Keynote Speakers

POGLED KOMPONISTA NA AKUSTIKO (ODNOS KOMPONISTA/INTERPRETA DO AKUSTIKE)

Vinko GLOBOKAR

Kultura in natura; komponiranje in dekomponiranje; komponist sestavlja glasbene parametre v strukture, akustičar razstavlja zvočne fenomene v znanstvene podatke. A) Zaključek dobe gradnje akustičnih inštrumentov: 1) Odkritje novih barvnih in artikulacijskih možnosti na orkesterskih inštrumentih (dušilci, multifonični zvoki pri pihalcih in trobilcih, istočasno igranje in petje ali govor v eni cevi, deformiranje zvoka ...). 2) Prehod iz čistega tona v šum ali ropot. 3) Mikrointervali (spektralna glasba). 4) Nove tehnike v produciranju zvoka (cirkularno dihanje, igranje pri vdihavanju). 5) Jezikoslovje kot model za kontrolo in opis barvnih inštrumentalnih odtenkov.B) Elektronska glasba in računalniška sredstva: 1) Analogna sredstva (generatorji, modulatorji, filtri ...). 2) Spektralna analiza inštrumentalnih zvokov. 3) Sinteza novih zvokov. 4) Kontrola difuzije zvoka in njegovo lokaliziranje. 5) Psihoakustični fenomeni (trajni glissando). 6) Računalnik kot sredstvo za inovacijo kompozicijskih algoritmov. C) Spekulacije o bodočnosti: 1) Sejem inštrumentov (Pariz, Frankfurt). 2) Privatizacija v produciranju glasbe in pojav "samplinga". 3) Konsumiranje glasbe in njena polucija. Predavanje bo podprto s primeri na inštrumentu (pozavni).

CLASSROOM ACOUSTICS - ACOUSTICAL CONDITIONS IN SCHOOLS AND THEIR IMPACT ON PUPILS

August SCHICK1, Maria KLATTE1, Markus MEIS2, Christian NOCKE3

1 Oldenburg University, Institute for Research Into Man-Environment-Relations, Germany, 2 Oldenburg University, Hearing Center

3 Akustik Buero Oldenburg

Despite the fact that "good acoustics" possess evident significance regarding successful learning in school, room acoustic criteria often only play a subordinate role when building schools. Therefore, classrooms often show substantial deficits regarding room acoustics: They are too reverberant, speech intelligibility is too low, and background noise levels are too high. For some time now, our research group has been occupied with the acoustic conditions in schools and their effects on well-being, health, and mental performance of students and teachers. In addition, constructional and electroacoustic measures to improve classroom acoustics are evaluated. In this work, the significance of good hearing conditions in schools is documented and a realistic cost-benefit analysis regarding room acoustical improvements is presented.

INVERSE NUMERICAL ACOUSTICS

Andrew F. Seybert

University of Kentucky, Department of Mechanical Engineering, Lexington, KY 40506-0503 USA

This paper explores the use of inverse numerical acoustics to reconstruct the surface vibration of a noise source. Inverse numerical acoustics is mainly used when measuring the surface vibration directly is not practical or not possible. This approach uses the measured sound pressure at a set of field points and the Helmholtz integral equation to reconstruct the normal surface velocity. The number of sound pressure measurements is considerably less than the number of surface vibration nodes. A brief guideline on choosing the number and location of the field points to provide an acceptable reproduction of the surface vibration is presented. The effect of adding a few measured velocities to improve the accuracy will also be discussed. Other practical considerations such as the shape of the field point meshes, effect of experimental errors and reconstruction accuracy will be presented. Examples will include a diesel engine and an open duct.

UNDERSTANDING HELICOPTER ROTOR NOISE THROUGH DEDICATED WIND TUNNEL AND FLIGHT TESTS

Hanno Heller

Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Entwurfsaerodynamik und Strömungstechnik, Abteilung Technische Akustik, Lilienthalplatz 7, 38108 Braunschweig,

Germany

Although significant advances have been made in the past few years in understanding helicopter rotor noise, there is still no break-through in sight towards the "24-hour/green helicopter", i.e. a helicopter which was acoustically unobtrusive allowing round the clock operation. In Europe intensified efforts are underway towards (1) controlling helicopter rotor noise at the very aeroacoustic sources, and (2) developing noise abatement flight procedures which are acceptable both to the pilot (who must fly them in addition to his/her normal piloting work load) and to the passenger (who requires a comfortable ride). Advanced rotor blade designs which would be inherently quiet ("low source noise") as well as progress made in guiding helicopters through Global Positioning Systems (GPS) show the way. This paper treats advances made in these respects. Starting with a brief recapitulation of the basic physics of rotor noise generation, the paper will discuss topical wind tunnel and flight experiments which significantly improved the current understanding of rotor noise and its control at the source and which point towards noise abatement flight procedures. Europe, within its various joint research projects - both recently concluded ones and planned ones - is working towards the ultimate goal, the acoustically unobtrusive "24-hour helicopter".

SOUND INSULATION IMPROVEMENT OF TRADITIONAL MASONRY WALLS: AN OVERVIEW

Roberto ZECCHIN, Antonino DI BELLA

Dipartimento di Fisica Tecnica, University of Padova, Via Venezia 1, 35131 Padova, ITALIA

The increasing attention paid to noise pollution in the built environment leads to look for more and more improvements in the characteristics of partitions in buildings. Recent laws and regulations take care of this concern and fix minimum values of acoustical insulation according to different requirements. It is quite easy to obtain even very high sound reduction indexes by resorting to lightweight walls, e.g. by means of combinations of plasterboard layers and porous filling, but in many cases tradition, structural and safety requirements, impose the use of masonry walls, mainly in the residential field. The type of bricks or blocks and the wall thickness so far used are often insufficient to cope with the above mentioned limits and the user expectative. Therefore new solutions have to be set up and assessed, taking into account cost, thickness (which involves loss of surface area), easiness of construction and robustness. In this paper an overview of recent achievements is reported and some criteria of selection among different solutions are discussed.

DEVELOPMENT AND USE OF A NEUROSURGICAL ULTRASOUND ENDOSKOPE PROBE

Bojan Ivančević

FAKULTET ELEKTROTEHNIKE I RAČUNARSTVA, Zavod za elektroakustiku, Unska 3, HR-10000 ZAGREB

Minimally invasive ultrasonic surgery is the most recent field of application of ultrasound in medicine. Due to the principle of ultrasonic surgery (direct cutting, cavitation, fragmentation and thermal damage), the irreversible changes in tissues and organs are reported. The aim of thies study has been to optimize construction of an endoscopic contact ultrasonic probe (ECUP) with respect to some specific technical, medical and operational/ergonomic requirements. On the basis of the theoretical model, the ECUP was constructed and verified through extensive experiments. The ECUP has been realized as a rod-type resonant vibrating system, consisting of a half-wave lenght transducer of piezoceramic material, and a resonant wave-guide in the form of a specially shaped velocity transformer. Special attention has been paid to the electroacoustical characteristics of the transducer as well as of the specially shaped wave guide. Neurosurgical treatments of brain tumors can result with damage to healthy tissue (because of focussing of high-energy ultrasound). In order to avoid this the 2D and 3D simulation of ultrasound field in the human scull was developed. To check the precision of simulation the measurements on real scull were carried out. The ECUP was tested in clinical applications (more then 40 patients were succefully operated).

ULTRASOUND ENHANCES THROMBOLYSIS

Dr. Branka Devcic-Kuhar

Technische Universität Wien, Institut für Allgemeine Physik, Wiedner Hauptstrasse 8-10/E134, A-1040 Wien

Thrombotic occlusion of the coronary artery results in myocardial infarction, one of the major causes of death in the western world. Also, acute peripheral occlusions leading to limb ischemia are a severe clinical problem requiring immediate thrombolytic therapy. The most powerful blood clot dissolver yet known is the fibrin-selective recombinant tissue plasminogen activator (rt-PA). However, penetration of rt-PA from the surrounding blood into the thrombus is a very slow process and a rate-limiting step in reestablishment of blood flow and mainteinance of viability of the affected region, but it can be enforced if taking place in an ultrasound field (sonothrombolysis). In our four-years research on sonothrombolysis, we studied the effects on thrombolysis enhancement of ultrasound of therapeutic quality, which is commonly and safely used in physical therapy. We also developed a new method of visual detection of fibrinolytic reactants within the blood clot. This method enabled us to localize fibrinolytic components in the thrombus and to study the effect of ultrasound on their spatial distribution. We have shown for the first time that ultrasound facilitates the access of rt-PA to the deeper layers of the clot, thus leading to significantly faster clot dissolution.

THE ITALIAN EXPERIENCE IN IMPLEMENTING THE EUROPEAN DIRECTIVE 2000/14/CE: THE CASE OF CONSTRUCTION MACHINES

Eleonora Carletti

IMAMOTER Institute - National Research Council of Italy, Via Canal Bianco, 28 - 44044 Cassana (Ferrara) - Italy

The 2000/14/EC Directive is the new European legislation concerning the limitation of noise emissions in the environment by equipment for use outdoors. It has been published by the European Parliament on July 2000 and has been in force all over the European Community since January 2002. This Directive covers a wide range of different machines and lays down the requirements with regard to permissible noise levels, noise test codes, marking and conformity assessment procedures. Although its extremely flexible frame well suits with the innovative concepts related to the New Approach, its practical implementation has been showing serious difficulties to ensure a uniform enforcement among all the Member States. The paper, after a short introduction on the contents and the novelties introduced by this legislation, will just point out on the technical problems accompanying its application. In particular, the settling up of suitable procedures for the correct assessment of the experimental data uncertainties and the guaranteed sound power level will be presented. Finally, the case of construction machines will be described with the purpose to show whether and to what extent the technical progress in this specific field will guarantee the fulfilment of the reduced noise limits starting from 2006 (stage II of the Directive).

VIRTUAL PROTOTYPING TODAY: INDUSTRIAL IMPACT AND FUTURE TRENDS

Giuseppe Miccoli

Institute for Agricultural and Earthmoving Machines - IMAMOTER, National Research Council of Italy - C.N.R., Via Canal Bianco, 28 - 44044 Cassana (Ferrara) - Italy

The National Agency for Finite Element Methods and Standards (shortly NAFEMS) is a non-for-profit UK company. Its specific aim consists on promoting knowledge and diffusion of simulation computational codes normally based on the finite element method and related technology. NAFEMS Steering Committees have been set up in USA, Germany and Italy to co-ordinate local activities and interaction with members involved in many different types of engineering simulation, covering both products and processes. The NAFEMS technical activities are coordinated by working groups, like Education & Training, CAD/CAE Integration, CFD, Process Optimisation. These working groups identify areas of interest to the analysis community that require new educational materials to be developed. That is achieved by primer/review publication, course/master organization and International/European project involvement. The aim of the paper consists on showing the activities carried out by NAFEMS and its Italian Steering Committee, the author being a member of both. Simulation computational codes state-of-the-art and effectiveness are illustrated, based on case histories, applications and results already achieved. Simulation/analysis tools and virtual prototyping turn out to be promising and powerful for both industrial and academic world. NAFEMS can be considered a landmark in support of both of them.

BISPECTRAL ANDWAVELET ANALYSES: APPLICATIONS IN MECHANICAL ENGINEERING

Miha BOLTEŽAR

Faculty of Mechanical Engineering, University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, SLOVENIA

Two modern signal-processing methods will be addressed: bispectral and wavelet analyses. These techniques are able to detect non-linearity and non-stationarity, respectively. First, some basic principles of both will be explained, together with our own theoretical research. This includes an assessment of the estimation quality of the bispectrum regarding the presence of harmonic components and noise in the signal, and the influence of the edge-effect and noise when estimating scalograms within the wavelet transform. Our own applications include the detection of the quadratic phase coupling in a multi-degree-of-freedom vibrational system, chatter detection in the cutting process as well as faults identification using bispectral analysis. The application of wavelet analysis will be shown as damping identification of vibrating continuous systems and faults identifications, specifically on DC electric motors.

NOISE SYNTHESIS TECHNOLOGY USING MODIFIED SUBSTRUCTURING APPROACH

Goran Pavic

Laboratoire Vibrations - Acoustique Institut National des Sciences Appliquées de Lyon, 69621 Villeurbanne, France

Noise Synthesis Technology (NST) is an approach aimed at helping low noise design of many industrial products. It is applicable to products where noise is generated by individual sources (components) implanted into an otherwise noiseless main frame (housing). Examples are household appliances, HVAC installations, outdoor machinery, communication equipment, computation equipment etc. In such products noise is transmitted to the surroundings as direct air-borne noise, structure-borne noise (via feet, cables etc) and frequently fluid-borne noise (via pipes etc). Although often being more detrimental than the first one, the latter two noise mechanisms are rarely dealt with in industrial conditions. The originality of NST is that it predicts trends in the overall noise by combining data from real components with a main frame generic modelling based on existing products. Such an evolutionary approach has the advantage of being potentially simple enough for use by the industry. It provides a systematic step-by-step access to noise control. The underlying prediction technique is sub-structuring. The whole product is subdivided into three classes of objects: source(s), connections and main frame. The acoustical assembling is done by satisfying continuity conditions at the interfaces. The noise sources as well as the connections source - main frame are characterised in a deterministic way, by adapted measurements and/or computation. The novelty is in the representation of the main frame. It is represented in a statistical way, by its baseline (generic) characteristics on which is added the fuzz, i.e. the statistical uncertainty. This specific representation was shown to be particularly well adapted to mass industrial products.

