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Jun 2012

Volume 131, Issue 6, pp. EL421-4870

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Propagation of sound from a monopole source above an impedance-backed porous layer

Kai Ming Li and Sheng Liu

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4376-4388 (2012); (13 pages)

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In this article, the propagation of sound from a monopole source above an impedance-backed porous layer is examined. The sound fields can be expressed in an integral form that is amenable to further analysis. A standard method of steepest descents is applied to evaluate the integral where the method of pole subtraction is needed to obtain a uniform asymptotic solution for the sound field above the plane surface. To obtain a numerical solution, the location of the pole was determined numerically by means of the Newton-Raphson method. Based on the pole location, the sound fields can then be calculated numerically. It has been demonstrated that the use of a plane wave reflection coefficient to calculate the sound fields is a special case of the asymptotic formula when the pole is located further away from the saddle point.
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43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.20.Fn Scattering of acoustic waves
43.20.El Reflection, refraction, diffraction of acoustic waves
43.28.Kt Aerothermoacoustics and combustion acoustics

Efficient computation of the sound fields above a layered porous ground

Sheng Liu and Kai Ming Li

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4389-4398 (2012); (10 pages)

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An efficient computation of sound fields due to a monopole source placed above a porous layer is presented. This paper examines an improved scheme whereby the steepest descent path is selected for the numerical evaluation of the Sommerfeld integral. Along the steepest descent path, a standard Gaussian-Hermite quadrature can be used to calculate the sound fields effectively. The suggested numerical scheme is accurate at all frequencies except in the very near field. The proposed method is more numerically efficient than other computational schemes, especially at long ranges and high source frequencies.
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43.28.Js Numerical models for outdoor propagation
43.20.Fn Scattering of acoustic waves
43.20.El Reflection, refraction, diffraction of acoustic waves

Acoustic reconstruction of the velocity field in a furnace using a characteristic flow model

Yanqin Li, Huaichun Zhou, Shiying Chen, Yindi Zhang, Xinli Wei, and Jinhui Zhao

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4399-4408 (2012); (10 pages)

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An acoustic method can provide a noninvasive, efficient and full-field reconstruction of aerodynamic fields in a furnace. A simple yet reasonable model is devised for reconstruction of a velocity field in a cross section of a tangential furnace from acoustic measurements based on typical physical characteristics of the field. The solenoidal component of the velocity field is modeled by a curved surface, derived by rotating a curve of Gaussian distribution, determined by six characteristic parameters, while the nonrotational component is governed by a priori knowledge. Thus the inverse problem is translated into determination of the characteristic parameters using a set of acoustic projection data. First numerical experiments were undertaken to simulate the acoustic measurement, so as to preliminarily validate the effectiveness of the model. Based on this, physical experiments under different operating conditions were performed in a pilot-scale setup to provide a further test. Hot-wire anemometry and strip floating were applied to compare with acoustic measurements. The acoustic measurements provided satisfactory consistency with both of these approaches. Nevertheless, for a field with a relatively large magnitude of air velocities, the acoustic measurement can give more reliable reconstructions. Extension of the model to measurements of hot tangential furnaces is also discussed.
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43.28.We Measurement methods and instrumentation for remote sensing and for inverse problems
43.28.Vd Measurement methods and instrumentation to determine or evaluate atmospheric parameters, winds, turbulence, temperatures, and pollutants in air
43.60.Pt Signal processing techniques for acoustic inverse problems
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