Mechanism And Modeling Of Magnetic Field Produced By Dynamical Seawater And Underwater Metal Targets

Now the underwater target is detected mainly by active sonar or passive sonar.In order to hide the submarines,various countries make the sound field reflexed or radiated by the submarine similar to that of the ocean background by using noise elimination technology,leading to the higher difficulty of sonar detection.Due to the high frequency electromagnetic wave that decays rapidly in the sea water,it is not possible using the high frequency electromagnetic wave to detect submarines.Therefore,the method that using the low frequency electromagnetic wave to detect target is an important means to detect underwater targets.In this paper,the magnetic field of the ocean background and that of the metal target are studied,the magnetic field models are established to detect underwater targets.The main works are as follows:1.Firstly,the common sea spectrum models,the directional function,and the method of modeling sea surface are introduced briefly,and the sea surface is modeled by the linear superposition method,and the magnetic field of sea wave cutting the earth's magnetic field is simulated.Then,a simple idealized treatment of ocean current model is carried out,ocean current model is considered as an infinite flow with constant velocity,the distributed magnetic field model of ocean current is built.Lastly,the long internal wave and the short internal wave are analyzed and modeled,and the spatial distribution characteristics of the magnetic induction field for the internal wave are obtained.2.The Kelvin wake generated by the ship is constructed and analyzed,and the different wake waves are obtained at the different speeds of different hulls.And its magnetic induction magnetic field is calculated.Based on this,the spatial distribution characteristics of the magnetic induction field is summarized.It is found that the variation law of the magnetic induction magnetic field along the x-axis and the y-axis meets sinusoidal characteristics,and the magnetic peak appears in the area with lager ups and downs located at the trailing angle of 16 degrees to 19.5 degree.3.The magnetic field model of vertical and horizontal electric dipole in low frequency in seawater is analyzed and simulated detailedly.The calculated results show that the low frequency horizontal electric dipole can be used to equal excitation current source of the hull or submarine generally.4.The magnetic field model in seawater generated by an iron sphere is analyzed and studied.Firstly,the submarine is simplified into an iron sphere,and the expression of the induced magnetic field inside and outside the sphere is derived.And then,the total induced magnetic field generated by the sphere at the uniform magnetic field,meanwhile,the near-far field distributions of the induced magnetic field in x,y,and z component are given at the different seawater depth,different frequency excitation and different detection positions.