The Modal Analysis And Structure Optimization On Body-in-White Of A Car

The integral body of car is the matrix to assemble engine and interior trimming, it has many parts and the structure is complex. It withstands the inertia force when the car at the condition of starting, braking, turning etc,and the excitation from road and engine, has complex sound and vibration characteristics. It is an important link which influences the ride comfort of the car, so the design and optimization on the body-in-white has become increasingly attractive.Based on the vibrating theory, finite element method and experimental modal analysis, this dissertation studied the dynamic characteristic of a car which was being improved in a corporation on the MSC.nastran platform. Firstly, it dealt with the guideline to build finite element model, and cleared the CAD model and predigested some characters, accomplished the FE model. Studied the theory of numeric modal analysis and the method that how to identify the numeric modal parameter, put the FE model into Nastran for modal analysis and got the numeric modal parameter. Implemented the experimental modal analysis on the body-in-white, identified experimental modal parameter, and compared the numeric modal parameter with the experimental modal parameter, validated the FE model. Then, this dissertation implemented the first modal sensitivity analysis for the validated FE modal base on the thickness of some parts on the body, taking example for the roof, discussed the relationships between the first modal sensitivity and the thickness. Finally, taking the thickness of the thirty one parts which have higher modal sensitivity as design variables, improving the first natural frequency as goal, optimized the structure of the body-in-white, and ameliorated the dynamic characteristic.In research, found the relationship between the first modal sensitivity and the thickness is not a linear function, then brought forward could not standpoint that could not ensure design variants base on specific modal sensitivity, and supervised the optimization, enhanced the rationality of modal optimization algorithm. The dissertation is from the practical project, and the research can directly apply on practical project.