bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconstruction of acoustic field horizontal layer in diffusive ambience
Authors: Pozera Arunas , Volkovas Vitalijus
Published: May 2008

This study introduces a method how to minimize the number of acoustic measurements in the diffusive ambience in order to reconstruct the horizontal layer of primary acoustic field. This reconstruction means determination of the level of the sound pressure at any point of surface, e.g. worker's occupational place, where there are a lot of sound sources. A mathematical modeling, based on regularity of sound spread, is used in the study. The elements of active experiment are applied in the research, the adequacy of mathematical model is evaluated by Fisher criterion, and the mathematical model of horizontal layer of the acoustic field is based on the polynomial of the regressive equation. The results are compared to the measurements received in the real experiment. This study also pays great attention to local and the EU legal regulations about the noise standards at the worker's occupational place and the measures to be taken to lower the noise level. The device of sound measurement INVESTIGATOR type 2260 and MAPLE 11 mathematics software tool have been used in the research.
Analytical validation of time-step interpolation in transient insular nodal analysis
Authors: De Rybel Tom , Marti José , Hodgson Murray
Published: May 2008

The transient insular nodal analysis method (TINA) combines elements from the finite differences (FD) and transmission-matrix methods (TLM) in one unified approach. In contrast to existing TLM-FD methods, TINA uses time-decoupled cells, avoiding the need for solving large system matrices. The time-decoupled cells allow for easy parallelisation, and the solution of large systems in detail. Due to the use of an exact transmission-line model in the cells, wave propagation can be computed without the need for discretisation of the equations, nor the use of prediction, yielding an unconditionally stable method. Boundary conditions are implicit, and are solely defined by the wave speed and characteristic impedance of the medium. One key difference with the TLM method is how cells whose transmission time is not an integer multiple of the simulation time step are integrated in the simulation. These mismatches occur due to the the varying wave speeds of the different media in the cells. In TINA, the match is obtained through interpolation, as opposed to the stub-matching methodology employed in TLM. In this paper, we will demonstrate the validity of the interpolation approach analytically, as well as compare the TINA method to a theoretical case.
Green roofs to enhance quiet sides
Authors: Van Renterghem Timothy , Botteldooren Dick
Published: May 2008

In this paper, the finite-difference time-domain method is used to study sound propagation over a green roof in an urban situation. Sound propagation between adjacent city canyons is considered, and the focus is on the reduction of the sound pressure level in the non-exposed canyon due to the presence of a vegetated (green) roof. Numerical calculations have been conducted for both intensive and extensive green roofs, showing that an important reduction of the sound pressure level in the shielded canyon can be achieved, compared to a rigid roof. In case of an extensive green roof, there is a strong dependence on the substrate layer thickness; a maximum reduction of 10 dB at the octave band of 1000 Hz was found. For intensive green roofs, the influence of the substrate layer thickness is limited.
Low noise truck study for distribution in urban areas
Authors: Blairon Nicolas , Carton Bruno
Published: May 2008

Today, vehicle noise is identified in opinion pools as one of the main annoyance source in urban areas. To face this issue, truck manufacturers are today developing low noise vehicles in order to allow their customer to deliver goods in urban areas during night. An acoustic research program has been launched by Volvo 3P (Volvo Trucks, Renault Trucks and Mack Trucks): the LUT project as Low Noise Urban Truck. The partners of the project are Michelin, the Institut National des Sciences Appliquées de Lyon (INSA) - a French university - and Marmonier - a noise shield manufacturer. This project has been founded by ADEME The target in terms of noise reduction is ambitious because the low noise truck will emit an acoustic power four times lower than today's vehicles in specific rolling conditions! Methods and tools have been developed to analyze the vehicle noise sources in urban conditions and define acoustic solutions to reduce the main vehicle noise sources.
Quantification of structural damping of a multi-layered windshield at low and medium frequencies
Authors: Etchessahar Manuel , Gagliardini Laurent
Published: May 2008

Structural damping is known as one of the most efficient design variable in order to reduce structure-borne noise. At low and medium frequencies (100-500 Hz), the vibro-acoustic behavior of the car is essentially governed by large panels as windshield, roof or front panel for example. In order to improve the car body design regarding cost, weight, performances and reliability, one must have a good understanding of the damping performances of these large panels submitted to various operating conditions. In a previous paper, the authors have proposed an improved method for structural damping numerical assessment of structural elements with non uniform damping using a stochastic distribution of input forces. In the present paper, this method is applied to quantify the structural damping of a multi-layered windshield at low and medium frequencies. Effects of the geometry, of the viscoelastic properties of the PVB layer and of the windshield glue bead on the total damping properties will be studied.
Improving sound propagation modeling for wind power projects
Authors: Duncan Eddie , Kaliski Kenneth
Published: May 2008

