bluuebunny/crossref_metadata_2025 huggingface dataset:
Ocean acoustic tomography: Travel-time inversion in the eastern Fram Strait
Authors: Skarsoulis Emmanuel , Piperakis George , Kalogerakis Michael , Sagen Hanne
Published: May 2008

The Fram Strait is the main passage through which the mass and heat exchange between the Atlantic and the Arctic Ocean takes place. In the framework of DAMOCLES project (EU/FP6) a tomography experiment is planned to be conducted at latitude of 78N50 between 1E and 7E. A near-real-time discrete inversion scheme has been developed relying on the matched-peak inversion approach seeking to maximize agreement between theoretical and observed peaks. The model relations between model parameters (temperature distributions) and travel times are implemented using a ray-tracing code accounting for the effects of range dependence. The parameter space is discretized and the corresponding model relations are stored in a database for later use - stored model relations greatly accelerate the inversion process. In the absence of real measurements the performance of the inversion scheme was tested using synthetic data relying on 3-year long time series of temperature data. The particular propagation conditions give rise to different inversion errors at different depths, with the minimum obtained at 250 m depth, in the core of the northward flowing Atlantic water. For the implementation of the tomographic analysis a software system called SMTAS has been developed running in a dedicated server connected to the internet.
Temperature and size-dependence of the vaporization threshold of phase-shift emulsions
Authors: Porter Tyrone , Zhang Peng
Published: May 2008

Acoustic cavitation has proven to be important for several therapeutic applications of ultrasound. However, acoustic cavitation is difficult to initiate and sustain in the absence of cavitation nuclei, particularly in tissue. Phase shift emulsions are ideal candidates for cavitation nuclei for in vivo applications. These emulsions, which consist of superheated liquid perfluorocarbon droplets enclosed by albumin shells, may be vaporized with acoustic pulses, a process known as acoustic droplet vaporization (ADV). In this study, we determined the ADV threshold at 2 MHz as a function of temperature and droplet size. Studies were conducted with micro- and nano-sized emulsions in a closed-flow system immersed in a temperature controlled water bath. The emulsions were injected into a flow system and exposed to high intensity focused ultrasound (HIFU; acoustic parameters: 2 MHz, 10 cycles, 100 Hz pulse repetition frequency). A portable diagnostic ultrasound scanner was used to monitor for vaporization. Upon vaporization, the peak rarefactional pressure of the acoustic pulse and the water bath temperature were recorded. It was determined that the vaporization threshold was independent of droplet size and inversely proportional to temperature. The utility of these emulsions in cancer therapy, particularly for bubble-enhanced heating during HIFU exposure, will be discussed.
Quantitative intravascular ultrasound elasticity imaging as an imaging biomarker in clinical trials
Authors: Van Der Steen Ton , Schaar Johannes A. , Mastik Frits , Garcia Hector , Danilouchkine Mike , Baldewsing Radj , Serruys Patrick W.
Published: May 2008

The composition and morphology of an atherosclerotic lesion are currently considered more important determinants of acute coronary ischemic syndromes that the degree of stenosis. When a lesion is unstable, it can rupture and cause an acute thrombotic reaction. An unstable plaque can be characterized by a lipid core that is covered by a thin fibrous cap, which has been locally weakened by inflammatory cells. Intravascular Ultrasound Palpography is an intravascular ultrasound based technique that is capable to measure the local strain in coronaries and atherosclerotic plaque. This strain is induced by varying intraluminal pressure. This lecture will show principles of the technology and how this technology is used in clinical trials. Results from a trial with traditional lipid lowering treatment (IBIS1) and from a trial on the efficacy of a new medication (IBIS2) will be presented. Furthermore the potential of Intravascular Ultrasound Modulography will be discussed. This work is financially supported by the Dutch Technology Foundation, The Dutch Heart Foundation and a research grants from Volcano Corporation and Glaxo Smith Kline
Recent progress of acoustic microscopy for medicine and biology
Authors: Saijo Yoshifumi , Kobayashi Kazuto , Iwamoto Takahiro , Okada Nagaya , Tanaka Akira , Hozumi Naohiro
Published: May 2008

Dramatic shortening of the calculation time provided by the recent progress of the computer technology has made biomedical researchers possible to assess nonlinear acoustic phenomena in soft materials which had been assumed as acting linearly. Besides, the spread of Windows-based personal computer and peripheral devices enabled easier and cheaper configuration of the whole acoustic microscope system such as pulse generation, analogue/digital conversion, mechanical scanning and image processing. According to these progresses, conventional acoustic microscopy with only C-mode imaging has widened its data acquisition mode to B-mode, C-mode, surface acoustic impedance mode, and three-dimensional (3D) imaging. The base of our acoustic microscope system was consisted of (1) PVDF transducer with the central frequency of 100 MHz, (2) ultrasonic pulser made of high speed semiconductor switching, (3) mechanical scanner using two linear servo motors, (4) high speed PCI card digitizer with the sampling frequency of 2 GHz, and (5) personal computer controlling the whole system. For skin imaging, 3D imaging of the fingerprint was reconstructed by consecutive B-mode imaging. Surface acoustic impedance imaging of the fingerprint can be obtained by just putting a finger on a thin plastic plate of the transducer. Conventional C-mode imaging of thinly sliced skin sample presented quantitative values of thickness, attenuation and sound speed of the tissue.
Improved cancer detection and classification using multi-parameter quantitative ultrasound
Authors: Oelze Michael L. , O'Brien, Jr. William D.
Published: May 2008

