degrees of freedom (three translational and three rotational) for each contact point and the transfer mobilities between; each contact point, each degree of freedom and each degree of freedom at each contact point. In practice reliable measured data for some degrees of freedom is difficult to obtain, so simplified source characterisation methods are required, for example using only certain degrees of freedom. The novel contribution of this paper is to investigate the variance in the predicted structure borne sound power transmission calculated when some degrees of freedom are missing, and when the source is approximated as a single equivalent excitation. The investigation was carried out using numerical simulations of simplified source and receiver structures.
The effect of acoustic waves on stick-slip behaviour in sheared granular media, with implications to earthquake processes
Authors: Johnson Paul A. , Savage Heather , Knuth Matt , Gomberg Joan , Behringer Robert , Marone Chris
Published: May 2008

We are studying the effects of acoustic waves on sheared granular material, with two goals in mind: one is to understand the intriguing physics that arises in this experimental system, and the other is to see if such experiments offer insight into earthquake processes, in particular the phenomenon where one earthquake triggers another nearby, or distant, earthquake ('dynamic earthquake triggering'). We conducted laboratory experiments of stick-slip in granular media using a double-direct, shear apparatus, while applying low amplitude vibration as well as pulsed waves. We find that vibration and pulses significantly perturb the shearing behaviour of the granular material, and that the manifestation of vibration is extremely complex, including strong material memory of the acoustic perturbation, that persists. We note that the wave disturbance must take place near the critical point, where the granular material is near failure, otherwise no effect is observed. Also, horizontal loads on the system can eliminate the effect if they arelarge (⩾4-5 MPa).
Static and dynamic nonlinear behaviors of unconsolidated granular media
Authors: Lu Zhiqu , Sabatier James M.
Published: May 2008

Unconsolidated granular media such as sands, soils, and glass beads, exhibit astonishing static and dynamic nonlinear behaviors that are quite different from those of elastic materials such as liquids and crystalline solids. They can generally classified as mesoscopic hysteretic nonlinear materials since hysteresis is a universal phenomenon for these materials. In order to understand the mechanism and to quantify the nonlinearity of unconsolidated granular materials, a series of studies have been conducted on re-molded unconsolidated soils. The systematic research consists of three parts: (1) a triaxial cell test with pre-defined stress-paths and sound speed measurement, focusing on the exploration of the role of hysteresis in both linear and nonlinear acoustics; (2) the phase shift method, using non-classical nonlinear acoustic theory to measure the hysteretic nonlinearity parameter; (3) the study of fluid effects on the hysteretic nonlinearity parameter. The study reveals many static and dynamic nonlinear behaviors of soils, including: nonlinear stress/strain relationship, hysteresis loop, end-point memory, much greater dynamic elastic modulus than static elastic modulus, strain-amplitude dependence of elastic modulus, linear resonant frequency shift and phase shift relationships against strain, extremely high values of the hysteretic nonlinearity parameter, harmonics generation, and moisture effects.
Theoretical study of the diffraction fields generated by a fluid-loaded plate with two-surface corrugation
Authors: Herbison Sarah W. , Declercq Nico F.
Published: May 2008

A renewed interest has recently emerged in the study of the interaction of elastic waves with periodic structures, including periodically corrugated surfaces. From prior theoretical and experimental studies of the diffracted fields generated by such surfaces, it is well known that periodically corrugated surfaces can be used to generate ultrasonic surface waves, which are especially important in the field of ultrasonic non-destructive evaluation. In general, anomalies appear in the reflection and transmission spectra due to the presence of the corrugation, and these anomalies can be correlated with the surface waves generated. The present work has extended the theory of diffraction on periodically corrugated surfaces to the case of a fluid-loaded plate with both sides corrugated. The unique filtering effects and diffraction phenomena that can be achieved with such a structure are examined and related to the creation of surface and plate waves.
Sound absorption of advanced textile materials
Authors: Bolkovac Ivan , Domitrovic Hrvoje , Bozic Martina
Published: May 2008

Today's acoustic applications demand an ever greater array of materials used for acoustic treatment of spaces for both professional or non-professional use. Elements like absorbers, diffusers and silencers are met with increasingly strict demands, both aesthetic and functional. That is the reason why we were interested in acoustic qualities (absorption coef.) of different kinds of textile materials that could be used in building or finishing such elements. Textile materials range from conventional to high-performance textiles. The latter, with their advanced qualities (both acoustic and mechanical) promise a much wider area of application and further specialized use, both as stand-alone elements or their parts.
Flow resistivity profile inversion for a porous medium
Authors: Depollier Claude , Sebaa Naima , Naas Mouna , Castagnede Bernard R. , Fellah Zine , Lauriks Walter
Published: May 2008

