The qualitative behaviour of dynamic physical systems
Qualitative representations concentrate on general behaviours rather than numerical accuracy. This thesis introduces methods for producing qualitative descriptions of dynamically changing quantities. A distinction is made between scalar and vector representations of quantities, and several qualitative vector operations are defined, including a qualitative calculus. These operations correspond closely to their normal numerical counterparts. A systematic approach to a model-based method is presented for the analysis of physical systems, which allows the derivation of behaviour for a range of operational conditions. A simple electrical example is used to illustrate completeness of results. The use of qualitatiave reasoning for design support is shown with reference to thermal conditions in a chemical reactor. Qualitative methods are examined in the context of steady-state conditions, instabilities, and potential fault indicators. Application to control problems is illustrated by a system of coupled tanks. Progressively more complex controllers are introduced using different strategies to improve control. The problem of scaling qualitative relationships to external conditions is related to equivalent work in fuzzy logic. Detection of slow trends in system behaviour is shown through a qualitative representation of a car suspension system, which relates changes in component values to changes in system behaviour.