Quantitative ultrasound (QUS) has been used successfully to differentiate benign from malignant solid tumors in animal models of breast cancer. In these studies, QUS made use of estimates of average scatterer diameter (ASD) and average acoustic concentration (AAC) from the ultrasonic backscatter. However, initial attempts to classify different kinds of malignant tumors based on ASD and AAC estimates were not successful. New models for ultrasonic backscatter were created by considering the cytoskeletal structure of cells. In addition, the homodyned K distribution was used to model the amplitude of the envelope from regions-of-interest in the malignant tumors. The homodyned K distribution yielded two parameters: the S parameter, which quantified the randomness of scatterer spacings, and the β parameter, which quantified the amount of clustering of scatterers in the interrogated tissue. Statistically significant differences (P < 0.05) were observed between average S and β parameters from the malignant tumors. Furthermore, statistically significant differences (P < 0.05) were observed between ASD and AAC estimates from the malignant tumors using the new scattering models at ultrasonic frequencies above 16 MHz. The use of four parameters, as opposed to two, improved the ability to uniquely classify different kinds of malignant tumors. [Supported by NIH R01CA111289.]
Transient elastography in heterogeneous tissues
Authors: Bastard Cécile , Oudry Jennifer , Mofid Yassine , Sandrin Laurent
Published: May 2008

The Fibroscan® (Echosens, Paris, France) is a transient elastography based device used to quantify liver fibrosis by following the propagation of a low frequency shear wave and measuring the mean Young's modulus of the liver. This device has been successfully applied to homogeneous tissues such as liver in patients with chronic hepatitis C. Current developments in transient elastography are now headed toward the characterization of heterogeneous tissues. The estimation of the shear wave velocity can be achieved by solving the elastic wave equation taking into account either the 1D, the 2D, or the 3D components of the displacement spatial derivatives. The objective of this study is to characterize focal nodules in human liver and to quantify heterogeneous fibrosis. We present the methods used to estimate the local shear wave velocity and the results of experiments conducted on heterogeneous phantoms and in the liver in vivo.
An acoustic technique for mapping and sizing particles following needle-free transdermal drug and vaccine delivery
Authors: Condliffe Jamie , Schiffter Heiko , Coussios Constantin C.
Published: May 2008

Needle-free ballistic particle injection enables painless transdermal delivery of pharmaceuticals. To improve the efficacy of this technique, a non-invasive method of assessing particle penetration depth, distribution and changes in particle size following injection is required. Polydisperse distributions of polystyrene particles, mean diameter 25 μm, and insulin particles, mean diameter 44 μm, were injected into both tissue-mimicking phantoms and porcine skin, which they penetrate to a mean depth of 300 μm. Following injection, the surface of the targets was scanned using a 50 MHz focused ultrasound transducer driven in pulse-echo mode. The received waveforms were post-processed to estimate particle penetration depth and distribution in the plane perpendicular to injection. The targets were then sectioned and optical microscopy was used to validate the acoustic results. Furthermore, computational implementation of an exact solution for sound scattering by an elastic sphere allows prediction of the frequency response of the insonified particles. Direct comparison of the theoretical model with the frequency content of experimental data is shown to provide an accurate means of estimating particle size, and is being extended to correlating particle size with penetration depth. The acoustic technique shows great promise as a non-invasive means of mapping, sizing, and assessing stability of drug particles following needle-free injection.
On the need for basic theoretical, numerical, and experimental research in the development of useful standards for focused ultrasound therapy
Authors: Kaczkowski Peter , Bailey Michael R. , Khokhlova Vera A. , Sapozhnikov Oleg A.
Published: May 2008

High intensity focused ultrasound (HIFU) is rapidly gaining widespread clinical use in China, and is undergoing regulatory evaluation in Europe and the US for many target diseases. There is rising concern within the HIFU community that no standards exist for measuring or reporting of HIFU fields, inhibiting broad clinical adoption of HIFU. This paper addresses current technical gaps for the development of such standards. High power and strong focusing combine to make accurate measurements of focal fields difficult. No simple way exists to extrapolate in-water field measurements directly to patients, and thus to calculate temperature rise and therapeutic dose in tissue. To arrive at a set of characteristic parameters for HIFU systems that are both clinically relevant and are practical to measure reliably, we believe several avenues of research are needed. Numerical models that include nonlinear acoustic propagation must be carefully validated with experiments, and both numerics and experimental methods must be standardized for broad dissemination. Mechanisms of enhanced tissue heating due to nonlinear effects must be experimentally quantified, and robust accurate models developed. These advances in understanding must be transitioned into practical recommendations for standard metrics and methodologies to facilitate industrial development and regulatory oversight.
Towards a standardized approach for quantifying inertial cavitation activity
Authors: Collin Jamie R. , Webb Ian , Roy Ronald A. , Coussios Constantin C.
Published: May 2008

