ABSTRACT

The paper addresses the problem of thrusters interactions and thrusters identification for the purpose of dynamic positioning (DP) operations and DP capability prognosis. Carried out analyses are based on numerical and experimental methods. The computations show satisfactory compliance with the experimental results and indicate which thrusters orientations are most favorable in DP operations in terms of efficiency. The presented research results improve the understanding the mechanism contributing to thrust losses. This, in turn enables one to carry out more accurate DP performance predictions which result in more efficient DP operations. As a continuation of the study, application of the identified thrusters and thrusters interactions models to the DP simulator can show the actual effect of the determined models.

INTRODUCTION

For few decades now the offshore industry is developing extensively. First, the direction was development of sourcing nonrenewable energy (oil). Today, on the contrary, the aim is to increase the share of renewable energy in the global market. Thus, one of activities towards this goal is development of wind and wave power plants at sea. A variety of ship types is utilized to maintain those offshore structures. The ships dedicated to this task are equipped with the dynamic positioning (DP) system which enables operations at fixed position and heading.

One of the components of the DP system is Thrust Allocation (TA). TA requires optimization as the DP system is usually over actuated. The input data to the TA have a crucial impact on the vessel response and efficiency. Typically, fuel consumption and wear and tear of the thrusts are used to construct the objective functions of the optimizing TA algorithm. The thruster models and thrust losses due to hull-thruster and thruster-thruster interactions greatly impact the DP performance as they dictate the thruster orientation (avoidance of selected regions) and lower the thrust nominal capacity. The thrust is a direct extortion on the hull therefore, an accurate model of the thrusters and losses can make a significant difference to the thrust allocation hence also station keeping.

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