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COB84 CÁLCULO DO ESPALHAMENTO ACÚSTICO ATRAVÉS DO MÉTODO DE SIMULAÇÃO POR FONTES ELEMENTARES/ CALCULATION THE SCATTERING BY THE METHOD OF SOURCE SIMULATION TECHNIQUE
Paulo Henrique Trombetta Zannin
Departamento de Engenharia Mecânica - Centro Politécnico - Universidade Federal do Paraná, CEP 81531-990 Curitiba, Brasil - Caixa Postal 19011 - E-mail: zannin@demec.ufpr.br
One method to calculate the acoustic scattering from a body with given surface velocity is described here. The method consists in approximating the scattered field of auxiliary radiators in a way that allows a good agreement between tehm both. The error due to this approximation can be minimized in several ways. However, in the present contribution only the method of minimal squares was used. In this paper the acoustic scattering due to the presence of one cylinder with variable surface impedance was investigated both theoretically and experimentally using the method of the source-simulation-technique.
Keywords: Espalhamento acústico, radiação, multipolo, monopolo - scattering, radiation, multipole, monopole.
COB202 SIMULAÇÕES NUMÉRICAS E ENSAIOS EXPERIMENTAIS DA RESPOSTA ACÚSTICA DE ALTO-FALANTES/NUMERICAL MODELING AND MEASUREMENTS OF THE ACOUSTIC RESPONSE OF LOUDSPEAKERS
André L. Goldstein & Samir N. Y. Gerges
Laboratório de Vibrações e Acústica, Depto.de Engenharia Mecânica - UFSC -CP: 476,CEP 88040-900 Florianópolis, SC, Brasil
E-mail: andre@gva.ufsc.br , gerges@mbox1.ufsc.br
The frequency response prediction of loudspeakers is a problem that have closed form analytical solution only for low frequencies and simple geometry. In this paper it is investigated the use of the finite element method and the boundary element method implemented in commercial software for extend the prediction of loudspeaker response for higher frequencies considering the flexible behavior of the diaphragm. The modeling of a commercial loudspeaker is performed and its frequency response and directivity is calculated. The computational results are compared with measurements realized in a hemi anechoic chamber showing good agreement.
Keywords: Simulação de Alto-falantes, Método de Elementos Finitos, Método de Elementos de Contorno / Loudspeaker Simulation, Finite Element Method, Boundary Element Method
COB414 ONDAS ACÚSTICAS EM CORPOS DELGADOS - UMA FORMULAÇÃO INTEGRAL / ACOUSTIC WAVES ON THIN BODIES - AN INTEGRAL FORMULATION
José Jeferson ro Rêgo SilvaÄ , Henry PowerÅ & Luiz Carlos WrobelÆ
Ä DECIV/UFPE – Av. Acad. Hélio Ramos, s/n,CdU,50.740-530, Recife/PE, Brasil. E-mail: jjrs@npd.ufpe.br
Å WIT/CMI – Ashurst Lodge, Ashrust, Southampton, SO40 7AA, UK. E-mail: henry@wessex.witcmi.ac.uk
Æ Dep. Mech. Eng./Brunel Univ. – Uxbridge, Middlesex UB8 3PH, UK. E-mail: luiz.wrobel@brunel.ac.uk
This paper presents an advanced boundary element method to deal with scattering of sound waves by curved thin bodies. The formulation employed involves a hypersingular integral equation obtained from the normal derivative of the Helmholtz integral representation formula, considering the thin body of very small thickness as an open surface. The hypersingular integral, interpreted in the sense of Hadamard finit part integral, requires more attention in its numerical treatment, mainly when modelling curved surfaces. A general algorithm to numerically evaluate the hipersingular integral based on the concept of finite part integration is implemented to enable the use of higher-order isoparametric boundary elements, to model curved sound barriers.
Keywords: Acústica, Corpos delgados, Elementos de contorno, Integral hipersingular. Acoustic, Thin bodies, Boundary elements, Hypersingular integral.
COB426 Modelagem de Transdutores Piezoelétricos de Potência / MODELING POWER PIEZOELETRIC TRANSDUCERS
Julio C. Adamowski, Marcelo Y. Matuda, Flávio Buiochi, Celso M. Furukawa
Escola Politécnica da Universidade de São Paulo, Dep. de Engenharia Mecânica
Av. Prof. Mello Moraes, 2231, CEP 05508-900, São Paulo, Brasil. E-mail: jcadamow@usp.br
Two methods are presented for modeling power piezoelectric sandwich transducers, composed of a stack of piezoelectric ceramics terminated at both extremities with steel masses. The piezoelectric ceramics are rings connected by a bolt that passes through their centers and is clamped at both ends to apply tension to the stack. This transducer may be solved by a very efficient analytical method called Chain Matrix, which uses electric and acoustic matrices to describe the interactions between successive layers. Chaining these matrices provides a model of the complete transducer. The second modeling method is based on the finite element method. Both methods allow to calculate the electrical impedance of the transducer to determine the resonant and antiresonant frequencies. To achieve different optimization criteria, parameters of the transducers may be changed and the results rapidly examined. These methods were applied to construct a prototype transducer. Experimental and simulated results showed good agreement. In conclusion, these modeling methods are accurate, constituting a useful tool for designing power transducers.
