bluuebunny/crossref_metadata_2025 huggingface dataset:
Networking and Fusion of Disparate Acoustic Sensors for Battlespace Applications
Authors: Pham Tien , Whipps Gene
Published: May 2008

A network of distributed acoustic sensor systems on the ground and/or in the air can be used effectively for autonomous and remote intelligence, surveillance, and reconnaissance (ISR) applications. However interoperability of disparate sensor systems is a major challenge for current coalition force applications. Specifically, a network of acoustic sensor nodes can exhibit heterogeneity in a variety of dimensions. At the sensor-level, the acoustic sensors can vary in their types (e.g., cardioid vs. omni-direction) and in their responsiveness to transient and continuous sources. At the node-level, the acoustic systems can vary in their array configuration, platform mobility, node reactiveness (e.g., timeliness of response), and information processing and output. At the network-level, the acoustic systems can vary in their communication protocols and access mediums. Current R&D efforts within the US-UK International Technology Alliance seek to develop a "sensor fabric" technology to seamlessly connect disparate systems for networked sensing applications. Results from a recent field experiment to detect and locate moving ground targets, weapon firings, and explosions via a network of disparate acoustic sensor systems and sensing platforms (e.g., PDA's, workstations, motes and unattended ground sensor systems) are presented.
Performace Bounds for a Multi-Array Network Approach to Gunfire Detection and Localization
Authors: Roan Michael , Hoppe Elizabeth , Johnson Marty
Published: May 2008

Acoustics-based gunfire detection and sniper localization have become important in both military and civilian sectors. For the case of rifle fire, most current localization algorithms rely on estimating parameters using the projectile's cone-shaped shockwave and the muzzle blast. Previous studies have attempted to quantify shockwave detection performance as a function of range for various approaches such as wavelet matched filtering for the "N" shaped shockwave. Accurately detecting the shockwave is important because the shockwave shape can be used to determine bullet trajectory if the bullet velocity is known. A second layer of direction of arrival (DOA) estimation can be added by using the time difference of arrival between the shockwave and the muzzle blast. These DOA methods require a two step process of detection and estimation. In this work, a signal model is developed for a network of microphone arrays that receives the acoustic waveform generated by supersonic projectiles. The best-case localization performance of the multi-array network is quantified via the Cramer-Rao lower bound on the error in estimating shooter position. Results are illustrated using simulated data to generate CRLB ellipses on shooter position estimation error and via live fire experiments using several calibers and a multi-array network of microphones.
Phase calibration of hydrophone and its application in the reconstruction of underwater acoustic waveforms
Authors: Wang Yuebing , Li Shui , Huang Yongjun
Published: May 2008

Abstract: In this paper, both the reciprocal method and the optical method for the calibration of plural sensitivities of hydrophones are reviewed firstly. Then an experimental system is introduced in which with a 1.5MHz focusing transducer acting as a position indicator, phase responses of hydrophones can be calibrated easily and accurately. Measurements are carried out for different types of hydrophones and results are given in the frequency range 20kHz to 400kHz. Finally, with the plural responses of hydrophones included in the construction for the transfer function of the receiving system, acoustic waveforms produced by a projector are reconstructed in wide band from received signals, and a few conclusions are summarized from the experiment.
Imaging of Large-Scale Sediment Transport Dynamics with Multibeam Sonar
Authors: Simmons Stephen M. , Parsons Dan R. , Best Jim L. , Malzone Chris , Keevil Gareth M.
Published: May 2008

Multibeam Echo-Sounder (MBES) systems have developed rapidly over recent decades and are routinely deployed to provide high-resolution bathymetric imaging. Modern data handling and storage technologies have facilitated the logging of the back-scatter information previously discarded by these systems. This paper develops a novel methodology to exploit this logging capability to quantify the concentration and dynamics of suspended sediment within the water column. This development provides a multi-purpose tool for the holistic surveying of sediment transport by imaging suspended sediment concentration, associated flow structures and providing concurrent high-resolution bathymetry. This paper presents the results obtained from the deployment a RESON 7125 MBES in the field, with the aim of examining the dynamics of suspended sediment transport over dune bedforms and in the region of flow mixing between large rivers of significantly different suspended sediment concentration. Results from controlled tank tests are also presented, obtained using different types and mixes of sediment. The results demonstrate the capability of MBES systems to successfully resolve the contrast in suspended sediment concentrations. The large sets of data recorded in the two-dimensional MBES swath enables the real-time monitoring of suspended sediment transport and related flow processes on a scale previously unrealisable with single-beam acoustic systems.
On the acoustics of a specifically designed library discussion room with corrugated ceiling
Authors: Declercq Nico F. , Dewijngaert Katrien , Vanderhaeghe Katelijn , Verleysen Patricia
Published: May 2008

