Computer Modeling

█ JUDSON KNIGHT

Modeling, in the technical use of the term, refers to the translation of objects or phenomena from the real world into mathematical equations. Computer modeling is the representation of three-dimensional objects on a computer, using some form of software designed for the purpose. Among the uses of computer modeling are war games and disaster simulations, situations in which computers offer a safe, relatively inexpensive means of creating or re-creating events without the attendant loss of life or property.

Mathematics, Computers, and Modeling Software

Mathematical modeling dates to advances in geometry and other disciplines during the late eighteenth century. Among these was the descriptive geometry of French mathematician Gaspard Monge, whose technique was so valuable to Napoleon's artillery that it remained a classified defense secret for many years. Nearly one and a half centuries later, at the end of World War II, mathematicians and scientists working for the United States war effort developed a machine for readily translating mathematical models into forms easily grasped by non-mathematicians.

That machine was the computer, and during the last two decades of the twentieth century, varieties of three-dimensional modeling software proliferated. These included any number of computer animation and gaming packages, as well as varieties of computer-aided design/computer-aided manufacturing (CAD/CAM) systems. CAD allowed engineers and architects, for instance, to create elaborate models that allowed them to "see into" unbuilt structures, and to test the vulnerabilities of those structures without risking lives or dollars.

One notable variety of three-dimensional software is virtual reality modeling language, abbreviated VRML and pronounced "ver-mal." Necessary for representing three-dimensional objects on the World Wide Web (that portion of the Internet to which general users are most accustomed), VRML creates a virtual world, or hyperspace, that can be viewed through the two-dimensional computer screen. By pressing designated keys, the user is able to move not only up, down, right, and left, but forward and backward, within this virtual world.

Disasters, Wars, and Other Simulations

After the space shuttle Columbia crashed on February 1, 2003, analysts at the National Aeronautics and Space Administration (NASA) used modeling software applied by the National Transportation Safety Board (NTSB) for studying crashes. In applications such as those for the NASA and NTSB studies, the purpose is to understand not only what happened, but how and why it happened, and what caused it.

The more data available on a disaster, the better the model, and this in turn gives investigators more accurate tools for analysis. In the end, however, there is no substitute for human reasoning. For example, an NTSB simulation of the Swissair Flight 111 crash in September 1998 tracked the course of a fire from the cockpit that eventually brought down the plane, but it did not explain what caused the fire.

Still, the simulation is invaluable inasmuch as it provides human minds with an extraordinarily accurate and vivid source of information as to the exact sequence of events that took place during a disaster. NASA analysts used computer modeling to study the first great shuttle disaster, that of Challenger in 1986, but the technology of 2003 was vastly superior. Not only was a $2,000 computer capable of running simulations that required a $75,000 machine 17 years earlier, but advances in graphics—spurred, ironically, by the seemingly frivolous demands of gaming and the movies—had resulted in a vastly more accurate picture of what happened.

War games and terror simulations. The connection between entertainment and simulation in general, as well as computer modeling technology in particular, has not been lost on the U.S. security and defense leadership. In the immediate aftermath of the September 11, 2001, terrorist attack, federal officials brought together a team that included David Fincher, director of Seven and Fight Club; Steven E.

De Souza, screenwriter for Die Hard; and Spike Jonze, director of Being John Malkovich. The assignment placed before these creative minds was one ideally suited to Hollywood: to imagine scenarios in which terrorists attacked the United States.

These scenarios, along with other forms of input, have helped form the basis for simulations by groups such as the Institute for Creative Technologies (ICT), a research center at the University of Southern California at Los Angeles. ICT is one of many entities in which the federal government invests nearly $100 million a year for the purpose of developing military simulations—studies that, unlike the disaster models for NTSB or NASA, are concerned not so much with what has happened as with what could happen. The Department of Defense also has its own simulation think tanks, including the U.S. Army Simulation, Training, and Instrumentation Command, known as STRICOM.

Simulations developed by ICT are mind-boggling in their degree of verisimilitude. The "virtual humans" on screen are not automatons; rather, they have been programmed with personalities and emotions, like characters in a movie. Cutting-edge computer technology makes it possible to even simulate smells. In an unusual merger of public and private sectors, ICT has sold commercial versions of games it co-produced with the U.S. Army.

The purpose of simulations produced by ICT and others involved in computer modeling goes far beyond mere entertainment: at a fraction of the expense and risk involved in war games involving real troops and equipment, commanders and their subordinates can study and learn from battle. Computer modeling also makes it possible to study dozens of different terror, but without any human or financial cost. By providing laboratories for instruction, simulations may prevent losses in real situations.

█ FURTHER READING:

BOOKS:

Danby, J. M. A. Computer Modeling: From Sports to Spaceflight—From Order to Chaos. Richmond, VA: Willmann-Bell, 1997.

Emmer, Michele. The Visual Mind: Art and Mathematics. Cambridge, MA: MIT Press, 1993.

Modeling and Simulation: Linking Entertainment and Defense. Washington, D.C.: National Academy Press, 1997.

ELECTRONIC:

Lee, David B., Lt. Col., USAF. "War Gaming: Thinking for the Future." Airpower Journal <http://www.airpower.maxwell.af.mil/airchronicles/apj/3sum90.html> (March 14, 2003).

U.S. Air Force Wargaming Institute. <http://www.cadre.maxwell.af.mil/wargame/main.htm> (March 14, 2003).

U.S. Army Program Executive Office for Simulation, Training, and Instrumentation. <http://www.stricom.army.mil/> (March 14, 2003).

SEE ALSO

Internet
NASA (National Air and Space Administration)
NTSB (National Transportation Safety Board)
Supercomputers

Computer Modeling

Computer modeling is a general term that describes the use of computers to simulate objects or events. As such, it is sometimes known as computer simulation. Forensic applications of computer modeling can produce purely graphical results (for example, the face of an unknown murder victim reconstructed from a skull) or mathematical idealizations of physical, chemical, biological, or geological processes (for example, calculations performed to estimate the speed of a vehicle before an accident). Most forensic computer models are extensions of graphical and mathematical techniques that have been used by forensic scientists for many years, but which have become much more complicated and visually compelling because of continuing advances in computer technology.

Craniofacial reconstruction (re-building the shape of the skull and face) is one example of a purely empirical graphical forensic technique that is adaptable to computer modeling. The traditional approach is to shape layers of clay placed on a cast of a skull in order to produce a likeness of an unknown person. The thickness of clay on different parts of the skull is constrained by information from tissue thickness databases, which were originally obtained from cadavers but now measured using techniques such as computerized tomography (CT) scans, magnetic resonance imaging (MRI), or ultrasound imaging of living subjects. This has been an important advance, because cadaver measurements represented only a small segment of the general population.

In computer-assisted craniofacial reconstruction, a virtual representation of the skull is created using a laser scanner or stereo photography to produce a three-dimensional mesh of points. Tissue thickness at selected points on the skull is specified mathematically, often using statistical relationships derived from large CT scan or MRI database, and the shape of the face is modeled as a smooth three-dimensional surface that passes through the measurement points. The main weakness of any craniofacial reconstruction technique is that the soft tissue thickness is always an estimate and it is difficult to infer facial characteristics reflecting age, weight, sex, and ethnicity from skull shape (although this information can be inferred from a complete skeleton). Superficial characteristics such as hair color and skin texture are impossible to infer from skull shape and are only artistic embellishments. Therefore, a general resemblance between a craniofacial reconstruction and a deceased person is the best that can be achieved.

Process-based forensic computer models combine equations describing physical or chemical processes with empirical information in order to reconstruct sequences of events. One widely used computer program for automobile accident reconstruction, known as SMAC (Simulation Model of Automobile Collisions), was originally developed by the National Highway Traffic Safety Administration. It uses Newton’s laws of force and motion to simulate colliding automobiles as moving bodies in much the same way that one might simulate the collision of billiard balls. Factors such as road condition and tire type are incorporated using empirical coefficients, and the model input is adjusted until the output agrees with observations made at the accident site. Whereas this kind of computer model might calculate the energy at impact, it would not explicitly simulate the crumpling and deformation of the automobiles. Computer animation can be used to visualize the results of process-based models by depicting the automobiles as specific makes, models, and colors rather than nondescript masses or by incorporating realistic topography and scenery to simulate the accident scene. This kind of animation, in which variables such as vehicle position and speed are the result of scientific analysis and inference, is known as forensic animation.

A more sophisticated kind of process-based computer modeling involves the detailed simulation of physical or chemical processes in two or three dimensions (and often over time) in order to reconstruct an event or process. For example, a sophisticated accident model might simulate the bending and buckling of each structural member in an automobile rather than just the total amount of energy absorbed by one moving mass colliding with another. Another example is the use of computer models to simulate the two and three-dimensional movement of chemicals contaminating an aquifer. In order to obtain accurate results using this kind of model, geologists must collect detailed information about the materials comprising the aquifer by drilling test wells, taking samples of the aquifer materials, and conducting a variety of tests. The velocity and chemical composition of the ground-water are then calculated at many thousands, and perhaps even millions, of points within the simulated aquifer and the model is calibrated by adjusting the input until the results agree with observed conditions. Experts can use this kind of model to infer the source of the contaminants or the time that they entered the aquifer, which can be important in legal proceedings such as the well-known lawsuit concerning groundwater contamination in Woburn, Massachusetts. Fire scientists likewise use computational fluid dynamics models to simulate the spread of fires in buildings, and other computer models can be used to simulate the mechanics of solid objects, the flow of fluids, and chemical reactions. As computer models become more complicated, however, they also become more difficult to apply because the quality and quantity of input increase dramatically. As is the case for simple process-based models, the results of multidimensional can be visualized using static and animated computer graphics.

