Scattering From The Elastic Spherical Shell In The Fluid

The detection and classification of the submarine targets need the deep understanding of the target scattering.The submarine targets such as sea mine and submarines are man-made objects,however,the traditional research focus on the rigid body which is not the very need in the practical use.The form function describes the frequency response of target,this is very important for the detection and classification of target.The research of scattering from the elastic spherical shell focuses on the calculation of form function with the target parameters known,however,the time series of scattering signal is received by the hydrophone.Can the form function be extracted from the time series?Extracting the form function from the time series of scattering signal is verified in this text.To extract the form function,the components of time series should be classified.The analytical theories mainly are RST(resonance scattering thoery) and Sommerfeld-Waston transformation.RST is adopted in this text to analyse the scattering from elastic spherical shell,Scatt&OASES3D numerical method simulates the scattering and gets the time series of scattering signal.The time series of scattering signal contains the specular wave and other elastic components, there are time intervals between them because of the difference of propagating path.The time intervals from the analytic method and simulation method are compared and coincided very well,so the components of scattering signal are classified very well.The resonance scattering is separated into background component and resonance component,the background component and resonance component correspond to the specular waves and resonance waves respectively.Because the specular waves and elastic components isolate,the specular waves can be taken as the incident waves after calibration,then the form function can be achieved by the definition equation.The form function is extracted from the time series of scattering signal using the method above,it coincides the form function calculated using the RST in general.However,there are differences near the resonance frequency,the reason is that energy couples more into the spherical shell at the resonance frequency.Because the incident wave will be affected by the waveguid,it isn't easy to be determined.The method of extracting the time series without incident wave known is more stable.The estimation of group velocity is a relatively independent problem,Wigner- ville distribution is used to analyse the time series of scattering signal and the dispersion and time delay phenomenon are revealed.The group velocity in the elastic spherical shell can be calculated by the propagation path and the difference of the two wavelets' group delay,it coincides with the result from the Resonance Scattering Theory.Group velocity relates to the target material very much,so it's important for the detection of target.The scattering from thin spherical shell has the midfrequency enhancement phenomenon which is very different from thick spherical shell.After studying the phenomenon,the outer radius a and thickness h can be expressed by the frequencyω_p of greatest enhancement and echo delay△t.The echo delay can be read from the time series from the numerical model,the form function can be extracted from the time series using the method in this text,then the radius and thickness can be estimated.