| Physical system behavior follows the general principles of conservation of energy and continuity of power, but may exhibit nonlinearities that result from small, parasitic effects, or occur on a time scale much smaller than the time scale of interest. At a macroscopic level, the detailed continuous behavior may appear to be discontinuous, thus the system is efficiently described by a mixed continuous/discrete, hybrid, model. In continuous modes the energy distribution describes the system state. Discrete configuration changes in the model may cause discontinuities in the energy distribution governed by the principle of conservation of state, and may trigger further configuration changes till a new real mode is achieved where no further changes occur. The intermediate, mythical modes between two real modes have no physical representation. The principle of invariance of state applies to derive the energy distribution in a mode as a function of the energy distribution in the preceding real mode. When a loop of consecutive instantaneous mode changes occurs time stops progressing. This conflicts with known physical system behavior, therefore, the principle of divergence of time forms an important model verification mechanism. The principle of temporal evolution of state requires the energy state to be continuous in left-closed time intervals to ensure proper causal attribution.;From another viewpoint, abrupt faults in process components can be modeled as discontinuities that take system behavior away from its nominal, steady state, operation. To quickly isolate the true faults, well constrained hybrid models avoid the inherent intractability problems in diagnostic analyses by integrating and facilitating the (1) generation of behavioral constraints from physical laws, (2) expression of system dynamics as energy transfer between constituent elements, and (3) modeling of steady state behavior as a special case of dynamic behavior. The analysis of transients is paramount to accurate and precise fault isolation. However, this is a difficult problem which can be further complicated by operator intervention, and intermittent and cascading faults, therefore, quick capture and analysis of transients is the key to successful diagnosis.;This thesis develops a formal hybrid modeling theory based on physical principles, a model verification method, and a physically correct behavior generation algorithm. Next, it describes a methodology for monitoring, prediction, and diagnosis of dynamic systems from transient behavior, based on the developed hybrid bond graph modeling paradigm. Simulation results from diagnosing a high-order, nonlinear, model of a liquid sodium cooling system in a nuclear reactor demonstrates the success of the approach. |
