A tree search algorithm for uncertainty-considered consecutive discharging and loading operations between ship and offshore platform

Abstract

This paper presents a combinatorial optimization problem for consecutive discharging and loading operations on a floating cargo-handling platform which is a new maritime technology for liquified natural gas redistribution. Because the discharging and loading process involves complex operations with stochastic and sequential nature, a Markov decision process model is formulated for the problem description with the objective of minimizing the ship turnaround time. Then, a tabu-based tree search algorithm allowing a look-ahead at future states is developed. Two sets of practical rules are proposed to control the local tree structure in terms of depth and breadth. The ship stability is also considered. A comprehensive analysis is conducted to determine the most suitable operation strategy for a specific platform design, followed by the analyses of the impacts of strategy parameters, ship size, operation uncertainties. The results show that a customized strategy that considers the dual-cycling operation outperforms other strategies.