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Published Articles

The Volume 11, No 1, March 2006

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Dynamic Characteristics of a Cantilever Beam with Transverse Cracks

R. K. Behera, D. R. K. Parhi, S. K. Sahu


It has long been observed that the dynamic response of a structure changes due to the presence of a crack. Scientific analysis of such phenomena can be utilised for fault diagnosis and the detection of cracks in structures. The present investigation is an attempt in that direction. Theoretical expressions have been developed in order to determine the natural frequencies and mode shapes for an elastic cantilever beam with two cracks using flexibility influence coefficients and a local stiffness matrix. The numerical results for the beams without cracks, with one crack, and with two cracks are compared. It has been observed from the numerical results that there are appreciable changes in the vibration characteristics of the cantilever beam with and without cracks. This method can be utilised for multi crack identification of structures.

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Analysis of Multiple-duct Variable Area Perforated Tube Resonators

T. Kar, P. P. R. Sharma and M. L. Munjal


Conical concentric tube resonators are often used in commercial automotive mufflers. These are characterised by wave-coupling phenomenon across interacting ducts. Using a one-dimensional control volume approach, a mathematical model is presented for a generalised configuration of variable area perforated tube resonators. The analysis is applied to different configurations that account for waves in the incompressible mean flow and in the acoustic coupling between the interacting ducts due to the admittance of the intervening perforates. The problem has been solved by means of the Peano-Baker's series of matrix calculus, and the transmission loss results have been outlined. The predictions have been validated against the three-dimensional finite element analysis.

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On Some Recent Advances in Aeroacoustics

Luis Manuel Braga da Costa Campos


A brief survey of the current status of aeroacoustics is used to identify eight aeronautical problems of concern needing attention: 1) acoustic fatigue of structural panels due to high-intensity noise (150 dB plus); 2) active cancellation of discrete tones in aircraft cabins; 3) estimation of the directivity and spectrum of jet noise; 4) noise radiation from a propellers; 5) influence of blade-vortex interaction on the noise of helicopter rotors; 6) noise due to the turbulent boundary layer over aircraft cabins; 7) sound attenuation in jet engine ducts by acoustical liners with non-uniform impedance; and 8) shielding of engine noise by aircraft structures, e.g. wings or fuselages. The motivation to study each problem is explained, followed by the formulation of a model, an outline of the solution and an illustration of results, often in comparison with experimental results from projects conducted in cooperation with the aeronautical industry. It is concluded that aeroacoustics has been, and is likely to remain an area of intensive research as air transport grows and environmental concerns give rise to an increasing impetus for new solutions to noise issues.

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