Establishment of Prediction on Unstable Ship Motions under Extreme Sea States

(1)比较了世界领先机构的几个数值模型和倾覆模型试验，结果表明，完整船舶在随浪和四分浪中倾覆的定性预报是可能的，但没有一个数值模型能够定量预测倾覆。(2)它们表明，这些模型可以估计破损船舶在横浪中倾覆的临界波高，但都不能解释倾覆前的横倾角。(3)对于完整船舶在随浪和四分浪中的主要倾覆模式之一，建立了一个定量预测随浪和四分浪倾覆的模型，并用倾覆模型试验进行了验证。新模型考虑了波浪对船舶运动水动力导数的影响，以及大横倾角对水动力导数的影响。(4)对于可能导致随浪倾覆的船头俯冲，提出了一种新的计算方法，并通过试验进行了验证。(5)对于破损船舶的数值模拟，建立了考虑船体渐进水淹对船体水动力影响的新理论，并证明了这种影响是显著的。此外，数值模拟和物理模拟之间的差异被解释为一种由于舱水淹没而产生的减摇水舱效应。(6)对于基于分段线性方法的倾覆概率计算方法，通过数值研究考察了海浪统计的影响，结果表明，考虑操作影响的计算概率与实际伤亡统计具有可比性。

(1)Comparison of several numerical models from the world leading institutes and capsizing model experiments showed that qualitative prediction of capsizing for intact ships in following and quartering waves was possible but no numerical model could quantitatively predict capsizing.(2)They showed that the models could estimate critical wave height of capsizing of damaged ships in beam waves but none could explain roll angles before capsizing.(3)For broaching, e.g. one of the major capsizing modes of intact ships in following and quartering waves, a model to quantitatively predict capsizing due to broaching was newly developed and validated with the capsizing model experiments. The new model takes into account the wave effect on hydrodynamic derivatives with respect to ship motions and hydrodynamic forces due to large heel angles.(4)For bow-diving that could result in capsizing in following waves, a new calculation method to predict its onset was proposed and well validated with experiments.(5)For numerical modeling of damaged ships, a new theory was formulated to take the effect of progressive flooding into the hull on hydrodynamic forces acting on the hull into account and demonstrated that such effect is significant. Moreover, the difference between the numerical and physical modeling was explained as a kind of anti-rolling tank effect due to flooded compartments.(6)For a calculation method of capsizing probability based on a piece-wise linear approach, effect of wave statistics was investigated with numerical studies and then it was shown that calculated probability with operational effects could be comparable to actual casualty statistics.