ORCID Profile
0000-0002-3520-1377
Current Organisations
RMIT University
,
University of Technology Sydney
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Acoustics and Noise Control (excl. Architectural Acoustics) | Mechanical Engineering | Numerical Modelling and Mechanical Characterisation
Industrial Energy Conservation and Efficiency | Expanding Knowledge in Engineering |
Publisher: Elsevier BV
Date: 12-2020
Publisher: World Scientific Pub Co Pte Ltd
Date: 19-09-2020
DOI: 10.1142/S2591728520500140
Abstract: Surface waves have been extensively studied in earthquake seismology. Surface waves are trapped near an infinitely large surface. The displacements decay exponentially with depth. These waves are also named Rayleigh and Love waves. Surface waves are also used for nondestructive testing of surface defects. Similar waves exist in finite width three-dimensional plates. In this case, displacements are no longer constant in the direction perpendicular to the wave propagation plane. Wave energy could still be trapped near the edge of the three-dimensional plate, and hence the term edge waves. These waves are thus different to the two-dimensional Rayleigh and Love waves. This paper presents a numerical model to study dispersion properties of edge waves in plates. A two-dimensional semi-analytical finite element method is developed, and the problem is closed by a perfectly matched layer adjacent to the edge. The numerical model is validated by comparing with available analytical and numerical solutions in the literature. On this basis, higher order edge waves and mode shapes are presented for a three-dimensional plate. The characteristics of the presented edge wave modes could be used in nondestructive testing applications.
Publisher: Elsevier BV
Date: 09-2009
Publisher: Informa UK Limited
Date: 03-2012
Publisher: Acoustical Society of America (ASA)
Date: 07-2020
DOI: 10.1121/10.0001568
Abstract: Unlike the audio sound generated by traditional sources, the directivity of that generated by a parametric array loudspeaker (pal) deteriorates significantly after passing through a thin partition. To study this phenomenon, the pal radiation model based on the Westervelt equation, and the plane wave expansion method are used to calculate the sound fields behind a sheet of aluminum foil and a porous material blanket under the quasi-linear assumption, where the paraxial approximation is assumed only for ultrasonic waves. The audio sounds generated by a point monopole and a traditional directional source are presented for comparison. Both simulation and experiment results show that the transmitted sound from a pal behind the thin partition is small and less focused on the radiation axis because most of the ultrasounds forming the directivity of the pal is blocked by the thin partition which has little effect on the traditional audio sources.
Publisher: Acoustical Society of America (ASA)
Date: 05-2017
DOI: 10.1121/1.4983192
Abstract: This article develops a numerical model suitable for analysing elastic wave scattering in buried pipelines. The model is based on a previous so-called hybrid approach, where a nominally infinite length of pipe is split up into uniform and non-uniform regions. The key challenge for buried structures is in enforcing the appropriate boundary conditions in both the axial and radial directions, which must encompass the entire length of the structure, as well as the surrounding material. Accordingly, the focus of this article is on developing a model suitable for accurately applying these boundary conditions, and so the analysis is restricted here to the study of axisymmetric defects and to an incident sound field that consists of the fundamental torsional mode only. It is shown that this problem may be addressed in a numerically efficient way provided one carefully choses a perfectly matched layer for the surrounding material, and then integrates over this layer using a complex co-ordinate stretching function. This enables the use of mode matching to deliver a convergent system of equations that enforce the appropriate axial and radial boundary conditions.
Publisher: Acoustical Society of America (ASA)
Date: 03-2020
DOI: 10.1121/10.0000793
Abstract: It has been reported that audible sounds can be heard behind a parametric array loudspeaker in free field, which cannot be predicted by existing models. A non-paraxial model is developed in this paper for the finite size and disk-shaped parametric source based on quasilinear approximation and disk scattering theory. The sounds on both front and back sides are calculated numerically and compared with the existing non-paraxial model for the parametric source installed in an infinitely large baffle. Both simulation and experiment results show that audible sound exists on the back side. The mechanism of the phenomenon is explored.