Invited and Contributed Papers

NUMERICAL ANALYSIS OF WAVE PROPAGATION IN AN ULTRASONIC FLOWMETER

Michal BEZDEK1¤, Alfred RIEDER1¤, Hermann LANDES2, Torsten STRUNZ1¤, Reinhard LERCH2

¤1 Endress+Hauser GmbH+Co. KG, Am Lohm¨uhlbach 12, 85356 Freising, Germany 2 Department of Sensor Technology, University of Erlangen-Nuremberg, Paul-Gordan-Str.

3/5, 91052 Erlangen, Germany

In this paper, a state-of-the-art computer simulation tool is presented. It is applied in order to investigate the wave propagation phenomena in a sample transit time ultrasonic flowmeter. 3D and 2D finite element models including the piezoelectric transducers are setup. Therewith the full electro-acoustic coupling is taken into account using an electric excitation of the transmitter and providing the electric output signal of the receiver. Furthermore, the solid-fluid interaction is implemented and the acoustic field in the fluid is obtained by means of solving the convected wave equation. Various simulation results are presented including the problem of parasitic waves traveling through the pipe wall. Finally, a simple simulation-based optimization procedure is proposed.

A MICROPROCESSOR CONTROLLED MULTI-CHANNEL MEASUREMENT SYSTEM FOR RESONANT PIEZOELECTRIC BAW SENSORS

Reinhard SCHNITZER, Martin GRÖSCHL, Ewald BENES

Institute of General Physics, Vienna University of Technology, Wiedner Hauptstraße 8/134, A-1040 Vienna, Austria

A new microprocessor controlled multi-channel measurement system for resonant piezoelectric bulk acoustic wave (BAW) sensors measuring different physical quantities, like temperature, viscosity and humidity, is presented. The measurement principle for all supported sensors is based on the determination of the sensor's electrical admittance as a function of frequency in the vicinity of resonant frequencies. The physical measurand quantity is calculated out of one or two resonant frequencies and in some cases the quality factor of the sensor by using the appropriate sensor function for each type of sensor. Special demands on the electronics for resonant sensors are described. Kernel measurement electronics are used to transform the admittance values of the sensor to voltage signals which can be acquired by the computer. Two different types of such kernel electronics are compared with respect to their principal capabilities for resonant sensor applications. The multi-channel measurement system is controlled by an industrial PC (NI PXI). Basic features of the sensor family and the measurement electronics are discussed.

ASSESSMENT OF THE TITANIUM WIRE AS A ENDOSCOPIC SURGICAL TOOL

Alan Štimac

Brodarski Institute, Acoustics Department, Ave. V. Holjevca 20, HR-10 020 Zagreb, Croatia

During scientific-research programmes in the Republic of Croatia, a possibility to apply high-power ultrasonic point sources for minimally invasive neurosurgery has been noticed. Earlier experiences with applications of high energy ultrasound have induced the idea of ultrasonic energy transfer through an elastic wire waveguide. The scope of this study is to present the results of theoretical and experimental research in the field of generation and propagation of high-power ultrasound along the titanium wire as a endoscopic surgical tool. On the basis of the theoretical calculations for generation and transmission of ultrasonic waves from the ultrasonic transducer, through the mechanical concentrator to the endoscopic tool, the ability for adaptation to different surgical applications have been described. In the experimental part, methods for verification of the theoretical results have been presented. This includes methods for validation the performance of the 1,6 mm titanium wire as an endoscopic tool and experimental methods for assessment of electric and acoustic characteristics.

ESTIMATION OF SPACE ACOUSTICAL QUALITY BASED ON ENERGY RATIO OF SOUND

Siniša Fajt, Antonio Petošić, Bojan Ivančević

Faculty of Electrical Engineering and Computing, Department of Electroacoustics, Unska 3, 10000 Zagreb, Croatia

Measuring procedure of achieving energy-time curves (ETC) is applied and supported by time delay spectrometry (TDS), which is implemented on time-energy analyzer (TEF) and objective parameters of clarity (C), definition (D) and ratio between reflected and direct energy (R) as ratio between reflected, direct and total energy. Inter-relations are set in order to enable estimation of other parameters based on measurement of only one energy parameter. Based on measurements in two architectural identical, but according to acoustic characteristics two different rooms, and additional analysis and calculations connected with number of people in a hall, objective parameters are evaluated according to earlier adopted optimal conditions involving certain deviations from the values.

PARAMETRIČNI SPEKTRALNI ANALIZATOR

Samo BEGUŠ, Dušan FEFER

Fakulteta za Elektrotehniko, Univerza v Ljubljani, Tržaška 25, 1000 Ljubljana, SLOVENIJA

High resolution parametric spectral analyser is can to change two parameters of a measurement in real time. It uses a computer sound card for signal acquisition. According to the measurement two parameters could be changed with the serial interface (external signal generator control) or with the two sound card output signals. The parameters could be the frequency or the amplitude of the sound card output signals. Analyser could be used for audio systems measurements, motor noise measurements in different operating points and loads. The results could be processed and presented in time or frequency domain.

A NEW ULTRASONIC FLOW-METER FOR DETERMINING THE VOLUME FLOW OF GASES IN PIPES AT HIGH TEMPERATURES

Rüdiger Reitinger, Andreas Schröder, Martin Gröschl, Ewald Benes

Vienna University of Technology, Institutes of General and Theoretical Physics, Wiedner Hauptstr. 8/134, A-1040 Vienna, Austria

A new method for measuring the volume flow of gases in pipes at elevated temperatures of some hundred degrees Celsius, by means of ultrasonic waves generated and detected by capacitance transducers, is suggested. Hence, as common ultrasonic capacitance transducers are made of materials not resistant against high temperatures, a special transducer for this application had to be developed.Various materials for each component of the transducer were investigated by taking into account their physical properties at raised temperatures as well as at room temperature. Specific manufacturing processes for coating the backplates with different insulating materials are introduced, and the experimental setup for the volume flow measurements is presented. Special attention is dedicated to a range of different insulating materials, used as dielectrics. Their capability to withstand high electric fields at increased temperatures is investigated, as this is the main criterion, whether they can be used to electrically insulate the two electrodes of the transducer during operation without being destroyed by dielectric breakthrough. Furthermore, the mechanical stress between the back panel and the coating material at elevated temperatures is regarded.

THE ULTRASONIC H-SHAPE SEPARATOR: HARVESTING OF THE ALGA SPIRULINA PLATENSIS UNDER ZERO-GRAVITY CONDITIONS

E. Benes1, M. Groeschl1, H. Nowotny1, H. Böhm1, J.B. Power1, K.C. Lowe1, L.G. Briarty1, M.R. Davey2

1 Vienna University of Technology, Institutes of General and Theoretical Physics, Wiedner Hauptstr. 8/134, A-1040 Vienna, Austria

2 School of Biological Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK

Conventional ultrasonic bio-cell filters require the supporting effect of gravity and therefore are sometimes referred to as ultrasonically enhanced settlers. In contrast to those, the new h-shape resonator utilizes the acoustic radiation forces directly for dividing the liquid flow lines into cleaned and particle-enriched portions that are directed to separate outlets. Therefore the direct ultra-sonic separation concept of the h-resonator does not rely on gravity. A mathematical model based on a complete flow and force field simulation has been developed that allows for the prediction of the separation performance figure (Litres/W h) for any given sample suspension. Calculation of the particle traces was performed in two steps. First the velocity and the streamlines of the fluid were determined by solving the Navier-Stokes equation with the software Package FLUENT®. In the second step, Newton's equation of motion for the suspended particles was solved to obtain the particle traces. The simulation results for a suspension of polystyrene spheres of 40 micrometer in diameter were compared to the respective experimental results. In addition, sample suspensions of yeast cell cultures of various concentrations were investigated. The h-separator was also tested successfully with suspensions of the blue-green alga Spirulina platensis under microgravity conditions in the recent ESA 29th zero-g parabolic flight campaign within the frame of the ESA Melissa project. This work was supported by the European Commission, TMR Network Contract No. ERBFMRXCT97-0156 (EuroUltraSonoSep).

VISCOSITY MONITORING WITH A QUARTZ CRYSTAL THICKNESS SHEAR RESONATOR

Martin Gröschl*, Rudolf Thalhammer*, Ewald Benes*, Helmut Nowotny**

*Vienna University of Technology, Institute of General Physics,

**Institute of Theoretical Physics, Wiedner Hauptstr. 8, A-1040 Vienna, Austria/Europe

The paper describes a novel quartz crystal sensor for the measurement of the density-viscosity product of Newtonian liquids. The sensor element consists of two circular quartz crystal plates with an air-gap in between and the liquid sample in contact with the outer plate surfaces. Plano-convex AT-cut quartz crystals arranged in mirror symmetric crystallographic orientation and vibrating in an even-symmetric thickness-shear fundamental mode at 2.77 MHz are utilized. The two outer plane sides of the crystals are fully covered by gold electrodes, which are both connected to ground potential. This special mirror symmetric set-up allows the compensation of spurious displacements in the circular clamping zones of the

two crystals. The measurement values of the sensor are the fundamental resonance frequency f and the associated resonance Q-value, which are analytically dependent on the density-viscosity product of the liquid in contact with the sensing surfaces. The quartz crystals, together with a miniature platinum resistance temperature sensor, are mounted in a stainless steel housing. In contrast to an earlier report [1] about a sandwich resonator sensor, which entrapped the liquid sample in between two quartz plates, the immersible sensor presented here is not restricted to low viscosity samples. For Newtonian liquids, the double-quartz sensor features high absolute accuracy and reproducibility without the need of calibration and without any fitting parameter. The sensor covers a viscosity range from almost zero (air!) up to 2000 cP, and is not restricted to electrically insulating liquids. Non-Newtonian behaviour can be identified and the complex mechanical impedance of non-Newtonian fluids can be determined at high shear rates (107 s-1). The flange mounted immersible sensor was employed successfully in rough industrial environment for on-line monitoring viscosity and temperature of waffles dough flowing through the dough supply pipe of a waffles production plant (Manner®-Schnitten, Wien, Austria). The high viscosity resolution could be demonstrated by adding small amounts of water (1 vol.% or 0.5 vol.%, respectively) for which corresponding decreases in dough viscosity could be observed. Dough viscosity is an essential parameter for quality control in waffles production. This work was supported by MANNER AG, Wien, Austria, and by the European Commision within the GROWTH shared-cost RTD funding scheme, project QxSens No. GRD1-2001-41816. [1] R. Thalhammer, S. Braun, B. Devcic-Kuhar, M. Gröschl, F. Trampler, E. Benes, H. Nowotny, and M. Kostal, Viscosity sensor utilizing a piezoelectric thickness shear sandwich resonator, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 45, pp. 1331-1340, 1998.

ULTRASOUND ENHANCED DE-MIXING OF OIL-WATER EMULSIONS

Christian Hauser, Stefan Radel, Martin Gröschl, Ewald Benes

Vienna University of Technology, Institut für Allgemeine Physik, Wiedner Hauptstr. 8/134, A-1040 Vienna, Austria

Ultrasonic filters are successfully used for the retention of suspended biological cells and mainly applied in the field of biotechnology. In theory, the same principle of particle manipulation exploited when separating biological cells can be applied to the droplets in an emulsion. However, a difference exists in the sign of the acoustic contrast factor on which the ultrasonic forces depend. Batch separators were used for experiments where the ultrasonic field coagulates the small droplets to bigger agglomerates. The smaller surface to volume ratio of the agglomerates allows the subsequent de-mixing of the emulsion by gravity. Various samples of industrial interest ranging from bio-Diesel to washing liquids for the printing industry were chosen for examination. It was shown that ultrasonic treatment within specially designed resonators was applicable for the de-mixing of emulsions. The effect of the ultrasound was evaluated in comparison to un-sonicated controls. Pictures of samples and controls will be shown to demonstrate the effect of the ultrasonic treatment.

ULTRASOUND GENERATION IN AIR WITH FOCUS ON RECENT DEVELOPMENTS OF CAPACITANCE ULTRASONIC TRANSDUCERS

Andreas Schröder, Rüdiger Reitinger1, Martin Gröschl1, Ewald Benes1

Laboratory for Analysis and Architecture of Systems, 7 Avenue du Colonel Roche, F-31077 Toulouse, France

1 Vienna University of Technology, Institute of General Physics, Wiedner Hauptstr. 8/134, A-1040 Vienna, Austria

This paper is focussed on ultrasonic transducers for sound generation in air. In addition to the commonly known and widely used transducers based on the piezoelectric principle, there are other transducers utilizing different physical principles for sound generation that offer advantages in certain applications. A short survey of the problem of sound generation in air will be given and the most important ultrasonic transducers used for this purpose will be introduced. Fundamental transducer properties and basic applications will be discussed. For specific measurement applications the capacitance ultrasonic transducer shows advantages when compared to piezoelectric transducers. Recent developments in the field of capacitance transducers conducted at the Institute of General Physics will be presented. The concept of transducer characterization will be discussed. As an example, measurement results achieved with specially developed high temperature resistant capacitance transducers are presented and the design rules for obtaining certain desired transducer properties will be explained. Future developments and new applications that become feasible due to these developments will be discussed.

