We study a new facility protection problem in which one must allocate scarce protection resources to a set of facilities given that allocating resources to a facility only has a probabilistic effect ...on the facility's post-disruption capacity. This study seeks to test three common assumptions made in the literature on modeling infrastructure systems subject to disruptions: 1) perfect protection, e.g., protecting an element makes it fail-proof, 2) binary protection, i.e., an element is either fully protected or unprotected, and 3) binary state, i.e., disrupted elements are fully operational or non-operational. We model this facility protection problem as a two-stage stochastic program with endogenous uncertainty. Because this stochastic program is non-convex we present a greedy algorithm and show that it has a worst-case performance of 0.63. However, empirical results indicate that the average performance is much better. In addition, experimental results indicate that the mean-value version of this model, in which parameters are set to their mean values, performs close to optimal. Results also indicate that the perfect and binary protection assumptions together significantly affect the performance of a model. On the other hand, the binary state assumption was found to have a smaller effect.
Discrete event simulation is used to evaluate a novel configuration of the exit roller in the composure area of security checkpoints, which is designed to address the failures of the current exit ...roller configuration. The paper presents in detail the conceptual modeling of a two-lane system with the current configuration, and an additional model, featuring the new design in one of the lanes. The second model is used to evaluate statistically whether there is any reduction in the passengers’ system time from directing the passengers to the lane having the new design, based on the number of items passengers carry. Lastly, we perform an analysis to examine the range of arrival rates for which a single lane, featuring the new design, could replace a traditional two-lane system.
In circuit board manufacturing, the production sequencing problem with sequence dependent setups is complicated by the fact that the amount of setup required depends on not only the setup directly ...before the current setup, but can depend on all of the preceding setups. We present a case study that examines the use of a heuristic for estimating the expected number of setups from the sequence dependent setups. Our method is based on estimating the expected number of setups which may occur given a board-feeder setup configuration. Once estimates for the sequence dependent setups are established, they can be used to measure the similarity between boards in clustering algorithms and in nearest neighbor heuristics for group sequencing. The method is tested on an actual printed circuit board assembly system. Then, using a simulation of the assembly system, we compare the sequences generated using the expected number of setups distance measure and the Hamming distance measure to optimal sequences. Our results indicate that grouped sequences generated by using the expected number of setups had significantly better makespan performance when compared to sequences based on the more traditional Hamming distance for the particular system under study. The significant gains in makespan resulted in only moderate increases in work in process and slight increases in manual station utilization.
This research extends a static threshold based control strategy used to control headway variation to a dynamic threshold based control strategy. In the static strategy, buses are controlled by ...setting a threshold value that holds buses at a control point for a certain amount of time before allowing the bus to continue along the route. The threshold remains constant each time the bus stops at the control point. The dynamic strategy involves the same principle of holding buses at a bus stop; however, a different threshold value is chosen each time the bus holds at a control point. The results indicate that in cases where the static threshold is set equal to the scheduled headway, very low headway variation and passenger system times result; however, passengers on board the bus are penalized by extra delay on the bus while waiting at the control point. The dynamic strategy reduces the penalty to passengers delayed on-board the bus at a control point at the expense of a slight increase in overall passenger system time.The results indicate that in most cases, the tradeoff of the slight increase in waiting time for the significant decrease in on-board delay penalty makes the dynamic strategy an acceptable choice.
Flexible automation in the form of robotic couriers holds the potential for decreasing operating costs while improving delivery performance in hospital delivery systems. This paper discusses the use ...of simulation modeling to analyze the costs, benefits, and performance tradeoffs related to the installation and use of a fleet of robotic couriers within hospital facilities. The results of this study enable a better understanding of the delivery and transportation requirements of hospitals. Specifically, we examine how a fleet of robotic couriers can meet the performance requirements of the system while maintaining cost efficiency. We show that for clinical laboratory and pharmaceutical deliveries a fleet of six robotic couriers can achieve significant performance gains in terms of turn-around time and delivery variability over the current system of three human couriers per shift or 13 FTEs. Specifically, the simulation results indicate that using robotic couriers to perform both clinical laboratory and pharmaceutical deliveries would result in a 34% decrease in turn-around time, and a 38% decrease in delivery variability. In addition, a break-even analysis indicated that a positive net present value occurs if nine or more FTEs are eliminated with a resulting ROI of 12%. This analysis demonstrates that simulation can be a valuable tool for examining health care distribution services and indicates that a robotic courier system may yield significant benefits over a traditional courier system in this application.
We develop a methodology for using bar code scanner timing information from an automated shop floor data collection system to estimate operation times within a flexible manufacturing system ...environment. The purpose of the methodology is to estimate mean operation times for multiple product types when the scanning only occurs when products arrive to and depart from a machine center. This methodology partially reconstructs the shop floor operations from captured bar code scanner timing information and then through the use of regression techniques estimates the mean operation times for each of the product types. This paper develops and evaluates the methodology within an operational context. The accuracy and precision of the estimators is evaluated via discrete event simulation under various experimental conditions to identify key factors which effect the performance of the estimators. We identified guidelines for achieving estimator accuracy and we applied the estimator to an actual industrial situation.
An optimization framework for the evaluation of queueing approximations is proposed and illustrated on a queueing approximation for the two-type stoppage machine interference model. The optimization ...framework combines infinitesimal perturbation analysis and stochastic approximation in order to optimize the approximation’s error function using simulation. The optimization procedure attempts to find the worse case error of the approximation and the associated parameter values. The optimization framework is compared against the standard factorial design approach for queueing approximation evaluation. The results indicate the potential of evaluating queueing approximations using an optimization framework. In addition, the performance of the machine interference approximation is shown to be worse than previous results indicated using factorial design approaches. This research illustrates to practitioners how queueing approximation evaluation is performed and should indicate to researchers new directions to take in queueing approximation evaluation methodology.
Purpose The purpose of this paper is to address the inefficiency in resource allocation for disaster relief procurement operations. It presents a holistic and reconfigurable procurement auctionsbased ...framework which includes the announcement construction, bid construction and bid evaluation phases. Designmethodologyapproach The holistic framework is developed in a way that auctioneers and bidders compete amongst each other in multiple rounds of the procurement auction. Humanitarian organization in disaster locations are considered as auctioneers buyers and suppliers are considered as bidders. Findings Unique system parameters e.g. announcement options, priority of items, bidder strategies, etc. are introduced to represent the disaster relief environment in a practical way. The framework is verified by simulation and optimization techniques using the system characteristics of the disaster relief environment as an input. Based on the parameters and their values, behavioural changes of auctioneers and suppliers are observed. Originalityvalue Combining the three phases of procurement auctions is unique both in the auction literature and in the disaster relief research, and it helps the humanitarian organizations supply the immediate and longterm requirements in the disaster location more efficiently.
Manufacturing firms rely on automatic data collection systems to replace labor-intensive data collection methods. Most systems concentrate on locating and counting parts without regard to transaction ...times; however, by capturing and processing event times, additional system characteristics can be inferred. Using product arrival and departure event transactions based on bar code technology, this research develops a methodology for estimating the amount of workload in a workcenter with a parallel server structure commonly found in practice. This paper presents an evaluation of the accuracy and precision of the resulting workload estimators under conditions of varying product mix. It was found that the relative proportion of products in the production mix can have a significant effect on estimator performance. For production mixes that change infrequently, the estimator was within 5% of the true workcenter load in 98% of the experiments. The estimator is simple and can be continually updated as new data are collected. This research illustrates the value-added benefits to be gained in utilizing bar code timing information for developing estimates of workcenter load especially within computer-automated shop floor control systems.
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