Transient Radiated Sound Vector Field Of Annular Transducer In The Shallow Sea With A Thermocline

This thesis is focused on the transient acousitc vector field excited by an overflow-type annular transducer in the shallow sea with a thermocline.The reasons for studying this problem are as follows:a).In the shallow sea area,the thermocline often occurs due to the influence of the solar radiation and wind-driven agitation during the summer and autumn.Theoretical investigation on the propagation of the sound excited by different types of sound sources in the shallow sea with the thermocline plays an important role in the underwater acoustic communication and underwater acoustic detection.B).The annular transducer that utilize liquid cavity resonance has excellent performances,such as broadband,high power,and deep water resistance.It is widely used in the underwater acoustic engineering,such as the aviation sonar and underwater acoustic communication network.Therefore,it is necessary to study the propagation of the transient sound excited by the annular transducer;c).The acoustic vector field contains far more rich information than the scalar field.Compared with the scalar field,the vector field can provide vector information such as the sound pressure gradient,particle velocity and particle acceleration.Therefore,the acoustic vector field has great potential in sound detection and ground sound inversion.Firstly,the guided wave propagation dispersion equation in the multi-layered liquid is derived and numerically solved.The circular frequency-wavenumber(?-?,),phase velocity,and group velocity dispersion curves of the propagation of guided waves in the shallow sea with the thermocline are obtained,based on which the influence of the thickness variation of the upper and lower layers on dispersion characteristics is studied.It is found that the group velocity dispersion curve corresponding to the mth(m>1)mode propagating in the shallow sea with the thermocline has a fluctuating frequency band.However,this band cannot be found in the group velocity curves corresponding to the guided waves in the uniform shallow sea.Furthermore,based on the vector displacement wave equation,the analytical solutions of the transient radial displacement,axial displacement and sound pressure excited by the annular transducer in shallow water with the thermocline are derived.The transient acoustic vector fields excited by the annular transducer in a uniform liquid layer and three sets of thermocline with different thickness combinations are numerically simulated.Those numerical results are used to analyze the influence of the thermocline and the thickness variation of the upper and lower layers on the transient displacement and the transient sound pressure.The theoretical and numerical results obtained in this thesis are useful to the underwater acoustic engineering experiments,for example,underwater acoustic communication and acoustic detection experiments,carried out in the shallow sea with the thermocline,in which annular transducers are used.