Study On Propagation Characteristics Of Seabed Wave In Shallow Sea By The Excitation Of Vibration Targets

This paper introduces the background and application of ship seismic wave propagation in shallow sea,and expounds the research history,development and current situation of seismic waves at home and abroad.The method of locating the targets in the water using seismic waves caused by the radiation signals of ships is proposed.Firstly,a two-dimensional elastic wave equation in homogeneous elastic medium is used to simulate the propagation of the ideal elastic wave.The acoustic model of the shallow sea is established by the two-dimensional acoustic wave equation in the homogeneous acoustic medium to simulate the acoustic propagation in the ideal seawater.A set of fluid-solid boundary conditions is introduced on the basis of the ocean-earth model to simulate the seismic wave area propagating into the distance near the seabed interface.By introducing the numerical dispersion elimination algorithm in the finite difference grid,the numerical dispersions of the seabed wave area were eliminated and compensated.The effective data extraction and transformation was got by the simulated seabed wave area.The polarization characteristics of the seismic waves near the fluidsolid interface in the shallow sea were studied.The body waves and the Scholte wave were identified and distinguished,but the time difference of the shear waves was not easy to extract due to the attenuation and short of the source distance.In the direction parallel to the interface and the depth direction below the interface,the propagation attenuation characteristics of the Scholte wave at the horizontal and vertical of the particle velocity were analyzed in the form of graphs and tables,respectively according to three different medium with different degrees of softness and hardness.The dispersion characteristics of Scholte wave in the fluid-solid interface and the Scholte wave energy distribution in the shallow seabed seismic wave were studied simultaneously.It is proved that the Scholte wave is the slowest and with the lowest frequency in the shallow seabed flow-solid interface.With the increase of the source distance,the energy will become the largest and the propagation distance is the farthest and easy to identify.The longitudinal waves are the fastest and the most frequent in the each wave train,and the energy decays rapidly as the source distance increases.The shear wave is in the range of Scholte and longitudinal wave in the matter of propagation velocity,frequency and energy distribution.When the source distance is near,it is also difficult to identify.Therefore,the application of target detection has extensive value by seabed interface wave in shallow sea.At last,the seismic records near the seabed interface are acquired by simulation using the known parameters of the seabed medium.By means of the hydrophones above seabed interface and the seismic sensors beneath the interface,the seismic waves induced by the target in the sea are studied and used to achieve target detection and location in water.