Control and Simulation of a Thruster-Assisted Moored Offshore Vessel in Sea-ice

Abstract

The exploration of the northern seas is constantly raising new and interesting research topics in order to adapt our technology to handle this extraordinary harsh climate. Darkness, remoteness, cold and harsh weather, and not at least, drifting ice and icebergs, are making the conventional equipment used further south useless. The ice loads are largely different from open water sea loads, while remoteness and the harsh environment makes safety an even more important issue. The Arctic conditions are difficult to recreate due to the inpredictability and large variations in ice features, and going up there with all the needed equipment is particularly expensive. It is possible to create realistic ice features in a model basin, but it takes time and effort compared to open water. This is why a numerical computer simulator is an attractive option. This thesis is investigating the properties of the Numerical Ice Tank (NIT) simulator developed at NTNU in order to implement a high fidelity turret mooring model into it. A finite element based mooring model is implemented and tested in the NIT. Controller strategies for adaption into ice infested areas are discussed and tested in the simulator. A theoretical background on dynamic positioning (DP), position mooring (PM), controller design, arctic conditions and mathematical modelling is pro- vided.