Full PaperArup, Manchester, UK
ABSTRACT
This paper provides a state of the art review of the assessment of construction groundborne noise and vibration im-pacts that arise from subsurface works, which need to be identified and addressed in the planning, design and con-struction of tunnels. Through a review of published information and description of recent project-specific research, methods of prediction, assessment, measurement and mitigation of these impacts are described. The significance of any effects arising from these impacts is dependent upon the overlying receptors. Assessment for facilities ranging from nanotechnology to human comfort and building damage are considered, including recent work to establish ac-ceptability criteria for construction works taking place adjacent to existing subway tunnels. The need to specify mon-itoring equipment correctly is discussed. Options for mitigating the effects of construction vibration are described.
Woods Hole Oceanographic Institution, Woods Hole, MA 02543 USA
ABSTRACT
In this paper, we review some recent new results in shallow, coastal waters from both ocean acoustics (the study of how sound propagates and scatters in the ocean) and acoustical oceanography (the study of ocean processes using acoustics as a tool).
Institute of Sound and Vibration Research, University of Southampton, Highfield, Southampton SO17 1BJ, UK
ABSTRACT
The main source of noise from railway operations is associated with the wheel/rail contact. It is now widely estab-lished that railway rolling noise is caused by the "roughness" of the wheel and rail running surfaces; this roughness induces vibration of both wheel and track and the vibration radiates sound. A review is presented of the theoretical modelling that has led to this conclusion, following which the implications of this for noise control as well as for leg-islation are discussed. Legal limits for the noise emission from road vehicles and aircraft have been in force for many years. By contrast the noise emission from rail vehicles has only recently been subject to legal limits, introduced in Europe through the Technical Specifications for Interoperability. This has been facilitated by the theoretical knowledge embodied in models of rolling noise. Finally, the scope for using "virtual testing" based on calculations to partially replace costly field tests is discussed.
(1) Arup Acoustics, Melbourne (2) Arup Advanced Technical Group, Sydney
ABSTRACT
Heavy mechanised construction works, for example, excavation, piling and vibratory compaction cause groundborne vibration due to the interaction of the machines with the ground. This construction vibration can be perceptible to humans, often adversely impacts on sensitive receivers located very close to the construction site and in extreme cases may cause structural damage to nearby buildings. An assessment of construction vibration impacts is therefore usually restricted to sites directly adjacent to construction sites. However, laboratory buildings for nano-science, electronics lithography, high-magnification electron microscopy or imaging are significantly more sensitive to vibration than conventional commercial or residential buildings. A theoretical analysis indicates that it is possible that construction vibration from particular machinery could exceed the usual sensitive laboratory vibration velocity limits (eg VC-E, 0.3 micrometers/s) at distances up to 100-150 m from the construction site. This could necessitate the implementation of restrictive limitations on construction sites at relatively large distances from laboratory buildings to avoid adverse impacts on vibration sensitive equipment and processes. In this study, predictions of vibration from typical heavy construction works at long distance using both geometric spreading and frequency dependant attenuation models. The results of the predictions are compared to long-distance vibration velocity measurements undertaken on typical development sites due to the operation of bored piling and vibratory compaction equipment. The measurement results show good agreement with the empirical predictions, and show that vibration from heavy construction works can be expected to exceed VC-E at distances of 100-150m from the construction site.
Water and Environment, SKM, Brisbane, Australia
ABSTRACT
This paper considers what is practical in managing construction noise by presenting results from noise monitoring conducted for the construction of Hinze Dam Stage 3 in Advancetown, Australia. A continuous noise monitoring program was used to compare construction noise levels to project day time noise limits of Leq,1hour 58 dB(A), and L1,10min 63 dB(A). Both statistical indicators and sound recordings were used to analyse and identify construction related exceedances on a weekly basis. No official noise complaints were received with regards to project construction activities. However, construction activities did result in exceedances of noise limits and twenty four noise related enquiries were addressed by the Hinze Dam Alliance from 2007 to May 2011. There is currently little formal guidance on noise limits for construction. Given the expectation large infrastructure projects will continue to be developed in Queensland it is recommended we develop a suitable set of noise goals that are practical to implement and protect the noise amenity of the community.
Professional Services Division, RailCorp, George Street Burwood, NSW
ABSTRACT
Construction works can cause significant noise and vibration impacts if not managed properly. Often a lack of project information at the environmental assessment (pre-approval) stage leads to generalised statements about noise and vibration impact and lists of standard management practices. Generalised statements can greatly hinder an understanding about expected noise impacts and lists of standard management practices can make it appear that no further consideration of noise management is needed. Many construction noise impact statements focus on quantifying the expected construction noise levels, however few follow this with a clearly documented examination of what feasible and reasonable practices will be applied to manage the identified impacts. This paper presents two case studies based on real life construction projects. The first case study illustrates what can happen on a medium-sized construction project in an urban area without a noise management plan in place, and to also outline what can be the key features of a noise management plan. The second case study outlines how a clear and concise construction noise management plan prepared during the post-approval stage can greatly assist in communicating to the project team, regulator and the community what are the identified noise impacts and how will they be managed. Also discussed is an 'impacted zone' approach for large and complex projects to precisely understand the extent and location of noise impacts.
Urban Research Program, Griffith School of Environment, Griffith University, Brisbane, Australia
ABSTRACT
Noise generated by surface and air transport is routinely considered in EIA of transport projects. Sophisticated tools are utilised in prediction, noise mitigation, and assessment of noise impacts. These estimate human annoyance - even though there is a well-documented range of health effects of transport noise beyond annoyance. Focus on "annoyance" alone has had two important consequences. Firstly, it tends to have little traction with decision-makers. Secondly, despite the availability of assessment tools at the project level, there has been little consideration of transport noise at strategic levels. The extent of annoyance is a useful criterion in choosing between alternative highway routes at the project level, but not to assess impact of, say, area-wide transport options. This has now changed. Accumulated evidence regarding health effects of environmental noise has been published by the WHO Regional Office for Europe as initial guidance for quantitative risk assessment of environmental noise—based on Environmental Burden of Disease (EBD) methodology and the metric Disability-Adjusted Life Years (DALY). Synthesized reviews of health effects of environmental noise (cardiovascular disease, cognitive impairment, sleep disturbance, annoyance, hearing impairment and tinnitus), and exemplary estimates of the burden of its health outcomes now allow for inclusion of transportation noise in quantitative Heath Impact Assessments at aggregated strategic levels—in regional or national transport planning, and in assessment of policy options such as road pricing, land use planning, energy costs, modal shifts etc. that can influence the exposure of populations to transport noise at strategic levels
(1) Leibniz Research Centre for Working Environment and Human Factors, Ardeystr. 67, 44139 Dortmund, Germany (2) Unit for Experimental Psychiatry, Division of Sleep and Chronobiology, University of Pennsylvania School of Medicine, 1013 Blockley Hall, 423 Guardian Drive, Philadelphia, PA, USA
ABSTRACT
This paper deals with noise-induced sleep disturbances that are regarded as the most deleterious effects of noise with aftereffects on mood and performance the next day. In the long run noise-induced sleep disturbances are assumed to contribute to the genesis and manifestation of multifactorial diseases. The paper gives a rough overview over the state of the art and of the possibility to prevent or at least to reduce these effects and oulines eventually future research in this area.
(1) Faculty of Architecture, Design and Planning, The University of Sydney
ABSTRACT
Room impulse responses (RIRs) are very commonly used to represent the acoustic response of rooms for the derivation of acoustical parameters and for auralization. This paper presents a set of signal processing techniques that can be used to enhance the usefulness of recorded RIRs for convolution-based room simulations (which could be classed as a type of auralization), which include using the noise floor to extend the decay, and manipulating the RIR to represent arbitrarily different yet plausible room conditions. The paper also considers how the manipulation of the decay slope can be used to make other features of RIRs more audible, which could have applications in RIR sonification.
Faculty of Architecture, Design and Planning, The University of Sydney, NSW 2006, Australia
ABSTRACT
Predicting the diffuseness of a sound field in a small room through theoretical modelling is a task currently receiving much attention. The emphasis of such work has been upon establishing a relationship between the measurable proper-ties of diffusing surfaces and their effects on the sound field they contain. Although several theoretical perspectives have been taken on this problem, one currently popular theoretical model lends itself to rigorous testing using sets of room acoustic measurements made in rooms allowing variable diffusion treatments. This is the focus of the work pre-sented in this paper. It is proposed here that the success of theoretical modelling for room acoustics is best evaluated using such diffuseness measurements, as they provide the opportunity to test predictions in real world case studies.
Faculty of Architecture, Design and Planning, University of Sydney, NSW 2006, Australia
ABSTRACT
When a visual stimulus is not present, the room reflected sound from one's own voice has been shown to be an important cue in determining the characteristics of rooms. The room reflected sound can vary with interaural changes that are sometimes accompanied with head movements. Such head movements, when incorporated in room acoustical simulations, are expected to increase the level of "presence" within simulations. But whether this headtracking is detectable by talking-listeners hearing a room's response to the projection of their own voice has not been studied. In this pilot study, five participants performed ABX headtracking detection test by projecting their voice in six real rooms that were simulated in real-time, with an accurate binaural reproduction of room reflections. The results indicate that headtracking is detectable for the rooms tested, which ranged in volume from 125 m^3 to 7650 m^3, after equalizing for Type 1 and Type 2 errors. Most consistent detection was noticed in a room with the highest early IACC.
(1) Maritime Platforms Division, Defence Science and Technology Organisation, Fishermans Bend VIC 3207, Australia. (2) School of Mechanical Engineering, The University of New South Wales, Sydney NSW 2052, Australia.
ABSTRACT
A resonance changer is a device which may be installed in the propulsion system of a marine vessel to reduce the axial vibration transmission from the propeller to the hull. This device is a hydraulic system incorporated in the thrust bearing, which operates analogously to a Helmholtz resonator. Previous work by the authors has examined optimisation of the resonance changer parameters to reduce the acoustic signature of maritime platforms. In those studies, prediction of the low frequency axisymmetric structure-borne noise was carried out using both analytical and fully coupled finite-element/boundary-element models. This paper further develops the analytical model, by including a description of the propeller radiation and its coupling with the hull. The sound power is expressed as the combination of sound radiation from the hull and the direct dipole sound radiation from the propeller. Results calculated from both models are presented for comparison and discussed.
School of Mechanical Engineering, The University of Adelaide, Adelaide, S.A. Australia
ABSTRACT
An adaptive-passive quarter-wave tube resonator silencer was experimentally tested using recorded in-duct recipro-cating engine exhaust noise. The exhaust noise was re-played through a loudspeaker attached to one end of a duct, and the adaptive passive system was able to track changes in engine speed and provide attenuation of the noise at the fundamental firing frequency of the engine and the third harmonic. The control system used a novel method of de-termining the phase angle of the transfer function between the pressure in the quarter wave tube and the main duct by using a sliding-Goertzel algorithm to calculate the Fourier coefficients.
School of Mechanical and Manufacturing Engineering, The University of New South Wales, NSW 2052
ABSTRACT
Computational optimisation techniques are applied to maximise the acoustic performance of mufflers used in sleep apnoea devices. The mufflers are small and irregularly shaped, and as such their compact nature introduces complexities in the optimisation problem. A continuous positive airway pressure (CPAP) muffler comprising three inter-connected chambers was examined, with and without the presence of foam. The optimisation process involved development of an integrated model to couple the genetic algorithm function within Matlab with an acoustic finite element model of the muffler, with an objective to minimise the transmission loss of the muffler. Optimisation of the geometry of the CPAP muffler in the absence of foam was initially performed. The inclusion of foam was then considered and optimisation of the foam dimensions at various frequency ranges was conducted. Results are compared with the transmission loss of the CPAP muffler for which the reactive and resistive components were simultaneously optimised.
School of Mechanical Engineering, University of Western Australia
ABSTRACT
Vibration analysis has been applied to power transformer condition monitoring in the last few decades. It uses the characteristic vibration of the transformer to detect and diagnose transformer failures. Because the winding insulation paper degradation is a very common and serious power transformer failure, this paper is concerned with the effect of ageing of winding insulation paper on the vibration of a simplified "winding model", comprising a single layer of concentric circular rings wrapped with insulation paper. The insulation paper undertakes high thermal and electrical pressure in an operational transformer, and the average molecular of cellulose chains decreases with age which causes both the insulation abilities and mechanical strength of the paper degrade. By testing the vibration of the concentric rings with different ageing papers, it is found that the natural frequencies of the rings shift to low frequency end when the mechanical strength of the paper decreases. A mechanical model of the rings with paper is provided here to identify the relationship between the paper mechanical properties with their corresponding vibrations. Based on the work reported in this paper, it is believed that the ageing extent of winding insulation paper can be detected by monitoring the vibration of the winding.