Publisher: Elsevier BV
Date: 08-2005
Publisher: Elsevier BV
Date: 09-2015
Publisher: RWTH Aachen University
Date: 2019
Publisher: Acoustical Society of America (ASA)
Date: 2023
DOI: 10.1121/10.0016816
Abstract: A steerable parametric array loudspeaker (PAL) aims to steer a highly directional audio beam without the need to mechanically rotate the source. The Gaussian beam expansion (GBE) method is often used to model PALs because it is a computationally efficient approach, however the method relies on a paraxial approximation that can result in significant inaccuracies at large steering angles. To address this limitation, a steerable non-paraxial GBE is proposed in this article, where the mainlobe of the steered ultrasonic beam is included in the calculation by rotating the coordinate system. A non-paraxial approximation is then used to improve the accuracy of the method when integrating the virtual audio sources. The numerical results obtained using the proposed method are compared against those using the conventional GBE, as well as an exact solution. For a typical configuration, it is shown that for a conventional GBE the prediction error can be more than 30 dB at large angles, whereas the proposed method reduces this to less than 1 dB. The advantage of the proposed method is more significant at large steering angles, low audio frequencies, and those locations outside of the paraxial region. This improvement in performance is achieved with a computational cost that remains the same as the conventional GBE.
Publisher: Acoustical Society of America (ASA)
Date: 07-2003
DOI: 10.1121/1.1582448
Abstract: A numerical technique is developed for the analysis of dissipative silencers of arbitrary, but axially uniform, cross section. Mean gas flow is included in a central airway that is separated from a bulk reacting porous material by a concentric perforate screen. The analysis begins by employing the finite element method to extract the eigenvalues and associated eigenvectors for a silencer of infinite length. Point collocation is then used to match the expanded acoustic pressure and velocity fields in the silencer chamber to those in the inlet and outlet pipes. Transmission loss predictions are compared with experimental measurements taken for two automotive dissipative silencers with elliptical cross sections. Good agreement between prediction and experiment is observed both without mean flow and for a mean flow Mach number of 0.15. It is demonstrated also that the technique presented offers a considerable reduction in the computational expenditure when compared to a three-dimensional finite element analysis.
Publisher: Elsevier BV
Date: 02-2019
Publisher: Wiley
Date: 2000
DOI: 10.1002/1097-0363(20000815)33:7<993::AID-FLD40>3.0.CO;2-A
Publisher: Acoustical Society of America (ASA)
Date: 10-2022
DOI: 10.1121/10.0014832
Abstract: A steerable parametric array loudspeaker (PAL) can electronically steer highly directional audio beams in the desired direction. The challenge of modelling a steerable PAL is to obtain the audio sound pressure in both near and far fields with a low computational load. To address this issue, an extension of the spherical wave expansion is proposed in this paper. The steerable velocity profile on the radiation surface is expanded as Zernike polynomials which are an orthogonal and form a complete set over a unit circle. An expression for the radiated audio sound is then obtained using a superposition of Zernike modes. Compared to the existing methods, the proposed expansion is computationally efficient and provides a rigorous transformation of the quasilinear solution of the Westervelt equation without paraxial approximations. The proposed expansion is further extended to accommodate local effects by using an algebraic correction to the Westervelt equation. Numerical results for steering single and dual beams are presented and discussed. It is shown that the single beam can be steered in the desired direction in both near and far fields. However, dual beams cannot be well separated in the near field, which cannot be predicted by the existing far field models.
Publisher: Elsevier BV
Date: 11-1998
Publisher: Elsevier BV
Date: 02-1999
Publisher: Elsevier BV
Date: 11-2022
Publisher: Elsevier BV
Date: 05-2007
Publisher: Elsevier BV
Date: 12-2016
Publisher: Elsevier BV
Date: 08-2015
Publisher: Elsevier BV
Date: 2019
Publisher: Acoustical Society of America (ASA)
Date: 06-2020
DOI: 10.1121/10.0001473
Abstract: Long range ultrasonic testing of pipelines sends an ultrasonic wave along a pipe wall and then detects scattering from defects present. It is well known that scattering by pipe fixtures and fittings, such as a flange, can cause distortion and interfere with the ability to identify defects. This article develops a theoretical model to investigate scattering from a flange in a fluid-filled pipe with elastic walls. Mode matching is used as this is a computationally efficient way to examine long lengths of pipe and for enforcing the appropriate axial continuity conditions over area discontinuities. A recent article presented a mode matching approach for a similar problem, and it is demonstrated here that a re-casting of the equations is necessary to ensure all of the appropriate matching conditions are enforced. Mode matching predictions are also compared with an alternative point collocation approach in order to provide an independent benchmark. Excellent agreement between mode matching and point collocation is demonstrated, and reflection and transmission coefficients are generated in order to show the resonant behaviour of a flange and illustrate that its influence is significant and strongly frequency dependent.
