This paper studies a storage yard management problem in a transshipment hub where the loading and unloading activities are both heavy and concentrated. In order to reduce the number of reshuffles, which helps to reduc...
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This paper studies a storage yard management problem in a transshipment hub where the loading and unloading activities are both heavy and concentrated. In order to reduce the number of reshuffles, which helps to reduce the vessel turnaround time, the port operator uses the consignment strategy to group export and transshipment containers according to their destination vessel. To reduce the potential traffic congestion of prime movers, a high-low workload balancing protocol is used. A mixedintegerprogramming model is formulated to determine the storage locations of incoming containers, the number of incoming containers and the smallest number of yard cranes to deploy in each shift. An iterative improvement method is developed to solve the problem, in which a tabu search based heuristic algorithm is used to generate an initial yard template, and then the generated yard template is improved by an improvement algorithm iteratively until an optimal or a satisfactory solution is obtained. Experiment results show that the proposed method can generate excellent results within a reasonable time, even for the extreme cases.
Today's competitive and volatile market requires flexibility, quality and efficiency front the logistics operations, In this context, warehouses are ail important link of the logistic chain and warehouse managemen...
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ISBN:
(纸本)9781424422883
Today's competitive and volatile market requires flexibility, quality and efficiency front the logistics operations, In this context, warehouses are ail important link of the logistic chain and warehouse management plays ail important role over customer's service. Throughout this work we analyze a mathematical model aiming to support warehouse management decisions. A ease study is used for that purpose and the model jointly identifies product allocation to the functional areas in the warehouse, as v, ell as the size of each area. This case study also evaluates file performance of the model when real data is used. Model is solved using LINGO 9.0 mixed-integer commercial solver, and potential savings achieved using tire proposed technique are discussed.
This paper presents a mixed-integer optimization approach to the yearly hydrothermal scheduling problem. The proposed method is applied to a hydrothermal system comprising 29 thermal units and 13 hydroplants, includin...
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ISBN:
(纸本)9781424417438
This paper presents a mixed-integer optimization approach to the yearly hydrothermal scheduling problem. The proposed method is applied to a hydrothermal system comprising 29 thermal units and 13 hydroplants, including 2 pumped storage plants, similar to the Greek Power System. The generation scheduling model is based on an hourly load curve. Perfect competition assumption is adopted and an thermal generators are assumed to bid their marginal cost. A large mixed-integer programming problem is formulated and implemented in GAMS. Binary variables represent thermal unit hourly commitment status. Results on an hourly basis, including thermal unit commitment and dispatch, hydroplant generation and pumping and system marginal price are presented.
This article deals with the optimal short-term scheduling of single stage batch plants with sequence-dependent changeovers together with the optimal selection of the number of batches to produce. The novelty of the ar...
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This article deals with the optimal short-term scheduling of single stage batch plants with sequence-dependent changeovers together with the optimal selection of the number of batches to produce. The novelty of the article is that instead of following the traditional approach of considering one processing task per batch, all batches of the product are now aggregated into a single task. integer variables that hold the number of batches to produce are used to characterize these aggregated tasks. Two conceptually different continuous-time models are proposed. They rely on either multiple time grids or global precedence sequencing variables for event representation and generate a mixedinteger linear program. The new formulations are compared to a traditional resource-task network multiple time grid approach as well as to a recent bounding model with immediate precedence sequencing variables. The results for several example problems show the new multiple time grid formulation as the best overall performer. When compared to the traditional approach, one order of magnitude savings in computational effort are achieved due to the need of fewer event points to get to the global optimal solutions. (C) 2007 American Institute of Chemical Engineers.
We present an approach for the design, evaluation and implementation of remanufacturing processes in a given facility. Based on the description of the market situation and involved actors, a planning method is derived...
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ISBN:
(纸本)9781424422722
We present an approach for the design, evaluation and implementation of remanufacturing processes in a given facility. Based on the description of the market situation and involved actors, a planning method is derived. Data acquisition procedures for product, process and facility are described. Two mixedinteger programs are developed;the first one optimizes the remanufacturing process and evaluates its economic viability and the second sequences the remanufacturing tasks. Additionally, the paper describes the technical implementation into a software and the exemplary application on the product category Flat Screen Monitors.
