Shape optimization of a vehicle hat-shelf - Improving acoustic properties for different load cases by maximizing first eigenfrequency

This paper presents design optimization of the geometry of a vehicle hat-sh elf. At first two existing finite element discretizations are investigated for two different element types. The structural model is then parameterized . Only four design variables have been chosen to control the shape modifica tion of the hat-shelf. The aim of this paper is to decrease the vehicle int erior noise due to three different excitations for two cases of fluid dampi ng. With respect to the support conditions of the hat-shelf these three loa d cases and the two cases of different damping are considered simultaneousl y by maximizing the lowest eigenfrequency of the structural model. Although remarkable differences in the natural frequencies are discovered for the f our discretizations, a similar dependence of the objective function in term s of the design variables is observed. Thus, a multigrid strategy can be ap plied. The coarsest mesh is used to obtain suitable initial sets of optimiz ation variables, one of the finer meshes serves for a pre-optimization and the finest mesh is optimized to find the final set of parameters. While the lowest eigenfrequency of the original model is found at about 31 Hz, the c orresponding value in the optimized variant exceeds 100 Hz being the upper bound of the frequency range under consideration. Evaluation of the noise t ransfer function proves that this strategy decreases its average between 4. 4 and 13.9 LIB. (C) 2001 Elsevier Science Ltd, All rights reserved.