Journal
JOURNAL OF OCEAN UNIVERSITY OF CHINA
Volume 18, Issue 4, Pages 812-822Publisher
OCEAN UNIV CHINA
DOI: 10.1007/s11802-019-3912-8
Keywords
nonlinear roll damping; parametric identification; nonlinear restoring moment; asymptotic method; linear exponential approximation
Categories
Funding
- National Natural Science Foundation of China [5160 9224]
- Major Program of National Natural Science Foundation of China [51490675]
- Fundamental Research Funds for the Central Universities [201513056]
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Damping is critical for the roll motion response of a ship in waves. A common method for the assessment of damping in a ship's rolling motion is to perform a free-decay experiment in calm water. In this paper, we propose an approach for estimating nonlinear damping that involves a linear exponential analytical approximation of the experimental roll free-decay amplitudes, followed by parametric identification based on the asymptotic method. The restoring moment can be strongly nonlinear. To validate this method, we first analyzed numerically simulated roll free-decay data using rolling equations with two alternative parametric forms: linear-plus-quadratic and linear-plus-cubic damping. By doing so, we obtained accurate estimates of nonlinear damping coefficients, even for large initial roll amplitudes. Then, we applied the proposed method to real free-decay data obtained from a scale model of a bulk barrier, and found the simulated results to be in good agreement with the experimental data. Using only free-decay peak data, the proposed method can be used to estimate nonlinear roll-damping coefficients for conditions with a strongly nonlinear restoring moment and large initial roll amplitudes.
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