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AAS2015: Acoustics 2015 - Hunter Valley
Active Noise and Vibration Control
Assessment and prediction of structure-borne rail noise in domestic dwellings
Exhaust silencer using water injection
Measurements of underwater noise from the RV Investigator
Design and analysis of a thermoacoustic heat engine
Mechanical design of flow control of the exhaust noise from a v6 petrol engine
Simplified prediction of sound radiation due to bending mode resonances of submerged cylinders
Determining the speed of a variable speed wind turbine from the vibration response
Control of transformer noise using an independent planar virtual sound barrier
Effects of turbulent flow characteristics on wind-induced noise generation in shielded microphones
Leading edge noise prediction using a hybrid RANS-BEM technique
Localisation of flow-induced noise source generated at the Aeolian tone using hybrid CFD-BEM and time-reversal methods
An experimental investigation of flow-induced noise mechanism of a flexible flat-plate trailing-edge
Analytical noise modelling of a centrifugal fan validated by experimental data
Time delay estimation of acoustic tones under low SNR conditions
Aeroacoustic investigation of the effect of a detached flat plate on the noise from a square cylinder
The effect of a serrated trailing edge on self-noise reduction of a flat plate
Directivity analysis of sound in turbulent exhaust jets with laminar cross-flow: A numerical study
Numerical experiments of aerofoil noise: the role of direct numerical simulations in understanding and controlling noise
The effect of trailing-edge elasticity on its noise radiation
An experimental investigation of turbulent boundary-layer interaction with different serrated trailing-edge configurations
An experimental investigation of the flow-induced noise generated by a porous trailing-edge of a flat-plate
A revision of a previous discussion on the correctness of Curle's and the Ffowcs Williams and Hawkings equations
Architectural and Building Acoustics
Acoustic properties of vacuum insulating glazing
Overview of the revision of AS/NZS 2107
In-situ testing of gym floor impact isolation
The acoustic design of 'The Triffid' music venue, Brisbane
Comparative analysis of on-site STIPA measurements with EASE predicted STI results for a sound system in the railway station concourse
An engine for real-time audiovisual rendering in the building design process
Boundary element modelling of fractal and other enhanced bandwidth schroeder diffusers
An assessment of different sized open plan and enclosed kindergarten classroom listening environments
Investigating concert hall acoustics from musicians' perspective: summary of results from a survey of two touring chamber orchestras
A BEM study on the effect of source-receiver path route and length on attenuation of direct sound and floor reflection within a chamber orchestra
Preliminary study on the speech privacy performance of the Fabpod
Improving sound diffusion in a reverberation chamber
Computational Acoustics
Finite elements in vocal tract acoustics: generation of vowels, diphthongs and sibilants
Case study of the sound reduction of various residential glazing treatments
Low frequency noise and environmental assessment
The second mining boom: what can we learn from mining of long term environmental monitoring data?
Fundamental Acoustics
Locally resonant sonic crystal barrier for low frequency noise control
On the completeness and orthogonality of the acoustic modes of an open cavity
Ultrasonic retrieval of anisotropic stiffness tensor for trees
Near-field acoustic holography and non-negative intensity for prediction of sound radiation
Wave propagation in infinite periodic structures taking into account energy absorption
Acoustic performance of periodic composite materials
Generation and Mitigation of Noise on Mine Sites
Haul truck sound power assessment
Noise management improvements at the Mount Thorley - Warkworth mining complex
Acoustic signature of open cut coal mines
The generation and propagation of noise from large coal mines, and how it is managed in NSW
Exploring uncertainty in low frequency noise (LFN) measurement and control: Documenting spatial variability
Innovating noise management: how can low-tech thinking improve the yield from high-tech management tools?
Meteorological factors affecting environmental noise propagation over several kilometres
Haul route modelling
Working with the community to minimise mine noise impacts at Bulga Coal
Acoustical behaviour of conical muffler with single-inlet and single-outlet: a 3-D semi-analytical approach
Standards – constraining instrumentation innovation?
You can't measure it but you can know it: precisely synthesising acoustic flow
A comparison of tonal noise regulations in Australia
Low Frequency Noise
Marine Environmental and Bio Acoustics
Autonomous processing of sidescan sonar imagery for unmanned underwater vehicles
Determining the even harmonic attenuation at which the 'clarinet-like' timbre of complex tones becomes dominant
Analysis and evaluation of irregularity in pitch vibrato for string-instrument tones
Deriving a timbre space for three types of complex tones varying in spectral roll-off
Physiological and Psychological Acoustics
A soundscape approach for assessing indoor aural comfort subjected to road traffic noise
The influence of room reflections on subwoofer reproduction in a small room: Binaural interactions predict perceived lateral angle of percussive low-frequency musical tones
Sonar Signal Processing
Performance of adaptive beamformers for extracting audio signals
Transportation Noise
Noise monitoring and extraction of new information from older instruments and archives
Refinement of exhaust system noise from large diesel engines using one dimensional (1D) simulation
Alternative systems for road surface CPX measurements
OBSI measurements for the purpose of calibrating road surface corrections for CoRTN based road models
Quasi-periodic noise barrier with Helmholtz resonators for tailored low frequency noise reduction
RONDA - Pavement noise measurements
Proposed methodology for the assessment of noise in a route selection process
Investigation of additional insertion loss from T-profile and absorptive noise barriers
Broadband transmission loss performance of a hemispherical end-chamber muffler with single end-inlet and single/double end-outlet
Low noise road surfaces: So far, so good – and the best is yet to come
Development of new external noise limits for electric rolling stock on the transport for NSW network
Improving brake squeal propensity prediction by model updating
Underwater Acoustics and Noise
A high-resolution underwater acoustic communication propagation simulator with multi-path transient sea-surface interactions
Prediction of bubble generation based on acoustic emission
An analytical model for noise radiated from axial vibration of a simplified pressure hull of an underwater vehicle
Coherent leakage of sound from a mixed layer surface duct - Revisited
Challenges in the prediction of underwater noise due to propellers
Acoustic propagation over the continental slope and deep basin off Eastern Australia
High resolution undersea acoustic data acquisition using single-board microcontrollers
Modelling shallow water sound transmission by using a simple analytical formula based on the effective depth approximation
A case study of damage effects to residential buildings caused by vibratory compaction equipment
Estimation of bearing forces in rotating machinery: A problem revisited
Determining the static stiffness of structures: a comparison of methods involving measurement of displacement and measurement of acceleration response
Development and testing of a tuneable damped spring system for treadmill vibration isolation
Analysis of thin curved flexible structures for space applications
Fault severity trending in rolling element bearings
Detecting changes in gear surface roughness using vibration signals
Preliminary modelling of a marine propulsion system
Wind Turbine Noise
Wind turbine amplitude modulation noise due to time-dependent interference
Microphone wind speed limits during wind farm noise measurements
Workplaces, OH&S Noise Exposure and Hearing Protection
Hearing and leisure noise
All rights reserved. Permission is granted for any person to reproduce a part of any abstract provided that the permission is obtained from the author(s) and credit is given to the author(s) and these conference proceedings.
Chadha, Supreet Singh (1), Kanapathipillai, Kana (1)
(1) UNSW Australia, Australia
The aim of this paper is to provide findings based on a study on the existing structure-borne rail noise levels in order to facilitate the decision making on any future expansions in Sydney. The study focuses on prediction of structure-borne noise levels using an algorithm which takes into account the geology, the vibration transfer coupling between the ground and a typical dwelling, the efficiency of the floor to re-radiate the vibration and typical acoustic properties of a dwelling. With the experimentation conducted in various locations around Sydney, a consensus was drawn on the noise and vibration assessment according to the geology of the region. The predicted structure-borne rail noise is to be juxtaposed with the measured data to suit the conditions in the areas concerned.
Full Paper
Cotton, Brandan (1), Damin, Lewis (1), Silvestri, Anthony (1), Howard, Carl (1)
(1) The University of Adelaide, Australia
This paper describes results from the development of a water injection noise control system applied to an exhaust duct. A mist of water is introduced into an exhaust duct by injectors into the gas flow and is used to reduce the sound pressure level in the exhaust by several mechanisms, particularly through the absorption of energy required for the evaporation of the water vapour. This noise control method is investigated firstly with the aid of CFD software and then tested experimentally. The results from the CFD showed that there are significant reductions in temperature, pressure and hence energy of the flow. The experimental prototype injection system showed inconclusive results due to systematic error. The instrumentation noise floor in every test was approximately 100dB when the water injectors were activated. It is expected that the increase in the noise floor is created by the injected water causing vibrations in the pipe walls which is picked up by the microphone. It is proposed that a water injection based noise attenuation device could be effective with different implementation based on research theoretical results.
Duncan, Alec (1), Kloser, Rudy (2), Sherlock, Matthew (2)
(1) Curtin University, Australia (2) CSIRO Marine and Atmospheric Research, Australia
Australia's Marine National Facility, operated by CSIRO, has recently taken delivery of a new, $126 million, multi-purpose blue-water marine research vessel, RV Investigator. The ship is equipped with an extensive suite of active acoustic instrumentation that include an omnidirectional sonar, three multibeam echosounders, six split beam scientific echo sounders, two acoustic Doppler current profilers and a sub-bottom profiler. Permanently installed seismic compressors also prepare the ship to undertake geophysical survey missions. The ship has been designed to maximise the performance of these systems through innovative hull design to minimise air bubble entrainment under the acoustic transducers, and by reducing the underwater sound radiated from the ship through an innovative propulsion system, coupled with advanced isolation of vibration from the primary power generation machinery. This paper discusses some recent underwater noise measurements that were carried out in southern Tasmanian waters following Det Norske Veritas (DNV) guidelines in order to determine baseline underwater noise signatures for the vessel, and to characterise the noise performance of the various acoustic instruments. The baseline measurements obtained are compared to the ship's design criteria of DNV Silent-R and the expected background wind and thermal noise. The potential variability in vessel noise spectra obtained when following DNV noise measurement guidelines are also discussed.
Griscti, Henry (1), McPeake, Jordan (1), Scott, Bradley (1), Howard, Carl (1)
Thermoacoustic heat engines (TAEs) are a well-established technology, however practical applications are limited. TAEs operate when a temperature gradient is applied that causes acoustic oscillations. This paper presents a tutorial on how to design and build a TAE. Focus is given to the design process and analysis of the TAEs performance in order to describe how it was developed and provide a standard to which future TAEs can be assessed.
Hunter, Morgan (1), Leclercq, Damien (1), Howard, Carl (1)
The concept of reducing petrol engine exhaust noise by regulating exhaust gas flow has been previously investigated theoretically and demonstrated. One method by which this can be achieved is by the optimal regulation of the gas flow by accurately controlling an oscillating valve. This paper describes design improvements of a standard butterfly valve configuration by utilising a linear electromagnetic shaker and a rocker arm, to regulate the flow of exhaust gases from a petrol engine. By redesigning the mechanism and increasing the stiffness of the system, so that its natural frequency was close to the cylinder firing frequency, permitted the valve to oscillate at high amplitudes using minimal force applied by the actuator. Experimental results of this flow control valve design showed that the noise at the engine firing frequency was attenuated by over 10dB.
Kinns, Roger (1), Wu, Hongjian (2), Peters, Herwig (2), Kessissoglou, Nicole (2)
(1) RK Acoustics, United Kingdom and UNSW Australia, Australia (2) UNSW Australia, Australia
The aim of this work is to explore the nature of radiation from bending modes of a submerged tube with variation in mass distribution along the length of the tube. The bending modes of a fluid-loaded tube are initially predicted using a simple finite element shell model, where the effects of water loading are modelled by adding mass to that of the tube itself. The sound radiation is then predicted using an array of transverse dipoles whose strengths are proportional to the local cross-sectional area and vibration amplitude. The effects of retarded time are taken into account for directions that are not normal to the tube. For comparison with the semi-analytical approach, a fully coupled finite element/boundary element model of the fluid-loaded tube was also developed. Results from both techniques show that variation of the mass distribution of the fluid-loaded tube has a large impact on the radiated sound power and directivity of the radiated sound pressure due to low order bending modes.
Randall, Robert (1), Coats, Michael (1), Smith, Wade (1)
Condition monitoring of wind turbines is very important to minimise maintenance costs (virtually the only costs once they are installed), and to maximise production. New diagnostic techniques have had to be developed to deal with the varying speed and load of the most efficient turbines, but these are greatly aided by having a measure of the speed. This paper shows how the speed of a wind turbine was extracted very accurately from the response vibration signal, making use of a phase demodulation method for determination of a rotational angle vs time map, as used for order tracking. The angle vs time relationship can be determined by the phase demodulation method to any degree of resolution if the corresponding carrier frequency and its sidebands are isolated in the frequency domain with no encroachment from adjacent components. For the case used here for demonstration of the method, the speed range of each signal section had to be limited to about � 15% to avoid overlap. The overall signal was divided into eight overlapping sections, in each of which a suitable candidate harmonic was isolated, and phase demodulated in two iterations, the second able to use higher harmonics for increased accuracy once separated by the first iteration. Specially designed window functions allowed the results from each section to be smoothly joined. Noise from the differentiation of these phase curves to rotational speed was removed by two methods, which gave very similar results; lowpass filtration in the frequency domain (which however gave some distortion at the two ends) and polynomial curve fitting, which was chosen in this case. The final speed vs time record over the whole record length could then be order tracked using the speed curve itself (integrated to obtain a phase vs time map) to express it as speed vs rotation angle.
Tao, Jiancheng (1), Qiu, Xiaojun (2), Pan, Jie (3)
(1) Nanjing University, China (2) RMIT University, Australia (3) The University of Western Australia, Australia
A virtual sound barrier (VSB) can be applied to reduce transformer noise radiated outward from an opening of an enclosure without scarifying natural ventilation and lighting. Although a traditional independent VSB system consisting of multiple single channel active noise control systems has shown practical potential for solving the noise problem of real transformers, the instability associated with the system decentralization needs to be investigated. In this paper, a stability assessment method is proposed for the independent VSB system consisting planar arrays of control loudspeakers and error microphones first. Then the distance between the control loudspeaker and its collocated error microphone that is required for stability is investigated based on the frequency characteristics of the noise and the Green's function in free field. Finally, the system stability and the noise reduction performance of a 44-channel independent VSB system installed at the room opening of an onsite 110 kV transformer are presented.
