Numerical Computation Of Ship Motions And Added Resistance In Regular Waves With Large Amplitude

The prediction of the added resistance of ships in waves with large amplitude is a key point to the calculation of the Minimum Propulsion Power.The strongly nonlinear feature of hydrodynamic forces of ships in large amplitude waves is one of the hard issues in the seakeeping field.In this thesis,two CFD solvers,SURF and StarCCM+,are used to calculate the ship motions and added resistance of the S175 containership under different wave lengths and wave amplitudes.The computational results show that the CFD methods are more accurate than the potential methods and the influence of wave amplitude can be considered by the CFD methods.To investigate the interactions between diffraction and radiation in large amplitude waves,the simulations of diffraction problems in which the ship is fixed in waves and the simulations of radiation problems in which the ship is forced to oscillate in calm water are carried out.The results show that the decomposition of diffraction and radiation does not work well for the added resistance and higher harmonic surge forces obtained by the integration of pressure and shear on the hull.The nonlinear interactions between diffraction and radiation become stronger as the wave amplitude increases.Further,the added resistance is calculated using the wave profiles obtained by CFD methods.It turns out that the collapsing of wave profiles near the bow leads to the decrease of the added resistance coefficient with the increase of wave amplitude.Finally,the nonharmonic variations of the time history of resistance can be explained by the instantaneous pressure distributions on the hull surface.The shape of wetted surface and the pressure on wetted surface change dramatically due to the interactions between large waves and large ship motions.The increase of added resistance in larger waves is found to be induced at the waterline near the bow.