Relative measures of the energy radiated as broadband noise emissions by inertially cavitating bubbles, such as the mean square voltage received using a passive cavitation detector (PCD), have been recently shown to be directly relatable to cavitation-mediated bioeffects. Even though numerous techniques exist to detect inertial cavitation qualitatively, there is presently a lack of a unified approach that makes it possible to quantify and compare levels of cavitation activity across different experimental setups and conditions. A technique has been developed that uses a calibrated sound source, a hydrophone, and a point spherical scatterer of known frequency response embedded in a tissue-mimicking material to achieve an absolute calibration of a PCD on receive. This makes it possible to relate the PCD signal during inertial cavitation activity to the acoustic power radiated as broadband noise in the proximity of the bubble cloud. The technique is validated against PCD measurements of single-bubble inertial cavitation activity in a tissue-mimicking material and compared to theoretical predictions using the Keller-Miksis model. Calibrated measurements of acoustic power radiated as broadband noise emissions could thus provide a quantitative measure of cavitation dose that can be directly related to resulting bioeffects, such as increased sonoporation or enhanced heating.
An autonomous moored ocean profiler
Authors: Cray Benjamin
Published: May 2008

An unconventional set of environmental and acoustic data, measured from an autonomous moored ocean profiler, is presented. The profiler is a programmable robotic underwater winch and data acquisition system that cycles vertically through the water column. The system profiles at pre-determined time intervals, surfaces to transmit data via RF links, and can be deployed for up to 180 days. Built by WETLabs Incorporated (Western Environmental Technology Laboratories) for the Naval Underwater Systems Center (NUWC), the system is outfitted with three environmental sensors and two acoustic vector sensors. The environmental sensors include; a Nortek Vector velocimeter which samples current components and characterizes surface wave velocities, a Seabird FastCAT Conductivity, Temperature, Depth (CTD) sensor; and a Wetlabs Fluorometer-Turbidity optical sensor that measures both chlorophyll-a and turbidity. The Wilcoxon acoustic vector sensors measure acoustic pressure and the three components of acoustic particle acceleration. Wilcoxon Research (a subsidiary of Meggitt Corporation) and Applied Physical Sciences (APS) have developed underwater acoustic vector sensors for many applications. The quality and sensitivity of these vector sensors has steadily improved. A review of early (pre-2002) vector sensor development efforts is discussed.
Broadband transducers for underwater communications
Authors: Brown David , Bachand Corey , Aronov Boris
Published: May 2008

Properties of underwater acoustic cylindrical piezoelectric (PZT) transducers currently used for broadband underwater communications with unmanned underwater vehicles (UUV) and new transducers under development utilizing single crystal relaxor ferroelectrics (PMN-PT) with significantly higher material coupling coefficients and lower sound speed are presented. Characteristics including resonance frequency, coupling coefficient, transmit (TVR) and receive (OCVS) frequency response, maximum drive and achievable source levels, tuned and untuned power factor, and directivity factors are discussed. Results for experimental calibrations and field tests will be compared with detailed equivalent electrical circuit models of the transducer and transducer channel. Work supported in part by BTech Acoustics and Office of Naval Research.
Acoustical methods for azimuth, range and heading estimation in underwater swarms
Authors: Zimmer Uwe R. , Kottege Navinda
Published: May 2008

Acoustical Methods for Azimuth, Range and Heading Estimation in Underwater Swarms Enhanced, embodied autonomy in small submersibles enables the design and deployment of practical swarms of autonomous underwater vehicles (AUVs). The swarming paradigm requires for each vehicle location awareness of at least its near neighbors. The Serafina AUV swarming project additionally requires a localisation system which could cope with the dynamic and fast changing vehicle configurations while being small, reliable, robust, and energy efficient and not dependent on pre-deployed acoustic beacons. The short-range acoustical relative localisation system proposed here, uses hyperbolic and spherical localization concepts and provides each vehicles with the azimuth, range and heading of its near neighbours. The implementation utilises an acoustically transmitted MLS signal which provides extremely high robustness against interference by stochastic and systematic disturbances which are typical for underwater environments. The azimuth is obtained via hyperbolic positioning with improved resolution and accuracy with respect to conventional methods. Range and heading estimation is achieved by two independent methods for increased robustness; one uses the implicit synchronisation provided by the underlying inter-vehicle communication scheduling system to measure the difference of TOAs of an acoustic and a long-wave radio signals; the second relies on TDOAs and a reverse hyperbolic localisation scheme.
A comparison of measured and theoretical performance of a co-centred rigid and open spherical microphone array
Authors: Jin Craig , Parthy Abhaya , Van Schaik Andre
Published: May 2008

