A Relax-and-Fix Algorithm for a Maritime Inventory Routing Problem.

This work presents a relax-and-fix algorithm for solving a class of single product Maritime Inventory Routing Problem. The problem consists in routing and scheduling a heterogeneous fleet of vessels to supply a set of ports, keeping inventory at production and consumption ports between lower and upper limits. Two sets of constraints are proposed both for tightening the problem relaxation and for obtaining better integer solutions. Four MIP-based local searches to improve the solution provided by the relax-and-fix approach are presented. Computational experiments were carried out on instances of the MIRPLIB, showing that our approach is able to solve most instances in a reasonable amount of time, and to find new best-known solutions for two instances. A new dataset has been created by removing the clustered characteristics of ports from the original instances, and the effectiveness of our method was tested in these more general instances.