Schedule robustness in the periodic supply vessels planning problem with stochastic demand and travel time

The periodic supply vessel planning problem (PSVPP) consists in determining a periodic schedule and the respective fleet composition for servicing offshore units on a regular basis. One of the challenges for the PSVPP is determining reliable schedules with a good compromise between reliability and cost. This work extends the PSVPP by including stochastic demand and travel time. We also introduce a novel methodology based on a voyage-based model to deal with the schedule robustness. Basically, key statistical parameters related to the routes' demand and execution time are generated. They are used together with a set of probability combinations to incorporate the schedule reliability into the optimization model. Therefore, schedule reliability is an input parameter in the optimization model. The instances used in the study are based on real data from Brazil. A comparison of the new methodology to conventional approaches is presented, and a Monte Carlo simulation is used to evaluate the quality of the solutions. The proposed methodology is able to generate robust schedules at a lower cost compared to the conventional approaches. The proposed methodology might be applied to other stochastic problems, where schedule reliability is a key parameter for the problem.