Composite particle algorithm for sustainable integrated dynamic ship routing and scheduling optimization

Ship routing and scheduling problem is considered to meet the demand for various products in multiple ports within the planning horizon. The ports have restricted operating time, so multiple time windows are taken into account. The problem addresses the operational measures such as speed optimisation and slow steaming for reducing carbon emission. A Mixed Integer Non-Linear Programming (MINLP) model is presented and it includes the issues pertaining to multiple time horizons, sustainability aspects and varying demand and supply at various ports. The formulation incorporates several real time constraints addressing the multiple time window, varying supply and demand, carbon emission, etc. that conceive a way to represent several complicating scenarios experienced in maritime transportation. Owing to the inherent complexity, such a problem is considered to be NP-Hard in nature and for solutions an effective meta-heuristics named Particle Swarm Optimization-Composite Particle (PSO-CP) is employed. Results obtained from PSO-CP are compared using PSO (Particle Swarm Optimization) and GA (Genetic Algorithm) to prove its superiority. Addition of sustainability constraints leads to a 4–10% variation in the total cost. Results suggest that the carbon emission, fuel cost and fuel consumption constraints can be comfortably added to the mathematical model for encapsulating the sustainability dimensions

Optimizing the inventorying and distribution of chemical fluids: An innovative nested column generation approach

Vendor-managed-inventory is a successful business practices based on the cooperation between a supplier and its customers in which demand and inventory information from the customers are shared with the supplier. This practice is gaining popularity in the chemical industry and relies on the inventory-routing-problem, which integrates inventory management, vehicle routing, and delivery scheduling decisions. This one is a difficult combinatorial optimization problem both theoretically and practically. However, because of the large expenses involved in distribution and inventorying of chemical products, it is attractive to make use of optimization tools for exploiting as many degrees of freedom as possible with the goal of minimizing both distribution and inventorying costs. Consequently, we propose a nested column generation algorithm for solving an inventorying and distribution problem that models the delivery of several chemicals fluids. The approach is building on a column generation & incomplete branch-and-price algorithm in which for each delivery route, the delivery patterns of fluids are also determined by column generation. We detail the implementation and provide computational results for realistic test instances.Fil: Coccola, Mariana Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Mendez, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Dondo, Rodolfo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Modelos de otimização para a distribuição de combustíveis em curta distância marítima

