bluuebunny/crossref_metadata_2025 huggingface dataset:
Source detection and tracking in 3-D space using efficient subspace methods
Authors: Barnhill Colin
Published: May 2008

This presentation will demonstrate the versatility and robustness of a MUSIC-based subspace algorithm for acoustic source detection and tracking. The new algorithm (MUSIC3D) is designed for use with spherical arrays and performs three dimensional source detection and tracking. MUSIC3D operates on a spherical decomposition of the received array signals which results in its high efficiency. Spherical decomposition of the array signals allows for data reduction, frequency selection, and direct subspace calculations. The appeal of the MUSIC3D algorithm is that it offers a large variety of implementations which can be tailored for specific environments, signal sources or noise sources. Source tracking is accomplished through a combination of a Kalman-based filter and the MUSIC3D algorithm.
Insights to dolphin sonar discrimination capabilities with human listening experiments
Authors: Au Whitlow W. , Delong Caroline M.
Published: May 2008

Dolphins have a very keen sonar system that is able to make fine discriminations between complex targets such as proud and buried mines. To understand the cues that dolphins use for fine target discrimination, human listening experiments have been conducted with echoes from real targets using a simulated broadband dolphin echo-ranger. Echoes are stretched in time to translate the echoes into the human auditory range. The human performance is usually as accurate as the dolphin, with the additional benefit of being able to get feedback on cues used. Various types of discrimination and detection experiments have been conducted paralleling dolphin sonar experiments. Discrimination of material composition of cylinders and spheres, detection of target in clutter and cylinder wall thickness difference discrimination experiment have been performed. The human listeners performed as well or better than the dolphins at the task of discriminating between a standard target and comparison targets. Click pitch, echo duration, time-separation pitch and timbre are some of the cues used by human listeners to discriminate targets. Dolphins may use some of the same echo features as humans. Human listening studies can quickly identify salient combinations of echo features that permit object discrimination and also help refine dolphin experiments.
Incorporation of acoustic level analysis with sonar operator workstation workflow using hierarchical hidden Markov models
Authors: Nevitt Justin , Ballas James
Published: May 2008

Future Anti Submarine Warfare (ASW) systems will be highly automated, and utilize multiple sonar signal processing, non-acoustic information, off platform information, and environmental information to maximize the detection, tracking, and classification of undersea threats. Recently, a hidden Markov model (HMM) was developed to describe and characterize the workflow strategies that expert sonar operators used during the IUSW-21 (Integrated UnderSea Warfare for the 21st Century) Sea Test. Abandoning the normative workflow designed into the system, the sonar operators developed and utilized unanticipated strategies to gather evidence to confirm or disconfirm automated classifications or to manually classify contacts. The workflow included detailed visual inspection of and listening to the sonar return. This initial HMM did not include a characterization of the auditory processing. Hidden Markov models are well suited to this purpose. Adding this component to the operator workflow was achieved by a hierarchical HMM which represents the acoustic processing as an embedded HMM in the overall workflow HMM. The resulting model is not just an operator workflow but defines a system processing model that could be used as a framework to develop automated processing of selected components.
The hydrophone free-field calibration in the non-anechoic water tank using continuous radiation mode
Authors: Isaev Alexander , Matveev Anton
Published: May 2008

Anechoic chambers are used at free-field measurements in acoustic. Quality of the anechoic chamber estimate by comparing the dependence of sound pressure with distance between a projector and the receiver with the inversely proportional law. Creation of an anechoic water tank is a difficult technical problem. Therefore measurements in a water tank usually use tone burst radiation technique. In a non-anechoic water tank it is possible to provide free-field conditions at a continuous radiation mode. It is achieved by using a signal with the distributed spectrum and mathematical processing of results of measurements. The measurement procedure and results of free field calibration of this method are considered in the paper. Efficiency of measuring procedure was estimated by a check of the inversely proportional law in conditions of a non-anechoic water tank.
Vector-phase methods of bottom reflecting properties research in shallow shelf area
Authors: Ermolaeva Elena , Goncharenko Boris , Gordienko Valery
Published: May 2008

It is known, that parameters of bottom have essential influence on the signal propagation in the shallow water. Variation of the attenuation coefficient can amount to tens dB. Therefore, research of bottom properties and its structure (first of all - thickness and acoustics parameters of alluvial soil) is actual problem, especially at low frequencies. Using of receivers, which record both sound pressure and its gradient make it easier to solve this problem in a number of cases. The following methods are considered: impedance method, which is based on direct measurement of relation between pressure and vertical component of oscillatory velocity in one point on the water/ bottom boundary; method, which is based on measuring phase difference between pressure and horizontal or vertical component of particle velocity; method in which additive combination of sound pressure and vertical component of oscillatory velocity are used. The essence of the last method consists in formation of minima of reception system directional characteristic in the direction at the signals extending from surface to bottom and reflected from bottom. The suggested methods of acoustic characteristics research of a ground repeatedly have been checked in shallow shelf area of the Baltic and the Black seas, and also in conditions of shallow inland water areas.
Correcting bathymetry measurements for water sound speed effects using inversion theory
Authors: De Plaa Jelle , Snellen M. , Simons Dick G.
Published: May 2008

