Structural, Behavioral and Functional Modeling of Cyber-Physical Systems
Building preliminary mathematical models to simulate system behavior is an essential part of designing dependable cyber-physical systems (CPS). This thesis presents the implementation of a visual modeling environment that supports compositional component-based modeling and simulation of cyber-physical systems. For this purpose, we have designed a domain specific modeling language (DSML), then implemented two model interpreters, and a MatlabŸ block- and function- library to support the model building and simulation tasks. The modeling language employs the hybrid bond graph formalism to facilitate building cross-domain physical system models, and an extended version of the Grafcet model of computation to formally represent and analyze the discrete behavior evolution of the hybrid system. Domain models complying with the DSML capture the Functional, Behavioral and Structural aspects of the system, by explicitly modeling the interaction of the physical processes and the controlling computational units. The associated model interpreter automates the generation of hybrid simulation models. Grafcet models also incorporate logical constraints to express functional requirements for the system in the form of Hoare triples. Finally, the thesis also presents a case study, which describes the approach to model building and simulation of the Reverse Osmosis subsystem of the NASA Advanced Life Support System. The original test results from the testbed at NASA Johnson Space Center confirm the correctness of our model and simulation results.