Besset S., Jezequel L.

Modal analysis methods have long been studied because the use of generalized coordinates makes it possible to reduce calculation costs. The modal analysis method that we will use deals with coupled fluid-structure systems. Complex systems, including structural and acoustic parts, are described using generalized coordinates. Thus, the systems we will study will be made of fluid cavities, structural plates and hollow parts. Hollow parts will be analyzed using a « modal finite element » method that we will explain in the paper. Mass and stiffness matrices of the complete system are used to optimize structural parts of the system, in order to reduce the pressure level in the acoustic part. This optimization aims at modifying the geometry of the hollow parts of the structure. First, a genetical optimization will be done to generate a « pareto set ». Secondly, a more precise optimization will be processed. The first optimization allows to find points that are not so far from an optimized point. The second one uses a point resulting from the first optimization to start an algorithm that find the best point around the starting point. Both of these optimization methods need criteria. As the system has been studied using modal analysis methods, mass and stiffness matrices of the system are made of mode matrices. Thus, we will use modal criteria, given by parts of these mass and stiffness matrices.