Design Methods Of Ship Structure With Metamaterials And Performance Analysis

Vibration of ship structures is always the main cause to crack or fatigue failure,and the higher concealment of ships and submarines is required by the improvement of noise monitoring.Therefore,there is great significance to improve the the concealment,safety and comfort of the ships to reduce the vibration of the main engine by some reasonable design.Auxetic porous metamaterials are made up of unit cells forming by translation or rotation,which can also be seen as the application structure formed by series and parallel connection of one unit cell.The Poisson's ratio,relative density stiffness and frequency of an unit cell can be affected by many parameters such as unit cell angle,ratio of height to width or thickness.In this paper,the theoretical expression is deduced based on the theory of elastic homogenization and finite element method,then the dynamic and static mechanical performance of honeycomb cell at different angles and different ratios of height to width is analyzed under different connection conditions,which can provide a theoretical reference for the design of complex auxetic metamaterial structures and wide application prospect.Traditional marine vibration isolation equipment such as base or floating raft has been deeply studied at home and abroad.It is difficult to take account of the vibration function and lightweight design requirements without considering new forms of structure or new materials.Consequently,the floating raft structure and auxetic metamaterial structure are analyzed theoretically,then the design scheme of vibration isolation floating raft based on the auxetic metamaterial structure is proposed.On the basis of that,2 typical floating raft structures and 2 newly designed floating raft with auxetic metamaterial structure are established in FEM software to explore the application of 4 different types of floating rafts in vibration reduction performance under a ship main engine excitation.The results show that the auxetic metamaterial raft can improve the vibration level drop in some frequency bands,reduce the vibration intensity transmitted from the main engine to the bottom plating of ship,and at the same time reduce the weight of the floating raft significantly.A double-layer cylindrical shell with auxetic metamaterial rib is designed,which shows lightweight and excellent vibration reduction performance.Under the premise of bearing capacity of the structure,We explore its application in the cabin of submarine in order to reduce the vibration and noise caused by power equipment.The stiffness of the double-layer cylindrical shell can be changed by adjusting the width of the metamaterial rib,and the vibration isolation and sound radiation performance of the double-layer cylindrical shell can be changed by adjusting the thickness,angle and the number of cell layers of the metamaterial cell.The influence of metamaterial cell layers on the vibration isolation and acoustic radiation performance of double-layer cylindrical shells is studied by keeping the total mass of the ribbed plates unchanged,and the influence of the width of the supermaterial ribbed plate,the Poisson's ratio of the cell and the number of the cell layers on the strength,natural frequency,acceleration response level,vibration level drop,vibration transfer rate and radiated sound power of the double-layer cylindrical shell are given.Compared with conventional double-layer cylindrical shells,the lightweight advantage and low noise performance of double-layer cylindrical shells with auxetic metamaterial rib are proved.In view of the excellent performance of auxetic metamaterial rib in vibration and noise reduction of double cylindrical shells,it is further applied to the structural design in the cabin of a submarine power equipment.By changing the double-layer shell stiffened plate to the auxetic metamaterial rib,it can reduce the hull vibration and underwater radiation noise caused by the vibration of power equipment,and at the mean time,it can reduce the weight of the hull structure.In this paper,the finite element model of submarine is established to analyze the vibration and underwater radiated noise.We compared the vibration acceleration levels of the cabin shells designed by the metamaterial rib and the ribbed plate under different mass constraints by adjusting the cell plate thickness of the auxetic metamaterial rib.And the radiated sound power level and radiation directivity of the submarine are calculated by the coupled indirect BEM.compared with the submarine structure with the ribbed plate,the auxetic metamaterial rib shows better noise reduction performance in the total synthetic sound power.Using the auxetic metamaterial rib can prevent transmitting energy of the mechanical vibration to the outer shell effectively.It is proved that there is practical application prospect of auxetic metamaterial rib.