School of Mechanical Engineering, University of Adelaide, SA, Australia
ABSTRACT
In the sport of archery, recent developments in materials technology have seen the introduction of carbon-fibre aluminium composite arrows. Archery performance has been shown to be dependent on the vibrational behaviour of arrows (including the natural frequencies and mode shapes). This paper investigates the vibration of composite archery arrows through analytical and finite element modelling. Computer models used in this paper employ modal analysis to identify the significant modes of vibration. Results from the numerical simulations are also compared to experimental measurements using a Polytec scanning laser Doppler vibrometer (PSV-400). Experiments use both mechanically and acoustically coupled vibration actuators to vibrate the composite arrow structure. Evaluation of the modal behaviour shows good agreement between the theoretical models and the experiments.
(1) School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, Australia (2) Palmer Technologies Pty Ltd, Newstead, Australia
ABSTRACT
Spectral Analysis of Surface Waves (SASW) is a widely used and accepted method in Geotechnical and Civil Engineering applications for estimating material properties in layered structures based on the dispersion characteristics of surface waves. This project aims to extend existing half space theory to analyse layered structures of finite depth. The excitation frequency and signal analysis need to be adapted and optimised to suit the physical properties of the layered structures and associated wave interactions from the layer interfaces. The material properties of the layered substructure can be estimated by evaluating the Rayleigh Wave dispersion characteristics as a function of frequency. Layer thicknesses and the structural integrity of the samples being tested can be interpreted from the averaged disper
Gippsland School of Information Technology, Monash University, Melbourne, Australia
ABSTRACT
One of the prevalent issues in condition based maintenance (CBM) is to predict the residual life of the equipment. This paper propos-es a novel framework to predict the remnant life of the equipment, called Residual life prediction based on optimally parameterized Wavelet transform and Mute-step Support vector regression (RWMS). In optimally parameterized wavelet transform, a generalized criterion is proposed to select the wavelet decomposition level which works for all the applications and decomposition nodes are selected by characterizing their dominancy level based upon relative fault signature-signal energy contents. The prediction model is based on multi-step support vector regression (MSVR) and prediction accuracy is improved in comparison with the techniques based on support vector regression (SVR). Performance of RWMS is evaluated in terms of Root Means Square Error (RMSE), studies show that proposed algorithm predicts the residual life of the equipment accurately.
(1) Faculty of Architecture, Design and Planning, The University of Sydney, NSW 2006, Australia (2) Faculty of Arts, The University of Sydney, NSW 2006, Australia
ABSTRACT
The messa di voce (MDV) is a vocal exercise used by singers, consisting of a crescendo and decrescendo on a single sustained note. In this study we analysed recorded MDVs sung by tertiary singing students to examine the extent to which MDVs have a linear crescendo and linear decrescendo. The MDVs studied were recorded over a 3-year period, as a cohort of classical singing students progressed through their tertiary education and training. Previous studies of MDV envelopes have examined the envelopes in decibels, but in the present study we use envelopes derived from a dynamic loudness model. We did not find an overall tendency for increased linearity as students mature.
School of Physics, University of New South Wales, Sydney NSW 2052, Australia
ABSTRACT
Traditional didjeridus have a broad range of unknown bore geometries, and consequently have advantages for examining relationships between subjective and physical parameters. This study involved 7 experienced players assessing each of 38 traditionally made didjeridus in terms of 8 subjective parameters. Their assessments were then correlated with detailed measurements of acoustic input impedance spectra and geometry. There was a small, but useful, consistency in the rankings of the 7 players, although it was surprising that backpressure was the least consistent term, because this term is widely used by both didjeridu and brass players. A high degree of positive correlation existed between most of the parameters (clarity, resonance, loudness, vocals, overtones and overall quality). The other two parameters studied (backpressure and speed) were correlated with each other, although not significantly correlated with the other parameters. The parameters clarity, resonance and backpressure made the most important contributions to the overall quality of an instrument. In general there was a strong negative correlation with the characteristic impedance of the instrument for overtones, vocals, resonance, loudness and overall quality. The parameter speed was found to be positively correlated with the frequency of the first (or lowest) frequency resonance. Assessments of PVC pipes were consistent with these results. The overwhelming preference of the assessors was for instruments with a low magnitude of impedance across the spectrum particularly in the 1 to 2 kHz region; a feature that allows time-varying resonances of a player's vocal tract to have a dominant influence over the spectral envelope of the sound
(1) School of Physics, University of New South Wales, Sydney NSW 2052, Australia (2) CNRS GIPSA Lab, Grenoble, France
ABSTRACT
The wide range of the singing voice, from below C2 (65 Hz) to above F6 (1397 Hz), requires a number of strategies that can involve different mechanisms of laryngeal vibration and various adjustments of the vocal tract resonances. The adjustments are made because a vocal tract resonance can boost the radiation of a voice harmonic when it falls close to a resonance frequency. Here we report how singers with different voice categories tune their vocal tract resonances. For the lower voices, the lowest resonance R1 is sometimes tuned to a high harmonic, while high voices consistently tune R1 to the fundamental over a range of about C5 to C6 (523 to 1046 Hz). The second resonance, R2, can be simultaneously tuned to the second harmonic in the pitch range C5 to F5 (523 to 700 Hz). At the very highest pitches, sopranos can no longer increase R1 sufficiently and must then switch to adjusting R2 so its frequency is close to that of the fundamental.
School of Mechanical Engineering, The University of Adelaide, SA 5005, Australia
ABSTRACT
Advances in nanotechnology have provided acoustic researchers with a number of new materials with nanofibres and nanopores that can potentially be implemented as an acoustic porous absorber. The molecular behaviour of these new nanoscopic materials may have a significant influence on their sound absorption; in addition, their properties could play an important role in reducing the absorber thickness compared to the currently available materials. However, the absorption mechanisms of nanoscopic fibres are not fully understood and the application of numerical and analytical modelling methods to this problem is still at an early stage. This paper presents a review of numerical methods which have been implemented for various micro- and nano-scale analyses of relevance to the acoustics of nanofibres. The review is focused mainly on the application of non-continuum particle based approaches such as the Lattice Boltzmann Method (LBM) and the Direct Simulation Monte Carlo (DSMC) method, since it is expected that the flow behaviour for nanoscopic fibres will be in a transitional flow regime due to the high Knudsen number. The acoustic absorption mechanisms are thus likely to deviate from the continuum phenomena and modelling approaches applicable to flow associated with larger scale fibres. It is intended that this review will provide an overview of the potentially applicable approaches for the exploration of absorption mechanisms of nanoscopic fibres.
Faculty of Architecture, Design and Planning, The University of Sydney, NSW 2006, Australia
ABSTRACT
The use of an impedance tube to determine normal transmission loss (TLnormal) of single panels of typical building materials was undertaken and compared with measured field incidence transmission loss (TLfield) evaluated from the two room method. This comparison was undertaken to investigate Sharp's theoretical relationship between TLnormal and TLfield, using a small sample-set of some different types of common building materials. TLfield data for the materials (orthotropic coated steel sheeting, isotropic low-density Autoclaved Aerated Concrete [AAC] panel, AAC panel plus plasterboard) was obtained from the NATA certified results from the National Acoustic Laboratories at Chatswood, Australia. Samples of similar and other materials were prepared and measured in the Bruel and Kjaer 4206T impedance tube. This paper investigates the relationship between TLnormal and TLfield and compares them to a result predicted by Sharp's modelling. The experimental techniques used and results obtained are discussed, along with limitations of the impedance tube method and some suggestions for potential improvements.
(1) Akustikbüro Oldenburg, Oldenburg, Germany (2) BARRISOL S.A.S, Kembs, France
ABSTRACT
The theory of micro-perforated panel sound-absorbing constructions has been introduced by D.-Y. Maa in 1975. Since then many variations of micro-perforated sound absorbing devices and materials have been introduced. Materials that have been used to be micro-perforated have been metal, wood, plastics and many others. In 2001 a nearly invisible micro-perforation has been introduced to the stretched material making it highly sound absorptive. In this contribution measured sound absorption coefficients of various set-ups with micro-perforated stretched foils and different other acoustic materials will be presented. Finally applications will be shown.
School of Mechanical and Manufacturing Engineering The University of New South Wales Sydney, Australia
ABSTRACT
Many commercial partitions such as walls, windows and doors can provide reasonable sound insulation in medium and high fre-quency ranges. Those structures often perform in the mass control region of the acoustic spectrum and follow the "Mass Law" model. However, the Mass Law often does not provide adequate noise insulation at low frequencies. Hence other methods of increasing the sound insulation are required. One of those methods involves attaching to the vibrating structure a tuned mass or Tuned Vibration Absorber (TVA).While the TVA was invented over a century ago and was used successfully to reduce structural vibrations, applica-tions to acoustics problems are relatively new. Most of researches in the last decade focused on TVA tuned to the excitation frequen-cies and the TVAs were not always optimised or they have been designed with little damping. This paper investigates the effect of attaching a highly damped TVA on sound transmission loss of panels. The numerical simulations show that significant reduction in vibration and sound transmission is achieved at the first panel resonance.
Maritime Operations Division, Defence Science & Technology Organisation and University of Sydney Institute of Marine Science
ABSTRACT
Active acoustics, which makes use of the echo of a transmitted signal, has long been used to obtain information about the ocean and the marine animals. Applications range from water depth measurement by echo sounders to mulitbeam sonar imaging of the sea floor, from sonars for fish detection to those for naval defence. Listening, or passive acoustics, has been less widely used, but this is changing, with significant recent developments. This paper discusses some of these developments, their potential and the challenges. Sound propagates through the ocean with far less absorption loss than in the atmosphere, so that sources in the ocean are audible at much greater distances than might be expected from our terrestrial experience. This allows passive acoustics to be effective over large areas and distances, in some cases up to hundreds of kilometres. Signals from individual sources can provide information about the source, its behaviour, location and environment. Breaking waves across the open ocean produce broad band noise that is very well correlated with wind speed, so acoustic receivers can be used to for long term measurements wind speed at sea. Rain on the sea surface also produces broad band noise that is related to rainfall rate. The dominant sources of noise for both breaking waves and rain are the bubbles formed as air is entrained, either as the wave breaks or as the rain droplet penetrates the surface. These bubbles play an important role in the transfer of gases (e.g. CO2) and aerosols between the ocean and the atmosphere, so acoustics has a role in climate studies. Marine animals make extensive use of sound in an environment where vision is very limited. Passive acoustics provides information about their behaviour by tracking animals using their sounds and by understanding the function of their signals. Their sounds provide cues for estimating their abundance and distributions, in many cases on scales that would not be possible by other means. The ambient noise of reef ecosystems is indicative of the animals that contribute to it and may also be an indicator of the health of the ecosystem
(1) Defence Science and Technology Organisation, P.O. Box 1500, Edinburgh, SA 5111, Australia (2)Centre for Marine Science & Technology, Curtin University of Technology, GPO Box U1987, Perth WA 6845, Australia
ABSTRACT
The transmission of sonar signals in a surface ducted environment, or in a shallow ocean, is affected by reflection losses at the ocean surface, when wind action or swell causes the surface to be roughened. Under these circumstances, the amplitude of the specular reflection of sound at the ocean surface is reduced by a number of complex phenomena, including: the sea surface shape; acoustic shadowing of parts of the surface to sound incident at small angles; diffraction of sound into the shadow zones; coherence of sound scattered at the specular angle; and bubble formation from white-caps. Recent work has shown that the inclusion of these effects within a ray model of transmission is a formidable prospect, as ray theory cannot describe all the phenomena, and the inclusion of acoustic wave effects in combination with a ray model is required. This paper addresses several of the complexities, in the search for a comprehensive solution to this modelling issue. In particular, the appropriateness of the Small-Slope Approximation roughness model used by Williams et al. (JASA, 116, Oct. 2004) is investigated, using a Parabolic Equation (PE) model, for extended combinations of wind speed and acoustic frequency. Also, the refraction near the ocean surface caused by wind-induced bubbles (e.g. Ainslie, JASA, 118, Dec. 2005) is investigated by use of the PE model. Lastly, the surface loss values obtained for received coherent sound pressure are compared with those relevant to received root-mean-square sound pressure. The paper speculates on the prospects for the near future development of a surface loss model that includes all relevant effects.
