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TECHNICAL PAPERS

Simulating and Measuring Structural Intensity Fields in Plates Induced by Spatially and Temporally Random Excitation

[+] Author and Article Information
Michael J. Daley

Akustica, Inc., 2403 Sidney St, Suite 270, Pittsburgh, PA 15203mdaley@akustica.com

Stephen A. Hambric1

Applied Research Laboratory, The Pennsylvania State University, PO Box 30, State College, PA 16804sah@wt.arl.psu.edu

$m$ denotes the mode order along the length of the plate (11.2 cm) and $n$ the mode order along the width (7.5 cm), where the mode order indicates the number of antinodes, or peaks, in the mode shape.

The resonance frequencies of the 12th and 15th modes could not be reliably extracted from the measurements, and are therefore not included in the figure.

1

Corresponding author.

J. Vib. Acoust 127(5), 451-457 (Jan 06, 2005) (7 pages) doi:10.1115/1.2013299 History: Received August 11, 2004; Revised January 06, 2005

Abstract

The structure-borne power in bending waves is well understood, and has been studied by many investigators in ideal beam and plate structures. All studies to date, however, have considered only the structural intensity induced by deterministic, localized drives. Since many structures of practical interest are excited by spatially random pressure fields, such as diffuse and turbulent boundary layer pressure fluctuations, techniques for measuring and predicting the structural intensity patterns in flat plates excited by such fields are presented here. The structural intensity at various frequencies in a simply supported, baffled, flat plate driven by a diffuse pressure field is simulated using analytical techniques and measured by post-processing data from a scanning laser Doppler vibrometer and reference accelerometer using finite differencing techniques. The measured and simulated fields are similar, and show intensity patterns different from those caused by deterministic point drives. Specifically, no clear source regions are apparent in the randomly driven intensity fields, although the energy flow patterns do clearly converge toward a point damper attached to the plate.

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Figures

Figure 4

Diagram of plate—dimensions in centimeters

Figure 5

Photograph of plate, clamped to its massive brass base frame

Figure 6

Modeled and measured natural frequencies of simply supported plate

Figure 7

Measured operating deflection shape of plate at (3,1) natural frequency

Figure 8

Schematic of Point Damper

Figure 1

Free body diagram of differential element of plate

Figure 2

Diagram of response array used for 13 point finite differencing scheme. S-I vector is computed at center point (point 2).

Figure 3

Schematic diagram of system used for simulations

Figure 10

Schematic diagram of measurement setup

Figure 11

Simulated and measured velocity spectra; mode orders for which S-I fields are computed are annotated

Figure 12

Predicted S-I field at (2,1) resonance frequency

Figure 13

Measured S-I field at (2,1) resonance frequency

Figure 14

Predicted S-I field at (3,1) resonance frequency

Figure 15

Measured S-I field at (3,1) resonance frequency

Figure 16

Predicted S-I field at (2,3) resonance frequency

Figure 17

Measured S-I field at (2,3) resonance frequency

Figure 9

Measured and theoretical spatial correlation functions for diffuse acoustic field at the (3,1) resonance frequency of the plate

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