Optimizing fuel consumption in thrust allocation for marine dynamic positioning systems

In offshore maritime operations, automated systems capable to maintain the vessel’s position and heading using its own propellers and thrusters to compensate exogenous disturbances, like wind, waves and currents, are referred to as Marine Dynamic Positioning (DP) Systems. DP systems play a central role in assuring the mission of the vessels, such as for drilling, pipe-laying, coring, and ocean observation operations. At the same time, vessels operations are the primary cause of fuel consumption, having a strong impact on the overall footprint of the vessel. For this reason, in this paper, we will face the problem of optimising the propellers thrust allocation, namely determining
thrust and direction of each propeller and thruster in an overactuated vessel, to maintain its position and heading, while minimising the fuel consumption. State of the art approaches simplify this problem by roughly approximating it and obtain a simple, mostly convex, optimisation problem. This allows to solve
it in near-real time allowing its exploitation on-board during operation by simply integrating it in the automation system. In this paper, we deal with the problem of improving the current approaches with a twofold contribution. On one hand, we will exploit a detailed modelling approach of the physical system,
resulting in an high fidelity representation of the optimisation problem. On the other hand, we will study and manipulate the resulting optimisation problem in such a way that it is still possible to solve it in near-real time on conventional on-board computing platform. Authors will leverage on a Platform Supply
Vessel, equipped with 6 thrusters, as case study to evaluate the quality of the proposal. Results will show that, leveraging on the proposed approach, it is possible to achieve up to 5% of fuel savings with respect to conventional approaches.