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Scheduling Problem (scheduling + problem)
Kinds of Scheduling Problem Selected AbstractsEconomic Lot Scheduling Problem with ReturnsPRODUCTION AND OPERATIONS MANAGEMENT, Issue 4 2006Ou Tang Motivated by a case study of a company that produces car parts, we study the multi-product economic lot scheduling problem for a hybrid production line with manufacturing of new products and remanufacturing of returned products. For this economic lot scheduling problem with returns (ELSPR), we consider policies with a common cycle time for all products, and with one manufacturing lot and one remanufacturing lot for each product during a cycle. For a given cycle time, the problem is formulated as a mixed integer linear programming (MIP) problem, which provides the basis for an exact solution. The application of this model for one of the core products of the case study company indicates a 16% reduction in cost compared to the current lot scheduling policy. [source] Out-of-Core and Dynamic Programming for Data Distribution on a Volume Visualization ClusterCOMPUTER GRAPHICS FORUM, Issue 1 2009S. Frank I.3.2 [Computer Graphics]: Distributed/network graphics; C.2.4 [Distributed Systems]: Distributed applications Abstract Ray directed volume-rendering algorithms are well suited for parallel implementation in a distributed cluster environment. For distributed ray casting, the scene must be partitioned between nodes for good load balancing, and a strict view-dependent priority order is required for image composition. In this paper, we define the load balanced network distribution (LBND) problem and map it to the NP-complete precedence constrained job-shop scheduling problem. We introduce a kd-tree solution and a dynamic programming solution. To process a massive data set, either a parallel or an out-of-core approach is required. Parallel preprocessing is performed by render nodes on data, which are allocated using a static data structure. Volumetric data sets often contain a large portion of voxels that will never be rendered, or empty space. Parallel preprocessing fails to take advantage of this. Our slab-projection slice, introduced in this paper, tracks empty space across consecutive slices of data to reduce the amount of data distributed and rendered. It is used to facilitate out-of-core bricking and kd-tree partitioning. Load balancing using each of our approaches is compared with traditional methods using several segmented regions of the Visible Korean data set. [source] Scheduling time-critical requests for multiple data objects in on-demand broadcastCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 15 2010Victor C. S. Lee Abstract On-demand broadcast is an effective data dissemination approach in mobile computing environments. Most of the recent studies on on-demand data broadcast assume that clients request only a single-data-object at a time. This assumption may not be practical for the increasingly sophisticated mobile applications. In this paper, we investigate the scheduling problem of time-critical requests for multiple data objects in on-demand broadcast environments and observe that existing scheduling algorithms designed for single-data-object requests perform unsatisfactorily in this new setting. Based on our analysis, we propose new algorithms to improve the system performance. Copyright © 2010 John Wiley & Sons, Ltd. [source] Using parallelization and hardware concurrency to improve the performance of a genetic algorithmCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 4 2007Vijay Tirumalai Abstract Genetic algorithms (GAs) are powerful tools for solving many problems requiring the search of a solution space having both local and global optima. The main drawback for GAs is the long execution time normally required for convergence to a solution. This paper discusses three different techniques that can be applied to GAs to improve overall execution time. A serial software implementation of a GA designed to solve a task scheduling problem is used as the basis for this research. The execution time of this implementation is then improved by exploiting the natural parallelism present in the algorithm using a multiprocessor. Additional performance improvements are provided by implementing the original serial software GA in dedicated reconfigurable hardware using a pipelined architecture. Finally, an advanced hardware implementation is presented in which both pipelining and duplicated hardware modules are used to provide additional concurrency leading to further performance improvements. Copyright © 2006 John Wiley & Sons, Ltd. [source] Robust Resource Allocation Decisions in Resource-Constrained Projects,DECISION SCIENCES, Issue 1 2007Filip Deblaere ABSTRACT The well-known deterministic resource-constrained project scheduling problem involves the determination of a predictive schedule (baseline schedule or pre-schedule) of the project activities that satisfies the finish,start precedence relations and the renewable resource constraints under the objective of minimizing the project duration. This baseline schedule serves as a baseline for the execution of the project. During execution, however, the project can be subject to several types of disruptions that may disturb the baseline schedule. Management must then rely on a reactive scheduling procedure for revising or reoptimizing the baseline schedule. The objective of our research is to develop procedures for allocating resources to the activities of a given baseline schedule in order to maximize its stability in the presence of activity duration variability. We propose three integer programming,based heuristics and one constructive procedure for resource