Статьи журнала - Техническая акустика
Все статьи: 276
Design and optimization of a new range of low sound emission generating set
Статья научная
This work provides an integrated approach developed with the aim of reducing the noise of generating sets, and the results obtained. The methodology and the procedures employed, with the indications obtained from theoretical analysis, are extendable to a vast range of industrial machines. The approach described has been applied to some PRAMAC Lifter generating set, presenting a high value of sound power, in order to reduce it accordingly with the value provided by the recent normative. Two production series generating sets were examined. The first, named S 12000, is a petrol engine generating set, with a 10,8 KVA alternator power and 614 cm3 of cubic capacity; the second, named S 6000, is a diesel engine, with a 5,5 KVA alternator power and 406 cm3 of cubic capacity. The implementation of the method described in the paper concerns the design of a new frame for the two machines and the development of new acoustical muffler.
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Design of tunable filter by Kerr effect used in optical communications
Статья научная
The discovery of photonic Band-gap (PBG) materials and their use in controlling light propagation is a new and exciting development. An optical design of a wavelength-selective tunable filter permitting to select a channel of 1 nm of spectral width among 40 channels situated between 1550 nm and 1590 nm is considered in this paper. Guided modes in a two dimensional dielectric photonic crystal (PC) waveguides are studied by the transfer matrix method (TMM) and Galerkin method. A cavity (localized defect) between two waveguides in the PC structure is introduced. Among several wavelengths circulating into the first guide, the resonance wavelength with the defect can be extracted by coupling effect, and then is injected into the second guide. The tuning effect is obtained by Kerr effect applied in the cavity.
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Design optimization of double-chamber mufflers on constrained venting system by ga method
Статья научная
Whilst the space volume of mufflers in a noise control system is often constrained for maintenance in practical engineering work, the maximization on muffler's performance becomes important and essential. To efficiently depress the venting noise, a high performance of double-chamber muffler is then proposed and investigated in this paper. To assess the optimal solution in the muffler design, the genetic algorithm (GA), a stochastic algorithm, is also applied, accordingly. This paper presents the GA application for the size optimal design of doublechamber muffler under space constraints and dealing with broadband noise. Using technique of four-pole matrix for sound transmission loss (STL) calculation in conjunction with the GA technique, the optimisation was carried out. Before GA operation, a single-chamber muffler is simulated and compared with the experimental data for accuracy check of mathematical model. Thereafter, a simple program of noise control at the pure tone of 500 Hz has been pre-run to verify the correctness of genetic algorithm before the optimal design of broadband noise was performed. Results show that both the accuracy of mathematical model and the correctness of GA method are acceptable. Consequently, the GA optimization on double-chamber muffler proposed in this study may provide a quick and correct approach.
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Design sensitivity analysis of statistical energy analysis models using transfer path approach
Статья научная
Statistical Energy Analysis (SEA) is an attractive tool to predict noise and vibration at high frequencies. It provides an ideal framework to carry out optimisation and sensitivity analysis. Design Sensitivity Analysis (DSA) using SEA helps the designer in making changes, by indicating the model parameters that cause the greatest benefit in either narrow or broadband noise and/or vibration reduction. This paper describes a simple and effective way of getting design sensitivities of noise and/or vibration response (or objective function formed using total energy response) to subsystem damping in SEA contest. Final form of design sensitivity vector, derived using Transfer Path Approach (TPA), suggests that the method is equally applicable for analytical and experimental DSA. A general proof for convergence of sensitivity vector thus derived is given to support the approach. Example of an automobile model, formed from 2 acoustic spaces and 24 plates, is given to validate and demonstrate the method.
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Development of moving sound source localization system
Статья научная
This paper proposes a novel approach of moving sound source localization using adaptive time delay estimation (TDE) algorithm and active-positioning of microphone arrays. Using the adaptive TDE that continuously estimates the time differences between the captured signals in the microphones sensors, the activepositioning controller keeps track of the source direction by rotating arrays mechanically. Theoretical analysis and computer simulations of the convergence characteristics of the proposed TDE algorithm are presented. The activepositioning array guarantees the highest delay-position sensitivity with smaller number of microphones than the fixed arrays. The overall performance is shown by using an experimental prototype system.
