bluuebunny/crossref_metadata_2025 huggingface dataset:
Bach on other planets or why acoustic sensors make sense in planetary science
Authors: Petculescu Andi , Leighton Timothy G.
Published: May 2008

The European Huygens probe, which landed on Titan in 2005, is the only planetary probe so far to incorporate passive and active acoustic sensing. Acoustic wave motion is intimately coupled with an atmosphere and thus can give first-hand information on that environment. Motivation for acoustic sensing in planetary atmospheres abounds: anemometry, turbulence measurements, soil characterization, sound generation by lightning, acoustics of liquid hydrocarbon flows, cryovolcanoes, dust devils, quantitative fluid spectroscopy, thermometry, atmospheric boundary layers etc. In this paper it is shown quantitatively how the environments of Mars, Venus, and Titan affect the generation and propagation of audible sound differently. To exemplify, a musical fragment with a rich frequency content was chosen (Bach's Toccata and Fugue in D-minor played by one of the authors) and passed through the three planetary ''filters.'' Appreciation of the nature of these sounds will inform the design of acoustic sensors for future space probes. Furthermore, a demonstration that the physics is sufficiently understood to predict these sounds indicates that the same understanding can be applied quantitatively to interpret alien sounds to estimate the environmental conditions.
Acoustic Anemometry on Mars
Authors: Williams Jean-Pierre , McEwan Ian
Published: May 2008

Acoustic anemometers provide wind measurements with high sensitivity, temporal resolution, and accuracy, and are in many ways superior to the hot wire technique anemometers currently and previously flown to Mars. An anemometer is under development that employs an internal model of how sound is changed by a particular gas mixture with respect to wind speed and temperature to derive these values. This is done by measuring the transfer function (attenuation and phase versus frequency) of sound between two transducers with a very wide spread-spectrum signal and comparing this with its internal model. While sonic anemometry is the premier technique for research studies of winds on Earth, the acoustic properties differ substantially from atmosphere to atmosphere and it is not valid to assume that an existing terrestrial system can provide heritage for a planetary instrument. Further, current multi-gas acoustic models rely on constants derived from experiments performed in conditions far from the planetary application intended here. Since the parameters of the model must be well defined in our approach, the instrument's ability to accurately measure transfer functions will be used in experiments to improve our knowledge of the behavior of various calibrated gas mixtures over relevant temperatures and pressures.
Solid-fluid coupling on planets: from seismology to acoustics and beyond
Authors: Garcia Raphael F. , Lognonné Philippe , Occhipinti Giovanni
Published: May 2008

On Earth, solid-fluid coupling is responsible for acoustic signals created by quakes or volcanic eruptions which have been observed by infrasonic sensors or through ionospheric perturbations produced by infrasounds. Similarly volcanic explosions, ocean surface waves and ocean internal gravity waves are producing seismic signals. A specific normal mode coupling theory has been developed for the whole solid/ocean/atmosphere Earth system in order to model these phenomena. Recent developments for the observation and modeling of the infrasonic waves created by quakes and tsunamis have focused on the ionospheric perturbations produced by the exponential amplification of vertically propagating infrasonic and gravity waves. On Earth, these tools are particularly interesting for the observation of seismic surface waves and tsunamis in the open ocean where sensors are not present. However, the interest is even stronger to infer the internal structure of planets for which the deployment of seismometers is almost impossible. Theoretical modeling of solid/atmosphere coupling on Venus is presented, including open questions concerning the attenuation of infrasounds by Venus atmosphere. An attempt to observe quake signals with VIRTIS instrument on board Venus Express ESA mission is also described. Finally, a mission analysis tool and other ideas for future planetary investigations of atmospheric acoustic normal modes are discussed.
Impact of acoustic boundary conditions on confined combustion noise
Authors: Lamraoui Ammar , Richecoeur Franck , Schuller Thierry , Ducruix Sébastien
Published: May 2008

The noise produced by aircraft engines at take-off and landing can be very harmful for airport neighbors, an issue that became recently particularly crucial. While combustion instabilities, where a strong coupling between flames and acoustic modes of the combustion chamber cause very high levels of harmonic sound, the wide bandwidth noise emitted by confined flames in stable situations is less well-documented. It has been recently shown by Tran et al. (2007) that varying the burner upstream acoustic boundary condition was a very efficient method for damping combustion instabilities and creating ideal conditions for the study of combustion noise. In the present study, the noise level induced by stable combustion is investigated for various upstream conditions. The test bench consists in a swirl stabilized burner, connected to a rectangular combustion chamber, equipped with microphone ports for acoustic measurements. The 40 kW burner is composed of two identical stages fed with air and propane. A photomultiplier equipped with a narrow band filter measuring the CH* spontaneous emission from the flame is used to study heat release fluctuations in the flame. Time-resolved measurements are carried out and spectral analysis of pressure measurements and light emissions are performed for various inlet impedances.
Green's function model for a Rijke tube with a distributed heat source
Authors: Heckl Maria A.
Published: May 2008