allocation. We derive lower bounds for schedule stability and report on computational results obtained on a set of benchmark problems. [source] Conception of self-construction production scheduling systemELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 1 2010Hai Xue Abstract With the high speed innovation of information technology, many production scheduling systems have been developed. However, a lot of customization according to individual production environment is required, and then a large investment for development and maintenance is indispensable. Therefore now the direction to construct scheduling systems should be changed. The final objective of this research aims at developing a system which is built by it extracting the scheduling technique automatically through the daily production scheduling work, so that an investment will be reduced. This extraction mechanism should be applied for various production processes for interoperability. Using the master information extracted by the system, production scheduling operators can be supported to accelerate the production scheduling work easily and accurately without any restriction of scheduling operations. By installing this extraction mechanism, it is easy to introduce a scheduling system without a lot of expense for customization. In this paper, first a model for expressing a scheduling problem is proposed. Then the guideline to extract the scheduling information and use the extracted information is shown and some applied functions are also proposed based on it. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 93(1): 19,29, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10188 [source] Solving resource constrained multiple project scheduling problems by random key-based genetic algorithmELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 8 2009Ikutaro Okada Abstract In this paper, we propose a hybrid genetic algorithm with fuzzy logic controller (flc-rkGA) to solve the resource-constrained multiple project scheduling problem (rc-mPSP) which is well known as an NP-hard problem and the objective in this paper is to minimize total complete time in the project. It is difficult to treat the rc-mPSP problems with traditional optimization techniques. The new approach proposed is based on the hybrid genetic algorithm (flc-rkGA) with fuzzy logic controller (FLC) and random-key encoding. For these rc-mPSP problems, we demonstrate that the proposed flc-rkGA to solve the rc-mPSP problem yields better results than several heuristic genetic algorithms presented in the computation result. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(8): 25,35, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10101 [source] A heterogeneous computing system for data mining workflows in multi-agent environmentsEXPERT SYSTEMS, Issue 5 2006Ping Luo Abstract: The computing-intensive data mining (DM) process calls for the support of a heterogeneous computing system, which consists of multiple computers with different configurations connected by a high-speed large-area network for increased computational power and resources. The DM process can be described as a multi-phase pipeline process, and in each phase there could be many optional methods. This makes the workflow for DM very complex and it can be modeled only by a directed acyclic graph (DAG). A heterogeneous computing system needs an effective and efficient scheduling framework, which orchestrates all the computing hardware to perform multiple competitive DM workflows. Motivated by the need for a practical solution of the scheduling problem for the DM workflow, this paper proposes a dynamic DAG scheduling algorithm according to the characteristics of an execution time estimation model for DM jobs. Based on an approximate estimation of job execution time, this algorithm first maps DM jobs to machines in a decentralized and diligent (defined in this paper) manner. Then the performance of this initial mapping can be improved through job migrations when necessary. The scheduling heuristic used considers the factors of both the minimal completion time criterion and the critical path in a DAG. We implement this system in an established multi-agent system environment, in which the reuse of existing DM algorithms is achieved by encapsulating them into agents. The system evaluation and its usage in oil well logging analysis are also discussed. [source] A case of rule-based heuristics for scheduling hot rolling seamless steel tube productionEXPERT SYSTEMS, Issue 3 2006Jianxiang Li Abstract: A production scheduling problem for hot rolling seamless steel tube at Tianjin Pipe Corporation of China is studied. Considering the complexity of the problem and the acceptable time for solving it, a rule-based heuristic approach is proposed and implemented. The proposed approach is a bottleneck scheduling method and considers simultaneously all production processes in three production units and ,optimizes' them as a whole. Additionally, the running result shows, on average, that a 3% increase in throughput and a 5% reduction in late deliveries have been achieved since the system implementation. [source] Flexible flow shop scheduling: optimum, heuristics and artificial intelligence solutionsEXPERT SYSTEMS, Issue 2 2005Hong Wang Abstract: For the past three decades or so the flexible flow shop (FFS) scheduling problem has attracted many researchers. Numerous research articles have been published on this topic. This study reviews research on the FFS scheduling problem from the past and the present. The solution approaches reviewed range from the optimum to heuristics and to artificial intelligence search techniques. I not only discuss the details from the selected methods and compare them, but