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Differences in dummy-head hrtfs caused by the acoustical environment near the head
Статья научная
Filtering of the Head-Related Transfer Functions (HRTFs) is the first and most important part during the perception of directional information in spatial hearing. A computer-controlled dummy-head measurement system was installed in an anechoic room with 1 degree horizontal and 5 degrees vertical resolution. Differences in the measured HRTFs caused by changes of the acoustical environment near the head are calculated. Effects of "everyday objects" like caps, hair, glasses and clothing on the fine structure of the HRTFs are presented.
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Статья научная
This paper presents an ultrasonic transducer modeling with VHDL-AMS standard (Very High speed integrated circuits Hardware Description Language - Analog and Mixed Signal) referenced IEEE 1076.1, integrated in a global measurement cell modeling dedicated to biological tissues ultrasound characterization. Usual modeling of ultrasonic transducer are based on electrical analogy and are not simulated in the global measurement environment which must include non linear medium behavior and electronic coupling. The ultrasonic transducer modeling proposed is simulated with the nonlinear acoustic load and electronic excitation. It was composed by a first element with a piezoceramic ring structure vibrating at a frequency of 2,25 MHz in thickness mode. The second element is stuck into the center of the first. This geometrical form is a disc vibrating at 4,5 MHz in thickness mode too. Nonlinear B/A parameter is used to characterize medium with a comparative method. The measurement cell is composed by a piezoceramic transducer which is implemented with the Redwood's electric scheme and a metallic reflector into a Plexiglas structure. The analyzed medium is placed between the transducer and a metallic reflector. Medium is modeled with take into account the nonlinear propagation with B/A parameter. The usual transmission line model has been modified to take into account the nonlinear propagation for a one dimensional wave. Simulations of the transducer pulse response and impedance show a VHDL-AMS model in good agreement with measurement. Results simulation of the measurement cell modeling are in agreement with well known B/A values of biological mediums.
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Double glazing vibroacoustic behaviour
Статья научная
The dynamic behaviour of a double glazing system requires the modelling dynamic behaviour of panels, air cavity, and fluid structure interaction. The associated energy functional formulation is established. Its discretisation by finite element methods leads to dynamic system equation. Modal approach, based on the decomposition of the modal pressure in a statical pressure and dynamical one, permits the determination of eigenfrequencies and eigenmodes of coupled system and the resolution of dynamical equations projected on the modal basis. Vibratory analysis allows to conclude the existence of two eigenmodes families for which the vibroacoustic coupling between panels and air cavity is absent for the first one and strong for the second one. Moreover, the established dynamic responses of a double glazing system show an important reduction of energy transmitted in comparison with simple panels.
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Electrodynamic loudspeaker modelling and characterization
Статья научная
The modelling and the simulation software are important tools in the design process of radiator systems. Also, for the manufacturers of such systems their characterization is necessary in the quality control. This work deals with the modelling, the simulation and the characterization of an electrodynamic loudspeaker. The measured characteristics are the electrical complex impedance, the frequency response and the Harmonic Distortions (HD) including 2nd, 3rd and Total Harmonic Distortion (THD). Comparisons of computed and measured frequency response and electrical complex impedance are shown. Thiele-Small parameters are deduced from the electrical complex impedance measurement. Besides these characteristics, the visualization of sound fields is useful for understanding the directional radiation of sound emitted from such loudspeaker. For that, the transverse acoustical beam section of sound pressure field is done using acoustic intensity measurement. Matlab based programs are developed for the simulation of these characteristics and for the processing and the visualization of acoustic pressure field.
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Exact solution of linear parametrically excited system with transient frequency modulation
Статья научная
To demonstrate the dangers of neglecting the transient characteristics of frequency modulation in linear parametrically excited systems a model equation with variable frequency that includes components of transient behavior is investigated. The transient components of the frequency modulation decay periodically and asymptotically with time leading to a periodic closed cycle form. The exact analytical solution of the model equation is derived for the first time in the present work by introducing a transformation that maps the original model into a system of two solvable equations. The extensive investigation of the general solution and its components demonstrates that the transient characteristics of the frequency variation cannot be ignored. In fact cases where theses characteristics can result in bounded or unbounded response of the system are presented. In general transient frequency characteristics continue to drastically affect the structure and the amplitude of the general solution long after they become indistinguishable in the frequency modulation. Numerical solutions of the model equation are also presented to further support the conclusions made in this paper.
