Stochastic estimation methods for non-linear ship roll motion

Abstract A method is developed for estimating the parameters in a single-degree-of-freedom non-linear equation of motion, suitable for representing the rolling motion of a ship in an irregular sea. It is assumed that the excitation is unmeasurable but can be modelled as a stochastic process. The estimation technique is thus based on the processing of a record of the roll motion alone. For the purpose of validating the method, it is applied to simulated data corresponding to both white noise and correlated noise inputs. The simulation results enable the accuracy of the estimated result, with respect both to bias and variability, to be assessed in a range of typical cases.