عنوان مقاله [English]
Many oil and gas producers operate offshore installations that need regular supplies of commodities from land. Specialized offshore supply vessels are used to bring supplies from onshore supply depots out to offshore installations. To achieve a cost-effective supply service, a good planning of supply vessels is required. The supply vessel planning problem is a maritime transportation
problem consisting of determining the optimal fleet composition of offshore supply vessels and their corresponding weekly voyages and schedules. Traditionally, the vehicle routing problem is a pure delivery or pickup problem. In many practical situations, however, the vehicle is often required to simultaneously drop off and pick up goods at the same stop points. The objective of the problem is to develop a set of routs to service all customers while minimizing total distance travelled. In addition, some constraints, such
as capacity or total durations, must not be violated. In vehicle routing problem with pickup and delivery, customers are divided into two sets. The first set is linehaul customers, each requires pickup goods; the second set consists of customers who require delivery goods. The crucial assumption in this problem is that all delivery customers must be visited before pickup customers. In vehicle routing problem with simultaneous pickup and delivery,all customers' need pickup and delivery goods.
In this study, in order to obtain an optimal supply vessel planning and propose an efficient model, which is well- adapted to the real- life situations, some additional properties, such as simultaneously pickup and delivery, are considered. In addition, an exact method consisting of two phases is presented.