1,029 research outputs found

    Scheduling Ocean Transportation of Crude Oil

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    Management Science, 33, p. 335-346. (Nominated for 1987 International Management Science Achievement Award.)The article of record as published may be found at http://links.jstor.org/sici?sici=0025-1909%28198703%2933%3A3%3C335%3ASOTOCO%3E2.0.CO%3B2-FNominated for 1987 International Management Science Achievement Award.A crude oil tankerscheduling problem faced by a major oil company is presented and solved using an elastic set partitioning model. The model takes into account all fleet cost components, including the opportunity cost of ship time, port and canal charges, and demurrage and bunker fuel. The model determines optimalspeeds for the ships and the best routing of ballast (empty) legs, as well as which cargos to load on controlled ships and which to spot charter. All feasible schedules are generated, the cost of each is accurately determined and the best set of schedules is selected. For the problems encountered, optimal integer solutions to set partitioning problems with thousands of binary variables have been achieved in less than a minute

    A Multiple Ant Colony Metaheuristic for the Air Refueling Tanker Assignment Problem

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    The performance of the Nuclear Facility (NFAC) incident module in modeling a nuclear reactor accident is evaluated. Fallout predictions are compared with air concentration measurements of I-131 in Europe over a five-day period. Two categories of source term specifications are used: NFAC-generated source terms based on plant conditions and accident severity, and user-defined source terms based on specifying the release of I-131. The Atmospheric Transport Model Evaluation Study report source term provided the needed detailed release information. The Air Force Combat Climatology Center provided weather data covering Europe during the release\u27s 11-day duration. For the NFAC-generated source terms as few as 20% and as many as 52% of the values are within the intended accuracy, depending on which source term specification was selected. For the user-defined source terms, values ranged 35% to 56% being within the intended accuracy, again depending on which source term specification was used. Performance improved in all cases for monitoring sites closest to Chernobyl, with up to 87% of the values falling within the intended accuracy. This indicates there may be a limit for selecting the spatial domain, making HPAC more useful as a tool for smaller spatial domains, rather than on a continental scale

    Ship Routing with Pickup and Delivery for a Maritime Oil Transportation System: MIP Modeland Heuristics

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    This paper examines a ship routing problem with pickup and delivery and time windows for maritime oil transportation, motivated by the production and logistics activities of an oil company operating in the Brazilian coast. The transportation costs from offshore platforms to coastal terminals are an important issue in the search for operational excellence in the oil industry, involving operations that demand agile and effective decision support systems. This paper presents an optimization approach to address this problem, based on a mixed integer programming (MIP) model and a novel and exploratory application of two tailor-made MIP heuristics, based on relax-and-fix and time decomposition procedures. The model minimizes fuel costs of a heterogeneous fleet of oil tankers and costs related to freighting contracts. The model also considers company-specific constraints for offshore oil transportation. Computational experiments based on the mathematical models and the related MIP heuristics are presented for a set of real data provided by the company, which confirm the potential of optimization-based methods to find good solutions for problems of moderate sizes

    Bio-Inspired Multi-Agent Technology for Industrial Applications

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    The Developmental Test Scheduling Problem

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    Developmental testing of aircraft systems in the United States Air Force requires a complex set of resources for each test. The optimal scheduling of those resources is the job of the 412th Test Wing at Edwards Air Force Base. With more than 20 different Combined Task Forces requesting resources for roughly 300 flying missions each week, manual scheduling is a difficult task. The current process takes a team of schedulers several days to get a workable result from which they can start tailoring the final schedule. While concepts and techniques can be taken from industry scheduling problems, the body of knowledge as it relates to developmental test scheduling is sparse. The contribution of this paper is to initially document the Developmental Test Scheduling Problem, define it in structured terms for which a solution methodology can be designed, and present an Integer Programming based solution. The design allows for a scheduler to tailor an initial answer to fit nuanced and timely objectives and constraints. For this prototype effort the problem is scoped to the Iron Resources while bearing in mind the extensibility of the approach to Range Resources. This study and prototype will demonstrate results that will create an initial schedule in several hours and serve as a good starting point for the final schedule