also provide insights and suggestions for future research. [source] An intelligent logistics support system for enhancing the airfreight forwarding businessEXPERT SYSTEMS, Issue 5 2004H.C.W. Lau Abstract: Recent research related to the aircraft container loading and scheduling problem for airfreight forwarding business has seen significant advances in terms of load plan optimization, taking into account the cost and volume of packed boxes. In today's competitive industrial environment, it is essential that freight forwarders are able to collaborate with carriers (airline companies) to achieve the best possible selection of logistics workflow. However, study of contemporary research publications indicates that there is a dearth of articles related to the design and implementation of an intelligent logistics system to support decision-making on carrier selection, aircraft container loading plans as well as carrier benchmarking. This paper presents an intelligent logistics support system (ILSS) which is able to provide expert advice related to the airfreight forwarding business, enhancing the logistics operations in relevant activities within the value chain of tasks. ILSS comprises a heuristics-based intelligent expert system which supports carrier searching and cargo trading planning as well as load plan generation. The proposed approach is meant to enhance various operations in the airfreight forwarding business, adopting computational intelligence technologies such as rule-based reasoning to provide domain advice and heuristics to support the generation of load plans. After potential outcomes are generated by the heuristics-based intelligent expert system, a neural network engine is applied to support prediction of unexpected events. To validate the viability of this approach, a production system using the ILSS has been developed and subsequently applied in an emulated airfreight forwarding environment. The application results indicate that the operation time from searching for potential carriers to the execution of the order is greatly reduced. In this paper, details related to the structure, design and implementation of the ILSS are also covered with the inclusion of the actual program codes for building the prototype. [source] Human and machine effects in a just-in-time scheduling problemHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 4 2009Tamer Eren In this article, single-machine scheduling problems with learning effects of setup and removal times and deterioration effects of processing time are considered. The objective function of the problem is minimization of the weighted sum of total earliness and total tardiness. To get an exact solution to the problem, a mathematical programming model is proposed. Also the model is tested on an example. To the best of our knowledge, no work exists in the literature that considers the problem presented in this article. © 2009 Wiley Periodicals, Inc. [source] A personal perspective on problem solving by general purpose solversINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 3 2010Toshihide Ibaraki Abstract To solve the problems that abound in real-world applications, we are proposing an approach of using general-purpose solvers, as we cannot afford to develop special-purpose algorithms for all individual problems. The existing general-purpose solvers such as linear programming and integer programming are very useful but not sufficient. To improve the situation, we have developed solvers for other standard problems such as the constraint satisfaction problem and the resource-constrained project scheduling problem among others. In this article, we describe why general-purpose solvers are needed, what kinds of solvers we considered, how they were developed and where they have been applied. [source] Tight bounds for the identical parallel machine scheduling problemINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 6 2006Mohamed Haouari Abstract We address the problem of minimizing makespan on identical parallel machines. We propose new lower bounding strategies and heuristics for this fundamental scheduling problem. The lower bounds are based on the so-called lifting procedure. In addition, two optimization-based heuristics are proposed. These heuristics require iteratively solving a subset-sum problem. We present the results of computational experiments that provide strong evidence that the new proposed lower and upper bounds consistently outperform the best bounds from the literature. [source] A solution approach for log truck scheduling based on composite pricing and branch and boundINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 5 2003Myrna Palmgren Abstract The logging truck scheduling problem is one of the most complex routing problems where both pick-up and delivery operations are included. It consists in finding one feasible route for each vehicle in order to satisfy the demands of the customers and in such a way that the total transport cost is minimized. We use a mathematical formulation of the log truck scheduling problem where each column represents a feasible route. We generate a large pool of columns based on solving a transportation problem. Then we apply a composite pricing algorithm, which mainly consists of pricing the pool of columns and maintain an active set of these, for solving the LP relaxed model. A branch and price approach is used to obtain integer solutions in which we apply composite pricing to generate new columns. Numerical results from case studies at Swedish forestry companies are presented. [source] Constructing nurse schedules at large hospitalsINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 3 2003Tiago M. Dias Several heuristics, based on evolutive