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Journal of the Acoustical Society of America

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Nov 2004

Volume 116, Issue 5, pp. 2697-3225

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Guided wave propagation in three-layer pavement structures

Nils Ryden and Michael J. S. Lowe

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2902-2913 (2004); (12 pages) | Cited 11 times

Online Publication Date: 09 Nov 2004

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A study on guided waves in a layered half-space with large velocity contrasts and a decreasing velocity with depth is presented. Multiple mode dispersion curves are calculated in the complex wave number domain, taking into consideration the attenuation caused by leakage into the underlying half-space. The excitability of the modes by a vertical point force on the surface is also calculated. Results show that the measurable wave field at the surface of a pavement structure is dominated by leaky quasi-Lamb waves in the top and second layers. The fundamental antisymmetric mode of vibration is the dominating mode generated in the stiff top layer. This mode drives the complete system and continuity across the boundaries generates higher order modes in the embedded second layer. The interaction of leaky Lamb waves in the first two layers results in large variations in the excitability and the attenuation, so that only the waves corresponding to certain portions of the dispersion curves are measurable remote from the source at the pavement surface. It is concluded that these portions of dispersion curves can be individually resolved in practice, by using multichannel processing techniques. This holds the potential for a refined nondestructive testing technique for pavements. © 2004 Acoustical Society of America.
Show PACS
43.35.Pt Surface waves in solids and liquids
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission

Line source representation for laser-generated ultrasound in an elastic transversely isotropic half-space

David H. Hurley and James B. Spicer

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2914-2922 (2004); (9 pages) | Cited 3 times

Online Publication Date: 09 Nov 2004

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Theoretical and experimental results are presented for a laser line source in an elastic, transversely isotropic half-space. The thermoelastic source (laser source) is represented as an appropriately weighted shear stress dipole applied at the sample surface. The plane of isotropy coincides with the half-space boundary. Analytical expressions representing the out-of-plane displacements for the surface wave and for the epicentral cases are given for all crystal classes that exhibit elastic transverse isotropy. In addition, quasianalytical results are given for observation points off the epicentral axis. Theoretical wave forms for all of the source/observation geometries considered are compared with experimental wave forms generated in single crystal zinc samples. The close comparison between experiment and theory confirms, for this particular line source orientation and crystal symmetry, that a laser line source is accurately modeled using an equivalent boundary stress. © 2004 Acoustical Society of America.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.20.Bi Mathematical theory of wave propagation
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

A resonant, self-pumped, circulating thermoacoustic heat exchanger

G. W. Swift and S. Backhaus

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2923-2938 (2004); (16 pages) | Cited 3 times

Online Publication Date: 09 Nov 2004

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An asymmetrical constriction in a pipe functions as an imperfect gas diode for acoustic oscillations in the pipe. One or more gas diodes in a loop of pipe create substantial mean flow, approximately proportional to the amplitude of the oscillations. Measurements of wave shape, time-averaged pressure distribution, mass flow, and acoustic power dissipation are presented for a two-diode loop. Analysis of the phenomena is complicated because both the mean flow and the acoustic flow are turbulent and each affects the other significantly. The quasi-steady approximation yields results in rough agreement with the measurements. Acoustically driven heat-transfer loops based on these phenomena may provide useful heat transfer external to thermoacoustic and Stirling engines and refrigerators. © 2004 Acoustical Society of America.
Show PACS
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.25.Nm Acoustic streaming
43.25.Qp Radiation pressure
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