Research On Residual Ultimate Strength Of Damaged Hull Structure

Ultimate strength is the most critical indicator of the safety of a ship’s structure.Insufficient ultimate strength of a ship will lead to the catastrophic consequence of the hull beam being broken into two sections.Due to the complexity of the hull’s own structure and the non-linearity of the material,the problem of the ultimate strength of the ship is very complicated.Ultimate strength problems are generally studied using model experiments and numerical methods.Model experiments of ultimate strength are destructive experiments,which require high experimental conditions and huge costs.Numerical method is another powerful method to study the ultimate strength,but the dispersion of the calculation results obtained by different numerical methods is still large.Therefore,it is a common requirement of the shipbuilding industry and the shipping industry to evaluate the calculation cost and accuracy of numerical methods and achieve the purpose of calculating the ultimate strength quickly and accurately.This paper uses model tests,numerical methods to study the ultimate strength of intact and damaged hull structures,compares the results of experimental and numerical methods,and the characteristics of different numerical methods.The research results have great engineering application value.As a new shipbuilding material,aluminum alloy is increasingly used in the construction of large hovercrafts,small waterplane catamarans and other ships.In this paper,a non-linear finite element method is used to develop a load-end shortening curves library for aluminum alloy materials,and a calculation program is developed in conjunction with Smith Method,which can quickly evaluate the ultimate strength of aluminum alloy boats in intact and cabin-breaking conditions.One of the current development trends is the transition of ship structure design from fixed value design method to reliability design method based on probability and statistics.This paper analyzes the time-varying reliability of hulls due to corrosion damage.The calculation results have important reference value for assessing the safety of the hull throughout its life cycle and the life extension plan of aging ships.The main contents and results of the research work in this article include:(1)Aiming at the problem of local denting of the hull structure under the actual engineering background,a stiffened plate model and test fixture were designed,and a uniaxial compression test of the stiffened plates under the condition of simple support was carried out to study the stiffened the residual ultimate strength of the stiffened plates.A reliable nonlinear finite element analysis process was established to solve the problem of lack of experimental verification of finite element analysis in existing research.(2)For the box girder of long-span deck structure,model test,nonlinear finite element method and Smith method were used to calculate the ultimate strength,and the accuracy and application cost of nonlinear finite element and Smith method were evaluated.The maximum stresses that can be endured by the structural component are compared with the calculation results based on the Smith method,and the accuracy of the load shortening curve of the Smith method is evaluated from the component level.(3)The non-linear finite element method is used to calculate the load-end shortening curves of the aluminum alloy structural units.The load-end shortening curves library is established by transforming different and values for the Smith method to call during the calculation process.(4)The improved Smith method takes into account the effects of translation and rotation of the neutral axis of the damaged section on the ultimate bearing capacity of the section.Based on this method,the residual ultimate strength of the large aluminum alloy hovercraft under collision and ground damage conditions is calculated.(5)Based on the optimized search algorithm and Smith method,an efficient calculation agent model for the ultimate strength of hull girder is established,and the function of quickly obtaining the statistical characteristics of ultimate strength of hull girder through large-scale sampling is realized.(6)Summarizes the application of reliability analysis methods in existing ship and marine structure codes.The reliability analysis of the ISSC large bulk carrier with corrosion damage is carried out,and the reliability index curve of the bulk carrier in the life cycle is obtained,and the sensitivity analysis of related parameters is performed.