bluuebunny/crossref_metadata_2025 huggingface dataset:
Relations between acoustic parameters and perceptual properties: an approach by regressions tree applied to car door closure sounds
Authors: Bezat Marie Céline , Roussarie Vincent , Kronland-Martinet Richard , Ystad Solvi
Published: May 2008

The aim of this study is to identify perceptually pertinent parameters for the evaluation of car door closure sounds. For this purpose, door closing sounds are finely decomposed into perceptual properties: analytical properties (which are obtained thanks to sensory analysis), natural properties (linked to perception of sources and events) and evocations. The acoustic characterisation of the sound is then processed by means of an analysis-synthesis model which aims, not at reproducing the exact replica of the door closing sounds, but to synthesize sounds that preserve perceptual properties with a reduced number of signal parameters. The model consists in decomposing the sound in several independent impact sources, each impact being modelled by a set of gains and damping factors in frequency bands. Listening tests on controlled sounds are then carried out to observe the effects of acoustic parameters on the perceptual properties. The complex relations between acoustic parameters and perceptual properties are finally established via regressions tree analyses.
Measurement of the acoustic pressure distribution occurring around an aerial substation adjacent to apartment buildings
Authors: Borucki Sebastian , Boczar Tomasz , Cichon Andrzej
Published: May 2008

The subject matter of the research work presented in this paper refers to the measurements of the values of the acoustic pressure levels (noise) occurring around a main feeding-point aerial substation adjacent to apartment buildings. The paper presents the values of the noise accompanying the particular power devices, mainly transformers, during their regular operation. The main aim of this research work was the comparison and assessment of the acoustic pressure values measured with the permissible values defined by environmental standards binding in Poland. The research analysis carried out proved that during a long-term operation of power appliances installed in substations the acoustic pressure level that they emit into the environment is not constant but is subject to changes. Thus the increase of the noise level above the permissible values can be the cause of violation of environmental standards. Due to a significant increase of people's awareness and readiness to claim their rights, the main consequence of violating the standards is a growing number of claims. Therefore it is imperative that the level of the acoustic pressure be monitored during routine tests, especially around high-power transformers.
Effects of personal stereo use: pilot results from 20 university students
Authors: De Santis Eric , Ordoñez Rodrigo , Reuter Karen , Hammersho/i Dorte
Published: May 2008

Modern personal stereo systems have the ability to store thousands of music files in small, relatively low-cost, compact devices. The popularity and widespread presence of the MP3 player cannot go unnoticed in contemporary society. Given a sufficient noise level and listening duration, consumers are at risk of developing a noise-induced hearing loss. A study into the effects of personal stereo use will be carried out with the intention of investigating common noise exposure levels in realistic settings, user listening habits and the hearing status in a group of listeners. Noise exposure levels are to be obtained by using the manikin technique described in the ISO 11904-2 standard. The questionnaire to be presented to interested participants is designed to report personal stereo listening habits and to screen subjects for the hearing status evaluation. The hearing status of selected subjects will be evaluated through the use of conventional and possibly extended high-frequency audiometry, transient-evoked otoacoustic emissions and distortion product otoacoustic emission fine structures.
Classroom noise in schools containing children learning English as a second language
Authors: Ramirez Gina
Published: May 2008

This study analyzes the acoustics of two elementary schools containing both native English speaking children and large English learning populations, to determine if facilities are best being utilized acoustically. As stated by the ASA, children learning English require a more favorable signal-to-noise ratio and should thus be instructed in quieter learning environments. The study examined at least 20 classrooms in each facility by measuring ambient noise level and reverberation time by methodologies outlined in the ANSI S12.60 (2002) standard. Creating a noise mapping allowed for the evaluation of each school based on utilization of pre-existing facilities. Based on preliminary results all classrooms tested failed to meet the maximum A-weighted steady background noise level specified in the standard furthermore schools placed English learning students in environments that were up to 10 dB louder than classrooms used for native English speaking students, demonstrating that more attention to ambient noise level and its effect on speech intelligibility is needed when planning the layout of learning facilities containing large English learning populations. The ongoing analysis of the data aims at assessing the impact of the measured acoustical environments in terms of perceived intelligibility by using a survey tool among the student population.
Optimization of compact finite difference method for wave acoustic simulation
Authors: Tsuru Hideo , Iwatsu Reima
Published: May 2008

Recently, the finite difference method, a tool for wave acoustic simulations, can be applied to practical analysis. However, the numerical dispersion which makes propagation speed in simulations change according to the wave length, is a severe problem to maintain high accuracy in the analysis. The numerical error accompanied by the time integration hinders to carry out an accurate simulation. An examination of a compact finite difference scheme which can approximate differentiation precisely on a comparatively large grid spacing was made. It was shown that the adjusting the coefficients in the compact finite difference scheme can simulate a wave propagation accurately with a small amount of computation. The improvement method of the time integration was also discussed. The possibility of improvement of accuracy through a multi-step integration is shown.
Assessment of noise impacts of the air traffic
Authors: Ohlau Katrin , Bickel Peter , Friedrich Rainer
Published: May 2008