Centre for Marine Science and Technology, Curtin University, Perth Australia
ABSTRACT
The interaction of sound with an arbitrarily shaped underwater object must in general be treated as a coupled interaction between the fluid and structure, due to the acoustic impedance properties of water. Typically, this type of problem is solved by building a numerical model of the exterior fluid and interior solid regions and then simultaneously solving the coupled system of equations, on the common fluid-structure interface. These models are restricted by their high cost in terms of computational time and memory. The fast multipole method (FMM) significantly reduces these requirements and is applicable to many types of boundary integral equations. For simple structures, a coupled model using the FMM for both the fluid and structure will provide a substantial increase in the possible model size or frequency limit compared to traditional methods. This paper discusses such a model and presents initial non-coupled results in the form of acoustic scattering and target strength results for the rigid BeTSSi submarine model.
(1) School of Engineering and Advanced Technology, Massey University, Palmerston North, New Zealand (2) Atkinson and Rapley Consulting, Palmerston North, New Zealand (3) Elliott Sound Products, Thornleigh, Australia
ABSTRACT
In measuring the environmental noise level for such purposes as compliance monitoring and nuisance noise assess-ment, the most often used statistic is the A-weighted sound pressure level (SPL), often reported as a centile ex-ceedance (e.g. L10, Lden or Ldn) averaged over a time interval such as 10 minutes or 24 hours. This statistic can not be relied upon in situations where noise has 'special audible characteristics,' such as modulation or tonality, since in-creases in the sound pressure level (SPL) of the loudest n% of sound will be ignored. Furthermore, the use of A-weighting underestimates the lower-frequency sounds, which have recently been shown to be perceived by humans through alternative mechanisms, therefore different measures are required. The analysis of large amounts of data for compliance monitoring can be a time-consuming process. Errors can occur due to inappropriate analysis methods or flawed understanding of the noise under investigation. This paper reports on: (1) some of the current issues with us-ing the A-weighting and exceedance statistics as measures of loudness; (2) the development of several alternative measures to analyse environmental sounds from various sources that exhibit 'special audible characteristics' (includ-ing wind farms and impulsive noise); (3) the requirements of automated, standardised methods of data reporting, analysis and assessment for large and complex data sets and (4) the development of a new sound measurement tool that implements the proposed analysis techniques while extending the acoustic spectrum down to less than 1 Hz: the Spectro-Acoustic Meter (SAM).
(1) Department of Transport and Main Roads, 477 Boundary Street, Brisbane. 4000 Queensland. Australia (2) Queensland University of Technology, George Street, Brisbane, Queensland, 4001. Australia.
ABSTRACT
This paper outlines a study to determine the correlation between the LA10(18hour) and other road traffic noise indicators. It is based on a database comprising of 404 measurement locations including 947 individual days of valid noise measurements across numerous circumstances taken between November 2001 and November 2007. This paper firstly discusses the need and constraints on the indicators and their nature of matching a suitable indicator to the various road traffic noise dynamical characteristics. The paper then presents a statistical analysis of the road traffic noise monitoring data, correlating various indicators with the LA10(18hour) statistical indicator and provides a compre-hensive table of linear correlations. There is an extended analysis on relationships across the night time period. The paper concludes with a discussion on the findings.
Aviation and Airports, Australian Government Department of Infrastructure and Transport, Canberra, Australia
ABSTRACT
In 2000 the Australian Government Department of Transport and Regional Development published a discussion pa-per entitled "Expanding Ways to Describe and Assess Aircraft Noise". The discussion paper was released in response to public concerns about the transparency and comprehensibility of technical aircraft noise metrics. Since the release of the "Expanding Ways" paper there has been a progressive adoption of flight path based noise descriptors and of "Number Above" (N70) noise contours both in Australia and overseas. This paper explores the evolution in aircraft noise descriptors and concludes that the skill set of the aircraft noise specialist now needs to be much broader. If the aircraft noise practitioner is to have a real influence on decisions, he/she has to operate at a number of different levels, using multiple noise metrics, and needs to be an effective communicator as well as a technical expert.
Formerly Manager, Noise Strategies, Noise Policy Section, NSW Department of Environment, Climate Change and Water
ABSTRACT
The problems and challenges of regulating environmental noise are surveyed with a focus on addressing dose/response relationships. The extent of government noise policy in NSW is discussed with reasons for the current structure and examples of its application. An account is given on the evolution of government policy since the 1970s especially for NSW from the standpoint of personal experience during that period, which includes the national approach to aircraft noise impact assessment. Aspects of policy development in that history are described with insights into the political background driving that development and the administrative difficulties faced by regulators, both in terms of the politics and the science. Specific examples are described that illustrate the results of policy and legislative application. This history provides a perspective on the current policy position in NSW and likely future issues and directions for governments and regulators are discussed.
Air Noise Environment Pty Ltd
ABSTRACT
The 4.8 kilometre Clem7 tunnel passes underneath the Brisbane river, providing a direct connection between the northern and southern Brisbane suburbs. During the design and construction phases of the project, various acoustic design issues were addressed. These included airborne noise emissions from the electrical and mechanical plant servicing the Clem7 tunnel. Computational acoustic model predictions of plant noise emissions from the ventilation building outlets, and the various tunnel portals were completed using specialist acoustic software. This paper presents an overview of the key acoustic design issues associated with the mechanical and electrical plant noise sources for the Clem7 tunnel. The modelling methodology and acoustic control solutions that were adopted are described, and the outcomes of the acoustic monitoring during the commissioning phase are presented.
Savery and Associates Pty Ltd
ABSTRACT
Environmental noise is a significant constraint upon the development and operation of the booming coal seam gas (CSG) industry in Australia. The CSG industry (upstream) is proposed to cover a large area of Queensland and NSW on the eastern seaboard of Australia. The project scales are enormous and unprecedented, representing many billions of dollars in development costs and many thousands of gas wells and numerous major compression facilities, gathering and transmission pipelines, power generating plants and water treatment plants across a vast area. The proposed CSG developments pose significant challenges for regulators, proponents and acoustic engineers with respect to noise regulation, assessment, planning, temporary and permanent noise mitigation, suitable engineering solutions, ongoing maintenance and monitoring. The upstream CSG areas have very low background noise levels and at times meteorological conditions that are conducive to long range noise propagation. The gas processing compression facilities and associated power and water treatment plants are very large and are comprised of multiple units, with noise emissions having both tonal and low-frequency characteristics. To supply gas to the processing facilities, well must be drilled, flow enhanced (fracced), made-over and regularly maintained and connected by a pipe gathering system to the compression plants. Wells are typically drilled on a 700m grid. The regulators in Qld are endeavouring to control CSG noise by enforcing very strict noise limits for well development, construction, itinerant activities and operations. The noise limits for development and operations are applied at receptor locations as cumulative limits of noise from all CSG sources. Compliance with the cumulative noise limits may still mean that CSG noise will be clearly audible at times, even at very large distances from the sources. The challenge for the CSG industry and their acoustic engineers is to determine what represents "best acoustic practice" for this new industry in all of its development activities, operations and maintenance and to deal with practices, plant and equipment that were deployed prior to determination of best acoustic practice for the industry. The challenge for the regulators is to set appropriate noise limits and conditions that enable best acoustic practices for the industry to be developed.
Wilson, Ihrig & Associates, Inc. 6001 Shellmound St., Suite 400 Emeryville, California 94608 USA
ABSTRACT
Rail based transportation systems produce noise and vibration that can cause annoyance or problems in the community without application of appropriate mitigation. Standards and recommended criteria have been developed to control the levels of noise and vibration to minimize impact on the nearby community. Unfortunately unanticipated community complaints of excessive noise and vibration still arise after system startup or modifications. Practical experience has shown that many of these complaints have merit and that they are usually caused by unforeseen technical or administrative reasons. A review of some of these cases at different rail transit properties in the United States indicates that although resolution is most often achieved, the process may take considerable resources and time.
(1) School of Mechanical Engineering, The University of Adelaide, SA 5005, AUSTRALIA (2) PE&I Cell, CSIR-IMMT, Bhubaneswar, Orissa 751013, INDIA
ABSTRACT
Active headrests produce a quiet zone near the occupant's head using active noise control. It has been shown that active headrest algorithms using virtual microphones are better than those using physical microphones, as they have the ability to shift the zone of quiet away from the location of the physical microphones towards the ears of the occupant. Recently, the virtual microphone arrangement based ANC method was used for an active headrest application, in which it was assumed that the primary pressures at the physical and virtual microphone locations are similar. In this paper the previous work is extended to incorporate the remote microphone technique, which is a better estimation algorithm as it incorporates an extra transfer function between the physical and virtual microphone. Experiments using two secondary speakers, and two physical and two virtual microphones are carried out to compare the results from both algorithms. The paper comprises of the detailed multichannel virtual microphone algorithm for a headrest and the experimental results.
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, Australia
ABSTRACT
This paper theoretically investigates the application of tuned vibration absorbers and hybrid passive/active inertial actuators to reduce the vibrational responses of plates and shells. The passive/active actuators are initially applied to a simple plate. A model of a submerged hull consisting of a ring stiffened finite cylinder with bulkheads and external fluid loading is then considered. The fluctuating forces from the propeller result in excitation of the low frequency global hull modes. Inertial actuators and tuned vibration absorbers are located at each end of the hull and in circum-ferential arrays to reduce the hull structural response at its axial resonances. The control performance of the hybrid passive/active inertial actuator, where the passive component is tuned to a structural resonance, is compared to the attenuation achieved by a fully passive tuned vibration absorber. This work shows the potential of using hybrid pas-sive/active inertial actuators to attenuate the global structural responses of a submerged vessel.
School of Mechanical Engineering, The University of Adelaide, Adelaide, S.A. Australia
ABSTRACT
Adaptive-passive vibration and acoustic control systems can provide significant attenuation without requiring significant power compared to an active control system. The control system includes an algorithm to evaluate a cost-function to be minimised, which is typically a time-averaged multiplication of the vibration or noise on the resonator and at a point in the system where the disturbance is to be minimised. This conventional algorithm of cost-function evaluation is suitable for simple systems. A new cost-function evaluation algorithm is proposed based on the sliding-Goertzel algorithm, that is tolerant of multiple harmonics and high background broadband noise. The algorithm was demonstrated on an experimental rig of an adaptive tuned vibration neutraliser and a two-stage vibration isolation system.
Maritime Platforms Division, Defence Science and Technology Organization, 506 Lorimer Street, Fishermans Bend, Victoria 3207, Australia
ABSTRACT
This paper discusses the design and evaluation of a pole placement controller for reducing vibration of structures. The design of the controller involves shifting the poles of a transfer function describing the structure's dynamic behaviour by using a feedback control gain. The feedback control gain is chosen to minimise the vibration response of the structure. The performance of the controller is evaluated by simulation using a dynamic model of a plate estimated from experimental data. The experimental data consisting of natural frequencies, structural damping and eigenvectors are used to construct to a state-space model where the state vector is multiplied by the control gain to produce a control input. The effect of pole location and the effect of excitation type on structural response and control voltage required are discussed in detail. Also, the effect of measurement noise on the robustness of the controller is investigated. Results show that the controller produces a significant reduction in the plate vibration.
Centre for Marine Science and Technology, Curtin University, Perth, Western Australia
ABSTRACT
The underwater acoustic communication channel is characterised by transient signal fading across multiple propagation paths and much greater time spread between first and last arrivals than in terrestrial wireless systems. At useful transmission distances of a few kilometres the channel is significantly bandwidth-limited in the tens of kHz by ab-sorption at higher frequencies, and unlike most terrestrial wireless radio-frequency channels, relative transmitter/receiver motion and sea-surface motion leads to significant signal Doppler effects. A dynamic underwater acoustic channel simulator is being developed to test and improve the effectiveness of point-to-point signal transmission by underwater acoustic modem systems. The simulator will enable testing of modems and signalling strategies in diverse transient acoustic propagation and background noise conditions in a cost-effective manner. The purpose of this paper is to outline the modelling challenges that are being addressed.
