February 1999 Imagine New Worlds By James J. Swain Imagine a world in which Y2K is only a memory and speedy megaships ply the ocean at 40 knots carrying cargo between Europe and America in half the time that it takes today. These monster ships would represent huge capital investments, and the ships could not afford to sit idle. To be economically viable, these ships will have to be rapidly loaded and unloaded in ports specially constructed to quickly handle their cargo as well as their deep draft. These ships and their voyages, the methods of loading them to facilitate their speedy turnaround in port, and even the surges in containers that their arrival would cause are already being imagined and studied using simulation. How will cash be handled in the future? Soon consumers may carry their cash electronically, using smart cards supplied by and periodically replenished at banks. What will this world be like? What should the capacity of the cards be, and what safety features will be necessary to protect businesses and consumers from fraud? In a simulated world we can model the give and take between security and likely threats, the interaction between fraud, and the algorithms used to thwart or blunt these attacks. We may even be able to determine how the fraudulent value diffuses through the monetary system in order to quantify the costs of defense and risks of loss. Meanwhile, in even less benign worlds, military planners study how to fight wars that they hope will never occur. Using simulation, they can study equipment that may not even be built using warriors that don't exist employing tactics that may have to change and change again as threats evolve in this possible world. Simulation provides great flexibility, of course, with the added advantage that the blood and damage is only simulated. Simulation has an economic impact here, in helping to pick good designs prior to production. There is also the time factor — learning how to employ new weapons prior to their use rather than after. The great power and flexibility of simulation has made it a popular tool, and each year the tool becomes easier to use and more powerful. Simulation can be viewed as a crystal ball, a probe for what the future holds under rules that we believe govern the world amid changes that are to be made to that world. The adept can construct possible future worlds in order to study tradeoffs between various choices in their various combinations and configurations. The increasing power of animation means that simulation output can also be viewed like a movie where the simulator serves as a director of a simulated cast. The final product is not entertainment, but a story about how things might be and how they would look and feel. Experiments that were not promising are much like outtakes on realities that never were. This use of simulation for visualization will intensify as virtual reality is incorporated into simulation technology. The two preceding views of simulation treat it as a mere application program. In fact, the relation between simulation and computers and computer networks is more nearly that of symbiosis. The idea of simulation is not new, and can be realized with pencil and paper — but from the very beginning the stored program computer was recognized as an ideal way to implement simulation, and the personal computer has made simulation accessible nearly everywhere. But the influence is hardly one way. Simulation is used to study the organization of computer hardware and its interaction with software, to model the chips that will form the heart of the computer, and to increase the efficiency of the manufacturing processes that place this equipment into our hands. Simulation has had an influence on programming as well — the current object paradigm for software has its roots in the simulation language Simula. We can expect that the symbiosis will continue and even strengthen in the years to come. The maturing computer networks will make it possible for simulations to be used anywhere, while distributed simulation will widen the scope of simulation from single models operating alone to simulation programs interacting to represent larger and more complex systems. Simulation will evolve together with the computers and the networks that simulation utilizes. Survey This survey is the fourth biennial survey of simulation software for discrete event systems simulation and related products [Swain, 1997]. As in previous surveys, the information on the pages that follow was provided by the vendors based upon a survey of important product features, price and platform. We have concentrated upon products that run on desktop computers with an emphasis on discrete event simulation, as being the most suitable for usage in management science and operations research. Simulation products whose primary capability is continuous simulation (systems of differential equations) or training (e.g., aircraft and vehicle simulators) are omitted here. There are 54 products listed in this survey, making it the largest survey in the series. The range and variety of these products continues to grow, reflecting the growth and increasing sophistication of the user base. The information presented has been chosen to provide a general gauge of the product's functionality, special features and price. A separate listing gives contact information for all of the vendors whose products are in the survey. Many of the vendors provide Web sites to obtain immediate and detailed descriptions of their products and services. The interaction between vendors and their customers has developed as products have matured, and most of the vendors maintain contact with their users through product mailings, newsletters, their own Web sites and annual user group conferences. These user group conferences showcase the application and usefulness of their products, nurture close contact with their users, and allow the users to learn from each other. In addition to user groups, there are a number of organizations and conferences devoted to application and methodology of simulation. Articles on simulation methodology and applications appear in the INFORMS publications Management Science, Operations Research and Interfaces. The College on Simulation sponsors simulation sessions at the national INFORMS meetings and regular awards for both the best simulation publication and the Lifetime Achievement Award for service to the area of simulation. For further information about the College on Simulation and its activities, visit their Web site at www.isye.gatech.edu/informs-sim. This Web site also contains links to many vendors of simulation products and sources of information about simulation. The College is also a co-sponsor of the annual Winter Simulation Conference. This year's conference will be held Dec. 5-8 at the Pointe Hilton at Squaw Peak in Phoenix, Ariz. The program includes introductory and advanced tutorials, computer, manufacturing and military applications, and presentations and exhibits by many of the vendors in this survey, as well as methodology and analysis sessions. Further details and registration information are available from the permanent Winter Simulation Conference Web site, www.wintersim.org. Other sponsors of the conference can be linked from this Web