SOUND ANALYSIS AND QUALITY CONTROL OF VACUUM CLEANER MOTORS

Uroš Benko1, Joža Tavčar3, Janko Petrovčič1, Đani Juričić1, Jožica Rejec3, Aneta

Stefanovska2

1 Jožef Stefan Institute, Department of Systems and Control, Jamova 39, 1000 Ljubljana, Slovenia

2 University of Ljubljana, Faculty of Electrical Engineering, Tržaška 25, 1000 Ljubljana, Slovenia

3 Domel d.d., Otoki 21, 4228 Železniki, Slovenia

Abstract: Relentless competition in the field of household appliance manufacturing has urged the manufacturers to produce high quality products available by the lowest possible prices. High quality products can be attained only by highly automated production with best possible quality assurance end test, which in first place prevents the faulty products to leave the manufacturer and secondly it enables on-line control of the assembly line. The paper addresses a possibility of fault detection of vacuum cleaner motors based on a sound analysis. Its contribution is threefold. First, on the basis of a thorough physical insight into a device's operation, a detailed analysis of sound sources is performed. Second, proper experimental measurement scenario is proposed and third, an explanation of fault detection based on a rather simple signal processing tools is described. An emphasis is laid especially on the faults with mechanical and aerodynamic origin. Finally, an outline of diagnostic system build upon an experimental study done on more than 200 motors is presented.

POTRJEVANJE SUMA KRONIČNE SENZORINEVRALNE NAGLUŠNOSTI KOT POKLICNE BOLEZNI (UPOŠTEVANJE STAROSTNE KOREKCIJE IZGUBE

SLUHA)

Škibin L.*, Bilban M.**, Deželak F.**

*Dispanzer medicine dela, prometa in športa - Zdravstveni dom Sežana, Partizanska cesta 24, Sežana, Slovenija

**ZVD - Zavod za varstvo pri delu d. d., Bohoričeva 22a, Ljubljana, Slovenija

Hrup je še vedno ena glavnih fizikalnih škodljivosti pri delu predvsem v industriji. Poklicna okvara sluha zaradi hrupa je najpogostejša poklicna bolezen v razvitih in nerazvitih državah. Sum na kronično senzorinevralno naglušnost kot poklicno bolezen je lahko podan v primeru biauralne, starostno korigirane okvare sluha srednje, težke ali zelo težke stopnje ali enostranske popolne gluhosti. Sum na poklicno bolezen poda pooblaščeni zdravnik - specialist medicine dela, prometa in športa. Namen raziskave je bil preveriti oz.pripraviti nov predlog podlag diagnostike in verifikacije poklicne bolezni zaradi auralnih učinkov hrupa. Zato smo v raziskavo vključili številne dejavnike, ki bi lahko vplivali na slušno okvaro ter pri tem posebno pozornost posvetili eventuelnim kemijskim ototoksikom in doslednem upoštevanju starostne korekcije ugotovljene slušne okvare, kar menimo, da sta bila ta dva dejavnika, vsaj v našem prostoru, do sedaj v veliki meri spregledana. Ugotovili smo, da delež sumov na poklicno okvaro sluha zaradi izpostavljenosti hrupu brez starostne korekcije izgube sluha presega 10%, kar je zgornja meja deleža preobčutljivih ljudi za okvaro sluha zaradi hrupa, da se delež sumov na poklicno okvaro sluha zaradi hrupa statistično pomembno veča z leti izpostavljenosti hrupu, da je večji pri delavcih, ki so hkrati izpostavljeni tudi kemičnim ototoksikom, kot pa tistih, ki so izpostavljeni le hrupu in da starostna korekcija okvare sluha statistično pomembno zniža delež sumov na poklicno okvaro sluha zaradi hrupa. Zato predlagamo, naj se pri verifikaciji dosledno upošteva starostna korekcija izgube sluha, v obsegu in vsebini preventivnih zdravstvenih pregledov delavcev izpostavljenih hrupu pa poudari pomen upoštevanja vseh dejavnikov, ki lahko vplivajo na okvaro sluha. Na podlagi tega je tudi v promociji zdravja potrebno dati večji poudarek preprečevanju vseh škodljivih dejavnikov, ki posledično okvarjajo sluh, tako v delovnem okolju kot v življenju nasploh.

METODA ROBNIH ELEMENTOV V AKUSTIKI

Furlan M.1 in Boltežar M.2

1 ISKRA Avtoelektrika d.d, Šempeter pri Gorici, Slovenia 2 Univerza v Ljubljani, Fakulteta za strojništvo, Aškerčeva 6, 1000 Ljubljana, Slovenia

V prispevku so predstavljeni osnovni prijemi za reševanje zunanjih akustičnih problemov s pomočjo metode robnih elementov (MRE) ter njena izvedba v programih za reševanje dvodimenzionalnih, tridimenzionalnih ter tridimenzionalnih aksisimetričnih problemov. Prikazana je tudi integracija programa v komercialni programski paket metode končnih elementov (MKE), ki primarno služi kot orodje za določitev strukturnega odziva oz. vzroka za zvočno polje, sekundarno pa za pripravo in kasnejšo obdelavo akustičnega modela. Programi MRE so verificirani na akustičnih problemih, kjer je poznana analitična rešitev. Sama verifikacija je izvedena s poudarkom na raziskavi vpliva gostote diskretizacije na natančnost izračuna zvočnega polja. Poleg tega je zaradi narave numeričnega problema oz. sistema linearnih enačb, ki pri tem nastane, ovrednotena tudi hitrost reševanja problema glede na izbiro metode reševanja nastalega sistema linearnih enačb.

NUMERICAL METHODS IN ACOUSTICS MODELING / AUDITORY AND SPEECH ACOUSTICS. A MULTI-THREADED SOLVER FOR AUDITORY

COMPUTATIONS IN THE MSO

Claus Weiland

J W Goethe-University Frankfurt, Germany

Low frequency sound localization is currently explained by models, which are based on processing of interaural time delays (ITD) in systematically ordered coincidence detector cells. Common simulation approaches on this topic consist on simplified 'point neuron' models (lacking dendritic compartments) of time coding units. Facing the functional architecture of the underlying Medial Superior Olivary Nucleus (MSO), the morphology of the MSO shows contrary to point neuron-based models a rich structural variety: Several neuronal types can be recognized, each building a specific pattern of connections to other neurons. Having this structural complexity in view, modeling MSO cells leads to an intensive use of computational resources, which suggest the need for parallel simulations. The paradigmatic approach for the simulation of complex neuronal systems is compartmental modeling, a method derived from physical cable theory. Here finite element discretization is used to simplify the differential equations representing the spread of activation in a neuronal system. Aim of this talk is to show how a now common approach in parallel shared memory programming - based on the proposed standard application interface (API) OpenMP - could be used to distribute algorithms for compartmental models of the auditory system across actual shared memory platforms.

NOISE GENERATION BY VACUUM CLEANER SUCTION UNITS

Mirko Čudina1, Jurij Prezelj1, Jožica Rejec2

1 University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva 6, 1000 Ljubljana, SLOVENIA

2 DOMEL Železniki, Otoko 21, 4228 Železniki, SLOVENIA

A vacuum cleaner is one of the most powerful noise sources in housekeeping. The main noise source within the vacuum cleaner is the suction unit consisting of a commutator electric motor and a centrifugal blower working on a common shaft. The total noise is generated partially by the blower and partially by the electric motor, and consists so of aerodynamic, mechanical and electromagnetic noise origins. All these noise origins depend on the suction unit geometry, its size and shape, and on the operating conditions, i.e. speed and load. The amount of the dust particles in the dust bag is permanently increasing so that the system characteristic becomes steeper and steeper until it reaches zero flow rate, and at some blower geometry it reaches before a region of instability. The instability is a consequence of rotating stall and surge phenomenon. As a result an additional vibration and noise is generated. The emitted noise depends on the suction unit geometry and configuration and on the operating conditions. In the present paper an overview is given for suction units with and without vaned diffuser and at different operating conditions.

VPLIV HRUPA PRI POUKU V OSNOVNI ŠOLI

Ina Čarič*, Mirko Čudina**

*Osnovna šola Spodnja Šiška, 1000 Ljubljana **Fakulteta za strojništvo, Aškerčeva 6, 1000 Ljubljana

Pri pouku v osnovni šoli je hrup lahko zelo moteč faktor; ta vpliva na koncentracijo, pomnjenje, komunikacijo, razumevanje razlage in splošno počutje. V šolskih prostorih ga povzročajo učenci sami s svojimi aktivnostmi, v učilnice pa prihaja tudi od zunaj kot posledica prometa ali dejavnosti otrok na šolskem igrišču. Hrup, ki ga povzročajo učenci, se razlikuje glede na njihovo dejavnost in dnevni čas. Zunanji hrup pa je odvisen od položaja učilnice glede na prometnice in druge vire zunanjega hrupa. Vpliv hrupa na učence in učitelje v šoli smo ugotavljali z meritvami ravni hrupa v različnih prostorih šole in s pomočjo anket, ki smo jih izvedli med učenci in učitelji. Meritve so pokazale, da je raven hrupa v obravnavani šoli tudi v času, ko v njej ni pouka, na meji dovoljene ravni (40 dB(A)), ali pa jo celo presega. Med poukom so ravni hrupa daleč nad dovoljeno ravnjo. Ankete so pokazale, da učitelje hrup najbolj moti pri komunikaciji z učenci in pri delu, ki terja visoko stopnjo koncentracije. Učenci se spet zaradi hrupa ne morejo zbrati, si snov težje zapomnijo ali ne razumejo razlage. Ugotovili smo tudi, da so mlajši učenci na hrup bolj občutl

AN ULTRASONIC METHOD FOR DETERMINING THE MECHANICAL CONSTANTS OF THE SHIP SHAFT

Dragoljub Svilar

Brodarski institut d.o.o. Zagreb, V. Holjevca 20, Croatia

An ultrasonic method that enables determination of all important mechanical constants within a generally solid medium of the cylindrical form is considered. It is intended primarily for the determination of the shear modulus of rigidity G, Young's elasticity modulus Y, Lame's constant and Poisson's ratio of the materials used in the construction of ship propulsion shafts. Mechanical parameters, derived from the linear theory of elasticity, are determined from the propagation medium density and the speed of longitudinal and transversal waves at the location where the torque of the shaft is measured. Method is based on precise measurement of the ultrasonic pulse time of flight.

CHARACTERIZATION OF VALVE NOISE

Egon Susič

Danfoss Trata, Laboratory for Acoustics and Vibrations, Jožeta Jame 16, Ljubljana Slovenia

Water flow trough a control valve can produce an audible and predominantly annoying noise. This noise can be heard when control valve is installed together with other district heating appliances in building living area or when noise is propagating over piping of heating system and consequently, heating radiator acts as a loudspeaker. Therefore, the need of noise reduction demands changes in valve design. Internal valve parts that determine flow path and local singularities are usually subject of acceptable changes. To relate geometrical features of internal parts to noise characteristics we have designed a multi-channel measuring system. This system provide us with empirical data of valve and water flow parameters. Simultaneously to this, the noise is characterized by measured spectra and level. Different flow phenomena as for example, turbulent flow, two phases flow, whistling, cavitation, etc. cause typical noises that have characteristic spectra, while noise levels are not necessarily different. To visualize relations between emitted noise end parameter of interest, spectra are plotted in respect to complete span of parameter of interest. By identifying typical spectra it can be localized the problematic area, transitions between noise phenomena and critical values of parameters. Analysis of trade-off relations of noise and shape features help our designers to improve noise performances of valves.

"INTEGRATION OF LOW-NOISE ROAD SURFACES WITH OTHER ABATEMENT MEASURES" WITHIN THE FRAMEWORK OF THE EU PROJECT "SILVIA - SUSTAINABLE ROAD SURFACES FOR TRAFFIC NOISE CONTROL"

Ernst Pucher, James Girard, Johann Litzka, Jürgen Haberl

Vienna University of Technology, A-1060 Vienna, Getreidemarkt 9/315

The SILVIA project aims at providing decision-makers with a tool allowing them to rationally plan traffic noise control measures. The main final product will be a European Guidance Manual on the Utilisation of Low-Noise Road Surfacings" integrating low-noise surfaces with other traffic noise control measures including vehicle and tyre noise regulation, traffic management and road and building noise protection equipment. Low noise road surfaces can achieve substantial reductions in street traffic. However, in order to take advantage of the low noise surfaces, the integration of the surfaces with other noise abatement measures must be explored. This is accomplished in work package WP5 of the project. The objectives are: ¨ To describe noise reduction solutions taking into account the combination of pavement and tyre design. ¨ To address noise reduction possibilities by assessing other vehicle noise sources (e.g. reducing engine and drive train noise). ¨ To discuss the acoustical optimisation of local conditions (urban, semi-urban and rural roads, crossings, roundabouts, etc). ¨ To consider traffic management measures for noise control and the effect of these on mobility.

¨ To estimate the noise reduction of low-noise pavements when combined with noise barriers and earth mounds, and when used on bridges. Preliminary examinations have demonstrated that the behaviour of the pavement referring to the tyre noise is different for passenger car tyres and the tyres of trucks. A road surface for low tyre noise of trucks might be different from a pavement for low passenger car tyre noise. The influence of operating conditions - cruise-by and accelerated pass-by as well as driving in a gradient and curve - on the noise will be investigated. Special regard will be drawn to the share of the drive train noise of important vehicle concepts. Where noise problems are most severe, a combination of noise reducing measures will be required and it will not always be possible to simply add the acoustic benefits of each to obtain the combined effect. This is the case where a low-noise surfacing is used with roadside noise barriers and earth mounds. The combined effect can be less than the added benefits and the discrepancy tends to increase with barrier height. The aim will be to provide guidance on the way in which the discrepancy varies under different conditions. Integrating low-noise surfaces with other abatement means, the results of the above effort will be used to produce a guidance manual on "Advanced Low-Noise Highway Design" to help decision-makers to rationally plan noise control measures taking into account full life-cycle costs. Exploitation and dissemination will involve: kick-off seminar for stake holders, formation of reference group, guidance manual, layman's digest, web site, specific session at a European Conference, final seminar recommendations to EU WG8 "Traffic Noise" and WG10 "Cost/Benefit Analysis".

