Full PaperUNSW Sydney
ABSTRACT
The flow-induced noise produced by a surface-mounted three-dimensional (or finite length) airfoil is important for many aerodynamic and hydrodynamic applications. Examples include wing-fuselage junctions, turbomachinery blade, rotor tip and end-wall flows, and ship appendage and hull-junction flows. This paper provides an overview of the three-dimensional airfoil noise program at UNSW Sydney. In general, there are four flow regimes for a three-dimensional airfoil. These are the airfoil-wall junction flow featuring a horseshoe vortex that wraps around the airfoil base; turbulent flow interaction with the leading edge; trailing edge flow whose structure depends upon the Reynolds number; and the tip flow that consists of vortices that form as the flow wraps around the free-end of the airfoil. The acoustic signature and turbulent noise sources associated with each of these flow regimes will be examined using anechoic wind tunnel measurements obtained with acoustic array, unsteady surface pressure and turbulence measurement methods.
University of Technology Sydney
ABSTRACT
The impact of the invention of the laser cannot be overstated. In vibration and acoustics engineering, the laser Doppler vibrometer has revolutionised the means by which scientists and engineers can interpret and control the natural and man-made environment, both on and off the planet. Combining high sensitivity, dynamic and frequency ranges, non-invasiveness and high spatial resolution, laser Doppler vibrometers (LDVs) have received significant and increasing attention in both research and industry. This paper will briefly investigate the origins, working principles and evolution of LDVs, focusing on industrially relevant, practical applications. Particular focus will be on overcoming specific challenges associated with making successful measurement campaigns in challenging scenarios, including directly from rotating equipment and from vibrating platforms, a UTS topic of interest.
(1) Defence Science and Technology Group (2) UNSW Sydney
ABSTRACT
Acoustic metamaterials are rationally designed composites for which the effective material properties go beyond those of their bulk ingredients. A simple design of an acoustic metamaterial for maritime applications comprises a lattice of resonant scatterers embedded in a host elastic matrix. This composite design facilitates multiple scattering of waves and strong acoustic coupling between scatterers. Due to their extraordinary wave manipulation capabilities and the tremendous progress in fabrication technology, acoustic metamaterials are becoming immensely popular for noise control. However, the analytical and numerical treatment of acoustic metamaterials is still a challenging undertaking. The Maritime Division of the Defence Science and Technology and the School of Mechanical and Manufacturing Engineering at UNSW have developed a range of analytical and numerical tools to determine the acoustic performance of metamaterials for maritime applications. To this end, we have translated some well-known analytical results from electrostatics, fluid dynamics, diffusion kinetics, and solid-state physics to develop homogenisation and effective boundary approximation approaches. This paper provides an overview of our approaches for tailored designs of acoustic metamaterials.
Flinders University
ABSTRACT
Despite widespread community acceptance of renewable power generation to reduce CO2 emissions and natural resource impacts, large-scale expansion of wind farms has prompted significant community debate regarding adverse health impacts of wind farm noise (WFN). Our research has aimed to investigate this issue by identifying, quantifying, and characterising the components of WFN that are responsible for annoyance and sleep disturbance. In this study, we carried out 1-year-long acoustic and meteorological measurements at three residences located near different wind farms, allowing detailed characterisation of WFN and its relationship with meteorological conditions. At two of these residences, participants recorded their subjective annoyance, providing insight into the relationship between specific noise features and human response. To detect amplitude modulation (AM), which is a particularly annoying component of WFN, we used a novel detection algorithm which significantly outperformed previous methods. Application of this algorithm revealed that AM prevalence was 2 to 5 times higher during the nighttime compared to the daytime. Annoyance due to WFN was reported most often during the nighttime and early morning, consistent with the measured AM prevalence. Participants most often described the noise as a "swish" or "swoosh" and the presence of these signal components was confirmed via spectral analysis.
(1) Acoustic Studio
ABSTRACT
The Australian rail industry has made remarkable progress over the last fifteen years to better understand rail noise and devise mitigation strategies. There have been significant developments in curve noise, locomotive noise, and general rolling noise, both in understanding their root causes in Australia and in how to reduce these types of noise. But the industry has been slow to implement these developments and risks losing its reputation as an environmentally friendly mode of transport. This paper explores the successes, failures, and untapped opportunities in regards to implementing noise mitigation. We emphasise understanding the broader rail system and the drivers of rolling stock and network operators, and how acousticians can leverage this broader context. We then examine rail noise mitigation through the lens of opportunity cost. With reference to recent examples, and the current rail infrastructure boom, we pose a challenge to regulators, planners, operators and proponents to be open to different ways of implementing mitigation.
(1) UNSW Sydney (2) Bundeswehr University Munich
ABSTRACT
Measurements of the far-field sound radiated by two and three-dimensional supercritical airfoils operating in a low Mach number flow were performed in an anechoic open-jet facility. For the three-dimensional case, two aspect ratios (AR = span/chord) of 1.0 and 1.5 were considered. The far-field sound was measured using a 64 microphone phased array placed outside the flow region and the array output was beamformed to reveal the acoustic sources. The results show that the trailing-edge noise from the 2D airfoil is larger than the 3D cases up to a frequency of 5 kHz, while above 7 kHz, the 3D airfoils generate more noise. Further, for the 3D airfoils, trailing-edge is the dominant noise source at 4 kHz, whereas at 8 kHz the source is concentrated near the free-end of the trailing-edge. Qualitatively, the source behaviour is the same for both ARs, but the airfoil with lower AR generates less broadband noise.
(1) Defence Science and Technology Group (2) YTEK Pty Ltd
ABSTRACT
Vehicles moving through a fluid all suffer from unwanted noise and vibration from turbulent boundary layer excitation. Industries involved with designing planes, trains and automobiles have consequently invested heavily in its control. Large levels of noise and vibration can negatively impact on passenger and crew comfort as well as contributing to environmental noise. This paper details a novel approach for estimating the unsteady pressure at the trailing edge (TE) resulting from the turbulent boundary layer of a rotating propeller blade. This methodology is based on the semi-empirical method of Brooks, Pope and Marcolini known as the BPM method. Using a spanwise-strip implementation, the far-field TE noise is calculated for multiple points along the TE of the propeller surface of interest and at different positions of the propeller rotation. To provide quantitative validation of the numerical model, we present a comparison of estimated noise and trailing edge pressure characteristics with results obtained via experiment in the open literature. The noise estimates shown provide varying agreement using predictions of the flow field from the original empirical relationships and with those calculated using Reynolds Averaged Navier Stokes (RANS) CFD and the potential flow panel code XFOIL. The derived surface pressure characteristics are useful when evaluating the unsteady loading from the blade boundary layer flow.
(1) UNSW Sydney
ABSTRACT
Airfoil-turbulence-interaction noise, which is created whenever turbulent flow encounters an airfoil, is a major contributor of unwanted noise emitted by aircraft, turbomachinery and alike. The experimental study presented here is the precursor to a larger investigation of the impact of complex turbulence on noise generation at the airfoil's leading-edge and airfoil-wall junction. In the current study, we examine links between the experimentally acquired properties of isotropic turbulence and the sound radiation of the immersed airfoil. This is achieved by varying the in-flow turbulence intensity using two different turbulence grids. A NACA0012 airfoil was analysed at a range of geometric angles of attack up to 16 degrees and Reynolds numbers of 1x105 up to 3x105. Stereoscopic Particle Image Velocimetry (SPIV) was conducted beforehand to capture the turbulence characteristics of the free flow. Additionally, acoustic beamforming with a phased microphone array provides insight into the sound generation at the leading-edge. Pressure taps along the centre chord-line were used to measure the mean static pressure, thereby allowing for an open-jet deflection correction of the angle of attack.
