Multiple Model Adaptive Dynamic Positioning

This paper describes a procedure to design multiple model adaptive controllers for Dynamic Positioning (DP) of ships and offshore rigs subjected to the influence of sea waves, currents, and wind loads. To this effect, a linear design model is obtained, based on practical assumptions, describing the dynamics of the vessel. Four Linear Quadratic Gaussian (LQG) DP controllers (with the same structure) are designed, covering the different sea conditions from calm to extreme seas. Tools from multiple model adaptive control (MMAC) theory are used to exploit the information provided by the different observers (models) in order to select the appropriate controller. Numerical simulations carried out using a high fidelity nonlinear DP simulator illustrate the efficiency of the MMAC techniques proposed. To bridge the gap between theory and practice, the results of the simulations were experimentally verified by model testing with a DP operated ship, the Cybership III, under different simulated sea conditions in a towing tank equipped with a hydraulic wave maker.