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Vol 38 No 1

CONTENTS

April 2010


ARTICLES

Analysis and reduction of blade passing noise of the entecho mupod
J. Pan, H.M. Sun, B.S. Walsh, K.D. Do, P. O?Neill and J. Ranasinghe
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A numerical and experimental study of the transmission loss of mufflers used in respiratory medical devices
P. W. Jones and N. J. Kessissoglou
PDF Full Paper

Use of PiP to investigate the effect of a free surface on ground vibration due to underground railways
Simon Jones, Mohammed Hassein and Hugh Hunt
PDF Full Paper

NoteView: A computer program for the analysis of single-line musical performances
D. Gunawan and E. Schubert
PDF Full Paper

Acoustics Forum: What is offensive noise? A case study in NSW
Renzo Tonin & Associates
PDF Full Paper

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Analysis and reduction of blade passing noise of the entecho mupod

Pan1 , J., Sun. H. M., Walsh, B. S., Do, K. D., O?Neill, P. and Ranasinghe, J.
School of Mechanical Engineering, The University of Western Australia, Crawley WA 6009

Vol. 38, No. 1 pp 7 - 12 (2010)
ABSTRACT: Rotor-stator interaction has been identified as the dominant noise source of the Mupod, a vertical take-off and landing aircraft, developed by Entecho, a WA company. This paper reports field measurement results of blade passing noise of the
Mupod together with its analysis and control. The blade passing event was simulated in a wind tunnel experiment. The flow speed, rotor blade position and rotor stator blade spacing were varied while the chord-wise pressure distribution of the leading
surface of the rotor blade was measured by an array of 6 flush mounted microphones. The features of the pressure distribution on the rotor blade influenced by an upstream stator blade were used for the qualitative analysis of the sound radiation from
the Mupod. The result of the reduction of the blade passing noise using angled stator blades is also presented.

A numerical and experimental study of the transmission loss of mufflers used in respiratory medical devices

P. W. Jones and N. J. Kessissoglou
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney NSW 2052, Australia
This e-mail address is being protected from spambots. You need JavaScript enabled to view it , This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 38, No. 1 pp 13 - 19 (2010)
ABSTRACT: Mufflers are incorporated into continuous positive airway pressure (CPAP) devices to reduce noise in the air paths to and from the flow generating fan. The mufflers are very small, irregularly shaped, and are required to attenuate noise up to 10kHz. It is important that the acoustic performance of these mufflers is reliably predicted and optimised, in order to improve the user experience and maximise compliance with the CPAP therapy. In this study, the acoustic performance of three reactive muffler designs similar to those used in CPAP devices is presented. Transmission loss predictions obtained using analytical and finite element methods are compared with experimental data measured using a test rig based on the two-microphone acoustic pulse method. The analytical methods were found to be unsuitable for predicting the transmission loss of CPAP muffler designs due to the complexity of the muffler geometries. Good agreement between the finite element and experimental results were obtained.

Use of PiP to investigate the effect of a free surface on ground vibration due to underground railways

Simon Jones1, Mohammed Hussein2 and Hugh Hunt1
1University of Cambridge, Engineering Department, Trumpington Street, Cambridge CB2 1PZ, UK
2Department of Civil Engineering, University of Nottingham, University Park, Nottingham, NG7 2RD
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Vol. 38, No. 1 pp 20 - 24 (2010)
ABSTRACT: The Pipe-in-Pipe model (PiP) is a quick and accurate tool for calculating vibration from underground railways and for assessing the performance of vibration countermeasures. The original model formulation simulates a tunnel buried in a fullspace but has recently been extended to account for a free-surface (i.e. halfspace). Results from the two versions are compared to quantify the effect of the freesurface on soil power spectral density (PSD) values. The study suggests that it is reasonable to assume the PSD surface results predicted from the free-surface model will be approximately 6dB more than those predicted by the fullspace model when the tunnel is at a depth of two tunnel-diameters or more. For tunnel depths less than two tunnel-diameters it seems beneficial to account for the free surface in the simulation as there is significant variation in the results invalidating the 6dB assumption.

NoteView: A computer program for the analysis of single-line musical performances

D. Gunawan1 and E. Schubert1*
1Empirical Musicology Group, School of English, Media and Performing Arts,
University of New South Wales, NSW 2052, Australia
* This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 38, No. 1 pp 25 - 30 (2010)
ABSTRACT: Newly developed software, NoteView, is used to analyse the fundamental frequency (F0) and categorical as well as microtonal pitch from audio recordings of music performances from a single line (monophonic) instrument. The code is based on the SWIPE algorithm developed by Camacho and Harris. The features of the interface are described and a comparison of two performances of a familiar piece played by a professional French horn player is used as an example for the purpose of investigating the pitch stability of the two renditions. Results produced by NoteView indicate that pitch pairs across the two performances differed by a mean of 7 cents, and that within-note standard deviation was typically 6 cents. These results are examined using the various customisable views and statistics returned by the software. Some of the features and limitations of NoteView are discussed. The software is currently implemented in Matlab and is freely available from the UNSW Empirical Musicology web site http://empa.arts.unsw.edu.au/research-and-creative-practice/research-projects/ empirical-musicology/.

Acoustics Forum: What is offensive noise? A case study in NSW

Renzo Tonin, Renzo Tonin & Associates (NSW) Pty Ltd,
PO Box 877 STRAWBERRY HILLS NSW 2012, This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 38, No. 1 pp 31 - 33 (2010)

 

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