Experimental Investigation of the Bending Vibrations of a Fast Vessels

Nowadays, the larger flexibility of ship structures, as well as wave-load spectra shifted to higher frequencies due to high-speed operating regimes, allow the onset of significant vibration phenomena. Recently, there has been increasing interest in combining seakeeping with vibration tests that may result in a deeper physical insight into this topic. In fact, experimental investigations on physical scaled models may benefit general purpose techniques for structural dynamic analysis in order to provide an interesting point of view of the hull vibration problem. The application of methods for modal identification, such as the Output-Only techniques, fi ts the present identification problem, particularly, where the main source of excitation for the structure is the ambient excitation due to the sea waves. In this paper, the tests carried out in a towing tank basin with an elastically scaled and segmented model are analysed in order to investigate the bending response, ie. bending vibrations modes (shape, frequency and damping) and whipping oscillations. The modal parameters of the "dry" and "wet" modes of the elastic segmented model are identified with the Output-Only technique, based on the Frequency Domain Decomposition. Then, the ship response is analysed in terms of response amplitude operators and recorded time-histories. The correspondence with the full-scale ship, and the dependence of the aforementioned estimations with respect to the forward speed, are highlighted in the paper.