We present a method to accurately estimate the bathymetry and water sound speed in shallow waters using overlapping swaths obtained from a Multi-Beam Echo Sounder (MBES). The method is designed to correct the errors in the bathymetry manifested mainly in the outer beams of the MBES. The errors are caused by deviations in sound speed, which occur, for example, in estuaries where fresh river water mixes with seawater. Simulations show that we are able to simultaneously estimate the mean sound speed and the bathymetry. This is accomplished by minimizing the differences between the MBES measurements in the overlap region using a Levenberg-Marquardt optimization routine. We also present an application of the method to real data obtained at the fairway to the harbour of Rotterdam, The Netherlands. Analysis shows that the inverted sound speed agrees well with the measured sound speed at the transducer. However, the uncertainties are larger when the track-to-track distance is ̃2 times the depth. Therefore, we also discuss the optimal distance between sailed tracks. The method appears to be a promising tool for the accurate mapping of sea floors in shallow-water areas with a complex sound-speed profile.
Cost Benefit Analysis of Acoustic Treatments for Entertainment Venues
Authors: Borgeaud David M.
Published: May 2008

Fortitude Valley, in Brisbane City, Australia is an inner city area combining retail, commercial, residential, and entertainment uses. It has been the starting point for several major Australian bands. To address the increase in apartments in the Valley, the Brisbane City Council has developed a noise policy (called The Valley Music Harmony Plan) using entertainment precincts with specific noise criteria within the Valley, to allow informed decisions to be made regarding future development while minimising potential noise conflicts. An earlier paper by the Author has addressed the ambient noise mapping undertaken for the Valley, and this paper discusses the results of the cost benefit study undertaken into the acoustic treatment of selected venues. The purpose of this work was to provide Council with information on both the feasibility of treating the entertainment venues to reduce noise emissions and the order of cost for the treatments. The study of four venues found that attenuation of 3 - 22dB(A) or 1 - 17dB(C) could be achieved with asociated costs ranging from $30,000 to over $400,000 (Australian dollars). The costing work provided invaluable knowledge in the development of the Valley Music Harmony Plan.
Air Absorption Error in Room Acoustical Modeling
Authors: Wenmaekers Remy H. , Hak Constant C. , Martin Heiko J. , Van Luxemburg Laurentius C.
Published: May 2008

Most statistical and ray-tracing computer models take into account the absorption of sound by air when calculating the reverberation time. Extensive research by many scientist lead to the standardized calculation model for pure tone air absorption. The phenomenon was discovered from a room acoustical point of view by Sabine, while the further development of the calculation model took place in the fields of physics and environmental noise. As a result, several parameters and units are used for the same phenomenon. However, air absorption is calculated for pure tones, while room acoustics calculations are performed for frequency bands. Most computer models use the center frequency of the normalized frequency bands to calculate the air absorption by the pure tone method. Frequency band reverberation measurements under laboratory and practical conditions show that errors larger than the JND are made in calculating the air absorption by this 'center frequency method'. No literature is found that provides an accurate air absorption calculation for frequency bands.
FEM based prediction model for the impact sound level of floors
Authors: Rabold Andreas , Düster Alexander , Rank Ernst
Published: May 2008

Up to now the research and development in the field of building acoustics is based mainly on experiments. The consequence of this approach is that the development and optimization of a new building component is a very tedious and expensive task. A considerably reduction of these costs could be achieved, if the optimization relying on experiments would be replaced - at least to some extent - by a computational approach. Common prediction models of the impact sound level from lightweight floors are based on measured impact sound level data for the component parts under consideration. These models are very useful for the evidence of performance of known building components, but they are not suited for the development of new components. An alternative approach in this context is the application of the finite element method (FEM). Based on a FE model, a modal- and spectral analyses provides the framework for an optimization of the building component. This contribution will present the overall approach consisting of the three-dimensional modeling of a lightweight-floor and the excitation source (tapping machine), the subsequent modal- and the spectral- analyses and the computation of the radiated sound from the floor.
Human footsteps induced floor vibration
Authors: Bard Delphine , Sonnerup Julia , Sandberg Göran
Published: May 2008

