Establishment of Prediction on Unstable Ship Motions under Extreme Sea States

(1)通过对世界领先研究机构的几种数值模型和倾覆模型试验的比较，可以对完整船舶在跟随波和分波下的倾覆进行定性预测，但没有数值模型可以定量预测倾覆。(2)结果表明，这些模型可以估计出受损船舶在波束波下倾覆的临界波高，但都不能解释倾覆前的横摇角。(3)针对完整船舶在随波和分波中主要倾覆方式之一的拉削，建立了拉削倾覆的定量预测模型，并通过倾覆模型实验进行了验证。新模型考虑了波浪对船舶运动的水动力导数的影响和由于大跟角引起的水动力力。(4)针对潜艏后浪可能导致倾覆的情况，提出了一种新的计算方法来预测潜艏后浪的发生，并通过实验进行了验证。(5)对于受损船舶的数值模拟，提出了考虑进流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，数值模拟与物理模拟的差异被解释为一种由淹水舱室引起的防滚舱效应。(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波浪统计的影响，结果表明，计算出的具有操作效应的概率与实际伤亡统计是相当的。

(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.