Using Modelica Models for Qualitative Reasoning

Applications of qualitative reasoning to engineering design face a knowledge acquisition challenge. Designers are not fluent in qualitative modeling languages and techniques. To overcome this barrier, we perform qualitative simulation using models solely written in Modelica, a popular language for modeling hybrid systems. We define the relationship between the results of the Modelica and qualitative simulations and describe how qualitative simulation from numerical models can assist designers. We discuss challenges and solutions for abstracting equations into constraints, determining initial conditions, continuous behavior, and discrete events. In particular, we identify three places where additional constraints should be derived from Modelica equations, and describe how we bridge the gaps between Modelica and existing qualitative simulation work on discrete behavior. Our system has been integrated with the OpenModelica1 tool and we discuss its potential design applications.