Qualitative Simulation For Biw Stiffness And Beam Cross-section Optimization

Automobile industry has experienced rapid development in recent years. A large number of facts show that, the sooner that CAE technology is applied in vehicle development, the better that the cost and the development cycle time will be decreased. At the same time, modern cars are using integral chassis and body construct, where the stiffness performances of an auto body in white (BIW) play an important role in the static and dynamic characteristics of the vehicle system. Thus in the stage of auto body conceptual design, using the body stiffness to determine conceptual design schemes among a variety of potential structures has great significance to reduce developing time. This paper focuses on how to use CAE technology to do the qualitative simulation for BIW stiffness, which is of great importance in conceptual design phase, and also presents an optimization approach for the cross-section of thin-walled beam. And on this basis, this paper introduces a self-developed system which can realize CAE simulation of BIW stiffness on the platform of UG NX.Firstly, this paper discusses a construction method of a parametric wire-frame geometric model for BIW. Based on this wire-frame model and the building of the beam cross-section library, the finite element mode of BIW can be quickly set up to achieve the stiffness evaluation during the conceptual design phase. Then the calculation of bending stiffness and torsional stiffness is carried out between the simplified model and detailed model, the results indicate that the difference of values was within 10%, which verifies that the conceptual simulation model is reasonable and effectiveness.Secondly, shape optimization techniques for the cross-section of thin-walled beam were systematically studied in this paper. Through the research of cross-section shape control methods, scale vector is finally chosen to be applied as the control technique for shape optimization. Meanwhile, numerical approximate functions for the section properties such as area, moment of inertia, and torsional constant are derived by using the response surface method. Afterwards, based on the sensitivity analysis and the theory above, shape optimization of beam cross-section is applied in a real case. The results show that body mass was decreased by 3.8%, bending and torsional stiffness were increased by 3.89% and 7.12%,which achieves the initial optimization of the beam cross-section in conceptual design phase and can be a guide for the subsequent design. Finally, this paper introduces a self-developed system which can realize CAE analysis of BIW stiffness on the platform of UG NX. It also describes the two key technology involved in the system development process, parameter and modular oriented solution, together with the implementation of C++ program for the realization of the simulation system. Meanwhile, the system functions and operation manual are also presented at the end of the paper.