A Rijke tube is an open-ended tube with a compact heat source (flame or hot gauze) inside. The heat source is commonly modelled by the "nτ law", which assumes a point source releasing heat at a rate that is proportional to the velocity (delayed by a time lag τ) at the heat source. The present paper aims to extend this model to include distributed heat sources. A distributed source is simulated by a row of point sources with individual heat release rates and time lags. The acoustic processes in the tube will be modelled by Lighthill's acoustic analogy equation, combined with a Green's function approach. The occurrence of thermo-acoustic instabilities will be predicted for different properties of the heat source. Geometrical complications in the tube, such as a blockage and a jump in cross-section, as well as a jump in mean temperature, will be taken into account.
Influence of Temperature Gradients on the Sound radiated from Flames
Authors: Piscoya Rafael , Ochmann Martin
Published: May 2008

The far field pressure of a turbulent flame can be determined using the standard boundary element method (BEM) if the sound pressure or its derivative is known at a closed surface (control surface) surrounding the flame, as long as the medium outside the control surface is homogeneous. If temperature gradients are present, the homogeneous Helmholtz equation is no more valid. In that case, the wave equation can be rewritten in form of an inhomogeneous Helmholtz equation with a source term that depends also on the unknown pressure. Using the "Dual Reciprocity BEM" the integral form of this wave equation can be solved involving only surface integrals, so that the sound field can still be computed from field values at the control surface. The cases under study consider a volume of hot gas with a temperature distribution that is prescribed or obtained from a CFD simulation. The influence of the temperature gradients on the sound field can be evaluated by comparison of characteristic quantities like sound power and radiation patterns, with and without temperature gradient.
Localization of Sound Sources in Combustion Chambers
Authors: Pfeifer Christian , Moeck Jonas P. , Enghardt Lars , Paschereit Christian Oliver
Published: May 2008

To optimize the efficiency and to minimize the emissions of pollutants, modern combustion chambers for aeroengines or stationary gas turbines run in high temperature ranges with lean fuel-air mixtures. The disadvantage of this combustion mode is its susceptibility to the formation of thermoacoustic instabilities. These self-excited oscillations are an unacceptable noise source and, furthermore, they reduce the durability of the combustion chamber significantly. The focus of this paper is the localization of combustion noise sources in enclosed combustion chambers. This can be achieved using the acoustical nearfield information from pressure measurements with wall-flush mounted sensors. The spatially bounded region, where the sound sources are suspected, is discretized by a grid of monopole sources. A system of linear equations for the source strengths is built based on the relations between the sound sources and the sound pressure field, theoretically caused by the assumed sources of the grid. The source strengths are calculated by inverting the system of equations. A spatial variation of the source grid allows the scan of likely regions of sound sources to finally deduce their original distribution. Numerical simulation results will be shown to illustrate the potential and the limits of the proposed method.
Frequency sweeping and fluid flow effects on particle trajectories in ultrasonic standing waves
Authors: Lipkens Bart , Dionne Jason , Costolo Michael , Rietman Edward
Published: May 2008

Particle concentration in ultrasonic standing waves by the acoustic radiation force is discussed. The acoustic radiation force is a function of the density and compressibility of the fluid and the suspended particles. A two-dimensional theoretical model is developed for particle trajectory calculations. An electro-acoustic model is used to predict the acoustic field in a resonator. The results of the linear acoustic model are used to calculate the acoustic radiation force acting on a particle suspended in the resonator. A particle trajectory model is developed that integrates the equation of motion of a particle subjected to a buoyancy force, a fluid drag force, and the acoustic radiation force. Computational fluid dynamics calculations are performed to calculate the velocity field. For a fixed frequency excitation, the particles are concentrated along the stable node locations of the acoustic radiation force. Through a periodic sweeping of the excitation frequency particle translation is achieved. Two types of frequency sweeps are considered, a ramp approach and a step-change method. Numerical results of particle trajectory calculations in a resonator with dimensions much larger than a typical wavelength are presented. A movie of experimental observations of particle trajectories is shown to illustrate the method.
Viscoelastic material monitoring using an acoustical cylindrical spectrometer
Authors: Wilkie-Chancellier Nicolas , Martinez Loic , Griesmar Pascal , Serfaty Stéphane
Published: May 2008