Predictions for the low frequency sound waves propagation in a porous medium needs the knowledge of the flow specific resistance of the medium. We present a scheme for the flow resistivity profile inversion for a layered medium. In the framework of the fluid equivalent model a closed-form relation of the resistivity profile with the Fourier transform of the reflection is derived. It provide a straightforward way to perform the reconstruction of the profile. The result show a strong correlation between the flow resistivity profile and the reflection coefficient in this model. Some numerical simulations are given as examples of the applicability of this scheme.
An index to quantify the through-thickness symmetry of sound absorbing materials
Authors: Salissou Yacoubou , Panneton Raymond
Published: May 2008

In this work, an extension of the theoretical formulation of the transfer matrix to non symmetrical sound absorbing porous materials is carried out. From this extension, an index of asymmetry is proposed and discussed. This index allows one to quantify the through-thickness asymmetry of a sound absorbing porous material. This index may be used for quality control or to assess the symmetry of the material in terms of its acoustic properties (absorption, reflection, impedance, propagation constant). To validate the application of the index of asymmetry, samples made up from two layers of porous materials are studied. Each so-constructed two-layered sample is seen as an equivalent asymmetrical single porous layer with a sudden change in its physical properties. The acoustic properties of each sample are then measured in the direct and inverted configurations (i.e., when both sides of the sample are facing successively the incident wave). Their values are compared in terms of the asymmetry index of the equivalent single layer. From these tests, an index value is suggested. Above this value, the acoustic properties of a sound absorbing material should be considered as being not symmetrical.
Film thickness determination by laser ultrasonics
Authors: Lemaire Michaël , Jenot Frédéric , Ouaftouh Mohammadi , Xu Wei Jiang , Duquennoy Marc , Ourak Mohamed , Côte Renaud , Salenbien Robbe , Sarens Bart , Lauriks Walter , Glorieux Christ
Published: May 2008

The thickness of films deposited on substrates is crucial for their thermal, electrical, optical behaviour. These properties are essential in thin film applications, especially in the field of microelectronics. In this study, we are interested in thickness determination of silver and gold films deposited by evaporation on a silicon substrate by using an ultrasonic non-destructive technique. In particular, the well-known laser ultrasonic technique is used to generate and detect the surface acoustic waves. Results obtained by two complementary methods allowing a non-contact measurement in a large bandwidth (from 5 MHz to 200 MHz) are presented, and the dispersion of the Rayleigh wave propagation velocity is analyzed to determine the film thickness.
Line-focus beam photoacoustic imaging of surface and undersurface defect simulated on a planar specimen
Authors: Hoshimiya Tsutomu , Hatake-Yama Mika
Published: May 2008

A theoretical formulation of photoacoustic (PA) imaging with a line-focus beam (LFB) for surface and undersurface simulated defect was performed. Equivalence between 2D surface defect photoacoustic tomography (PAT) and X-ray CT was derived. PAT imaging experiment was carried out A second harmonics of a LD-pumped YAG laser was used as a LFB. The laser power was 45mW. The length and width of a laser beam on a specimen was 25 mm times 0.65mm The measured area was 27mm x 27mm, while the reconstructed area was 18mm x 18mm. 64 times 64 resolution image was reconstructed from the rotation and translation scanning. Reconstructed PA image agreed with the PA image obtained with a point-focus PA imaging. The frequency dependence of thermally diffused image agreed well with the theoretical prediction (thermal diffusion length is inversely proportional to the square root of modulation frequency) Under surface PAT image was obtained by a thermal wave diffraction formula, and the simulated image agreed well with the experimental data.
Generation of Acoustic Wavelength Shorter Than 10nm By Means Of Nonlinear Acoustic
Authors: Zhang Shuo , Péronne Emmanuel , Belliard Laurent , Perrin Bernard
Published: May 2008

As the size of the structure decrease toward the nanoscale, their acoustic properties get closer to the THz range. Traditional techniques based on piezoelectric transducer or the Brillouin diffusion can hardly reach the adequate frequency range. However, if we tightly focus short optical pulses, we can expect to generate high frequencies due to nonlinear effect during the propagation of the acoustic pulses. Moreover, such small source could be used to image buried structures. We have developed an pump-probe experiment based on a Ti:Sa oscillator using microscope objectives and 2 axis displacement stage to study nonlinear propagation and diffraction of acoustic wave in 3 dimension. We have studied 356-μm thick GaAs substrate and have demonstrated the generation of acoustic longitudinal wavelength as short as 10 nm. Due to the acoustic dispersion during the propagation, acoustic solitons are observed for high excitation power. Thanks to the use of interferometric detector, the acoustic pulses are characterized in great details. Such experimental development can help us to study the properties of transmission and reflection of buried nanosystem such as single quantum well or phonon nanocavities.
LED-based Stroboscopic Schlieren System
Authors: Hanhijärvi Kalle , Kassamakov Ivan , Aaltonen Juha , Hæggström Edward
Published: May 2008