There is a discussion room at the library of Viipuri in Finland where the ceiling has been especially designed to enhance the acoustics and make every position within the room acoustically equivalent. In other words no matter where a speaker is standing, he is supposed to be heard equally well all over the room. For that purpose a corrugated ceiling has been constructed that must distribute sound optimally, at least from the point of view of a ray theoretical analysis. The numerical study presented here shows that the corrugation is such that the ray approach is not exactly valid and a plane wave expansion technique shows that the acoustics is much worse than it is supposed to be. A detailed description of the sound distribution as a function of the position of the sound source and the receiver is presented. The acquired knowledge is important for future construction of similar rooms.
Acoustic climate inside a canteen and mitigation solutions
Authors: Marsico Giuseppe , Brambilla Giovanni , Curcuruto Salvatore , Clapiz Monica , Betti Rinaldo , Riccardi Michele
Published: May 2008

The acoustic environment inside a canteen is an important feature to guarantee speech intelligibility and speech privacy, as well as to reduce the exposure levels. Unfortunately this aspect is not always properly taken into account as others, like cleanliness. This paper describes the case-study of the canteen at the National Agency for Environmental Protection (APAT), having a capacity of 220 seats. The acoustic environment has been characterized by measuring the main acoustic descriptors for speech intelligibility (Reverberation Time, STI, C80 and D50) and evaluating the noise exposure levels for the users. The comparison of the results with the recommended values showed a bad situation, especially in the speech frequency range, which requires acoustic corrections to improve the quality of the acoustic environment. To identify these corrections a numerical model of room acoustics, implemented on a commercial software, has been used to evaluate the effects produced by different corrections. The proposed correction improves the acoustic performances up to a good level, without modifying the structural parts and existing walls. Moreover, the solution allows to maintain the hall's usability without obstructing user mobility, screening natural lighting and reducing number of seats.
Localization of brief sounds by a bottlenose dolphin
Authors: Zaslavski Gennadi L.
Published: May 2008

Spatial hearing in dolphins is believed to be similar to that in humans. The same binaural phenomenon known for humans is used to explain sound localization in dolphins. However, the ability of a bottlenose dolphin to localize a sound in the vertical plane as accurate as in the horizontal plane appears to undermine binaural phenomenon concept in dolphin sonar. We found that directionality of the bottlenose dolphin transmit beam could account for most results on the bottlenose dolphin underwater object localization. In this paper passive localization and spatial discrimination of brief signals by a bottlenose dolphin is examined. The bottlenose dolphin was found capable of discriminating clicks with different intensity as well as a click and brief noise pulse simultaneously transmitted via transducers separated in azimuth by less than 1°. The dolphin was also able to discriminate a lead from a lag noise pulse at the transducer azimuth separation as small as 0.3°-0.4° and the lag delay as small as 20 microseconds. The results are discussed with regard to the bottlenose dolphin auditory time resolution and so called precedence effect phenomenon well known for the binaural system of humans.
Annotated odontocete recordings for developing automated detection and classification methods
Authors: Mellinger David K. , Klinck Holger , Heimlich Sara , Nieukirk Sharon
Published: May 2008

A free archive has been developed for research in automatic detection/classification of cetacean sounds. The archive contains many datasets, with each dataset comprising recordings and metadata for a given species and geographic area. This archive differs from other sound archives in three important respects: (1) Recordings are annotated to indicate where in time and frequency the sounds of a given species occur. These annotations are done manually to remove the bias of any automatic detection system. (2) The archive deliberately includes poor-quality recordings, recordings encountered in any realistic detection/classification application. (3) Since performance of detection/classification methods depends heavily on the SNR of target sounds, the archive includes each vocalization's SNR so performance can be effectively represented. Until recently, most recordings in the archive were of baleen whales [Mellinger and Clark, Applied Acoustics 67(11), 2006]. However, datasets for toothed whales and dolphins are now being incorporated. Initial efforts have been focused on beaked whales because of high interest for management and because of the difficulty of visual detection. To date, recordings of Cuvier's, Blainville's, Baird's, and Arnoux's beaked whales have been entered into the archive, as have those of bottlenose whales, pilot whales, and some delphinid species. Further contributions are welcomed.
Killer whales (Orcinus orca) and Bell Laboratories: What can information theory tell us about the communication system of this species
Authors: Lehmann Kenna D. , Wood Jason D.
Published: May 2008

In the 1950's Shannon and Weaver developed information theory as a statistical tool to determine the structure and organization within communication systems. More recently information theory has been applied to the study of animal communication. We gathered acoustic recordings of the Southern Resident killer whales in the inland waters of Washington State, USA, and British Columbia, Canada, from both land based and boat based acoustic arrays. Recorded calls were categorized using the accepted call catalog for this population. In this paper we will present our results from applying various Shannon entropies to the documented call sequences. One notable result is that the call repertoire is more redundant than is ideal to convey the maximum amount of information. This may be a result of their particular social system and behavioral ecology, or may be an indication of the amount of noise present in their acoustic environment. Comparisons will also be made with measures of information theory in other species.
Narrow band high frequency clicks from Hourglass dolphins (Lagenorhynchus cruciger)
Authors: Kyhn Line A. , Tougaard Jakob , Wahlberg Magnus , Beedholm Kristian , Madsen Peter T.
Published: May 2008

