The Modal Analysis Of BIW

Forecasting the stiffness characteristics , the strength characteristics and the modal characteristics of auto parts during the process of the vehilcle design is a neccesary step to reduce the time of design .The finite element thoery offers an advanced method .During the analysis of the 3D digital model ,we can find the problem exist in the initial stages of design. It not only help us save the time but also save the money.The modal of vehicles relate to the characteristics of NVH ,which is the promission of comfort and security .In this dissertation , the modal of a car body will be analyzed by using FEA software, then we will proof the correctness of the FEA model analysis result by another result we obtained in the car body experiment.The FEA is applied to study the weld spots on the car body that has a great influence on the correctness of the FEA model. Five models used to replace the weld spots are disscussed .Considering the accurate rate of the analysis result and the time cost to build the model, the beam element is disscussed to be the best. After we found the right method to build a FEA model, we meshed the model and had the modal parametersare analyzed using nastran.we forecasted the characteristics based on the modal result.According to the method of the car body modal experiment, the modal experiment was performed. Furthermore, the relativity between the different modal results was compared and researched through modal assurance criterion (MAC). It found that the forecasting is very good.A mass reduction design of light-duty truck chassis frame was discussed. A plane was given. According to the request of mass reduction,the thickness of the tube beams are optimized through sensitivity analysis. Compared with the tradional chassis frame , The results demonstrate that the new chassis with tube beams has the advantages of both better mass reduction and modal ,which is significative for the whole truck..