Sound propagation from wind power projects can be modeled in the same manner as other more common outdoor noise sources, but are these models suited to wind turbines' uniquely high source heights, operating under high wind conditions, and various degrees of terrain ruggedness. In "Propagation Modeling Parameters for Wind Turbines" (K. Kaliski and E. Duncan, Proceedings of Institute of Noise Control Engineers NOISECON 2007), the effects of ground attenuation and various adjustments for wind conditions on sound propagation modeling were discussed. This paper continues the discussion and explores the accuracy of existing sound propagation modeling methods for wind power projects including ISO 9613 and other standards. Model data for wind power projects and the implications of various terrain and ground coverage will be discussed.
Prediction of flow induced noise in rotating devices using nonmatching grids
Authors: Grabinger Jens , Karic Branimir , Triebenbacher Simon , Kaltenbacher Manfred , Becker Stefan , Lerch Reinhard
Published: May 2008

With increasing number of electrical devices, e.g. air conditioning systems, used in homes and offices, noise pollution is becoming a more and more relevant topic. A large amount of this noise is generated by turbulent flows and laminar flows at leading and trailing edges, where mainly tonal noise is generated. The objective of our contribution is to investigate shape optimizations of rotating devices in order to reduce their noise levels. For this purpose, we conduct a simulation of the turbulent flow in a ventilator. The acoustic source terms are obtained from the fluid dynamics solution by using Lighthill's acoustic analogy. The acoustic domain is decomposed into a rotating part and a fixed part. The coupling between these two parts is enforced at their interface by a mortar finite element method, which uses Lagrange multipliers in order to ''glue'' the geometrically independent parts together. The mortar method takes into account the movement of the rotating part through a moving nonmatching grid, that is recomputed at each time step.
Aeroacoustic Computation of Ducted-Fan Broadband Noise Using LES Data
Authors: Reboul Gabriel , Polacsek Cyril , Lewy Serge , Heib Sebastien
Published: May 2008

Following large efforts to reduce tone noise during the last decades in modern high-bypass ratio turbofans, fan broadband noise reduction has become now an industrial priority. A hybrid computational method providing source-to-far-field predictions of broadband noise due to rotor-stator interaction is presented. The acoustic model is based on the loading term of the FWH (Ffowcs Williams and Hawkings) equation with a modal Green's function valid for an infinite annular duct, and a Kirchhoff approximation for the free-field radiation. The aerodynamic sources on the airfoils required by the model are expected to be directly issued from a LES (Large Eddy Simulation) computation. The method is applied to a simplified configuration tested in a laboratory rig. The first part of the study is concerned with the assessment of in- duct acoustic field. Usual assumptions about coherence and energy distribution between the acoustic modes are analyzed. PSD (Power Spectrum Density) are calculated through several ways. The second part is focused on the ability to generate an equivalent PSD by means of equivalent source distributions. The purpose is to validate a practical way for coupling LES with Computational Aero-Acoustics Euler solver, in order to include realistic geometry and mean flow effects.
Study of a thermoacoustic-Stirling engine
Authors: Tijani Hassan , Spoelstra Simon , Poignand Gaelle
Published: May 2008

During the last decade most efforts in thermoacoustics have been focused on the development and understanding of the traveling-wave thermoacoustic systems. These systems get much attention because they employ the inherently efficient Stirling cycle. This makes them much more efficient that the standing-wave counter parts which are intrinsically irreversible. A 1 kW thermal power thermoacoustic-Stirling engine is designed and performance measurements are performed. The engine incorporates a compact acoustic network to create the traveling-wave phasing necessary to operate in a Stirling cycle. The acoustic network consists of a regenerator unit, an acoustic compliance and a feedback inertance. The design, construction and performance measurements of the traveling-wave thermoacoustic engine will be presented and discussed.
Recent developments on heat to electricity thermoacoustic conversion
Authors: Huelsz Guadalupe , Piñeirua Miguel , Castrejon-Pita Alfonso A. , Gomez Fabrisio
Published: May 2008

In this work we present recent developments for the conversion of heat into electricity based on the combined effects of a thermoacoustic prime mover coupled to a magnetohydrodynamic generator where different working fluids can be optimally chosen for each process. We consider the acoustically produced oscillatory motion of a liquid drop confined into a horizontal squared cross section capillary tube as a possible flow configuration for the system. We investigated the energy losses of the system and concluded that this system would be a convenient configuration for small systems. [Work supported by CONACYT 25116 project]
Miniaturation of thermoacoustic refrigerators
Authors: Li Yan
Published: May 2008

The possibility to miniature thermoacoustic refrigerators is theoretically investigated. Both standing-wave and traveling-wave systems are considered. In the consideration of standing-wave refrigerators, a system consisting of a resonator tube (50 cm) with a closed end and a PVC stack (length 5 cm) is taken as a reference. Helium is used at a mean pressure of 10 bars and an amplitude of 1 bar. The operating frequency is 1 kHz. The variation of the performance of the refrigerator when scaled down in size is computed under the prerequisites that the temperature difference over the stack or the energy flux or energy flux density are fixed. The analytical results show, as expected, that there is a limitation for scaling-down of a standing-wave thermoacoustic refrigerator due to heat conduction. Similar scaling trends are also shown in traveling-wave refrigerators. The traveling-wave reference system consists of a feedback inertance tube of 0.567 m long, inside diameter 78 mm, a compliance volume of 2830 cm3 and a 24 cm thermal buffer tube. The regenerator is sandwiched between two heat exchangers. The system is operated at 125 Hz and filled with 30 bar helium gas. Again, the thermal conductance forms a practical limitation in down-scaling.
Intensity measurement of a periodic acoustic shock wave in a resonator
Authors: Biwa Tetsushi , Yazaki Taichi
Published: May 2008