The source properties of toothed whale echolocation clicks are essential for evaluating the performance of biosonar systems. However, such data only exist for a small number of free ranging toothed whale species. Here we present a quantitative analysis of the first recordings of echolocation sounds from hour glass dolphins (Lagenorhynchus cruciger) made in the Drake Strait. Recordings were made with a vertical array of four broad-band, calibrated hydrophones that allows for acoustic localization and source parameter derivation. Only apparent on-axis clicks were used for analysis. Hour glass dolphins produce clicks with a mean peak and centroid frequency around 128kHz, a narrow, mean RMS bandwidth of 10kHz with no energy below 100kHz and a mean signal duration of 161μs. Echolocation clicks of hour glass dolphins are thus of the high frequency narrow band-width type (NBHF type) found in porpoises, a few delphinids of the Cephalorhynchus genus and the pygmy sperm whale Kogia breviceps, but are strikingly different from other dolphins. Acoustic convergence from vastly different genera and ecotypes suggest that evolution of NBHF clicks are adaptations to special auditory processing or acoustic crypsis rather than to habitat.
Geoacoustic uncertainties in matched-field inversions of ship-noise data
Authors: Tollefsen Dag , Dosso Stan E.
Published: May 2008

This paper applies geoacoustic inversion to ship-noise data recorded on a horizontal array deployed on the seafloor in an experiment conducted by FFI in the Barents Sea. A Bayesian matched-field inversion method is employed which quantifies geoacoustic uncertainties and allows for quantitative comparisons of results from different data sets. Estimates of sediment parameters and their uncertainties were obtained by inversions of low-frequency narrowband data from a quiet research ship at source-array ranges of 1-6 km and different orientations with respect to the array, as well as from a merchant ship at ranges of 6-8 km. Multiple, independent data segments are included in the inversion and shown to significantly reduce geoacoustic parameter uncertainties. The effect of the state of prior information on the ship track (e.g., well known or unknown) on geoacoustic information content is also examined. Estimates of the sound-speed profile and density of sediment are compared with results from inversion of data from a towed controlled-source, and with reference values from other geophysical data collected in the area.
Numerical simulation of shock wave generation and focusing in shock wave lithotripsy
Authors: Krimmel Jeffrey , Colonius Tim
Published: May 2008

Shock wave lithotripsy is a procedure where focused shock waves are fired at kidney stones in order to pulverize them. Lithotripters with different source mechanisms and reflector shapes (or lenses) are in clinical use, but prediction of focal region pressure is made difficult by nonlinearity and cavitation. We report on development of a numerical simulation framework aimed at accurate prediction of focal region pressures and bubble dynamics. Shock wave generation and beam focusing are simulated via the Euler equations with MUSCL-type shock-capturing scheme and adaptive mesh refinement (AMR). Electrohydraulic, electromagnetic, and piezoelectric-array lithotripters are modeled with axisymmetric geometries. In the electrohydraulic case, an expanding bubble model simulates spark firing. In the piezoelectric case, a boundary condition prescribing the motion of individual elements is used. Calculated peak pressures and pulse widths agree well with experimental data for the electrohydraulic and electromagnetic lithotripters. For the piezoelectric case, peak pressures are increasingly over-predicted by the model when more elements are fired, and reasons for this discrepancy will be discussed. Finally, we compare the spatial and temporal characteristics of the focal pressure fields for several clinical lithotripters in the context of observed stone comminution efficacy and tissue damage. This work is supported by NIH grant PO1 DK043881 and ONR Grant N00014-06-1-0730.
Photoacoustic microscopy for high-resolution imaging
Authors: Bost Wolfgang , Lemor Robert M.
Published: May 2008

Photoacoustics is a hybrid technology based on the photoacoustic effect that detects absorbed photons ultrasonically. Photoacoustic imaging combines ultrasonic resolution with high contrast due to light absorption depending on the physiology of the examined biological tissue. The resolution of conventional systems is not sufficient for in-vitro measurements of small tissue samples or individual cells. In this work, we present a high-resolution photoacoustic microscopy platform based on the SASAM acoustic microscope that allows high resolution imaging on living cells. The system based on an inverted optical microscope consists of a laser source for optical multi wavelength excitation (diode- and solid-state-laser) which emits nanosecond laser pulses with a wavelength in the near infrared spectrum (optical window). It allows the usage of different ultrasound transducers in the frequency range up to 300MHz. In addition to the photoacoustic imaging mode, all common optical modalities are implemented. Pure acoustic imaging mode is used for reference imaging. The developed photoacoustic microscopy platform is a system for high-quality volumetric imaging in different scanning modes. 3D offline reconstruction is possible based on the presented 2D imaging. The system was characterized by in-vitro measurements with a lateral resolution better than 100μm in the confocal mode.
Imaging tissue and wavefront control: Application to acousto-optics and photoacoustics
Authors: Ramaz François , Bossy Emmanuel , Loriette Vincent , Gigan Sylvain , Boccara Albert-Claude
Published: May 2008