Against the background of the generally increasing traffic and especially the expansion plans in doubling the air traffic until 2020, this paper presents an assessment of noise effects of air traffic and underlines its future meaning. In several projects including the EC funded projects HEATCO (Developing Harmonised European Approaches for Transport COsting and Project Assessment), GRACE (Generalisation of Research on Accounts and Cost Estimation) and ASSET (ASsessing SEnsitiveness to Transport), methodologies for assessing noise including aircraft noise have been developed, improved and applied. The methodologies focus on the impact pathway approach, i.e. first noise levels are estimated, and then level- response functions are applied to calculate health impact and annoyance level distributions. Afterwards it is evaluated by transforming the impacts into monetary levels. Our studies for assessing annoyance have been carried out with the contingent valuation method. Results of the monetary valuation will be shown for the airports Frankfurt, Hamburg, Berlin-Tegel, Düsseldorf, Köln/Bonn, München and Stuttgart. The total air traffic noise costs for Germany range from EUR 150 million to EUR 1200 million per year.
Efficiency of shielding effect on installed double stream nozzles
Authors: Aeberli Sébastien
Published: May 2008

In spite of acoustic improvements on jet noise brought by innovative technologies such as chevrons, a way to ensure important acoustic gains is to optimize the power plant integration on aircrafts in order to benefit of the shielding effect due to wing, empennage and fuselage surfaces. In this presentation, these effects are illustrated thanks to a jet noise test campaign at 1/10th scale in an anechoic chamber as part of a European project. This campaign gives a better understanding of shielding effect by a wing and also of the acoustic impact of pylon azimutal direction on two representative BPR 9 nozzles (Baseline - smooth - and Low Noise - with chevrons). The efficiency of shielding effect on jet noise sources in these configurations is assessed.
Study of the surface traffic inside the Cluj-Napoca urban agglomeration
Authors: Solea Geamilia , Arghir Mariana , Borza Dan , Runcan Mariana
Published: May 2008

The environment's protection is one of the most actual problems, because of the fact that pollution is a major danger for planet life. The environment's pollution is caused because some pollution agents are in too large a quantity for a long time and they become dangerous for human health, for the flora, for the fauna and for the constructions too. The pollution sources can be classified as natural and artificial sources. The quality of the environment from a specific area at a certain time can be determined by: a) the air quality; b) the water quality; c) the soil quality; d) the health level of the population; e) the decrease of animals and plants species that are accounted for. In the paper there are given the urban traffic on the principal routes inside the Cluj-Napoca municipality. The traffic is the constituent part of the research activity of the national project having the destination the monitoring of the noise and vibrations into an urban agglomeration, applied to the Cluj - Napoca town. This study is the first step for the "noise map" asked for by the Romania integration in the European Union for the team researchers of TUCN under the the direction of Dr. Mariana Arghir.
Low frequency noise reduction from building technical equipment: A case study
Authors: Kondylas Kathleen , Fuller Chris R. , King Joseph A. , Levit Natalia
Published: May 2008

Mechanical equipment (fans, chillers, motors) produces airborne and structure-borne noise with a significant low frequency component. However, in many applications, mitigation of the low frequency noise requires implementation of significant mass barrier in combination with an air space. This work presents case studies on the use of a novel lightweight and thin acoustical material to mitigate low frequency noise from mechanical equipment. This advanced material, based on patented distributed absorber technology, was used to treat the metal housing of the mechanical equipment. The novel material effectively increased transmission loss of the metal housing below 300 Hz. The total noise reduction was 10-14 dB (A) with 5 dB improvement over typical flexible acoustical blankets below 300 Hz.
Experimental and numerical study of the ground transmission of structure-borne sound generated by trams
Authors: Coquel Guillaume , Jean Philippe A. , Villot Michel
Published: May 2008

The increase of railway traffic in urban areas leads to developments in modelling and understanding the propagation of structure borne sound through soil, foundation and structure. Vibration propagation through the ground, is still not well known. The present paper focuses on the propagation of trams vibrations (20-250Hz) in the ground and the energy transmission to the structure. In the first part, calculations performed using a 2D code based on a FEM/BEM approach are compared to measurements performed on a test site. The railway excitation is produced with a vibrator in order to recreate a line of uncorrelated forces. Soil properties are evaluated by an analysis of surface waves. Both bending and in-plane waves are measured on the structure. The ratio of the soil velocity over the structure velocity is computed in order to evaluate the accuracy of the computation. A 2,5D modelisation is also performed in order to evaluate the effect of a point source on the velocity fields on the soil and on the structure. In the second part, a parametric study using the 2D code is performed on typical cases in order to evaluate the modification of vibration transmission from the ground to the foundation.
Sound Quality Evaluation for the Axle Gear Noise in the vehicle
Authors: Lee Hyun Ho , Kim Ho Wuk , Lee Sang Kwon
Published: May 2008