A periodic shock wave of a gas column is formed in a duct, when the gas column is sinusoidally driven near the resonance frequency. This phenomenon has been one of the fundamental problems in nonlinear acoustics and has been studied extensively both theoretically and experimentally. In this work, we study the nonlinear effect leading to the shock formation through measurements of the acoustic intensity. A gas column of atmospheric air is filled in a resonator with a length of 1.15 m and internal radius of 10.5mm, and driven by an oscillating piston at 144.4 Hz near the fundamental resonance frequency. Pressure and axial acoustic particle velocity of the gas column are measured as a function of the resonator axis using small pressure transducers and a laser Doppler velocimeter. We show the spatial distribution of the acoustic intensity associated with the fundamental and the second modes, from which we show the nonlinear interaction between these oscillating modes.
Transition to turbulence and acoustic Rayleigh streaming in thermoacoustic devices
Authors: Baillet Helene , Valière Jean-Christophe , Moreau Solenn , Marx David
Published: May 2008

Thermoacoustic engines and refrigerators with practical levels of heating or pumping power must generally operate at high pressure amplitudes. When used to describe the behavior of such high-amplitude thermoacoustic devices, the well-established foundations of thermoacoustics, based on the acoustic approximation, reach their limits. It is necessary to gain a deeper understanding of the high-amplitude phenomena in order to improve the performances of thermoacoustic devices, and efforts of several research groups have been directed towards this goal over the last decade. In this presentation, we will consider recent advances in the understanding of some of the gas-dynamics phenomena leading to limitation of devices performances, namely transition to turbulence and acoustic Rayleigh streaming. The common point for these phenomena is that they owe their origin in the dynamic of oscillating flows in very near wall regions, so that their quantification implies measurements of acoustic particle velocity in adverse conditions. Recent progresses in Laser techniques used to perform such measurements will therefore also be reviewed.
PIV contribution for measuring acoustic and streaming flow in thermoacoustic systems, using phase average dynamics
Authors: Baltean Carlès Diana , Debesse Philippe , Lusseyran François , François Maurice-Xavier
Published: May 2008

The present study deals with the experimental challenge of the measurement of the velocity field generated by a thermoacoustic wave. The system consists in a cylindrical standing-wave resonator, filled with gas confined at high mean pressure, driven by a thermoacoustic prime-mover. The axial and radial components of fluid velocity are measured using Particle Image Velocimetry (PIV) with an optical flow technique. The average cycle of acoustic oscillation of the velocity field is reconstructed from a temporally under-sampled set of PIV snapshots, using an embedding method for building out a suitable phase space based on Singular Value Decomposition (SVD). This reconstruction allows us to extract both oscillation component of the velocity field (with the harmonic content) and time-averaged component of velocity (streaming flow). The measurements are confirmed using a second experimental procedure, based on a classical phase-averaged method: velocity measurements are synchronized with the pressure signal, the fundamental time period being decomposed in 16 phases. The measurements are repeated for different values of the drive ratio (acoustic pressure/mean pressure). The results are compared with available theory. Different experimental methods used in measuring the velocity field in thermoacoustic systems are analysed and compared with the present method.
Time-domain modelling of thermoacoustic devices: Reflections from the stack
Authors: Kleiven Stig , Larsson Krister , Kropp Wolfgang
Published: May 2008

Thermoacoustic devices are today mainly simulated using frequency-domain models. Contrary to frequency-domain models, time-domain models may include time-varying boundary conditions and time varying effects. Furthermore, effects like reflections from the stack can be visualised which, in turn, can improve the understanding. The primary aims were: (1) to study the initial behaviour of the acoustic field in a thermoacoustic device using a time-domain method; and (2) to compare the results from the simulations with experiments. Since time-domain techniques are computational expensive, the detailed Finite-Difference Time-Domain (FDTD) method are combined with the quicker Equivalent Source Method (ESM). The acoustic field in the stack, only including viscous effects, was modelled using the FDTD method, and the ESM was used outside the stack. The experimental setup consisted of a loudspeaker connected to a circular tube containing a ceramic stack with rectangular pores. From the results of both the simulations and the experiments, clear reflections from the stack were seen. Since these reflections influence the total acoustic field in thermoacoustics devices, time-domain methods provide useful tools for further development of thermoacoustic devices.
Acoustic Bloch oscillations, Wannier-Stark ladders and negative refraction in ultra- and hypersonic superlattices
Authors: Kosevich Yuriy A.
Published: May 2008