Although optical waves do not exhibit the same ability to be manipulated as e.g. electromagnetic waves up to a few GHz or acoustic waves, for which field emitters-detectors are available, various tools are nevertheless available in the optical domain which open the path to tricks which can be used in the context of sound-light detection. In the purely optical domain, one knows the impact of deformable mirrors led to adaptive optics which is now coupled to OCT for retinal examination. Real time holography leads to complex wavefront synthesis and are useful in acousto-optics (AO) to monitor very complex speckle field distributions. Phase conjugation which is in certain conditions equivalent to time reversal, starts to be used for wavefront retrieval after propagation in turbid media, one can think to use it for AO signal monitoring; moreover matrices of spatial light modulators allow to control light not only spatially but also in the frequency domain and open the field to new astonishing experiments. We will discuss a few applications and perspectives offered by these new devices to the field of biomedical imaging.
Acoustic modeling for designing sonic logging tools
Authors: Kinoshita Toshihiro , Hori Hiroshi
Published: May 2008

Formation acoustic properties such as velocity and attenuation provide useful information regarding rock type and formation fluid. Sonic logging is one of the principal measurements to evaluate the presence of hydrocarbons in the well and to enable an efficient and safe production of oil. Unfortunately the sonic measurement is affected by the tool itself. Suppressing or attenuating the tool wave, which propagates along the logging tool and is received by the sensors, is directly related to the accuracy of the answer products. In order to improve the measurement quality and to increase the efficiency of logging operations, the structure of sonic logging tools must be well understood. A sonic tool with known effects is decidedly more complex and acoustic modeling incorporating the tool structure details is becoming essential to better sonic tool design. The methodology of numerical modeling used to predict the response of a sonic tool is to be presented.
Use of rapid protyping techniques in transducer manufacture
Authors: Hutchins David , Billson Duncan R. , Bradley Robert J. , Ho Kwok S.
Published: May 2008

This paper will describe the use of a rapid protyping technique, known as micro-sterolithography, for the manufacture of ultrasonic transducers. There are two main types to be described. The first is a MEMS-type capacitive transducer, this being an example of a capacitive micromachined ultrasonic transducer (CMUT). This can be made with all the main structural elements fabricated from polymers, so that no silicon processing is required. Experiments have investigated the properties of these devices, operating in air, water, and in contact with a metal surface. The technique has also been used to make electromagnetic acoustic transducers (EMATs), by forming the main structure from polymers and including a metal coil. These are interesting developments, which may have application to the fabrication of many types of acoustic MEMS devices.
Increasing power-efficiency of a micro-machined pump transducer for a parametric transmitting array in air
Authors: Lee Haksue , Moon Wonkyu
Published: May 2008

Parametric array applications in air, such as high directional loudspeaker system, have been studied with a large radiator (generally D⩾300mm) to generate high intensive sound beams required for nonlinear interactions. However, conventional transducer requires high electrical power because its electro-acoustic efficiency is too low due to an acoustic impedance mismatch. For mobile applications, a high efficient transducer is required. As an alternative pump transducer, a feasibility of a micro-machined ultrasonic transducer is studied. The efficiency can be improved by applying a thin-film membrane, overcoming the impedance mismatch. The efficiency of micro-machined transducer is simulated with a reduced dynamic model and compared with that of a conventional transducer. Two types of unimorph piezoelectric micro-machined ultrasonic transducers are designed and fabricated as small pump transducers for a ranging sensor and a loudspeaker. The electro-acoustic efficiency and dynamic characteristics related with primary wave generation are mainly examined in this work. The radiation characteristics, directional beam patterns and axial pressure distributions, of primary and secondary waves are also measured and compared with theoretical results. Throughout this work, feasibility of the proposed pump transducer is shown, but further work is also required for practical applications. [Research supported by MRCnd and ADD-UD070054AD of DAPA]
A developmental approach to voice science
Authors: Stadler Elmer Stefanie
Published: May 2008

Vocal development had been studied mostly with a focus on speaking, and only rarely, on singing. Traditional theories on singing development are often based on wrong premises, e.g. eurocentrism, and reliable analyses of singing are missing or selective. A new theory - inspired by the principles of Piaget's theory -, and a new methodology - based on acoustic measures - are proposed. The voice starts to organise at birth, and gradually adapts to the cultural surrounding and its conventions concerning language, music, and social rules. Vocal and musical behaviour are highly adaptive and constructive, and concern two symbolic systems: music and language. The child develops the voice by playing and imitating. The development proceeds from sensorimotor activities towards more and more conscious actions and thoughts. In order to study children's singing, computer aided programs were devised to analyse and represent pitch, timing, pitch qualities, and syllables. This method yields complex configurations of these parameters describing children's song singing. Detailed descriptions allow to reconstruct the strategies children apply to invent or learn new songs. The empirical results from children at various ages demonstrate that the focus on the analysis of the organisation of the vocal expression is a promising research strategy.
Rate of change of Fo in performance singing
Authors: Scherer Ronald C. , Radhakrishnan Nandhu , Boominathan Prakash , Tan Haidee
Published: May 2008