Publisher: Elsevier BV
Date: 02-2018
Publisher: Acoustical Society of America (ASA)
Date: 02-2021
DOI: 10.1121/10.0003498
Abstract: A numerical technique is proposed for synthesizing realizations of airfoil surface pressure induced by incoming turbulence. In this approach, realization of the surface pressure field is expressed as a set of uncorrelated wall plane waves. The litude of these plane waves is determined from the power spectrum density function of the incoming upwash velocity fluctuation and the airfoil aeroacoustic transfer function. The auto-spectrum of the surface pressure is obtained from an ensemble average of different realizations. The numerical technique is computationally efficient as it rapidly converges using a relatively small number of realizations. The surface pressures for different airfoils excited by incoming turbulence are numerically predicted, and the results are compared with experimental data in the literature. Further, the unsteady force exerted on an airfoil due to the airfoil-turbulence interaction is also computed, and it is shown to be in very good agreement with analytical results.
Publisher: ASA
Date: 2019
DOI: 10.1121/2.0001205
Publisher: Acoustical Society of America (ASA)
Date: 10-2008
DOI: 10.1121/1.2967837
Abstract: Sound propagation in an acoustic waveguide is examined using a hybrid numerical technique. Here, the waveguide is assumed to be infinite in length with an arbitrary but uniform cross section. Placed centrally within the guide is a short component section with an irregular nonuniform shape. The hybrid method utilizes a wave based modal solution for a uniform section of the guide and, using either a mode matching or point collocation approach, matches this to a standard finite element based solution for the component section. Thus, one needs only to generate a transverse finite element mesh in uniform sections of the waveguide and this significantly reduces the number of degrees of freedom required. Moreover, utilizing a wave based solution removes the need to numerically enforce a nonreflecting boundary condition at infinity using a necessarily finite mesh, which is often encountered in studies that use only the standard finite element method. Accordingly, the component transmission loss may readily be computed and predictions are presented here for three ex les: an expansion chamber, a converging- erging duct, and a circular cylinder. Good agreement with analytic models is observed, and transmission loss predictions are also presented for multimode incident and transmitted sound fields.
Publisher: Acoustical Society of America
Date: 2017
DOI: 10.1121/2.0000636
Publisher: Elsevier BV
Date: 04-2019
Publisher: Acoustical Society of America (ASA)
Date: 05-2012
DOI: 10.1121/1.3699196
Abstract: A numerical model based on a hybrid finite element method is developed that seeks to join sound pressure fields in interior and exterior regions. The hybrid method is applied to the analysis of sound radiation from open pipes, or ducts, and uses mode matching to couple a finite element discretization of the region surrounding the open end of the duct to wave based modal expansions for adjoining interior and exterior regions. The hybrid method facilitates the analysis of ducts of arbitrary but uniform cross section as well the study of conical flanges and here a modal expansion based on spherical harmonics is applied. Predictions are benchmarked against analytic solutions for the limiting cases of flanged and unflanged circular ducts and excellent agreement between the two methods is observed. Predictions are also presented for flanged and unflanged rectangular ducts, and because the hybrid method retains the sparse banded and symmetric matrices of the traditional finite element method, it is shown that predictions can be obtained within an acceptable time frame even for a three dimensional problem.
Publisher: Elsevier BV
Date: 08-2009
Publisher: Elsevier BV
Date: 06-2022
Publisher: Elsevier BV
Date: 02-2016
DOI: 10.1016/J.ULTRAS.2015.09.019
Abstract: Viscoelastic coatings are often used to protect pipelines in the oil and gas industry. However, over time defects and areas of corrosion often form in these pipelines and so it is desirable to monitor the structural integrity of these coated pipes using techniques similar to those used on uncoated pipelines. A common approach is to use ultrasonic guided waves that work on the pulse-echo principle however, the energy in the guided waves can be heavily attenuated by the coating and so significantly reduce the effective range of these techniques. Accordingly, it is desirable to develop a better understanding of how these waves propagate in coated pipes with a view to optimising test methodologies, and so this article uses a hybrid SAFE-finite element approach to model scattering from non-axisymmetric defects in coated pipes. Predictions are generated in the time and frequency domain and it is shown that the longitudinal family of modes is likely to have a longer range in coated pipes when compared to torsional modes. Moreover, it is observed that the energy velocity of modes in a coated pipe is very similar to the group velocity of equivalent modes in uncoated pipes. It is also observed that the coating does not induce any additional mode conversion over and above that seen for an uncoated pipe when an incident wave is scattered by a defect. Accordingly, it is shown that when studying coated pipes one need account only for the attenuation imparted by the coating so that one may normally neglect the effect of coating on modal dispersion and scattering.
