Study On The Direct Calculation Method Of Deadship Stability Based On 6-DOF Nonlinear Time Domain Motion Model And The Corresponding Application

IMO?International Maritime Organization?second generation intact stability criteria are expected to be finalized in 2019,while nowadays,numbers of sample ships are calculated for its perfection.Deadship condition,which means a ship exposed to the combination of beam wave and wind will roll intensely and even capsize,is recognized as one of the most dangerous stability failure modes.Based on the unified model which considers maneuvering and seakeeping performance,a 6-DOF nonlinear time domain numerical motion model that can be used by direct calculation of deadship stability is established and improved.With the help of this model,some factors that will have impacts on the motion response and capsizing features of deadship stability are discussed,like drift motion,initial heeling angle,wave spectrums,peak frequency and so on.With the method of spectrum analysis,statistical analysis of roll motion in random as well as the efficient and convenient assessment of capsizing probability is conducted in the situation of deadship condition in irregular waves.Meanwhile,based on the 2^nd level vulnerability criteria of deadship stability,with the method which can linearize the curve of righting arm,the capsizing probability is able to be calculated.In addition,some sensible factors that can impact the capsizing probability significantly are discussed.The 6-DOF nonlinear time domain numerical motion model is verified to be accurate and reliable.As the model can investigate the motions and the interactions of some significant degrees of freedom in deadship condition under combination of wind and waves,it has some research values.As the significant variation of GM in waves for very large containerships,strict demands are raised to this ship type for the evaluation and safety assessments of parametric roll.Targeting at a 10000TEU containership sailing in head sea,ship velocity and wave conditions are taken into consideration to this 6-DOF time domain numerical motion model.After each loading condition has been calculated step-by-step,sensible conditions about parametric roll are explored.Finally,according to the results,corresponding safety assessments and some avoidance measures are proposed,such as reducing the height of center of gravity and raising speed moderately.In addition,if wave predictions can be detected in advance,the circumstance when natural rolling period being twice as much as encountering period should be avoided,which deserves the most sensible factor for inducing parametric roll.As a result,the remarkable engineering application and value for reference can be recognized.