Farassat's methods in marine propeller hydroacoustics

The aim of this work is to show the potential of the Acoustic Analogy in the analysis of ship underwater noise, moving from an isolated marine propeller in a uniform flow to a ship scaled model in a steady course. In particular, some formulations proposed by Feri Farassat are used to conduct an investigation on many interesting and rather unknown aspects of the problem: the identification of the most significant noise sources of a ship, the mutual hydroacoustic interactions between its structural subcomponents, the versatility and effectiveness of the Acoustic Analogy in dealing with issues within this research area. Sample numerical results are presented, that were obtained by coupling an incompressible RANS code, including a Level-set approach to account for the fundamental time evolution of the free surface, to a FWH-based hydroacoustic solver, here suitably designed to manage the huge set of data coming from a full-unsteady hydrodynamic simulation. A surprising outcome is that, contrary to popular belief and regardless of the low blade rotational speed, a reliable hydroacoustic analysis of a marine propeller seems to require the computation of the FWH nonlinear quadrupole sources and cannot leave apart an accurate estimation of the three-dimensional turbulence and vorticity fields.