We present a comparison of the measured and theoretical performance of a dual co-centred spherical microphone array that consists of an open spherical microphone array with a smaller, rigid spherical microphone array at its centre. The dual co-centred spherical microphone array has 64 microphones, with 32 microphones on the open spherical microphone array of radius 6.30 cm and 32 microphones on the rigid spherical microphone array of radius 1.63 cm. We have previously shown [1] that this even distribution of microphones, between the two spherical microphone arrays, provides a greater frequency range of operation for a third-order, 64-channel spherical microphone array compared to a single rigid 64-channel spherical array. The performance of the dual co-centred spherical microphone array is measured in an anechoic chamber using a speaker mounted on a robotic arm. A comparison is made between the theoretical and measured directivity pattern for various frequencies. [1] A. Parthy, C. Jin, and A. van Schaik "Optimisation of Co-centred Rigid and Open Spherical Microphone Arrays," in Proc. of 120th Audio Engineering Convention, Paris, France, May 20-23, 2006.
Acoustics of open fittings
Authors: Blau Matthias , Sankowsky Tobias , Stirnemann Alfred , Oberdanner Hannes , Schmitt Nicola
Published: May 2008

The use of so-called "open fittings" instead of individual ear shells has become very popular in hearing aid fitting, in particular because the open fittings avoid the occlusion effect, but also because they are more comfortable, easier to manufacture, and cosmetically preferred. On the other hand however, there are acoustical issues with open fittings, including the mixture of direct and amplified sound, a poor low-frequency performance, an increased risk of feedback and a supposedly less reproducible position of the sound delivering device (tubing or speaker) in the ear canal, which in turn may result in a greater variability of acoustic parameters such as RECD and REOG. The two latter issues are addressed here in a study with 20 subjects, for individual shell and a number of open fittings, comprising closed and open domes of different diameters with tubings as well as with ear canal receivers. It was observed that in comparison to individual shell fittings, the open fittings did not exhibit higher interindividual differences of RECD and REOG, but up to 15 dB (closed domes) to 25 dB (open domes) lower feedback thresholds.
Estimation of maximum stable gain in a hearing aid
Authors: Merks Ivo L. , Recker Karrie , Natarajan Harikrishna P. , Theverapperuma Lalin S.
Published: May 2008

Feedback cancellation (FBC) algorithms have become an important part of hearing aids, allowing the Maximum Stable Gain (MSG) to be increased by up to 25 dB beyond what is possible without an FBC. Although FBC algorithms have improved the usability of hearing aids, it is difficult to predict the MSG for a given individual with a particular hearing aid. Knowledge of this information would enable the audiologist to make more informed decisions regarding the appropriateness of a hearing aid/earmold, and it could be used to counsel the patient regarding feedback. A method of estimating the MSG of a hearing aid with and without an FBC will be presented. The method uses a finite impulse response filter to approximate the acoustic path. The filter coefficients are estimated during the initialization of the FBC. From these filter coefficients, the MSG for the hearing aid with and without FBC are calculated. This method has been implemented in the firmware and fitting software. Using a variety of device styles, microphone modes and feedback paths, it has been verified that the estimated MSG matches the actual MSG within 6 dB for 90% of hearing aids.
"Auditory scene analysis" in hearing instruments
Authors: Froehlich Matthias
Published: May 2008

The term "auditory scene analysis" generally refers to a categorization of a given acoustic situation based on the acoustic signal only, where the results determine the subsequent processing of the acoustic signal within some auditory context. According to this definition, several approaches can be differentiated in the field of hearing instrument development. They differ in the computational complexity of the particular analysis methods applied, as well as in the subsequent action. Some of these approaches have been realized in commercially available hearing instruments, others lie still ahead. A simple example of the former category is noise reduction algorithms that address different classes of noises, examples of the latter are MPEG4-like virtual arrangements of media objects. In the presentation, different approaches will be discussed in terms of potential benefit and technical realization, as well as their limitations. For approaches already realized in commercially available hearing instruments, the expected benefit will be aligned with results from clinical studies.
Real-world effectiveness of directional microphone hearing aids
Authors: Bentler Ruth
Published: May 2008

Single, dual, triple, and array microphone designs that are static, automatic and/or adaptive are now available in marketed hearing aids. The cost of designing and producing these more sophisticated systems is significant; yet, studies of user benefit are often equivocal, particular those involving self-report or field-obtained measures. In a series of studies we have attempted to characterize (model) the function of a number of these designs in simple and complex environments in an effort to explain the results obtain in both laboratory and field studies. Rather than directivity limitations, factors such as internal noise, loudness preference and visual cues have all been implicated in the limited user benefit, and will be discussed in this presentation.
A two-stage binaural speech enhancement approach for hearing aids with preserving binaural benefits in noisy environments
Authors: Li Junfeng , Sakamoto Shuichi , Hongo Satoshi , Akagi Masato , Suzuki Yôiti
Published: May 2008

