Index of content:
Volume 109, Issue 3, March 2001
- GENERAL LINEAR ACOUSTICS 
109(2001); http://dx.doi.org/10.1121/1.1336500View Description Hide Description
The results of a numerical study of vibration localization due to stiffener variability in a framed shell are reported. An axisymmetric finite element (FE)–infinite element model is used to obtain predictions in good general agreement with previously reported experimental results. Over the frequency band of this study, up to three times the ring frequency, two structural resonances dominate the vibratory response of the shell for high circumferential orders Localization is shown to be linked to the sensitivity of the local resonance frequencies of the system to specific geometrical parameters. Specifically, rib thickness variations strongly affect the first pass band, while rib spacing variations strongly affect the second pass band.
109(2001); http://dx.doi.org/10.1121/1.1348296View Description Hide Description
The scattering of a plane acoustic wave by an infinite penetrable or impenetrable circular cylinder, parallel with another one, also penetrable or impenetrable, of acoustically small radius, is considered. The method of separation of variables, in conjunction with translational addition theorems for cylindrical wave functions, is used. Analytical expressions are obtained for the scattered pressure field and the various scattering cross sections, for normal incidence. Numerical results are given for penetrable and impenetrable cylinders.
109(2001); http://dx.doi.org/10.1121/1.1348297View Description Hide Description
The problem of the scattering of harmonic plane waves by a rough half-plane is studied here. The surface roughness is finite. The slope of the irregularity is taken as arbitrary. Two boundary conditions are considered, those of Dirichlet and Neumann. An asymptotic solution is obtained, when the wavelength of the incident wave is much larger than the characteristic length of the roughness l, by means of the method of matched asymptotic expansions in terms of the small parameter For the Dirichlet problem, the solution of the near and far fields is obtained up to The far field solution is given in terms of a coefficient that have a simple explicit expression, which also appears in the corresponding solution to the Neumann problem, already solved. Also the scattering cross section is given by simple formulas to It is noted that, for the Dirichlet problem, the leading term is of order which, by contrast, is different from that of the circular cylinder in full space, that is, of order Some examples display the simplicity of the general results based on conformal mapping, which involve arcs of circle, polygonal lines, surface cracks and the like.
109(2001); http://dx.doi.org/10.1121/1.1348299View Description Hide Description
Propagation of flexural guided waves in a fluid-loaded transversely isotropic cylinder is studied. Numerical results are presented for a cobalt cylinder immersed in water. The phase velocities are not significantly affected except for several modes in which the energy leakage occurs into the fluid over certain frequency ranges. Attenuation spectra for the leaking modes are plotted.