This work investigates the availability of the baseline approach proposed in the previous researches, and expands the applicability of the method for noise and vibration optimization. Based on the s-plane extension theory, baseline was formed by introducing a virtual damping in the transfer function calculation formula. Sensitivity analysis based on baseline was conducted to predict the changing tendency by structure modification in the target frequency range. The validity of the proposed method is examined through numerical simulation with two finite element (FE) models. A simple hollow rectangular parallelepiped model was constructed for confirming the effect of baseline sensitivity analysis as a structural vibration reduction treatment. And a vehicle frame-panel structure was constructed for confirming the proposed method as a noise optimization example. In view of the model in discussion, the sum of squares sensitivity or root-mean-square sensitivity was calculated to determine the mass attachment location. The conventional sensitivity values using FRFs without virtual damping(FRF method) were also calculated for comparing with baseline sensitivity results. The FE models with mass attachment based on sensitivity analysis results were calculated for confirming the vibration reduction effects. The result shows that FRF method has a greater decrease at some single peak in the target frequency range, while the baseline method has a better reduction performance at multiple peaks in the target frequency range. The selection strategies of the two methods for the mass attachment location and the change of mode shape after mass attachment were discussed. The baseline sensitivity method presented in this study provides a feasible approach for noise and vibration performance improvement in the medium frequency band.

This paper proposes a stiffness sensitivity analysis with principal strain application to decrease the out-of-plane vibration, which is the main source of the sound radiation of mechanical structures with thin plate parts. The sensitivity is evaluated as a differential coefficient of the target response with respect to the design variable, e.g., stiffness or mass. For suppressing the out-of-plane vibration, we pay attention to finding an appropriate location on the structure to add local stiffness. The location is decided according to stiffness sensitivity analysis results. The compliance frequency response function (FRF) is considered as the target response, and the thickness of stiffener is considered as the design variable. The validity of the proposed method is examined through numerical simulation with a finite element method (FEM) model of a thin plate. The modal principal strain distributions, stiffness sensitivity, and FRF changes by local thickening are calculated based on 4 selected natural modes. It is also examined by the experimental approach. The expected reduction of the response is attained by adding the stiffener (a thin stainless plate) to the appropriate location on the plate.

Poroelastic materials are wildly used as sound absorbing applications in automobile design. It plays an important role not only as absorbers in acoustical treatments but also as dampers on the structure to reduce the structure-borne noise. In this paper, single or multiple layers of poroelastic materials (felt type) are attached to the bottom plate of an acoustic box, which is designed as a simplified experimental model of the vehicle cabin. The reduction of system response amplitude at the first natural frequency is observed by the attachment of felt layers, and the additional damping and equivalent mass are evaluated by the variation of the resonant peak. A simplified finite element (FE) model of the acoustic box with felt layers is constructed in commercial FE program. Frequency response analysis is conducted, and the vibration reduction effect caused by sound absorbing materials is estimated. The simulation results are in good agreement with the experimental results.