algorithms and local search, are used to solve the nurse scheduling problem at a large hospital. Due to several intricate and specific restrictions imposed on the schedules, the problem is a difficult one to solve by hand. Moreover, some of the restrictions have a subjective value attached to them, and this constrains the use of exact methods that search for global optima. In order to facilitate the use of the solver modules by the hospital staff, a user interface was also implemented. [source] Minimizing Total Tardiness: A Case Study in an Autoparts FactoryINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 4 2002Leandro Kiyuzato The application of heuristic procedures for solving a real scheduling problem that arises in an autoparts factory is reported in this paper. Due to the characteristics of the environment, the measure of performance considered is the minimization of the total tardiness of the jobs. The original problem is reduced to the single machine scheduling problem, and the dispatching rules EDD (earliest due date), SPT (shortest processing time), and the PSK algorithm are used to obtain approximate solutions. Computational tests and a comparison with the usual schedule are presented. [source] Scheduling Part-Families Under FMS: To Mix or Not to Mix?INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 2 2001Henry C. Co This paper considers the issue of whether to mix part-types in one or several of the families to be produced in a flexible manufacturing system (FMS). For this input control problem in an FMS, we have derived conditions that support the mixing of a part-type, which can share the setup of other part-types, in deterministic environment. The problem is identified as a special economic lot scheduling problem (ELSP), and is formulated as a linear programming problem. Analytical insights are derived by considering the special case with three part-families. The results are illustrated with a numerical example. [source] A travelling salesman problem with allocation, time window and precedence constraints , an application to ship schedulingINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 3 2000K. Fagerholt Abstract A Travelling Salesman Problem with Allocation, Time Window and Precedence Constraints (TSP-ATWPC) is considered. The TSP-ATWPC occurs as a subproblem of optimally sequencing a given set of port visits in a real bulk ship scheduling problem, which is a combined multi-ship pickup and delivery problem with time windows and multi-allocation problem. Each ship in the fleet is equipped with a flexible cargo hold that can be partitioned into several smaller holds in a given number of ways, thus allowing multiple products to be carried simultaneously by the same ship. The allocation constraints of the TSP-ATWPC ensure that the partition of the ship's flexible cargo hold and the allocation of cargoes to the smaller holds are feasible throughout the visiting sequence. The TSP-ATWPC is solved as a shortest path problem on a graph whose nodes are the states representing the set of nodes in the path, the last visited node and the accumulated cargo allocation. The arcs of the graph represent transitions from one state to another. The algorithm is a forward dynamic programming algorithm. A number of domination and elimination tests are introduced to reduce the state space. The computational results show that the proposed algorithm for the TSP-ATWPC works, and optimal solutions are obtained to the real ship scheduling problem. [source] Learning scheduling control knowledge through reinforcementsINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 2 2000K. Miyashita Abstract This paper introduces a method of learning search control knowledge in schedule optimization problems through application of reinforcement learning. Reinforcement learning is an effective approach for the problem faced by the agent that learns its behavior through trial-and-error interactions with a dynamic environment. Nevertheless, reinforcement learning has a difficulty of slow convergence when applied to the problems with a large state space. The paper discusses the case-based function approximation technique, which makes reinforcement learning applicable to the large scale problems such as a job-shop scheduling problem. To show effectiveness of the approach, reinforcement learning is applied to acquire search control knowledge in repair-based schedule optimization process. Preliminary experiment results show that repair-action selection made by learned search control knowledge succeeded in improving scheduling quality efficiently. [source] An experimental analysis of decision channeling by restrictive information displayJOURNAL OF BEHAVIORAL DECISION MAKING, Issue 5 2002Manouchehr TabatabaeiArticle first published online: 15 OCT 200 Abstract This study focuses on the effect of restrictive information display on decision performance. Specifically the study examines whether two-channeled and one non-channeled computerized information display systems result in significant differences in decision accuracy. The two-channeled information display systems are designed to encourage two general information processing patterns commonly observed in the experimental literature examining multi-alternative, multi-attribute choice decisions: information processing by alternative and information processing by attribute. An information display program was developed which used restrictive information display to operationalize the channeled versus non-channeled manipulation. Channeling was implemented either by displaying information only by alternative or by displaying information only by attribute. The task was an operations scheduling problem that subjects completed under