Publisher: Acoustical Society of America (ASA)
Date: 10-2005
DOI: 10.1121/1.2010267
Abstract: A numerical model based on the finite element method is developed for a finite length, HVAC splitter silencer. The model includes an arbitrary number of bulk-reacting splitters separated from the airway by a thin perforated metal sheet and accommodates higher-order modes in the incident sound field. Each perforated sheet is joined to rigid, impervious, metallic fairing situated at either end of a splitter. The transmission loss for the silencer is quantified by application of the point collocation technique, and predictions are compared to experimental measurements reported in the literature. The splitter fairing is shown to significantly affect silencer performance, especially when higher-order incident modes are present. It is concluded that laboratory measurements, and theoretical predictions, that are based on a predominantly plane wave sound source are unlikely to reflect accurately the true performance of an HVAC silencer in a real ducting system.
Publisher: Acoustical Society of America (ASA)
Date: 12-2020
DOI: 10.1121/10.0002912
Abstract: This article presents a finite element based solution of the exact governing wave equation for a stratified inhomogeneous moving media. The model is applied to a two dimensional range independent problem in outdoor sound propagation in which the ground is treated as perfectly reflecting. The sound pressure field is expanded as a sum over eigenmodes propagating in the range direction, and the semi analytic finite element method is used to solve the governing eigenequation. This delivers faster solution times when compared to traditional finite element based methods while simultaneously accommodating continuous variations in fluid properties in the vertical direction. In principle, the method converges toward the exact solution and so delivers a benchmark method for range independent problems. The method is shown to provide excellent agreement with analytic solutions, and good convergence is demonstrated for more complex problems, including temperature inversions and logarithmic profiles for wind velocity. Finally, qualitative comparisons are made against infrasound predictions, including those obtained using wide angle parabolic equations. The method is shown to provide a focussed image of the sound pressure field over large distances, as well as to reproduce multiple turning points and ground interactions.
Publisher: Acoustical Society of America (ASA)
Date: 03-2021
DOI: 10.1121/10.0003606
Abstract: The near and far fields of traditional loudspeakers are differentiated by whether the sound pressure litude is inversely proportional to the propagating distance. However, the audio sound field generated by a parametric array loudspeaker (PAL) is more complicated, and in this article it is proposed to be ided into three regions: near field, Westervelt far field, and inverse-law far field. In the near field, the audio sound experiences strong local effects and an efficient quasilinear solution is presented. In the Westervelt far field, local effects are negligible so that the Westervelt equation is used, and in the inverse-law far field, a simpler solution is adopted. It is found that the boundary between the near and Westervelt far fields for audio sound lies at approximately a2/λ – λ/4, where a is transducer radius and λ is ultrasonic wavelength. At large transducer radii and high ultrasonic frequencies, the boundary moves close to the PAL and can be estimated by a closed-form formula. The inverse-law holds for audio sound in the inverse-law far field and is more than 10 meters away from the PAL in most cases. With the proposed classification, it is convenient to apply appropriate prediction models to different regions.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2023
Publisher: Acoustical Society of America (ASA)
Date: 02-2021
DOI: 10.1121/10.0003567
Abstract: This article uses a normal mode approach to predict atmospheric sound propagation over a locally reacting impedance plane. The semi-analytic finite element method is used to compute the normal modes, which enables the exact governing wave equation for a moving fluid to be solved in two dimensions. A locally reacting surface is added using the general Ingard–Myers boundary condition, and the transmission loss is obtained for cylindrical and spherical spreading for range independent problems. The approach developed in this article will, in principle, converge toward the exact solution and so has the potential to provide benchmark predictions for complex, range independent, outdoor sound propagation problems. Predictions are shown to provide good agreement with benchmark solutions available in the literature, including those with a logarithmic wind velocity profile. Results are also reported for a combination of a logarithmic wind velocity profile and a temperature inversion for ranges of up to 5 km. Finally, transmission loss predictions are reported for a relatively wide frequency range, and it is concluded that finite elements can provide an alternative approach for computing range independent outdoor sound propagation that converges to the exact solution.
