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Unformatted text preview: 2/11/2007 Industrial Data and Systems Analysis 1 Discrete Event Simulation Peter L. Jackson Professor School of O.R. and I.E. 2/11/2007 Industrial Data and Systems Analysis 2 Overview • Motivation: The Cookie Problem • A Model of Behavior: Discrete Event Simulation • A Graphical Language • Programming a Simulation in MS Excel 2/11/2007 Industrial Data and Systems Analysis 3 Key Lessons (Preview) • Discrete event simulation is a highly flexible method of describing the behavior of a system • Basic simulation services can be implemented in MS Excel, but require user coding in VBA • The structure of a simulation model can be described with an event graph • Building, running, and analyzing a simulation model is a structured process 2/11/2007 Industrial Data and Systems Analysis 4 Before You Buy a Simulation Package • See how you would use it to model the following situation: An oven takes 13.5 minutes to bake cookies. The oven can hold up to two trays of cookies. The number of trays in the oven does not affect baking time. The trays can be of different types of cookies but you cannot open the door while the cookies are baking. That is, you can put trays into the oven only after the current oven cycle has ended. Trays of chocolate chip cookies arrive every t c minutes. Trays of peanut butter cookies arrive every t p minutes. What is the average number of trays of peanut butter cookies waiting to be cooked, assuming t c is uniformly distributed over [9,18] and t p is uniformly distributed over [12,16]? 2/11/2007 Industrial Data and Systems Analysis 5 The Cookie Problem Trays of p.b. arrive every 14 minutes on average Trays of c.c. arrive every 13.5 minutes on average Queues of trays can build up due to randomness of arrivals Oven cycle is 13.5 minutes but cannot be interrupted Oven capacity is two trays (can be of mixed type) Maximum throughput is 2 trays every 13.5 minutes 2/11/2007 Industrial Data and Systems Analysis 6 Questions • Maximum throughput is 2 trays/13.5 min. What will be the average throughput ? • Easy, determined by average arrival rate • If there is no randomness, what will be the maximum number of trays in queue? 2/11/2007 Industrial Data and Systems Analysis 7 Questions (continued) • If arrivals are random (uniformly distributed), what will be the average number of trays in queue? • Cannot tell, using analytical methods • Must simulate • Answer depends on scheduling rule • “Always fill oven” or “cook on arrival” • If arrivals are random, what will be the average number of p.b. trays in queue? • Answer depends on priority rule • Ex. “Minimize the c.c. queue” 2/11/2007 Industrial Data and Systems Analysis 8 Discrete Event Simulation • The system is described by a state • The state changes only at discrete points in time, called events • The interval between events is called a delay , or duration. The delay could be random • Events can trigger other events depending on conditions...
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This note was uploaded on 01/09/2009 for the course ORIE 312 taught by Professor D.ruppert,p.jacks during the Spring '08 term at Cornell.
 Spring '08
 D.RUPPERT,P.JACKS

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