A new and very efficient ultrasonic superlattice is realized for the study of such fundamental effects of quantum transport in a perturbed periodic potential as acoustic Bloch oscillations, Wannier-Stark ladders and resonant Landau-Zener tunneling. The acoustic equivalent of the Wannier-Stark ladders is employed in a set of water cavities, with a gradient of the thicknesses, in a simple water-solid multilayer system. Bloch oscillations in different acoustic minibands are observed as time-resolved oscillations of the transmisssion of ultasonic pulses with corresponding spectral positions and widths. Acoustic Bloch oscillations with different temporal periods for the pulses centered in two neighboring acoustic minibands are observed. Experimental observations are in very good agreement with the transfer-matrix simulations [1]. The propagation of acoustic pulse in an even acoustic miniband in orthogonal or oblique with respect to the superlattice axis direction will result in negative refraction and Bloch oscillations of acoustic pulse with "negative effective mass", which can be visualized by mapping out of acoustic pressure field. Hypersonic phononic structures, which can be fabricated with the use of interference lithography, render possible the observation of all the abovementioned acoustic phenomena in the hypersound frequency range. 1. H. Sanchis-Alepuz, Yu. A. Kosevich, and J. Sanchez-Dehesa, 2007, Phys. Rev. Lett. v. 98, 134301.
Measurement of the velocity dispersion and attenuation in a liquid metal at GHz frequencies
Authors: Wright Oliver B. , Perrin Bernard , Matsuda Osamu , Gusev Vitali
Published: May 2008

Ultrashort optical pulses are used to excite and interferometrically detect picosecond longitudinal acoustic pulses in thin films of liquid mercury sandwiched between sapphire plates. By analysing consecutive acoustic echoes we derive the dispersion of the ultrasonic attenuation and sound velocity for this liquid at frequencies up to 10 GHz. Two types of optical detection, from the same side of the film as the excitation light and from the opposite side to the excitation light, are presented. Significant effects of structural relaxation are observed and are compared to a simple model that indicates the presence of picosecond relaxation times in mercury.
Pulse laser induced wave propagation in graded media and focusing devices
Authors: Vollmann Jacqueline , Bryner Juerg , Aebi Laurent , Dual Jurg
Published: May 2008

Near-infrared-laser pulses having durations of 100 fs are used to excite elastic waves thermoelastically propagating in a sub-THz frequency range. The elastic waves interact with inhomogeneities and carry information to the surface. The arrivals of the elastic pulses at the surface lead to transient changes of the optical reflectance which are monitored with short laser pulses which have a defined and controlled time delay relative to the initial pulses. Two activities of the research group are presented: The reflection and transmission behavior of acoustic waves propagating in graded media shows a frequency dependent nature and can therefore be used for filtering purpose. Time-boundary value problems are solved for various gradients with a finite-difference method. Results of the numerical simulation are presented and compared with laser-acoustic measurements. A 'classical' photoacoustic set-up provides an in-depth resolution of about 5 nm whereas the lateral resolution is in the order of 5 to 10 microns. To enhance the lateral resolution of the pump-probe technique, the elastic wave propagation along structures with arbitrary tip-like geometries consisting of orthotropic material is analyzed. With such structures representing ultrasonic lenses, the elastic energy is focused to a spot size given by the sharpness of the tip thereby leading to a higher lateral resolution.
Imaging of 3D acoustic wave-fronts by means of picosecond laser ultrasonics in GaAs substrate
Authors: Péronne Emmanuel , Belliard Laurent , Zhang Shuo , Rossignol Clément , Perrin Bernard
Published: May 2008

Picosecond ultrasonic experiments are widely used as pump-probe technique using longitudinal acoustic pulses and measuring time dependence of the signal. We present an experiment which combines an interferometer with the control of the pump-probe spatial overlap. Such set-up can perform a new kind of bulk phonon imaging based on ultrafast optical generation and detection scheme. When ultrafast acoustic longitudinal wave propagate in crystals they generate coherent transverse acoustic wave by diffraction. Transverse waves are known to give rise to phonon focusing patterns. The imaging of such patterns in time and space allowed us to partially reconstruct the wave front surface of bulk acoustic wave in crystals. The data may be viewed as 2D slices of the 3D acoustic wavefront revealing the basic anisotropy of the solid with unprecedented micronic lateral and in-depth resolution. Measurements are carried out in a 356 μm-thick GaAs sample as an example, but many different experimental conditions are compatible with the present set-up. This technique provides a new way to perform phonon energy and phonon polarisation dependent experiment with high frequency phonons.
Surface acoustic waves propagating on microstructured phononic crystals
Authors: Profunser Dieter M. , Wright Oliver B. , Matsuda Osamu , Tanaka Yukihiro , Khelif Abdelkrim , Laude Vincent , Benchabane Sarah
Published: May 2008

