Low-noise Optimization Design On Ship Grillage Structures

Ship is a large and complex structure composed of various grillage structures.During the voyage,it is inevitably affected by multiple excitations such as power plants,shafting,and external flow fields.These excitations affect the overall vibration and sound radiation level of the ship through the transmission of the ship’s slab structure,thus threatening the comfort and safety of the ship.Therefore,the low noise optimization design of ship’s slab structure is a very necessary research topic.In this paper,numerical analysis and experimental research are carried out to optimize the low noise design of ship grillage structures.Firstly,the research methods of structural vibration and sound radiation are introduced,and the research methods of structural vibration and sound radiation calculation by scholars at home and abroad are summarized.The method of studying the acoustic radiation of ship slab structure is finite element/boundary element method in this paper.The research status of the influence factors and laws of vibration and sound radiation of ship grillage structures is summarized,which lays a foundation for the research of this paper.The research status of low noise optimization design of ship plate structure 1s analyzed,which points out the direction for the research.The benchmark model for acoustic radiation analysis of ship grillage structures 1s established,and its modal characteristics,vibration characteristics and radiation noise characteristics are analyzed.The effects of design variables such as plate thickness,side-length ratio,stiffening form,rib spacing and inertia moment on acoustic and vibration characteristics of grillage structures under uniform or concentrated forces in air environment are explored.The conclusion show that the parameters such as rib spacing,rib number and inertia moment of ribs can significantly affect the acoustic and vibration characteristics of the slab structure with less weight change.Choosing the spacing of ribs,rib number and inertia moment of ribs as design variables,the layout transformation method of the slab structure is proposed,and the low noise optimization design method of the ship slab structure in the air environment is established.The method is based on the finite element method and boundary element method combined with multi-island genetic algorithm.On this basis,the low noise optimization design of one-way and two-way stiffened frame structure in air environment is carried out and the vibration and noise reduction effects are obvious.The goal of low noise plate structure design is completed in the design stage.In order to prove the validity of the low noise optimization design method for ship slab structure adopted in this paper,the transfer function test of the low noise slab structure is carried out.The error between the test results and the numerical analysis results can meet the engineering requirements,which fully proves the validity of the low noise optimization design method for ship slab structure in this paper.Finally,this paper proposes a low noise optimization design method for hull plate considering fluid load,and the practical effect of this method in ship application is analyzed.Taking the structure of propeller-shaft-stem as the optimization objective,the main excitation sources and transmission paths are analyzed,the slab area to be optimized is determined,and the optimization scheme of stem structure is given according to the low noise optimization method considering fluid load.The analysis results of actual ship show that the low noise optimization design of this paper has achieved the optimization goal.In this paper,the effects of structural design variables on the characteristics of vibration and sound radiation are studied,the methods of low noise ship slab structure optimization design in different environments are established,the validity test of low noise optimization method and the practical effect analysis of low noise optimization on actual ship are earried out,which provides ideas and methods for the low noise design of ship grillage structures.