(1) RMIT University (2) Defence Science and Technology Group (3) UNSW Sydney
ABSTRACT
Large eddy simulation (LES) has the potential to be a high-fidelity approach for predicting broadband noise from turbulent boundary layer flow, with the predicted surface pressure fluctuations providing an input to acoustics analogies. However, the practical application of conventional wall-resolved LES is limited by high computational cost. Therefore, wall-modelled LES (WMLES) has been investigated as a means to reduce this cost. Simulations were carried out using OpenFOAM, with channel flow as a test case. Predictions from both wall-resolved and wall-modelled approaches were compared against data from direct numerical simulation (DNS). The accuracy of WMLES was found to be comparable to that of wall-resolved LES over most of the channel, while incurring less than a tenth of the cost. However, near-wall accuracy of the boundary layer statistics from WMLES was reduced, resulting in a reduction in accuracy for the estimated wall pressure fluctuations. As an alternative approach, a semi-analytical method has been tested, which does not rely on the pressure fluctuations. Instead, a model derived from a Fourier transform solution of the pressure Poisson equation was implemented, with the boundary layer parameters supplied by LES. The accuracy of the resulting spectra for each LES method is discussed.
(1) UNSW Sydney
ABSTRACT
An experimental study on aeroacoustics of low Mach number flow over a forward-backward facing step (FBS) with aspect ratio of 8 is presented. The height of the step being considered was 50% of the incoming boundary layer thickness (h/d = 0.5) and the Reynolds number based on the step height Reh ranged from 1.4 x 10^5 to 2.8 x 10^5. The acoustic measurement was conducted using a 64-microphone-phased array in the UNSW Anechoic Wind Tunnel (UAT). The beamforming results show that the noise source locates at the leading edge of the step. The sound spectra obtained from the centre microphone of the array show that noise produced by the step is generally broadband without any distinct tonal noise. The data at different flow speeds collapse well using the scaling law proposed by Doolan and Moreau (2014).
(1) Monash University
ABSTRACT
An analysis of the symmetry-locking mechanism in screeching twin-jet systems dominated by axisymmetric modes is performed in this work. The different waves supported by the flow in a range of jet conditions are obtained by means of a twin-jet vortex sheet model, which considers the shear layer as an infinitesimal region. Analysis of the bands of existence of upstream waves in the flow suggest that the jet separation greatly affects the ability of the flow to support anti-symmetric screech modes, while symmetric modes remain relatively unaffected by this parameter. Comparison with acoustic data shows that most tones lie in the frequency bands of existence of guided jet modes, supporting the hypothesis that resonance is closed by these waves. The dominant symmetry for each condition is obtained by means of a symmetry-imposed spectral proper orthogonal decomposition of schlieren data, which provides both mode shapes and energies of the most amplified coherent structures in the flow. Overall, it is shown that symmetric modes are more energetic for very low spacings, and no clear dominance is found for large spacings.
(1) Defence Science and Technology Group (2) UNSW Sydney (3) Swedish Defence Research Agency
ABSTRACT
Noise generated by turbulent flow over high-aspect ratio bluff bodies is of interest in many engineering applications including the design wind turbines, aircraft and marine vessels. This study investigates the noise produced by a large span circular cylinder in cross-flow at a Reynolds number based on diameter (ReD) of 22,000. Large eddy simulations and the Ffowcs Williams and Hawkings acoustic analogy were used to simulate the aerodynamic and aeroacoustic fields around both full- and reduced-span cylinders, with aspect ratios of 18.75 and 4.0 respectively. At ReD=22,000, there is well-documented evidence of a low-frequency modulation of the fluctuating lift force, which is evident in the present results. The modulation means that very long runtimes are required to reach statistical convergence for the full-span cylinder. The modulation is not observed in the reduced-span simulation results, which significantly reduces the time taken to reach statistical convergence. The sound pressure levels (SPL) predicted from the full-span simulation are consistently 3-6 dB below experimental values. The SPLs predicted by scaling the reduced span simulation were in better agreement with the measured values, particularly around the vortex shedding frequency. These results show that more accurate far-field acoustic predictions can be obtained by scaling the results from the reduced-span simulation, when compared to the full-span predictions.
(1) UNSW Sydney
ABSTRACT
This paper presents an experimental investigation of the tip vortex formation noise produced by a wall-mounted finite airfoil. To characterise the noise at the wingtip, acoustic measurements taken in the UNSW open jet anechoic wind tunnel with a planar microphone array are presented for a NACA 0012 airfoil with varying aspect ratios at different geometric angles of attack and chord-based Reynolds numbers. Measurements of the mean streamwise total pressure field at the wingtip using a single pitot probe for selected test cases are included to link the flow dynamics with noise production. Furthermore, the flow interaction between the wingtip and the wing-wall junction region and its effect on tip noise generation for a low aspect ratio (AR = 0.2) NACA 0012 airfoil will also be examined.
(1) UNSW Sydney (2) Defence Science and Technology Group (3) Technical University of Munich
ABSTRACT
A technique to investigate the contributions of aeroacoustic sources to the sound power is presented. The method combines the Lighthill source distribution with an acoustic impedance matrix constructed from radiation kernels of the free-field Green's function. By calculating the contributions of aeroacoustic sources to sound power, the location and nature of the dominant flow noise sources are identified. To demonstrate the technique, the flow noise produced by a pair of co-rotating vortices is examined. The aeroacoustic contribution of each component of the Lighthill tensor is determined for a range of wavenumbers, with key findings discussed.
(1) Consultant Engineer (2) Pulse White Noise Acoustics (3) UNSW Sydney
ABSTRACT
Buildings are an enormous consumer of energy, due to air leaks alone buildings waste up to 5% of all energy worldwide. Building envelope airtightness is therefore of paramount importance to minimise energy consumption and to meet cut carbon emissions by 2050, as set out by the Australian Government. Air permeability rate testing is also becoming a requirement for various building rating systems such as WELL and Green Star and must be performed to obtain the relevant credit points. The commonly used current standard measuring technique for air permeability is the blower door test, while thermography and smoke pens are widely used for air leak detection. All these methods have in common, that a difference of either pressure or temperature between inside and outside of the building must be established. Moreover, the blower door test is labour and time intensive. To meet the demand for increased building airtightness and testing, more efficient methods areneeded. Following the principle that sound travels the same path as leaking air, acoustic based techniques are proposed. Among those techniques the acoustic imaging shows best potential benefits. This paper provides a short summary of the research published in this area and the plan for further research.
(1) University of Technology Sydney (2) INSA-Lyon (3) Naval Group Research (4) Technical University of Munich
ABSTRACT
In many engineering applcations it is important to identifiy the regions on a vibrating structure which radiate energy to the far field. This work analytically formulates a surface contribution technique based on non-negative intensity in the wavenumber domain to investigate the surface areas on a vibrating planar structure that are contributing to the radiated sound power in the far field. The non-negative intensity is derived in terms of the cross spectrum density function of the stochastic field and the sensitivity functions of either the acoustic pressure or normal fluid particle velocity. A simply-supported baffled panel excited by a turbulent boundary layer or an acoustic diffuse field is considered to illustrate the technique. The region of the panel contributing to the radiated sound power are identified. The non-negative intensity distribution is shown to be dependent on stochastic excitation. It is also observed that the more the non-negative intensity distribution is localised within the panel surface, the more effective the panel radiates sound to the far field.