FILTERBANKS FOR AUDITORY MODELING AND CODING

Christian FELDBAUER, Gernot KUBIN

Signal Processing and Speech Communication Laboratory, Graz University of Technology, Graz, Austria

Auditory modelling is a well-established methodology that provides insight into human perception and that performs signal analysis which allows to extract those signal features which are most relevant for the listener. Recently, we have successfully demonstrated [Kubin&Kleijn, ICASSP'99] how auditory analysis can be combined with auditory synthesis to achieve efficient and robust coding of speech and audio signals. In this approach, audio signals are converted into auditory movies using a cascade of decimated filterbanks whose characteristics are matched to the human hearing system. We provide an extensive overview of such auditory filterbanks, including frequency warping by all-pass transforms, and demonstrate a new perfect reconstruction solution for decimated frequency-warped filterbanks.

ACOUSTIC SENSORS FOR THE DETECTION OF BIOANALYTES - ENZYMES, VIRUSES AND CELLS

F.L. Dickert, R. Bindeus, S. Gazda-Miarecka, K.J. Mann, C. Schirk and O. Hayden

Institute of Analytical Chemistry, Vienna University, Währingerstr. 38, A-1090 Vienna, Austria

Acoustic transducers as QCMs and SAWs are universally applicable as mass sensitive devices in combination with a coating for analyte recognition. Usually 10 MHz quartz micro balances or 430 MHz lithiumtantalate shear wave devices are suitable for detecting the biological analytes in aqueous solution. The QCMs were produced from the quartz blanks by screen printing applying a gold paste followed by a burning process. The surfaces of organic and ceramic coatings were structured by a self organisation process to generate suitable hollows for the re-inclusion of enzymes, viruses and cells. The principle of self organisation can be realized by assembling thioles on the gold surfaces. In this case chains of different length and functionality were applied. Thus, these surface modifications yield an optimized interaction to biological particles. Furthermore, the strategy of molecular imprinting can be generally used to achieve a selective moulding of surfaces. For this purpose polymer layers were applied to the devices by a spin off process yielding coatings in a roughness of approximately 1nm as shown by AFM. On the top of these layers, structuring can be performed by a stamping process with cells or viruses, which were assembled on very flat surfaces. The viruses form ordered structures similar to liquid crystals, the degree of order is favoured by cooling the selfassembled particles. Another possibility, which is preferably applied for enzymes is selforganising of polymers around the bioanalytes, e.g. enzymes in ultrathin layers in a thickness from 10 to 20 nm. In this case the diameter of these particles is not much larger than the surface roughness and thus stamping is not the best method. All monofunctional and multifunctional building blocks for enzyme embedding were water soluble. Thus, the enzymes are not denatured during this procedure and in combination with mass sensitive devices a discrimination between native and denatured enzymes is possible. The incorporation process of enzymes and viruses into these layers is monitored by mass-sensitive devices. Even a single cell is detectable by a SAW device. The extent of coverage of the surface can be deduced from titration curves which can be described by either a BET or more Langmuir' behaviour. Astonishingly, both for bacteria and viruses non-Sauerbrey sensor responses are observed which are similar to viscoelastic polymers.

FRONTEND SAW AND BAW SIGNAL PROCESSING DEVICES

Franz Seifert

Institute of Industrial Electronics and Material Sciences, University of Technology, Vienna, Austria

In small receiver / transmitter (T/R) sets (e.g. mobile phones) surface acoustic wave (SAW) filters are applied in the T/R frontend. In T-operation these devices have to handle up to 1 Watt RF-power at frequencies up to 2.5 GHz, and in R-mode an insertion attenuation as small as 2 dB is required to keep the noise figure low. This R-requirement is sufficiently met with present SAW technology but power loading together with bandwidth constraints of filters in T-mode touches the limits of SAW technology. Recently, for the problem of power loaded steep skirt filters a combination of SAW and bulk acoustic wave (BAW) devices came into discussion. We describe design of frontend systems with SAW and BAW devices.

THE NOISE MAPPING OF A RURAL LAND IN A NARROW VALLEY

Marina Clerico*, Gabriella Soffredini**

*Safety Engineering Researcher, Politecnico di Torino **Student - Politecnico di Torino

The problems connected to the community noise, whose importance has been fixed by DIR 2002/49/CE, require both an evaluation of acoustical conditions and a land's management with the aim of containing and eliminating acoustical impact caused by different sources (stationary and infrastructural), to improve or maintain environmental acoustical quality. In Italy, the body of the specific legislation identifies in the noise mapping, the instrument put in charge of territorial acoustical management. The methodology of noise mapping, which was born and tested basing on conditions of an urbanized and flat land, is still testing. Different characteristics, about topography or urbanisation's level of a land, determine the necessity of specific and detailed studies, co-ordinate with town planning instruments and with development territorial plans and suitable with the existent acoustical conditions. This research is about a study case, which the first aim is the realization of the first phases of noise mapping , for a narrow valley characterised by rural conditions with strong infrastructural setting, facing the theme of compatibility among nearby areas. There is considerable importance about congruity test between theorical choices and the present acoustical conditions, this purpose can't leave out of instrumental evaluation. This remark is based on the importance of the topography and the consequent alteration of the meteorological parameters with reference to sound propagation.

ACOUSTICAL CHARACTERISATION OF BACKGROUND NOISE AT GTP MOLVE III

Goran Hudec

Faculty of Textile Technology, University of Zagreb, Pierottijeva 6, 1000 Zagreb, HRVATSKA

Gas Treatment Plant (GTP) Molve III is major Croatian energy resource. Here purification and distribution of natural gas are performed. Technological safety and environment impact improvement are matters of concern and implementation of acoustic emission (AE) leak monitoring system is considered. Application of a AE leak monitoring system under industrial conditions is a problem setting specific demands. As a fisrts step acuostic background noise monitoring is established. Noise would be monitored all around a year in different climate conditions at a choice of technologicaly characteristic production locations. The main reason for change in background noise are normal production activities and in a monitoring program for each location some characteristic production procedures are identified. In the paper some results considering acoustic noise beckground monitoring at a GTP Molve III compared with earlier screening measurements at a same monitoring points are presented. In a conclusion some modifications in monitoring program are discused..

THE INFLUENCE OF WALL MATERIAL ON THE RADIATED SOUND OF THE FLUTE

Widholm G., Linortner R.

Institut fuer Wiener Klangstil, University of Music Vienna, A-1010 Wien, Singerstrasse 26a

The discussion on the influence of the material of wind instruments on the sound colour is unending. While acousticians speak mostly of a negligible influence, players are convinced that the material highly influences the color of the radiated sound. This paper reports experiments done with 7 different flute materials and 110 testpersons, where the price of the instruments lies between EUR 2000.- and 70,000.-. Deatailed surveys and listening tests indicated players´ preferences and the recognizability or non- recognizability of the used material. The results concerning the sound color and the dynamic range are obtained by special sound analysis methods. Sound examples will be given and the audience is invited to judge themselves.

STANDARDIZED MEASUREMENTS FOR LOUDSPEAKERS

Marko Horvat, Hrvoje Domitrović, Mladen Maletić

University of Zagreb, Faculty of Electrical Engineering and Computing, Department of Electroacoustics, Unska 3, HR-10000 Zagreb, Croatia

In the world of modern science and technology, there are many engineers, scientists and equipment manufacturers working independently of each other on creating similar products or developing new technologies. In order to avoid confusion and incompatibility between those products or technologies, they strive to agree on sets of rules called standards, by which certain products shall be manufactured or certain technologies implemented. Furthermore, the measurements taken on finalized products have to be standardized also, for the measurements to be repeatable and the characteristics and parameters obtained to be comparable. The world of audio technology is no exception. This paper offers a brief overview of standards, defined and approved by International Electrotechnical Commission (IEC), for loudspeaker measurements, both loudspeaker drive units and loudspeaker systems. Measurement conditions, test signals, acoustic environment, loudspeaker mounting shall be described as well as the most important parameters and characteristics an audio engineer is interested in, such as the impedance curve and parameters derived from it, voltage and power characteristics, frequency-related characteristics, sound pressure and sound power characteristics, directional characteristics, amplitude nonlinearities as well as the methods of obtaining them.

THE ACOUSTICAL REDESIGN OF EXISTING STUDIO AND CONTROL-ROOM

Maja Rojc, Mladen Maletić, Hrvoje Domitrović

University of Zagreb, Faculty of Electrical Engineering and Computing, Department of Electroacoustics, Unska 3, HR-10000 Zagreb, Croatia

To accurately perceive stereo images and enjoy a hightened spatial impression with a sense of immersion or envelopment in the sound field one must control the interference of early reflections and create a uniform diffuse sound field with significant lateral components in the room. Reflections which are too eraly and/or too strong with respect to the direct sound cause false localization and frequency coloration. While absorption is certainly helpful in optimizing a listening or microphone position, it should not be used in excess. Therefore to mimize reflections at a listening position, we can make boundary surfaces diffusive or absorptive, alternatively we can angle and splay boundary so reflected energy can be directed away from the listening position. To process spatial information, the auditory system demands that the direct sound be isolated by at least 10 ms from the indirect reflected sounds of the room. It is important to create the uniformly dense reflection pattern so that no point in time or angular direction is favored. The quality of acoustical solution is controled during the design and construction phase in real room, using MLS acoustical measurements

ATTENUATION OF DETONATOR EXPLOSION IN TESTING ELECTRICAL DETONATORS

Igor Zorić, Dalibor Kuhinek, Davor Kirin

University of Zagreb, Faculty of Mining, Geology and Petroleum, Engineering, Pierottijeva 6, 10000 Zagreb, CROATIA

During standard testing of electrical detonators, some of them require firing likewise. In this process, very high temperature is reached and the noisy explosion of a relatively high level is heard, while parts of metal shell of a detonator are scattered in all directions. This is the reason why the testings are carried out outdoors, accompanied by necessary human and equipment protection measures, or indoors, where the detonators could be tested in a specially designed high-pressured sealed testing apparatus. Outdoors' areas for testing are selected to be far enough from towns and places, whereas the handling with high-pressured apparatuses is awkward and demands for more time spent in testing. Therefore we undertook to construct the open-testing apparatus, where the effective attenuation of detonator explosion could be applied. This paper gives the results obtained in usage of the constructed open-testing apparatus with the application of standard attenuation elements.

THE SENSITIVITY OF AUDIO DISTORTION MEASUREMENT METHODS

Djurek, Ivan; Domitrović, Hrvoje; Maletić, Mladen

Faculty of EE and Computing, Dept. of Electroacoustics, Unska 3, HR-10000 Zagreb, Croatia

Distortion measurements should give us objective evaluation and comparison of different electroacoustical devices. Ordinary methods for distortion measurements give us partial information about certain devices, because used test signals don't have characteristics of natural signals - speech and music. Proposed combined audio test signal (CATS) consists of three sawtooth signals, and has characteristics of natural signals. Frequency components of the CATS spectrum are unevenly distributed, so intermodulation components fall between components of the original spectrum at the input of the measured system. Using peak search method intermodulation components can be extracted form original signal, and their comparison can be made. Proposed audio pseudo-random test signal is compared with other audio distortion measurement signals and methods. Comparison is made with investigations of the sensitivity by experimental measurements on electrical circuits, which simulate basic distortion mechanisms. Electrical circuits are made with combination of two operational amplifiers, resistors and zener diodes. The results show that the ordinary methods for measurements of total harmonic distortion are not relevant for dynamic distortions. Every used method has low sensitivity for at least one distortion mechanism. Correlation functions between different methods are obtained in order to predict measurement results obtained with one method from another one.

APPLICATION OF DIGITAL MIXING CONSOLES FOR MULTITRACK RECORDING AND MUSIC PRODUCTION

Davor Grgesina*, Bojan Ivančević**

*HRVATSKA RADIO-TELEVIZIJA, HRVATSKI RADIO, RJ Tehnika radija, Prisavlje 3, HR-10000 ZAGREB

**FAKULTET ELEKTROTEHNIKE I RAČUNARSTVA, Zavod za elektroakustiku, Unska 3, HR-10000 ZAGREB

Introduction of digital mixing consoles for multitrack recording and music production has a lot of important advantages due to analogue, because of their today's technological degree. Some of them will be highlighted here. Powerfull digital signal processing (DSP), realised by means of digital filters implemented into "floating point" DSP integrated circuits and controlled by appropriated software, enables a realisation of outstanding dynamic and frequency characteristics in sound processing. Some mesurements of THD and frequency response at one channel module confirm mentioned. Microphone preamps, placed directly into studio space in form of stageboxes, enable analogue microphone signal amplifying with high S/N value, splittig of each amplified microphone signal for Public Addresse (PA) system supplying, conversion to digital form and transmission in time divided multiplex (TDM) form via fiber optic or coax to the main DSP unit. Gain control of each microphone input is done from appropriate channel module by means of separate control circuit based on "ethernet" networking. Built-in integral input/output routing matrix, enables desired switchings of all input and output signals directly, which eliminates a requirement of classic patch pannels.

