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Vol 32 No 1

CONTENTS

April 2004


ARTICLES

A Novel Approach for Integrated Fault Diagnosis Based on Wavelet Packet transform
S. Zhang, J. Mathew, L. Ma and Y. Sun
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Determining Individual Member Stiffness of Bridge Structures Using a Simple Dynamic Procedure
J. Li, B. Samali and K. Crews
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Crack Detection in Welded Mechanical Structures Using Coupled Vibrations
D. Liu, H. Gurgenci and M. Veldt
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Dynamic Modelling and Applications for Passenger Car Powertrains
A.R. Crowther and N. Zhang
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Identification of Transient Axial Vibration on Double-Suction Pumps During Partial Flow Operation
M.R. Hodklewlcz and Jo Pan
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ACOUSTICS FORUM:

How to Build a 100 Watt Loudspeaker
N. Fletcher
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A NOVEL APPROACH FOR INTEGRATED FAULT DIAGNOSIS BASED ON WAVELET PACKET TRANSFORM

Sheng Zhang, Joseph Mathew, Lin Ma and Yong Sun
School of Mechanical, Manufacturing and Medical Engineering,
Queensland Univesity of Technology, Brisbane, QLD 4001, Australia

Vol. 32, No. 1 pp 5 - 8 (2004)
ABSTRACT: Integrated machine fault diagnosis is usually conducted by considering different types of signals so as to improve the accuracy of diagnosis. This paper presents a novel approach for integrated machine fault diagnosis based on the vibration signals alone. Wavelet packet transform is adopted to analyze the vibration signals, followed by the selection of best bases. We consider each best basis as a local site, then extract features from it and make a local decision using probabilistic neural networks. The local decisions from each best basis are fused to be a global conclusion using a weighted average method. The whole diagnosis process is implemented under a uniform framework. An experimental case shows that this approach improves the accuracy of diagnosis.

DETERMINING INDIVIDUAL MEMBER STIFFNESS OF BRIDGE STRUCTURES USING A SIMPLE DYNAMIC PROCEDURE

Jianchun Li, Bijan Samali and Keith Crews
Centre for Built Infrastructure Research, Faculty of Engineering,
University of Technology, Sydney, NSW, Australia

Vol. 32, No. 1 pp 9 - 12 (2004)
ABSTRACT: A reliable determination of the structural condition of timber bridges presently requires costly load testing. A new dynamic based testing method was developed by authors to reduce the cost and shorten the testing time. The method has been successfully used to undertake field-testing of more than 40 timber bridges across NSW: The dynamic testing procedure involves the attachment of accelerometers underneath the bridge girders. The bridge girders are then excited .by a modal hammer. The method requires tests with and without extra mass, so that the overall flexural stiffness of the bridge can be obtained. However, in order to accurately estimate the load carrying capacity of the bridge, it is necessary to obtain the stiffness values of individual members from test results without complicating the current testing procedure. In this paper, the authors review the dynamic testing procedure and propose a method to determine individual member stiffness for a bridge structure based on the field dynamic testing data. The outcomes of this work not only enable more accurate prediction of the load carrying capacity of the bridge but will also identify defective members of the bridge structure.

CRACK DETECTION IN WELDED MECHANICAL STRUCTURES USING COUPLED VIBRATIONS

D. Liu1,2, H. Gurgenci1,2 and M. Veidt2
1CRCMining, 2436 Moggill Road, Pinjarra Hills, QLD 4069, Australia
2Department of Mechanical Engineering, The University of Queensland, QLD 4072, Australia

Vol. 32, No. 1 pp 13 - 18 (2004)
ABSTRACT: Detection of a fatigue crack in a welded frame structure is studied in this paper using coupled response measurements. Similarity to real engineering structures is maintained in the fabrication of the test frame with hollow section chords and branch members. The fatigue crack was created by a special reciprocating mechanism that generates cyclic stress on a beam member of the structure. The methodology of coupled response measurements is first demonstrated on a single hollow section beam by analytical simulation and experimental validation. The issues of using this approach for fatigue crack detection in real structures are then examined. Finally, the experimental results of the frame under different scenarios are presented. The existence of the crack is clearly observable from the FRF plots. It is suggested that this approach offers the potential to detect cracks in welded frame structures and is a useful tool for routine maintenance work and health assessment

DYNAMIC MODELLING AND APPLICATIONS FOR PASSENGER CAR POWERTRAINS

A.R. Crowther and N. Zhang
Faculty of Engineering, University of Technology, Sydney
PO Box 123 Broadway, NSW 2007, Australia

Vol. 32, No. 1 pp 19 - 24 (2004)
ABSTRACT: Torsional finite elements for direct, geared, branched and grounded connections are presented. For a simple three-degrees-of-freedom powertrain model the finite elements are defined and the global system assembly is detailed. The appropriateness of the finite element method for powertrain systems is illustrated via examples for modelling manual, automatic and continuously variable transmissions. The use of custom elements is discussed for an element for toroid-roller contact and for a two-stage planetary gear set. A test rig is presented and model verification is discussed.

IDENTIFICATION OF TRANSIENT AXIAL VIBRATION ON DOUBLE-SUCTION PUMPS DURING PARTIAL FLOW OPERATION

M.R.Hodkiewicz and J.Pan
School of Mechanical Engineering,
The University of Western Australia, Crawley WA 6009

Vol. 32, No. 1 pp 25 - 32 (2004)
ABSTRACT: The impeller in double-suction pumps is hydraulically balanced in the axial direction due to symmetry in the flow entering the two opposing suction eyes. While an assumption of axial balance is valid at design flow, process plant experience has shown that partial flow operation can result in dynamic axial displacement of the impeller causing mechanical seal and bearing failures. This paper investigates the effects of flow reduction on the axial vibration response of three sets of double-suction pumps and identifies transient axial vibration at partial flow using Short Time Fourier and Discrete Wavelet Transform techniques.

 

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