The Method Research On Controlling The Self-noise Of Sonar Platform

Sonar is a device that make use of the propagation of sound wave to detect?locate?track?navigate and communicate the underwater targets.It plays an important role for ships,since it can effectively avoid dangerous accidents by improving the detection ability of sonar,which will enhance the survive ability of ships.A large number of exports around world has made deeply research of improving the detection ability and the concealment performance of the sonar.It is the key point that reducing the self-noise of sonar platform to improve the ability of sonar.By the analysis of the influence factors characteristics of self-noise,we can find out the efficient ways to reduce the self-noise.And then we can improve the ability of sonar.The self-noise of sonar platform includes three main noise source: hydrodynamics noise,propeller noise and mechanical noise.Hydrodynamics noise is the main noise component when ships speed is over 10k/h;propeller noise is another main underwater noise source which will effected the intensity of The self-noise of sonar platform and will increase with 5th~6th power of speed;mechanical noise mainly influence the low frequency.In this paper,the main work is based on the structural feature of sonar platform.By adding sound insulation board in the platform and covering An-echoic coating,propeller noise and mechanical noise can be controlled.And a series of numerical simulation and experiments has been finished to verify the efficient of those measurements.Hydrodynamics noise component is mainly generated around ship bow.A new acoustic structure has been designed to make sure that the ship bow acoustic window has the Sufficient strength and good acoustic transmission ability at same time.The research result shows that: by covering the acoustic an-echoic coating with the periodic arrangement cavity,the additional impedance of baseboard can be increased efficiently,and vibration of baseboard will be reduced.What's more,impedance mismatching between water and acoustic an-echoic coating has been increase,and that ensure the vibration transmission loss will increase efficiently.In general,the acoustic anechoic coating with the periodic arrangement cavity has a better sound insulation ability in the high frequency.In this paper,four kinds of sound insulation board has been designed.Among these sound insulation board,The concave Angle type sound insulation board has the best noise reduction performance with mechanical noise;while the Convex Angle type sound insulation board is the worst.The plane surface type sound insulation board and cambered surface type sound insulation board have nearly the same performance that is between the concave Angle type sound insulation board and the Convex Angle type sound insulation board.And the reason of that situation is that the curvature is quite small.By increasing the curvature may decrease the noise reduction ability with mechanical noise.As for propeller noise,the type of sound insulation board makes little difference in noise reduction.As for hydrodynamics noise,several types of sound transmission board has been designed in this paper.The numerical simulation in ANSYS and experience in water tank was done.By which shows that we should as much as possible to reduce the thickness of the plate and the height of the rib,to meet the structural strength requirements.In this paper,a new kind of Titanium alloy ribbed sound transmission board has been designed.It has a good sound transmission ability and also meets the acoustic requirements.