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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.

A method for analyzing and decreasing booming noise in the cabin of a minivan using acoustic excitation tests has been developed. To ensure a pleasant ride for passengers of minivans equipped with four-cylinder engines, decreasing cabin noise from secondary components of engine revolution has become a priority. “Booming noise” in the cabin originates from engine vibration that passes through engine mounts to shake the body structure and body panels. To decrease the level of sound pressure resulting from this shaking, one effective approach is to reduce the level of the mechanical-acoustical transfer function (MATF) in the interval from engine mounts to passengers' ears. This paper reports on a specific method for reducing the level of MATF. In this method, a speaker is positioned near a passenger's ear to measure the vibration-response level at the points where engine mounts are installed when exciting the body structure, and the level is reduced by modifying the body structure.

The load path U* analysis is an effective tool for investigating the load paths in body structures. In the present study, a new index U** is introduced to investigate structures under distributed loading. The new parameter U** is a complementary concept of U*. Although the conventional index U* cannot be applied to cases of distributed loading conditions, the new index U** can be applied to those cases. This paper describes the application of a load path U** analysis to improve efficiently the first eigenvalue of the vertical bending mode in a vehicle body structure model. It also explains how target parts for shape optimization are interpreted on the basis of a load path U** analysis when a load is applied to reproduce the first vertical bending mode.

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.

The accuracy of the vibro-acoustic coupled system model for the low frequency range depends on how accurately modal characteristics are represented at the input, output, and the structure-acoustic coupling surface. This study focus on extracting the detailed acoustic mode shapes on the coupling surface for the improvement of the model accuracy. In order to extract the acoustic mode shapes on the coupling surface from an experimental test, the applied method is initially evaluated by FE model results. As the next step, the same procedure in the previous step is applied to the test data of an actual vehicle for the purpose of extracting the detailed acoustic mode shapes at the coupling surface of the body structure and cabin interior acoustic field.

Finite element models based on the design drawing information are widely applied in the early development stage in the automotive industry. During this stage, the performances of noise and vibration of a vehicle are evaluated by the calculation using FE models. Therefore, it is extremely important to secure the accuracy of the calculation by FE models. Otherwise the problem does not solved with the countermeasures implemented in FE models. To predict sound pressure levels in the passenger compartment, an acoustic model for the compartment must be precisely created. Experimental analysis have shown in the past that narrow air gaps between interior trim parts or between a trim part and a body structure have a high impact on the acoustic transfer functions even in the low frequency range where the issues on booming noise and road noise are often addressed.