Mitigation of vibration of ship structure via local structural modifications

This article presents a methodology for the reduction of ship structure vibration through local structural stiffness modifications. To identify the locations in the ship structure where the modifications should be made, three design criteria are considered: structural intensity, von Mises stress, and displacement. Two simple cases of cantilever beam and simplified ship were first tested under a harmonic excitation force at a frequency near resonance. The methodology was subsequently applied to a containership model subjected to propeller excitation forces. It is found that the von Mises stress is the most effective criterion in identifying the critical regions for structural modification. By increasing the thickness of plates in small localised regions, the global vibration level in the ship structure can be reduced by 50% when the excitation is near the resonant frequencies. The improvement varies with the structural damping present, and also on the model of mass distribution in the ship.