relevant to the purposes of this study. Tracing the series of analytic choices above in the context of a particular example should help illustrate where potential areas of analytic uncertainty and error can enter into a representative application of simulation-based prediction.

2.2 PROJECTILE-IMPACT EXAMPLE PROBLEM

Consider the situation depicted in Figure 2.1, which is an example adapted from Thompson (1972). The system under consideration consists of a cylindrical aluminum rod impacting the center of a cylindrical aluminum plate at high speed. This kind of system could be informative when trying to understand the behavior of a projectile impacting armor.

At the start of the problem, the cylindrical rod is moving downward at high velocity and is just touching the thick plate (Figure 2.1, left). The image on the right in Figure 2.1 represents a “slice” through the center of the system and uses color to represent density.

Assume that interest centers on the problem of predicting the behavior of the rod and plate system. First, it must be decided which aspects of the system behavior are required to be predicted—the QOIs. There are several possibilities: the depth of penetration of the plate as a function of impactor velocity, the extent of gross damage to the plate, the fine-scale metallographic structure of the plate after impact, the amount of plate material ejected backward after the rod impact, the time-dependent structure of loading and unloading waves during the impact, and so on. In general, the number of possible QOIs that could be considered as reasonable candidates for prediction is large. Which aspects are important is application-dependent—depending, for example, on whether application focus is on improving the performance of the projectile or of the armor plate—and will influence to a large degree the simulation approach taken by the analyst.

A question that emerges at this stage is the degree of accuracy to which the prediction needs to be made. This also depends on the application under consideration. In this rod and plate example, it may be that the primary QOI

image

FIGURE 2.1 Aluminum rod impacting a cylindrical aluminum plate.



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