three levels of time pressure. The results indicate statistically significant effects on decision accuracy for both the type of information display and time pressure manipulations. The highest decision accuracy was observed when information was displayed by alternative and when subjects were under highest levels of time pressure. Copyright © 2002 John Wiley & Sons, Ltd. [source] Scheduling dispensing and counting in secondary pharmaceutical manufacturingAICHE JOURNAL, Issue 5 2009Michele Ciavotta Abstract In this article, we describe a general methodology for operations scheduling in dispensing and counting departments of pharmaceutical manufacturing plants. The departments are modeled as a multiobjective parallel machines scheduling problem under a number of both standard and realistic constraints, such as release times, due dates and deadlines, particular sequence-dependent setup times, machine unavailabilities, and maximum campaign size. Main characteristics of the methodology are the modularity of the solution algorithms, the adaptability to different objectives and constraints to fulfill production requirements, the easiness of implementation, and the ability of incorporating human experience in the scheduling algorithms. Computational experience carried out on two case studies from a real pharmaceutical plant shows the effectiveness of this approach. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Capacitated lot-sizing and scheduling with parallel machines, back-orders, and setup carry-overNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2009Daniel Quadt Abstract We address the capacitated lot-sizing and scheduling problem with setup times, setup carry-over, back-orders, and parallel machines as it appears in a semiconductor assembly facility. The problem can be formulated as an extension of the capacitated lot-sizing problem with linked lot-sizes (CLSPL). We present a mixed integer (MIP) formulation of the problem and a new solution procedure. The solution procedure is based on a novel "aggregate model," which uses integer instead of binary variables. The model is embedded in a period-by-period heuristic and is solved to optimality or near-optimality in each iteration using standard procedures (CPLEX). A subsequent scheduling routine loads and sequences the products on the parallel machines. Six variants of the heuristic are presented and tested in an extensive computational study. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 2009 [source] A branch-and-cut algorithm for the quay crane scheduling problem in a container terminalNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2006Luigi Moccia Abstract The quay crane scheduling problem consists of determining a sequence of unloading and loading movements for cranes assigned to a vessel in order to minimize the vessel completion time as well as the crane idle times. Idle times originate from interferences between cranes since these roll on the same rails and a minimum safety distance must be maintained between them. The productivity of container terminals is often measured in terms of the time necessary to load and unload vessels by quay cranes, which are the most important and expensive equipment used in ports. We formulate the quay crane scheduling problem as a vehicle routing problem with side constraints, including precedence relationships between vertices. For small size instances our formulation can be solved by CPLEX. For larger ones we have developed a branch-and-cut algorithm incorporating several families of valid inequalities, which exploit the precedence constraints between vertices. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2006 [source] Analysis of algorithms for two-stage flowshops with multi-processor task flexibilityNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2004George L. Vairaktarakis Abstract In this article we introduce a 2-machine flowshop with processing flexibility. Two processing modes are available for each task: namely, processing by the designated processor, and processing simultaneously by both processors. The objective studied is makespan minimization. This production environment is encountered in repetitive manufacturing shops equipped with processors that have the flexibility to execute orders either individually or in coordination. In the latter case, the product designer exploits processing synergies between two processors so as to execute a particular task much faster than a dedicated processor. This type of flowshop environment is also encountered in labor-intensive assembly lines where products moving downstream can be processed either in the designated assembly stations or by pulling together the work teams of adjacent stations. This scheduling problem requires determining the mode of operation of each task, and the subsequent scheduling that preserves the flowshop constraints. We show that the problem is ordinary NP-complete and obtain an optimal solution using a dynamic programming algorithm with considerable computational requirements for medium and large problems. Then, we present a number of dynamic programming relaxations and analyze their worst-case error performance. Finally, we present a polynomial time heuristic with worst-case error performance comparable to that of the dynamic programming relaxations. © 2003 Wiley Periodicals, Inc. Naval Research Logistics, 2004. [source] Scheduling of depalletizing and truck loading operations in a food distribution systemNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 3 2003Zhi-Long Chen Abstract This paper studies a scheduling problem arising in a beef distribution system where pallets of various types of beef products in the warehouse are first depalletized and then individual