Numerical methods in underwater acoustics - sound propagation and backscattering

This report summarizes an overview given at the XXXII Symposium on Hydroacoustics (SHA 2015) over several modelling techniques that are used in the context of military applications at the Research Department FWG of the German Bundeswehr Technical Centre for Ships and Naval Weapons, Maritime Technology and Research (WTD 71). For the modelling and understanding of sound propagation a physical model consisting of a tank for scaled measurements and the corresponding numerical simulation is presented. The basic formalism of stochastic ray tracing of the German Navy sonar simulation MOCASSIN is explained and compared to traditional deterministic ray tracing including the comparison with measurements. Strategies for the approximate calculation of the sonar target strength of large underwater objects with the use of boundary element methods, fast multipole methods and a ray-based algorithm are presented and the results of the calculations of several test objects are shown.