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Dec 1986

Volume 80, Issue S1, pp. S1-S128

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back to top Session P. Shock and Vibration III: Radiation Loading on Elastic Structures
Invited Papers
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Asymptotic solution to low‐frequency fluid‐loaded structure problems (A)

D. G. Crighton

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S32-S32 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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This paper will review the structural and acoustical features of asymptotic solutions recently obtained for fluid‐loaded structure problems. In the cases treated here, the structure is plane (a thin plate or membrane) and driven by a source of concentrated mechanical excitation. The asymptotic results, based on the smallness of the fluid‐loading‐at‐coincidence parameter, hold generally at frequencies below coincidence, but assume particularly simple forms at much lower frequencies. Problems discussed will include semi‐infinite and finite unribbed structures (with details of resonance, mode shapes, and forced response), and infinite and semi‐infinite ribbed structures. An aspect subject to particular study will be the nonlocal (i.e., non‐added‐mass) effects of fluid loading; and generally, the aim is to expose fundamental mechanisms for structural vibration with heavy fluid loading, and to provide benchmarks for computational schemes. [Work supported by ONR.]
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Fluid‐loading effects upon scatter of elastic waves at discontinuities (A)

P. W. Smith, Jr.

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S33-S33 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Vibratory waves in structures constructed of many plate or shell elements joined together are scattered by the discontinuity of elastic properties at the junctions. Descriptions of that scatter (reflection, transmission, and radiation into adjacent fluid) are important in analyzing the behavior of realistically complex structures. Results of analyses that have included significant fluid loading are reviewed and their implications for structural response discussed.
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Finite element treatment of exterior fluids in fluid‐structure interaction problems (A)

Gordon C. Everstine

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S33-S33 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Several finite element solution approaches are described for fluid‐structure interaction problems involving an exterior fluid. The specific problems of interest are those of acoustic radiation and scattering from submerged elastic structures subjected, respectively, to internal time‐harmonic mechanical loads or an incident time‐harmonic wavetrain. These problems can be solved by combining a finite element model of the structure with a fluid loading computed using finite element, boundary element, infinite element, or decoupling techniques. Formulations are presented and compared for fluid domains modeled using an added mass matrix, the doubly asymptotic approximation (a decoupling technique), explicit fluid finite elements, and the Helmholtz exterior integral equation. With the exception of the integral equation treatment, all these fluid‐loading approaches can be implemented using the standard finite element modeling capabilities available in structural analysis computer codes such as NASTRAN. The most accurate fluid treatment is obtained with the Helmholtz integral equation although this is at somewhat greater computational cost than that required using the less precise approaches.
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Doubly asymptotic approximations in acoustics, elastodynamic, and electromagnetic scattering (A)

Thomas L. Geers

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S33-S33 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Doubly asymptotic approximations (DDAs) are differential equations that describe the dynamic interaction between a scatterer and a surrounding wave‐propagating medium. They find application in problems of acoustic, elastodynamic, and electromagnetic scattering by bodies of complex geometry and structure through the utilization of boundary element and finite element techniques. DAAs have been successfully developed and applied for acoustic scattering, have been developed for elastodynamic scattering, and are under development for electromagnetic scattering. In this paper, systematic formulations of DAAs for the various field equations are presented, and their behavior in canonical problems is examined. The utilization of increasingly higher‐order DAAs is explored and the point of diminishing returns is sought.
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