Volume 124, Issue 4, October 2008
Index of content:
- STRUCTURAL ACOUSTICS AND VIBRATION 
124(2008); http://dx.doi.org/10.1121/1.2968705View Description Hide Description
In 1821, Fresnel obtained the wave surface of an optically biaxial crystal, assuming that light waves are vibrations of the ether in which longitudinal vibrations (waves) do not propagate. An anisotropicelastic medium mathematically analogous to Fresnel’s crystal exists. The medium has four elastic constants: a -wave modulus, associated with a spherical wave surface, and three elastic constants, , , and , associated with the shear waves, which are mathematically equivalent to the three dielectric permittivity constants , , and as follows: , , , where is the magnetic permeability of vacuum and is the mass density. These relations also represent the equivalence between the elastic and electromagnetic wave velocities along the principal axes of the medium. A complete mathematical equivalence can be obtained by setting the -wave modulus equal to zero, but this yields an unstable elastic medium (the hypothetical ether). To obtain stability the -wave velocity has to be assumed infinite (incompressibility). Another equivalent Fresnel’s wave surface corresponds to a medium with anomalous polarization. This medium is physically unstable even for a nonzero -wave modulus.
124(2008); http://dx.doi.org/10.1121/1.2973233View Description Hide Description
This paper deals with wave conversion phenomena through a study of the acoustic scattering from a stiffened cylindrical shell at normal incidence. The analysis presented follows the experimental study which explored the acoustic wave propagation and scattering processes in the case of air-filled submerged cylindrical shells having internal axial solder [J. Chiumia, N. Touraine, D. Décultot, G. Maze, A. Klauson, and J. Metsaveer, J. Acoust. Soc. Am.105, 183–193 (1999)]. The significant observed phenomena were generation, reflection, and conversion of circumnavigating waves at the solder. The present work confirms the presence of the three phenomena through a theoretical approach based on the elasticity theory. In particular, resonances with new feature whose frequencies are very close to those of the wave are highlighted here. The origin of this new resonance feature is identified and can be associated to wave type conversions between and Lamb waves, occurring when these propagating waves encounter the solder. The air-filled stainless steel studied tube submerged in water has an internal lengthwise solder, which is, in theoretical computations, considered as an internal axial mass layer. The reduced frequency range of the study is between 25 and 90, (: wave number in water; : external radius of the shell).
124(2008); http://dx.doi.org/10.1121/1.2973237View Description Hide Description
An analytical model is presented to describe the vibration of a truncated conical shell with fluid loading in the low frequency range. The solution for the dynamic response of the shell is presented in the form of a power series. Fluid loading is taken into account by dividing the shell into narrow strips which are considered to be locally cylindrical. Analytical results are presented for different boundary conditions and have been compared with the computational results from a boundary element model. Limitations of the model to the low frequency range are discussed.