site. Trends in Simulation Software Simulation software is an increasingly mature technology. The underlying methodology (e.g., the next event calendar and random number generation) is well-established and essentially the same for all products. Much of the difference between products is in the basic constructs provided for modeling and in their user interfaces. Most of the systems have graphical interfaces based upon either the process description or network paradigms. There is little programming required and most parameters and options are specified by means of pull-down menus. Increasingly, animation facilities are built into the basic modeling capability, so that a minimum level of animation is immediately available. In some cases, the built-in animation can be quite sophisticated. As the user base of the software increased, it became feasible to tailor the interface to specific application, such as manufacturing, services such as healthcare and logistics, telecommunications and business processes. In some cases, this meant much more than simply altering the model-building interface; as simulation products become more focused, it is also possible to imbed more detailed and specific information into the model. For instance, COMNET includes predefined constructs for particular transmission cables and protocols, while MEDMODEL provides logic and animation icons for typical elements of a healthcare service facility. One group of products can be characterized in the integration of the model building functions in their interface. Ease of use and comprehensiveness are found in products such as AUTOMOD, PROMODEL, TAYLOR II and WITNESS, for example. Other products have evolved using a hierarchical structure. For instance, ARENA, Extend and SLX have multiple layers of generality. The lowest-level elements can be built into modules that either represent commonly encountered composite elements (e.g., in a manufacturing setting, the combination of input conveyor, buffer, server and perhaps inspection station) or specialized modules for a specific application area (e.g., a work unit plus animation). Such a structure appears to promise many of the advantages of an applications-oriented simulator, while access to the lower levels of the hierarchy permit the generality associated with a general-purpose simulation language. In parallel to other computer software, simulation software is increasingly able to share information with other applications. Many of the products here can accept information from a variety of spreadsheets or database formats, and can output data to them as well. Most of the products also provide access to procedural languages which can be linked to the simulation code (whether C code or Visual Basic), which can access specialized information sources or perform specialized computations, such as scheduling and decision-making within the simulated system. Simulation packages are increasingly integrated through the vendor-provided add-on software for such tasks as costing, scheduling, input modeling or experimentation run control (specification of runs, collection of run data, and analysis of the results). Several of the programs can perform some automated optimization, particularly for determining the best of specified set of choices or for factorial experiments. Input modeling modules can be used to display, summarize and analyze raw data and rank fitted distributions based upon the data. For those products that don't include input modeling, there are two products in this survey which will provide input modeling: ExpertFit and Stat::Fit. Each can be used to observe data to a wide variety of distributions and can then specify the syntax for realization of the fitted distributions for almost all of the simulation programs. Perhaps the most interesting development for simulation is the interaction between the World Wide Web and simulation. In recent years the development of portable programming codes such as Java means that simulations can be run on any machine, regardless of source. The Web is also being utilized for interactive distributed simulations between dispersed sites. These distributed simulations can be used to enlarge the domain of the simulations (cooperating companies can run their simulations together in order to simulate joint operations), or simulations can be run interactively in a "gaming" mode, to see how a given configuration or strategy will compete in the uncertain marketplace. The distributed simulation could also be logical, as when a control system is run in conjunction with a simulation in place of the real system. Applications The growth of simulation applications has expanded in the last two years. Improvements in simulation interfaces and the development of application-oriented simulators will increase the accessibility of simulation. Animated simulation output provides credibility and an immediacy for model developers, which is harder to achieve with sample statistics. Transportation is a growing area of simulation use. Examples of simulation use can be cited for all modes of shipment; and most major carriers, whether air, rail, ship or truck, now employ simulation to study and streamline their operations. Ports and air terminals use simulation to determine their capacity and to improve their operations. Carriers use simulation to rationalize their operations and to fine-tune their dispatching policies. Pressures to remain cost competitive while enhancing the level of performance have made simulation critical throughout the transportation industries. The military employs simulation to model almost all aspects of its operations from the unit level to large commands. These simulations are used to pre-test prototype equipment, to develop and evaluate doctrine, and for training. Simulation can be used in place of component units to exercise commanders. Developments in distributed simulation will make it possible to link individual trainers (e.g., tank or aircraft simulators) so that simulation can supplement more expensive field training for unit training. For this reason, the military has been a leading proponent of animation and interconnected simulations, and is already interested in combining these into "virtual" simulations. Simulation use is also heavy throughout the commercial world. As service systems become automated, simulation is used to tune equipment configurations and to predict performance. Sensitivity studies are also made of these systems to examine system robustness and likely failure modes. Service industries use simulation to test scheduling algorithms and to ensure that performance can be maintained under a wide variety of operating conditions. References Swain, J. J. (1997),"Simulation Goes Mainstream," OR/MS Today, Vol. 24, No. 5, pp. 35-37. James J. Swain is associate professor in the ISEEM Department at the University of Alabama in Huntsville. He is active in the INFORMS College on Simulation and the Winter Simulation Conference. He can be reached via e-mail at swain@ise.uah.edu. Be sure to visit the 1999 Simulation Survey web pages. Table of Contents OR/MS Today Home Page OR/MS Today copyright © 1999 by the Institute for Operations Research and the Management Sciences. All rights reserved. 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