Acoustic sensors often have a plane geometry due to manufacturing constrains. In the present work, the cylindrical geometry is investigated with a normal incident beam in order to suppress the edge effects on mode conversion. The experimental setup uses an aluminium cylindrical shell. A classical immersion transducer (2 MHz central frequency) sends a plane pulse wave on the shell at normal incidence. A second immersion transducer can turn around, enabling the observation of the waves scattered by the cylindrical shell. Previous works have shown that the acoustic field scattered by the shell as a rainbow structure enabling the acoustic spectrometry of the material poured inside the shell. From these results, the present study proposes an acoustical model linking the resonances parameters to the material ones, enabling the monitoring of time varying viscous materials. Several gelation monitoring experiments are performed and analysed using the proposed model. Results are in good agreement with quartz sensor measurements and offer a good alternative to wide frequency range measurements.
Determination of the width of an axisymmetric deposit on a metallic pipe by means of Lamb type guided modes
Authors: El Moussaoui Mustapha , Chati Farid , Leon Fernand , Klauson Aleksander , Maze Gerard
Published: May 2008

The non-destructive evaluation of pipes using guided waves is extensively used for the detection and the size estimation of defects. The important number of investigations concerning with the interaction between a guided wave and a defect show the growing need to improve our knowledge of this phenomenon in order to detect and to characterize as well as possible the defect. This work is devoted to the evaluation of the width of an axisymmetric resin deposit coupled to the wall of a metallic tube by means of longitudinal modes S0, S1. To that end, we interest to damping of these modes provoked by the deposit. The study is carried out both from the numerical point of view and from the experimental point of view in considering a deposit of variable width. The finite element method is employed to model the propagation and the diffraction of Lamb-type waves. The experiment is based on the generation of axisymmetric waves on the section of a tube by a piezoelectric transducer. Measurements of temporal echoes reflected by the deposit and transmitted after the deposit are achieved. A mathematical law of the attenuation as function of the width is deduced for each wave.
Scattering by a defect in an elastic waveguide: Coupling of finite elements and modal representations
Authors: Baronian Vahan , Bonnet- Ben Dhia Anne-Sophie , Chambeyron Colin , Luneville Eric
Published: May 2008

The potentiality of guided ultrasonic waves in nondestructive testing is currently investigated. Indeed, guided waves can allow a rapid inspection of large areas and of non accessible parts of particular structures like plates or pipes, compared to conventional techniques. This work concerns the numerical finite element computation, in the frequency domain, of the diffracted wave produced by a defect (crack, heterogeneity, discontinuity, local bend etc.) located in an infinite elastic waveguide. The computational domain is chosen as a portion of the waveguide, containing the perturbation, and our purpose is to build transparent conditions on its artificial boundaries by using modal representations. This cannot be achieved in a classical way, due to nonstandard properties of elastic modes. However, a biorthogonality relation is established which allows to derive a transparent condition relating hybrids displacement/stress vectors. An original mixed formulation is then implemented, whose unknowns are the displacement field in the bounded domain and the normal component of the normal stresses on the artificial boundaries. Numerical validations are presented in the two-dimensional and three-dimensional cases.
Low frequency composite acoustic sensor for highly absorbing media characterization
Authors: Skaf Alain , Nassar Georges , Lefebvre Fabrice , Nongaillard Bertrand
Published: May 2008

Ultrasonic techniques are widely used in nondestructive testing and evaluation of media. But when media are highly absorbing, it becomes often impossible to operate at classical ultrasonic frequencies. In this work, we propose a low frequency acoustic device to characterize such highly absorbing media. This device is composed of a piezoelectric disc embedded in a metallic ring. The technique consists in bringing into resonance the entire structure. Firstly, we will study analytically and numerically the main resonance modes of the sensor, which are the flexion modes and the radial modes. The results of the modelization are compared to measurements obtained through an impedance analyzer. In a second part, we will use this model of sensor to characterize two different media. The first type consists of a series of polymer disks with different viscoelastic properties. Using radial modes of vibration, we will characterize these polymer disks through measurement of the acoustic velocity. After that, we will characterize using the flexion modes a very complex medium which present a highly absorbing phenomenon such as dough in the fermentation phase. The measurements show the aptitude of this technique to follow the evolution of the physical properties of complex media.
Subjective verification of simulation of a vehicle pass-by
Authors: Kaczmarek Tomasz
Published: May 2008

The simulation of a moving vehicle can be a very powerful tool for investigating the perception of vehicle motion (velocity, acceleration, road traffic annoyance studies etc). Before applying a simulated vehicle in psychoacoustic noise annoyance studies, one should perform a subjective validation of this tool. The present paper presents the subjective validation of simulation method created by the author. Real pass-by recordings were used to calculate the one-third octave power spectra of a vehicle. Based on these spectra, the simulated pass-bys were created. The simulation was validated in terms of annoyance level and perception of velocity by comparing (in psychoacoustic experiment) the original pass-bys with their simulated replicas. Two types of engines - otto and diesel - were tested, for velocities ranging from 30-110 km/h. For velocities above 50 km/h, the annoyance of simulated pass-bys is very close to the original signal. For lower velocities, simulated pass-bys result in lower annoyance ratings. The solution to the problem would be a reconstruction of the tonal components from the exhaust system.
'Behavioral Relevance' as a guiding principle in investigating the perception of sound source properties
Authors: Neuhoff John
Published: May 2008

