Numerical and experimental studies of nonlinear wave loads of ships:Dissertation

Extreme wave loads have to be defined in the ultimate strength assessment of ship structures. Nonlinearities in extreme wave loads can be significant in high waves. Numerical and experimental studies of nonlinear wave loads are presented in this work. A nonlinear time domain method has been developed and the fundamentals of the method are given. The method is based on the source formulation expressed by means of the transient three-dimensional Green function. The exact body boundary condition is satisfied on the instantaneous floating position of the body. The free surface boundary condition is linear. The time derivative of the velocity potential in Bernoulli's equation is solved with a similar source formulation to that of the perturbation velocity potential. The verification of the method is presented for a hemisphere and cones. Wigley hull forms are used to validate the calculation method in regular head waves and calm water. Model tests of a roll-on roll-off passenger ship with a flat bottom stern have been carried out. Model test results of ship motions, vertical shear forces and bending moments in regular and irregular head waves and calm water are given. The nonlinearities in ship motions and hull girder loads are investigated using the calculation method and the model test results. The nonlinearities in the hull girder loads have been found to be significant. The calculation method is used to predict rigid hull girder loads for the model test ship. It is shown that the time domain calculation method can be applied to ship-wave interaction problems to predict the nonlinear wave loads