Research On Design Methods Of Auxetic Cellular Structures For Vibration Reduction And Defensive Structures Of Ships

With the requirements on ship comfort and safety,vibration reduction and impact resistance design of ships have become a key problem in high performance ships.From the main design principles of ship vibration reduction structures and defensive structures,it can be concluded that the structure should not only have the ability to efficiently isolate or absorb external energy(vibrational energy,noise energy,armor-piercing kinetic energy,explosive impact energy,etc.),but also should have appropriate stiffness that can play the role of the main structure.It emphasizes the integration of structural bearing capacity and special functions.However,traditional ship vibration reduction and impact resistance materials and structures are mostly made up of ordinary materials and structures,which is difficult to further improve the performance of them.Based on the design of vibration reduction bases,defensive structures and buffer bulbous bows,this dissertation is aimed to explore the application of negative Poisson's ratio materials and structures in the field of ship engineering.The vibration reduction and impact resistance mechanism,the optimization design theory and the test verification technology of the auxetic cellular base isolation system were studied;the influence of the number of honeycomb layers and geometric parameters on the penetration resistance in the air and water and underwater explosion resistance performance of honeycomb sandwich defensive structures were analyzed;a buffer bulbous bow with auxetic honeycombs was designed and its crashworthiness was studied by the FEM.The dissertation includes the following parts:(1)The overview of research on the ship vibration isolation systems,sandwich defensive structures and negative Poisson's ratio materials and structures is made.Meanwhile,the research significance and main contents of this dissertation are proposed.(2)Poisson's ratio and relative density of the re-entrant,the star-shaped and the arrow-shaped honeycombs are deduced theoretically.The influence of the geometric parameters on the mechanical properties of the honeycombs are also analyzed by the FEM.What's more,the frequency response test of the re-entrant honeycombs is conducted and a good agreement between the numerical results and experimental data is achieved.(3)Two types of ship vibration isolation shock honeycomb bases with positive Poisson's ratio effect and negative Poisson's ratio effect are designed.By keeping the weight of the honeycomb core,the effects of the thickness and layers of honeycombs on base isolation performance and impact resistance are studied.The varying curves of isolator stress,natural frequency,vibration level and vibration level difference versus cell wall thickness are obtained and proved that cellular base has good impact resistance isolation and negative Poisson's ratio has better performance.Dynamics optimization models of the hybrid base designed with thickness of face plates,brackets and honeycomb cells as variables are investigated in two cases,one with vibration reduction performance constraints and the other with both vibration reduction and shock resistance performance constraints.Optimization results indicate that by applying auxetic honeycomb hybrid structure and synthetic dynamics optimization design,excellent performance in vibration reduction and shock isolation can be obtained in the base design.This analysis is followed by static,modal,and frequency response tests,which verified the results of the numerical analysis.(4)The processes of a missile impinging on and penetrating auxetic cellular sandwich structures and traditional defensive structures,namely single-layer steel plate and double-layer steel plate,are simulated by nonlinear finite element software.The results indicate that when the weights of the structures are the same,the traditional defensive structures have better performance.Meanwhile,structural passive defense has been unable to deal with high speed projectiles and only the active defense takes effect.By reducing the number of the cell layers and increasing the cell thickness and Poisson's ratio,the impact resistant performance of the auxetic cellular sandwich structure can be improved obviously.(5)The failure modes of the auxetic cellular sandwich structures and traditional defensive structures under underwater explosion shock are simulated and the comparative analysis of their explosion resistance performance are also conducted.What's more,effects of different design parameters on auxetic cellular sandwich defensive structure,like thickness,size and Poisson's ratio of the honeycombs,are studied and compared.Numerical results show that compared with traditional defensive structures,auxetic cellular sandwich defensive structure has better impact resistant performance,which can be enhanced by increasing the layers and Poisson's ratio of the honeycombs,and is more suitable for underwater explosion protection.The impact resistant performance of the auxetic cellular sandwich structures is affected by the parameters such as cell shape,cell thickness,cell layer number and Poisson's ratio.It is suggested that the optimization design method should be applied to coordinate these different parameters.(6)A general numerical simulation and evaluation procedure for the accident of ship collision is proposed.By applying structural dynamic finite element numerical simulation technology and acoustic numerical simulation technology,detailed models for accident analysis of ship collision are presented.Collision process,structure damages,vibration of ship structure and noise resulting from collision are calculated.Crews' perceptions of impact noise in cabins are discussed with relevant maritime codes and regulations.Based on the good energy absorption and impact resistance performance of the auxetic cellular structures,a buffer bulbous bow with auxetic honeycombs is designed and its crashworthiness is studied by the FEM.The results show that the crashworthiness of the auxetic bulbous bow is better than that of the traditional ones.