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Vol 40 No 3

CONTENTS

December 2012


LETTERS

Response to: S. Cooper, Wind farm noise - an ethical dilemma for the Australian Acoustical Society, Acoustics Australia 40(2), 139-142 (2012)
Renzo Tonin
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Response to: S. Cooper, Wind farm noise - an ethical dilemma for the Australian Acoustical Society, Acoustics Australia 40(2), 139-142 (2012)
Timothy Marks, Christophe Delaire, Justin Adcock and Daniel Griffin
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Response to: S. Cooper, Wind farm noise - an ethical dilemma for the Australian Acoustical Society, Acoustics Australia 40(2), 139-142 (2012)
Kym Burgemeister
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PAPERS

Reduction of flow induced airfoil tonal noise using leading edge sinusoidal modifications
Kristy Hansen, Richard Kelso and Con Doolan
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Modelling of pile driving noise by means of wavenumber integration
Tristan Lippert and Stephan Lippert
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The vibrations of bubbles and balloons
Kirsty A. Kuo and Hugh E.M. Hunt
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The sound of music: Order from complexity
Neville H. Fletcher
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Design of Helmholtz resonators in one and two degrees of freedom for noise attenuation in pipelines
S. Mekid and M. Farooqui
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Vibration field of a double-leaf plate with random parameter functions
Hyuck Chung
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TECHNICAL NOTES

Adding noise to quiet electric and hybrid vehicles: An electric issue
Ulf Sandberg
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Acoustical impacts of future generation road vehicles
Matthew Stead, Adrian White and Deb James
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NEWS

News
New Products
Meeting Reports
Future Conference
Diary
Sustaining Members
Advertisers Index


Reduction of flow induced airfoil tonal noise using leading edge sinusoidal modifications

Kristy Hansen, Richard Kelso and Con Doolan
School of Mechanical Engineering, University of Adelaide, Adelaide, Australia This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 40, No. 3 pp 172 - 177 (2012)
ABSTRACT: Significant tonal noise reduction has been achieved using sinusoidal protuberances, also known as tubercles, on the leading edge of a NACA 0021 airfoil for a Reynolds number, Re ~ 120,000. It has also been observed that the overall broadband noise is reduced for a considerable range of frequencies surrounding the peak in tonal noise. It is postulated that tonal noise elimination is facilitated by the presence of streamwise vortices generated by the tubercles and that the spanwise variation in separation location is also an important factor. Both characteristics modify the boundary layer stability, altering the frequency of velocity fluctuations in the shear layer near the trailing edge. This affects the coherence of the vortex generation downstream of the trailing edge, hence leading to a decrease in trailing edge noise generation. An additional effect is the confinement of the suction surface separation bubble to the troughs between tubercles, which may reduce the boundary layer receptivity to external acoustic excitation. Investigations have also revealed that the smallest wavelength and largest amplitude tubercle configuration have the lowest associated tonal and broadband noise.

Modelling of pile driving noise by means of wavenumber integration

Tristan Lippert and Stephan Lippert
Institute of Modelling and Computation, Hamburg University of Technology, Germany This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 40, No. 3 pp 178 - 182 (2012)
ABSTRACT: A method for the acoustic simulation of pile driving is presented using the wavenumber integration (WI) approach, in combination with a recently suggested array of point sources, to represent the pile. The fundamentals of the WI are briefly discussed, as are the main acoustic characteristics of pile driving. A reference finite element model is set up to demonstrate these main features and is further compared to a literature example, to ensure its validity. Subsequently, the obtained results are compared to the solutions from WI simulations on the same example. The results are found to be in excellent qualitative agreement, therefore the WI technique seems to be very promising with respect to the acoustic long range prediction in pile driving.

The vibrations of bubbles and balloons

Kirsty A. Kuo and Hugh E.M. Hunt
Faculty of Engineering, University of Cambridge, Trumpington St., Cambridge CB2 1PZ, UK This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 40, No. 3 pp 183 - 187 (2012)
ABSTRACT: Bubbles and balloons are two examples of structures that feature a pressure difference across the skin, a thin, tensioned membrane, and a doubly curved interface surface. While mathematical models have been formulated for bubble vibrations, no such model exists for balloon vibrations. This paper reviews a model of bubble vibrations, and compares its predicted natural frequencies and modeshapes to those of a rubber balloon. It is shown that the bubble model consistently underpredicts the balloon?s natural frequencies, and it is concluded that the nonlinear elasticity present in the balloon skin accounts for this result.

The sound of music: Order from complexity

Neville H. Fletcher
Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200 This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 40, No. 3 pp 188 - 193 (2012)
ABSTRACT: Musical and biological sounds have the property of being well organised and usually strictly harmonic in spectrum, though there are a few notable exceptions such as the shimmering crash of a cymbal or the cry of the sulphur-crested cockatoo. It turns out, however, that this apparent simplicity is constructed by the interaction of highly nonlinear feedback generators linked to resonators whose vibrational modes are not in simple harmonic frequency ratios. This paper explores the way in which this apparent simplicity emerges from complex interactions in the generation of instrumental sound and in the songs of humans and other animals.

