Research On Mechanical Symmetry Concept, Function And Acquisition Of Application Knowledge

There widely exists symmetry in mechanical systems, covering the mechanical systems from small standard parts to large machine system. Symmetry is embodied by the visual geometrical structures, the abstract functions and the principles of mechanical systems. Deep and systemic research on mechanical symmetry can guide the application of symmetry to better realize the function of mechanical systems, improve their performance, meet their design restrictions, and finally increase the technical, economic and social performances of mechanical products. Moreover, research on symmetry will also benefit innovative design, and escalate the market competitiveness of mechanical products. After synthetic analysis on the research history and situation of symmetry in different domains, aiming at the drawbacks of current research in mechanical symmetry, research on mechanical symmetry concept, function and acquisition of application knowledge is carried out. The main research and primary contributions are reflected in the following four aspects:Firstly, the concept system of mechanical symmetry was established. After the research on the existence of symmetry in mechanics and other domains, the concept and hierarchical structure framework of mechanical symmetry was proposed. By summarizing and extending of concept framewrok of biologic symmetry and physical symmetry, the ontology framework of biology symmetry and physics symmetry was established, and then a symmetry ontology framework for general systems was presented. By combining the above works with the analysis of a large number of instances of mechanical symmetry, the framework of mechanical symmetry ontology, categorized into function symmetry, principle symmetry, structure symmetry, was set up. Furthermore, the definitions of different kinds of mechanical symmetry were put forward and their existence and working principles in mechanical systems were illustrated. Then the application strategies of structure symmetry, principle symmetry and function symmetry on improving and innovating products were discussed. Finally, the commonness of symmetry in natural and engineering systems, including hierarchical structure, correlation, multi-body, multi-element, multi-dimension and combination was discovered.Secondly, the research on knowledge discovery method of mechanical structure symmetry design and an algorithm for mining associating rules based on transaction attribute combination and comparative pattern mapping (CPM) was conducted. There existed much regular symmetry application knowledge in the large number of symmetry instances. The application of KDD (Knowledge Discovery in Database) in the knowledge discovery of symmetry instances and utilization of computer-aid methods to mine design knowledge in deep-level is the basis to promote the correct application of symmetry in mechanical design. An instance-based knowledge discovery process and method for mechanical structure symmetry design was proposed. And then the basic knowledge database of structure symmetry design, the model of structure symmetry instance and the template of structure symmetry design knowledge were established. A mining algorithm for associating rules based on transaction attribute combination and comparative pattern mapping (CPM) was presented aiming at the databases with a large mount of attributes but a small mount of transactions. By comparing CPM algorithm and classical algorithms, it is indicated that CPM has a satisfactory effect in calculating associating rules for databases with multiple attributes, especially for low supporting associating rule. By using knowledge discovery method of mechanical structure symmetry design and the CPM algorithm to mine associating knowledge from symmetric instances and abstract the associating knowledge, the general structure symmetry application knowledge could be obtained.Thirdly, the application knowledge of mechanical structure symmetry were established. By applying the knowledge discovery method of mechanical structure symmetry design to mine the associating knowledge from vast symmetric instances, the associating knowledge was sorted, summarized and abstracted and some application knowledge of symmetry in mechanical structure design was proposed. The bidirectional associating knowledge between design demands, general design principle and structure symmetry was proposed. Some knowledge of applying structure symmetry in realizing design function demands and design performance demands were proposed. Correctly applying the mechanical structure symmetry application knowledge could be beneficial for realizing design demands better, increasing the technical, economic and social performances of mechanical products, improving design efficiency and implementing product innovation with rapid response to consumers'demands.Fourthly, research on realization and application of computer-aided knowledge discovery system for mechanical symmetric instances was put forward. On the basis of above theory, the knowledge discovery system for mechanical symmetric instances (KDDMSI) was established. The software framework included basic knowledge management module, symmetric instance management module and symmetry design knowledge mining module. By applying the KDDMSI system in mechanical structure symmetry design knowledge discovery, a lot of mechanical symmetry associating knowledge was mined.