A gear whine sound due to the axle system is one of the most important sound qualities in a sport utility vehicle (SUV). In the previous works about the gear whine sound, it was known that it is difficult to evaluate the gear whine sound objectively by using the only A-weighted sound pressure level because of the masking effect. In this paper, for the objective evaluation of the axle-gear whine sound, the characteristics of the axle-gear whine sound is at the first investigated based on the synthetic sound technology and the new objective evaluation method for the axle-gear whine sound is developed by using the sound metrics, which is the psychoacoustic parameters, and the artificial neural network (ANN) used for the modeling of the correlation between objective evaluation and subjective evaluation. This model is successfully applied the objective evaluation of the axle-gear whine sound for real sport utility vehicles and the output of the model are compared with subjective evaluation. The results have a good correlation over 90 per cent.
Mapping urban noise quota generated by a transport service
Authors: Luzzi Sergio
Published: May 2008

The paper refers to a recent noise mapping experience, regarding the determination of quotas generated by urban transport services in complex areas. The first results of this study have been presented at Euronoise 2006 in Tampere and at Transport Noise 2006 congress in Saint Petersburg. Now the study is completed. Italian Law established that noise levels produced by buses, coaches and trams, must respect noise limits of area and road buffers classification. Public and Private transport companies are directly requested to point out their specific contributions levels and action plans for the reduction of those levels. At the same time, data for 2002/49/EC Directive have to be collected by them and given to authorities in agreement with formats and standards. The original methodology of source analysis, noise mapping and action planning studied and experienced by the authors in the Florentine area, applies a multi-variable couple-checking algorithm for the optimal choice of critical sites, to the whole road network of each company, reducing the number of calculations and conducting measurement campaigns only for the chosen critical "pivot" scenarios. Noise contribution quotas, generated by bus and coach traffic on linear sources and road systems, have been investigated and considered in models.
Management of the Tourist & Entertainment Noise Using Noise Mapping Technique
Authors: Štimac Alan , Globevnik Aleš , Kuhelj Lilijana
Published: May 2008

In countries with strong orientation in tourism and entertainment, especially during summer months, noise problems are always present. This paper represents some applications of noise mapping techniques for the management of tourist & entertainment noise that were conducted in Croatia and Slovenia. The noise mapping techniques were applied for the prediction of noise levels on several places inside the cities of Varaždin and Pola (Croatia) including famous Roman amphitheatre, and in the city of Nova Gorica (Slovenia) especially during entertainment live-shows (concerts, movie festival etc). Such approach enables the city authorities to prepare the base for the implementation of noise policy with introducing such a system that would represent background documents for providing criteria of setting out areas on one side intended to entertainment and quiet areas on the other. For the daily activities in areas that are the most attractive for tourists, noise-modelling techniques have been used for predicting noise emitted from pubs and bars including terraces and loudspeakers. Such approaches have been used by city authorities to establish technique for "fixed quotas" that will be able to designate maximum area of terraces concerning number of seating places in relation with the type of bar/pub and noise emission.
Mapping of noise caused by military airplane operation
Authors: Kamenicky Milan , Petrak Peter
Published: May 2008

Noise from military airplane operations is a serious problem in affected surroundings of military airports. Usually, military airplane noise emission data are not available in databases of common programs, which causes problems in noise load modeling. In such cases it is necessary to obtain emission data by measurement. Measurement must be performed in modes which are not used in ordinary airplane operation. Based on these measurements, acoustic emission data will be processed in the required form according to a used mathematical model. This paper will include examples of acoustic data acquisition and their utilization in mapping of noise load caused by military airplane operations in the surroundings of military airports. Also, verification of data acquired by prediction and measurement in the airport surrounding ordinary airplane operations will be present.
Effect of limitations of ray-tracing software on predicting community from petrochemical plants
Authors: Brittain Frank , Hale Marlund
Published: May 2008

Ray-tracing software has proven to be a valuable and powerful tool to predict community noise from outdoor petrochemical and power plants. Accurate predictions are necessary to determine noise reductions needed to meet regulations and/or project noise limits, and then to determine individual equipment noise limits, select add-on noise controls, and confirm the plant will comply with its noise limits. Modeling using ray-tracing software is much more powerful and versatile than a spreadsheet model, which had often been used. Ray tracing and similar image source software have many limitations, particularly for outdoor petrochemical and power plants. To effectively use ray-tracing software, the user needs to understand those limitations. For example, ray tracing does not adequately predict for configurations where distances are significant compared to the wave length of sound, reflections from dense pipe racks, or screening by pipelines and equipment. This paper identifies and discusses some of the limitations of ray-tracing software for predicting community noise. Examples are given. This paper emphasizes limitations of ray-tracing methodology, and not those arising from atmospheric effects.
The railway noise reductions achieved in the Silence project
Authors: Poisson Franck , Gautier Pierre Etienne
Published: May 2008

