Nonlinear wave loads on a ship advancing in waves

Based on the strip theory, a method for predicting the nonlinear wave loads of a ship advancing in large oblique waves is proposed in the paper. With the previous well progress in the hydrodynamics, the hydrodynamic coefficients and forces can be well estimated. Therefore in the study, the authors consider the ship as a free-free beam and use the simple beam theory to estimate the corresponding sea loads along the ship hull, e.g. wave bending moment, shear force and torsion moment at any ship section. The numerical solutions for the linear analysis in frequency domain are firstly made and the accuracy has been verified by comparing with the existing experimental data and theory done by others. With the well developed linear theory, the analytical model of the nonlinear wave loads for a ship in large oblique waves are further developed The time domain analyses including the instant grid generation technique (IGGT) for the corresponding sea loads are made. Besides, to avoid the numerical drift phenomena in the sway and yaw mode motion, the Artificial Restoring Force Technique (ARFT) and Digital Filter Technique (DFT) are applied to solve five coupled equations of motions. A series of analyses are made in the paper and some valuable suggestions are also submitted, which will be helpful for the researchers to do the related works. The calculation procedures developed here may be considered as a useful analytical tool for predicting the ship motions and wave induced loads.