Alamshah, Vahid (1), Zander, Anthony (2), Lenchine, Valeri (3)
(1) Resonate Acoustics, Australia (2) The University of Adelaide, Australia (3) SA Environment Protection Authority, Australia
Outdoor noise measurements can be highly affected by the wind-induced noise generated by turbulence structures present in the flow and wakes generated at the air and windshield interface. Various commercially available windshields were tested in a small anechoic wind tunnel in order to investigate the effects of turbulent flow properties on the wind-induced noise in shielded microphones. To distinguish the contribution of wind-induced noise from the acoustic signal an Incoherent Output Power analysis between two microphone signals has been used. The effects of mean flow velocity, turbulence intensity and average length scales on the wind-induced noise in shielded microphones were evaluated. An incremental trend with increasing airflow velocity has been found for the wind noise spectral amplitudes. The findings indicate a dependency between turbulent scales and the wind- induced noise levels at low frequencies. The overall wind-induced noise was found to be insensitive to the incoming flow turbulence intensity levels which may suggest that other parameters of the incoming flow turbulence, such as turbulence scale, are more important for the processes of wind-induced noise generation.
Croaker, Paul (1), Doolan, Con (1), Kessissoglou, Nicole (1)
The noise produced by turbulent flow incident on the leading edge of an airfoil is predicted using a hybrid RANS-BEM technique. Hydrodynamic data including turbulent kinetic energy and turbulent dissipation rate are obtained from a steady-state Reynolds Averaged Navier-Stokes (RANS) simulation of turbulent flow past the airfoil. Using a model of the turbulence cross spectrum, statistical noise sources are obtained and then combined with a boundary element method (BEM) model of the airfoil to predict the far-field sound. The results from the hybrid RANS-BEM technique are presented for turbulent flow incident on a NACA0012 airfoil at a Reynolds number based on chord of Rec = 6.0 � 10^5 and a Mach number of M = 0.12. The results are compared with experimental and analytical results from literature.
Croaker, Paul (1), Mimani, Akhilesh (2), Doolan, Con (1), Kessissoglou, Nicole (1)
(1) UNSW Australia, Australia (2) The University of Adelaide, Australia
This paper presents a novel simulation technique based on the hybrid computational fluid dynamics (CFD)-boundary-element method (BEM) and the aeroacoustic Time-Reversal (TR) source localisation method to analyse the flow-induced noise generated at the Aeolian tone due to a circular cylinder located in a low Mach number flow. To this end, the hybrid CFD-BEM method is used to obtain the far-field acoustic spectrum of (1) the direct acoustic pressure field generated by flow over the cylinder,
(2) the acoustic field scattered by the cylinder and (3) the total acoustic field at all four computational boundaries. The acoustic spectrum shows the occurrence of an Aeolian tone for all three cases whereby the acoustic pressure time-history at the boundary nodes is synthesised by assuming a sinusoidal signal at the Aeolian tone frequency. The aeroacoustic TR simulation was implemented by numerically solving a set of 2-D Linearised Euler Equations (LEE) and enforcing the time-reversed acoustic pressure history as input at the computational boundaries. The TR source maps indicate a lateral quadrupole source nature due to the direct field whilst a lift-dipole source nature is indicated due to the scattered and total acoustic pressure fields. The results of the TR simulations is consistent with previous works, thereby demonstrating the validity of the novel technique proposed in this work for analysing flow-induced noise problems.
Das, Chandrashnata (1), Mimani, Akhilesh (1), Porteous, Ric (1), Doolan, Con (2)
(1) The University of Adelaide, Australia (2) UNSW Australia, Australia
The Trailing-Edge (TE) of aircraft wings generates significant noise which is problematic for communities. This paper investigates a possible noise reduction mechanism by using an airfoil with a flexible TE made from Nylon 6 material. Experiments were carried out in an Anechoic Wind Tunnel (AWT) at low-to-moderate Reynolds number 2.8 x 105 < Re < 4.3 x 105, based on the chord length. To this end, two different flexible TE models with different chord-wise lengths are studied and their results are compared with that obtained for the rigid TE models (made of aluminium) at different free-stream velocities. A spiral array comprising of 31 microphones were used to record the acoustic pressure data for the different test-cases during aeroacoustics experiment. The Power Spectral Density (PSD) spectra obtained from single microphone measurements indicate a noise reduction of 4 dB (on average) whilst using a flexible TE in comparison to its rigid counterpart, thereby demonstrating the effectiveness of a flexible TE for reducing noise. Cross-spectral Conventional Beamforming (CB) was implemented using the recorded acoustic pressure for the TE models considered to obtain a source map. The source maps indicate a dominant TE noise source at high-frequencies (i.e., in the one-third octave bands with centre frequencies 3150 Hz onwards) whilst a dominant Leading-Edge (LE) noise source is observed in the one-third octave bands whose centre frequencies are 2000 Hz and 2500 Hz (the mid-frequency range) which is in agreement with the results of previous investigations.
Faverjon, Beatrice (1), Doolan, Con (1), Moreau, Danielle (1), Croaker, Paul (1), Kinkaid, Nathan (1)
This study focuses on the understanding and modelling of noise radiated from a mine ventilation fan, with the ultimate aim of designing quiet fan impellers. Experimental measurements are presented that suggest that the main noise sources on mine ventilation fans are related to the impeller and consist of tonal components created by the passage of the blades past the volute tongue and broadband noise associated with turbulent flow interacting with the blades. Two models, one analytical and one semi- empirical, have been developed to predict the broadband components of the radiated noise. Given the assumptions made, the computed far field noise compares well with experimental data. The models are therefore good candidates for use in designing new, quieter mine ventilation fan systems in the future.
Franklin, Stephen (1), Meade, Joshua (1), Finn, Anthony (1)
(1) The University of South Australia, Australia
This paper describes a novel approach for autonomously detecting and tracking aircraft in the vicinity of an unmanned aerial vehicle (UAV). The time difference of arrival (TDOA) of acoustic tones originating from distant aircraft are correlated between spatially distributed microphone pairs located onboard the UAV. The geometry of multiple microphone pairs then allows the elevation and azimuth of the approaching aircraft to be estimated, despite the high levels of narrow- and broadband noise emanating from the engine firing sequence, propeller, airflow over the microphones and mechanical vibration. The technique enables estimation of the signal at levels 20 dB below the broadband noise floor. Potential detection ranges in excess of 1 km are demonstrated when the signal processing is combined with careful suppression of the many noise sources onboard the UAV.
Jagtap, Aniket (1), Porteous, Ric (1), Mimani, Akhilesh (1), Doolan, Con (2)
This paper presents an experimental investigation of the aerodynamic noise generated by a square cylinder in the presence of a detached thin flat-plate located in its wake. Experiments were performed in an Anechoic Wind Tunnel (AWT) at Reynolds numbers between 1.55 x 10^4 < Re_D < 2.3 x 10^4 (D being the width of the cylinder) and Mach numbers of 0.07 < M0 < 0.1. A flat-plate with a length L = D was placed along the centreline of the wake at a gap distance G from its trailing-edge (TE). The gap was varied between 0 < G < 4D whereby the aeroacoustic behaviour was studied using microphone measurements. It was found that the thin detached flat-plate reduced the Sound Pressure Level (SPL) by approximately 7 dB at the Aeolian tone frequency.
Karimi, Mahmoud (1), Croaker, Paul (1), Doolan, Con (1), Kessissoglou, Nicole (1)
The noise generated by a flat plate with both sharp and serrated trailing edges under quadrupole excitation is predicted using a periodic boundary element technique. The flat plate is modelled as a continuous structure with a finite repetition of small spanwise segments. As such, the matrix equation formulated by the periodic boundary element method for this acoustic scattering problem can be represented as a block Toeplitz matrix. To solve the linear system of equations, the original matrix is embedded into a larger and more structured matrix called the block circulant matrix. The discrete Fourier transform is then employed in an iterative algorithm to solve the block Toeplitz system. Noise reduction plots are shown as a function of source location at different frequencies illustrating the effects of serrated edges on the scattered acoustic field.
Leav, Orddom (1), Cazzolato, Benjamin (1), Howard, Carl (1)
It is commonly assumed directivity of sound from exhaust stacks is axisymmetric, which is a reasonable assumption below cut-on and in the absence of flow or elevated stack temperatures. This paper shows that the sound directivity is non-spherical when there is a laminar cross-flow across the outlet of an exhaust stack that ejects hot subsonic gas. This computational study uses computational fluid dynamics to model the heated jet exhausting into a mean laminar cross-flow and the linearised Euler equations, solved using the finite element method, to model the propagation of sound. This non- spherical spreading is due to the refraction of sound in the shear layer and diffraction at the edge of the stack outlet. Furthermore, the laminar mean cross-flow causes asymmetric spreading of the acoustic field, as the exhaust flow is also non-axisymmetric. The implications of these findings suggest that community noise level predictions from stacks may be under-predicted due to the altered directivity of the exhaust stack caused by cross-flow and refraction effects from hot exhaust gases.
Sandberg, Richard
The University of Melbourne, Australia
Aerofoil self-noise is the noise produced by the interaction between an aerofoil with its own boundary layers and wake and is of concern as it is an important contributor to the overall noise in many applications, e.g. wind turbines, cooling fan blades, or air frames. The continued growth of available computing power has made direct numerical simulations (DNS) of compressible flows with application to aerofoil noise possible. In this review paper, challenges associated with such simulations and numerical details of a DNS code that is able to exploit modern high-performance computing systems are presented. DNS data of flow at moderate Reynolds number are used to evaluate the accuracy of approximations commonly made in deriving trailing edge noise theories. Data from simulations of flow over NACA-0012 aerofoils with straight and serrated flat-plate trailing-edge extensions are presented to highlight the potential of DNS to study noise reduction technologies.
Schlanderer, Stefan (1), Sandberg, Richard (2)
(1) The University of Southampton, United Kingdom (2) The University of Melbourne, Australia
This work aims to investigate the effect of trailing-edge elasticity on trailing-edge noise radiation. To that end a highly accurate and well-validated DNS-code was coupled to a structural solver. The moving body is represented by a novel boundary data immersion method. The effect of trailing-edge elasticity on pressure fluctuations in the far field and the power spectral density are investigated. Our results indicate that depending on the frequency the elastic trailing-edge either acts as a noise amplifier or damper. In-depth spectral analysis of the noise directivity provides insight into the origin of the excess noise observed for the elastic trailing-edge at certain frequencies.
Sivakumar, Aravind (1), Porteous, Ric (1), Mimani, Akhilesh (1), Doolan, Con (2)
The paper presents an experimental investigation of a turbulent boundary-layer interaction over a single large triangular serration at the Trailing-Edge (TE) of an airfoil on the flow-induced noise. Experiments were conducted at low-to-moderate Reynolds number given by 1.8 x10^5 < Re_c < 5.7 X 10^5, where c is the chord of airfoil. Six different TE serration geometries were studied: Three serrations with a single large triangular geometry at the TE, two serrations with varying orientation relative to the airfoil, and a straight-edged reference plate (in which the TE triangular serration is not considered). The airfoils with different TE configurations were placed in an anechoic wind tunnel in amean flow field with free-stream velocities of 25, 30 and 35 m?s?1. The radiated acoustic pressure field was recorded using a spiral microphone array located in the far-field. It was found that a significant noise reduction up to 6 dB was obtained when the included angle of the triangular serration was less than 45??, which was in agreement with Howe's theory. The Conventional Beamforming (CB) source maps confirmed that the noise reduction was obtained by varying the included angle of the triangular serrations. It was observed that the maximum noise attenuation occurred at frequencies above 5 kHz, where the TE noise dominates over the Leading-Edge (LE) noise. For frequencies below 5 kHz, the LE noise sources dominate over the TE noise.
Sudhakaran, Rahul (1), Mimani, Akhilesh (1), Porteous, Ric (1), Doolan, Con (2)
This paper presents the results of an experimental investigation to study the effect of a porous airfoil Trailing-Edge (TE) with different open-area ratios at Reynolds number by 2.9 x 10^5 ? Rec ? 4.06 x 10^5 (based on the chord length) and the zero angle of attack (?=0) on the flow-induced noise generation mechanism. Acoustic pressure measurements were taken in an Anechoic Wind Tunnel (AWT) using a spiral array of 31 microphones. Five different TE configurations were considered; these are airfoil with a porous TE modelled by 15, 36, 45 and 72 slits and a reference non-porous plate. A comparison of the Power Spectral Density (PSD) graphs of a porous TE with that obtained due to reference non-porous plate indicates up to 5 dB reduction (on an average) in the noise levels between the frequency range given by 2500 Hz to 8000 Hz due to the use of porous TE. The results obtained from the cross-spectral Conventional Beamforming (CB) algorithm indicate that the noise generation source is closer to the TE at these frequencies. However, in the mid-frequency range between 2000 Hz to 2500 Hz, the noise from the Leading-Edge (LE) is comparable to that observed at the TE. This is hypothesised to be due to the interaction between the LE and the boundary-layer exiting the contraction-outlet.
Zinoviev, Alex
Defence Science and Technology Group, Australia
It is well known that noise generated by fluid flow around propellers and hulls of maritime platforms significantly contributes to their acoustic signature. The level of this noise is often determined by means of Curle's and the Ffowcs Williams and Hawkings (FW-H) equations, according to which the noise level depends on the total force acting upon the rigid boundary and the velocity of the boundary. The author and his previous co-author claimed that these equations are incorrect and suggested another equation where the noise level was determined by the acoustic pressure and its normal derivative, i.e. the potential component of velocity, on the boundary. The purpose of this paper is to reconsider the arguments which the author and his co-author presented during the discussion on the correctness of these equations. It is shown that the FW-H equation in the integral form and the equation derived previously by the present author can be obtained from the FW-H equation in the differential form utilising different ways of evaluating integrals of the source terms. It is demonstrated that the equation derived by the author does not contradict the FW-H and Curle's equations and is another form of these equations expressed via a different set of variables. It is concluded that viscous stresses as well as the rotational component of velocity do not contribute to the acoustic radiation from a rigid boundary in fluid flow.
Ashmore, Nathan (1), Cabrera, Densil (1), Kocer, Cenk (1)
(1) The University of Sydney, Australia
Vacuum Insulating Glazing (VIG) is a technology that is capable of meeting increasingly stringent global standards for low thermal emittance (U-values) windows in the built environment; however, little acoustic data is available to describe the sound insulation performance of this approach to glazing. Rhetoric suggests that the vacuum element greatly improves sound insulation compared with conventional windows, which suggests the need for an investigation to test the hypothesis that VIG provides superior acoustic performance compared to monolithic glass of equal thickness. Sound reduction index (R) values were measured using the field sound intensity method (ISO 15186-2). Measurements correspond well with theory and reference data above 250 Hz, where the performance is determined by a combination of mass-law behaviour and a coincidence dip around the critical frequency. The results suggest that the mass-law behaviour is well predicted from the VIG's surface density (equivalent to a monolithic panel) and the coincidence dip is well predicted from the critical frequency of the individual layers of the VIG unit.