The European project Silence is dedicated to the reduction of railway and roadway noise in urban areas. Within the framework of the subproject E and G, the reduction of the railway noise is addressed. Source ranking of state of the art rolling stocks has been carried out. Then, the Diesel engine, the exhaust, the cooling unit, the electrical engine, the wheels and the track have been optimised by the manufacturers and prototypes have been constructed. The most promising have been selected through laboratory measurement to be installed on the trains and trams. Last measurement campaigns have been carried out to characterise the combination of optimised rolling stocks running on optimised track. Then, relevant reductions of the pass-by noise have been achieved for electrical and Diesel multiple unit trains, freight trains and trams. In the same time, a software called VAMPPASS has been developed in subproject B to simulate the time signal of a train pass-by. The paper focuses on the results of the last measurement campaigns which validate the noise reduction achieved on the global pass-by noise of several rolling stocks and tracks. A comparison with the reduction predicted by VAMPPASS will be also presented. Some improvement of the solutions will be also addressed.
Principles for selection of rail fastening systems for control of railway noise and vibration
Authors: Cox Stephen J.
Published: May 2008

Railways generate noise and vibration as trains pass along the track. It is usually ultimately noise that causes annoyance to those above or alongside the track, but this noise is often generated as a result of vibrations transmitted along and away from the track. Examples of ground-borne vibration at the surface above railway tunnels; airborne noise from trains passing at grade; and noise from trains passing over structures such as viaducts and bridges are each considered in turn. The selection of suitable rail fastening systems, and in particular their stiffness, to control each of these problems is discussed. This often requires compromise - for example, reduction of the noise emitted from the rail may suggest a high stiffness, while reduction of noise from the supporting structure may require a low stiffness. These considerations lead to different solutions to different problems. Some general conclusions are drawn as to how, and to what extent, each of the different types of railway noise and vibration problem may be addressed by modifications to the track fastening system.
Comparing railway noise prediction results for passenger trains using various models
Authors: Reiter Malgorzata , Kostek Bozena
Published: May 2008

Railway noise modeling is a requirement for all European countries. Under the European Directive on the Assessment and Management of Environmental Noise, 2002/49/EC all member states were obliged to create strategic noise maps of the major railways by June 30th, 2007. Some of the participating states have their own national schemes dedicated to noise prediction. For those not having their own noise prediction model, the recommendation is to use the Dutch SRM II Model. The most important assessment criterion is an inaccuracy value, which is defined as a difference between the result calculated based on a model and the actual measurements under the same atmospheric conditions simulated. Therefore, it is essential to check out which of the main calculation schemes produces most accurate results. Therefore, all above models were implemented numerically and calculations of the noise maps were performed with the use of: Schall 03 developed in Germany, Dutch SRM II and the Nordic model engineered in Norway. Those models were tested employing sample passenger trains data exploited in Gdansk, Poland. Noise maps were drawn in CadnaA software and then were compared to the field noise measurement test results.
Brake noise measurements on mixed freight trains with composite brake blocks
Authors: Jansen Erwin H. , Dittrich Michael G. , Sikma Erik L.
Published: May 2008

In the Netherlands, the noise emission of shunting yards, which are often located in urban areas, are a source of disturbance. The noise emission of shunting yards is legislated in terms of maximum allowable equivalent sound pressure levels and peak noise levels of the façade of residences. Brake noise is known to be a major contributor to the total sound emission of shunting yards, in particular from trains with cast-iron block brakes. Within the scope of the Dutch Innovation Programme on Noise Reduction, the rolling noise reducing effect of alternative composite block brakes, such as LL and K blocks, was successfully demonstrated. Additionally, the effect of composite brake blocks on braking noise was studied. For this purpose, noise measurements were conducted on mixed freight trains according to the applicable protocols. Measurements were conducted on trains slowing down from a speed of 30 km/h to a standstill and trains passing-by with brake systems applied. Some composite brake blocks show a considerable reduction of both braking pass-by levels and peak noise levels. Results are presented. If squeal noise is absent, braking noise of most considered brake blocks show a speed dependency similar to that for rolling noise.
Prediction method for structure borne noise generated in buildings by tools such as drills
Authors: Villot Michel , Jean Philippe A.
Published: May 2008

Tools such as drills generate structure borne noise which propagate in the building structure and radiate loud noise even in rooms far from the source. This paper presents a method for predicting this type of noise, frequent in buildings under construction or renovation. First the structural power injected by the tool to the receiving structure (floors or walls) is estimated from field measurements of the vibrational (bending) energy stored in the receiving plate. Then the vibration propagation through the building structures and the noise radiated in the receiving room is estimated using Statistical Energy Analysis (SEA), where both bending and in plane waves are taken into account. Comparisons between predictions and results measured in an apartment building under construction show that SEA gives quite acceptable results down to 1/3 octave 50 Hz for structure borne sound sources such as drills.
A combined approach for base isolation design
Authors: Neves E Sousa Albano , Guerreiro Luís , Gomes Rui
Published: May 2008