Publisher: Elsevier BV
Date: 03-2023
Publisher: Elsevier BV
Date: 2016
Publisher: Elsevier BV
Date: 06-2001
Publisher: Acoustical Society of America (ASA)
Date: 10-2020
DOI: 10.1121/10.0002161
Abstract: The reflection of audio sounds generated by a parametric array loudspeaker (PAL) is investigated in this paper. The image source method and the non-paraxial PAL radiation model under the quasilinear approximation are used to calculate the reflected audio sound from an infinitely large surface with an arbitrary incident angle. The effects of the surface absorption in the ultrasound frequency range are studied, and the simulation and experiment results show that the reflection behavior of audio sounds generated by a PAL is different from those generated by traditional audio sources. The reason is that the reflected sound generated by the PAL consists of the reflection of audio sounds generated by incident ultrasounds and the audio sounds generated by the reflected ultrasound, and it is the latter that determines the directivity of the reflected audio sound.
Publisher: Acoustical Society of America (ASA)
Date: 04-2006
DOI: 10.1121/1.2172168
Abstract: This article presents an analytic mode-matching approach suitable for modelling the propagation of sound in a two-dimensional, three-part, ducting system. The approach avoids the need to find roots of the characteristic equation for the middle section of the duct (the component) and is readily applicable to a broad class of problems. It is demonstrated that the system of equations, derived via analytic mode-matching, exhibits certain features which ensure that they can be recast into a form that is independent of the roots of the characteristic equation for the component. The precise details of the component are irrelevant to the procedure it is required only that there exists an orthogonality relation, or similar, for the eigenmodes corresponding to the propagating wave forms in this region. The method is applied here to a simple problem involving acoustic transmission through a dissipative silencer of the type commonly found in heating ventilation and air-conditioning ducts. With reference to this ex le, the silencer transmission loss is computed, and the power balance for the silencer is investigated and is shown to be an identity that is necessarily satisfied by the system of equations, regardless of the level of truncation.
Publisher: Elsevier BV
Date: 12-2023
Publisher: Acoustical Society of America (ASA)
Date: 03-2022
DOI: 10.1121/10.0009750
Abstract: This work investigates the scattering by a rigid sphere of audio sound generated by a parametric array loudspeaker (pal). A computationally efficient method utilizing a spherical harmonic expansion is developed to calculate the quasilinear solution of audio sound fields based on both Kuznetsov and Westervelt equations. The accuracy of using the Westervelt equation is examined, and the rigid sphere scattering effects are simulated with the proposed method. It is found the results obtained using the Westervelt equation are inaccurate near the sphere at low frequencies. Contrary to conventional loudspeakers, the directivity of the audio sound generated by a pal severely deteriorates behind a sphere, as the ultrasounds maintaining the directivity of the audio sound are almost completely blocked by the sphere. Instead, the ultrasounds are reflected and generate audio sound on the front side of the sphere. It means that a listener in front of the pal will hear the audio sound scattered back after introducing the sphere as if it is reflected by the sphere. The experiment results are also presented to validate the numerical results.
Publisher: Elsevier BV
Date: 09-2013
Publisher: Institute of Noise Control Engineering (INCE)
Date: 08-2021
DOI: 10.3397/IN-2021-2721
Abstract: An analytical model to predict the vibrational response of a simply supported rectangular plate embedded in an infinite baffle with an upper free surface under heavy fluid loading and excited by a point force is presented. The equations of motion of a thin plate are solved using modal decomposition technique by employing admissible functions for an in-vacuo plate and by directly solving the Helmholtz equation for acoustic waves in a fluid. The vibrational response for a flat plate in an infinite baffle and unbounded domain (semi-infinite domain) using analytical formulation available in literature is initially computed. These results are then compared against present results to observe the effect of a free surface. Predictions from analytical models are validated by comparison with results obtained by numerical models. The proposed analytical approach presents a novel formulation to describe a fluid-loaded flat plate in a waveguide and an efficient method for predicting its vibrational response.
