Operational modal analysis on the hydroelastic response of a segmented container carrier model under oblique waves

Both vertical and torsional mode shapes of a segmented container carrier model towed in a model basin are estimated using the operational modal analysis. The operational modal analysis targets to identify the modal properties of a structure using measured data collected during the operation without any information about the excitation. The proper orthogonal decomposition, which is also known as Karhunen-Loeve decomposition, was used for the extraction of mode shapes, and the random decrement technique was applied for the derivation of free decay signal. The segmented hull model of 10,000 TEU container carrier with the scale of 1/60 was towed in a model basin under head and oblique waves and the strain time histories at the designated locations along the continuous backbone were measured. The sectional load, which was estimated based upon the measured strain, was processed using the proper orthogonal decomposition to obtain both vertical and torsional vibration modes. Finally, the free decay signal of each modes was extracted out of the processed data using the random decrement technique and wet damping ratios as well as damped natural frequencies were estimated.