In this study, some strategies of optimization have been designed, for the problem of ship silencing. Specific criteria can be expressed for this problem. We present principles of attenuation ensuring their application in practice. These criteria can be written in terms of dynamical flexibilities and transmissibilities over a wide range of frequency. We show how to improve the dynamical behaviour of structures with respect to the criteria: two methods are presented for the design of dynamic absorbers. Both can deal with experimental data. Then, we present one method of structural optimization. The objective is to minimize the mass of the structure with constraints on point flexibilities and transmissibilities. This method is based on two conecpts: first, the modal approach with modal effective parameters and second the algorithm is built upon Kühn-Tucker optimality condition. At last, we show how this approach can be extended to the optimization of composite structures, by taking into account the structural damping with a complex mode shapes formulation. Numerical results are presented.