UNSW Canberra
ABSTRACT
Anita Lawrence was a pioneer in acoustics in Australia and a pivotal contributor to the formation and development of the Australian Acoustical Society (AAS). She was involved at the outset and continued throughout the decades. She contributed greatly to the international reputation for AAS via her role in the hosting of international meetings in Australia. In addition to initiating courses to provide acoustic education, her contributions were broad and included important research findings relevant to the Australian context and the development of Australian Standards. Her passion for acoustics, especially for quality of acoustics inside and outside buildings, has led to a legacy in her generous donations to the University of New South Wales. Her bequest is to be used solely to provide scholarships for PhD students studying acoustics within the School of the Built Environment. This paper will outline some of the achievements of Anita Lawrence.
(1) The University of Sydney
ABSTRACT
Seat preference in a concert hall is affected by both auditory and visual conditions. While traditional concert hall preference studies have mainly focused on auditory preference, visual preference has drawn more recent attention, as the importance of audio-visual interaction has been emphasized. For combined audio-visual studies, using virtual reality simulation with head-tracked audio provides more flexibility and control compared to in-situ studies, while maintaining most spatial information that would be lost in experiments merely using photos and/or binaural recordings. Furthermore, with the popularization of head-mounted virtual reality devices and the ease of online file transfer, the experiments need not be limited to laboratories. This paper provides an overview of techniques used for such experiments and briefly discusses relevant findings.
Acoustic Directions
ABSTRACT
The simple method that J. H. Rindel recently published to predict patron noise in eating establishments is based on a model of the Lombard Effect. This method provides a substantial increase in accuracy over the commonly-used prediction method which assumes raised voices and 10*log(number of talkers). A key outcome of the Lombard model is that noise levels increase by approximately 20*log(number of talkers). Although Rindel's method is not yet widely used in Australia, it is now documented in the Patron Noise Guideline prepared by the Association of Australasian Acoustical Consultants. Rindel's statistical method has several simplifications, which can potentially result in over or under predictions. The proposed extension to this statistical method includes the use of octave-band room constants and the contribution of the direct field of talkers, which allow it to be used in situations with low reverberation such as outdoor terraces. The extended method is illustrated with a comparison of predicted and measured noise levels in two situations; the first is a busy Sydney bistro with patron numbers varying from 40 to 160 over an afternoon; the second is a restaurant, before and after sound absorption was installed. The effects on the predictions of the key parameters of Lombard ratio and Speaking Group Size are also explored.
Marshall Day Acoustics
ABSTRACT
The recently opened Phoenix Central Park is a building space dedicated to art, performance, nature and culture. The result of an open architectural brief based around the German concept of gesamtkunstwerk, that is, a total work of art. At the heart of the building is an intimate performance space, with a folded bell shaped internal form. The space does not have a stage or traditional seating, but instead invites artists to perform from anywhere in the space and audiences to likewise find their own place to experience the performance. The first acoustic challenge was to determine what the space should sound like, given an open brief and few boundaries of how the space would be used. The design challenges increased as the form of the space evolved with complex geometries and the need for a coherent singular expression and not with acoustics as an add-on. The finishes presented unique challenges, including gilded/gold leaf acoustic panels and ultimately a singular bell shaped room constructed with stepped and contoured free-formed cross laminated (CLT) components incorporating tuned acoustic resonators. The Phoenix opened in 2020 and has been well received by audiences and critics alike.
University of Technology Sydney
ABSTRACT
This paper introduces the newly built sound transmission loss suite at the Centre for Audio, Acoustics and Vibration (CAAV) at the University of Technology Sydney. This report covers vital parameters of the transmission loss suite when testing a typical heavyweight masonry wall, including the background noise, the spatial variations of the sound pressure level, the reverberation time, the absorption coefficients and the transmission loss. The averaged overall background noise level inside the receiving room is 21.3 dB or 15.5 dBA, approaching the test system/equipment's range. The standard deviation of the sound pressure levels in each test room is less than 1.6 dB in one-third-octave bands with centre frequencies between 100 Hz and 5000 Hz. The weighted sound reduction index (Rw) of the test wall is 66 dB with spectrum adaptation terms (C and Ctr) being -1 dB and -6 dB for the A-weighted pink noise spectrum and urban traffic noise spectrum, respectively.
SoundBASE Consulting Engineers
ABSTRACT
Two case studies involving the reduction of structureborne noise due to use of boxing bags and the dropping of heavy barbells during deadlifts are presented. The boxing bag isolation varied from the usual installation method as the client wanted to suspend the boxing bags via framework suspended from the underside of the suspended concrete slab above. The deadlift isolation involved testing different rubber tiles on an on-ground concrete slab to reduce the structureborne noise moving laterally into the adjoining commercial tenancy. The results of in-situ testing are presented along with lessons learnt during the studies.
Resonate Consultants Pty Ltd
ABSTRACT
This paper presents the design, installation and outcomes of a bespoke weightlifting platform within a university-based Exercise Physiology Laboratory. The Exercise Physiology laboratory is located within a medical research building which houses vibration sensitive research functions including microscopes. The Exercise Physiology Laboratory has a requirement for elite level athletes to conduct heavy weightlifting movements including deadlifts and overhead presses. Weight placement on the floor without appropriate treatment demonstrated that adjacent spaces would be adversely impacted by these activities. A targeted vibration isolation platform was designed to mitigate these potential impacts.
ACOR Consultants Vic Pty Ltd
ABSTRACT
In architecture and civil engineering there is a growing interest in the study of the dynamics of structures. The dynamic effects are due to various actions, but their influence is widened or reduced according to the design of the structure. Structures can be highly susceptible to the action of dynamic loads produced by the action of wind, earthquake, industrial activities, blasting activities, construction sites, road vehicles, trains, building services and human activities. Noise and vibration can have significant environmental impact on buildings and structures and can damage track components, crack roadways, unsettle foundations, affect sensitive equipment, impact human comfort and damage structures. Structure-borne noise and vibration can be a major and often overlooked consideration in the planning, design and operation of existing or new developments. A reliable, considered approach to assessing noise and vibration is needed to achieve outcomes that meet client expectations while maintaining on-going compliance with relevant standards and regulatory and planning requirements. The proposed paper will focus on a general overview of the structure-borne noise and vibration risks, associated with new developments that are adjacent to existing rail lines during the early design stages, from commercial and residential buildings to sensitive research facilities. It will further explain the general description of the design process, including problem descriptions, measurements of ground and structural vibration levels at the proposed site, vibration criteria, finite element analysis and provisions of the isolation system required to be considered at the building to achieve the relevant criteria. The procedures proposed are mainly aimed at structural and civil engineers who are working in construction and environmental engineers who are not specialists in vibro-acoustics.
(1) University of Adelaide
ABSTRACT
Experiments and numerical simulations have shown that sound radiated from vertically orientated hot exhaust stacks is strongly refracted away from the exhaust plume. In gentle cooler horizontal cross-flow, the plume bends downwards, which subsequently leads to increased refraction of the sound towards the horizontal plane downwind from the stack outlet. This paper builds upon previous research and reports on field trials of the sound directivity measured from a 250kW gas turbine (Turbine Technologies Minilab SR-30 Gas Turbine). The turbine was operated at two turbine shaft speeds, approximately 45,000RPM and 75,000RPM delivering exhaust jet flow speeds and temperatures of Mach Mj = 0.06-0.12 and Tj = 400oC-560oC, respectively, and with wind conditions ranging from calm to 8m/s. It was found that previous research could be reproduced in the field, with SPLs downwind of the exhaust stack 10-12 dB higher than spherical spreading predicts. The paper concludes with guidelines for acousticians to assist in far-field predictions of sound pressure levels arising from hot exhausts such as those found in gas turbine power plants.