Johan Sundberg has had a strong interest in the vocal behavior of singers of different styles and nationalities. This tribute talk emphasizes the voluntary change of rate of fundamental frequency in performance singing of ornaments and vibrato. The "taan" gestures from Northern Indian classical singing, the "pulse patterns" in Carnatic Southern Indian classical singing, and pitch change in classical western coloratura singing constitute the primary corpus for this study of Fo rate change. Rate of Fo change varied from approximately 20 to 120 ST/s for soprano pitch change, 8 to 20 ST/s for the Southern Indian pulse patterns, and 7 to 60 ST/s for the Northern Indian taan gestures. What these rates depend upon and rates from other ornaments will be discussed, as well as the relation to maximum Fo rates in the literature, performance needs, perceptual characteristics, and control.
The influence of plectrum thickness on the radiated sound of the guitar
Authors: Carral Sandra , Paset Martin
Published: May 2008

It is generally thought that the human ear is very sensitive to subtle changes in sounds. In the context of musical instruments, one important aspect to study is how much the physical attributes of any given instrument have to differ so that a human can perceive a difference in the produced sound. In the case of the guitar, it is unquestionable that when the string is plucked at a particular position, some of the differences on the produced sound of the instrument are introduced by changes in how the player plucks the string (playing technique). However, given the wide variety of plectrum types, materials and thicknesses, it is hypothesised that the player is not the only parameter that influences the sound, but that the plectrum itself plays a significant role in the sound production. This paper presents a study whereby a guitar is played with three plectra of different thicknesses with an artificial plucking machine. The radiated sound is recorded, and subsequently analysed using the program SNDAN. Physical and psychoacoustical attributes of the sound are calculated from the resulting analysis. A thorough comparison of these results obtained for the three different plectra is presented and discussed.
Transparent boundary condition for acoustic propagation in lined guide with mean flow
Authors: Redon Emmanuel , Ouedraogo Boureima , Bonnet-Ben Dhia Anne-Sophie , Mercier Jean-Francois , Chambeyron Colin
Published: May 2008

A finite element analysis of acoustic radiation in an infinite lined guide with mean flow is studied. In order to bound the domain, transparent boundary conditions are introduced by means of a Dirichlet to Neumann (DtN) operator based on a modal decomposition. This decomposition is easy to carry out in a hard-walled guide. With absorbant lining, many difficulties occur even without mean flow. Since the eigenvalue problem is no longer selfadjoint, acoustic modes are not orthogonal with respect to the L2-scalar product. However, an orthogonality relation exists which permits writing the modal decomposition. For a lined guide with uniform mean flow, modes are no longer orthogonal but a new scalar product allows us to define the DtN operator. We consider first the case of an infinite rectangular two-dimensional lined guide with uniform mean flow in order to present the methodology. Then, some extensions will be presented: non-uniform two-dimensional geometries by calculating potential mean flow, and cylindrical axisymmetric three-dimensional problems with uniform mean flow.
Upgraded BB64700 locomotives - Noise Management Plan during the redesign process
Authors: Dalle Sebastien
Published: May 2008

To extend the working life of its BB 64700 locomotives, SNCF decided to upgrade a fleet of 19 tractive units. Priorities for the upgrading work include changing the motor and its cooling system, adding air conditioning to the cab while meeting new environmental obligations and improving cab acoustics. An acoustic model that combines calculations and experimental data is used as a platform to specify maximum allocated acoustic power to each system suppliers. The global approach to sub-structuring and acoustic synthesis is based on decomposition of the product in a main structure and several noise sources, and that their acoustic and vibration energy propagates via different identified transfer paths. The model, which is updated throughout the design process, serves as a decision tool to enable corrective action plans if a clause might be not respected. In the context of this project, measured noise levels on the upgraded locomotive meet SNCF specifications for interior and exterior acoustic according to the defined operating conditions (idling, max load traction).
Non stationary tire-road noise analysis using large array beam forming in the time and frequency domains
Authors: Ollivier François
Published: May 2008