Burgess, Marion (1), Gabriels, Norbert (2)
(1) UNSW Australia, Australia (2) Gabriels Environmental Design, Australia
On behalf of its members, the Australian Acoustical Society was the lead organisation in the application to Standards Australia in 2013 for a project on the review of AS/NZS 2107 "Acoustics� Recommended design sound levels and reverberation times for building interiors". The basis of this request was that the version from 2000 needed updating to revise the text, include more spaces relevant to the current building designs, remove spaces that are no longer relevant and revise the levels for both design sound levels and reverberation times. The project was approved by Standards Australia and the committee commenced the work. A draft was sent out for public review and almost 500 comments were submitted highlighting the importance of this standard to the acoustics community in Australia and New Zealand. Many of these comments were common indicating that discussion on the draft had been undertaken by groups; another good sign. A two day meeting was held in March 2015 for the committee to go through the comments and amend the draft as necessary to produce a final version. The revisions aim to maintain the same intent for what is clearly a well-respected and important document. In this paper an overview will be provided of the process and changes that have been made in the standard.
Hayne, Michael
Floth Sustainable Building Consultants, Australia
In response to complaints about structure-borne noise, in-situ floor impact isolation testing was conducted of a gym floor. The gym was located on the ground floor of a multi-storey residential apartment building. The impact of free weights being dropped onto the existing gym floor was causing structure-borne noise to be clearly audible within residential apartments located up to six floors above the gym. Using a 42.5kg dumbbell dropped from the same height above the floor surface, the existing gym floor was tested along with various samples of rubber flooring mats and a timber floating floor. The airborne sound generated by the dumbbell impacts was measured in the basement directly below the ground floor test location to provide an accurate indication of the impact isolation provided by the various flooring systems. At the completion of the installation of the upgraded gym floor additional in- situ testing was conducted to evaluate the effectiveness of the completed floor.
Hough, Cameron (1), Burgemeister, Kym (1)
(1) Arup, Australia
The Triffid is a new 800 capacity live music venue in the inner Brisbane suburb of Newstead, consisting of a conversion of a WW2-era 'Nissen Hut' type warehouse and an adjacent beer garden. Acoustic challenges included sound insulation design to allow performance by bands in the live room at levels above 100 dB(C) while keeping within the structural capacity of the 70-year old building structure. The semi-cylindrical room cross-section was a particular challenge for the room acoustic design of the live room, coupled with the architectural desire to preserve the visual look of the existing room with its concave shape and exposed radial 'rib' beams. The room acoustic design for the Triffid includes an innovative two-stage design solution involving hand-perforating the existing roof structure to act as a tuned resonant sound absorber, with a new roof structure external to the building to provide the required sound insulation. Additional internal room acoustic treatments were designed using the transfer-matrix absorption prediction method and modelled using the Odeon room acoustics software package. Concurrent to the main venue design, a partial roof structure for the adjacent beer garden was designed to control environmental noise emission from patron noise from the beer garden. A lightweight polycarbonate noise barrier design was developed for use in the beer garden enclosure. Noise emission from the beer garden was compared against published papers for the prediction of noise from small/medium crowds. The results of measurements taken in the completed beer garden compare closely to the predicted noise emission from comparable-sized groups of patrons.
Lau, Akil (1), Rowe, Deon (1)
(1) Aurecon, Australia
Houtgast and Steeneken designed the Speech Transmission Index (STI) test signals (modulated, speech-shaped noise) and its measurement methodology in 1970. The underlying basic principle of the STI is preservation of speech intelligibility during transmission. This is achieved by maintenance of the natural intensity fluctuations in the speech spectra. The design of the test methodology was such that they measured the natural modulations in a way that measurements could be carried out precisely and effectively, notwithstanding the constraints of the environment. Limitations associated with on-site STI testing accounts for certain deviations in the final results. Speech Transmission Index for Public Address (STIPA) is a simplified version of the standard STI method which is dedicated for sound level meters. STIPA measurements were conducted at a train station concourse by the Direct method (using speech signal modulation) and the Indirect method (using pink noise for impulse response) in accordance with [5]. A detailed acoustic model of the concourse was also created using EASE version 4.3 for STI predictions. The software Enhanced Acoustic Simulator for Engineers (EASE) uses MTFs (Modulation Transfer Functions) as a basis for high accuracy STI predictions. The software uses seven averaged frequency dependent octave band impulse responses to calculate the Modulation Transfer Index (MTI) values by means of 14 modulation frequencies. This paper evaluates the deviation in the measured STIPA results versus EASE-predicted STI results for the sound system in the railway station concourse and investigates the primary causes for the variation in the results.
Lindebrink, Josefin (1), N�tterlund, J�rgen (1)
(1) Tyr�ns, Sweden
The gathering of information or data in shared models is becoming more frequent in the course of planning new buildings and environments. Three-dimensional visualizations of such models are often utilized as means for verifying the final design proposal. Simulations offer opportunities for an overall impression of environments prior to construction. They also support and improve communication between disciplines, allowing design decisions to be evaluated on a perceptual basis. TyrEngine is an application built to enable real-time visualizations based on a computer game engine. It is currently a part of Tyr�ns visualization toolset and can be freely distributed with no additional licence costs. Aimed specifically to provide aid in the planning process, visuals can be generated from a variety of geometrical input formats, such as those common to CAD. In this paper the addition of acoustic information through auralization is discussed. In addition, results are presented from initial tests to acoustically couple motion utilizing the engine's inherent features. With evolving techniques for performing auralization, it has become a more integrated phase in the acoustic design of environments. Acoustic simulations are often utilized when existing building regulations do not stipulate design criteria or as means to determine such specific to a project. Hybrid simulations as proposed in this paper have the potential to widen the discussion on complex spatial features and aid discussions on quality of built environments.
Lock, Andrew (1), Holloway, Damien (1)
(1) The University of Tasmania, Australia
It is well established that Schroeder diffusers may be used as surface treatment to promote diffuse sound fields in auditoria over a target frequency range. Quadratic Residue Diffusers are very effective within a design frequency bandwidth, and this frequency bandwidth may be significantly extended by a nested or fractal design. Publicly available data typically publishes diffusion coefficients separately for the parent diffuser and the child diffuser, with some ambiguity surrounding the effect the two levels have on each other, and the performance at 'crossover' frequencies. This paper uses an optimised 2D boundary element method to investigate the differences in results when the parent and child diffusers are modelled separately, and as an integrated design. It is found that the scattering properties of the child diffuser are significantly modified by the well of the parent diffuser in which it is placed. More interestingly, the excellent scattering properties of the fractal design may be achieved with only a minor loss of bandwidth using a far simpler and more robust geometry in which the child diffuser is replaced by a concave surface at the base of the well in the parent diffuser. The paper outlines the optimisation of the boundary element code for this task, and compares results for a variety of well bottom shapes with the fractal design.
Mealings, Kiri (1), Demuth, Katherine (1), Buchholz, Jorg (2), Dillon, Harvey (2)
(1) Macquarie University, Australia (2) National Acoustics Laboratories, Australia
Open plan classrooms, where several class bases share the same space, have recently re-emerged in Australian primary schools. This paper compiled the results of three recent studies to compare both the acoustic parameters and speech perception test results in four different Kindergarten classrooms (an enclosed classroom with 25 students, a double classroom with 44 students, an untreated linear fully open plan triple classroom with 91 students, and a purpose-built semi-open plan K-6 classroom with 205 students) with the children's ratings about how well they could hear their teacher. Compiling these results allowed a regression analyses to be undertaken to establish the acoustic limits needed for children to rate they could hear their teacher 'well' (here defined as the 'hear well' criteria). Ambient noise levels, intrusive noise levels, and teacher's speech levels were recorded during different activities and room impulse responses were recorded for different teaching scenarios. From these recordings average noise levels, signal-to-noise ratios, speech transmission index scores, and reverberation times were calculated. These parameters were compared to the current Australian/New Zealand acoustic standards for classrooms (AS/NZS2107:2000), the acoustic recommendations in the literature for classrooms with 5-6-year-old children, and the derived 'hear well' criteria. The results revealed much higher intrusive noise levels in the two largest open plan classrooms (especially the untreated triple classroom), resulting in signal-to-noise ratios and speech transmission index scores to be well below the 'hear well' criteria. Results from the speech perception task also revealed poorer scores and slower response times in the triple open plan classroom compared to the other classrooms. Additionally, children's speech perception abilities decreased the further away they were seated from the teacher in the classrooms with higher noise levels resulting in scores outside the 'hear well' criteria. These results suggest students may have difficulty listening and learning in open plan classrooms and teachers are likely to strain their voice from needing to speak above a comfortable level to be heard. Additionally, the regression analysis results from the children's questionnaires confirmed that the acoustic recommendations suggested in the literature need to be met in order for the children to be able to hear their teacher 'well'. These results suggest that it may be beneficial for Australia to implement acoustic standards for unoccupied and occupied classrooms and have enforced criteria for classroom designs to ensure they meet these standards so children are comfortable and able to learn effectively in every educational setting.
Panton, Lily (1), Holloway, Damien (1), Cabrera, Densil (2)
(1) The University of Tasmania, Australia (2) The University of Sydney, Australia
Through a collaboration with the Australian Chamber Orchestra (ACO) and their sister group ACO2, subjective musician assessments of the acoustics in sixteen Australian concert venues have been obtained. The musicians were asked to rate venues on key acoustical aspects, including on Reverberance, Hearing Self, Support, Ensemble, Clarity, Warmth, Timbre, Communication with the main Auditorium, Echoes and Overall Acoustic Impression. This work differs from previous subjective stage acoustics studies in several significant respects. First, the sets of venues (8 for each orchestra) were assessed with the same repertoire, and over a short concert tour. This eliminated many variable elements in the assessments, and ensured that the comparisons were made by the subjects within the timespan of good acoustic memory, which is known to be short. Additionally, the chamber orchestra configuration performing without a conductor is postulated to be the ideal medium for such a study. Larger orchestras would rarely work without a conductor; hence many of the ensemble and balance problems that depend on good acoustics become less critical. The results from the two surveys indicate that Ensemble and Support are the most important subjective characteristics for a chamber orchestra, and were highly correlated with the Overall Acoustic Impression. This work is part of a larger project in which these subjective assessments will be used to compare with both traditional acoustic measurements on stage with omnidirectional source/receiver, as well as novel measurements employing a spherical microphone array.
Panton, Lily (1), Holloway, Damien (1)
In past work stage acoustic parameters have been used with limited success to assess musicians? subjective impressions of acoustic conditions. These parameters are commonly measured either on unoccupied stages, or on stages with furniture only (no musicians) but with a radius of 2 m cleared around both the source and receiver. This study investigates the validity of undertaking such measures on unoccupied stages, by considering the difference in on stage sound fields with and without a chamber orchestra present. This paper uses a previously validated BEM (boundary element method) model of a chamber orchestra for this investigation, and examines six source-receiver paths within the orchestra, two distinct paths each of three different lengths. Consideration is also given to the impact of randomly perturbing the orchestra for each of the six paths, and to the most appropriate distance to clear around the source and receiver to avoid significantly impacting results while maintaining a realistic stage set-up. Using the results of the BEM orchestra model, it was found that, in contrast to the 2.0 m normally recommended, a clear radius of 0.5 m was a good compromise between giving consistent results and clearing too much from the stage for meaningful results. It was also found that the attenuation was strongly affected by path length, but weakly affected by the path route or by perturbations of the orchestra set-up, and corrections are proposed to empty stage measurements (of direct sound and floor reflection only) to account for the presence of an orchestra on stage, for several source-receiver distances.
Qiu, Xiaojun (1), Cheng, Eva (1), Burnett, Ian (1), Williams, Nicholas (1), Burry, Jane (1), Mark, Burry (1)
(1) RMIT University, Australia
This paper reports the preliminary measurement results for characterising the speech privacy performance of an open ceiling meeting room called Fabpod in RMIT University, where the Speech Privacy Class standardized in the ASTM E2638 was adopted in the measurements to rate the speech privacy performance. The background sound pressure level inside and outside the Fabpod and the sound pressure level differences at different locations inside and outside the Fabpod with different sound source locations were measured in one third octave bands from 50 Hz to 10000 Hz. Based on the measurement results, the Speech Privacy Class of the Fabpod was calculated. The conclusion is that the Fabpod cannot meet the normal speech privacy criteria and the meeting inside the Fabpod can easily be overheard outside. Speech privacy is affected by many factors including the speech attenuation from the sound source to the receiver and the level of the background noise. The speech attenuation from the sound source to the receiver depends on the height of the wall or barrier, the sound absorption coefficient of the ceiling and the distance between the sound source and receiver. To achieve acceptable speech privacy for the Fabpod, all design parameters have to be tuned to near optimum values. The measures that can be used to increase the speech privacy of the Fabpod are discussed.
Vallis, Jack (1), Hayne, Michael (2), Mee, David (1), Devereux, Richard (3), Steel, Andrew (4)
(1) The University of Queensland, Australia (2) Floth Sustainable Building Consultants, Australia (3) Acran, Australia (4) Ultrafonic, Australia
Accurate test data of the acoustic properties of materials are critical for effective engineering noise control and general acoustic design. Acoustic test facilities are custom built to enable the measurement of various acoustic parameters such as sound reduction, sound power and absorption. However these facilities have been plagued with poor inter-laboratory results due to the lack of sufficiently diffuse sound fields. This paper quantifies the acoustic utility of a reverberation chamber, specifically with regards to its diffusion levels and analyses the effect that diffuser panels have on variations in the uniformity of the sound field. The diffusion levels are analysed using the spatial uniformity of sound pressure levels, spatial uniformity of reverberation times and the degree of time series fluctuations in an impulse response. In addition the facility has been modelled with a ray-tracing program to assess the significance that the diffuser panel orientations have on the diffusion levels of the sound field. The results from these quantifiers indicate that the orientations of the diffuser panels do not have a significant effect on the diffusion levels of the sound field.
