Analytical evaluation of the output variability in production systems with general Markovian structure

Performance evaluation models are used by companies to design, adapt, manage and control their production systems. In the literature, most of the effort has been dedicated to the development of efficient methodologies to estimate the first moment performance measures of production systems, such as the expected production rate, the buffer levels and the mean completion time. However, there is industrial evidence that the variability of the production output may drastically impact on the capability of managing the system operations, causing the observed system performance to be highly different from what expected. This paper presents a general methodology to analyze the variability of the output of unreliable single machines and small-scale multi-stage production systems modeled as General Markovian structure. The generality of the approach allows modeling and studying performance measures such as the variance of the cumulated output and the variance of the inter-departure time under many system configurations within a unique framework. The proposed method is based on the characterization of the autocorrelation structure of the system output. The impact of different system parameters on the output variability is investigated and characterized. Moreover, managerial actions that allow reducing the output variability are identified. The computational complexity of the method is studied on an extensive set of computer experiments. Finally, the limits of this approach while studying long multi-stage production lines are highlighted. © 2013 Springer-Verlag Berlin Heidelberg

Throughput enhancement with parallel redundancy in multi-product flow line system

We develop a new analytic approximation method to replace a set of parallel machines by an equivalent machine in a series-parallel flow line with finite buffer. We develop our method based on discrete state Markov chain. The proposed technique replaces a set of parallel machines at a work centre by an equivalent machine in order to obtain a traditional flow line with machines in series separated by intermediate buffers. We derive equations for the parameters of the equivalent machine when it operates in isolation as well as in flow line. The existing analytic methods for series-parallel systems can tract only lines with a maximum of two machines in series and a buffer in-between them. The method we propose in this thesis can be used in conjunction with an approximation method or simulation to solve flow lines of any length. We also model and evaluate the performance of series-parallel systems manufacturing more than one product types with predefined sequence and lot size. We address this issue for a considerable longer flow line system with finite buffer which is common in industry. We consider the set-up time of the machines as the product type changes, deterministic processing times and operation dependent failures of the machines. We analyze the effects of buffer and number of machines in parallel on the performance of series-parallel systems

An Analytical Approach to Cycle Time Evaluation in an Unreliable Multi-Product Production Line with Finite Buffers

This thesis develops an analytical approximation method to measure the performance of a multi-product unreliable production line with finite buffers between workstations. The performance measure used in this thesis is Total Cycle Time. The proposed approximation method generalizes the processing times to relax the variation of product types in a multi-product system. A decomposition method is then employed to approximate the production rate of a multi-product production line. The decomposition method considers generally distributed processing times as well as random failure and repair. A GI/G/1/N queuing model is also applied to obtain parameters such as blocking and starving probabilities that are needed for the approximation procedure. Several numerical experiments under different scenarios are performed, and results are validated by simulation models in order to assess the accuracy and strength of the approximation method. Consequent analysis and discussion of the results is also presented

Manufacturing flow line systems: a review of models and analytical results

The most important models and results of the manufacturing flow line literature are described. These include the major classes of models (asynchronous, synchronous, and continuous); the major features (blocking, processing times, failures and repairs); the major properties (conservation of flow, flow rate-idle time, reversibility, and others); and the relationships among different models. Exact and approximate methods for obtaining quantitative measures of performance are also reviewed. The exact methods are appropriate for small systems. The approximate methods, which are the only means available for large systems, are generally based on decomposition, and make use of the exact methods for small systems. Extensions are briefly discussed. Directions for future research are suggested.National Science Foundation (U.S.) (Grant DDM-8914277

Analysis of Erlang transfer lines

Ankara : The Department of Industrial Engineering and Institute of Engineering and Science of Bilkent University, 1997.Thesis (Master's) -- Bilkent University, 1997.Includes bibliographical references leaves 64-68Transfer lines are widely used in the modeling and analysis of complex production systems. The literature is mostly devoted to the analysis of transfer lines with exponential processing times. However, most of the time a part is |)rocessed through stages(phases) of exponential processing times. It is possil)le to model such systems by means of processing times that are A,·—Erlang distributed. In the modeling and solution of these systems, significant difficulties arise due to the nature of the problem. In this thesis, we propose a -Markov model for transfer lines consisting of n reliable machines with A—Erlang processing times and finite buffers. The arrivals to the system is Poisson distributed. A program coded in C which is capable of solving the Markov model of a three machine transfer line is also developed. Besides the commonly used performance measures, such as utilization of the machines, mean throughput, mean WIP level, we calculate the variance of VVIP so that it is possible to construct confidence intervals.Dönmez, NebahatM.S

Performance of merging lines with uneven buffer capacity allocation: the effects of unreliability under different inventory-related costs

