Numerical Simulation Study Of Sound Propagation Loss In Shallow Sea

In the domestic hydroacoustic community,shallow sea research is also more advantageous.In this thesis,we combine theoretical and other experimental studies of shallow sea hydroacoustic investigations to investigate the shallow sea hydroacoustic propagation properties and analyze the physical mechanism of their formation.Also,from these properties,the sound propagation losses in several typical environments are derived and verified using computer simulations or ocean data.Specific studies include:(1)The characteristics of acoustic propagation in surface waveguides are studied,and the classical medium frequency equation is modified to verify the optimal range at the frequency scale when the sonar is actively transmitting and passively receiving from the propagation loss perspective.In order to improve the performance of the sonar when working in the shallow equatorial region to accurately predict the El Ni?o phenomenon,the relationship between the location of the sound source in the surface waveguide and the output acoustic frequency is analyzed using the principle of the mirror method and the simple positive wave model: firstly,for the shortcoming that the classical cut-off frequency formula of the surface waveguide does not consider the depth of the sound source,a correction factor is introduced to consider the effect of the depth of the sound source on the cut-off frequency;secondly,numerical simulations are performed.Then,numerical simulations are performed.Using the computing power of modern computers,a finite difference numerical method is used to simulate the behavior of the surface waveguide and calculate its cutoff frequency versus the location of the sound source;finally,the accuracy is verified in terms of propagation loss through simulation modeling.(2)Using the theory of acoustic waves in fluids and solids,the propagation loss equation under the ice-water layer medium is derived,and the characteristics of acoustic propagation in waters under the ice surface are calculated.In order to calculate more accurately the difference between the reflected acoustic waves at the interface of sound waves incident to sea ice and air,firstly,the solid reflection characteristics are added to the calculation of the propagation loss equation through the theory of sound transmission in solids;secondly,environmental factors are introduced to modify the equation to obtain the physical parameters of sea ice and seawater.The number of variables of the propagation loss equation is further simplified by snell’s law;finally,the integration of the propagation loss is solved by interpolation and simulation modeling is performed to obtain the relationship between frequency and propagation loss at the ice interface.(3)The effect of underwater rigid spheres on acoustic scattering is studied,and the influence of incident acoustic frequency and particle scale on directivity is proposed.The frequency selection for long-range propagation in the case of suspension is verified from the perspective of propagation loss in a non-uniform suspension environment.In order to verify the general law of incident wave frequency and directivity,firstly,the scattering characteristics of a rigid sphere are analyzed by a simple normal wave model;secondly,the rigidity condition is got rid of and the solid scattering attenuation coefficient is introduced to modify the propagation loss equation;finally,the effect of incident wave frequency on propagation loss is obtained by simulation modeling,and the optimal long-distance propagation frequency in this environment is obtained by comparing with the appeal law.