Speech enhancement is one of the most crucial functions, if not the most, in hearing aids, as hearing impaired people have great difficulty in understanding speech in noisy environments. In this paper, we propose a two-stage binaural speech enhancement approach for hearing aids, which consists of interference estimation by pre-trained adaptive filters and speech enhancement using the Wiener filters. Main attention is then paid to the theoretical analysis of this system and the experimental comparisons with the traditional binaural speech enhancement approaches. The comparisons are conducted with the following two considerations: interference suppression performance and the ability in preserving binaural cues which give birth to listener's own “binaural gain.” We finally give the general discussion on this proposed binaural speech enhancement algorithm from the viewpoints of theory, through implementation, to evaluation.
Magnetostrictive compacted sonar transducer design
Authors: Butler Stephen C. , Slaughter Julie
Published: May 2008

A compact modular high power magnetostrictive sound source that is capable of producing scanning Cardioid beams every 45 degrees in the horizontal plane and operates over one octave has been fabricated. The device consists of 8 transducer elements in the form of a ring that radiates acoustic energy radially outward. This design uses the operation principles of a peizoceramic transducer of similar design [J. L. Butler and A. L. Butler, J. Acoust. Soc. Am. 119, 3409 (2006)], which operated in a higher frequency band. The sound source can be driven to form omni-directional, dipole, and quadrupole beam patterns. By combining the measured electrical drive and acoustic pressure amplitude and phase coefficients of these beam patterns a narrower type Cardioid beam pattern is generated. The transducer elements are of a tonpilz type vibrator consisting of magnetostrictive Terfenol-D drive rods sandwiched between radiating head mass and a tail mass that is common to all elements with tie bolts consolidating the parts together. The Terfenol-D rods are interlaced with rare earth magnets to provide the DC magnetic bias field for the AC drive field provided by a coil. FEA models using ATILA and COMSOL are used for structural and magnetic analysis predictions of the device. [Work supported by ONR.]
Calibration of apparatus for wave separation in wind instruments
Authors: De Sanctis Giovanni , Van Walstijn Maarten
Published: May 2008

Knowledge of the forward and backward traveling waves inside the bore of a wind instrument is a useful starting point for the estimation of its playing parameters. These are mainly parameters describing the mouthpiece embouchure and the states of the tone holes. Due to the highly nonlinear behaviour of the excitation mechanism, a precise estimation is needed. The separation method under investigation relies on a model inversion, starting from the pressure measured by three microphones. For this reason the estimation is very sensitive to the relative positions of the microphones, and the latter must therefore be known very precisely. A geometrical measurement would not be reliable because of construction tolerances, including uncertainties about the acoustic centers of the microphones; therefore the distances are gathered through audio measurements. A number of approaches to such a calibration of the measurement system have been investigated, using a purposely constructed apparatus which will also be described.
Frequency and phase characteristics of the edge tone
Authors: Paál György , Vaik István
Published: May 2008

Extensive experimental and computational work was performed to characterize the edge tone phenomenon. The dependence of the oscillating frequency on some of the main parameters of the configuration including the nozzle-wedge distance and the profile and the mean velocity of the jet was measured. The frequency was obtained from the FFT of a pressure sensor signal. The measured and computed frequencies are compared and show a very good agreement. For both the CFD simulations and the experiments the phase of the oscillation and the pressure at specified points on the wedge are correlated. For the experiments the phase of the flow oscillation is determined with the help of flow visualization pictures obtained by a high speed digital camera. From the CFD results spatial distribution of acoustical sources are also observed and correlated with pressure distribution on the wedge and with the phase of the oscillating flow. Some aspects of the initial transients are also presented.
Documenting the acoustics of the Silbermann pipe organ at the Catholic Cathedral in Dresden before and after the restoration of 2002
Authors: Ahrens Christian , Braasch Jonas , Schmidt Sebastian
Published: May 2008

Gottfried Silbermann's pipe organ at the Catholic Cathedral of the Saxonian Court in Dresden was, with 47 stops, the largest instrument he had ever built. The instrument was evacuated during World War II and luckily survived intact, while the church itself was badly damaged. The instrument received a more romantic sound ideal after its resurrection in 1971. The biggest deviation from the original concept of Silbermann was the change from church pitch (A4=415 Hz) to chamber pitch (A4=440 Hz). In 2002, the instrument was renovated again with the goal to restore the instrument to the original design of 1755. The work was commissioned to two local organ builders, Kristian Wegscheider and Jehmlich Orgelbau, and the authors received the unique opportunity to measure the instrument before and after the restoration. During the measurements, the pipes of each stop were recorded in the near field in steps of a third. The acoustical comparison between each pipe before and after the restoration shows significant differences that match the informal observations of expert listeners. In general, the pipes received more energy in the higher partials and had a better attack response. Another interesting finding is the improvement of the pipes' formants after the restoration.
Correlations between the turbulent and the acoustic fields of a hot co-axial jet simulated by large-eddy simulation
Authors: Bogey Christophe , Coiffet Francois
Published: May 2008