The generation of the impact sound by the act of the human walk involves two factors, the characters of the footfall and the shape of the induced floor deflection. The footfall noise is created by the impact excitation and the characters of the footfall depend on the foot-ware: the heels and the frequencies of the footfall. The shape of the floor deflection depends rather on the geometrical walking pattern and the construction of the floor structure. In this investigation, the vibration patter of the light-weight construction floor is created by the same walking object, a male with common height. The excitation from the person to the floor in the FE simulations is a function of the length of the foot and the weight of the walking object. The geometrical time history is of the foot step allows it to have different directions in the room. Since the excitation is assumed to be deterministic, differences between the excitation frequencies are estimated from the video records. The goal of this investigation is to determine the difference of the floor structure deflections between two different walking paths: one is perpendicular to the bearing beams and the other is the diagonal path.
Parameter survey of a rib stiffened wooden floor using sinus modes model
Authors: Sjökvist Lars-Göran , Brunskog Jonas , Jacobsen Finn
Published: May 2008

In buildings built with new techniques there exists a need for better understanding of their acoustical performance. The development of large wooden houses slows down by the uncertainty and costly testing that have to be performed many times before gaining good results. A greater understanding of the sound insulation for lightweight buildings have the possibility to speed up the development of new techniques and in the end give tenants better quality of life. This study uses Fourier sinus series to calculate the vibrations on a rib stiffened plate. The beams are modelled as line forces and moments that reacts onto the plate vibrations. A parameter study is performed with the aim to identify the most important parameters and their behaviour. The preliminary results show that the attenuation of the system is by far most evident in the direction across the beams. The influence from the basic input parameters on the attenuation is then studied. And it is preliminary shown that the placement of the excitation force within a bay actually is irrelevant for the calculated attenuation.
Innovative building systems to improve the acoustical quality in lightweight masonry constructions: Application of resilient joints at junctions - PART 2: Study cases modelled according to the standard 12354-1 (2000)
Authors: Crispin Charlotte , Ingelaere Bart , Wuyts Debby
Published: May 2008

An important brick manufacturer in partnership with the BBRI has suc-ceeded to propose efficient acoustic solutions for this kind of lightweight materials by treating the flanking transmission using flexible interlayers at junctions and foundations. A large measurement campaign has been carried out to study the efficiency of the resilient joint and to provide a prediction model on airborne sound insulation in brickwork constructions. The prediction model used is based on the standard 12354-1 but was adapted in order to take into account higher orders for the flanking transmission paths. This adapted model thus allowed to study different applications of the flexible joint and their contribution to the improvement of the global sound insulation. This paper presents a discussion on the calculation model, the input data and some early results.
The interaction of emitted pulses and echoes in a whale's biosonar: A partial contribution to biosonar automatic gain control
Authors: Supin Alexander Y. , Nachtigall Paul E. , Breese Marlee
Published: May 2008

In a false killer whale Pseudorca crassidens, echo perception thresholds were measured using a go/no-go psychophysical paradigm and one-up-one-down staircase procedure. Electronically synthesized echoes were triggered by whale-emitted echolocation pulses, and the echo amplitudes were presented proportional to the triggering biosonar pulse amplitudes, thus imitating the basic feature of real target echoes. Echo thresholds were measured in terms of attenuation relative to the source level of the biosonar pulses. The echo threshold dependence on echo delay was investigated. With increasing echo delay, the threshold echo attenuation decreased from -49.3 dB at 2 ms to -79.5 dB at 16 ms, with a regression slope of -31.5 dB per delay decade. At delays longer than 16 ms, the threshold remained nearly constant around -80.4 dB. This echo threshold dependence on delay is interpreted as a release from forward masking by the preceding emitted pulse. This release may well compensate for the echo level decrease with distance which is from 20 to 40 dB per distance decade, depending on target properties. This compensation may keep the echo sensation level independent of, or little dependent on, target distance. Supported by Office of Naval Research (USA), Ministry of Science and Education (Russian Federation).
Optimal source tracking in an unknown ocean environment
Authors: Wilmut Michael J. , Dosso Stan E.
Published: May 2008

This paper develops and compares two approaches to localizing and tracking a low-level acoustic source when ocean environmental properties are unknown. Both approaches are based on a Bayesian formulation in which source and environmental parameters are considered random variables constrained by noisy acoustic data and by prior information on parameter values (e.g., physical limits for water-column and seabed properties) and on inter-parameter relationships (e.g., limits on horizontal and vertical source speed). One approach is based on determining the source track and environmental parameters that maximize the posterior probability density (PPD) using adaptive hybrid optimization. A key to solving this challenging problem efficiently is that the Viterbi algorithm is applied to compute the highest-probability source track for each environmental realization considered in the optimization-this provides the optimal track while requiring the optimization is applied only to environmental parameters. The second approach involves integrating the PPD over unknown environmental parameters to represent source-track information as a series of joint marginal probability surfaces over range and depth. The Viterbi algorithm is applied to extract the optimal track from these surfaces. For realistic environmental models (e.g., more than a dozen unknown parameters), the integration is carried out using efficient Markov-chain Monte Carlo methods.
Photoacoustic imaging for characterising the structure and function of vascular networks
Authors: Beard Paul C.
Published: May 2008

