• Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Journal of the Acoustical Society of America

SECTION LISTING

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Nov 1990

Volume 88, Issue S1, pp. S1-S200

Return to All Sections
back to top
RSS Feeds
back to top Session 3SA: Structural Acoustics and Vibration: Plate and Shell Vibration and Acoustics
Contributed Papers
FREE

Finite difference modeling and slowness‐time analysis of modes in a submerged steel plate (A)

J. Robert Fricke and Arthur B. Buggeroer

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S51-S51 (1990); (1 page)

Online Publication Date: 14 Aug 2005

Full Text: | Download PDF

Show Abstract
This presentation illustrates one of the capabilities of a numerical laboratory in the study of acoustic‐elastic wave interaction. Because of the simultaneous presence of many modes of vibration, multipath, and mode conversion, physical experiments are difficult to instrument well enough to unravel the wave interactions. As an alternative, numerical results from a 2‐D finite difference solution to the elastodynamic equations mimic the physical interaction of a transient acoustic pulse with a finite elastic object. In this case the field variables of velocity and stress are computed directly and instrumentation is not an issue. In the experiment presented here, a 500‐Hz center frequency pulse insonifies a submerged steel plate with dimensions ≈2λ × λ/20, where λ is the wavelength in steel. Diffractions from the ends of the plate are observed as well as the flexural and longitudinal plate modes that arise from the coupling of acoustic to elastic energy. In addition, radiation of acoustic energy into the water from the ends of the plate is seen when the flexural and longitudinal modes impact from the interior. A fundamental question of the scattering process is how much of the insonifying acoustic energy is converted into elastic energy in the plate. While the plate modes occur simultaneously and overlap in the time domain, they can be separated into isolated regions of the slowness‐time domain. The isolation of the modes in this domain enables estimates of the energy partitioning to be made. From a time series recorded just below the midline of the plate, a slowness spectrum clearly shows the flexural and longitudinal modes in isolation. In addition, the continual reflection of these modes from the ends of the plate, i.e., the multipath, is seen as they travel back and forth. Quantitative estimates of energy partitioning are possible from the slowness spectra.
FREE

Application of the reciprocity theorem in the problem of an infinite elastic plate (A)

Anthony J. Rudgers

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S51-S51 (1990); (1 page)

Online Publication Date: 14 Aug 2005

Full Text: | Download PDF

Show Abstract
At the 116th Meeting of the Acoustical Society of America, an equivalent‐network representation of an elastic plate was reported [A. J. Rudgers, “Equivalent‐network representation of an infinite elastic plate subject to plane‐wave excitation,” J. Acoust. Soc. Am. Suppl. 1 84, S184 (1988)]. The circuit equations describing this network are identical to the equations arising from the theory of linear elasticity that describe the two‐dimensional elastic behavior of an infinite plate subject to arbitrary plane‐wave excitation at its surfaces. It was noted that gyrators are required in the equivalent network, in order to make the network obey the equations of linear elasticity theory. The presence of gyrators in the equivalent network, however, implies that the elastic plate is a nonreciprocal system, with the nonreciprocal effects being associated with elastic mode conversion at the plate surfaces. Because the appearance of nonreciprocal effects in the elastic‐plate problem is unexpected and, perhaps, surprising, it is useful to examine the question of reciprocity from a more general standpoint—from a standpoint that does not require one to consider any particular equivalent‐network representation of the plate. The present work reports the application of a general version of the reciprocity theorem in the plate problem.
FREE

Experimental measurement of structural power flow on L‐shaped plates subjected to mechanical and acoustic excitation (A)

J. M. Cuschieri

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S51-S52 (1990); (2 pages)

