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Published Articles

The Volume 6, No 1, March 2001

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Adaptive IIR Filters for Active Noise Control

C. Mosquera, J.A. Gomez, F. Perez, M. Sobreira and E. Alexandre


This work is concerned with the performance of adaptive filters with both poles and zeros in active noise control (ANC) applications. This filtered-error type of application makes it necessary to modify classical adaptive algorithms to cancel the noise. A well established theory exists for filtered-error adaptive FIR filters, especially for the FxLMS algorithm. However, when it comes to filtered-error adaptive IIR (Infinite Impulse Response) filters, convergence conditions are not so well understood. IIR filters are specially suited to those scenarios where feedback from the cancelling loudspeaker to the primary source presents high values, and the performance of the cancellation with a fixed filter is not as good as desired. In this work we present the study of the convergence of a family of adaptive IIR algorithms appropriately modified for handling filtered-error situations. Some results based on real measurements are also presented.

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Subjective Response to Environmental Noise of Locomotives in the UK

A.E.J. Hardy and R.R.K. Jones


The environmental noise characteristics of locomotives are significantly different from those of railway coaches, particularly at low speeds. This difference is primarily due to the presence of exhaust and engine carcass noise in the case of diesel locomotives, and cooling fan noise for both diesel and electric locomotives. As a result, simple indices alone, such as the A-weighted sound level, are not always adequate for the quantification of noise from these vehicles, either for the purposes of specification or for environmental impact assessment. The paper presents the results of listening tests for locomotives, and discusses potential indices for the quantification of subjective response to them. Reference is made to a diesel locomotive that is known to be subjectively quiet due to careful design. The specification approach adopted for this locomotive is discussed, together with improvements that might be made to similar specifications in the future.

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Characterisation of Transient Behaviours in Rotordynamic Vibrations from Experimental Data Using Harmonic Wavelets

Valeta Carol Chancey, George T. Flowers and Candice L. Howard


Wavelets are versatile tools for the analysis of vibration signals. Wavelet-based methods are especially valuable for the analysis of vibrations that are not steady state. However, it is sometimes difficult to extract physically relevant patterns from the great wealth of information contained in the wavelet decomposition of a vibration signal. By examining the absolute values of harmonic wavelet coefficients, the application of harmonic wavelets to the vibration analysis of rotating machinery is explored. The basics of the strategy are explained. Example experimental data collected from a bench-top test rig with a journal bearing exhibiting oil whirl was analysed to illustrate the proposed methods.

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An Effective and Portable Electronic Stethoscope for Fault Diagnosis by Analysing Machine Running Sound Directly

Peter W. Tse, Guang H. Xu, Liangsheng Qu, Soundar R. Kumara


Machine sound is a typical kind of non-stationary signal which carries information regarding the operating conditions of the machine. In the past, human ears have been used for detecting any abnormality occurring in a machine as this method is simple and fast. However, the audible range of human hearing is broadband and has a low signal-to-noise ratio, making the method inefficient. The invention of the Fast Fourier Transform (FFT) for vibration-based machine fault diagnosis has helped to increase the efficiency of diagnosis. However, FFT fails to detect the transitory characteristics of signals that are fault-related. Moreover, the cost of a FFT based analyser is expensive and the accessibility of a wired transducer is limited. Therefore, we are proposing the use of the hearing method again ? not with a pair of human ears, but with an electronic stethoscope. We use Continuous Wavelet Transforms (CWT) to remove the noise from raw machine running sound signals and to detect nonstationary impulses generated from the impacts of defective components. The method of Trajectory Parallel Measure (TPM) is then used for fault detection and classification. From the results of the tests on a number of similar types of gas engines, the concept of the electronic stethoscope has been found to be feasible and promising. This electronic stethoscope uses CWT and TPM to diagnose faults by analysing the machine running sound directly.

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Active Attenuation of Sound Radiation from a Circular Fluid-Loaded Plate

Lucyna Leniowska, Ryszard Leniowski


This paper is concerned with the problem of suppressing the far-field sound pressure radiating from a circular plate located in a finite baffle and which interacts with a fluid. The sound field is reduced by applying a control force directly at a point on the plate surface. For the system under consideration a state - space model is constructed. The optimal control problem is solved by including an additional term in the performance which is proportional to the squared farfield sound pressure radiated, in addition to the customary two terms which depend on the vector of state variables and on the control effort. The control input that minimises this performance is derived by applying Hamiltons principle.

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