A stroboscopic Schlieren system is proposed to characterize acoustic fields in transparent media. Schlieren imaging has been used to visualize beam profiles of ultrasonic transducers mostly in liquids. The method is sensitive to gradients in refractive index, and can thus be used with solids and fluids. A stroboscopic illumination synchronized with the ultrasonic vibration (controllable phase delay between the illumination and the ultrasonic drive signal), allows obtaining an image of a propagating tone burst. An LED source provides relatively fast response time for high measurement bandwidth. Incoherent light doesn't suffer from unwanted interference, as with laser sources. Our setup employs two 90° off-axis parabolic mirrors. Non-reflected light is blocked with spatial filtering which is achieved with a knife-edge, placed at the focal point of the focusing mirror. We first present a time-averaged Schlieren image of the acoustic field of a 7.5 MHz focusing transducer, as a proof-of-principle result. Then a custom-built LED-based stroboscopic illumination system is used to visualize wave propagation in water emitted by a high power 20 kHz transducer. Schlieren imaging is useful in applications, where non-contact characterization of acoustic fields is necessary.
Vector surface velocity measurement using contour scanning laser vibrometers for the detection of landmines
Authors: O'Malley Patrick F. , Teresa Woods J. , Vignola Joseph F. , Judge John A. , Jarzynski Jacek
Published: May 2008

Much work has been done studying the detection of buried landmines using acoustic excitation and measuring the vibration response of the ground using Laser Doppler Vibrometry (LDV). We examine the benefits of measuring the full three-dimensional velocity response of the ground surface when a landmine is present. Three-dimensional velocity measurements provide a richer data set for identification of buried targets and avoid potential errors associated with projecting the surface velocity vector onto a single laser line of sight direction. We present results of a study conducted using landmines buried in sand in a laboratory environment. The data were obtained using a novel five-axis laser vibrometry system, which uses a single point LDV system to measure the surface of the sand from multiple angles at each measurement location. Data will be presented showing the consequences of a buried landmine on the three-dimensional velocity response of a contoured ground surface.
Elastic-anisotropic properties of rocks along the Finnish Drill Hole (OKU) section in the depth range down to 1 km
Authors: Kovalevskiy Mikhail
Published: May 2008

The Finnish drill hole OKU was drilled in the south-eastern Baltic Shield (Finland). The drill hole limiting depth is 2516m. The goal of investigations was determination of elastic and non-elastic characteristics of 14 rock samples taken within 1.0km depth. The determinations were done on the basis of the latest improvement of the acoustopolarization method with devices for determining elastic properties [1]. The study of the rock sample properties from the drill hole section showed that they are all elastic anisotropic and pertain to the transverse-isotropic and orthorhombic symmetry types. A slight change in the compression and shear wave velocities with depth can be observed. The effect of linear acoustic anisotropic absorption has been registered in the samples. The nature of this effect manifestation is related to the presence of microcracks of the natural character. The effect of depolarization of shear waves was registered in some samples which suggests the presence of the angular unconformity between the directions of the LAAA elements and elastic symmetry elements. The pattern of change in the anisotropy factors for compression and shear waves with depth is manifested in a similar way. REFERENCES 1. Gorbatsevich F.F. Acoustopolariscopy of rocks. Apatity, Acad. Sciences, 1995, 204 p.
Features of acoustic emission at various influences on rock samples
Authors: Voznesenskiy Alexander S. , Viljamov Sergey V.
Published: May 2008

In the report special features of acoustic emission (AE) in the rock samples during its deforming, loading, dissolving and heating are discussed. The AE-activity and spectral characteristics of AE at the frequency band from on 30 kHz up to 500 kHz versus time at various influence stages and forms are analyzed. For example the amplitudes at the frequencies 30-90 kHz during deforming of carnallite are higher than these ones during its dissolving. It means the cracks at the deforming are about 4-10 mm and these ones at the dissolution are about 1-3 mm. These results can be used for the recognition of influence forms and stages.
A numerical study of the onset of granular avalanches
Authors: Staron Lydie
Published: May 2008

