Study On Modal-Based Structural Optimization Of Body-in-White

As the most important structure of the automobile for realizing the using function, the quality of car body has an important relationship with the user satisfaction. And the BIW modal characteristic is one of the most important aspects of the car body qualities. BIW modal characteristic is a reflection of the vibration performance of car body. Low steps of modal also can be a reflection of the stiffness of the car body structure. Acquisition of the car body modal parameters is the premise of optimization design for car body.The subject made the BIW modal analysis as the key core of the research. The research contents were included as follows:(1) The basic method of BIW computational modal analysis was summarized. Base on previous research, the induction of principles for BIW modeling methods was made, including rationality of geometrical simplification, normative of mesh and equivalence of connecting methods.(2) Completed the BIW geometry modeling in CATIA V5, and the FEM modeling in Hypermesh 8.0. The BIW modal parameters were acquired by analysis in Nastran 2005.(3) With the basis of multi-degree of freedom system complex modal analysis and the theory of system identification, the principle of EMA of car body was described. Then the EMA was made by using LMS testing system.(4) Combined with the EMA theory and the FRF acquired as basis, the estimations of the modal parameters were made by the method of LSCF assisted by LSCE. Then three methods are used to validate modal results:Frequency Response Function Synthesis, Modal Assurance Criterion, Modal Participation, and the analysis were made for the results.(5) According the comparing of the results of EMA of FEM, the modal parameters of the BIW were obtained, including natural frequencies and modal shapes.(6) The description and optimization of vibration for thin panels on car body are studied by using the method of mode shapes optimization of car roof base on acoustic radiation theory of thin panel; and the interior noise optimization of a concrete car was made from this breakthrough point.According to the discussions of the six aspects above, from BIW modeling to body-structure optimization, a complete studying thought was formed. The potential of vibration and noise reduction from the aspect of structure optimization was emphatically studied in the subject; it provides some kind of reference value for the dynamic performance optimization of car-body.Innovations involved in the subject as follows:(1) The core factors of accuracy of BIW modeling were concluded, including rationality of geometry simplify method, the quality of mesh, the equivalence of connecting method; They are regarded as the guiding principles of BIW modeling.(2) Being different from the previous research that using the vibration frequency as the optimizing variable, the modal shape optimizing method were introduced in the paper. And the statistical description method of thin panel vibration was introduced.