Statistical Characteristics of Whipping Response of a Large Container Ship Under Various Sea States and Navigational Conditions Based on Full-Scale Measurements

The recent increase in the size of container ships has resulted in lower natural frequency of the hull girder vertical bending and torsional vibrations; this has caused great concern regarding excessive whipping in these responses to incident waves. To accurately account for whipping in ship design, it is important to understand the relationship between the whipping response and sea states in which the ship operates. However, there has been little reported to date on this specific topic. In this study, we quantitatively analyze the influence of various sea states and navigational conditions on the whipping response in hull girder bending vibration and torsional vibration. Full-scale measurements of an 8,600 TEU container ship were taken over four years and two months. Longitudinal stresses in way of four corners at the mid-ship section were measured and then decomposed into four components: hull girder vertical bending stresses, horizontal bending stresses, warping stresses, and axial stresses. Furthermore, components of the high-frequency vibrational responses and wave frequency wave responses were decomposed, and the probability distribution of peak values of each component was calculated. Then, the values corresponding to 1/1000 expected maximum stresses were obtained, allowing for statistical investigation. Moreover, a whipping factor was obtained in order to evaluate the correlation with sea states, navigational conditions, etc. By providing quantitative analysis of the relationship between whipping and sea states/navigational conditions, our study will contribute to future ship design to ensure better operation safety and longer hull life.