(1) Global Acoustics (2) Dept of Planning, Industry and Environment, NSW (3) Sydney Metro, NSW
ABSTRACT
Predicting noise impact is a valuable tool for acoustic consultants. In Australia, five common models are used to determine the propagation loss from a source to a receiver; being ISO-9613-2, CONCAWE, ENM, CNOSSOSEU, and NORD2000. Emissions data for common construction equipment is used to compare the predicted A and C-weighted levels from these models to show there are large differences in predictions, even for simple scenarios.
University of Technology Sydney
ABSTRACT
It is common in Australia to encounter complex meteorological conditions such as temperature inversions, especially at night. These climatic conditions can have a significant effect on the propagation of sound, and this can influence the noise levels experienced by local communities from activities such as mining. It is, therefore, desirable to understand how the propagation of sound is influenced by climatic conditions, especially in the planning and monitoring of noise generating activities. A new approach to modelling outdoor sound propagation is presented here, which uses the semi analytic finite element method to generate solutions to the exact governing wave equation for a two dimensional problem. This approach allows arbitrary wind and temperature profiles to be included, so that exact solutions can be generated for temperature inversions in the presence of wind. Sound transmission loss predictions will be presented for range independent problems in the presence of different temperature inversions, as well as ground conditions. It will be shown that the semi analytic finite element method enables solutions to be generated for large ranges, and predictions will be presented here for ranges of over 5 km. This method is, however, currently limited to range independent problems, and so the extension of the approach to range dependent problems, such as the inclusion of noise barriers, hills and other terrains will also be discussed.
(1) UNSW Sydney
ABSTRACT
Prediction of road traffic noise is important for environmental impact assessments. In this work, a GIS-based heavy vehicle noise emission model is presented. The GIS-based model accounts for the influence of translational vehicle dynamics for a heavy vehicle on grade to enable accurate prediction of vehicle speed as well as operating conditions such as acceleration and deceleration. These kinematic variables in turn assist with accurate estimation of engine noise and rolling noise. To illustrate the model, a case study based on a freight route of the Great Western Highway in New South Wales is presented.
Robert Fitzell Acoustics
ABSTRACT
Land-use planning and assessment is envisaged by many to involve orderly and uncontentious procedures contributing constructively to how we protect community assets and the environment more generally. However most decisions are made in a local or parochial context with an underlying assumption that impacts and outcomes are considered in close proximities to the land boundaries. These local decisions can lead to cumulative outcomes that, progressively and sometimes instantly, entirely change the nature of nearby lands. This insular perspective is allowed perpetuate by the absence of legislative definitions for fundamentally important terms - impact, amenity and reasonableness - leading to assessment reports that do not consider the potential impact from a proposed land use in an appropriate way. This has aggravated public misunderstanding of the assessment process such that expectations and outcomes are commonly disarticulated. Acoustical assessment reports frequently refer to amenity loosely and encourage an emphasis on sound level criteria referencing sometimes inappropriate regulatory authorities. This paper examines the issues involved in these circumstances and attempts to establish more rigorous procedural foundations that may help ameliorate the risk of unsatisfactory unforeseen outcomes.
(1) Renzo Tonin & Associates
ABSTRACT
Over the last decade Metropolitan Sydney has been changing as a multitude of major infrastructure projects are constructed, including South West Rail Link (Glenfield to Leppington), Sydney Metro North West, Sydney Metro City and South West, WestConnex, Parramatta Light Rail, Northern Beaches Hospital road upgrade and Western Sydney Airport. Projects in the pipeline include Sydney Metro West and Sydney Metro Western Sydney Airport, Western Harbour Tunnel, Warringah Freeway Upgrade, Beaches Link to name a few in Sydney. Minimising construction noise and vibration impacts has been a significant consideration in the planning and management of these projects. This paper looks at how construction noise and vibration has been managed on some large infrastructure projects over the last decade. It looks at what some of the key learnings have been and how we might take this forward into a 'golden century of infrastructure investment'.
(1) Resonate Consultants
ABSTRACT
For the first time in South Australia, a newly implemented building standard provides a deemed-to-satisfy protocol for the mitigation of aircraft noise for affected constructions in general accordance with AS2021:2015. With the implementation of the Planning and Design Code in South Australia, residential developments are required to adhere to building requirements outlined in the Ministerial Building Standard - 010 (MBS 010), in which aircraft noise intrusion has been introduced. Implementation of these updated methods in MBS 010 is aimed to simplify the assessment of aircraft noise intrusion and reduce the costs associated with the development application process for residential homeowners. This paper details the methodologies, aircraft noise modelling and general development of the deem-to-satisfy and performance solution protocols outlined in MBS 010. This includes development of the Aircraft Noise Reduction (ANR) contour which describes the predicted maximum noise level from aircraft movements surrounding the subject aerodrome, deemed-to-satisfy construction assumptions and the constraints of this new assessment methodology.
Recognition Research Pty Ltd
ABSTRACT
The 2018 revision of 'AS1055 Acoustics - Description and measurement of environmental noise' included an informative Appendix E, which provided an objective method for assessment of impulsive noise. The intent of the Appendix was to provide a standard method for impulse assessment in Australia, as at present there is no other objective method to assess such impulsive characteristics. Assessment in those States requiring 'I' (or Impulse) time response can't be implemented as there is no current international standard for the 'I' time constant in sound level meters and many sound level meters do not include it because of that. The paper describes how to apply the Standard method, which uses 'F' (or Fast) time weighting and compares results of analyses of three different and common types of impulsive industrial noise sources using 30ms, 20ms and 10ms time intervals allowed in the standard to identify if there was any difference between their calculated impulse adjustment. The 100ms and 50ms intervals were also used for comparison and 100ms was found to provide a relatively simple screening method. Because of the potential for variation in adjustment value identified using different sample intervals, jurisdictions using Appendix E of AS1055:2018 should clearly state the sample interval to be used; if one value is to be used, 10ms is recommended.
(1) Defence Science and Technology Group (2) University of Sydney
ABSTRACT
Workplace health and safety regulations for the protection of hearing are well established but there appear to be no similar regulations for divers working underwater. Apart from the noise of machinery used by divers, they will also be subject to noise from many other sources because sound travels with much less absorption attenuation than in air. Regulations developed for airborne noise cannot be applied directly to underwater noise because the human auditory system functions differently in water compared with air. This difference is due to the large impedance difference in the two media. Hearing evolved in water so the terrestrial ear has evolved substantial adaptations (mainly the ossicular chain in the middle ear) to ensure that most of the energy incident on the external ear is transmitted to the cochlea or inner ear where the sound is sensed. The fluid in the cochlea has a similar acoustic impedance to that of water so that without the impedance matching of these adaptations, more than 99.9% of the energy would be reflected and less than 0.1% would reach the cochlea. In water, there is no need for the impedance matching. How then does the sound travel from water to the cochlear and how does this affect sensitivity? There have been a small number of measurements of hearing sensitivity underwater and although the results show significant variation between studies, they provide a basis for establishing a benchmark sensitivity when assessed with the theoretical considerations discussed above. This paper will compare the mechanism of transmission of sound from air to the cochlea with possible mechanisms for transmission from water to the cochlear and consider what can be inferred about hearing sensitivity underwater. It will compare this with the underwater hearing sensitivity measurements and suggest how criteria developed for hearing protection in air can be adjusted to establish criteria for underwater noise exposure.