THE COMPARISON OF ROOM IMPULSE RESPONSE MEASUREMENT SYSTEMS

Ivo Mateljan

Faculty of electrical engineering, R. Boskovica bb., 21000 Split, Croatia

The paper describes evaluation of cross-correlation based systems for measurement of the room impulse response. Various types of excitation signals are used: white noise, pink noise, aperiodic sweep, MLS, random phase multisine and periodic chirp. Criteria to evaluate the quality of impulse response estimation were: a) random and stationary noise rejection, b) rejection of nonlinearities introduced by measuring system, c) immunity to time non-invariant environment disturbances and d) averaging time necessary to achieve reliable estimation. The measurement system uses high quality PC soundcards and software which gives user friendly access to setup of many acoustical measurements. Signal generation can be done with adjustable rms levels and crest factor of noise-like signals. Measurements were done in a large hall and in a small room, with controlled noise level. Time-invariant ambient were simulated by varying the ventilation fan speed and power. The work clearly shows that systems with low-crest random phase pink multisine and logarithmic sweep excitation outperform systems with white spectrum excitation. It is shown that choice of optimal signal depends on measurement environment. In an environment with a high noise, random phase pink multisine gave the best estimation, otherwise excellent result were obtained with a logarithmic sweep excitation.

DIGITAL HEARING AIDS AND BINAURAL AMPLIFICATION

Branka Alčin, Jagoda Vatovec

University Department of Otorhinolaryngology and Cervicofacial Surgery Clinical center, Ljubljana, Zaloška 2, Ljubljana

This paper presents the advantages of digital hearing aids and the indications for prescribing them to hearing impaired patients. We discuss the benefits of binaural amplification according to different acoustic situations, type and grade of hearing loss and age categories of hearing aid users. The results of the questionary about the satisfaction with the hearing aid application between our patients at the Audiologic Department of the University Department of Otorhinolaryngology and Cervicofacial Surgery in Ljubljana during the period from 31st December 2001 to 31st December 2002 are presented.

RECENT ADVANCES IN THE DESIGN AND ANALYSIS OF MICROACOUSTIC LIQUID SENSORS

J. Kuntner, B. Jakoby

Vienna University of Technology, Industrial Sensor Systems E366 Gusshausstrasse 27-29/366, A-1040 Vienna, Austria

Microacoustic sensors have proven to be powerful tools in a number of applications ranging from chemical sensing to viscosity and density sensing in fluids. For liquid media, shear polarized modes have been utilized as they do not lead to an unwanted excitation of compressional waves in the liquid, which would lead to a serious damping of the sensor. Transverse shear mode resonators, most often based on quartz, are a prominent example for this latter type of device. Although the microacoustic modes oscillating in these sensors are dominantly shear polarized, compressional waves are still excited, which is related to the non-uniform distribution of the mechanical discplacement across the sensing surface. The effects associated with these spurious compressional waves recently have been investigated experimentally. In this contribution we discuss these issues and present a finite element analysis of the oscillating device, which leads to more insight into the excitation of the spurious compressional waves.

VPLIV HRUPA NA DELO IN ZDRAVJE DELAVCEV V VZGOJNO-VARSTVENIH

ZAVODIH

Tatjana Gazvoda*, Jožef Horvat**

*Zdravstveni dom Novo mesto, Dispanzer za medicino dela, prometa in športa Kandijska cesta 4, 8000 Novo mesto, SLOVENIJA

**Univerza v Ljubljani, Visoka šola za zdravstvo, Poljanska 26, 1000 Ljubljana, SLOVENIJA

Problem Cilj te študije je bil prikazati ekološke razmere, v katerih delajo vzgojiteljice, med njimi predvsem problem hrupa. Skupina strokovnjakov je v nekaj vzgojno-varstvenih zavodih (vrtcih) izvedla analizo delovnih mest in okolja vzgojiteljev. Pri tem interdisciplinarnem postopku se ocenijo obremenitve, škodljivosti in zahteve delovnega mesta glede na naslednje dejavnike: · organizacija dela, · ekološke razmere, · fiziološki pogoji dela, · psihološki pogoji dela in · ergonomski pogoji dela. Na osnovi dobljenih rezultatov se izdela načrt merske analize in predvidijo možne ergonomske rešitve. Rezultat analize je zdravstvena ocena oziroma ocena tveganja, v kateri so upoštevane: · stopnja tveganja za poškodbe pri delu, · težavnost dela, · potreba po preventivnih zdravstvenih pregledih,

· ustreznost dela za mladino, ženske, nosečnice, kronične bolnike, invalide in · potreba po posebnem režimu pitja tekočin. Način reševanja Z obdobnimi preventivnimi zdravstvenimi pregledi in merjenjem počutja pri delu ter ekološkimi meritvami se potrdijo vplivi dela na nastanek zdravstvenih okvar. Delovno okolje oz. ekološke razmere v vrtcih se ocenjujejo na podlagi veljavne zakonodaje za delovne prostore in tehničnih predpisov za gradnjo in rekonstrukcijo vrtcev. Za to študijo so bili merjeni in ocenjevani mikroklima, osvetljenost in hrup. Rezultati izsledkov Mikroklimatske razmere v vrtcu so bile v dovoljenih mejah, v zimskem času večinoma v za posamezne starostne skupine normativno predpisanih mejah. Delovni prostori v vrtcu morajo biti dobro ter enakomerno osvetljeni, in sicer z indirektno ali enakomerno razpršeno svetlobo. Osvetljenost v večini igralnic v vrtcih ustreza normativno predpisanim vrednostim oz. jih celo presega. Za ocenjevanje hrupa je delovno mesto vzgojiteljev uvrščeno v drugo kategorijo, kjer se ekvivalentne dovoljene ravni gibljejo med 45 db(A) in 55 db(A). Zahtevo po tako nizki dovoljeni ravni lahko razumemo kot preventivni ukrep, potreben zaradi dela z majhnimi otroki. Izmerjene so bile izjemno visoke ravni hrupa, ki kot take obremenjujejo tako vzgojiteljice kot otroke. V nekaterih vrtcih so bile maksimalne ravni, torej občasna izpostavljenost, celo višje, kot jih normativi dopuščajo za delo ob stroju. Ekvivalentne ravni hrupa v nekaterih igralnicah (do 81,9 dB/A) kažejo na izpostavljenost hrupu kot v industrijskih obratih šivalnic ali pletilnic. Tolikšen hrup pa ne le močno moti koncentracijo, temveč že otežuje normalno sporazumevanje med vzgojiteljico in otroki.

MODELLING WAVE AND FLUID PROPAGATION IN WIND INSTRUMENTS -METHODS AND APPLICATIONS

Kausel, Wilfried; Kuehnelt, Helmut

Institut fuer Wiener Klangstil (Musical Acoustics), University of Music and Performing Arts Vienna, Singerstrasse 26°, A-1010 Wien

Two completely different aims are motivating scientists to simulate sound production in musical instruments. The first one is real time production of virtual instrument sounds, as realistic as possible, offering all the natural expressivity to composers or performers. The end justifies the means - the implemented algorithms do not need to be physical but have to be computationally efficient. The second aim is to understand the mechanisms of sound production well enough in order to help builders and players of musical instruments to better control sound characteristics or to improve playing techniques. For this purpose accuracy of sound modelling is not primarily relevant, yet may prove validity and relevance of the modelled physical effects. For the sake of understanding the basic interactions between player and instrument, initial models tend to be as simple as possible. With growing understanding more higher-order effects are usually added, yielding a more and more realistic synthetic sound and explaining more of the possibilities of interaction between artist and instrument. Current approaches to model wave propagation in one-, two-, and three-dimensional acoustical systems are reviewed and actual ways to model sound production mechanisms in various instruments are discussed.

NONLINEAR ENHANCEMENT AND SATURATION PHENOMENA IN HIGH INTENSITY FOCUSED ULTRASOUND BEAMS

V. A. Khokhlova*, L. A. Crum**

*Department of Acoustics, Faculty of Physics, M. V. Lomonosov Moscow State University, Leninskie gory, Moscow 119992, Russia

**Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle, WA 98105, USA

Effect of nonlinear acoustic wave propagation is strongly pronounced for both therapeutic and diagnostic modern ultrasound devices. It is necessary, therefore, for given output of the focused ultrasound source, to predict in situ values of acoustic pressure or intensity. Nonlinear enhancement of energy concentration at focus compared to the linear gain can be observed for moderate source output due to better focusing of higher harmonics. Nonlinear saturation phenomenon is caused by effective absorption of acoustic energy at the shocks for higher source output. There is no general analytic result that includes a combined effect of nonlinearity, diffraction, and absorption in a focal region. In the present work numerical simulations of focused ultrasound beams have been performed in a wide range of source parameters and properties of propagation medium. Acoustic beams with initial Gaussian amplitude shading are considered. Asymptotic frequency domain numerical algorithm which enables modelling of strongly distorted waves with shocks using relatively few number of harmonics is employed. The results of simulations are compared with the known analytic and numerical results. The effect of absorption and linear focusing gain on nonlinear enhancement of acoustic energy concentration and saturation level is discussed. Work supported by the CRDF and ONR.

DIRECT EVALUATION OF A NOISY VESSEL PASSIVE DETECTION STRUCTURE

Kosta Ugrinovic

Faculty of Natural Sciences, Mathematics and Education, Nikole Tesle 12/III, HR-21000 Split, Croatia

The paper treats direct evaluation of the statistical optimum detection of the noisy vessel in the presence of deep-sea ambient noise. The noisy vessel underwater noise is supposed to be an extremely weak Gaussian stochastic process that is due to vessel cavitation phenomenon. The deep-sea ambient noise is supposed to be a Gaussian stochastic process as well. The mathematical model of the power spectral density referring to the noisy vessel noise consists of a nonwhite wide-band component due to vessel cavitation. The mathematical model of the power spectral density referring to the deep-sea ambient noise is a nonwhite wide-band component. The evaluation of the statistical optimum noisy vessel detection is considered in the frequency domain.

ACOUSTIC MODIFICATION OF THE "TREŠNJA" THEATRE

Kristian Jambrošić, Bojan Ivančević

FAKULTET ELEKTROTEHNIKE I RAČUNARSTVA, Zavod za elektroakustiku, Unska 3, HR-10000 ZAGREB

The "Trešnja" theatre, built 15 years ago, was made exclusively for children plays. Its interior is made colorful and twitching, but with some serious mistakes in its acoustical properties. One of them was an ineffective layout of the reflecting surfaces of the walls and ceiling with the consequence that the last 6 rows of the stand had low levels of sound loudness coming from the stage and low intelligibility. An inexpensive modification was required to solve this problem using strictly physical means, without the help of loudspeakers. The ceiling could not be altered, although that would be the most logical and effective way of improvement. A series of ETC measurements on the most critical spots revealed the problem in an objective way. With inclination modification of a part of the sidewalls and with reducing the absorption of the back wall, an improvement in acoustical properties was achieved. This improvement was again checked with measurements of ETC-s on the same spots.

MODELS OF THE SEAT TO HEAD TRANSMISIBILITY FUNCTION OF THE SEATED HUMAN BODY EXPOSED TO FORE AND AFT VIBRATION

Jovanka Lukic, Miroslav Demic

University of Kragujevac. Faculty of Mechanical Engineering Kragujevac, Sestre Janjic 6, 34 000 Kragujevac, Serbia and Montenegro

Depending on type of vehicles, the influence of fore and aft vibration on driver cannot be neglected. Literature reviewed has been shown that most papers considered human exposed to vertical vibrations. The number of papers considering the influence of fore and aft vibration on human with respect to seat to head transmissibility function is small in comparison with number of papers considering driving point mechanical impedance or apparent mass. Experimental results obtained for group of thirty subjects exposed to broadband random for and aft vibration was base for development appropriate seated human body model. Derived models with characteristics generated by parameter optimization showed good agreement with experimental results. The best model comprised of two degree of freedom systems in parallel combined with a rigid mass in contact with seat to head transmissibility function.

WHICH FACTORS MAKE A TRUMPET RESPONSE WELL?

Bertsch Matthias

Is there a connection between what we feel when playing an instrument and what we can measure? Physical models and measuring tools have been developed for a better understanding of brass instruments and to provide objective physical documentation of their acoustics. Musicians and instrument makers still criticize the enormous gaps between the physicsbased parameters and the empirically reported feelings of brass players on quality aspects of their instruments. Deviations between played and measured parameters like intonation and their variability have already been focused on in earlier studies. Attempts for a theoretical explanation of these deviations using physical modeling continues. For musicians, one of the most important quality factors of a brass instrument is its response. A new series of playing tests has been designed to correlate empirical data with objective physical parameters (impedance measurements). International Instrument makers provided special test instruments (modular trumpets). <BR> This paper will show the difficulties in defining response and setting up suitable playing tests. Preliminary results and correlations of the data will be presented.