Granular media can either exist in a jammed state, in which their behaviour can be seen as solid-like, or they can exist in a dilute state and flow as a fluid would. In this contribution, we are interested in the mechanisms prevailing in the transition between solid-like and fluid-like behaviour, specifically in the case of the onset of granular avalanches. Therefore, discrete numerical simulations of granular flows are carried out. The focus is set on the analysis of the stick-slip dynamics preceeding the trigger of the avalanche; the existence of precursors to the flow, and their distribution in space and time will be investigated.
Wave propagation in stratified fluid flows: Application of the Stroh formalism to Lagrangian acoustic perturbations
Authors: Poncelet Olivier , Ottenio Mélanie
Published: May 2008

We consider the problem of harmonic waves propagating in non uniform fluid flows in presence of either solid interfaces (elastic walls), or jumps of mechanical properties or jumps of fluid convection-speed. The acoustic field is described by taking into account Lagrangian perturbations referred to an Eulerian frame related to the moving fluid. In contrast to the case of eulerian perturbations, the lagrangian description enables us to introduce the acoustical displacement in the problem and therefore to write the continuity conditions in a simple and unambiguous way: normal acoustical displacement is always continuous through an interface between either solids or (moving) fluids; the normal acoustical stress is also continuous in most of the practical cases (boundary layers, vibrating walls). We express the wave equation as an ordinary differential system by making use of the Stroh formalism from which analytical and semi-analytical results can be obtained for any arbitrary profile of the flow properties. This formalism, coupled with Peano-Neumann series expansion and Frobenius power series, enable us to compute modes dispersion in elastic ducts, and reflective properties of a mixing layer in between two fluids in relative motion. Some analytics on those problems is provided.
Object-related negativity indexes perception of sounds beyond the echo threshold
Authors: Sanders Lisa D. , Zobel Benjamin , Keen Rachel , Freyman Richard L.
Published: May 2008

The ability to isolate a single sound source among concurrent sources and reverberant energy is crucial for understanding the auditory world. The precedence effect describes an experimental finding that when listeners are presented with identical sounds from two locations with a short onset asynchrony, they report hearing a single source with a location dominated by the lead sound. We recently showed that event-related potentials (ERPs) elicited by click pairs differ for trials on which listeners do and do not report hearing the lag sound as a separate source. Specifically, when participants report hearing two sounds, we observe a negativity between 100 and 250 ms, previously termed the object-related negativity (ORN). These results indicate that the precedence effect reflects top-down cognitive influence over early neurosensory processing. Additionally, the study provides support for the claim that the ORN, initially reported for sounds perceived as two concurrent pitches, indexes auditory object perception. The effects on the ORN of repeating identical click pairs, a condition that has previously been shown to increase echo thresholds, will also be discussed in the context of listeners forming complex models of room acoustics based on what they hear in a specific setting.
Masking release based on fine-grain temporal pitch cues in speech-like stimuli - mechanisms and implications for the cocktail-party phenomenon
Authors: Clark Nicholas R. , Krumbholz Katrin
Published: May 2008

One of the most important cues for segregating wanted from unwanted sounds when listening in noisy environments is temporal regularity (or harmonicity), which gives rise to the perception of pitch. This study measured masked signal detection thresholds when both the signal and the masker are complex tonal stimuli similar to speech. Detection was considerably easier when the pitch of the masker differed from that of the signal. A control experiment involving non-simultaneous masking revealed that this pitch-based release from masking was not due to spectral differences between the signal and the masker. A second experiment investigated the effect of a pitch difference between the signal and the masker on the audibility of certain perceptual features of the signal when the signal is presented at a supra-threshold level. Two features were used that are known to be particularly important for speech perception: amplitude modulation and spectral profile related to formant frequencies. The supra-threshold tasks enabled to quantify the unmasking effect of pitch on the processing of these features over and above the effect on the signal detection threshold. The results provide new insights into the low-level processes involved in the cocktail-party phenomenon. Acknowledgement: Work supported by the Medical Research Council.
Perceptual sensitivity to high-frequency interaural time differences created by rustling sounds
Authors: Wiegrebe Lutz
Published: May 2008

