On the distribution of throughput of transfer lines

Ankara : Department of Industrial Engineering and the Institute of Engineering and Sciences of Bilkent University, 1998.Thesis (Master's) -- Bilkent University, 1998.Includes bibliographical references leaves 86-107A transfer line corresponds to a manufacturing system consisting of a number of work stations in series integrated into one system by a common transfer mechanism and a control system. There is a vast literature on the transfer lines. However, little has been done on the transient analysis of these systems by making use of the higher order moments of their performance measures due to the difficulty in determining the evolution of the stochastic processes under consideration. This thesis examines the transient behavior of relatively short transfer lines and derives the distribution of the performance measures of interest. The proposed method based on the analytical derivation of the distribution of throughput is also applied to the systems with two-part types. An experiment is designed in order to compare the results of this study with the state-space representations and the simulation. They are also interpreted from the point of view of the line behavior and design issue. Furthermore, extensions are briefly discussed and directions for future research are suggested.Deler, BaharM.S

Empirically derived methods for analysing simulation model output.

Often in simulation procedures are not proposed unless they are supported by a strong mathematical background. As will be shown in this thesis, this approach does not always give good results when the procedures are applied to complex simulation models, especially on output analysis. For this reason we have used an empirical rather than a theoretical approach for dealing with some of the output problems of simulation. The research carried out has dealt mainly with queuing networks. The first problem we address is that of the identification of possible unstable queues. We also deal with the problem of the identification of queues that may require a long simulation run length to reach the steady state. The method of replications is used for the estimation of terminating and sometimes of steady state parameters. In this thesis we study the relationship that exists between the number of replications used in the simulation and the simulation run length required for the parameter being estimated to reach the steady state. We also study the influence of the random number streams on the values of the mean estimates as a function of the number of replications. One of the most commonly discussed problems related to the estimation of steady state parameters is that of the initialisation bias problem. Two methods are proposed in this thesis to deal with this problem. In one of the methods we propose an effective procedure that can be used for the estimation of the number of initial observations that are to be deleted. The second method, is based on a basic forecasting technique called weighted averages and does not require the elimination of any of the initial observations. Another topic that has been studied in this thesis is the batch means method which is employed for the estimation of steady state parameters based on a single but very long simulation run. We show how a new sampling method called Descriptive Sampling is well suited for the estimation of steady state parameters with the batch means method. We also show how some of the procedures proposed in the literature for use in the batch means method do not work well in simulation models for which no analytical answer exists. The thesis demonstrates that empirically derived methods can be practically effective and could form future theoretical research