Correlations between the turbulent and the acoustic fields of a high-speed hot co-axial jet are calculated, in order to study noise generation mechanisms by a causality method. The jet flow was computed by a large-eddy simulation using specific aeroacoustic schemes. The simulation also provided directly the near-presure field, which was then extrapolated in the far field by solving the linear acoustic equations. The causality method is applied using flow quantities such as the velocity components, density, and temperature in the jet and the far field pressure, in the temporal as well as in the spectral domains. To exhibit and characterize the regions of noise generation, we are focusing on the correlation peaks, and in particular their location and corresponding frequencies. Moreover, there is an attempt to link the noise generation with the jet turbulence properties including intermittency and convection velocity. For instance, the turbulence at the end of the primary potential core was found to show high correlations with the far field pressure and significant intermittency, in a similar way as in single-stream jets.
Numerical study of the influence of temperature and microjets on the radiated noise for a subsonic jet
Authors: Huet Maxime , Rahier Gilles , Vuillot François
Published: May 2008

Jet noise remains the principal nuisance source for an aircraft at take-off conditions. A previous work [1] showed that using micro-jets could be effective to modify the turbulence development and thus decrease the radiated pressure. This micro-jets effect is numerically studied for two jets. LES simulations of a cold (M = 0.9) and a hot (M = 0.636) jets, with and without micro-jets, are computed and the acoustic post-processing is performed using the Ffowcs-Williams and Hawkings surface formulation. The temperature effect on the noise is analyzed for the reference computations and, with micro-jets, the noise reduction is compared to measurements for a similar configuration [1]. Aerodynamic comparisons with experiments give a good comparison, excepted a too short potential core and overestimated turbulent kinetic energy. The noise decrease with the higher temperature and the modifications of the spectral densities are well captured by the simulations. The micro-jets provide a reduction up to more than 2 dB for the best angles. Turbulence modification is still under investigation and results will be presented. [1] Castelain, T., Béra, J., Sunyach, M., and Juvé, D., “Effect of microjets on a high-subsonic jet. Parametric study of far-field noise reduction,” 12th AIAA/CEAS Aeroacoustics Conference (2006).
Turbulent flow noise around a zero-incidence airfoil
Authors: Marsden Olivier , Bogey Christophe , Bailly Christophe
Published: May 2008

A large eddy simulation (LES) of the flow around a NACA 0012 airfoil at zero incidence, at a chord-based Reynolds number of 500,000 and a Mach number of 0.22, is presented. The aim is to show that high-order numerical schemes can successfully be used to perform direct acoustic computations of compressible transitional flow on curvilinear grids. At a Reynolds number of 500,000, the boundary layers around the airfoil transition from an initially laminar state to a turbulent state before reaching the trailing edge. Results obtained in the LES show a well-placed transition zone, and turbulence levels in the boundary layers in agreement with analytical developments as well as experimental data. Furthermore, the radiated acoustic field is determined directly by the LES, without the use of an acoustic analogy. Third-octave acoustic spectra are compared to experimental data, with deviations of around 3 dB per band exhibited.
A numerical insight into the effect of confinement on trailing edge noise
Authors: Le Garrec Thomas , Gloerfelt Xavier , Corre Christophe
Published: May 2008

The flow and the acoustic field around a 3D NACA 0018 airfoil at Reynolds 160 000 with an angle of attack of 6° are investigated numerically by direct noise computation to make comparisons with the experimental results of Nakano et al. (Experiments in Fluids, 2005) and the numerical simulations of Kim et al. (Heat and Fluid Flow, 2006). The direct noise computation of the flow around a 3D airfoil reaches the limits of current computational capacities. Indeed the main difficulty of such simulations comes from the large disparities between the fine scales of turbulence and the large wavelengthes of acoustic radiation which impose severe constraints on the meshes. In order to limit the number of points and to reduce the calculation cost, a multisize-mesh multitime-step strategy is adopted. The main purpose of the paper is to study numerically the influence of the confinement due to the top and bottom surfaces of the wind tunnel used in the experiments of Nakano et al. on the flow around the airfoil. The numerical results for a confined airfoil will be compared to the results obtained when the top and bottom walls are removed. So the noise can be directly linked to the vortices which develop in the wake of the airfoil.
Modeling and prediction of fan noise
Authors: Envia Edmane
Published: May 2008