Keywords: Chain matrix, finite element method, power piezoelectric transducer, ultrasound, piezoelectric transducer.
Matriz em cadeia, método dos elementos finitos, transdutor piezoelétrico de potência, ultra-som.
COB427 Medição da viscosidade DINÂMICA de líquidos por ultra-som / ULTRASONIC MEASUREMENT OF DYNAMIC VISCOSITY OF LIQUIDS
Flávio Buiochi, Julio C. Adamowski & Celso M. Furukawa
Escola Politécnica da Universidade de São Paulo, Dep. de Engenharia Mecânica
Av. Prof. Mello Moraes, 2231, CEP 05508-900, São Paulo, Brasil. E-mail: fbuiochi@usp.br
This paper describes an method for measuring the viscosity of liquids using ultrasound. From several signals reflected inside a measurement cell, the density, the attenuation coefficient and the propagation velocity of the liquid can be calculated and related to its dynamic viscosity. The method employs a double element transducer (DET) which consists of a piezoelectric ceramic transmitter and a large aperture PVDF membrane receiver separated by a solid buffer rod. Between the receiver and the liquid there is a reference solid rod. The attenuation coefficients of the liquids are calculated from the measured reflection coefficient for the interface of reference rod and the liquid, and the propagation velocity is calculated from the transit time between this interface and a metal reflector placed at the opposite wall of the chamber. The effect of acoustic diffraction is eliminated by using the DET, because the receiver is somewhat larger in diameter than the transmitter. For testing this method, a sensor was implemented, and measurements of viscous liquids, such as, automotive oils, were conducted at 1.4MHz. The determination of the dynamic viscosity requires the calibration of the measurement system, using a viscometer.
Keywords: Viscosity measurement, absorption coefficient, ultrasound, instrumentation. / Medição de viscosidade, coeficiente de absorção, ultra-som, instrumentação.
COB1192 INFLUÊNCIA DA COMPOSIÇÃO DO TRÁFEGO SOBRE O RUÍDO GERADO POR RODOVIAS BRASILEIRAS TÍPICAS / COMPOSITION EFFECTS ON THE TRAFFIC NOISE OF TYPICAL BRAZILIAN ROADS
Arcanjo Lenzi1 e Joel M. Alves Filho2
1 - Laboratório de Vibrações e Acústica (LVA) Depto de Engenharia Mecânica, UFSC cp. 476
CEP 88040-900 -tel. 048 234 0689 - fax 048-234 1519 - Florianópolis - SC e-mail: arcanjo@emc.ufsc.br
2 - Departamento de Engenharia Mecânica e Produção
Universidade Estadual do Maranhão - UEMA - CEP 65.055-390 - São Luis - MA - Brasil.
This work deals with a road traffic noise investigation at Florianópolis (SC, Brazil). Seeking to determine the relationship between L10 and Leq levels and traffic composition and volume flow. L10 prediction equation obtained from 149 measurements is compared to equations based on similar works made in other countries. A Statistical analysis indicated good correlation (r =0.61) for L10 predictions and a satisfactory correlation (r = 0.49) for Leq predictions.
Keywords: Ruído de Tráfego, Composição do Tráfego, Road Traffic Noise, Traffic Composition
COB1193 PROPAGAÇÃO DO SOM EM LÂMINAS DE ÁGUAS RASAS POR ACÚSTICA DE RAIOS / Sound Transmission in ShaLlow Waters by Ray Acoustics
Ricardo Vitoy1, Arcanjo Lenzi1
1 - Laboratório de Vibrações e Acústica (LVA) Depto de Engenharia Mecânica, UFSC, cp. 476 - CEP 88040-900 -tel. 048 234 0689
fax 048-234 1519 - Florianópolis - SC, email: arcanjo@emc.ufsc.br
Due to its vast territorial extension, with extense coast and large hidrographic basins, Brazil still has many unexplored natural resources. The development of SONAR systems would certainly be helpful for underwater mining purposes and to the fishing industry. This work deals with sound propagation analysis in shallow water by Ray Acustics models. The effects of bottom irregularities on the sound propagation are analyzed.
Keywords: Acústica de Raios, Águas Rasas, Propagação do Som - Ray Acoustics, Shallow Waters, Sound Propagation
COB1327 Avaliação acústica de danceteria por modelo reduzido / ACOUSTIC EVALUATION OF DISCO HALL BY REDUCED MODEL
Moysés Zindeluk1, J. Flávio s. Feiteira1, Paulo M. Massarani2
1 Laboratório de Acústica e Vibrações da COPPE - PEM / UFRJ
CEP - 21945-900 Ilha do Fundão RJ, Brasil - E-mail: moyses@serv.com.ufrj.br
2 Laboratório de Ensaios Acústicos - INMETRO, CEP - 25250-020 Xerém RJ, Brasil - E-mail: laena@inmetro.gov.br
An example of the conjugated use of reduced models and digital signal processing to preview the acoustic behaviour of complex shaped halls is here reported. The main concern with the disco hall studied was its very tall, multiplane with cylindrical top glass roof. The roof intersects the main building, which is octogonal, with three cylindrical cavities aside. This is very difficult to numerically simulate, especially for transient response. The 1:20 model built, with patches of absorbing material to correct for absoption of surfaces was used mainly for impulsive response determination. Virtual reality sound files, of voice and music were successfuly synthesised by convolution, helping, together with the time frequency representations, to develop the acoustic treatment, which virtually eliminated the observed echoes and room modes, without "drying out" the room response.
Keywords: Room Acoustics, Reduced models, Signal Processing, Experimental techniques, Time-Frequency Representation. Acústica de Salas, Modelos Reduzidos, Processamento de Sinais, Técnicas Experimentais, Representação Tempo-Freqüência.
COB1384 UNCERTAINTY AND COMPATIBILITY ANALYSIS OF ACOUSTIC POWER DETERMINATION BY INTENSITY AND PRESSURE MEASUREMENT TECHNIQUES
A. Massacesi, N. Paone*, G. L. Rossi *, E. P. Tomasini*
ELICA SpA, Stab. E Casoli, Contrada Serralta, 49/A, 60049 Serra San Quirico, (AN), tel 0732 610637, fax 0732 610639
* Università di Ancona, Dipartimento di Meccanica, Via Brecce Bianche, 60131 Ancona, tel 071 2204487, fax 071 2204418
European Machinery Directive states that all machine producers must declare the noise level, in terms of acoustic power and/or acoustic pressure in a significant point, emitted by each kind of machine on the market. Recently a new standard to perform sound power measurements by intensity methods has been introduced. In this work results of sound power obtained by intensity techniques and traditional pressure measurements inside reverberating room are compared. Measurements have been performed according to two international standards: the first based on acoustical intensity mapping around the source (ISO-9614-1); the second based on averaged pressure measurements inside a reverberating room (ISO 3741). Tests has been performed in two laboratories. The noise source analysed is a range hood. Repeated measurements on different models of range hood by both techniques allowed to obtain an estimate of uncertainty and to perform a compatibility analysis. Also advantages and disadvantages of both techniques for the particular noise source tested are highlighted.
Keywords: Acoustic intensity, sound power measurements, uncertainty.
COB1396 PISTONFONE PARA CALIBRAÇÃO DE HIDROFONES EM BAIXAS FREQÜÊNCIAS / PISTONPHONE FOR CALIBRATING HYDROPHONES AT LOW FREQUENCIES
Fernando L. de Magalhães, Manoel Marteleto & Orlando J. Ribeiro Afonso
Instituto de Pesquisas da Marinha - Grupo de Sonar - Rua Ipiru n°2, Ilha do Governador, Rio de Janeiro, Brasil, CEP 21931-090
E-mail: fermag@pobox.com
This paper describes the main acoustic parameters related to the development of a non conventional pistonphone for calibrating hydrophones at low frequencies. While in the usual models the internal acoustic field is analytically calculated from the displacement measurements of a stiff piston source, in the model here proposed the calibration curves are obtained by using a standard hydrophone in a comparison calibration process and adopting a comercial loudspeaker as the excitation source. The system is designed for production, testing and field use in the largest possible frequency ranges from 10 Hz to 1 KHz. The hydrophones are placed in a water-air chamber with dimensions established from the application of theorical models to define the dynamical behaviour of the acoustic means. The initial results obtained from a prototype of the pistonphone are presented.
Keywords: Acústica - Transdutores - Hidrofone - Calibração - Pistonfone / Acoustics - Transducers - Hydrophone - Calibration - Pistonphone