New buildings in the vicinity of underground railway lines should be protected against noise and vibrations induced by railway traffic. In the present paper a case study is presented. A 2D FEM model of the tunnel, ground and building was built in order to identify the transfer function of vibration from the tunnel to building foundations. A 3D model of the building was built, including not only structural elements, but also other non structural walls, in order to identify the transfer function of vibration from foundations to walls and floors. As the impedance of heavy walls and floors is much higher than the acoustic impedance of air, the numerically assessed vibration fields of walls and floors were used to calculate sound fields in rooms by means of natural mode analysis. The vibration and sound fields were then compared with comfort criteria in order to design a base isolation system. With this combined approach, the analysis was performed up to 170 Hz, which is more than one can usually do with integrated 3D models.
Investigation of a vibro-acoustic reciprocal method to derive the contact forces of building equipment
Authors: Schevenels Pieter , Dijckmans Arne , Van Der Linden Peter J. , Vermeir Gerrit
Published: May 2008

Structure-borne sound caused by installations can be derived from the injected structure-borne sound power into the connected building element. Theoretically, this is as simple as summing the products of force and velocity at each contact point of the installation. The velocity can be well approximated by the velocity measured close to the contact point. But to measure the force, installation and building element would have to be separated to insert a force sensor. This is generally impractical or even impossible. In this paper, a method is analyzed to derive the force between an installation and a building element in a vibro-acoustic reciprocal way. First, a dedicated volume sound source is placed in an adjacent room and the transfer function of its volume acceleration with the acceleration of the building element is determined. Next, the sound pressure is measured at the source's position while the installation is operating. Since most installations have an important lower frequency contribution, below 50 Hz, the sound source must cover this frequency range with sufficient level. Moreover, an accurate measure of the in-situ volume acceleration of the used source is required. Finally, the method is compared to other methods that approximate the injected structure-borne sound power.
Stick-slip dynamics of a granular medium
Authors: Petri Alberto , Baldassarri Andrea , Dalton Fergal , Pontuale Giorgio , Zapperi Stefano
Published: May 2008

Under certain limits, granular materials share many features with fluids and solids. Most of the time, however, they exhibit peculiar features which originate in the non-equilibrium and dissipative character of the grain dynamics. We have investigated the dynamics of a granular medium in a channel, when subject to continuous shear stress from a plate connected to a motor by an elastic spring. We have shown [1] that the statistical features of granular stick-slip dynamics are not simply Gaussian and that [2] can be described in a quantitative way by a simple stochastic equation. Extant work, such as the statistical properties of friction in solid-on-solid systems, further suggests that a large class of driven instabilities can be described in terms of similar general mechanisms. The intensity of the acoustic signals emitted by the granular medium during the slip events displays a non trivial correlation with the plate velocity. [1] F. Dalton et al., Phys. Rev. Lett. 95, 138001 (2005) [2] A. Baldassarri et al., Phys. Rev. Lett. 96, 118002 (2006)
Monitoring changes in crustal properties with seismic noise
Authors: Campillo Michel , Brenguier Florent , Hadziioannou Celine , Shapiro Nikolai , Larose Eric
Published: May 2008

The seismic noise is a continuous source of waves due to the interaction between the solid Earth and its fluid envelopes. Theoretically, the time correlation of the field measured at two distant points allows retrieving the Green function between the points for a random distribution of sources or in presence of a diffuse field. We use this property and study the stability of the correlation functions. We show that the velocity measurements made with correlations are very stable. Using doublet analysis, we found that that we can monitor relative velocity changes smaller than 10-4. We present applications to the forecast of volcanic eruptions and to the monitoring of an active fault.
Force fluctuations in granular disks near the jamming threshold
Authors: Ecke Robert E. , Bandi Mahesh , Rivera Michael K.
Published: May 2008

We study experimentally the force fluctuations felt by a probe disk as it is dragged at a nominally constant rate through a two-dimensional bi-disperse system of randomly packed photo-elastic disks. As the packing fraction increases from loose packing to a value where the disks are jammed, lines of connected force - stress chains - develop that couple the entire domain. We consider the transition from an unjammed state with no long range force distribution to a jammed state with stress chains spanning the system size. We characterize this transition using the measured force fluctuations and the determination of stress chains as visualized by the photo-elastic disks. Length and time scales obtained from these measurements are used to describe both the transition to jamming and the nature of the jammed state. The reorganization of disks and the force fluctuations have a stick-slip character in the jammed state.
Irreversible interaction of sound waves with dense granular matter
Authors: Laurent Jérôme , Brunet Thomas , Jia Xiaoping
Published: May 2008

