Simulation Modeling Handbook

A Practical Approach

Christopher A. Chung, Christopher A. Chung

• Publisher: CRC Press
• Year: 2003
• ISBN:
  9781135513603
• Edition: 1
• Topic: Computer Science
• Subtopic: Computer Engineering
• Index: Computer Science

The use of simulation modeling and analysis is becoming increasingly more popular as a technique for improving or investigating process performance. This book is a practical, easy-to-follow reference that offers up-to-date information and step-by-step procedures for conducting simulation studies. It provides sample simulation project support materi

1
Introduction

“Where do we begin?”

1.1 Introduction

The objective of this chapter is to provide the simulation practitioner with some basic information about simulation modeling and analysis. Experienced practitioners using the handbook for reference purposes are advised to bypass this chapter and proceed to the appropriate chapter. Practitioners who have never received training in simulation or whose training is dated are strongly recommended to work through not only the examples but also the sample problems at the end of the chapter.

The chapter includes:

• An introduction to simulation modeling and analysis
• Other types of simulation
• Purposes of simulation Advantages and disadvantages
• Advantages and disadvantages of simulation
• Famous simulation quotes
• Basic simulation concepts A comprehensive example of
• A comprehensive example of a manual simulation

1.2 Simulation Modeling and Analysis

Simulation modeling and analysis is the process of creating and experimenting with a computerized mathematical model of a physical system. For the purposes of this handbook, a system is defined as a collection of interacting components that receives input and provides output for some purpose. Included within this field are traditional simulation and training simulators. In general, the distinction is as follows. Traditional simulation is used for analyzing systems and making operating or resource policy decisions. Training simulators are used for training users to make better decisions or improving individual process performance. A short section is included at the end of the handbook that discusses the basic nature of simulators.

The vast majority of this handbook concentrates on the field of simulation versus simulators. Although many different types of systems can be simulated, the majority of the systems that we discuss in this handbook are manufacturing, service, or transportation related.

Examples of manufacturing systems include:

• Machining operations
• Assembly operations
• Warehousing

Machining operation simulations can include processes involving either manually or computer numerically controlled factory equipment for machining, turning, bending, cutting, welding, and fabricating. Assembly operations can cover any type of assembly line or manufacturing operation that requires the assembly of multiple components into a single piece of work. Material-handling simulations have included analysis of cranes, forklifts, and automatically guided vehicles. Warehousing simulations have involved the manual or automated storage and retrieval of raw materials or finished goods.

Examples of service systems include:

• Hospitals and medical clinics
• Materials-handling equipment
• Retail stores
• Food or entertainment facilities
• Information technology
• Customer order systems

Hospital and medical clinic models can be simulated to determine the number of rooms, nurses, and physicians for a particular location. Retail stores may need to know how many checkout locations to utilize. Entertainment facilities such as multitheater movie complexes may be interested in how many ticket sellers, ticket checkers, or concession stand clerks to employ. Information technology models typically involve how many and what type of network or support resources to have available. Customer order systems may need to know how many customer order representatives are needed to be on duty.

Examples of transportation systems include:

• Airport operations
• Port shipping operations
• Train and bus transportation
• Distribution and logistics

Airport operations simulations have been performed on airport security checkpoints, check-in counters, and gate assignments. Port shipping operations can include how many cranes and trucks are needed to offload transportation ships. Train and bus transportation can include analysis involving routes. Distribution and logistics studies have included the analysis of shipping center design and location.

1.3 Other Types of Simulation Models

The types of simulation models previously discussed are not the only types of simulation model that the practitioner may encounter or have a need for. Another type of computer simulation model is the computer simulator. Though the distinction between simulation models and computer simulators may differ somewhat among practitioners, the following discussion may help differentiate these two types of simulation.

So far, the types of simulation models that we have discussed have been models of actual or proposed systems. Models of the systems are normally created with different resource or operating policies that have been previously determined to be of interest. After the simulation runs, the output measures of performance are compared between or among the models. Thus, the ultimate use of the models is to make resource or operating policy decisions concerning the system.

Simulators are also models of existing or proposed systems. In contrast to simulation models, resource and operating policy decisions are not made beforehand. These types of decisions are actually made during the simulation run. Thus, the output measures are observed not only at the end of the run but, more importantly, during the simulation run. The practitioner or user can see the effects of executing different resource and operating policy decisions in real time. Thus, the purpose of the simulator is not to make a decision but to expose the users to the system and to train them on how to make decisions. These types of simulators are often referred to as training simulators.

Although the principal focus of this book is on developing and analyzing simulation models, a short section has been included on simulators in Chapter 12, “Training Simulators.”

1.4 Purposes of Simulation

The simulation modeling and analysis of different types of systems are conducted for the purposes of (Pedgen et al., 1995):

• Gaining insight into the operation of a system Developing operating or resource policies to improve
• Developing operating or resource policies to improve system performance
• Testing new concepts and/or systems before implementation
• Gaining information without disturbing the actual system

1.4.1 Gaining Insight into the Operation of a System

Some systems are so complex that it is difficult to understand the operation of and interactions within the system without a dynamic model. In other words, it may be impossible to study the system by stopping it or by examining individual components in isolation. A typical example of this would be to try to understand how manufacturing process bottlenecks occur.

1.4.2 Developing Operating and Resource Policies

You may also have an existing system that you understand but wish to improve. Two fundamental ways. of doing this are to change operating or resource policies. Changes in operating policies could include different scheduling priorities for work orders. Changes in resource policies could include staffing levels or break scheduling.

1.4.3 Testing New Concepts

If a system does not yet exist, or you are considering purchasing new systems, a simulation model can help give you an idea how well the proposed system will perform. The cost of modeling a new system can be very small in comparison to the capital investment involved in installing any significant manufacturing process. The effects of different levels and expenses of equipment can be evaluated. In addition, the use of a simulation model before implementation can help refine the configuration of the chosen e...