Experimental investigation on wave-induced bending moments of a 6,750-TEU containership in oblique waves

Abstract

This study aims at the experimental investigation of wave-induced motions and loads of a containership model without forward speed in -120 degree oblique regular waves to study the influence of the wave steepness and provide reference data for future benchmark studies. A mooring system with 4 horizontally arranged spring lines was used to maintain the heading angle of a 1/65 scaled 9-segmented model designed to be as rigid as possible.Focuses were on studying the nonlinear effects due to the wave steepness on the vertical bending moment (VBM) and horizontal bending moment (HBM) near amidships, and 6-DOF motions at the center of gravity (COG) of the model. Several wave series that are distinguished by wave steepness were considered in the experiment accordingly. Each series consists of waves with various periods that were intended to cover the peak of the wave bending moment transfer functions. Through this, the nonlinear wave effects on the responses of the rigid body at various periods were determined. It was confirmed that the steeper wave contributes to the increase in the higher-order harmonic components including slamming events in the bending moments measured. The change in the characteristics of the wave bending moments according to the change in wave steepness was found to be very different from the linear response.A detailed discussion was made on the influence of the mooring system on the asymmetric horizontal bending moment (HBM) and the change in the average yaw motion. Experiments with and without a mooring system under the same wave condition were conducted, and the effect of the mooring system was identified. It was qualitatively confirmed that the mooring system’s restoring moment correlates with the asymmetric HBM and average yaw movement change.