Research On Qualitative Modeling For Conceptual Design

Product conceptual design activities play an important role in product life cycle. As effective auxiliary product design and analysis tools, qualitative methods and digital prototyping can extend engineers'design mentality and provide new tools for product innovation. Traditional quantitative digital prototyping is lack of the support of non-number and inaccurate data on reason the system behavior. In fact, there is a large number of qualitative knowledge exist in conceptual design stage. Directed towards those reasons a concept of qualitative digital prototyping is proposed in this dissertation, and some key technical problems are researched.After the author analyzed and concluded the product conceptual design features, researched the traditional digital prototyping modeling and simulation theoretical, referenced the qualitative modeling and simulation theoretical, the concept of qualitative digital prototyping that defined from object, function, capability and technology is proposed in this dissertation. An object-oriented framework strategy is used to implement the framework of the qualitative digital prototyping to illustrate the structure of qualitative digital prototyping.The organic connections and interaction relationships exist between the system elements which recognized in product conceptual design stage, and structural analysis method has advantage in relationship analysis between the system elements, so a qualitative digital prototyping modeling method which based on structural modeling method is proposed in this dissertation. In this method, the interaction relationships between system elements are analyzed and described by structural modeling method first. And second, the relevant constraints which in accordance with the form of algebraic constraint and qualitative constraint in qualitative simulation models are generated between the elements which have direct causal relationships. Third, the all constraints generated in second step are filtered by constraint consistency, behavioral consistency and dimensional consistency. Finally, the qualitative differential equations which can directly use for simulation are generated.Because of Kuipers Qualitative Simulation method actually has the feature of the constraint satisfaction problems; it can be looked as solving a class of constraint satisfaction problem. In order to improve simulation efficiency and facilitate system modeling, the author use constraint logic programming language improves Kuipers Qualitative Simulation method. According to the constraint solving is based on "first generate and then to examine" principle, the constraint solving ability is added on the basis of the logical language, and it may be make it more suitable for the application of qualitative knowledge and programming.Because of qualitative simulation method is sufficient and completeness, it easy leads to the simulation contain a large number of redundant result. If the model size relatively large, the matching combination and global consistency filtering will be very difficult. Directed towards those problems two different model decomposition methods which based on strongly connected graph and genetic algorithm are proposed in this dissertation. According to the actual situation of object system, user can select different method to decompose the system model. After accomplish the model decomposition, a new simplified system model which composed by subsystems will be obtained. Each subsystem can simulate separately. Matching combination and redundant behavior filtering are distributed separately in each subsystem, the simulation efficiency will be greatly improved and the difficult of simulation will be reduced.The ambiguity which caused by qualitative computing will be reduced if we Introduce the quantitative knowledge into qualitative simulation. Synthesized the qualitative and quantitative knowledge can construct the system model at different levels, and more precise define the system and its behavior. In order to reduce the simulation branch of unnecessary, save a lot of unnecessary calculations, improve simulation efficiency, and meet different application requirements, fuzzy-based qualitative and quantitative synthesized simulation method is proposed in this dissertation. Fuzzy-based simulation method provides a method for effective application the quantities knowledge in conceptual design stage.