摘要:

Wavenumber integration (WI) techniques are well established for analysis of wave propagation in laminated or stratified media, inherently satisfying all boundary and radiation conditions. However, their area of applicability is restricted to separable geometries such as infinite laminated plates and cylindrical or spherical shells. In structural acoustics the boundary element method (BEM) is traditionally applied to determine the radiated and scattered field in the surrounding fluid, requiring a discretization of the entire surface of the structure under consideration, with the interior being treated by, e.g., finite elements. Here, a hybrid WIBEM approach is applied to study the wavenumber conversion induced by facets such as stiffeners and grooves in an otherwise perfectly laminated medium. By choosing the Green's function for the laminated medium, only the interface between the facet and the layered medium contributes to the surface integral in Green's theorem. Thus, only the boundary of the inhomogeneity needs to be discretized, leading to a highly efficient numerical implementation. The method is applicable to all problems where the major part of the structure is of separable geometry. Thus, in particular, it is intended for analysis of scattering and radiation by coated cylindrical shells with attached structures. In contrast to traditional BEM approaches, the scattered field is determined in the wavenumber domain, allowing direct physical interpretation in terms of modal coupling. Here the approach is illustrated by analyzing the wavenumber conversion in flat, coated plates with irregularities such as stiffeners and grooves. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2028086

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Recent experimental results (to appear) by Williams and colleagues at NRL suggest that wave propagation concepts apply to vibrations caused by point excitations on circular shells even at frequencies substantially below the ring frequency. A previous analysis by Pierce and Kil [ASMEJ. Vib. Acoust. (1990)] has given general dispersion relations for such waves, but with detailed analysis only for frequencies far above the ring frequency. The present paper examines the propagation in the opposite limit. In this limit two types of propagating waves are excited, which in the axial direction correspond to shear waves in bulk media [phase velocity equal to (G/p)1/2] and to longitudinal waves in rods [phase velocity equal to (E/p)1/2]. At low frequencies these waves are nondispersive with phase velocities that do not vary with frequency. The propagation, however, is anisotropic and the mode that nominally coresponds to shear waves has zero phase velocity for propagation in the circumferential direction. Hence wave fronts for the two types of waves are not circular; the “shear wave's” lines of constant phase resemble figure‐eight's aligned in the axial direction; those for the mode that nominally corresponds to the longitudinal (thin rod) mode resemble ellipses elongated in the axial direction. Numerical examples are also presented for amplitudes and radiation patterns associated with point excitation. [Work supported by ONR and by the William E. Leonhard endowment to Pennsylvania State University. The author acknowledges the advice of A. D. Pierce.]

ISSN:0001-4966    

DOI:10.1121/1.2028095

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This paper is addressed to the macromechanical analysis of dynamics of an elastic ship laminae within the effective stiffness concept of composites. The laminae that may possess arbitrary number of layers is immersed within an ideal fluid of infinite extent. In the first part, a variational principle [N. Sarigül and M. C. Dökmeci, AIAA J.20, 1173–1175 (1984)] is extended by Friedrichs's transformation [M. C. Dökmeci, IEEE Trans.UFFC‐35, 775–787 (1988)] so as to formulate a unified variational principle of fluid‐solid interaction. In the second part, a set of two‐dimensional governing equations of laminae is systematically derived by means of a variational principle together with a series representation in the thickness coordinate for the fields of displacement and hydrodynamic pressure that are chosen as a basis of derivation. The significant effects of laminated composites are considered, including those of the dynamic interactions between, and the hydrodynamic pressure on, the layers. The governing equations accommodate all the types of motions of laminae. In the third part, emphasis is placed upon a theorem of uniqueness in solutions of the governing equations and special cases.

ISSN:0001-4966    

DOI:10.1121/1.2028098

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP