Identification of nonlinear ship motion using perturbation techniques

Abstract

This thesis presents an identification scheme for the dynamic model of a ship at sea. We determine the form of the governing differential equations for a ship which is free to pitch and roll, but constrained in all other degrees of freedom, using a perturbation-energy technique. This technique approximates energy expressions and applies Lagrange's equations for quazi-coordinates to develop the equations of motion. When formulating the energies, we take advantage of the ship's symmetry to reduce the number of terms. The equations of motions are approximated such that they contain quadratic and cubic nonlinear terms. Having the form of the governing equations, we set up the parametric identification procedure. Using the method of multiple scales, we exploit resonances and obtain expressions containing subsets of the parameters to be identified. Then we outline a scheme which uses these expressions in conjunction with experimental data to identify the ship parameters.