(1) Airservices
ABSTRACT
Aircraft noise pollution continues to be a major part of adverse community reaction towards airports and air navigation service providers. With the ease of access to noise and flight operations data, community opposition to airport growth is increasing and is originating from areas further away from airports. Recent studies of airports in Hobart, Sunshine Coast and Brisbane have shown that adverse public reaction to aircraft noise can be high at distances of 30km to 50km along a flight path where predicted noise levels are low. This highlights the need for accurate noise modelling and the importance of noise modelling results to inform major community engagement activities. Noise modelling accuracy can be improved through validation with real world measured data. The key goal is to continually improve the practice of noise modelling to better predict noise levels in community areas both close to and far from airports so mitigation actions or noise improvements can be implemented.
(1) Australian Acoustical Society, Victoria Division
ABSTRACT
In response to the COVID 19 pandemic in 2020, the government of the Australian state of Victoria implemented short term travel restrictions in the city of Melbourne that resulted in an approximate halving of road traffic volume. The Victorian Division of the Australian Acoustical Society took the opportunity to monitor traffic noise at twenty six sites during this time. Due to a prohibition on unnecessary travel, the sites were at individuals' home addresses. Monitoring was repeated at several of the sites following a return to near-normal traffic volumes. This paper presents the results of this monitoring work and compares the noise levels during "lockdown" versus "normal".
(1) UNSW Sydney (2) Defence Science and Technology Group
ABSTRACT
The effect of hydrostatic pressure on the acoustic performance of a metamaterial attached to a rigid backing and submerged in water is presented. The metamaterial design consists of a polydimethylsiloxane (PDMS) matrix embedded with an array of spherical voids. A nonlinear finite element model is developed that considers deformation of the voided inclusions caused by hydrostatic pressure as well as the rheology of the viscoelastic material. An increase in the hydrostatic pressure is shown to significantly affect the volume of the voids which in turn affects the sound reflection from the coating. Results from the numerical model developed here are compared with results from the literature, showing good agreement.
(1) University of Technology Sydney
ABSTRACT
Mechanical waves and sound waves have complex propagation characteristics that are manipulated by periodic structures such as elastic metamaterials and phononic crystals for the purposes of wave guiding, vibration isolation and sound absorption. System parameters are tuned to induce auxetic physical properties such as negative effective mass density and negative Poisson's ratio. Locally resonant metamaterial (LRM) uses Fano-type interference to manipulate elastic wave propagation from the host structure by formation of a band gap due to local resonance. Not restricted by the Bragg interference limit, such sub-wavelength structures are particularly effective in attenuation of the low frequency oscillations. Tunability of the lower and upper bounds of the band gap through simple geometrical and material variations has made the LRMs a strong candidate for the noise and vibration control of automotive and industrial applications. In this study, we demonstrate a tunable LRM design that can be fabricated by injection moulding and vacuum casting. The mould for the fabrication of the resonator features a cylindrical hollow section. Pins of different diameter can be inserted into the mould to vary the material distribution in the cavity, thereby changing the resonance. A numerical model using COMSOL Multiphysics has been developed to investigate the dispersion mechanism. A parametric study of the pin diameter with respect to target band gap frequency demonstrates the capability of broadband vibration attenuation while keeping the overall size of the resonator small and constant. These results are promising for practical implementation of LRMs.
(1) UNSW Sydney (2) Defence Science and Technology Group
ABSTRACT
Sound absorption by an acoustic coating comprising a hexagonal lattice of hard spherical inclusions embedded in a soft elastic medium is analytically and numerically investigated. The analytical approach approximates each layer of inclusions in the direction of sound propagation as a homogenised layer incorporating local resonance of the inclusions and multiple scattering of waves between the inclusions in the lattice. The analytical results for sound absorption are in excellent agreement with finite element simulations that exactly model the geometric and material properties of the coating.
University of Technology Sydney
ABSTRACT
Limited reproducibility of absorption coefficients measured in different laboratories has been observed in the recent inter-laboratory test. This measurement uncertainty can result from the room acoustic design variance amongst laboratories and the material selection for qualification tests. Sound absorption measurements were performed in the reverberation room at the University of Technology Sydney, with test sample sizes and materials under different room acoustic conditions by installing different numbers of diffusers. With the measured data, initial work was made to decompose the sound absorption components based on the geometric feature of the test specimen, which is potential to assist the assessment of the diffuseness of the test facility and the optimization of diffuser installation.
(1) Transport for NSW
ABSTRACT
The mode of public transport known as light rail has been prioritised by the NSW Government, funding three (3) infrastructure projects since 2010 to serve and revitalise the growing Sydney and Newcastle communities. Light rail connects communities and helps both locals and visitors move around more freely and explore what regions have to offer. Transport for NSW's light rail portfolio includes Newcastle Light Rail, Sydney Light Rail (Inner West Light Rail, and CBD & South East Light Rail) and Parramatta Light Rail. This paper demonstrates how these three case studies have implemented the Rail Infrastructure Noise Guideline (RING) and Road Noise Policy (RNP) criteria to comply with the planning approval requirements, while outlining the challenges encountered that are not addressed in these guidelines. The impact of noise and community response to at-property treatments due to light rail operations is also discussed.
(1) Acoustic Studio (2) Revelstoke, Canada
ABSTRACT
Over a year's vibration data was collected from a monitor located adjacent to the rail corridor in Sydney. The results allow detailed analysis of long-term vibration trends by train type and track. The results also provide insight into the repeatability of short-term vibration monitoring, such as the common approach of attended measurements of around 20 trains.
(1) Acoustic Studio (2) Hushpak Engineering (3) University of Technology Sydney
ABSTRACT
Mitigating engine exhaust noise from older locomotives is a substantial challenge. The engine noise is broadband, but also includes prominent low-frequency tones that vary with engine speed. There is very little space inside the locomotive, so while a silencer would ideally be as large as possible, it must fit within tight constraints around other locomotive equipment. Many older locomotives have two-stroke engines that are highly sensitive to back pressure and were designed to run with direct ventilation to atmosphere. This imposes tight constraints on the flow resistance that a silencer can introduce, thereby constraining the design options.
(1) SLR Consulting Australia
ABSTRACT
In NSW, vibrations from train passbys that result in human comfort concerns are assessed in terms of Vibration Dose Values (VDVs). Measuring VDVs requires the use of instrumentation that can either measure VDVs directly or record waveforms that enable VDVs to be calculated through post-processing. However, when rail vibration is measured within buildings, ground-borne noise is often of primary concern with human comfort vibration relegated to being a secondary concern or an afterthought. Ground-borne noise is often measured in terms of one-third octave band vibration spectra and VDVs or waveforms are not recorded in many cases; in these instances, VDVs can only be calculated using the eVDV method detailed within BS 6472. It is not clear how much error/conservatism may be introduced with this approach with respect to rail vibration. This paper compares the estimated VDVs (eVDVs) calculated from one-third octave band acceleration spectra, from total root-mean-square (RMS) acceleration and from Peak Particle Velocities (PPVs) with the VDVs calculated from velocity waveforms recorded on the same device simultaneously. The comparison considers results collected from two locations in the Sydney metropolitan rail network. Different methods for calculating eVDVs are examined as well as the influence of different weighting functions.
(1) Mott Macdonald (2) Jacobs
ABSTRACT
An analysis of noise generated from railway operations on Sydney Harbour Bridge is presented based on a hybrid analytical and experimental method. The approach includes vibro-acoustic testing of the rails, rail deck and supporting structures. The mobility of the rails and rail supports is determined along with the rail vibration decay rate. Measurements of operational vibration on the rails and at a matrix of locations on the bridge structure are used to quantify the energy averaged vibration velocity for each bridge component. The data gathered from testing is used to validate Finite Element and Statistical Energy Analysis models and to calculate the sound power contributions of the train wheels, rails and bridge components. The validated models are used to predict the change in component and overall sound power levels due to the replacement of the existing timber transom rail deck and timber walkways with a low maintenance continuous concrete rail deck.
