Shape Optimization Of Ships’ Local Structure With The Improved Kriging Approximation And Parameter Fusion

Local structures of ships,such as deck openings,hatch corners and elbow toes,tend to occur stress concentration due to the discontinuity of structure shape.If only the local structure is strengthened,it will increase the weight of the structure.Therefore,it is necessary to explore structural design with lighter weight and uniform stress by means of shape optimization.There are mainly three aspects involved in the study of shape optimization of local hull structures.First,we need to choose the appropriate initial shape type.You can also customize any suitable shape.Second,to select intelligent optimization algorithm with better search ability to ensure that the optimal geometric boundary shape of the structure can be obtained.Third,it is necessary to improve the efficiency of shape optimization and reduce the cost of optimization by replacing part of finite element calculation with approximate model.Firstly,an improved partition and generalization Kriging approximation model(PGKAM)is proposed.One of the improvements about partition is to divide each dimension of sampling point’s data in the design space into two or four equal parts.The Optimal Latin Hypercube Design sampling is applied in each partition.Then different Kriging approximation models are established among different partitions.The other improvement is combining Gauss and exponential correlation function by introducing of proportional coefficient,which increases the type of correlation function and thereby improves the generalization performance of approximation model.With testing the Schaffer function N.1,the PGKAM has been proved more accurate in predicting multi-dimensional response values.By integrating with parametric modeling and PGKAM,certain optimization problems of bracket and hatch corner’s boundary shape are carried out.In the process of shape optimization,firstly,the global initial optimal solution is obtained from the improved approximate model with the Multi Island Genetic Algorithm.Then the scope of the optimization variables is trimmed base on the initial solution.With costing few FEM calculations,the exact optimal design variables are able to found efficiently in a small scale.The results illustrate that the partition and generalization Kriging approximation model has higher prediction accuracy than the conventional Kriging model in the prediction of multi-dimensional responses.Phased shape optimization methodology ensure the ideal stress distribution and weight optimization results be capable of obtaining when error is minimum and the calculation burden is lessened,which is helpful to the lightweight analysis of ship structure.Finally,a shape optimization scheme based on Parameter Fusion and Abaqus’ s adaptive mesh redesign module is proposed.In the Parameter Fusion optimization scheme,shape type factor is introduced to distinguish different shape designs.And different types of shape structures are linked by global design variables and local design variables.By optimizing the shape of the bracket on a plate,it is shown that the parameter fusion can increase the diversity of structural shape optimization,which spare the evaluation of the optimization results among different types of shapes and improve the efficiency of structural shape optimization.