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RESEARCH PAPERS

Identification of Small-Sized Cracks on Cross-Stiffened Plate Structures for Ships

[+] Author and Article Information
A. Budipriyanto, M. R. Haddara

Faculty of Engineering and Applied Sciences, Memorial University, St. John’s, NL, Canada A1B 3X5

A. S. Swamidas

Faculty of Engineering and Applied Sciences, Memorial University, St. John’s, NL, Canada A1B 3X5swamidas@engr.mun.ca

J. Eng. Mater. Technol 128(2), 210-224 (Oct 08, 2005) (15 pages) doi:10.1115/1.2172625 History: Received October 20, 2004; Revised October 08, 2005

Abstract

In this paper we discuss the results of experimental and numerical studies carried out for monitoring the integrity of a $1∕20th$ model of the side shell of a ship’s structure, using its vibration responses. The model was tested for different crack development scenarios under random exciting force having a dominant spectral frequency much lower $(≈2Hz)$ than the first natural frequency of the structure $(≈580Hz)$. Sensor locations were justified based on modal responses under intact and damaged conditions. A damage detection procedure using the root mean square response modal amplitudes is also presented.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

Figure 1

Finite element mesh of the (a) prototype and (b) model

Figure 2

Notation for plate dimensions

Figure 3

The first five natural frequencies of the model and prototype

Figure 4

The first five modes of vibration of the prototype (left) and the model (right)

Figure 5

Location of cracks introduced in the model

Figure 6

Changes in the natural frequencies due to cracks for the first five modes

Figure 7

Node numbering for the transverse web frame and longitudinal of interest

Figure 8

Displacement shapes in the y direction of the longitudinal for crack cases #1 to #4: (a ) Mode 1 (b ) Mode 2 (c ) Mode 5, 엯: intact, ◻: case #1, ◇: case #2, ▵: case #3, +: case #4

Figure 9

Displacement shapes in x-direction of the web frame for crack cases #5 to #8: (a ) Mode 1 (b ) Mode 2 (c ) Mode 5, 엯: intact, ◻: case #5, ◇: case #6, ▵: case #7, +: case #8

Figure 10

Displacement shapes in the z direction of the web frame for crack cases #5 to #8: (a ) Mode 1 (b ) Mode 2 (c ) Mode 5, 엯: intact, ◻: case #1, ◇: case #2, ▵: case #3, +: case #4

Figure 11

Normalized responses of the longitudinal, web frame and side shell plate for damage cases #1 to 4, 엯: intact, ◻: case #1, ◇: case #2, ▵: case#3, +: case #4 (a ) Normalized acceleration responses of the longitudinal. (b ) Normalized acceleration responses of the web frame. (c ) Strain responses at the side shell plate.

Figure 12

Normalized acceleration responses of the longitudinal and web frame for damage cases #5 to #8, 엯: intact, ◻: case #5, ◇: case #6, ▵: case #7, +:case #8 (a ) Normalized acceleration responses of the longitudinal. (b ) Normalized acceleration responses of the transverse web frame.

Figure 13

(a) Accelerometer and (b) strain gauge locations and numbers

Figure 14

Diagram of experimental setup

Figure 15

Identified natural frequencies at different sampling rates (intact case)

Figure 16

Computed and averaged measured natural frequencies from accelerometers (left) and strain gauges (right) for damage cases #1 to #4.

Figure 17

Computed and averaged measured natural frequencies from accelerometers (left) and strain gauges (right) for damage cases #5 to #8.

Figure 18

The damping ratio measured using acceleration and strain responses for cases #1 to #4 for modes 1, 2, and 5.

Figure 19

The damping ratio measured using acceleration and strain responses for cases #5 to #8 for modes 1, 2, and 5

Figure 20

The eij values obtained from accelerometer #1 for modes 1, 2, and 5: (a ) Mode 1, (b ) Mode 2, (c ) Mode 5 (crl—crack location)

Figure 21

Diagnosis for crack size and location using the equivalue eij plots of several acceleration responses for various crack cases

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