Photoacoustic imaging is a new non invasive soft tissue imaging method in which low energy nanosecond pulses of visible or near infrared (NIR) laser light are used to excite subsurface ultrasound waves. The distinguishing advantage of the technique is that provides the high contrast and spectroscopic based specificity of optical techniques along with the high spatial resolution of ultrasound. Haemoglobin represents the most important source of naturally occurring photoacoustic contrast due its relatively strong optical absorption in the visible and NIR making the technique particularly well suited to imaging blood vessels. In addition, functional information can be provided by obtaining images at multiple wavelengths and applying a spectroscopic analysis to quantify the concentrations of endogenous chromophores such as oxy and deoxyhaemoglobin. These attributes make the technique well suited to studying a wide range of tissue abnormalities such as tumours and other pathologies characterised by changes in the structure and oxygenation status of the vasculature. A novel optical ultrasound imaging system has been developed and used to obtain 3D images of the superficial vascular anatomy of the mouse brain, skin and implanted tumours and demonstrate the spectroscopic capability of the technique.
Theory and applications of frequency domain photoacoustic microscopy
Authors: Murray Todd W. , Bramhavar Suraj , Sampathkumar Ashwin , Pouet Bruno
Published: May 2008

In frequency domain photoacoustic microscopy, the pulsed laser source used for ultrasound excitation in conventional photoacoustic imaging is replaced by a low power, amplitude modulated laser source. The acoustic signals are detected using an interferometer or contact transducer, coupled to a RF lock-in amplifier or vector network analyzer. The detection bandwidth reduction afforded by this technique allows for a significant improvement in signal-to-noise ratio (SNR) over systems using pulsed laser excitation. In this paper, the method of frequency domain photoacoustic microscopy is reviewed and compared to the pulsed-laser based approach. Methods for processing the frequency domain data to extract the information of interest are discussed, along with the effects of measurement bandwidth and frequency resolution. A new technique to optically downshift acoustic signals detected using an optical interferometer to a fixed intermediate frequency is presented, which allows for the detection of high frequency (100's of MHz- GHz) acoustic signals using low frequency, low cost detection electronics. Several applications of frequency domain photoacoustic microscopy are presented including the inspection of thin films and environmental barrier coatings and the photothermal operation of nano-electro-mechanical systems. Finally, potential applications of this technique for the characterization of biological media are discussed.
Photoacoustic tomography with a single detector in a reverberant cavity
Authors: Cox Ben , Beard Paul C.
Published: May 2008

In biomedical photoacoustic tomography (PAT), acoustic pulses, generated by the absorption of pulses of near-infrared light, are recorded on an array of ultrasound detectors, and the measured pressure time series are subsequently transformed into an image of the absorbed optical energy density within the tissue. For high resolution imaging, large-area detector arrays with a high density of sensitive, small elements are required. Such arrays can be expensive, so reverberant-field PAT is proposed as a means of obtaining PAT images using smaller arrays or even a single detector. By recording the reflections from a reverberant cavity surrounding the detector(s), in addition to the primary acoustic waves, sufficient information can be captured to allow a PAT image to be reconstructed, without the requirement for a large-area array. Image reconstruction, time reversal, non-uniqueness, and related ideas in quantum chaos will be discussed.
Hybrid photoacoustic - ultrasound transmission parameter imaging in a miniature photoacoustic imager
Authors: Manohar Srirang , Willemink Rene G. , Van Hespen Johan C. , Van Leeuwen Ton G.
Published: May 2008

Photoacoustic imaging is based on detecting laser pulse induced ultrasound transients from absorbing structures in tissue. The technique combines the advantages of a high optical absorption exhibited by tumors for example with the high resolution possible with ultrasound. A conventional photoacoustic imager operating in a CT geometry comprises a light source, an ultrasound detector array and a coupling medium usually water between the subject under investigation and detector. The imaging protocol usually consists of obtaining projections at angles around the subject. Recently we reported a method of measuring the local speed-of-sound variations by the addition of an absorber to the conventional imager, arranged between the light source and subject. This generates an ultrasound signal which interacts with the subject which can then be detected at the far-end by the detector. This allows the measurement of the integrated speed-of-sound (SOS) at projections around the subject leading to the formation of SOS images. In this article we discuss further analysis of the ultrasound obtained at projections to obtain images of the acoustic attenuation as well. In addition conventional photoacoustic images of the subject are also formed. The principle is demonstrated on well-characterized phantoms and we discuss the potential applications of this technique.
Silicon Micromachined Energy Concentrating Acoustic Transducers for Biomedical Applications
Authors: Lal Amit , Ramkumar Abhishek , Araz Muhamet
Published: May 2008