We investigate the interaction between high frequency surface acoustic waves and periodic microstructured patterns that form phononic crystals. The experimental method combines an optical pump-probe setup with interferometric detection and provides picosecond temporal and micron spatial resolutions. Surface acoustic waves with frequency components up to 1.3 GHz are imaged in real-time propagating over the periodic metamaterial. We used a DRIE (deep reactive ion etching) process to fabricate 2D air-silicon phononic crystals in the form of a square lattice. We present real-time animations of surface acoustic waves scattered by the phononic crystals. In particular we describe the frequency and angular dependence of the surface acoustic wave reflection from a 2D phononic crystal boundary. Fourier analysis allows us to reveal details of the acoustic band structure including gaps. The presence of such phononic band gaps enables us to visualize surface acoustic waves in waveguides, cavities and other phononic circuits at GHz frequencies.
Opto-acousto-optic evaluation of the physical properties of nanoporous materials
Authors: Mechri Charfeddine , Ruello Pascal , Nsenkoue M , Mounier Denis , Breteau Jean-Marc , Edely Mathieu , Minhao Y , Gibaud Alain , Povey I , Pemble M , Romanov Sergei , Baklanov Mikhail , Verdonck P , Gusev Vitali
Published: May 2008

The porous materials with the characteristic dimensions of the pores from few nanometers up to a few hundred of nanometers find applications in microelectronic industry (as low-k materials), in photovoltaics and for developing of effective chemical sensors. When the pores are ordered in a spatially periodic structure, these systems present photonic and/or phononic properties which are of a prime interest in applied optics and telecommunication (light and/or phonons spectrum control). Here we report how the methods of picosecond laser ultrasonics based on the generation and detection by lasers of the acoustic waves with frequencies in the band of 10 GHz - 1 THz (with the lengths of hundreds of nanometers down to few nanometers) are applied for the evaluation of the mechanical and optical properties of these materials.
Thermomechanical behavior of surface acoustic waves in ordered arrays of nanodisks studied by near-infrared pump-probe diffraction experiments and finite element simulations
Authors: Giannetti Claudio , Banfi Francesco , Nardi Damiano , Revaz Bernard , Ferrini Gabriele , Vavassori Paolo , Metlushko Vitali , Parmigiani Fulvio
Published: May 2008

The ultrafast thermal and mechanical dynamics of a two-dimensional lattice of metallic nanodisks has been studied by near-infrared pump-probe diffraction measurements over a temporal range spanning from 100 fs to several nanoseconds. The experiments demonstrate that in these systems a surface acoustic wave (SAW), with a wave vector given by the reciprocal periodicity of the two-dimensional array, can be excited by ̃120 fs Ti:sapphire laser pulses. We unambiguously show that the observed SAW velocity shift originates from the mechanical interaction between the SAWs and the nanodisks, while the correlated SAW damping is due to the energy radiation into the substrate. In order to clarify the interaction between the nanodisks and the substrate, numerical calculations of both the elastic eigenmodes and the time-dynamics of the system, following the impulsive heating excitation by the laser, are performed. Simulations based on finite-elements analysis, together with a wavelet analysis of our experimental data, suggest the opening of a band-gap at the centre of the super-Brillouin zone. The modes at the centre of the super-Brillouin zone are excited following laser excitation, as opposed to thermal population, of the elastic modes.
Measuring the Extreme Conditions Created During Cavitation
Authors: Suslick Kenneth S.
Published: May 2008

Extreme temperatures and pressures are produced through acoustic cavitation: the formation, growth and collapse of bubbles in a liquid irradiated with high intensity ultrasound. Single bubbles have generally been assumed to give higher temperature conditions than bubble clouds, but confirmation from the single buble sonoluminescence (SBSL) emission spectra have been problematic because SBSL typically produces featureless emission spectra that reveal little about the intra-cavity physical conditions or chemical processes. Here we present definitive evidence of the existence of a hot, highly energetic plasma core during SBSL. From a luminescing bubble in sulfuric acid, excited state to excited state emission lines are observed both from noble gas ions (Ar+, Kr+, and Xe+) and from neutral atoms (Ne, Ar, Kr, and Xe). The excited states responsible for these emission lines range from 8.3 eV (for Xe) to 37.1 eV (for Ar+) above the ground state. Observation of emission lines allows for identification of intra-cavity species responsible for light emission; the energy levels of the emitters indicate the plasma generated during cavitation is comprised of highly energetic atomic and ionic species.
Cavitational activity in bacterial biofilms exposed to 1 MHz ultrasound
Authors: Everbach Erich C. , Velez Roby , Vollmer Amy C.
Published: May 2008

An exposure system was previously developed to quantify destruction of bacterial biofilms by 1 MHz c.w. ultrasound at 0.8 MPa peak-to-peak acoustic pressure amplitude (JASA 122(5):3052, 2007). Bacterial killing is quantified via confocal microscopy using florescent E. Coli and image processing. Recently, a passive detector of inertial and stable cavitation was included, relying upon the presence and character of acoustic emissions. The detector, a PVDF array placed on the microscope slide forming the base of the exposure chamber, produces a proxy measure of cavitational activity during ultrasound exposure. Acoustic pressure thresholds for biofilm destruction and cavitational activity suggest that inertial and stable cavitation both play a role in biofilm destruction by ultrasound.
Emotion and meaning in interpretation of sound sources
Authors: Bergman Penny , Vastfjall Daniel , Fransson Niklas , Sköld Anders
Published: May 2008

