On the torsional vibratory response of 13000 TEU container carrier - full scale measurement data analysis

The torsional vibratory response of large container carriers has been suspected to be the main source of fatigue damage to the hatch corner structure, and has attracted considerable attention from ship designers. In line with this, this paper presents the results of the full scale measurement data analysis of a 13000TEU container carrier voyaged between Europe and China, with particular focus on its torsional vibratory response. First, the torsional mode shapes were extracted using the acceleration data measured at five different locations along the ship length and the natural frequencies were estimated by taking a Fourier transform of the modal magnitude time histories., The modal damping ratios were estimated based on the extracted time histories of the torsional modal magnitude and the correlation between the natural frequencies and damping ratios was examined. Modern signal processing techniques, such as the proper orthogonal decomposition and random decrement technique, were used for data analysis. Finally, a different level of contribution of the mode shapes to the total fatigue damage was investigated after decomposing the strain signal into different modal components. The torsional response of the vessel was not significant during its measurement campaign period.