Reflector Responses: A Comparison between ODEON’s Modified Ray Tracing Algorithm and a Filtered Boundary Element Method Model (original) (raw)
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Acoustical Society of America. Journal, 2006
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A transparency model and its applications for simulation of reflector arrays and sound transmission
The Journal of the Acoustical Society of America, 2006
Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Applied Acoustics, 2008
The phased beam tracing method (PBTM) was suggested as a medium-frequency simulation technique for the calculation of impulse response, although main assumptions of geometric acoustics still hold. The phased method needs the reflection coefficient for characterizing the acoustic property of a surface and the complex wave number for describing the propagation characteristics. In this study, two types of approximate real reflection coefficients derived from the measured absorption coefficient were tested for a practical applicability. As a test example, pressure impulse responses and energy impulse responses computed from the PBTM were compared with those from the measurement and the ordinary beam tracing method. The PBTM employing the approximate reflection coefficients greatly increased the accuracy of the prediction compared to the ordinary beam tracing method, in particular at the medium-frequency range in octave bands above the Schroeder cutoff frequency. A comparison was made between angle-dependent and angle-independent reflection coefficients in the calculation of acoustic measures. Although the angle-dependent reflection coefficient yielded best matched results with measured data, but the simple angle-independent reflection coefficient can be also used with a reasonably good precision.
1970
The paper is devoted to the theoretical analysis of interactions between a receiving array and a neighbouring structure as well as their consequences on the sonar function. The boundary element method is applied to solve the scattering problem for two bodies. Two configurations are considered: a cylindrical array placed in front of a thin rigid panel, both considered as two-dimensional bodies and the association of a spherical array and a thin soft disc. In both examples, the support of the sensors of the arrays are assumed perfectly rigid. The two-dimensional problem is solved using the Helmholtz integral representation; the threedimensional scattering problem using the axisymmetric formulation of the previous representation. Numerical results are used to compute directivity patterns as a function of the steering direction. Degradations produced by shielding and scattering phenomena such as the shift of the maximum level or the increase of the side lobe level are illustrated with d...
Experimental verification of the acoustic computer model using triangle reflector
Objective of this study was experimental verification of the acoustic computer model, which enables calculation of the signals reflected by triangles arbitrally oriented in space. Verification of the computer model was carried out comparing the C-scan images of triangle reflectors, obtained experimentally and by simulation in the case when ultrasonic beam is reflected by triangle reflectors, reflecting surfaces of which are perpendicular and inclined with respect to the symmetry axis of the directivity pattern. Comparison of the experimental and simulated results of the inclined triangle reflector revealed some discrepancies. In order to find out the reason of these discrepancies the assumption was made that during rotation of the triangle reflector, the rotation axis was not strictly perpendicular to the incident ultrasonic beam, but that it was slightly deflected. In order to check this hypothesis modelling was also performed at different transducer deflection angles from its supp...
Practical methods to define scattering coefficients in a room acoustics computer model
Applied Acoustics, 2006
To predict acoustics of rooms using computer programs based on geometrical assumptions, it is important that scattering is included in the calculations. Therefore scattering is usually included in terms of scattering coefficients which are assigned to each surface telling the software the ratio between the part of the reflected energy which is not being reflected specularily and the total reflected energy. However the effective scattering coefficient of a surface depends not only on the roughness of the surface material indeed diffraction caused by limited dimensions of the surface as well as edge diffraction also causes scattering. For complex rooms it can be difficult to give a reasonable estimate to the magnitudes of scattering coefficients if these should also include diffraction and even if these frequency dependent coefficients could be obtained in the design phase, the processes of obtaining the data becomes quite time consuming thus increasing the cost of design. In this paper, practical methods to define scattering coefficients, which is based on an approach of modeling surface scattering and scattering caused by limited size of surface as well as edge diffraction are presented. The predicted and measured acoustic parameters in real rooms have been compared in order to verify the practical approaches recommended in the paper.
The Journal of the Acoustical Society of America, 2009
This paper presents a computational technique using the boundary element method for prediction of radiated acoustic waves from axisymmetric surfaces with nonaxisymmetric boundary conditions. The aim is to predict the far-field behavior of underwater acoustic transducers based on their measured behavior in the near-field. The technique is valid for all wavenumbers and uses a volume integral method to calculate the singular integrals required by the boundary element formulation. The technique has been implemented on a distributed computing system to take advantage of its parallel nature, which has led to significant reductions in the time required to generate results. Measurement data generated by a pair of free-flooding underwater acoustic transducers encapsulated in a polyurethane polymer have been used to validate the technique against experiment. The dimensions of the outer surface of the transducers ͑including the polymer coating͒ were an outer diameter of 98 mm with an 18 mm wall thickness and a length of 92 mm. The transducers were mounted coaxially, giving an overall length of 185 mm. The cylinders had resonance frequencies at 13.9 and 27.5 kHz, and the data were gathered at these frequencies.
Proceedings of the ICA congress, 2019
The level of detail of a simulated model as well as the assignment of the materials acoustic properties have been largely debated and optimal guidelines have been determined based on the approximations of the scattering algorithm of the simulation tools. These aspects are of great importance when investigating the differences between geometrical-acoustic (GA) based and wave-based methods. To this aim the present study refers to objective and subjective evaluations of wave-based simulations (finite difference time domain method) in a shoebox concert hall, which has been previously studied through GA-based methods. Three models, that consider 1) reflective, 2) low scattering, and 3) high scattering conditions of one of the long lateral walls, have been simulated in order to determine the conventional acoustic parameters such as early decay time (EDT), reverberation time (T30), clarity (C80), definition (D50). GA-based and wave-based simulation results have been compared to measured data. Furthermore, a preliminary subjective investigation has been performed in order to determine the sensitivity of listeners to the surface diffusivity variations in different listening positions.