Design And Noise Reduction Characteristics Analysis Of A Skin Structure With Built-in Vibration Isolation Unit

Submarine,torpedo and other underwater vehicles,as an important part of the marine military force,have been highly valued by countries all over the world.In order to meet the growing needs of national security strategy,countries have put forward higher requirements for the fast and stealth aspects of underwater vehicles.Therefore,how to improve the concealment performance of underwater vehicles has become a research hotspot in the field of ship machinery and drag and noise reduction.By adding vibration isolation devices between the vibration source and the foundation,the elastic deformation of the vibration isolation system can significantly reduce the transmission of mechanical vibration and noise when the disturbance source is activated.Therefore,based on the excellent characteristics of vibration and noise reduction of the ship vibration isolation system,a new skin structure is proposed in this paper by installing a micro vibration isolation unit in the flexible skin,and then the noise reduction characteristics and mechanism of the skin are systematically studied.This paper mainly carries on the following aspects:Firstly,based on the working characteristics and design requirements of the skin structure,a new type of fluid noise reduction skin structure is constructed,which combines the ship's vibration isolation system and the technology of fluid drag reduction and noise reduction on flexible surfaces.The skin is mainly composed of surface restraint layer and vibration isolation unit,which can effectively restrain the transition of boundary layer,reduce the generation of turbulent fluctuation and achieve effective control of convective noise.Secondly,the two-way fluid-solid coupling control equation is established;the flow information of skin surface under fluctuating excitation is obtained using large eddy simulation method,and the turbulent pressure distribution patten of the surface of skin structure in the axial and circumferential directions is obtained;the influence of skin structure on the fluctuating pressure of the object surface is investigated by comparing the fluctuating pressure distribution patten with or without skin.The results show that the designed skin structure has a good effect on reducing turbulent fluctuating pressure.Then,based on the obtained turbulent flow information,FW-H acoustic equation and boundary element method,the spatial distribution of flow noise around the skin is solved by using Fluent and LMS Virtual.Lab software,and the sound information around the skin is obtained.By comparing the sound pressure value of flow noise around the flat structure with or without the skin,it is determined that the skin structure has good noise reduction effect.By comparing and analyzing the flow noise at different velocities,it is known that the flow noise will gradually increase with the increase of flow velocity,and the change range is larger in the near field area,but smaller in the far field area.Finally,based on the analysis theory of flow stability and the criterion of boundary layer stability,the characteristic equation of boundary layer stability is deduced by combining the small disturbance control equation of fluid,solid and the continuity condition of fluid-solid coupling surface.Based on the time-space theory,the characteristic equation of boundary layer stability is solved,and according to the distribution of characteristic roots,the effect of material characteristics of skin structure on boundary layer stability is explored.The results show that with the increase of tension coefficient and damping coefficient,the stability of boundary layer flow is better,while excessive support stiffness will have adverse effects on the stability of boundary layer.The noise reduction mechanism of skin structure is described from the perspective of stability.