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Flow-induced vibration of a y-shaped tube conveying fluid
Статья научная
This work investigates out of plane vibration of a Y-shaped tube conveying fluid with clamed ends conditions. The mathematical model is based on the equation of motion of each tube coupled with matched boundary conditions at the junction of the three segments. The resulting equations are then resolved using Galerkin approach. The resulting eigen-values, eigen-function and shape modes are found numerically. A stability analysis of the solution is then performed. The effect of geometrical and flow parameters on the vibration of the Y-shaped tube conveying fluid is investigated. Results show that for small length of branching side compared to the supplying tube and for zero branching angle then the first three non-dimensional frequency is close to those of straight single tube with clamped-clamped conditions. Moreover, neutral stability regions were observed in firs, second, and third modes for large range of dimensionless flow velocity. Results further demonstrate that an increase in dimensionless flow velocity results in decreasing of the non-dimensional frequency for the first three modes. Effect of branching angle and geometrical configuration of the mode shape and frequency is also investigated.
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Force chains in granular media and ultrasound impulse propagation in sand specimen under load
Статья научная
An analysis of the pattern of stress chains in dense and loose sand and velocity of ultrasound impulse propagation in quartz sand under loading explains the mechanisms by which granular materials, such as loose and dense sand, respond to external loads. Experiments were carried out in pure marine quartz sand under load in a triaxial test camera.
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Fourier and wavelets for blind image restoration
Статья научная
This paper describes a technique for the blind deconvolution based on the wavelet domain deconvolution that comprises Fourier-domain followed by wavelet-domain noise suppression, in order to benefit from the advantages of each of them. The algorithm employs regularized Wiener filter, which allows it to operate even when the system is non-invertible. In fact, we model such image to be the result of a convolution of the original image with a point spread function (PSF). This PSF depends mainly on the image formation system. Unfortunately, it is often very difficult to model this PSF from the physical data, for this reason we consider the problem as a blind deconvolution. First, the identification of the blur is based on maximum likelihood and the solution is obtained iteratively by successive estimations of the PSF from the noisy blurred image. We propose a blind restoration by estimating the noise variance, the point spread function (PSF) and the original image from a blurred and noisy observation. Our method is based on regularized Wiener filter and RDWT (redundant discrete wavelet transform). We illustrate the results with simulations on some examples.
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Fuzzy sliding mode control for a self-controlled synchronous motor drives
Статья научная
The application of fuzzy sliding mode control for improving the dynamic response of self controlled synchronous motor is presented. A fuzzy sliding logic controller is designed based on similarity between the fuzzy logic controller and the sliding mode control. The proposed scheme gives fast dynamic response with no overshoot and zero steady-state error. It has an important feature of being highly robust, insensitive to plant parameters variations and external disturbances. The design procedure is established to control the speed of a self controlled synchronous motor. The simulation results show that the controller designed is more effective than the conventional sliding mode controller in enhancing the robustness of control systems with high accuracy.
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Harmonic reduction based on active solutions
Статья научная
Most electronic systems use one or more switch mode power converter that will tend to draw current from the power line in a non sinusoidal shape. This input current characteristic results in current distortions that can contribute as well to the degradation of the supply voltage as to the negative disturbance effects of any connected equipment on the same line (interference, heating, noises, etc.). These problems have led to the creation of design standards and to develop interface systems which improve the power quality. Due to the high harmonic distortion of the wave of the current, it is necessary to develop solutions for their possible reduction. Consequently, the Power Factor Correction (PFC) stage of the front-end converter has become an important accessory. Operating principles, simulations and features of active solutions are discussed in this paper.
