A computer program called "the explicit global-modeling tool" implements a dynamic method of operation by which researchers can (1) determine global flow-path changes that occur during computational simulations of the behaviors of engineering systems; (2) analyze both normal and faulty qualitative system behavior; and (3) identify the corresponding local changes, caused by operational events or failures, in mathematical models of such systems. The program is a generic device-modeling tool that effects a software version of human qualitative analysis of device behavior.

Although progress has been made in qualitative modeling and analysis of perturbations in electrical circuits, by use of graph clustering (which is a continuous system-modeling method), the method implemented in the explicit global-modeling tool provides a significant advance over the continuous system-modeling method. In continuous system modeling, conventional numerical analysis is used to compute quantitative values of the behavior of a system and its components in each steady state. Analysis of dynamics involves solving equations for all proposed topologies and comparing these results to derive changed values; this is a very complex process, and in order to be able to effect the process, one must identify the dynamic topologies and appropriate simplifications and statistical assumptions for the system to be analyzed.

In contrast, the explicit global-modeling tool implements a method compatible with local modeling, discrete simulation, and analysis. Far less complex than any computer program developed previously for the same purpose, this program disentangles important global system-power-transmission variables from local component variables. This program thus supports abstracted general-purpose local mathematical models, and does not require the development of multiple-system, configuration-specific mathematical models for each component as is required in continuous system modeling.

The basis of the design of the explicit global-modeling tool is a data structure and algorithms in which flow-path elements communicate with one or more parent objects. Each parent object represents a subgraph of an overall flow network in a modeled system. During simulations, the elements report information on their local states, and the parent objects report to their elements the statuses of flow-related attributes of the subgraphs — e.g., whether an external flow into a subgraph occurs because of sources external to that subgraph.

The qualitative method of abstraction used in the explicit global-modeling tool supports the use of discrete-event-simulation approaches in analyzing analog systems. The power-transmission abstraction and clustering approach also afford broad applicability to several discrete and analog domains, and to such analysis domains as reliability block-diagram analysis. The program has already been demonstrated to be especially useful in applications of the type for which it was designed; namely, analysis of spacecraft equipment systems. Other, industrial uses are expected to evolve as the program becomes modified in subsequent development efforts.

This work was done by Jane T. Malin of Johnson Space Center and Land D. Fleming of Hernandez Engineering, Inc. This invention has been patented by NASA (U.S. Patent No. 5,732,192). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to

the Patent Counsel, Johnson Space Center, (281) 483-0837

Refer to MSC-22618.

NASA Tech Briefs Magazine

This article first appeared in the December, 1998 issue of NASA Tech Briefs Magazine.

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