(1) SLR Consulting Canada (2) SLR Consulting Australia
ABSTRACT
The combined roughness of the wheel/rail interface is an important factor in railway rolling noise emissions. Although it is widely acknowledged that track condition influences noise levels, the potential changes over time due to wear and maintenance cycles are rarely addressed in impact assessments for proposed new systems in NSW. Instead, it is commonly assumed that track will be maintained in good condition with noise emissions that are stable. This assumption may be disconnected from the reality of light rail and metro transit maintenance practices. A series of case studies and measured data is provided to illustrate the range of different rail roughness conditions and corresponding noise levels that can be observed over time on real-world operating systems. On some systems, there is relatively little variation in rail roughness over time and train noise emissions are very similar at comparable locations. Others can see see dramatic increases in noise soon after rail grinding. A case study is provided where measurements at different tangent track locations on the same network with the same rolling stock indicate a difference of 26 dBA in passby noise levels, attributable to rail condition and maintenance state.
GHD Pty Ltd
ABSTRACT
The Transport for NSW Rail Noise Database (RNDB) has served as an invaluable source of reference data for railway noise assessments in NSW. However, for freight trains, the data is limited to tangent track only and arguably by its relatively small sample size. This paper presents a methodology to obtain passby data from a single channel microphone located close to track, with linkages to databases containing relevant operational details including speed and train consists. The paper also presents a comparison of the RNDB against selected measurement campaigns undertaken since the last revision of the RNDB, offers some insights into curve gain in NSW and observations pertinent to refining currently adopted noise modelling methods.
(1) Stantec
ABSTRACT
This paper presents a software that allows users to experience a high quality auralisation in a virtual reality scenario. The novelty of this new software iteration relies on the ability to simultaneously auralise two different noise sources while continuously and dynamically update the acoustic output at the user position within VR scenario. We use convolutions with pre-computed ambisonics impulse responses as the basis for our method.
The University of Adelaide
ABSTRACT
An algorithm and network is described in this paper that implements a sliding Discrete Fourier Transform, such that it outputs an estimate of the DFT value for every input sample. Regular DFT algorithms calculate a complex value that is proportional to the amplitude and phase of an equivalent sine wave at the selected analysis frequency. The analysis frequency that can be select is typically an integer multiple of the frequency increment of the DFT algorithm, and this might not necessarily correspond to the desired analysis frequency. The sliding DFT algorithm proposed here overcomes this limitation, and permits the analysis frequency to be any value up to half the sampling frequency. The proposed sliding DFT algorithm is demonstrated by analysing a synthetic sine wave, and the exhaust noise from a V8 diesel engine.
GHD Pty Ltd
ABSTRACT
Ambient vibration tests for large structures have become more popular as a tool to identify fundamental or lowest natural frequencies. Ambient vibration analysis is pertained to "response only" methods where the characteristics of excitation are not known. Different techniques are utilised to post-process data. The quality of the ambient monitoring data used for subsequent post-process is critical for further analysis, independently of the method used for structural dynamics analysis.
A data pre-processing procedure was suggested for the rectification of data collected during ambient vibration tests. It is suggested to make the decision on the validity of data acquired during particular time periods based on the comparison of descriptive statistics such as skewness and kurtosis with reference magnitudes. A high deviation of the skewness and kurtosis from the reference magnitudes can be used as an indication that the data may be invalid. An example in the paper utilised the Jarque-Bera test for normal distribution to rectify data for subsequent fundamental frequency identification. The method was successfully implemented for the analysis of a large amount of data collected during an ambient vibration test of a dam structure.
(1) University of Technology Sydney
ABSTRACT
Gas Metal Arc Welding (GMAW) is a welding process which involves forming an electric arc between a consumable wire electrode and a metal work piece while protecting the arc from contaminants using a shielding gas. In this form of welding, there are several varying ways in which the molten droplets can be transferred from the end of the welding wire into the weld pool known as transfer modes. Identifying these transfer modes is crucial in monitoring and controlling the welding process, especially in automated applications such as industry 4.0 manufacturing lines. Currently in industry, these transfer modes can be identified by expert welders by using the sound signal that is generated throughout the welding process. However, there has been limited research on using the acoustic signal to detect these transfer modes in automated welding applications.
This paper explores a new method of automatic GMAW transfer mode detection using machine learning techniques to analyse the acoustic signal generated during the welding process. Several time and frequency domain features are extracted from the acoustic signal and used to train a support vector machine classifier to accurately classify the transfer modes. In addition to this, a new feature selection algorithm is proposed to improve the prediction accuracy of the support vector machine classifier and a final prediction rate of 96% was achieved. This high prediction rate demonstrates the feasibility and promising accuracy of using the acoustic signal as a basis for transfer mode classification in future smart welding technology with real-time adaptive feedback control.
(1) WSP Australia (2) University of South Australia
ABSTRACT
Contemporary learning environments are typically designed to be large areas with fluid boundaries and can facilitate cohorts well in excess of 50 students in one space; indeed the terms "open plan" and "flexible" are synonymous when describing modern learning areas. In these scenarios it is common for high amplitude, random and modulating noise levels to be generated during teaching and learning activities. It is well documented that random modulating noise environments can disadvantage some learners. Research has shown that the inclusion of additional environmental auditory stimuli (such as music or white noise) can improve task orientated outcomes through triggering stochastical resonance. However stochastical resonance is highly dependent on both the character of the added stimulus and the individuals neuronal signalling. The use of music or white noise is a common tool utilised by educators although it is likely that the approach tends to be haphazard with the sources played at "low" or "background" level. This research attempts to bridge the current gap by analysing a response (distraction or concentration) of students to predetermined levels of white noise, a natural environmental soundscape or low bpm instrumental music. The study was carried out in a modern teaching and learning environment in South Australia with two separate cohorts of students. This study also takes the opportunity to investigate the response of students to a typical open plan classroom soundscape.
(1) Environment Protection Authority Victoria
ABSTRACT
In response to the COVID-19 pandemic, the State Government of Victoria implemented strict measures, including several periods of "lockdown" that involved strict constraints on travel, and required people to work from home where possible. For most Victorians, these restrictions led to reduced noise from road traffic and from aircraft, however they appear to have resulted in increased exposure to other sources of noise. The number of pollution reports received by Environment Protection Authority (EPA) in relation to noise more than doubled in the period from January to July 2020 (which covered several episodes of lockdown) compared with the same period in the previous year (with no lockdowns). This paper investigates the evolution of noise reports during 2020 and 2021, giving regard to the alleged noise source categories used in their triage.
(1) University of Adelaide
ABSTRACT
Many studies have shown that hospital staff and patients are subject to noise levels in excess of those specified in the World Health Organization (WHO) guidelines. This article presents the results of a single-centre study of noise in four wards in an acute hospital in Adelaide, Australia The study measured noise in multi-bed bays, as well as nurse stations, and involved continuous noise monitoring between one and three days. For 4-bed and 6-bed patient bays, as well as nurse stations, the maximum, minimum and average equivalent 1-minute A-weighted sound levels were relatively constant from 22:00 until 06:00, increase from 06:00 until 09:00, remain raised until 18:00, and then decrease from 18:00 until 22:00. Measured average equivalent A-weighted noise levels for nurse stations and patient rooms were 56.6 dB(A) and 54.8 dB(A) respectively. Noise levels were higher in the 6-bed bays compared to the 4-bed bays with average equivalent A-weighted noise levels of 55.7 and 54.3 dB(A) respectively. The results were consistent with similar hospital studies, with noise levels exceeding WHO guidelines for patient comfort.
