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TECHNICAL PAPERS

Nonlinear Roll Damping of Ship Motions in Waves

[+] Author and Article Information
Xiaorong Wu

School of Engineering,  Griffith University, Gold Coast, QLD 9726, Australia

Longbin Tao1

School of Engineering,  Griffith University, Gold Coast, QLD 9726, AustraliaL.Tao@griffith.edu.au

Yuanlin Li

Department of Naval Architecture & Ocean Engineering,  South China University of Technology, China

The exciting moment by wind is ignored in this study.

1

Address all correspondence to this author.

J. Offshore Mech. Arct. Eng 127(3), 205-211 (Mar 24, 2005) (7 pages) doi:10.1115/1.1951780 History: Received November 10, 2003; Revised March 11, 2005; Accepted March 24, 2005

Nonlinear roll damping has a profound influence on ship motions and stability in ocean waves. In this study, an experimental investigation is conducted on the nonlinear roll damping of a ship in regular and irregular waves. The random decrement method, previously used in linear roll damping prediction, is extended to nonlinear roll damping estimation in the data process. The accuracy of the nonlinear roll damping obtained by using the random decrement method is found to be dependent on the values of the threshold and segment number.

Copyright © 2005 by American Society of Mechanical Engineers
Topics: Motion , Waves , Damping , Ships
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References

Figures

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Figure 1

(a) Time record of roll motion in irregular waves. (b) Decay curve obtained from a rolling time record

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Figure 2

Procedure of a roll damping analysis of a model ship

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Figure 3

The sketch of experimental setup

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Figure 4

Time history of ship roll motion in regular waves

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Figure 5

Roll decay curve in regular waves

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Figure 6

Roll time record in irregular waves

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Figure 7

Roll decay curves in irregular waves

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Figure 8

Roll decay curves for different values of threshold (m=120)

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Figure 9

Roll decay curves for a different number of segments (rd=20)

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Figure 10

A comparison of roll decay curves with and without a negative value of threshold

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Figure 11

Roll decay curves of the model ship in calm water and in regular waves

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Figure 12

Nonlinear roll damping moments in calm water and in regular waves

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Figure 13

A comparison of the curves of extinction in calm water and in irregular Waves (θm represents the mean value of the roll angels in the two consecutive roll Period)

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Figure 14

The values of roll damping processed using a different number of segments at rd=20

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Figure 15

Nonlinear roll damping moments in irregular waves with different thresholds at m=120

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Figure 16

The values of roll damping processed by different thresholds at m=120

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