Study On Fatigue Strength Evaluation Of Super-Large Container

With its high efficiency of loading and unloading,fast turnover speed,low operating costs,container ships have become one of the mainstream ship.The hull structure of container ship is different from that of other ship types.Its capacity of bending and torsion is greatly weakened because of its large opening area.Therefore,it is necessary to evaluate its fatigue strength.Especially in recent years,large-scale and high-speed container ships have been developed.In order to reduce production cost and increase economic efficiency,a large number of high-strength steels have been widely used,leading to local stresses' increase in hull structures.The fatigue problem has become more and more important and become a factor can not be ignored.In this paper,the fatigue evaluation of super-large container ships is studied,and a 9200TEU super-large container ship is taken as a case study to study the fatigue evaluation method suitable for its structural characteristics.This paper discusses the theoretical basis of the simplified method,spectral analysis method and design wave method respectively,and uses these methods to evaluate the super-large container ship's fatigue strength of typical fatigue hot spots.And the problems of PCL language automatic loading and hot spot stress extraction during fatigue strength evaluation are analyzed and studied.In addition,due to the relevant parameters' relatively large impact to the fatigue assessment results in fatigue cumulative damage theory,these related parameters were also studied.Through the use of BV and CCS ftigue rules for super-large container ship fatigue strength assessment,It's found that:On the whole,the distribution of the dangerous components of the results of these two kinds of rules is consistent.The fatigue damage calculated by the BV and CCS rules is relatively small in the upper side of the ship,and the fatigue damage in the bilge and bottom areas of the hull is large.Because the curvature of the bilge structure of the hull is relatively large and the stress is more concentrated and the external dynamic load is relatively large.The results of the BV and CCS rules are quite different from the fatigue evaluation results of the same longitudinal joints.The CCS standard evaluation results are more stringent than the BV specifications except the inner shell longitudinal joint.Through the use of spectral analysis and design wave method of these two direct calculation method for super-large container ship fatigue strength assessment,It's found that:The hatch corners and keyhole structures of container ships are the areas where the fatigue damage of container ships is more serious,so it is necessary to pay more attention to the checking of fatigue strength.Fatigue damage of the fatigue hotspots near the ship's amidships is generally larger than that of the bow and stern regions,due to the higher alternating stresses in the vicinity of the amidship than the bow and stern areas.Fatigue evaluation spectral analysis method and design wave method can reflect the more serious region and structure of fatigue damage of hull structure,but the two methods of fatigue damage results' deviation is relatively large.It can be seen that the fatigue wave design method is not accurate than spectral analysis method,but its evaluation result is more strict than spectral analysis method.Therefore,in the evaluation of fatigue,spectral analysis method has clear physical meaning,clear process and more accurate fatigue evaluation results.It is recommended to use spectrual analysis method for fatigue evaluation.While the design wave method is not as accurate as the spectral analysis method,but the calculation results are more conservative,less work than the spectral analysis method,which can be added as a spectral analysis method.Based on the study of fatigue cumulative damage relevent parameters,It's found that:The level of overrun probability and the parameters of weibull shape of fatigue damage theory have a great impact on the final fatigue damage results.The fatigue damage result increases with the increase of the shape parameter,so the bigger the shape parameter,the more the fatigue evaluation result is conservative.The level of overrun probability 10-2 is the least affected by the change of shape parameter value in each probability level and the range of overrun probability levels[10-1,10-2]is also the largest contribution to fatigue damage.