The Modal Analysis On Body-in-white Of A Car

Body is the key assembly of a car. Its structure determines the mechanics characteristics of the whole car. The modal analysis of body-in-white(BIW) can not only examine the integrative stiffness performance ,but also provide a guidance for people on structure optimization and response analysis. Based on the theory of finite element method(FEM)and modal,this paper mainly performs modal analysis of a car BIW by using ANSYS6.0 software. The validity of FEM's result is proved by experiment.Every component is built up through three dimensions CAD software. The interference among components is eliminated through assembly. Then the model is input into ANSYS program by port. The whole BIW is meshed by using shell and beam element in order to establish the detailed model for FEM modal analysis.During calculation, the influence of strengthen rib,thickness of sheet mental and connecting relation etc. on modal parameter is discussed. The result shows that reasonable setting of strengthen rib will increase special frequence greatly while the mass increases a little. In addition,the method dealing with connection will influence the result in some degree.The study of FEM and experiment modal analysis is performed. Furthermore ,The relativity between the two is compared and researched through modal assurance criterion(MAC).It is found that MAC of mode shapes from first to sixth is all larger than 0.8,that is to say, the relativity is very good.Evalution on the vibration characteristics of the body structure is performed. The structure modification is made by means of sensitivity to thickness of sheet mental. Finally,the paper carrys out a harmonic analysis to validate the validity of constructure modifcation.