Nested Column Generation Applied to the Crude Oil Tanker Routing and Scheduling Problem with Split Pickup and Split Delivery

The split pickup split delivery crude oil tanker routing and scheduling problem is a difficult combinatorial optimization problem, both theoretically and practically. However, because of the large expenses in crude oil shipping it is attractive to make use of optimization that exploits as many degrees of freedom as possible to save transportation cost. We propose a nested column generation algorithm for this particular split pickup split delivery problem which bears several complexities such as a heterogeneous fleet, multiple commodities, many-to-many relations for pickup and delivery of each commodity, sequence dependent vehicle capacities, and cargo quantity dependent pickup and delivery times. Our approach builds on a branch-and-price algorithm in which the column generation subproblems are solved by branch-and-price themselves. We describe our implementation in the branch-cut-and-price framework SCIP and give computational results for realistic test instances. The high quality schedules we obtain for these instances improve on those in previous studies. © 2012 Wiley Periodicals, Inc. Naval Research Logistics 59: 298–310, 2012