Silicon's high maximum ultrasonic particle velocity, high thermal conductivity, and low internal loss, make it an ideal material for for high-intensity ultrasonic actuators. We have designed and microfabricated silicon ultrasonic horns, which when actuated at their λ/2 longitudinal resonance (using ceramic PZT transducers) concentrate ultrasonic energy and magnify displacements. By incorporating microprobes at the high energy sites we have successfully demonstrated reduction of penetration force on biological tissues. We have also reported cardiac action potential measurement from multiple sites simultaneously within the heart wall by incorporating platinum electrodes on the microprobes. We have reported on mechanical and spatial characterization of seminiferous tubules in the testis in order to extract sperm for artificial insemination. We are currently exploring silicon ultrasonic horns in detecting testicular and prostate cancer in the early stages. In addition, silicon ultrasonic horns can be used for low power ultrasonic pumping and also atomization. By using bulk micromachining techniques an enclosed conduit is opened along the horn. Due to the highly amplified acoustic field at the tip, fluid enclosed in the channel can be atomized from the tip. Reversibly when the tip is immersed in fluid, fluid can also be pumped into the channel due to changing boundary conditions.
Vibrational Characteristics of Harp Soundboards
Authors: Waltham Chris
Published: May 2008

The musical quality of a harp depends on many factors, but key among these is the soundboard. This work sets out to define general vibrational qualities of a good harp soundboard. First, in order to understand the relationship between the vibrational behavior of a bare soundboard and that of the completed instrument, a 36-string harp was built from scratch. Measurements were made at each stage of construction and compared to finite-element calculations. The results showed how the bare soundboard properties affect those of the finished harp. Second, the soundboards of several harps of different sizes were assessed by measuring the admittances along the string bar. These data, and the views of the musicians who play the harps, showed that the most crucial relationship is that between the modal shapes and frequencies of the soundboard, and the position and pitches of the strings attached to it. This allows a general statement to be made about the vibrational qualities of a good soundboard, and suggests a recipe for improving poor soundboards.
Applications of Near-field Acoustic Holography on Small Apertures
Authors: Scholte Rick , Lopez Ines , Roozen N.b. , Nijmeijer Henk
Published: May 2008

Small, finite measurement apertures are a major impediment for accurate and fast application of near-field acoustic holography (NAH). In theory, FFT-based NAH methods are very powerful and acquire extremely fast inverse calculations of the sound field. However, in practice the usually small amount of sensors in a measurement array limit the possibilities of classical implementations of NAH, especially near the edges of the array or measurement grid. An alternative method to, for example, spatial windowing, patch NAH, SONAH, etc. is the recently introduced border-padding technique. This method makes it possible to apply FFT-based NAH with a large increase of accuracy compared to the original methods, specifically at the measurement grid edges, while maintaining the high speed of the inverse process PNAH is known for. This work focuses on the application of border-padding and the practical implementation in a newly developed PNAH system. It illustrates a large variety of extended possibilities for PNAH that border-padding enables. Apart from the earlier introduced standard border-padding, experimental results are shown for a highly improved border-padding method. Measurements and calculations on industrial products illustrate the wide applicability of the presented method.
Regularization method applied to deconvolution problem in Real-Time Acoustic Holography
Authors: Paillasseur Sebastien , Thomas Jean-Hugh , Pascal Jean-Claude
Published: May 2008

Near-field Acoustic Holography (NAH) [Maynard et Williams, 1985] is a measuring process for locating stationary sound sources from measurements made by an antenna of microphones positioned near the acoustic source plane. In order to characterize non-stationary sources, a new formulation has been introduced [Grulier, 2004] to propagate signals on a forward plane using a convolution product with an impulse response in the time-wavenumber domain. The purpose of this study is to solve the deconvolution problem in order to introduce the Real-Time Acoustic Holography and to test its accuracy. Taking the evanescent waves into account improves the spatial resolution of the solution but makes the deconvolution problem "ill-posed". Thus, the inverse of the impulse response is neither unique nor stable. Then, regularization methods that consist of giving an other constraint to the solution to solve this problem are studied. In particular, the standard Tikhonov regularization is used, which is based on the minimisation of the solution's energy, combined with generalized cross validation to estimate the regularization parameters. This method provides an image representation of the time dependent pressure of the source plane in order to localize and characterize the different sound sources.
Precise localisation of noise source using statistically optimal beamforming and post -processing deconvolution
Authors: Pascal Jean-Claude , Li Jing-Fang , Carniel Xavier , Hass Axel , Bollade Laurent
Published: May 2008

