摘要:

How should a multi-product manufacturing firm design production facilities? How many facilities should it have? How many and which products should be assigned to each facility? What batch sizes/scheduling rules are appropriate for facilities making more than one product? These are questions that have become more relevant now as advances in manufacturing technologies offer an increasing array of equipment choices. In this article, we introduce models that can help operations managers answer the above questions. For a specific product mix, these models lead to explicit expressions for the number of facilities, the number of products assigned to each facility and their corresponding capacities. We evaluate the effect of different operating parameters and scheduling policies on the optimality of different configurations. In particular, we show that the choice of the scheduling and batch sizing policies can have a significant effect on the nature of the optimal mix of flexible and dedicated facilities as well the size of these facilities.

ISSN:0740-817X    

DOI:10.1080/07408179808966482

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We study the multiple lot sizing problem with interrupted geometric yield distribution. Compared to the binomial and discrete uniform yields, the lot sizing problem with interrupted geometric distribution is less studied. We present results characterizing the behavior of the cost function and optimal lot sizes. These results help us understand the imperfect processes described by the interrupted geometric distribution. We also develop bounds which lead to an efficient numerical procedure with an approximately linear computation time for large problems.

ISSN:0740-817X    

DOI:10.1080/07408179808966483

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Most scheduling literature considers a “one-job-on-one-processor” pattern, which assumes that a processor processes exactly one job at a time. In this paper we consider a new scheduling problem with a “multiple-job-on-one-processor” pattern, where several jobs can be processed by a single processor simultaneously, provided that the total size of the jobs being processed does not exceed the capacity of the processor at any point in time. This problem is motivated by the operation of berth allocation, which is to allocate vessels (jobs) to a berth (processor), where the vessels, if small in dimension, may share the berth with some other vessels for loading/unloading the goods. We consider the problem to minimize the makespan of the schedule. The well-known First-Fit Decreasing heuristic is generalized and applied to several variations of the problem, and the worst-case behavior of the generalized heuristics is studied. Worst-case error bounds are obtained for those models. Computational experiments are conducted to test the heuristics. The results suggest that the heuristics are effective in producing near-optimal solutions.

ISSN:0740-817X    

DOI:10.1080/07408179808966484

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this paper, we consider a class of batching and scheduling problems in the two-machine flowshop where one of the machines is a discrete processor and the other one is a batch processor. The jobs are processed separately on the discrete processor and processed in batches on the batch processor. The processing time of a batch is equal to the total processing time of the jobs contained in it, and the completion time of a job in a batch is defined as the completion time of the batch containing it. A constant setup time is incurred whenever a batch is formed on the batch processor. The problem is to find the optimal batch compositions and the optimal schedule of the batches so that the makespan is minimized. All problems in this class are shown to be NP-complete in the ordinary sense. We also identify some polynomially solvable cases by introducing their corresponding solution methods.

ISSN:0740-817X    

DOI:10.1080/07408179808966485

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper develops a contingent claims model of an optimally controlled production process characterized by financial and operational risks. Financial risk is depicted by the uncertainty in output prices as determined in competitive markets. Operational uncertainty is portrayed through the risk of system failures which we represent by a nonhomogeneous Poisson process. In the analysis, failure propensity is functionally specified by the system's age, rate of production, and system maintenance expenditures. In this environment, the model obtains an optimal production and maintenance policy maximizing the value of the production effort. Determination of the optimal policies results through the application of stochastic control techniques where production and maintenance expenditure rates are taken as adapted real-valued processes. Further extensions of the model include the analysis of an insurance option on failure repairs and the consequent moral hazard implications. We demonstrate that an appropriately established insurance premium must reflect the producer's operating policy in place and the extent to which operating policies may be modified to maintain the same level of operating risk, as in the absence of an insurance option. The framework presented provides insight into key strategic factors that affect the management of process operations, operating flexibility issues and their resulting economic value.

ISSN:0740-817X    

DOI:10.1080/07408179808966486

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this paper the problem of finding efficient orderpicking routes is studied for both conventional warehouses, where pickers have a central depot for picking up and depositing carts and pick lists, and modern warehouses, where orderpicking trucks can pick up and deposit pallets at the head of every aisle without returning to the depot. Such environments can be found in many warehouses where paperless picking is performed from pallet locations with pickers having mobile terminals receiving instructions one by one. In order to find orderpicking routes with a minimal length in both the situations of a central depot or decentralized depositing, we extend the well-known polynomial algorithm of Ratliff and Rosenthal [1] that considered warehouses with a central depot. In practice, the problem is mainly solved by using the so-called S-shape heuristic in which orderpickers move in a S-shape curve along the pick locations. The performance of the new algorithm and the S-shape heuristic are compared in three realistic orderpicking systems: (1) narrow-aisle high-bay pallet warehouse; (2) picking in shelf area with decentralized depositing of picked items; and (3) conventional orderpicking from wide-aisle pallet locations. The new algorithm gives a reduction in travel time per route of between 7 and 34%. It turns out that the reduction in travel time strongly depends on the lay-out and operation of the warehouse.

ISSN:0740-817X    

DOI:10.1080/07408179808966487

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper describes the core algorithm used in an implementation of a scheduler currently being installed in a major Asian railway. It extends previous work on a greedy heuristic for scheduling trains, to provide a powerful and practically useful method that is fast enough for real-time use in many cases. Real-world railway systems have constraints that do not fit easily into a simple mathematical formulation. The algorithm described here makes it straightforward to incorporate many such realistic features.

ISSN:0740-817X    

DOI:10.1080/07408179808966488

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Several recent studies have explored the concurrent deployment of different priority rules at different processing stages of a manufacturing system. This study investigates the same issue by combining three popular simple priority rules with a combinatorial rule. In a three-stage flow shop, these rules are combined into 64 combination schemes and their performance compared under two shop load levels with two due date setting methods. The performance criteria considered are: mean lateness; mean tardiness; maximum tardiness; and per cent of tardy jobs. The results indicate that the rule combinations are a better strategy than their pure forms when various performance measures are jointly evaluated. Particularly, selected combinations of the Modified Shortest Processing Time, Shortest Processing Time, and the Earliest Due Date rules appear to be very effective. While the extent of shop load level shows little impact on the relative performance of the schemes, the endogenous method of due date setting consistently yields better results than the exogenous method.

ISSN:0740-817X    

DOI:10.1080/07408179808966489

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor