The Study Of Numerical Simulation Method On Parametric Rolling Of Containership In Head Waves

The parametric rolling is a severe stability problem of ships, which endanger the crew's lives and our property. In the present thesis, multi-level numerical models classified by different complexity and nonlinearity are developed to evaluate this phenomenon. The 1DOF Mathieu Equation is the elementary level, which explains the mechanism of parametric resonance. The second level employs a 3DOF weakly nonlinear model, where Radiation/Diffraction forces are kept linear and represented by impulse response function,while the Froude-Krylov forces are evaluated on the instantaneously wet surface of the ship with high order Stokes wave theory. Despite of the fact that this method is commonly used in industry, there are still some improper places in the basic theory, which have great influence on motion response. In the present work,the Cummins's method combined with STF to calculate ship motion in time domain is reconstructed and some additional terms are derived.On the other hand,a 2D simplified body-exact solver is developed to solve the nonlinear Radiation/Diffraction force, which is implemented by the third level. In this level, the Froude-Krylov forces are calculated on the instantaneously wet surface of the ship and 3DOF motion equations are solved in time domain. The last two models are employed to simulate the parametric rolling of one container ship and the numerical results are validated by experimental data. The influence of initial roll angle, roll damping, wave steepness and encounter frequency on the development of parametric rolling is discussed.