Centre for Marine Science & Technology, Curtin University of Technology, GPO Box U1987, Perth WA 6845, Australia
ABSTRACT
Several simple spreading laws have been proposed to allow estimates of underwater sound levels to be made without the complication of numerical modelling. Underwater acoustic propagation depends in an involved way on a number of geometric and environmental parameters, including source, receiver and water depth, and water column and seabed acoustic properties. As a result, there are many scenarios in which the use of these formulae lead to large errors. However, there would be a place for a formula that could provide an upper limit on received sound levels in a particu-lar situation as this would enable sound sources that had a very low probability of posing an environmental hazard to be quickly eliminated from further consideration. Such a formula is proposed in this paper and its bounds of applica-bility are explored by comparison with numerical model results for several scenarios.
(1) School of Mechanical and Chemical Engineering, University of Western Australia, Australia (2) Defence Science and Technology Organisation, Australia
ABSTRACT
Subarray beamforming has been identified as a signal processing technique to potentially reduce the effect of aerody-namically induced flow noise against a target signal which is difficult to target with full array beamforming due to its near-field and non-stationary nature. Previously the technique had been proposed yet was not fully investigated nor adequately compared to its full array adaptive counterpart. In this study the nature of flow noise and its implications to the effectiveness of the subarray technique have been investigated through an idealised mathematical model. The result demonstrates the potential to achieve considerable array gains against traditional adaptive beamforming, heav-ily dependent on flow noise characteristics, and the choice of subarray configuration is justified by a trade-off in faster adaption times against the accuracy of the cross-spectral matrix estimate.
(1) Defence Science and Technology Organisation, HMAS Stirling, WA (2) Centre for Marine Science and Technology, Curtin University of Technology, Bentley, WA
ABSTRACT
This paper reports on an underwater acoustic sensor used to demonstrate dynamic configurable Field Programmable Analogue Array (FPAA) devices. A single FPAA device was connected to a microcontroller and programmed to sweep through a set of fractional one-third octave filters with centre frequencies from 100 Hz through 20 kHz. Fourth order filters were designed using a cascading topology and approximated using two second order filters available in the FPAA. Sweep timing characteristics were controlled by the microcontroller to allow for settling time and a predetermined estimation uncertainty for each fractional octave band. Laboratory testing compared the filters with the relevant ANSI standard. Field measurements were conducted in the shallow waters of Cockburn Sound. Results of laboratory and field measurements are presented and discussed.
Defence Science and Technology Organisation P.O. Box 1500, Edinburgh, SA 5111, Australia
ABSTRACT
In active sonar, the echo from a target is the convolution of the source waveform with the impulse responses of the target and the propagation channel. The transmitted source waveform is generally known and replica-correlation is used to increase the signal gain. This process is also called pulse compression because for broadband pulses the re-sulting correlation functions are impulse-like. The echo after replica-correlation may be regarded as equivalent to that received by transmitting the impulsive auto-correlation function of the source waveform. The echo energy is spread out in time due to different time-delays of the multipath propagation and from the scattering process from the target. Time spreading leads to a reduction in the peak power of the echo in comparison with that which would be obtained had all multipaths overlapped in time-delay. Therefore, in contrast to passive sonar where all energies from all sig-nificant multipaths are included, the concept of transmission losses in the active sonar equation needs to be handled with care when performing sonar performance modelling. We show modelled examples of echo time spreading for a baseline case from an international benchmarking workshop.
Urban Research Program, Griffith School of Environmnet, Griffith University, Nathan 4111, Brisbane, Australia
ABSTRACT
The role and application of the concept of the soundscape, vis-à-vis that of environmental noise management, needs elaboration. In noise control, sound is a waste product, managed to reduce the immision of sounds that cause human discomfort. The soundscape approach, by contrast, considers the acoustic environment as a resource, focussing on sounds people want, or prefer. Quiet is not a core requirement for acoustic preference in the outdoor acoustic environment. Core requirements include that soundscape and landscape are congruent, and that wanted sounds in a place are dominant over, or not masked by, unwanted sounds. Soundscape design, planning and management, based on this principle, are a useful augmentation to environmental noise management approaches, expanding the scope of application of the tools of acoustic specialists.
(1) Engineering and Technology Division, Queensland Department of Transport and Main Roads, Brisbane, Australia (2) Assets and Operations Division, Queensland Department of Transport and Main Roads, Brisbane, Australia (3) Integrated Transport Planning Division, Queensland Department of Transport and Main Roads, Brisbane, Australia
ABSTRACT
A transport system generates environmental emissions such as noise, vibrations, air emissions and particles and light, which can have adverse impact on the health, well-being and quality of life for the occupiers of development contig-uous with transport noise corridors. The Department of Transport and Main Roads (TMR) has developed a policy po-sition statement which outlines TMR's position in relation to the development of land that is impacted by environ-mental emissions from Transport Operations and Infrastructure (TOI) which includes busways, light rail, railways and State-controlled roads. Together with the application of the Queensland Development Code (QDC), Mandatory Part 4.4, Buildings in a Transport Noise Corridor (QDC MP4.4), TMR's aim is to ensure development proposals for new environmentally sensitive development within transport noise corridors are designed and constructed in a way to protect occupants from significantly adverse impacts resulting from environmental emissions generated by existing and future transport operations. One of the major sources of environmental emissions is transport noise. When de-signing a new noise sensitive land use, developers must ensure that the predicted impact of transport noise by future transport operations is attenuated. The transport noise criteria listed in TMR's Policy Position Statement, Develop-ment on Land Affected by Environmental Emissions from Transport and Transport Infrastructure (PPS) is relevant to new noise sensitive land use proposed contiguous with a transport corridor.
(1) ASK Consulting Engineers, Brisbane, Australia (2) Griffith University, Brisbane, Australia
ABSTRACT
The topic of noise attenuation through a façade with an open window has received little attention, especially within Australia. The objective of this study was to obtain field measured noise reduction data for open windows at Queensland style residences. Specifically those with timber, brick veneer and double brick facade constructions targeting the Leq and Lmax noise descriptors, using road traffic noise and car door slams as the noise sources. To investigate this topic, a simultaneous multiple microphone monitoring methodology was developed using adapted testing procedures outlined in both AS 2702 (Acoustics - Methods for the measurement of road traffic noise) and ISO 140-5 (Acoustics - Measurement of sound insulation in buildings and of building elements).This study has obtained noise reduction results which can be compared to the 5 dB(A) open window attenuation assumption presented by the Queensland Government's "Planning for Noise Control Guideline" (PNCG) and the Brisbane City Councils "Noise Impact Assessment Planning Scheme Policy" (NIAPSP). The results of this investigation were also compared with internal noise prediction methods currently available to be used by acoustic consultants.
(1) School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, NSW 2052, Australia (2) School of Mechanical Engineering, Prince Mohammad Bin Fahd University, Al Khober 31952, Kingdom of Saudi Arabia
ABSTRACT
Lumped Parameter Models (LPMs) are widely used to simulate the dynamics of mechanical systems such as shafts and gears in a gearbox. In addition to simulating the complex behaviour between the various components, LPMs can also be used to simulate vibration signals in the presence of gear and bearing faults. However, the limited representation of the modes of the gearbox casing and the internals (shafts and gears) in the LPM model results in poor spectral matching over a wide frequency range. Finite element analysis (FEA) provides an alternative approach to simulate the dynamic behaviour of the structure. However, the use of FEA results in a large number of degrees-of-freedom (DOF), requires large computing resources and presents additional difficulties to simulate the entire system's response in the presence of nonlinearities and gear and bearing faults. The limitations of LPM and FE models are addressed in this paper by using finite element model reduction techniques. FE model reduction based on Craig-Bampton component mode synthesis (CMS) is used to extract greatly reduced mass and stiffness matrices of the gearbox components (internals and casing) based on the frequency range of interest. The extracted mass and stiffness matrices are imported and assembled into the dynamic model of the gearbox previously developed using Simulink®. The model has the capability of simulating time-varying stiffness nonlinearities and geometric faults for both gears and bearings. The reduced matrices comprising both physical and modal coordinates enable inclusion of component flexibility in the dynamic model up to a specified frequency defined by the number of modes included. The dynamic model was solved interactively to obtain simulated vibration signals in the presence of localised and extended bearing faults. The simulation results indicate a much better correspondence with the measured signals.
School of Mechanical Engineering, University of Adelaide, Adelaide, Australia
ABSTRACT
Vibration isolation systems incorporating linear mechanical springs exhibit the undesirable characteristic of changing resonance frequency with changing payload mass. Previous research at the University of Adelaide and elsewhere has demonstrated the theoretical feasibility of vibration isolation devices utilising magnetic springs as a means of achieving a constant resonance frequency across a range of payload masses due to their nonlinear force-displacement relationship. A conceptual prototype design is presented for a levitating magnet vibration isolation device which aims to achieve a load-independent resonance frequency across a range of payload masses via the use of inclined magnetic springs. Quasi-static and dynamic system models which informed the design process are presented, as well as a finite-element model aimed at validating the assumptions of the quasi-static system model for a select set of system states. Challenges related to the conflicting design requirements of stability, low transmissibility and load-independent resonance frequency are addressed, and an experimental framework for testing the real prototype is outlined.
Maritime Platforms Division, Defence Science and Technology Organisation, 506 Lorimer Street, Fishermans Bend, VIC 3207.
ABSTRACT
The structural vibration induced by machinery often needs to be assessed during the concept design phase in order to determine the configuration of machinery that minimises transmitted vibration, in addition to satisfying other design constraints. However, detailed information about machinery and the foundation's structure may not be available, and in these cases simplified analytical models can be used to assess potential designs. This paper derives the equations of motion for generalised two-stage and two-stage rafted vibration isolation systems using a matrix methodology. The supported mass and intermediate masses are assumed to be rigid and supported by isolators with arbitrary locations and orientations. The use of the methodology is illustrated for three common isolator configurations: single stage isolation; two-stage isolation; and two-stage rafted isolation, and the characteristics of each are discussed.
(1) School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, NSW 2052, Australia (2) Universität der Bundeswehr, Werner-Heisenberg-Weg 39, 85577 Neubiberg, Germany
ABSTRACT
By identifying the efficiently radiating acoustic radiation modes of a fluid loaded vibrating structure, the storage requirements of the acoustic impedance matrix for calculation of the sound power using the boundary element method can be greatly reduced. In order to compute the acoustic radiation modes, the impedance matrix needs to be symmetric. However, when using the boundary element method, it is often found that the impedance matrix is not symmetric. This paper describes the origin of the asymmetry of the impedance matrix and presents a simple way to generate symmetry. The introduction of additional errors when symmetrizing the impedance matrix must be avoided. An example is used to demonstrate the behaviour of the asymmetry and the effect of symmetrization of the impedance matrix on the sound power. The application of the technique presented in this work to compute the radiated sound power of a submerged marine vessel is discussed.
School of Mechanical and Chemical Engineering, The University of Western Australia, Crawley, WA 6009, Australia
ABSTRACT
As one of the most expensive and critical parts of power systems, power transformer maintenance and condition monitoring attracts increasing attention. Vibration analysis, which can be made either by experimental measurements or from predictions, is a promising technique in the healthy diagnosis of the power transformers. This paper presents the study of vibration characteristics of a power transformer mainly based on FEM. An improved FEM simulation scheme including electromagnetic simulation and the structural dynamic response analysis is presented. The complex vibration behaviour of the transformer is studied. Furthermore, this vibration model combining with vibration measurement may provide a potential method of diagnosing the failure modes of power transformer, such as looseness of clamp pressure and winding deformation. The reliability of the model scheme is verified by experimental measurement of a 10 kVA power transformer.
School of Mechanical Engineering, University of Adelaide, Adelaide, Australia.
ABSTRACT
The prediction capability of a RANS-based Statistical Noise Model (RSNM) is assessed by applying it to a sharp-edged symmetric flat strut at a Reynolds number of Re = 500,000 and zero angle of attack. The method uses a rigid-half-plane Green's function to calculate the far-field spectra generated by the turbulence in the vicinity of the trailing edge. Because the exact form of the turbulent sources is in general not available, a model of the turbulent velocity cross-spectrum must be assumed. The cross-spectrum model must accurately reflect the frequency and phase distribution in the boundary layer close to the trailing edge, but is otherwise arbitrary. The model used in this study is Gaussian, containing velocity, time and length scales that are defined in terms of the turbulence statistics obtained from a steady RANS solution. The predicted sound spectrum shows the correct slope and levels for frequencies ranging from 300 Hz to 2 kHz.
