Study On Structural Strength Of Ultra Large Containerships With Considering The Effects Of Springing And Whipping

Driven by the fierce market competition in the shipping industry,the dimensions of container ships have been becoming increasingly larger.The increase of scale and carrying capacity leads to the decrease of the natural frequency of the the container ship.The phenomenon of slamming caused by bow flare and high speed of the container will be obvious during the voyage.Theoretical analysis and experiment data show that springing and whipping will occur so frequently during navigation,which can make a significant impact on the fatigue and ultimate strength of the target ship.In this paper,the numerical method is used to compute and study on the load response of an ultra large container ship which can carry more than 20000 containers,the fatigue strength under the effect of springing and the ultimate strength under whipping effect are computed.What‘s more,this paper introduces the hydroelastic model test of ultra large container ships,and gets the conditions for model test and whipping load by computation.The results of model test and numerical calculation are compared,and the coincidence degree between them is high.The specific research contents of this paper are as follows.?1?By comparing the dry modes results of the hull under considering the modes of bending-torsional coupling and not considering the modes of bending-torsional coupling,it is found that the bending-torsional coupling modes of the target ship can not be neglected.The linear wave load response characteristics of the target ship are calculated and it is found that the phenomenon of the springing is very obvious.The nonlinear wave load of the target ship is calculated,and the frequency spectrum analysis and extreme value fitting analysis of the load time series are carried out.At last,the calculation results of the loads considering the modes of bending and torsion coupling and not considering the modes of bending and torsion coupling were compared and analyzed.?2?The content of wave load model test of target ship is introduced.For a particular target load,the sea condition that has the largest contribution to the long-term target load and the sea condition that can easily cause the springing and whipping can be chosen for model test and load computation.Determine the regular wave test conditions by studying on the target load response.By comparing the experimental results and numerical results of motion and load,it is found that there is a good agreement between them.?3?The structure response characteristics of the target ship are calculated and analyzed and the fatigue damage of each hot spot is calculated by spectral analysis.It is found that the elastic effect greatly aggravates the fatigue problem by comparing between the rigid body theory calculation results and elastical body theory calculation results.The ultimate bending moment of the section was calculated by the Smith method and the ultimate strength of the target ship was checked according to"Ch5,Sec2"in the"Structural Rules for Container Ships"^[50]of the French Bureau Veritas and the effects of whipping on the wave load is studied.