Full scale cruise ship dynamic identification using operational modal analysis on sea trial data measurements

Description

High operational vibrations in ships can lead to discomfort for passengers and crew and cause structural fatigue and cracking. Reducing these vibration levels under working conditions requires an understanding of both the characteristics of the excitation sources and the vibrational structural dynamic behaviour of the system in question. For accurate forced response vibration calculations, it is crucial to correctly identify resonant frequencies, mode shapes, and damping values through experimental methods, as these are essential for validating the results. Experimental Modal Analysis (EMA) is a widely used technique across many engineering fields that allows for the identification of modal parameters. However, EMA cannot be applied under operating conditions; it requires artificially exciting the system and measuring both the input force and the output response vibrations on an experimental grid of the structure. This identification technique can be challenging, costly, or even unfeasible for large and massive structures such as cruise ships. As an alternative, Operational Modal Analysis (OMA) can be used to experimentally extract modal parameters from response-only measurements. This paper presents the identification of two similar cruise ships using OMA, utilizing data collected during sea trials from endurance, crash stop, and propeller run-up tests. The testing procedures and the results obtained are presented and compared.

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