A Modeling and Simulation Primer

Welcome to the world of modeling and simulation (M&S). M&S is being used worldwide by the military, industry, and academia as a technological enabler to enhance training, analysis, and acquisition activities.

Military forces have determined that M&S can provide a realistic, and sometimes cheaper, way to train. Ammunition, fuel, and repair parts are expensive. M&S provides a method for training individuals and units in a safe environment, while optimizing the expenditure of your precious, limited resources. Military analysts use M&S to help shape the size, composition, and structure of forces to meet national military requirements, and to assess the sufficiency of operational plans. The military acquisition community uses M&S: (1) to evaluate requirements for new systems and equipment; (2) to conduct research, development and analysis activities; (3) to develop digitized prototypes and avoid the building of costly full scale mockups; and (4) to plan for efficient production and sustainment of the new systems and equipment when employed in the field.

Industry uses M&S in much the same way. The quality of training and analysis activities can be dramatically enhanced through the effective and efficient integration of M&S capabilities. Commercial firms incorporate M&S into all phases of the development of new products, covering the entire life cycle from concept development to sustainment. Academia has become a hotbed of M&S activities as this technology is used to augment instruction and research in a wide array of academic settings.

At the present time, the use of M&S is expanding dramatically. We intend to provide you with some basic information on M&S in the rest of this paper to allow you to better understand the potential positive impact of this exciting technological capability.

Let's start with some basic terms and points of discussion:

A model is a physical, mathematical or logical representation of a system, entity, phenomenon, or process. There is no movement in a model. Think of a plastic replica of an airplane or a car, or a mathematical equation that predicts the probability of an event occurring. These are examples of models.

A simulation is the implementation of a model over time. It shows how the model works. It is a technique used for testing, analysis, or training, where a model can represent “real world” systems or concepts. A simulation moves. You can see the model(s) in the simulation moving—whether it shows military units moving across a battlefield or engine parts moving in a simulated car engine.

Modeling and simulation (M&S) provides virtual duplication of products and processes, and represents those products or processes in readily available and operationally valid environments. Use of such models and simulations can reduce the cost and risk of “life cycle” activities.

M&S should be applied throughout a system’s life cycle in support of systems engineering activities. Systems engineers integrate the use of modeling and simulation tools and technology into all development / management activities, as well as, plan for life-cycle application, support, and reuse of models and simulations. Since M&S plays such a big role in test and evaluation, system engineering planning must be especially clear in integrating testing and M&S activities.

The Classes of Simulations

The U.S. Department of Defense has established three classes of simulations - virtual, constructive, and live:

Virtual simulations represent systems both physically and electronically. Think of a video game or a cockpit mockup used to train pilots--these are virtual simulations.

Constructive simulations represent systems and their employment through the use of extensive, complex mathematical and decision-based modules and statistical techniques. A constructive simulation is a computer program. The user inputs data to cause an event to occur, then gets the results. For example, a military user may input data on a military unit telling it to move and to engage an enemy target. The constructive simulation determines the speed of movement, the effect of the engagement with the enemy, and any battle damage that may occur. Results can be provided digitally or visually, depending on the type of simulation used.

Live simulations are simulated operations conducted by real operators using real equipment. Military training events using real equipment are live simulations. They are considered simulations because these events are not conducted against a live enemy.

How can you trust the model or simulation? How do you know if it is providing an accurate representation of reality?

You establish confidence in your model or simulation through formal verification, validation, and accreditation (VV&A). VV&A is usually identified with software, but the basic concept applies to hardware as well.

Verification is the process of determining that a model implementation accurately represents the developer’s conceptual description and specifications. It answers the question, “Did we build it correctly?”

Validation is the process of determining the manner and degree to which a model is a accurate representation of the real-world from the perspective of the intended uses of the model, and of establishing the level of confidence that should be placed on this assessment. It answers the question, "Did we build the right thing?”

Accreditation is the formal certification that a model or simulation is acceptable to be used for a specific purpose. A recognized subject matter expert in the field can accomplish accreditation. Accreditation answers the question, “Does it meet my needs?”

Let's discuss the realism of the model or simulation. When discussing realism, we use two basic terms—Fidelity and Resolution. Cost is a factor as realism can be expensive in terms of resources and computing power.

Fidelity is the degree to which aspects of the real world are represented in M&S. It is the foundation for development of the model and subsequent VV&A. Fidelity is a measure of how the model or simulation acts. Does it act like the real thing?

Resolution is the degree to which physical (appearance) aspects of the real world would be represented. Resolution is a measure of how the model or simulation looks. Does it look like the real thing?

Cost is a serious issue in terms of both fidelity and resolution. Both require money and computing power. The key is to require only what is needed to do the job. The correct balance between cost and fidelity/resolution should be the result of a requirements needs analysis.

Future of M&S

Advanced M&S may integrate a mix of computer simulations, actual warfighting systems, and weapon system simulators. The entities may be distributed geographically and connected through a high-speed network. Warriors at all levels will use M&S to challenge their military skills at tactical, operational, or strategic levels of war through the use of synthetic environments representing every potential opponent in any region of the world, with realistic interactions. Acquisition personnel may use the same synthetic environments for research, development, and test and evaluation activities. M&S will increasingly be used to improve efficiency and effectiveness in engineering development functions. Acquisition personnel will also use synthetic environments to support the acquisition decision-making process.