Söderman, U., Top, J., and Strömberg, J. E. (1994). Modelling Physical Systems with Changing Structure. Technical Report LiTH-IDA-R-94-06, Department of Computer and Information Science, Linköping University, Sweden. (bibtex),
Abstract: Causality plays an important role in essentially any aspect of reasoning about physical systems. However, causal directedness is problematic when the physical structure, i.e. the interaction between subsystems changes. This is due to the fact that causality is a global property. This problem can in principle be solved by specifying acausal models and to derive causality afterwards for the complete model. This is possible because physical systems are connected through bilateral signal flows, with no a priori fixed direction.Sofar, there has been no systematic and efficient way to represent acausal models of structures that undergo change. This would be an important feature of automated modelling and reasoning systems. In this paper we propose the definition of an ideal, generic switching element solving exactly this representation problem. The definition also adds a new ontological primitive to the bond graph language, though the general definition is not restricted to any specific modelling approach. Furthermore, the clear and explicit bond graph method to derive the overall causality can be reused unaltered. Several examples are presented to illustrate our approach.
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