In this talk, we will describe quantitatively the irreversible interaction between sound and the granular medium under low confining pressure (< 0.1 MPa). Both resonance measurement and pulsed wave propagation show that as the acoustic pressure goes up to a few percent of the confining pressure, the dynamic bulk modulus and shear one can be reduced to 10% and 20%, respectively. This observation of modulus softening is qualitatively in agreement with the prediction by a model based on the Mindlin hysteretic nonlinearity at the grain contact level. Beyond certain thresholds of acoustic amplitude, the irreversible sound-granular matter interaction is accompanied by continue or intermittent sample compactions. No visible grain motion is observed at this stage; however the multiply scatted shear waves [1] allow probing a significant evolution of the contact networks, which coincide with slow recovery of elastic moduli. This work may have the implication for better understanding the physical origin of dynamic triggering of the fault core [2]. [1] X. Jia, "Coda-like multiple scattering of elastic waves in dense granular media," Phys. Rev. Lett. 93, 154303 (2004) [2] P.A. Johnson & X. Jia, "Nonlinear dynamics, granular media and dynamic earthquake triggering," Nature 437, 871-874 (2005)
Acoustic emissions for the prediction of avalanches
Authors: De Guibert Pierre , Gibiat Vincent , Plazza Eric
Published: May 2008

Although we know well enough the main zones where occur avalanches, the main difficulty results in forecasting avalanches because of the constant evolution of the snow coat. The coat, composed of various slopes have different properties according to the weather conditions not only during falls but also after. Weather modifications after snow falls generate instability of slopes which create stress, fissure and failure states. These different states generate acoustic emissions whose parameters can lead to forecast avalanches. The aim is to detect in situ these precursors, that initiate a low frequency signal. We have settled an experiment to monitor and register this signal. It includes two geophones to detect the acoustic signals, an acquisition system, one aerial of temperature sensor and a wireless connection to a deported PC. The system is controlled by ADSL in our offices. It will be shown on examples that any movement of the snow cap provides a signal. The rate of repetition of these elementary signals is the indication of an increasing instability of the snow precursor to an avalanche. By comparing the acoustic signals to temperature variation evolution of the snow pack we could define an alarm degree allowing to secure the area.
Dynamic asperity failure triggering during the rupture process
Authors: Larmat Carene
Published: May 2008

Dynamic triggering by the transient deformations associated with seismic waves has been proposed as an alternative mechanism for inducing aftershocks in contrast to the Coulomb stress. This idea is supported by observations of triggered seismicity like for the Mw=7.3 Landers earthquake (1992), the Mw=7.1 Hector Mine (1999), and after the Mw=7.4 Izmit earthquake for which small events began in Greece immediately after the passage of the mainshock surface waves (Brodsky et al., 2000). Gomberg et al. (2003) conducted a rigorous analysis of aftershock distribution for 15 mainshocks and showed that most of the triggered events are located in the rupture direction which corresponds to a maximum of the radiated seismic energy. Another argument is the fact that the correctly scaled amplitude of the dynamic deformations are consistent with laboratory observations of failure processes (Gomberg & Johnson, 2005). Finally, work by Felzer and Brodsky (2006) indicates that aftershocks are due to dynamic triggering rather than quasistatic stress changes. Thus instabilities can be triggered as aftershocks as well as at remote distances by seismic waves, suggesting asperities located on the mainshock fault may fail due to transient strains. In this study, we propose to explore that hypothesis.
Breathing in Granular Chains and Conversion of Wave Energy to Useful Forms
Authors: Sen Surajit
Published: May 2008

Estimates suggest that a meter of a wave front carries ̃ 100 kW of power. A significant amount of renewable energy is hence dissipated across the time scale of minutes as surface gravity waves dissipate on any beach. Given that the majority of the world population lives near the ocean, it makes sense to explore the conversion of wave energy into electrical energy. Here we consider a new concept - that of a potentially scalable system that converts wave energy into energy in mechanical pulses and then to voltage drops. The envisioned system would exploit the well studied physics of nonlinear repulsion between elastic grains encased in cylinders to continuously convert the incident wave energy into dispersionless energy bundles, which can be subsequently converted to stress pulses in a piezo-electric slab. The key points involved in the concept will be presented.
Wave propagation in wetted Hertzian granular chains: analysis of a single contact dynamics
Authors: Job Stéphane , Santibañez Francisco , Melo Francisco
Published: May 2008

