Research On Structure Lightweight Design Of River-sea-going Ship Based On Ultimate Strength

In order to satisfy the national requirements,develop the golden waterwayof Yangtze river and promote the river-sea-going transportation,it is necessary to take optimization research on the structure of river-sea-going ship to make it environmental friendly and have a demonstration effect.Using ultimate strength criterion as optimization objective can be more effective for that it is more accurate.This essay was based on the method of ultimate strength and structural optimization method,and set both ultimate strength and weight as objectives.The ultimate behavior was considered in both bending and combined torsion and bending conditions.The rule was also adopted and investigated as it may affect the optimization result.The main contents and results are as follows:(1)The methods and their characteristics of ultimate strength were compared.Meanwhile,structural optimization theory and optimize platform were introduced.Finally,non-linear finite element method was used to calculate ultimate strength and Isight was used to drive the simulation.(2)Take Nishihara box girder as example,modeling method of a parametric model of box girder was studied,especially considering the spacing of longitudinal stiffeners.Driving Abaqus by Isight,and Optimal Latin hypercube design is chosen for sampling,sensitivity was studied.Otherwise,design of experiment and multi-objective method such as NCGA and NSGA-Ⅱ was compared for the further study.(3)Based on the modeling method which was studied before,the parametric model of river-sea-going ship’s middle section was built.The number of design variables,which include thickness,spacing and material,is 44.As the spacing is variable,the minimum sizes according to the ‘River-Sea-Going Construction Specifications’ were dynamical.So,the checking program was wrote by Matlab and set as restriction.Sensitivity analysis was conducted on the result of design of experiment,and the pareto front was also can be drawn.Finally the rules’ effects could be analyzed and optimal structure could be given.(4)The big opening of container ships might cause torsion loading seriously.So,on the basis of modal test and simulation of ultimate strength under torsion and bending,a smaller model which contains 3 frames was proposed as optimization target.Parametric model was built by modify an existing model.Combining with above method and strategy,the effects of torsion could be analyzed and optimal structure could be given.(5)Some ideal results were obtained after optimization calculation towards hog and sag condition.Under bending loading,ultimate strength of structures whose weights are the same increases at most 19.6% and 16.3%(due to the uses of high-strength steel),weights of structures whose capacities are the same decrease 4.5% and 6.3%.Under combined torsion and bending loading,ultimate strength increase 3.4% and 5.6%,weights decrease 1.6% and 2.7%,which were compared in the same condition.