Online Publication Date: 14 Aug 2005

Full Text: | Download PDF

Show Abstract
Analytical results on the structural power flow through an L‐shaped plate subjected to mechanical and acoustic excitation have been presented in previous ASA meeting papers. To verify some of these results, experimental measurements have been performed on a similar L‐shaped plate as used in the anaytical studies. Two sets of experimental results have been obtained. One set is for simulated results that show the discrepancies created by the selected measurement schemes. The second set of results is for actual measurements that use a four‐accelerometer measurement scheme. In the case of the acoustic excitation, measurements were also performed of the acoustic intensity incident and reradiated from the two components of the L‐shaped plate. The results of this experimental analysis show that there is good agreement between the measured experimental results, the simulated experimental results, and the analytical results. The accuracy of the measured data as compared to the analytical data is very much influenced by the type of measurement scheme that is selected to perform the measurements. [Work supported by NASA Langley Research Center.]
FREE

On direct method of calculation of degenerate elastodynamic solutions of elastic wave propagation in a thick plate (A)

Agha J. Ghorieshi

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S52-S52 (1990); (1 page)

Online Publication Date: 14 Aug 2005

Full Text: | Download PDF

Show Abstract
The elastostatic eigenvalue equations are commonly obtained by taking the limit of their elastodynamic counterparts as frequency tends to zero. However, this limiting procedure is not convenient. It is cumber‐some when applied to the solutions obtained using Stokes' potentials and, in the case of utilizing Lame's potentials, it does not produce static solutions that are a function of position alone. In this paper it is shown that the exact solutions of elastostatic problems can, in general, be obtained in a straightforward manner by the use of harmonic potentials without recourse to any special limiting form of analysis. This method is applied to an infinite, elastic thick plate with traction‐free parallel surfaces and the elastostatic eigenvalue equation. It is shown that the problem can be solved exactly in terms of harmonic functions, one of which is a scalar and the other of which is a vector. It is noted that results are in agreement with the published solutions.
FREE

Vibroacoustic behavior of point‐driven and cavity‐backed circular plates with general boundary conditions (A)

L. Cheng and J. Nicolas

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S52-S52 (1990); (1 page)

Online Publication Date: 14 Aug 2005

Full Text: | Download PDF

Show Abstract
This paper discusses the vibroacoustic response of point‐driven circular plates coupled to a cylindrical hard‐walled cavity. Particular attention is paid to the modeling of the boundary conditions of the plates. It is an extension of the previous work [L. Cheng and J. Nicolas, J. Acoust. Soc. Am. Suppl. 1 87, S136–S137 (1990)] in which a circular plate was modeled as part of the structure. The plate is assumed to be elastically supported by rotational and translational springs along the edge. With this model, both classical and intermediate cases can be easily simulated only by making different combinations of the elastic parameters. A variational formulation associated with Rayleigh‐Ritz procedure is used for the plate by choosing simple polynomials as trial functions. For the cavity, the Green's function based on cavity modes is adopted. Numerical results are presented to address the following topics: (1) effect of the classical boundary conditions of the plates and its interpretation; (2) consequences of the elastic supporting on the cavity sound field; and (3) some guidelines for the design of such systems in practice.
FREE

A new formulation for the sound radiation in a heavy fluid from a rectangular plate with elastic boundary conditions (A)

A. Berry

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S52-S52 (1990); (1 page)

Online Publication Date: 14 Aug 2005

Full Text: | Download PDF

Show Abstract
This paper considers the dynamic response and acoustic radiation of a fluid‐loaded, baffled, rectangular plate elastically restrained against deflection and rotation along the four edges. Classical methods using in vacuo plate eigenfunctions to formulate the fluid‐structure coupling are essentially limited to the simply supported case, and lead to considerable difficulty, both theoretical and numerical. The proposed approach employs a variational formulation coupled to a Ritz method for the structural motion. Choosing simple polynomials to generate the set of trial displacement functions and expanding the acoustic Green's function of the unbounded fluid medium in MacLaurin series allows an analytic solution for both the resistive part and the reactive part of the radiation impedance. In essence, the method furnishes a decomposition of the radiator in monopoles,dipoles,…,2n‐upoles. The analytic solution of the fluid‐structure coupling greatly improves the computation costs and generality is gained for the boundary conditions of the plate, as compared to available methods. The convergence of the method is illustrated in the case of simply supported, clamped, free, and guided plates immersed in water. The effect of mass addition and stiffening is also investigated.
FREE

