Research On Sound Field Calculation Based On Normal-mode Theory

The ocean sound field is usually described by pressure field and particle velocity field. While pressure is a scalar value, particle velocity is a vector one, which has both intensity and phase information simultaneously. With the development of vector hydrophone technology and vector signal processing techniques, researches on particle velocity field have shown more and more advantages than those on pressure field. So the main work of this thesis focuses on the numerical calculation and simulation of vector field.Normal-mode model is chosen during the sound field computation, and the eigenvalues and eigenfunctions involved are calculated by the finite-difference method. According to Euler Equation, particle velocity can be worked out with numerical differential of the pressure.Calculation programs for transmission loss and phase difference are accomplished with computer. Considering user's convenience, GUI (Graphic User Interface) software with the program forenamed is implemented based on MATLAB platform. Using the software, simulations for sound field are done, especially for the velocity field, which indicate obvious characteristics of normal modes. Calculations of source-centered, circle-distributed points are done using the software. Phase flips and pass-through characteristics highly correspond to theories and experiments, which validate the algorithm and simulation routine's rationality. As actual ocean environments are usually complex, sound fields with sea surface roughness, typical SSP, layered media and attenuation are calculated and influences of these factors are analyzed comparing with the ideal single layer sound field. Finally, the sound field of a more practical environment is calculated using both the routines mentioned above and Kraken normal modes, and the results have good consistency.