Research regarding the perception of sound focuses in large on the acoustical properties of the sound. We argue that, for a more complete picture of sound perception, one must take the non-physical properties into account. By changing the emotional descriptor of a sound the perception in terms of level of annoyance will change. The present study investigates how a priming picture placing the origin of the sound in either a positive or negative environment affects the level of annoyance to same sound. Three different sounds were used in the experiment, all based on pink noise. The participants were, in the beginning of each sound, exposed to a picture telling where the sound originated. The picture was either a positive environment (a picture of a waterfall) or a negative environment (a picture of a larger factory). While listening to the sounds the participants completed different performance tasks. In the end of each sound the participants rated the level of annoyance. Results show that the annoyance ratings are significantly lower when primed with a positive picture. Results also indicate that for more attention demanding tasks this correlation is stronger. The findings are discussed in relation to theories of sound perception.
Comparative Study of Wideband Subspace Direction of Arrival (DOA) estimation methods
Authors: Khan Sheraz
Published: May 2008

Signal subspace Methods like ESPRIT, MUSIC and MATRIX PENCIL, provides high resolution Direction Of Arrival (DOA) estimation in comparison to traditional Delay and Sum and Capon methods, which are limited by sensor spacing. However underwater Acoustics signals are inherently wideband in nature and most of these Subspace methods works on narrowband signals. Currently modified version of these methods for wideband signals are emerging. These methods are broadly classified as Coherent and Incoherent methods depending upon how signals of different frequencies have been merged. Performances of these methods are evaluated using extensive Monte-Carlo simulations under various protocols by comparing there Mean Square Error in DOA estimation and by their respective resolution power. This comparison study is also complemented with real acoustic data from public domain.
Application of statistical methods in underwater signal classification
Authors: Bissinger Brett E. , Culver Richard Lee , Bose Nirmal K. , Jemmott Colin W.
Published: May 2008

The overall goal of our work is to utilize knowledge of the ocean environment to improve sonar detection and classification performance. Source classification and localization in the underwater environment is a challenging problem in part because propagation through the space- and time-varying medium introduces multipath, variability, and decorrelation to the signal. Traditional underwater signal classification has relied on parametric methods such as the likelihood ratio tests. Recent research has explored non-parametric methods like maximum entropy and maximum likelihood with favorable results. This talk considers other, more contemporary non-parametric methods, e.g. principle component analysis, independent component analysis and support vector machines, and compares their structure and performance with previous results. Work supported by Office of Naval Research Undersea Signal Processing.
Bayesian linear regression onto data-driven dictionaries with application to music transcription
Authors: Févotte Cédric
Published: May 2008

In this work, we describe a linear regression technique where features of the dictionary (the collection of explanatory variables) are learnt from the data itself. Our Bayesian setting allows to add regularization constraints on both the explanatory variables and the regressors that fit physical properties of sound. More precisely, smoothness constraints can be imposed on the first ones while time-persistency and/or sparse constraints can be imposed on the second ones. When applied to music, we observe that the retrieved explanatory variables bear a semantic value and that the overall process yields a compact data-driven object-based transcription of the original signal.
Bayesian model selection applied to room-acoustic energy decay analysis
Authors: Jasa Tomislav , Xiang Ning
Published: May 2008

The previous work of Xiang et al. [Xiang & Goggans, J. Acoust. Soc. Am. 110 (2001), pp. 1415-1424; 113 (2003), pp. 2685-2697; Xiang & Jasa, J. Acoust. Soc. Am. 120 (2006) pp.3744-3749] successfully applied the Bayesian formulism to estimate multiple decay parameters from Schroeder decay functions measured or calculated in acoustically coupled spaces. In this work we consider a more difficult problem of determining the correct decay model in the presence of energy decay data within the Bayesian framework. We will compare the Annealing/Thermodynamic algorithm [Neal, R. M., Statistics and Computing 11 (2001), pp. 125-139], the Nested Sampling algorithm [Silvia & Skilling, Data Analysis: A Bayesian Tutorial, Oxford Science Publications (2006)], and a combined Variational/Markov Chain Monte Carlo approach in order to determine the correct decay model. The advantages/shortcomings of these methods are discussed in the context of the decay model selection and parameter estimation using experimentally measured data from real coupled spaces.
The effects of the internal waves on the statistic characteristics of the sound fields in the 2001 ASIAX South China Sea Experiment
Authors: Wu Lixin , Wang Jun , Wang Shaoqiang , Lynch James F. , Duda Timothy
Published: May 2008