Conventional data-independent beamforming with microphone array is widely used to locate sound sources and build acoustic model of equipments, engines and vehicles. The particularities of this technique are the use of a relatively few number of microphones and a simple signal processing. So, this technique is fast and easy to use. Other approaches using experimental data for computing the steering vector have been proposed to increase the resolution, for example, minimum variance method, and high-resolution methods. However these methods are often delicate to put in use in acoustic engineering where they are often reproached for lack of robustness in perturbed acoustic fields. Whereas, the most used methods nowadays are those by which the determination of the steering vector is data-independent. Among those methods we consider a method using a Statistically Optimal Array Processing (SOAP) completed by techniques of post-processing deconvolution, by which the resolution of the conventional beamforming is considerably increased, particularly at low frequencies. Some relevant indicators evaluate the performance of the proposed method by using perturbed data and by comparing between conventional and high-resolution beamformers. Examples of industrial measurements in a multi-sources environment demonstrate the practical interest of this technique.
Directional Recording and Analysis of Sounds from Musical Instruments
Authors: Zotter Franz
Published: May 2008

The sound of musical instruments doesn't radiate omni directionally into the sound field. Moreover, each component of the sound (e.g. a partial) can have its own directivity pattern which, in turn, may also vary over time. In general, the radiated sound in free space will have a different timbre at different locations around the sound source. In many cases the description of a particular radiation pattern contour may not be valid for other instruments, tones, playing techniques or even the same musical gesture on the same instrument. Consequently, this work focuses on the synchronous capture and analysis of musical sound sources with a spherical microphone array. In order to analyze the directivity in its very detail, a spatial model for radiated sound is suggested. Assuming coherent signals, a common signal decomposition is applicable. The relations between the signal components yield the desired directivity patterns. Spherical harmonics interpolation between the discrete measurement points allows for the estimation of the radiation in a continuous angular space.
Improving the localisation of sources based on shaped arrays with a reduced number of microphones
Authors: Lamotte Lucille L. , Leclere Quentin
Published: May 2008

The capacity of hardware today allows carrying out noise sources locali-sation without moving the microphone array at a limited financial and time cost. The single shot measurement processed with beamforming is comfortable for the user. But the quality of the results limits the interest of such systems: bad resolution, low dynamics and no quantitative levels. This article proposes complementary methods to beamforming to improve the results based on the same single measurement. First a near field beamforming algorithm is developed improving the resolution, and then an inverse method is applied based on the transfer function between the sources and the acoustic pressure at microphone positions or on the hologram in order to "clean" the localisation map and give quantitative results.
Tyre/road noise prediction: A comparison between the SPERoN and HyRoNE models - Part 1
Authors: Beckenbauer Thomas , Klein Philippe , Hamet Jean-François , Kropp Wolfgang
Published: May 2008

The SPERoN and HyRoNE models predict the pass-by tyre/road noise of a passenger car from intrinsic characteristics of the road surface. Both models are hybrid: they combine statistical laws with physical models. With a computing time of a few minutes (very quick compared to full physical models), they provide operational tools for tyre/road noise prediction. Particular fields of interest are road surface optimisation with respect to noise at the laboratory scale, conformity of production of a new surface and acoustic monitoring of roads. They are now implemented as user-friendly stand-alone applications. The presentation will address the principles of the models, their performances and their respective main fields of application. Part 1 will address the principles of the models and their respective fields of application.
Experimental study of dynamical contact forces for tyre/road noise application
Authors: Cesbron Julien , Anfosso-Ledee Fabienne , Duhamel Denis , Yin Hai Ping , Le Houedec Donatien
Published: May 2008

This paper deals with the experimental study of tyre/road contact forces in rolling conditions for tyre/road noise investigation. In situ measurements of contact forces and CPX noise levels were carried out for a slick tyre rolling on six different road surfaces at rolling speeds between 30 km/h and 50 km/h. Contact stresses were measured at a sampling frequency around 10000 Hz using a single array of digital pressure sensitive cells both in the transverse and in the longitudinal directions. The contact areas obtained during rolling were smaller than the one measured in statics. This could be due to an influence of the viscoelastic behavior of the rubber of the tyre tread during rolling. Additionally the global energy of the longitudinal contact forces at different speeds were in the same order for the six road surfaces, while their spectrums at different speeds were quite different. This may be explained by a spectral influence of the vibration of the tyre during rolling. Finally, the levels of longitudinal contact forces and CPX noise measured at 30 km/h were correlated. A high positive correlation was found around 800 Hz, which frequency could be directly linked to the road texture.
Monitoring 20 Silent Roads Over 10 Years In The Municipality Of Groningen
Authors: Van Keulen Wim
Published: May 2008

The municipality of Groningen in the northern part of the Netherlands has a wide experience with the application of silent roads. This experience covers a period of about 20 tracks with 2-layered porous asphalt and various types of thin layers. These tracks have been and are monitored regularly. The obtained data from 10 years monitoring offer a vast amount of valuable information on noise reduction, durability, maintenance, costs, contracts and policy. The municipality of Groningen in the northern part of the Netherlands has a wide experience with the application of silent roads. This experience covers a period of about 20 tracks with 2-layered porous asphalt and various types of thin layers. These tracks have been and are monitored regularly. The obtained data from 10 years monitoring offer a vast amount of valuable information on noise reduction, durability, maintenance, costs, contracts and policy.
A quiet poroelastic road surface manufactured in a normal asphalt mixing plant
Authors: Nilsson Nils-Åke , Ulmgren Nils , Sandin Ake
Published: May 2008