Perceiving a sounding object is the result of a complex interaction between physical, physiological, and cognitive factors. However, early in the history of modern psychacoustics, the difficulty in generating complex, controlled, dynamic stimuli limited many investigations of auditory perception to monaural presentation of static sine wave tones or bursts of noise. Thus, very influential models of auditory processing were developed using sounds that are not frequently encountered in a natural listening environment. Although this approach was useful in developing models of the function of the peripheral auditory system, it was less so in developing models of auditory cognition and behavior. If one accepts the position that our perceptual abilities have evolved specifically to help us survive and deal with the stimuli that occur in a natural environment, perhaps it is not surprising that there are differences in processing naturally occurring stimuli and those that are more artificial. Recent paradigmatic shifts spurred by technical innovations have spawned more ecologically valid investigations of complex auditory perception and cognition that include the perception of sound source properties. The future for this approach is promising if "behavioral relevance" can serve a guiding principle.
Classification of everyday sounds: Influence of the degree of sound source identification
Authors: Houix Olivier , Lemaitre Guillaume , Misdariis Nicolas , Susini Patrick
Published: May 2008

Based on a review of everyday sound classification studies, we define three types of similarity that might underlie the formation of categories: acoustical similarity, related to the perception of the sound signal properties; causal similarity, related to the perception of the cause of the sound; semantic similarity, related to the meaning of the sounds. This study focuses on the influence of the degree of sound source identification on the type of similarity used during a free sorting task. Our hypothesis is that well-identified sounds will lead to categories based on causal or semantic similarities, while non-identified sounds will lead to categories based on acoustical similarity. First we measure the causal uncertainty of each sound of a set of kitchen sounds. We ask to participants to describe the cause of the sounds in order to measure the degree of identification for each sound. The results of a free sorting task on this sound corpus indicate that participants groups together sounds according to our assumptions. The classification of the well-identified sounds shows a clear distinction between classes of sound events (gas, liquid, solids, motor) confirming a taxonomy proposed in literature. [Work supported by the CLOSED project of the NEST program]
Verbal imitations of sound events enable recognition of the imitated sound events
Authors: Aura Karine , Lemaitre Guillaume , Susini Patrick
Published: May 2008

We report a study investigating how verbal imitations of sound events might convey information enabling the recognition of the imitated sounds. We sampled twenty-eight sounds across a taxonomy of kitchen sounds, obtained from a previous experiment focused on the perceived properties of the causes of the sounds. First, we recorded speakers while imitating the sounds. They were specifically required not to use words. Then we selected the imitations of six speakers (three men, three women) imitating twelve sounds. Finally a group of twenty listeners performed a sorting task (they had to group together imitations thought to imitate the same events), and were asked to describe how they built each category. The categories of imitations, obtained from a hierarchical tree representation, fit very well with the categories of the original sound events. This suggests that speakers have succeeded in capturing the information sufficient to enable listeners to recognize the sound events. This is further confirmed by the analyses of the verbalizations. Phonetic analyses show that imitations grouped together share some phonetic similarities, yet the main similarities seem rather to be based on prosodic indexes (duration, intonation, rhythmic patterns). [This work is founded by the FP6 NEST Pathfinder European project CLOSED]
A History of Binaural Interaction Modeling - Walks with Jens Blauert
Authors: Colburn H Steven , Carr Suzanne , Wan Rui
Published: May 2008

Jens Blauert has been cut an impressively wide path through diverse areas of binaural and spatial hearing. He has consistently integrated viewpoints based on empirical results, intuitive interpretations, and mathematical and computational models of binaural interaction and spatial hearing. This talk focuses on the development of ideas about binaural interaction as represented in quantitative models and the strong influence that Blauert exerted on these models. These influences start with simple models of the extraction and use of interaural time and level differences, include mechanisms that incorporate complex interactions of these differences, and lead to models that are appropriate for the interpretation of complex acoustic scenes. Finally, some current modeling activities will be outlined and related to these historical developments. [Work supported by the US National Institutues of Health DC00100.]
Localization-based segregation of acoustic sources: Advantages and limitations
Authors: Divenyi Pierre
Published: May 2008