Guasch, Oriol (1), Arnela, Marc (1), Pont, Arnau (2), Baiges, Joan (2), Codina, Ramon (2)
(1) Universitat Ramon Llull, Spain (2) Universitat Polit�cnica de Catalunya, Spain
Most physics related to voice production takes place in our larynx and in our vocal tract. In this work we will focus on the latter and show its role in the generation of vowels, diphthongs and sibilants. A review will be made of the involved partial differential equations and the finite element methods (FEM) used to solve them. These equations may range from the irreducible wave equation in the case of vowels, to its mixed formulation in an Arbitrary Eulerian-Lagrangian (ALE) framework in the case of diphthongs, or to the incompressible Navier-Stokes equations, which are solved to obtain the acoustic source terms of acoustic analogies in the numerical generation of sibilants. Yet, it is well-known that for mixed problems in general, the standard Galerkin FEM suffers from oscillations which make necessary to resort to some kind of numerical stabilization. The variational multiscale methods (VMM), also often referred to as subgrid scale stabilization (SGS) methods, offer a nice way out to this situation by splitting the problem unknowns into large scales, resolvable by the computational mesh, and small scales whose effects onto the large ones have to be modeled. The additional terms in the variational equations arising from the modeled subscales not only account for stabilization but also offer many other advantages that will be outlined in the present work. As regards the numerical examples, three-dimensional simulations of vowels and diphthongs will be presented, as well as a simulation on sound generated by flow past a sharp edge at the exit of a rectangular duct, which is important for understanding some basic features of sibilant production.
Barry, Greg (1), Jurevicius, Darren (1), Stead, Matthew (1)
(1) Resonate Acoustics, Australia
This paper presents the results of a case study of the achievable sound reduction of glazing treatments for a typical South Australian residential property. A loudspeaker, located externally, was used to generate a broadband noise signal and the resultant internal noise levels were measured for each glazing treatment. The treatments included retrofitting a double hung timber window, built in the late 1800's, with Magnetite glazing systems of different thicknesses and air cavity sizes, as well as upgrading the existing window suite with thicker laminated glass and acoustically rated seals. The study compares each glazing system and discusses the effect that each window upgrade has on predicted internal noise levels from a road traffic noise source.
Ishac, Najah
EMM Consulting Pty Limited, Australia
This paper reviews the NSW Environment Protection Authority (EPA), Department for Environment, Food and Rural Affairs (DEFRA) (UK) and other approaches to the assessment of low frequency noise (LFN) and the relative success or otherwise of these in environmental noise impact assessment. The EPA through its policy provides guidelines for applying 'modifying factor' adjustments to account for LFN impacts. Where there is a difference of 15 decibels or more between the measured 'C' weighted and measured 'A' weighted levels, the policy applies a penalty of 5 dB to the measured noise at the assessment location. The policy also provides similar correction factors to account for tonal and intermittent sources of noise. The EPA's policy has been tested for 15 years and has had serious challenges in practice at large distances from sources. For example, sources that do not emit low frequency dominant spectra would pass the INP test in the near field, but by virtue of increased atmospheric absorption over distance at higher frequencies, would fail (e.g. greater than 3 km) and therefore attract the 5 dB penalty. This can lead to perverse outcomes where properties further from the source with lower noise are defined as more impacted than those that are closer to the source. The DEFRA process involves measuring the noise in third octave bands between 10 Hz and 160 Hz within an unoccupied room where the alleged LFN source has been observed. If the measured Leq exceeds the predefined levels in any one-third octave band, then this indicates the potential for the low frequency noise to be subjectively classed as a nuisance. The DEFRA process also provides some consideration of the threshold of acceptability for pure and 'beating' tones by the application of a 5 dB penalty. Some European countries adopt similar approaches to DEFRA and others apply an absolute overall difference criterion similar to the INP. Other alternate methods include recommended overall dBC values where annoyance can be expected. A case study is used in the paper and includes measurement data for locations at varying distances (kilometres) from major industrial facilities to show where LFN impacts are expected according to the application of various guidelines. The focus of the case study is on rural environments with relatively low ambient noise and sparsely populated land. In providing this comparison of approaches, an alternate criteria is developed and is compared to others with regard to practical application and effectiveness of identifying nuisance low frequency noise. The alternate criteria is aimed at providing a direct and practical compliance approach to the assessment of LFN impacts.
Sparke, Clayton
Advitech Pty Ltd, Australia
The mining investment boom established an environment that encouraged rapid and widespread deployment of environmental monitoring resources in the NSW Hunter Valley. While continuous environmental monitoring is not a new phenomenon, the growth of continuous environmental monitoring networks across the Hunter Valley is unique in its yield of data with very high spatial and temporal resolutions, across a wide variety of metrics. In this study, prospecting in long term monitoring datasets was undertaken to explore whether correlations may be observed between typical environmental variables. The prospecting was undertaken to demonstrate the types of analyses and opportunities that might be available to well- designed data mining projects, and understand whether these analyses may be relevant to improving our understanding of environmental baselines on a regional scale.
Fard, Samaneh M.B. (1), Kessissoglou, Nicole (1), Peters, Herwig (1)
Sonic crystals are periodic arrangements of sound scatterers in a homogeneous fluid medium, where there exists a large impedance mismatch between the scatterers and fluid. Sonic crystals are receiving recent interest as noise barriers for reduction of road traffic noise. The use of a sonic crystal noise barrier is particularly attractive for difficult-to-address low frequency traffic noise sources. In addition to the potential to design sonic crystal barriers to target specific frequency ranges, another benefit in their use is that they allow the free flow of air, thus reducing the effect of wind loading on barriers. The acoustic performance of sonic crystals can be enhanced by replacing the scatterers with locally resonant elements. This paper examines the acoustic performance of a periodic array of rigid perforated cylindrical shells as a potential noise barrier. A parametric study to investigate the effect of the number and size of the perforations on the sonic crystal barrier insertion loss is presented.
Leader, James (1), Pan, Jie (1)
(1) The University of Western Australia, Australia
The modal representation of closed acoustical systems such as rooms and enclosures is well known and is commonly used to find the forced response at a given frequency as the superposition of the modes. In open systems such as parallel noise barriers, open enclosures or reactive type duct mufflers, the modal representation may be incomplete due to radiation losses encompassed by the imaginary part of the eigensolution. This has been declared as an open problem in the literature, with sound field predictions being found accurate only at the resonant frequencies. In the present study, the completeness and orthogonality of the quasinormal modes is investigated using the example of a two- dimensional open cavity system.
Legg, Mathew (1), Bradley, Stuart (1)
(1) The University of Auckland, New Zealand
Acoustic non-destructive testing techniques have been developed to measure properties, such as stiffness, of standing trees and logs. Previous work using this technique to measure the stiffness of standing trees provides results that are biased towards the outerwood stiffness, which is higher than the average through the cross-section of the stem. In this paper, we explore a multipath acoustic technique for measuring components of the anisotropic stiffness matrix of tree stems, which describes the mechanical properties of wood. This technique uses anisotropic ultrasonic wave propagation velocity measurements made across a log, allowing calculation of an average stiffness through the log's cross-section. This result was compared with those obtained using the traditional acoustic technique for standing tree and acoustic resonance techniques for logs.
Liu, Daipei (1), Zdenek, Havranek (2), Peters, Herwig (1), Marburg, Steffen (3), Kessissoglou, Nicole (1)
(1) UNSW Australia, Australia (2) Brno University of Technology, Czech Republic (3) Technische Universit�t M�nchen, Germany
In this work, near-field acoustic holography and non-negative intensity methods are used to predict the radiated sound of a vibrating structure. Near-field acoustic holography (NAH) is an experimental technique to reconstruct the acoustic field on the surface of the structure. The sound pressure field was measured using a microphone array close to the structural surface. The normal velocity of the plate was also measured. Supersonic intensity was calculated using experimental data based on the NAH measurements. Non-negative intensity is a quantity which allows the surface contributions of a vibrating structure to the radiated sound based on acoustic radiation modes to be predicted. An example of a point driven plate is used to compare these two source localization techniques. Results show that both techniques are successful in predicting the sound radiation patterns and yield similar results for all frequencies considered.
McMahon, Darryl
This paper explores the possibility of generalised periodic structure waves (PSW) that include the well-known Bloch-Floquet (BF) waves as a special case. We consider two types of structure waves (SW) in an infinite, uniform, one dimensional structure of equally spaced scatterers that also absorb energy. For the first structure wave type (SW1), forward transmission and backward reflection phase shifts are independent of wave propagation direction. For a second structure wave type (SW2), the phase shifts have opposite signs for opposite directions of propagation. Examples of SW1 are bending waves, such as flexural waves of a plate, and for SW2 longitudinal waves, such as acoustic waves in a fluid. The differences in amplitudes and phases of the forward and backward SW within any "cell" between adjacent scatterers are found to be equivalent to continuous PSW convolved with a periodic structure function. Finding the PSW dispersion relations requires a function that is the solution of a quadratic equation derived from imposing the same relative SW amplitudes and phases in all cells. Conservation of energy identifies physically acceptable PSW. For no energy absorption and backward and forward scatter phase shifts differing by �p / 2 , PSW of the first type (PSW1) are BF waves that propagate unattenuated in passing bands and are evanescent in stopping bands. Including energy absorption for the same phase shifts, PSW1 propagation occurs at all wavenumbers but is attenuated. This extends the BF dispersion relations to include energy absorption which blurs the distinction between passing and stopping bands. For other scatterer phase shifts, PSW1 may still be possible but only at discrete wavenumbers. In contrast PSW of the second type (PSW2) are only consistent with conservation of energy at discrete stopping wavenumbers that are the Bragg reflection condition. PSW1 also exhibit Bragg reflection, but as a narrow stopping band for small scatterer reflectivity and energy absorption. A theory for incoherent wave energy scattering in an infinite periodic structure is also developed, and its results for energy reflection, transmission and absorption are similar to those of PSW1 except for coherence effects.
Sharma, Gyani Shankar (1), Eggler, Daniel (1), Peters, Herwig (1), Kessissoglou, Nicole (1), Skvortsov, Alex (2), MacGillivray, Ian (2)
(1) UNSW Australia, Australia (2) Defence Science and Technology Organisation, Australia
Sonic crystals are finite arrays of periodically arranged scatterers, for which very low noise transmission occurs in certain frequency bands known as stop bands or band gaps. The location of these band gaps can be tuned by changing the spacing between adjacent scatterers in the periodic array. Sonic crystals are receiving recent interest for practical applications ranging from vibro- absorbing coatings for attenuation of structure-borne noise to acoustic barriers for environmental noise reduction. In this work, analytical and numerical models of a simple sonic crystal comprising periodically arranged inclusions in a host medium are developed. The analytical model is based on the effective medium approximation method, whereby the composite material is modelled as a homogeneous viscoelastic material, determined by the volume fraction of the inclusions in the composite. A finite element model of the sonic crystal using the commercial software COMSOL Multiphysics is also developed. The acoustic performance of the sonic crystal array obtained analytically and numerically is compared.
Curran, Joel (1), Welbourne, Tony (1), Welbourne, Jeremy (1)
(1) Global Acoustics Pty Ltd, Australia
Part of the noise impact assessment (NIA) process of current or proposed open cut mines involves predictive noise modelling of mining scenarios to determine an area of affectation. Crucial to predictive noise modelling is accurate sound power level data of the mobile mining equipment to be utilised. ISO [1-3] (International Organisation for Standardisation) and AS [4] (Australian Standard) documents, along with industry developed methodologies, exist for this task and should be utilised when determining equipment sound power levels to be used in NIA modelling, and, determining compliance of equipment eventually used in production with sound power limits extracted from the NIA process. However, these standards and methodologies are often not employed, or are so reduced in scope and detail, that the resultant data is of questionable value and use. Use of questionable methodologies and resultant sound power level data has, in the authors' experience, lead to incorrect model results, sound power specifications not suitable for the intended mine, determination of an incorrect noise affectation area, and, ultimately, significant cost to the mine. Haul trucks are generally the most numerous plant type on a mine site and, as such, accurate determination of haul truck sound power is vital. Two levels of haul truck sound power assessment are presented (compliance and screening) and critical variables for each level of assessment are highlighted and discussed. Results from each level of assessment are compared, showing an agreement between the two methodologies of less than 2 dB/dB(A) (absolute). A theoretical exercise is also undertaken to highlight the effect on results of reducing the number of microphone positions used in determining compliance sound power.
Gleeson, Gerard
Rio Tinto Coal, Australia
Managing noise emissions from mining fleet is a key environmental aspect for the Mount Thorley – Warkworth mining complex (MTW). Effective mitigation strategies are required to ensure compliance is achieved, and impacts on near neighbours are minimised. There are three core components to MTW's noise mitigation strategy which are (1) sound attenuation of the mining fleet; (2) effective reactive management mechanisms; and (3) proactive management mechanisms. Following approval of the (now disapproved) Warkworth Extension Project, MTW commenced a project to attenuate 100% of the mining fleet. Without 'off the shelf' options for Komatsu 830E-1AC trucks, MTW partnered with the equipment manufacturer and third party companies to design and fit noise attenuation packages. So far the attenuation project has yielded promising results, by halving the perceptible noise level of the fitted trucks. MTW has developed one of the most comprehensive noise monitoring networks in the industry. This includes four directional real time monitors in the Bulga community, supporting on-ground noise assessments undertaken on a night-to-night basis by the MTW Community Response Officer. Committed to the use and success of real-time noise monitoring systems, MTW has supported the development of a first-of-class directional noise monitoring system known as the Environmental Noise Compass. This new technology combines a large microphone array and advanced signal processing methods (borrowed from sonar applications) to target the lower frequency bands typically dominated by mining noise. Installed in the Bulga area in December 2013, the ENC represents a first for the mining industry, and a clear demonstration in continuous improvement. Use of predictive noise models in a mining context are still in their infancy. Simple assessments of wind speed, direction and temperature inversion provide good indicators but are not always reliable. The extensive amount of data collected by the MTW monitoring network has allowed for a detailed study to be undertaken. The data is used to better understand the meteorological factors which are common to the nights which have seen the highest noise levels (i.e. worst case conditions), and better prepare for such events.
Parnell, Jeffrey
NSW Department of Planning and Environment, Australia
The NSW Department of Planning and Environment (DPE) has a regulatory role in managing the noise from coal mines. Currently there are 56 coal mines in NSW which generally have Leq(15 minute) noise criteria in the order of 35 to 40 dB(A) at the nearest private residences. As a consequence of its responsibilities, DPE undertakes a range of high quality audits and noise monitoring studies. This paper presents a brief selection of ancillary data that has been extracted from those studies. The object of this exercise was: to document the noise signature of coal mines; to better understand how to measure mine noise in a noise environment dominated by insect, frog and bat noise; and to identify if there are any shortcomings or areas of potential improvement in the way low frequency noise is identified. The exercise found that under normal meteorological conditions, differential attenuation over large distances effectively reduces the spectral energy > 630 Hz to very low levels, (if not below the threshold of hearing) with both dB(A) and dB(C) of mine noise usually being controlled by sub 250 Hz energy. The use of low pass filtering as an effective tool to eliminate extraneous high frequency noise such as that from frogs and insects was validated by the exercise. The exercise also found that the characteristic peaks in the 16 and 25 Hz range are unlikely to be audible unless the overall level of mine noise is in excess of at least 45 dB(A). Consequently, it is recommended that these frequencies should not be included in an assessment of low frequency annoyance (with reference to a C – weighted level).
