Study on Optimized Design of Ship Structure

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Optimized design of double hull structure for VLCC has been investigated.One tank structure based on plastic design is considered here.Since finite element method, which is mostly used for recent engineering problems, requires a lot of computing resources, the matrix transfer method is used in the one tank structure.The matrix transfer method is coupled with gframe structure method in order to compute 3-dimensional elastoplastic analysis.Weight and costs for constructing one tank are taken as objective functions.Finite elememt analysis is performed only for double bottom and bilge hopper tank structure based on the results obtained from the previously mentioned matrix transfer method.Optimization preocess is performed based on the finite element analysis for this localized structure.Only elastic design is considered in this optimization with applying resign constraint to the effective stresses in each element.Sensitivity analysis is introduced in this optimization in order for reducing computational load in finite element analysis.As an optimization technique, multiplier method is utilized resulting in removing the limitation on the initial condition.Since it is impossible to have continuous design variable in the real ship hull structure design, discrete design variable is also studied here.2 step optimization processes are held in this study for this purpose.In the first optimization step, all design variable are treated as continuous.In the second step, thicknesses of plates are set to be constant, while all other design variable are still taken as continuous.This 2 step optimization technique allows us to involve discrete design variable easily.Several problems are solved by the above mention method.Results show that the method introducted in this study gives us effective ship structure design.Both weigh and cost in constructing ship structure are decreased by using this method