In the framework of the REBECA Project founded by the ADEME, one seeks to provide a description of the tire-road noise source from the exterior of the vehicle perspective. Far field acoustic imaging techniques were proposed to identify the sources. Therefore an optimised array of 120 microphones, 4 m in diameter, was modelled and built. Measurements of the noise produced by a car mounted on a roll were performed in a semi anechoïc room. The front car axle was driven at various constant speeds and to rising speeds as well. Beam formed images and point signals have been post-processed with a 125 kHz sampling rate in order to derive space and time analysis of the pressure field in the vicinity of the tire-roll contact point. The high rate movies processed clearly exhibit periodic phenomena generated around the contact point, while the tire structure borne source appears to be insignificant. Results of frequency and order analysis are also presented in this attempt to provide an interpretation of the tire/road contact noise in terms of source models.
The effect of grinding and grooving on the noise generation of Portland Cement Concrete pavement
Authors: Wulf Tanya , Dare Tyler , Bernhard Robert
Published: May 2008

In this investigation, studies have been done to understand the effects of various grinding and grooving parameters to investigate their effect on noise generation at the tire-pavement interface. Grinding uses diamond-infused blades that are closely-spaced such that the fins between the blade tracks break off exposing an entirely new surface. For grooving, the blades are more widely spaced such that the fins do not break off and the surface texture remains largely unchanged except for grooves that are used for moisture control. Both procedures, used independently or in combination, have an effect on the noise produced by the tire-pavement interaction. Variation of grinding parameters was shown to have as much as a 3 dB effect on noise generation. Variation in grooving parameters has a secondary effect, which allows grooves to be added to texture without overall effect on overall noise. This paper will illustrate the effects on noise of the different parameters, such as grinding depth, blade width, and blade spacing, for grinding and grooving.
ONERA's activities on airframe noise numerical simulation
Authors: Manoha Eric
Published: May 2008

Airframe noise, or noise generated by flow around the airframe (high lift devices, landing gears and cavities), is a major contributor to the overall noise of large commercial aircraft in the approach phase. For several years, ONERA has been involved in the development of methodologies for the numerical simulation of airframe noise. These hybrid methods generally combine (i) CFD computations for the near field flow, including unsteady CFD techniques such as LES, DES and NLDE, and (ii) acoustic (CAA) propagation techniques in the mid- and far-field. A large range of acoustical methods is available for the propagation of sound waves in uniform or heterogeneous mean flows, either from the family of integral methods (Lighthill, FWH, BEM) or in the domain of (non-linear or linearized) Euler equations in perturbation. The key challenges of these hybrid methodologie are (i) the ad-hoc coupling between individual techniques and (ii) the availability of reliable and dedicated experimental database for the validation. The paper presents a survey of ONERA's activities in this field, with applications to (i) single symmetrical airfoil, (ii) high lift wing with deployed slat and flap, (iii) landing gears and (iv) cylindrical cavities.
A phase-pegistration acoustic method for nondestructive testing of porous materials
Authors: Tsaplev Valery M.
Published: May 2008

The well-known method of complex vibrator is modified for the purpose of meas-urements of complex elastic moduli (Young's and shear moduli) and corresponding values of internal friction, that change under the influence of different external factors. These external factors are: mechanical uniaxial compressive or tension stresses, temperature, electric and/or magnetic fields, etc. Different variants of phase-control methods in the self-excitation system of the complex vibrator are considered depending on the connection of the active piezoelec-tric bars: active external control or adaptive self-control at prescribed level of the in-put excitation level. The system contains the recording device to record quick changes of elastic and unelastic parameters of the test specimen. The system also contains the termostatic switch with the active control device to provide the specimen temperature control at prescribed algorithm. The method is used for the nondestructive testing of the acoustic properties of different materials under the influence of the stepwise applied mechanical stress.
Nonlinear-nonequilibrium wave propagation in sandstones
Authors: Pasqualini Donatella , Tencate Jim A. , Habib Salman
Published: May 2008

The transition from linear to nonlinear-nonequilibrium dynamical elasticity in rocks is of considerable interest in seismic wave propagation as well as in understanding the basic dynamical processes in consolidated granular materials. We have carried out a careful experimental investigation of this transition for Berea and Fontainebleau sandstones. These experiments have showed the existence of two strain regimes. At low strain (10-9 up to 10-7) the rocks behave elastically as classical (Landau-Lifshitz theory) nonlinear materials. At higher strains memory effects due to a driven nonequilibrium state complicate the characterization of the nonlinear behavior. The understanding of this second region is not trivial. The main focus of this work is to review the behavior of the low strain, nonlinear region and to report on new experiments meant to understand more about the behavior in the nonequilibrium regime.
Scattering of Rayleigh wave by microcrack with interacting faces
Authors: Lomonosov Alexey M. , Hess Peter
Published: May 2008

