Research On Vibration Reduction And Shock Resistance Characteristics Of Foundation With Auxetic Structure

The vibration generated during the operation of the mechanical equipment is transmitted to the hull through the foundation,meanwhile,the impact on the hull is also transmitted to the mechanical equipment through the foundation.The traditional base is usually welded by steel structure which has a small damping and is limited to suppress vibration.Some special structural materials with negative Poisson’s ratio effect are found in recent years which have some excellent mechanical properties such as impact resistance,energy absorption and vibration isolation.Therefore,the research on the vibration reduction and shock resistance performance of the foundation plays an important role in the designing of ships.In order to improve the vibration and shock resistance of the base of the ship and enhance the sound and vibration performance of the ship,the negative Poisson’s ratio structure is applied to the foundation in this paper.The main work are shown in the following:The expression of the Poisson’s ratio for negative Poisson’s ratio unit cell is deduced firstly.And then the Poisson’s ratio of negative Poisson’s ratio cells with different concave angles in cells is calculated.The influence of structural parameters on the static properties of negative Poisson’s ratio cells is analyzed.The results show that the stiffness of the cell increases with the increase of the cell wall thickness,and decreases with the increase of the concave angle of the cell.The effects of cell arrangement on static and dynamic characteristics of the structure is studied.The results show that the cell structure parameters and the way of arrangement for cells have a significant influence on the static and dynamic characteristics of negative Poisson’s ratio structure.A negative Poisson’s ratio foundation is designed,and a finite element model of negative Poisson’s ratio foundation-ship vibration reduction system is established.The influence of the cell structure parameters on the vibration reduction performance of negative Poisson’s ratio foundation is investigated.The total vibration level difference of the base decreases with the increase of the cell wall thickness and increases with the increase of the concave angle in the cell.A negative Poisson’s ratio base structure defect is simulated by missing a cell wall.The influence of different structural defects on vibration damping performance of the base is explored.And it is found that the structural defect may make the vibration reduction performance of the base worse.Through comparative analysis,it is found that the negative Poisson’s ratio base has better vibration reduction effect than the conventional base.The effects of the cell wall thickness,concave angles of the cell,the thickness of the base panel,and structural defects on the impact resistance of negative Poisson’s ratio base are investigated.The results show that the larger the cell wall thickness is,the better for impact resistance of the base is.As the concave angle inside the cell increases,the vertical resistance of the base becomes worse,meanwhile,the longitudinal impact isolation coefficient of the base firstly increases and then decreases.In addition,the thickness of the base panel has no obvious influence on the impact resistance of the base.Defects in the structure may make the impact resistance of the base worse.Appling the designed negative Poisson’s ratio base to the underwater structural cabin,the underwater vibration and sound radiation calculation model of the cabin structure with negative Poisson’s ratio base is established.Based on the FEM model,the influence of structural parameters of negative Poisson’s ratio base on the underwater acoustic and vibration characteristics of the cabin is analyzed by the FEM-BEM.The research shows that as the cell wall thickness increases,the noise reduction performance of the cabin structure at100-200 Hz is better.And the larger the concave angle of the base cell,the worse the noise reduction performance of the cabin structure.The structural defect of the negative Poisson’s ratio foundation has little effect on the noise reduction performance of the cabin structure.The acoustic and vibration characteristics of underwater structure cabin with negative Poisson’s ratio base and conventional base are compared and analyzed.It is found that the negative Poisson’s ratio base has better vibration reduction effect;In the low frequency range,the cabin with negative Poisson’s ratio base has a lower underwater radiated sound pressure level.