Radiation from an elastic slab under line and point excitation (A)

Patrick Leehey and Yuksel Gut

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S52-S52 (1990); (1 page)

Online Publication Date: 14 Aug 2005

Full Text: | Download PDF

Show Abstract
Solutions are obtained for acoustic radiation into a dense fluid on one side of an infinite elastic slab of thickness h for pure‐tone line and point excitations on the other side (where a vacuum is assumed). These results are compared with the corresponding solutions obtained using the Euler thin plate assumption. Comparisons show that significant excess radiation is predicted under the thin plate assumption even for frequencies sufficiently low that the plate free‐bending wavelength is appreciably greater than h. These results suggest that the spatial extent of the excitation must also be of order h or greater for the plate approximation to be valid. Implications for the excitation of a structure by a turbulent boundary layer and for radiation associated with structural discontinuities are discussed. [Work supported by ONR.]
FREE

Intensity vector and power flow in an infinite cylindrical shell excited by a point force (A)

Giorgio V. Borgiotti and Eric Rosen

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S53-S53 (1990); (1 page)

Online Publication Date: 14 Aug 2005

Full Text: | Download PDF

Show Abstract
The time harmonic forced vibration of a finite cylinder excited by a point force of arbitrary orientation is analyzed by using wave techniques. The vibrational response is constructed as superposition of propagating and attenuating characteristic waves of the structure (“waveguide modes”). The propagating modes are associated with the flow of mechanical power, whereas the attenuating modes are associated with reactive energy stored in the neighborhood of the excitation. Under the assumption of a linear dependence upon the radial coordinate within the shell thickness, the elastodynamic field is completely identified by 15 quantities, 10 of them being forces and moments resultant per unit length—either circumferential or longitudinal—and the other 5 being linear or angular velocities. The 2‐D shell intensity vector has a simple expression in terms of these quantities. Numerical calculations of the intensity vector field for point forces of different orientations are presented. [Work supported by the Naval Research Laboratory.]
FREE

Effects of rib stiffeners on the wave‐number sensitivity of a cylindrical shell to flow excitation (A)

Y. F. Hwang and P. C. Shang

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S53-S53 (1990); (1 page)

Online Publication Date: 14 Aug 2005

Full Text: | Download PDF

Show Abstract
The wave‐number sensitivity (square of the absolute of a normalized spatial Fourier transform of a mode function) of a structural mode determines the degree of the coupling between a structure and the flow‐induced pressure field. It is of engineering interest to evaluate relative contributions to the coupling in the two regions of the wave‐number domain: the high‐wave‐number region, at and near the hydrodynamic coincidence, and the low‐wave‐number region, at and near the modal wave number. Modes in a cylindrical shell can be classified as primarily radial (or flexural), longitudinal (or membrane), or circumferential (or torsional); only the radial modal components are responsible for the coupling with the pressure field. For some unstiffened cylindrical shells (an infinite shell or finite shells with radial constraint at the boundary), these modes are elastically uncoupled. This paper compares the wave‐number sensitivity of an unstiffened shell and that of a rib‐stiffened shell that is calculated from the finite‐element model of the structure. It is found that a circular rib stiffener may cause an elastic coupling between the flexural and membrane modes. This elastic coupling tends to increase the low‐wave‐number sensitivities of the modes that are predominantly flexural and the high‐wave‐number sensitivities of the modes that are predominantly membrane. [Work supported by ONR.]
Return to All Sections
Close

Home Publications Meetings Contact ASA Site Map Back to Top

Copyright © Acoustical Society of America

close