Analytical Method For Stress Around Hole In Hull Structural Member And Optimization Design For The Hole Shape

In the ship structure,it is inevitable to cut holes in the plate of some structures in order to meet the practical need of various functional requirements,and to reduce the weight of structure.However,when the plate is subjected to external loads,high stress values occur at the edge of the plate,causing stress concentration.Excessive hole-edge stresses can make the plate yielding or cracks,contributing to damage and shorten the overall service life of the structure.In addition,with the increasing of requirements in shipbuilding,the need for holes in hull structure diversifies.According to specific stress conditions and construction requirements,designers design hole shapes and hole sizes from the perspective of both security and economy.For a hull,however,the security is always contradictory to the economy.To ensure a better design result in the end,the structure needs to be optimized.Therefore,the study can be conducted on stress distribution around holes in the hull structure and the optimization of the hole to meet the need of security and economy for a hull.This study is of great significant to a low construction cost of the hull and a boost of international competitiveness in domestic shipyard.This study focuses on the stress distribution around holes in thin plates.The complex solution is adopted to get the theoretical values of the hole-edge stress.The BESO algorithm is adopted to optimize the hole shape.Firstly,methods on the stress function around holes in thin plates are sorted out.Secondly,based on the rational mapping,a new variable is introduced and an improved mapping function formula is proposed.With the improved mapping function formula,the waist and rounded square are mapped from a unit circle.Developing a calculation program combining the mapping function with the stress function to obtain the hole-edge stress around different hole shapes.Based on the theoretical calculation of different hole types,a improved BESO algorithm is adopted to optimize the design of the existing hole shapes.The content of this research are as follows:(1)Complex function methods dealing with the hole-edge stress of isotropic two-dimensional flat plate are sorted out.A new semi-analytic method dealing with the hole-edge stress of finite thin plate with different holes is introduced.It could provide the basis for theoretical solutions in the following research.(2)Theories of the mapping function that maps different holes into circular holes are analyzed.Based on the rational mapping,a new variable is introduced and an improved mapping function formula is proposed.The range of mappable graphs is expanded and the ranges and rules of each parameter in the formula are given.(3)The waist and the rounded square holes are the calculation object.The obtained specific mapping function combined with the reconstructed stress function and Maplesoft are used to compile the calculation program to solve the corresponding hole-edge stress.Based on that,the accuracy of the improved mapping function formula proposed in this research is verified by comparing the analytical results with the finite element simulation results.(4)Based on the traditional BESO algorithm,an improved optimization algorithm for plates with holes is proposed.The stress concentration factor is introduced to improve the calculation method of the element deletion rate and the addition rate.The average stress of multiple elements around an element serves as a criterion for deleting or adding elements.As the optimal end condition,the hole-edge stress value can be selected freely.The improved BESO algorithm program is written by APDL language of ANSYS,and then it can be used to optimize thin plates with different hole shapes.Finally,designing line of the optimized results,and providing practical reference for engineering applications.