Regulating noise impacts from large coal mines is difficult, particularly given the potential topographical and meteorological variations that can occur over setbacks of up to 5 km between mine sites and potentially impacted receivers. In NSW, the Industrial Noise Guideline is used to determine noise criteria for sensitive noise receivers that may be impacted by mine noise (such as residences). In many instances, this results in noise criteria being established at levels as low as Leq(15 minute) = 35 dB(A). Exceedance of this criterion may be negotiated by agreement, but exceedances of more than 5 dB may require the mine to offer property acquisition. Despite having some of the most stringent noise criteria in the world, regulators still receive a high number of complaints from residents surrounding mine sites. This paper examines the generation and propagation of mine noise, methods used to manage to project noise objectives (including reactive and predictive measures), and the regulatory regime that underpins these objectives.
To understand whether the phenomenon of spatial variation is a significant source of uncertainty in measurements of Low Frequency Noise, operator attended monitoring was undertaken at several points along a transect in the far field of known sources of Low Frequency Noise. Results indicate that in some instances, small but statistically significant variations in both 1/3 octave and broadband SPLs may be returned when measurement locations are varied by distances of 5m to 15m. Results of the assessment are presented to help explore the potential impact that this phenomenon may have on uncertainties in impact assessment, or in defining baseline conditions for design of Low Frequency Noise controls.
While increasingly sophisticated methods have been developed to interpret remote and real-time monitoring of industrial noise levels, constraints around automation of these analytical methods remain. The optimisation of real-time noise management is constrained by differing stakeholder comprehensions of the role that technology plays in noise monitoring, and the role that noise monitoring plays in noise management. A high level review of typical noise monitoring and management practices was undertaken to identify potential barriers to optimisation, and identify assumptions that may prevent the integration of emerging monitoring technologies and historical analysis methods. Several case studies are presented to demonstrate how the design and implementation of hi-tech tools (remote, automated noise monitoring systems) can be enhanced through the integration of relatively simple (low-tech) logic, to leverage better outcomes for noise management. It is hoped that assumptions pertaining to the deployment of conventional analysis methods into a technology and management environment that pursues autonomous manipulation of large datasets can be challenged, validated or better documented.
Todoroski, Aleks
Todoroski Air Sciences, Australia
Temperature inversion and wind conditions are known to have a significant effect on noise propagation over long distances. Consideration of such conditions is a challenging part of assessing environmental noise propagation over several kilometres in environments with relatively low background noise levels. To consider these phenomena, noise consultants generally use standard commercial noise models, which apply correction factors, linear vertical approximations of the prevailing weather conditions, or assume horizontally uniform weather conditions. These assumptions, whilst not ideally reflective of real world weather conditions will produce generally reliable assessments of noise overall, but for any specific period, these assumptions may lead to inaccurate assessments of short term noise levels. This is especially the case when there are significant spatial or temporal changes in the wind direction, wind speed or temperature in the period under consideration. As a result, the assumptions underpinning commercial noise models are not well suited to real time or predictive/forecast management of short term noise impacts over long distances. Understanding the nature of these non-linear, time and space varying weather conditions can lead to more accurate noise assessments. Examples of temperature profile measurements and new techniques to consider these influences in a three dimensional time and space varying field are outlined, including predictive/forecasting noise modelling for management of industrial noise levels.
Welbourne, Tony (1), Welbourne, Jeremy (1)
(1) Global Acoustics, Australia
Development of an open cut mine requires a noise impact assessment to determine the likelihood of affectation. Open cut mines typically comprise one or more pits and associated dumps. Transport of waste from pit to dump involves large trucks (haul trucks) travelling on earthen roads (haul routes). Haul trucks are inherently noisy, and, their emissions vary, as does the speed of travel. These variations need to be factored into any predictive noise model where a time based result is required, for example LAeq,15-minute. Past practice was to model haul truck emissions simply by placing truck sources in the model, the number of which corresponded to the number of trucks at the mine. Current best practice is to model haul routes as strings of relatively short segments; each having a specific period LAeq sound power determined by a set of relevant variables. The accuracy of this method has been evaluated by comparison of a validated model using 15-minute haul route source locations for trucks as logged in a mine GPS database, and a theoretically developed model using current best practice.
Wolfenden, Scott
Bulga Coal, Australia
Bulga Open Cut (BOC) is a large open cut mine located in close proximity to the local wine and tourism industry near the villages of Broke and Bulga in the Hunter Valley. It forms part of Bulga Coal, a Glencore operated business which also includes Bulga Underground Operations (BUO) and a shared Coal Handling and Preparation Plant (CHPP) and rail load out facility. The mine has gained a high level of acceptance within the local community because it listened to noise concerns raised by the community and responded appropriately. In late 2009 following community concerns regarding mine noise impacts, the mine undertook an investigation and consulted with both the local community and the NSW Department of Planning and Environment. Subsequently, Bulga Coal committed to a number of initiatives including: 1. Contemporised the noise criteria and management within the Development Approval; 2. Invested $173million on a fully noise attenuated mining fleet; and 3. The development of a real-time noise monitoring management system implemented by a control room to proactively reduce noise impacts. Bulga Coal has continued to educate mining supervisors and the entire workforce on the importance of reducing mining noise impacts from operations and has continually refined and improved the noise management system. A key design element of the recently approved Bulga Optimisation Project (December 2014) is the establishment of a large noise and visual bund. The outer face of the bund will be constructed during daytime only in order to reduce the noise impacts on the community. The Bulga Optimisation Project has extended the mine life by approximately 20 years and was approved with minimal community opposition. Initially, the noise impacts are very similar to the existing operational scenario and then progressively reduce after the first few years due the establishment of the noise and visual bund. The development of the bund is in addition to the changes to the mine plan to mine away from neighbouring communities to reduce noise impacts.These initiatives have enabled Bulga Coal to operate an open cut mine in near proximity to the local wine and tourism industry with a high level of community acceptance.
Mimani, Akhilesh
The University of Adelaide, Australia
This paper analyses the acoustical attenuation behaviour of a conical chamber muffler having a Single- Inlet and Single-Outlet (SISO) by means of a 3-D semi-analytical formulation based on modal expansion of the acoustic field and the Green's function approach. The 3-D acoustic field inside the rigid-wall conical chamber is expressed in terms of the spherical Bessel and Neumann functions of non-integer order, the Legendre and associated Legendre functions of integer order and non-integer degree and the circular functions. The conical chamber muffler is characterised using the uniform piston-driven model in terms of the impedance [Z] matrix parameters (equivalently, the acoustic pressure response function) obtained by computing the average of the 3-D Green's function over the surface area of the inlet/outlet ports modelled as rigid pistons. The 3-D semi-analytical approach enables one to taken into account, effect of relative azimuthal angular location between the inlet and outlet ports on the TL performance by consideration of the non-axisymmetric or azimuthal transverse modes (in addition to the symmetric transverse modes) in the modal summation of the acoustic field. The Transmission Loss (TL) graphs computed by using the 3-D semi-analytical formulation are found to be in an excellent agreement with that obtained from the 3-D FEA, thereby validating the technique presented in this work. Design guidelines for obtaining a broadband TL performance are suggested in terms of optimal (polar and azimuthal) angular and radial location of the ports on the appropriate pressure nodes which is a practically useful outcome of this investigation.
Hawkins, Roger
Palmer Acoustics Pty Ltd, Australia
Is our instrumentation moving with the times? Our current instrumentation owes it genesis to the condenser microphone, simple valve amplifiers and moving coil displays. The existence of highly integrated alternative devices for sound measurement, Micro-Electro-Mechanical-Systems microphones, are now familiar to all users of modern smart phones but not (yet) widely to acousticians. The standard for instrumentation, currently IEC 61672-1:2002 describes instruments with an analogue front end and a "don't care" processing engine and sets, as it must, accuracy and stability requirements. The analogue part effectively precludes a fully digital system, from getting certification. Are the standards, formed last century, holding back some potential advances to the betterment of measurement and data processing? This paper, using a currently available MEMS data logging sound level meter as an example, looks at the advantages of a fully digital device and poses the question "Why Not?"
Smith, John (1), Chu, Derek (1), Wolfe, Joe (1)
Typical acoustic currents are usually far too small to be measurable with any precision. This paper presents a technique that uses an impedance head to generate with precision a desired, acoustic current waveform, usually periodic. An impedance head with multiple microphones, after a suitable calibration procedure, allows calculation of the acoustic pressure and current waveforms at the appropriate reference plane. The current waveform injected by such a device is a complicated function of the waveform supplied to the transducer driving the impedance head, the acoustic properties of the impedance head itself, the frequency responses of the transducer and microphones, and the frequency responses of the electronic circuitry involved. It is possible however, using an iterative technique, to adjust the waveform driving the input transducer so that the waveform of the current injected into the device under study has the desired waveform. In this fashion an impedance head can be used to synthesise and to inject a precisely known acoustic flow waveform. As an application we report that the synthesis of a model glottal flow waveform which is then input to a rigid, unvarying physical model of the vocal tract. This allows, for the first time, the rigorous evaluation of the various techniques that are used to determine the acoustical properties of the vocal tract and the glottal waveform under a wide range of conditions.
Evans, Tom (1), Cooper, Jon (1)
Tonal noise, or tonality, as a component of environmental noise can be an important factor in the annoyance of people listening to that noise. Environmental noise with audible tonal components generally results in higher levels of annoyance than broadband noise at a similar level. To reflect this, specific assessment methodologies are applied to tonal noise in environmental noise regulations around Australia as well as internationally. Typically these assessment methodologies seek to determine whether a peak in a frequency spectrum exceeds a criterion level and, if so, what penalty should be added to the measured noise level such that it better reflects the likely annoyance. While tonal regulations are in place throughout Australia, there is a significant variance in the level of tonality at which they require a penalty to be applied. The differences can be particularly significant for tonal frequencies lower than 200 Hz. In many cases, the level at which a penalty applies does not accurately reflect the findings of dose response studies into tonal noise. Additionally, the standard application of a flat 5 dB penalty in many cases, regardless of the amount by which the tonal component exceeds the criterion, makes the regulations relatively inflexible. This paper reviews tonal noise criteria applied throughout Australia and compares them to each other as well as to international criteria and the findings of dose response studies to tonal sources. The tonal assessment criteria are used to assess examples of tonal noise from some sources to review the difference in outcome between the regulations.
Hamilton, Les (1), Cleary, Jane (1)
(1) Defence Science and Technology Group, Australia
Unmanned Underwater Vehicles can autonomously obtain high quality sidescan sonar backscatter swathe imagery of the seabed by traversing pre-programmed tracks at a set height above the bottom where they are relatively undisturbed by wave action. Some survey activities could be more efficient if the UUVs had some machine intelligence or decision making capability. For example, UUVs could be programmed to survey seabeds of particular interest at slower speeds to obtain more detail, or might resurvey particular areas using more detailed search patterns. Onboard processing for this purpose requires fast algorithms and robust decisions. Ongoing work in autonomously characterizing sidescan sonar imagery for seabed type is described. Humans can readily recognize patterns and textures indicative of particular seabed types, for example, sand has characteristic ripple patterns. Can Unmanned Underwater Vehicles be given the capability to autonomously mimic human visual perception?
Manor, Ella (1), Martens, William (1), Bassett, Mark (1)
It is well known that complex harmonic tones can be varied in their timbral character by adjusting the relative amplitudes of selected sets of harmonics, most obviously exemplified by the reduction of even-harmonic amplitudes to create a 'Clarinet-like' timbre. What is not well known is how great the reduction in even harmonics must be, relative to the odd harmonic amplitudes, in order for the 'Clarinet-like' timbre to be clearly distinguished from the timbre of other complex tones containing energy distributed over all harmonics. For example, a complex waveform with more of an 'Oboe-like' timbre will exhibit an orderly progression of harmonic amplitudes that decrease with increasing frequency. A slight deviation from this progression in which the amplitudes of all even harmonics are reduced as a group, for example by a common attenuation factor of 3dB, does not shift timbre identification responses away from predominantly 'Oboe-like' to predominantly 'Clarinet-like.' It was one motivation for the current research to determine how great the amplitude reduction in the group of even harmonics must be in order for the number of 'Clarinet-like' responses made by a panel of listeners to come to dominate the observed number of 'Oboe-like' responses. A second motivation for the research reported here was to determine how to adjust the relative amplitude of harmonics of a complex tone containing only odd harmonics in order to match the perceived 'sharpness' of a complex tone containing energy distributed more evenly over all harmonics. This was an important question to ask in this investigation because the perceived sharpness of these two complex tones clearly differed even though the rate of spectral roll-off was matched between them. Having the answer to the second question posed above regarding the means by which tonal 'sharpness' can be held constant, a more satisfying answer to the first question is made possible. The answer is more satisfying because it eliminates the confounding influence of changes in the perceived 'sharpness' of timbres occurring within the sequence of complex tones, in which the physical boundary between complex tonal stimuli identified as having 'Oboe-like' versus 'Clarinet-like' timbre was determined. Using a measure termed the 'Even-harmonic Attenuation,' the timbral transition point in categorical response proportions could be associated cleanly with a position on a physical stimulus continuum for such complex tones. This position was determined to be around 9 to 12 dB for the stimuli presented in this study.