It has been suggested [Divenyi, P., & Oliver, S.K., (1989), JASA 85, 2042-2052] that segregation of simultaneous pairs of sounds in the horizontal plane requires both resolution of the azimuthal separation between the sources, and correct assignment of each signal to the correct source. In fact, contrary to our a priori expectations, localization did not emerge as the dominant dimension underlying segregation of source pairs: its importance often fell behind that of segregation based on differences of spectral or temporal envelope structure, except for some listeners. Nevertheless, the possibility remains that these limitations can be attributed to localization dominance by one of the sources or both. The dual requirement of localization and signal-to-source assignment, in addition to reverberation, may represent a limiting factor for the role of localization in the cocktail-party effect.
Binaural technology for e.g. rendering auditory virtual environments
Authors: Hammersho/i Dorte
Published: May 2008

Jens Blauert's research up through the late 1960s and later, pioneered the field of binaural technology and auditory virtual environments. He mastered the measurement of head-related transfer functions (HRTFs) before the term was introduced, and his methods were standard for decades. While most acknowledge his efforts in understanding the binaural hearing and the significance of inter-aural differences, appreciation is also in place for his evaluation of localization with identical ear input signals. The relations between the hearing's "directional" bands and the transfer functions' "boosted" bands, helped mediate the understanding that if the transfer functions could be mastered, then important dimensions of the auditory percept could also be controlled. He early understood the potential of using the HRTFs and numerical sound transmission analysis programs for rendering auditory virtual environments. Jens Blauert participated in many European cooperation projects exploring this field (and others), among other the SCATIS project addressing the auditory-tactile dimensions in the absence of visual information.
Semio-acoustics: a domain of communication acoustics
Authors: Jekosch Ute
Published: May 2008

For user-oriented design of modern information and communication systems we investiate the perception of acoustic signals as sign carriers: How do listeners process acoustic/auditory events when they treat them as information carriers and which meaning do they associate with them? Sign carriers (in our case the acoustic signals) transport information across space and time. When being perceived, they are decoded, analyzed and interpreted with regard to their cultural meaning and their relevance for the actual living and communication situation. These processes are universal to a certain degree. It is the aim of our research in Dresden to investigate the fundamental structures and organisational principles underlying this assignment of meaning to acoustic and their accompanying auditory events. In this talk, some semio-acoustic paradigms will be introduced. As a Ph.D. student of Jens Blauerts' and as a post doc in his team, the semio-acoustic approach has developed as a logical continuation of his way of thinking, of his research approaches, and of his scientific goals, based on and fed by his basic statement: Communication acoustics is not conceivable without audition, and only if we are able to understand auditory events, and even cognitive processes, we are able to make use of acoustic communication and information technology in a user-friendly way.
Vibroacoustic Simulation of Partly Immersed Bodies by a Coupled Fast BE-FE Approach
Authors: Brunner Dominik , Junge Michael , Cabos Christian , Gaul Lothar
Published: May 2008

Simulation of vibroacoustic behavior of submerged bodies necessitates dealing with fluid-structure coupled problems. In case of a high density of the fluid, the feedback of the acoustic pressure onto the structure cannot be neglected and a fully coupled system must be investigated. In this work, the finite element method (FEM) is used for the structural part. The commercial finite element package ANSYS is applied for setting up the mass and stiffness matrices. The boundary element method (BEM) is well suited for simulating the sound propagation in the unbounded exterior acoustic fluid domain. Here, the fast multipole method (FMM) is applied to overcome the known bottleneck of classical BE-methods. In the case of partly immersed bodies, Dirichlet boundary conditions on the fluid surface additionally have to be incorporated. This is done by applying a halfspace formulation. The extension of the FMM to this scenario is discussed. Iterative preconditioned solvers are employed and the numerical efficiency is discussed. The applicability of the coupling scheme is demonstrated using a realistic model problem.
A half-space BEM for the simulation of sound propagation above an impedance plane
Authors: Brick Haike , Ochmann Martin
Published: May 2008

The Boundary-Element-Method is a powerful tool for the simulation of sound radiation and scattering. Classically, it was developed for the free 3D-space, but it can be modified easily for half-space solutions as long as the half-space is delimited by a perfectly rigid or soft plane. In this case, the Green's function, the core of the BEM, can be derived from a simple image source ansatz, which however cannot be used for a more general impedance boundary condition. The alternative, an additional discretisation of a finite but large part of the plane leads to an enormous increase of the size of the set of equations. In this presentation, an appropriate Green's function will be introduced, which is able to describe the sound propagation above an impedance plane and is suitable for an implementation into a BEM code. It bases on the superposition of sound sources with complex source points. The numerical evaluation of this Green's function will be presented along with several test cases including sound radiation from burning flames above ground and tire-road noise. The computational costs of the developed "Complex-Source-Point-BEM" (CBEM) in comparison with a classical BEM together with a discretisation of the impedance plane will be discussed.
A GWBEM method for high frequency acoustic scattering
Authors: Perrey-Debain Emmanuel , Bériot Hadrien , Ben Tahar Mabrouk , Vayssade Catherine
Published: May 2008

