Modelling and experimental investigation of icevaning control for arctic offshore vessels

Abstract

This dissertation presents a new control algorithm for the dynamic positioning (DP) system of the Arctic offshore vessels, which introduces the icevaning phenomenon in the Arctic operation, as well as a series of experimental results to evaluate the feasibility of the proposed control algorithm. For the development of the new icevaning control algorithm, a mathematical model for an Arctic offshore vessel is summarized. Moreover, a simple and computationally efficient approach for ice load generation in time-domain analysis based on the concept of the ice load spectrum is introduced. To realize the icevaning action of the Arctic offshore vessels without any measurement and estimation of the ice drifting, a task space and a null space are defined and the control law is formulated in the task space. A backstepping technique is utilized to handle the nonlinearity of the Arctic offshore vessel's dynamic model and the Lyapunov stability theory is applied to evaluate the stability of the proposed control algorithm. In addition, thrust allocation methods under mechanical and operational constraints for the Arctic DP system, which generally exhibits over-actuated characteristics, are introduced. The validity and feasibility of the proposed methods are demonstrated with extensive numerical simulations. Moreover, a series of experimental tests is conducted in the ice tank of the Korea Research Institute of Ships and Ocean Engineering. The practical feasibility of the proposed approaches is examined with the model test results.