This study addresses a real-life multiship routing and scheduling application with inventory constraints that arises in pickup and delivery operations of different types of crude oil from various offshore oil rigs (platforms) to coastal terminals. Oil transportation largely results from the need to maintain inventories at each supply point (platform) between minimum and maximum levels, considering production rates in these operational points, and to meet demands of different oils in the terminals within the planning time horizon. Routing and scheduling of the available fleet aims to obtain solutions of minimum total costs, subject to various constraints such as the maximum volume of cargo carried on each ship, simultaneous cargo unloading in some terminals, conditions that rule ship docking in offshore platforms and terminal berths, among others. In this research, we modify and extend inventory constrained maritime routing and scheduling models to appropriately represent the problem of a case study at a Brazilian company and to solve small-to-moderate instances based on real data. We also present a matheuristic to deal with larger problem instances. Solution evaluation by company experts indicates that the model and this hybrid heuristic properly represent the problem and highlights the potential of their application in practice.

This paper proposes a technique for solving the multiobjective environmental/economic dispatch problem using the weighted sum and ε-constraint strategies, which transform the problem into a set of single-objective problems. In the first strategy, the objective function is a weighted sum of the environmental and economic objective functions. The second strategy considers one of the objective functions: in this case, the environmental function, as a problem constraint, bounded above by a constant. A specific predictorcorrector primal-dual interior point method which uses the modified log barrier is proposed for solving the set of singleobjective problems generated by such strategies. The purpose of the modified barrier approach is to solve the problem with relaxation of its original feasible region, enabling the method to be initialized with unfeasible points. The tests involving the proposed solution technique indicate i) the efficiency of the proposed method with respect to the initialization with unfeasible points, and ii) its ability to find a set of efficient solutions for the multiobjective environmental/economic dispatch problem.

No abstract

No abstract

ResumoO presente artigo discute um problema real de roteirização de navios e controle de estoque nos pontos de suprimento (plataformas offshore) e atendimento de demanda nos pontos consumidores (terminais costeiros) presente nas operações de coleta e entrega de diferentes tipos de óleo cru de empresas petrolíferas. O transporte dos produtos é em grande parte o resultado da necessidade de manutenção dos estoques em cada plataforma entre níveis mínimos e máximos. A roteirização e programação da frota visa a obtenção de soluções de mínimo custo variável, e deve considerar diversas restrições operacionais, dentre as quais destaca-se a viabilidade de atracação de navios em portos dos pontos operacionais e descarregamentos simultâneos em terminais com mais de um berço. Neste trabalho, exemplares com dados reais obtidos a partir de um estudo de caso em uma empresa petrolífera nacional, foram resolvidos a partir da implementação de um modelo linear inteiro misto que descreve o problema e por um método heurístico de busca local. Palavras-chave: Problema de roteirização e controle de estoque, transporte marítimo de petróleo, limitação de berços, heurística de busca local. AbstractThis paper discusses a real ship routing problem with inventory control in supply points (offshore platforms) and demand requirements in consumers points (coastal terminals) which appear in pickup and delivery operations of different types of crude oil. The transportation of the products is largely the result of the need to maintain the inventory in each platform between minimum and maximum levels. The routing and scheduling of the fleet aims to obtain minimum variable cost solutions, and should consider several operational constraints, such as the feasibility of docking the vessels at the ports and simultaneous dockings in terminals with more than one berth. In this work, real data examples from a case study in a national oil company, were solved by means of an implementation of a mixed integer linear model that describes the problem and by a local search heuristic.