This paper presents an integer-linear programming approach for a cell formation problem (CFP) in a dynamic environment with a multi-period planning horizon. The objectives are to minimize the inter-cell movement and m...
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This paper presents an integer-linear programming approach for a cell formation problem (CFP) in a dynamic environment with a multi-period planning horizon. The objectives are to minimize the inter-cell movement and machine costs simultaneously. In dynamic environments, the product mix and demand are different but deterministic in each period. As a consequence, the formed cells in the current period may not be optimal for the next period. Thus, the reconfiguration of cells is required. Reconfiguration consists of re-forming part families, machine groups, and machine relocation. The CFP belongs to the category of NP-hard problems, thus we develop an efficient simulated annealing (SA) method to solve such a problem. The proposed mathematical model is optimally solved and the associated results are compared with the results obtained by the SA run. The results show that the gap between optimal and SA solutions is less than 4%, which indicates the efficiency of the developed SA scheme.
This paper addresses the problem of identification of hybrid dynamical systems, by focusing the attention on hinging hyperplanes and Wiener piecewise affine autoregressive exogenous models, in which the regressor spac...
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This paper addresses the problem of identification of hybrid dynamical systems, by focusing the attention on hinging hyperplanes and Wiener piecewise affine autoregressive exogenous models, in which the regressor space is partitioned into polyhedra with affine submodels for each polyhedron. In particular, we provide algorithms based on mixed-integer linear or quadratic programming which are guaranteed to converge to a global optimum. For the special case where the estimation data only seldom switches between the different submodels, we also suggest a way of trading off between optimality and complexity by using a change detection approach. (C) 2003 Elsevier Ltd. All rights reserved.
Given rational numbers C-0,...,C-m and b(0),...,b(m), the mixing set with arbitrary capacities is the mixed-integer set defined by conditions s + C(t)z(t) >= b(t), 0 = 0, z(t) integer, 0 <= t <= m. Such a set...
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ISBN:
(纸本)9783540688860
Given rational numbers C-0,...,C-m and b(0),...,b(m), the mixing set with arbitrary capacities is the mixed-integer set defined by conditions s + C(t)z(t) >= b(t), 0 <= t <= m, s >= 0, z(t) integer, 0 <= t <= m. Such a set has applications in lot-sizing problems. We study the special case of divisible capacities, i.e. C-t/Ct-1 is a positive integer for 1 < t <= m. Under this assumption, we give an extended formulation for the convex hull of the above set that uses a quadratic number of variables and constraints.
We study the convex hull of the feasible set of the semi-continuous knapsack problem, in which the variables belong to the union of two intervals. Besides being important in its own right, the semi-continuous knapsack...
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ISBN:
(纸本)3540221131
We study the convex hull of the feasible set of the semi-continuous knapsack problem, in which the variables belong to the union of two intervals. Besides being important in its own right, the semi-continuous knapsack problem is a relaxation of general mixed-integer programming. We show how strong inequalities that are valid for the semi-continuous knapsack polyhedron can be derived and used as cuts in a branch-and-cut scheme for mixed-integer programming anal problems with semi-continuous variables. We present computational results that demonstrate the effectiveness of these inequalities, which we call collectively semi-continuous cuts. Our computational experience also shows that dealing with semi-continuous constraints directly in the branch-and-cut algorithm through a specialized branching scheme and semi-continuous cuts is considerably more practical than the "textbook" approach of modeling semi-continuous constraints through the introduction of auxiliary binary variables in the model.
We present an approach for the design, evaluation and implementation of remanufacturing processes in a given facility. Based on the description of the market situation and involved actors, a planning method is derived...
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ISBN:
(纸本)9781424422722
We present an approach for the design, evaluation and implementation of remanufacturing processes in a given facility. Based on the description of the market situation and involved actors, a planning method is derived. Data acquisition procedures for product, process and facility are described. Two mixedinteger programs are developed;the first one optimizes the remanufacturing process and evaluates its economic viability and the second sequences the remanufacturing tasks. Additionally, the paper describes the technical implementation into a software and the exemplary application on the product category Flat Screen Monitors.
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