Two-Stage Optimization on Vessel Routing and Hybrid Energy Output for Marine Debris Collection

The harm of marine debris (MD) to the environment and human beings has been paid more and more attention. At present, the most effective way to collect macro-MD floating on the sea is to send vessels. We employ vessels equipped with a hybrid energy system (HES) composed of photovoltaic (PV), battery and diesel to carry out MD cleanup. We propose a two-stage optimization approach for vessel routing and energy management strategy. In the first stage, the vessel routing problem with a drifting time window is modeled to minimize the vessel travel time considering continuous speed. The drifting time window means that multiple time windows are set on the MD trajectory, which is used to depict its dynamic nature. An adaptive large neighborhood search algorithm considering an elitist strategy coupled with speed optimization is designed to solve this problem. In the second stage, a mixed integer linear programming model for energy management strategy is established to minimize the total cost, including the power generation cost of diesel and PV, the battery charge, and discharge and carbon tax costs. The model takes the power load balance, the power limit of each part of the hybrid energy system and the battery charge and discharge state as constraints. The correctness of the proposed models and the effectiveness of the proposed algorithm are verified by a numerical example. The results not only show the advantages of hybrid energy vessels in energy saving and emission reduction but also show that the drifting time window can provide a rich and effective route selection solution. Some suggestions for rational utilization of hybrid energy vessels with long and short trips are put forward.