A one-dimensional dry granular medium, a chain of beads which interact via the nonlinear Hertz potential, exhibits strongly nonlinear behaviors. When such an alignment contains some viscous fluid between grains, it exhibits new interesting features. We report some recent experiments, analysis and numerical simulations concerning nonlinear wave propagation in dry and wet chains of spheres. We consider first a monodisperse chain as a reference case. We then analyze how the pulse characteristics are modified in the presence of an interstitial viscous fluid. The fluid not only induces dissipation but also strongly affects the intergrain stiffness: in a wet chain, wave speed is enhanced and characteristic pulse duration is shorter. Our observations are in a satisfactory agreement with ultrasound propagation measurements in 3D wetted granular beds reported in the literature. Recent experiments performed with a single sphere colliding a wall covered by a thin film of fluid allowed us to determine the rheology of the contact dynamics, and confirmed that a complex elastohydrodynamic interaction takes place close to solids contact.
Dynamic effective mass of granular media
Authors: Johnson David L.
Published: May 2008

We report an experimental and theoretical investigation of the frequency-dependent effective mass, M(ω), of loose granular particles which occupy a rigid cavity to a filling fraction of 48%. We demonstrate that this is a sensitive and direct way to measure those properties of the granular medium that are the cause of the changes in acoustic properties of structures containing grain-filled cavities. The dominant features of M(ω) are a sharp resonance and a broad background, which we analyze within the context of simple models as well as with molecular dynamic simulations. We find that: a) These systems may be understood in terms of a height-dependent and diameter-dependent effective sound speed (∼ 130 m/s) and an effective viscosity (∼ 2× 104 Poise). b) There is a dynamic Janssen effect in the sense that, at any frequency, and depending on the method of sample preparation, approximately one-half of the effective mass is borne by the side walls of the cavity and one-half by the bottom. c) On a fundamental level, dissipation is dominated by adsorbed films of water at grain-grain contacts in our experiments, not by global viscous damping.
Acoustic waves in granular materials
Authors: Luding Stefan , Mouraille Orion
Published: May 2008

The numerous sound propagation mechanisms in granular materials are rather complex and strongly depend on the material micro-scale parameters, such as inter-particle friction or damping. The use of DEM (Discrete Element Simulations) allows us to tune these parameters and hence to understand their influence. In both regular (crystal-like) and polydisperse (sand-like) systems of spheres, a small perturbation is created on one side of the simulation box and examined during its propagation and on arrival at the opposite side. Starting from a regular packing, a tiny size variation comparable to the typical contact deformation already changes sound propagation considerably [1]. The transmission spectrum becomes discontinuous, i.e., a lower frequency band is transmitted well, while higher frequencies are not, mainly due to scattering effects. Furthermore, the wave propagation and transmission properties are studied on fully polydisperse, frictional and cohesive packings under increasing load until breakage of the material [2]. [1] O. Mouraille and S. Luding, Sound wave propagation in weakly polydisperse granular materials, Ultrasonics, submitted. [2] O. Mouraille, O. Herbst and S. Luding, Testing cohesive and frictional granular materials with the discrete element model, in preparation.
Surface elastic waves in granular media under gravity and their relation to booming avalanches
Authors: Bonneau Lénaïc , Andreotti Bruno , Clement Eric
Published: May 2008

Due to the nonlinearity of Hertzian contacts, the speed of sound c in granular matter is expected to increase with pressure as P1/6. A static layer of grains under gravity is thus stratified so that the bulk waves are refracted toward the surface. The reflection at the surface being total, there is a discrete number of modes (both sagittal plane and transverse ones) localized close to the free surface. The shape of these modes and the corresponding dispersion relation are investigated in the framework of an elastic description taking into account the main features of granular matter: the nonlinearity between stress and strain and the existence of a yield transition. We show in this context that the surface modes localized at the free surface exhibit a waveguide effect related to the nonlinear Hertz contact. Sound propagation measurements in a laboratory scale channel as well as in the field (slip face of a singing dune), will be presented and compared to the theoretical predictions. Finally, these results will be used to constrain the possible dynamical mechanisms at the origin of booming avalanches.
Information losses minimization in spectral devices based on acousto-optic Bragg cells
Authors: Gurevich Boris S. , Gurevich Simon B. , Andreyev Sergey V. , Belyaev Andrey V.
Published: May 2008

Spectral devices such as spectrophotometers are intended, as many other devices, for information transmission and processing. Hence, they can be characterized by specific information characteristics such as information transmission capability and information capacity, which can be connected with some physical and technical parameters of the devices. The use of acousto-optic components in these devices introduce some peculiarities in information transmission and processing in spectrophotometers. We have considered the information transmission limitations based on signal and noise in acousto-optic Bragg cells. The spectral resolving power is also considered as one of decisive characteristics influencing on acousto-optic spectral device transmission capability.
Peculierities of acoousto-optic interaction in nanodimensional laser heterostructures
Authors: Kulakova Liudmila
Published: May 2008