A poroelastic road surface for low tire/road noise has been developed. It is manufactured using conventional asphalt mixing plants and conventional paving machines. Crumb rubber was added to the mix for attaining the desired elastic characteristics. The crumb rubber was subject to a long term pre-treatment before feeding it to the plant mixer. This ensures both long term durability and excellent adhesion to the binder. The crumb rubber grain size and amount in the mix has been carefully tuned to the aggregate grain size. By the pre-treatment of the crumb rubber the crumb rubber amount can be freely selected since it is not locked to the amount of binder (as for the hot bitumen pre-mixer technique) Single layer poroelastic road surface sections has been paved in Gothenburg. The reduction of noise relative to a SMA16 was found to be 4-6 dB(A) depending on the vehicle speed and amount of crumb rubber. The surface is almost unaffected by wear after 6 months winter traffic with studded tyres. Tuning the recipe for further increased reduction of the tire/road noise continues. Fundings from European Commission (project Quiet City Transport (QCITY)) is acknowledged.
Measurement techniques for airframe noise source identification
Authors: Burdisso Ricardo A.
Published: May 2008

Despite the significant progress achieved over the last three decades, noise pollution generated by aircraft around airports is still an obstacle to the further growth of the aviation industry. The engines and airframe constitute the main sources of the overall aircraft noise. Airframe noise is as important as the engine noise on approach due to the engines operating at low thrust. High-lift devices and landing gears are the dominant airframe noise components. Many efforts have recently been devoted to accurately locate and control the specific components of the airframe noise. Experimental studies on airframe noise include full-scale flight tests, and tests conducted on isolated small-scale models in both hard-walled and anechoic wind tunnels. These experimental efforts on airframe noise have been greatly helped by the advent of the microphone phased array technology. This presentation will focus on microphone phased array measurement techniques, in particular for model scale testing in wind tunnels. Issues such as beamforming algorithms, data corrections, effect of flow and acoustic environment on the measurements (hard-wall vs anechoic tunnels), etc. will be discussed. Illustrative results from experimental measurements of landing gear and high lift devices performed at the Virginia Tech wind tunnel will also be presented.
Reduction technologies and prediction of high lift noise
Authors: Delfs Jan W.
Published: May 2008

In the final approach phase airframe noise represents the ultimate aircraft noise barrier for future aircraft when equipped with quiet UHBR engines. This paper presents some of the main dependencies of high-lift noise sources on flow conditions as derived from extensive noise testing at DLR. Some successful reduction technologies for high-lift noise are discussed in view of their influence on the noise generation mechanisms. The remainder of the paper focusses on the numerical prediction of high-lift noise. The prediction concept as implemented in DLR's PIANO code is discussed. It is based on a two step approach, a) the computation of the time averaged turbulent flow field as a result of a CFD(=Computational Fluid Dynamics) simulation and b) the highly accurate CAA (=Computational Aeroacoustics) simulation of perturbations about this mean flow. The prediction relies on an advanced stochastic modelling of the turbulence related sources and thus avoids time consuming turbulence simulations. The method represents an accurate yet "low cost" prediction of high-lift noise. This is particularly important for real applications at flight (very high) Reynolds numbers and corresponding design trade-off studies, which typically require the computation of large numbers of configurations. Examples for such kind of applications are given.
On the reduction of flap side edge noise
Authors: Hutcheson Florence , Brooks Thomas F.
Published: May 2008

Results from flap side edge noise reduction experiments are presented. The test model used was a NACA 632-215 main-element airfoil with a half-span Fowler flap. The flap side edge was flat for the baseline configuration. The effect that small geometric variations of the flap edge have on the noise spectra is shown, and noise measurements from a "continuous mold-line link" (CML) flap configuration are presented. These measurements are compared to those obtained from the baseline flap. The results indicate that a large level of noise reduction is achieved using the CML flap. Finally, Particle Image Velocimetry (PIV) measurements of the flow in the region of a flap side edge are presented for a blowing flap configuration. In this active control approach, air was blown from small slots located along the side edge of the flap to weaken the vortex system that is present in that region of the flap. These measurements are presented to show the effects that the flap tip jets have on the structure of the flap side edge flow, and the potential that this blowing flap configuration has in reducing flap side edge noise.
Contemporary soundscape of ancient theatres
Authors: Chourmouziadou Kalliopi , Kang Jian
Published: May 2008