COMPARATIVE STUDY OF THE TRAFFIC NOISE EMISSION FOR CHARACTERISTIC TYPES OF ASPHALT MIXTURES WHICH ARE IN USE FOR

ROAD SURFACES IN SLOVENIJA

PRIMERJALNA ŠTUDIJA EMISIJE PROMETNEGA HRUPA ZA PRIMERE

ZNAČILNIH ASFALTNIH ZMESI, KI SE UPORABLJAJO ZA IZDELAVO VOZNIH POVRŠIN CEST V SLOVENIJI

Mihael Ramšak

Zavod za gradbeništvo Slovenije, Dimičeva 12, 1000 Ljubljana

V prispevku je predstavljena primerjalna študija emisije prometnega hrupa za primere značilnih asfaltnih zmesi, ki se uporabljajo za izdelavo voznih površin cest v Sloveniji. Študija je bila v letu 2002 izvedena za naročnika Družbo za avtoceste Republike Slovenije. Za vsako vsako izbrano vrsto vozne površine smo ugotavljali maksimalno raven zvoka mimovozečega osebnega vozila, in sicer pri enakomerni hitosti ter z motorjem v prostem teku. Na istih merjenih odsekih cest so bile poleg tega izvedene meritve globine hrapavosti vozne površine z namenom oceniti, ali razlike v globini hrapavosti vplivajo na emitirani zvok in v kolikšni meri. V prispevku je predstavljena metodologija izvedbe študije ter ugotovitve. Ugotovljeno je, da globina hrapavosti ne vpliva na emisijo zvoka pri vseh merjenih voznih površinah enako. V nekaterih primerih se z večanjem globine hrapavosti emisija hrupa poveča, v nekaterih pa se lahko celo zmanjša.

AKUSTIČEN VENTILATOR

Mitja Kočevar

ISKRA Avtoelektrika d.d, Šempeter pri Gorici, Direkcija razvoja

Članek prikazuje konstrukcijo ventilatorja za alternatorje z konvencionalnim načinom hlajenja (zunanji ventilator). Za novo tržišče je bilo potrebno spremeniti konstrukcijo obstoječega ventilatorja, ker le-ta ni zadoščal varnostnim predpisom. Obstajala je možnost poškodbe uporabnika ob delovanju alternatorja. Potrebno je bilo narediti "varni" - akustični ventilator. Varni ventilator ne sme imeti na prednji strani nobenih reber oziroma neravnosti, ki bi poškodovala človeka v primeru dotika. Po pregledu tržišča - konkurence in teoretičnih izračunih smo na vzorcih ventilatorjev izvajali naslednje meritve: - hrup alternatorja, - temperature podsestavov, - karakteristike alternatorja. Testne ventilatorje smo oblikovali po aerodinamičnih pravilih. Definirali smo material, število in višino lopatic ter kote med mjimi. Med seboj se ventilatorji razlikujejo po obliki same lopatice - spreminjamo izstopni kot lopatice. S izstopnim kotom vplivamo na izstopno hitrost zraka, le ta pa vpliva na vse iskane parametre analize (hrup, temperaturo in karakteristiko alternatorja ter vhodno hitrost zraka). Cilj naloge je bil izdelati varni ventilator, ki naj bi bil tišji od sedanjega, hkrati pa naj bi boljše hladil podsestave alternatorja. Področje za RR alternatorjev

EVALUATION OF THE FACTORS AFFECTING NOISE BARRIER PERFORMANCE

Neşe Yügrük Akdag

Building Physics Department, Architectural Faculty, Yildiz Technical University, 80750, Beşiktaş, Istanbul, Turkey.

In order to achieve an effective and economic noise control, the noise problem should be taken into account in land use planning process and building design process, respectively. One of the most common tool that is used to reduce environmental noise such as road traffic noise and railway noise is noise barrier. This paper presents some general determinations on the factors affecting barrier's performance. By using SoundPLAN 5.0 simulation program, the barrier noise reduction is calculated for different barrier height, different receiver distances and heights. The distribution of noise behind the barrier is illustrated by the noise maps and the single point receiver results are presented by the graphics. The outcomes show that, if the receiver height is lower than the barrier height, noise attenuation provided by the barrier is more effective for the receivers close to the barrier. If the receiver height is equivalent to the barrier height, the noise attenuation does not change in a considerable amount in all receiver distances from the barrier. On the other hand, in the case of higher receiver locations than the barrier, the decreasing in noise is more effective for the receivers further from the barrier.

PRIMERJAVA METOD DOLOČANJA ZVOČNE MOČI VIRA Z MERJENJEM ZVOČNEGA TLAKA, ZVOČNE INTENZIVNOSTI IN HITROSTI VIBRACIJ

Nikola Holeček

GORENJE, Velenje, Partizanska 18, Velenje

Zvočno moč ne merimo neposredno, ampak posredno z merjenjem zvočnega tlaka, zvočne intenzivnosti in z merjenjem hitrosti vibracij. Z metodo merjenja zvočnega tlaka so na voljo štiri metode: primerjalna metoda, absolutna metoda v prostem ali difuznem zvočnem polju in z merjenjem v cevi. Z metodo merjenje zvočne intenzivnosti merimo v diskretnih točkah ali pa s skaniranjem (sweeping). Zvočno moč vira lahko določimo tudi iz emitiranega zvoka z merjenjem hitrosti vibracij na zunanji površini vibrirajoče strukture (zunanja merilna površina stroja). V članku so prikazani rezultati določanja zvočne moči na praktičnih primerih po omenjenih metodah v gluhi sobi in odmevnici. Podana je diskusija dobljenih rezultatov in analizirani vplivni motilni inputi na relativno mersko napako.

PREDICTION OF AEROACOUSTIC NOISE AROUND BLUFF BODY

Peter Tibaut*, Branislav Basara*, Mirjam Snellen**, Leonard van Lier**, Joachim Golliard**

*AVL LIST GmbH, Graz, Austria

**TNO TPD , Delft, The Netherlands

Despite significant progress in computational sciences, challenges persist in the accurate numerical simulation of a turbulence as a very important basis for many multi-physics phenomena e.g., combustion, spray in IC engines and aeroacoustics. In order to reduce the severe computational requirements of second moment closure turbulence models, more robust approach for industrial problems has been pursued. The paper assesses the use of the most popular standard k-e model and the hybrid turbulent model for simple bluff body, and their impact on steady and transient RANS calculations. The Hybrid Turbulence Model is examined as an alternative solution, e.g. the recent proposal of combining the Boussinesq's concept with the second moment closure. Further CAA analysis, which consists of the unsteady acoustic source generation based on the RANS data and the calculation of the propagation of the pressure fluctuations using the linearized Euler equations, has been performed by using hybrid turbulence model results. The paper compiles the work performed by TNO TPD and AVL List GmbH using the in-house commercial CFD software AVL SWIFT.

TEORIJA AKUSTIČNEGA POLJA

Mateja PLOJ VIRTIČ, Aleš BELŠAK, Boris ABERŠEK

Pedagoška fakulteta, Univerza v Mariboru, Koroška cesta 160, 2000 Maribor, SLOVENIJA

The paper deals with the theoretical calculation of an acoustic field by means of acoustic analogy. Using basic equations of stream mechanics (continuity equation, equation of movement and equation of state) homogeneous stream equations of linear acoustics were received. The non-homogeneous equations were received by using continuity and movement equations and the problem of producing sound by streaming is derived back to the classical acoustic problem. This acoustic analogy is known as Lighthill's analogy. A source tenet that could be monopole, dipole or quadropole is presented later. Acoustic analogy formulations by Ribner, Powel and Howe are also mentioned.

UNATTENDED ACOUSTIC SENSORS FOR LAW ENFORCEMENT APPLICATIONS

Predrag Vukadin

Brodarski institut d.o.o., Av. V. Holjevca 20, 10020 Zagreb

Acoustic technology has attracted considerable interest in recent years in the surveillance applications due to its numerous advantages. Acoustic sensors are passive, can detect, localize and identify target at long ranges, have non-line-of-sight detection capabilities and are jam resistant. They can be used as standalone units, as a cueing devices for other sensors (image, IR), or can be networked by data links. They can be hands placed or deployed from aircraft and helicopters. This work exploits the multi-discipline scientific and technological requirements for the development of such sensor. This would include sound propagation studies and full scale measurements, acoustic signature databases, array processing, localization and tracking algorithms and target identification and pattern recognition algorithms.

TURBULENCE INFLUENCING ULTRASONICALLY ENHANCED SETTLING OF YEAST IN WATER-RICH ETHANOL MIXTURES

S. Radel1, A. J. McLoughlin2, W.T. Coakley3, M. Groeschl1, E. Benes1

1 Vienna University of Technology, General Physics, Wiedner Hauptstr. 8/134, A-1040 Vienna, Austria

2 UCD, Industrial Microbiology, Belfield, Dublin 4, Ireland

3 School of Biosciences, University of Wales, Cardiff, U.K.

Ultrasonic resonators are successfully used for the separation of suspended particles or cells, e.g. as cells filters in biotechnology [1]. These systems are based on the radiation forces spatially re-arranging the particles in the pressure nodal planes of the quasi-standing ultrasonic wave field. Suspensions of yeast in water-rich ethanol mixtures show an unexpected breakdown of the spatial distribution above certain concentrations of ethanol and the cells are turbulently mixed in the separation system. This has earlier been reported to go along with an impaired viability of yeast in a 12% (v/v) ethanol-water mixture [2]. The scope of the presented paper was to further examine this breakdown. Movies of normal banding and the different behaviour in the presence of ethanol will be shown. This work was supported in part by the European Commission, TMR Network Contract No. ERBFMRXCT97-0156 (EuroUltraSonoSep).

THE ACOUSTIC ECHO CANCELLATION FOR HANDS-FREE COMMUNICATOR

Rudi Čop

Fakulteta za pomorstvo in promet, Pot pomorščakov 4, 6320 Portorož

This paper compares convergence properties of two FIR filter adaptation algorithms used in echo cancellation systems based on energy decay property of reverberant sounds, sound field reproduction and control. The problem of acoustic echo cancellation arises wherever a loudspeaker and a microphone are placed such that microphone picks up the signal radiated by the loudspeaker and its reflections at the borders of the encounter. Because of acoustic feedback electro-acoustic circuit may become unstable and produce howling. Introduction of short term delay into signal path to avoid howling is unacceptable in most hands-free application as tolerable delay times are specified by International Telecommunication Union (ITU). With increasing more signal processing power available in recent years application of an adaptive filter parallel to the loudspeaker-enclosure-microphone system (LEM system) is econonically feasible. Stereophonic systems require independent adaptation of filtering for each channel because both channels are highly corelated and there is no unique solution for impulse responses of the echo-cancellation filters to be applied to both channels. Moving object and or changing the temperature results also in time-variable impulse response and adaptivity is of key importance in echo-cancellation applications.

ADVANCED ULTRASOUND IMAGING AND IMAGER QUALITY CONTROL

Jaroslav SATRAPA*, Georg DOBLHOFF*, Hans-Jürgen SCHULTZ**

*Tissue Characterization Consulting (TCC), Lenaustr. 10, A-4850 Timelkam, Austria Institut für Allgemeine Physik IAP Vienna University of Technology

**Ultrasound Consultant HMSE, Frahmredder 116 d, D-22393 Hamburg, Germany

Ultrasound imagers are in a permanent development progress thanks to the advances in electronics and piezoceramic technology. The complexity of these advances creates new practical and theoretical problems in measuring imager quality. The current methods of visual image quality assessment with phantoms are no more adequate to the new challenge. The AIUM and IEC standards of quality measurement take the imager quality rather to be a 2D than 3D problem although all ultrasound beams formers are unconditionally 3D. In the search for an adequate solution the conventional quality parameters e.g. axial, azimuthal and elevational resolution have been substituted by spatial resolution and signal to noise ratio (SNR) measurements as a superior alternative and a more familiar approach from the point of view of clinical assessment of imager quality. The 2D phantoms are substituted by suitable 3D phantoms and visual assessment is replaced by 3D phantom image processing as an incorruptible way of quantitative quality determination. The new approach has been automated as far as possible and provides a practical tool for fast quality measurement of ultrasound imagers in hospitals and clinics.

UGOTAVLJANJE DELEŽEV HRUPA HIŠNIH INŠTALACIJ, KI SE PRENAŠA IZ STROJNICE V STANOVANJA PO ZRAKU IN PO konstrukcija stavbe

Savo Volovšek

Zavod za gradbeništvo Slovenije, Dimičeva 12, 1000 LJUBLJANA

V zvezi s hrupom, ki se iz strojnice prenaša v stanovanja, se pogosto postavi vprašanje, ali se ta hrup prenaša po zraku (zaradi premajhne zvočne izolacije konstrukcij, ki ograjujejo strojnico) ali kot strukturni zvok po konstrukcijah stavbe (zaradi neprimerne izvedbe namestitve oz. pritrditve naprav v strojnici). Podatek o deležih hrupa, ki se iz strojnice prenaša po zraku in po konstrukcijah je tudi bistvenega pomena pri načrtovanju ukrepov za zaščito pred hrupom hišnih inštalacij. V prispevku je prikazan način, kako lahko z meritvami ugotovimo deleža hrupa, ki se prenašata iz strojnice po zraku in po konstrukcijah stavbe.