Fan noise is a significant contributor to the total noise signature of a modern high bypass ratio aircraft engine and, with the advent of ultrahigh bypass ratio engines like the geared turbofan, it is likely to remain so in the future. As such, accurate modeling and prediction of the basic characteristics of fan noise are necessary ingredients in designing quieter aircraft engines in order to ensure compliance with ever more stringent aviation noise regulations. In this paper, results from a comprehensive study aimed at establishing the utility of current tools for modeling and predicting fan noise will be summarized. It should be emphasized that these tools exemplify present state of the practice and embody what is currently used at NASA and industry for predicting fan noise. The ability of these tools to model and predict fan noise is assessed against a set of benchmark fan noise databases obtained for a range of representative fan cycles and operating conditions. Detailed comparisons between the predicted and measured narrowband spectral and directivity characteristics of fan noise will be presented in the full paper. General conclusions regarding the utility of current tools and recommendations for future improvements will also be given.
Contra-rotating fans noise prediction for jet engine performance optimization
Authors: Au Dax , Leblanc Alexandre
Published: May 2008

This work fits within the framework of the European research project VITAL, which is dedicated to the development of technologies aimed at reducing the environmental impact of jet engines. In this respect, a new concept of ducted contra-rotating fans is investigated. The present contribution to this project is to elaborate a noise prediction tool for performances optimization. On the basis of the helicoidal surface theory, Hanson previously developed a harmonic formulation for the propfan rotor/rotor interaction. This method is here extended in order to take into account the duct effects and the noise radiated by the rear struts. A computer program has been written to predict the pressure distribution in the near field and to estimate the noise spectra in the far field. The results are validated with computational fluid dynamics simulations and compared with available public data. Those predictions are then included in a global noise computation with the other engine acoustic sources (coaxial jet, combustor and so on), and a multidisciplinary optimizer is used for the engine noise minimization.
Computational AeroAcoustics of Realistic Co-Axial Engines
Authors: Redonnet Stephane , Mincu Ciprian D. , Manoha Eric , Druon Yann , Caruelle Bastien
Published: May 2008

This study, that is relevant from the turbofan engines noise prediction/reduction, aims at CAA-computing the aft fan noise propagation/radiation of a realistic full-3D exhaust (with pylon and internal bifurcations), the latter being affected of (i) typical in-flight (take-off) thermodynamic conditions and of (ii) a representative fan noise modal content. As for previous studies conducted over baseline geometries, this CAA computation is conducted following the usual hybrid process, where a preliminary aerodynamic calculation provides a heterogeneous steady mean flow on which an acoustic calculation is then conducted A RANS computation is first performed, delivering the stationary jet mean flow characterizing the 3D exhaust in its typical 'take-off flight' (M∞ = 0.25). A CAA grid (22 blocks, 28 millions cells) is then derived from the CFD one, before the RANS steady jet mean-flow is interpolated on it. After what the CAA computation is computed, a fan noise mode (26, 1) being emitted at a reduced frequency of kR = 30 (1 BPF) in the upstream of the engine's secondary exhaust, and numerically propagated along and outside the latter. Finally, a Kirchhoff post-treatment provides the far-field radiation characterizing these engine geometry, modal content and thermodynamic conditions.
Action planning procedures and realized action plans of municipalities and cities - results from the implementation of END
Authors: Petz Markus
Published: May 2008

For many federal states of Germany the Strategic Noise Maps were calculated and published in 2007. For some cities it will be shown, how a standard procedure for preparation of a noise action plan was defined together with responsible authorities from the municipality. The chosen procedure also considered the deadline for finalisation and the commencement of an action plan at July, 2008. Based on Strategic Noise Maps and hot spot analyses a catalogue of measures for noise reduction within a community was investigated and evaluated (cost/effectiveness). Together with representatives of traffic-, town- and environmental planning departures of the municipalities efficient measures were discussed and selected considering other local planning interests, financial possibilities and public acceptance. The draft action plan were published and public demurs have been weighted. In July, 2008 the action plans came into force.
NERS-analysis extended to include noise levels measured on city courtyards
Authors: Malm Peter , Stenman Åsa , Hammarlund Thomas
Published: May 2008

One of the goals for the EC financed Integrated Project Quiet City Transport (QCITY), is to provide European city administrations with validated analysis tools and technical noise control solutions for the efficient production of noise action plans. A part of the QCITY project work is to produce complete noise maps and hot-spot analysis for the entire Gothenburg area. Earlier studies have shown that calculated noise levels from traffic at inner city courtyard are lower compared to actual measurements. Gothenburg city have performed over 700 measurements on city courtyards. The measurements are included in the NERS-analysis to show the influence of the actual courtyard noise levels. The study covers a smaller area in the central part of Gothenburg where the measurements have been made.
Auralisation and psychoacoustic evaluation of traffic noise scenarios
Authors: Guidati Sandro
Published: May 2008