Ancient drama is performed every summer in ancient theatres in the Mediterranean countries, especially in Greece. In many cases the performance conditions in terms of acoustics are poor, due to the effects of external noise sources. There is often a motorway constructed near an archaeological site, without careful consideration regarding the impact on the overall soundscape. Previous studies have demonstrated the effectiveness of purposely designed scenery on improving the internal acoustic conditions, and this study investigates the contribution of scenery to the improvement of the acoustic environment of ancient theatres in terms of reducing nearby traffic noise. The acoustic simulation for the theatre of Philippi, with scenery design in the form of a background wall in different sizes, suggests that there is a decrease in traffic noise by about 4dB. Further improvements have also been demonstrated with noise barriers of various heights and lengths. Different levels of traffic flow have been examined. It is expected that the results will be verified by on-site measurements and recordings of summer performances will be presented during the conference.
Thermal ageing evaluation with nonlinear elastic wave spectroscopy method of carbon fiber reinforced plastic composite plates
Authors: Guenab Faouzi , Duflo Hugues
Published: May 2008

The excellent and specific properties of composite materials in the various fields such as aeronautics, transport, energy, the nuclear power and civil engineering led to the need of knowing their behaviours in presence of defect (crack, ageing, delamination...). Therefore, the aim of this paper is to study the thermal ageing of the carbon fibre reinforced composite plates, using their nonlinear behaviours. The method used to achieve this work is the NEWS method (Non-linear Elastic Wave Spectroscopy), where two alternatives of this one are used. The first one is SIMONRUS which involves a study of the nonlinear response of a single resonant mode of the plate according to various amplitudes of excitation. In this case, the nonlinear phenomena analysed are resonance frequency shift and damping characteristic of different level ageing of plate. The second one consists in studying the frequential response and the harmonics generated at the multiple of a resonance frequency f (at f, 2f, 3f...) caused by the ageing. Evolution of non linear effetcts are then correled to ageing duration
Finite element simulation of the linear and nonlinear interaction of progressive acoustic waves with a standing acoustic wave field
Authors: Lamkanfi Ebrahim , Declercq Nico F. , Van Paepegem Wim , Degrieck Joris
Published: May 2008

Throughout the 20th century studies have been published on the scattering of sound by sound. It has been shown that a combination of nonlinear effects and diffraction effects exists. Approximate models have been developed and some have been verified by experiments. The report presents a finite element simulation of the effect and results in exact solutions for configuration under consideration. It is shown that, depending on the amplitude of the standing wave field, orthogonally incident sound waves diffract. A simplified model is developed for linear interactions, followed by a more realistic model incorporating nonlinear elastic effects. The study is performed in a liquid and also in a solid. Analysis is achieved by Fourier transformation and a comparison is made with diffraction laws governed by the grating equation. For simplicity a 2D model is presented that is extendible however to a 3D problem should that be necessary. Comparison with some of the earlier published approximate results is also performed. The study shows the detailed influence of the amplitude on the strength of the diffraction effect.
Chirp-coded excitation applied with advanced pulse inversion for nonlinear acoustics in complex steel samples
Authors: Dos Santos Serge , Goursolle Thomas , Drab Martin , Slunecko Tomas
Published: May 2008

Nonlinear acoustics for nondestructive testing is still an emergent technique in complex materials with localized cracks because linear effects can be cancelled using specific symmetries for the pre- and post-signal processing. The local nonlinear signature is accessible even in complex aeronautic structure by using the symmetry properties: i. e. time reversal invariance and pulse inversion associate to chirp-coded excitation. Excitation Symmetry Analysis Method [Dos Santos et al., JNLM, 2007] which is an extension of the pulse inverted method for extraction of third order nonlinearity is applied experimentally for the measurement of relative level of nonlinearity on a airplane steel bracket, on which visible crack was created by fatigue tests. This pre-processing method has been coupled to a 100-250 kHz bandwidth chirp-coded ultrasonic excitation, realized at various amplitude (A, A/2, 31/2A/2, etc.), and performed with DAKEL IDK09 200 kHz PZT sensors. Signal processing based on correlation measurements, allow an extraction of the nonlinear signature versus fatigue level. Experiments and data processing have been conducted with a 12 bit DAKEL-DTR system in the bandwidth 80-800 kHz and compared with a continuous 4 channel acoustic emission device.
The atmospheres of Mars, Venus and Titan: observed and modelled structures
Authors: Lebonnois Sebastien
Published: May 2008

In our solar system, three bodies possess atmospheres presenting similar characteristics with our own environment: our neighbours Mars and Venus, and also Saturn's largest satellite Titan. The comparative study of these different atmospheric systems provides many insights on their respective behaviour, and helps understand the processes at work within these complex systems. In this review, the observed vertical and latitudinal structures of these atmospheres are presented, including their variability and seasonal evolution. Waves that have been observed are also shown, e.g., thermal tides, gravity waves. Global Climate Models that have been developed to study such atmospheric systems are also presented. Using these tools, production and role of the different waves present in each atmosphere may be studied.