See also Forensic science; Geospatial imagery.

William C. Haneberg

Computer Modeling

Computer modeling is a general term that describes the use of computers to simulate objects or events. As such, it is sometimes known as computer simulation. Forensic applications of computer modeling can produce purely graphical results (for example, the face of an unknown murder victim reconstructed from a skull ) or mathematical idealizations of physical, chemical, biological, or geological processes (for example, calculations performed to estimate the speed of a vehicle before an accident). Most forensic computer models are extensions of graphical and mathematical techniques that have been used by forensic scientists for many years, but which have become much more complicated and visually compelling because of continuing advances in computer technology.

Craniofacial reconstruction (re-building the shape of the skull and face) is one example of a purely empirical graphical forensic technique that is adaptable to computer modeling. The traditional approach is to shape layers of clay placed on a cast of a skull in order to produce a likeness of an unknown person. The thickness of clay on different parts of the skull is constrained by information from tissue thickness databases, which were originally obtained from cadavers but now measured using techniques such as computerized tomography (CT) scans, magnetic resonance imaging (MRI), or ultra-sound imaging of living subjects. This has been an important advance, because cadaver measurements represented only a small segment of the general population. In computer-assisted craniofacial reconstruction, a virtual representation of the skull is created using a laser scanner or stereo photography to produce a three-dimensional mesh of points. Tissue thickness at selected points on the skull is specified mathematically, often using statistical relationships derived from large CT scan or MRI database, and the shape of the face is modeled as a smooth three-dimensional surface that passes through the measurement points. The main weakness of any craniofacial reconstruction technique is that the soft tissue thickness is always an estimate and it is difficult to infer facial characteristics reflecting age, weight, sex, and ethnicity from skull shape (although this information can be inferred from a complete skeleton). Superficial characteristics such as hair color and skin texture are impossible to infer from skull shape and are only artistic embellishments. Therefore, a general resemblance between a craniofacial reconstruction and a deceased person is the best that can be achieved.

Process-based forensic computer models combine equations describing physical or chemical processes with empirical information in order to reconstruct sequences of events. One widely used computer program for automobile accident reconstruction , known as SMAC (Simulation Model of Automobile Collisions), was originally developed by the National Highway Traffic Safety Administration. It uses Newton's laws of force and motion to simulate colliding automobiles as moving bodies in much the same way that one might simulate the collision of billiard balls. Factors such as road condition and tire type are incorporated using empirical coefficients, and the model input is adjusted until the output agrees with observations made at the accident site. Whereas this kind of computer model might calculate the energy at impact, it would not explicitly simulate the crumpling and deformation of the automobiles. Computer animation can be used to visualize the results of process-based models by depicting the automobiles as specific makes, models, and colors rather than nondescript masses or by incorporating realistic topography and scenery to simulate the accident scene. This kind of animation, in which variables such as vehicle position and speed are the result of scientific analysis and inference, is known as forensic animation.

A more sophisticated kind of process-based computer modeling involves the detailed simulation of physical or chemical processes in two or three dimensions (and often over time) in order to reconstruct an event or process. For example, a sophisticated accident model might simulate the bending and buckling of each structural member in an automobile rather than just the total amount of energy absorbed by one moving mass colliding with another. Another example is the use of computer models to simulate the two and three-dimensional movement of chemicals contaminating an aquifer. In order to obtain accurate results using this kind of model, geologists must collect detailed information about the materials comprising the aquifer by drilling test wells, taking samples of the aquifer materials, and conducting a variety of tests. The velocity and chemical composition of the groundwater are then calculated at many thousands, and perhaps even millions, of points within the simulated aquifer and the model is calibrated by adjusting the input until the results agree with observed conditions. Experts can use this kind of model to infer the source of the contaminants or the time that they entered the aquifer, which can be important in legal proceedings such as the well-known lawsuit concerning groundwater contamination in Woburn, Massachusetts. Fire scientists likewise use computational fluid dynamics models to simulate the spread of fires in buildings, and other computer models can be used to simulate the mechanics of solid objects, the flow of fluids, and chemical reactions. As computer models become more complicated, however, they also become more difficult to apply because the quality and quantity of input increase dramatically. As is the case for simple process-based models, the results of multidimensional can be visualized using static and animated computer graphics.

see also Accident reconstruction; Aircraft accident investigations; Crime scene reconstruction; Fire investigation.