This simulation study investigates whether machine efficiency, mean time to failure (MTTF) and mean time to repair (MTTR) significantly affect the performance of uneven buffer capacity allocation patterns for merging lines. Also studied is the trade-off between increasing throughput via bigger buffers and their associated inventory-related costs, since previous studies have shown that higher overall buffer capacity and higher average inventory content result in higher throughput. Results suggest that an ascending buffer allocation pattern (concentrating buffer capacity towards the end of the line) produces higher throughput in shorter, more unreliable lines; whereas the balanced pattern shows better performance in longer, more reliable lines. Increasing average buffer capacity per station and/or having higher average buffer content was found to be more cost-effective in lines with lower machine inefficiency, shorter MTTF and MTTR, and longer lines. Results differed between reliable and unreliable lines since reliable lines were particularly penalised by buffer capacity investiment/maintenance costs due to a relatively low increase in throughput resulting from the addition of extra buffer capacity

Serial production line performance under random variation:Dealing with the ‘Law of Variability’

Many Queueing Theory and Production Management studies have investigated specific effects of variability on the performance of serial lines since variability has a significant impact on performance. To date, there has been no single summary source of the most relevant research results concerned with variability, particularly as they relate to the need to better understand the ‘Law of Variability’. This paper fills this gap and provides readers the foundational knowledge needed to develop intuition and insights on the complexities of stochastic simple serial lines, and serves as a guide to better understand and manage the effects of variability and design factors related to improving serial production line performance, i.e. throughput, inter-departure time and flow time, under random variation

Analyses of serial production lines and assembly systems for throughput and inyerdeparture time variability

Ankara : Department of Industrial Engineering and the Institute of Engineering and Science of Bilkent Univ., 1998.Thesis (Master's) -- Bilkent University, 1998.Includes bibliographical references leaves 77-81In this thesis, we study three different but closely related production system design problems. First, we investigate the effects of various design factors such as number of stations, buffer capacity, allocation of bulfers and location of a bottleneck on the interdeparture time variability of serial production lines. In the second part, we study the effects of number of component stations, processing time distributions, buffers and buffer allocation schemes on throughput and interdeparture time variability of assembly systems. As an alternative to work transfer, we introduce variability transfer and assess its effectiveness. We analyze the anomaly displayed by optimal throughput for some processing time distributions and uncover the underlying details of this behavior. In the third part, we analyze serial production lines and assembly systems under constant workload condition. In addition to investigating the problem of determining the optimal system size, we examine the effects of other design factors such as buffers and material handling time on throughput, interdeparture time variability and cost related measures. Each part reveals several important findings. We also discuss the managerial implications of these findings to present guidelines for the practitioners.Kök, Abdullah GürhanM.S

Stratégies de production manufacturière dans un environnement de chaîne d'approvisionnement : approche dynamique stochastique

Ce projet porte sur le controle des activites operationnelles de la production dans un environnement de chaine d'approvisionnement. Nous nous adressons aux problemes de controle des rythmes de production, des actions de mise en course ainsi que des strategies de maintenance preventive de systemes manufacturiers contraints par un environnement interne et/ou exteme non fiables. A cet egard, nous cherchons a determiner des stratégies integrees de production et d'approvisionnement, en presence de plusieurs foumisseurs potentiels. Nous proposons une approche sequentielle de resolution basee sur la modelisation mathematique et la resolution numerique ainsi que la simulation, les plans d'experiences et les algorithmes genetiques. La premiere partie de l'approche basee sur la theorie de commande optimale et/ou impulsionnelle est indispensable pour avoir une base solide permettant de proposer des strategies de controle qui s'approchent de I'optimum. Quant a la deuxieme partie de I'approche, elle vient completer la premiere afin de developper des processus decisionnels des activites manufacturieres bases sur les politiques developpees. De plus, elle permet d'etendre les dites strategies pour couvrir des systemes plus complexes. A un niveau opérationnel de decision, nous demontrons la grande utilite de la combinaison des deux approches susmentionnees qui peut s'averer incontoumable pour amener des solutions a des problemes A^P-difficiles. L'application de 1'approche aux systemes etudies nous a permis de proposer des strategies de production plus realistes et plus économiques. La prise en consideration du systeme manufacturier dans son environnement exteme, nous a permis de mettre en evidence I'importance d'une gestion integree des fonctions de production et d'approvisionnement. A cet egard, les politiques de controle proposees nous ont permis de reduire jusqu'a 10 % le coiit total, encouru quand il s'agit d'une gestion dissociee. Cette these amene des solutions a une classe de problemes de modelisation dynamique stochastique de systeme manufacturier et ce, a plus qu'un niveau de la hierarchie de déecision. De plus, elle met en application une approche globale de resolution permettant de developper des processus decisionnels de gestion. Cette approche peut surmonter les problemes lies a la resolution des modeles mathematiques quand il s'agit de systemes de faille reelle