Doutoramento em Matemática e AplicaçõesO transporte marítimo e o principal meio de transporte de mercadorias em todo o mundo. Combustíveis e produtos petrolíferos representam grande parte das mercadorias transportadas por via marítima. Sendo Cabo Verde um arquipelago o transporte por mar desempenha um papel de grande relevância na economia do país. Consideramos o problema da distribuicao de combustíveis em Cabo Verde, onde uma companhia e responsavel por coordenar a distribuicao de produtos petrolíferos com a gestão dos respetivos níveis armazenados em cada porto, de modo a satisfazer a procura dos varios produtos. O objetivo consiste em determinar políticas de distribuicão de combustíveis que minimizam o custo total de distribuiçao (transporte e operacões) enquanto os n íveis de armazenamento sao mantidos nos n íveis desejados. Por conveniencia, de acordo com o planeamento temporal, o prob¬lema e divido em dois sub-problemas interligados. Um de curto prazo e outro de medio prazo. Para o problema de curto prazo sao discutidos modelos matemáticos de programacao inteira mista, que consideram simultaneamente uma medicao temporal cont ínua e uma discreta de modo a modelar multiplas janelas temporais e taxas de consumo que variam diariamente. Os modelos sao fortalecidos com a inclusão de desigualdades validas. O problema e então resolvido usando um "software" comercial. Para o problema de medio prazo sao inicialmente discutidos e comparados varios modelos de programacao inteira mista para um horizonte temporal curto assumindo agora uma taxa de consumo constante, e sao introduzidas novas desigualdades validas. Com base no modelo escolhido sao compara¬das estrategias heurísticas que combinam três heur ísticas bem conhecidas: "Rolling Horizon", "Feasibility Pump" e "Local Branching", de modo a gerar boas soluçoes admissíveis para planeamentos com horizontes temporais de varios meses. Finalmente, de modo a lidar com situaçoes imprevistas, mas impor¬tantes no transporte marítimo, como as mas condicões meteorológicas e congestionamento dos portos, apresentamos um modelo estocastico para um problema de curto prazo, onde os tempos de viagens e os tempos de espera nos portos sao aleatórios. O problema e formulado como um modelo em duas etapas, onde na primeira etapa sao tomadas as decisões relativas as rotas do navio e quantidades a carregar e descarregar e na segunda etapa (designada por sub-problema) sao consideradas as decisoes (com recurso) relativas ao escalonamento das operacões. O problema e resolvido por um metodo de decomposto que usa um algoritmo eficiente para separar as desigualdades violadas no sub-problema.Maritime transportation is a major mode of transportation of goods worldwide. Most of cargo of the maritime transport accounted for liquid cargo oil and petroleum products. As Cape Verde is an archipelago, maritime transportation is of great importance for the local economic activity. We consider a fuel oil distribution problem where an oil company is responsible for the coordination of the distribution of oil products with the inventory management of those products at ports in order to satisfy the demands for the several oil products. The objective is to determine distribution policies that minimize the routing and operating costs, while inventory levels are maintained within given limits. For convenience, the planning problem is divided into two related subproblems accordingly to the length of the planning horizon: A short- term and medium-term planning. For the short-term planning problem we discuss mathematical mixed integer programming models that combine continuous and discrete time measures in order to handle with multiple time windows and a daily varying consumption rate of the various oil products. These models are strengthened with valid inequalities. Then the problem is solved using a commercial software. For the second subproblem several mixed integer formulations are discussed and compared for a short time horizon, and assuming constant consumption rates and new valid inequalities are introduced. Then, based on the chosen model, we compare several heuristic strategies that combine the well-known Rolling Horizon, Feasibility Pump and Local Branching heuristics, in or¬der to derive good feasible solutions for planning horizons of several months. Finally, as weather conditions and ports congestion are very impor¬tant in maritime transportation, we present a stochastic model for a short sea shipping problem, where traveling and waiting time are random. The problem is formulated as a two stage recourse problem, where in the first stage the routing and the load/unload quantities are defined, and in the second stage (subproblem) the scheduling of operations is determined. The problem is solved by a decomposition method that uses an efficient separation algorithm to include inequalities from the subproblem

