Efficiency Evaluation Of Flexible Configurations In Queueing Systems

Nowadays,with the deepening of economic globalization,customers' demands are becoming more diversified.The uncertainty of the demand market,the in-crease of price competition,and the shorter upgrading cycle of product have made manufacturers and service companies face with unprecedented challenges.In or-der to maintain superiority in the fierce competition environment,enterprises cannot rely solely on production capacity,quality,or price as their management strategy.Flexibility,as an advantageous tool in shielding against risks,is now being highly regarded by domestic enterprises.What's more,flexible structures have been widely applied in manufacturing and service systems because of their quick responsiveness to uncertain requirements.In a production system,for example,if a product can only be served by a single product line after entering the system,it will be defined as a dedicated system.If a product can be produced by multiple servers,it will be defined as a flexible structure.Furthermore,the flexible structure can be divided into total flexible structure and partial flexible structure.We know that the construction cost of total flexible system is extremely high,so it is important to think about whether we can design a partial flexible structure,which can also perform as well as total flexible system.This research will mainly consider a special partial flexible structure:chaining configurations.The main contents of the research are as follows:The research backgrounds of the thesis,relevant academic achievements both in domestic and overseas,and the structure and the stream of the research is in-troduced in Chapter 1.Besides,several concepts and theorems are summarized in Chapter 2,which will lay the foundation of the research.Efficiency of k-chain configuration in loss system,queueing system,and preemptive priority queueing system are evaluated in Chapter 3,4 and 5,respectively.First,loss system is a special kind of stochastic system,in which arriving customers find no available servers will be lost.By redefining the state space of such a system,more efficient algorithms are designed to compute the performance of k-chain,dedicated system-s,and total flexibility systems numerically.The key performance measure is the percentage of lost customers,which is influenced by system size,flexibility,and traffic intensity.The numerical results are summarized in several observations and recommendations for flexibility design in loss system are raised.Second,in a first-come-first-served(FCFS)queueing system,arriving customers which located no available servers will join the queue.Similar to the loss system,the system state space are redefined and the performance of these different configurations are calculated.The key performance measure is average waiting time,which is also influenced by system size,flexibility,and traffic intensity.Finally,a parallel queue with 2-chain configuration is studied.In the system,each server serves its own customers with preemptive priority.The stability condition of the system is derived and the system performance with average queue length and idle rate of each server is evaluated by using two approximation methods,namely,steady-state method and matrix-analytic method.In addition,the results of these two methods with that of simulation are compared.At the end of this thesis,the main contributions of the research are concluded,we emphasize its creation and shortcomings,and points out the possible directions of future research.The purpose of this paper is to evaluate the efficiency of k-chain configuration in stochastic systems,and hope that the research shed some new light on flexibili-ty design.The gaps of the research are:(i)The majority of existing works focus on newsvendor settings,however,in this research,the efficiency of chaining configu-rations in stochastic systems where the arriving process is random and the service times are uncertain is examined.Studies on such field are limited.(ii)Due to the-oretical intractability of queueing systems,most results from previous literatures involving flexible system performance is obtained through simulation.Borrowing from the results of two related works)the system state space is redefined and efficient algorithms are designed to evaluate the performance of chaining configu-rations.The thesis finds that although 2-chain configuration performs pretty well under some circumstance,it is less effective in loss system,(iii)Different from the previous research,this research first studies 2-chain configuration in a queueing system with preemptive priority and derive the stability condition of such sys-tem.Furthermore,two approximation methods have been proposed to evaluate the system performance.