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Nikolay I. Ivanov, Baltic State Technical University (Russia)
Alexander V. Omelchenko, Baltic State Technical University (Russia)
Michael M. Samoylov, Baltic State Technical University (Russia)
Vladimir N. Uskov, Baltic State Technical University (Russia)
Natalia V. Zuyzlikova, Baltic State Technical University (Russia)
Excessive noise is still one of the harmful reality of our surrounding and consequently it is still in the focus of investigations for many specialists. Often it is not possible to reduce noise in the source as well as by active way and therefore it becomes necessary to use passive noise control means. This paper is devoted to investigation of acoustical shields which might be used at work places situated as inside buildings as at open places and on machines and to a possibility of optimization of shield parameters. A method for calculation of acoustical shields effectiveness and the procedure of analytical optimization are described in the paper. It is suggested that there are two most important actions should be done in order to reduce noise which are, first of all, providing the required noise reduction levels, and, the second, making this with the lowest expenses. It was derived that in that case, cost of a shield will depend on its material and square. The algorithm and software for interactive optimization, in other words, selection of the parameters of a shield providing required noise reduction with minimal cost, is obtained. Examples of numerical simulation are also presented.
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Ben Cazzolato, University of Adelaide (Australia)
Carl Q. Howard, University of Adelaide (Australia)
Colin H. Hansen, The University of Adelaide (Australia)
Classical analytical models used for prediction of the performance of reactive silencers are limited to conditions where the dimensions of the duct and resonators are small compared to the wavelength of the sound. Finite Element Analysis does not suffer from such limitations and has therefore been used to analyse the design of a reactive silencer for the exhaust stack of a {980MW} power station. To assist in the design process, resonators of various dimensions were analysed using FEA which has led to the derivation of expressions for the resonance frequencies of slot-type rhomboid shaped resonators as a function of the geometry. An important design issue is the influence that adjacent resonators have on the overall performance of the system. It was found that when resonators of similar resonance frequency are in close proximity, they can interact and lead to a decrease in the overall performance compared to that of a single resonator.
sv970350.pdf (Scanned) TOPAlan Cummings, University of Hull
Hybrid modal/ray acoustics models for high frequency multimode sound propagation through finite-length dissipative duct silencers are being investigated and in this paper, the very simplest of these - involving no mean fluid flow, two dimensional sound propagation, a locally reacting duct liner and no area change in the silencer - is described. A mode matching scheme is also outlined. Numerical predictions of silencer attenuation from the hybrid model and the mode matching model are compared to experimental data taken from a two-dimensional silencer apparatus, and favourable agreement is noted.
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Pavel V. Vorobjev, Baltic State Technical University (Russia)
Lyudmila Ph. Drozdova, Baltic State Technical University (Russia)
Michael M. Samoylov, Baltic State Technical University (Russia)
External acoustical field of a vehicles is characterized by plenty of components which are generated by different sources. These sources are noise of engine and its units, noise of transmission, noise of elements of a vehicle body, noise of intake and exhaust systems, etc. But, as follows from practice, noise of internal combustion engine (ICE) exhaust gases represents the main part of external acoustical field of a vehicle. Exhaust noise reduction is one of the main and the most complicated problems. Traditional solution of this problem is elaboration of effective exhaust noise muffler. Such mufflers, as a rule, should be of 0.5-1.5 m in length to provide desirable effectiveness for each 100 horse power (hp.) of ICE. Moreover traditional exhaust mufflers usually cause 40-80 mm of mercury column (mm m.c. ) of pressure losses. Thus, to reduce noise of exhaust gases in vehicle with more than 500 hp. ICE it is required a muffler of traditional construction which should be not less than 250-300 liters of volume, what brings problems of its placement at a vehicle, taking into account strong requirements to vehicle overall dimensions and weight. Therefore the vehicles which have the restrictions concerning their dimensions and weight often are produced without any muffler. This fact cause high acoustical overloads in the environment and, as a consequence, confine the application of such machines in national economy. Therefore authors propound a new noise reduced construction to be placed at ICE exhaust of such vehicle. Developed noise reduced construction allows to avoid specific disadvantages of traditionally used mufflers mentioned above. Worked out noise reduced construction consists of a set of metal nets of different cross sections, it has small overall dimensions and do not generate additional ICE exhaust pressure losses. This construction was installed at a heavy vehicle with 870 hp. engine with dimensions of exhaust cross section of 1x0.3 m. Tests showed that installation of developed -construction gives ICE exhaust gases pressure loss of not more than 10 mm m.c. while acoustical effectiveness of the construction consists 4-12 dB in the frequency range of 100-8000 Hz.
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C.D. Field, University of Sydney (Australia)
F.R Fricke, University of Sydney (Australia)
This paper continues ongoing research into the use of quarter-wave resonators for the attenuation of noise entering buildings. Previous work involving scale model experiments demonstrated the effectiveness of a multi-cavity resonator system, achieving significant attenuation in the third octave bands to which the resonators were tuned (Field and Fricke 1995a, 1995b, 1995c, 1996). Results for experiments with a full scale prototype are now presented, demonstrating the feasibility of such a device for the attenuation of noise entering buildings.
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Jae Eung Oh, Hanyang University (Korea)
Kwang Hee Han, Hanyang University (Korea)
The intake noise of a vehicle is analyzed and reduced by using the transfer matrix method as well as the FE analysis code, NIT/SYSNOISE. A speaker excitation system is also proposed, which can analyze the acoustic characteristics of the intake system. It is easy to analyze the intake noise in the laboratory environment, and can be used at an early design stage of the intake system development. And this study proposes the improvement to reduce the level of the intake noise. It is to select the optimum position of a resonator and verified by NIT/SYSNOISE, FE analysis commercial software and testing the prototype and a proposed speaker excitation system.
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Seung Chul Kwak, LG Electronics Inc (Korea)
Ho Seon Rew, LG Electronics Inc (Korea)
Duck Joo Lee, Korea Advanced Institute of Science and Technology (Korea)
To investigate the pressure pulsation in a resonance tube, a computer program based on the unsteady compressible Euler equations has been developed. The convective terms are constructed using a Roe*s approximate Riemann solver and for high accuracy MUSCL is employed. To limit oscillations near shocks , Koren*s differentiable limiter is adopted and an explicit two-step Runge-Kutta method is used for time integration. Various characteristic boundary conditions suggested by Thompson, Watson-Myers and Hwang are tested and discussed to understand their physical meanings. Through the above tests , appropriate boundary conditions are selected and applied to simulate the pressure pulsation in the resonance tube. The calculation results are compared with the experiment by Merkli and Thomann. The computed amplitude and the period of pressure pulsation are in good agreement with experiment. It is believed that the practical engineering problems in acoustics can be directly simulated using Euler or Navier-Stokes equations with appropriate boundary conditions
sv970118.pdf (Scanned) TOPM.L. Munjal, Indian Institute of Science (India)
A majority of the present-day automobile exhaust systems make use of three-pass mufflers that are characterized by low back pressure and good acoustic performance because of interaction of waves in the three pass tubes with those in the annulus. A frequency-domain one-dimensional transfer matrix model is presented here for an extended-tube three-pass perforated element muffler. Transmission loss values computed therefrom have been shown to reduce to those of the flush-tube configuration in the limit. Finally, results of parametric studies are reported in order to help muffler designers in synthesizing an efficient muffler configuration within a given overall length of the chamber.
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