摘要:

We develop a method for quoting manufacturing due dates to achieve a target service level (percent of orders filled on-time). We posit a very general function for determining leadtimes as a function of work in process and use a control chart method for adjusting the parameters in this function over time. We make almost no assumptions about the nature of the underlying production system (i.e., we do not require any particular distribution of process times, nor do we require that the system be in steady state). Using simulation we show that our method is very accurate for a simple case where an exact analytic solution is possible and that it outperforms other due date quoting methods from the literature in more complex situations.

ISSN:0740-817X    

DOI:10.1080/07408170008967437

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We consider a manufacturing system where the quality of the end product is uncertain and is graded into one of several quality levels after production. We assume stochastic demand for each quality level, stochastic production times, and random quality yields. We also assume downward substitutability (i.e., customers who require a given product will be satisfied by a higher quality product at the same price). The firm produces to stock and has the option to refuse satisfying customers even when it has items in stock. We formulate this problem as a Markov Decision Process in the context of a simple M/M/l make-to-stock queue with multiple customer classes to gain insight into the following questions: (i) how does the firm decide when to produce more units (i.e., what is the optimal production policy?) and (ii) how does the firm decide when to accept/reject orders and when to satisfy customers demanding lower quality products using higher quality products? In the case of two product classes, we completely characterize the structure of the optimal production and acceptance/substitution policies. However, the structure of the optimal policy is complicated and we therefore develop a simple heuristic policy for any number of classes which performs very well. We finally extend our heuristic to the system where production occurs in batches of size of larger than one, the system where there is a setup cost for initiating production, and the case where processing time distribution is Erlang.

ISSN:0740-817X    

DOI:10.1080/07408170008967438

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We study an assembly system, in which each end product consists of two different components. The components are produced in batches, with possible defective units. The proportion of defective units in each batch is itself a random variable, known only in terms of its distribution. Defective units can be identified and corrected through an inspection-repair procedure, before final assembly taking place. We are concerned with developing an optimal inspection policy that minimizes the total expected cost due to inspection, repair, and warranty. Particularly, we focus on policies that have simple threshold structures and a near-optimal performance.

ISSN:0740-817X    

DOI:10.1080/07408170008967439

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We treat the scheduling of a single server in a finite-buffer capacity, multi-class, make-to-order production system subject to inventory holding costs, set-up times, and customer rejection costs. We employ theoretical and numerical analysis of a Markov decision process model to investigate the structure of optimal policies and the performance of heuristic policies. We establish the monotonicity of optimal performance with respect to the system parameters. Based on our insights, we provide a heuristic policy called the Capacitated Modified Index Rule (CMIR) for capacitated scheduling with customer loss penalties. The CMIR heuristic can easily be precomputed and stored for real-time control. Numerical benchmarking with respect to the optimal performance as well as an existing heuristic suggests that CMIR is very effective.

ISSN:0740-817X    

DOI:10.1080/07408170008967440

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper demonstrates that an important role of intermediaries in supply chains is to reduce the financial risk faced by retailers. It is well known that risk averse retailers when faced by the classical single-period inventory (newsvendor) problem will order less than the expected value maximizing (newsboy) quantity. We show that in such situations a risk neutral distributor can offer a menu of mutually beneficial contracts to the retailers. We show that a menu can be designed to simultaneously: (i) induce every risk averse retailer to select a unique contract from it; (ii) maximize the distributor's expected profit; and (iii) raise the order quantity of the retailers to the expected value maximizing quantity. Thus inefficiency created due to risk aversion on part of the retailers can be avoided. We also investigate the influence of product/market characteristics on the offered menu of contracts.

ISSN:0740-817X    

DOI:10.1080/07408170008967441

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Scheduling outpatients and medical operation rooms has the following structure:Nusers are given appointment times to use a facility, the duration required by the facility to service each user is stochastic. The system incurs a “user idle cost” if a user arriving at the appointed time finds the facility still engaged by preceding users, while a “facility idle cost” is incurred if the facility becomes free before the next user arrives. We develop an accurate procedure to compute the expected total system costs for any given appointment schedule. Compared to earlier related procedures, ours is much faster and can handle larger problems as well as very general service-time distributions. We then show that this fast computation procedure enables one to determine easily the “lowest-cost appointment schedule” for any given “job” (i.e., “user”) sequence. This in turn will enable one to search for the optimal job sequence that has the best “lowest-cost appointment schedule”.

ISSN:0740-817X    

DOI:10.1080/07408170008967442

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An appointment policy is established for a specific outpatient system, with the goal of reducing a combination of patients' expected waiting times and doctor's expected overtime. Service times are stochastic, and patients are assumed to be punctual if they show for their appointments. Substantial reductions in waiting times can be obtained over traditional scheduling practices, and the procedure is easily implemented by a naive scheduler once the optimal policy is established.

ISSN:0740-817X    

DOI:10.1080/07408170008967443

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper, we model the situation where operator maintenance activities improve the failure process of equipment. We analyze the business decision to reduce both the mean and variance of the production cycle time and the overall inventory level through an investment in planned autonomous maintenance. We answer: (i) when do optimal autonomous maintenance decisions most improve inventory levels?; and (ii) how do capacity restrictions, equipment characteristics the maintenance response function, and product characteristics impact the autonomous maintenance investment decision? Extensive numerical analyses are performed to develop an approximation to the optimal response for both inventory and autonomous maintenance investments over a wide range of problem parameters. Our solutions provide guidelines on how much time should be invested in autonomous maintenance activities and describe when companies can most benefit from autonomous maintenance programs that increase equipment reliability. We determine the investment in autonomous maintenance activities as a function of available capacity, equipment reliability and demand characteristics.

ISSN:0740-817X    

DOI:10.1080/07408170008967444

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Aviation safety analysis is increasingly needed in regulating air traffic and safety, in light of the rapid growth in air traffic density. With the recent advances in computer technology, large amounts of multivariate aviation safety data are now routinely collected in databases. Many existing analysis methods prescribed in those databases and corresponding safety indictors are based on classical statistical analysis, and their applicability are considerably restricted by the requirement of normality. An alternative nonparametric methodology based ondata depthis pursued in this paper. For a given multivariate sample, a data depth can be used to measure their depth or outlyingness with respect to the underlying distribution. The measure of depth leads to a center-outward ordering of the sample points. Derived from this ordering, Liu (1995) introduced a simple, yet effective, control chart for monitoring multivariate observations. The control chart is combined here with properly chosen false alarm rates to develop meaningful threshold systems for multivariate aviation safety data for both regulating and monitoring purposes. The developed procedure is applied to the aviation inspection results collected by the Federal Aviation Administration (FAA) inspection system. The threshold system serves as a standard for evaluating the performance of aircraft operators, and provides clear guidelines for identifyingunexpectedperformances and for assigning appropriate corrective actions.

ISSN:0740-817X    

DOI:10.1080/07408170008967445

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper addresses resource sharing in a multiclass service center. The flow of service requests from each class of customers are regulated by a class manager who attempts to maximize the class net benefit (throughput reward less delay cost). Relaxed asynchronous algorithms are proposed for obtaining a Nash equilibrium among these competing classes in which each manager iteratively updates his throughput strategy in response to local (and possibly delayed) information on the strategies of the others. The novelty of these flow-control algorithms are in the relaxation, whereby each manager employs a strategy update that is a convex combination of his previous strategy and his best-reply strategy to current information. Alternatively, this relaxation can be viewed as an exponential smoothing of all previous best-reply strategies. For a particular number of classes with specified cost/ reward parameters, relaxation conditions for asymptotic convergence to the unique interior Nash equilibrium are presented. For more than two classes, it is shown that relaxation not only accelerates convergence (at least in a special case), but also is a necessary condition for convergence. Due to an equivalent functional form, these results can be directly translated to a network of users employing a power criterion, a common objective in the communications literature.

ISSN:0740-817X    

DOI:10.1080/07408170008967446

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor