MODELLING AND CONTROL FOR DYNAMIC POSITIONED VESSELS IN LEVEL ICE

The aim of this paper is to propose a mathematical model for simulating the behaviour of a dynamic positioned (DP) vessel operating in level ice. The process of ice-vessel interaction is assumed to be a sequence of breaking events of the ice plate. Each breaking event is a cycle of crushing and bending. The form of the edge of the broken ice floe due to bending is assumed to be circular. The ice load due to bending, submersion, and velocity dependence is constant and is calculated from the ice resistance. The simulated ice load will be validated and compared to the empirical ice resistance. Based on the level ice model, a new output feedback controller for DP will be proposed. Furthermore, a supervisory switching mechanism is proposed to cope with the in-and-out of ice regime scenario. The proposed controller is validated through the simulations which showed that the proposed controller performed better in level ice than the conventional one for open water. The study confirms the importance of the ice-load model for DP control design.