(1) School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, Australia (2) Institute of Mechanics, Universitat der Bundeswehr Munchen, Neubiberg, Germany
ABSTRACT
A meshfree multipole moment preserving condensation (MmMPC) method is proposed to spatially condense the volumetric quadrupole sources based on Lighthill's acoustic analogy that are extracted from computational fluid dynamics (CFD) data. The purpose of the method is to reduce both the amount of data that must be stored during the CFD analysis and the number of acoustic sources driving the subsequent acoustic propagation analysis, while preserving the accuracy of the predicted sound pressure field. The method uses a distribution of particles with quintic kernels to integrate the acoustic sources and employs a multipole expansion of the harmonic free-field Green's function to preserve the multipole moments of the underlying acoustic sources. The directivity of the sound pressure field due to the quadrupole sources are presented for the first four harmonics of the vortex shedding frequency for flow past a circular cylinder with Reynolds number, ReD=100 and Mach number, M=0.02. Using the MmMPC method, the number of acoustic sources is reduced by a factor of 120 with the associated far-field sound pressure levels within 0.5 dB of the non-condensed results for all four harmonics.
School of Mechanical Engineering, The University of Adelaide, Adelaide, SA, 5005 Australia
ABSTRACT
This paper explores the noise reduction potential of sawtooth trailing edge serrations on a flat plate at low-to-moderate Reynolds number. The noise radiated by a flat plate with both sharp and serrated trailing edges has been measured in an anechoic wind tunnel at the University of Adelaide. The noise measurements have been taken at a range of flow speeds (Reynolds numbers of Rec < 4.5 x 10^5, based on chord) for two different sawtooth geometries. Trailing edge serrations are found to achieve an average attenuation of up to 7 dB over a certain Strouhal number range, where Strouhal number is St = fδ/U∞, f is frequency, δ is boundary layer thickness and U∞ is the free stream velocity. The results of this study are compared with theoretical noise reduction predictions showing that significant differences
exist between measurements and theory.
School of Mechanical Engineering, The University of Adelaide, Adelaide, SA, 5005 Australia
ABSTRACT
Airfoils operating at low-to-moderate Reynolds number may produce noise that contains one or more high amplitude tonal components. Many previous researchers have attributed airfoil tonal noise to a feedback loop between instabilities in the laminar boundary layer and the acoustic waves produced at the trailing edge. There is, however, limited experimental evidence to verify this proposed hypothesis. This paper presents results of an empirical study on the tonal noise produced by a sharp-edged flat plate at low-to-moderate Reynolds number (0.7 x 10^5 < Rec < 2.3 x 10^5, based on chord). Simultaneous measurements of the far-field noise and flow about the plate's trailing edge have been acquired in an anechoic wind tunnel at the University of Adelaide. An empirical formula is derived to estimate the tonal frequencies produced by flow past the flat plate. A feedback model based on that developed by Tam (1974) is applied to the experimental data to demonstrate that the characteristics of the flat plate tonal noise and flow fields do not support an aeroacoustic feedback mechanism. The vortex shedding model developed by Moreau et al. (2011) is reviewed to show that in this particular case, the tonal noise appears to be governed by vortex shedding processes at the trailing edge.
School of Mechanical Engineering The University of Adelaide
ABSTRACT
In order to produce aircraft, turbo-machinery and helicopters with low acoustic signatures and without annoying tones, it is essential to understand the noise generated by airfoils. A series of experiments were carried out in the an-echoic wind tunnel facility at the University of Adelaide with subsonic, low Mach number turbulent flow over a wall-mounted finite-length NACA 0012 airfoil of span 124 mm and chord 67 mm (aspect ratio of 1.851). Acoustic data were acquired using two phase-matched microphones, one mounted 560 mm above and the other 560 mm below the trailing edge of the airfoil, for flow conditions in the Reynolds number range of 2.2 104 - 1.675 105. Experiments were conducted for airfoil geometric angles of attack (α) of 0º, 5º and 10º. From the experimental measurements, it is evident that the noise spectra contained broadband noise together with tonal components of various frequencies and sound pressure levels. In this paper, the effect of the airfoil tip on its tonal noise behavior and the effects of Reynolds number and angle of attack on the far-field noise radiated from the airfoil are presented and compared with experi-mental and numerical investigations carried out by others for similar geometries and flow conditions.
Rail CRC, School of Engineering, University of Queensland, Brisbane, QLD 4072, Australia
ABSTRACT
Wear-type rail corrugation is a significant problem in the railway transport industry. Some recent work has suggested that speed control can be used as an effective tool to minimize the rate of corrugation growth. This has brought about the need to model corrugation growth under variable passing speed. Variable speed rail corrugation growth modelling normally consists of either numerical simulation of a sequence of varied speed wheel passes or direct integration of a probabilistic passing speed distribution function; both of which are computationally expensive. This paper investigates the use of the statistical moments of the speed probability density function to greatly improve the computational speed of variable speed corrugation growth models and compares results of changing standard deviation and skewness to numerical integration models. It also identifies the effects of individual statistical moments on corrugation growth to provide better insight into control methods. The new modelling method correlated well with the numerical integration models for small standard deviations in speed (less than 10%) and highlighted a need to consider kurtosis in predicting the performance of speed control based corrugation mitigation schemes. For larger standard deviations in speed, higher than 4th order effects need to be considered.
University of Queensland and ISVR(Institute of Sound and Vibration)
ABSTRACT
Several theoretical models are available for predicting railway rolling noise. However, the TWINS (Track-Wheel Interaction Noise Software) model, based on the mechanics of the vehicle and track interactions, agrees well with field measurements. Full-scale validation experiments have shown that the TWINS model gives reliable predictions under European conditions. In this paper, the development of the TWINS calculation procedure in MATLAB as part of RailCRC Project No.1-105 Improved Noise Management is detailed. Details of the prediction modules, Graphical User Interface and validation under European conditions are provided as well as the sensitivity analysis of the MATLAB model (called 'RRNPS', meaning Railway Rolling Noise Prediction Software). The predictions of this model are compared with those from the TWINS model and results show the RRNPS model gives reliable predictions under European conditions. Subsequently this model is used to predict how pad and ballast dynamic properties affect the sound powers from the wheel and rail.
(1) AECOM, Level 28, 91 King William Street, Adelaide, South Australia 5000 (2) AECOM, Level 8, 540 Wickham Street, Fortitude Valley, Queensland 4006
ABSTRACT
There are a number of standards and guidelines which are used in Australia for the assessment of wind farm noise. While there is some variation in the lower noise limit applied, the standards and guidelines typically set noise criteria for wind farms as 40 dB(A) or the background noise level + 5 dB(A), whichever is the greater. Additionally, they provide different methods for measuring compliance once the wind farm is operational. This paper examines the differences that result when assessing compliance against the various measurement and analysis procedures. Compliance measurements from a number of receivers surrounding several wind farm sites are used in the analysis. Differences of between 1.9 and 4.3 dB(A) are observed between the highest and lowest assessment results obtained at individual receivers, although this range is reduced to 1.9 - 2.7 dB(A) when LAeq results that appeared to be influenced by extraneous noise are discarded. These results complement the findings of our other paper which compares predicted levels against the compliance measurement results, and can be used to compare predictions against wind turbine noise levels measured and analysed using different methodologies.
AECOM, Level 28, 91 King William Street, Adelaide, South Australia 5000
ABSTRACT
Wind farms are an important source of renewable energy but should also comply with environmental noise regula-tions. To maximise the energy output of wind farms whilst still meeting the relevant noise regulations, it is important that an accurate environmental noise prediction method be used during the planning stage. This paper presents a comparison of four commonly applied prediction methods against measured noise levels from the operational wind farm conducted in accordance with the applicable guidelines in South Australia. The results indicate that the methods typically over-predict wind farm noise levels but that the degree of conservatism appears to depend on the topography between the wind turbines and the measurement location. This could have important implications for the planning stage of new wind farms in South Australia where environmental noise levels represent a design constraint.
Science & Assessment Division, SA EPA, GPO Box 2607 Adelaide SA 5001, Australia
ABSTRACT
Noise exposure from wind farms is one of major factors forming negative public opinion regarding this source of re-newable energy. Due to strict compliance requirements, the noise contribution from wind farms at relevant receiver locations may be comparable to or less than the background noise. Measurement and calculation of wind farm noise becomes a challenging task at a distant receiver. In cases where it is proposed to upgrade an existing wind farm to ac-commodate a greater number of turbines, it is important that the contribution of the existing wind farm can be ex-tracted from the overall noise measurements. Many regulatory procedures are based on reporting of total noise meas-ured over 10 minute intervals. Possible short term fluctuations in noise from wind turbines during this interval due to variations in turbine operating regimes and atmospheric conditions is a potential cause of concern for residents. This paper details an assessment of the noise contribution from a wind farm with a focus on a shorter time interval. The re-sults of the monitoring indicate that, when measured over shorter periods, normally variation in the noise contribution of the wind farm when compared with 10 minute values is either insignificant or moderate. If the data is well refined from extraneous noises, the scattering of data points is less than is normally reported as a result of an unattended monitoring. Comparison of the directional noise contribution with data gathered by traditional methods shows that noise contribution from the wind farm may not be adequately calculated if the data post- process is made in accord-ance with conventional procedures.
Danish Road Directorate, Road Institute, Hedehusene, Denmark
ABSTRACT
A comprehensive method for mapping traffic noise levels is an indispensable tool for road administrations in their ef-fort to mitigate traffic noise. Nord2000 is a new generation prediction method for environmental noise. Predictions can now be made of third-octave band levels of road traffic noise propagating over complex terrain under almost any weather condition. This allows accurate computation of yearly average noise levels as required by the European di-rective on environmental noise. The Danish Environmental Protection Agency in 2007 decided that computation of surface transportation noise shall be carried out using Nord2000. At the same time the yearly average Lden was intro-duced as the Danish noise measure to characterize population exposure to transportation noise. Computations are made by commercially available software, and test cases have been defined as a measure to prove software compli-ance. For rough estimates freeware is provided for looking-up pre-calculated noise levels in typical cases. Road sur-face conditions are taken into account by correcting default values for the pavement lifetime average condition. Noise barriers now seem to come out slightly less effective than before, when noise levels were predicted for conditions of a slight downwind perpendicular to the road.
School of Mechanical Engineering, The University of New South Wales, Sydney, Australia
ABSTRACT
Traditionally noise measurements are taken on a horizontal plane, largely ignoring the vertical propagation. This ver-tical propagation is of particular importance in the CBD as it is characterised by high rise offices where workplaces are often exposed to noise generated from traffic jams. These excessive noise levels could lead to interference with communication or cause distraction as well as several other health problems. To study the vertical noise propagation, a suitable area within the CBD was selected, of which, a simulated model was created. Results from the simulation were verified with real world noise level measurements, which showed a 6 dB(A) decay over the first 50 m of height, and a maximum decay of 4 dB(A) at heights over 50 m up to 140 m.
Maritime Platform Division, Defence Science and Technology Organisation, PO Box 4331, VIC 3001, Australia
ABSTRACT
In this study, the turbulent flows over a hydrofoil and the bare-hull SUBOFF are simulated using the unsteady/steady RANS model of FLUENT in order to show the distribution of noise sources. The sound radiation from hydrofoils with different spanwise dimensions and from SUBOFF is predicted for a model quadrupole source using the Boundary Element Method of SYSNOISE. It has been found that the scattered field for quadrupoles near the solid surface is mostly dipolar and that the scattering is more efficient when the sources are close to the edges. The trailing edge is a very efficient scatterer. The radiated field by the sources on the body of the hydrofoil and on the SUBOFF hull away from edges is mainly due to the radiation of the quadrupoles, and the scattering is very weak.
