Study on Optimized Design of Ship Structure

对超大型油轮双壳结构的优化设计进行了研究。文中考虑了一种基于塑性设计的油罐结构。由于有限元方法主要用于解决当前工程问题，需要大量的计算资源。单舱结构采用矩阵传递法，将矩阵传递法与框架结构法相结合进行三维弹塑性分析。以单舱重量和造价为目标函数。根据矩阵传递法的计算结果，只对双层底舱和舱底舱结构进行有限元分析。对这种局部结构进行了基于有限元分析的优化处理。在优化过程中只考虑了弹性设计，并对每个单元的有效应力施加了重新设计约束。在优化中引入了灵敏度分析，以减少有限元分析的计算量。作为一种优化技术，该优化方法在有限元分析的基础上进行了优化由于在实际船体结构设计中不可能有连续的设计变量，因此本文还对离散设计变量进行了研究。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，板的厚度是恒定的。这种两步优化方法使得我们可以很容易地将设计变量离散化。用上述方法解决了几个问题。结果表明，本文所介绍的方法给出了有效的船体结构设计方法。该方法降低了建造船体结构的重量和成本

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