ITDs are recruited to localize sounds in azimuth. ITDs can be extracted from low-frequency sounds or from the envelopes of high-frequency, complex sounds. Studies of the latter have included amplitude-modulated or transposed tones. A recent study showed that not the degree of envelope fluctuation, as quantified by the envelope 4th moment, determines sensitivity to envelope ITDs but the envelope spectrum and with it the interaural cross-correlation function of the auditory envelopes provide a good description of envelope ITD sensitivity. Here we use a different class of high-frequency stimuli, namely noise stimuli generated with different degrees of roughness which resemble natural rustling sounds. Stimuli are generated with a Gaussian-noise carrier and an aperiodic, rectangular modulator of statistically different duty cycle. The results show that ITD sensitivity increases both with increasing roughness and increasing bandwidth of the rustling sounds. While the effect of bandwidth on ITD sensitivity is in line with previous conclusions, the effect of roughness is not. ITD sensitivity for rustling sounds elicited ITD thresholds as low as 32 μs, i.e., considerably lower than reported in previous studies with transposed stimuli. The data show that high-frequency rustling sounds provide strong temporal localization cues which the auditory system can effectively exploit.
Lateralization of unidirectional frequency sweeps at high frequencies
Authors: Hsieh I-Hui , Saberi Kourosh
Published: May 2008

The ability to lateralize FM sweeps at high frequencies was investigated in a 2IFC 2-down 1-up adaptive design. Four conditions were examined in which the unidirectional FM stimulus swept either up or down in frequency, and either linearly or logarithmically between 3 and 8 kHz with the onset frequency roved by 15% on each presentation. The signal was an interaural delay in the waveform's fine-structure and hence its instantaneous frequency. The waveforms to the left and right ears had simultaneous envelopes and were filtered with the inverse of the headphone transfer functions to eliminate frequency-dependent interaural level differences. Results showed that sweep durations exceeding 25ms produce near-chance performance. Thresholds monotonically improved with increasing sweep rate to a lower asymptote of approximately 100 microseconds. Counterintuitive reversals of lateral position percepts were observed for down-sweeps which were inconsistent with lateralization based on envelope outputs of frequency-matched filters.
Are interaural time and level cues processed by separate or integrated networks in the human auditory cortex
Authors: Edmonds Barrie A. , Krumbholz Katrin
Published: May 2008

Listeners use two cues to localise the position of a sound source in the horizontal plane: interaural time differences (ITDs) and interaural level differences (ILDs). It is thought that these two cues are encoded separately at the level of the brainstem, but are likely to be combined at higher levels in order to produce a representation of sound azimuth. In the current study, we used electro-encephalography (EEG) to investigate whether the cortical representation of a stimulus containing both ITDs and ILDs reflects separate processing of ITDs and ILDs or a combined code for perceived sound location. Stimuli were presented over headphones using a continuous stimulation paradigm; a diotic control sound was presented for 1.5 seconds followed immediately by a dichotic test sound for 250 milliseconds. Evoked responses were recorded for test stimuli containing an ITD only, an ILD only, or both an ITD and an ILD indicating either the same or opposite source azimuths. When the two cues were in opposition, the stimuli were perceived as central and were indistinguishable from the diotic control sound. However, they still elicited a strong cortical response. This suggests that ITDs and ILDs are encoded separately in the auditory cortex.
Analysis of everyday sounds which are extremely annoying for children with autism
Authors: Johansson Örjan , Lindegren David
Published: May 2008

Extreme sensitivity to noise is a problem that almost all autistic children suffer from. A sound that is extremely annoying does not need to be loud. However, the characteristics and temporal variations of these sounds are sparsely investigated. The aim of this study is to increase the knowledge about these extremely annoying sounds so they can be avoided by better design criteria for classrooms and venues like that. By interviewing teachers and parents a number of everyday sounds were identified and binaurally recorded. Examples are vacuum cleaners, ventilation noise, washing machines and pouring water. Detailed psychoacoustic analyses of this type of sounds were achieved by a listening test procedure in three parts. First 16 children composed different types of vacuum cleaner sounds trying to minimize annoyance in two different tests, a) keeping original sound pressure level. b) adjusting to acceptable loudness. In the second part, teachers working with autistic children performed a listening test to evaluate some of the composed sounds from part 1 and modified versions of them. The third part was performed by children to validate the results. The results showed that Roughness, Loudness and an index defined as High frequency tonality were the most important characteristics.
Effect of reverberation on loudness perception
Authors: Raimond Andrew , Watkins Anthony J.
Published: May 2008

Stimuli with a slow-attack/fast-decay (S-F) envelope are judged to be louder than stimuli with a temporally-reversed, equal-energy version of the same envelope (fast-attack/slow-decay or F-S). It may be that the energy in the tails of F-S stimuli is discounted from loudness judgments because it is perceptually attributed to room reverberation. Here we examine the characteristics of real-room reverberation that affect loudness perception, particularly the way that reverberant tails tend to be de-correlated at the two ears. Our experiments used reverberation from real-room measurements of binaural room impulse responses (BRIRs). We ask if the perceived reduction in loudness of F-S stimuli relative to S-F stimuli is still apparent with dichotic sounds processed by the BRIRs.