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TECHNICAL PAPERS

Structural Acoustic Problems With Absorbent Layers Within Laminated Composite Enclosures

[+] Author and Article Information
Arup Guha Niyogi

Department of Civil Engineering, Jadavpur University, Kolkata, West Bengal, India, PIN-700 032agṉju@yahoo.com

J. Vib. Acoust 128(6), 705-712 (Apr 20, 2006) (8 pages) doi:10.1115/1.2345671 History: Received December 13, 2004; Revised April 20, 2006

Studies on coupled structural acoustic problems within laminated composite enclosures are presented. Isoparametric quadratic boundary element formulation for the acoustic domain is coupled to the structural properties of the enclosure through mobility relations obtained from free vibration finite element analysis of the dry enclosure visualized as a folded plate with first order transverse shear deformation and rotary inertia. Velocity amplitudes and forcing frequency is specified over certain parts of the boundary. The rest is interactive boundary. Absorbent layers at the boundary are accommodated through admittance relation. Results show that impact of absorbent layers is frequency dependent while modifying structural damping has a better prospect.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 5

Vibrating boundary having normal velocity us, with surface acoustic admittance Y

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Figure 8

Acoustic response at the center of the right wall and the center of the domain, obtained by BE analysis for the 8×2×2 mesh in Fig. 7 and a one-dimensional analytical solution

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Figure 9

SPL at the center of the right wall in the rigid enclosure of Fig. 7 with absorbent layer

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Figure 10

SPL at the center of the rigid enclosure in Fig. 7 with absorbent layers

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Figure 11

Detail of the folded plate cavity. (a) A box with four rigid and two flexible walls, and (b) the equivalent flexible folded plate structure.

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Figure 12

(a): SPL at the center of the right wall for a CSA problem involving absorbent layer at (1) left wall only, and (2) left and right wall for 0.001–600.001rad∕s; (b): SPL at the center of the domain for a CSA problem involving absorbent layer at (1) left wall only, and (2) left and right wall for 0.001–600.001rad∕s

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Figure 13

(a): Study of the effect of variation of modal damping ratios on the SPL at the center of the right wall. No absorbents added on walls. (b): Study of the effect of variation of modal damping ratios on the SPL at the center of the acoustic domain. No absorbents added on walls.

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Figure 1

Positive directions of displacement and stress resultants

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Figure 2

(a): Deformation of the plate along a section parallel to the x-z plane; (b): deformation of the plate along a section parallel to the y-z plane

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Figure 3

Global (x′,y′,z′) and local (x,y,z) axes for a typical folded plate finite element

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Figure 4

(a): Transformation of translations from local (x,y,z) axes to global (x′,y′,z′) axes; (b): transformation of rotations from local (x,y,z) axes to global (x′,y′,z′) axes

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Figure 6

Non-dimensionalized acoustic admittance (ρcY) measured with impedance tube (4)

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Figure 7

Geometry of the rigid acoustic container

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