Simulating the dynamic response of a complex structure to its environment requires the formulation of a suitable mathematical model of the structure in its environment and efficient solution algorithms for calculating the response. Also required are methods for specifying the problem in a convenient way, and methods for viewing the results. The finite element method provides a universal tool for formulating mathematical models, as its pervasive use attests. The method is ideally suited to the digital computer, the mathematical model being formulated by a computer program. However, a complex problem's definition and its specification to a computer system can require considerable human effort. By modeling a complex structure as an assemblage of substructures, the human effort can be subdivided and the total effort reduced.