Internal waves are one of primary sources of ocean variations in shallow water. The temporal-spatial stability of sound channel may be degraded by the activities of internal waves. We present analyses of statistic characteristics observed in acoustic signals transmitted by two 400Hz sources moored as part of ASIAEX 2001 South China Sea (SCS) experiment. One source was 31.3 km offshore from the receiving array, and the other was 20.6 km alongshore from the array. Time series of signal intensity measured at individual phones of a 16-element vertical line array and a 32-element horizontal line array. temporal-spatial correlations were observed from 2 May to 17 May 2001. The temporal-spatial decorrelation scales are closely related to internal wave properties. The largest internal wave, especially solitary wave packets, are the principal contributors to reduction of the temporal-spatial decorrelation scales. We also present elementary analyses of higher-order statistics (HOS), such as bispectrum, bicoherency coefficients, etc.
Applying the Data Nullspace Projection Method to a Geoacoustic Bayesian Inversion in a Randomly Fluctuating Shallow-Water Ocean
Authors: Lynch James F. , Lin Ying-Tsong , Newhall Arthur
Published: May 2008

Bayesian inversion techniques which are commonly used in geoacoustic inversion can suffer the effects of uncertain water-column fluctuations. To reduce these effects, one could also invert for the fluctuating water-column parameters; however, there are issues with this approach. One obvious problem is that the dimensions of parameter space will increase, so that Bayesian inversion may not be efficient. Another issue arises from the temporal and spatial randomness and variability of the water-column parameters; this requires extra effort in handling the randomness and variability in the inversion procedure. In this paper, we propose another approach to the problem. The data nullspace projection method, which has been applied to perturbative inversion, is extended to Bayesian inversion using acoustic modal wavenumbers and group velocities. The idea of this method is to project acoustic data onto a subspace that is insensitive to uncertain water-column fluctuations, and use the projected data to invert for bottom properties. The advantage of this approach is that we do not need to invert for water-column parameters, so that the inversion requires less operations than the previous approach. A numerical simulation demonstrates the feasibility of the projection approach. It is then applied to real data collected in the SW06 experiment.
A modified dnoidal model for internal solitary waves and its effect on sound transmission
Authors: Wang Shaoqiang , Wu Lixin , Hu Changqing
Published: May 2008

A new solution of KDV equation in the form of dnoidal function is developed in this paper. Based on this new solution, a modified solution of KDV equation with slowly varying parameters in the form of dnoidal function is derived. Numerical simulation shows that the wave pockets scale of the modified solution is only 1/5 to the solution in the reference (JASA, 108(3), pp 957-972), and also the equilibrium positions are different. Comparing the solutions with slowly varying parameters with the published data of internal solitary waves in the ocean indicates that the modified solution is better for the description of the dnoidal wave. Based on the modified solution of KDV equation with slowly varying parameters, a modified model for dnoidal wave is given and its effect on sound transmission is discussed in this paper.
Pulse tube measurement of bulk modulus of visco-elastic composite materials: Theory and practice
Authors: Brazier-Smith Peter R. , Clark Allan R.
Published: May 2008

A method for the determination of the bulk moduli and loss factors of micro-voided composite materials is presented. The method requires that the reflection and transmission coefficients of a tile of uniform thickness are determined in both amplitude and phase as functions of frequency. Reduction to the bulk modulus and loss factor then proceeds by using the analytic properties of a function of a complex variable derived from the reflection and transmission coefficients. A pulse tube is used for the determination of the complex reflection and transmission coefficients. Although other measurement techniques are available, the pulse tube has proved to be versatile in covering a large range of the frequency-temperature master curve for typical composite materials used in underwater acoustics. It achieves this versatility by using an anti-freeze/water mixture as the medium following which measurements can be made over a range of different temperatures.
A new integral equation method for elastic composites
Authors: Willoughby Natasha J. , Parnell William J. , Abrahams I David
Published: May 2008

A new integral equation approach to elastodynamic homogenization has been proposed [1] to determine the effective properties of periodic fibre reinforced composite materials in the case of SH wave propagation. When all the fibres are aligned in the same direction and considered infinite in extent, the microstructure is two-dimensional. The integral equation method is based on Navier's equations of elasticity in integral equation form, and uses the notion of separation of scales and averaging to find explicit expressions for the effective properties in a convenient form. Here we discuss an extension to the in-plane problem: the response of periodic fibre reinforced composites to time harmonic (low frequency) P/SV wave propagation. For simplicity, we assume all fibres are identical and of circular cross-section, and that both host and fibre phases are isotropic; additionally we restrict attention to lattice geometries which result in, at most, orthotropic elastic symmetry. The governing equations are presented and the effective quasi-static material properties are determined via the integral equation methodology. Results are presented for the effective material properties and compared with existing methods. [1] W.J. Parnell and I.D. Abrahams. "A new integral equation approach to elastodynamic homogenization". Submitted to Proc. Roy. Soc. A, 2007.
Experimental study of piezoelectret foams as underwater sensors
Authors: Haberman Michael , Embleton Steven
Published: May 2008