Publisher: Elsevier BV
Date: 12-2014
Publisher: Acoustical Society of America (ASA)
Date: 04-2021
DOI: 10.1121/10.0004407
Abstract: Applying the finite element method to problems in atmospheric sound propagation is challenging because the use of a standard approach, such as meshing the entire domain, quickly delivers a prohibitive problem size. The finite element method does, however, offer many advantages such as the ability to accommodate continuous variations in fluid properties, as well as scattering from obstacles of complex geometry. This means the method is ideally placed to provide benchmark solutions for more popular approaches. Accordingly, ideas for developing more efficient versions of the finite element method suitable for atmospheric sound propagation are explored here for two dimensional problems. These are based on the use of one dimensional normal mode expansions, and then mapping these on to two dimensional solutions for non-uniform obstacles. The normal mode solution for a range independent inhomogenous moving fluid is presented, and numerical mode matching techniques are introduced to demonstrate the inclusion of a point source. The extension of these mode matching methods to accommodate scattering from obstacles is then discussed, and the conditions necessary to deliver efficient finite element solutions are reviewed.
Publisher: Elsevier BV
Date: 09-1999
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2022
Publisher: Elsevier BV
Date: 12-2014
Publisher: Elsevier BV
Date: 08-2012
Publisher: SAGE Publications
Date: 02-2007
DOI: 10.1260/095745607780154318
Abstract: Mathematically modelling sound propagation in splitter silencers has the potential to provide a fast and effective method for optimising silencer design, and for alleviating the need to undertake repetitive and expensive experimental measurements. Moreover, understanding the physics behind sound attenuation in silencers will ultimately help to improve in situ silencer performance and to avoid current problems whereby commissioned silencers do not provide the attenuation expected from laboratory measurements. Accordingly, a mathematical model is discussed here that is capable of predicting silencer insertion loss and predictions are compared with experimental measurements. Results demonstrate the potential of this model for predicting silencer performance under laboratory conditions, but also illustrate that multi-modal sound fields significantly affect silencer performance so that laboratory tests are unlikely to represent accurately in situ silencer performance.
Publisher: Acoustical Society of America (ASA)
Date: 04-2000
DOI: 10.1121/1.428466
Abstract: A numerical solution is presented to the problem of nonisentropic acoustic wave motion in a circular capillary tube in the presence of both axial mean flow and a background axial temperature gradient. The effects of the radial components of the acoustic velocity are included in the analysis. The main application area is in the study of the acoustic effects of catalytic converters. The solution makes use of a series expansion and is valid for small relative changes in the background temperature, which are typical of this application area. Various solutions to the problem have been obtained previously, using different simplifications to the complete problem which is considered here. It is shown that each of the simplifications results in errors for the predicted attenuation of at least 20 dB/m, using conditions typical for catalytic converters. In particular, the isentropic assumption is shown to be invalid.
Publisher: Acoustical Society of America (ASA)
Date: 05-2014
DOI: 10.1121/1.4869089
Abstract: Splitter silencers are found in ventilation and gas turbine systems and consist of parallel baffles of porous material placed within a duct so that they split the mean gas flow. Theoretical investigations into dissipative splitter silencers have generally been limited to two dimensions and this limits the analysis to finding the silencer eigenmodes or, for a finite length silencer, to rectangular baffles only. In this article a numerical point collocation approach is used to extend theoretical predictions to three dimensions. This facilitates the analysis of more complex silencer designs such as “bar” silencers and theoretical predictions are validated by comparison with experimental measurements. The insertion loss of different silencer designs is evaluated and the performance of a bar silencer is compared to traditional designs for rectangular and circular ducts. It is shown that a bar silencer with a volume of material identical to an equivalent parallel baffle design delivers a significant improvement in insertion loss at higher frequencies, although this is at the expense of a small reduction in performance at low frequencies. It is also shown that under most circumstances it is possible to get good agreement between prediction and experiment even for relatively large Helmholtz numbers.
Publisher: Acoustical Society of America (ASA)
Date: 05-2020
DOI: 10.1121/10.0001261
Abstract: The existing non-paraxial expression of audio sounds generated by a parametric array loudspeaker (pal) is hard to calculate due to the fivefold integral in it. A rigorous solution of the Westervelt equation under the quasilinear approximation is developed in this paper for circular PALs by using the spherical harmonics expansion, which simplifies the expression into a series of threefold summations with uncoupled angular and radial components. The angular component is determined by Legendre polynomials and the radial one is an integral involving spherical Bessel functions, which converge rapidly. Compared to the direct integration over the whole space, the spherical expansion is rigorous, exact, and can be calculated efficiently. The simulations show the proposed expression can obtain the same accurate results with a speed of at least 15 times faster than the existing one.