(1) School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, Australia (2) Human Protection and Performance Division, Defence Science and Technology Organisation, Melbourne, Australia
ABSTRACT
A computationally efficient method to approximate the total sound power and far-field acoustic intensity spectra generated by turbulent flow past a rigid body is proposed. The method is based on Proudman's analytical formula for the sound generated by isotropic turbulence. This formula expresses the sound intensity of locally isotropic turbulence for low Mach numbers in terms of the kinetic energy of the turbulence, k, and its dissipation rate, e. In this work, the approach is extended to non-uniform turbulent flows and the associated acoustic spectra are expressed in terms of the standard steady-state variables, k and e, conventionally used in computational fluid dynamics (CFD). Since these steady-state variables of turbulent flow are much easier to calculate than the non-stationary turbulent fluctuations used in traditional formulations for the flow sound, this approach dramatically reduces the computational burden of the flow noise calculation. Such a computationally efficient method for predicting flow noise is essential for conducting extensive "what-if" studies such as shape optimisation to reduce flow noise. The final expressions for the proposed method are calibrated against experimental and numerical data for flow noise of turbulent jets and boundary layers. The method is then applied to study the coefficient of drag and Mach number dependence of the sound generated by flow past a slender body.
Maritime Operations Division, Defence Science and Technology Organisation, Edinburgh, 5111, Australia
ABSTRACT
The purpose of this study is to compare the well-known Ffowcs Williams and Hawkings (FW-H) equation of aeroacoustics with the non-uniform Kirchhoff equation derived previously by the author. The purpose of this comparison is the clarification of the issue of possible equivalence of the two equations, as they produce equivalent predictions for radiated sound in many cases despite having different appearance. The comparison is done by reconsidering the original derivation by Ffowcs Williams and Hawkings. It is shown that one set of conditions within the medium inside the rigid body leads to the FW-H equation, whereas another set of conditions leads to the non-uniform Kirchhoff equation. As the conditions within the rigid body can be chosen arbitrarily, it is concluded that the two equations are equivalent and the non-uniform Kirchhoff equation represents a new form of the FW-H equation.
(1) Track Engineering, RailCorp, Level 13, 477 Pitt St Sydney NSW 2000, Australia (2) School of Civil, Mining, and Environmental Engineering, University of Wollongong, Wollongong NSW 2500, Australia (3) Railway Dynamics Division, Railway Technical Research Insititute, Hikari-cho, Kokubunji, Tokyo 185-8540, Japan
ABSTRACT
The prestressed concrete railway sleepers (or railroad ties), which are installed in railway track systems as the crosstie beam support, are designed to carry and transfer the wheel loads from the rails to the ground. It is well known that railway tracks are subject to impact loading conditions, which are attributable to the train operations with either wheel or rail abnormalities such as flat wheels, dipped rails, etc. These loads are of very high magnitude but short du-ration. In many cases, it has been reported from the fields that concrete sleepers are lacking of support due to mud pumping or excessive but localised track settlement, so-called "voided sleepers". This paper presents a numerical study to evaluate dynamic responses of the voided concrete sleepers to impact loading. A simplified finite element model of concrete sleepers was developed and validated against experimental data. The model has then been used to evaluate the effect of voids on the dynamic responses of concrete sleeper to a typical impact loading. The outcome of this study will help engineers to determine the life of assets and to investigate the failure mode of concrete sleepers and associated track components in actual ballasted tracks. It also gives better insight into the dynamic behaviour of voided concrete railway sleepers.
Wilson, Ihrig & Associates, Inc., 6001 Shellmound St., Suite 400, Emeryville, California 94608 USA
ABSTRACT
A major challenge for new performing arts centers in major cities is to achieve sufficiently low levels of background noise. Thus there is the need to isolate the new structures from vibration sources typically found in urban downtown areas. This paper provides background information, typical design details and procedures used to ensure that the groundborne noise and vibration from outside activities will be inaudible or sufficiently low inside performing arts venues. Specific design procedures are presented with respect to the Four Seasons Centre for the Performing Arts, Canada's first purpose-built opera house located in Toronto. Results of follow-up measurements are presented which confirmed that the vibration design effectively mitigated the outside vibration and noise intrusion inside the auditori-um to achieve background noise levels from exterior sources equivalent to the threshold of human hearing.
(1) China Ship Scientific Research Centre, China (2) Nanjing Metro, China (3) Pandrol Rail Fastenings Ltd., Australia
ABSTRACT
Pandrol Ltd. has been supplying its low stiffness VANGUARD rail fastener to metro operators throughout China since 2004. The Pandrol VANGUARD system uses the principle of rubber in shear to support the running rail by the web and the underside of the railhead, which allows the fastener to develop very low vertical support stiffness. This is demonstrated by the reduction of secondary (or re-radiated) noise inside buildings adjacent to metro tunnels. In 2009 Nanjing Metro made a trial fitting of Pandrol VANGUARD on Line 1. It was retrofitted in place of the existing slab track fasteners thus the performance differences between the two could be measured in terms of the insertion loss. The China Ship Scientific Research Centre was commissioned by Nanjing Metro to make relevant measurements of noise and vibration. This paper describes the results in terms of vibration measured inside the tunnel, the ground vi-bration above the tunnel and noise inside a building above the trial site.
(1) School of Engineering and Advanced Technology, Massey University, Palmerston North, New Zealand (2) Atkinson and Rapley Consulting, Palmerston North, New Zealand
ABSTRACT
It is current practice to measure sound pressure levels (SPL) from wind farms at a handful of locations in the surrounding countryside. These can be placed near sensitive areas such as residences to provide an indication of the SPL at that point and are used in conjunction with sound level prediction software to infer sound level throughout the affected areas. This paper reports a literature review of human perception of low-frequency sound before describing investigations into sound levels at the Makara wind farm near Wellington, New Zealand where the interference of low frequency sound from the multiple wind turbines form stable SPL patterns. The low frequency emissions from multiple wind turbines were simulated and validated against measurements from microphone arrays. Ten sound frequencies from 1/3 octave immission spectra were chosen from recorded measurements on the site ranging from 55 Hz to 315 Hz. The simulation used the positions of 14 wind turbines closest to a microphone array as point sources of the sounds. Results show that the combined frequencies from a single turbine produced SPL patterns within a 100 m-by-100 m area that varied by 2-5 dBLin whereas the combined sounds from all 14 turbines varied by 6-13 dBLin. Validation of these results was achieved by using three 2-by-4 microphone arrays with 1 m, 2 m and 3 m separation between the microphones. These recorded variations of 6-11 dBLin in their 15-minute, SPL averages. Additional validation was also shown by direct observation; the sound from the wind turbines was observed to appear and disappear within two to three paces between fixed locations. The conclusion is that measurements of low frequency sound levels can vary considerably over even very short distances and that point measurements may not represent the sound levels throughout their immediate neighbourhood.
School of Mechanical Engineering, University of Adelaide, Adelaide, SA, Australia
ABSTRACT
The aerodynamic noise production mechanisms of modern horizontal axis wind turbines are reviewed. An engineering analysis of the time and frequency scales from three noise sources, leading edge turbulence interaction noise, trailing edge noise and blade-tower interaction noise is presented. The analysis shows that noise sources are present from low-frequencies (1-4 Hz) to over 500 Hz for a representative wind turbine. The results of the analysis are used to explain amplitude modulation observed during noise measurements at a European wind farm. The paper concludes with a description of conceptual ideas for the control of wind turbine noise.
Savery & Associates Pty Ltd, Brisbane, Australia
ABSTRACT
Noise measurements undertaken during the environmental impact assessment process typically consist of overall levels only, using broad-band noise loggers without spectral capability. This temporal information does not provide enough insight into the noise sources surrounding the noise logger to accurately determine the ambient noise levels for the duration of the year. Several one-third octave noise loggers were used in combination with meteorological measurements at two different reference heights, to evaluate the spectral content of baseline noise records as well as the contribution from seasonal and episodic biological noise. Examples are presented that contrast the conclusions that can be drawn from spectral noise monitoring compared with broad-band noise logging for both the determination of rating background noise levels in the gas fields and noise criteria for a wind farm.
(1) Noise Measurement Services Pty Ltd, Brisbane, Australia (2) School of Public Health, Auckland University of Technology, Auckland, New Zealand
ABSTRACT
On a decibel-for-decibel basis, wind turbine noise is commonly judged as significantly more problematic than most other community noise sources. As a relatively new source of community noise, however, methodological issues remain as to how wind farm noise should be measured, and how data should be collected to afford valid health assessments of turbine noise. Maintaining public health while ensuring that wind farm developments are not unnecessarily blocked has created a tension between the communities asked to host wind farms and those developers wishing to build them. Between them stand local and state regulatory authorities who are increasingly required to judge the risks and benefits of wind farms based on scant data, or technical arguments that go far beyond their expertise. Issues with measurement include, but are not limited to, terrain effects, seasonal and meteorological effects, the validity of averaging, single microphone vs. array recordings, coherent addition of periodic noise sources, level measurements vs. dynamic measurements, selection of frequency weightings, and the effects of thermal stratification on wind shear. Individual responses to wind farm noise are barely related to current acoustical indices and can instead be deconstructed from a set of interacting factors, including noise sensitivity, attachment to place, age, and procedural fairness. A further issue centres on how "health" should be defined, and the best outcome measures to use when judging the impacts of turbine noise. This paper identifies current and advanced wind turbine noise prediction, measurement and assessment issues and uses examples of individual experiences of turbine noise to emphasise the importance of "getting it right".
Ron Rumble Renzo Tonin, Brisbane, Australia
ABSTRACT
The prediction of carpark noise presents a significant challenge to Acoustic Engineers. This paper aims to provide a method for prediction of carpark noise that can predict spectral Leq, L1, L10 and Lmax. The basis for this method is an application of the Bavarian State Office for the Environment (Bayerisches Landesamt für Umwelt - BayLfU) traffic noise study to Australian conditions. Measurements of carpark noise were made at carparks with low, medium and high rates of turnover per parking space. The noise associated with an individual parking procedure was measured for procedures on smooth bitumen, rough bitumen and coarse gravel. The overall sound pressure level from one parking procedure on smooth bitumen was 64dB(A), with a +3dB correction required for rough surfaces. The BayLfU model, a German study into noise emissions from carparks, presents a method for calculating the LAeq overall sound level. The model does not provide methods for calculating spectra for the noise. Predictions of carpark noise for the BayLfU model are based on a 63dB(A) measurement for one parking procedure. When comparing the noise measurement results with predictions calculated using the BayLfU model, it was found that the BayLfU model slightly under-estimated noise emissions. By correcting predictions made with the BayLfU model to the parking procedure measurements, estimations of carpark noise were very close to the measured levels for medium and high turnover carparks.
Maritime Platforms Division, Defence Science & Technology Organisation, 506 Lorimer St, Fishermans Bend VIC 3207.
ABSTRACT
Plates and shells with beam stiffeners are common structural elements in ships, aircraft and land vehicles. Several approaches can be used to model the dynamics of these elements. One is to smear the mass and stiffness of the beam stiffeners to give an orthotropic plate or shell which models the low-frequency response well. Another is the use of periodic structure theory to give a compact result for the vibration transmission with evenly spaced stiffeners considered discretely. This paper considers a cylindrical shell with ring stiffeners as an example problem and compares the performance of the smeared model with that of the discrete-stiffener approach. A method that could be used to investigate the effect of some randomisation in stiffener spacing is also described.
(1) School of Mechanical and Chemical Engineering, University of Western Australia, Crawely WA 6009, Australia (2) Defence Science and Technology Organisation, HMAS Stirling, Rockingham WA 69582, Australia
ABSTRACT
This paper summarizes the experimental results of underwater vibration of a torpedo-shaped structure under axial excitation. Through the comparison of the vibration of the structure in water with that in air, we have found that the peak frequencies and corresponding mode shapes of the wet structure may differ significantly from those of the dry structure. This paper explains the change of the modal characteristics of the wet in terms of the coupling of the dry structural modes. The possible links between the wet and dry modes of the same structure are further illustrated by the vibration modelling a fluid-loaded plate.
(1) Atkins, Perth, Australia (2) Department of Mechanical Engineering, Curtin University, Perth, Australia
ABSTRACT
Many types of slender or thin walled structures experience forces which traverse across them. For example: vehicles passing over a bridge, overhead crane operations and liquid "slug" movement in spanning pipelines. This moving force can initiate a large dynamic stress within the structure and is often important for assessing structural fatigue. For many of these force/structure scenarios, modelling of the force as a concentrated point force would be an adequate simplifying approximation. In some cases, however, it may not be appropriate to simplify the distributed force into a single point force. For instance, slug lengths in pipelines can be significant in relation to span lengths. There is currently no guidance in the literature regarding the distribution effect of the force on the response of a struc-ture under a moving force. This paper investigates the dynamic response of an elastic, simply supported beam under the influence of a moving distributed force, with varying distribution to span length ratios. In addition, it examines the speed of the traversing force, which is also highly influential on the dynamic response of the beam. This investi-gation is undertaken using an explicit transient dynamic finite element formulation of a simply supported beam. Guidelines are provided to discriminate between those scenarios when it is appropriate to simplify a distributed mov-ing force as a concentrated force, and those when it must be modelled as the original distributed force.