cases are loaded via conveyors to the trucks which deliver beef products to various customers. Given each customer's demand for each type of beef, the problem is to find a depalletizing and truck loading schedule that fills all the demands at a minimum total cost. We first show that the general problem where there are multiple trucks and each truck covers multiple customers is strongly NP-hard. Then we propose polynomial-time algorithms for the case where there are multiple trucks, each covering only one customer, and the case where there is only one truck covering multiple customers. We also develop an optimal dynamic programming algorithm and a heuristic for solving the general problem. By comparing to the optimal solutions generated by the dynamic programming algorithm, the heuristic is shown to be capable of generating near optimal solutions quickly. © 2003 Wiley Periodicals, Inc. Naval Research Logistics, 2003 [source] Using Lagrangean relaxation to minimize the weighted number of late jobs on a single machineNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 3 2003Stéphane Dauzère-Pérès This paper tackles the general single machine scheduling problem, where jobs have different release and due dates and the objective is to minimize the weighted number of late jobs. The notion of master sequence is first introduced, i.e., a sequence that contains at least an optimal sequence of jobs on time. This master sequence is used to derive an original mixed-integer linear programming formulation. By relaxing some constraints, a Lagrangean relaxation algorithm is designed which gives both lower and upper bounds. The special case where jobs have equal weights is analyzed. Computational results are presented and, although the duality gap becomes larger with the number of jobs, it is possible to solve problems of more than 100 jobs. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 50: 2003 [source] Minimizing weighted earliness and tardiness penalties in single-machine scheduling with idle time permittedNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 8 2002Jaw-Yeh Chen Abstract In this paper, a single-machine scheduling problem with weighted earliness and tardiness penalties is considered. Idle time between two adjacent jobs is permitted and due dates of jobs could be unequal. The dominance rules are utilized to develop a relationship matrix, which allows a branch-and-bound algorithm to eliminate a high percentage of infeasible solutions. After combining this matrix with a branching strategy, a procedure to solve the problem is proposed. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 760,780, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10039 [source] Robust ship scheduling with multiple time windowsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2002Marielle Christiansen We present a ship scheduling problem concerned with the pickup and delivery of bulk cargoes within given time windows. As the ports are closed for service at night and during weekends, the wide time windows can be regarded as multiple time windows. Another issue is that the loading/discharging times of cargoes may take several days. This means that a ship will stay idle much of the time in port, and the total time at port will depend on the ship's arrival time. Ship scheduling is associated with uncertainty due to bad weather at sea and unpredictable service times in ports. Our objective is to make robust schedules that are less likely to result in ships staying idle in ports during the weekend, and impose penalty costs for arrivals at risky times (i.e., close to weekends). A set partitioning approach is proposed to solve the problem. The columns correspond to feasible ship schedules that are found a priori. They are generated taking the uncertainty and multiple time windows into account. The computational results show that we can increase the robustness of the schedules at the sacrifice of increased transportation costs. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 611,625, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10033 [source] An integer programming model for the weekly tour scheduling problemNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2001Tolga Çezik Abstract We study a workforce planning and scheduling problem in which weekly tours of agents must be designed. Our motivation for this study comes from a call center application where agents serve customers in response to incoming phone calls. Similar to many other applications in the services industry, the demand for service in call centers varies significantly within a day and among days of the week. In our model, a weekly tour of an agent consists of five daily shifts and two days off, where daily shifts within a tour may be different from each other. The starting times of any two consecutive shifts, however, may not differ by more than a specified bound. Furthermore, a tour must also satisfy constraints regarding the days off, for example, it may be required that one of the days off is on a weekend day. The objective is to determine a collection of weekly tours that satisfy the demand for agents' services, while minimizing the total labor cost of the workforce. We describe an integer programming model where a weekly tour is obtained by combining seven daily shift scheduling models and days-off constraints in a network flow framework. The model is flexible and can accommodate different daily models with varying levels of detail. It readily handles different days-off rules and constraints regarding start time differentials in consecutive days. Computational results are also presented. © 2001 John Wiley & Sons, Inc. Naval Research Logistics 48: 607,624, 2001. [source] | ||||||||||||||||||||||