Inventory routing problem with stochastic demand and lead time

In the supply chain, the integration of the different processes is critical to obtain high levels of coordination. Inventory control and its distribution are two of these processes whose coordination have been demonstrated by researchers as key in order to gain efficiency and effectiveness. They affect the synchronization of the supply chain management. With the intention to contribute to the integration of these processes and improve the problems of demand variability, we propose an integration of operations research area and the help of metaheuristics in a multi-objective approach. The expected results are to reduce the costs associated with inventory and its distribution, as well as to reduce the uncertainty in making decisions based on demand. This thesis presents methods for obtaining and analyzing near optimally solutions for dynamic and stochastic inventory-routing problems. The methods include retailers selection and clustering methods, algorithms and experiments on benchmark instances. We focus on problems with one and several suppliers that serve several dispersal geographically retailers. The thesis contains four parts. In Part I, we focus on the literature review. We first provide an overview of the literature on problems related to the coordination of the inventory and its distribution. Then we make a point in four elements: information management, inventory policies, stochastic demand and optimization methods. Also, we provide a scientometric analysis of the documentation collected in the last ten years. We provide a thorough review of papers working with dynamic and stochastic demand. The contributions of this part are i) the review of papers working with stochastic demand and stochastic lead times focusing on its stochastic and multi-depot aspects, ii) identify critical factors for the performance of many logistics activities and industries, iii) have shown that studying the behavior of the demand and the lead time are essential in order to achieve a useful representation of the system to take proper decisions and iv) provide the trends and patterns in the research in IRP problems. In Part II, we focus on the methodology of the research and of development. We first introduce the problem, state of the science, the gaps in the literature, variables under study, the instruments applied and assumptions. The development methodology is presented by a general model to address this type of research proposed in this thesis. Here, the general development process, decomposition of the problem and how the possible solutions are explained.. The importance of the this chapter is provided an effective way to face IRP problems. In Part III, the foundations in formulations for IRP problems are proposed. We begin with the formulation of the TSP problems with variants for one and many suppliers, likewise for VRP and IRP problems. The contributions of the model presented here aim identifying the variables and mathematical models frequently used to deal with these problems. In Part IV, we perform a single criteria objective and multi-criteria analysis of the solutions for one and many suppliers instances. Our methods yield significant improvements over a competing algorithm. Our contributions are i) propose three new customer selection methods for a dynamic and stochastic inventory-routing vii problem, ii) perform a multi-criteria analysis of the solutions, comparing distribution versus inventory management, iii) perform a single criteria objective experiment on benchmark instances from the literature.En la cadena de suministro, la integración de los diferentes procesos que la conforman, es fundamental para obtener altos niveles de coordinación. El control del inventario y su distribución son dos de estos procesos, cuya coordinación ha sido demostrada por los investigadores como clave para lograr mejoras en eficiencia y efectividad. Estos a su vez, afectan la sincronización y la administración de la cadena de suministro. Con el propósito de contribuir en la integración de éstos procesos y mejorar los problemas derivados de la variabilidad de la demanda, se propone usar los fundamentos del área de investigación de operaciones y la ayuda de metaheurísticas en un enfoque multi-obejtivo. Los resultados esperados son reducir los costos asociados a los procesos de inventario y distribución, así como también reducir la incertidumbre en la toma de decisiones a partir de la demanda. Ésta tesis presenta métodos para el análisis y obtención de soluciones cercanas a las óptimas para problemas de inventario y routeo, dinámico y estocástico. Los métodos incluyen selección de retailers y métodos de clustering, algoritmos y experimentos en instancias de prueba disponibles en la literatura. Se hace énfasis en instancias de un solo proveedor y varios proveedores que sirven varios retailers distribuidos geográficamente. La tesis está organizada en cuatro partes. En la Parte I, se revisa la literatura, para ello, primero se presentan los problemas relacionados con la coordinación del inventario y su distribución. Ésta revisión resalta cuatro elementos que han sido identificados como claves en la literatura como son: la administración de la información, políticas de inventario, demanda estocástica y métodos de optimización. Luego, se presenta un análisis cienciometrico de la literatura encontrada en los últimos 10 años. La revisión de la documentación se realiza de manera exhaustiva trabajando con demanda dinámica y estocástica. Las contribuciones de esta parte son: i) proporcionar una revisión pertinente y actualizada de artículos que emplean demanda estocástica, enfatizando en sus elementos dinámicos y estocásticos, así como también en aspectos que permitan abordar problemas con múltiples depósitos, ii) identificar factores críticos para el desempeño de actividades logísticas, iii) Demostrar que el estudio de la demanda es esencial para lograr una representación útil del sistema, la cual influye en la toma de decisiones y iv) proporcionar tendencias y patrones en la investigación de problemas de IRP. En la Parte II se aborda la metodología de la investigación y de desarrollo. Primero, se presenta el problema, el estado de la ciencia y los gaps encontrados en la literatura. Luego se identifican las variables de estudio, los instrumentos aplicados y los supuestos utilizados. La metodología de desarrollo es presentada por medio de un modelo general para abordar éste tipo de investigaciones que nosotros proponemos en ésta tesis. Esta metodología aborda aspectos como: el procedimiento general de desarrollo, la descomposición del problema y la forma en que se prueban las posibles soluciones. En la Parte III, se presentan los fundamentos en la formulación de IRP. Primero se formulan los problemas TSP con variantes para un solo depósito y también paramúltiples depósitos, igualmente se hace para VRP e IRP. La contribución de los modelos presentados son la identificación de las variables y los modelos matemáticos que frecuentemente son usados para tratar con éste tipo de problemas. En la Parte IV se presentan dos experimentos. El primero para el análisis de instancias con uno sólo depósito y en el segundo para analizar instancias con múltiples depósitos. Los métodos usados producen mejoras sobre resultados obtanidos con algoritmos similares. Las contribuciones de ésta parte son: i) proponer tres nuevos métodos para la selección de retailers para IRP dinámicos y estocásticos, ii) realizar análisis multi-criterio de las soluciones, comparando la distribución con la administración del inventario y iii) realizar análisis de un solo objetivo sobre instancias de pruebas proporcionada por la literatura existente

