Identification of Dynamically Positioned Ships
Thor Inge Fossen, Svein Ivar Sagatun, Asgeir Johan Sorensen · Modeling Identification and Control A Norwegian Research Bulletin · 1996
. Today's model-based dynamic positioning (DP) systems require that the ship and thruster dynamics are known with some accuracy in order to use linear quadratic optimal control theory. However, it is difficult to identify the mathematical model of a dynamically positioned (DP) ship, since the ship is not persistently excited under DP. In addition, the ship parameter-estimation problem is nonlinear and multivariable, with only position and thruster state measurements available for parameter estimation. The process and measurement noise must also be modeled in order to avoid parameter drift due to environmental disturbances and sensor failure. This article discusses an off-line parallel extended Kalman filter (EKF) algorithm utilizing two measurement series in parallel to estimate the parameters in the DP ship model. Full-scale experiments with a supply vessel are used to demonstrate the convergence and robustness of the proposed parameter estimator. Key Words. Dynamic positioning syste...