Prediction And Evaluation Of Modes For Conceptual Car Body

The car industry act as a pillar for the national economy, the level of industry and technology is highly reflected by the car industry. Along with the swift growth of Chinese economy, car has become consumable for the household. The car output is also increasing speedly. While facing the intense market competition, all the car enterprises strive to promote the product research speed and release the latest car model to the market continuously. The concept design is a important phase in the product reseach. In the fast moving and complex market circumstance, enterprises need correct prediction and make decision promptly. Therefore quick design of product is a key point to deal with the fast moving market and innovation. In the concept design phase of car structure, as there is no detailed model of car body, the simplified model of car body is needed to evaluate and optimize the disign plan.The reseach of this thesis is completed in a cooperated project by Jilin University and China FAW Group Corporation R&D Center.The purpose is to develop a set of CAE softwares using in the area of car concept design--The quick design and optimization system of conceptual car body. The finite element in this software is composed by beam, plate, and joint element. Static and dynamic stiffness can be analysed.With the target of car weight, stiffness, mode and design variable of section mechanical property, it can undertake multi-purpose optimization design under the multi-workinng condition. The multi-objective optimization model can be solved by GA and PSO methods, which provide Pareto optimum solution. After giving the optimum sector mechanical property, this software can furthur give the most optimized cross-sectional shape.The second chapter in this paper gives a general overview of the importance of T-joints and the present study in the field of concept car body. It introduces three kind of joints(the T-joints of super element,shell element and beam element reduced by Guyan),and evaluates them respectively and makes comparison with them. Three kind of joints(the T-joints of super element,shell element and beam element reduced by Guyan) are introduced and compared with each other. Then the necessity and present situation of thin-walled box beams used in the frame construction of car body is elaborated. One-dimensional C0 beam element based on the present theory is employed for numerical analysis. Using kinematic variables representing torsion, warping and distortion, shown in this paper, is suitable for both static and dynamic analyses. Five numerical examples have confirmed that the present elements accurately predict the dynamic behaviour of the coupled deformations of torsion, warping, and distortion.In Chapter 3, we firstly introduce the development and the current researches of structural dynamic optimization, point out the meaning of prediction of frequency extreme in structural dynamic optimization, and then discuss the computational methods of prediction of frequency extreme. A large amount of examples of trusses and rigid frame structures show that adding the prediction of frequency extreme can avoid wasting computational resources resulting from non-solution of the problem at extremely low computing costs. The work is helpful for the structural dynamic optimization of concept car body.Chapter 4 is about dynamic stiffness sensitivity analysis of white-car body. Data are collected by stochastic excitation in laboratory, and are also processed by computer systems to analyze and determine an efficient transfer path. Key positions which have a strong influence on body stiffness in vibration are chosen to analyze the peak value of frequency response function, mean square deviation and sensitivity. The analysis and test results supply a dynamic modification method in order to realize design parameters systematic optimization. Data collection should be correct and effective, and the scheme selection of computer data processing should be rational As a result, systematic optimization based on dynamic modification can be realised.The comparation of modal analysis between detailed and simplified car body is analysed in Chapter 5. This finite element modal is verified to be accurate and feasible by the experimental test.