Fatigue Strength Assessment And Optimization Design Of The Typical Joint In Very Large Container Ship

Very large container ships have the characteristic of large openings,which results in the torsional stiffness of very large container ships being lower than that of ordinary ships.CCS didn’t consider the influence of torsion on the fatigue life of ship structures in the simplified method of the 2015 version "Guide for Fatigue Strength of ship Structure",so the research that whether the simplified method is appropriate for the fatigue life assessment of large opening vessels such as container ships needs to be studied.And also with the energy conservation and environmental protection gradually being valued by people,the shipbuilding industry as a traditional resource high-consumption industry,ship lightweight has become a hot research topic.This paper is based on the impact of torsion on the fatigue life of container ship hull structure and how to improve the fatigue life and reduce the weight of the ship structure.The main research contents of this paper are as follows:(1)The research significance of fatigue strength assessment and ship lightweight for very large container ships is introduced,and the research status of these two problems is described in detail.(2)The method of calculating the fatigue life for the ship structure by the CCS specification is introduced,which include the simplified algorithms and spectral analysis method,S-N curve method and fracture mechanics method.(3)The steps of the spectral analysis method are introduced.The finite element model of two very large container ships was established in Patran.The finite element mesh of the fatigue hotspots for the two ships was refined.The wave load calculation software WALCS was used to predict the wave pressure of the two container ships,and the stress response of fatigue hotspot was finally predicted.(4)The influence of torsion on the fatigue lives of longitudinal stiffeners in very large container ships is studied.Based on the simplified method and the spectral analysis,the fatigue life of some longitudinal stiffeners at the L/4,L/2 and 3L/4 sections distanced from stern for the two ultra large container ships are evaluated respectively,and then compared with the two methods.Finally,based on the stress range fitted by spectral analysis,the proportion of torsion-induced alternating stress in the whole stress range is analyzed by the design wave approach.(5)Optimization design of a circular hatch corner at the rear end of the cabin in a container ship is carried out.The BP neural network is applied to construct the proxy model of design variables and objective functions.The proxy models are optimized with the multi-objective particle swarm optimization(MOPSO).The improved minimum distance method is used to quickly select a set of optimal results from the set of non-inferior solutions,and the fracture mechanics method is adopted to calculate the fatigue life of the optimized hatch corner.