This paper considers the problem of scattering of a time-harmonic acoustic incident wave by a hard obstacle. The numerical solution to this problem is found using a Galerkin Wave Boundary Element Method (GWBEM) whereby the functional space is built as the product of conventional low order piecewise polynomials with a set of plane waves propagating in various directions. In this work we present strategies for finding the appropriate plane wave basis locally on each boundary element in order to deal efficiently with very irregularly meshed structures exhibiting both large smooth scattering surfaces as well as corners and small geometrical features. Numerical results clearly demonstrate that these improvements allow the handling of scatterers with complicated geometries while maintaining a low discretization level of 2.5 to 3 degrees of freedom per full wavelength.
An overview of models for viscothermal wave propagation, including fluid structure interaction
Authors: Beltman Willem M. , Wijnant Ysbrand H. , Nijhof Marten J.
Published: May 2008

In acoustics, the standard wave propagation models neglect the effects of viscosity and thermal conductivity. When waves propagate in narrow tubes or thin layers these simplifications might not be accurate. This paper presents an overview of models that take the effects of inertia, viscosity, thermal conductivity and compressibility into account. Based on the use of dimensionless parameters, three classes of models are outlined. The most important dimensionless parameter is the shear wave number, an unsteady Reynolds number that indicates the ratio between inertial and viscous effects. These viscothermal wave propagation models can be coupled to structural models to capture the fluid structure interaction. Analytical solutions can be found for these coupled analysis cases only for simple geometries and boundary conditions. For more complex geometries, numerical models were developed. Examples of applications of these models are also presented.
Improvements on the directional characteristics of a calibration sound source using the Boundary Element Method
Authors: Cutanda Henriquez Vicente , Barrera-Figueroa Salvador , Juhl Peter
Published: May 2008

The project Euromet-792 aims to investigate and improve methods for secondary free-field calibration of microphones. In this framework, the comparison method is being studied at DFM in relation to the more usual substitution method of microphone calibration. The design of the sound source is of particular importance to achieve a sound field that reaches both microphones with the same level and that is sufficiently uniform at the microphone positions, in order to reduce the effect of misalignment. An existing sound source has been modeled using the Boundary Element Method, and the simulations have been used to modify the source and make it suitable for this kind of calibration. It has been found that a central plug, already present in the device, can be re-shaped in such a way that makes the sound field on the microphone positions more uniform, even at rather high frequencies. Measurements have been carried out in order to verify the goodness of this solution.
Analysis of the resonance frequency shift in cylindrical cavities containing a sphere and its prediction based on the Boltzmann-Ehrenfest principle
Authors: Santillan Arturo , Cutanda Henriquez Vicente
Published: May 2008

It is known that forces generated by high-level acoustic waves can compensate for the weight of small samples, which can be suspended in a fluid. To achieve this, a standing wave is created in a resonant enclosure, which can be open or closed to the external medium. This phenomenon, called Acoustic levitation, has numerous applications in containerless study and processing of materials. Although it is possible to levitate a sample for long periods of time, instabilities can appear under certain conditions. One of the causes of oscillational instabilities is the change of the resonance frequency of the cavity due to the presence of the levitated object. The Boltzmann-Ehrenfest principle is used to find an analytical expression for the resonance frequency shift in a cylindrical cavity produced by a small sphere, with kr < 1, where k is the wavenumber and r is the radius of the sphere. The validity of this expression has been investigated by means of the Boundary Element Method and experiments. In addition, the effect of the dispersion of the sound field by the sphere and the boundaries of the cavity on the resonance frequency shift has been analyzed using the BEM.
Experimental and numerical investigation of the dynamics in spatial fluid-filled piping systems
Authors: Herrmann Jan , Haag Thomas , Gaul Lothar
Published: May 2008

Hydraulic piping systems, such as fluid-filled break and fuel pipes in automotive applications, undergo strong acoustic excitation due to pressure pulsations of pump and valve operation. By fluid-structure coupling the sound transmission within the pipe may lead to a structural excitation of other car components causing excessive noise levels or even structural failure. In order to obtain a complete and reliable understanding of the wave propagation and vibration phenomena in spatial piping systems, a test rig is presented, consisting of a pressure source and a fluid-filled break pipe with an attached target structure. With this experimental setup, it is possible to quantify the acoustic sound transmission and to examine the dynamic behavior by transfer functions. The experimental results are compared with harmonic and transient finite element simulations employing efficient model order reduction techniques for the fluid-structure coupled system. This research focuses on the identification of hydraulic resonances and the optimal mounting of the fluid-filled break pipe in order to minimize the structure-borne sound induced on the target structure.
Active Tracking using the Invariance Extended Kalman Filter (IEKF)
Authors: Zurk Lisa M. , He Chensong , Quijano Jorge E. , Hempel Christian
Published: May 2008