(1) GHD Pty Ltd
ABSTRACT
Identification of the contribution from multiple noise sources is critical for suggesting potential noise mitigation measures. Structural noise radiation of planar structures located on industrial sites frequently provides significant contribution to noise levels measured at affected receivers. One of the methods to estimate sound power (SPW) radiated from walls, enclosure roofs, or industrial buildings is the measurement of vibration over the radiating surface. Theoretically the SPW emitted by a planar structure is proportional to product of the squared vibrovelocity averaged over the radiating surface, area of the surface, the radiation efficiency, and a few other ancillary parameters. Radiation efficiency of simple plates has its peak at a critical frequency and tends to be unity at higher frequencies. Industrial enclosures and building are frequently built from reinforced concrete, brick, and mortar. They represent inhomogeneous structures, and the radiation efficiency of these structures is more complex than it is for metal plates. Sound intensity measurements of planar structures installed in an electrical substation site were undertaken using a sound intensity probe. Vibrovelocity estimates were also obtained to compute indirect estimates of the radiated sound power. Radiation efficiency was analysed in third octave frequency bands using the SPW and vibrovelocity estimates. It was shown that radiation efficiency has a more complex character in comparison with metal plates, showing that vibration measurements of these types of structures and materials for estimation of radiated sound power may not always provide good representation of such complex structures.
(1) SLR Consulting Australia (2) WSP Australia
ABSTRACT
Vibrating screens are commonly used to separate and classify material across a variety of processing industries. The operation of the screens can be a source of noise (unwanted sound) within communities and environments near to processing plants and industrial premises. The emissions can include prominent low frequency sound which has the potential to impact public health and wellbeing. The nature of potential impacts associated with low frequency noise can be contentious, particularly where the low frequency sound is not always audible (often referred to as infrasound). Decisions to rectify low frequency noise problems require a detailed understanding of the mechanisms which generate the low frequency sound during the operation of the vibrating screens. This paper considers vibrating screens as sources of low frequency noise and discusses techniques to diagnose and quantify the low frequency sound emissions.
(1) University of Technology Sydney
ABSTRACT
Breakout from ducts can be a major source of noise on industrial sites. The emitted noise is harmful at sufficient levels and must be reduced. Reducing noise levels using appropriate methods after the fact can be both costly and time consuming. This can be avoided by correctly predicting duct transmission loss before the duct is installed and choosing a suitable construction. In this paper the breakout from circular ducts will be presented as part of a parametric study. Parameters such as duct radius and wall thickness will be used to allow for a suitable choice of duct construction. In practical systems duct radii can be several metres in diameter and this is reflected by the range of the study. The breakout noise is calculated using a semi analytic finite element method. The first step in this method requires determination of the duct's modal properties which is calculated using a numerical eigenvalue analysis. The waves are then propagated along the duct using an analytic expression. A monopole sound source is used to excite the system, simulating the complex acoustic field within HVAC ducts with the transmission loss calculated from the difference between radially propagating sound power to axially propagating sound power.
(1) Defence Science and Technology Group, Sydney
ABSTRACT
Defence Science and Technology Group (DSTG) undertook measurements of flow noise on a Geospectrum M20 acoustic velocity sensor from 15-17 June 2020 as part of a joint AUS/US program to reduce flow noise on acoustic vector sensors. The aim of the trial was to measure the flow noise associated with the sensor both with and without a flow shield, at a variety of angles to the flow, to determine if the flow shield reduced the noise. The measurements were undertaken in a water supply canal on the outskirts of Sydney which provided a quiet environment without the noise from pumps associated with conventional flow tanks. The measurements suggested a simple flow shield could greatly reduce the flow noise and confirmed the suitability of the canal for future trials. While most measurements were conducted with a fixed flow, towards the end of the trial the canal was "turned off", leading initially to a period of increased flow velocity followed by reduced flow velocity. A sharp increase in flow noise with increased flow velocity was noted. Some suggestions are made for refinement of techniques to assist in future trials.
(1) Defence Science and Technology Group
ABSTRACT
With suitable processing, a broadband acoustic signal received at a short range in a shallow ocean may be used to invert the Weston alpha parameter (Weston, D. E., J. Sound Vib. 18, 271-287, 1971) appropriate for the local seabed. Based on this, adequate simulations of sound transmission to much longer range may be obtained. The broadband signal may be an impulse, or continuous random emission, across the frequency band of interest. As no sensor calibration is required for the technique, there is considerable opportunity for legacy time series data to be re-processed to carry out the inversion. Application of the inversion technique is demonstrated using previously unpublished legacy impulse data, and simulations of transmission to longer range are obtained. These simulations are then compared with legacy at-sea measurements of transmission. Both the inversion technique itself and the application of the inverted data are not without a number of issues. These are considered with reference to practical cases.
(1) JASCO Applied Sciences (Australia) (2) University of Tasmania (3) Nautilus Collaborations (4) JASCO Applied Sciences (UK)
ABSTRACT
Underwater acoustic seal deterrent systems are increasingly used internationally to mitigate interactions between seals and marine fish farming operations, however none have been utilised in Australian waters or with Australian fur seals. The OTAQ SealFenceTM system was examined at a site on the Tamar River, Tasmania via a detailed modelling and field characterisation study. The modelling study considered a source spectra derived from measurements, along with different sea states and applied a statistically justifiable representation of multiple operational devices. The measurement study was conducted using fixed and mobile recorders during different sea states, and re-modelling was undertaken to allow comparison between similar scenarios. Understanding the propagation of signals from individual and multiple devices in a specific location is essential when estimating effects. Confidence in the predicted ranges to effect thresholds for seals and other marine fauna (e.g., cetaceans and fish), is an important part of an impact assessment required prior to further system use. The characterisation results have provided the basis for understanding potential effects of the SealFenceTM on marine fauna, and the representation will be used to underpin the feasibility of the next project phase; a long-term behavioural response study to examine the system efficacy on Australian fur seals.
(1) Defence Science and Technology Group
ABSTRACT
The level and vertical directionality of ambient noise in shallow oceans may each be influenced by the acoustic reflectivity properties of the seafloor. Components of ambient noise interacting with the seafloor at small grazing angles may be either strongly reflected or absorbed, depending on seafloor density, sound speed and attenuation, and the speed of shear waves in the seafloor. The nature of the seafloor reflectivity near normal incidence is almost entirely determined by the product of the sound speed and density for the seafloor material. In a brief study, estimates are made of the vertical directivity of the ambient noise generated by dipole surface sources, with consideration to the influence from reflections from several, quite different, seafloor types. This work includes the derivation of several simple expressions for resultant noise intensity and their comparison with numerical integrations. As these expressions are in terms of the geoacoustic properties of the seafloor, it suggests that prediction of ambient noise characteristics may be viable.
(1) Defence Science and Technology Group (2) YTEC Pty Ltd
ABSTRACT
The paper deals with a reduced order analytical model of the vibration response of a NACA0015 cantilevered hydrofoil excited by honeycomb-generated turbulence. The statistical stochastic excitation model employs strip theory with the intensity and the integral length-scale of the turbulence being the input parameters. The structural response is calculated as the product of the total hydrodynamic response function with the frequency spectrum of the space-time velocity correlation function. The total hydrodynamic response is represented by the combination of Sears' model of unsteady hydrodynamic gust combined with Theodorsen's theory for the lift and moment due to the heaving and pitching motion of the strip coupled with Euler-Bernoulli and torsional equations of the cantilevered hydrofoil motion. The comparison of the predicted structural velocity spectra with available experimental results shows good agreement for the first bending mode but overpredicts the amplitude at higher frequencies. Finally, a finite/boundary element model developed using COMSOL Multiphysics, provides further cross-verification with the aim of understanding some of the limitations of the simplified analytical model.