Design of Helmholtz resonators in one and two degrees of freedom for noise attenuation in pipelines

S. Mekid and M. Farooqui
King Fahd University of Petroleum and Minerals, Department of Mechanical Engineering, Dhahran, 31261, Saudi Arabia 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. 40, No. 3 pp 194 - 202 (2012)

ABSTRACT: A thorough design methodology of one and two degrees of freedom Helmholtz resonators leading to optimised transmission loss is described and validated in this paper. Numerical simulations of acoustic wave propagation in pipelines fitted with designed resonators have shown great agreement with analytical modelling and experimental tests. The Helmholtz resonator concept has been analysed in various configurations to evaluate the effect of the size and arrays on the overall noise attenuation performance. Using this method to directly dimension geometry aspects of the resonators followed by numerical computation of the sound pressure levels has shown that considerable sound attenuation could be achieved.

Vibration field of a double-leaf plate with random parameter functions

Hyuck Chung
School of Computing and Mathematical Sciences, Auckland University of Technology, PB 92006, Auckland, New Zealand This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 40, No. 3 pp 203 - 210 (2012)
ABSTRACT: This paper shows how to compute vibrations of a double-leaf plate with random inhomogeneities in its components. The components are two plates and reinforcement beams. The modelling method is based on the variational principle for elastic plates and beams. In addition to the deformation of individual components, the model includes contributions from junctions between components, e.g., rigidly of the connection between a beam and a plate. The model does not restrict the junctions to be perfectly straight. The beams are allowed to have a small random twist. The junction rigidity is included as potential energy in addition to the strain and the kinetic energies of the components. The random inhomogeneities are simulated as continuous smooth random functions. A random function is realized using a predetermined probability density function and a power spectral density function. The vibration is then computed from a set of random functions. The numerical simulations show that the random stiffness affects the behaviour of the structure in a wide frequency range. Whereas the junctions affect the a lower frequency vibrations. The root-mean-square velocity of surface vibration level shows changes at resonance frequencies depending on the random functions.

Adding noise to quiet electric and hybrid vehicles: An electric issue

Ulf Sandberg
Swedish National Road and Transport Research Institute (Vti), Linkoping, Sweden This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 40, No. 3 pp 211 - 220 (2012)
ABSTRACT: It has been suggested that hybrid and all-electric automobiles are so quiet at low speed in electric drive that they constitute a safety hazard for pedestrians and bicyclists. This trait has been especially troubling to vision-impaired people who rely on sound cues to avoid approaching vehicles. Assumptions have been made linking the quietness of such vehicles with fatalities and serious injuries. The U.S. Pedestrian Safety Enhancement Act of 2010, requires the use of Audible Vehicle Alerting Systems (AVAS) in hybrid and all electric vehicles. Rules are now being developed and are expected to be issued by January 2014. Similar regulations are being promulgated in Japan and the European Union. The UN/ECE is developing a Global Technical Regulation after extensive preparatory work. SAE International and ISO are developing a method of measuring the lowest accepted noise level for vehicles. This article first notes firm evidence that the noise difference between electric-driven and internal combustion engine (ICE) vehicles exists only at speeds below about 20 km/h; also that AVAS makes vehicles traveling at low speeds detectable from a longer distance, absent masking background noise. Some electric and hybrid cars on the market already have AVAS installed. The author explores the assumptions related to the problem in regard to traffic safety and the harmful effects of noise on humans. One statistical study from the United States seems to suggest that vehicles driven in electric mode cause relatively more accidents involving pedestrians than do ICE vehicles. However, multiple studies in the U.S., Japan and Europe leave this causal relationship unconfirmed. The author then shows that quiet vehicles, very hard to hear when approaching at low speeds, existed in urban traffic already many years before hybrid cars became common, and if quietness would create accidents this should have been apparent already earlier and not be something occurring only when hybrid and electric cars entered the market. A number of non-acoustical ways to alert pedestrians, not the least blind people, of quiet vehicles near them are discussed and suggested in the article. The article also describes the intensive work to explore the problem as well as to develop and specify AVAS systems that has been made from 2008 until now. The author argues that it would be more beneficial to human health and safety to reduce the maximum noise of vehicles rather than increasing the minimum noise of them. Consequently, the article ends with the recommendation to discontinue the work with AVAS, to limit rather than require the use of such systems, and instead focus on limitation of the worst masking noise emissions in urban areas.

Acoustical impacts of future generation road vehicles

Matthew Stead, Adrian White and Deb James
Resonate Acoustics, Australia This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 40, No. 3 pp 221 - 224 (2012)
ABSTRACT: Future generation transportation has inherently lower noise emissions which are driven by changes to regulation, improved technology and because of consumer expectations. Lower noise emissions will have an impact on infrastructure projects in terms of reduced capital costs and also improved amenity for the communities surrounding the infrastructure. It has been found that hybrid and electric vehicles will have the greatest impact on lower speed roads (80 km/hr or less) and only marginal impact for 100 km/r roads because tyre noise is the dominant source rather than propulsion noise at this speed. Results of these findings for major road infrastructure routes are presented for consideration by authorities, designers and contractors.

 

Newsflash

PROPOSED INTERNATIONAL YEAR OF SOUND 2019

Let's make 2019 the International Year of Sound!

Click here to see draft prospectus. Suggestions for major activities that would be truly international to strengthen the application are welcomed.

 

ACOUSTICS 2017

Perth, Western Australia 19-22 November 2017