Martens, William
The University of Sydney, Australia
In describing musical performances, the use of the term vibrato can imply any periodic (or quasi- periodic) fluctuation in pitch, amplitude, or timbre of a sustained musical tone. The current study focused only upon analysis and evaluation of 'pitch vibrato' observed in recorded performances on a number of string instruments (three violins, a viola, a cello, and a bass violin). In order to gain a better understanding of the identifiable auditory attributes associated with the perception of pitch vibrato as performed, a multi-parameter vibrato synthesis algorithm was employed in the creation of a set of stimuli for evaluation by human listeners. Besides rate and depth of pitch modulation, a third parameter was included in the synthesis that allowed for a manipulation of the quasi-periodic nature of simulated vibrato intended to mimic performed vibrato. Control for this third parameter, effectively capturing the amount of irregularity in pitch modulation, was enabled via adjustment of the Q value of a resonant low-pass filter that was used to either spread or concentrate a modulation signal's energy around the nominal pitch modulation frequency (vibrato rate). A high Q value was associated with pitch modulation that sounded very regular, practically sinusoidal at the sub-audio vibrato rate (when the Q value exceeded around 30). Lower Q values were associated with irregular sounding pitch modulation that was heard as more rough, and could become very rough at the lowest Q values (below Q=3). Performances recorded without substantial pitch vibrato were processed via a delay-modulation algorithm that employed a collection of the synthesized modulation signals in an attempt to match the character and quality of vibrato performances recorded on the same instruments. A group of fifteen listeners was employed to determine how detectably different the synthetic vibrato was as the Q value was varied, and to what extent changes in Q value influenced the perceived 'fluctuation strength' of the synthetic vibrato.
Martens, William (1), Bassett, Mark (1), Manor, Ella (1)
Three types of complex harmonic tones were created by adjusting the relative amplitudes of selected sets of even-numbered or odd-numbered harmonics, relative to the more homogenous pattern of harmonic amplitudes associated with an 'Oboe-like' timbre, which timbre comprised the first of the three types of tones employed in this study. The other two types of tones were produced either by the reduction of even-harmonic amplitudes to create a 'Clarinet-like' timbre, or by the reduction of odd- harmonic amplitudes to create an 'Organ-like' timbre. In all three cases the overall harmonic amplitude envelope could be described by a simple spectral roll-off parameter, that parameter being the rate of amplitude attenuation over increasing frequency, measured in dB/octave. For each of these three types of complex harmonic tones, further variation was introduced into the stimulus set by small adjustments in the rate of spectral roll-off in harmonic amplitude (which included four attenuation rates that ranged from 3 dB/octave to 7.5 dB/octave, in incremental steps of 1.5 dB/octave). Thus a set of 12 timbres was constructed that differed perceptually along one continuous dimension (identified with the auditory attribute termed 'sharpness') and one categorical dimension (related to perceived musical-instrument character, nominally identified as 'Oboe-like', 'Clarinet-like' and 'Organ-like'). All pairwise comparisons of these 12 timbres were presented to four listeners for evaluation in terms of overall timbral dissimilarity for each pair, without regard to particular identifiable auditory attributes. The collected dissimilarity ratings were treated as estimates of inter-stimulus distances between the Cartesian coordinates of the stimuli configured in a two-dimensional (2D) perceptual space, which was derived using INdividual Differences SCALing (INDSCAL) analysis. INDSCAL was employed to produce two useful outputs: First it produced the abovementioned perceptual space (termed 'Stimulus Space') for the group of four listeners as a whole. Second, it produced estimates of the differences in weighting that each of the four listeners placed on the resulting dimensions (which weightings are captured by INDSCAL in terms of a 'Subject Space'). The INDSCAL analysis of data from these four listeners revealed very small differences in the perceptual salience that each dimension holds for each listener. Finally, the group Stimulus Space coordinates on the continuous perceptual dimension (identified with the 'sharpness' attribute) were modelled using a two-term regression equation that included the conventional physical measure designed to predict variation in 'sharpness' and also a term confirming significant dependence on the odd-to-even harmonic amplitude ratios of the tones.
Sheikh, Mahbub Alam (1), Lee, Siew-Eang (2)
(1) Vipac Engineers and Scientists, Australia (2) National University of Singapore, Singapore
Soundscape is defined as the acoustic environment as perceived and understood, by people, in context. It relates the aural space to the living environment towards the enhancement of acoustic experience. Soundscape approach is mostly used to investigate people's positive perception of outdoor environmental noise such as in parks, town squares, rural environments and recreational areas etc. However, it is rarely used in indoor residential context to assess acoustic comfort subjected to different environmental noises, for example road traffic noise - a major source of noise annoyance in cities. In addition, the use of psychoacoustic investigation is rather limited in literature in context of acoustic comfort in residential environment which often is useful in identifying specific soundscape quality. In this research a psychoacoustic experiment was carried out to investigate indoor acoustic comfort subjected to road traffic noise. A multidimensional evaluation by semantic differential analysis was carried out about subjective perceptions of different road traffic sounds. Statistical analyses were then carried out to correlate different psychoacoustic quantities with different perception dimensions in the semantic space. The research investigation revealed that subjective perception across different bipolar perception dimensions investigated are strongly and significantly correlated to Loudness and Roughness of the road traffic noise.
Spargo, David (1), Martens, William (1), Cabrera, Densil (1)
In free field listening, interaural differences provide auditory information that enable listeners to identify the lateral angle of sound sources very accurately. When listening in rooms, however, performance is greatly reduced by the presence of room reflections, particularly for sources containing energy primarily at low frequencies. Within the frequency band of speech signals, the influence of room reflections on directional hearing has been well established; however, less is known about the influence of room reflections on low-frequency directional hearing. Headphone-displayed binaural simulation of subwoofers located at 17 positions in a small reverberant room were prepared by convolving a dry source with binaural room impulse response measurements made using a Head and Torso Simulator (HATS). In an identification task using percussive low-frequency musical tones as sound sources, perceived lateral angles of these sources were reported by 10 listeners, for comparison with the actual subwoofer angles. The peak in the interaural cross correlation function of the binaural stimuli predicted observed lateral angle judgement data much better than did the actual subwoofer angles. A multivariate regression analysis revealed that including interaural coherence (IC) as an additional predictor of lateralisation judgements improved the amount of variance for which the regression model could account, suggesting that IC effectively modulated a listener's ability to utilise interaural time difference (ITD) cues.
Bao, Chaoying
The need to extract a single audio signal of interest from a multi-source and noisy environment is common across many disciplines. Adaptive beamforming, due to its superior interference rejection and noise suppression, is a preferred processing technique for obtaining high quality audio in noisy environments. In this paper, we compare the performances of two different types of adaptive beamformers for the purpose of extracting audio signals. One of the beamformers is the robust Capon beamformer (RCB) where the beamforming part is carried out in the frequency domain, resulting in low computational complexity but relatively high latency. The other beamformer is the block constrained least mean square beamformer (BCLMSB) where the beamforming part is carried out in the time domain. It has relatively higher computational cost but no latency. The performances of these two adaptive beamformers are evaluated in terms of fidelity of the beamformer output and robustness of the system under various conditions.
Adams, Keith
B&K EMS, Australia
Several thousand permanent monitoring terminals have been deployed around the world for monitoring aircraft noise. A large proportion of these were designed more than twenty years ago, primarily to record A-weighted levels, but later enhanced to include levels pertaining to C- and Z- weighting, third octaves, effective perceived noise, stationary loudness, and more recently, non- stationary or dynamic loudness. In addition, acoustic recording of events with levels above a prescribed threshold and neural network classification were added. Noise events are frequently caused by more than one type of sound source, so that it becomes important to quantify the aircraft contribution to the noise impact. In addition to the enhanced facilities of noise monitoring terminals, the sonograms of the acoustically recorded noise events prove to be especially useful. In many cases a quick glance at the sonogram will reveal the presence of several other noise sources, such as barking dogs, loud birds, trains and other ground-based sources. Moreover, the sonogram permits the speed of trains and aircraft, with surprisingly good agreement with aircraft speed data obtained from radar, to be estimated. Distinctions between different types of jet, turbo-prop and helicopter aircraft show up readily on the sonograms. In this paper, examples of sonogram evaluations will be presented, including cases where non-aircraft noise events have been wrongly ascribed to certain aircraft movements, or the wrong type of aircraft has been ascribed to the noise event. The methodology can similarly be applied to other situations of environmental noise to reveal more details of the noisescape.
Bowden, David (1), Forrest, James (1)
The airborne noise levels for large capacity diesel engines must meet legislative requirements as a minimum and may have additional constraints on level and spectral content. Exhaust system testing and development for this class of engine is generally limited to confirmation testing due to limited availability of test facilities, high cost of test hardware and testing, limited physical access, and low production volumes. Large diesel engines differ significantly from those used for automotive applications in regard to gas flow characteristics, exhaust system design, and operational modes. This study evaluates the applicability of an automotive industry one dimensional (1D) simulation software suite (Ricardo WAVE�) to the refinement of large diesel engine exhaust system performance and describes the modelling approach used. The Defence Science and Technology Group (DSTG) has developed a computer based capability for modelling the acoustic response and flow performance of exhaust systems and exhaust system components representative of large diesel engines. This capability can be used for exhaust system components, complete exhaust systems, and full engine installations. A virtual transmission loss test bench approach was employed to reduce simulation run times compared to that of complete engine installations. The modelling was conducted in order of increasing complexity where simple models were validated before progressing to more complex models. Published research and data were used for validation. The modelling capability described in this study permits assessment and development of exhaust systems, with or without engine source data, at lower cost. Savings are achieved through a reduction in test samples and physical testing.
Chiles, Stephen
NZ Transport Agency, New Zealand
Road surface noise can be measured by microphones mounted in close proximity to the tyre/road interface on a moving vehicle. The draft standard ISO/DIS 11819-2 defines the "CPX" measurement method that has been widely adopted by many road authorities and researchers. In New Zealand two CPX measurement systems have recently been developed in general accordance with this standard, but using different approaches: one with a conventional trailer, and the other with instrumentation fitted to a car. There are also differences in the instrumentation and data processing architecture between the systems. This paper compares the designs of the two systems and provides commentary on the requirements of the draft standard.
Cockings, Tom (1), Sburlati, Dominic (1), Harrison, Matthew (1)
(1) SLR Consulting Australia Pty Ltd, Australia
In Australia, road traffic noise models are calibrated against noise measurements made simultaneously with the measurement of meteorological conditions and traffic volume and composition. Road traffic noise influencing factors, such as vehicle speed and traffic composition, are measured in order to remove as much systematic error from the calculation method prior to applying an overall calibration factor to the predictions to account for the difference between the measured and predicted traffic noise level results. Although a road surface correction is generally applied to the predictions to account for quiet road surface treatments, such as Stone Mastic Asphalt (SMA), it is not yet common practice for acoustic consultants to directly quantify one of the key road traffic noise influencing variables: road surface correction. Without direct measurement of the road surface correction, it is often difficult to accurately calibrate road traffic noise models for long alignments, or different carriageways, with different surface types. SLR Consulting has developed an innovative and practical method whereby acoustic consultants can construct, calibrate, and operate a low-cost road surface correction measurement system using standard acoustic measurement equipment and low-cost 3D printed parts. The proliferation of road surface correction measurement systems will hopefully lead to the standardisation of road surface correction validation, leading to more accurate computer noise modelling across Australia. The ability to accurately measure the road surface correction will minimise one of the largest remaining sources of systematic error in our road noise modelling methodology. This will result in reduced variation between the "calibrated" model and the measured noise level at individual monitoring locations (minimising the standard deviation between predicted and measured noise levels).
Fard, Samaneh M.B. (1), Peters, Herwig (1), Kessissoglou, Nicole (1), Marburg, Steffen (2)
(1) UNSW Australia, Australia (2) Technische Universit�t M�nchen, Germany
Barriers are generally less effective at low frequencies due to easier diffraction of long acoustic wavelengths over the top edge of a barrier. The effectiveness of a barrier is also highly dependent on its design. This paper examines the acoustic performance of a noise barrier embedded with Helmholtz resonators along the top edge of the barrier using a quasi-periodic boundary element technique. Using the quasi-periodic approach, the length of a nominally infinitely long barrier is truncated using a finite number of periodic sections. A Helmholtz resonator tuned to a specific low frequency is included in each periodic section of the barrier. High insertion loss at the tuned frequency is observed. Compared to insertion loss results for an equivalent straight barrier in the absence of the embedded Helmholtz resonators, greater attenuation in the barrier shadow zone at the tuned frequency can be achieved.
Gange, Michael (1), Brown, Robin (2), Tardio, Darren (2), Hang, Kevin (3)
(1) Renzo Tonin & Associates NSW Pty Ltd, Australia (2) Renzo Tonin & Associates VIC Pty Ltd, Australia (3) UNSW Australia, Australia
Road traffic noise affects approximately 8 million people in Australia with 2 million seriously affected, far more than from other forms of transportation. As the principal source of road noise is from the tyre/pavement interface, it is important to understand and quantify pavement noise and to catalogue ongoing performance. A new instrument is now available in Australia for this work comprising a special purpose noise trailer. RONDA (ROad Noise Data Acquirer) is a CPX trailer conforming to international standard ISO/CD 11819-2, intended for measuring road pavement noise. The trailer is of the open frame type without an enclosure and is the first of its kind in Australia. A description of the design of the trailer is provided together with the results of initial testing on asphalt pavements.
Harrison, Matthew (1), Kean, Simon (2), Hinze, Benjamin (1)
(1) SLR Consulting Australia Pty Ltd, Australia (2) Roads and Maritime Services, Australia
A methodology has been developed by the authors to address the issue of determining a transparent process whereby the selection of various routes for a new road can be ranked in terms of their noise impact on affected communities. A rating scale has been proposed to enable these rankings to be easily combined with the rankings of other environmental considerations in a multi-criteria assessment (MCA) framework associated with the project. The approach relies on the rating of "noise annoyance" to rank the proposed route options. The proposed procedure uses the annoyance response relationships for Day-Night levels (DNL) documented within the Environmental Health Perspectives magazine article "Annoyance from Transportation Noise: Relationships with Exposure Metrics DNL and DENL and their Confidence Intervals". These relationships are also cited in the European Commission's "Position Paper on Dose Response Relationships between Transportation Noise and Annoyance (2002)". The DNL level can be directly calculated using the current New South Wales (NSW) Road Noise Policy (RNP) noise metrics for day and night noise levels (i.e. L_Aeq,15hr and L_Aeq,9hr). The assessment methodology includes an additional consideration for the level of annoyance caused by an abrupt increase in noise level at route opening which mirrors the consideration of noise level increase provided in the RNP.
Jurevicius, Darren (1), Evans, Tom (1)
This paper presents the findings into a study of the relative performance of custom-design noise walls of different heights, with and without T-profile noise wall tops of various dimensions. The study was undertaken at a test facility using noise walls of heights 2.4 m and 3.5 m, with T-profile widths of 600 and 1200 mm. The testing was undertaken using measurement positions of varying height behind the wall, with a loudspeaker used to generate an MLS-type signal. The impulse response was stored for post-processing and calculation of the spectral insertion losses was carried out for each test. Additionally, the influence of absorptive treatment on the T-profile was tested. These results were compared to the untreated T-profile, the standard noise wall and a standard noise wall with an absorptive capping but without a T-profile. The reduction achieved with the T-shaped profile is quantified in terms of both an additional spectral insertion loss relative to the base wall as well as the equivalent reduction in noise wall height that can be obtained while maintaining performance by using the modified top. The performance of the different noise wall configurations is also compared to the theoretical and tested performance of other modified noise wall types. Finally, the practical application of the tested insertion loss results to predicted noise levels is discussed.