Long‐term effects of short planning horizons for inventory routing problems

This paper presents a detailed study concerning the importance of the planning horizon when solving inventory routing problems (IRPs). We evaluate the quality of decisions obtained by solving a finite-horizon IRP. We also discuss the relevance of explicitly considering profit maximization models rather than the traditional cost minimization variant. As a means to this end, we describe four classes of the IRP corresponding to different types of markets. Two of them lead to nonlinear models, which are linearized. Furthermore, we provide a deterministic simulator to evaluate the long-term effects arising from using planning horizons of varying lengths when solving the IRP. A computational study is performed on cases generated from benchmark data instances. The results confirm that the long-term performance of the IRP decisions is, in part, contingent on the length of the selected planning horizon. They also show that considering profit maximization instead of cost minimization leads to different decisions, generating considerably more revenue and profits, albeit not nearly as much as suggested by individual solutions to static IRPs with short planning horizons. Keywords: profit maximization, path flow, linearization, end effect, simulationpublishedVersio

Discrete time and continuous time formulations for a short sea inventory routing problem

We consider a fuel oil distribution problem where an oil company is responsible for the routing and scheduling of ships between ports such that the demand for various fuel oil products is satisfied during the planning horizon. The production/consumption rates are given and assumed to be constant. We provide two alternative mixed integer formulations: a discrete time model adapted from the case where the production/consumption rates are varying and a classical continuous time formulation. We discuss different extended formulations and valid inequalities that allow us to reduce the linear gap of the two initial formulations. A computational study comparing the various models accordingly to their size, linear gap and running time, was conducted based on real small-size instances, using a commercial software

An operational model for liquefied natural gas spot and arbitrage sales

As more buyers become interested in the spot purchase of liquefied natural gas (LNG), the share of spot trade in LNG business increases. This means that the cash flowing into the upstream of LNG projects is a combination of that generated by deliveries to long-term contract (LTC) customers and uncommitted product and arbitrage spot sales. LTC cash flows are more predictable while uncommitted product and arbitrage cash flows, affected by the dynamics of supply and demand, are more volatile and therefore less predictable. In this research, we formulate an inventory routing problem (IRP) which maximizes the profit of an LNG producer with respect to uncommitted product and arbitrage spot sales, and also LTC deliveries at an operational level. Using the model, the importance of arbitrage, interest rates and compounding frequency in profit maximization, and also the significance of interest rates and fluctuation in spot prices in decision-making for spot sales of uncommitted product are studied. It is proven that writing traditional LTCs with relaxed destination clauses which assist in arbitrage is beneficial to the LNG producer. However, in contrast to what was predicted neither the interest rate nor the compounding frequency has any importance in profit maximization when no change of selling strategy is observed. Apart from these, it is shown that there is a trade-off between the expectation of higher spot prices and the inventory and shipping costs in decision-making for spot sales of uncommitted product in the LNG industry. Finally, it is observed that the interest rate can affect the set of decisions on spot sales of uncommitted product, although the importance of such changes in profit remains to be further explored