Publisher: Acoustical Society of America (ASA)
Date: 02-2022
DOI: 10.1121/10.0009587
Abstract: This paper investigates the feasibility of remotely generating a quiet zone in an acoustic free field using multiple parametric array loudspeakers (PALs). A primary sound field is simulated using point monopoles located randomly in a two-dimensional plane, or three-dimensional (3D) space, whereas the secondary sound field is generated by multiple PALs uniformly distributed around the circumference of a circle sitting on the same plane as the primary sources, or on the surface of a sphere for 3D space. A quiet zone size is defined as the diameter of the maximal circular zone within which the noise reduction is greater than 10 dB. The size of this quiet zone is found to be proportional to 0.19λN for N secondary sources with a wavelength λ when the primary and secondary sources are in the same plane, whereas it is found to be 0.55λN1/2 for the 3D case. The size of the quiet zones generated by PALs is similar to that observed with traditional omnidirectional loudspeakers however, the effects of using PALs on the sound field outside the target zone is much smaller due to their sharp radiation directivity and slow decay rate along the propagation distance. Experimental results are also presented to validate these numerical simulations.
Publisher: Acoustical Society of America (ASA)
Date: 11-2013
DOI: 10.1121/1.4821214
Abstract: Acoustic intensity is normally treated as a real quantity, but in recent years, many articles have appeared in which intensity is treated as a complex quantity where the real (active) part is related to local mean energy flow and the imaginary (reactive) part to local oscillatory transport of energy. This offers the potential to recover additional information about a sound field and then to relate this to the properties of the sound source and the environment that surrounds it. However, this approach is applicable only to multi-modal sound fields, which places significant demands on the accuracy of the intensity measurements. Accordingly, this article investigates the accuracy of complex intensity measurements obtained using a tri-axial Microflown intensity probe by comparing measurement and prediction for sound propagation in an open flanged pipe. Under plane wave conditions, comparison between prediction and experiment reveals good agreement, but when a higher order mode is present, the reactive intensity field becomes complicated and agreement is less successful. It is concluded that the potential application of complex intensity as a diagnostic tool is limited by difficulties in measuring reactive intensity in complex sound fields when using current state of the art acoustic instrumentation.
Publisher: Acoustical Society of America (ASA)
Date: 11-2021
DOI: 10.1121/10.0007280
Abstract: In this work, a cylindrical expansion for the audio sound generated by a steerable baffled parametric array loudspeaker (PAL) based on the phased array technique is derived from the Westervelt equation. The expansion is a series of twofold summations with uncoupled angular and radial components in the cylindrical coordinate system. The angular component is determined by the trigonometric functions, and the radial component is an integral containing the Bessel functions and an arbitrary excitation velocity profile. The numerical results for a typical steerable PAL are presented and compared to those obtained using the convolution model. It is found that the prediction of the audio sound using the proposed cylindrical expansion improves the agreement with the experimental results when compared to the existing models. This is because no further approximations are required in the cylindrical expansion of the quasilinear solution of the Westervelt equation, whereas the complex near field nonlinear interactions between the ultrasonic waves cannot be correctly captured in a convolution model. The proposed cylindrical expansion does, therefore, provide an alternative approach to modeling a phased array PAL and high accuracy with a relatively low computational cost.
Publisher: Informa UK Limited
Date: 12-2010
Publisher: Elsevier BV
Date: 2015
Publisher: Acoustical Society of America (ASA)
Date: 12-2007
DOI: 10.1121/1.2793614
Abstract: An analytic mode matching scheme that includes higher order modes is developed for a straight-through circular dissipative silencer. Uniform mean flow is added to the central airway and a concentric perforated screen separates the mean flow from a bulk reacting porous material. Transmission loss predictions are compared with experimental measurements and good agreement is demonstrated for three different silencers. Furthermore, it is demonstrated that, when mean flow is present, the axial kinematic matching condition should equate to that chosen for the radial kinematic boundary condition over the interface between the airway and the material. Accordingly, if the radial matching conditions are continuity of pressure and displacement, then the axial matching conditions should also be continuity of pressure and displacement, rather than pressure and velocity as previously thought. When a perforated screen is present the radial pressure condition changes, but the radial kinematic condition should always remain equivalent to that chosen for the axial kinematic matching condition here, results indicate that continuity of displacement should be retained when a perforated screen is present.
Publisher: Elsevier BV
Date: 03-2014
Start Date: 01-2019
End Date: 07-2022
Amount: $415,893.00
Funder: Australian Research Council
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