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Published Articles

The Volume 9, No 4, December 2004

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Gradient Optimisation Methods for the Positioning of Active Noise Control Actuators in Enclosures

G.N. Charalampopoulos, S.T. Mouzakitis and C.G. Provatidis


This paper discusses the problem of finding the optimum locations and strengths of a number of secondary sources in an interior active noise control problem. The analysis of the acoustic field is performed using the finite element method, while the positions and strengths of the secondary sources are determined by various optimisation schemes. These schemes are compared to each other in terms of computational effort and efficient prediction of the global optimum when tested in two-dimensional rectangular cavities. The results indicate that a new optimisation method, based on the combination of evolution and deterministic Newton methodology, is best used for this type of problem in most cases.

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Optimisation of Constrained Multi-layer Absorbers by Using Genetic Algorithms

Ying-Chun Chang, Long-Jyi Yeh and Min-Chie Chiu


For maintenance and access purposes, it is necessary to minimise the thickness of a sound absorption control system. In this paper, the maximal sound absorption under space constraints is studied. The genetic algorithm (GA) is adopted as the optimiser, and the GA searching technique is presented. Case studies of optimisations on normal incidence sound absorption with respect to three kinds of sound absorbers (single-layer, double-layer, and triple-layer) at the pure tone of 350 Hz under a fixed thickness are introduced. The optimised parameters include 1) absorbing material; 2) diameters of holes on the perforated plates; 3) perforated ratios of the perforated plates; and 4) the flow resistivities of the absorbing materials. Before optimisation, the accuracy of a single-layer absorber mathematical model is tested. Thereafter, the optimisations of three kinds of sound absorbers with one to three layers are exemplified. Consequently, results reveal that the sound absorption at the desired frequency is almost maximised. The more layers there are in the sound absorber, the higher the broadband. The optimal design of a multi-layer sound absorbers system proposed in this study can provide a quick and efficient approach (without redundant testing).

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A Theoretical Study of Convergence Characteristics of a Multiple Channel ANC System

Guoyue Chen, Kenji Muto


Most active noise control (ANC) systems are based on feedforward structure with adaptive filters, which are updated with the filtered-x LMS algorithm or the multiple error filtered-x (MEFX) LMS algorithm. The convergence characteristics of these algorithms have been studied mostly in the time domain, and it was found that the convergence properties are subject to the distribution of the eigenvalues of the autocorrelation matrix of the filtered reference signal. Analysis in the time domain, however, requires a great deal of computation, and its physical meaning is unclear. This paper presents a method for evaluating the adaptive algorithm for the ANC system with multiple noise sources and multiple control points in the frequency domain. In this method, the convergence characteristics of the MEFX LMS algorithm are evaluated separately by the determinant or eigenvalues of the matrix, which are composed of transfer functions between the secondary sources and the control points, and the correlations among the outputs of the reference sensors.

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Dynamic Characteristics of a Four-Bar Linkage with a Composite Coupler

Raghu Echempati


Most modern machinery and automated industrial mechanical equipment operates at high speeds to attain high productivity. Damping plays a prominent role in controlling vibration in structural members of these mechanical systems. Depending upon the specific application and the type of desired dynamic properties, different engineering materials with improved vibrational and damping characteristics are being used by many researchers and by several industrial manufacturers. A four-bar mechanism is one such application that must have the basic characteristics, such as low inertia, high strength, and stiffness, to enable smooth power transmission without excessive vibrations and deflections. In order to study the overall dynamic performance of four bar mechanisms, in this research, it is proposed that the isotropic metal members be replaced by composite materials. The work presented in this paper deals with an experimental study of the dynamic response of the coupler link of four-bar linkage mechanisms fabricated from different hybrid glass-graphite/epoxy pultruded composite beams. The response characteristics include the determination of midpoint strain, the system damping, and the fundamental frequency of the couplers. These characteristics are compared with coupler links made out of steel and aluminum. This study is very useful in exploring whether pultruded composites can potentially be used in high-speed industrial mechanism devices.

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