【作者】 高歌；

【导师】 胡平；

【作者基本信息】 吉林大学 ， 车身工程， 2008， 博士

【摘要】 提高轿车车身开发技术的水平对于提高我国汽车产业的整体核心竞争力有很重要的战略意义。本文应用知识工程的理论到车身设计领域,在深入研究汽车造型和空气动力学的CFD分析的基础上,开展了概念车身局部参数化建模与CFD仿真一体化的方法研究,开发出了一系列基于知识工程的面向CFD分析的概念车身局部参数化设计系统。本文在综合评述国内外知识工程、参数化设计及CFD仿真模拟领域研究成果的基础上,进行了概念车身局部参数化建模与CFD仿真一体化的理论研究;结合KBE知识工程和CFD分析前的模型清理和建模的特点,首次提出了面向CFD分析的车身局部参数化的概念,分析了参数化车身结构设计特点,系统阐述了知识驱动的车身零部件的设计方法,这些方法是实现车身结构设计的参数化、自动化和知识化的重要基础。以轿车底部模型为研究对象,在UG/NX软件平台上开发出实用性较强的知识驱动的“CAS_CFD地板快速设计模块”,通过CFD的模拟和与实际数据的对比,证明该模块在实际使用中具有较强的实用性和准确性。以车轮模型为研究对象,在UG/NX平台上开发了知识驱动的“CAS_CFD轮胎快速成型模块”,将通常的CFD分析所用车轮建模标准化,参数化,使得用户只需要输入轮胎的基本参数(如215/55 R17)即可制作出满足CFD分析的轮胎模型,该系统针对CFD工程师在以往简化车轮模型、几何清理,车轮与地面接触部分特殊处理等问题,使轮胎建模流程简化,缩短建模周期。以三厢轿车尾翼(后扰流板)为研究对象,参照尾翼对轿车高速时的影响以及CFD分析的规律,将尾翼与车身装配布置的知识经验与UG/NX软件平台相结合,开发出了“CAS_CFD轿车尾翼快速设计模块”,针对造型需要加装尾翼的车身设计方案和CFD工程师快速建模分析的需要,将尾翼的设计和与车身的装配关系参数化、自动化,使其设计、修改与CFD分析周期大大缩短,提高了车身设计的效率和分析的准确性。以车身附件后视镜为研究对象,参照人机工程学相关后视镜视界法规及后视镜对外流场的影响因素,将后视镜布置的经验与UG/NX软件平台相结合,开发出了“CAS_CFD后视镜与车身夹角快速计算模块”。该系统结合空气动力学分析,用于计算满足驾驶员视野的左、右后视镜与车身夹角的快速计算,达到降低气动阻力及提高燃油经济性的目的,提高了车身开发效率,产品设计精度和准确性。更多还原

【Abstract】 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.更多还原