Scattering of short Rayleigh pulse by a partially closed surface-breaking microcrack is studied both experimentally and numerically. The microcrack was generated by a nonlinear surface wave with shock. In practice such type of cracks corresponds to fatigue or thermally generated ones. The crack was irradiated by a probe laser-generated Rayleigh. The scattered acoustic field at the surface, monitored by means of optical detector, consisted of the reflected and transmitted Rayleigh waves, longitudinal and shear acoustic waves excited by mode-conversions at the crack. Characteristic size of the crack was 50-100 μm, experimental bandwidth was 5-200 MHz. Scattering was simulated numerically in finite differences. For modeling the partially closed crack we proposed a simple one-parameter model, which takes into account weak interaction between the crack faces. It was shown, that interaction changes the predicted frequency-dependent transmission and reflection coefficients significantly. On the basis of fitting the simulated acoustic field to the measured one, the evaluation of the crack size has been performed. In this work frequency dependence of the following three parameters were employed for that purpose: transmission and reflection coefficients, and the time delay of the transmitted pulse. Obtained estimates were compared to the direct microscopic measurement of the crack.
Foundations of the ultrasonic non-destructive method of determination of stresses in near-the-surface layers of solids
Authors: Guz Alexander
Published: May 2008

The ultrasonic non-destructive method under consideration is intended for measurements of uniaxial and two axial stresses in the near-the-surface layers of relatively rigid materials (metals, alloys and similar material). This method is intended for measurements of the actual, assemble, operating, preload prestress and other stresses. Above mentioned stresses must be considered as initial or residual stresses taking into account the theory [1] under consideration. In this case the disturbances (displacements and stresses of the 3-D linearized theory [1] of elastic waves in bodies with initial or residual stresses) arise due to ultrasonic vibrations. Description of the non-destructive method under consideration and information on instruments and devices for measurements are presented. Some examples of non-destructive determination of stresses in near-the-surface layers of materials are presented also as applied to the residual stresses arising at electric welding and to the operating stresses arising at loading. Additional information is presented in monograph [1]. References: 1.Guz A.N. Elastic waves in bodies with initial (residual) stresses. Kiev: "A.C.K." Publishers, 2004. – 672 p. (In Russian).
Use of microphones to record windspeed and turbulence in planetary environments
Authors: Lorenz Ralph D.
Published: May 2008

A major feature of any planetary acoustic measurement is noise due to ambient winds, or to the motion of the measurement platform through the air. Venera 13 and 14 recorded sound on the surface of Venus: the amplitude of the microphone signal was interpreted (by dynamic pressure scaling) to recover a windspeed. The Huygens probe at Titan also recorded sound levels during descent and on the surface with a passive microphone and an acoustic sounder. The author has made passive microphone measurements made on a rotating aerospace vehicle (an instrumented Frisbee) which show spin modulation and a variation with flight speed and angle of attack. He has also used microphones as a crude wind sensor on an array of 20 meteorological stations used to study dust devils in Arizona. All of these observations will be reviewed. Lessons learned for future planetary measurements, and prospects and methods for microphonic anemometry (especially with limited telemetry bandwidth) will be discussed.
Sound production by partially premixed flames in a stagnation flow
Authors: Schuller Thierry , Duchaine Patrick , Zimmer Laurent
Published: May 2008

In the perspective of combustion noise reduction, understanding mechanisms of sound generation from combustion of non perfectly mixed reactants is a major challenge. Sound production is thus investigated for vortices impinging a flat laminar flame in a stagnation flow. Such a configuration helps to better understand sound production from turbulent flames. A study with different compositions of the main flow and surrounding gases - mixtures of nitrogen, air and methane - is carried out under the same mean flow and perturbations conditions. Time traces of radiated sound pressure and chemiluminescence emission from radical species present in the reaction zone are characterized together with detailed imaging of the flame and flow motions. Elements of classical combustion noise theory are used to identify the main noise sources when air or fuel is entrained by the vortex interacting with the flame.
Low-order modelling of unsteady flame behaviour in a spray combustor
Authors: Arthur David M. , Dowling Ann P. , Cant Stewart
Published: May 2008

The effect of mass flow rate perturbations on the stability of a liquid-fulled annular aeroengine gas turbine is investigated using a three-dimensional uRANS code. The simulations are performed on a single sector of an idealised annular gas turbine geometry. A Lagrangian fuel spray description is used with a Monte Carlo solution of Williams' spray equation. Broadband mass flow fluctuations are imposed at the combustor inlet and dilution ports, and the effect on heat release is quantifed using flame transfer functions. The excitation of inlet and dilution flows leads to signifcant unsteady combustion and the implications for self-excited oscillations are considered. The numerical results are then compared to a low-order model which is developed to account for the different physical mechanisms responsible for unsteady heat release when the inlet and dilution port air mass flow rates are perturbed. The low-order model is used to predict the possibility of self-excited oscillations as well as to investigate the potential of altering the phase and relative magnitude of the inlet and dilution port excitation as a possible means of controlling thermoacoustic oscillations.
Numerical prediction of interaction between combustion, acoustics and vibration in gas turbines
Authors: Pozarlik Artur , Kok Jim B.
Published: May 2008

