Structural-acoustic optimization of a partial fuselage with a standard finite element code

The present work is part of an ongoing research program to develop and validate a robust computational tool to minimize noise transmission into stiffened cylinders through the modification of the structural design. The paper presents the results of an optimization study for sizing the stiffener cross sections (frames and stringers) of a stiffened cylinder. The optimization problem is formulated to minimize the interior noise environment subject to constraints on the structural weight of the cylinder. Previous work has demonstrated that a coupled formulation yields designs that successfully minimize the interior noise levels in idealized fuselage models. This noise reduction goal can be achieved while still keeping the structural weight within acceptable engineering bounds. A preliminary application considering an unstiffened fuselage model has been extended to the stiffened cylinder model. According to the existing literature, two different optimization strategies have been selected. In the first, the minimization of the structural weight was searched while imposing a maximum permissible bound on the internal noise levels. In the second, the more interesting, the minimization of the internal noise levels has been attempted while imposing a maximum permissible bound on the structural weight. Both optimizations were performed at a specific excitation frequency. The most promising aspect, and the major improvement of the application presented herein, is related to the feasibility of using the same commercial FEM code for the structural dynamics, the internal acoustics and the optimization procedure. Furthermore, it has been also tested the possibility to perform a multi-frequency and/or a multi-constraint optimization. Also in these latter cases, even if they are very preliminary, the results are promising. © 2001 by the authors.