The evaluation of vehicle noise is mostly done using the A-weighted sound pressure level, e.g., the Lmax for pass-by noise or the Leq for community noise. Unfortunately, the dB(A)-value does not reflect the annoyance effect of vehicle noise correctly. During the first phase of the European Research Project QCity a metric for psychoacoustic evaluation of single pass-by events has been developed. In the next step this metric is adapted for the evaluation of complex traffic scenarios calculated by traffic flow simulations. Psychoacoustic evaluation requires time signals. Single values or third octave spectra are not sufficient to investigate all relevant effects (e.g., annoying time patterns, masking). The time signals are calculated combining advanced resynthesis with exterior noise simulation techniques. Hereby, it is possible to investigate the effect of e.g., low noise surfaces or various traffic control measures (traffic light vs. roundabout). Since a standard traffic scenario includes a very large number of single pass-by events special focus lies on fast processing techniques. This paper gives an overview of the developed algorithms and presents first results of the psychoacoustic evaluation of traffic scenarios.
Some algebra and statistics on isolated noise events
Authors: Maurin Michel
Published: May 2008

Noise indices related to isolated emerging noise events are calculated on variable finite durations ΔTev, as opposed to instantaneous levels or indices on constant conventional periods ΔT (1 h, 24 h, ...). Here they are defined by TEL (transit exposure levels) or LeqΔTev on every ΔTev. There are classical formulas to pass from many TELi to the Leq on a longer period including many events. When TELi are supposed equal to TEL one gets classicaly LeqΔT = TEL + 10 log n + K, (CNR, NEF for instance). In algebra, the approach develops some algebraic relations and conditions between total duration ΔT, the global part of all ΔTev,i and their number n, in a way that TEL is clearly emerging from noise level without the isolated events. It is a manner to find a general result like “events kill events,” say that too many events render not emerging any new one. One finds the same with a statistical approach and other appropriate technics (quantiles for instance). And coming on with probabilistic tools, the Bêta distribution renders possible some characterisation of the graphical look of the time evolution of noise level during ΔTev. This work has partly been done with V. Catto of Lyon 1 University.
Acoustical design margins: Uncertainty in prediction and measurement of community noise
Authors: Putnam Robert , Hetzel Roland
Published: May 2008

Compliance with regulatory requirements for sound levels in communities adjacent to industrial or power generating facilities is typically a contractual commitment, with the potential for significant financial penalties in the event of noncompliance. Uncertainties at any stage of the design, specification or prediction of plant sound level may be accounted for as part of the overall plant acoustical design margins. There are also additional uncertainties in terms of compliance sound measurement surveys, that are commonly referred to as either “test tolerance,” or “instrumentation tolerance and measurement uncertainty.” From the viewpoint of the plant equipment supplier all of the uncertainties associated with equipment design and specification are simply additive to all of the uncertainties of compliance measurements, since they all contribute to, or affect the selection of, the overall plant acoustical design margin. The discussion will address the types of uncertainties in source sound power levels and measurement error, tolerances, and confidence limits of field sound surveys, highlighting some seldom-treated aspects of uncertainty. Measurement uncertainties and the applicable combinatorial rules will be treated.
The United Kingdom noise mapping experience
Authors: Hawkins Nick , Parry Graham
Published: May 2008

The paper describes the noise mapping of the Bristol and Bournemouth agglomerations for the United Kingdom Noise Mapping Initiative in compliance with the European Directive on Environmental Noise and the challenges of delivering both compliant noise mapping, noise mapping outputs and shape files, and the associated methodology reports. The paper examines the noise model utilised for the mapping, the various efficiencies built into the system to provide error checking, the external data acquisition and the effects that any uncertainties may have in strategic noise mapping. Additionally, the use of a GIS based toolkit for identifying and amending the location of noise barrier objects was utilised.
City noise mapping without traffic data
Authors: Droin Laurent , Odent Pierre
Published: May 2008

The authers have a large experience on transport and noise planning and mapping with projects on many communities of different size in France. Within the time scale of a mapping project, it is very common to have a large variation of the accuracy in traffic data, especially for roads (largest source data base). In many cases, no traffic data is available on less exposed roads. This paper illustrates how variation of input data accuracy and lack of data were tackled in both large and small territories (population between 50 000 and 1 000 000) in order to provide maps with the required accuracy and information for political action and communication.
Limits and advantages of Good Practice Guide to Noise Mapping
Authors: Licitra Gaetano , Memoli Gianluca
Published: May 2008

The Pisa Noise Mapping Project has recently presented to the public what turned out to be the first noise map for road traffic in Italy, developed taking into account the Good Practice Guide version 2 (GPG2) of WG-AEN and the main results of the IMAGINE project. This paper will discuss the results of this noise map, relative to road traffic, in terms of Lden and Lnight and their uncertainties, obtained by comparing the calculated values with a set of noise measurements taken across the territory. The uncertainties so defined were compared with the ones predicted by GPG2 considering, in particular, two different ways to model the source. To do this, input traffic flow were assigned first by taking direct measurements and performing a road classification and then, at a second stage, using a static traffic model (the latter method should give less uncertainty, according to GPG2). The expected change in uncertainty will be discussed, together with advantages and disvantages of the two different choices. A comparison of exposed population with other EU realities will be also presented.