(1) Defence Science and Technology Group (2) Curtin University
ABSTRACT
The power spectrum densities of underwater noise recorded on the seafloor at a site northwest of Australia were compared for the same wind speeds in summer and winter, when the predominant sound speed profiles were distinctly different for underwater sound propagation, with the primary difference being the presence/absence of the surface acoustic duct in the top mixed layer in the colder/warmer seasons respectively. For the same wind speeds in different seasons, little differences were found between the noise levels at frequencies where wind-generated noise dominates, indicating that the sound speed profiles had little effects on wind-generated underwater noise. Acoustic modelling showed that the surface acoustic duct trapped only an insignificant amount of noise energy propagated within a narrow range of shallow grazing angles from distant sources and most of the noise was contributed from a local surface area with relatively steep propagation angles to the receiver.
(1) University of Technology Sydney (2) INSA-Lyon (3) Defence Science and Technology Group
ABSTRACT
The results on the acoustic response of a heavy fluid-loaded baffled plate excited by a harmonic point force are presented. The displacements of the fluid-loaded plate are decomposed on the basis of the in-vacuo plate modes and the radiated acousic waves are determined solving the Helmholtz equation in a fluid. The Green's function for the acoustic waveguide domain formed by the baffled plate and the free surface is modelled by the source-image method. Predictions for the radiated sound power from the plate and pressure spectra are calculated for varying depths of the free surface and compared against results from an unbounded domain to infer the effect of the free surface on the acoustic response of the plate. The proposed analytical model is verified by comparison with finite element simulations.
(1) UNSW Sydney (2) Defence Science and Technology Group
ABSTRACT
Sound radiation from a submerged, structurally excited, cylindrical shell with an acoustic coating applied to the external shell surface is presented. The coating is composed of a soft elastic medium embedded with a circumferential array of periodic resonant inclusions. The layer of soft material encompassing the resonant inclusions is approximated as a homogeneous medium with effective material and geometric properties. Results show that local resonance of inclusions leads to sound reduction in a broad frequency range. The effects of variation in the size and number of resonant inclusions on the radiated pressure of the submerged cylindrical shell are observed.
(1) University of Technology Sydney (2) UNSW Canberra
ABSTRACT
Globally, naval mines and unexploded ordinance litter large areas of the ocean floor, resulting in many coastlines being abandoned due to their deadly and indiscriminate threat. Recent developments in state of the art Mine Like Object (MLO) countermeasure have seen the use of Unmanned Underwater Vehicles (UUV), equipped with advanced active sonar systems, becoming more effective at identifying, classifying, and clearing these threats. Such systems rely heavily on large databases of known MLO acoustic signatures, which are typically characterised by their resonant behaviour. Whether originally designed to sit on the seabed or not, many MLOs have ended up buried under the seabed, becoming less visible, but no less of a threat. In order to accurately identify MLOs as they become "lost" in the seabed, it is necessary to track how their acoustic signatures change when their boundary conditions move from water to saturated sand. In this paper, the change in resonant behaviour of several simplified shell geometries has been estimated when sat proud on the seabed vs. when in shallow burial beneath it. These scenarios have been modelled numerically, as is typical for the creation of the MLO reference database, and analytically for validation. The results show how embedding the objects within saturated sand results in a decrease in the resonant frequencies for all geometries.
(1) Defence Science and Technology Group, Victoria
ABSTRACT
This paper presents the modelling and analysis of local masses and their effect on the radiated sound pressures from an underwater enclosure. The underwater enclosure is modelled as a submerged cylindrical enclosure with ring stiffeners. To simulate the structure-borne and airborne noise transmission, machine noise is characterised by forces applied along the enclosure in three directions and by acoustic sources located inside of the enclosure. An analytical approach is presented where the inertial force of an added mass is modelled by including a mass-induced pressure in the cylindrical shell equations of motion of the enclosure. Thus, an analytical model implementing the approach can have a number of local masses attached to the surface of the enclosure, which gives insight into how the local masses affect the inherent modal amplitudes for given modal forces. These modal amplitudes determine the radiation characteristics of the underwater structure. The influence of mass sizes and locations on the structure is discussed. For benchmark example cases, the analytical results are compared with those from numerical finite element / boundary element models with good agreement.
(1) Norman Disney & Young
ABSTRACT
Auralisation is a powerful tool for presenting acoustic design options to stakeholders, enabling them to preview the acoustic environment using appropriately processed audio signals. Current state-of-the-art auralisations require a dedicated listening room with very low reverberation times, very low background noise, and a multi-channel loudspeaker setup. More recently, auralisations have been coupled with virtual reality (VR) visualisations to enhance the user experience, through use of VR headsets. Recent computational power increases in portable consumer-grade devices, such as smart phones and tablets, have meant that rendering a 3D augmented reality (AR) or VR simulation is now a possibility on such devices. AiHear is an AR/VR auralisation application which utilises the portable device platform in conjunction with an off-the-shelf (calibrated) headphone setup to playback accurate auralisation audio. This paper looks at some of the technical challenges associated with successfully implementing an AR/VR auralisation application for use on a low-cost consumer-grade platform.
(1) SLR Consulting Australia Pty Ltd (2) GHD
ABSTRACT
Marine pile installation using impact hammer is a common practice during many nearshore and offshore construction activities. The associated noise emissions have the significant potential to adversely impact on the surrounding marine environment. Predicting sound radiation from marine impact pile driving activities based on numerical simulations has been proved to benefit not only the assessment of resulted marine environmental impact, but also the investigation of effective mitigation measures to minimise the impact. In this paper, we present a finite element (FE) model for the prediction of noise emissions from marine impact pile driving based on the software COMSOL, where the characteristics of the sound field in the near field are investigated. Based on this FE model, the radiated sound signals at a set of receivers placed at different distances and depths within the water column from a driven pile have been calculated, and the sound signals in the time domain have been analysed to characterise the attenuation over distance. This FE model has been validated based on comparisons with previous benchmark case studies.
(1) Department of Psychology, University of California, UC San Diego (2) Sydney Conservatorium of Music, University of Sydney
ABSTRACT
Songbird vocal communication signals (birdsongs) often evolve in secondary sexual selection contexts and are shaped by female preferences. Such female preferences to male songs are typically linked to information-theoretic features of song complexity such as repertoire size or syntax of discrete song elements. Recent discoveries of similar structures between birdsong and human music suggest, however, that musical features of song complexity may also be relevant to female preferences. Australian pied butcherbirds (Cracticus nigrogularis) exhibit songs with recombinatory syntax and structural similarities to human music, but the depth of their song complexity remains ill-defined. To holistically examine pied butcherbird song complexity, we characterized relevant features of song complexity through a combination of symbolic sequence and musical rhythm analysis. This integrated approach reveals long-range dependencies in pied butcherbird songs, in which song elements are dependent on song history, and strong categorical song rhythms, in which the temporal spacings between song element onsets occur at discretely organized intervals. As categorical song rhythms can facilitate song history encoding, it may be critical in enabling long-range dependencies in pied butcherbird songs. A systematic conception of song complexity that takes into account such potential interactions between song features stands to benefit songbird communication research.