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Image analysis and pattern recognitionas tools in map interpretation
Статья научная
In this article we propose a methodology, which uses image analysis and pattern recognition techniques for the acquisition and the interpretation of cartographic documents. The main subject on map interpretation is to make easy their exploitation by proposing some steps allowing the transformation of the maps in paper form to a numerical storage of information in computers. Our approach is aiming to construct a system that can generate a symbolic description of the map. This approach includes color segregation, buildings localization, symbols identification, roads extraction and related character string recognition. All the information must be encoded. A color scanner generates a multicolor raster image of the map. This image is split into layers of predefined map colors. Each layer is then vectorized. To signify the feasibility of the proposed system, a brief description of the system is discussed and some experimental results are shown.
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Impact of tram traffic on noise and vibrations
Статья научная
The most important form of the public transport in town Zagreb is tramways, with 120 km of the tram tracks and 450,000 passengers transported every day. The noise and vibrations are today one of the major causes of reduced quality of life in the urban environments. That is confirmed by more and more frequent complaints from the citizens living and working in the urban areas along the traffic corridors with heavy road and tram traffic. This paper shows the survey on impact of tramway traffic on noise levels and vibrations. The tram vehicles from four manufacturers were considered: Duro Dakovic (Croatia), CKD Tatra (Czech Republic), Dьwag (Germany) and Koncar (Croatia), which are used by the Zagreb Electric Tramways (ZET) company. The research also covered the new, low floor tram type TMK 2200, manufactured in Zagreb, and started being exploited in June 2005. The results of this research helped ZET to decide on the tram types first to be replaced with the new ones, and also provided specific guidelines for design and maintenance of the tram tracks, all that to undertake adequate measures to reduce noise and vibrations.
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Implementation the active noise control to fan airborne noise of multimedia projector
Статья научная
Implementation the active noise control technology using Digital Signal Processing (DSP) core is presented. The case of airborne noise for EPSON projector fan is studied. The noise source ranking based on separate running method has been implemented to reveal the most significant noise source among three fans incorporated into multimedia projector. A short duct system containing noise cancelling speaker, reference and error microphones and DSP board with ported adaptive feed forward algorithm to cancelling critical tonal components of the fan noise were applied. The suppression of 6…10 dB for airborne noise of the fan in multimedia projector at tonal frequencies was obtained.
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Статья научная
In this paper, first, partly is noted the suggestions by well-known philosophical emphasis of Herakleitos, Hegel etc. (i.e., several of famous other philosophers) based on their original standpoint that the truth exists not in fragmentarily individual things but only in their relational fact or process (i.e., event) itself through some concrete self-exercise of existing contradiction. That is, it is stated that a central core and/or primary existence is not in only mutual intermediation of time series type among past, present and future, but also mutual intermediation and/or relationship among different environmental factors in especially dynamic styles (more explicitly, some temporal) harmony and/or objectively latent (severe or hierarchical) contradiction. It seems true even if apparently it has no connection according to only our individual professional sense. After all, such a viewpoint of "Relationism(us)-First" seems to be exceedingly important to all things including our human being evolving after the beginning of only material nature with Big Bang. Two kinds of actual example of the above (hierarchical type) mutual correlation in the time series and mutual correlation distributed in the space among different environmental factors are considered. More concretely, the proposed method is applied especially to the acoustic environment in the actual indoor living surroundings. Then, the mutual intermediation among sound and light waves (served for utility) and leaked EM waves (served for risk) around personal computer under playing a game is investigated through some principle experiment. As the result, some effectiveness of the proposed methodology is experimentally confirmed by taking the mutual intermediation among only physical environmental factors as an example.
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Limit-cycle properties of a Rijke tube
Статья научная
Thermoacoustic instability appears when unsteady heat release is favourably coupled with acoustic pressure perturbations. The important technical applications involving thermoacoustics are combustion instability in rocket motors and low-pollutant lean flames; noisy industrial burners; pulsed combustors; and thermoacoustic engines. The simplest device for studying thermoacoustic instability is a Rijke tube. In this work, a series of experiments is carried out to determine the nonlinear behavior of the transition to instability and the excited regimes for an electrically driven Rijke tube. A hysteresis effect in the stability boundary is observed. A mathematical theory involving heat transfer, acoustics, and thermoacoustic interactions is developed to predict the transition to instability and limit-cycle properties.
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