In the report, we present results of study of acousto-optic and acousto-electron interactions in active and optical resonator regions of nano-dimensional laser heterostructures. It was established that an ultrasonic wave introduced into a laser heterostructure produces modulation of the laser radiation frequency with a period equal to that of the acoustic wave. The static and dynamic analysis of the spectral parameters change under the ultrasonic strain has been fulfilled. The appreciable contribution of the acousto-optic interaction (comparable with the acousto-electron), resulting in the modulation in time of the positions of the heterolaser optical resonator lines was found out. The assumption about basic influence of quasi-two dimensional configuration of the laser optical resonator on the photoelastic properties causing unexpectedly large acousto-optic efficiency is stated.
3D Simulation of periodic surface wave inter-digital transducer using finite element/boundary element analysis
Authors: Ballandras Sylvain , Daniau William , Wilm Mikaël , Reinhardt Alexandre , Lardat Raphaël , Steichen William
Published: May 2008

Spectacular advances have been made during the past years in the development of surface acoustic wave thanks to technology improvements but also to a strong effort in the modelling and design of such devices, taking into account their actual structure to benefit from second order effects (for instance the influence of the metal strip shape used in inter-digital transducers on the wave propagating under periodic gratings). In this paper, we present a 2D-periodic 3D-simulation approach to compute the spectral response of one period of a surface wave transducer, accounting for the actual shape of the electrodes as well as realistic guiding conditions and acoustic properties of the propagation surface. The idea consists in meshing the inhomogeneous part of the transducer, i.e. the electrodes and the bus bar, as well as a thin layer of the substrate to match the finite element section with surface boundary elements simulating the acoustic contribution of the substrate (propagation and radiation). Periodic boundary conditions are applied in both surface direction, allowing for the exploitation of spectral Green's function-based boundary elements, but additional absorbing conditions are added in the transverse direction (from both part of the bus bars) to suppress any unwanted modes generated by the mesh.
Pendellösung phenomenon in two-dimensional sonic crystals
Authors: Angelov Mitko , Torrent Daniel , Cervera Francisco , Sanchez-Dehesa José
Published: May 2008

The phenomenon of "Pendelösung" oscillations, which is well known in X-ray diffraction [P.P. Ewald, Phys. Z. 14, 465 (1913); Ann. Phys. 54, 519 (1917); Rev. Mod. Phys. 37, 189 (1965)] is predicted here and experimentally verified for the case of two-dimensional sonic crystals made of hexagonal arrays of fluidlike cylindrical bars embedded in water. The dependence of diffraction intensity is studied as a function of layer thickness; i.e., of the layer number N. Nearly periodic oscillations have been observed at specific frequencies and the oscillation period is also a function of the frequency. The periodic behaviour is evidence of the exchange of energy between two modes in the sonic crystal. [Work supported by MEC of Spain.]
Lossy propagation of the Gulfstream Quiet Spike
Authors: Salamone Joe
Published: May 2008

The Gulfstream Quiet Spike is a telescoping nose extension with multiple segments of decreasing diameter intended to reduce the outdoor loudness of a sonic boom. This work examines the influence of the atmosphere on a propagated sonic boom signature for this device. First, atmospheric data, averaged by season, has been collected as a function of latitude to reasonably bound the range of meteorological conditions. These atmospheric profiles are subsequently input to nonlinear, lossy propagation code that computes the primary sonic boom carpet for a supersonic aircraft in steady, level flight. This code is an augmented implementation of the KZK model equation for one-dimensional propagation. The confluence of shocks generated by the Quiet Spike remains distinct and do not coalesce, as intended per the design. The amplitudes, rise times and spacing of the shocks from the individual spike segments are strongly governed by dispersion and attenuation. Loudness levels calculated from the resulting ground signatures show an observable change of over 4 dB at certain azimuths due to the various atmospheric conditions. Based on these results, minor design changes are recommended to improve the acoustic performance of the Gulfstream Quiet Spike.
Study of full band gaps and propagation of acoustic waves in two-dimensional piezoelectric phononic plates
Authors: Hsu Jin-Chen , Wu Tsung-Tsong
Published: May 2008

Acoustic wave propagation in periodic structures composed of multi-constituents, namely the phononic crystals (PCs), has received much attention in the past decade. Recently, PCs constructed in the form of plate structures with two-dimensional lattices have been investigated, and some important phenomena, such as the full band-gap and waveguiding effects, induced by the periodicities of the phononic plates were reported. One of the virtues using Lamb waves is to perfectly confine the acoustic energy within the plate thickness and guided in structures with only 2D lattices rather than 3D lattices; however, the additional free surfaces derive much more complicated characteristics which are still awaiting study further. In this study, we investigate the band-gap and propagation properties of waves in two-dimensional phononic plates that consist of either elastic or piezoelectric materials by employing a revised full 3D plane wave expansion (PWE) method and so on. To apply the PWE method efficiently, Fourier expansions are performed in the thickness direction for an imaginary 3D periodic structure by stacking the phononic plates and vacuum layers alternatively. Moreover, effects of piezoelectricity, lattices, and filling ratios on band gaps are discussed.