A Hybrid System Dynamics-Discrete Event Simulation Approach to Simulating the Manufacturing Enterprise
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A HYBRID SYSTEM DYNAMICS-DISCRETE EVENT SIMULATION APPROACH TO SIMULATING THE MANUFACTURING ENTERPRISE by MAGDY HELAL M.Sc. Benha Higher Institute of Technology, 1999 B.Sc. Benha Higher Institute of Technology, 1993 A dissertation submitted in partial fulfillment of the requirements for the degree of the Doctor of Philosophy in the Department of Industrial Engineering and Management Systems in the College of Engineering and Computer Science at the University of Central Florida Orlando, Florida Summer Term 2008 Major Professor: Luis Rabelo © 2008 Magdy Helal ii ABSTRACT With the advances in the information and computing technologies, the ways the manufacturing enterprise systems are being managed are changing. More integration and adoption of the system perspective push further towards a more flattened enterprise. This, in addition to the varying levels of aggregation and details and the presence of the continuous and discrete types of behavior, created serious challenges for the use of the existing simulation tools for simulating the modern manufacturing enterprise system. The commonly used discrete event simulation (DES) techniques face difficulties in modeling such integrated systems due to increased model complexity, the lack of data at the aggregate management levels, and the unsuitability of DES to model the financial sectors of the enterprise. System dynamics (SD) has been effective in providing the needs of top management levels but unsuccessful in offering the needed granularity at the detailed operational levels of the manufacturing system. On the other hand the existing hybrid continuous-discrete tools are based on certain assumptions that do not fit the requirements of the common decision making situations in the business systems. This research has identified a need for new simulation modeling approaches that responds to the changing business environments towards more integration and flattened enterprise systems. These tools should be able to develop comprehensive models that are inexpensive, scalable, and able to accommodate the continuous and discrete modes of behavior, the stochastic iii and deterministic natures of the various business units, and the detail complexity and dynamic complexity perspectives in decision making. The research proposes and develops a framework to combine and synchronize the SD and DES simulation paradigms to simulate the manufacturing enterprise system. The new approach can respond to the identified requirements in simulating the modern manufacturing enterprise systems. It is directed toward building comprehensive simulation models that can accommodate all management levels while explicitly recognizing the differences between them in terms of scope and frequency of decision making as well as the levels of details preferred and used at each level. This SDDES framework maintains the integrity of the two simulation paradigms and can use existing/legacy simulation models without requiring learning new simulation or computer programming skills. The new framework uses a modular structure by which the SD and DES models are treated as members of a comprehensive simulation. A new synchronization mechanism that that maintains the integrity of the two simulation paradigms and is not event-driven is utilized to coordinate the interactions between the simulation modules. It avoids having one simulation paradigm dominating the other. For communication and model management purposes the SDDES formalism provides a generic format to describe, specify, and document the simulation modules and the information sharing processes. The SDDES controller which is the communication manager, implements the synchronization mechanism and manages the simulation run ensuring correct exchange of data in terms of timeliness and format, between the modules. It also offers the user interface through which users interact with the simulation modules. iv In loving memory of my Mother v ACKNOWLEDGMENTS I would like express my appreciation to my advisor Dr. Luis Rabelo who with his advice and continuing support made this research possible. I’m thankful and grateful to all of my committee members for their support and for taking part in the committee. I’m especially thankful to Dr. Albert Jones of NIST for his valuable insights and feedback. And I’m grateful to Dr. Robert Armacost for his support and advise in the time when I needed them the most. I appreciate all encouragement and help from all faculty and staff of the Industrial Engineering and Management Systems Department at the University of Central Florida. And my sincere thanks and gratitude to Sandra Archer, Director of the Office of University Analysis and Planning Support for her understanding, support, and help and to the good friend Mohammad Fayez, Ph.D. for his encouragement. vi TABLE OF CONTENTS LIST OF FIGURES ..................................................................................................................... xiii LIST OF TABLES .........................................................................................................................xx CHAPTER 1: INTRODUCTION ...............................................................................................1 1.1 The Purpose of This Research ...............................................................................................6 1.2 Research Premises and Directions ........................................................................................6 1.3 Contributions .........................................................................................................................7 1.4 Chapter Outline .....................................................................................................................8 CHAPTER 2: LITERATURE REVIEW ....................................................................................9 2.1 The Manufacturing Enterprise System ..................................................................................9 2.2 The Enterprise Resource Planning System .........................................................................14 2.3 Enterprise Modeling and Integration ...................................................................................16 2.4 Simulation Modeling ...........................................................................................................17 2.4.1 Discrete event simulation .............................................................................................20 2.4.1.1 Output analysis in DES ..................................................................................... 22 2.4.2 Continuous simulation .................................................................................................26 2.4.2.1 System Dynamics simulation ............................................................................ 27 2.4.2.2 Generic mathematical formulas for the stocks and flows ................................. 33 2.4.2.3 The stock management model .......................................................................... 39 vii 2.5 Hybrid Simulation ...............................................................................................................42 2.5.1 The dynamics of hybrid systems ..................................................................................45 2.5.2 The hybrid state transition machine .............................................................................46 2.5.2.1 The AnyLogic software package ...................................................................... 50 2.5.2.2 Commentary on using the state chart and AnyLogic ........................................ 56 2.5.3 The DEVS-based hybrid simulation ............................................................................57 2.5.3.1 The DEVS formalism ....................................................................................... 58 2.5.3.2 The DESS formalism ........................................................................................ 60 2.5.3.3 The DEV&DESS formalism ............................................................................. 61 2.5.3.4 Commentary on the DEV&DESS formalism ................................................... 64 2.5.3.5 Using the DEV&DESS formalism ................................................................... 68 2.5.4 On the current hybrid simulation approaches ..............................................................69 2.6 Distributed Simulation ........................................................................................................71 2.6.1 Distributed simulation in industry ...............................................................................73 2.7 Simulating the Manufacturing Enterprise ...........................................................................75 2.7.1 Contrasting DES and SD .............................................................................................92 2.7.2 Attempts for more comprehensiveness ......................................................................103 2.8 The Gap in Simulating the Manufacturing Enterprise ......................................................107 CHAPTER 3: SYNCHRONIZATION IN DISTRIBUTED SIMULATION .........................110 3.1 Conservative Time Management .......................................................................................115 3.2 Optimistic Time Management ...........................................................................................116 3.3 The Time Bucket Approaches to Time Management