Research On Local Parameterization Modeling Of Concept Car Body And CFD Simulation

Car body development is a complex iteration of"design—evaluate—modify". The period of car body development is not only determined by the design speed, but also determined by whether the design can do the right choice in the early design to avoid the future modification and decrease the number of design iterations. The second factor will help the car body design enter one-way highway.The research works are supported by the Great Industrialization Project of National Automobile Industry (No.2004-2563) of National Development and Reform Commission"CAD/CAE/CAM Software Platform of Car Body Digital Fine Design and Manufacturing"(FGGJ 2040) and the key project of National 985 Innovation Platform"The Key Technology of Digitalization of Car Body Design and Manufacturing". And the research is also the important part of"KMAS System of Fast Fine Design, Manufacturing and Analysis of Car Body Structure and Parts"which gained 2007 National Sci-Tech Progress Award (II).Based on the achievements in knowledge engineering, parameter designing and CFD simulation areas, this thesis focuses the theories on building model with component's parameters of concept car body and CFD simulating integration. Using the KBE knowledge engineering and model clearing and building before CFD analyzing, a new concept that building model with component's parameters is developed for CFD analyzing. And the characteristics of car body structure designing with parameters are analyzed. The method of designing components of car body knowledge driven is introduced theoretically. These are keys in designing car body structure parametrically, automatically and theoretically. Using the fast design method based on designing car components with parameters for CFD analysis, the designers can move many future analysis works to the early period of car body design. The pre-analysis will help the designers find the potential problem and issues and avoid those issues emerged in the later period of design. In this period, the expense is very high for correction and modification to the initial design, so the design process will be delayed greatly. Moreover, the key techniques of fast car body part automatic modeling system are also studied in this paper. Those techniques can make the designers escape from some boring modeling processes and adopt them to more valuable innovation.Following techniques are applied in the fast design system of car body and parts. 1,CAS_CFD Floor FormingThe CFD analysis is necessary for aerodynamic optimization of car body. A floor model must be cleared and built before CFD simulating and analyzing. The step is necessary and time consuming in the processes of CFD analyzing about car body. In traditional simulating methods, the shape and characteristic of the floor are ignored so that the results of aerodynamic lift are unreliable. This thesis develops"CAS_CFD Floor Fast Design Module"in UG/NX platform. Using the module, the designer can design the floor knowledgeably, parametrically and quickly based on the floor's shape and characteristic. A floor model is built using this module based on a car body CAS model. And the contrast of this model and traditional model is researched in Fluent software. The simulation results show that the model built in"CAS_CFD Floor Fast Design Module"is reliable and efficient.2,CAS_CFD Wheel Fast Design ModuleWheel shaping is one part of body shaping and in same type. Due to its'variable shapes, the workload of clearing and simplifying wheel model counts about 20% in whole. In traditional ways, the engineers usually trade wheels as simple cylinders to reduce workload. And the shape of wheel rim is ignored too. These often amplify error in calculation. The aerodynamic drag force concerning wheel counts about 30% in whole aerodynamic drag force. So an accurate wheel model that provides fundamental characteristics will greatly increase accuracy of CFD calculation. This thesis develops"CAS_CFD Wheel Fast Design Module"in UG/NX platform to reach the goal. Using this module, the designer can knowledgeably, parametrically and quickly build wheel model that provides fundamental and aerodynamic characteristics. The CFD calculations show that the module is reliable for CFD analyzing and increases the efficiency in designing period.3,CAS_CFD Spoiler FormingThe aerodynamic lift is one of the aerodynamic forces that push on car when car is driving. The aerodynamic lift will damage the car's safety. To reduce the aerodynamic lift, rear spoiler is an efficient way and it meets the different demands of customers'. In designing and refitting period, the CFD calculations will help designer to decide whether or not the rear spoiler is used. Thesis develops"CAS_CFD Wheel Fast Design Module"in UG/NX platform to reach the goal. A rear spoiler of three-box car is researched in this thesis. Depending on the theories of aerodynamic lift under high speed and CFD analysis, the influences of two parameters, the angle of Spoiler and the distance of Spoiler, are analyzed aerodynamically. And by using the knowledge and experience about body assembly in UG/NX platform, the CFD engineer can design rear spoiler and assemble it parametrically and automatically for model fast building and analyzing. The efficiency and accuracy are increased by using this module. 4,CAS_CFD Angle between Body and Rearview Mirror Fast Design ModuleThe optimal angle between body and rearview mirror, without damaging the driver's view, can reduce the aerodynamic drag and improve car's aerodynamic and fuel economy. Based on the theory of driver view designing and national standards, this thesis develops"CAS_CFD Angle between Body and Rearview Mirror Fast Design Module". By using this module, the designer can design the angle between body and rearview mirror knowledgeably, parametrically and quickly to reduce aerodynamic drag concerning the angle. The CFD calculation and analysis results show that the module is usable and efficient in car body part designing period. And it provides a new idea and a new method in applying knowledge engineering and the theories about CFD to car body part assembly.This research is basing on the confederate development with UGS PLM Company (USA). Four car-body-part design modules were developed in UGS NX platform. And all those modules are tested and evaluated by some CAS,CAD and CFD customers.The responses from customer show that these modules can help user predict some potential design issues, and correct their design to avoid the emergency of critical problem in later design phase. Fast modeling system will help user escape from some boring manual modeling process and pay more attention to the innovation. More over the KBE technique will help the company capture the design experiment and knowledge of designs, and share those experiment and knowledge in the company.