INTRODUCTION TO THE ART AND SCIENCE OF SIMULATION
Robert E. Shannon Industrial Engineering Texas A&M University College Station, Texas 77843-3131 U.S.A.
ABSTRACT This introductory tutorial presents an over view of the process of conducting a simulation study of anydiscrete system. The basic viewpoint is that conducting such a study requires both art and science. Some of the issues addressed are how to get started, the steps to be followed, the issues to be faced at each step, the potential pitfalls occurring at each step, and the most common causes of failures. 1 INTRODUCTION Simulation is one of the most powerful tools available to decision-makers responsiblefor the design and operation of complex processes and systems. It makes possible the study, analysis and evaluation of situations that would not be otherwise possible. In an increasingly competitive world, simulation has become an indispensable problem solving methodology for engineers, designers and managers. We will define simulation as the process of designing a model of a real system andconducting experiments with this model for the purpose of understanding the behavior of the system and /or evaluating various strategies for the operation of the system. Thus it is critical that the model be designed in such a way that the model behavior mimics the response behavior of the real system to events that take place over time. The term's model and system are key components of our definitionof simulation. By a model we mean a representation of a group of objects or ideas in some form other than that of the entity itself. By a system we mean a group or collection of interrelated elements that cooperate to accomplish some stated objective. One of the real strengths of simulation is the fact that we can simulate systems that already exist as well as those that are capable of beingbrought into existence, i.e. those in the preliminary or planning stage of development.
In this paper we will be discussing the art and science of moving a modeled system through time. Simulation is the next best thing to observing a real system in operation since it allows us to study the situation even though we are unable to experiment directly with the real system, either because the system doesnot yet exist or because it is too difficult or expensive to directly manipulate it. We consider simulation to include both the construction of the model and the experimental use of the model for studying a problem. Thus, we can think of simulation modeling as an experimental and applied methodology, which seeks to: ♦ Describe the behavior of a system. ♦ Use the model to predict future behavior,i.e. the effects that will be produced by changes in the system or in its method of operation. 2 ADVANTAGES AND DISADVANTAGES
Simulation has a number of advantages over analytical or mathematical models for analyzing systems. First of all, the basic concept of simulation is easy to comprehend and hence often easier to justify to management or customers than some of the analytical models. Inaddition, a simulation model may be more credible because it's behavior has been compared to that of the real system or because it requires fewer simplifying assumptions and hence captures more of the true characteristics of the system under study. Additional advantages include: ♦ We can test new designs, layouts, etc. without committing resources to their implementation. ♦ It can be used to explorenew staffing policies, operating procedures, decision rules, organizational structures, information flows, etc. without disrupting the ongoing operations. ♦ Simulation allows us to identify bottlenecks in information, material and product flows and test options for increasing the flow rates. ♦ It allows us to test hypothesis about how or why certain phenomena occur in the system.