The axially short circular/elliptical cylindrical chamber is often used as a flow-reversing or straight- flow end-chamber in a multi-pass perforated duct muffler, a typical component of a modern-day automotive exhaust system. However, due to its small expansion volume, such short end chambers yield low acoustic attenuation (expressed in terms of Transmission Loss (TL)) in the low-frequency range, induce a large back pressure and increasing the chamber length results in the occurrence of a trough (due to the first axial mode) at a lower frequency that deteriorates the TL performance. In view of these limitations, the use of a different geometry, namely, a rigid-wall hemispherical cavity as a flow-reversal end-chamber muffler is investigated for potentially enhancing the TL performance over a wider frequency range, especially at low frequencies. To this end, this paper analyses the TL performance of a hemispherical end-chamber muffler having a single end-inlet and single/double end- outlet by means of a 3-D semi-analytical formulation based on the modal expansion of the acoustic field and the Green's function approach. The 3-D acoustic field inside the rigid-wall hemispherical end-chamber is expressed in terms of the orthogonal modal functions. The hemispherical end-chamber muffler system is characterised using the uniform piston-driven model in terms of the impedance [Z] matrix parameters obtained by computing the average of the 3-D Green's function over the surface area of the ports which are modelled as rigid pistons. The TL graphs computed by using the 3-D semi- analytical formulation are found to be in an excellent agreement with that obtained from the 3-D FEA, thereby validating the technique used here. Furthermore, the 3-D modal expansion method enables one to take into account, the relative polar angular location between the ports and also determine their optimal radial offset distance (corresponding to appropriate pressure nodes on the end face) to obtain a broadband TL performance. A comparison of the TL performance of the optimised hemispherical end- chamber muffler with that of an equivalent circular end-chamber having an equal volume demonstrates a significantly higher frequency range over which a broadband attenuation is obtained by using the hemispherical cavity. Similarly, a comparison with the TL graph of an equivalent axially short circular end-chamber indicates that the former exhibits higher attenuation in the low-frequency range.
Sandberg, Ulf
Swedish National Road and Transport Research Institute VTI, Sweden
Low Noise Road Surfaces (LNRS), in this presentation surfaces offering at least 3 dB of noise reduction compared to common asphalt surfaces, have been used occasionally since the 1980's for road traffic noise abatement. However, it is not until the latest 10-15 years that they have become sufficiently developed to combine noise-reducing efficiency with a reasonable longevity. This development is still ongoing and the future looks even brighter. Simultaneously, in Europe, work is underway to produce an objective classification procedure for noise properties of LNRS, making it possible for road authorities to require the use of certain "noise classes" of pavements on certain road sections. This presentation will provide glimpses of the latest achievements, mainly in Europe, and also peek into the crystal ball. After briefly mentioning some historic curiosities, the author will summarize the development of Low Noise Road Surfaces in the last three decades of the 20th century in USA, Europe and Japan. After that, he will make a state-of-the-art review, including but not limited to single-layer and double-layer porous asphalt pavements and thin asphalt layers (TAL). Special focus will be on double-layer porous asphalt concrete (DPAC) pavements, including their application in both sub-urban and urban areas. Noise reduction, economy, safety, durability and longevity will all be dealt with. Some important design issues for optimization of LNRS will be mentioned. After that, some innovative surfaces will be described and the present research status of these be summarized. This includes, for example, the creation of extra negative textures, Helmholtz-resonator layers, and poroelastic road surfaces (PERS) in Europe and Japan. It must be realized that quietness from a road has a cost; often a quite dramatic cost. Nevertheless, when the indirect cost of noise exposure of humans is considered, the use of LNRS often becomes a winning solution. It is often also a winning solution against noise barriers. Several road authorities in Europe and East Asia have realized this and consequently accept rather substantial extra pavement costs for the sake of noise reduction. Finally, the author will open a slot in his personal crystal ball, with the aim of exploring the possibilities in the near future to achieve even better LNRS than the best available practice today. Hopefully, this might reveal the Oracle's best-kept secrets on which knobs to turn, and in what direction, in order to improve the performance towards higher noise reduction and/or longer lifetime than possible today.
Vegh, Serge
Transport for New South Wales, Australia
In December 2014, the Asset Standards Authority (ASA) of Transport for NSW (TfNSW) published a new version of the TfNSW Rolling Stock General Interfaces engineering standard. It included a new set of clauses covering external (environmental) noise limits for Electric Multiple Unit (EMU) rolling stock. The previous limits were aimed at diesel locomotives which have higher values than would be expected for an EMU, with EMU noise limits traditionally being addressed in contract specifications for each class. Clauses covering external noise limits for EMU rolling stock in use within the Sydney Metropolitan network were previously dictated within procurement contracts. The catalyst for the project was the acquisition of a new fleet of intercity EMU rolling stock for the NSW Network. The development of this new standard involved collaboration between the ASA Rolling Stock and Environmental sections to develop a document that was: 1) assured and justified; 2) met stakeholder requirements; 3)drove continual improvement in the noise footprint; and 4) in line with the TfNSW open market acquisition strategy with a focus on commercial off the shelf EMU rolling stock. This paper discusses the process to develop, the lessons learnt and the impacts of the new standard on the framing of TfNSW rolling stock standards, focused on noise and vibration emissions, and how this compares to limits set around Australia and the world. The project considered actual measurement data from local and international sources including current TfNSW EMU rolling stock, current and previous regulations, standards and specifications. The project allowed for alignment of the testing methodology to the applicable International Standard (ISO 3095). It also focused on improving the testing framework and criteria drawing from lessons learnt from previous acquisitions to reduce the ability to structure testing and reporting with a particular bias or weighting and to ensure that everyone was on the same page. A key deliverable to this was the standardisation and publication of distance correction formulae for both stationary and moving measurements. Stakeholder engagement and review of the draft standard extended to approximately 25 organisations ranging from TfNSW divisions and operating entities, including Sydney Trains and NSW TrainLink, the NSW Environmental Protection Agency, national and international rolling stock suppliers and the noise consultancy community. This assured TfNSW that the standard could be met by rolling stock suppliers, executed by noise consultants and accepted by the customer and community impacted by noise.
Zhang, Zhi (1), Oberst, Sebastian (1), Williams, Jack (1), Lai, Joseph (1)
Brake squeal as a significant warranty-claim related costs problem to the automotive industry is difficult to model numerically and analyse because of inherent nonlinearities, uncertainties in material properties, contact and boundary conditions, and system complexity. Often, model components are linearised and not experimentally validated. Sophisticated contact or friction models as well as stiffness in joints are often not considered owing to difficulties in experimental validation. In this study, a full brake system is modally updated at the component level and then at the subassembly level (pad assembly alone, pad in bracket). Squeal prediction using the complex eigenvalue analysis on a finite element model of the system is compared to squeal results from a noise dynamometer test. The results are discussed with respect to further refinement of the modelling approach and improvements to brake squeal prediction.
Caley, Michael (1), Duncan, Alec (1)
(1) Curtin University, Australia
A channel simulation has been developed to explore the fine time-scale Doppler and multi-path arrival-time delay spreading imparted to underwater communication signals by interaction with the transient ocean surface. The simulation provides a configurable ocean test-bed for the purpose of testing and developing acoustic signal data coding and decoding strategies that are more reliable and resistant to the natural reverberation, arrival delay distortion and Doppler distortion that are inherent in relatively shallow underwater signal propagation. The simulator operates by calculating the transmit impulse response for successive realisations of a three-dimensional ocean surface with configurable sea and swell parameters. A unique transmit impulse response history is calculated for each of the underlying flat-surface ray-paths, capturing time-varying fluctuations of the rough surface around the mean-plane response. The realism of the synthetic multi-path channel response history is then evaluated against an experimental channel.
Chen, Li (1), Trinh, Vinh (1), Yang, William (2), Mohanarangam, Krishna (2)
(1) Defence Science and Technology Group, Australia (2) CSIRO Mineral Flagships, Australia
The noise associated with gas discharged from a submerged nozzle is of great interest to many industries because of its important applications. For example, it can be used to size bubbles and to detect gas flow rate. However, the physics associated with the acoustic emission due to bubble formation is complex, particularly when a large number of bubbles are involved, and has not been fully understood. In this study, the dynamics of the bubble formation from a submerged nozzle has been studied experimentally using the Particle Droplet Image Analysis (PDIA) technique. An improved model for prediction of the bubble generation rate and size distribution based on acoustic emission is presented. The experimental study is carried out in a large water tank, of dimensions 10 m x 10 m x 6 m, using multiple hydrophones. The water tank is carefully calibrated in order to provide free-field measurements. The predicted bubble generation rate and size distribution have been compared with the experimental data. It has been found that the predicted results are in good agreement with the experimental measurement, implying that an accurate prediction of acoustic emission associated with a bubbling plume from a submerged nozzle can be achieved by using the model.
Hall, Marshall V.
Marshall Hall Acoustics, Australia
An analytical model is presented for the hull vibration and sound pressure radiated when a large empty cylindrical hull submerged in water is excited by an axial thrust along a central propeller shaft. The model, which is based on the Donnell-Mushtari coupled equations of motion for axial and radial vibration of a cylindrical shell, yields frequency-dependent phase velocity and attenuation of those vibrations. The amplitudes of the vibrations that travel along a hull and reflected by both ends are described in terms of the incident thrust. A solution is obtained for the consequent radiated sound pressure. Both unstiffened and stiffened shells are considered, in which the analytical model for the stiffened shell is based on a smeared approach. Results from the analytical model presented here are compared with the analytical results from literature. The main contribution of this work is to consider phase velocities that vary with frequency and their effect on the radiated sound pressure.
Jones, Adrian D. (1), Duncan, Alec (2), Zhang, Yong (1)
(1) Defence Science and Technology Organisation, Australia (2) Curtin University of Technology, Australia
The coherent leakage of a signal from a mixed-layer surface duct with no rough surface scattering is a subject which received considerable attention decades ago. As is well known, coherent leakage of sound from a surface duct reduces progressively as frequency rises from below a nominal trapping frequency to higher values. Considered as modal leakage, or attenuation, the rate of coherent leakage with range for a surface ducted scenario is related to the imaginary part of the horizontal wave number, and may be determined through the use of a modal model of transmission. Such a calculation is performed through an iterative technique, and so when speed is desirable in the calculation, use of a direct analytic expression for leakage would be preferred. To that end, a brief study was made of the suitability of some of the expressions derived originally by Furry and described by Pederson and Gordon (JASA, 47, 304-326, 1970), as the basis for such a determination for the first acoustical mode, in particular. This work includes comparison of leakage rates obtained from expressions based on early work by Furry against results from both the ORCA modal model, and from simulations based on the wave number integration model SCOOTER, for a mixed-layer surface ducted scenario with frequencies relevant to the onset of duct trapping. The work also includes a brief review of some of the early literature relating to leakage of sound from the surface duct.
Kinns, Roger (1), Peake, Nigel (2), Kessissoglou, Nicole (1)
(1) UNSW Australia, Australia (2) The University of Cambridge, Uinted Kingdom
The aim of this paper is to explore techniques that are being developed by the authors and their colleagues to estimate underwater noise radiated by marine propellers. Some fundamental aspects of propeller noise prediction are considered, including the nature of broadband noise due to flow over propeller blades and the effects of rotating and fluctuating forces that lead to tonal components in the underwater noise spectrum. It is shown how research in aeroacoustics can be applied at the much lower Mach numbers associated with marine propellers. A major challenge in surface ship design is prediction of the onset of cavitation, occurring when the pressure in the flow over the rotating propeller drops below the vapour pressure of water, and of its effect on the spectrum of underwater noise as ship speed increases. Acoustic sources change from higher order sources such as dipoles and quadrupoles, to monopole sources that have much greater acoustic efficiency. Furthermore, these cavitation sources are sensitive to the properties of water, including temperature and air content, as well as sea state and ship heading. Overall propeller noise increases progressively with speed, with changes in the spectral shape that bias the content to lower frequencies. The nature of the spectral changes, and the combination of experimental and numerical methods that can be used to estimate cavitation noise are discussed.
Robertson, Robin (1), Hartlipp, Paul (1)
Sound propagation in Australian waters is of keen interest to the Royal Australian Navy (RAN) and the Maritime Division of the Royal Australian Air Force (RAAF) as it affects sonar operations in one of their prime operating regions. Off eastern Australia, temperature fields are affected both by the East Australian Current (EAC), eddies generated by the EAC, and internal tides. The ocean's temperature structure off eastern Australia can be divided into three basic regimes: the strong southward EAC region (240-280S, the EAC separation region (200-320S), and the 'river' of eddies region (320-380S) south of the separation zone. Although the internal tides in this region are small, nevertheless, they modify the sound speed profile, with the potential to affect acoustic propagation on time scales of the daily and twice daily tidal cycles and the 15-day spring-neap tidal cycle. A primitive-equation model (Regional Ocean Modelling System (ROMS)) with tidal forcing provided temperature and salinity fields, from which horizontally and vertically dependent sound speed fields for the waters off eastern Australia were generated and saved at hourly intervals for 60 days. Using these sound speed fields and the Bellhop acoustic ray tracing software, the effects of the EAC, eddies and internal tides on sonar propagation were investigated. Both ray paths and Transmission Loss were analysed for dependencies on both latitude and the tidal cycles. Acoustic rays propagation and Transmission Loss at 50 Hz were determined for sound speed fields for 100 different snapshots, each separated by at least 1 hour for 25 latitude cuts (240-360S at 0.50 intervals), for 6 different source depths (2, 50, 100, 200, 300, and 500 m), yielding a total of 15,000 cases. The two most significant factors in ray propagation and Transmission Loss were latitude and source depth. North of 290S, Transmission Loss was higher in the first 50 km. A large eddy was found to disrupt the beam patterns and increase Transmission Loss and an offshore seamount was found to terminate the sound channels that formed at that latitude and also increasing Transmission Loss. Observation of the rays indicated two primary sound channels centred around 1400 m depth; one 1000 m wide from 900 to 1900 m and a wider channel 2000 m from 400 to 2400 m. More rays propagated within the sound channels with deeper source depths, particularly the narrower (900-1900m) sound channel. The sound speed changed with the semidiurnal and diurnal tidal cycles, but tidal impacts on the acoustic propagation was overwhelmed by that of eddies and topography.