The turbulent flame in the lean combustion regime in a gas turbine combustor generates significant thermo-acoustic instabilities. The flame can amplify fluctuations in the released heat, and thus in the acoustic field as well. The induced pressure oscillations will drive vibrations of the combustor walls and burner parts. Stronger fluctuating pressure results in stronger fluctuations in the wall structure. Due to fatigue the remaining life time of the hard ware will be reduced significantly. This paper investigates modeling of acoustic oscillations and mechanical vibrations induced by lean premixed natural gas combustion. The mutual interaction of the combustion processes, induced oscillating pressure field in the combustion chamber, and induced vibration of the liner walls are investigated with numerical techniques. A partitioned procedure is used here: CFX-10 for the CFD analysis and Ansys-10 for the CSD analysis are coupled to give insight into a correlation between acoustic pressure oscillations and liner vibrations. These results will be compared with the available experimental data. The data are gathered in a purpose built 500 kW/5 bar premixed natural gas test rig.
Thickness determination of a multilayered system of different materials by natural frequencies
Authors: Zhou Changzhi , Li Mingxuan , Mao Jie , Wang Xiaomin
Published: May 2008

This paper is focusing on the relationship between the natural frequencies of a multilayered system of different isotropic elastic materials and the thickness of each layer. A relevant ultrasonic method for thickness determination of a multilayered system by natural frequencies has been developed. The natural frequencies are numerically calculated from the normally incident reflection coefficient of a "steel-epoxy resin-aluminum-thin polymer" structured lamination. Some natural frequencies are sensitive to one layer thickness in certain range while the others are invariable. This phenomenon is explained by the defined strain energy ratio, and used for our thickness inversion. The measured natural frequencies of a specimen show good agreement with the theoretical ones. All the natural frequencies are taken into account, and the simulated annealing method is employed for the thickness inverse calculation of the multilayered structure. The average relative errors of calculated thickness of the each layer are -0.7%, 35%, -1.3% and -6.1%, corresponding to the real values: 1957μm, 16μm, 1913μm and 54μm.
Factoring end-user expectations into the sound design process of computer keyboards
Authors: Boulandet Romain , Lissek Hervé , Sauvage Sylvain , Robert Jacques
Published: May 2008

The poor acoustic comfort of usual commercial products is often perceived as annoying. Today, more and more companies have realized that sound can be an important component of product attributes and image. They are interested in having acoustic guidelines for enhancing their products sound quality. The objective of this research is to quantify the objective and subjective noise production of computer keyboards, and hence to translate the pleasantness in an objective way. Our strategy consists in developing both benchmarks and listening tests to ensure that sound design process never looses sight of the end-users expectations. The presented work proposes an original methodology to define what keystroke sound matches the image of a pleasant keyboard. We also approach what acoustic characteristics have a significant influence on the global appreciation of keystroke sounds. Good results have been obtained showing a strong correlation between perceptive cues and metrics.
Detection of missing modal frequencies
Authors: Stoelinga Christophe N. , Lutfi Robert A.
Published: May 2008

The amount of information about a source that can be recovered from sound is naturally limited by the ear's ability to resolve individual modal frequencies unique to that source. To measure these limits, listeners were asked to detect, in a standard two-interval, forced-choice task with feedback, which of two sounds on each trial contained a missing partial. The frequencies of the partials corresponded to the ideal modes of a simply-supported, rectangular plate. Plate surface areas and height-wide ratios were chosen to produce the same bandwidths (125-1125, 250-2250 or 500-4500 Hz) for different numbers of partials (11, 16 or 24). Overall level of the sounds was roved to discourage detection based on simple level differences. Detection of five highly-practiced listeners was largely independent of the frequency of the lowest partial, being best for partials 1-3, 1-4 or 1-6 for 11, 16 or 24 partials in total, respectively. Mutual masking among the higher-number partials is given as the likely cause. The results are discussed in terms of their implications for the identification of rudimentary source attributes from sound. [Work supported by NIDCD grant 5 R01 DC006875].
A means for comparing normal and impaired listeners in spatial hearing
Authors: Hafter Ervin R.
Published: May 2008

In our computer controlled Simulated Open Field Environment (SOFE), a computer generates simulated sources and echoes in an anechoic chamber. The SOFE has evolved over many years through ideas and hard work from a superb group of graduate students and post docs including Francoise Briolle, Tom Buell, Poppy Crum, Eric Jensen, Kourosh Saberi, Chris Stecker, Bernhard Seeber, and Miriam Valenzuela, as well as advice from such luminaries as Georg von Bekesy, Arnold Leiman and, of course, Jens Blauert. The ready use of Head Related Transfer Functions (HRTFs) with headphones raises the question, "Why the SOFE?" The answer is that each subject enters the environment with his or her natural HRTF and hearing apparatus intact, thus allowing comparisons between patients with cochlear implants or hearing aids, as well as listeners with normal hearing. Since its inception, this environment has been used to examine precedence, the role of relative level in echo suppression, multiple factors in auditory motion perception, and ventriloquism. This presentation will review some of the more interesting results.