Optimization Design Of Ship Bracket Structures

Safety of the ship's structure,which occupies the important status in ship design, is the primary issue that designers, builders and operators pay most attention to. Ship structures are usually connected by traditional triangular brackets which cause stress concentration at the connections between ship structures and the bracket. Researches have shown that damage mainly occurs in the brackets, and reducing the tensile stresses at the brackets is the main method to improve this situation. A new design method of brackets is proposed in this paper, in which sub-modeling technology is employed to conduct the refinement stress analysis of the brackets, and optimization is applied to improve the stress concentration.Firstly, sub-modeling technology is employed to conduct the refinement stress analysis of the brackets by finite element analysis software Ansys. Based on the global analysis results, a connection between the bulkhead near the bow and the second platform is selected to conduct the optimization. The validity that proposed sub-modeling technology can be applied to examine the strength of the brackets is demonstrated by using the path interpolation method. Stress analyses of cases with and without the bracket are conducted in this paper to consider the role of the bracket in the connection structure by sub-modeling technology. The results show that the bracket reduces the stress concentration at the connection between the bulkhead girder and the second platform girder, and enhances the girders' bending characteristic, but causes stress concentration at the junction between the bracket and the girders.The shape and topology optimization are used to reduce the stress concentration respectively. In the shape optimization, changes in length of the brackets are defines as the design variables,the stress of the girder webs and the stress of the girder panels, which is close to the bracket, are considered as the constraints. The stress of the bracket is considered as the objective. The topology optimization is conducted by two steps. At the first step, material distribution of the bracket is defined as the design variable while the stress of the girder, close to the bracket, is considered as the constraints and the stress of the connections, between the bracket and the girders, is considered as the objective. A new type of bracket structure is obtained once the proper engineered treatment is applied to the topology optimization results of the bracket. At the second step, material distribution of the new bracket flange is defined as the design variable. The stresses of the girder webs and the stresses of the girder panels, which are close to the bracket, are considered as the constraints. The stress of the bracket webs is considered as the objective. The optimized bracket's stress concentration is improved greatly.The presented method may provide reference for strength analysis and optimum design of similar structures.