Hull vibration analysis of river boats

Ship structural design is done today resorting to powerful numerical tools. Ship structures come out to be optimal regarding load and failure mechanisms; in spite of this they come to lose that residual capability which in past gave a valuable benefit to overcome certain undesirable side effects. Such effects are not acceptable when ship’s structures are prone to develop high levels of vibrations excited by propulsion plant or other sources. In this frame, the paper investigates a river ship case, where preliminary calculations of structural dynamic response to vibrations induced by on board sources gain a relevant role in defining the minimum thickness of plates and supporting structures’ topology. River ship hulls have indeed light structures due to low demanding environments, which lead to an increase of vibration effects on accommodation decks. The approach here discussed is based on direct calculations of the hull’s structures dynamic response, performed in the frequency range where first harmonic frequencies of main excitation sources play a relevant role in inducing local and global vibration effects. The critical aspect of interaction between structure and fluid will be dealt with by an implicit modeling of the surrounding water around the hull. The aim of the study is to give the reader basic tools to implement, in the ship’s hull preliminary design stage, free and forced vibration analyses in order to support decision making about the hull scantling when vibration effects are not negligible.