The pressure received from a moving source in a shallow water channel has a frequency dependent structure that is imposed by the propagation characteristics of the channel. While an exact description of this structure requires fine knowledge of the channel properties (including bottom composition), an approximate relationship which utilizes the so-called waveguide invariant can be used to describe the intensity variations as a function of frequency versus range. This relationship has been extensively explored and utilized for application to passive sonar systems. Recent work has demonstrated that a similar structure, called the active invariance, may be present in active sonar. In this paper the active invariance relationship is incorporated into an extended Kalman filter (EKF) to create a new tracking formulation called the Invariance EKF (IEKF). The IEKF differs from the conventional formulation by incorporating the time-dependent frequency content into both the state space representation and the update equations, where the relationship between target position and frequency is given by the active invariance expression. Performance of the IEKF relative to conventional approaches is explored with normal mode simulations and bistatic data collected in the Maltese channel. Sponsored by ONR-321US
A comparison of hydrophone near-field scans and optical techniques for characterising high frequency sonar transducers
Authors: Humphrey Victor F. , Robinson Stephen P. , Theobald Peter D. , Hayman Gary , Cooling Martin P.
Published: May 2008

Two potential methods of fully characterising the response of high frequency sonar transducers and arrays operating in the frequency range 100 kHz to 500 kHz are compared. In the first approach two-dimensional planar scans, with a spatial resolution of better than half a wavelength, are performed in the acoustic near-field using a small probe hydrophone. The measured two-dimensional data are propagated numerically using a Fourier Transform method to predict the far-field response. Alternatively the data can be back-propagated to re-construct the pressure distribution at the source, a powerful diagnostic technique which can identify defects in transducers and array elements. The second approach uses a scanning laser vibrometer to measure the velocity of the transducer surface; with the resulting velocity data also being used to predict the far-field response by numerical propagation. The two approaches are compared for a number of devices. Comparison of the propagated hydrophone near-field scan data with direct measurements at these ranges shows very good agreement, indicating the usefulness of the method for deriving far-field transducer responses from near-field measurements in laboratory tanks. The potential limitations introduced to the optical approach by the acousto-optic effect are discussed.
Frequency and grain size dependence of longitudinal wave velocity in granular marine sediments
Authors: Kimura Masao
Published: May 2008

Frequency dependence of longitudinal wave velocity in granular marine sediments is important in underwater acoustics. Also, the grain size dependence is significant for the identification of sediments. In this study, the measurements of the velocity of three kinds of sands with different grain sizes are carried out in the frequency ranges from approximately 5 kHz to 500 kHz in the laboratory. The velocity at a low frequency is measured by using an acoustic tube method. Time-of-flight method is used for the measurements of the velocity at higher frequencies. These measured results are compared with the calculated results by using the Biot-Stoll model and a modified gap stiffness model incorporated into the Biot model (BIMGS model). It is shown that the frequency and grain size dependence of velocity can be explained by using the BIMGS model.
Effect of bending portions of the air column on the acoustical properties of a wind instrument
Authors: Félix Simon , Nederveen Cornelis J. , Dalmont Jean-Pierre , Gilbert Joël
Published: May 2008

The need to keep long wind musical instruments compact imposes the bending of portions of the air column. Although manufacturers and players mention its effects as being significant, the curvature is generally not included in physical models and only a few studies, in only simplified cases, attempted to evaluate its influence. The aim of our study is to quantify the influence of the curvature by modelling the wave propagation in an air column with a multimodal formalism. In a duct with a circular cross-section and a finite curvature, two infinite sets of coupled first-order differential equations are constructed for the components of the pressure and axial velocity, projected on the local transverse modes. From these an impedance matrix is defined, which can be easily calculated, particularly when considering a duct with a piecewise constant curvature. Influence of the curvature on the input impedance, effective length, or playing frequencies is then quantified, displaying notably a dependence to frequency such that, compared to an equivalent straight tube, the shift in resonance frequencies in a tube with bent sections is not always positive, as generally stated. Results are independently corroborated by numerical - finite differences - computations.
Associations between road traffic noise level, road traffic noise annoyance and high blood pressure in the HYENA study
Authors: Babisch Wolfgang , Houthuijs Danny , Pershagen Goran , Katsouyanni Klea , Velonakis Manolis , Cadum Ennio , Jarup Lars
Published: May 2008

