Study on Optimized Design of Ship Structure

研究了VLCC双壳结构的优化设计。这里考虑的是一种基于塑性设计的储罐结构。由于有限元法是解决现代工程问题的主要方法，需要大量的计算资源，因此在单罐结构中采用矩阵传递法。将矩阵传递法与框架结构法相结合，进行三维弹塑性分析。以建造一个储罐的重量和成本为目标函数。本文仅对双层底舱和舱底料斗舱结构进行了基于上述矩阵传递法计算结果的有限元分析。在有限元分析的基础上对该局部化结构进行了优化处理。该优化只考虑弹性设计，对每个单元的有效应力施加一定的约束。为了减少有限元分析的计算量，在优化中引入了灵敏度分析。作为一种优化技术，乘数法消除了对初始条件的限制。由于实际船体结构设计中不可能有连续的设计变量，因此本文也对离散设计变量进行了研究。为此，本研究采用两步优化流程。在第一步优化中，所有的设计变量都被视为连续的。在第二步中，将板的厚度设置为恒定，而所有其他设计变量仍然是连续的。这种两步优化技术使我们能够轻松地涉及离散设计变量。用上述方法解决了几个问题。结果表明，本文所采用的方法为船舶结构设计提供了有效的依据。采用该方法可以降低船舶结构的重量和成本

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