This work explores the use of piezoelectret foams (PF) as acoustic sensors for underwater applications. PF material (Emfit Ltd.) provides an intriguing alternative to piezoelectric ceramics and piezopolymers due to their low density, minimal thickness, and potential for easily creating sensors of complex geometries. The foams consist of a continuous polymer containing electrically polarized elliptical voids. Typical density, thickness, and low frequency receive voltatge sensitivity (RVS) values of these foams are 300 kg/m3, 80 μm, and -175 dB re 1V/μPa, respectively. This work presents experimentally obtained RVS of piezoelectret sensors with rigid and pressure release backing. The results show PF sensor RVS is comparable to conventional sonar transducers at low ambient pressures with RVS degradation as ambient pressure increased. The results are compared with theoretical predictions using microelectromechanical mean field theory and equivalent circuit models. Theoretical predictions explain the observed sensitivity degradation due to void closure caused by the applied pressure. To overcome the performance degradation, two pressure tolerant sensor design concepts are proposed and tested. The designs aim to employ PF elements for high ambient pressure applications while leveraging foam density and thickness to create lightweight, low profile sensors.
Shear wave speed increases with depth to the one-sixth power in sandy/silty marine sediments
Authors: Pierce Allan D. , Carey William M.
Published: May 2008

Gravity holds the sediment's particles in loose contact; the strength varies with depth. The distribution in shapes, sizes, and orientations is presumed independent of depth. Each particle is subject to several contact forces, and also to a buoyancy force exerted by the surrounding water. An externally imposed shear stress results in distortions in the individual grains, the nature and magnitudes of which depend on the contact areas between the grains, which in turn depend on depth. A derivation making use of fundamdental mechanics, the theory of elasticity, and Hertz's theory of contact yields shear modulus G as a dimensionless quantity times g1/3(ρs-ρw)1/3E2/3d1/3, where d is depth into the sediment and E is the elastic modulus of the solid material in the grains. The dimensionless quantity depends on Poisson's ratio and porosity. The shear speed (G/ρav)1/2 consequently varies with depth as d1/6. The prediction is consistent with data reported in the past by Stoll, Yamamoto, and Hamilton; the discrepancy of the theoretical prediction of 0.167 with experimentally derived exponents of the order of 0.25, although not viewed as significant, is discussed, and it is suggested that such may be caused by the variation of porosity with depth.
Sound focusing and scanning in shallow water with background internal wave field
Authors: Lunkov Andrey A. , Pereselkov Sergey A.
Published: May 2008

Sound field focusing and scanning with focal spot are investigated for shallow water and long distances (up to 30km). It is studied the availability of horizontal and vertical scanning for controlling long-range low-frequency bottom reverberation as well. These researches are carried out by using numerical modeling for typical acoustic waveguides including random ones with background internal waves. The acoustic field is focused with vertical array by phase conjugation of sound wave from probe source placed at preset point. Horizontal scanning with the focal spot is performed by radiation frequency tuning. It is demonstrated that the best feasibility for scanning and hence for controlling bottom reverberation takes place for the regular waveguide under winter conditions when sound speed depends on depth only slightly and background internal waves are nonexistent practically. As an example for these conditions we can control the bottom reverberation on interval ̃ 5km in the neighborhood of preset point. In summer for near bottom sound waveguide the range of distances for which it is practicable is much narrower even without internal waves. For the waveguide with intense background internal waves the control of long-range bottom reverberation becomes impossible. The work was supported by RFBR Project 05-02-16842.
An optimized source transmission scheme based on pressure sensitivity kernels
Authors: Raghukumar Kaustubha , Cornuelle Bruce , Hodgkiss William , Kuperman William A.
Published: May 2008

A first-order Born approximation is used to obtain the pressure sensitivity of the received signal to small changes in medium sound speed. The pressure perturbation to the received signal caused by medium sound speed changes is expressed as a linear combination of single-frequency sensitivity kernels weighted by the source signal in the frequency domain. This formulation is used to optimize the pressure sensitivity kernel to give a new source transmission that can produce a focal spot and at the same time, to have less sensitivity to sound speed fluctuations than time-reversal. The formulation allows for a trade-off between quality of focal spot and sensitivity to environmental fluctuations. The optimized new source transmission uses knowledge of the medium statistics and is related to the regularized inverse filter.
Analytical Time Domain Analysis of an Acoustic Waveguide
Authors: Sertlek Hüseyin Ö. , Aksoy Serkan
Published: May 2008

A new analytical time domain Normal Mode solution for one layer acoustic channel in two dimensional Cartesian coordinates is presented in this paper. The method is based on the separation of variables technique for the time domain wave equation. Dirichlet boundary condition is applied on the upper and lower boundaries of the channel. Klein-Gordon equation is obtained and solved by using the Green function. The fundamental advantage of this new technique is not necessary to use the Fourier Transformation to obtain time domain response of arbitrary acoustical source signal in the waveguide. In order to validate the obtained results, first of all, the Fast Fourier Transform is applied to the time domain analytical data, then, the comparisons are given between KRAKEN program and a new analytical time domain Normal Mode solution in the sense of Transmission Loss relating to ranges. The excellent agreement is obtained between the results.