(1) School of Mechanical Engineering, University of Western Australia, Crawley WA 6009, Australia (2) College of Marine Engineering, Northwestern Polytechnical University, Xi'an Shaan 710072, China
ABSTRACT
Many structures have apparent symmetries, implying symmetrical mode shapes of vibration. Practically many of those structures show asymmetric mode shapes. Slight variations in structure geometry, boundary conditions and material properties are often the cause of such asymmetric vibration properties. In this paper, the finite element method is applied to analyze the vibration characteristics of a cylinder with a slightly varying diameter. The results indicate that some mode shapes of the cylinder vibration are very sensitive to the small diameter variation. The numerical results of the cylinder vibration are verified experimentally.
Environment Division, RailCorp, Sydney, Australia
ABSTRACT
This paper provides an overview of some recent developments in rail noise management practice with a particular focus on some of the challenges (both technical and non-technical) that often confront the implementation of effective mitigation. The paper illustrates these challenges by reference to a range of operational rail noise and vibration examples covering: ground-borne noise, in-tunnel noise, train horns, wheel squeal, stabling yards and level crossings.
(1) Professional Services Division, RailCorp, 36-46 George St Burwood NSW 2134 (2) Environment Division, RailCorp, 477 Pitt St Sydney NSW 2000
ABSTRACT
The measurement of passby noise for type testing of rail vehicles in Australia is governed by AS2377-2002 Measurement of Noise from Railbound Vehicles. This standard is referenced by many organisations including RailCorp (ESR0001-100 Minimum Operating Standards for Rolling Stock - General Interface Standards), ARTC (WOS 01.150 Environmental Interface) and Queensland Rail (EMS/STD/46/004 Code of Practice - Railway Noise Management), and therefore type tests for rail vehicles on most Australian rail networks are conducted in accordance with its recommendations. AS2377 lags behind the latest European standards such as ISO3095 Measurement of Noise Emitted by Railbound Vehicles (draft 2010) in two important areas however; it provides no guidance regarding the acoustic scale roughness of the rails, and the track decay rate, of the test track section. This paper explores the implications of these oversights, provides examples of the resulting changes in noise that can result, with implications for compliance with RailCorp's EPA licence, and describes how these important track properties are handled in ISO3095.
(1)University of Wollongong, NSW, Australia (2)Railcorp, NSW, Australia
ABSTRACT
The decay rate of rail vibration as a function of the distance from the excitation source is a key factor determining the general rolling noise contribution from the rail. A higher decay rate results in a shorter effective rail radiating length and therefore less noise emission from the rail. For the purpose of estimating rail noise radiation and evaluating the effectiveness of rail damping measures, the decay rate has to be determined accurately. The conventional impact hammer approach requires several hours of on-track time and normally manual data processing. An alternative method by using a passing train as the source of excitation requires track access to attach the sensors only and data processing can be automated. Results from the two methods have been compared for two elevated track situations. It was discovered that there is significant variation between the results obtained from the two methods. The reasons for the discrepancies may include the effect on the damping characteristics of the rail fastening system of the train's presence. The train pass-by method shows a good consistency over different train pass-bys.
School of Mechanical and Mining Engineering, The University of Queensland & CRC for Rail Innovation, Brisbane, Australia
ABSTRACT
In order to validate prediction models of wheel squeal, a two-disk rolling contact test rig has been developed to inves-tigate fundamental squeal behaviour. This test rig has been modified to allow for a range of angles of attack to be set and measured accurately, with a relative error about 1%. On the other hand, in order to perform a controlled investi-gation of the effects of humidity on wheel squeal, a humidity control system was set up in the enclosure of the test rig. Squeal noise was recorded at the different angle of attack, rolling speed and relative humidity, and the analysed results not only indicate the effect of these parameters initially, but also correlate well with the results from modal test and FEA. Furthermore, the test rig was retrofitted to measure the lateral force at the rolling contact patch with strain gauges on leaf springs.
Renzo Tonin & Associates (NSW) Pty Ltd
ABSTRACT
Electricity substations and their associated transformers are necessary for community power needs. In NSW these substations are often located in rural areas where background noise is low. Noise "hum" from the transformers can be an issue for residents located nearby to the substation, and the tonal and low-frequency nature of the noise can add to the annoyance. The NSW Industrial Noise Policy applies penalties for these noise characteristics when assessing such sources. This paper analyses noise measurements of substations in rural areas. One-third octave band noise measurements were conducted both close up to the transformers, and also in the residential community. The meas-urement results show that although tonal and low frequency characteristics might be evident close up to the trans-formers, these characteristics dissipate over distance and the INP penalties do not necessarily apply at the residential receiver.
(1) Renzo Tonin and Associates (NSW) Pty Ltd (2) University of Technology Sydney
ABSTRACT
Currently there are regulations and guidelines that governing bodies have adopted when dealing with the emission of noise that make reference to or imply the term of inaudibility when setting criteria to be met for mechanical plant and music noise after restricted hours. However, to date no such criteria has been established that can predict the inaudibility of these sources when combined with ambient backgrounds. As a result, stakeholders are met with uncertainty and designers are left with an inadequate subjective term when attempting to meet location-specific noise criteria. This paper involves an investigation into the possibilities of conducting a psychoacoustic experiment that will test for the inaudibility of mechanical plant and music noise in the presence of ambient background noise typical of the home environment situated in urban and suburban locations. This paper attempts to provide the framework for future larger scale investigations and provides the relevant findings and a methodology to assist in reducing the subjective nature of the responses observed. Through these future investigations, objective definable criteria from which to establish the inaudibility of mechanical plant and music noise in the presence of ambient background noise may be established.
Faculty of Architecture, Design and Planning, The University of Sydney, NSW 2006, Australia
ABSTRACT
The directivity of an electroacoustic sound source can be controlled by dividing its surface into independently controlled elements, and there have been several approximately spherical loudspeaker arrays developed from this idea recently. This paper describes a virtual dodecahedral loudspeaker array, which is achieved using a sealed loudspeaker possesing a single driver (through successive measurements). We compare the measured spatial response of this loudspeaker to a computer modelled loudspeaker array in terms of the applicable spherical harmonics.
(1) gfai tech GmbH, 12489 Berlin, Germany (2) Signal Processing, Society for the Promotion of Applied Computer Sciences (GFaI) eV, 12489 Berlin, Germany (3) HW Technologies, Telopea NSW 2117, Australia
ABSTRACT
Many acoustic indicators used in the standards of room acoustics consist of global criteria which allow characterizing the most important properties of a room relatively well. In addition to the well-established and standardized methods, the application of three-dimensional microphone arrays in connection with calculations in the time domain (delay and sum beamforming) can give far more detailed insights. However, the application of 3D-beamforming requires a geometric CAD-model of the room which is often not readily available in practice. This paper shows an approach that is based on using a 3D-scanner to quickly acquire the geometry information of the room. The scanning times achieved are in the range of a few minutes. The scan points recorded by the scanner are algorithmically processed to a sufficiently dense and homogenous 3D-mesh. The room model computed this way then forms the base for the following acoustic 3D-beamforming. This combined system of scanner and array allows a very fast evaluation of interiors. The advantages, the possible application ranges as well as the limits of the method will be discussed, and practical application examples from real environments will be shown.
Faculty of Architecture, Design and Planning, University of Sydney, Australia
ABSTRACT
Typical attempts to collect sets of head-related transfer functions (HRTFs) attempt to remove from the derived transfer functions the acoustical properties of the sound source used to make those measurements. This is done so that the directionally-dependent variations in the binaural response at the receiver's location can be independently characterised. For sound sources that are far from the receiver's location, this is appropriate and relatively straightforward to achieve. However, at close range (e.g., at distances between source and receiver position of less than 1 meter), characterising the variation in derived transfer functions that is dependent upon the acoustical characteristics of an orally-radiated source becomes potentially useful. The measurements reported here attempted to capture both source and receiver characteristics for a particular case, that in which the sound source is radiated from the mouth of an anthropomorphic manikin, and is received at the ear of a nearby manikin. Substantial range-dependent variation in the measured transfer functions was observed, clearly due to the presence of reflections between the surfaces of the source manikin and the receiver manikin's head. These results have implications for spoken telecommunication applications employing headphone-based virtual acoustic simulations.
Scientific Acoustics, Toowoomba, Australia
ABSTRACT
The performance of a public address system for a road tunnel is currently specified in project documents in terms of the required Speech Transmission Index ( STI ) (Typically 0.5 or greater in line with AS1670.4 ) to be delivered throughout the tunnel in the presence of substantial background noise. The derivation of a guaranteed level of performance from a loudspeaker system in such an environment requires precise data defining the tunnel's acoustic properties and physical properties as well as loudspeaker acoustic data and physical dimensions. Commission testing is commonly performed using one of the currently available systems compliant with IEC 60268-16, such as the NTI'XL2' and "Talkbox" system. This paper aims to evaluate the quality of outcomes derived from existing design approaches using currently available software such as Ease 4.3, Easera 1.1 and an NTI XL-2 analyser system. Tests were conducted entirely within the software platforms. The results show that reliability of Tunnel acoustic calculations, in particular, reverberation time, is not good. Substantial variations can be attributed to (a) challenges in dimensioning software models, (b) challenges in obtaining sufficiently accurate absorption coefficients whether approximated or measured ( c ) challenges in obtaining reliable test data on real, completed, tunnels. Challenges were also encountered in obtaining certifiable octave band noise data, which, when coupled with unreliable reverberation time calculations, further reduced the reliability of Loudspeaker system performance calculations. The hostility of the acoustic environment in the tunnels under investigation was dictated by non negotiable material choices thereby further limiting the designers choice of a suitable device. Substantial differences were found in the relative merits of different loudspeakers and system topographies. The requirement for a flat frequency response was found to be somewhat subjective in nature given the high priority requirement to achieve a minimum STI reading according to a test system using STIPa audio signals.
Stacey Agnew Pty Ltd, Brisbane, Australia
ABSTRACT
Long reverberation times and high background noise levels associated with jet fans degrade speech transmission in road tunnels. Sound attenuation and reverberation time measurements in the Sydney Harbour Tunnel are used here to calibrate a mathematical model used to estimate speech transmission index STI. This study forms a basis for future work in the evaluation of acoustic design alternatives for public address systems required for communication to motorists who may become stranded within the tunnel during normal operations or tunnel emergencies.
Photonics Research Laboratory, School of Engineering, Edith Cowan University, Joondalup, Australia
ABSTRACT
In this study, acoustic emissions (AEs) were detected through a variety of different flooring materials using a fibre Bragg grating (FBG). The AEs were generated using a low velocity impact test, and by footstep. The acoustic vibrations cause a strain in the optical fibre, and hence alter the wavelength reflected by the FBG. This strain iduced wavelength shift can then easily be detected by converting this wavelength shift into an intensity change. This is done using an intensiometric detection system, where a laser is tuned to the 3dB point of the FBG, and the optical power transmitted and reflected is modulated by the spectral shift of the FBG. The intention is to use FBGs as an in-ground intrusion detection system to detect the AEs generated by an intruder walking within range of the sensors. This type of intrusion detection system can be applied to both external (in soil, etc) and internal (within the foundations or flooring of the home) security systems. The results show that the AEs can clearly be detected through wood, ceramic tiles, aluminium and concrete.
(1) Acoustics Group, Department of Information Technology, Ghent University, Gent, Belgium (2) IBCN, Department of Information Technology, Ghent University, Gent, Belgium
ABSTRACT
The research project IDEA: intelligent distributed environmental assessment, is aimed at using new capabilities of-fered by consumer hardware to deploy sound monitoring methodologies that approach human environmental sound perception as closely as possible. The low cost noise measurement nodes deployed in the network pre-process the sound to a data set that can be transmitted continuously to the central servers. On these servers basic acoustic features are extracted and a self organizing map is trained to represent commonly co-occuring ones. Once an initial mapping is available all incoming sound is analysed and recorded when (1) the combination of features is not recognized, indi-cating unexpected sounds; (2) the feature set matches so closely a unit in the map that the sound can be used as a pro-totype. Unrecognized sounds trigger attention which leads to further training of the self organized map and potential alerts. The implementation of the above methodology resulted in a tool that allows getting detailed and useful infor-mation on the sounds that people will observe in a certain environment by mapping frequency of occurrence - and dominance of different classes of sounds that can easily be auralised for example in the context of soundscape design.
