摘要:

AbstractA simulation of ferry traffic in the Aegean islands, which is being used as a decision aiding system for regional development, is presented. The model has been developed using SIMSCRIPT II.5 and its major variables and parameters, for which data are available, consist of types of vessels, harbour layouts, weather conditions, passenger and vehicle demand, types of vehicles, and loading and unloading times. The model has inbuilt flexibility to consider additional variables and parameters depending on data availability and scenarios to be examined. The graphics interface is based on a chart of the Aegean Islands and the various types of vessels appear as dynamic entities on the screen either moving or queuing outside busy ports. Itineraries are defined through the graphics editor on the basis of coordinates on the chart. It has been used for studying the scenarios to compare many combinations of various types of vessels, various types of harbour layout, differing routes, passenger and vehicle demands, and even the establishing of new ports. It can also be used to aid decision making about non-profit making itineraries which could then qualify for government subsidies.

ISSN:0160-5682    

DOI:10.1057/jors.1996.19

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractIn winter, when roads may become dangerously slippery due to frost, ice or snow, a de-icing agent (usually salt) is spread on them by a local authority for safety reasons. A gritter only needs to travel once down all those roads requiring treatment, as it can spread the salt onto both sides of the carriageway. The problem studied is how to design routes for gritters which will minimise costs. This problem is a type of Capacitated Arc Routeing Problem including consideration of multiple depot locations, limited vehicle capacities, time constraints on when roads must be gritted, roads with different priorities for gritting, the existence of one-way roads and salt-refilling locations. The objective function to be optimised depends on both the total distance travelled and the number and capacity of the gritters. A heuristic algorithm is devised with a computer program which allows user-interaction, and provides a practical tool for planning gritter routes. The model is linked to a GIS containing information on the road network for the County of Lancashire. Test results from the interactive algorithm are found to outperform another existing approach which solves the same problem.

ISSN:0160-5682    

DOI:10.1057/jors.1996.20

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe problem of missing values is common in statistical analysis. One approach to deal with missing values is to delete the incomplete cases from the data set. This approach may disregard valuable information, especially in small samples. An alternative approach is to reconstruct the missing values using the information in the data set. The major purpose of this paper is to investigate how a neural network approach performs compared to statistical techniques for reconstructing missing values. The backpropagation algorithm is used as the learning method to reconstruct missing values. The results of back-propagation are compared with results from two methods, viz., (1) using averages, and (2) using iterative regression analysis, to compute missing values. Experimental results show that backpropagation consistently outperforms other methods in both the training and the test data sets, and suggest that the neural network approach is a useful tool for reconstructing missing values in multivariate analysis.

ISSN:0160-5682    

DOI:10.1057/jors.1996.21

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractA number of pull production systems reported in the literature are found to be equivalent to a tandemqueue so that existing accurate tandem-queue approximation methods can be used to evaluate such systems. In this study, we consider developing an exact performance evaluation model for a non-tandemqueue equivalent pull production system using discrete-time Markov processes. It is a periodically controlled serial production system in which a single-item is processed at each stage with an exponential processing time in order to satisfy the Poisson finished product demand. The selected performance measures are throughput, inventory levels, machine utilizations and service level of the system. For large systems, which are difficult to evaluate exactly because of large state-spaces involved, we also propose a computationally feasible approximate decomposition technique together with some numerical experimentations.

ISSN:0160-5682    

DOI:10.1057/jors.1996.22

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractLot-sizing and scheduling comprises activities that have to be done repeatedly within MRP-systems. We consider the proportional multi-item, capacitated, dynamic lot-sizing and scheduling problem that is more general than the discrete lot-sizing and scheduling problem, as well as the continuous set-up lot-sizing problem. A greedy randomized algorithm with regret-based biased sampling is presented. We partition the parameter space of the stochastic algorithm and choose subspaces via sequential analysis based on hypothesis testing. The new methods provided in this paper, i.e. the randomized-regret-based backward algorithm, as well as the controlled search via sequential analysis, have three important properties: they are simple, effective and rather general. Computational results are also presented.

ISSN:0160-5682    

DOI:10.1057/jors.1996.23

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThis paper presents a newly developed hierarchical control model for several PERT type projects being realized simultaneously. The model has two objectives: to minimize the number of control points for an on-line control at the project level, and to maximize the probability that the slowest project can meet its due date on time (company level). On-line control is carried out separately for each project in order to minimize the number of control points subject to a chance constraint, which seeks to prevent deviation from the planned trajectory. If at the control point it is anticipated that the project will not be on target subject to the chance constraint, then an emergency is called. Under emergency conditions the company level is faced with the stochastic problem of budget reassigning among the projects enabling the faster projects to help the slower ones. A numerical example is presented.

ISSN:0160-5682    

DOI:10.1057/jors.1996.24

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractA repairable-item provisioning system with two levels of repair is presented. Under the assumption that the machine time-to-failure and the repair times are exponentially distributed, a new algorithm is developed to compute the long-run average number of machines operating. Using the new algorithm we determine the optimal number of machines and repair channels at the two repair centres to minimize cost and meet a service-level constraint. The algorithm, which is based on Little's result in queueing theory and the theory of regenerative processes, is extremely efficient in terms of computer storage and execution time.

ISSN:0160-5682    

DOI:10.1057/jors.1996.25

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractWe look at a conference scheduling problem with the objective of maximizing the ability of participants to attend sessions of interest. This problem was addressed in an article by Eglese and Rand; conference scheduling has otherwise received little attention in management science literature. Related problems of class- and exam-scheduling have been extensively studied and published, yet few cases consider participant (e.g. student) preferences. Our formulation, which a variation of that used by Eglese and Rand, includes prioritized preferences for conference sessions, as well as schedule resource constraints. The purpose of this paper is to extend the previous work by exploring the impact of various scheduling decisions on participant satisfaction (measured by enrollment in desired sessions). We use a previously published algorithm to look at issues such as conference length and make general observations that may aid the conference-scheduling decision maker.

ISSN:0160-5682    

DOI:10.1057/jors.1996.26

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe problem of scheduling jobs on a single machine is considered. It is assumed that the jobs are classified into several groups and the jobs of the same group have to be processed contiguously. A sequence independent set-up time is incurred between each two consecutively scheduled groups. A schedule is specified by a sequence for the groups and a sequence for the jobs in each group. The quality of a schedule is measured by two critera ordered by their relative importance. The objective is to minimize the maximum cost, the secondary criterion, subject to the schedule is optimal with respect to total weighted completion time, the primary criterion. A polynomial time algorithm is presented to solve this bicriterion group scheduling problem. It is shown that this algorithm can also be modified to solve the single machine group scheduling problem with several ordered maximum cost criteria and arbitrary precedence constraints.

ISSN:0160-5682    

DOI:10.1057/jors.1996.27

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractWhen several suppliers are concurrently used to replenish one stock item, it is often of interest to compute the mean and the variance of the effective lead time, i.e., the minimum of all lead times. However, in many cases, especially with non-identical lead time distributions, these quantities do not have closed form expressions and their calculation can be complicated. Difficulty in computation also arises in evaluating demand during lead time, even if there is only one supplier. This paper presents a numerical integration method using Gaussian quadrature to evaluate the effective lead time mean and variance, re-order level and the probability of stockout during the effective lead time. The Gaussian quadrature rules are easy to implement and several data sets are used in the paper to demonstrate the method.

ISSN:0160-5682    

DOI:10.1057/jors.1996.28

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor