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1.
We study the vessel arrival process in bulk ports handling either cargo containers or minerals. Then we introduce the SHIP/G/1 queue to be able to study the queueing behavior at the port. We present approximations for the asymptotic probabilities of delay and the number of vessels at the port. Numerical examples show the accuracy of the approximations. In appendices, we provide details of the analysis of the number of vessels at the port and the correlation properties of the vessel arrival process. 相似文献
2.
Jagerman David L. Balcıoglu Barış Altıok Tayfur Melamed Benjamin 《Queueing Systems》2004,46(3-4):481-506
It is known that correlations in an arrival stream offered to a single-server queue profoundly affect mean waiting times as compared to a corresponding renewal stream offered to the same server. Nonetheless, this paper uses appropriately constructed GI/G/1 models to create viable approximations for queues with correlated arrivals. The constructed renewal arrival process, called PMRS (Peakedness Matched Renewal Stream), preserves the peakedness of the original stream and its arrival rate; furthermore, the squared coefficient of variation of the constructed PMRS equals the index of dispersion of the original stream. Accordingly, the GI/G/1 approximation is termed PMRQ (Peakedness Matched Renewal Queue). To test the efficacy of the PMRQ approximation, we employed a simple variant of the TES+ process as the autocorrelated arrival stream, and simulated the corresponding TES +/G/1 queue for several service distributions and traffic intensities. Extensive experimentation showed that the proposed PMRQ approximations produced mean waiting times that compared favorably with simulation results of the original systems. Markov-modulated Poisson process (MMPP) is also discussed as a special case. 相似文献
3.
Gokmen Tayfur Hakki Erhan Sevil Erkin Gezgin Serhan Ozdemir 《Mathematical and Computer Modelling》2009,49(3-4):709-720
This study developed a variant of genetic algorithm (GA) model called the trait-based heterogeneous populations plus (TbHP+). The developed TbHP+ model employs a memory concept in the form of immunity and instinct to provide the populations with a more efficient guidance. Also, it has an ability to vary the number of individuals during the search process, thus allowing an automatic determination of the size of the population based on the individual qualities such as character fitness and credit for immunity. The algorithm was tested against the classical GA model in convergence and minimum error performance. For this purpose, 5 different mathematical functions from the literature were employed. The selected functions have different topological characteristics, ranging from simple convex curves with 2 variables to complex trigonometric ones having several hilly shapes with more than 2 variables. The developed model and the classical GA model were applied to finding the global minima of the functions. The comparison of the results revealed that the developed TbHP+ model outperformed the classical GA in faster convergence and minimum errors, which may be explained by the adaptive nature of the new paradigm. 相似文献
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We consider a multi-period inventory model with raw material procurements carried out via a reverse auction. Bids are multi-dimensional,
and they consist of supplier information of price, shortage quantity and lead time. This work is an extension of our earlier
work that has focused on multi-dimensional procurement auctions in single-period inventory models, to multi-period settings.
The new model is based on a hybrid approach combining stochastic dynamic programming and simulation. 相似文献
6.
We consider a decentralized, pull-type manufacturing system with each stage having its own input and output stock keeping activities. Material handling between stages is carried out according to a fixed quantity, non-constant withdrawal cycle. We approximate the system behavior using a two-node decomposition approach, which decomposes the system into smaller subsystems. The analysis of two-node subsystems is achieved using a matrix-recursive approach due to phase-type modeling of certain random variables. Our solution algorithm resolved a major difficulty (due to batch transfers) in the analytical approach to study multi-stage manufacturing systems. We also discuss system behavior and suggest several rules-of-thumb to improve system performance. 相似文献
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Devising manufacturing/distribution strategies for supply chains and determining their parameter values have been challenging problems. Linking production management to stock keeping processes improves the planning of the supply chain activities, including material management, culminating in improved customer service levels. In this study, we investigate a multi-echelon supply chain consisting of a supplier, a plant, a distribution center and a retailer. Material flow between stages is driven by reorder point/order quantity inventory control policies. We develop a model to analyze supply chain behavior using some key performance metrics such as the time averages of inventory and backorder levels, as well as customer service levels at each echelon. The model is validated against simulation, yielding good agreement of robust performance metrics. The metrics are then used within an optimization framework to design the supply chain so as to minimize expected total system costs. The outcome of the optimization framework specifies how to move inventory throughout the supply chain and how to set inventory control parameters, i.e., reorder levels and replenishment batch sizes. 相似文献
9.
Procurement is one of the major activities in the Manufacturing Resource Planning (MRP II), which is closely coupled with
inventory management. Any improvement in this area will have a direct impact on the performance of the entire supply chain.
Auction mechanism can be a successful procurement method when there are several potential suppliers available. In this paper,
we consider a single-period inventory model when the selection of the supplier is done through a reverse auction with bids
consisting of several attributes, namely price, shortage quantity, and lead time. The multi-dimensionality of the bid increases
the complexity of the underlying problem creating a need for an approach to determine an approximate optimal target level.
This is needed for the initiation of the auction and the procurement process. Monte-Carlo simulation method was used to investigate
the performance of the approximation. Simulation results show that the analytical method provides an acceptable approximation
for the optimal target inventory level. 相似文献
10.
We consider a single-server queue subject to multiple types of operation-independent interruptions motivated by operations
and vessel queueing at entrances of waterways. A case in point is the Strait of Istanbul. We are using waiting-time arguments
and service completion time analysis to obtain the expected waiting time of a customer (vessel) in the aforementioned queue
with single-class of customers and k non-simultaneous and possibly simultaneous service interruptions. In the analysis, we have used arguments and assumptions
from the Strait of Istanbul that are also valid for narrow waterways at large. 相似文献