TRANSIENT FLOW REGIME DRIVEN BY ACOUSTICAL WAVES IN POROUS MEDIA

Y.M. Shtemler1, I.R. Shreiber2 and A. Britan1

1Department of Mechanical Engineering, 2Department of Chemical Engineering 2Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105, Israel

The impact of hydraulic resistance is markedly underestimated in the early stages of the boundary layer formation and expansion to the porous bed capillary center. The early stage of flows induced by acoustical waves is considered in gas-filled solid porous beds. In the long-wave and low-viscosity limit an explicit solution for a step-wise pressure pulse is adapted for description of transient waves propagating with sound velocity as weak-shock waves but spreading and attenuated as diffusion waves. The results of the modeling are in fair agreement with experimental data. Inapplicability of method of "bases" for measurements of the wave-front propagation velocity is established. The criterion is developed distinguishing two scenarios of transitions from transient-to-diffusion regime in narrow and wide porous bed capillaries based on instability of unsteady boundary layers in porous bed capillaries. The criterion provides a triggering mechanism for transition from the transient to the Darcy or Forchheimer resistance laws and for explanation of multiplicity of diffusion regimes at the Darcy and Forchheimer resistance laws.

SOUND PROPAGATION IN SOLID-PARTICLES SEEDED GAS-LIQUID FOAMS

Ben-Dor G., Britan, and A. Shreiber, I

Shock Tube Laboratory, Department of Mechanical Engineering, Ben Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel,

This paper is focused on the capabilities of gas-liquid foams to attenuate acoustic waves. It is shown that small additives of solid particles to the gas-liquid foam increase both the sound velocity and the attenuation coefficient of sound. An important finding is that when the concentration of the additives becomes large the attenuation coefficient decreases. A simple physical explanation of this effect suggests that the hydrodynamic resistance of the Plateau-Gibbs channels to the flow of liquid through them largely governs the phenomenon of sound attenuation. Small concentrations of additives increase this resistance and cause a growth in the attenuation coefficient. When the concentration of the particles reaches some critical value, the particles block the Plateau-Gibbs channels and stop the filtration. The attenuation coefficient of the sound wave decreases while the sound velocity in such three-phase foams increases. An inspection of our developed model provides the reasons to this new phenomenon referred to as effect of the foam's clarification.

NUMERIC ANALYSES OF THE FREE HUMAN ARM OSCILLATIONS

Slavka Mitić* and Sretko Bulatović**

* Prof. Dr. Slavka Mitić, dipl. inž. maš.

** Mr Sretko Bulatović, dipl.inž. zaštite na radu, Fakultet zaštite na radu, Čarnojevića 10a, 18000 Niš

In order to set the right estimation of the arm movement, constantly exposed to various forces, the acknowledgement of free circular frequencies as well as free oscillation forms, is of a great importance. Problems dealing with the determination of the free oscillation vectors and the values of free frequencies represent the subject of the oscillation theory. A brief summary of the analitic procedure from the oscillation theory was given as a necessity for the filfillment of the numeric procedure, for the linear oscillation system without damption and with n degree of freedom. Numeric procedure for two arm movement models was done, using the method of final elements, for the determination of free oscillation frequencies. The first one, the two-dimensional (2D) dynamic model, constructed for the plane arm movement, and the second one, the tree-dimensional (3D) dynamic model, for the space arm movement. Both 2D and 3D models used ANSYS program package and in both cases, the results of the numeric experiment constructed as the first five forms of free oscillations, were shown.

INFLUENCE OF FATIGUE PROCESS ON THE VIBROACOUSTICAL SIGNAL OF

THE GEARS Stanislaw RADKOWSKI

Institute of Machinery Design Fundamentals, Warsaw University of Technology Narbutta 84, 02-524 Warsaw, Poland

A toothed gear is one of the most critical elements of a power transmission system. Transmission error in a toothed gear is considered to be one of the main reasons of increased vibration and noise in the whole power transmission system. Despite numerous publications devoted to the analysis of vibroacoustic properties of toothed gears, the approach allowing for the development of a diagnosis and forecast of gear residual service life as a function of wear and fatigue has not been developed yet. The paper includes the analysis of the possibilities of accounting for these factors in a dynamic model being a simulation of a toothed gear. Assuming that that the parameters of the propagation path remain unchanged, we introduced a disturbance, in the form of accordingly modified contact conditions, into the process of generation of a vibroacoustic signal by a pair of toothed wheels. We took a look at modeling of the influence of rigidity changes in individual elements of the system as well as of the wear-related growth of pitch play in individual kinematic pairs. Particular attention was devoted to the issue of modeling of the impact that the degree of wear and tear of pairs of toothed wheels has on the frequency structure of the generated signal. We noted that the wear and tear processes not only have influence on the change of signal power distribution among the individual components of the meshing harmonic, but they above all lead to changes of amplitudes in the modulated bandwidths surrounding the relevant frequencies and they lead to generation of additional components in the low frequency bandwidth. In addition, in the model we analyzed the possibility of applying a drive in the form of synchronic electrical motors with permanent magnets, in which case we also accounted for the noisiness of a toothed gear. The analysis has been completed with a presentation of a diagnostic parameters set generated by a toothed gear in the function of service life and it is pointed to the possibility of using vibroacoustic signals for detecting damage in its early stage of development.

A STUDY ON SOUND ABSORPTION IN SOME TECHNOLOGICAL MATERIALS

Vasile N. Dima, Emil E. Barna

Physics Faculty, University of Bucharest, PO Box MG-11, Bucharest, Romania

The paper presents a study on the sound absorption by different phono-absorptant solid materials used, mainly, in the automobile industry, but in other fields as well. The measurements were performed using an electro-acoustic device functioning on the principle of the stationary waves that develop between the direct wave and the the wave that is reflected by the specific material that is being analyzed. The energetic absorption coefficient was measured, in percentages, in the 100 to 2000 Hz audio frequency interval, at constant temperature. The absorption coefficient was obtained from the sound pressure values corresponding to the maxima and minima in the stationary wave. The experimental data outputted is presented numerically and graphically. The average relative error for the present measurements is 1%.

EXPERIMENTAL DETERMINATION OF SOUND ABSORPTION COEFFICIENT AND COMPLEX MODULUS OF ELASTICITY IN TECHNICAL ACOUSTICS

Volčík, V; Lapčík, Jr., L; Vašina, M.

Tomas Bata University in Zlin, Faculty of Technology, Department of Physics and Material Engineering, Nám. T. G. Masaryka 275, 762 72 Zlín, Czech Republic

The paper deals with experimental determination of sound absorption coefficient and complex modulus of elasticity of the soft polyurethane composite matrix based samples. Measurements were carried out on samples with three different thicknesses and with different amount of bonding agent in sample. Measurement of sound absorption coefficient was carried out on Brüel&Kjar 2034 analyzer with Kundt's tube. The complex modulus of elasticity was determined on vibration analyzer .

A STUDY OF THE LOW NOISE ENGINE INLET SHAPE BY USING OPTIMAL DESIGN

Wan-Ho Jeon*, Huinam Rhee**

*Digital Appliance Research Lab. LG Electronics Inc. 327-23, Kasan-dong, Kumchon-gu, 153-802, Seoul, Korea

**School of Mechanical and Automotive Engineering, Sunchon National University, Sunchon, Junnam, Korea, 540-742

A computer program to design an optimal shape of engine inlet is developed. It is based on a computationally efficient thin-shell BEM with a numerical optimization algorithm. The design goal in the present study is to obtain the engine inlet shape which radiates the minimum far field acoustic pressure. To do this, the far field acoustic pressure is used as objective function and the design sensitivity is obtained by finite-difference method. Finally, engine inlet design is performed with various constraint and the results are compared with scarf inlet shape.

VIBRATIONS IN LAYERED ORTHOTROPIC SOILS

Holger Waubke

Acoustics Research Institute, Austrian Academy of Sciences Reichsratsstrasse 17, 1010 Vienna, AUSTRIA

Fourier integral transform about time and horizontal coordinates in space reduces linear partial differential equation to an ordinary differential equation related to the vertical axis. For isotropic medium Helmholtz potentials are used to separate the vector differential equations into scalar ones. Using the complete differential matrix for an anisotropic linear material and applying Fourier integral transform additionally with respect to the vertical direction gives a homogenous linear set of equations. The matrix depends on the wavenumbers in all three directions in space and on angular frequency. The horizontal wave numbers and the angular frequency are fixed. Decomposing the matrix into eigenvectors and eigenvalues of the vertical wave number gives the desired decoupling of the coupled shear-compression wave types. Analytical back transform about the vertical axis is possible if the homogenous solutions are converted to generalized functions. An analytical back transform results in complex exponential functions for the three wave types. The wavelengths and -velocities depend on the calculated eigenvalues. Applying this method allows to extend the solution procedure formerly used for isotropic medium to any kind of linear anisotropy. Numerical back transform is needed about the horizontal axis to calculate frequency spectra for any desired position in space. Prediction of vibrations induced by railways will be a typical application for this method.

A NUMERICAL STUDY ON THE FLOW NOISE OF A SIDE MIRROR OF CAR

Young-Soo Won*, Jang-Hyung Cho**

* CMStech Ltd. 1101 Daerung-Techtown III, 448, Kasan-dong,

**Kumchon-gu, Seoul, Korea, 153-804

The flow noise of a side mirror of car is numerically analyzed. The unsteady flow field is calculated by node based CFD scheme. The flow noise of side mirror is calculated by one of the acoustic analogy - Ffowcs-Williams and Hawkings equation. The acoustic pressure is predicted by using unsteady aerodynamic force on the side mirror and back plate. In order to validate the accuracy of numerical scheme, an airfoil and sample side mirror are analyzed. The shape of side mirror is half circle and the flow noise of sample side mirror is compared to the measured one. The predicted acoustic spectrum is similar to the measured one. By using this method, side mirror of newly designed car model is analyzed and the acoustic source region is identified.

NEW CROATIAN "LAW ON NOISE PROTECTION"

Miljenko Henich*, Zoran Veršić**

*"SONUS" d.o.o., Benešićeva 21, 10000 Zagreb, CROATIA

**University of Zagreb, Faculty of Architecture, Kačićeva 26, 10000 Zagreb, CROATIA

New croatian "Law on noise protection" was published in official journal Narodne novine No. 20/03 and entered into force on the 15.february 2003. The Law was prepared basically on the experience with implementation of former law taking into account EU Directives, EN and ISO standards which are adopted as HRN (croatian standards). The principal idea of the Law is prevention, assuring health protection from noise in time, in most efficient and cheapest way. Because noise protection is an interdisciplinar matter, Law covers all actions where noise can be influenced. Protection begins with land use planning, continues with whole process of building the objects which must be protected from noise and objects containing noise sources, includes working area, handicraft, industry, noise sources in the open area and takes care on sound power of noise sources. Account is taken on touristic noise problems, and noise bound of music emmitions, sports and recreation acivities. Introduced is the obligation for settlements of preparing noise maps and action plans. Initiated is an expert exam for all pearsons involved in implementation of the Law and the accreditation of involved labors following HRN EN ISO/IEC 17025. Nine forseen regulations elaborating in details implementation of Law must be prepared up to end of August 2003.

PSIHOAKUSTIKA

Peter Špec

Študent na Fakulteti za elektrotehniko, računalništvo in informatiko, Univerza v Mariboru, Smetanova 13, 2000 Maribor, SLOVENIJA

Psychoacoustics is a relatively young science, although many prominent scientists wrote about and studied it, like Platon, later Shumann, Carl Stumpf and the others. Psychoacoustics is multidisciplinary science, and one needs knowledge about acoustics, anatomy and psychology to understand it. In this article, correlation between sound, structure of a human ear and psychophysical phenomenon is described. In this article some basic definitions and phenomenon are described. Ability of human to detect different frequency signals under changing conditions is explained. Further, a correlation between frequency and note is described. Another phenomena of detecting and identifying signals masked by background noise are discussed. On the and sensitivity of human hearing to amplitude, harmonics and phase distortions of audio reproduction systems is analyzed.

REGULATION OF COOKING STOVE BY BOILING STATE DETECTION BASED ON ACOUSTIC SIGNALS

Albin Smrke*, Jurij Prezelj**

* Poudarek d.o.o., Ljubljanska 108,1230 Domžale, Slovenija

** Fakulteta za strojništvo, Aškerčeva 6, 1000 Ljubljana, Slovenija

The number of labor - saving appliances used in households is rising. This is one of the main reasons for increasing of energy consumption. It is estimated that 20% of all energy is used in households. Design of efficient consumer appliances is a trend all over the world. The market has already defined several regulations, which classify appliances according to the energy consumption levels. The regulation of cooking appliance energy efficiency is not included and its formation is at the beginning. In response to the market needs for energy efficiency in cooking systems, a multi sensor wireless approach for optimizing cooking efficiency was invented and patented. In this article a method of determining the boil states of liquid, by using audible sound as information, is presented. Sound, generated by the liquid as it is heated, is measured and processed to determine the boiling states. Derivative inflection points, zero slope points, and acoustic signal frequencies are utilized to determine the pre-boiling, boiling, boiling-dry, and boiling-over states of the cooking process.

SIMULATION OF ACTIVE NOISE CONTROL IN DUCT

Jurij PREZELJ, Mirko ČUDINA

Univerza v Ljubljani, Fakulteta za strojništvo, Aškerčeva 6, 1000 Ljubljana, SLOVENIA

The main purpose of this work is to determine the influence of different test signals on adaptive algorithm performance, and to determine the impulse response of the unknown system. The influence of microphone position on the active noise control process was also tested by simulation. In order to achieve credible simulation, all the components of the active noise control system have to be identified with accurate impulse response. Impulse response of the acoustic path can easily be measured with sound impulse and two fast and paired microphones. Generation of sound impulse is pretentious. Deviation from ideal conditions results in estimation error of an acoustic path impulse response, and inserts a deviation in simulation. Therefore another approach for system impulse response identification using adaptive LMS filtering was introduced. The algorithm compares input and output of unknown system, with input and output of the model and corrects the model until the error reaches minimum. In order to obtain credible results of active noise control simulation, impulse response of the each part of the active noise system was measured using four different test signals; white noise, frequency sweep and impulses with two different lengths. Simulation of active noise control process was afterwards conducted using this measured impulse responses.

VPLIV ODMEVNOSTI PROSTORA V PREDAVALNICI NA RAZUMLJIVOST GOVORA

Ina Čarič*, Jurij Prezelj**, Mirko Čudina**

*Osnovna Šola Spodnja Šiška, Gasilska 17, 1000 Ljubljana, Slovenija

**Faculty of Mechanical Engineering, University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, Slovenija

Students of Faculty for mechanical engineering were complaining that lectures in classrooms are hard to follow, and in some classrooms taking notes in last rows is impossible. In order to establish reason for bad intelligibility of speech in the classrooms reverberation time T60 was measured using three different sound sources: high energy spark, bursting of the balloon and reference source with pink noise. Reverberation time was measured in five classrooms and at twelve positions, where subjective measurements of speech intelligibility were also conducted. Reverberation time was compared with the measured speech intelligibility. Signal to noise ratio was also measured at all positions and compared to the speech intelligibility as well. Measurement results of the T60 with different sources were also compared to each other.

WELDING NOISE SIMULATIONS USING ADAPTIVE DIGITAL FILTER

Jurij PREZELJ, Ivan POLAJNAR, Mirko ČUDINA

University of Ljubljana, Faculty for Mechanical Engineering, Aškerčeva 6, 1000 Ljubljana, Slovenia

During Gas Metal Arc Welding (GMAW) process strong side affects are present such as emission of UV light, heat, vibrations, acoustic emission and generation of audible sound. The main objective of our research is to obtain information about ongoing welding process using audible sound. On the basis of experimental and theoretical work we found most significant audible sound sources in time and space during GMAW process. A mathematical model for calculating sound from welding current is presented. Further, a use of digital adaptive least mean square algorithm for finite impulse response filter is presented, that can be implemented in real time digital signal processing for calculation of welding process parameters. Advantage of using audible sound, as a signal for GMAW process, in comparison to welding voltage signal and welding current signal, is that sound caries some additional information about the process. Additional advantage of sound is simplicity of its detection.

WAVE PROPAGATION IN FLUID-FILLED VISCOELASTIC PIPES

Matjaž PREK

Fakulteta za strojništvo, Univerza v Ljubljani, Aškerčeva 6, 1000 Ljubljana, SLOVENIJA

In viscoelastic pipes, where the material properties depends on a complex bulk modulus as well as on a complex shear modulus, the sound field within the fluid is affected. Coupling between the pipe wall and the fluid decreases the sound speed in the fluid. Likewise, the speed of sound in fluid is frequency-dependent. Wavelet transform of non-stationary sound signal was used to identify the frequency-dependent fluid sound speed. This method provides a view to frequency dependent transfer characteristics of fluid - pipe coupled system. The results showed that, in the case of propagating small disturbances (such as acoustic waves), the pipe wall inertance has a minor influence on the wave propagation characteristics. The elastic reaction of the wall to expansion of the cross section greatly exceeds the inertial reactions.

FLOW INDUCED NOISE IN FLUID VALVE

Matjaž Prek

Fakulteta za strojništvo, Univerza v Ljubljani, Aškerčeva 6, 1000 Ljubljana, SLOVENIJA

A predictive method was used to estimate the noise generated in fluid valve model. The prediction is based on hydroacoustic scaling rules and experimental data to relate the noise level and spectrum to the geometry and flow conditions within the valve. A comparison of the predicted mechanisms with the experimental data indicated that the scaling rules could be further improved by a re-examination of the influence of the impact factors, namely the flow and geometrical conditions. An interesting consequence of the measurement results is the influence of the valve diameter and opening on the noise generating mechanism. It appears that the noise source characteristics changes between the monopole and dipole type as the basic noise generation mechanism, depending on geometrical conditions.

MEHANIZMI GENENERIRANJA HRUPA IN VIBRACIJ V ENOSMERNIH ELEKTROMOTORJIH

Martin FURLAN1, Miha BOLTEŽAR2

1 Iskra Avtoelektrika d.d. Polje 15, 5290 Šempeter pri Gorici, SLOVENIJA

2 Fakulteta za strojništvo, Univerza v Ljubljani, Aškerčeva 6, 1000 Ljubljana, SLOVENIJA

V prispevku so opisani osnovni mehanizmi generiranja hrupa in vibracij v enosmernih elektromotorjih. Glede na znano razdelitev virov hrupa in vibracij v električnih strojih smo le-te obravnavali kot magnetne, mehanske in aerodinamične. Za vsak pomembnejši vir hupa in vibracij, ki nastopa v enosmernem elektromotorju, smo natančneje opisali njegov mehanizem generiranja ter navedli značilnosti. Posebno pozornost smo namenili razlagi mehanizmov generiranja magnetnega hrupa ter hrupa ščetk in ventilatorskega hrupa, ki imajo pogosto prevladujoč vpliv v skupnem hrupu enosmernih elektromotorjev. Navedeni in na dejanskih primerih prikazani so osnovni prijemi za zmanjševanje hrupa in vibracij omenjenih virov. Poleg tega so navedene tudi metode za njihovo identifikacijo ter različni prikazi rezultatov meritev hrupa in vibracij, ki omogočajo njihovo identifikacijo.

IZVEDBA, VERIFIKACIJA IN INTEGRACIJA METODE ROBNIH ELEMENTOV ZA REŠEVANJE AKUSTIČNIH PROBLEMOV V PROGRAMSKI PAKET METODE

KONČNIH ELEMENTOV

Martin FURLAN1, Miha BOLTEŽAR2

1 Iskra Avtoelektrika d.d. Polje 15, 5290 Šempeter pri Gorici, SLOVENIJA

2 Fakulteta za strojništvo, Univerza v Ljubljani, Aškerčeva 6, 1000 Ljubljana, SLOVENIJA

V prispevku so predstavljeni osnovni prijemi za reševanje zunanjih akustičnih problemov s pomočjo metode robnih elementov (MRE) ter njena izvedba v programih za reševanje dvodimenzionalnih (2D), tridimenzionalnih (3D) ter tridimenzionalnih aksisimetričnih (3A) problemov. Prikazana je tudi integracija programa v komercialni programski paket metode končnih elementov (MKE), ki primarno služi za določitev strukturnega odziva kot vzroka za zvočno polje, sekundarno pa za pripravo in kasnejšo obdelavo akustičnega modela. Programi MRE so verificirani na akustičnih problemih, kjer je poznana analitična rešitev. Sama verifikacija je izvedena s poudarkom na raziskavi vpliva gostote diskretizacije na natančnost izračuna zvočnega polja. Poleg tega je zaradi narave numeričnega problema oz. sistema linearnih enačb, ki pri tem nastane, ovrednotena tudi hitrost reševanja problema glede na izbiro metode reševanja nastalega sistema linearnih enačb.

ZMANJŠEVANJE HRUPA MAJHNIH ENOSMERNIH ELEKTROMOTORJEV

Martin FURLAN1, Jože KOVAČ1, Andrej ČERNIGOJ1, Dušan LIČEN1 in Miha BOLTEŽAR2

1 Iskra Avtoelektrika d.d. Polje 15, 5290 Šempeter pri Gorici, SLOVENIJA

2 Fakulteta za strojništvo, Univerza v Ljubljani, Aškerčeva 6, 1000 Ljubljana, SLOVENIJA

V prispevku so opisani osnovni numerični in eksperimentalni prijemi, ki smo jih uporabili pri analizi in zmanjševanju hrupa majhnih enosmernih elektromotorjev. Prikazani so rezultati ovrednotenja vzbujevalnih magnetnih sil, dobljeni z metodo končnih elementov (MKE), ter spektralna analiza hrupa in vibracij pri različnih pogojih obratovanja elektromotorja. Slednja poda celovito sliko o karakterju hrupa in vibracij. Uporabljeni kombinirani analitično eksperimentalni pristop k zmanjševanju hrupa temelji na numeričnem modeliranju, ki omogoča boljše razumevanje mehanizma generiranja hrupa, ter na eksperimentalnem delu, kjer se karakterizirajo viri hrupa in vibracij v enosmernem elektromotorju. Tak pristop nam pomaga pri izbiri učinkovitih ukrepov za zmanjšanje hrupa. Končno so na prototipih izvedeni in ovrednoteni ukrepi za zmanjšanje hrupa.

DAMAGE DIAGNOSTICS OF A GEAR UNIT

Aleš Belšak1, Mateja Ploj Virtič2, Jože Flašker1

1 University of Maribor, Faculty of Mechanical Engineering, Smetanova 17, 2000 Maribor,

2 University of Maribor, Faculty of Education, Koroška 160, 2000 Maribor, Slovenia

The influences of various defects of a single-stage gear-unit upon the vibrations they produce are dealt with. Different methods are applied to analyse time signals obtained by experiments. Significant changes in tooth stiffness are caused by a notch in the tooth root. A notch has been made with the purpose of simulating the conditions close to the ones in concern to a fatigue crack in a tooth root. Different lengths lead to the increase in amplitudes of certain frequencies in the spectrum, which is one of the most important factors indicating changes in a gear-unit. The appearance of sidebands round the fundamental frequencies and their higher harmonics is also a very important factor indicating defects in a gear-unit.

PROBLEMATIKA HRUPA V KOMANDNI SOBI BLOKA 4

Nikola VLAHOVIĆ*, Ferdinand DEŽELAK*

*Termoelektrarna Šoštanj d.o.o., Cesta Lole Ribarja 18, 3325 Šoštanj, SLOVENIJA

**Zavod Republike Slovenije za varstvo pri delu, Center za ekologijo in toksikologijo in varstvo pred sevanji, Bohoričeva 22a, 1105 Ljubljana, p.p.2227, SLOVENIJA

This article considers some noise and vibration problems in the command room of block 4 in the power plant station Šoštanj. When meassuring noise in this room, the experts established higher noise levels than allowed. This noise originates from the machine room of the block IV. The most sensitive part in the partition wall between the machine and control room is a big glass window. Despite lead added, this glass does not provide satisfactory airborne sound isolation. The noise in machine room is wideband, but a considerable part of ¸its energy is in the high frequency region, especially near 1250 and 3150 Hz, as a result of some pumps operation. When evaluating the influence of this noise to the working environment, additional safety rules must be applied. The noise in control room does not present a serious health hazard, which workers are exposed to, but it can interfere with their mental activities, communication abilities and quality of work. The meassuring results indicate, that noise levels on the most exposed positions in the control room exceed 60 dB(A). The results stated are applied as a basis for further noise control meassures. The previous analysis shows, that noise control meassures at the noise sources only is very difficult to carry out. For this reason the antinoise meassures are focused to noise propagation paths.

A CONTRIBUTION TO THE INVESTIGATION OF THE "VIBRATION STRIPS"

Alija CIGIĆ, Šimun BOGDAN, Davorka ŠARAVANJA

Faculty of Mechanical Engineering, University of Mostar, Matice hrvatske bb, 88000 Mostar, BOSNIA AND HERZEGOVINA

In this paper a methodology and observation results ''vibration strips'' using in solving acute problem in city road traffic are presented.Obtained dates indicates that using of ''vibration strips'' in city road traffic had an opposite effect than the desired. Contrary to our expectations, a number of traffic accidents with fatal consequences have been increased, while a noise level on the frequent road as a result of passing over ''vibration strips'' were too high.

UGOTAVLJANJE STANJA ZOBNIŠKIH GONIL

Aleš Belšak, Jože Flašker

Univerza v Mariboru, Fakulteta za strojništvo, Inštitut za konstruiranje in oblikovanje Smetanova 17, 2000 Maribor, Slovenija

Eden izmed načinov ugotavljanja stanja gonila predstavlja merjenje vibracij skupaj z ostalimi obratovalnimi parametri. Vse z nalogo zaznati napake oz. poškodbe v gonilu še pred odpovedjo delovanja. Opisan je način merjenja, predvsem pa analiza signalov, na podlagi katere je mogoče ugotoviti spremembe v delovanju posameznih komponent gonila. Najpomembnejši izvori vibracij so notranji izvori: ubiranje zob, vrtenje ležajev in torzijske vibracije. Tako izmerjene vibracije pri gonilu s poškodbo ali napako identificiramo kot spremembo značilnosti signala v časovnem oz. frekvenčnem prostoru. Že z analizo izmerjenega časovnega signala je razvidna prisotnost sprememb, ki pa se mnogo bolje identificira še v frekvenčnem oz. časovno frekvenčnem prostoru. Za lažjo identifikacijo sprememb, pa je dobrodošla povezava informacije o vrtljajih. Vrtljaji namreč lahko med obratovanjem nihajo oz. niso konstantni, še posebej, če gre za meritve gonil na strojih ali napravah pod obremenitvijo v industriji. Zaradi tega je frekvenčna slika, še posebej pri frekvenčni analizi višjih harmonikov popačena. Če so odstopki preveliki, lahko izvedemo rekonstrukcijo signala na način obdelave po delih ali z metode prevzorčenja. Odločitev je odvisna tudi od načina nadaljnje obdelave. Pri frekvenčni analizi je tako slika višjih harmonikov jasnejša. Tudi klasične statistične metode analize časovnega signala pridobijo na svoji vrednosti, čeprav je njihova uporabnost močno omejena.