Travaglione, Ben (1), Munyard, Andrew (1), Matthews, David (1)
There are a number of situations in the undersea environment in which it would be useful to have a low-cost, low-power, deployable, high resolution acoustic data acquisition system. Thanks to the rapid technological advances within the mobile computing industry, there are now a number of small, low- cost, single-board microcontrollers available that lend themselves to the tasks of data acquisition and processing. In this paper, we show how a single-board microcontroller, along with a 24-bit analogue- to-digital converter chip, and some amplification and filtering circuitry can be combined with a PVDF hydrophone to record and analyse high resolution acoustic data. We compare the performance of this low-cost acoustic data acquisition system with a commercial alternative.
Zhang, Zhi Yong
Defence Science & Technology Organisation, Australia
Understanding and modelling the transmission of underwater sound is critical for predicting the performance of acoustic sensing systems. Complicated mathematical models based on various approaches have been developed in past decades to predict sound transmission in the complex underwater environments. These complex models require detailed environmental inputs, longer execution time, and do not always show explicitly the effects of specific environment factors. For quick engineering assessments or sonar operations analysis, it would be advantageous to develop simple parameterised sound transmission formulas that capture the main features of underwater sound propagation using the fewest possible parameters. In this paper, we give a simple formula for incoherently averaged transmission loss in shallow water environments by taking into account the effects of energy spreading, absorption, and leakage out of boundaries. The formula is based on extension of earlier work by using the concept of effective depth to include the effect of normal mode penetration into the seafloor on modal attenuation. Comparison with measurement data at several shallow water sites worldwide shows that the formula are capable of producing the main features of shallow water sound propagation in environments with different types of seafloors. The formulas are useful for estimating sound transmission losses in generic yet representative underwater environments where detailed environmental knowledge is lacking or the fine details of underwater sound propagation is not required.
Bao, Berney (1), Matthews, David (2), Munyard, Andrew (3), Sun, Hongmei (1), Pan, Jie (1)
(1) The University of Western Australia, Australia (2) Defence Science and Technology Group, Australia and The University of Western Australia, Australia (3) Defence Science and Technology Group, Australia
The ability to visualise the vibration of a structural surface is a big advantage when analysing the modal characteristics of the structure. This can be done using many accelerometers but can be a laborious, time consuming process. In addition, for small structures the accumulative effects of accelerometer mass can soon become a problem and adversely affect the measured natural frequencies. An alternative is to use a scanning laser doppler vibrometer (SLDV) where the surface can be scanned to passively obtain the surface velocity. These systems are very useful but can be expensive and difficult to use in confined spaces or within fluids. This paper investigates using Polyvinylidene fluoride (PVDF) polymer film as an alternative method for visualizing the surface vibration. PVDF film has been widely investigated as a sensor and transducer material due to its high piezo-, pyro- and ferro-electric properties. In can be easily fabricated into thin sheets (~ few micrometers) and as a result it is ideal for making small, very light piezoelectric sensors. An array of seventeen PVDF sensors was constructed and attached to a thinly clamped steel disk. The output of the array was recorded for the first six resonant frequencies of the disk and compared to simultaneous results obtained using a SLDV.
Jurevicius, Darren (1), Stead, Matthew (1), Barry, Greg (1)
This paper presents the findings into a study of vibration magnitude versus potential damage caused by vibratory compaction equipment at two residential properties located in South Australia. The two residential properties under investigation are classified as 'Contributory' in the local Historic Conservation Policy Area by Council and were constructed between the late 1800's and early 1900's. Vibratory compaction equipment was operated near to the properties at varying distances and machine settings with the primary objective to relate the measured vibration magnitude to cosmetic or structural damage, and to compare the results to the German Standard DIN 4150-3, 1999, Structural vibration – Part 3: Effects of vibration on structures. The secondary objective was to relate the measured vibration magnitude to subjective human perception and other observed ancillary effects to assist with community consultation activities that occur as part of major infrastructure projects. The results from the two objectives are presented and discussed in this paper.
Kinns, Roger (1), McColl, John H (2)
(1) UNSW Australia, Australia (2) The University of Glasgow, United Kingdom
Development of a new ship machinery installation may require combinations of prime movers, electric motors, generators, gearboxes and other items that have not been used previously. Large items of this type are expensive to develop, so that only existing production items are likely to be affordable. Modern quiet ship design requires careful attention to the source characteristics of the individual machinery items as well as the dynamic characteristics of any new combination, so that fluctuating forces transmitted to the hull via mounting systems and flexible connectors in the final installation are within acceptable limits. Almost periodic components, which arise at multiples of machine rotational frequency, are of particular concern. Machine source properties are often known only in terms of the vibration characteristics of previous installations, not in terms of the disturbing forces that cause that vibration. The aim of the techniques described in this paper is to allow deduction of those disturbing forces from a matrix of transfer functions at each frequency of interest, measured with an existing machine in operation. The number of forces to be estimated must be less than the number of structural degrees of freedom. Those degrees of freedom arise from rigid body motions and machine flexural properties, which may change significantly when shafts are rotating. Also, the matrices must be redundant in order to allow estimation of the accuracy of derived force estimates. The larger the machine, the greater the number of degrees of freedom that are likely to arise at a given frequency. A first use of the methodology was to establish the bearing forces in a marine turbo generator (TG) set with plain journal bearings. Measurements of transfer functions were made with the machine stationary and then with the machine in normal operation. Direct and reciprocal measurements in different directions were made for a large number of locations on the machine structure and bearings, covering the frequency range up to more than twice shaft rotational frequency. There were large differences in some frequency ranges between the static and operational conditions. Vibration due to machine operation was then measured to allow deduction of bearing forces using the transfer function matrices. Repeat measurements were made to establish whether machine source properties changed significantly with time, while statistical techniques were also used to identify and eliminate any suspect measurements. Those early experiments are described in this paper with a view to future application of similar techniques.
Miller, Aaron (1), Duschlbauer, Dominik (1)
Two different methods of estimating the static stiffness of structures are compared. In the first approach, the structure is loaded with a known quasi-static force and its displacement is measured. The second approach is based on impact tests with a rubber tipped hammer where the dynamic response of the structure is determined and the static stiffness is obtained by extrapolating the receptance spectrum towards zero Hertz. This paper compares the results of both methods from measurements taken on an existing bridge, and discusses the relationship between the measured static stiffness using the force-displacement method and the dynamic approach based on impact tests.
Mitchell, Andrew (1), Mitchell, Lloyd (1), Murray, Tim (1)
(1) Embelton Noise and Vibration, Australia
Effective isolation of vibration generated by treadmill usage is a challenge due to the frequencies at which footfall typically occurs. Vibration theory suggests that an effective isolation system should have a fundamental frequency significantly lower than that of the excitation; however in practice this approach would require springs of very high static deflection, resulting in a tall, heavy and potentially unstable running platform. One solution is to use an isolation system with a fundamental frequency above the footfall frequency, but below the fundamental frequency of the structural floor. In this scenario, the isolators will reduce vibration transmitted at and above the fundamental frequency of the structural floor, but may amplify vibration at lower frequencies. Introducing damping to the isolation system can assist in moderating this amplification; however, too much damping may compromise isolation efficiency at higher frequencies. In a particular case where a treadmill platform was installed on a gym floor slab with a fundamental frequency of 11 Hz, computer modelling indicated that a damping ratio of approximately 0.2 would be optimal. To test this result, a damped spring system was developed by Embelton, in which the amount of damping could be varied. This paper presents an overview of the computer modelling and subsequent testing of the damped spring system, with reference to the above case study.
Oberst, Sebastian (1), Griffin, Doug (1), Tuttle, Sean (1), Andrew, Lambert (1), Boyce, Russell R. (1)
With the advent of affordable nano-satellite designs (off-the-shelf payloads, standardised launch geometries), increasingly enterprises, governmental agencies and universities have started developing their own space programs to explore the environment of Low Earth Orbits. Thin, flexible and unfolding/deployable structures are common space engineering antenna and solar panel designs owing to their lightweight and ideal packaging characteristics, which are, however, difficult to experimentally validate in a 1-g environment. Further, curvatures or discontinuities to increase functionality without violating prioritised design criteria may lead to system-level trade-offs: stability issues arising from buckling in combination with micro-vibrations which feed back to the satellite's attitude behaviour. It appears that the literature lacks a systematic investigation of these aspects. On-Earth experimental validations (static experiments, model updating) are the starting point for studying the response to static/dynamic loading of thin curved flexible structures such as deployable high frequency antennas. Linear and nonlinear buckling modes owing to varying loadings (aerodynamic drag, solar radiation pressure, residual gravity and magnetic body forces) are found together with a high sensitivity to torsional modes' frequency changes under micro-vibrational forcing.
Siew, Win Sum (1), Smith, Wade (1), Peng, Zhongxiao (1), Randall, Robert (1)
Fatigue-induced fault propagation is the most common cause of failure in rolling element bearings. As most classic diagnostic indicators do not trend monotonically with wear development, the ability to assess fault severity remains limited at present. This paper aims to expand current understanding and establish a correlation between the vibration signal and the actual extent of fault propagation. To achieve this, an extensive test program was undertaken using a laboratory test rig fitted with bearings initially seeded with small faults on the inner race. Vibration data from the rig was collected and analysed systematically at regular time intervals. Concurrently, the defect size and raceway topography were examined using laser scanning microscopy. The results from both sources were then combined to provide valuable insight into the effectiveness of common vibration indicators for fault trending. Through a detailed comparison of these indicators, a method of tracking fault severity is suggested which will aid greatly in the prognostics of rolling element bearings.
Yang, Yunzhe (1), Smith, Wade (1), Borghesani, Pietro (2), Peng, Zhongxiao (1), Randall, Robert (1)
(1) UNSW Australia, Australia (2) Queensland University of Technology, Australia
The detection of gear wear from vibration signals is generally achievable once the wear has progressed to a 'macro' level, in which the tooth profile has changed appreciably. A typical example is the 'double scalloped' wear pattern – involving substantial material loss either side of the (largely unaffected) pitchline – which is diagnosable from an increase in the amplitude of the second harmonic of gearmesh frequency. Yet macro level wear is often preceded and accompanied by micro-level surface roughness changes, arising from either abrasive wear or contact fatigue pitting. These micro- and macro-level phenomena interact with one another, and so to be able to accurately predict wear rates in operating gears requires knowledge of their surface roughness state – information not easily obtainable without stopping the machine and taking detailed measurements. This paper investigates the use of vibration signals for estimating gear tooth surface roughness. Measurements from a laboratory spur gearbox test rig are used, and the rig is fitted with gears of modified surface roughness. It is proposed that changes in surface roughness would be detectable from the nature of amplitude modulation of the random vibrations produced from asperity contacts between the teeth when they slide against one another. Such a signal – random but with cyclic modulation – is known as second-order cyclostationary, and the study finds that the degree of second-order cyclostationarity in the measured signals is strongly correlated with gear surface roughness. In comparison, the RMS and kurtosis of the vibration signal are found not to be as strongly correlated with roughness. The findings will be very important for gear prognostics, where knowledge of wear rate is critical in estimating the remaining useful life of gears.
Youssef, Andrew (1), Dylejko, Paul (2), Andrew, Guzzomi (1), Jie, Pan (1)
(1) The University of Western Australia, Australia (2) Defence Science and Technology Organisation, Australia
In order to transmit thrust effectively a marine propulsion system is made up of mechanically stiff components. Consequently, unsteady propeller loads are also effectively transmitted to the hull structure. At low speeds, these result in tonal oscillations at the blade-passing frequency and its harmonics. At high speeds, broadband vibration is generated by cavitation and turbulence ingestion. The relative magnitudes of the axial, tangential and radial unsteady forces acting on the propeller are dependent on the non-uniform hull wake and propeller design. Much of the previous research has focussed on studying the effect of these components independently. This paper theoretically investigates the three-dimensional vibrational behaviour of the propulsion system to gain insight into the relative importance of the different excitation mechanisms and transmission paths. The propeller blade dynamics are included by considering an equivalent beam. This work provides the foundations for further efforts, which will investigate the vibration attenuation through the propulsion system of marine vessels.
Bradley, Stuart
The University of Auckland, New Zealand
Trailing edge noise from a turbine blade comprises sources which move in a circle so that the direct sound path and ground reflected sound paths to a receiver periodically vary. At any one listener location, there is therefore a fluctuating intensity. A simple ray model shows that this mechanism enhances the characteristics of wind turbine amplitude modulation noise, and can lead to a sharper onset of the higher intensity sound at some frequencies. This time-dependent interference mechanism does not depend on intermittent stall, although increased source intensity obviously leads to increased modulation noise.
Cooper, Jon (1), Evans, Tom (1)
Guidelines and Standards which set environmental noise criteria often include clauses which prescribe a limit as to the allowable wind speed during noise measurements. It is common practice for this limit to be 5 m/s at the microphone, although 3 or 10 m/s are sometimes also adopted. The purpose of this limit for general environmental noise measurements may be to limit wind induced background noise, adverse propagation affects, wind induced noise on the microphone, or a combination of these. In the case of wind farm background noise assessments, the purpose of the measurements is to quantify the increase of wind induced background noise and a wind speed limit of 5 m/s at the microphone is typically adopted, with the sole aim of ensuring that wind induced microphone noise does not adversely affect the measurements by way of artificially increasing background noise. This paper examines the rationale for limiting wind speeds at the microphone to 5 m/s, and shows through field measurements that this limit does not guard against adverse effects of wind induced microphone noise. An alternative approach for preventing adverse effects of wind induced microphone noise is proposed.
Williams, Warwick
National Acoustic Laboratories, Australia
This presentation reports on the examination of the relationship between self-reported noise exposure during leisure activities and audiological indicators: including measured hearing threshold levels (HTL) and tinnitus. The research was conducted by cross sectional survey of 1432 individuals from 11 to 35 years old. Methodology included of a full audiometric assessment including otoscopy, pure tone audiometry (PTA) (air-and bone-conduction), otoacoustic emissions (OAE) and tympanometry. A comprehensive questionnaire gathered information on demographics, hearing health status and participation in work, non-work and leisure activities. Using the history of work, non-work and leisure noise exposure a cumulative life time noise exposure was estimated. No correlation was found between cumulative life time noise exposure and audiometric PTA or OAE parameters. However, tinnitus was found to frequently occur at what would be considered as low exposure levels.