Research On Modeling And Rule Of Infrasound Propagation In Shallow Sea

Shallow water sound propagation is an important research problem in underwater acoutics. Since nowadays the working frequency of sonar becomes much lower, vector sensors and related signal processing technique has been applied widely and developed rapidly; the seismic wave caused by ship noise or ocean environmental factors, as a new kind of physical field has important application foreground in underwater target detection, mine exciting and ocean kinetics monitoring. Therefore the propagation law and modeling method for infrasound vector field and seismic wave fields in shallow water with irregular elastic bottom had been researched in this thesis. Some new researching results had been got as following:(I) Modeling methods for infrasound vector field and seismic wave fields in shallow water with elastic bottom1. FFM for calculating diplacement fields in ocean and seismic wave in bottom had been developed Diplacement fields and seismic wave, which excited by point sound source, had been formulated in cylindrical coordinates with layered elastic bottom, displacement fields had been caculated by using FFM.2. Elastic parabolic approximation method for calculating diplacement fields in ocean and seismic wave in bottom had been developedNumerical method for diplacement field and seismic wave calculation had been introduced, based on elastic parabolic approximation method and using inverse operator. For which, in comparison with numerical difference method, larger step in range can be used and results will be given more rapidly.Using this method with the help of coordinate mapping, numerical solution of wave propatation for case of irregular elastic bottom had been obtained. This method had also been generalized for seismic wave predicting and analysis beyond shoreline. 3. The validity and accuracy of these methods had been proved by comparison with other propagation model and experiment dataThe validity and accuracy of these methods had been proved by comparison with KrakenC and SAFARI model. For the first time in China, ocean experiment had been carried out for measurement of seismic wave caused by ship. The seismic wave signal had been successfully received by measuring system placed on offshore coast. Comparison of experimental data with result calculated using simulating model had been given, the two results consistent to each other.(II) Researchiong propagation law for infrasound propagating in shallow water with irregular elastic bottom1. The study of seismic wave propagation mechanism in shallow water. Using Pekeris waveguide model with layered elastic ocean bottom, a simple numerical model of acoustic vector field has been developed in Cartesian coordinates; the particle orbits and displacement of the Scholte wave as well as sub-interface wave have been studied, the dispersive characteristics have been also researched.2. The displacement field distribution of acoustic vector and seismic wave in Pekeris waveguide with elastic bottom The parameters'effects on amplitude of the acoutic vector fields and seismic wave have been also analyzed, these parameters include wave speeds of the compressional and the shear wave, water depth, source frequency, depth of source location, coefficient of medium absorption, sound speed profile, etc.3. Acoustic energy leakage in shallow water with sloping elastic bottom In wedge with elastic bottom, the field distribution of acoustic vector and seismic wave field had been analysed, results indicate that the energy of sound wave leaked into the bottom along the decrease of water depth, the place, where leakage occurred, can be determined by the ratio of the ocean depth to the wavelength, as predicted by normal mode theory.4. The field distribution of seismic wave beyond shoreline The parameters'effects on amplitude of seismic wave have been also analyzed, these parameters includedepth of source location, source frequency, wave speeds of the compressiona the shear wave l, etc.The research can provide a physical foundation for underwater targets detection using acoustic vector fields and seismic wave fields.