Acoustic stealth and discreteness of underwater vehicles are important issues in underwater acoustics. These vehicles are constituted of shells which are periodically reinforced by ribs. Acoustic fields radiated or scattered by such structures are strongly affected by phenomena related to this periodicity such as Bragg diffraction and Bloch-Floquet waves. The introduction of a slight modification of each rib is considered here to reduce this signature for radiation problem, scattering problem or both radiation and scattering problems. Geometrical and material parameter variations used to obtain these new solutions may also be constrained by technological limitations. In a classical process, the design would be realized by experts using tools and methodologies that have been developed over the years. Another approach of the problem consists in using optimization algorithms (genetic, greedy, etc.) which have to be coupled to simulation models of the acoustic radiation and scattering problems. This approach is considered here in the case of a plate periodically reinforced by ribs. Simulation results are reported and the impact of the choice of the objective function, the parameter to be varied, the simulation model and the optimization algorithm on the final performance are also discussed.