The HYENA study is a multi-centred study regarding the effects of aircraft noise and road traffic noise on blood pressure (BP) which was funded by the European Community. Study subjects were 4,861 males and females aged between 45 and 70 years, who had lived for at least 5 years in the vicinity of any of six major European airports. Aircraft noise contours and road traffic noise levels were modelled using the Integrated Noise Model (INM) and national calculation methods. The noise levels were linked to each participant's home address (most exposed façade) using graphical information systems (GIS). Noise annoyance was assessed using the 11-point ICBEN scale. High blood pressure was determined by measurements of systolic and diastolic blood pressure, anti-hypertensive medication and self-reported doctor diagnosed hypertension. The focus here is on the effects of road traffic noise. The road traffic noise level (LAFm, 24 hours) and noise annoyance due to road traffic noise were both significantly associated with high blood pressure. The association between road traffic noise and high blood pressure was stronger for the road noise level than for the road noise annoyance (90th percentile vs. 10th percentile of the exposure distributions).
Updates on Prominent Discrete Tone Procedures in ISO 7779, ECMA 74, and ANSI S1.13
Authors: Hellweg Robert
Published: May 2008

There are two alternative procedures for determining if a tone is prominent, i.e. a "prominent discrete tone" in ISO 7779, ECMA 74 and ANSI S1.13: the Tone to Noise Ratio (TNR) method and the Prominence Ratio (PR) method. Both of these procedures have been used by the computer industry for more than a decade. Recent revisions to these procedures have refined the calculation of the critical bandwidth and modified the both procedures for low level tones. This paper describes these changes and the rationale behind them. Examples are presented that demonstrate the features of each procedure. The paper presents an overview on the applicability and limitations of each procedure.
Effects of notches on span wise correlation of surface pressure fluctuations downstream of a wall-mounted spoiler
Authors: Mejia Paloma , Park Jong Beom , Mongeau Luc
Published: May 2008

Leading edge spoilers are widely-used for suppressing flow-induced cavity resonance such as buffeting due to open sunroofs in moving cars. Spoilers deflect the grazing flow over the opening into a region of greater flow velocity, thereby increasing the critical velocity. Notched spoilers have been observed to enhance resonance suppression while moving the flow reattachment region upstream, resulting in a decreased drag. The mechanisms involved in the effectiveness of the notched spoiler were investigated experimentally and numerically. Static and dynamic pressures on the surface behind a wall mounted notched spoiler were measured, and the spatial correlations of the measured pressures were compared to those for a spoiler without notches. The span wise pressure correlation was decreased by the presence of the notches, suggesting a breakdown of the span wise leading vortices predominantly responsible for the cavity excitation. Numerical flow simulations were performed using the lattice Boltzmann method (LBM) with turbulence modeling. Surface pressure results were compared with experimental data to better highlight surface pressure trends.
Simulation of vehicle interior wind noise at low frequencies: a case study
Authors: Powell Robert , Khatib-Shahidi Bijan
Published: May 2008

Quietness of passenger vehicle interiors has become a critical-to-quality metric in designing modern passenger vehicles. At the same time, the necessity of bringing fresh designs to market quickly has greatly compressed the development time available to achieve the desired refinement of interior noise and vibration. This has forced manufacturers to place increasing responsibility on analytical simulations in developing countermeasures for noise problems. One aspect of car acoustics that has not received very much attention from the simulation community is the wind noise created by external air flow at speed. Significant contributions to interior loudness can come from underbody air flow, while improvements in simulation efficiency of Computational Fluid Dynamics (CFD) flow models and Finite Element Analysis (FEA) vehicle vibration and acoustic models now make it feasible to analytically simulate interior noise caused by wind excitation. This lecture describes a case study where existing vehicle models were adapted to first build a wind load case from CFD, and then to apply it in estimating and reducing interior noise in FEA. Topics to be covered include: spatial discretization of continuous panel pressures, application of random loads to deterministic vehicle FEA models and diagnostic imagery for visualizing noise and vibration responses.
Modeling and characterization of rattle noise encountered in an automotive environment
Authors: Desvard Ludovic , Hamzaoui Nacer , Duffal Jean-Marc
Published: May 2008

In an automotive cockpit, rattle noises deal with all noise due to normal impacts which radiate as annoying noises for customers. The state of the art shows studies focused on one automotive subsystem, describing the specific associated physic. The method proposed, in this study, is to generate automotive rattle noises using simple geometries. The interest of this approach is to know all the parameters of the system (impact location, material, geometries, excitation...) and to precisely describe the physical phenomena related to the apparition of rattle noises. Firstly an experimental bench was proposed to generate rattle noises using simple geometries. These rattle noises are similar to those encountered in an automotive environment. This experimental approach allows to measure the vibrational behaviour and the radiated sound of the system under a random impact excitation. Then an analytical model, which describes the experimental approach, is developed to predict the radiated sound, knowing the displacement of the impactor. Numerical and experimental results are compared. Finally, thanks to the experimental approach, a database of rattle noises is created and used to find metrics to quantify the annoyance.