    A Combined Adaptive Tabu Search and Set Partitioning Approach for the Crew Scheduling Problem with an Air Tanker Crew Application

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    This research develops the first metaheuristic approach to the complete air crew scheduling problem. It develops the first dynamic, integrated, set-partitioning based vocabulary scheme for metaheuristic search. Since no benchmark flight schedules exist for the tanker crew scheduling problem, this research defines and develops a Javaâ„¢ based flight schedule generator. The robustness of the tabu search algorithms is judged by testing them using designed experiments. An integer program is developed to calculate lower bounds for the tanker crew scheduling problem objectives and to measure the overall quality of solutions produced by the developed algorithms

    Analyzing the Interdiction of Sea-Borne Threats Using Simulation Optimization

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    Worldwide, maritime trade accounts for approximately 80% of all trade by volume and is expected to double in the next twenty years. Prior to September 11, 2001, Ports, Waterways and Coastal Security (PWCS) was afforded only 1 percent of United States Coast Guard (USCG) resources. Today, it accounts for nearly 22 percent of dedicated USCG resources. Tactical assessment of resource requirements and operational limitations on the PWCS mission is necessary for more effective management of USCG assets to meet the broader range of competing missions. This research effort involves the development and validation of a discrete-event simulation model of the at-sea vessel interdiction process utilizing USCG deepwater assets. A discrete-event simulation model of the interdiction, control and boarding, and inspection processes has been developed and validated. Through a simulation optimization approach, our research utilizes the efficiency of a localized search algorithm interfaced with the simulation model to allocate USCG resources in the interception, boarding, and inspection processes with the objective of minimizing overall process time requirements. The model is tested with actual USCG data to gain insight on the development of efficient and effective interdiction operations

    A Capacitated Facility Location Approach for the Tanker Employment Problem

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    Air refueling is conducted to provide rapid response, increased range, and extended airborne operations for bombers, fighters, airlift, command and control, and intelligence, surveillance, and reconnaissance aircraft. The planning and scheduling of limited tanker resources during employment operations is a major concern for Air Mobility Command (AMC). AMC does not currently have a simple tool that runs in a short amount of time to aid in planning operations. The tool developed allows AMC to input several sorties consisting of various aircraft types and armaments. Each sortie contains a base of origin, and is assumed to be attacking or patrolling in an engagement zone defined by the user. The user is also able to specify the locations of military tanker aircraft. The main goal of the tool is to assign the tankers to anchor areas, surrounding the engagement zone so that all receivers can be refueled during their attack operations. Secondary goals include minimizing the number of tankers required (or maximizing the number of receivers supported), and limiting the total flight distance for the tanker aircraft. The TET tool uses the heuristic technique tabu search to determine an assignment of tankers and sorties to anchor areas during employment

    An Adaptive Tabu Search Heuristic for the Location Routing Pickup and Delivery Problem with Time Windows with a Theater Distribution Application

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    The time constrained pickup and delivery problem (PDPTW) is a problem of finding a set of routes for a fleet of vehicles in order to satisfy a set of transportation requests. Each request represents a user-specified pickup and delivery location. The PDPTW may be used to model many problems in logistics and public transportation. The location routing problem (LRP) is an extension of the vehicle routing problem where the solution identifies the optimal location of the depots and provides the vehicle schedules and distribution routes. This dissertation seeks to blend the PDPTW and LRP areas of research and formulate a location scheduling pickup and delivery problem with time windows (LPDPTW) in order to model the theater distribution problem and find excellent solutions. This research utilizes advanced tabu search techniques, including reactive tabu search and group theory applications, to develop a heuristic procedure for solving the LPDPTW. Tabu search is a metaheuristic that performs an intelligent search of the solution space. Group theory provides the structural foundation that supports the efficient search of the neighborhoods and movement through the solution space
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