Prediction of extreme loads on ultra-large containerships with structural hydroelasticity

Abstract

Design rules for very large seagoing vessels are undergoing changes owing to the hydroelasticity of the ship. The hydroelasticity of the ship is in the form of wave-induced vibrations such as springing and whipping, which are known to aggravate fatigue and extreme loads. The present study deals with a method for the estimation of extreme loads. The method consists of a preliminary analysis of linear responses of motions and loads, and a sequential analysis of the nonlinear extreme load. First, a full-time series of the linear response is obtained using response amplitude operators and wave spectra. Next, the candidate waves of extreme event are extracted from the full-time series based on the linear response. The linear response may be a motion or a load depending on the target value of the sequential analysis. Finally, the sequential analysis is conducted using a fully coupled model of the three-dimensional Rankine panel method, three-dimensional finite-element method, and two-dimensional generalized Wagner model with the candidate waves. The method is validated for a nonlinear hogging moment in a short-term sea state and applied for a long-term prediction of an extreme hogging moment on an ultra-large containership. The extreme values of linear and nonlinear loads are compared in terms of the most probable value and probabilistic distribution.