AECOM, Brisbane, Australia
ABSTRACT
With the rapid increase in the use of smartphones such as the Apple iPhone and Android-based phones, a range of low cost acoustic tools are now available to acoustic professionals and the general public. This paper explores some of the software tools currently available for smartphone devices, evaluates their measurement accuracy and dis-cusses their potential place in the acoustic professionals testing and analysis kit. The results of several experiments comparing the results from "traditional" sound level meters and smartphones are presented. Tested scenarios include sound pressure measurements from various sources and room acoustic measurements. A review of the shortfalls of the smartphone based tools currently available is also undertaken. The results of the study show that these new de-vices can provide useful results under some measurement conditions. However there is as yet no substitute for a sound level meter designed and calibrated in accordance with the relevant international standards.
Defence and Systems Institute, University of South Australia, Mawson Lakes, SA 5095, Australia
ABSTRACT
A novel technique for remotely monitoring the near-surface air temperature and wind fields based on measurements of the Doppler shift in frequency exhibited as a result of the varying propagation delays between an unmanned aerial vehicle UAV and different acoustic ground receivers is presented. The technique measures the onboard spectrum of sound signals emitted by the engine of an UAV, transmits them to the ground using high bandwidth radio communications and compares them to the Doppler shifted spectra received over propagation paths to several ground-based acoustic receivers. The data are then converted into effective sound speed values using tomographic techniques to reconstruct a two-dimensional grid of spatially varying atmospheric temperature and wind fields.
(1) Faculty of Engineering and Surveying, University of Southern Queensland, Toowoomba, Australia (2) Gas Detection Australia, Toowoomba, Australia
ABSTRACT
The work presented in this paper addresses the problem of creating a low-cost, intrinsically safe, low-level gas sensor for mining and transportation applications. The system is to have no electrical connection to the remote sensor head, and as such relies on optical transmission via fibre. An integral component is the acoustically resonant chamber, which is excited by an appropriate laser excitation. The laser is modulated at the resonant frequency of the chamber to create periodic heating, causing expansion. This is followed by cooling and thus contraction, resulting in a periodic pressure wave. The pressure wave is amplified in the resonant chamber, and then measured using an optical microphone approach. This makes the sensor inherently safe, as there are no electronics at the sensor head nor electrical connections required. A particular challenge associated with this approach is the acoustic signal generation and extraction from very high levels of noise. This paper gives a background on the photo-acoustic method, and describes our approaches to the development of physical hardware and processing algorithms required for an embedded sensor.
Technical Operations, Department of Environment and Resource Management, 400 George Street, Brisbane, Australia
ABSTRACT
A methodology to assess the environmental impacts from high power underwater sound sources on marine mammals and fishes is presented. The methodology was first developed for low frequency navy sonar and was later extended to different types of high power underwater sound sources, including underwater blasting for demolition and shock testing and seismic surveys. The methodology assumes that any species of marine mammal or fish may be present and defines several impact zones corresponding to different impacts, including inner ear injuries, temporary threshold shift in hearing, fish kill, and also safe stand-off distances for divers. The size of the impact zones depends on several key factors including the level of the anthropogenic sound radiated underwater, its nature such as the duration and frequency characteristics, and the sound propagation characteristics of the marine environment which are dependent on such factors as water depth and sea bed material. The methodology was first developed and tested by the UK Ministry of Defence to conduct underwater environmental impact assessments to protect underwater wildlife from the procurement of a low frequency sonar. It was later successfully applied to the demolition of the North Sea petrochemical Phillips 66 Maureen oil platform sub-structure. The methodology can be tailored to any specific marine species or generalised when any type of marine animal may be present in a location. This means the methodology can be applied to a wide range of projects that need to use high level underwater sound sources which may impact on marine fauna. The implementation of the methodology has ensured no incidents have occurred during the deployments of all low frequency sonar trials in the UK.
9 Moya Crescent, Kingsgrove NSW 2208
ABSTRACT
The Cooks River is a 23-km meandering urban waterway of south-western Sydney, and empties into Botany Bay. The tidal section is around 11 km long and supports significant numbers of mangroves, birds, and fish. Due to the tides, the salinity fluctuates but falls off slowly with distance upstream. Underwater ambient noise has been measured from 18 bridges over the lower 12 km of the river. Apart from occasional traffic noise that transmits into the river from some bridges, the only sounds heard underwater have the characteristics of (saltwater) snapping shrimp. The Sound Pressure Level of the strongest snaps is in the neighbourhood of 180 dB re 1 microPa^2 at positions up to 3 or 4 km upstream from the river mouth, but then falls steadily as the measurements are repeated further upstream, although a previous survey of snapping shrimp distribution with a dipnet found a population 9 km upstream. The present finding is however consistent with previous findings for benthic life generally, which suggests that the snapping shrimp distribution may be limited by available food. The quieter sounds upstream are due to propagation of sound from the shrimp within 4 km of the mouth rather than more local shrimps, even though there are three 90-degree bends in the river course upstream of 4 km. Previous work has found that much of the riverbed is mostly sand, and should thus be a good reflector of sound.
Global Detection Systems, Sydney. Adjunct Principal Research Fellow. School of Engineering & Physical Sciences, James Cook University
ABSTRACT
Acoustic methods to mitigate bycatch in gillnet fisheries commenced in the mid 1980's after 14,000 dolphins died in NW Australian waters. Similar events in the North Pacific resulted in the development of acoustic pingers (≈ alarms) and an assessment of sonar aspects of fishing gear. Biosonar studies indicated toothed whales had capabilities to detect nets although mortalities continued. Alert animals (all cetaceans) detected obstacles while inattentive animals were at greatest risk. Uptake of pingers within mitigation strategies has been patchy. In hindsight after three decades, some pingers have been poor while others were used inappropriately in order to attain equivocal results to facilitate fishery closures. Even when the same pinger/species combinations outside Australia proved highly successful there is a reluctance to recognise the technology in Australia. In 1992 the International Whaling Commission considered that bycatch mortality would eventually be eclipsed by mammals depredating fish product from commercial fishing operations. Toothed whales and pinnipeds now take significant percentages of the world catches of line based fisheries and aquaculture facilities. Australia no longer has large scale drift net fisheries. There is however, a need to alert mammals with passive biosonar (dugongs, dolphins and baleen whales) and active sonar (dolphins) if the acoustic signatures of the net and vessel were not detected. There is also a need to dissuade toothed whales from the immediate vicinity of smaller nets to prevent the growing problem of depredation of the net catch so prevalent internationally. Achieving these effects with pingers at low Source Levels is a current challenge for pinger manufacturers recognising the problems associated with continual sound exposure. A 4th generation pinger is demonstrating significantly reduced longline depredation and reduced entrapment in fish trawls and purse seines. Interference of returning biosonar echoes to depredating toothed whales using pingers and logistically appropriate sonar reflective material are also showing potential.
A recent development is an offshore GPS gear localisation buoy for the fishing industry with an acoustic detection capability to identify depredation on fishing gear. This capability will permit fishery operators to take steps to minimise depredation interaction time along with the exposure time to pingers and sonar reflective techniques. An overview of marine mammal bycatch and depredation mitigation is presented. However, commercial fisheries usually adapt to cost benefits much faster than directed research projects indicating that economic indicators for mitigation will always be the gauge as an indicator for success. Understanding the sonar basis for depredation would provide the rigour to this process.
(1) Centre for Marine Science and Technology, Curtin University, Perth, Western Australia (2) Defence Science and Technology Organisation, Sydney, NSW (3) Institute of Marine Science, University of Sydney, Sydney, New South Wales, Australia (4) Scottish Oceans Institute, University of St. Andrews, Scotland
ABSTRACT
Combined visual and acoustic surveys for beaked whales (BWs) were carried out between 15th August and 25th September 2008, and between 8 July and 2 August 2009 in an area of the Coral Sea used for naval exercises. These surveys were part of a collabora-tive project between the Universities of Sydney, Queensland, Curtin University and the Defence Science and Technology Organisa-tion (DSTO) aimed at trialling methods for detecting BWs, and determining their distribution across the exercise area. One of the methods trialled in the survey was the deployment of high-frequency (HF) noise loggers on drift moorings for 2-3 days at a time. A HF noise logger was developed by the Centre for Marine Science and Technology (CMST) at Curtin University specifically for this project. The HF noise loggers were deployed autonomously on drift moorings for durations ranging from 1 hour to over 3 days dur-ing the Coral Sea surveys. Over the two surveys, there were 14 deployments in the survey area, which combined recorded 225 hours of underwater sound sampled at 192 ksps. Thousands of clicks that are likely to be BW echolocation clicks were detected in the HF noise logger recordings.
(1) National Acoustic Laboratories, Australia (2) Hearing Co-operative Research Centre, Sydney, Australia
ABSTRACT
The aim of the study was to establish the accuracy with which individuals can estimate the noise level of everyday events to which they are exposed. A group of 45 volunteer participants was recruited to wear personal noise exposure meters for periods of up to five days. The volunteers kept diaries of their daily events and were requested to estimate the noise level of all events on a 1 to 10 Likert scale. The results showed that participants could successfully estimate the noise level of daily events, suggesting that individuals are able to make reasonable estimates of the noise level of events they experience. This result is of potential significance for those interested in producing effective hearing health awareness programs in that individuals may be able to assess their own degree of hazard exposure.
AECOM, Brisbane QLD 4006, Australia
ABSTRACT
Hospitals include a multitude of different spaces with a wide range of sensitivity and privacy requirements. Each space may be used for a variety of activities that have differing sensitivity levels and generate varying levels of noise. Similar types of spaces within the same hospital can also have quite different design considerations depending on the department and users. This information is often not fully captured in the project brief, nor in prescriptive healthcare guidelines. Consequently, the practicality of achieving acoustical criteria must be considered. Operational constraints such as cleanability, hygiene and access requirements can limit the use of some acoustic treatments, and in some circumstances restrict the ability of a space to achieve certain acoustic outcomes. This paper provides a discussion of the approach to acoustic design of hospital projects and the factors that should be considered in the acoustic design approach. A review of international healthcare guidelines has been undertaken and the requirements qualified against real world mitigating factors. Two case studies are included to highlight the difficulties that occur in the design of real healthcare facilities. These case studies demonstrate that while health care guidelines are a useful starting point, these guidelines must be moderated with an understanding of the user groups and design constraints. In this way, project specific design criteria and solutions can be developed that are workable and still deliver key design outcomes.
(1) Ron Rumble Renzo Tonin, 96 Petrie Terrace, Petrie Terrace QLD Australia 4000 (2) School of Mechanical and Mining Engineering, The University of Queensland, Brisbane, Australia 4072
ABSTRACT
The prediction of crowd noise is a problem faced by acoustical consultants. Although consultants are frequently required to predict noise emissions from activities involving crowds of people, there are no reliable prediction methodologies available. In the past, reliance has been made upon the adoption of results measured at similar venues or by extrapolating the vocal effort from an individual to derive the overall level for a defined crowd size. Applying these methodologies can result in prediction errors as large as 15dB(A), indicating that they do not correctly characterise this type of noise. To derive an appropriate prediction methodology, the authors have investigated the factors that influence the generation of crowd noise such as the Lombard effect, crowd size, orientation of individuals within the crowd and whether individuals act together as a synchronised source or behave randomly. Using these factors as a basis, a series of controlled and uncontrolled experiments have been conducted in order to derive a set of equations that are suitable for use by consultants to predict the noise emissions from small to medium sized crowds (up to 100 people) located in out-door spaces.
School of Mechanical Engineering, The University of Adelaide, Adelaide, SA, 5005
ABSTRACT
This paper presents the results of research into the effectiveness of auditory warning signals for emergency vehicles. Recommendations are provided to improve the effectiveness of warning sirens to alert motor vehicle drivers. Physical and psychoacoustic issues are explored, along with consideration of various mounting locations for siren loudspeak-ers.