Parametric identification for ship roll motion

Zhang, Yanming (1993) Parametric identification for ship roll motion. Masters thesis, Memorial University of Newfoundland.

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Abstract

This thesis presents a systematic study of the parametric identification and probability description of ship roll motion. A new method for parametric identification using modulating function technique is proposed. The method provides an easier way of solving a wide range of ship roll parametric identification problems including parametric identification from free roll decay data, forced roll data and randomly excited roll data. Another advantage is that it can he used to estimate the parameters of nonlinear damping moment, nonlinear-time-dependent restoring moment and the strength of excitation from measured roll response without necessarily knowing the excitation. This makes the prediction of ship dynamic stability possible because the ship roll parameters can be obtained from only the roll response of a ship. Furthermore, the new method avoids a main source of computational error which results from the numerical differentiation of the measured data which is used by many current parametric identification methods, and therefore it can produce more accurate results. -- The second part of the work deals with the probability description of roll motion. From estimated roll parameters, the joint probability distribution of roll angle and velocity as well as probability distribution of peaks of roll motion are derived using the Markov approximation. -- The method has been validated by applying it to analyse several ship roll data including the following, (1) experimental roll data of four ship models; (2) numerically simulated roll data; (3) measured roll data of a full scale ship at sea. In all the above applications, the proposed method has been found to produce more satisfying results. -- The probability distributions of the roll angle, roll velocity and peaks of roll motion obtained by a numerical approximation also show a good agreement with the relevant histograms of the experimental data. All these results suggest that the proposed method is a successful approach for the ship roll motion study.

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