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This paper presents an optimization method of damping material attached on vehicle body panels incorporated with trimmed body calculation up to 400 Hz. Damping sheets are modeled by using shell elements whose neutral plane are located away from the middle plane of the elements. In this method the offset value must agree with the average of the thicknesses of a panel and a damping sheet attached on it. Therefore, we implement the function that can automatically change the offset values according to the change of the thicknesses of damping sheets during the iterative calculations of optimization. Interior sound pressure levels are employed as the constraint conditions by utilizing the precise acoustic cavity models that have been recently developed. The developed optimization technique is applied to reduce the weight of the damping sheets on the floor panels of a sedan car.

This paper proposes a new hierarchical optimization technique for the vehicle body structure, by combining topology optimization and shape optimization based on the traction method. With the proposed approach, topology optimization is first performed on the overall allowable design domain in 3D. The surface is extracted from the optimization result and converted to a thin shell structure. Shape optimization based on the traction method is then applied to obtain an overall optimal body shape. In the shape optimization process, iterative calculations are performed in the course of consolidating parts by deleting those whose contribution is small. The result obtained by applying this method to the front frame structure of a vehicle is explained. The resultant optimal shape has stiffness greater than or equal to the original structure and is 35% lighter. This confirms the validity of the proposed technique. It was found, however, that some issues remain to be addressed.